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Stantec Consulting Services Inc. 1409 North Forbes Road, Lexington KY 40511-2024

July 22, 2016 File: rpt_001_LTR_175665216 Revision 0

Frost Brown Todd LLC 400 West Market Street 32nd Floor Louisville, Kentucky 40202

RE: Initial Safety Factor Assessment Spurlock Ash Pond EPA Final CCR Rule East Kentucky Power Cooperative H.L. Spurlock StationMaysville, Kentucky

1.0 PURPOSE

This letter documents Stantec’s certification of the Initial Safety Factor Assessment for the Spurlock Station’s Ash Pond. Based on this assessment, the Spurlock Ash Pond is in compliance with the factors of safety specified in the EPA Final CCR Rule at 40 CFR 257.73(e)(1)(i), (ii), (iii) and (iv).

2.0 SAFETY FACTOR ASSESSMENT

The safety factor assessment conducted pursuant to 40 CFR 257.73(e) addresses the following factors of safety:

• Long-term, maximum storage pool loading condition,

• Maximum surcharge pool loading condition,

• Seismic,

• Liquefaction

Stantec compiled and reviewed available historical site, topographic and geotechnical data. A complete listing of documents reviewed is included in the attached document.

Based upon our document review, Stantec identified one cross section that had been previously analyzed and identified as the most critical cross section. This cross section is designated Section A-A’, and it was analyzed for the required EPA Final CCR Rule load cases.

July 22, 2016 Page 2 of 3

Re: Initial Safety Factor Assessment Spurlock Ash Pond EPA Final CCR Rule East Kentucky Power Cooperative H.L. Spurlock StationMaysville, Kentucky

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3.0 SUMMARY OF FINDINGS

The attached document presents the Initial Safety Factor Assessment analyses at Section A-A’. The calculated Factors of Safety are shown in the table below. The results show that the calculated Factors of Safety exceed the minimum values required under the EPA Final CCR Rule 40 CFR 257.73(e).

Plant Facility Critical Cross

Section EPA Criteria EPA Required

FOS Factor of

Safety (FOS)

EKPC Spurlock Station

Ash Pond A-A’

Long-term maximum storage pool loading condition

1.5 1.8

Maximum surcharge pool loading condition

1.4 1.8

Seismic 1.0 1.3

Liquefaction 1.2 1.4

July 22, 2016

Page 3 of 3

Re: Initial Safety Factor Assessment

Spurlock Ash Pond EPA Final CCR Rule

East Kentucky Power Cooperative

H.L. Spurlock Station

Maysville, Kentucky

4.0 QUALIFIED PROFESSIONAL ENGINEER CERTIFICATION

I, Don W. Fuller II, being a Professional Engineer in good standing in the State of Kentucky, do

hereby certify, to the best of my knowledge, information, and belief that the information

contained in this certification is prepared in accordance with the accepted practice of

engineering. I certify that pursuant to 40 CFR 257.73(e)(2), the safety factor assessment for the

Spurlock Station Ash Pond was conducted in accordance with and demonstrates compliance

with the factors of safety specified in 40 CFR 257.73(e)(l )Ci), (ii), (iii) and (iv).

SIGNATURE

DATE: July 22, 2016

ADDRESS: Stantec Consulting Services Inc.

1409 North Forbes Road

Lexington, Kentucky 405 l l

TELEPHONE: (859) 422-3000

ATTACHMENTS: Safety Factor Assessment Calculation Package

Design with community in mind

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Initial Safety Factor Assessment

East Kentucky Power Cooperative Spurlock Ash Pond H.L. Spurlock Station

Prepared for: Frost Brown Todd LLC 400 West Market Street 32nd Floor Louisville, Kentucky 40202-3363

Prepared by: Stantec Consulting Services Inc. Lexington, Kentucky

July 22, 2016

Revision Record Revision Description Prepared By Checked By Approved By

Sign-off Sheet

This document entitled, "Initial Safety Factor Assessment," was prepared by Stantec Consulting Services Inc. ("Stantec") for the account of Frost Brown Todd LLC (the "Client") representing East Kentucky Power Cooperative. Any reliance on this document by any third party is strictly prohibited. The material in it reflects Stantec's professional judgment in light of the scope, schedule, and other limitations stated in the document and in the contract between Stantec and the Client. The opinions in the document are based on conditions and information existing at the time the document was published and do not take into account any subsequent changes.

