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Appendix D Geotechnical Investigation Report

1.0 INTRODUCTION 1.1 BACKGROUND

The City of Santa Maria Department of Public Works (City) is in the process of developing a future

solid waste disposal site on a portion of a 4000-acre parcel south of the City of Santa Maria in an

unincorporated portion of northern Santa Barbara County, California (Figure 1). The future City of

Santa Maria Integrated Waste Management Facility (IWMF) lies between Highway 101 to the west

and Dominion Road to the east in an area known as the Las Flores Ranch. This parcel is currently

jointly owned by the City and the Chevron Company and is the site of past oil extraction operations.

This geotechnical investigation report has been prepared as part of the master planning work

conducted to evaluate the viability of the project site as a municipal solid waste disposal site. Field

investigations were conducted specifically to identify fatal flaws and to obtain site-specific geologic,

seismic, hydrogeologic, and geotechnical design criteria to develop environmental impact, master

planning, and permitting documents. Bryan A. Stirrat & Associates (BAS) managed this project as

lead consultant. Geologic/geotechnical field work, design analyses, and preparation of this report

were conducted by GeoLogic Associates (GLA).

1.2 PURPOSE AND SCOPE

The purpose of this geotechnical investigation was to assess the geological, hydrogeological, seismic

and geotechnical mechanical conditions within and in the vicinity of the IWMF as they influence the

development of the proposed waste management facility.

For reporting purposes, the investigation was divided into four principal areas of evaluation: Site Geology Subgrade and Fill Slope Stability Leachate Generation Analysis Groundwater Environment

The geologic/geotechnical investigation for the evaluation employed a wide array of methods to

evaluate site geology, groundwater, and geotechnical conditions. These included: Review of Local and Regional Geologic Studies; Interpretation of Aerial Photographs; Geologic Mapping; Excavation and Logging of Test Pits and Trenches; Seismic Refraction and Shear Wave Velocity Surveying; Excavation, Logging, and Sampling of Exploratory Boreholes;

Geotechnical Investigation Report City of Santa Maria Integrated Waste Management Facility

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Installing, Developing, and Sampling Groundwater Monitoring Wells; Performing Aquifer Tests; Analyzing Representative Lithologic Samples; Performing Slope Stability Analyses; and Infiltration Analysis.

The proposed landfill development was analyzed using appropriate engineering and geologic

techniques to address the proposed conceptual-level subgrade and final fill slope designs in light of

local earth materials, synthetic and natural liner components and local hydrogeology.

1.3 REGULATORY REQUIREMENTS

Siting and design of municipal solid waste facilities is governed by Chapter 3 of Title 27 of the

California Code of Regulations (27 CCR). Table 1 contains a summary of the relevant regulations

and the corresponding section(s) of this report that address these requirements.

1.4 REPORT ORGANIZATION

This technical report is organized into text sections with support data compiled in 11 appendices (A

through K). Four large plates showing current and planned site conditions and relationships

complete the document. Specific topics and appendix titles are identified in the Table of Contents.

Report text follows a sequential numeration by major topic. Subsections follow the same sequencing

to facilitate easy reference. Illustrations, figures, and tables are identified by numeric code

corresponding to the relevant text section.


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2.0 SITE DESCRIPTION

2.1 SITE LOCATION AND ACCESS

The IWMF is approximately 7 miles south of the Santa Maria city center (Figure 1). Access to the

site from Highway 101 is an unnamed exit that is approximately 2.5 miles north of Palmer Road and

3.75 miles south of Clark Avenue. The site can also be reached from Dominion Road through a

gated cattle crossing approximately 1.7 miles south of Clark Avenue. Within the IWMF property are

a number of graded dirt roads and paved asphalt roads, providing access to most of the site to stock

two-wheel drive vehicles. The site is currently jointly owned by the City of Santa Maria and

Chevron Company. Two active oil transmission pipelines cross the property, and these lines are

managed by Greka Petroleum. A local cattle rancher uses much of the property for free-range

livestock grazing.

2.2 TOPOGRAPHIC SETTING AND DRAINAGE PATTERNS

The IWMF is located in the moderate-relief Solomon Hills of northern Santa Barbara County. The

site encompasses fairly gentle canyonland bounded by a north-south trending ridgeline on the

western side of the proposed development, though the site topography has been significantly

modified by oil-field operations that occurred at this site during the last century. These operations

created numerous road cuts, oil well pads, and canyon fills that generally altered the subdued,

rounded nature of the original topography.

The proposed IWMF will occupy two canyons, herein referred to as the “northern” canyon and the

“southern” canyon. These two canyons descend from the western ridgeline, draining in a

northeasterly direction. The headwaters of a third canyon are located at the eastern edge of the

proposed development, between the northern and southern canyons. Ground surface elevations range

from approximately 1260 feet above mean sea level (msl) along the western ridgeline to about 840

feet amsl at the mouth of the northern canyon. The northern canyon is a tributary to Bradley Canyon,

while the southern canyon is tributary to Cat Canyon. Both Bradley Canyon and Cat Canyon drain to

the northeast into the Santa Maria Valley.

Site access off Highway 101 occupies two southwest draining tributaries to the north-draining

Solomon Canyon, which flows into Solomon Creek near the community of Orcutt. The site

topography is depicted on Plate 1. 2.3 VEGETATION

Vegetation at the proposed IWMF includes a variety of grasses, oak, and chaparral. Much of the


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native vegetation has been denuded by grazing livestock. Canyon areas are dominated by mature oak

trees, and a few south-facing slope areas are covered by moderately dense chaparral. A more

complete and detailed description of the site flora will be provided by the City’s biological

consultant.

2.4 PROPOSED IWMF DEVELOPMENT

As currently envisioned, the City of Santa Maria plans to develop the project area as a municipal

solid waste disposal site with ancillary facilities, including access roads, a scale house, equipment

service yard, and landfill offices (Plate 1). Access to the site will be by way of a new road to be

developed off Highway 101 that provides an entrance to the site from its southernmost point. The

proposed disposal site refuse footprint encompasses approximately 286 acres spanning the two

canyons. The site will be developed with 2.5:1 (horizontal:vertical) perimeter subgrade slopes

extending from the western ridgeline at an average elevation of about 1240 feet above mean sea level

(amsl) down to relatively flat floor areas. Completing the proposed excavation plan will result in

removal of approximately 30 million cubic yards of soil and bedrock. The subgrade will generally

follow pre-existing drainage patterns in that the southern half of the site will continue to drain out

from the mouth of the southern canyon, and the northern half of the site will continue to drain out

from the mouth of the northern canyon. The southern floor will have a minimum elevation of about

980 feet amsl, while the northern floor will have a minimum elevation of about 860 feet amsl. The

floor areas will drain to their respective canyon mouths at an average gradient of 3 percent. All

subgrade areas to receive wastes will be covered with a composite liner system. As currently

envisioned, the composite liner system will include:

From top to bottom on floor areas:

A two-foot thick layer of protective soil, A filter geotextile, A 12-inch sand, gravel, and perforated pipe Leachate Collection and Removal System (LCRS), A cushion geotextile, A 60-mil High Density Polyethylene (HDPE) geomembrane that is textured on both sides, A Geosynthetic Clay Liner (GCL), and A six-inch layer of select low permeability soils.

From top to bottom on side-slope areas: A two-foot thick layer of protective soil, A geocomposite LCRS, A 60-mil HDPE geomembrane that is smooth on top and textured on the bottom, and A GCL, and Prepared subgrade.


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The proposed IWMF is designed with disposal airspace of approximately 133 million cubic yards.

The final refuse fill will be constructed at 2.5 to 1 slope gradients with a top deck elevation ranging

from 1420 feet amsl in the south to approximately 1510 feet amsl in the north. The top deck of the

landfill will form a sinuous shape that generally follows the original configuration of the western

ridge line as shown on Plate 2.


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3.0 PREVIOUS INVESTIGATIONS, DATA REVIEW AND RELATED STUDIES

The studies presented herein are the first site-specific geologic, hydrogeologic, seismic, or

engineering studies conducted for the IWMF. Based on our research, no previous studies of the site

have been conducted. Data compiled from oil field exploration are considered proprietary, and were

not available for review. Regional geologic studies that include the subject property have been

conducted by various private and governmental organizations. A brief synopsis of those

investigations is provided below.

Woodring, W.P. and Bramlette, M.N., 1950, Geology and Paleontology of the Santa Maria

District, California. United States Geological Survey Professional Paper 222. This professional paper provides detailed descriptions of all regional geologic units, including comprehensive descriptions of lithology, fossil occurrence, and areal distribution of the Orcutt Sand, Paso Robles Formation, and Careaga Sand (Formation). The study was undertaken to assess potential oil-bearing resources in the Santa Maria District.

Dibblee Geological Foundation Maps of the Santa Maria Area, 1994. Geologic maps and cross

sections of the Orcutt and Sisquoc quadrangles (including the proposed IWMF area) illustrate the stratigraphic and structural relationships of the Orcutt Sand, Paso Robles Formation, and Careaga Formation. Surface relationships are based on past work by others, supplemented with field checking of geologic contacts, and includes numerous field-measured bedding plane and structural attitudes. Subsurface relationships are based on oil well data and extrapolation. These maps contain detailed interpretations about the nature of folding and faulting in the vicinity of the site.

United States Geological Survey monitors a series of groundwater monitoring wells

approximately 2 miles east of the site in the Santa Maria Valley. Data from these wells were used to extrapolate groundwater elevations at the site for the purposes of estimating groundwater depths beneath the proposed IWMF.

Tom Gibbons (personal communications) provided historical topographic maps of the study area

depicting the locations of former oil-field operations, including oil wells, transmission pipelines, sumps, cuts and fills.

Additional published sources used in preparation of this report or in the engineering analyses

presented herein are cited in the text, and fully referenced in Section 12.0 of this report.


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4.0 FIELD INVESTIGATION

Each aspect of geotechnical investigation is described in detail below. The locations of all

geophysical lines, boreholes, test pits, and monitoring wells completed during this investigation, and

from previous studies, are shown on Plate 3. Prior to field investigation, Underground Services Alert

was contacted to clear the proposed excavation sites. All field work that required ground disturbance

was conducted under the supervision of a field biologist to ensure that potential tiger salamander and

fairy shrimp habitats were not irreparably damaged. At drilling sites surrounded by numerous

burrows, plywood sheets were laid over the burrows at the direction of the field biologist for

protection. Prior to drilling monitoring wells and piezometers, well permits were obtained from the

Santa Barbara County Public Health Department. 4.1 GEOLOGIC MAPPING

Initial geologic mapping was performed in November 2006, and continued throughout the duration of

field work to fill in data gaps that emerged from other investigation findings. Data were plotted on

a site topographic map to enable accurate location of outcrops and other pertinent structural and

stratigraphic information. Pocket transits were used to triangulate outcrop locations and measure

structural orientations. Mapped data were digitized in AutoCAD format to generate the

accompanying geologic map and cross sections of the IWMF site (Plates 3 and 4, respectively).

4.2 SEISMIC SURVEYING

Two seismic refraction profiles and seven refraction microtremor (ReMi) surveys were conducted to

evaluate the rippability and strong ground motion response of bedrock and soils within the proposed

IWMF site. Seismic surveying methods and results are summarized below and the profile array

locations are shown on Plate 3.

Seismic Refraction Surveys - The rippability predictions were based on seismic velocities measured

along two profiles. Since all areas of the site to be developed are directly underlain by the relatively

homogeneous Paso Robles Formation or nonlithified materials, two seismic refraction profiles were

deemed sufficient to determine rippability.

For the seismic refraction surveys, seismic waves were generated by striking a 20-pound sledge

hammer on a metal strike plate at each shot point. The seismic refraction method uses an array of 4.5

hertz surface geophones to detect changes in wave velocities caused by vertical and lateral changes in

material density. The waves travel from the shot point down into the ground and are refracted along

material boundaries, such as bedding planes, unconformities, or formational contacts, that have

different densities, and therefore, different velocities. If the lower material has a higher velocity, then


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the waves are refracted upward and can be sensed by the surface geophones. If the lower material's

velocity is lower, then the waves are refracted downward and never measured. The two arrays were

arranged as follows:

Profile Orientation Length Geophone Array Shot Points SR-1 West to East 220 feet 12 geophones at

20-foot spacing 5 shot points.

Shot 1: 20 feet east of Geophone 1, Shot 2: 50 feet along the geophone array,

Shot 3: 110 feet along the geophone array, Shot 4 : 170 feet along the geophone array,

Shot 5: 20 feet west of Geophone 12.

SR-4 Northwest to Southeast

604 feet 24 geophones at 26-foot spacing

9 shot points: Shot 1: 20 feet northwest of Geophone 1, Shot 2: 52 feet along the geophone array,

Shot 3: 130 feet along the geophone array, Shot 4: 208 feet along the geophone array, Shot 5: 286 feet along the geophone array, Shot 6: 364 feet along the geophone array, Shot 7: 442 feet along the geophone array, Shot 8: 520 feet along the geophone array, Shot 9: 20 feet southeast of Geophone 24.

The refraction data were collected with a DAQ Link II 24 channel-seismograph connected to the

array of geophones. The acquired data was processed for GLA by Optim LLC using their SeisOpt

ReMi software (Optim, 2004). The results of the two-dimensional seismic refraction surveys are

presented in Appendix A in the form of color-coded contours of compressional wave velocity.

Results - Travel times of the compressional waves and geophone-shot point array geometry were

used to calculate seismic velocities and corresponding thicknesses of subsurface velocity zones using

Snell's law (Dobrin,1960). Material rippability was estimated from these velocities using the

Caterpillar, Inc. (1994) empirical tables. According to these charts, material with a seismic velocity

of up to 7000 feet per second (ft/sec) is considered rippable with a Caterpillar D9 dozer with a single-

shank ripper.

As shown on the seismic refraction illustrations in Appendix A, the highest compressional-wave

velocity recorded along SR-1 is on the order of 6000 ft/sec, at depths of about 60 feet toward the

eastern half of the array. Proposed subgrade excavations in this area are less than 60 feet, indicating

that material excavation can be conducted using typical earth-moving equipment.

A change in the proposed IWMF design occurred after field work was completed. The revised

design includes removal of the ridgeline separating the northern and southern canyons. While no

significant changes in lithology are anticipated based on extrapolation of exploratory borehole and


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test pit data, additional seismic refraction surveys should be conducted in this area to verify the

rippability of this area.

Refraction Microtremor (ReMi) Surveys – Nine two-dimensional (2-D) refraction microtremor

(ReMi) shear wave velocity surveys were performed by GLA to evaluate soil profiles along the

canyon bottoms and to establish average shear wave velocities for the purpose of determining a site

seismic response. In contrast to seismic refraction surveys, which record compressional waves, the

ReMi surveys record shear waves. Furthermore, the ReMi method uses a passive source, such as

ambient noise from vehicles, equipment, or pedestrian traffic, to construct a one-dimensional (1-D)

average shear wave velocity model from data collected along an array of geophones. By sequentially

analyzing data subsets along the array, a series of 1-D models can be aggregated to create a 2-D shear

wave velocity model. The arrays were established as follows:

Profile Orientation Length Geophone Array SR-1 West to East 220 feet 12 geophones at 20-foot spacing

SR-2/2a South to North 450 feet 2 overlapping arrays - 24 geophones

at 15-foot spacing with a 17-geophone overlap

SR-3 North to South 220 feet 12 geophones at 20-foot spacing

SR-4 Northwest to Southeast

604 feet 24 geophones at 26-foot spacing

SR-5 South to North 275 feet 12 geophones at 25-foot spacing

SR-7 West to East 275 feet 12 geophones at 25-foot spacing

SR-11 North to South 220 feet 12 geophones at 20-foot spacing

The ReMi data were collected using the same equipment using for the seismic refraction surveys.

