surface water and geomorphology herrera report-oct 2005

SURFACE WATER AND GEOMORPHOLOGY TECHNICAL REPORT

Pioneer Aggregates Mining Expansion

and North Sequalitchew Project

Prepared for

Huckell/Weinman & Associates

October 2005

Note: Some pages in this document have been purposefully skipped or blank pages inserted so that this document will copy correctly when duplexed.

SURFACE WATER AND GEOMORPHOLOGY TECHNICAL REPORT

Pioneer Aggregates Mining Expansion

and North Sequalitchew Project

Prepared for

Huckell/Weinman & Associates 270 Third Avenue, Suite 200

Kirkland, Washington 98033

Prepared by

Herrera Environmental Consultants, Inc. 2200 Sixth Avenue, Suite 1100

Seattle, Washington 98121 Telephone: 206/441-9080

October 28, 2005

Contents

1.0 Introduction...............................................................................................................................1

2.0 Affected Environment...............................................................................................................3

Sequalitchew Creek ..................................................................................................................3 Stream Discharge ............................................................................................................5 Water Quality ..................................................................................................................6 Geomorphology ..............................................................................................................7 Hydraulic Modeling of Existing Conditions .................................................................11

Fort Lewis Diversion Canal....................................................................................................12 Canal Discharge ............................................................................................................13 Water Quality ................................................................................................................13

Sequalitchew Creek Springs ...................................................................................................14 Near-Shore Springs.................................................................................................................14 Kettle Wetland ........................................................................................................................15 Old Fort Lake..........................................................................................................................15 Pond Lake ...............................................................................................................................15 Brackish Marsh.......................................................................................................................16 Historical Geomorphic Conditions .........................................................................................16 Existing Geomorphic Conditions ...........................................................................................16

Nisqually Reach (Puget Sound) ....................................................................................17

3.0 Significant Impacts of the Proposed Action ...........................................................................19

Construction............................................................................................................................19 Stormwater Management ..............................................................................................19 Site Clearing and Grading.............................................................................................20 North Sequalitchew Creek Construction.......................................................................20 Access Road and Pedestrian Bridge Construction ........................................................26 Conveyer System Construction.....................................................................................27

Operation ................................................................................................................................27 Mining and Processing ...........................................................................................................27

North Sequalitchew Creek ............................................................................................27 Sequalitchew Creek.......................................................................................................32 Kettle Wetland ..............................................................................................................34 Fort Lewis Diversion Canal/Sequalitchew Lake...........................................................34 Old Fort Lake ................................................................................................................35 Pond Lake .....................................................................................................................35 Brackish Marsh .............................................................................................................35 Post-Reclamation Stormwater Management.................................................................36 Near-shore Springs........................................................................................................37 Shipping Activities........................................................................................................37

i

Impacts of the Project Alternative ..........................................................................................37 Water Resources............................................................................................................37 Geomorphology ............................................................................................................37

Impacts of the No Action Alternative.....................................................................................38 Monitoring and Mitigation Measures .....................................................................................38

Water Quality ................................................................................................................38 Geomorphology ............................................................................................................39

Significant Unavoidable Adverse Impacts .............................................................................40 Proposed Action............................................................................................................40 Project Alternative ........................................................................................................42

4.0 References...............................................................................................................................43

ii

Tables

Table 1. Discharge summaries (monthly means) for Sequalitchew Creek and Fort Lewis Diversion Canal from 1977 through October 2004. ........................................49

Table 2. Water quality standards (freshwater) and designated uses (Chapter 173-201A-200 WAC) (Ecology 2003) applicable to surface waters of the project site including Sequalitchew Creek and the Fort Lewis Diversion Canal. ..................50

Table 3. Water quality data for Sequalitchew Creek collected in the ravine bordering the southern boundary of the Glacier site from September 1999 to September 2000. ...........................................................................................................................51

Table 4. Water quality data for the Fort Lewis Diversion Canal collected near the eastern boundary of the Glacier site from September 1999 to September 2000. ...........................................................................................................................53

Table 5. Brackish Marsh salinity measurements (ppt) collected during low, ebb, high, and flood tides on April 14 and April 19, 2004..........................................................55

Table 6. Water quality standards (marine waters) and designated uses (Chapter 173-201A-210 WAC) (Ecology 2003) applicable to the Nisqually Reach of Puget Sound (Extraordinary Quality). ..................................................................................56

Table 7. Marine water quality data collected from Ecology’s long-term ambient water quality monitoring station GOR001 in the Nisqually Reach of Southern Puget Sound from October 1996 to September 2002. ..........................................................57

Table 8. Table of estimated ground water quality concentrations and North Sequalitchew Creek Concentrations within the mine expansion area compared to background concentrations in Sequalitchew Creek and Washington State surface water quality standards (Chapter 173-201A-200 WAC) (from Pacific Groundwater Group [PPG 2005]).............................................58

Table 9. Best estimate of predicted annual average flows in Sequalitchew Creek with the additional flows from North Sequalitchew Creek upstream and downstream of the proposed confluence at RM 0.8 (Anchor 2004d).........................60

Table 10. Best estimate of peak storm flows in Sequalitchew Creek under existing and future conditions (Anchor 2004d). .............................................................................61

Table 11. Estimated peak storm flows in the proposed North Sequalitchew Creek used by Aspect to assess reclamation stormwater conditions within the mine expansion area (Aspect 2004b)...................................................................................62

iii

Figures

Figure 1. Proposed Glacier Mine expansion area, surface water features, and surface water monitoring stations, DuPont, Washington........................................................63

Figure 2a. Sequalitchew Creek reach boundaries and landslides mapped by GeoEngineers..............................................................................................................65

Figure 2b. Sequalitchew Creek reach boundaries and landslides mapped by GeoEngineers (continued). .........................................................................................67

Figure 3. Landslide and debris fans in the lower Sequalitchew Creek ravine as interpreted from shaded relief lidar digital elevation model. .....................................69

Figure 4a. Sequalitchew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results. ........................................................71

Figure 4b. Sequalitchew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results (continued). ....................................73

Figure 5. Potential depositional and erosional reaches predicted by hydraulic modeling of existing conditions in Sequalitchew Creek (GeoEngineers 2004b). ......................75

Figure 6. Sequalitchew Creek outlet and Diversion Canal surface water flow directions, DuPont, Washington...................................................................................................76

Figure 7. Kettle wetland water levels at the existing Glacier Mine site from July 1999 to October 2002 (CH2M Hill 2003a)..........................................................................77

Figure 8. Brackish Marsh salinity sample locations near the existing Glacier Mine, DuPont, Washington...................................................................................................79

Figure 9. Historical maps of Lower Sequalitchew Creek. .........................................................81

Figure 10. Current conditions within the Brackish Marsh during low tide. ................................83

Figure 11. Potential depositional and erosional reaches predicted by hydraulic modeling of proposed conditions in Sequalitchew Creek (GeoEngineers 2004b). ....................85

Figure 12a. Sequalitchew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers. .............................................87

Figure 12b. Sequalitchew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers (continued). .........................89

Figure 13a. Sequalitchew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers. ............................................................................91

Figure 13b. Sequalitchew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers (continued)..........................................................93

Figure 14. Model predicted change in ground water level near Sequalitchew Creek..................95

iv

Surface Water and Geomorphology Technical Report

1.0 Introduction

This report provides surface water and geomorphology technical detail and support to the Supplemental Environmental Impact Statement (SEIS) for the expansion of Glacier Northwest’s mining operations in DuPont, Washington. Glacier Northwest proposes to expand its current mining operations by approximately 200 acres by mining adjacent land located mostly to the east of the current mine area. Under the proposed action, Glacier proposes to capture ground water entering the mine expansion area from the east and convey it south to Sequalitchew Creek via North Sequalitchew Creek, a newly constructed stream channel. The following technical report describes surface water and geomorphic existing conditions (affected environment), as well as analyzes potential impacts to surface water resources and geomorphology from the proposed 200-acre expansion. In addition, proposed monitoring and mitigation measures for the proposed project are presented.

wp4 /02-02403-000 surface water and geomorphology tech report.doc

October 28, 2005 1 Herrera Environmental Consultants


2.0 Affected Environment

Major surface water resources within the vicinity of the existing mine and proposed mine expansion area include: Sequalitchew Creek and its associated wetlands and springs, Fort Lewis Diversion Canal, Sequalitchew Lake, Old Fort Lake, and the Nisqually Reach of southern Puget Sound. In addition, numerous small kettle lakes and wetlands located in the vicinity of the project are described below.

The proposed mine expansion area is located in the Chambers-Clover basin (Water Resource Inventory Area [WRIA] 12), which has a drainage area of 171 square miles. This basin is located within the Puget lowlands ecoregion and has an average annual precipitation of approximately 40 to 44 inches/year (Anchor 2004c). Sequalitchew Creek (Segment No. 12-0019), located entirely within the Chambers-Clover Creek Watershed, drains a watershed covering 38.4 square miles and discharges into the Nisqually Reach of Puget Sound (WDF 1975). The headwaters of the Sequalitchew Creek drainage basin are located in Kinsey Marsh on the east side of Interstate 5 (I-5). Runoff from the Kinsey Marsh flows 3.8 miles in Murray Creek into American Lake on the west side of I-5. The water level in American Lake (1,162 surface acres) occasionally overflows the outlet weir and discharges into Sequalitchew Lake (81 surface acres) (Figure 1).

Sequalitchew Creek

Sequalitchew Creek is formed at the outlet of Sequalitchew Lake. The Sequalitchew Creek channel downstream of Sequalitchew Lake extends for approximately 1.5 miles through Edmond Marsh. The lower 1.5 miles of Sequalitchew Creek, between Edmonds Marsh and the Puget Sound shoreline, descends through a steep-walled ravine that parallels the southern boundary of the proposed mine expansion area and existing mine. The channel drops approximately 220 feet in elevation in 7,750 feet (average slope of 2.8 percent) between Center Drive below the upland plateau and the brackish marsh located directly upstream of the BNSF Railroad embankment. The floor of the ravine gradually widens in the downstream direction from a minimum of 40 feet at the ravine head to a maximum width of roughly 400 feet near the railroad embankment at the brackish marsh.

Ravine slopes on either side of the stream channel over much of its length range from 30 to 80 percent for an average of 60 percent. Near the mouth, Sequalitchew Creek passes through a 240-foot long box culvert (5 feet wide and 5 feet high) under the Burlington Northern-Santa Fe Railroad (BNSF) railroad tracks before discharging into Puget Sound. The lower 300 feet of Sequalitchew Creek above the BNSF railroad tracks is tidally influenced as evidenced by tidal channels and a Class 1 estuarine wetland (per the City of DuPont rating system and identified as the Brackish Marsh throughout this section).

Several springs, which provide flow to Sequalitchew Creek, are located on the north and south banks from approximately 0.6 to 1.1 miles upstream of the mouth. An abandoned small-gauge




railroad grade that parallels the north creek bank intercepts these springs and collects the runoff in drainage ditches that are culverted under the rail bed and drain into Sequalitchew Creek. The springs daylight along the side slopes of the ravine at the contacts between layers of different permeobilites and provide most of the flow into Sequalitchew Creek along this reach (CH2M Hill 2003b).

Natural conditions at the mouth of the creek were substantially altered by construction of the BNSF RR along Puget Sound in 1912 (Andrews and Swint 1994). The railroad embankment isolated the delta from shoreline processes along Puget Sound and transformed the delta into a one-half-acre brackish marsh. Since construction of the embankment, the exchange of freshwater and saltwater has occurred through the long box culvert beneath the railroad.

Historically, Sequalitchew Creek has been subjected to chronic and extensive sediment inputs throughout the project area as a result of pre-project land use (i.e., deforestation of ravine slopes and construction of the railroad grade). The dominant mechanisms delivering sediment to the creek channel include erosion of poorly consolidated hillslopes, soil creep, shallow landslides, slumping, and ground water seeps. The Sequalitchew Creek valley has the potential to contribute sediment due to the underlying geology of relatively unconsolidated sediments and high ground water table. Extensive forest clearing in the early 1900s likely increased the rate of sediment input to the creek. Given that flows in Sequalitchew Creek were naturally moderated by ground water and upstream wetlands, it is likely the sediment inputs resulting from forest clearing overwhelmed the creek’s sediment transport capacity. When the quantity of sediment input to a reach exceeds the output, sedimentation decreases the depth and increases the width of flow, further diminishing the sediment transport capacity. Bar formation and increased flow widths would have further aggravated erosion of adjacent hillslopes. Local bank erosion is observed where the channel is wide under existing conditions. The Fort Lewis diversion canal (an upstream system of weirs that diverts flow away from Sequalitchew Creek) built in the 1950s, further diminished the creek’s sediment transport capacity by reducing stream flows.

Historically, two potential pollutant sources existed near the DuPont mine site. Fort Lewis Army Reservation Landfill No. 5 located 0.5 mile east-northeast of the mine site was used for the disposal of reservation wastes from 1967 to 1990. The landfill was designated as a Superfund site pursuant to the Comprehensive Environmental Response Compensation and Liability Act (CERCLA), when in 1987, sampling indicated that the landfill had contaminated the ground water with elevated levels of heavy metals and organic compounds (U.S. EPA 2003). Closure of the landfill was begun in 1987. Additional sampling after the closure of the landfill found contaminant concentrations in ground water samples below state and federal cleanup standards, and on May 22, 1995, the site was deleted from the National Priorities List (U.S. EPA 2003).

The old DuPont Works Plant, located south of the existing mine site, manufactured forty grades of dynamite including water gel, nitroglycerine, ammonia explosives, and black powder from 1909 to 1977. Several remedial actions have been taken to remove contaminated material from the site after the Weyerhaeuser and DuPont companies signed a Consent Decree with the Washington Department of Ecology in pursuant to the Model Toxics Control Act in 1991 (URS 2000). The final environmental impact statement (FEIS) proposed action involves


Herrera Environmental Consultants 4 October 28, 2005


constructing a golf course to provide a cap/containment facility for the former explosives plant (URS 2000).

Stream Discharge

The hydrology of Sequalitchew Creek is characterized by three reaches: an upper, losing reach; the ravine, a middle gaining reach; and a lower, losing reach (CH2M Hill 2003b). The upper reach extends from the outlet of Sequalitchew Lake through Edmond Marsh to a point west of Center Drive. This upper reach infiltrates to recharge the Vashon Aquifer (CH2M Hill 2003b). As the stream approaches the western end of Edmond Marsh, flows infiltrate the highly permeable Vashon outwash materials. Surface flows do not extend downstream past Edmond Marsh, except during high flow conditions.

During the winter, flows are regulated by a series of outlet weirs designed to manage the level of Sequalitchew Lake by diverting excess discharge into the Fort Lewis diversion canal. Several beaver dams on the stream cause the level of the stream to rise and back up, forcing discharge into the diversion canal (Aspect 2004a). The Army removed some of the beaver dams near Sequalitchew Lake in the summer of 2004, as they have reportedly done historically. The beavers typically rebuild the dams. Because of the very low stream gradient along this reach, the beaver dams can cause the water to reverse its flow direction with a water level rise of 1 to 2 feet. Effect of the beaver dams results in water levels in upper Sequalitchew Creek and Edmond Marsh that are higher than water levels at either end. Thus, Sequalitchew Creek discharges both down its historical channel to the west and through the Diversion Canal to the northwest (Aspect 2004a) (Figure 1). In addition, one stormwater outlet from Fort Lewis flows into Hamer Marsh and one flows into Bell Marsh, adding additional surface flow to the stream. See the Diversion Canal discussion below for a more detailed description of surface water flow pathways.

The middle reach extends from west of Center Drive downstream through the ravine to the “Kitsap Cutoff,” the northern edge of the Olympia beds (CH2M Hill 2003b). This reach is typically dry between the west end of Edmond Marsh and the ravine springs (Aspect 2004a). This higher gradient portion of the creek receives discharge from several small springs from both the north and south sides of the steep-walled ravine (CH2M Hill 2001). These springs provide a perennial water source for the creek (CH2M Hill 2001, 2003b).

The stream channel within the lower reach, which extends west of the Kitsap Cutoff to Puget Sound, consists of the highly permeable sands and gravels of the DuPont Delta formation. This permeable layer causes water within the creek to infiltrate and recharge the ground water of the DuPont Aquifer, measurably decreasing the discharge of the creek compared to the middle reach (CH2M Hill 2003b).

Sequalitchew Creek discharge has been monitored periodically for several decades. Two studies conducted during the 1970s and 1980s measured discharge in lower Sequalitchew Creek. A study by Thut et al. (1978) from 1977 to 1978 measured monthly discharges in Sequalitchew Creek ranging from 0.1 to 12.8 cfs. Similar results were found by Firth (1991) from 1984 to 1987 in lower Sequalitchew Creek, where monthly discharge averaged between 1.0 and 9.4 cfs.




The most recent Sequalitchew Creek discharge data were collected by Aspect Consulting (Aspect) (2004a) and CH2M Hill (2001, 2003a) (Table 1). CH2M Hill monitored Sequalitchew Creek discharge from October 1999 through September 2002 at a monitoring station located approximately 700 feet upstream of the mouth. Stream flow monitoring activities at this lower monitoring station were subsequently assumed by Aspect, which has published discharge data through October 2004 (Aspect 2004b). From November 1999 to October 2004, the mean monthly discharge at the lower monitoring station ranged from 0.2 to 2.9 cubic feet per second (cfs). In addition, Aspect began operating a second upper flow monitoring station located upstream of the proposed confluence with North Sequalitchew Creek (Aspect 2004a). From November 2003 to October 2004, the mean monthly discharge at the upper station has ranged from 0.4 to 2.5 cfs. At both stations, the highest discharges were measured during the wet season (November through June) and the lowest discharges were recorded at the end of the dry season (October/November).

Discharge measured in the lower reach indicates the creek does not respond quickly to rainfall events, with minimum flows often lagging 1 to 2 days after a major rainfall event (i.e., >0.50 inches in 24 hours) (CH2M Hill 2001). The presence of Sequalitchew Lake, several large wetlands in the headwaters of the creek, and several beaver dams in the Sequalitchew Creek headwaters help detain and retard stormwater runoff. Because the flows in the lower reach of Sequalitchew Creek are supported by ground water discharge, there is a time lag in the stream’s response to storm events. Water flow through the subsurface (downstream of Center Drive) moderates the discharge rates creating the lag in stream flow response. In addition, very little, if any, surface water from the mine site enters Sequalitchew Creek (CH2M Hill 2001). The majority of the precipitation infiltrates the highly permeable gravel deposits of the DuPont Delta and Vashon Drift units underlying the site (CH2M Hill 2001).

