report for the 2015 inspection of the ash ponds at … · november 2015 2 1529064 2015-11-20 ash...

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REPORT FOR THE 2015 INSPECTION OF THE ASH PONDS AT LITTLE FLINT CREEK

Benton County, Arkansas

Submitted To: American Electric Power 1 Riverside Plaze

Columbus, Ohio 43215-2373 Submitted By: Golder Associates Inc. 3730 Chamblee Tucker Road Atlanta, GA 30341 USA Distribution: American Electric Power – 6 Copies

Golder Associates Inc. – 2 Copies November 20, 2015 1529064

FIN

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1 2015-11-20 Ash Pond Inspection Report (FINAL) .docx Golder Associates Inc.

3730 Chamblee Tucker Road Atlanta, GA 30341 USA

Tel: (770) 496-1893 Fax: (770) 934-9476 www.golder.com

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November 20, 2015 1529064

Mr. W. Greg Carter, P.E. – Region 5 Engineer American Electric Power 1 Riverside Plaze Columbus, Ohio 43215-2373 RE: FINAL REPORT FOR THE VISUAL INSPECTION OF

LITTLE FLINT CREEK ASH PONDS COMPLEX BENTON COUNTY, ARKANSAS Dear Mr. Carter:

Golder Associates Inc. (Golder) is pleased to submit the attached Final Visual Inspection Report for Little Flint Creek Bottom Ash Ponds performed on September 10, 2015. The inspection was performed by Mr. Rafael Ospina, P.E. and Michael Chilson, P.E., under the direction of W. Randall Sullivan, P.E. (Arkansas). Mr. W.G. Carter, Gary Zych, and H.E. Rice with AEP-SWEPCO were present during the inspection. This work was performed in accordance with our Proposal dated May 1, 2015, Blanket Contract 2631379X103, and Letter of Authorization (LOA) 263137900001x168 dated June 23. 2015.

We appreciate this opportunity to provide engineering services to AEP. Please do not hesitate to contact one of the undersigned if you have any further questions, require additional information, or would like to discuss the conclusions presented in this report.

Sincerely,

GOLDER ASSOCIATES INC.

Josh Nasrallah, PG Michael T. Chilson, P.E. Senior Geological Engineer Senior Civil Engineer

cc: Randy Sullivan, P.E. (AR Lic. # 8575) – Golder Associates Inc.

Attachments: 2015 Inspection Report

MTC/WRS/sp

November 2015 ii 1529064

2015-11-20 ash pond inspection report (final).docx

Table of Contents 1.0 INTRODUCTION .............................................................................................................................. 1

1.1 Background .................................................................................................................................. 1

1.2 General Description of Dams ....................................................................................................... 2

2.0 SUMMARY OF VISUAL INSPECTION TERMS .............................................................................. 4

3.0 VISUAL OBSERVATIONS ............................................................................................................... 5

3.1 Upstream Slope ........................................................................................................................... 5

3.2 Crest ............................................................................................................................................. 5

3.3 Downstream Slope ....................................................................................................................... 5

3.4 Abutment and Groins ................................................................................................................... 6

3.5 Spillway Structure ........................................................................................................................ 6

3.6 Monitoring Instrumentation and Downstream Drainage .............................................................. 7

4.0 ASSESSMENT OF RECENT INSTRUMENTATION DATA ............................................................ 8

5.0 CONCLUSIONS AND RECOMMENDATIONS................................................................................ 9

List of Tables Table 1 Observed Deficiencies and Recommendations

List of Figures Figure 1 Location Map Figure 2 Piezometer Locations Figure 3 Location of Dam Deficiencies Figure 4 Piezometer Trend

List of Appendices Appendix A Dam Inspection Checklist Appendix B Photographs

November 2015 1 1529064


1.0 INTRODUCTION

1.1 Background American Electric Power (AEP) Service Corporation Civil Engineering administers the dam inspection and

maintenance program at AEP facilities. AEP contracted with Golder Associates Inc. (Golder) to complete

the annual inspection of Little Flint Creek Reservoir (Cooling Lake) and Bottom Ash Ponds at the AEP

Flint Creek Power Station in Benton County, Arkansas (Figure 1). These inspections were completed to

fulfill, in part, the requirements of the Arkansas National Resources Commission’s Dam Safety Program,

and to provide AEP an evaluation of the facility to assist in the prioritization of maintenance activities. The

Little Flint Creek Dams were last inspected by Golder on November 8, 2012. Golder understands that

additional internal inspections have been performed by AEP personnel since then.

Mr. Rafael I. Ospina, P.E. and Mr. Michael T. Chilson, P.E., of Golder, under the direction of Mr. W.

Randall Sullivan, P.E., with Mr. Greg Carter, P.E., Mr. Gary Zych, P.E. and Mr. H.E. Rice of AEP visually

inspected the Ash Ponds on September 10, 2015. This report contains Golder’s observations,

photographs, conclusions and recommendations for AEP’s Ash Ponds at the Little Flint Creek Station.

The dam inspection checklist was submitted to AEP on September 19, 2015, and is included in Appendix

A. The severity of noted deficiencies and the adequacy of freeboard and spillway capacities were

assessed based on the operation of the dam at the time of visit. No analytical assessment of the

hydrologic or hydraulic performance of the dam and components was made. Geotechnical analysis was

also not performed to assess the stability of the different components of the primary and secondary ash

pond’s dams.

At the time of the inspections, the temperature was about 81̊ F under sunny and clear skies. Two days

prior to the inspection on September 8, 2015, 2.2 inches of rain fell on site as recorded by AEP plant

personnel. This rainfall resulted in the activation of the Primary Pond’s auxiliary spillway.

The following documentation, provided by AEP, was reviewed and utilized during the preparation of this

report:

Flint Creek, Drawing Number 1-30301-01-A, Bottom Ash Pond, Bottom Ash Storage Cell Location Plan Map, dated 2006.

Ash Pond Dike, Drawing No. FCX-3 Sheets 1, 2 & 3; Drawing No. FCX-29 Sheets 1 and 2; and Drawing FCX-104 Sheets 1 and 2.

Monument and piezometer monitoring data.

Emergency Action Plan for the Cooling Lake dam.