The acquired data was processed for GLA by Optim LLC using their SeisOpt ReMi software (Optim,

2004). The results of the 2-D shear wave velocity survey are presented in Appendix A in the form of

color-coded contours of shear wave velocity. These results indicate average shear wave velocities of

350 to 400 meters per second. The measured shear wave velocities were used to evaluate site

response to strong ground motions as presented in Section 6.3 of this report.

4.3 TEST PIT LOGGING

Test pits were excavated to supplement geologic surface mapping in areas of dense vegetation or

surficial soils. Forty-three test pits, ranging in depth from about two to 12 feet and from about five to

over 50 feet long, were excavated throughout the site using a rubber-tired backhoe. Where the test

pit depth exceeded four feet, the excavation was stepped so that no wall exceeded four feet in height.


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Test pit walls were hand-cleaned to expose geologic features. Geologic information, including soil

type, geologic contacts, bedding plane, fracture, and slip surface orientations, fracture in-filling, and

water seepage, was recorded on log forms. After logging, the test pits were backfilled with excavated

soils and wheel-rolled by the backhoe. Test pit locations are plotted on Plate 3 and logs are

contained in Appendix B. Test pit geological findings are summarized on Table 2. 4.4 EXPLORATORY BORINGS

Three drilling methods were utilized to evaluate deeper subsurface conditions. Bucket-auger borings

were used to permit downhole logging by a field geologist and facilitate collection of large bulk soil

samples. Since the bucket-auger excavation capability can be restricted by the nature of the

formation and/or by the presence of significant groundwater, hollow-stem auger drilling methods

were used to access geologic conditions below the depth attainable using bucket-auger methods.

Finally, air- and mud-rotary drilling techniques were used to drill monitoring well borings. Each

drilling technique, along with corresponding sampling and logging are described in detail below.

The locations of exploratory boreholes and monitoring wells completed during this investigation are

shown on Plate 3. Boring logs are included in Appendix C (C1 - bucket auger boring logs, C2 –

hollow-stem auger borings, and C3 – air/mud rotary borings). Table 3 summarizes the geologic

observations made in each borehole during the investigation.

4.4.1 BUCKET-AUGER DRILLING

Eleven bucket-auger boreholes (BA-1 through BA-11) were drilled to depths ranging between 32 and

140 feet. Drilling was conducted by Al-Roy Drilling of Yorba Linda, California between December

7 and 22, 2006.

Bucket-auger drills use a large-diameter, steel digging bucket with auger-bottom cutting teeth. The

bucket is turned by a telescoping Kelly bar which, together with the bucket, provide the weight

applied to the cutting head. As the bucket is rotated, soil and rock are cut and forced inside. When

the bucket is full, it is raised to the surface and the cuttings are released by opening the bottom. To

accommodate the sampling and borehole exposure logging requirements of this project, a 24-inch

diameter bucket was used.

Sample Collection - Bucket-auger drilling allowed collection of disturbed bulk samples, relatively

undisturbed drive samples, and grab samples from the sides of the borings. Bulk samples were

generally obtained at 10-foot intervals or at each substantial change in lithology. Bulk samples

represent approximately 20 to 40 pounds of cuttings from a single bucket load that are placed in a

heavy plastic bag, labeled, and sealed with electrical tape. Grab samples of important geologic


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features, such as shear planes, were also obtained by the geologist during downhole logging.

Specimens were carefully extracted from the borehole wall using hand tools and placed in a labeled

plastic bag. Drive samples were obtained at five or ten-foot intervals using a modified California

split spoon sampler fitted with 12 brass rings which was in turn attached to the kelly bar and lowered

down the hole. The sampler itself has a 2.4-inch inner diameter and a 3.25-inch outside diameter.

With the sampler resting on the bottom of the hole, a 12-inch interval was marked on the kelly bar or

cable to measure depth of penetration. The Kelly bar was then raised 12 inches and released to drive

the sampler into the substrate. Upon 12 inches of penetration, the number of blows and drive energy

were recorded, and the sample was retrieved. The brass rings containing the specimen were carefully

removed, and up to six brass rings were placed in labeled, plastic-lined tubes for subsequent

laboratory testing. The soil from the remaining rings and the sampler shoe were used to classify

sample materials and to develop the lithologic log. The sample tube was sealed with electrical tape

and placed in an insulated box to minimize disturbance during transport. At the conclusion of bucket

auger drilling, all soil and rock samples were transported to GLA’s geotechnical laboratory for

analysis.

Logging - Initial bucket auger drilling logs were prepared by observing the bucket returns and drive

samples. Materials were examined and the following information was recorded on the boring log, as

appropriate: Sample depth. Sample recovery. Blow counts per foot. Standard stratigraphic nomenclature or Unified Soil Classification System (USCS) soil type. Lithologic composition for bedrock. Mineralogical composition. Color according to Munsell soil and/or rock color chart. Field estimate of moisture content (e.g., dry, moist, wet). Field estimate of consistency (e.g., soft, firm, stiff, hard). Field estimate of plasticity. Degree of weathering. Degree of induration. Bedding characteristics, including thickness and angle of dip. Fracture characteristics, including fracture intensity, width, infilling, textures and dip. Presence of fossils or microfossils. Other pertinent characteristics.

Downhole logging was performed in all bucket-auger boreholes. Before the geologist entered the

hole, a four-gas meter was lowered down the hole to monitor the air for explosive gases, hydrogen

sulfide, carbon monoxide, and oxygen content. In addition, the geologist and drilling personnel

evaluated the borehole stability from the ground surface to ensure that caving was not likely. Once


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the air quality and initial borehole stability were determined acceptable, a five-foot temporary surface

casing was installed at the ground surface to minimize sloughing, a weighted tape measure was

lowered down hole to serve as a depth reference during logging, and the safety cage was prepared

with an internal light, the four gas meter, and a fresh-air line. The geologist entering the borehole

was required to wear a hard hat, steel-toed boots, and a safety harness attached to the cage. The

geologist also carried a hand pick, pocket transit, and log sheets to excavate, measure, and record the

geologic features exposed. The information obtained downhole was used to supplement the surface

logging described above. Where present, the geologist recorded the following:

Strike and dip of bedding. Strike and dip of faults, joints, and fractures. Depth of landslide slip surface or shear zones. Depth where groundwater entered the borehole. Depth and orientation of geologic contacts. Other pertinent geologic features.

Logs of all bucket-auger borings drilled during this investigation are presented in Appendix C1.

Bucket Auger Borehole Abandonment - After logging the bucket-auger boreholes, each was

backfilled by pushing the cuttings into the hole. After two to three cubic yards of soil had been

placed in the hole, the soils were compacted using a tamping plate attached to the Kelly bar.

Tamping continued until there was no visible change in the Kelly bar elevation. Soil

addition/tamping continued until the borehole was completely backfilled. Excess soil was spread out

on the site, though burrows were avoided.

4.4.2 HOLLOW-STEM AUGER DRILLING

Initially, the proposed piezometers were to be drilled using hollow-stem auger methods, which allows

collection of disturbed and undisturbed samples. Because groundwater was significantly deeper than

first anticipated, only four of the original seven piezometer boreholes were drilled, and those that

were drilled were used for geotechnical evaluation to supplement the bucket auger drilling and

logging information.

Between January 3 and 10, 2007, four hollow-stem auger boreholes (P-1, P-2, P-4, and P-5) were

drilled by Test America Drilling of Anaheim, California. Hollow-stem auger borings ranged from 35

to 274 feet in depth, with a piezometer constructed in borehole P-1. Boreholes were advanced using

10-inch diameter augers driven by a CME 75 rig. All hollow-stem auger drilling and sampling

equipment was steam-cleaned prior to drilling each boring. Decontamination water was discharged

to the ground in a manner that did not cause erosion, excessive runoff, or damage to nearby burrows.


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Sample Collection - Bulk samples were collected at significant changes in lithology by shoveling

soils into large sample bags as they came to the surface along the outer edge of the auger stems.

Drive samples and Standard Penetration Test (SPT) samples were collected at alternating 5-foot

intervals. SPT samples were used to gauge soil density and log soils. Drive samples were collected

in split-spoon samplers lined with brass rings, and were retained for subsequent laboratory analyses.

Brass rings were extracted from the sampler and then placed in a lined and labeled plastic tube for

transport to the laboratory. The sample shoe was also used to log soil and bedrock lithology.

Piezometer boring P-5 was drilled through an area of known oil well drilling mud. In addition to the

geotechnical sampling, soil samples collected from this boring were also analyzed for total petroleum

hydrocarbons by EPA test method 1664. Soil samples were placed in laboratory-supplied 8-ounce

glass jars, labeled, and placed in an ice-filled cooler with the completed chain-of-custody

documentation for transportation to the laboratory. Analytical results are provided in Appendix G,

and the results are summarized in Table 4.

Logging – Lithologic logging was conducted by recording the lithologies observed in the SPT and

split-spoon samples. Materials were examined and the samples were logged using the same criteria

followed during logging of the drive samples collected during bucket auger drilling. In addition the

borehole was periodically monitored for explosive gases, hydrogen sulfide, carbon monoxide, and

oxygen content, and this data was recorded on the log sheet.

Borehole Abandonment - Of the piezometer borings, only boring P-1 encountered significant

groundwater within the original target depth. At this location, a 2-inch diameter polyvinyl chloride

(PVC) piezometer was constructed. Piezometer and monitoring well construction is described in

Section 4.5. All other hollow-stem auger boreholes were abandoned by filling the borehole with

Volclay® bentonite grout. The grout was filled to the ground surface, and then allowed to settle

overnight. Bentonite chips and soil cuttings were used to fill the annulus above the settled grout.

4.4.3 AIR/MUD-ROTARY/CASING-HAMMER DRILLING

Air-rotary/casing hammer (ARCH) drilling was used to attempt drilling wells MW-1 and P-2.

Drilling was performed by Test America Drilling of Anaheim California. Borings were advanced

using a 10-5/8-inch diameter tricone bit, and circulating high pressure air to remove cuttings. A

temporary 11-1/2-inch diameter casing was driven into the borehole immediately behind the drill bit

in order to maintain borehole stability. As a result of the great depth to groundwater and poorly

consolidated bedrock, the air-rotary boreholes could not be kept open at depth, and therefore the


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monitoring well borings had to be drilled using mud rotary methods.

Mud rotary drilling was conducted by Water Development Corporation of Montclair, California, to

complete monitoring wells MW-1 through MW-5 and piezometer P-2. Mud rotary methods use

similar 10-5/8-inch tricone bit, but employ a bentonite-polymer mud (instead of air) to circulate the

cuttings. The mud cools the drilling bits, extracts the cuttings, and stabilizes the borehole. Prior to

construction of monitoring wells in these boreholes, the mud is thinned, and then pumped into roll-

off bins for disposal.

Sample Collection and Logging – Air and mud rotary drilling method utilize a tricone bit that

pulverizes the bedrock, suspending the pulverized material in air or mud and preventing collection of

undisturbed samples. In lieu of obtaining discrete lithologic samples, gross lithologic changes were

recognized by logging drill cuttings from the discharge cyclone or mud pit and observing changes in

drilling behavior. In addition, after the borehole was advanced to its design depth, Pacific Surveys of

Rancho Cucamonga, California, logged the borehole using a gamma-ray electric logging tool to

assess lithology and a sonic variable density tool to determine the depth to groundwater. ARCH and

mud rotary drilling geologic and geophysical logs are presented in Appendix C3, monitoring well

permits are provided in Appendix D1, and monitoring well construction logs are presented in

Appendix D2.

Drilling Mud Storage and Disposal - After mud-rotary drilling was completed, the drilling mud was

pumped into roll-off bins and representative samples were collected to assess the presence of heavy

metals, petroleum hydrocarbons, and volatile organic compounds. Samples were analyzed for 17

metals, volatile organic compounds, diesel or gasoline-range petroleum hydrocarbons, oil and grease,

percent liquids, percent solids, and pH. Analyses were completed by BC Laboratories, Inc., a State

of California and federally certified environmental laboratory located in Bakersfield, California.

After laboratory results were received, and the mud was deemed to be free from constituents of

concern, the mud was pumped into transport vehicles for disposal at the City’s wastewater treatment

facility. The results of mud analyses are presented in Appendix E.

Borehole Abandonment - Air-rotary boreholes in which wells were not constructed were abandoned

using neat cement grout, which is a mixture of Portland cement with about 8 percent bentonite

powder. The grout was added to fill the hole, and allowed to settle overnight. If settlement was

greater than 10 feet, additional neat cement was added, otherwise, the remaining annulus was filled

with bentonite chips.


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4.5 MONITORING WELL AND PIEZOMETER CONSTRUCTION

Between February 8 and May 24, 2007, five monitoring wells and two piezometers were constructed,

ranging in depth from 35 feet (at P-1) to 802 feet (at MW-2). Piezometer P-1 was constructed by

Test America Drilling of Anaheim, California. Drilling and construction of all other monitoring

points were performed by WDC Exploration and Wells (WDC) of Montclair, California. All drilling

and well construction were performed under the direct supervision of the field geologist. Appendix

C3 contains the geologic and geophysical logs of the monitoring well boreholes, and the as-built

construction diagrams for wells MW-1 through MW-5 and piezometers P-1 and P-2 are presented in

Appendix D2.

Well Permits – Monitoring well construction permits were obtained from the County of Santa

Barbara Public Health Department. Permits were obtained for four monitoring wells and seven

piezometers. Since only two piezometers were constructed, the Public Health Department granted

verbal approval to construct well MW-5 under a permit for a piezometer that was not constructed.

Under the terms of the permit, the Public Health Department was notified prior to construction of

each well, providing their personnel the opportunity to inspect well construction practices. Copies of

the well permits are provided in Appendix D1.

Well Drilling and Design Parameters – Well depths were estimated by extrapolation of the regional

water table in the adjacent Santa Maria Valley. As described in Section 4.4, monitoring wells and

piezometer P-2 were drilled using mud rotary methods. This method enables drilling stable

boreholes to great depths but obscures geologic and groundwater information that can be obtained

from “dry” boreholes. As a result, geophysical logging was necessary to obtain the information

obscured by the drilling mud. Within one day of reaching the target depth, Pacific Surveys (the

geophysical contractor) was notified so that logging could be conducted shortly after reaching the

target depth. The use of drilling mud necessitated sonic variable density geophysical logging to

determine the depth to groundwater, and electric gamma logging was used to assess the general

lithologic character in the vicinity of the water table and aid in well design. After the geophysical

logs were reviewed, the total depth of the well was determined. With the depth to water often

exceeding 500 feet, screened intervals were typically set at 40 to 60 feet below the water table to

allow for fluctuation in the water level and to allow for a sufficient volume of water to fill the well

and discharge lines of future sampling pumps.

If the bottom of the borehole was greater than 60 feet below the water table, then the lower portion of

the borehole was sealed by placing a 50 percent sand/50 percent bentonite chip mixture in the bottom

of the hole through a tremie pipe. This lower seal was allowed to hydrate and settle overnight prior

to well construction.