Water Quality

Surface water quality standards for the State of Washington are established by Ecology in Chapter 173-201A WAC for the protection of public health and enjoyment, and designated beneficial uses (Ecology 2003). Sequalitchew Creek is designated as a salmon core rearing and migration stream (formerly as a Class AA [extraordinary] waterbody under the previous WAC designation and described in the original EIS [City of DuPont 1993]) by Ecology). Changes to the state’s water quality standards were adopted by Ecology on July 1, 2003 and were effective August 1, 2003. Water quality sampling results are compared to applicable state water quality standards in Table 2.

Section 303(d) of the CWA (and later revisions) requires all states to prepare lists of surface water that are not expected to meet applicable water quality standards after implementation of water quality based controls. This list, identified as the 303(d) list, is prepared by Ecology and submitted to the U.S. EPA. The most current listing is the 2004 303(d) list. To-date, Sequalitchew Creek has not been identified on Ecology’s 303(d) list as a threatened or impaired waterbody and is therefore not part of any existing or proposed TMDL. However, on the current 303(d) list, Sequalitchew Creek is listed as a “waters of concern” (Category 2) due to dissolved oxygen and temperature excursions beyond the applicable criteria (Ecology 2005a).




Sequalitchew Creek water quality was described in the original mine EIS, which characterized the stream as having good water quality and generally meeting Class AA water quality standards (City of DuPont 1993). As part of the North Sequalitchew Creek Project, water quality samples were collected monthly in Sequalitchew Creek from September 1999 through September 2000 (CH2M Hill 2001), with three additional dissolved oxygen measurements collected during the summer of 2002 (Table 3). In addition, a continuous temperature recorder was installed in Sequalitchew Creek in July 2000 to record daily temperature through December 2002. Water quality samples were collected approximately 700 feet upstream of the mouth of lower Sequalitchew Creek at the lower Sequalitchew Creek discharge gauge (Figure 1).

The sampling results (September 1999 through September 2000) indicate the waters of Sequalitchew Creek are generally cool, well oxygenated, with low concentrations of fecal coliform bacteria. During monthly sampling, measurements of pH, temperature, dissolved oxygen and fecal coliform bacteria met the applicable state criteria. Nitrate-nitrogen was detected at levels ranging from 0.28 to 0.82 mg/L, within the range presented in the original mine EIS (City of DuPont 1993). Total phosphorus concentrations were low to moderate, and ranged from 0.015 to 0.034 mg/L, with an average of 0.021 mg/L. TSS concentrations were low, with an average of 4 mg/L measured during sampling (CH2M Hill 2001). Because samples were not analyzed for turbidity, compliance with this standard cannot be determined. However, because of the well documented link between turbidity and TSS (Packman et al. 1999), the turbidity may also have been low during sampling.

During sampling, dissolved cadmium and lead concentrations were detected at concentrations exceeding state water quality chronic criteria for each metal (based on an average hardness of 44 mg/L) (CH2M Hill 2001). A dissolved cadmium sample collected in October 1999 measured 0.0009 mg/L, which exceeded the chronic criterion of 0.0006 mg/L. Two dissolved lead samples collected in May and July of 2000, both measuring 0.002 mg/L, exceeded the chronic criterion of 0.0010 mg/L.

CH2M Hill collected additional water temperature and dissolved oxygen data in Sequalitchew Creek as part of continued project monitoring. The continuous temperature gauge recorded two exceedances of the state temperature criterion (16°C) during August 2001 (CH2M Hill 2003c). In addition, three dissolved oxygen measurements were made during the summer of 2002 with one measurement in July (9.2 mg/L) and one measurement in August (9.3 mg/L) that failed to meet the state minimum criterion of 9.5 mg/L (CH2M Hill 2003c).

Geomorphology Historical Geomorphic Conditions

Sequalitchew Creek has responded to a series of changes in flow and sediment regimes throughout both geologic and more recent historical times. The ravine of lower Sequalitchew Creek was initially formed by a series of meltwater floods during glacial retreat (GeoEngineers 2004b). Peak flows within the channel likely declined rapidly following retreat of the glacier and cessation of meltwater floods. Erosion would have been further reduced as forest vegetation




became established. This post glacial reduction in sediment production, sediment-transporting flows, and increased hydraulic roughness within Sequalitchew Creek resulting from the accumulation of wood debris would have resulted in relatively little sediment export to Puget Sound. Thus as sea level rose, the creek mouth was probably characterized by a shallow embayment of open water such as depicted in historical maps of the creek and not a prominent delta (see Brackish Marsh discussion below). Prior to European colonization, the creek would have provided outstanding salmon habitat because of the perennial source of cold water, excellent substrate, abundant cover and shade, and high pool frequency created by in-stream large woody debris.

Historical accounts of resource use by indigenous cultures and early settlers in lower Sequalitchew Creek provide qualitative evidence of significant perennial flow prior to settlement of the region. Records from Euro-American explorers arriving in the 1780s suggest perennial flow and habitat conditions within Sequalitchew Creek were sufficient to sustain a productive salmon run that sustained the local tribal population. Discharge at the mouth of Sequalitchew Creek was also used to support a trading post established in 1821 and a water-powered sawmill that operated between 1859 and 1870. Later on, the E.I. DuPont de Nemours Company constructed a small dam and hydroelectric plant in the ravine in the early 1900s and maintained the dam until at least 1940 (Aspect 2004a). Drainage of Edmond Marsh for farming by the 1850s, and the development of Fort Lewis between 1908 and 1917, impacted flows to Sequalitchew Creek by reducing the storage capacity in the watershed. By the 1950s, flooding caused by increased runoff from impervious areas of Fort Lewis prompted construction of the current network of weirs and the diversion canal at the outlet of Sequalitchew Lake (Aspect 2004a) (Figure 1).

Construction of the diversion canal in the 1950s substantially reduced flows in Sequalitchew Creek. Prior to construction of the diversion canal, the peak discharge in Sequalitchew Creek for the 2-year storm event was estimated to range from 40 to 120 cfs, with an average value of 70 cfs (Aspect 2004a). Based on recent stream gauging and hydrologic modeling, the current estimate of the 2-year peak discharge is 10 cfs (Aspect 2004a). This major reduction in flow followed a period in which deforestation and development would have dramatically increased the sediment supply to the creek. The combination of an increase in sediment supply and reduction in sediment transport capacity is consistent with field evidence of sedimentation within the ravine. This material is currently held in storage within the ravine and available for transport to downstream depositional reaches in the event of increased flow. The principal sediment trap has historically been the tidal area currently occupied by the brackish marsh immediately upstream of the railroad grade, an area where sedimentation is likely to accelerate if stream flow is increased without compensating measures to reduce sediment delivery and improve transport capacity through the area of tidal influence (see Brackish Marsh discussion).

Field observations and the natural history of the region suggest sediment transport and storage within the creek would have been significantly influenced by large trees and in-stream woody debris. Large tree stumps observed on the slopes of the ravine indicate that wood recruitment to the creek would have included logs far larger than the creek would have been able to move, and thus logs and woody debris capable of influencing the creek morphology would have been




common. Large trees would also be expected to moderate erosion along adjacent hillslopes by reinforcing creek banks and promoting a relatively narrow and deep channel. Deforestation of the basin in the early 1900s is likely to have exposed the highly erodible glacial sediments to erosion and severely accelerated sediment input to the creek and sedimentation within the brackish marsh.

Existing Geomorphic Conditions

The existing geomorphic conditions of lower Sequalitchew Creek have been investigated for the proposed mine expansion project through field reconnaissance and modeling efforts. Field reconnaissance was completed in January 2004 by participants from GeoEngineers, CH2M Hill, and Glacier Northwest (GeoEngineers 2004b). Existing conditions in the brackish marsh were investigated by Anchor (2004c) during rising and falling tides in April 2004. Additional field reconnaissance of Sequalitchew Creek was performed by Aspect (2004a) in April 2004 and by Herrera in September 2003 and February 2005. Landslides were mapped in the field and interpreted from high-resolution topography of the project site.

The ravine below Center Drive has been divided into four reaches based on geology (location of Kitsap cutoff), extent of tidal influence, and channel morphology (GeoEngineers 2004b). Reach numbering (1 through 4) is upstream to downstream. Stream stationing, extending from Station 00+00 at the mouth, approximately 50 feet downstream of the 5-foot box culvert: to Station 70+00 (7000 feet) at the upstream end of the ravine, was established for purposes of hydraulic modeling and provides an additional reference for discussion (Figures 2a and 2b). The uppermost reach of the ravine is typically dry from the west end of Edmond Marsh to the first identified springs about 300 feet west of Center Drive. Flow at this location is intermittent. Remnants of the old dam and power works are located here as well.

Reach 1 begins at Station 70+00 in the ravine, approximately 750 feet downstream from Center Drive (Figure 2a). At this location, the ravine is roughly 60 feet wide and 40 feet deep. Reach 1 is located above the Kitsap Cutoff and is characterized by relatively low channel gradient and numerous ground water seeps emerging along the Olympia-Vashon contact. The average channel gradient varies from 1 to 2 percent, with the local maxima as great as 3.5 percent. The bankfull channel depth varies from 0.3 to 3 feet. Channel width varies from 5-7 feet upstream and increases to 15-40 feet near Station 35+00. Sediment comprising the channel bed is dominated by small gravel and cobbles and interstitial coarse sand and fine gravel. Stream morphology varies between a shallow, wide, braided channel spanning nearly the entire width of the ravine, to a relatively narrow channel confined against the ravine wall and causing local erosion. Deposition of sand within the active channel reflects the relatively low transport capacity within Reach 1. Consistent with sedimentation, the channel has relatively few pools, and the ones observed occur downstream of the wood debris obstructing flow.

Reach 2 extends from Station 30+00 to 18+00 and is located below the Kitsap Cutoff in unconsolidated outwash sand and gravel (Figure 2b). Channel gradient increases to 2-3 percent in Reach 2, with a local maximum of 4.5 percent. The width of the ravine bottom also increases downstream from 30 to 50 feet. Channel widths and depths in Reach 2 vary dramatically from




5-40 feet and 0.3-3 feet, respectively. Local surface raveling and exposed sediment at the toe of ravine slopes suggest active erosion by the stream in Reach 2. Where the channel widens, low-relief gravel bars provide additional evidence of recent scour and deposition, despite historically low flows. These observations clearly indicate that local sediment delivery from adjacent hillslopes still occurs and is likely to increase if flows are increased, unless mitigating actions are taken to keep erosive flows from abutting the hillslopes (such as placement of large woody debris). Elsewhere, the stream bed is locally armored with cobbles up to 6 inches in diameter. The downstream segment of Reach 2 between Stations 23+00 and 18+00 is similar to Reach 1 and consists of a poorly defined braided channel with little or no floodplain.

The width of the ravine increases in Reach 3 to about 250 ft at the downstream end of the reach (Station 5+00) (Figure 2b). Similar to the transition from Reach 1 to 2, the transition from Reach 2 to Reach 3 is marked by a change in channel morphology from a wide, shallow channel to a narrow channel incised into alluvium. Downstream of Station 16+80, channel morphology varies from a narrow channel confined against the toe of the ravine to a wide undefined channel with intermittent mid-channel gravel bars. A berm constructed between Stations 9+00 and 11+50 deflects the stream channel to the south side of the ravine and separates the creek from a 10-foot deep pit excavated along the north side of the ravine. At Station 10+00, the creek flows within a relatively narrow channel in the middle of the widening valley bottom and away from the toe of the ravine.

Reach 4 consists of a straight, plane-bed channel extending through the brackish marsh to the entrance of the box culvert at the foot of the railroad embankment (Figure 2b). The channel flows situated along the north side of the valley with its bed located below the brackish marsh, which forms the creek’s floodplain through Reach 4. The channel is armored with a layer of coarse gravel and is 9-10 feet wide and 1.0-1.5 feet deep. The channel does have some vegetated bars along its right bank indicating it has undergone periods of historic sedimentation. In addition, there are several distinctive gravel splays or finger-like deposits of gravel on top of the adjacent tidal marsh at the upstream end of the reach (Station 5+50). Channel gradient decreases from 2 percent to approximately 1.5 percent at the transition from Reach 3 to the brackish marsh at Reach 4. The gradient of the box culvert beneath the railroad embankment is 1.2 percent. The hydraulic gradient through Reach 4 is largely governed by the inlet elevation of the box culvert (-1.02 feet) and high tides, which can exceed 10 feet.

Woody debris within the creek has been recruited from adjacent hill slopes because there are relatively few trees within the ravine bottom. The majority of pools in the creek are formed downstream of logs and in places where the banks are stabilized by tree roots. Most of the wood debris consists of small trees, branches, and shrubs. Woody debris is not present in the tidally influenced segment of Sequalitchew Creek through the brackish marsh (Reach 4), reflecting low wood recruitment rates, insufficient transport capacity in the upstream reaches, and a low supply of bedload in Reach 4. The lack of wood within the brackish marsh also indicates that little wood debris is moving down the stream (coincident with a low sediment transport capacity) and what is moving downstream is trapped prior to reaching the brackish marsh. Some small wood debris may be flushed to Puget Sound during low tides. But if any significant quantities were




reaching the brackish marsh, then deposits of wood debris would be found along the high water margins of the marsh.

Ravine slopes throughout the reaches are vegetated by ground cover and a mixed deciduous-coniferous forest. The gradient of side slopes within the ravine ranges from 30 to 80 percent. Several landslide features were mapped during a field reconnaissance of the ravine above station 9+00 in January 2004 (GeoEngineers 2004b) (Figures 2a and 2b). Evidence of ancient landsliding was noted at Stations 9+00 and 12+00 in Reach 3. These landslides are at least a century old based on the presence of old-growth tree stumps in growth position on the surface of both features. A more recent landslide deposit was mapped on the ravine floor in Reach 2 at Station 23+50. This feature, a probable debris flow deposit, is about 40 years old based on the size of the largest tree growing on the deposit (GeoEngineers 2004b). High-resolution LiDAR topography of the project area became available after completion of field mapping. The landslide features identified in the 2004 field reconnaissance are delineated on a map showing the 2003 LiDAR of the project area (Figure 3). Material derived from historical or older landslides and chronic soil creep forms a nearly continuous sediment wedge along the toe of ravine slopes and serves as a readily available sediment supply when eroded by the creek. Local erosion of the sediment wedge occurs at sites where the creek flows along the valley edge. At these sites the sediment wedge has eroded and the hillslope is undercut and steepened (GeoEngineers 2004b). Unvegetated banks and ravine slopes with exposed sediment indicate ongoing input of sediment to the creek.

Based on observations of existing geomorphic conditions in the ravine, sediment production and delivery processes appear to be dominated by the erosion of existing landslide deposits, gravitational creep, surface weathering, and sediment mobilized by flow from seeps and springs. Sediment derived from hillslopes is typically delivered to margins of the valley bottom where it remains in storage until eroded or entrained by the creek.

Hydraulic Modeling of Existing Conditions

Existing hydraulic conditions in Sequalitchew Creek were evaluated by GeoEngineers (2004b) using the HEC-RAS model. HEC-RAS is a one-dimensional hydraulic model developed by the U.S. Army Corps of Engineers to estimate water-surface elevations for rivers and streams. HEC-RAS is typically used to evaluate stage and velocity relationships in a river given the channel geometry, roughness, and flow rate. The channel geometry used in the model was based on cross sections surveyed from the outlet of the box culvert at Puget Sound to the upstream end of Reach 1. Existing hydraulic conditions were simulated for the 2-, 5-, 10-, 25-, 50-, and 100-year recurrence storm flow events. Hydraulic conditions in Reach 4 were evaluated under conditions of both high and low tide. Simulated flows were developed using recent gauge data from lower Sequalitchew Creek and correlation with recent stream gauge data from adjacent stream systems. Simulation outcomes were compared with existing bankfull elevations inferred in the field in order to calibrate the simulated channel roughness.

Shear stress (i.e., force exerted on the bed by the stream) calculated by the HEC-RAS model provided the necessary hydraulic parameters to evaluate the potential for sediment transport




(erosion) and deposition along various reaches of the lower stream reach (GeoEngineers 2004). The total boundary shear stress is the stress exerted by flowing water on the streambed and changes with discharge, flow depth, and channel gradient. Critical shear stress for the bed is the stress required to initiate the movement of a particle and is an intrinsic property of the particle mass, shape, and size range of other particles on the bed. Because Sequalitchew Creek is armored with the coarsest particles, the critical shear stress for initial entrainment of the streambed was scaled to twice the critical shear stress for the 70th percentile grain size (GeoEngineers 2004b). Sediment deposition occurs when shear stress drops below the critical particle shear stress.

The modeling results of the shear stress analysis by GeoEngineers (2004b) indicated potential erosion in Reach 1 near Station 33+00 for storm events larger than the 2-year event (Figure 4a). However, the majority of potential erosion sites are located in Reach 2, where streambed gradients increase through the Kitsap Cutoff (Figure 4b). The results for Reach 3 indicate potential erosion for the 2-year storm near Station 10+80, downstream of the berm and 10-foot-deep depression. Two additional sites in Reach 3, at Stations 5+58 and 5+40, indicate potential bed erosion at the 25- and 50-year storm events just upstream of the brackish marsh.

Results also identify sites where declining shear stress would cause deposition of sediment. The shear stress analysis suggests a downstream pattern in the deposition of progressively finer sediment sizes through Reach 3. For instance, all grains in transport and larger than 8.2 mm would be deposited near Station 17+10 during 10-year flows, whereas grains larger than 6 mm would be deposited at Station 10+05 during 25-year flows (Figure 4b). Likewise, during 100-year flows, the maximum grain size transported through these reaches declines in the downstream direction from 12 mm at Station 17+10 to 10 mm at Station 10+05. Declining shear stress through the brackish marsh indicates Reach 4 is aggrading under existing flow conditions.

Relative trends in bed erosion and sediment deposition within Reaches 1 through 4 have been summarized by comparing the ratio between the simulated shear stress and critical shear stress during the 100-year event along a longitudinal profile of the creek (Figure 5). A ratio greater than 1 indicates conditions are favorable for sediment transport and bed erosion. When shear stress falls below the critical particle shear stress, sediment currently in transport would be deposited. Results of the shear stress analysis indicate Reaches 1, 3, and 4 act as sediment traps while most of Reach 2 is subject to erosion and exporting sediment under existing conditions (Figure 5). The simulated decline in shear stress to just a fraction of the critical shear stress is consistent with current observations of sedimentation in Reaches 3 and 4 and historical filling of the brackish marsh.