November 2015 2 1529064


1.2 General Description of Dams The Bottom Ash Pond is divided into two impoundments in series. The Primary (upper) Pond is an 820-

foot long cross-valley dam on an unnamed tributary to the Little Flint Creek. It discharges to the

Secondary Pond. The Secondary (lower) Pond is a 750-foot long cross-valley dam on an adjacent first

order stream. The Secondary Pond discharges directly to the Little Flint Creek Reservoir (downstream of

the ash ponds), which submerges the downstream toes of both the Primary and Secondary Ponds’

embankments.

GENERAL INFORMATION

Dam or Reservoir: Bottom Ash Ponds

Date of Construction: 1978 - Ponds at Flint Creek Station

Owner: AEP Southwest Electric Power

Type of Dam: Earth-Fill Structure

D/S Hazard: Not Classified

LOCATION

County: Benton County,

General Location: Approximately 4.5 miles north of Siloam Springs, AR

Stream and Basin: Little Flint Creek; Flint Creek Basin

SIZE – PRIMARY (UPPER) POND

Dam Crest Elevation1: 1,155 feet-msl

Maximum Water Level: 1,146 feet-msl (elevation of ASP weir)

Minimum Water Level: 1,143 feet-msl

Current Water Level2: 1,145 feet-msl (normal pool)

Height1: 45 feet

Surface Area 24 acres (current free water) – 42.8 acres (total area (Open Water): from 2009 EPA Survey)

Surface Area (Ash): 18.8 acres (current area) (42.8 – 24 = 18.8 acres)

Total Reservoir Capacity (below normal pool): 276 acre-feet (based on design contours)

Water Volume (below normal pool): 72 acre-feet (assumes solids sloped at 10h:1v)

Total Solids Volume: 422 acre-feet (within design foot print, above and below normal pool)

November 2015 3 1529064


SIZE – SECONDARY (LOWER) POND

Dam Crest Elevation1: 1,155 feet-msl

Maximum Water Level: 1,145 feet-msl (elevation of ASP concrete weir)

Minimum Water Level: 1,142.5 feet-msl (principal spillway concrete weir- normal pool)

Current Water Level2: 1,143.55 feet-msl

Height1: 35 feet

Surface Area: 6 acres (current free water at normal pool) (Open Water): Total Reservoir Capacity (at normal Pool): 11 acre-feet (Freese and Nichols Hydraulic Analysis, 2011)

Notes: 1.) From deign drawings references provided by AEP. 2.) Based on staff gauge reading during the inspection on September 10, 2015.

November 2015 4 1529064


2.0 SUMMARY OF VISUAL INSPECTION TERMS The summary of the visual observations presented herein uses terms to describe the general appearance

or condition of an observed item, activity or structure. Their meaning is understood as follows:

CONDITION OF DAM COMPONENT

Good: A condition or activity that is generally better or slightly better than what is minimally

expected or anticipated from a design or maintenance point of view.

Fair: A condition or activity that generally meets what is minimally expected or anticipated from

a design or maintenance point of view.

Poor: A condition or activity that is generally below what is minimally expected or anticipated

from a design or maintenance point of view.

SEVERITY OF DEFICIENCY

Minor: A reference to an observed deficiency (e.g., erosion, seepage, vegetation, etc.) where

the current maintenance condition is below what is normal or desired, but which is not

currently causing concern from a structure safety or stability point of view.

Significant: A reference to an observed deficiency (e.g. erosion, seepage, vegetation, etc.) where the

current maintenance program has neglected to improve the condition. Usually these

conditions have been identified in previous inspections, but have not been corrected.

Excessive: A reference to an observed deficiency (e.g., erosion, seepage, vegetation, etc.) where

the current maintenance condition is worse than what is normal or desired, and which

may have affected the ability of the observer to properly evaluate the structure or

particular area being observed or which may be a concern from a structure safety or

stability point of view.

November 2015 5 1529064


3.0 VISUAL OBSERVATIONS For location of monitoring instrumentation and observed deficiencies refer to Figures 2 and 3,

respectively. A summary of observed deficiencies during this inspection and recommended actions are

included in Table 1.

3.1 Upstream Slope The upstream slopes are depicted in Photographs 1, 2 and 3 (Primary Pond) and Photographs 12 and 13

(Secondary Pond). The upstream slope of the Primary Pond is mostly dry as dry ash and soil has been

stockpiled against the embankment. The upstream slope of the Secondary Pond is submerged under

water as solids are not generally deposited in the Secondary Pond.

There is undesirable overgrown vegetation within the riprap on the lower part of the slopes. Rills and

erosion gullies have formed above the riprap. There is some beach erosion along the shoreline of the

natural ground slope just north of the principal spillway of the Primary Pond. Surface scour erosion is

occurring near the stairs approaching the principal spillways of both the Primary and Secondary Ponds.

One animal burrow was identified on the upstream slope of the Secondary Pond embankment. There

were no signs of sloughing or slope instability.

The upstream slope of both the Primary and Secondary Ponds are in poor condition, mainly because of

the difficulty encountered inspecting the lower slopes.

3.2 Crest The surface of the crest of the dam is hard-packed earth and gravel for vehicular access. The crests of

the Primary and Secondary Ponds are generally well graded with the exception of tire rutting on the crest

near the north end of the Primary Pond embankment, shown on Photograph 5. The remaining crest of

both embankments was in good condition as shown on Photographs 6 (Primary Pond) and 14 (Secondary

Pond). As noted in the section above, some rilling and erosion gullies were observed along the upstream

slopes. These features can be caused by concentrated flows of stormwater run-off from the crest of the

berms at low points in the crest; however, there were no obvious depressions in the crest at these

locations.

3.3 Downstream Slope The downstream slope is depicted in Photographs 7 and 8 (Primary Pond) and Photographs 15 and 16

(Secondary Pond). The Little Flint Creek Reservoir submerges the downstream toe of the embankments

preventing full inspection of approximately 12 vertical feet of slope below the water surface. The riprap on

the slope above the water surface appears in fair condition along the Primary Pond, but is in poor

condition along the Secondary Pond due to significant vegetation growth within the riprap preventing

November 2015 6 1529064


adequate inspection. Grass above the riprap on both embankments was 12 to 18 inches in some places

which hindered the potential identification of additional animal burrows, especially along the Primary Pond

embankment where the surface was very irregular and loose. Two animal burrows, 12 to 18 inches wide

and deep, were identified on the downstream slope of the Primary Pond, but surficial animal activity was

evident throughout the site. Sapling trees, 1 to 2 inches in diameter, have established on the lower part of

the slope and near the shoreline of the Primary Pond embankment, and clusters of 2- to 3-inch diameter

trees have established on the slope of the Secondary Pond embankment within the riprap and shoreline.