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Well Construction - All wells were constructed in compliance with the California Department of

Water Resources (DWR) well standards as outlined in DWR Bulletin 74-90. With the exception of

Piezometer P-1, which was constructed with 2-inch diameter Schedule 40 PVC casing and screen, all

monitoring points were constructed using four-inch (nominal) inner diameter, Schedule 80 PVC

casing and well screen, connected by flush-threaded joints sealed with rubber O-rings. The well

screen was uniformly cut, with evenly distributed 0.020-inch wide, machine-cut slots. A flush-

threaded PVC cap was attached to the bottom of the well screen. All well casing and screen

materials used during this project arrived on the site in new condition, wrapped in plastic, and in

original factory packaging. During well construction, all casing lengths were assembled by hand

without the use of grease, solvents, or glues. The top of the casing was centered and supported by the

drill rig throughout construction, and stainless-steel centralizers were attached to the top and bottom

of the screen, and at fifty-foot intervals from the top of the screen to the borehole collar.

The monitoring well filter-pack material consisted of uniformly-graded, pre-washed Lonestar #2/12

sand, which was tremied in place as a water-supported slurry. The tremie pipe was maintained

within 10 feet of the top of the filter-pack to minimize free fall and potential bridging, and the depth

to the filter-pack sand was frequently sounded to ensure that bridging did not occur. Once the level

of the filter-pack was two to five feet above the top of the screen, the well was surged using a vented

surge block to settle the filter-pack and remove fine-grained material. After surging, the filter-pack

level was sounded again, and additional sand added, as necessary, to meet filter-pack design

specifications.

A bentonite seal was constructed above the filter-pack using a minimum of three feet of medium-

chipped bentonite. Bentonite chips were tremied in place as a water-supported slurry until the

bentonite-chip seal was at least three feet thick. Typically, the bentonite-chip seal was significantly

thicker to minimize the potential for the overlying grout to intrude into the well screen. The

bentonite-chip seal was allowed to hydrate for at least one hour before additional well materials were

placed.

After hydration of the bentonite-chip seal, a grout seal was placed from the chip seal to about four

feet from the ground surface. Grout consisted of Volclay® powdered bentonite and water blended at

a ratio of about 25 gallons of water per 40-pound sack of bentonite. The grout was mixed in a

cleaned aluminum tub using a compressed-air mixer, and mixing continued until the grout attained a

uniform consistency, free of dry product. The grout was then pumped into the borehole through a

tremie pipe placed about 10 feet above the top of the bentonite chip seal. As grout was added, the

tremie pipe was raised until the level of the grout was within four feet of the ground surface. The

grout was allowed to cure and settle for at least 24 hours, and additional grout was added, as


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required, to bring the level to design specifications.

The remaining borehole annulus was filled with cement, and all wells were completed at the surface

with PVC slip caps with a locking steel well cover in a three-foot square concrete surface

seal/monument centered around the steel well cover. To minimize damage by grazing cattle, no

traffic posts or bollards were set at this time. Table 5 summarizes well and piezometer construction.

Well Development - Each well was developed using a combination of surging and bailing. As noted,

following initial placement of the filter-pack, each well was pre-developed by surging the screened

interval with a vented surge block to remove entrained fines. During development, a four-inch-

diameter, four-foot-long steel bailer was used to work the sand pack and to remove drilling mud and

formational sediment that accumulated at the bottom of the well casing. Water was periodically

added to the well to aid in removal of the excess drilling mud from screen and filter pack. In

addition, deflocculant was added to some wells where the drilling mud was observed to be

particularly thick. Sediment-laden water and drilling mud were discharged to the roll-off bins, and

disposed of by the City. After the development water was observed to be relatively free of sediment,

the discharged water was periodically monitored for temperature, conductivity, and pH. Under ideal

conditions, well development is considered complete after a minimum of three well volumes has

been removed, the well water is visibly clear, and the temperature, pH, and conductivity of the

discharge water stabilizes (i.e., three consecutive readings of temperature, conductivity, and pH

within 10 percent of each other). However, since the groundwater itself contained substantial solids,

good water clarity was rarely achieved. Well development data are included on the well construction

logs in Appendix D2.

4.6 BAIL DOWN AND RECOVERY TESTING

Bail down and recovery tests were performed to estimate the hydraulic conductivity of the alluvium

or bedrock materials immediately surrounding the wells and piezometers. Bail down and recovery

testing was performed after final well development was completed and relatively stable groundwater

elevations were measured.

Prior to testing, the static water level in each well was measured using a decontaminated electric

sounder. Well water was then “bailed down” by evacuating a sufficient volume of water from the

well to substantially lower the water level, using WDC’s development rig. Subsequently, periodic

water level measurements were collected using the electric sounder until the water level had

recovered to within at least 80 percent of the static water level. Data collected from recovery tests

were used to approximate hydraulic conductivity values in the screened formation immediately

surrounding each well. The results of recovery tests are presented in Section 7.2.


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5.0 GEOTECHNICAL TESTING

5.1 INTRODUCTION

All of the relatively undisturbed, disturbed, and bulk samples obtained during the exploration

program were taken to the geotechnical laboratory where they were examined to verify field

classification. Representative samples of different soil and bedrock materials types were selected for

laboratory testing. The laboratory test program was designed to classify the predominant material

types encountered at the site and to measure their basic engineering properties, including: shear

strength, hydraulic conductivity, and the other physical and chemical properties required for design

of the proposed project.

The following laboratory tests were performed using the latest applicable American Society for

Testing and Materials (ASTM), U.S. Environmental Protection Agency (USEPA) or California

Department of Transportation (Caltrans) standards. In-Situ Moisture Content and Dry Density (ASTM D2216 and D2937) Particle Size Analysis (ASTM D422 and D1140) Atterberg Limits (ASTM D4318) Direct Shear (ASTM D3080) Flexible Wall Permeability (ASTM D5084) Corrosivity: Soluble Sulfate Content (Caltrans 417); Soil pH (USEPA 9045); and Electrical

Resistivity (Caltrans 532)

Laboratory test methods and results are discussed in this section, and test data are presented in

Appendix H.

5.2 OBJECTIVES AND PROGRAM DEFINITION

The laboratory geotechnical testing program was designed to evaluate the properties of subgrade

materials likely to be encountered or used as fill soils for construction of the proposed landfill

expansion and associated improvements. The primary objectives of the laboratory test program were

to:

Obtain engineering properties of subsurface geologic units (and compacted fill derived from them) in support of the design of stable subgrade slopes. The engineering properties required for slope stability evaluations include unit weight and shear strength. Properties required for compacted fills include unit weight, moisture content, shear strength, and maximum density/optimum moisture content.

Characterize the proposed cut materials to evaluate their suitability for use as the low-


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permeability soil element of a composite liner system, final cover soils or other fills that have an infiltration performance specifications. Tests assessed in-situ moisture content, grain size distribution, Atterberg Limits, maximum density/optimum moisture content, and laboratory hydraulic conductivity.

A brief description of the geotechnical testing program is presented below.

Subgrade Material Evaluation - Subsurface geologic units encountered in the proposed IWMF

include residual soil, old oil-field drilling muds, alluvium, colluvium, landslide debris and bedrock of

the Paso Robles Formation. Although the Careaga Sand was encountered during monitoring well

drilling, it is too deep to be of engineering significance for the proposed project. Since the proposed

subgrade slopes will result in removal of most of the shallower materials (i.e., drilling mud, residual

soil, alluvium, colluvium, and most landslide debris) the proposed subgrade will be underlain

primarily by weathered and unweathered bedrock of the Paso Robles Formation. As a result, the

majority of soils testing was performed on samples of this unit.

Index property tests, including Atterberg Limits, gradation, in-situ moisture content and dry density,

were performed on different soil and bedrock units for soil classification purposes.

Sulfate content, pH, and minimum resistivity were measured on representative subsurface samples to

evaluate the corrosion environment for the planned or foreseen structures.

The stability of the proposed subgrade slopes will be influenced primarily by local geologic structure

and the strengths and distribution of the geologic units. The strengths of subgrade materials were

estimated from laboratory direct shear and triaxial compression tests conducted on representative

undisturbed samples of the weathered and unweathered Paso Robles Formation. Direct shear tests

were performed at a strain rate of 0.0042 inch per minute on intact bedrock to determine cross-

bedding strengths. Ultimate shear strengths were determined by measuring the angle of internal

friction and cohesion after the sample had been sheared 0.25 inch.

Bedding planes were observed to be poorly developed in outcroppings and in the large-diameter

borings, and shearing was not observed in the boreholes or in the collected samples. To simulate

shear planes that might exist at the site, a sample of siltstone from borehole BA-4 was repeatedly

sheared to estimate bedding plane/slip surface strength characteristics. For this test, the sample was

first saturated and consolidated under applied vertical stresses, and then repeatedly sheared until a

steady-state strength was reached. The residual shear strength results best reflect weak bedding

plane/slip surface strength conditions when intact samples of bedding planes or slip surface cannot be

collected.


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Direct shear tests were also performed on remolded samples of these materials to evaluate shear

strengths of proposed engineered fills. Remolded samples were compacted to a relative compaction

of 90 percent as determined by ASTM D1557 to simulate engineered fill conditions.

Results of laboratory tests are summarized in Table 6, and individual test data are presented in

Appendix H.

Infiltration Performance – Laboratory permeability and soils classification tests were conducted on

in-place and remolded soil samples to evaluate their use as soil liner or cover materials. Specific

testing included gradation analyses, Atterberg Limits, maximum density/optimum moisture content

and hydraulic conductivity by flexible-wall permeameter. Hydraulic conductivity tests were

performed on undisturbed samples or on samples remolded to about 90 percent relative compaction.

Samples were tested at confining pressures of 1 to 5 psi, a range of values considered reasonable of a

final cover system, and considered very conservative for a composite liner system under anticipated

refuse loads. The results of laboratory tests on these materials are summarized in Table 6, and

individual test data sheets are included in Appendix H.

5.3 LABORATORY TEST RESULTS

The majority of the material to be excavated during development of the IWMF will be derived from

the Paso Robles Formation, and ultimately nearly the entire landfill will be directly underlain by this

formation. In addition, small quantities of canyon alluvium and colluvium/slide debris will be

removed. These native soils are derived from the Paso Robles Formation, and are generally similar

in lithologic characteristic.

Material Classification: Gradation and Atterberg Limit tests indicate that soils derived from the Paso

Robles Formation range from high plasticity clays (Unified Soils Classification - CH) to poorly

sorted cobbly sands (Unified Soils Classification – GW). The following table summarizes the

classification test results:

PARAMETER RANGE AVERAGE

In-Situ Moisture Content (%) 1.1 – 40.1 12.2 In-Situ Dry Density (pcf) 80.5 – 116.8 101.7 Fines Content (% minus 200) 8 - 100 37.1 Liquid Limit NP – 114 28.0 Plastic Limit NP – 41 13.8 Plasticity Index NP – 73 14.2

Shear Strength - Shear strength tests were performed on undisturbed and remolded samples of the

Paso Robles Formation to evaluate slope stability and engineered fills. The results from direct shear


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tests include:

PARAMETER RANGE AVERAGE Peak Value (18 Samples)

Friction Angle (degrees) 21 to 37 29.8 Cohesion (psf) 0 to 1800 950

Ultimate Value (18 Samples)

Friction Angle (degrees) 13 to 33 26 Cohesion (psf) 0 to 1200 458

Residual Value (1 Sample)

Friction Angle (degrees) 25 NA Cohesion (psf) 0 NA

Permeability - Laboratory analyses were performed on select undisturbed samples of the Paso Robles

Formation to determine its natural permeability as a hydrogeologic property for evaluating potential

contaminant transport. The permeability of undisturbed samples was analyzed at in-situ moisture and

density conditions.

The paucity of continuous fine-grained beds in the Paso Robles Formation suggests that this

formation could not be used as a source for the “clay” liner element of a composite liner system;

however, the materials could be considered for use as alternative final cover soils or other engineered

fills. Select bulk samples of this formation were remolded to approximately 90 percent of the

maximum dry density at 3 to 5 percent above the optimum moisture content. Samples were analyzed

at confining pressures ranging from 1 to 5 pounds per square inch, simulating near-surface conditions

of final cover soils or other engineered fills. The results are summarized below

SAMPLE TYPE

USCS CLASSIFICATION

PERCENT FINES

HYDRAULIC CONDUCTIVITY

(cm/s) Undisturbed SP 7.7E-4 Undisturbed SM 7.0E-4 Undisturbed SM-ML 29 2.3E-4 Undisturbed SC 1.3E-8 Undisturbed SM 3.6E-6 Undisturbed SC 3.7E-4 Undisturbed SC 12 6.0E-5 Undisturbed SM 9 4.8E-4 Undisturbed SM 1.2E-4 Undisturbed SM 5.5E-4 Remolded CH 82 7.0E-8 Remolded CH 87 2.9E-8 Remolded CH 100 4.3E-9 Remolded CL-ML 49 1.5E-5

Notes: SC – Clayey sand CH – High plasticity clay SM – Silty Sand CL – Low plasticity clay SP – Poorly graded sand ML – Low plasticity silt

Although the laboratory test data suggest that the hydraulic conductivities of some Paso Robles

Formation samples compacted to 90 percent might satisfy the regulatory requirement for a

prescriptive low-permeability soil liner material (i.e., 1 x 10-7 cm/s or less), field mapping and


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exploratory drilling suggest that these deposits are limited in aerial extent, and should not be relied

upon to provide the volume of low-permeability soil resources required for liner system construction.


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6.0 GEOLOGIC CONDITIONS

6.1 REGIONAL GEOLOGIC SETTING

The proposed IWMF is situated in the southernmost extent of the Coastal Ranges Geomorphic

Province, which extends approximately 600 miles north from the Santa Ynez River to the Oregon

border. In a general sense, the Coastal Ranges were initially formed in the Mesozoic era by

subduction of the Pacific plate beneath the North American plate and accretion of allocthonous

terrain to the continental landmass. During the Tertiary era, the development of the San Andreas

transform system resulted in a general relaxation of the portion of the westernmost portion of the

North American plate, creating deep ocean basins in much of the area now occupied by the Coast

Ranges. Over time, a change in the stress regime resulted in closure of these basins and uplift of the

terrain to form the modern Coast Ranges, including the local San Rafael Mountains and Solomon

Hills. The resulting terrain is characterized by north to northwest-trending moderate-relief ranges

separated by parallel valleys. Ranges are typically bounded by northwest-trending faults of the San

Andreas system, including the Hosgri, Nacimiento, and Rinconada faults.

The site is located in the north-central portion of the Solomon Hills, which are two upland areas

separated by the northwest-southeast trending Solomon Canyon and Orcutt Creek. The Solomon

Hills and the Casmalia Hills (west of the site) form the southern edge of the Santa Maria Valley.

These hills are gently undulating topographic highlands extending from the Pacific Ocean

(approximately 15 miles to the west) to the San Rafael Mountains (approximately 10 miles east of the

site). The Solomon Hills were formed by middle- to late-Tertiary compressional forces uplifting the

sedimentary and volcanic sequence. The oldest rock units underlying the Solomon Hills include

volcanic rocks assigned to the Franciscan Formation of probable Jurassic age (about 140 to 205

million years before present; mybp) and Jurassic metasedimentary rocks of the Knoxville Formation

(Woodring and Bramlette, 1950). A significant deposition hiatus occurred after Jurassic time so that

the next units are the Miocene-age (5 to 25 mybp) Lospe, Point Sal, and Monterey Formations and

the Obispo Tuff. The late Miocene to early Pliocene age (3.3 to 5.3 mybp) Sisquoc Formation

overlies the Monterey Formation, and it is overlain by the Foxen Claystone. The Pliocene sequence

(2 to 5 mybp) includes the Careaga Formation (Careaga Sandstone as defined by Woodring and

Bramlette, 1950), and the overlying Plio-Pleistocene age Paso Robles Formation. The Pleistocene-

age (11,000 to 1.6 mybp) Orcutt Sand is the youngest named rock unit in the Solomon Hills. The

regional geologic relationships are illustrated on Figure 2.