Fort Lewis Diversion Canal

The Fort Lewis Diversion Canal (Diversion Canal), which borders the western boundary of the Fort Lewis Military Reservation, was constructed in the 1950s to convey stormwater runoff from Fort Lewis to Puget Sound and to help control the water level in Sequalitchew Lake by serving




as an auxiliary outlet (Figure 1). Hydraulic structures (i.e., weirs) control the lake water level to prevent inundation of Sequalitchew Springs located near the eastern end of the lake, which serves as a major water source for Fort Lewis (CH2M Hill 2003b). The Diversion Canal is two miles long with trapezoidal-shaped channel, which is approximately 15 to 20 feet deep with a base width of 20 feet and 1H:1V side slopes (Aspect 2004a).

Sequalitchew Lake is located entirely on the Fort Lewis Military Reservation. The lake is approximately 81 acres in size and is shallow, approximately 17 feet deep. An 18-foot-wide concrete structure with wooden stop logs that can be raised or lowered to adjust the elevation of the lake acts as the outlet diversion weir for the Diversion Canal (Aspect 2004a). The weir is currently set at an elevation of 211.15 feet (by the army).

Stormwater runoff from the developed areas of Fort Lewis flows into the Diversion Canal, downstream of the lake outlet. The stormwater runoff is conveyed under Sequalitchew Creek via a culvert near the lake outlet (CH2M Hill 2003b). The Diversion Canal then routes water along the western boundary of the Fort Lewis Landfill No. 5, ultimately discharging into the Puget Sound near the Solo Point Sewage Treatment Plant (Woodward-Clyde 1990).

A series of weirs controls lake level and flows to the Diversion Canal and Sequalitchew Creek (Figure 6). At low lake levels, an adjustable height weir directs flows from the lake to Sequalitchew Creek, and at higher lake levels, lake outflow enters the Diversion Canal (CH2M Hill 2003c). To maintain flows in Sequalitchew Creek, a second weir structure prevents Sequalitchew Creek waters from flowing into the Diversion Canal. Beaver dams located downstream of the lake outlet can cause Sequalitchew Creek waters to back up, causing more water to flow into the diversion canal and reducing the flows to the creek (CH2M Hill 2003c).

Canal Discharge

Discharge data measured by CH2M Hill (2003c) and Aspect (2004a) indicate that much higher discharge flows through the Diversion Canal in comparison to the Sequalitchew Creek discharge. The average monthly discharge ranged from 2.0 to 21.9 cfs from December 1999 to November 2002 at Wharf Road (CH2M Hill 2003c) and from 1.5 to 11.3 cfs from May 2003 to October 2004 at the Diversion Weir (Aspect 2004a) (Table 1). In addition, daily winter storm discharge was measured as high as 40 to 50 cfs (CH2M Hill 2001). Aspect (2004a) also measured the discharge at three locations in the Diversion Canal to determine whether it was gaining or losing discharge. Aspect (2004a) determined that the first reach between the diversion weir and DuPont-Steilacoom Road gains discharge while the next two reaches lose flow at relatively constant rates.

Water Quality

A discussion of Diversion Canal water quality was not included in the original mine EIS (City of DuPont 1993). However, as a part of the baseline monitoring for the project, water quality samples were collected on a monthly basis in the Diversion Canal from September 1999 through




September 2000 (Table 4). Samples were analyzed monthly for dissolved oxygen and water temperature, and quarterly for conventional parameters and metals (Table 4). The analytical results indicate that the waters of the diversion canal generally have good quality, with the exception of elevated water temperatures during the late spring through early fall. During the monitoring period, state criteria were met for dissolved oxygen, fecal coliform bacteria, pH, and turbidity. A continuous temperature gauge was installed in July 2000, which recorded daily water temperatures through August 2002. Water temperatures exceeding the state criterion were measured during July, August, and September of 2000.

Additional temperature and dissolved oxygen data were collected in the Diversion Canal as part of continued project monitoring (CH2M Hill 2003c). The continuous recording temperature gauge recorded numerous exceedances of the state temperature criterion (16°C) during May through September 2001 and from late April through August 2002 when the continuous gauge was removed (CH2M Hill 2003c). In addition, three dissolved oxygen measurements were recorded during the summer of 2002 which did not meet the state minimum criterion of 9.5 mg/L (CH2M Hill 2003c).

Sequalitchew Creek Springs Several springs discharging from the Vashon aquifer are located along the north and south banks of the Sequalitchew Creek ravine, south of the existing mine and proposed mine expansion area. One major spring located on the north bank and two smaller seeps located along the south bank were sampled as part of the original mine EIS studies (City of DuPont 1993). The results of this monitoring indicate that the spring waters are of good quality (City of DuPont 1993). No new spring water quality or discharge data have been collected since completion of the original mine EIS. Similar to Sequalitchew Creek, elevated nitrate-nitrogen concentrations have been measured in these springs (City of DuPont 1993).

Near-Shore Springs Several near-shore springs are located along the Nisqually Reach of Puget Sound, adjacent to the western boundary of the existing mine site. Spring discharges originate from the DuPont Delta aquifer (CH2M Hill 2001). The largest spring (Large Beach Spring) is located in the intertidal zone approximately 1,600 feet north of the mouth of Sequalitchew Creek (Figure 1). This large spring enters Puget Sound at approximately 4 feet above mean lower low water (MLLW). Discharge data in the original mine EIS characterized the discharge from this spring as ranging from 11 to 18 cfs, depending on tide height (City of DuPont 1993). More recent data (CH2M Hill 2001) measured discharges of 9.1 and 14.9 cfs during September 1999 and August 2000, respectively. Several smaller near-shore springs, located about 600 feet north of the large spring, had discharge that ranged between 0.05 and 0.24 cfs (CH2M Hill 2001).

Based on the water quality data results presented in the previous mine EIS, waters of the large near-shore spring generally exhibit good quality (City of DuPont 1993). Significantly high




concentrations of sodium and chloride in addition to high specific conductivity measurements reported in the original mine EIS were attributed to saltwater intrusion into the spring (City of DuPont 1993). Salinity data were collected once in 1999 as part of the North Sequalitchew Creek project in the large beach spring and two smaller springs (CH2M Hill 2001). Salinity in the large beach spring was 5.3 parts per thousand (ppt), and was 7.7 ppt and 15.3 ppt in each of the smaller springs.

Kettle Wetland

The Kettle Wetland, located in a large closed depression (a geologic feature called a kettle) near the center of the existing mine site, is approximately 2.5 to 3 acres in size (CH2M Hill 2001) (Figure 1). This wetland is located within the Sequalitchew Creek drainage basin and is in hydrologic continuity with the Vashon aquifer, where the surface water level is an expression of the ground water table at that location (CH2M Hill 2003b). Based on the water quality data presented in the previous mine EIS, the Kettle Wetland has fair to good water quality (City of DuPont 1993).

Water levels in the kettle fluctuate seasonally, from 1-2 feet during the summer to 4-6 feet during the winter. The open water component width also varies seasonally from 50 feet during the summer to several hundred feet during the winter. Water levels in the wetland were monitored intermittently by CH2M Hill at a staff gauge installed in the wetland in 1999 (CH2M Hill 2003a). Monthly water level data from July 1999 to October 2002 are presented in Figure 7. During monitoring, water levels reached peak levels during the wet season (November through June) and tended to drop with decreasing precipitation, especially during late summer and early fall. At the staff gauge location, water levels over the monitoring period ranged from a high of 6.22 feet in December 1999 to the soil surface (0.63 feet) in October 1999.

Old Fort Lake

Old Fort Lake is a small kettle lake located south of Sequalitchew Creek and the proposed mine expansion area (Figure 1). The lake is located on the former DuPont Works Site now owned by the Weyerhaeuser Company. The lake is located in a kettle, and is supported hydrologically by the shallow Vashon aquifer. Thus, lake water levels fluctuate seasonally and are a reflection of the ground water table at this location. Old Fort Lake water quality data were not summarized as part of the original mine EIS and water quality data were not collected in Old Fort Lake as a part of the North Sequalitchew Creek Project.

Pond Lake Pond Lake is a surface water, isolated, kettle depression wetland that is approximately 1.8 acres in size located south of the Sequalitchew Creek (WSA 2005). Pond Lake is located between




Center Drive and Strickland Lake (Figure 1). Although Pond Lake has no surface water connections to other surface waters, it is apparently connected with ground water and its surface fluctuates throughout the year based on the local ground water elevation (WSA 2005). Pond Lake water levels fluctuate greatly; and lake periodically dries out for extended periods of time, such as, in 2001 and 2004 (WSA 2005). Pond Lake dries out completely at a ground water surface elevation of approximately 201 feet above sea level. Pond Lake water quality data were not summarized as part of the original mine EIS and water quality data were not collected in Pond Lake as a part of the North Sequalitchew Creek Project.

Brackish Marsh The brackish marsh is a one-half acre wetland located in the estuary of Sequalitchew Creek (Figure 8). The brackish marsh is situated on the southwest side of the main Sequalitchew Creek channel on the landward (upstream) side of the BNSF railroad berm (Figure 8). Historical records indicate that the Sequalitchew Creek estuary was once an open embayment along Puget Sound which would have had a tidal wetland fringe. Historical land use beginning with construction of the railroad embankment and upland development, led to gradual infilling of the Sequalitchew estuary, allowing emergent vegetation to become established. Infilling has further transformed emergent wetlands to upland vegetation.

Historical Geomorphic Conditions Early survey maps from the late 1880s and 1908 show Sequalitchew Creek draining into a small embayment along the coast of Puget Sound at the present location of the brackish marsh (Figure 9). Although construction of the railroad berm in 1912 isolated the mouth of Sequalitchew Creek from Puget Sound (Andrews and Swint 1994), sedimentation from deforestation of the basin likely initiated filling of the estuary, which probably consisted of a shallow embayment with intertidal mudflats and wetlands partially separated from Puget Sound. Topographic maps prepared after construction of the railroad embankment indicate the remnants of the embayment still existed in 1939 and 1947 as an open-water lagoon behind the railroad embankment (Figure 9). Aerial photography from 1990 and recent field reconnaissance indicate that considerable filling of the former embayment during the late 1900s transformed the saltwater lagoon into the current brackish marsh.

Existing Geomorphic Conditions The brackish marsh drains through a dendritic network of tidal channels that flow away from Sequalitchew Creek and merge into a main tidal channel, which then runs north along the railroad embankment and joins the creek at the box culvert entrance (see Figure 8). The hydrology and water level of the brackish marsh are tidally influenced by Puget Sound (Anchor 2004c). When the tide is 8 feet above mean lower low water (MLLW) or lower, flow in Sequalitchew Creek remains within its channel and bypasses the brackish marsh directly to the




box culvert (Anchor 2004c). When the tide rises to 9 feet above MLLW, salt water inundates the main tidal channel and fresh water from Sequalitchew Creek flows into the main dendritic channel of the marsh (Anchor 2004c). When the tide reaches 10 feet above MLLW or higher, the brackish marsh is completely inundated (Anchor 2004c).

Because the elevation of the culvert is within the intertidal zone, fresh water and sediment from Sequalitchew Creek are temporarily impounded behind the railroad embankment during high tide (Anchor 2004c). The impoundment creates conditions for the settling of fine-grained sediment throughout the brackish marsh within the area of inundation, as well as deposition of coarse bedload sediment where the creek enters the impounded area at the upper end of Reach 4. Significant quantities of sediment have historically been deposited and retained in the brackish marsh. During low tide, there is generally sufficient shear stress within the creek channel to move sediments deposited during high tide out to Puget Sound. Deposition within the brackish marsh is most likely to occur during high creek flow and high tides. These periods of deposition contribute to the ongoing aggradation of the brackish marsh. Field reconnaissance conducted by Herrera in February 2005 observed gravel splay deposits emanating from the main-stem channel and covering portions of the marsh surface (Figure 10). The combination of historical survey records and recent observations of coarse-grained alluvium several feet above sea level (in the area of the former salt water embayment) indicate historical sedimentation and filling of the wetland within the brackish marsh.

The current valley morphology and channelization of the creek into alluvial fan deposits is consistent with the sedimentation predicted by the declining shear stress simulated within the lower ravine and brackish marsh. HEC-RAS modeling conducted by Herrera of the mean high water (MHW) (approximately 9.5 feet North American Vertical Datum [NAVD], 13.5 feet above mean lower low water, see above), indicates that aggradation below Station 8+00 is tidally influenced, particularly when high tide coincides with significant sediment transporting events. Mean higher high water elevation to the 1988 NAVD is 10.5 feet and the highest observed water was 13.9 feet (at Olympia).

During April 2004, salinity in the brackish marsh and the lower Sequalitchew Creek reach was monitored on two separate occasions (Anchor 2004c). The salinity was measured at several stations during low and high tides, including an ebb tide during the second monitoring event (Table 5). The mid-depth salinity in the Sequalitchew Creek channel (SQ-1 through SQ-7) ranged from 0.1 to 27.6 ppt while the main dendritic channel (SQ-12, SQ-16, and SQ-17) mid-depth salinity ranged from 1.9 to 27.3 ppt. In general, salinity in the Sequalitchew Creek channel remained low (0.1 ppt) unless it became inundated with saltwater. The main dendritic channel tended to exhibit much higher salinity concentrations, especially during low tide periods when the marsh was not inundated with saltwater (Anchor 2004c).

Nisqually Reach (Puget Sound)

The Nisqually Reach of Puget Sound separates Anderson Island from the Nisqually Delta and borders the western shoreline of the project site. Water circulation in the Nisqually Reach is




determined by a complex mixture of forces, including tides, freshwater inputs, and winds (City of DuPont 1993). The Nisqually Reach hydrologic characteristics and water quality were described in the original mine EIS (City of DuPont 1993).

The Nisqually Reach is designated as an extraordinary marine water by Washington State Department of Ecology (Ecology 173-201A-085) (Table 6). Ecology has established several ambient water quality monitoring stations in the Nisqually Reach. The station used to characterize Nisqually Reach marine waters in the original mine EIS (Station Id: NSQ001) has not been monitored since July 1996. More recent water quality data are available from a nearby station in the reach (Station Id: GOR001) and are used to update the following water quality characterization (Ecology 2005). This station is located in Pierce County, just north of Anderson and Ketron Islands (Figure 1). The water quality data collected at this station from 1996 through 2002 are summarized in Table 7. Data collected in 2001 and 2002 are provisional and have not been finalized (Ecology 2005). Data were gathered at 0.5, 10, and 30 meters from October 1996 to January 2000 and thereafter, were collected from depths of approximately 1, 10, and 30 meters (Ecology 2005b).

Monitoring data indicate that marine waters of the Nisqually Reach have fair to good quality. During sampling, reach waters met state extraordinary criteria for pH and fecal coliform bacteria. However, the state extraordinary water temperature criterion (13°C) was exceeded 29 times during the late summer and fall (July through October). In addition, 45 dissolved oxygen measurements during the monitoring period did not meet the state minimum criterion of 7.0 mg/L. Because turbidity was not monitored, compliance with this standard is undetermined.

The Nisqually Reach/Drayton Passage area is on Ecology’s final 2004 303(d) list of threatened and impaired waterbodies for violations of the state standards for fecal coliform bacteria, dissolved oxygen, pH, ammonia-nitrogen, and temperature (Ecology 2005a). The Nisqually Reach/Drayton Passage area was also listed for fecal coliform bacteria on the 1996 list, but was not placed on the 1998 list (Ecology 2005a).

Ecology has initiated a South Puget Sound Model Nutrient Study (SPASM), which addresses concerns of eutrophication in South Puget Sound. However, to-date a TMDL (and proposed clean-up action) has not been established for the Nisqually Reach addressing the fecal coliform bacteria listing (McKee 2005). Ecology completed a quality assurance project plan for the Henderson and Nisqually TMDL Study that summarizes the existing Nisqually Reach data and presents a TMDL evaluation project design (Sargeant et al. 2003). That report will serve as a background study for establishing the Nisqually Reach TMDL. Several excursions beyond the criterion for dissolved oxygen at station NSQ001 were identified on Ecology’s 1998 303(d) list; however, these excursions were found to be a result of natural causes and no formal listing was made (Ecology 1998).




3.0 Significant Impacts of the Proposed Action

Construction Construction activities associated with the proposed mine expansion would include site clearing and grading, excavation of soils for the construction of North Sequalitchew Creek, pedestrian bridge construction (over North Sequalitchew Creek), access road construction (culvert placement), and conveyer system construction. All mining operation and processing facilities were constructed as part of the original mine facility and are not located within the proposed 200-acre mine expansion area. Impacts from the construction of these facilities are described in the original draft and final EIS for the mine (City of Dupont 1992, 1993). No additional facilities would be constructed in either the new mine expansion area or in the processing area that is already in operation with the existing permitted mine.

Glacier Northwest proposes dewatering to accommodate excavation and sand gravel extraction below the existing ground water table. The proposed dewatering plan would require the installation of a series of dewatering wells to pump and drawdown the Vashon aquifer so that excavation could occur under mostly dry conditions. Ground water would be discharged into Sequalitchew Creek at the approximate location of the proposed confluence with North Sequalitchew Creek (RM 0.8). During construction, the mining operations would remove the Vashon drift unit, located within the proposed mine expansion area. (See the ground water technical report for the discussion of impacts to ground water quality and quantity (PGG 2005).

Stormwater Management

A sediment pond and an infiltration pond would be used during construction (and operation) for the discharge of on-site stormwater (CH2M Hill 2003c). The sediment pond would be sized to treat up to the 10-year storm event and to treat ground water base flow (i.e., approximately 10 cfs) not captured by the dewatering wells (CH2M Hill 2003c). The infiltration pond would be sized to store and infiltrate the 100-year, 24-hour storm, including the 10 cfs of possible ground water baseflow (CH2M Hill 2003c).

During mine excavation, stormwater runoff and some ground water baseflow would accumulate in the bottom of the active excavation pit. This pit would be graded to allow for the captured water to collect at a low point, which would serve as a temporary sedimentation pond. If necessary, the collected water would be pumped to an on-site infiltration pond for discharge to ground water.

Current mining activities are covered under a Surface Mining and Associated Activities General Permit (WAG-50-1178) as part of the Ecology NPDES permit program. This permit covers the discharge for process water and stormwater associated with sand and gravel operations. Coverage under this permit allows for discharges to waters of the State of Washington subject to permit conditions under both the construction and operational phases of mining.