In preparing the document, Stantec did not verify information supplied to it by others. Any use that a third party makes of this document is the responsibility of such third party. Such third party agrees that Stantec shall not be responsible for costs or damages of any kind, if any, suffered by it or any other third party as a result of decisions made or actions taken based on this document.

Prepared by __ \ __ J_��=--�M�'--"..---,{;_� .... �� {) __ _ -�gmtum) 9--

Jason M. Curd, EIT

Reviewed by �riJ .�dflLigna ure)

Vincent J. Seve=E

Reviewed by,:?::;Je.� •�

(Signat e) Bret A. Lavey, PE

Reviewed by ��f(Signature)

Don W. Fuller, PE

Stantec

INITIAL SAFETY FACTOR ASSESSMENT

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Table of Contents

EXECUTIVE SUMMARY ............................................................................................................... I

1.0 INTRODUCTION ...........................................................................................................1.1 1.1 OBJECTIVE ....................................................................................................................... 1.1 1.2 OUTLINE OF RULE REQUIREMENTS ................................................................................. 1.1 1.3 DESCRIPTION OF STRUCTURE ........................................................................................ 1.2

2.0 PROJECT RECONNAISSANCE .....................................................................................2.1 2.1 REVIEW OF EXISTING DATA ............................................................................................ 2.1 2.2 DATA GAPS ..................................................................................................................... 2.1

3.0 SUMMARY OF FIELD INVESTIGATIONS AND LABORATORY TESTING ..........................3.1

4.0 DETAILED TASK ANALYSIS CRITERIA ............................................................................4.1 4.1 MATERIAL PROPERTIES ................................................................................................... 4.1 4.2 CRITICAL CROSS SECTION SELECTION ......................................................................... 4.2 4.3 WATER LEVELS ................................................................................................................. 4.3 4.4 ANALYSIS METHODOLOGY ........................................................................................... 4.4

4.4.1 Long-Term Maximum Storage Pool ........................................................... 4.4 4.4.2 Maximum Surcharge Pool .......................................................................... 4.5 4.4.3 Seismic Factor of Safety.............................................................................. 4.5 4.4.4 Liquefaction Potential ................................................................................. 4.5

4.5 ACCEPTANCE CRITERIA ................................................................................................ 4.6

5.0 ANALYSIS ASSUMPTIONS ............................................................................................5.1

6.0 ANALYSIS RESULTS .......................................................................................................6.1

7.0 CONCLUSIONS ............................................................................................................7.1

8.0 REFERENCES .................................................................................................................8.1

LIST OF TABLES Table 1. Factor of Safety Criteria ............................................................................................. 1.1 Table 2. Generalized Subsurface Conditions ........................................................................ 4.1 Table 3: Spurlock Ash Pond Soil Strength Parameters (Stantec 2013) ................................ 4.2 Table 4: Historic Slope Stability Analyses Results for Cross Section A-A’............................. 4.3 Table 5: Spurlock Ash Pond Water Elevations for Stability Modeling ................................. 4.3 Table 6: EPA Final CCR Rule Factor of Safety Criteria .......................................................... 4.6 Table 7: Initial Safety Factor Assessment Results for Spurlock Ash Pond ............................ 6.1


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LIST OF FIGURES Figure 1 Aerial View of Spurlock Station ................................................................................ 1.2 Figure 2 Plan View of Cross Section A-A’ (Stantec 2013) ................................................... 4.2

LIST OF APPENDICES

SLOPE STABILITY ANALYSIS ....................................................................... A.1

LIQUEFACATION POTENTIAL ANALYSIS .................................................... B.1


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Executive Summary

This Initial Safety Factor Assessment report documents the safety factor evaluation of The Spurlock Ash Pond. The evaluation was performed in accordance with section §257.73(e) of the EPA Final CCR Rule. The results of the Safety Factor Assessment are presented below.