Since the uplift of the Solomon Hills, erosional forces have modified these materials by rounding the

areas underlain by unconsolidated Tertiary rocks and steepening areas underlain by consolidated

Tertiary bedrock. Canyons are filled with alluvial soils derived from the exposed bedrock. The


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eastern group of the Solomon Hills is adjacent to the Cat Canyon Oil Field. This field was first

developed in 1908 and has produced on the order of 300 billion barrels of oil and 180 billion cubic

feet of gas (as of the year 2000, County of Santa Barbara Planning Division, 2005). Interpretation of

geology in this region is based on field mapping of exposed units and stratigraphic interpretation

from oil field drilling.

6.2 LOCAL GEOLOGIC SETTING

The elevations at the proposed IWMF site range from 1,250 feet along the southern perimeter of the

landfill to a low of 850 feet in the northeastern portion of the site. The site is roughly composed of

two canyons (one in the north and one in the southern portion of the site). The northern canyon drains

to the northeast (to an elevation of 850 feet) and the southern canyon drains generally to the east (to

an elevation of 975 feet).

As mapped by Dibblee (1994) and Tennyson (1992), the site is underlain almost entirely by the

Pliocene/Pleistocene-age Paso Robles Formation, though the Pleistocene-age Orcutt Sand crops out

in the northeastern portion of the property. In addition to these two units, artificial fill/drilling mud,

recent alluvium and colluvium, landslide debris, and the Careaga Formation were encountered during

the field investigation. Geologic conditions encountered during this investigation are depicted on

Plate 3. Descriptions of these units are described in detail below. 6.2.1 STRATIGRAPHY

Each of the soil and rock units encountered during our field investigations is described in detail

below (from oldest to youngest) with its map symbol indicated in parentheses.

Careaga Formation (Tc; not exposed) - The Pliocene-age Careaga Formation (also identified as the

Careaga Sandstone or Careaga Sand in the literature) does not crop out within the IWMF property,

but was encountered at depths of over 500 feet below the ground surface in each of the monitoring

well borings and in the piezometer P-2 boring. As described by Woodring and Bramlette (1950), this

formation includes an upper Graciosa Member – a coarse-grained sandstone, and a lower Cebada

Member – a fine-grained sandstone. Although these two members are differentiated in outcroppings

located approximately 5 miles south of the site, Dibblee (1994) does not differentiate these members

in the subsurface beneath the project area. Woodring and Bramlette (1950) indicate a formational

thickness ranging from 50 to 1450 feet; however, interpretation of oil well logs suggests a thickness

of about 300 to 500 feet within the project site.

Where encountered, the Careaga Formation was observed to be a dark gray, fine to medium grained

silty sandstone and mudstone with zones of scattered megafossils (typically bivalved mollusks) and


-25-

rare wood fragments. Though not observed in the drill cuttings during this investigation, Woodring

and Bramlette (195) indicate that the Careaga Formation may contain local tar deposits.

The contact between the overlying Paso Robles Formation and the Careaga Formation appears to be a

gradational coarsening upward sequence that was often punctuated by a distinctive color change from

the yellow brown or olive-colored Paso Robles Formation to the dark gray Careaga Formation. A

structure-contour map depicting the Careaga-Paso Robles formational contact as identified during

this investigation is presented on Figure 3.

Paso Robles Formation (QTp) – The late Pliocene to Pleistocene-age Paso Robles Formation

currently directly underlies approximately 90 percent of the proposed landfill site, and is expected to

underlie the more than 95 percent of project site once grading is completed. The Paso Robles

Formation is poorly indurated and erosion of the unit forms rounded hills and broad valleys.

Outcroppings are rare; occurring only in the more resistant beds (cemented sandstones and

conglomerates). This formation is undifferentiated and has a maximum exposed thickness of about

2000 feet in the region, but is no more than 700 feet thick within the IWMF study area.

The Paso Robles Formation was encountered in all exploratory borings, monitoring wells, and

piezometers, and in most test pit excavations. It is typically a light brown to yellowish brown

quartzofeldspathic sandstone and chert-rich conglomerate. Sandstones range from fine- to coarse-

grained, and are generally poorly cemented, though well-cemented marly sandstone beds up to four

feet thick crop out along the western ridgeline. Conglomerate beds range from one to 10 feet thick,

and are internally massive with poor imbrication. Conglomerates are typically clast-support with a

poorly sorted, fine-to coarse sand matrix. Clast size ranges from pebble to cobble, and clasts are

nearly always very well rounded and spherical to roller in shape. Conglomerates are dominated by

chert clasts, but also contain minor quantities of various porphyritic plutonic and aphanitic volcanic

rocks. Few claystone beds were encountered in the Paso Robles Formation, and these were typically

less than six inches thick. At borehole BA-8 and test pit TP-25, light yellowish brown, highly plastic

sandy claystone was encountered near the ground surface. At approximately three feet thick, this was

the most extensive clay encountered within the proposed development area.

Bedding in the Paso Robles Formation is poorly developed in outcrop and in the subsurface. The

formation is primarily cross bedded, though the position of the site on the eastern limb of the Las

Flores-Cat Canyon anticline results in a northeasterly dip despite the cross bedding.

Based on the observed lithologies and the moisture-density data obtained during this investigation,

the Paso Robles Formation appears to have a high percentage of diatomite in its fine-grained beds,

and appears to be derived from erosion and reworking of the Pliocene age Sisquoc Formation or the


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lithologically-similar Miocene-age Monterey Formation. Woodring and Bramlette (1950) indicate

that the Paso Robles Formation is primarily a non-marine, fluvial deposit with clays and limestone

deposits representing overbank or lagoonal depositional environments

Orcutt Sand (Qo) - The Orcutt Sand is a tan to rusty brown colored, poorly cemented, sand and

gravel terrace deposit of Pleistocene-age that occurs on the ridge tops in the northeastern portion of

the proposed landfill site. The Orcutt Sand is well exposed in road cuts along Dominion Road

northeast of the northern canyon, and crops out near the intersection of the road that joins the north

canyon with the south canyon. As observed in site exposures, the Orcutt Sand is no more than 5 feet

thick. Due to its limited thickness and lateral extent at the site, the Orcutt Sand has no engineering

significance to the proposed site development.

Landslide Deposits (Qls) – Although the proposed IWMF site has been extensively disturbed by past

oil field operations, altering much of the native terrain, two relatively large potential landslide

features and several small debris flows were identified in the northern canyon, and two potential

landslides were identified in the south canyon. Landslide “A” is located on the southern slope of the

northern canyon and was investigated by Test Pits TP-14, TP-15, TP-18, TP-19, and TP-20. A well-

defined slip surface was observed in test pits at the toe of the slide, and clay- and silt-filled tension

fractures were observed in the test pits excavated at the head scarp. Landslide “A” failed in the Paso

Robles Formation, and these deposits will be completely removed during subgrade excavation.

Landslide “B” is a postulated feature that is located near the northeastern corner of the property in the

northern canyon. The anomalous geomporphology in this area of the site suggests that a large block

of the Paso Robles Formation was displaced into the canyon. No basal slip surface was identified in

the test pits excavated at the lower portion of this feature. However, TP-4, which was excavated

across the saddle at the top of this feature, revealed a series of silt-filled fractures up to 3-feet wide

suggesting a landslide or fault.

In the south canyon, high-angle, clay gouge-filled fractures were observed in borehole BA-10 at a

depth of 25 feet, suggesting the presence of an old landslide. Bedding planes observed beneath this

feature were oriented consistently and coincident with local bedding plane orientations. These

observations suggest a small slope failure that will be removed during mass grading of the proposed

IWMF. A second potential landslide was postulated based on the geomorphology and downhole

visual logging of borehole BA-11. At this borehole, the orientations of shallow bedding planes were

not consistent with the regional dip of the Paso Robles Formation, and a silt-filled fracture was

observed at a depth of 8 feet. Below this depth, bedding orientations were consistent with the

regional dip. Both landslide features will be removed by the proposed grading for the IWMF.

It is important to note that development of the site as an oil field began before much of the formal


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geologic mapping, aerial photography, and documentation of this area occurred. As a result of the

extensive alterations of the native terrain, most of the geomorphic features that could have been used

to interpret the presence of landslides have been removed. Consequently, landslides other than those

identified above may exist within the IWMF development area.

Alluvium (Qal) - Alluvium was encountered in the bottom of both the north and south canyons in

boreholes P-1, P-2, P-4, MW-1, and MW-3, and in test pits TP-2, TP-3, and TP-29, and ranged from

about 20 to 30 feet along the upper reaches of the canyon thalwegs (at piezometers P-2 and P-4),

deepening to about 75 feet at well MW-1. The alluvium was described as very dark brown to dark

olive brown, poorly sorted fine to coarse sand with silt and scattered organic matter. Local layers of

gravel, pebbles, and cobbles were encountered.

Topsoil (Qts; on borehole and test pit logs) - Topsoil were encountered in nearly all test pits and

exploratory boreholes. Topsoils are derived from the underlying alluvium or bedrock and were

observed to be typically very dark brown to dark grayish brown, dry to damp, silty to clayey sand

with mixed with roots, organic matter, and cow manure. Where soils had developed over

conglomeratic bedrock, the topsoil contained highly weathered, angular fragments of pebbles and

cobbles.

Artificial Fill/Drilling Mud (Af) - Drilling and construction of oil wells during the last century

resulted in the generation and disposal of large quantities of drilling mud in the bottom of both

canyons. In some areas, the drilling mud is not distinguishable from the alluvial soils, but in the

upper reaches of the south canyon, distinctive deposits of drilling mud up to 27 feet thick were

identified in boring P-5. At this location, the fill soils were described as dark brown, well sorted,

rounded to subrounded sand with some silt. Rills eroded though this deposit revealed blebs of tar and

vegetation entrained in the soil. Drilling muds were also encountered in test pits TP-30, TP-31, and

TP-32. At the test pit locations, the drilling mud was typically dark grayish brown to brown fine-

grained sand or silty sand, and were characterized with distinct irregular hairline fracturing indicating

desiccation or compressional dewatering.

In addition to the drilling muds, small artificial fills were encountered along existing roadways and as

barrage dams across the thalweg of the southern canyon. The artificial fills for the roadways are

composed of reworked bedrock mixed with asphalt or tar. The barrage dams are typically 3 to 8 feet

in height and approximately 10 feet wide, and are composed of reworked drilling mud mixed with

native soil and bedrock. Four barrage dams were observed in the southern canyon. The northern

canyon floor has been extensively reworked and the distinction between native alluvium and drilling

mud is not clear.


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6.2.2 STRUCTURAL GEOLOGY

Bedrock within the proposed IWMF is situated on the eastern limb of the Cat Canyon-Los Flores

anticline (Plate 3), and as a result, bedding plane orientations in undisturbed bedrock is relatively

consistent across the site. The axis of the Cat Canyon-Las Flores Anticline (as mapped by Tennyson,

1992 and Dibble et. al, 1994) is just west of the western ridgeline. In general, the bedding in the

northern half of the site has a strike ranging from 30 degrees west of north to 5 degrees east of north,

with a dip ranging from about three to 9 degrees to the east-northeast. The bedding in the southern

half of the site has a strike ranging from 20 to 60 degrees west of north with a dip ranging from 3 to 6

degrees to the northeast.

No active faults are known to cross the site, and aside from fractures associated with slope failures,

only a few small, localized faults and fractures were observed in the study area. A minor vertical

fault striking approximately 50 degrees east of north was mapped along a road cut in the south

canyon near borehole BA-11. At this location, the Paso Robles Formation beds are offset several

feet. A similar pattern of jointing was observed on the road cut between the IWMF site and Highway

101.

6.3 SEISMICITY

This section of the geotechnical investigation report presents the general tectonic and seismic

framework of the area surrounding the proposed IWMF site and the seismic hazard assessment based

on known seismic sources.

6.3.1 SEISMIC FRAMEWORK AND POTENTIAL EARTHQUAKE SOURCES

The proposed IWMF is situated in the Solomon Hills, which are among the southernmost ranges of

the Coastal Ranges Geomorphic Province. The Solomon Hills are the surface expression of an

“upfold” or anticline uplifted along a fault zone extending along the northern flanks of this

topographic highland. Seismicity in this region is usually associated with translational breakage

along numerous strike-slip faults that are generally parallel to the San Andreas Fault, which is located

approximately 42 miles east of the site at its closest approach, though antithetic reverse/thrust faults

are also located within distances considered to be of engineering significance to the site. There is no

volcanic activity in the vicinity of the site.

Although no evidence of Holocene-age faulting on the property has been found either through a

review of available literature or through site investigations, and the proposed IWMF site is not within

or near any State of California Earthquake Fault Zones (as mandated by the Alquist-Priolo


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Earthquake Fault Zoning Act passed in 1974 and updated through 1999), several active or potentially

active faults are located within distances of engineering significance to the site, including the

Casmalia-Orcutt Frontal Fault, the San Luis Range Fault, the Los Alamos-West Baseline Fault, the

Lion’s Head Fault, the offshore North Channel Slope Fault, and the San Andreas Fault. These local

faults are further described as follows:

The Casmalia-Orcutt Frontal Fault is located 1.8 miles east of the site and trends northeast-southwest.

This reverse fault juxtaposes Quaternary age rock of the Orcutt Formation against older rocks of the

Tertiary Sisquoc and Careaga formations. Because Quaternary rocks are offset, this fault is classified

as potentially active (having movement from 11,000 to 2 million ago). The fault is approximately 29

kilometers (km; 17.5 miles) long and has a slip rate of 0.25 millimeters per year (mm/yr; 0.01

inch/year). The fault has a Maximum Credible Earthquake (MCE) Magnitude of 6.5 (USGS, 2002)

and an estimated Maximum Probable Earthquake (MPE) Magnitude of 5.5.

The San Luis Range Fault is a northwest-southeast trending fault 4.7 miles northeast of the site lying

just to the northeast of Santa Maria. This thrust fault has a slip rate of 0.2 mm/yr (0.01 inch/yr) and

is approximately 64 km (38.5 miles) long. The fault has a Maximum Credible Earthquake (MCE)

Magnitude of 7.0 to 7.2 (USGS, 2002) and an estimated Maximum Probable Earthquake (MPE)

Magnitude of 5.3.

The Los Alamos-West baseline Fault is 5.0 miles south of the site and is classified as active (having

Holocene movement within the last 11,000 years). The thrust fault has a slip rate of 0.7 mm/yr (0.03

inch/yr). The fault has a Maximum Credible Earthquake (MCE) Magnitude of 6.7 to 6.9 (USGS,

2002) and an estimated Maximum Probable Earthquake (MPE) Magnitude of 5.5.

The Lion’s Head Fault is an extension of the Casmalia Fault and lies 6.5 miles south of the site. This

reverse fault is approximately 41 km (24.5 miles) long and is identified as potentially active (having

Quaternary displacement from 11,000 to 2 million years ago). The fault has a Maximum Credible

Earthquake (MCE) Magnitude of 6.6 (USGS, 2002) and an estimated Maximum Probable Earthquake

(MPE) Magnitude of 5.5.