Site Clearing and Grading

Mine expansion area clearing and grading would be phased with mining and construction activities to minimize the area cleared at any one time. Site clearing and grading would consist of the removal of the topsoil and stockpiling this material on-site for re-use during site reclamation after mining operations have ceased.

An Erosion and Sedimentation Control (ESC) Plan would be prepared as part of the Stormwater Pollution Prevention Plan (SWPPP) completed for the proposed mine expansion as a requirement of the mine NPDES permit. With the employment of proper and usual ESC measures, impacts to receiving waters during clearing and grading are expected to be negligible. ESC measures outlined in this plan would minimize or eliminate impacts by providing adequate treatment through the use of best management practices during site clearing and grading. Sediment and erosion ESC measures proposed for the mine expansion area include:

Wetting roadways as necessary with water for dust control Truck wheel washing prior to off-site travel On-site infiltration of stormwater.

Within the mine expansion area, construction would remove vegetative cover and expose soils leaving this area prone to erosion during runoff events. The rate of surface water runoff from these areas could increase due to compaction of soils and lack of vegetative cover. If sediment enters any water resources, increases in turbidity, suspended solids, and settleable solids could occur. However, all storm water runoff on-site would be infiltrated to the shallow ground water aquifer, and not reach Sequalitchew Creek (via surface flow). Therefore, impacts to surface water resources are not expected.

Oil, grease, and total petroleum hydrocarbons (TPH) could leak or spill from construction equipment or petroleum product storage facilities. If an uncontrolled spill occurred, there would be the possibility that petroleum products could reach ground water under the construction area. These products could pose a risk to water quality at high concentrations. Release of petroleum hydrocarbons from heavy mining equipment and haul trucks is a significant concern to ground waters, but can be prevented by mitigation measures such as strict prohibition of oil/fueling dumping and contractual specification’s for accidental spill response and notification requirements, and catchment control of parking/staging areas for construction equipment. The mining SWPPP would include an Emergency Spill Cleanup Plan that outlines specific best management practices (BMPs) as they relate to accidental spills of fuel and oil and clean up provisions for any contaminated soils and construction waste.

North Sequalitchew Creek Construction

Construction of North Sequalitchew Creek would begin in the northern section of the proposed mine, then proceed to the south along the eastern property boundary of the proposed mine expansion area. Early phases of mining (approximately the first five years) would include the construction of 4,000 feet of North Sequalitchew Creek.




During stream construction, an impoundment berm would be constructed at the southern most end of the new stream channel, near its proposed confluence with Sequalitchew Creek, to collect runoff and ground water seeping from the materials during excavation and mining. This impoundment berm would remain in place during channel excavation to prevent turbid water and sediment from entering Sequalitchew Creek.

As mining operations remove sand and gravel, the stream channel and riparian buffer area for North Sequalitchew Creek would be excavated. The slope above the new stream would be stabilized and planted. After the stream channel is constructed and the vegetation along the slope and within the riparian corridors is established, pumping of the dewatering wells would be reduced. As the pumping is reduced, seeps would develop along the eastern riparian slope face and flow down to the channel. Measures to prevent erosion along this face may include piping this seepage down the face to the stream (CH2M Hill 2003b). The Vashon Drift consists of two aquifers, an upper and a lower aquifer, which are separated by a thin layer of till, and stratified silty ice-contact deposits which act as a confining layer (i.e., aquitard) between the two aquifers. Most of the flow to the new stream would come from the upper aquifer, which consists of top the 30 feet of the seepage face (CH2M Hill 2003b). The lower 40 feet of the seepage face would consist of the lower aquifer, which would have much lower yields (CH2M Hill 2003b). In addition, ground water would daylight within the newly established North Sequalitchew Creek channel along the impermeable Olympia Beds.

As the pumping of the dewatering wells is decreased, the expected flow in North Sequalitchew Creek would increase. As stream flows are established, flow would be monitored for total suspended solids, turbidity, dissolved oxygen, and temperature (CH2M Hill 2003c). Due to the lack of vegetative cover, sediment and fines would likely occur in runoff entering the stream. During this period, the project proposes to route this water to sediment pond(s) for treatment (CH2M Hill 2003c). North Sequalitchew Creek will be constructed with a variety of BMPs in place that are intended to protect water quality and meet applicable water quality standards. These BMPs would help reduce fines and suspended sediment that could potentially be transported from North Sequalitchew Creek to the mainstem creek when the two systems are connected.

After the flow into the stream has stabilized, the temporary impoundment berm would be removed, allowing flows from North Sequalitchew Creek to join Sequalitchew Creek. Turbidity levels may be elevated in both streams during the initial flow period when the streams are connected after berm removal. The estimated average monthly discharge of North Sequalitchew Creek in its lowest reach prior to entering the mainstem of Sequalitchew Creek is estimated to range between 6.4 (October) and 8.7 (March) cfs (Anchor 2004d). Water quality for the new stream is discussed below under Operational Impacts.

Sequalitchew Creek

During construction, surface water runoff from the mine expansion area would not discharge directly to Sequalitchew Creek because all storm water runoff would be infiltrated on-site. However, during construction, ground water (Vashon aquifer) in the mining area would be




intercepted by a series of dewatering wells and pumped to Sequalitchew Creek for discharge. The dewatering wells would be used for dewatering the mine expansion area until North Sequalitchew Creek is functioning and intercepts ground water flow. Pumped ground water would be piped from the mine expansion area to the south, down the steep ravine where it would discharge to Sequalitchew Creek via a rock pad and flow dissipater designed to prevent erosion of the ravine hill slope and stream channel. The flow dissipater would be located at approximately RM 0.8, near the proposed confluence of the two streams. The estimated dewatering rates would range from 7 cfs to 15 cfs with an average of 10 cfs (CH2M Hill 2003c). These volumes exceed the current flow in Sequalitchew Creek, where monthly average flows range from 0.2 cfs (September) to 2.9 cfs (March) (Anchor 2004b). However, these dewatering rates are well below the historic peak flows within the stream that occurred prior to the construction of the Fort Lewis diversion canal.

Water Quality

During construction, dewatering water (ground water) would be pumped via pipe(s) to Sequalitchew Creek for discharge. Because mine expansion area ground water quality data were not available, ground water quality data ranges were extrapolated by Pacific Groundwater Group (PGG) from water quality data collected as part of (1) the Landfill No. 5 Remedial Investigation (Woodward Clyde 1990), and (2) the 2002 quarterly ground water monitoring results reported for Landfill No. 5 by Anteon (2002) (PGG 2005). The range of predicted dewatering ground water quality for select parameters are compared to Sequalitchew Creek background water quality data and state surface water quality standards in Table 8. The estimated quality of the existing ground water is generally good (PGG 2005).

Temperature, turbidity, and dissolved oxygen were not estimated by PGG because background data for these parameters did not exist either as part of the Fort Lewis Remedial Investigation (Woodward Clyde 1990) or part of the 2002 and 2005 quarterly ground water sampling at Fort Lewis No. 5 landfill (Anteon 2002; PGG 2005). Further, they are not regulated parameters in state ground water quality standards (Chapter 173-200-040 WAC) (Ecology 1990).

Fecal coliform bacteria are regulated by state ground water standards, but were not sampled as part of the quarterly monitoring of Landfill No. 5 as reported by Anteon (2002). Because this data did not exist, PGG (2005) did not establish a background fecal coliform bacteria concentration for ground water in the vicinity of the site. However, the fecal coliform concentrations in the ground water would likely be low. Near the mine expansion area, there is not a significant subsurface fecal coliform bacteria source (i.e., septic systems, etc.). The City of DuPont (including Northwest Landing) is a sewered community. Further, fecal coliform bacteria do not survive in the subsurface environment for an extended period of time. Fecal coliform bacteria are not expected to exceed the state surface water criterion of 50 CFU/100 ml in Sequalitchew Creek.

During dewatering, the pumped ground water would be cool. In the project test wells, ground water temperatures ranged between 8°C to 12°C (CH2M Hill 2003c), meeting the state surface water standard of 16°C (Chapter 173-201A WAC). Because the dewatering water pumped from




the mine would be cool, it would not adversely impact Sequalitchew Creek water temperatures. Similar to temperature, turbidity is generally not a concern with ground water. The pumped ground water would not be allowed to discharge to Sequalitchew Creek until the wells have been properly purged and developed, and are free of sediment which may have been introduced during well drilling and installation.

The dissolved oxygen concentrations of the dewatering water may be lower than the state minimum criterion of 9.5 mg/L; however, the project proposes to utilize a rock pad and dissipater device that would aerate and increase the dissolved oxygen concentration in the water within in the discharge to meet this state standard (CH2M Hill 2003c).

Based on ground water quality data presented by PGG (2005), both ammonia and nitrate concentrations in the dewatering water would be within background range of the Sequalitchew Creek concentrations measured by CH2M Hill during baseline project sampling (Table 8). The predicted ammonia concentration in the ground water would be low (<0.1 mg/L) and would meet state water quality standards. The estimated nitrate-nitrogen concentration in the ground water would be low, and is expected to range between 0.0005 and 0.02 mg/L, which is lower than the stream background which ranged between 0.28 and 0.82 mg/L (Table 8) (PGG 2005). Nitrate-nitrogen is not a regulated parameter in the state surface water standards, but is a regulated parameter in state ground water standards and state drinking water standards. Both standards set the limit at 10 mg/L (Chapters 173-200-040 WAC and Chapter 246-290-310 WAC, respectively) based on human health concerns.

Monitoring of the dewatering water is a required element of the State’s sand and gravel general National Pollutant Discharge Elimination System (NPDES) permit. The permit requires dewatering discharges to surface water be monitored for turbidity, TSS, pH, temperature, and oil sheen.

During the last phase of construction, the berm between the active mine area and Sequalitchew Creek would be removed to connect North Sequalitchew Creek and Sequalitchew Creek, so that North Sequalitchew Creek discharge can flow into Sequalitchew Creek. During confluence construction, the Sequalitchew Creek channel would be disturbed, likely causing some sediment and fines to enter Sequalitchew Creek waters. Construction measures would employ BMPs to help minimize turbidity and sediment impacts from berm removal and confluence construction. In addition, when flows from North Sequalitchew Creek are introduced to Sequalitchew Creek, sediment from the disturbed channel areas would have the potential to be washed downstream causing temporary increases in turbidity.

Discharge

Based on preliminary work by CH2M Hill (2003c), the estimated dewatering rates would range from 7 cfs to 15 cfs with an average of 10 cfs. Dewatering volumes would exceed the average annual discharge in the stream of 1.4 cfs (from 1999 through 2004) below the proposed confluence of North Sequalitchew Creek (Anchor 2004b). These discharge rates are well below the historic range estimated for Sequalitchew Creek, where the 2-year storm flows were




estimated to range from 40 to 120 cfs prior to construction of the diversion canal by Fort Lewis (Aspect 2004a).

Geomorphology

Increased flows from mine dewatering would affect existing sediment transport processes in lower Sequalitchew Creek. Increased discharge from dewatering of the mine expansion could entrain greater amounts of sediment stored in the ravine bottom. Localized sections of the stream, particularly in Reach 2, already experience bed and bank erosion under the existing flow regime. Likewise, most of Reaches 3 and 4 show evidence of recent sedimentation reflecting insufficient transport capacity and inputs from Reach 2 and local bank erosion within Reach 3. This situation is likely to remain constant in most of these segments even after flows are increased – particularly in Reaches 3 and 4 which would be receiving more sediment from Reach 2. Based on the downstream trend in declining shear stress (i.e., the force exerted on the streambed by the water) reported by GeoEngineers (2004), sediment eroded from Reach 2 would likely be deposited in the upper portion of Reach 3. The resulting sedimentation within Reach 3 would increase the potential for channel migration into unconsolidated and easily eroded sediment along the toe of valley slopes during moderate to large flood events. This in-turn could trigger localized erosion of the hillslopes which could further overwhelm the stream with sediment beyond what the increased discharge would have the capacity to move.

Brackish Marsh Water Quality

The brackish marsh located near the mouth of Sequalitchew Creek would experience increased flows and water levels as ground water is pumped to the mainstem of Sequalitchew Creek (upstream of the brackish marsh) during mine dewatering during construction. Flow increases in the brackish marsh would be similar to those described above for Sequalitchew Creek, where flows in the stream channel could increase by 7 to 15 cfs (average of 10 cfs) during construction dewatering.

This initial increase in flow to Sequalitchew Creek would likely mobilize sediment and fines downstream as the wetted-width of the channel is increased, and as fine sediments and organics are washed downstream (Anchor 2004c). The project proposes to incrementally increase flows to Sequalitchew Creek to limit the amount of erosion upstream in Sequalitchew Creek and downstream deposition within the brackish marsh.

Sediment and fines entering the stream during dewatering activities could have the potential to increase turbidity downstream within the brackish marsh. Turbidity is a regulated parameter in the state surface water quality standards (Chapter 173-201a WAC). During construction dewatering, the project would have to maintain turbidity that is within 5 NTU over the background condition (in Sequalitchew Creek), as identified in the State’s surface water quality standards, unless otherwise specified in construction or mining permits issued for the project.




The increase in the amount freshwater entering the stream could alter the salinity of the water in the brackish marsh (Anchor 2004d). However, salinity is not a regulated parameter in state surface water quality standards for either freshwater or marine waters. Significant changes in salinity could, however, affect the plant and animal communities existing within the marsh. These are discussed in the Plants and Animals section of the SEIS, 3.4.

Geomorphology

Increased flows in Sequalitchew Creek during construction have the potential to impact the geomorphology and ecology of the estuary (Reach 4). The Sequalitchew Creek estuary consists of two distinctive geomorphic process domains: (1) a fluvial corridor along the north side of the ravine occupied by the stream channel, within which freshwater and sediment are not input to the estuary; and (2) a tidal marsh system occupied by a dendritic tidal slough network and salt marsh vegetation, within which salt water from Puget Sound is exchanged twice daily (i.e., a diurnal tide cycle). The confluence of these two geomorphic processes is located immediately upstream of the box culvert inlet. This domain configuration is characteristic of pocket estuaries throughout Puget Sound where fluvial corridors become confined along the perimeter of embayments by natural levees (created by deposition of coarse overbank sediments along margin of stream channels). These natural levees effectively increase the depth of the stream which in-turn increase sediment transport capacity and reduce the probability that tidal marshes are filled and converted to upland by stream sedimentation. The boundary between these two process domains in the Sequalitchew Creek estuary is not well defined. Most notably absent is a distinct levee. Because of this, Sequalitchew Creek has periodically delivered sediment to the brackish marsh with the resulting sedimentation filling portions of the salt marsh wetland.

The confluence of the tidal slough network and stream channel near the outlet to Puget Sound also contributes to sustaining the tidal marsh domain. During low tides, the outflow discharge from the tidal slough network effectively increases the stream discharge and sediment transport capacity in a locale particularly susceptible to sedimentation. The volume of water that enters and leaves between mean lower low water (MLLW) and mean higher high water (MHHW) is referred to as a tidal prism. The greater the tidal prism, the greater the ability of the system to sustain an outlet channel to Puget Sound.

Pocket estuaries in Puget Sound have been able to sustain salt marsh ecosystems for thousands of years through the natural segregation of the freshwater dominated fluvial domain and the saltwater dominated tidal marsh domain. This natural segregation inhibits sedimentation from filling tidal salt marshes and converting them to freshwater floodplains. The process is reflected in the fact that many pocket estuary tidal marshes are underlain by thick deposits of organic peat (created by tidal marsh vegetation) and little or no inorganic sediment representative of stream deposition. While the Sequalitchew Creek Estuary exhibits some of general attributes of an undisturbed pocket estuary, it has undergone rapid, historic infilling uncharacteristic of an undisturbed pocket estuary. Infilling of the Sequalitchew Creek estuary has resulted from historic land disturbance within the watershed and ravine. This historic trend has continued despite the reduced flow regime in the stream and is likely to accelerate if the stream discharge is increased, unless mitigating actions are taken. Implementing changes to the stream that emulate




a natural system (i.e., in-stream wood to trap sediment upstream of the estuary, construction of a low levee between the stream and tidal marsh, and excavation of historic infilling of the estuary to increase the tidal prism and re-establish tidal wetlands) would offset negative impacts. Together with the proposed increase in flow, such measures would result in a net environmental improvement to Lower Sequalitchew Creek and estuary.

The increased discharge from dewatering of the mine expansion could result in more frequent entrainment of sediment stored in the ravine bottom, both through an increase in basal shear stress on the stream bed and primarily through erosion along the margins of the stream where it abuts the sediment wedge along the toe of the ravine slopes. Based on the downstream trend in declining shear stress reported by GeoEngineers (2004b), sediment transported from the upper reaches would likely deposit in Reaches 3 and 4, aggrading the channel bed and the brackish marsh. Sedimentation within the brackish marsh could cause raised ground elevations, lower salinity, and a reduction in tidal flushing. Sedimentation within the marsh would be a significant impact because it would be analogous to filling a wetland and causing a major ecological transformation (i.e., conversion of salt marsh to freshwater floodplain and reduction in the tidal slough network). Ecological impacts to the marsh from increased flows are discussed in the Plant and Animal section of the SEIS.

Morphological adjustments in the ravine caused by increased flow could deliver more sediment to Reach 4 in the short-term. An increase in the bed elevation relative to the top of the existing stream bank would increase the frequency of sediment delivery to the brackish marsh and increase the probability of the stream channel being re-directed through the marsh (similar to the channel change on an alluvial fan or river delta). These changes would contribute to infilling of the brackish marsh. Additional fine sediment delivered by increased flow and held in suspension behind the railroad embankment during high tide, would cause additional aggradation within the brackish marsh. Aggradation would likely be greatest at the upstream end of the brackish marsh, and, with sustained sediment supply, continue on toward the railroad embankment through time. Sedimentation and accumulation of LWD within or directly upstream of the box culvert would eventually diminish conveyance between the brackish marsh and Puget Sound, further reducing the tidal prism. A reduction in tidal prism would decrease sediment transport capacity through the culvert despite added instream flows from North Sequalitchew Creek. This could further accelerate marsh infilling and associated impacts in Reaches 3 and 4. Monitoring of sedimentation rates within the stream channel and brackish marsh (Reaches 3 and 4) are recommended as part of project mitigation (see Mitigation Measures).