Description Required FOS from CCR Rule

Factor of Safety Report Reference

Static Factor of Safety Under Long-Term Maximum Storage Pool Loading

1.5 1.8 Section 6.0

Static Factor of Safety Under Maximum Surcharge Pool Loading

1.4 1.8 Section 6.0

Seismic Factor of Safety 1.0 1.3 Section 6.0

Liquefaction Factor of Safety 1.2 1.4 Section 6.0

The results of this Initial Safety Factor Assessment meet or exceed the minimum requirements of section §257.73(e) of the EPA Final CCR rule for long-term maximum storage pool, maximum surcharge pool, seismic, and liquefaction loading criteria.


Introduction February 12, 2016

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1.0 INTRODUCTION

1.1 OBJECTIVE

On April 17, 2015 the “Disposal of Coal Combustion Residuals (CCR) from Electric Utilities” (EPA Final CCR Rule) was published in the Federal Register. Stantec Consulting Services Inc. (Stantec) was contracted by Frost Brown Todd LLC representing East Kentucky Power Cooperative to analyze the Structural Integrity Criteria for the Spurlock Ash Pond CCR surface impoundment and to evaluate compliance with §257.73(e) of the EPA Final CCR Rule.

1.2 OUTLINE OF RULE REQUIREMENTS

As required by §257.73 of the EPA Final CCR Rule, an initial structural integrity evaluation is required by October 17, 2016 and must include an initial safety factor assessment for each existing CCR surface impoundment that meets the conditions of paragraph (b) as follows:

1. Has a height of five feet or more and a storage volume of 20 acre-feet or more, or

2. Has a height of 20 feet or more.

The safety factor assessment must document whether the calculated factors of safety for each existing CCR surface impoundment perimeter dike demonstrate the minimum safety factors specified in paragraphs §257.73 (e)(1)(i) through (e)(1)(iv) of the EPA Final CCR Rule for the critical cross section of the embankment.

Table 1. Factor of Safety Criteria

CCR Rule Criteria CCR Rule

Required FOS CCR Rule Reference

Long-term, maximum storage pool loading condition

1.5 §257.73(e)(1)(i)


1.4 §257.73(e)(1)(ii)

Seismic loading condition 1.0 §257.73(e)(1)(iii)

Liquefaction 1.2 §257.73(e)(1)(iv)


Introduction February 12, 2016


In addition, in accordance with paragraph (f)(2), the owner or operator of the existing CCR surface impoundment may elect to use a previously completed assessment to serve as the initial assessment required by paragraph (e) of the EPA Final CCR Rule provided that the previous assessment(s) was completed no earlier than 42 months prior to October of 2016 and meets the applicable requirements of paragraph (e) of the EPA Final CCR Rule.

1.3 DESCRIPTION OF STRUCTURE

The Spurlock Ash Pond is located in the northern portion of Kentucky within the Outer Bluegrass Physiographic Region. The topography within the Outer Bluegrass varies from rolling hills to relatively flat, low-lying areas adjacent to major drainage features. The Ash Pond is located near the northern boundary of Mason County, along the Ohio River. As such, the Ohio River will influence groundwater levels at the site. Topography within the vicinity of the Ash Pond is relatively flat, with local relief generally less than 10 feet. EKPC has determined that the Ash Pond is a CCR surface impoundment and, therefore, is subject to the EPA Final CCR rule.

Figure 1 below presents an aerial view of the Spurlock Station and Ash Pond.