No seeps were identified during this inspection. No signs of sloughing or slope instability were observed,

and no movement of fine soils.

3.4 Abutment and Groins A couple of historic sloughs with bulging at the toe appear to have occurred on the upstream side of the

abutment that separates the Primary and Secondary Ponds (upstream of the Primary Pond spillway). No

open cracks or unvegetated scarps were observed at these two locations during the inspection.

Erosion of significance was not observed along the groins of the upstream and downstream slopes of the

Primary and Secondary Pond embankments.

The riprap within the left downstream groin of the Primary Pond (at the mid-dam abutment between the

Primary and Secondary embankments) is in proper alignment; however there is overgrown vegetation

within the riprap. Trees, 1 to 2 inches in diameter, have established within the riprap along the right groin

of the Primary Pond’s downstream slope.

3.5 Spillway Structure The principal and auxiliary spillways at the primary and secondary impoundments were visually inspected,

and are generally in fair condition. The point of plant inflow was not observed as part of this inspection.

The principal spillway at the Primary Pond is a concrete drop-inlet structure. The conduit discharge was

submerged within the Secondary Pond and could not be inspected. The winch and concrete stop-log

system used to control the reservoir level of the Primary Pond appeared to be functional, and was not

necessary to adjust during the inspection (see Photograph 9).

The auxiliary spillway at the Primary Pond, shown in Photographs 10 and 11, is a grass-lined, earth-cut

channel in natural ground with a small concrete control weir. This structure and channel was cleaned of

debris and heavy vegetation following Golder’s 2012 inspection. The Primary Pond water level at the

time of the inspection was about 1 foot below the top of the weir (top of weir at elevation 1,146 feet-msl).

Seepage emanating through cracks in the concrete and from under the concrete weir was apparent at a

few locations along the length of the weir (See Photograph 11).

November 2015 7 1529064


The principal spillway at the Secondary Pond, shown in Photographs 17, 18, 19 and 20 is a concrete

structure with a series of horizontal orifices through which flow discharges to a weir box, through a rock-

lined channel and into the Little Flint Creek Reservoir. The trashrack and principal spillway structure were

relatively clean of brush and branches (Photograph 17). Some vegetation was growing within the riprap

of the exit channel. Additional riprap has been placed along the bank of the channel since Golder’s 2012

inspection to protect the channel from erosion, bank erosion has continued to occur on the right bank

near the discharge to the Little Flint Creek Reservoir during extreme flow events (Photograph 20). This

erosion does not pose an immediate risk to the Ash Ponds.

The auxiliary spillway at the Secondary Pond, shown in Photograph 17, is a grass-lined, earth-cut channel

in natural ground with a small flow control weir constructed across the auxiliary spillway channel. The

auxiliary spillway was not active at the time of inspection and no signs of erosion were observed.

Recycled concrete blocks have been placed on the downstream side of the weir to protect against erosion

and undercutting of the weir in the event of activation. The exit channel had some bare areas but it was

not clear if there had been recent maintenance activities in the area of the channel prior to the inspection.

3.6 Monitoring Instrumentation and Downstream Drainage Seven piezometers (A-1 to A-7) are located on the ash pond embankments (see approximate piezometer

locations on Figure 2). While the integrity of the piezometers was not verified during this inspection, the

flush mount covers of the piezometers were in fair condition (Photograph 6). AEP personnel measured

the piezometer water levels for the 2015 yearly inspection and provided the data to Golder for evaluation

and comparison with historic data. No embankment drains were observed.

November 2015 8 1529064


4.0 ASSESSMENT OF RECENT INSTRUMENTATION DATA Historic piezometer water level data is plotted in Figure 4. This figure shows the historic variation of

piezometric water levels with respect to the relatively constant pool levels of the Primary and Secondary

Ponds, and the more variable pool level of the Little Flint Creek Reservoir submerging the downstream

toes of the both embankments. In general, all piezometers respond consistently with the variation of the

pool level in the Little Flint Creek Reservoir, with piezometers A-3 and A-4 located on the crest of the

Primary Pond having a slightly slower and different response with less fluctuation.

Water levels in piezometers installed on the crest of the Primary Pond have varied historically by 2 to 4

feet, while piezometers installed on the crest of the Secondary Pond have varied historically by 4 to 6

feet. It was not possible to evaluate the sensitivity of historic pool water levels of the Primary and

Secondary ponds as these vary just within one to two feet. Based on the historic data, piezometric water

levels have been at their highest during the summer in 2015, which is consistent with a sustained high

water levels within the Little Flint Creek Reservoir operating at around elevation 1,139 feet-msl.

Golder does not have piezometer installation records and has not evaluated these piezometer levels as

they may affect dam stability. As recommended in previous inspection reports, Golder understands that

AEP is in the process of developing trigger levels for piezometeric readings.

No drain, channel or weir flows were measured. No monument survey data was provided to Golder.

November 2015 9 1529064

1 2015-11-20 ash pond inspection report (final) .docx

5.0 CONCLUSIONS AND RECOMMENDATIONS Table 1 summarizes the observed deficiencies and recommendations as a result of the 2015 inspection of

the Primary and Secondary Ash Ponds at Flint Creek Station.

Throughout the majority of the upstream and downstream slopes of both the Primary and Secondary Ponds, significant undesirable vegetation still remains growing through the riprap revetment hindering adequate inspection.

Beach erosion was observed in natural ground on the upstream slope, upstream of the Primary Pond spillway.

The Primary and Secondary Ponds are generally in fair condition.

The right bank of the Secondary Pond’s spillway exit channel has eroded near the discharges to the Little Flint Creek Reservoir. This does not pose an immediate risk to the Ash Ponds.

To address the deficiencies identified at the Bottom Ash Ponds, Golder recommends the following

remedial actions:

All vegetation should be cut and maintained less than 6 inches in height. Clear both slopes and riprap of undesirable vegetation and cut and remove all trees on the slopes. Seed and mulch areas without riprap to establish a good grass cover.