Access Road and Pedestrian Bridge Construction

Construction of access roads and the pedestrian bridge (over North Sequalitchew Creek) within the proposed gravel mining area would have no impacts on surface water resources in the vicinity of the project. The access roads and pedestrian bridge would be constructed prior to the operation of North Sequalitchew Creek when there is no flow within the stream channel. In addition, the berm separating the North Sequalitchew Creek construction activities and Sequalitchew Creek would be in place during construction of these features. The two access




road crossings of North Sequalitchew Creek would consist of bottomless box culverts. The pedestrian bridge would be constructed near the mouth of North Sequalitchew Creek, but prior to its connection with the mainstem of Sequalitchew Creek, thereby not impacting Sequalitchew Creek.

Conveyer System Construction

Construction of the conveyer system would not impact surface water resources. The conveyer system would not be constructed near any on-site or off-site water resources. Similar to other areas of the mine, stormwater runoff would be routed to a sedimentation pond and then to an infiltration pond, for discharge.

Operation

Operation activities associated with the mine expansion area would include mining, processing and shipping. Operation impacts associated with the processing plant, concrete facilities, barge loading facility and shipping were discussed in the original EIS (City of DuPont 1993) and subsequent SEIS (City of DuPont 1995). With the addition of the new mine expansion area, the types of impacts from operating these facilities would not differ from what was previously described in the original EIS (City of DuPont 1993) and the subsequent SEIS (City of Dupont 1995). However, the life of the mine would be extended by approximately 8-12 years while the expansion area is mined.

Mining and Processing

Glacier proposes to capture ground water entering the mine expansion area from the east and convey it off-site to Sequalitchew Creek via North Sequalitchew Creek, the newly constructed stream channel. Construction of this stream is described above in the Construction Impacts section. This new stream would be designed to create new fish habitat and increase flows in the lower mainstem of Sequalitchew Creek, thereby improving the existing aquatic habitat.

North Sequalitchew Creek

During the operational phase of mining, North Sequalitchew Creek would intercept ground water and allow mining excavation to occur under generally dry conditions. This newly constructed stream channel would replace the ground water intercept function provided by the dewatering wells during construction. The new stream channel would have a low gradient (0.5 percent) and a channel length of approximately 4,000 feet (Anchor 2004a). A detailed description of North Sequalitchew Creek is provided in the Fisheries Technical Report (Herrera 2005b).




Water Quality

Water quality data for North Sequalitchew Creek were predicted using data collected as part of the Landfill No. 5 Remedial Investigation (Woodward Clyde 1990) and as part of the 2002 and 2005 quarterly monitoring results of the landfill reported by Anteon (as cited in PGG 2005) and are listed in Table 8. The estimated quality of North Sequalitchew Creek would be good. The data presented in Table 8 indicate the stream would likely meet applicable state standards for metals, pH, and fecal coliform bacteria. However, dissolved oxygen, temperature and turbidity initially may not meet state water quality standards in the newly constructed stream because of the lack of mature riparian vegetation and the physical design of the stream channel. However, the project proposes corrective actions that would be taken to assure the newly constructed stream meets applicable water quality standards and such measures are described below (CH2M Hill 2003c).

Unlike the dewatering discharge to Sequalitchew Creek during construction, (which proposes to utilize a rock pad and dissipater to promote aeration), discharge from the seeps and springs to the new stream would occur as sheet flow or shallow channel flow, which initially may not introduce enough oxygen to the water to meet the state minimum criterion of 9.5 mg/L (Chapter 173-201a WAC). The proposed design of North Sequalitchew Creek would include elements, which would help aerate the water, to meet the state surface water quality standard. If dissolved oxygen is not meeting the standard, structural measures would be taken to introduce oxygen to the stream waters, such as constructed log weir drops in the stream channel to promote aeration (CH2M Hill 2003c).

Because the source of flow in North Sequalitchew Creek would be ground water seeps, water temperatures would be cool. However, during the initial operation, stream temperature could be a concern because the vegetation in the riparian corridor would not be fully established to provide adequate shading of the stream channel, especially during the dry season. Therefore, warming could occur. The stream design flow rate would be 1 foot per second (fps) (CH2M Hill 2003c) and at this flow rate the residence time in the stream would be approximately 3 hours which would allow for an increase in water temperature to occur. The planting design would initially include the installation of willows along the riparian corridor which would grow relatively quickly to provide shade. As with dissolved oxygen, water temperature in the new stream would be measured for compliance to the state standard prior to final stream construction and when flows are initially allowed to enter Sequalitchew Creek. Based on the preliminary design of this stream, water temperatures of 10°C to 14°C would be achievable in the new stream (CH2M Hill 2003c).

Even after bank and channel stabilization, sediment and fines may still enter the new stream. Because North Sequalitchew Creek originates from ground water, this source would generally be free of silt and sediment. However, as the ground water daylights onto the steep slopes above the channel and travels via overland flow to the stream below, flows would likely transport sediment and fines and deposit this material into the stream. The sediment could either settle to the bottom or be carried downstream. However, because the gradient of the new stream is relatively flat and the proposed velocities are low, the opportunity for flushing these fines and




sediments from the stream are low. As a result sediment build-up could occur and adversely impact salmon spawning areas in the new channel.

Because the stream would function as a dewatering channel during mining operations, it would be monitored per the requirements of the sand and gravel NPDES permit issued for the mining operation. Currently, the State general permit requires that dewatering water (North Sequalitchew Creek) that discharges to a surface water (i.e., Sequalitchew Creek) must be monitored for turbidity, TSS, pH, oil sheen, temperature, and flow.

Hydrology

Predicted flows in North Sequalitchew Creek were determined using the ground water modeling completed as part of the project (Aspect 2004a, 2004b; CH2M Hill 2003c). Based on the best estimate for average annual conditions, the predicted flow of North Sequalitchew Creek just above its confluence with Sequalitchew Creek would be 7.6 cfs Anchor 2004d) (see Table 9). Taking into account the sensitivity analysis of the ground water model, the best estimate for predicted average annual instream flows could range from 6.4 to 9.8 cfs at the confluence with Sequalitchew Creek (Anchor 2004d). The predicted low flow within the channel is 4 cfs (Ellingson 2005).

Hydraulic Modeling

CH2M Hill conducted hydraulic modeling of the proposed design for North Sequalitchew Creek using the U.S. Army Corps of Engineers HEC-RAS model which simulates the hydraulics of streams and open channel systems. The model was used to determine how different stream discharges would alter the stages and velocities within the channel and, in turn, what their affect would have on the riffle and pool depths of the proposed design. The sensitivity analysis involved running the model for 2, 4, 6 and 8 cfs. This range of flows includes both the low flow and average flow conditions and was conducted to analyze the proposed stream design stages and velocities at these different flow rates. For each flow rate in the modeled range, specific cross sections along the stream channel were selected for analysis. Based on the model results, modifications were then made to the channel geometry until the desired water depths and velocities were achieved within the channel for optimal fish habitat (CH2M Hill 2003c).

For the selected flow range 2, 4, 6, and 8 cfs, water depths in the riffle sections would range from 0.8 to 1.4 feet, with discharge ranging from 0.9 to 1.9 cfs (CH2M Hill 2003c). However, the model results for 2 cfs calculated a riffle depth of 0.3 feet, which would not meet the criteria for spawning habitat (CH2M Hill 2003c). Modeling results for the pool sections show that the water depths would range from 2.4 feet to 3.3 feet with a discharge ranging from 0.1 to 0.3 cfs (CH2M Hill 2003c). In addition, the stream predesign report completed in 2003 by CH2MHill (2003c), a depth of 1.5 feet for the central portion of the stream channel is sufficient to convey the 2-year flow and the floodplain would be able to accommodate the 100-year flow of 30 cfs (flows analyzed were based on the previous ground water modeling results).




Based on the most recent stormflow analyses for the 2-year, 5-year, 10-year, 25-year, 50-year and 100-year events, flows modeled within the channel ranged from 11.3 (2-year event) and 25.8 cfs (100-year event) (Anchor 2004d). The channel geometry modeled was similar to that used previously by CH2M Hill in their HEC RAS model analysis (Anchor 2004d). Anchor’s modeling results indicate that the highest water velocity value is found in the lower 1,000 feet of proposed stream channel (Station Id. 535.6). Model results show that the water velocities spike for sections modeled as rock vortex drops, such as Station Id. 535.6 (Anchor 2004d). Modeling results show that with the 2-year event, the predicted average velocity at this station (3.01 feet/second) would be sufficient to sort gravel (Anchor 2004d). This average velocity would not erode the channel banks or the thalweg (Anchor 2004d). The average velocity for the 100-year event would also occur at this same location and would be 4.53 feet/second (Anchor 2004d). Modeling results indicate major structural features in the channel would be stable at the 100-year event.

Geomorphology

North Sequalitchew Creek is the new stream channel that would be created as part of the proposed gravel mine expansion. The purpose of the new stream is to manage ground water entering the mine site while creating new riverine habitat. In order to reduce infiltration of surface water, the stream bed would be installed in the low-permeability Olympia Beds. A description of the proposed new stream channel is provided in three reports (Anchor 2004a, 2004d; Herrera 2005b) completed for the project and is summarized in the paragraphs below.

North Sequalitchew Creek would be approximately 4,000 feet long and would drop approximately 39 vertical feet in elevation between the headwaters and the confluence with Sequalitchew Creek. This configuration would provide an overall channel gradient of 1 percent, although the actual gradient would vary along the new channel alignment based on the elevation of the Olympia Beds beneath the proposed channel. Based on boring logs in the area, the new stream channel would be divided into three distinct reaches characterized by different channel gradients and habitat features.

The lower reach of North Sequalitchew Creek will be 900 feet long and would be constructed with a 2.0 percent gradient to make this the steepest reach of the new channel. Large boulders and coarse sediment would be used to construct grade control structures and to create a step-pool channel profile. The grade control structures would also be designed to stabilize the bed and prevent head-cut erosion. Large woody debris would be placed in the channel to promote gravel sorting and habitat diversity.

The middle reach would be 1,100 feet in length with a gradient of 1 percent. The elevation drop through the middle reach would occur over riffle segments constructed from coarse sediment. Each riffle segment would be located between channel bends and pools to create a meandering pool-riffle channel. Large woody debris and boulders would be used to provide gravel sorting, energy dissipation, and habitat function. Habitat features in the middle reach would be designed to enhance fish rearing functions.




The upper reach would be constructed at a relatively low gradient of 0.5 percent and extends 2,000 feet above the middle reach. The upper reach would include side channels designed to provide rearing and over-wintering habitat for salmon (cutthroat and coho). Side channels would be constructed at locations that optimize perennial flow from seeps and interconnections with the main channel.

The width of the new stream channel would vary between 10 and 20 feet and be constructed in a 40- to 50-foot wide floodplain corridor. Coarse, rounded sediment would be placed along the edges of the stream corridor. The coarse sediment would extend vertically from the top of the Olympia Beds to above the anticipated maximum flood stage and would control the width of the meander belt. The bed of the new channel would be seeded with sand and gravel appropriately sized to emulate natural sediment transport processes and the formation of habitat features. Pool formation and meander development would be encouraged by the placement of large woody debris and engineered log jams.

Grading required for the construction of North Sequalitchew Creek would result in a 75-foot-high slope on the east side of the stream. Slopes would range from 3H:1V (18 degrees) to 2H:1V (27 degrees) along the lower and upper reaches, with locally steeper slopes as steep as 1H:1V (45 degrees). The proposed slope angles are comparable to the naturally formed slopes above the Olympia Beds in the ravine of the mainstem Sequalitchew Creek. Slopes within the existing ravine range from 4H:1V to 2H:1V, with local areas as steep as 1.2H:1V. In addition, the natural variability in slope angles exhibited by the existing ravine suggests the morphology of the lower Sequalitchew Creek is controlled by the spatial variability in local material properties. It is expected that slope adjustments would occur along North Sequalitchew Creek and these adjustments would likewise have an impact on stream morphology and turbidity. While these impacts can be minimized with aggressive reforestation, they are unavoidable and the new stream channel would be regularly monitored for potential impacts resulting from hillslope erosion.

Based on the slope conditions within the existing Sequalitchew Creek ravine, the proposed slopes above the new stream will likely undergo a period of erosional adjustment for an unknown period of time, particularly before vegetation is established on new ravine slopes. Several measures would be implemented to address soil erosion from slopes prior to the establishment of vegetation (see the discussion of mitigation measures further along in this report). Hillslope runoff and runon to unstable areas would be diverted by horizontal benches and lined ditches installed on steep slopes. Unstable surfaces would be protected with a coir-mat or comparable erosion control blanket. The blanket would be staked to the ground surface to prevent the formation of gullies beneath the blanket. At a minimum, sloughing of surface material and shallow slope failures are expected to accumulate sediment at the toe of the hillslope (i.e., colluvial wedge), as has been observed in the existing ravine. Sediment stored in the stream floodplain would supply sediment (both fine-grained and essential, coarse-grained spawning gravels) to the stream system at a rate dependent on the supply from hillslopes and the migration rate of the active channel into sediment stored at the toe of the slope.




Sequalitchew Creek Water Quality

Because North Sequalitchew Creek flows into Sequalitchew Creek, the quality of Sequalitchew Creek waters would be influenced by the waters from this new tributary stream. Similar to the analysis presented above for the dewatering well impacts during construction (see Sequalitchew Creek discussion under construction impacts), the expected quality of the ground water source of North Sequalitchew Creek is generally expected to be good.

During the late summer and early fall when low flow conditions occur within the stream, elevated water temperatures and low dissolved oxygen concentrations may occur. During background studies for this project, elevated water temperature and low dissolved oxygen concentrations were measured during the summer which violated state surface water quality standards. With the addition of North Sequalitchew Creek flows, these conditions would still likely occur. However, the increased flows would help to elevate the dissolved oxygen concentrations in the stream by increasing velocities within the channel, which would promote aeration. In addition, instream water temperatures will be maintained by the low temperature ground water flowing into Sequalitchew Creek.

The potential for sediment movement within the channel because of the increase in flow is discussed below under Hydraulic Modeling.

Hydrology

The existing hydrology of Sequalitchew Creek would change because of the reduction of ground water input to the stream and addition of North Sequalitchew Creek flows. The North Sequalitchew Creek channel would intercept ground water which, under the existing conditions, partially flows into the mainstem of Sequalitchew Creek. Based on the ground water modeling and actual flow data collected in Sequalitchew Creek (Anchor 2004d), stream discharge would be reduced by about 0.5 cfs (from 1.0 cfs to 0.5 cfs) in the reach upstream of the proposed confluence of North Sequalitchew Creek. However, downstream of the confluence of North Sequalitchew Creek, the average annual stream discharge in the mainstem would increase by 6.7 cfs (Table 9).

The ground water model predicts that the average annual flow of North Sequalitchew Creek at its confluence with the main stem Sequalitchew Creek would be 7.6 cfs. The 7.6 cfs would combine with the 0.5 cfs in the mainstem resulting in an average annual flow of 8.1 cfs in the mainstem below the confluence (Anchor 2004b). This average annual flow represents an increase over the existing condition of approximately 6.7 cfs. The 2-year storm flow event in Sequalitchew Creek would result in flow of approximately 20.2 cfs including 10 cfs from North Sequalitchew Creek during the 2-year event (Table 10).

Hydraulic Modeling

A shear stress analysis was performed (GeoEngineers 2004b) to evaluate changes in sediment transport and depositional processes within the lower stream under the proposed flow conditions.




The shear stress analysis followed the same methodology described for existing conditions. The critical shear stress for initial entrainment of the streambed was scaled using the median particle size of the bed. Additional transport of fine sediment can occur from an armored bed or fine-grained patches before the armor layer is fully disturbed. The shear stress analysis also simulated conditions for sediment deposition of different particle sizes when the modeled shear stress dropped below the critical shear stress. Sediment deposition in a particular reach assumes that sediment is already in transport in the upstream reach.

Hydraulic modeling indicates the higher flow rates would result in correspondingly higher flow depths, channel velocities, and boundary shear stresses than for existing conditions. The average water surface elevations are expected to increase from 2.2 to 4.0 inches throughout the ravine, with the local maximum depth reaching 6 inches in Reach 2.

Relative trends in sediment transport and deposition in Sequalitchew Creek have been evaluated for the proposed conditions by comparing the ratio between shear stress and the critical shear stress required for bed entrainment. A comparison of existing conditions and proposed conditions are shown for the 100-year storm event (Figure 1). Results of the shear stress analysis indicate the upstream portion of Reach 1 would remain relatively stable under proposed conditions. Bed erosion is likely to continue in Reach 2, where shear stress under proposed conditions would be greater than the critical shear stress. Despite increases in flow, results indicate sediment deposition would continue in the upstream portion of Reach 3. The decline of shear stress through Reaches 3 and 4 to below the critical shear stress would allow continued filling of the brackish marsh under the proposed conditions. In general, increases in shear stress could shift the stream bed erosion thresholds to flow conditions having a lower recurrence interval, which could in turn increase the frequency of sediment transporting events within the ravine and delivery of sediment to the brackish marsh (Reach 4).

Geomorphology

The increase in flow under the proposed conditions has the potential to impact the morphology of Sequalitchew Creek. A comparison of model results between existing and proposed conditions indicate increases in bed erosion would occur at the downstream end of Reach 1 (Figure 12a). The greatest potential for mobilization of the channel bed from increased flows is likely to occur in Reach 2, where shear stress is projected to increase by 40 percent relative to existing conditions. This increase in shear stress is at least in part due to segments of the reach where the channel has been constricted by debris flow and alluvial fan deposits (Figure 12b). Localized increases in shear stress are expected to result in bed incision and/or bank erosion. Results of the hydraulic modeling suggest mobilization of the bed is likely to occur during a 2-year flow event. Depending on the supply and availability of coarse sediment, the increased shear stress is also likely to increase the degree of bed-surface armoring, which would condition the bed and increase the critical shear stress required for future bed mobilization.

Areas of potential adverse change and increase in-stream bed erosion within the ravine were identified (GeoEngineers 2004). The abrupt increase in stream flow and shear stress at the confluence of North Sequalitchew Creek and the main stem (Reach 1, Station 40+50) has the




potential to induce bank erosion and stream bed scour (Figure 13a). The shear stress analysis also identified two erosional and two depositional reaches within Reach 3 (Figure 13b). The coarsest fraction of sediment mobilized from Reach 2 is expected to be deposited near Station 17+00 in response to declining shear stress. Results of the shear stress analysis indicate bed mobilization at the downstream end of Reach 3 would occur during flow events with a greater recurrence interval. The analysis also identified a location near Station 10+30, where the increase in shear stress is approximately 25 percent greater than that for existing conditions. This station is located just downstream of the berm and 10-foot depression, and just upstream of a depositional reach where a reduction in shear stress occurs. The proximity of erosional and depositional reaches indicates the stream channel will respond relatively quickly to an increase in flow. Grade adjustment of the stream will be accompanied by localized channel widening and migration both of which entail bank erosion that will further increase the sediment supply to the stream. At locations such as Station 17+00, bank erosion could lead to a major change in the stream channel if flows gained access to this 10-foot depression along north side of the ravine. If the stream were to flow into this depression, it would significantly change the stream grade and initiate a headcut that would proceed upstream and further destabilize adjacent hillslopes. Sediment produced in the process would rapidly fill the depression. Until the stream readjusted a stable gradient, fish passage and water quality would likely be impacted.