These local faults govern the seismic hazard of the proposed landfill. Larger active regional faults

(such as the North Channel Slope Fault and the San Andreas Fault) are at a much greater distance

from the site, and as a result, pose a less significant concern with respect to strong ground motions.

A summary of active faults within 100 km of the site is provided on Table 7. Significant faults are

shown on Figure 4.


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6.3.2 SEISMIC HAZARD ASSESSMENT

Although Title 27 of the California Code of Regulations (27 CCR) requires that slope stability

analyses performed for a Class III municipal solid waste landfill be based on the expected Probable

Ground Acceleration (PGA) at the site associated with the Maximum Probable Earthquake (MPE),

more recent analyses are deriving the anticipated PGA from a Probabilistic Seismic Hazard

Assessment (PSHA) approach and not a deterministic approach. This trend applies to both the

geotechnical engineering profession as a whole, as well as to the preferences of individual Regional

Boards and is allowed for in 27 CCR which states that: “Data and procedures shall be consistent

with current practice …”.

A deterministic analysis derives the PGA at a site generated by an individual earthquake fault, and

the PGA is the largest acceleration value at the site based on all known fault sources. The

deterministic PGA at a site is a function of the site-to-source distance, the MPE magnitude, the

rupture scenario, and the selected attenuation relationship used to model the diminution of shaking

intensity with distance for all possible fault sources within a reasonable distance considered

individually.

Conversely, the PSHA, determines the PGA by assigning probability distributions at every step in the

process, including recurrence interval, magnitude, distance, rupture dimensions, and attenuation. Not

only does a PSHA consider all possible magnitudes of earthquake on all known causative faults, but

it also considers “background seismicity" (i.e. discrete faults that are currently unknown). The

results of a PSHA are expressed as a site PGA having a probability (P) of being exceeded in a certain

number of years (t). This probability may be expressed as:

(Kramer, 1996), where:

P = Probability of exceedance

λ = mean annual rate of exceedance (1/λ = earthquake return period)

t = time period of interest.

With this definition, it can be shown that a 10% exceedance probability in 50 years is equivalent to

an earthquake recurrence interval of 475 years. While not specifically defined by Title 27, the 10%-

in-50 year probability is nominally associated with a Maximum Credible Event (MCE) level event,

representing an event with a 475 year return period.

teP 1


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In order to select representative earthquake time histories for ground motion analyses, a single design

earthquake event, with a unique magnitude and source-to-site distance, is considered. To arrive at

these parameters in a PSHA, the data must be deaggregated to determine the modal event. The

PSHA modal event is the magnitude-distance pair, which results in the largest contribution to the

seismic hazard at a given site.

The PSHA-derived PGA at the site, which considers all possible events as discussed above, accounts

for source-to-site attenuation by means of one or more attenuation relationships. The attenuation

relationship selected for use should be consistent with the site conditions since some attenuation

relationships are for “Soil” or “Rock,” while others are more specific, such as “NEHRP Site C.”

National Earthquake Hazard Reduction Program (NEHRP) site classifications, which were adopted

in the 1997 Uniform Building Code (UBC), consider the seismic shear wave velocity within the top

30 m (100 feet) of soil (Vs-30), which can vary from less than 180 meters per second (m/s) for soft soil

(Type E) to greater than 1,500 m/s for hard rock (Type A). A benchmark site condition used by the

USGS to estimate seismic hazard is the NEHRP Type B/C boundary, which represents the boundary

between Type B (rock) and Type C (very dense soil/soft rock) with Vs-30 = 760 m/s (2,500 ft/s).

A 10%-in-50-year probability PSHA-based estimate of the PGA at the Type B/C boundary, as well

as the deaggregated modal magnitude and distance, were also obtained from a USGS website (USGS,

2002) for the site. The PGA value of 0.28g (Appendix I) is associated with a moment magnitude 6.6

event at a distance of 6.9 km (4.3 miles). Strictly speaking, these design events do not refer to a

specific fault, but are strongly influenced by the nearby Casmalia, San Luis Range, and Los Alamos

Faults.

A deterministic analysis was also performed to confirm that this approach would not yield a greater

PGA. As shown in Appendix I, calculated maximum probable earthquake (MPE) events near the site

were identified using the computer program EQFAULT (Blake, 2004a). Although the MPE values

are not currently reported by the USGS, the MPE values from Blake (2004a) were slightly increased

based on the results of the EQSEARCH analysis (Section 6.3.3) and to account for slight increase in

the MCE values in the last 10 years. The attenuation relationship used was based on data from Boore

et. al., (1997) and the site shear wave velocity obtained from the site geophysical evaluations. The

seven seismic traverses were analyzed for the shear wave velocity in the upper 100 feet of the

traverse. The average of the traverses yielded an average shear wave velocity of 375 m/s. The

program does not have an attenuation relationship for 375 m/s, so an attenuation relationship for 350

and 400 m/s were analyzed and averaged to evaluate the PGA. Accordingly, the deterministic

approach to the PGA (using EQFAULT) yielded a site acceleration of 0.27g. The controlling fault

was the Casmalia (Orcutt Frontal) Fault at a distance of 1.8 miles (2.9 km) with a MPE magnitude of

5.5. This value compares favorably with a PGA of 0.28g calculated from the probabilistic approach.


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A list of the faults within 60 miles (100 km) of the site, their MPE magnitudes and distance to the site

is presented in Appendix I.

6.3.3 HISTORIC SEISMICITY

A review of the previous seismic history of the site was performed to evaluate if historic events could

govern the seismic analysis. As presented in Appendix I, a review of these events was performed by

EQSEARCH (Blake, 2000) to catalogue historic earthquake epicenters within a 100 km radius of the

site. All catalogued earthquakes within the selected search radius with a magnitude greater than 5.0

occurring after 1800 are listed. Based on the available historic data, the site has experienced a

maximum acceleration of about 0.24g during a magnitude 5.7 earthquake which occurred on

December 12, 1902 at distance of about 4.0 miles (6.4 km). This is less than the site acceleration

calculated by the deterministic and PSHA approaches.

6.3.4 SEISMIC DESIGN SUMMARY

Based on the deterministic PGA of 0.27g, the largest historic PGA of 0.24g, and the PSHA PGA of

0.28g, we have chosen a site design PGA of 0.28g. The deaggregated modal event to be used for

design calculations will be a magnitude 6.6 event at a distance of 6.9 km (4.3 miles). This approach

will provide a greater magnitude event (and consequently a longer duration event) and a greater PGA

at the site than the deterministic MPE event of magnitude 5.5 at a distance of 1.8 miles (2.9 km).


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7.0 GROUNDWATER CONDITIONS

7.1 REGIONAL GROUNDWATER CONDITIONS

The proposed IWMF site lies within the Sisquoc Hydrologic Area of the Santa Maria Hydrologic

Unit, which encompasses roughly 1600 square miles between the San Luis and Santa Lucia Ranges

to the north, the San Rafael Mountains to the east, the Casmalia and Solomon Hills to the south, and

by the Pacific Ocean to the west (Figure 5). This area includes the Cuyama and Santa Maria-Sisquoc

river valleys, Orcutt Creek, and Huasna River. The Sisquoc Hydrologic Area occupies the southern

third of the Hydrologic Area and includes the Santa Maria-Sisquoc River Valley (and all its

tributaries) upstream of its confluence with the Cuyama River. Cat Canyon and the northern flanks

of the Solomon Hills, including the IWMF area, eventually drain into this portion of the Santa Maria-

Sisquoc River Valley. Water-bearing units in the Santa Maria Valley include recent alluvium and

dune sands, the Pleistocene-age Orcutt Formation, the Pleistocene-Pliocene Paso Robles and Pismo

Formations, and the Pliocene-age Careaga Formation. The average combined thickness of water-

bearing units is approximately 1000 feet, with a maximum thickness of about 3000 feet (CDWR,

2004). Groundwater generally flows from southeast to northwest under unconfined conditions,

though groundwater is confined near the coast.

According to the Central Coast Basin Plan (1994), all groundwater in the Santa Maria Valley is

considered to have beneficial use except where:

The total dissolved solids (TDS) concentration exceeds 3000 milligrams per liter (mg/L) or the

electrical conductivity exceeds 5000 microsiemens per centimeter (S/cm). Contamination exists that cannot reasonably be treated for domestic use. The groundwater source is not sufficient to supply an average sustained yield of 200 gallons per

day. The water is in collection or treatment systems of municipal or industrial wastewaters, process

waters, mining wastewaters, or stormwater runoff. The water is in systems for conveying or holding agricultural drainage waters.

Groundwater sampling and analysis and aquifer testing was conducted to determine if the

groundwater present beneath the site meets these requirements to be considered a beneficial use

resource, and the results of these analyses are presented in the following sections. 7.2 LOCAL GROUNDWATER CONDITIONS 7.2.1 GROUNDWATER OCCURRENCE

Within the proposed IWMF study area, three groundwater occurrences were identified. Perched

groundwater was identified in the canyon alluvium and uppermost weathered bedrock, groundwater


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seeps were identified in the Paso Robles Formation, and regional groundwater was encountered in the

Careaga Formation.

Alluvial Groundwater - Groundwater was encountered in the north canyon during drilling of

piezometers P-1 and P-2. Alluvial groundwater appears to be unconfined and perched, and does not

extend down-canyon to well MW-1. Based on the geologic logs of these borings, it appears that

groundwater is perched above thin limestone layers at or just below the contact with the underlying

Paso Robles Formation. A similar limestone layer was observed in the boring for piezometer P-4, but

no free groundwater was encountered. Piezometer P-1 was constructed to monitor alluvial

groundwater in the north canyon. Based on bail-down and recovery tests conducted in P-1, the

alluvium has a hydraulic conductivity of 1.60 x 10-1 feet per day (ft/day) to 6.55 x 10-1 ft/day. At P-

1, the saturated thickness is approximately 25 feet, and at P-2 the saturated thickness was observed to

be approximately 4 feet. Based on these measurements and observations, the alluvium has a

transmissivity of about 0.64 to 16.4 ft2/day. Alluvial groundwater is likely recharged from direct

infiltration of precipitation onto the canyon bottom and runoff from adjacent slopes. Some recharge

may occur from seepage through the adjacent Paso Robles Formation.

Based on preliminary designs for the proposed IWMF, nearly all of the canyon alluvium will be

removed during site development, and as a result, the alluvial groundwater is not expected to affect

construction and operation of the facility. The alluvium in the south canyon was not observed to be

saturated, but will also be removed during site development.

Groundwater in the Paso Robles Formation - Groundwater seepage was encountered in the Paso

Robles Formation throughout the study area, both in surface seeps as shown on the geologic map

(Plate 3) and in the subsurface as observed in the bucket auger borings BA-5 (from 13 to 18 feet bgs)

and BA-9 (at 29 feet bgs). The observed seeps do not occur over widespread areas and do not appear

to represent a continuous zone of saturation in the Paso Robles Formation. Rather, seepage was

typically observed as localized zones of moisture or small puddles of free water near the contact of

sandstone or conglomerate layers over cemented sandstone/limestone layer. During the span of this

investigation, seepage quantities were too small to measure in the field, though seepage flows may

increase following periods of prolonged or heavy rainfall.

Groundwater in the Careaga Formation - The most significant groundwater occurrence is in the

Careaga Formation, and this occurrence correlates with the regional groundwater table in the Santa

Maria Valley to the east of the site. Groundwater was encountered in the Careaga Formation in each

of the monitoring wells and in piezometer P-2 at depths ranging from 500 to 712 feet bgs. These

monitoring points are constructed specifically to screen the uppermost zone of saturation in the

Careaga Formation. The top of the saturated zone was identified in each of the monitoring well


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boreholes using sonic velocity/variable density surveys whereby a sound wave is generated by the

geophysical probe, and is lost in unoccupied pore spaces in the rock. When the pore spaces are filled,

the signal is reflected back to the probe indicating the presence of water (or other liquids).

Each well was screened across the upper 30 to 60 feet of the saturated zone. During well

development, water was removed at a sufficient rate from each well to substantially lower the water

level. Bail down and recovery testing was performed in the monitoring wells and piezometers to

estimate hydraulic characteristics of the screened intervals. Hydraulic conductivity values were

estimated using the computer program Aquifer Test Pro (Waterloo Hydrogeologic, 2002) according

to the solutions developed by Hvorslev and Bouwer and Rice. The Hvorslev Method calculates

hydraulic conductivity using rising head (recovery) data from the bail down test according to the

formula:

K = r2ln(Le/R) 2LeTo

Where: K = hydraulic conductivity (ft/day) r = well casing radius (ft) R = borehole radius (ft) Le = length of screen and filter-pack (ft) To = time for water to rise 37% of the initial change (days)

Allowing for potential error in the plot of the best fit line for available data, a range of To values was

used to calculate a suite of hydraulic conductivity values for the bedrock surrounding each well.

Calculations indicate that Careaga Formation 0.0203 ft/day (7.16 x 10-6 cm/s) in MW-4 to 0.00178

ft/day (6.28 x 10-7 cm/s) in piezometer P-2. Bail down and recovery test data and curve matching

output are presented in Appendix H.

Because other analytical solutions exist to determine the hydraulic characteristics in wells under

similar conditions, hydraulic conductivity values were also calculated using the Bouwer and Rice

method (Fetter, 1994). By comparing the results of the two analytical solutions, the results of the

recovery tests were verified to be reasonably accurate. The Bouwer and Rice method calculates

hydraulic conductivity using the following formula:

K = rc2ln(Re/R) ln(Ht/Ho)

2tLe

Where: K = hydraulic conductivity (ft/day) rc = well casing radius (ft) R = gravel envelope radius (ft) Re= effective radius over which head is dissipated (ft)


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Le = length of screen and filter-pack (ft) Ho = the drawdown at time t = 0 (ft) Ht = the drawdown at time t (ft)

t = time since H = Ho (day)

Since the variable Re cannot be reasonably estimated in a single well test such as those performed

during this investigation, the Bouwer and Rice method offers curve matching solutions to

approximate the value of this variable depending on whether the well screen fully or partially

penetrates the aquifer. Taking into account the well-specific geologic conditions, the Bouwer and

Rice method yielded hydraulic conductivity values for the Careaga Formation bedrock ranging from

0.0163 ft/day (5.75 x 10-6 cm/s) in well MW-4 to 0.00145 ft/day (5.12 x 10-7 cm/s) in piezometer P-2

(Appendix F; Table 8).

Bail down and recovery tests were performed after drilling muds and over 500 gallons of water were

removed from each well. As a result, the calculated hydraulic conductivity results are expected to be

representative of the formational materials and should not be affected by residual drilling mud.

Groundwater levels were routinely measured throughout the duration of field work and prior to

subsequent groundwater sampling events to estimate static water levels in each well. A contour map

depicting the potentiometric surface of the bedrock groundwater as of June 18, 2007 is presented as

Figure 6. Based on this groundwater elevation data, bedrock groundwater the site appears to flow in

a northeasterly direction at a gradient of about 0.05 to 0.07 ft/ft. This interpretation suggests that

wells MW-2 and MW-4 are upgradient of the proposed landfill, and wells MW-1, MW-3, and MW-5

are downgradient of the landfill. Piezometers P-1 and P-2 are located within the proposed disposal

site footprint and will be decommissioned prior to waste disposal activities. Based on this gradient, a

reasonable estimate of bedrock porosity, and the hydraulic conductivity values calculated above, the

seepage velocity in bedrock is calculated as follows:

V = KI

ne Where: V = Seepage velocity (ft/day) K = Hydraulic conductivity (ft/day) I = Hydraulic gradient (ft/ft) ne = Effective porosity (dimensionless)

Assuming that hydraulic conductivities calculated from the bail down and recovery tests are

representative of the Careaga Formation beneath the site, the seepage velocity beneath the proposed

IWMF ranges from 0.0003 ft/day to 0.0016 ft/day (0.11 to 0.58 feet per year).