Backfill animal burrows with compacted fill, seed and mulch to establish grass cover in the areas where burrows were observed on the upstream and downstream slopes of the Primary and Secondary Ponds.

Maintain an herbicide program to eradicate vegetation growing within the riprap revetments.

Place riprap along the shoreline and lower slope of the natural ground between the Primary Pond and the Secondary Pond. The use of riprap in this area would help minimize beach erosion as well as discourage animal burrowing which was identified by Golder during the 2012 inspection.

Backfill and regrade the crest of the Primary Pond where tire ruts were identified and any other depression that would cause ponding of water on the crest or concentrated run-off down the slopes to reduce the potential for development of rills or erosion gullies.

Continue to monitor the spillway weirs for changes in under seepage and potential erosion caused by the seepage.

Stabilize the Secondary Pond’s exit channel bank by flattening the slope and place riprap to provide erosion protection. Recycled concrete blocks may be used as an alternative to regular riprap as used at other locations along the channel. We recommend placing the concrete blocks or riprap on a flattened slope no steeper than 2h:1v and on geotextile filter fabric.

Re-establish vegetation in the exit channel downstream of the Secondary Pond auxiliary spillway concrete control structure.

November 2015 10 1529064


GOLDER ASSOCIATES INC. Michael T. Chilson, P.E. W. Randall Sullivan, P.E., Lic#8575 Senior Civil Engineer Principal and Practice Leader

MTC/WRS/sp

TABLES

1/1

Thick and tall brush and woody vegetation is growing on the lower portion of the slope within the riprap revetment preventing adequate inspection. 1 Significant Continue to clear overgrown vegetation and trees from the riprap and slopes.

Maintain a herbicide program to eradicate vegetation within riprap.

Shallow erosion gullies and rill erosion has occurred a several locations across the length of the Primary Pond embankment. The slope is generally uneven and irregular.

2, 4 Minor Backfill large voids with compacted fill and regrade the slope. Reestablish a good grass cover to prevent farther deterioration.

Beach erosion has occurred at the natural ground between the Primary and Secondary Pond embankments. 3 Minor Extend the riprap revetment along the upstream shoreline upstream of the

Primary Pond spillway.

Crest Fair Tire ruts have occurred at the right (north) abutment. 5 MinorResurface the crest using a road base material near the north end of the Primary Pond embankment, and any other depressions that might result in ponding water or concentrated runoff during rainfall events.

D/S Slope Fair The upper slope generally has a well maintained, good grass cover. The

lower slope brush and grass growing among the riprap revetment. 7, 8 MinorContinue to clear brush from the riprap and slope. Maintain herbicide program to eradicate vegetation in riprap. Maintain grass to < 6 inches to discourage animal burrowing and facilitate inspection of the slope.

Groins Fair Some vegetation was growing within the riprap at the left groin of the Primary Pond embankment. NA Minor Maintain herbicide program to eradicate vegetation within riprap.

Spillway FairSeepage is occurring from under the concrete weir and through cracks in the concrete weir. No erosion or scour occurring immediately downstream of the weir and in the flow away channel. Vegetation is appropriate.

9, 10, 11 Minor Monitor for increase of seepage through and deterioration of the concrete weir

Thick and tall brush and woody vegetation is growing on the lower portion of the slope within the riprap revetment. 13 Significant Continue to clear overgrown vegetation and trees from the riprap and slopes.

Maintain a herbicide program to eradicate vegetation within riprap.

One animal burrow was found on the slope, but other signs of animal activity were observed throughout the site. 12 Minor Backfill any animal burrows with compacted fill and regrass as needed.

Crest Good No issues identified. 5 NA No action recommended.

D/S Slope Poor

The upper slope generally has a well maintained, good grass cover. The lower slope has thick brush and woody vegetation growing among the riprap revetment. The lower slope could not be fully inspected.

15, 16 SignificantContinue to clear brush and trees from riprap and slope. Maintain herbicide program to eradicate vegetation in riprap. Maintain grass to < 6 inches to discourage animal burrowing and facilitate inspection of the slope.

Grass and brush growing within the riprap bank protection downstream of the spillway. No erosion or scour has occurred immediately downstream of the weir and vegetation in the overflow channel is appropriate.

17, 18, 19 Minor Maintain a herbicide program to keep vegetation from growing within the

riprap.

The right channel bank, downstream of the spillway, is eroding where the channel joins the Little Flint Creek reservoir. 20 Minor Cut the channel slope back, and protect it with riprap.

Piezos Fair Piezometers are functional and measured monthly. There are not set trigger levels. 6, 14 Minor AEP is in the process of setting trigger levels in piezometers to guide future

monitoring of the Primary and Secondary Pond embankments.

Table 1: Observed Deficiencies and Recommendations

Con

ditio

n *

(Goo

d/ F

air/

Poor

)

U/S Slope Poor

Stru

ctur

e

Dam

Com

pone

nt

Seve

rity

* (M

inor

/ Si

gnifi

cant

/ Ex

cess

ive)

Observations and Remarks Actions and Recommendations

Phot

ogra

ph

Prim

ary

Pond

Seco

ndar

y Po

nd

U/S Slope Poor

Spillway Fair

FIGURES

!

BOTTOM ASH PONDS

!

COOLING LAKE DAM

PROJECTAEP FLINT CREEK

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UPSTREAM SLOPE IS GENERALLY IRREGULAR WITHSHALLOW RILL AND GULLY EROSION THROUGHOUT.TOE OF SLOPE WITH RIPRAP AND HEAVILY VEGETATED.

"

STEEP SLOPE AT SHORELINE WITH BEACH EROSION

"

SEEPAGE THROUGH CRACKS AND UNDER THE CONCRETE WEIRSPILLWAY ACTIVATED SEPTEMBER 9, 2015 DURING RAINFALL EVENT

"

BURROW: 8"-12" WIDE AND DEEP."

MINOR SURFACE SCOUR AT STAIRS

"

LOWER PORTION OF SLOPE AND SHORELINE IS GENERALLYIRREGULAR WITH THICK BRUSH AND RIPRAP. LOWER SLOPE IS DIFFICULT TO INSPECT.