Declining shear stress through Reaches 3 and 4 under the proposed conditions (GeoEngineers 2004b) indicates that the progressive deposition of sediment in the brackish marsh will continue under the proposed conditions. The additional sediment transported to Reach 4 by the increased flows is likely to contribute to the ongoing aggradation of the brackish marsh. Although sediment deposited within the main stem in Reaches 3 and 4 during high tide would likely be entrained during low tide and transported to Puget Sound, fine-grained sediment and gravel deposited within the brackish marsh and dendritic tidal slough network will remain and contribute to gradual infilling of the tidal marsh area.

Kettle Wetland

The Kettle wetland located within the existing permitted mine area would be removed as part of expansion area mining operations. Proposed mitigation for removal of the Kettle wetland is discussed in Plants and Animals section of the SEIS, Section 3.4.

Fort Lewis Diversion Canal/Sequalitchew Lake

Changes in diversion canal water levels were not analyzed as part of the ground water modeling analysis for the project (CH2M Hill 2003b). However, subsequent modeling efforts incorporated the effect of the diversion canal into the ground water model (Aspect 2004a, 2004b). It was determined that most of the Diversion Canal recharges the Vashon Aquifer in the vicinity of the proposed project (Aspect 2004a, 2004b). However, one small reach near the diversion canal weir is a “gaining reach” and is recharged by ground water. Therefore, the proposed project may cause less water to be recharged to the diversion canal along this reach because of the drop in




area ground water levels. The ground water model did not analyze this decrease in baseflow (ground water discharge) to the Diversion Canal under future conditions (Aspect 2004a, 2004b).

Based on a ground water modeling analysis completed in 2004 (Aspect 2004b), Sequalitchew Lake is located outside of the outer boundary of any observable ground water drawdown effect from the project (Figure 14). Based on this analysis, there would be no observable effect on the lake water level or lake water quality from the proposed project.

Old Fort Lake

Because Old Fort Lake is hydrologically supported by the Vashon aquifer, lake water levels fluctuate similar to the changes in the ground water table in the vicinity of the lake. Based on the ground water modeling results, ground water levels could drop by approximately 0.25 feet in the vicinity of Old Fort Lake because of the project (Aspect 2004b).

Based on a ground water modeling analysis completed in 2004 (Aspect 2004b), Old Fort Lake is located outside of the outer boundary of any observable ground water draw down effect from the project (Figure 14). Based on this analysis, there would be no observable effect on the lake water levels or lake water quality from the proposed project.

Pond Lake

Based on the ground water modeling results in 2004, ground water levels could drop by approximately 0.5 feet in the vicinity of Pond Lake (Aspect 2004b) (Figure 14). Based on an analysis of the drawdown effects, in wetlands such as Pond Lake where seasonal saturation and inundation are controlled by the underlying ground water table, surface waters would dissipate two or three weeks earlier in the spring (Aspect 2004a, 2004b; PGG 2005; WSA 2004b). With the regional lowering of the ground water table, Pond Lake is predicted to dry out for longer periods (i.e., when the ground water elevation is less than 201 feet above sea level), and have a lower surface water elevation throughout the year (Aspect 2004b). Impacts to plant communities are discussed in the Plant and Animals section of the SEIS, Section 3.4.

Brackish Marsh Water Quality

The proposed project would increase the amount of flow into the mainstem of Sequalitchew Creek by the 6.7 cfs addition from North Sequalitchew Creek (Anchor 2004d). These flows would also alter the flow regime downstream in the Brackish Marsh which could affect salinity both in the water column and in the underlying soil.

Because the water quality in the newly constructed creek would be within the background range of existing Sequalitchew Creek, no measurable impacts to Brackish Marsh water quality are expected.




As part of background investigations for the proposed project, existing salinity conditions within the marsh (soil and water) were evaluated Anchor (2004c, 2004d). Salinity data were collected as part of background investigations for the proposed project in April 2004 (Anchor 2004c). Salinity data indicate that a freshwater lens exists within the brackish marsh and that highly saline conditions are present in the marsh during flood tide events. Salinity is not a regulated parameter in state water quality standards for either freshwater or marine waters (Chapter 173-201a WAC). Impacts to Brackish Marsh vegetation are discussed in the Plants and Animal Section of the SEIS, Section 3.4.

Geomorphology

Increased flows in Sequalitchew Creek from the new North Sequalitchew Creek have the potential to impact the existing sediment dynamics of the main stream channel (within the brackish marsh) and the dendritic channel network within the brackish marsh, much the same as the conditions described for construction. The increase in stream flows in Sequalitchew Creek upstream of the brackish marsh (contributed by North Sequalitchew Creek) would increase the potential for streambed erosion (GeoEngineers 2004b). Average annual flows in Sequalitchew Creek are expected to increase by 6.7 cfs (Anchor 2004d). Sediment eroded from the upper reaches of the ravine would likely be deposited in Reaches 3 and 4 in response to declining shear stress.

Aggradation in the main channel would increase the possibility of an avulsion and deposition of coarse sediment in the dendritic channel network of the marsh. Avulsion of the channel away from the current alignment could deposit considerable amounts of sediment within the main dendritic channel that runs along the toe of the railroad embankment. A shift in the main stem alignment away from the culvert inlet could accelerate filling of the dendrite channel network and reduction in the tidal prism.

Post-Reclamation Stormwater Management

After mining is complete, the site would be reclaimed and re-vegetated with ground cover that would provide permanent erosion control (CH2M Hill 2003c). A post reclamation stormwater modeling analysis was completed in 2004 (Aspect 2004a). For purposes of this analysis, the expansion area was subdivided into four subbasins (Aspect 2004a), identified as subbasin E1 (13 acres), E2 (34 acres), E3 (68.9 acres), and E4 (24.2 acres) (Aspect 2004a). After reclamation, most stormwater runoff generated within these subbasins would either infiltrate into the ground or flow as overland flow to North Sequalitchew Creek. Subbasin E1 (northern-most basin) would collect stormwater via the subsurface collection system that would daylight at the head of North Sequalitchew Creek. Stormwater runoff from subbasins E2, E3, and E4 would either infiltrate into the ground or flow via overland flow to North Sequalitchew Creek (Aspect 2004a). The total amount of stormwater (excluding ground water) entering North Sequalitchew Creek would range from 3 cfs during the 2-year event to 17 cfs during the 100-year event (Table 11).




Near-shore Springs

The capture of ground water in North Sequalitchew Creek would reduce the amount of discharge in the tidal springs located north of the confluence of Sequalitchew Creek. Based on the ground water modeling results, the ground water component of spring discharge would be reduced by 19 to 25 percent (Aspect 2004d) (Also see the ground water impact discussion for more detail).

Shipping Activities

Operation impacts to marine waters were discussed in the original EIS for dock loading operations and maritime traffic. With the addition of the new mine expansion area, the types of impacts arising from use of the loading dock and transporting gravel off-site via Puget Sound would not differ from what was described in the original mine EIS (City of Dupont 1993). However, because the life of the mine would be extended by approximately 8 to 12 years, the length of shipping activities and associated impacts would be extended over this period of time.

Impacts of the Project Alternative

The proposed Project Alternative will replace the proposed North Sequalitchew creek design with a gravel-filled interceptor ditch and a buried conveyance pipeline 5,000 feet long. The pipeline would be microtunneled approximately 500 feet through the berm between the excavated mine site and Sequalitchew Creek. The discharge point to Sequalitchew Creek would coincide with the proposed confluence of North Sequalitchew Creek (RM 0.8).

Water Resources

The proposed impacts to Sequalitchew Creek with the project alternative would be similar to the proposed action. The water quality of the proposed water discharged to Sequalitchew Creek via the pipeline discharge would have similar water quality as the proposed North Sequalitchew Creek (Table 8). However, water temperatures in the pipeline discharge would likely be lower than with proposed action, because the water will not have been subject to solar heating. In addition, dissolved oxygen concentration of the pipeline water may be lower than if the flows interacted directly with the atmosphere on the surface. With this project alternative, a construction access road would be built from the existing abandoned railroad bed (to the outfall area) to transport microtunneling equipment to the site. Stormwater BMPs would be employed during access road construction and use.

Geomorphology

The Project Alternative is anticipated to have similar effects on flow rates within Sequalitchew Creek as the Proposed Action. The excavated slopes above the interceptor ditch for the Project Alternative will be nearly identical to the excavation plan above the creek in the Proposed




Action. It is possible that fine sediment entering the proposed pipeline would be conveyed more rapidly to Sequalitchew Creek relative to sediment transport within North Sequalitchew Creek under the Proposed Action. Hydraulic roughness provided by pools, riffles, vegetation, and in-stream wood in North Sequalitchew Creek would moderate the supply of fine sediment to Sequalitchew Creek and provide more sediment storage capacity than the Project Alternative. Under the proposed interceptor trench design, sediment delivery to the drainage network from excavated slopes may be less than under the Proposed Action. Assuming the flow dispersion structure at the pipe outfall in Sequalitchew Creek is effective at dissipating energy, impacts to sediment transport and habitat forming processes within the existing creek resulting from the Project Alternative should be similar to the impacts described for the Proposed Action.

Impacts of the No Action Alternative

Under the no action alternative, the proposed mine expansion project would not occur and mining of the existing Glacier site would continue as currently permitted. Potential impacts to surface water resources, water quality, and hydrology would not differ from the impacts that were discussed in the original mine EIS (City of DuPont 1993). Continued diversion of discharge out of Sequalitchew Creek by the Diversion Canal would continue to limit stream hydrology and sediment transport. Erosion within the ravine would continue to supply sediment that cannot be transported out of the system by the limited stream discharge. Reaches within Sequalitchew Creek would continue to aggrade within the ravine, thereby compromising salmonid passage and habitat.

Monitoring and Mitigation Measures

The project proposes to monitor Sequalitchew Creek and the Brackish Marsh for possible impacts from the project prior to implementing possible mitigation measures outlined below. Possible monitoring and mitigation measures, including specific timeframes for monitoring/mitigation efforts, would be refined during the permitting process. Actual monitoring and mitigation measures would be determined by permit conditions and negotiations with the regulatory agencies.

Water Quality Proposed Monitoring

During construction of North Sequalitchew Creek, the project proposes to conduct the following water resource monitoring:

Prior to the surface water connection with Sequalitchew Creek, monitor North Sequalitchew Creek water quality until the stream stabilizes. Stream waters would be monitored for temperature, turbidity, total suspended solids and dissolved oxygen.




Monitor the mainstem of Sequalitchew Creek for possible erosion and turbidity during dewatering activities scheduled for the wet season.

Proposed Mitigation During construction and operation (unless otherwise noted), the following mitigation measures to protect area water resources are proposed:

Provide truck wash basins to minimize the introduction of sediments onto on-site or off- site roadways.

Infiltrate of all stormwater runoff on-site.

Employ stormwater BMPs as outlined in the SWPPP for mining operations.

Construct access road, bridges (bottomless box culverts), and a pedestrian bridge prior to connection (construction only).

Geomorphology Proposed Monitoring Monitoring for changes in channel geomorphology would consist of an annual stream reconnaissance of Sequalitchew Creek (below the proposed confluence) focusing on areas of potential erosion and deposition (as identified by GeoEngineers [2004b] and Anchor [2004d]). Monitoring would include the following:

Document physical changes on the ravine slopes (i.e., slumps and landslides). Monitoring would note size, area and location of these landslides and slumps.

Photo documentation of bank erosion, toe of slope erosion, etc.

Survey longitudinal profiles and/or channel cross-sections where deposition and erosion is likely or evident, or where the consequences of erosion/deposition could be significant.

Document changes in stream bed composition. At a minimum, this would include doing pebble counts at set points throughout the reach at the select cross-sections.

Data would be interpreted to: 1) identify the cause and/or source of the change; 2) determine whether the change is local or systemic in nature; and 3) determine whether mitigation measures should be implemented (Anchor 2004d). If, based on the monitoring results, it is determined that reaches are scouring or aggrading (including the brackish marsh), localized restoration measures could be put in place to ameliorate impacts. Measures such as placement of large woody debris would be an option.




In order to determine if reaches are aggrading or eroding as a result of the proposed project, a baseline monitoring program would be established in Sequalitchew Creek and the brackish marsh prior to project construction. Three years of baseline data in addition to the data collected thus far would be collected at selected transects throughout the four stream reaches (1 through 4). This information would be used to establish baseline rates for comparison during project construction and operation. In addition, prior to project commencement, depositional and erosion thresholds would be established prior to construction based on regulatory guidance (e.g., no net fill in jurisdictional wetlands) and best available science.

Proposed Mitigation Prior to project construction, the topographic depressions (e.g., 10 foot depression at Station 11+00) within the ravine bottom of Reach 3 would be filled with suitable material. This would be done to prevent adverse impacts that would result from the stream channel moving into the depressions (i.e., to prevent impacts, such as head-cutting and incision upstream of where creek enters the depressions). If these depressions are filled, adverse impacts can be avoided, otherwise significant impacts could occur.

Possible Mitigation The following mitigation measures could address potential geomorphic impacts of the project to Sequalitchew Creek if determined due to the monitoring.

Place large woody debris (LWD) in the ravine bottom to: curb erosion of adjacent hillslopes and toe-of-slope sediment wedges, control stream grade and limit head-cutting, trap sediment, increase pool frequency and channel complexity, and accelerate development of forested floodplains within the ravine bottom. LWD installations would be prioritized for those areas where flows currently abut sediment wedges or for hillslopes along the flanks of the ravine and channel segments most susceptible to bed erosion (Reach 2). LWD placement would be done during low flow conditions to ease potential impacts from disturbance in the channel, and to prevent potential adverse project impacts.

Measures to prevent bank and streambed erosion at the confluence of North Sequalitchew Creek should be employed. Measures could include armoring the streambed and banks, and placement of log structures to dissipate flow energy.

Significant Unavoidable Adverse Impacts Proposed Action Water Resources Construction of North Sequalitchew Creek and operation of the mine would impact water resources located in the vicinity of the proposed mine expansion area. Because the ground water




table would be lowered in the vicinity of the project, base flows within Sequalitchew Creek would be reduced upstream of the proposed confluence with North Sequalitchew Creek at RM 0.8; however much of this portion of the creek is currently dry (Anchor 2004b; CH2M Hill 2003b). However, discharge in Sequalitchew Creek downstream of the confluence with North Sequalitchew Creek would increase, starting with the construction phase from the addition of ground water pumped to the stream during construction dewatering, and would continue with the mining operations (and thereafter) from the additional flows contributed by North Sequalitchew Creek.

In addition, the project would lower the ground water table underneath the upgradient wetlands by up to 1.5 feet (Anchor 2004b) (Figure 14). South of the project site, the ground water table would be lowered by up to 0.5 feet at Pond Lake (Anchor 2004b) (Figure 14). No measures are proposed that would mitigate for the lowering of the ground water table in the vicinity of the project.

At the end of North Sequalitchew Creek construction, the berm between North Sequalitchew Creek and Sequalitchew Creek would be removed thereby allowing flows from the newly constructed stream to enter Sequalitchew Creek. During berm removal, even with the employment of BMPs to protect water quality, sediment and fines would likely enter Sequalitchew Creek.

Tidal springs discharge would be reduced because of up-gradient ground water capture in dewatering wells during construction, and as a result of ground water captured in North Sequalitchew Creek during mining operation. This capture is estimated to reduce the tidal spring discharge by 19 to 25 percent (Anchor 2004d).

Geomorphology

Construction of North Sequalitchew Creek would impact the geomorphology of the mainstem of Sequalitchew Creek by the increase in flows to the stream that would occur during mine construction and operation. Based on hydraulic modeling results conducted for this project (GeoEngineers 2004b), this increase in flow would increase erosion and sediment transport at various locations throughout the stream channel and are identified by reach on Figures 12a and 12b. The increase in sediment transport from these reaches would similarly increase sedimentation within those downstream segments having lower transport capacities.

Areas of potential adverse impact were identified as part of downstream geomorphic analysis (GeoEngineers 2004b) of the proposed confluence with North Sequalitchew Creek (Figures 13a and 13b). If recommended mitigation measures are not employed prior to project construction, unavoidable adverse impacts would likely result from the project. Mitigation measures to prevent bank and streambed erosion at the confluence of North Sequalitchew Creek should be employed. Even with LWD placement, some channel adjustment in the form of local erosion and sedimentation will be unavoidable.




Local erosion of the excavated hillslope east of North Sequalitchew Creek would occur with the proposed excavation plan due to local variations in geologic materials and ground water seepage. Outflow from the Vashon aquifer located high on the hillslope, would likely result in surficial erosion down the steep hillslope. Hillslope adjustment would likely impact North Sequalitchew Creek in the form of sediment input from slumps, slides, or surface erosion below seeps.

Project Alternative Water Resources

Significant unavoidable adverse impacts to Sequalitchew Creek and other surface water resources within the affected environment would be similar to those described for the proposed action. Pipeline discharge to Sequalitchew Creek would increase flows to Sequalitchew similar to the flow increases predicted with the proposed action. In addition, the ground water level drawdown in the area within the affected environment would be similar to the levels predicted with the proposed action resulting in the upstream segment above where the pipeline discharge would be located would go dry from the regional drawdown of the ground water table.

Similar to the proposed action the discharge in the tidal spring would be reduced by approximately 19 to 25 percent (Anchor 2004d).

Geomorphology

Significant unavoidable adverse impacts to sediment transport and habitat forming processes resulting from the Project Alternative would not differ from the impacts described for the Proposed Action, except that sediment delivery from excavated slopes to the pipeline may be less than supply to the daylighted creek in the Proposed Action. Even with the energy dissipation structure, increased flows downstream of the outfall may initiate short-term channel adjustments that are unavoidable and similar to the Proposed Action.




4.0 References

Anchor. 2004a. North Sequalichew Creek, Flow, Vegetation, and Slope Stability Evaluation. Pioneer Aggregates North Sequalitchew Creek Project. June 2004. Seattle, Washington.