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7.2.2 BEDROCK GROUNDWATER QUALITY

Groundwater samples were first collected from wells MW-1 through MW-5 on June 19 and 20, 2007.

The samples were collected with a stainless steel bailer that was decontaminated between each well

sample. Each sample was analyzed for general chemistry parameters (chloride, nitrate as nitrogen,

sulfate, and total dissolved solids), total petroleum hydrocarbons, and all constituents in Appendices I

and II of 40CFR Part 258.1. These constituents include: cyanide, sulfide, 17 metals, volatile organic

compounds (VOCs), semivolatile organic compounds (SVOCs), chlorinated herbicides,

organochlorine and organophosphorus pesticides, and polychlorinated biphenyls (PCBs). During

sampling, field measurements of pH, specific conductance, temperature, and turbidity were also

recorded. The results obtained from each well during the course of this investigation are compiled in

Table 9.

With the exception of four VOCs that were also detected in blank samples (suggesting field or

laboratory contamination), and one SVOC (bis[2-ethylhexyl]phthalate; also a common laboratory

contaminant), no organic compounds were detected in these samples. Analysis of the water quality

results from the first sampling period indicates that a few general chemistry constituent

concentrations exceed local, state, and/or federal standards (Table 6). Chloride concentrations in

samples from wells MW-1 and MW-2 exceed the Basin Objective established by the Central Coast

Regional Water Quality Control Board for the Sisquoc Hydrologic Area. The sulfate and total

dissolved solids concentrations measured in the sample from well MW-2 exceed the respective State

of California secondary drinking water standards for these constituents. These findings represent

background conditions for the proposed development.


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8.0 ENGINEERING ANALYSES

Engineering analyses were completed in support of the design of suitable slope orientations and

gradients and for adequate leachate collection at the proposed IWMF site. Slope orientations, phase

delimiters, and composite liner system designs were developed in coordination with Bryan A. Stirrat

& Associates (BAS). Iterative stability analyses were performed to evaluate the static and seismic

stability of the proposed subgrade and final refuse fill slopes. Individual phasing plan analyses will

be submitted under a separate cover as these designs are completed. The analytical methods, input

data, and results of the engineering analyses are described in the following sections.

8.1 SLOPE STABILITY

As the development of the IWMF is still many years away, only overall subgrade and completed final

fill slope geometries have been developed and analyzed. Phasing plans and interim slope

configurations have not yet been finalized. (Hypothetical interim refuse fill slopes were developed as

part of the this study to analyze minimum run-out lengths and maximum refuse height for refuse cells

design.)

Analysis of slope stability is mandated for subgrade slopes by 27 CCR Section 21750, which requires

stability analysis to ensure the integrity of the “Unit”, including its foundation, final slopes, and

containment systems under both static and dynamic (earthquake-loading or seismic) conditions

throughout the Unit’s life, closure period, and post-closure maintenance period. Although 27 CCR

requires that earthquake-loading conditions for Class III landfills must account for the peak ground

acceleration (PGA) associated with the MPE event, the analyses presented herein are based on a

PSHA that results in a higher PGA that is an MCE PGA equivalent. In accordance with 27 CCR

Section 21750, both subgrade and final refuse fill slopes must have a factor of safety of at least 1.5

under both static and seismic loads. If the factor of safety for a slope is less than 1.5, then a more

rigorous displacement analysis must be performed, and the results of this analysis must demonstrate

that a slope will experience minimal displacement during the design seismic event. A displacement

of 12 inches is generally considered the maximum movement that a slope can accommodate without

compromising the integrity of the composite liner system components and other environmental

control systems (Seed and Bonaparte, 1992), and this criterion was used to guide the design of slopes

under earthquake-loading conditions. Analytical methods and results are described in more detail

below.


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8.1.2 ANALYTICAL METHODS

Conventional two-dimensional static and pseudo-static stability analyses were performed using

Morgenstern-Price/constant side force option within the limit equilibrium slope stability SLOPE/W

computer program (GEO-SLOPE International, 2004). The SLOPE/W program calculates the

factor-of-safety for a user-specified geometry using a number of analytical methods to evaluate limit

equilibrium. A variety of search procedures were utilized to determine the critical potential failure

surface. When applicable, the analyses took advantage of a slip surface optimization procedure

within SLOPE/W wherein the lowest factor-of-safety potential slip surface at the end of standard

limit equilibrium iterations is further iterated on a segment-wise basis to find potentially lower factor

of safety (and often non-circular) slip surfaces. Use of this procedure will always result in a factor of

safety that is as low or lower than if it had not been used (i.e. it is conservative).

Slope stability under the design PGA for the project (discussed in Section 6.3) was first evaluated by

pseudo-static analysis using the slope stability analysis procedure described above. In most analyzed

iterations, the calculated pseudo-static factor of safety was less than 1.5, requiring additional analyses

to estimate the displacement anticipated during the PGA as allowed by 27 CCR Section

21750(f)(5)(D). As a result, pseudo-static factors of safety are not reported, and the computer-

generated stability analyses included in Appendix I do not contain the results of the traditional

pseudo-static analysis. The yield acceleration was determined for each cross section through an

iterative process of calculating the pseudo-static factor-of-safety for different applied seismic

coefficients until a factor of safety of 1.0 was obtained. Then seismically induced permanent

displacement was estimated using a procedure described by Bray and Rathje (1998) and Bray, et al.

(1998) which accounts for site-specific shear wave velocities, earthquake period, and the period of

waste to calculate a maximum horizontal equivalent acceleration (MHEA) with which the yield

acceleration is compared to determine seismically-induced displacement. Spreadsheets and

analytical output are presented in Appendix J.

8.1.3 GEOTECHNICAL PARAMETERS FOR SLOPE STABILITY

Geologic conditions modeled by the stability analysis were based on information obtained during

drilling and logging of boreholes and test pits, interpretation of geophysical data, and field mapping

of observed structural features. Resultant data and interpretations were plotted on a site topographic

map and extrapolated into the proposed development plans. Despite the presence of a few minor

landslide features, no evidence of major slope instability was observed during our investigation

within the proposed IWMF site.

The stability of the proposed IWMF subgrade, fill slopes, and proposed liner systems was then

evaluated using strength parameters from tests performed on materials recovered from the site during


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this investigation (Appendix H) and review of available literature for geosynthetic interface and

refuse strengths. Bedding observed in outcrop and within the borings was found to be discontinuous

or poorly defined and near horizontal, and as such, isotropic strengths were used. Parameters for the

isotropic bedrock conditions were analyzed using the data directly obtained in laboratory direct shear

tests. Ultimate normal and shear loads were plotted to create a composite cohesion intercept and

friction angle. Peak data was plotted in the same manner and used for pseudostatic analysis. To

check the sensitivity of the model, other strength configurations were also analyzed. Material

strength values used in this evaluation are presented on the following table.

PARAMETERS USED FOR STABILITY ANALYSIS

UNIT

UNIT WEIGHT (pcf)

COHESION

(psf)

ANGLE OF INTERNAL FRICTION (degrees)

Paso Robles Formation (peak) 115 750 31 Paso Robles Formation (ultimate) 115 300 28 Alluvium 125 200 30 Engineered Fill/Soil Liner 120 200 32 Refuse 80 200 30 Geotextile-Textured HDPE Interface 10 0 14 Geotextile-Smooth HDPE Interface 10 0 8 GCL Internal Strength (Non-Encapsulated) 10 400 8 GCL Internal Strength (Encapsulated) 10 400 14

Two different liner sections are proposed for the IWMF development. The proposed liner section for

subgrade areas steeper than 5:1 (slope areas) consists of prepared substrate overlain by a GCL, which

is overlain by an 80-mil single textured HDPE (texture side down) which is, in turn, overlain by a

geocomposite drainage layer covered with two feet of select protective soils. For floor areas (i.e.,

slopes <5:1), the proposed liner section consists of a 6-inch-thick low permeability soil layer overlain

by a GCL and an 80-mil double-sided textured HDPE membrane that will be covered, sequentially,

with a cushion geotextile, a 9- to 12-inch thick gravel and perforated pipe LCRS, a geotextile filter

layer, and a 24-inch thick protective soil layer.

Based on our experience and as presented in the table above, the interface shear strength between the

non-woven geotextile and the HDPE geomembrane or the internal strength of the GCL is likely to be

the governing critical interface for both back slope and floor liner stability. The shear strength of the

recompacted low permeability soil or engineered fills is not critical, as its as-built shear strength will

be specified to be greater than that of the other interfaces. Based on our analyses, GLA recommends

a portion of the GCL be encapsulated with an underlying geomembrane to minimize saturation

potential, and increase the internal shear strength of the GCL to improve stability of the overlying

refuse fill. In addition, compacted engineered soil fill berms are recommended at the mouth of the

northern and southern canyons (along Cross Section D-D’ and L-L’) to achieve the required refuse

fill stability.


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Long-term stability of the refuse slopes and liner sections is dependent on maintenance of drained

slope conditions to prevent elevated hydrostatic pressures within or below the liner system. The

analytical model assumes a fill sequencing plan that places refuse in single lifts (plus or minus 20

feet) uniformly across the entire floor of the development area. Filling with single lifts of uniform

thickness creates a slow loading process and thereby minimizes the potential for developing excess

pore pressures. It also minimizes eccentric loading and related instability. 8.1.4 SUBGRADE SLOPE STABILITY ANALYSES

General - The slope stability analyses completed for the proposed IWMF is based on the subgrade

and final refuse fill slope grading plans developed by BAS (Plates 1 and 2). The proposed grading

plan incorporates approximately 196 acres that are bound by perimeter ridgelines. The proposed

IWMF subgrade will range in elevation from 860 feet amsl at the northeastern corner of the northern

canyon to about 1250 feet along the western ridgeline. Bounding slopes will typically be cut at a 2:1

(horizontal:vertical) gradient between benches with 15-foot wide benches spaced at 40-foot vertical

increments, resulting in an overall slope ratio of 2.5:1. The floor area will be divided by a crestline,

where the southern half of the site will drain to the east out the mouth of the southern canyon, and the

northern half of the site will drain to the northeast out of the mouth of the northern canyon. The

gradient across the floor areas will be approximately 3 percent.

The proposed IWMF grading will remove alluvium, drilling mud, and other unqualified soils so that

the landfill subgrade is made up of bedrock of the Paso Robles Formation or engineered fills. Based

on field investigations, preparation of the subgrade should result in complete removal of identified

landslides. Overexcavation is recommended in the northern and southern canyons to remove

alluvium. Removals should be observed by a geologist/representative of the geotechnical consultant.

This material can be reused as compacted, engineered fill for the soil berms to be constructed across

the mouths of both canyons to provide subsurface drainage containment for the composite liner

system and enhance the stability of the overlying refuse fill slopes. Additional engineered fills may

also be required to bring native slopes up to design grades. The fill soils for these soil berms as well

as all other engineered soil fill should be moisture-conditioned and compacted to a minimum relative

compaction of 90 percent (based an ASTM Test 1557) under the observation and testing of a

representative of the geotechnical consultant.

The proposed IWMF development will ultimately be divided among eight phases (1A, 1B, and 2

through 7). The analyses described herein consider the final subgrade and final refuse fill slopes.

Phase-specific design analyses will be submitted under separate cover as the design process

advances.


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Analytical Results - Ten geologic cross-sections were developed to analyze the variable geologic

conditions and slope orientations presented in the proposed IWMF development plan (Plates 1, 3, and

4). Based on field investigations, the proposed grading plan (Plate 1) will result in removal of

surface soils, drilling mud, and landslide debris, and most of the alluvium. During grading, it is

anticipated that areas of remaining alluvium will be identified, removed, and replaced with

engineered fill. The completed grading plan will result in a subgrade that is underlain almost entirely

by the Paso Robles Formation, with minor amount of engineered fill replacing the alluvium.

Groundwater conditions encountered during this investigation suggest small areas of seepage may be

encountered, but the saturated areas and flow rates are sufficiently small so that these areas can be

intercepted and mitigated with local subdrains. Due to the granular nature of the Paso Robles

Formation, pervasive saturated conditions and accumulation of pore water pressures are not

anticipated. Consequently, stability analyses were performed assuming drained conditions with a

minimum five-foot separation between the groundwater surface and the subgrade.

Subgrade stability simulations were performed assuming isotropic strength conditions (i.e., the

strength of breaking across a bed is similar to the strength of breaking along a bedding plane), with

failures occurring along arcuate or rotational surfaces. This assumption is based on field

observations that the Paso Robles Formation, which will underlie approximately 99 percent all slope

areas of the site after grading is completed. The Paso Robles Formation has poorly developed

bedding planes (as described in Section 6 of this report), and jointing in the formation is also poorly

developed. These conditions suggest that geologic structure has little effect on stability and block

failure or failure along weak bedding planes is not likely. Consequently, isotropic strengths are more

representative of site conditions. (We note that the upper 5 to 10 feet of Section G-G’ may be

underlain by the Orcutt Sand, but its position in the slope has no measurable bearing on slope

stability).

The computer-generated analytical results are presented in Appendix J1, and are summarized on the

following table.

SUMMARY OF SUBGRADE SLOPE STABILITY ANALYSES

SECTION

SLOPE

HEIGHT

SLOPE

DIRECTION

CANYON

STATIC FACTOR

OF SAFETY

SEISMIC ANALYSIS YIELD

ACCELERATION DEFORMATION

(INCHES) A-A’ 160 feet Southeast Northern 1.65 0.37g 0 B-B’ 260 feet South Northern 1.59 0.33g 0 C-C’ 310 feet East Northern 1.54 0.30g 0 D-D’ 300 feet Northeast Northern 1.57 0.31g 0 E-E’ 230 feet East Between 1.54 0.31g 0 F-F’ 100 feet West Northern 1.68 0.43g 0


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SECTION

SLOPE

HEIGHT

SLOPE

DIRECTION

CANYON

STATIC FACTOR

OF SAFETY



(INCHES) G-G’ 140 feet Northwest Northern 1.68 0.39g 0 H-H’ 200 feet Southeast Southern 1.61 0.34g 0 J-J’ 250 feet Northeast Southern 1.58 0.32g 0

K-K’ 220 feet Northwest Southern 1.60 0.33g 0

As summarized in the above table, the static factor of safety for each cross section exceeds 1.5, which

is the minimum static factor of safety deemed acceptable by 27 CCR. In lieu of calculating

pseudostatic factors of safety, yield accelerations were calculated and compared to the PHSA for an

MCE-equivalent event. As shown in the above table, for each cross section, the yield acceleration

exceeds the PHSA (0.28g; Section 6.3.4). This indicates that an MCE-level earthquake would have

no measurable effect on any of the proposed IWMF subgrade slopes. In addition, permanent seismic

displacement was calculated in accordance with the Bray and Rathje (1998) method presented in

Appendix J. The results also indicate a negligible seismic displacement under the MCE event. This

analysis indicates that the proposed design meets the seismic design parameters for foundation slopes

under 27 CCR Section 20370.