"

SMALL EROSION FEATURE AT BASE OF STAIRS

"

BANK EROSION IN THE DISCHARGE CHANNEL

"

WIDESPREAD BRUSH AND RIPRAP ON THELOWER SLOPE IS DIFFICULT TO INSPECT.

"RILLING AND GULLY EROSION~6" TO 12" DEEP AND WIDE

"CLUSTER OF TREES ~2"-3" DIAM.

"

EXCESSIVE BRUSH AND GRASS, TREES 1" - 2" DIAMETER AMONG RIPRAP

!

PRIMARY PONDWATER LEVEL 1,145.5 FEET-MSLSEPTEMBER 10, 2015

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SECONDARY PONDWATER LEVEL 1,143.6 FEET-MSLSEPTEMBER 10, 2015

"SHALLOW TIRE RUTS

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DOWNSTREAM SLOPE IS GENERALLY WITH TALL GRASS 12" - 18" TALL, WITH LOOSE MATERIAL AND SHALLOW ANIMAL BURROWS ABOVE THE RIPRAP

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2 BURROWS: 12"-18" WIDE AND DEEP.

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APPENDIX A DAM INSPECTION CHECK LIST

150919 Flint Creek Ash Pond 10 Day Cover Letter.docx Golder Associates Inc.

3730 Chamblee Tucker Road Atlanta, GA 30341 USA

Tel: (770) 496-1893 Fax: (770) 934-9476 www.golder.com Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America


September 19, 2015 1529064 Mr. W. Greg Carter, P.E. – Region 5 Engineer American Electric Power Corporation – Southwest Power Company 1 Riverside Plaza Columbus, OH 43215-2373 RE: FLINT CREEK PLANT 2015 ANNUAL DIKE AND DAM INSPECTION, LITTLE FLINT CREEK

BOTTOM ASH PONDS, ARKANSAS

Dear Mr. Carter: Golder Associates Inc. (Golder) is pleased to submit the attached Inspection Checklist Forms for the annual safety inspection of the Flint Creek Plant Ash Ponds performed on September 10, 2015. The inspection was performed by Mr. Rafael Ospina, P.E. and Mike Chilson, P.E, under the direction of W. Randall Sullivan, P.E. (Arkansas). Mr. Greg Carter, Gary Zych, and H.E. Rice with AEP-SWEPCO were present during the inspection. The enclosed forms are to be submitted to the Arkansas Soil and Water Conservation Commission within 10 days of the inspection. The full report of the inspection will be submitted to you under a separate cover. The work was performed in accordance with our Proposal No. 1535398 dated May 1, 2015, Blanket Contract 2631379X103, and Letter of Authorization (LOA) 263137900001x168 dated June 23, 2015. If you have any questions, please do not hesitate to contact us. Very truly yours, GOLDER ASSOCIATES INC.

Rafael I. Ospina, P.E. W. Randall Sullivan, P.E, Arkansas #8575 Principal and Practice Leader Principal and Practice Leader Attachments: Inspection Checklists RIO/MC/WRS/rio cc: Gary F. Zych, P.E. – AEP Manager Geotechnical Engineering Group

NAME OF DAM: Flint Creek Plant Ash Ponds INSPECTION DATE:

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1 SURFACE CRACKING None Observed -- --

2 CAVE IN, ANIMAL BURROW None Observed -- --

3 LOW AREA(S) None Observed -- --

4 HORIZONTAL ALIGNMENT OK -- --

5 RUTS AND/OR PUDDLES Small depression across crest at north end of primary impoundment berm. -- -- 6 VEGETATION CONDITION OK - Road base aggregate -- --

7 ----- ----- -- -- --8 ----- ----- -- -- --9 SLIDE, SLOUGH, SCARP Non observed during this inspection. -- --

10 SLOPE PROTECTION Vegetation in riprap, need to eradicate vegetation/weeds with herbicide. -- -- 11 SINKHOLE, ANIMAL BURROW Animal burrow mid slope of south embankment. -- -- 12 EMB.-ABUT. CONTACT OK -- --

13 EROSION Minor erosion at both spillway access stairs. Beach undercutting. -- --

14 VEGETATION CONDITION Overgrown vegetation within the riprap shore protection. -- -- 15 SLOPE ANGLE Upper 1/3 of Secondary embankment increases in slope to 1.5-2.0:1 (h:v) -- --

16 ----- ----- -- -- --ADDITIONAL COMMENTS: REFER TO ITEM NO. IF APPLICABLE.

11) Overgrown vegetation in secondary pond needs to be cut and investigate area for additional animal burrows. Backfill all animal burrows identfied.

5) Fill/regrade depression.

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EEMBANKMENT

10) Clear vegetation on slope and riprap and maintain a herbicide vegetation/weed control program.

10/9/2015

13) A few 6" to 12" deep rilling and gully erosion developing in both north and south embankments. Beach undercutting of the natural ground north of the primary spillway in area

CHECK ()

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North (N) embankment

South(S) embankment

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Upstream

NAME OF DAM: Flint Creek Plant Ash Ponds INSPECTION DATE: 10/9/2015

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ADDITIONAL COMMENTS: REFER TO ITEM NO. IF APPLICABLE.

Inspected by: Rafael Ospina, Golder Associates Inc.

14) Overgrown grass above riprap in north embankment. Keep vegetation down to < 6" for proper inspection. Cut a few trees identified identified during the inspection.

Accompanied by: Gregg Carter and H.E. Rice, AEP

13) between north and south embankments. Regrade and vegetate eroded areas and place rip-rap protection to reduce beach erosion as appropiate.

CHECK ()

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EMBANKMENT

NAME OF DAM: INSPECTION DATE:

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17 WET AREA(S) (NO FLOW) None Observed -- --

18 SEEPAGE None Observed -- --

19 SLIDE, SLOUGH, SCARP None Observed -- --

20 EMB.-ABUT. CONTACT OK -- --

21 CAVE IN, ANIMAL BURROW Irregular surface above rip-rap with significant shallow animal burrow -- -- 22 EROSION None observed of significance -- --

23 UNUSUAL MOVEMENT None Observed -- --

24 VEGETATION CONTROL Thick vegetation among riprap, trees started to regrow on D/S slope -- -- 25 ----- ----- -- -- --

26 ----- ----- -- -- --

27 PIEZOMETERS/OBSERV. WELLS Not inspected by Golder during this Inspection. Water levels recorded by -- --

28 STAFF GAUGE AND RECORDER OK -- --

29 WEIRS NA - None observed -- -- --

30 SURVEY MONUMENTS NA - None observed -- -- --

31 DRAINS NA - None observed -- -- --

32 FREQUENCY OF READINGS Frequency of readings scheduled by AEP, at least quarterly -- -- --

33 LOCATION OF RECORDS Records kept with AEP Plant office -- -- --

34 ----- ----- -- -- --


10/9/2015Flint Creek Plant Ash Ponds

EMBANKMENT

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21) activity in north embankment. Two animal burrows 12" wide and 16" to 18" deep identified. Backfill all animal burrows identfied.