Anchor. 2004b. Fish Habitat Benefit Evaluation for Sequalitchew Creek, Pioneer Aggregates North Sequalitchew Creek Project. July 2004. Seattle, Washington.

Anchor. 2004c. Brackish Marsh Water Quality Evaluation for Sequalitchew Creek. Pioneer Aggregates North Sequalitchew Creek Project. Prepared for Glacier Northwest. July 2004.

Anchor. 2004d. Supplemental Report: North Sequalitchew Creek Project. Pioneer Aggregates North Sequalitchew Creek Project. December 2004. Seattle, Washington.

Anteon. 2002. Third Quarter 2002 Groundwater Monitoring Report. Prepared for Fort Lewis Public Works by Anteon Corporation.

Aspect. 2004a. Surface Water and Groundwater System with Predictions on Effects to Wetland Hydrology Upstream of Proposed North Sequalitchew Creek. Technical Memorandum. Seattle, Washington. Prepared for Glacier Northwest by Aspect Consulting, LLC, Seattle, Washington. July 2004.

Aspect. 2004b. Surface Water and Groundwater System, North Sequalitchew Creek Project. Supplemental Report. Seattle, Washington. Prepared for Glacier Northwest by Aspect Consulting, LLC, Seattle, Washington. December 2004.

CH2M Hill. 2001. North Sequalitchew Creek Project, Dupont, WA. Surface Water Investigation Report. Bellevue, Washington. Prepared for Glacier Northwest. April 2001.

CH2M Hill. 2003a. North Sequalitchew Creek Project, Dupont, WA. Surface Water Investigation Report. Bellevue, Washington. Prepared for Glacier Northwest. April 2003.

CH2M Hill. 2003b. Draft Final Groundwater Modeling and Analysis Report. North Sequalitchew Creek Project. Bellevue, Washington. Prepared for Glacier Northwest. May 2003.

CH2M Hill. 2003c. Final Draft Stream Predesign Report North Sequalitchew Creek Project. Bellevue, Washington. Prepared for Glacier Northwest. June 2003.

DuPont. 1993. Final Environmental Impact Statement. City of DuPont, Washington.

DuPont. 1995. Pioneer Aggregates Barge Loading Facility and DuPont Shoreline Master Program Amendment SEIS. City of DuPont.




Ecology. 1990. Water quality standards for ground waters of the State of Washington. Chapter 173-200 Washington Administrative Code (WAC). Washington State Department of Ecology, Olympia, Washington.

Ecology. 1995. Washington State Water Quality Assessment. Water Division, Water Quality Program. Ecology publication # WQ-95-65b. Washington State Department of Ecology, Olympia, Washington.

Ecology. 1998. Final 303(d) water quality limited list for Washington State. Washington State Department of Ecology, Olympia, Washington.

Ecology. 2002. Sediment quality in Puget Sound, Year 3 – Southern Puget Sound, July 2002. Information taken from the Washington Department of Ecology web site on March 30, 2005: <http://www.ecy.wa.gov/pubs/0203033.pdf>. Washington Department of Ecology, Olympia, Washington.

Ecology. 2003. Water Quality Standards for Surface Waters of the State of Washington. Chapter 173-201A WAC, amended July 1, 2003. Washington Department of Ecology, Olympia, Washington.

Ecology. 2005a. Washington State’s Water Quality Assessment [303(d) and 305(b) Report]. Washington Department of Ecology, Olympia, Washington. Information taken from the Washington Department of Ecology web site on October 28, 2005: <http://www.ecy.wa.gov/programs/wq/303d/2002/2004_documents/wq_assessment_cats2004.html>.

Ecology. 2005b. Long-term marine quality data. Taken from the Washington Department of Ecology web site on January 10, 2005: <http://www.ecy.wa.gov/apps/eap/marinewq/mwdataset.asp?ec=no&scrolly=12&htmlcsvpref=csv&estuarycode=1&theyear=1996&themonth=1&staID=55>.

Ellingson, Charles. 2005. Personal communication (e-mail to Jennifer Goldsmith, Herrera Environmental Consultants, Inc., Seattle, Washington). Pacific Groundwater Group, Seattle, Washington.

Firth, Barry K. 1991. Sequalitchew Creek Regulation Under the Shoreline Management Act. Weyerhaeuser. DuPont, Washington. June 3, 1991. In: Aspect Consulting, LLC, 2004, Supplemental Report, Surface Water and Groundwater System, North Sequalitchew Creek Project. Seattle, Washington.

GeoEngineers. 2004a. Geomorphic Evaluation Pioneer Aggregates North Sequalitchew Creek Project, DuPont, Washington. July 23, 2004.

GeoEngineers. 2004b. Revised Report Geomorphic Evaluation Pioneer Aggregates North Sequalitchew Creek Project, DuPont, Washington. November 1 2004.



http://www.ecy.wa.gov/pubs/0203033.pdf


GeoEngineers. 2005. Landslide identification at Sequalitchew Creek. Technical Memorandum File No. 4747-017-01, dated August 25, 2005. Bellevue, Washington.

Herrera. 2005a. Pioneer Aggregates Mining Expansion and North Sequalitchew Project Plants and Animals Technical Report. Herrera Environmental Consultants, Inc., Seattle, Washington.

Herrera. 2005b. Pioneer Aggregates Mining Expansion and North Sequalitchew Project Fisheries Technical Report. Herrera Environmental Consultants, Inc., Seattle, Washington.

McKee, Kim. 2005. Personal communication (e-mail with Alex Svendsen, Herrera Environmental Consultants, Inc., Seattle, Washington). Water Clean-Up Unit, Washington State Department of Ecology, Olympia, Washington.

Packman, James J., Karen J. Comings and Derek B. Booth. 1999. Using turbidity to determine totals suspended solids in urbanizing streams in the Puget Lowlands. Canadian Water Resources Association Annual Meeting, Vancouver, B.C., 27-29 October 1999, p. 158-165.

PGG. 2005. Groundwater Impact Analysis. Expansion of Glacier Northwest’s Pioneer Aggregate Mine DuPont, Washington. Pacific Groundwater Group, Seattle, Washington.

Sargeant, Debby, Mindy Roberts, and Barb Carey. 2003. Quality Assurance Project Plan Henderson and Nisqually TMDL Study. Washington State Department of Ecology, Olympia, Washington.

Thut, R.N. B.K. Firth, S.W. Vincent, D.J. McGreer, and T.S. Friberg. 1978. Water Quality Studies, Part 1: Freshwater. In: Supplemental Report, Surface Water and Groundwater System, North Sequalitchew Creek Project. 2004. Aspect Consulting, LLC, Seattle, Washington.

U.S. EPA. 2003. Fort Lewis (Landfill No. 5). Washington, EPA ID#WA9214053465. United States Environmental Protection Agency Region 10, Pierce County, Fort Lewis. <http://yosemite.epa.gov/r10/nplpad.nsf/88d393e4946e3c478825631200672c95/6dc93b881191135385256594005c0f16?OpenDocument>.

URS. 2000. Former DuPont Works Site Final Environmental Impact Statement. July 28, 2000. Information taken from the World Wide Web on April 15, 2003: <http://www.ecy.wa.gov/programs/tcp/sites/weyer/Weyer_TOC.htm>.

Washington State Department of Health. 2004. Drinking water standards for the public drinking water systems. Chapter 246-290 WAC. Olympia, Washington.

WDF. 1975. A catalog of Washington streams and salmon utilization. Volume 1: Puget Sound Region. Washington Department of Fisheries, Olympia, Washington.

Wetland Science Applications (WSA). 2005. Supplemental Analysis of Sequalitchew Creek Area Wetlands.




Woodward Clyde. 1990. Fort Lewis Landfill No. 5 Remedial Investigation/Feasibility Study Hydrology and Water Quality Technical Memorandum. Prepared for U.S. Army Corps of Engineers Seattle District by Woodward-Clyde Consultants, Seattle, Washington.



TABLES AND FIGURES


Table 1. Discharge summaries (monthly means) for Sequalitchew Creek and Fort Lewis Diversion Canal from 1977 through October 2004.

Diversion Canal Lower Sequalitchew Creek

Month Diversion Wier (5/03 to 10/04) a

Wharf Road (12/99 to11/02) b

Upper Sequalitchew

Creek 12/03 to 10/04 c

1977 to 1978 d

1984 to 1987 e

11/99 to 10/04 f

January 11.3 12.8 2.5 9.7 5.9 2.6 February – 14.3 1.4 12.8 8.5 2.7 March – 21.9 0.9 12.2 8.7 2.9 April 9.9 16.0 0.7 0.7 9.4 1.8 May 7.0 7.7 0.6 1.6 7.8 1.0 June 2.4 6.6 – 1.5 3.7 1.0 July 1.5 2.9 0.4 0.2 1.3 1.0 August 1.8 2.0 0.4 0.1 1.0 0.5 September 2.5 2.0 0.4 0.1 1.0 0.2 October – 5.5 0.4 0.1 1.4 0.3 November 6.4 9.9 – 2.4 3.7 0.7 December 8.9 14.7 2.0 10.5 5.1 2.7

Mean 5.7 9.7 1.0 4.3 4.8 1.4 a Mean monthly discharge gauged continuously by Aspect (2004b). b Mean monthly discharge gauged continuously by CH2M Hill (2003) presented in Aspect (2004a). c Mean monthly discharge gauged continuously above the proposed confluence of North Sequalitchew Creek (Aspect 2004b). d Data collected by Thut et al. (1978) presented in Aspect (2004b). e Data collected by Firth (1991) presented in Aspect (2004b). f Mean monthly discharge gauged continuously by CH2M Hill (2003a) from November 1999 to September 2002, subsequent

data gauged continuously by Aspect (2004b).




Table 2. Water quality standards (freshwater) and designated uses (Chapter 173-201A-200 WAC) (Ecology 2003) applicable to surface waters of the project site including Sequalitchew Creek and the Fort Lewis Diversion Canal.

Water Quality Parameter Salmon and Trout Spawning, Core Rearing, and Migration;

and Extraordinary Primary Contact Recreation

Fecal coliform bacteria Shall not exceed a geometric mean value of 50 colonies/100 mL, with not more than 10 percent of all samples exceeding 100 colonies/100 mL.

Dissolved oxygen Lowest 1-day minimum is 9.5 mg/L.

For lakes and streams, human actions considered cumulatively may not decrease the dissolved oxygen concentration more than 0.2 mg/L below natural conditions.

Temperature Highest 7-DADMax a is 16°C. When natural conditions exceed this limit, then human actions considered cumulatively may not cause the 7-DADMax temperature of that water body to increase no more than 0.3°C. Incremental temperature increases from non-point source activities shall not exceed 2.8°C.

For lakes, human actions considered cumulatively may not increase the 7-DADMax more than 0.3°C above natural conditions.

pH Shall be within the 6.5 to 8.5 with a human-caused variation within a range of less than 0.2 units.

Turbidity Turbidity shall not exceed 5 NTU over background turbidity when the background turbidity is 50 NTU or less, or have more than a 10 percent increase in turbidity when the background turbidity is more than 50 NTU.

Toxic, radioactive, or deleterious material concentrations

Shall be below concentrations that have the potential either singularly or cumulatively to adversely affect characteristic water uses, cause acute or chronic conditions to the most sensitive biota dependent on those waters, or adversely affect public health, as determined by Ecology.

Aesthetic values Shall not be impaired by the presence of materials or their effects, excluding those of natural origin, which offend the senses of sight, smell, touch, or taste.

Designated uses Shall include the following: salmon and trout spawning, core rearing, and migration; extraordinary primary contact recreation; domestic, industrial, and agricultural water supply; stock watering; wildlife habitat; harvesting; commerce and navigation; boating; and aesthetic values.

Source: Chapter 173-201A-200 WAC (Ecology 2003a). a 7-DADMax or the 7-day average of the daily maximum temperatures is the arithmetic average of seven

consecutive measures of daily maximum temperatures.




Table 3. Water quality data for Sequalitchew Creek collected in the ravine bordering the southern boundary of the Glacier site from September 1999 to September 2000. a

State Water Quality Standards c

Parameter (units) Mean b Minimum Maximum

Number of Samples Acute Chronic

Number of Observed

Exceedances of State Standard c

Alkalinity (mg/L) 39 15 55 12 na na na Ammonia – Nitrogen (mg/L) f 0.010 0.005 0.037 12 8.086 1.555 0 BOD (mg/L) 10 10 10 5 na na na Conductivity (µmhos/L) 116 89 150 12 na na na Dissolved Oxygen (mg/L) 11.9 10.6 13.6 8 > 9.5 mg/L 0 Fecal Coliform Bacteria (CFU/100 mL) 1.2 1.0 3.0 11 < 50 colonies/100 mL 0 Hardness (mg/L) 44 33 55 12 na na na Nitrate + Nitrite – Nitrogen (mg/L) 0.58 0.28 0.82 12 na na na TKN (mg/L) 0.25 0.25 0.28 12 na na na Orthophosphate (mg/L) 0.01 0.01 0.02 12 na na na Total Phosphorous (mg/L) 0.021 0.015 0.034 12 na na Na pH (standard units) 7.3 6.6 7.8 12 Between 6.5 and 8.5 0 Temperature (oC) 7.5 4.5 12.5 9 < 16oC 0 TSS (mg/L) 4 1 10 7 na na na Arsenic (mg/L) d,e 0.01 <0.01 <0.01 12 0.3600 0.1900 0 Cadmium (mg/L) d,e 0.0006 <0.0005 0.0009 12 0.0015 0.0006 1 Chromium (mg/L) d,e 0.001 <0.001 0.002 12 0.2749 0.0892 0 Copper (mg/L) d,e 0.001 <0.001 0.004 12 0.0077 0.0055 0 Iron (mg/L) e 0.02 <0.01 0.07 12 na na na Lead (mg/L) d,e 0.001 <0.001 0.002 12 0.0255 0.0010 2 Mercury (mg/L) e 0.0002 <0.0002 <0.010 12 0.0018 na * Nickel (mg/L) d,e 0.005 <0.005 <0.005 12 0.6931 0.0770 0



Surface Water and Geomorphology Technical Report Table 3 (continued). Water quality data for Sequalitchew Creek collected in the ravine bordering the southern boundary of

the Glacier site from September 1999 to September 2000.

State Water Quality Standards c

Parameter (units) Mean b Minimum Maximum


Number of Observed

Exceedances of State Standard c

Selenium (mg/L) d,e 0.01 <0.01 <0.01 12 0.0200 0.0050 *

Silver (mg/L) d,e 0.01 <0.01 <0.01 12 0.0008 na * Zinc (mg/L) d,e 0.003 <0.001 0.008 12 0.0560 0.0511 0 a CH2M Hill (2001). b Values that were less than the laboratory detection/reporting limit are included in the calculation of the mean using the reporting limit for that constituent. c Chapter 173-201A-200 WAC (Ecology 2003). d Water quality criteria calculated based on an average hardness of 44 mg/L. e Dissolved fraction of the concentration is presented in the data. f Water quality criteria based on the maximum pH and temperature values observed at the monitoring station. g The mean for fecal coliform bacteria is the geometric mean. na – Not applicable, no standard exists. * Detection limit above acute and/or chronic criteria. CFU/100 mL – Colony forming units per 100 milliliters. BOD – Biochemical oxygen demand. TKN – Total Kjeldahl nitrogen. TSS – Total suspended solids.




Table 4. Water quality data for the Fort Lewis Diversion Canal collected near the eastern boundary of the Glacier site from September 1999 to September 2000. a

State Water Quality Standards c Parameter (units) Mean b Minimum Maximum


State Standards Violations c

Alkalinity (mg/L) 48 42 52 4 na na na

Ammonia – Nitrogen (mg/L) f 0.040 0.031 0.053 4 13.585 1.352 0

BOD (mg/L) 10 10 10 2 na na na

Conductivity (µmhos/L) 110 100 120 1 na na na

Dissolved Oxygen (mg/L) 10.5 8.6 12.7 9 > 9.5 mg/L 3

Fecal Coliform Bacteria (CFU/100 mL) 9.7 2.0 31 4 < 50 colonies/100 mL 0

Hardness (mg/L) 43 41 46 4 na na na

Nitrate + Nitrite – Nitrogen (mg/L) 0.060 0.020 0.098 4 na na na

TKN – Nitrogen (mg/L) 0.29 0.25 0.36 4 na na na

Orthophosphate (mg/L) 0.010 0.005 0.006 4 na na na

Total Phosphorous (mg/L) 0.020 0.014 0.030 4 na na na

pH (standard units) 7.1 6.8 7.4 4 Between 6.5 and 8.5 0

Temperature (°C) 8.7 3.0 18.7 12 < 16 oC 4

TSS (mg/L) 4 2 6 2 na na na

Arsenic (mg/L) d,e 0.01 <0.01 <0.01 4 0.3600 0.1900 0

Cadmium (mg/L) d,e 0.0005 <0.0005 <0.0005 4 0.0015 0.0006 0

Chromium (mg/L) d,e 0.001 <0.001 <0.001 4 0.2749 0.0892 0

Copper (mg/L) d,e 0.001 <0.001 0.002 4 0.0077 0.0055 0

Iron (mg/L) e 0.23 0.12 0.42 4 na na na

Lead (mg/L) d,e 0.001 <0.001 <0.001 4 0.0255 0.0010 *

Mercury (mg/L) e 0.0002 <0.0002 <0.0002 4 0.0018 na *

Nickel (mg/L) d,e 0.005 <0.005 <0.005 4 0.6931 0.0770 0

Selenium (mg/L) d,e 0.01 <0.01 <0.01 4 0.0200 0.0050 *



Surface Water and Geomorphology Technical Report Table 4 (continued). Water quality data for the Fort Lewis Diversion Canal collected near the eastern boundary of the Glacier

site from September 1999 to September 2000.

State Water Quality Standards c Parameter (units) Mean b Minimum Maximum


State Standards Violations c

Silver (mg/L) d,e 0.01 <0.01 <0.01 4 0.0008 na *

Zinc (mg/L) d,e 0.002 <0.001 0.002 4 0.0560 0.0511 0 a CH2M Hill (2001). b Values that were less than the laboratory detection/reporting limit are included in the calculation of the mean using the reporting limit for that constituent. c Chapter 173-201A-200 WAC (Ecology 2003). d Water quality criteria calculate based on an average hardness of 43 mg/L. e Dissolved fraction of the substance is presented in the data. f Water quality criteria based on the maximum pH and temperature values observed during monitoring. na – Not applicable, no standard exists. * Detection limit above acute and/or chronic criteria. CFU/100 mL – Colony forming units per 100 milliliters. BOD – Biochemical oxygen demand. TKN – Total Kjeldahl nitrogen. TSS – Total suspended solids.