8.1.5 INTERIM REFUSE FILL SLOPE STABILITY

Interim refuse fill slope stability analyses were conducted to determine the maximum refuse height

and runout length relationships to provide guidance for future operations of the landfill.

General - In addition to evaluation of the proposed IWMF excavation slopes, the stability of interim

refuse fill configurations was assessed in light of the anticipated interface strengths of the various

components of the proposed composite liner system. Interim refuse fill slope stability was analyzed

based on the proposed excavation plans and composite liner system design, and was modeled by

creating a generic refuse fill configuration along the steepest floor gradient without toe confinement

or resisting forces other than those provided by the interface shear strength of the composite liner

system and weight of refuse along the base (floor) of the refuse slope. Both the HDPE/geotextile

interface (smooth HDPE on geotextile for slope areas and textured HDPE on geotextile for floor

areas) and the internal strength of the GCL were modeled to determine the most critical interface.

Analyses were conducted iteratively to evaluate the ratio of refuse height to runout length that would

result in a stable configuration if the refuse fill slope face is maintained at a 3:1 (horizontal:vertical)

gradient and the excavation slope was cut at a 2.5:1 (H:V) inclination. . Note that once the refuse fill

reaches its maximum design capacity, the fill will be buttressed by an engineered fill toe berm that

will provide additional resisting forces and allow a steeper final fill slope gradient than is possible in

an unsupported interim refuse fill slope.

Analytical Results – A generic cross section representing the most critical refuse fill orientation was


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analyzed with various refuse heights to determine the slope runout length needed to produce a

minimum 1.5 static factor of safety. The subgrade floor was modeled at a 3% grade. The results

indicate a minimum floor length and corresponding maximum refuse height as follows:

The SLOPE/W output is presented in Appendix J2. Additional interim refuse fill slope stability

analyses should be conducted for each development phase of the proposed IWMF to evaluate the

refuse embankments constructed to plan or maximum recommended heights at prescribed gradients

upon completion of each fill phase.

8.1.6 FINAL FILL SLOPE STABILITY ANALYSES

General - Final refuse fill slopes were analyzed using the final lines and grades developed by BAS

(Plate 2). As currently designed, the proposed final refuse fill configuration results in refuse placed

to a top deck elevation of approximately 1440 feet amsl above the southern canyon and to

approximately 1510 feet amsl above the northern canyon. Because the site is almost completely

surrounded by bounding ridgelines, only the two canyon mouth areas will have open refuse fill slopes

(Cross sections D-D’ and L-L’). These two areas represent the two critical refuse fill slope

geometries that were analyzed. As currently designed the refuse fills along these two geometries are

supported by 2.5:1 backslopes. The floor of the northern canyon will generally slope to the northeast

at 3 percent, and the floor of the southern canyon will slope to the east at approximately 3 percent.

The entire subgrade will be lined with a composite liner system as described in Section 2.4. The

southern canyon has a relatively narrow top deck, with an east-facing refuse fill slope that descends

Interim Refuse Fill Slope Stability Analysis

0

50

100

150

200

250

300

350

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Minimum Floor Length (feet)

Max

imu

m R

efu

se F

ill H

eig

ht

(Fee

t)

Applicable for refuse f ill slope = 3:1; subgrade slope = 2.5:1; f loor

gradient = 3%.100 feet

200 feet

300 feet

500

feet

1150

fee

t

1800

fee

t


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from a top deck elevation of 1440 feet amsl to a top of berm elevation of 1090feet amsl. The

northern canyon has a broader top deck with a maximum elevation of about 1500 feet amsl. The top

deck descends gently to the northeast to en elevation of 1477 feet then then steepens to a 2.5:1

(H:V) slope to a top of berm elevation of 1020 feet amsl. Both the northern and southern canyons fill

are supported by an engineered fill toe berm to provide resistance against sliding and containment of

leachate.

Analytical Results – Two critical cross-sections were developed to analyze refuse fill stability in the

area of the soil berms. Section D-D’ analyzes stability of the refuse fill along the northern canyon,

and Section L-L’ (modified slightly from section K-K’ to show the maximum final fill slope

gradient) analyzes stability of the refuse fill along the southern canyon. The critical interfaces

evaluated were along the base and slope liners (along the HDPE/geotextile interfaces and through the

GCL). In addition, the refuse was also analyzed for a potential failure through or along the base of

the engineered fill berm (although the factor of safety for this mode of failure was significantly

greater than the aforementioned interfaces, and thus is not presented). The following presents the

results of our analysis:

1) The GCL on portions of the floor in the area of the northern and southern canyons is

recommended to be encapsulated with geomembranes to justify an increase of the internal shear

strength of the GCL. For both the northern and southern canyons, the encapsulation of the GCL

must extend at least 400 feet upcanyon (below the refuse) of the base of the compacted soil

berm.

2) The compacted soil berm dimensions and refuse slope inclinations were back-calculated to

achieve a minimum factor of safety of 1.5 for each of the canyons as follows:

a) For the southern canyon area (as represented by Cross Section L-L’), a compacted soil berm

crest at elevation 1090 feet amsl is recommended. The downcanyon face of the soil berm

should be at an inclination of 2.5:1 (2:1 with benches) and the upcanyon face (refuse side) is

recommended to be 1.62:1 (1.5:1 with benches). The refuse fill slope was modeled at a 2.5:1

inclination (2:1 with benches).

b) For the northern canyon area (as represented by Cross Section D-D’), a compacted soil berm

crest at elevation 1020 feet amsl is recommended. The downcanyon of the soil berm should

be at an inclination of 2.5:1 (2:1 with benches) and the upcanyon face (refuse side) is

recommended to be 1.62:1 (1.5:1 with benches). The refuse fill slope was modeled at a 2.5:1

inclination (2:1 with benches).


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After the static analysis was completed, the slopes were analyzed for permanent seismic

displacement in accordance with the method presented in Bray and Rathje, 1998. The results are

presented in Appendix J3 and are summarized in the following table. Based on the above design and

the geotechnical parameter values outlined in Section 8.1.3, refuse fill stability analyses yielded the

following results.

SUMMARY OF REFUSE FILL SLOPE STABILITY ANALYSES

SECTION

REFUSE SLOPE

HEIGHT

SLOPE

DIRECTION

MAXIMUM SLOPE

GRADIENT

CANYON

STATIC FACTOR

OF SAFETY



(INCHES) D-D’ 480 feet Northeast 2.5:1 Northern 1.50 0.14g 0 L-L’ 350 feet East 2.5:1 Southern 1.50 0.14g 0

As shown above, the proposed IWMF refuse fill slopes are demonstrably stable under static and

dynamic (earthquake loads) provided that the GCL is encapsulated and the soil berm geometries are

constructed in accordance with the above assumptions and recommendations.

8.1.7 COVER STABILITY

The proposed landfill cover slopes are proposed at an inclination of 2:1 (horizontal to vertical) with

slope benches and a relatively top flat deck area with a slope ranging up to 3 percent (3 feet vertical

in a horizontal distance of 100 feet). The cover system design for the top deck and bench areas

consists of a 24-inch vegetative soil layer, over an optional geocomposite drainage layer, on a 60 mil,

double-sided, textured, LLDPE, over an additional 24 inch layer of foundation soil, on MSW. The

proposed cover for the slope areas consists of a 48-inch monolithic soil layer on MSW.

The critical interface for the deck/bench areas is anticipated to be the interface between the

geocomposite and the LLDPE. The critical interface for the slope areas is anticipated to be the

interface between the monolithic cover and the MSW.

We have analyzed the top deck/bench and slope cover systems for surficial stability. The results of

our calculations are presented in Appendix J3 (Tables J3-A and J3-B) and indicate a minimum static

factor of safety of 1.5 for both the deck and slope cover systems. The deck and slope cover systems

were additionally evaluated for permanent seismic displacement in accordance with the method

presented by Bray and Rathje (1998). The results of these calculations are presented in Table J3-C

and indicate that the calculated permanent seismic displacement under the loading of the MCE event

is negligible.


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8.2 LIQUEFACTION ANALYSIS

Liquefaction is a loss of the shear strength of a soil that occurs when the ground experiences strong

ground shaking. The phenomenon may result in large total and/or differential settlement beneath

structures founded on the liquefying soils. In order for the potential effects of liquefaction to be

manifested at the ground surface, the soils generally have to be granular, loose to moderately dense,

saturated relatively near the ground surface, and must be subjected to a sufficient magnitude and

duration of shaking.

According to the grading plans for the proposed IWMF, alluvium, oil-well drilling muds, and other

surficial soils will be removed so that the proposed refuse prism will be directly underlain by Paso

Robles Formation or engineered fills. With the removal of canyon alluvium, the nearest groundwater

will be on the order of 500 feet below the base of the landfill. Due to the lack of a near-surface

groundwater table, the relatively low design site acceleration, and the competency of the Paso Robles

Formation and engineered fills, the potential for significant, large-scale liquefaction effects and

associated dynamic settlement to cause damage to the composite liner system and other site facilities

is very low.

8.3 LEACHATE GENERATION ANALYSES

Leachate generation analyses were conducted to determine approximate peak daily leachate volumes

for design of the containment system storage tanks and to demonstrate that the head of leachate on

the low permeability elements of the composite liner system would be less than 30 centimeters as

required by 40 CFR Part 258. 8.3.1 GENERAL

According to 40 CFR Parts 257 and 258, landfills expanding laterally after October 9, 1993 must be

underlain by a composite liner system comprised of a low-permeability soil liner component, a

geomembrane component, and a leachate collection and removal system (LCRS). Together these

systems are designed to substantially reduce the potential for landfill-impacted fluid (leachate) to

infiltrate the substrate and commingle with the naturally occurring groundwater beneath the site.

Furthermore, 40 CFR Section 248.40(a)(2) states that the leachate control system should maintain

less than 30 cm of leachate head over the low-permeability liner components. Title 27 Section 20340

states that the LCRS shall be designed to prevent buildup of hydraulic head on the liner.

While the design and construction of the low-permeability natural and synthetic layers are important

for minimizing infiltration, proper design and construction of a high-permeability LCRS is equally

important to ensure that the collection capacity is adequate to minimize leachate head over the liner.


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Because the proposed composite liner system differs from the 40CFR prescriptive standard (primarily

by replacing the low permeability soil element with a GCL), it is important to demonstrate that the

LCRS can accommodate the anticipated leachate volumes.

To provide an assessment of the anticipated composite liner and LCRS performance, an assessment

of leachate generation potential at the proposed IWMF was undertaken using on-site soil

characteristics, local climatic data, and the proposed subgrade and final fill geometries for the site.

This information was used as input data for infiltration modeling that was completed using the

Hydrologic Evaluation of Landfill Performance - version 3.07 (HELP) model developed by the

United States Army Corps of Engineers. A summary of the model configurations for the proposed

composite liner system is presented below.

8.3.2 MODEL CONFIGURATION

The leachate generation model was created by simulating each of the proposed developments phases

and analyzing the effects of moisture application over the active life of each phase. Each phase was

divided into two sectors, reflecting floor and side-slope areas, with a one-acre unit representing the

average condition of each phase sector. Precipitation values were generated from the program and

used to evaluate the moisture application to the proposed development. The model was evaluated on

yearly cycles, updating the input parameters to reflect additional refuse and cover soil layers, and re-

initializing the moisture content of the waste based on the quantity of water in storage calculated

from the previous year’s analysis. Fill sequencing was based on the conceptual master plan prepared

by BAS, which accounts for ultimate subgrade and final fill configurations for each phase, but does

not provide a year-by-year account of fill sequencing. As a result, assumptions for fill sequencing

were conceived based on the generally accepted standards of practice for municipal solid waste

disposal operations. The modeling period ended at the active life of the landfill, as it was assumed

that the worst case scenario for leachate generation would occur during construction and active refuse

fill operations. The final cover constructed during landfill closure is designed to significantly reduce

infiltration, so it was assumed that the moisture application (and, therefore, potential leachate

generation) would decrease significantly following closure.

The following table summarizes the HELP model input parameters for a typical phase at the

proposed IWMF.

LAYER HELP LAYER TYPE COMMENTS and SPECIFICATIONS Interim Cover Vertical percolation This layer is assumed to be formed of poorly graded sand derived from the Paso Robles Formation. It is

also assumed that the landfill is efficiently managed, and that 90% of the sector area can be drained by surface runoff, and 10% of the sector area cannot be drained at any given time. Thickness = 6 inches (Specified Value) Saturated Hydraulic Conductivity = 3.7E-4 cm/sec. (Based on laboratory test data) Porosity = 46.3% (Estimated)


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Initial Moisture Content = 16.5% (Optimum Moisture Content based on laboratory test data)

Refuse Vertical percolation The field capacity of refuse was set at 29.2% and the initial moisture content was 12%. Based on HELP recommended values. Thickness = Multiple layers from 30 to 700 inches (Based on design plan, BAS 2007) Saturated Hydraulic Conductivity = 1.0E-3 cm/sec (HELP recommended value) Porosity = 67.1% (HELP recommended value) Field Capacity = 29.2% (HELP recommended value) Initial Moisture Content = 12%, and then re-initialized each year. (HELP Default/calculated value)

Operations layer

Vertical percolation This layer is assumed to be formed of poorly graded sand derived from the Paso Robles Formation. Thickness = 24 inches (Design specification) Saturated Hydraulic Conductivity = 3.7E-4 cm/sec. (Based on laboratory test data) Porosity = 46.3% (Estimated) Initial Moisture Content = 14.8% (Optimum Moisture Content based on laboratory test data).

LCRS (bottom only)

Lateral drainage A gravel blanket LCRS was defined for the bottom sector. Thickness = 12 inches (Design specification) Saturated Hydraulic Conductivity =0.3 cm/sec. (Design specification) Porosity = 39.7% (HELP Default value) Slope = 2% (Design Specification; minimum value for floor areas) Drainage Length = Varies by phase (average floor length of the phase)

Geocomposite (side-slopes only)

Lateral drainage The protective geotextile was defined as a lateral drainage layer for the side slopes sector to force HELP to report the flux conveyed to the bench drains. Thickness = 0.32 inches (Manufacturer specification) Saturated Hydraulic Conductivity =10 cm/sec. (Design specification) Porosity = 85% (HELP Default value) Slope = 50% (Design Specification; average value for slope areas) Drainage Length = Varies by phase (average floor length of the phase)

HDPE Flexible membrane liner A geotextile would be installed between the LCRS gravel and the FML to minimize abrasion during construction. Thickness = 80 mil (Design specification) Saturated Hydraulic Conductivity = 2.0E-12 cm/sec (HELP Default Value) Pinhole Density = 1 hole per acre (User-specified value) Installation Defects = 1 hole per acre (User-specified value) Placement Quality = Good (User-specified value)

GCL Barrier soil Geosynthetic clay liner would be placed on a prepared subgrade. Thickness = 0.24 inches (Manufacturer Design) Saturated Hydraulic Conductivity = 3.0E-8 cm/sec. (Design Specification)

The HELP program contains precipitation, evapotranspiration, solar radiation, and temperature data

from a weather station in Santa Maria, California, and these data were used in model simulations.

Rainfall runoff was estimated using HELP program default values, and user-selected values for soil

type, slope length and gradient, evaporative zone, and runoff area fraction that were based on site-

specific conditions or design parameters.