NAME OF DAM: INSPECTION DATE: 10/9/2015Flint Creek Plant Ash Ponds

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EMBANKMENT CHECK ()

ACTION NEEDED4 of 4

24) Cut trees/clear vegetation from riprap and maintain a herbicide grass/weed control program to eradicate vegetation within rip-rap.

27) AEP personnel the week prior to inspection. No issues with piezometers were reported by AEP.


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51 SLIDE, SLOUGH, SCARP None Observed -- --

52 EROSION Bank erosion on the right side where the channel enters the cooling lake. -- -- 53 VEGETATION CONDITION OK -- --

54 DEBRIS None Observed -- --

55 APPROACH AREA In fair condition -- --

56 ----- Seepage through cracks and under the concrete weir (12" high wall) of -- -- --

57 SIDEWALLS NA -- -- --

58 CHANNEL FLOOR NA -- -- --

59 UNUSUAL MOVEMENT NA -- -- --

60 APPROACH AREA NA -- -- --

61 WEIR OR CONTROL Seepage through cracks and under the concrete weir (12" high wall) of -- --

62 DISCHARGE AREA NA -- -- --

63 DRAINS NA -- -- --

64 ----- ----- -- -- --

65 INTAKE STRUCTURE NA -- -- --

66 TRASHRACK NA -- -- --

67 STILLING BASIN Submerged discharge. -- -- --

68 ----- ----- -- -- --


52) protection. Flatten east slope to provide an even surface and place additional rip-rap protection over geotextile fabric.

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61) principal spillway.

10/9/2015Flint Creek Plant Ash Ponds

SPILLWAYS

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70 INTAKE STRUCTURE Lower and Upper structures in fair condition 71 TRASHRACK Clear -- --

72 STILLING BASIN OK - -- --

73 PRIMARY CLOSURE NA -- -- --

74 SECONDARY CLOSURE NA -- -- --

75 CONTROL MECHANISM Weirs functional -- --

76 OUTLET PIPE Clear with submerged discharge. -- --

77 OUTLET TOWER NA -- --

78 EROSION ALONG DAM TOE None Observed -- --

79 SEEPAGE None Observed -- --

80 UNUSUAL MOVEMENT None Observed -- --

81 ----- ----- -- -- --

82 ----- ----- -- -- --


Flint Creek Plant Ash Ponds 10/9/2015

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71) Periodically clear algae from trash rack. Secondary pond spillway previously reconstructed using engineered design drawings.

16-1

CHAPTER 16: DAM INSPECTION AND MAINTENANCE CHECKLIST

THE EMBANKMENT Key things to look for: Any evidence of movement, either within the dam itself, at its ends, or in the material on which it rests; and excessive surface erosion or other damage to the embankment, or excessive seepage. Is the dam overgrown with underbrush or trees? SURFACE CRACKS

Yes No Remarks Maintenance Tips � � Are there any surface cracks?

May indicate movement within the dam.

Should be evaluated by a professional engineer.

� � Is there any unusual movement or cracking at or beyond the toe?

Dam or its foundation may be unstable.


SURFACE EROSION Yes No Remarks Maintenance Tips � � Is there erosion on upstream face from wave action or changes in pool level?

If severe or rapid, a serious problem.

If severe and progressive, protect upstream face with riprap or other form of wave protection.

� � Is there erosion from runoff, either rills, gullies or bare areas?

Erosion of any sort is a problem, as it tends to worsen with time if not corrected.

Improve grass cover; reshape embankment to improve drainage pattern.

� � Is there erosion from traffic (people, animals, vehicles)?

Any erosion is serious, as it will get worse with time if not corrected.

Try to keep all types of traffic to a reasonable level. Keep vehicles off dam. Stabilize crest roads to prevent rutting. Prohibit recreational vehicle traffic on slopes. Keep livestock off dam. Fill in existing ruts or eroded areas and reseed.

X

X

x

x

x

FLINT CREEK ASH POND SEPTEMBER 2015 INSPECTION

X

See Inspection Checklist Item 13

See Inspection ChecklistItem 13

16-2

EMBANKMENT (continued) ANIMAL BURROWS

Yes No Remarks Maintenance Tips � � Are there any animal burrows?

May provide passageways for water into or through the dam.

Fill burrows with earth or otherwise block entry. Try to keep woodchucks, muskrat and beaver away from the dam.

DEPRESSIONS

Yes No Remarks Maintenance Tips � � Are there depressed areas on the dam?

May have resulted from slope failures or settlement, or even piping.

If pronounced or progressive, must be evaluated by a professional engineer.

PIPING

Yes No Remarks Maintenance Tips � � Is there any evidence of piping? (This condition is evidenced by a muddy flow through the dam and/or the formation of soil deposits beyond the dam and depressions on its slopes.)

Piping is internal erosion within an embankment, or the progressive removal of soil particles adjacent to leaks through a soil mass.

Piping is always a serious condition, which can lead to failure of the dam. A piping condition must be evaluated by a professional engineer.

� � Does the crest appear to have shifted or settled excessively? (Look for cracks in the em-bankment and associated structures. Compare alignment with plans if they are available.)

Crest movement may indicate a stability problem. However, some settlement of a new fill, such as an embankment dam, is normal.

Must be evaluated by a professional engineer.

x

x

x

See InspectionChecklist Item 11 & 21

x

16-3

EMBANKMENT (continued) PIPING (continued)

Yes No Remarks Maintenance Tips � � If the upstream face is protected by riprap is it in good condition? (Riprap is a layer, facing, or protective mound of stone in random size pieces, randomly placed to prevent erosion, scour, or sloughing of an embankment or structure.)