Table 5. Brackish Marsh salinity measurements (ppt) collected during low, ebb, high, and flood tides on April 14 and April 19, 2004.

Date 4/14/2004 4/19/2004 Sample Depth Mid-depth Mid-depth Surface Station

Tide a Low High Ebb Low Ebb High Flood High SQ-1 0.6 27.6 25.8 0.6 1.3 27.6 0.4 5.9 SQ-2 0 0.1 0.1 0.1 0.2 27.2 0.1 4.5 SQ-3 0.1 0.1 0.1 0.1 0.1 25.5 0.1 1.4 SQ-4 0.1 0.1 0.1 0.1 0.1 25.7 0.1 0.5 SQ-5 0.1 0.1 0.1 0.1 0.1 0.1 0.1 nm SQ-6 0.1 0.1 0.1 0.1 0.1 0.1 0.1 nm SQ-7 0.1 0.1 0.1 0.1 0.1 0.1 0.1 nm SQ-8 dry dry Dry dry dry dry dry nm SQ-9 dry dry Dry dry dry 25.5 dry 5.7 SQ-10 dry dry Dry dry 16.6 26.9 dry 5.5 SQ-11 dry dry Dry 16.0 17.4 26.9 15.6 nm SQ-12 20.1 19.7 19.4 22.5 24.7 27.6 21.3 nm SQ-13 19.1 19.7 19 22.5 22.6 27.5 22 nm SQ-14 dry dry Dry dry dry 26.1 dry 9.4 SQ-15 dry dry Dry dry dry dry dry nm SQ-16 22.7 17.8 17.5 22.4 24.8 25.5 22.9 nm SQ-17 21.6 1.9 17.5 22.2 24 27.3 21.9 2.5 SQ-20 nm nm Nm dry dry 6.9 nm nm SQ-21 nm nm Nm dry dry 26.5 nm nm SQ-22 nm nm Nm dry dry 0.9 nm nm a The April 14, 2004 salinity measurement tidal elevations were +6.2 feet MLLW (low tide), +10.1 feet MLLW (high tide),

and +9.8 to +9.6 feet MLLW (ebb tide). The April 19, 2004 salinity measurement tidal elevations on were +0.5 feet MLLW (low tide), +13.1 feet MLLW (high tide), approximately +6.0 feet MLLW (ebb tide), and approximately +4.0 feet MLLW (flood tide).

nm = not measured.




Table 6. Water quality standards (marine waters) and designated uses (Chapter 173-201A-210 WAC) (Ecology 2003) applicable to the Nisqually Reach of Puget Sound (Extraordinary Quality).

Water Quality Parameter Criteria Applicable to Marine Waters of Extraordinary Quality

Fecal coliform bacteria Shall not exceed a geometric mean value of 14 colonies/100 mL, and not have more than 10 percent of all samples (or any single sample when less than 10 sample points exist) obtained for calculating the geometric mean value exceeding 43 colonies/ 100mL.

Dissolved oxygen Lowest 1-day minimum is 7.0 mg/L.

When a water body’s dissolved oxygen declines below this limit due to natural conditions, then human actions considered cumulatively may not cause the dissolved oxygen of that water body to decrease more than 0.2 mg/L.

Temperature Highest 1-DMax shall not exceed 13°C. When natural conditions exceed this limit, then human actions considered cumulatively may not cause the 7-DADMax temperature of that water body to increase no more than 0.3°C. Incremental temperature increases from non-point source activities shall not exceed 2.8°C.

pH Shall be within the 7.0 to 8.5 with a human-caused variation within a range of less than 0.2 units.

Turbidity Turbidity shall not exceed 5 NTU over background turbidity when the background turbidity is 50 NTU or less, or have more than a 10 percent increase in turbidity when the background turbidity is more than 50 NTU.

Toxic, radioactive, or deleterious material concentrations

Shall be below concentrations that have the potential either singularly or cumulatively to adversely affect characteristic water uses, cause acute or chronic conditions to the most sensitive biota dependent on those waters, or adversely affect public health.

Aesthetic values Shall not be impaired by the presence of materials or their effects, excluding those of natural origin, which offend the senses of sight, smell, touch, or taste.

Designated uses Aquatic Life Uses: salmon and other fish migration, rearing and spawning; clam, oyster, and mussel rearing and spawning; crustaceans and other shellfish (crabs, shrimp, crayfish, scallops, etc) rearing and spawning. Shellfish: shellfish harvesting. Recreational Uses: primary contact recreation. Miscellaneous Uses: wildlife habitat, commerce and navigation, boating, and aesthetics.

Source: Chapter 173-201A-210 WAC (Ecology 2003).




Table 7. Marine water quality data collected from Ecology’s long-term ambient water quality monitoring station GOR001 in the Nisqually Reach of Southern Puget Sound from October 1996 to September 2002. a

Parameter (units) Mean Minimum Maximum Number of

Samples

State Standard

Violations b

Ammonia - Nitrogen (mg/L) 0.014 0.010 0.045 57 na Chlorophyll a (µg/L) 3.92 0.19 17.82 89 na Conductivity (µmhos/L) Nm Nm nm nm na Dissolved Oxygen (mg/L) 8.0 5.5 13.5 153 45 Fecal Coliform Bacteria (CFU/100 mL) 1.3 1.0 5.0 52 0 Nitrite + Nitrate - Nitrogen (mg/L) 0.273 0.082 0.488 57 na Orthophosphate (mg/L) 0.110 0.052 0.272 57 na pH (standard units) 7.9 7.1 8.7 78 0 Phosphorous, Total (mg/L) Nm Nm nm nm na Salinity (parts per thousand) 28.9 25.6 30.3 165 na Temperature (°C) 11.0 7.4 15.0 165 29 Transparency, Secchi Disk (meters) 7.8 1.4 14.5 57 na a Data were gathered at 0.5, 10, and 30 meters in depth from October 1996 to January 2000 and thereafter, were collected from

depths of approximately 1, 10, and 30 meters (Ecology 2005). b Chapter 173-201A-210 WAC (Ecology 2003). c Turbidity standard exists, however, no turbidity data or background data were collected, thus, Class AA violations cannot be

determined. na – Not applicable, no standard exists. nm – Not measured. CFU/100 mL – Colony forming units per 100 milliliters.




Table 8. Table of estimated ground water quality concentrations and North Sequalitchew Creek Concentrations within the mine expansion area compared to background concentrations in Sequalitchew Creek and Washington State surface water quality standards (Chapter 173-201A-200 WAC) (from Pacific Groundwater Group [PPG 2005]).

Parameter

Estimated Ground Water Quality Range(PGG, 2005) a

Estimated Water Quality

of North Sequalitchew

Creek (PGG 2005) b

Sequalitchew Creek Surface Water Quality

Baseline Range (1999 to 2000)

(CH2Mhill 2000a and 2003b)

Below or Within Range of

Sequalitchew Creek Background

Water Quality?

Surface Water Quality Standard

(Chapter 173-201a WAC) c

Meets Surface Water Quality

Standard (Chapter 173-201A WAC)?

Alkalinity (mg/L) 45 to 47 46 15 to 55 Yes No Standard Not Applicable

Ammonia (mg/L) < 0.1 to 0.017 <0.017 0.005 to 0.037 Yes 8.0 (acute standard) Yes

Dissolved Arsenic (mg/L) <0.001to 0.001 <0.001 <0.01 to 0.01 Yes 0.360 (acute standard) 0.1900 (chronic standard)

Yes

Benzene (mg/L) <0.001 <0.001 Not Sampled Undetermined No Standard Not Applicable

Dissolved Cadmium (mg/L) <0.0002 <0.0002 <0.0005 to 0.0009 Yes 0.0014 (acute standard)0.0006 (chronic standard)

Yes

Chloride (mg/L) 3 3 Not Sampled Undetermined No Standard Not Applicable

Dissolved Chromium (mg/L) 0.001 0.001 <0.001 to 0.002 Yes 0.2697 (acute standard)0.0892 (chronic standard)

Yes

Total Copper (mg/L) 0.001 0.001 <0.001 to 0.004 (dissolved)

Yes 0.0077 (acute standard)0.0055 (chronic standard)

Yes

Total Iron (mg/L) 0.005 to <0.5 0.005 < 0.01 to 0.07 (dissolved)

Yes No Standard Not Applicable

Fecal coliform bacteria (org/100mls)

Not Modeled Not Modeled 1 to 3 Undetermined 50 CFU/100mls Undetermined, but likely

Total Lead (mg/L) <0.0004 to <0.001

<0.001 < 0.001 to 0.002 (dissolved)

Yes (ground water

predicted total lead not dissolved)

0.0255 (acute standard)0.001 (chronic standard)

Acute – Yes Chronic – Yes

Dissolved Nickel (ug/L) 0.0005 to 0.001 0.001 < 0.005 Yes 0.6931 (acute standard)0.0770 (chronic standard)

Yes



Surface Water and Geomorphology Technical Report Table 8 (continued). Table of estimated ground water quality concentrations and North Sequalitchew Creek Concentrations

within the mine expansion area compared to background concentrations in Sequalitchew Creek and Washington State surface water quality standards (Chapter 173-201A-200 WAC) (from Pacific Groundwater Group [PPG 2005]).

Parameter

Estimated Ground Water Quality Range(PGG, 2005) a

Estimated Water Quality

of North Sequalitchew

Creek (PGG 2005) b

Sequalitchew Creek Surface Water Quality

Baseline Range (1999 to 2000)

(CH2Mhill 2000a and 2003b)

Below or Within Range of

Sequalitchew Creek Background

Water Quality?

Surface Water Quality Standard

(Chapter 173-201a WAC) c

Meets Surface Water Quality

Standard (Chapter 173-201A WAC)?

Nitrate-nitrogen (mg/L) 0.0005 to 0.02 0.3 0.28 to 0.82 Yes No Standard Not Applicable

Dissolved Oxygen (mg/L) ND Not Modeled 10.6 to 13.6(2) Undetermined 9.5 mg/L Undetermined

pH (SU) 6.7 to 7.0 6.7 6.6 to 7.8 Yes 6.5 to 8.5 Yes

Phosphate (mg/L) Not Modeled Not Modeled 0.01 to 0.034 Undetermined No Standard Not Applicable

Sulfate (mg/L) 5to 6 5.4 Not Sampled Undetermined No Standard Not Applicable

Total Dissolved Solids (mg/L)

90 to 240 156 Not Sampled Undetermined No Standard Not Applicable

Temperature (°C) Not Modeled Not Modeled 4.5 to 12.5 Undetermined 16°C Undetermined

Turbidity (NTU) Not Modeled Not Modeled Not Sampled Undetermined 5 NTU over background Undetermined

Dissolved Zinc (mg/L) 0.0016 to 0.010 0.005 < 0.001 to 0.008 Yes 0.0560 (acute standard)0.0511 (chronic standard)

Yes

a Distal and ambient data were extrapolated by Pacific Groundwater Group (2005), (Table 2). See the ground water section of the DSEIS for a discussion of how data were extrapolated.

b The estimated concentration of in North Sequalitchew Creek at the confluence, Table 6 (PGG 2005). c Standards were evaluated using a hardness of 44 mg/L of CaCO3 (average hardness measured in Sequalitchew Creek during baseline sampling) (CH2M Hill 2001).




Table 9. Best estimate of predicted annual average flows in Sequalitchew Creek with the additional flows from North Sequalitchew Creek upstream and downstream of the proposed confluence at RM 0.8 (Anchor 2004d).

North Sequalitchew

Creek (at confluence)

Sequalitchew Creek (above confluence [RM 0.8])

Sequalitchew Creek (below confluence [RM 0.8])

Future Current Future Change Current Future Change

Observed Flows

Average Flow (cfs)

NA 1.0 1.4

Average Flow (cfs)

7.6 1.0 0.5 0.5 1.4 8.1 6.7 Best Estimate

Sensitivity Analysis (cfs)

6.4 to 9.8 1.0 0.5 0.5 1.4 6.9 to 10.3 5.5 to 8.9




Table 10. Best estimate of peak storm flows in Sequalitchew Creek under existing and future conditions (Anchor 2004d).

Existing Peak Flows (cfs) Location 2-Year 5-year 10-Year 25-Year 50-Year 100-Year

Based Lower Gauge Observations 10 14 17 22 26 31

Future Peak Flow Conditions (cfs)

Best Estimate 20.2 27.3 32.3 40.6 46.8 53.7




Table 11. Estimated peak storm flows in the proposed North Sequalitchew Creek used by Aspect to assess reclamation stormwater conditions within the mine expansion area (Aspect 2004b).

2-Year Event

5-Year Event

10-Year Event

25-Year Event

50-Year Event

100-Year Event

Stormwater (cfs) 3 5 7 10 13 17

Groundwater (cfs) 7 7 7 7 7 7

Total 10 12 14 17 20 24



Figure 2a. Sequaltichew Creek reach boundaries and landslides mapped by GeoEngineers.

Sou

rce:

Geo

Eng

inee

rs 2

004b

05-1

6-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

Sou

rce:

Geo

Eng

inee

rs 2

004b

05-1

6-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

Figure 2b. Sequaltichew Creek reach boundaries and landslides mapped by GeoEngineers (continued).

Sequalitchew Creek

Puget S

ound

Railro

adem

bank

ment

Existing Gravel Mine

0+00 5+00

60+00

55+0050+00

45+00

40+00

35+00

30+0025+0020+0015+00

10+00

0 500 1,000250Feet

K:\Pr

ojects

\02-02

403-0

00\P

rojec

t\GPS

point

s and

lidar.

mxd (

9/20/2

005)

GW

2004 topography provided by Puget Sound Lidar Consortium.

Figure 3. Shaded relief map developed from lidar topography and overlay of landslide and debris fans mapped during field reconnaissance (GeoEngineers 2004b, 2005).

LegendLandslides mapped during

1 inch = 500 feet

January 2004 field reconnaissance (GeoEngineers, 2004b)Centerline and approximate stationing

Figure 4a. Sequalitchew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results.

Sou

rce:

Geo

Eng

inee

rs 2

004b

05-1

6-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

Sou

rce:

Geo

Eng

inee

rs 2

004b

05-1

6-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

Figure 4b. Sequaltichew Creek selected erosional and depositional areas for current conditions based on hydraulic modeling results (continued).

100-year flow event, Sequalitchew Creek

0.001

0.01

0.1

1

10

100

0 500 1000 1500 2000 2500 3000 3500 4000

Distance from creek mouth (ft)

Rat

io o

f she

ar s

tress

to

criti

cal b

ed s

hear

stre

ss

0.001

0.01

0.1

1

10

100

Existing conditions

Reach 3Reach 4 Reach 2 Reach 1

Bed Entrainment

Sediment Transport

A


0.01

0.1

1

10

100

1000

0 500 1000 1500 2000 2500 3000 3500 4000


Rat

io o

f she

ar s

tress

to

criti

cal p

artic

le s

hear

stre

ss

0.01

0.1

1

10

100

1000

Existing conditions


DepositionDeposition

Sediment Deposition

B

Figure 5. Areas of potential sediment transport (A) and deposition (B) predicted from results of the HEC-RAS modeling for existing conditions in Sequalitchew Creek.

Figure 7

Kettle wetland water levels at the existing Glacier Mine site from July 1999 to October 2002 (CH2M Hill 2003a).

01234567

7/1/

1999

9/1/

1999

11/1

/199

9

1/1/

2000

3/1/

2000

5/1/

2000

7/1/

2000

9/1/

2000

11/1

/200

0

1/1/

2001

3/1/

2001

5/1/

2001

7/1/

2001

9/1/

2001

11/1

/200

1

1/1/

2002

3/1/

2002

5/1/

2002

7/1/

2002

9/1/

2002

11/1

/200

2

Sta

ff G

age

Wat

er L

evel

(ft)

Figure 7. Kettle wetland water levels at the existing Glacier Mine site from July 1999 to October 2002 (CH2M Hill 2003a).

(b)1908

(c)1939

(d)1947

(a) 1870

(e)1990

Figure 9. Historical maps of lower Sequalitchew Creek. (a) 1870 GLO Map, (b) 1908 Camp Lewis Map, (c) 1940 USGS topographic map (topography compiled in 1939), (d) 1994 USGS photorevised topographic map (topography compiled in 1947), and (e) 1990 aerial photograph showing sediment fill in brackish marsh.

Figure 10. Current conditions within the brackish marsh during low tide. (a) Panoramic view looking west from the eastern brackish marsh boundary. (b) View looking south from the old (abandoned) narrow gauge railroad grade.

(a)

(b)

Railroad Embankment

Brackish Marsh

Gravel Splay Deposits

Creek

Tidal Sloughs

Creek

Bar


0.001

0.01

0.1

1

10

100

0 500 1000 1500 2000 2500 3000 3500 4000


Rat

io o

f she

ar s

tress

to

criti

cal b

ed s

hear

stre

ss

0.001

0.01

0.1

1

10

100

Existing conditionsProposed conditions


Bed Entrainment

Sediment Transport

A


0.01

0.1

1

10

100

1000

0 500 1000 1500 2000 2500 3000 3500 4000


Rat

io o

f she

ar s

tress

to

criti

cal p

artic

le s

hear

stre

ss

0.01

0.1

1

10

100

1000

Existing conditionsProposed conditions


DepositionDeposition

Sediment Deposition

B

Figure 11. Areas of potential sediment transport (A) and deposition (B) predicted from results of the HEC-RAS modeling for existing and proposed conditions in Sequalitchew Creek.

Figure 12a. Sequaltichew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers.

Sou

rce:

Geo

Eng

inee

rs 2

004b

05-1

8-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

Sou

rce:

Geo

Eng

inee

rs 2

004b

05-1

6-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

Figure 12b. Sequaltichew Creek erosional and depositional areas for proposed conditions based on hydraulic modeling results by GeoEngineers (continued).

Figure 13a. Sequaltichew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers.

Sou

rce:

Geo

Eng

inee

rs 2

004a

05-1

6-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

Sou

rce:

Geo

Eng

inee

rs 2

004b

Figure 13b. Sequaltichew Creek areas of potential adverse change based on hydraulic modeling results by GeoEngineers (continued).

05-1

6-05

/rtb

/HE

C-O

-pjt/

02-0

2403

-000

-057

-001

/SE

IS

surface water and geomorphology herrera report-oct 2005

Technology

creek springs

old fort lake

pond lake

geomorphic conditions

surface water

pedestrian bridge construction

conveyer system construction

blank pages