For the first year simulation, the initial moisture content of the soil and refuse layers was established

based on laboratory test data or HELP recommended values. The results from the first year

simulation were used to re-initialize the moisture contents in the existing soil and refuse layers in the

next year’s simulation, while new soil and refuse layers were added using laboratory or HELP

recommended moisture values. This process continued until the phase model reached its design

capacity. This process allows the refuse to absorb, store, and transmit moisture down the profile to

the composite liner system, though it does not account for water use during microbial decomposition

of water removal by landfill gas extraction. As a result, it should be considered a relatively


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conservative model. 8.3.3 RESULTS

The HELP program output is included in Appendix K. (The first year model run for Phase 1A is

provided as a hard copy, and the remainder of the analyses for Phase 1A and the other phases are

presented on CD. Files can be viewed with any text editor.) The modeling results indicate that the

relatively low rainfall quantities for the site are not sufficient to overcome the combined

evapotranspiration rates and the field capacity of the waste and cover soils. These results suggest

that no leachate would be generated, even during initial waste placement operations. These results

were calculated using the recommended values for initializing the waste moisture content, and

reinitializing the waste moisture after each annual simulation. This scenario is likely to occur later in

the life of the landfill under optimal construction conditions; however, it is very unlikely to occur

early in the development of the site. As a result, GLA has evaluated monthly and annual leachate

generation records during the last five years for landfills along the central coast of California with

similar soils, climate conditions, and waste streams. Leachate generation rates from four landfills in

this region indicate average leachate generation rates ranging from 40 to 100 gallons per acre per

day. Using a conservative value of 150 gallons of leachate per day per acre, the proposed IWMF,

which will have a lined footprint of approximately 290 acres, can be expected to generate up 43,500

gallons of leachate per day. The northern canyon will drain approximately 194 acres, and therefore

can be expected to generate approximately 29,100 gallons of leachate per day. The southern canyon

will drain approximately 96 acres, and may be expected to generate approximately 14,400 gallons of

leachate per day.


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9.0 SUMMARY AND CONCLUSIONS GEOLOGIC CONDITIONS

1. The majority of the proposed IWMF is directly underlain by the Pliocene-Pleistocene Paso Robles Formation, a non-marine unit primarily composed of poorly bedded, poorly consolidated and lightly cemented sandstones and conglomerates. The Pleistocene Orcutt Sand is exposed at the northeastern corner of the property, but has no engineering significance to the proposed development. Alluvium and drilling muds occur on the bottom of both canyons.

2. As currently designed, the proposed IWMF excavation plan will remove most of the

mapped landslide debris, drilling mud, and alluvium in the proposed development area. Alluvium up to 40 feet thick will remain along the bottom of the northern canyon. This material must be removed and replaced with an engineered fill to minimize settlement and maintain drainage of the composite liner system.

3. Rippability studies indicate that the materials underlying the site can be excavated using

conventional earth-moving equipment. 4. Much of the Paso Robles Formation is poorly consolidated and uncemented. As a result,

the unit should be considered prone to erosion from high winds and heavy rainfall. 5. Based on field observations made during this investigation, the Paso Robles Formation

does not contain a sufficient volume of fine-grained sediments for construction of a prescriptive low-permeability soil liner component of a Title 27 composite liner system.

6. Extensive alteration of the natural terrain has occurred as a result of historical oil-field

operations at the site. As a result, much of the geomorphological evidence of landsliding has been obliterated. Additional landslides may be encountered during site development.

7. Both the northern and southern canyons are filled with drilling mud from past oil-field

drilling operations. Although most of the drilling mud deposits observed during this investigation had only minor petroleum hydrocarbons, oily liquid wastes were observed in two areas of the site.

8. Bedrock at the site occurs on the east-dipping limb of the Cat Canyon-Los Flores

Anticline. Bedding planes typically strike in a northwesterly direction and dip from 3 to 10 degrees to the northeast.

9. No active faults have been mapped at the site or trending toward the site. 10. The nearest active fault is the Casmalia-Orcutt Frontal fault, which is located

approximately 1.8 miles north of the site at its closest approach.

11. Seismic risk assessment indicates a peak horizontal ground acceleration for the site of


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0.28g for the MCE event. GROUNDWATER CONDITIONS

1. Groundwater at the proposed IWMF site was encountered in the alluvium, Paso Robles Formation, and in the Careaga Formation.

2. Groundwater in the Paso Robles Formation occurs as minor seeps where water infiltration

is impeded by local cemented or clayey layers. The seeps are localized and of very small volume. No continuous water-bearing zones were encountered in the Paso Robles Formations

3. Groundwater was encountered in the alluvium of the northern canyon at a depth of about

nine feet below the ground surface. Alluvial groundwater appears to be perched on cemented zones at the alluvium-Paso Robles Formation contact, and limited in areal extent.

4. Piezometer P-1 was constructed to monitor alluvial groundwater, and the hydraulic

conductivity of the alluvium at P-1 was measured at 0.16 to 0.65 ft/day (5.64 x 10-5 to 2.31 x 10-4 cm/s).

5. Regional groundwater was encountered in the Careaga Formation at depths ranging from

500 to 712 feet bgs. Comparison of first encountered groundwater to static water levels suggests that groundwater is semiconfined to confined. Five wells and one piezometer were constructed to intercept and monitor this water-bearing zone.

6. The hydraulic conductivity of water-bearing zone in the Careaga Formation is estimated

to range from 1.45 x 10-3 ft/day (6.28 x 10-7 cm/s) to 2.03 x 10-2 ft/day (7.16 x 10-6 cm/s) based on the results of bail down and recovery tests.

7. Groundwater potentiometric surface contours developed from static water levels suggest

that bedrock groundwater generally flows from southwest to northeast at a gradient of approximately 0.05 to 0.07 ft/ft and a velocity ranging from 0.0003 ft/day to 0.0016 ft/day.

8. As currently designed and based on the June 2007 groundwater equipotential map, there

will be a minimum 400-foot separation between wastes and first groundwater. 9. A comparison of the water quality results obtained from first sampling event with State

and Federal ARARs and the water quality objectives for the Sisquoc Hydrologic Subarea shows that chloride, sulfate, and total dissolved solids concentrations exceed water quality objectives in a sample from at least one well.

10. Aside from laboratory contaminants, no organic compounds were detected in samples

from the monitoring wells. No evidence of petroleum hydrocarbon contamination was detected in the first round of groundwater samples.


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SUBGRADE SLOPE STABILITY

1. Nine cross sections representing critical subgrade slope geometries were developed to

analyze the stability of the landfill subgrade. Slope geometries were iteratively analyzed, redesigned if necessary, and reanalyzed to develop slopes that meet the 27 CCR regulatory criteria for landfill foundation slope stability under static and dynamic conditions. As a result, the subgrade slopes along each of these nine cross sections have static factors of safety that equal or exceed 1.5, and have negligible displacements resulting from an MCE-equivalent scenario.

2. To meet the 27 CCR stability criteria, slope conditions were assumed to be drained, with a

minimum five-foot separation between groundwater and the subgrade surface. As indicated, all alluvium will be removed and replaced with engineered fill as necessary to achieve design grades. Groundwater seeps in the Paso Robles Formation were extremely light, and not likely to result in elevated pore-water pressures.

FINAL REFUSE FILL SLOPES

1. As currently designed, the proposed IWMF will be constructed almost entirely over the Paso Robles Formation bedrock. It will form a suitably strong and incompressible foundation for the proposed waste prism.

2. Two critical cross sections were identified along the axes of the northern and southern

canyons.

3. Stability analyses performed on these profiles indicate acceptable factors of safety under static conditions, and dynamic analyses indicated no measurable displacement when subjected to accelerations from an MCE-equivalent event. These results incorporate the recommendations made to the composite liner system configuration, GCL encapsulations in selected areas, toe berm geometries, and final refuse fill slope geometries.

LIQUEFACTION AND DYNAMIC SETTLEMENT

1. Site-specific geological and groundwater conditions suggest that liquefaction and associated dynamic settlement potential at the site is very low.

LEACHATE GENERATION

1. Leachate generation analyses were conducted using HELP version 3.07. Climate data were obtained from the program’s database for Santa Maria, and soils data were based on site-specific laboratory test data.

2. Analyses indicate that the high evapotranspiration rates and absorptive capacity of the soil

and refuse result in no measurable leachate generation over the active life of the proposed IWMF.


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3. Landfills along the central coast of California typically generated between 28 and 230

gallons of leachate per acre per day.


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10.0 RECOMMENDATIONS

GEOLOGY

1. Although the general geologic conditions are well documented throughout the proposed IWMF, this site has been extensively altered by historical oil-field operations and as a result, much of the original geomorphology has been destroyed. Therefore, all excavations should be examined by an engineering geologist during the construction phase to identify potentially adverse geologic conditions which could affect slope stability, placement of the proposed liner system or subdrains.

2. All soils, drilling mud, alluvium, landslide debris, and other compressible soils should be

removed and replaced with engineered fills to achieve the grades shown on the proposed excavation plan (Plate 1).

3. Master excavation and phasing plans should consider the low cohesion of the Paso Robles

Formation. Adequate slope protection, drainage structures, and sedimentation basins should be included in site development plans to accommodate erosion of bedrock that is exposed during grading.

4. Excavations may encountered previously-undocumented petroleum hydrocarbon deposits,

particularly in and around the canyon bottoms where oil-field drilling muds have accumulated. Hydrocarbon-impacted soils may contain volatile and noxious components, including hydrogen sulfide. As a result, air monitoring should be conducted during excavation of alluvium, drilling mud, or other non-lithified materials.

5. To accommodate changes in the proposed excavation plan, it is recommended that

additional seismic refraction surveys be conducted along the ridgeline between the northern and southern canyons to evaluate rippability of this area.

GROUNDWATER

1. Groundwater seepage in the Paso Robles Formation was observed to be limited during the course of this investigation. If heavier seeps or springs are encountered during site development, water accumulation should be prevented in areas to be overlain by the composite liner system. Accumulation of water or pore-water pressure may affect interim or long-term slope stability.

2. Groundwater elevations in the five monitoring wells (MW-1 through MW-5) and two

piezometers (P-1 and P-2) should be measured quarterly to further refine areas with seasonal fluctuations in the hydraulic gradient and groundwater flow direction.

3. The five new monitoring wells should be included in a routine groundwater sampling

program, and should be sampled and analyzed general chemistry parameters such as chloride, nitrate as nitrogen, pH, sulfate, total dissolved solids, and total petroleum hydrocarbons, as well as for the full list of analytes outlined in Appendices I and II of


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40CFR Part 258, initially to establish a baseline of data prior to waste placement. A reduced list of monitoring parameters may be established following evaluation of the baseline data.

4. A minimum of four background monitoring events should be completed before beginning

site development activities. 5. To facilitate sampling, dedicated submersible pumps should be installed in each

monitoring well. 6. After completing four background monitoring events, a groundwater monitoring and

reporting program should be developed and presented to the RWQCB.

SUBGRADE SLOPE STABILITY

1. The long-term stability of the slopes and liner sections are dependent on maintenance of drained slope conditions that prevent a build-up of hydrostatic pressure behind the liner. It is recommended that drainage provisions or contingencies be incorporated into the subgrade preparation prior to placement of the liner system.

2. All excavations should be examined by a geologist during construction to identify

potentially adverse geology that could be encountered and which may impact slope stability.

3. All engineered fills should be constructed under a program of continuous quality

assurance inspection and testing.

4. All alluvium, soils, undocumented fills, and other unacceptable foundation materials should be excavated prior to placement of the engineered fills and other improvements required for the development.

REFUSE FILL SLOPE STABILITY

1. The long-term stability of the slopes and liner sections are predicated on maintenance of drained slope conditions which prevent a build-up of hydrostatic pressure behind the liner and presumes implementation of a fill sequencing plan that ensures that fill is placed in single lifts (plus or minus 20 feet) uniformly across the floor of the development area. By filling in this sequence of single lifts of uniform thickness, the potential for eccentric loading and subsequent instability of the liner system is minimized.

2. In order to maintain stability of interim refuse fills, the waste geometry should be at least

six times as wide as it is high.

3. Interim refuse fill slopes should be no steeper than 3. to 1 (horizontal to vertical). 4. In order to attain acceptable factors of safety for the final refuse fill along the southern

canyon (Cross Section L-L’), the following is recommended:


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a. The GCL must be fully encapsulated for a distance of at least 400 feet upcanyon of the base of the soil berm.

b. The soil berm across the mouth of the southern canyon must have a minimum crest elevation of 1090 feet amsl, descending to the adjacent floor areas at an upcanyon slope of 1.62:1 (1.5:1 with benches) and a downcanyon inclination of 2.5:1 (2:1 with benches)..

c. The soil berm must be constructed as an engineered fill with a minimum relative compaction of 90 percent (based on ASTM D 1557). Earthwork operations should be performed under the full time observation and testing of a representative of the geotechnical consultant to document floor cleanouts, material preparation, and fill placement and compaction.

d. The refuse fill slope should extend from the top deck elevation of 1440 feet amsl to the crest of the soil berm at elevation 1090 feet amsl, to create an overall slope gradient no steeper than 2.5:1 (2:1 with benches).

5. In order to attain acceptable factors of safety for the final refuse fill along the northern

canyon (Cross Section D-D’), the following is recommended: a. The GCL must be fully encapsulated for a distance of at least 400 feet

upcanyon of the base of the soil berm. b. The soil berm across the mouth of the northern canyon must have a minimum

crest elevation of 1020 feet amsl, descending to the adjacent floor areas at an upcanyon slope of 1.62:1 (1.5:1 with benches) and a downcanyon inclination of 2.5:1 (2:1 with benches).

c. The soil berm must be constructed as an engineered fill with a minimum relative compaction of 90 percent (based on ASTM D 1557). Earthwork operations should be performed under the full time observation and testing of a representative of the geotechnical consultant to document floor cleanouts, material preparation, and fill placement and compaction.

d. The refuse fill slope should extend from the top deck elevation of 1477 feet amsl to the crest of the soil berm at elevation 1020 feet amsl, to create an overall slope gradient no steeper than 2.5:1 (2:1 with benches).

e.

6. As phasing plans are developed, the stability of each phase should be analyzed.

7. As soil stockpiling plans are developed, the stability of the stockpiles should be analyzed.


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11.0 CLOSURE

The data, analyses, conclusions and recommendation contained herein pertain only to the proposed

City of Santa Maria Integrated Waste Management Facility and assume that the geologic conditions

do not deviate substantially from those reported. If any variations or conditions are encountered that

are materially inconsistent with these findings, or if the proposed landfill development project differs

from that anticipated herein, GLA should be notified so that supplemental evaluations can be

provided.

It should also be recognized that geologic conditions exposed during construction may differ from

those encountered by field exploration. Therefore, all excavations should be examined by a geologist

during the construction phase to identify potentially adverse geology which could affect the

performance of landfill construction elements.

The findings of this report are considered valid as of the present date. However, changes involving

the earth and supported improvements do occur over time, whether due to natural processes or the

works of man on this or adjacent properties. In addition, changes in applicable or appropriate

standards and statutes may transpire from legislation, the judiciary and/or a broadening of technical

knowledge. Accordingly, the findings of this report may be invalidated wholly or in part by

conditions beyond our control.

This report has not been prepared for use by parties or projects other than those named above. It may

not contain sufficient information for other parties or other purposes. This document conforms to

generally accepted geotechnical practice and makes no other warranties, either expressed or implied,

as to the professional advice or data included. GeoLogic Associates John M. Hower, PG, CEG Joseph Franzone, PE, GE Senior Geologist Supervising Geotechnical Engineer


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