Effectiveness is lessened if riprap has slipped out of place, has been undermined, or has become overgrown with brush.

Restore riprap as necessary; keep free of trees and bushes.

� � If there is riprap in discharge channels or in the plunge pool downstream, is it in good condition?

Has riprap been displaced or overgrown?

Restore riprap as necessary; keep free of trees and bushes.

� � If drainage channels at ends of embankment are protected with riprap, is it in good condition?

Drainage along abutments often causes gullying if there is no protection.

Riprap or other form of slope protection should be used as necessary.

� � If there is riprap in miscellaneous areas (on downstream slope, on crest, etc.) is it in good repair?

Restore as necessary.

x

See Inspection ChecklistItem 10

See Inspection Checklist Items 14 and 24

x

x

x

16-4

EMBANKMENT (continued) ALIGNMENT Yes No Remarks Maintenance Tips � � Does the crest appear to have shifted or settled excessively? (Look for cracks in the em-bankment and associated structures. Compare alignment with plans if they are available.)

Crest movement may indicate a stability problem. However, some settlement of a new fill, such as an embankment dam, is normal.


SEEPAGE

Yes No Remarks Maintenance Tips � � If there are any drains to collect and remove, seepage, are they operating properly?

Check plans for the presence of drains and search the dam to see if any others are present.

Keep drains clear of any blockages and assure proper operation.

� � If there are foundation drain outlets, are they clear and flowing?

Foundation drains serve to collect seepage passing through the dam and conduct it away from the embankment.

Open outlets to such drains if they have become covered or clogged.

� � Are there wet spots or areas on the downstream face, at the toe, or beyond the dam? (Such spots are often indicated by a change in color or type of vegetation, such as from grass to cattails.)

Some seepage is normal for an earth dam. Be concerned if it appears to be excessive (a lot of standing water; very soft and marshy areas; evidence of a seepage line high on the downstream face).

Observe seepage areas periodically to detect changes in the amount of moisture, new flows, or muddy flows. If the upper limit of seepage is fairly high on the downstream face, the dam may be unstable.

x

N/A

N/A

x

See InspectionChecklist Item 17

X

16-5

EMBANKMENT (continued) SEEPAGE (continued) � � Are there seeps or springs with flowing water? Look closely for these at the ends of the dam, around any pipes passing through the embankment, on downstream face, at the toe of the dam and beyond, and at the base of trees on, near, or below the dam.

Flowing seeps or springs may indicate problems, and should be periodically monitored for changes in rate of flow or muddy flow. Creation of an impoundment often causes changes in the water table nearby.

Monitor seepage closely for any changes in amount, rate, extent, or clarity. Excessive or turbid seepage, or marked increases in rate of seepage, should be evaluated by a professional engineer.

� � Is there swamp or marsh type vegetation on downstream face or beyond the dam (cattails, tall grass, etc.)?

Swamp type vegetation indicates the presence of seepage.

Cut frequently to make observation of the area easier. Such growth can hide problems.

VEGETATION � � Is the dam overgrown with trees and/or underbrush?

One of the most frequent problems, and highly un-desirable. Roots may damage the embankment and allow water to pass into or through it. Trees may be uprooted in a storm and breach the dam.

Keep embankment faces free of trees and underbrush by periodic mowing. Remove existing trees and saplings, and establish and maintain a good grass cover on the dam.

See InspectionChecklist Items 14and 24

x

x

x

See InspectionChecklist Items 10, 14,and 24

16-6

EMBANKMENT (contined) OVERTOPPING � � Has the dam ever been overtopped by water flowing over it?

Past overtopping may have resulted in erosion of the crest and downstream face of the dam. Overtopping indicates that the emergency spillway is probably too small.

Restore eroded areas or other damage done to the dam by overtopping. Consider enlarging the emergency spillway, lowering the normal pool level to allow more storage capacity during floods, or perhaps raising the height of the embankment to decrease the possibility of future overtopping. Consult a professional engineer.

MODIFICATIONS � � Has there been any modification of the embankment, such as raising the crest, changing the shape or size of the principal spillway or the emergency spillway, or changing the shape or size of the embankment?

Inappropriate or unsuitable modifications can drastically affect the safety of a dam, even one that may have originally been properly designed and constructed.

Dams that have been appreciably modified since construction should be evaluated for stability by a professional engineer.

x

xx

See Check List Item 72 Additional Notes

16-7

THE PRINCIPAL SPILLWAY

Yes No Remarks Maintenance Tips � � Can water flow into the principal spillway without difficulty, as intended when constructed?

The riser, intake structure, or channel should be free of trash or other blockage.

Install a trash rack if one is not already in place. Periodically clear trash rack of any accumulated debris.

� � Is outlet pipe or discharge channel clear and open to allow the free passage of the principal spillway discharge?

Flows passing through the spillway should not erode or otherwise damage the dam.

Keep outlet pipe, plunge basin, and all other outlet works clear and in good repair.

� � Is the primary spillway structure in good condition (check concrete, wood, and metal portions for damage or deterioration)?

Such dam features as the principal spillway require continued maintenance like any other structure.

Repair and maintain as ap-propriate to insure the con-tinued useful life of the dam.

� � Does the lake have a drain that can be used to lower it in an emergency?

Lowering a lake may be necessary if the dam begins to develop problems.

Check plans or search dam for emergency drain system.

� � If there is an emergency drain, is it known to be in working condition? Danger: If a drain has not been used for a long time, it may be possible to open it but not close it, thus draining the lake.

Drain valves and other mechanisms should receive sufficient maintenance to insure that they remain in working order.

Maintain system so that it can be used in an emergency. Normally, the pool behind an earth embankment dam should not be lowered at a rate of more than 1 inch per day.

�� If there are other

gates, valves, or operating equipment, are these in working condition?

Such devices are vital to the effective and safe operation of the dam.

Repair and restore if necessary, and maintain in an operable condition.

x


x

x

x

N/A

N/A


16-8

THE EMERGENCY SPILLWAY

Yes No Remarks Maintenance Tips � � Can water flow into the emergency spillway without difficulty, as intended when con-structed?

To be effective, all portions of the spillway channel should be clear and unobstructed.

The approach channel should be kept free of trash, underbrush, or other blockage.

� � Is the discharge channel clear and open to allow the free passage of the emergency spillway discharge?

Spillway flows must be ef-fectively conducted away from the dam.

Clear as necessary.

� � Is the emergency spillway constructed in such a way that its flows will not erode other por-tions of the dam?

A berm is often constructed to keep spillway flows from encroaching on the embankment.

Reshape dam if necessary to take care of this problem.

� � Is the emergency spillway in good condition overall (check for erosion within the channel, adequacy of grass cover, etc.)?

Spillway erosion is a common problem.

Restore any erosion gullies or eroded areas. Provide channel protection (riprap, concrete, etc.) if necessary to eliminate recurring problems.

THE RESERVOIR AREA

Yes No Remarks Maintenance Tips � � Is serious wave erosion occurring along the shoreline?

Some minor erosion along a shoreline is to be expected.

Critical shoreline areas can be protected with vegetation or in some other manner.

� � Is a lot of sediment entering the impoundment, or has this happened in the past?

This may occur as a result of construction or agricultural activity in the watershed.

Dredging may be required to restore the lake.

x

x

See Inspection Checklist Items 53 & 54

x

x


x

x

Bottom Ash

X

16-9

RESERVOIR AREA (continued) � � Does the nature of the land surrounding the lake or its use present any problems?

Intensive agricultural or development activities in the watershed may precipitate problems associated with surface runoff or other difficulties.

Problems of this nature are often complex and may be beyond the owner’s direct control.

� � Is there any evidence of landslides or instability on the slopes around the reservoir?

A large landslide into a lake can subject a dam to overtopping or other damage.

Suspected or evident pro-blems of this type should be investigated by a professional engineer or engineering geologist.

DOWNSTREAM CHANNEL

Yes No Remarks Maintenance Tips � � Is the downstream channel free of obstructions, so that water in a flood will not back up against the toe of the dam?

The channel below a dam is often a neglected area.

Clear downstream channel if necessary.

WATERSHED AREA

Yes No Remarks Maintenance Tips � Have there been any major modifications or significant changes in the watershed drainage area, such as new urban developments (shopping centers, housing projects), clear cutting of woodlands, or other basic changes in land use.

Intensive agricultural or de-velopment activities in the watershed may precipitate problems associated with greater surface runoff or other difficulties.

Problems of this nature are often complex and may be beyond the owner’s direct control. Appeals to existing regulations dealing with erosion prevention, pollution control, etc. may be helpful.

x

x

x

x

APPENDIX B PHOTOGRAPHS

November 2015 B – 1 1529064

Appendix B Ash Pond Pictures V1.docx

Flint Creek Bottom Ash Ponds All other photographs were taken on September 9 and 10, 2015. PHOTO 1 Primary Pond Upstream Slope Thick brush and woody vegetation has grown throughout the riprap and at the toe. The thick and tall vegetation within a potential snake habitat makes the slope difficult and dangerous to inspect properly.

PHOTO 2 Primary Pond Upstream Slope Vegetation above the riprap has good coverage, but the surface is generally irregular with several shallow rills 6 to 12 inches deep.

November 2015 B – 2 1529064


PHOTO 3 Primary Pond Upstream Slope The slope at the shoreline just north of the principal spillway is over steep with beach erosion and overgrown vegetation. This area is located on the natural abutment between the Primary and Secondary Ponds.

PHOTO 4 Primary Pond Upstream Slope Surface scour erosion is occurring at the bare ground adjacent to the spillway access stairs.

PHOTO 5 Primary Pond Dam Crest Tire ruts on the crest near the west end of the berm appear to be related to a shallow trench excavated for the installation of utilities.

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PHOTO 6 Primary Pond Dam Crest The majority of the slope has a level gravel surface. The piezometers at the crest of the Primary and Secondary Impoundments have flush mounted protective covers and are in fair condition.

PHOTO 7 Primary Pond Downstream Slope Overgrown vegetation is above and within the riprap. Some 1- to 2-inch diameter trees have started to grow along the lower part of the slope near the shoreline. The grass above the riprap is 12 to 18 inches tall.

PHOTO 8 Primary Pond Downstream Slope The slope is generally irregular. Two large animal burrows, 12 to 18 inches wide and deep were identified. Overgrown brush is above and within the riprap revetment preventing the proper inspection of the slope and shoreline.

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PHOTO 9 Primary Pond Principal Spillway

PHOTO 10 Primary Pond Auxiliary Spillway AEP has significantly improved the maintenance condition of the weir and exit channel since Golder’s last inspection in 2012.

PHOTO 11 Primary Pond Auxiliary Spillway Seepage is occurring through hairline cracks in the concrete and from under the concrete weir.

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PHOTO 12 Secondary Pond Upstream Slope The upper part of the upstream slope has good grass cover. One animal burrow, 8 to12 inches wide and deep, was identified

PHOTO 13 Secondary Pond Upstream Slope Thick grass and brush has established throughout the riprap and shoreline. The thick and tall vegetation within a potential snake habitat makes the slope difficult and dangerous to inspect properly.

PHOTO 14 Secondary Pond Downstream Slope The majority of the slope has a level gravel surface. Utility lines were installed at the crest servicing the two spillways.

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PHOTO 15 Secondary Pond Downstream Slope The upper part of the upstream slope has good grass cover.

PHOTO 16 Secondary Pond Downstream Slope Thick brush and woody vegetation has established within the riprap and shoreline of the downstream slope preventing the proper inspection of the slope and shoreline.

PHOTO 17 Secondary Spillway Spillway Weir Recycled concrete slab pieces have been placed in the exit channel downstream of the weir for erosion and scour protection.

The concrete orifice and weir system appear to be adequately functioning.

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PHOTO 18 Secondary Spillway Spillway Weir The reservoir staff gage indicated a pool elevation at 1,143.55 feet-msl at the time of inspection.

PHOTO 19 Secondary Spillway Spillway Channel The channel is stable immediately downstream of the spillway weir.

PHOTO 20 Secondary Spillway Spillway Channel Stream bank erosion has occurred at the discharge to the Little Flint Creek Reservoir.


Golder Associates Inc. 3730 Chamblee Tucker Road

Atlanta, GA 30341 USA Tel: (770) 496-1893 Fax: (770) 934-9476

report for the 2015 inspection of the ash ponds at … · november 2015 2 1529064 2015-11-20 ash...

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