Figure 1 Aerial View of Spurlock Station


Project Reconnaissance February 12, 2016


2.0 PROJECT RECONNAISSANCE

2.1 REVIEW OF EXISTING DATA

The existing data review included the following documents:

• Dames and Moore (1972). “Subsurface Exploration Program – First Unit Spurlock Station”Prepared for East Kentucky Power Cooperative. Maysville, KY. 1972.

• Dewberry and Davis, LLC (2011). “Coal Combustion Residue Impoundment, Round 9 –Dam Assessment Report.” H.L. Spurlock Power Station, Spurlock Ash Pond. Prepared forEast Kentucky Power Cooperative. Maysville, KY. 2011.

• Environmental Protection Agency (2015). “Final Rule: Disposal of Coal CombustionResiduals from Electric Utilities”, Federal Register, April 17, 2015.

• GEO-SLOPE International, Ltd (2012). GeoStudio 2012, Version 8.12.3.7901. Calgary,Alberta, Canada. <www.geo-slope.com>.

• Stantec Consulting Services Inc. (2013). “EKPC Spurlock Ash Impoundment StructuralAnalysis, Geotechnical Investigation and Engineering Report.” Prepared for EastKentucky Power Cooperative, July 9, 2013.

• LIDAR Data received from EKPC on January 12, 2016

2.2 DATA GAPS

During the existing data review Stantec did not find any as built drawings or photographs of construction. These data gaps were acknowledged, but did not create the need for additional geotechnical drilling/sampling, instrumentation, laboratory testing, or field surveying.


Summary of Field Investigations and Laboratory Testing February 12, 2016


3.0 SUMMARY OF FIELD INVESTIGATIONS AND LABORATORY TESTING

Stantec Consulting Services Inc. (2013) performed drilling and sampling of three soil test borings along the northern embankment between the Ash Pond and the Ohio River between February 7 and February 14, 2013. Additional information was obtained from Dames and Moore (1971), which included soil parameters and a slope stability analysis. The geotechnical explorations, laboratory testing, and conclusions were used as the basis for this analysis and are found in the reports referenced in Section 2.1.


Detailed Task Analysis Criteria February 12, 2016


4.0 DETAILED TASK ANALYSIS CRITERIA

4.1 MATERIAL PROPERTIES

An overview of the subsurface conditions within the northern embankment of the Spurlock Ash Pond and the foundation soils is summarized in Table 2. Full details are presented in Stantec Consulting Services Inc. (2013).

Table 2. Generalized Subsurface Conditions

Approximate Elevation Materials Consistency/Density

El. 528 to El. 499 Embankment Fill – Lean Clay (CL) with Sand Medium Stiff to Stiff

E. 499 to El. 485 Alluvium - Lean Clay (CL) Stiff to Very Stiff

El. 485 to El. 478 Alluvium - Sandy Silt (CL / ML) Soft to Medium Stiff

El. 478 to El. 410 Alluvium - Silty Sand (SW-SM) Loose to Dense

During the 2013 geotechnical exploration, Stantec performed a laboratory testing program consisting of natural moisture content, particle size, Atterberg limits, soil classification, and consolidated-undrained (CU) triaxial testing (as applicable). All testing was performed in accordance with ASTM standards, and soil classification was performed in accordance with both the USCS and AASHTO soil classification systems. The test results were used to establish material properties for subsequent engineering analyses. The derived strength parameters used in this safety factor evaluation are presented in Table 3. The results of the laboratory testing and derivation of the strength parameters can be found in Stantec Consulting Services Inc. (2013).




Table 3: Spurlock Ash Pond Soil Strength Parameters (Stantec 2013)

Soil Horizon

Total Unit Weight (pcf)

Effective Stress Strength Parameters

c’ (psf)

ϕ’ (degrees)

Soil 1: Lean Clay with Sand (CL) (Embankment) 132 200 27

Soil 2: Lean Clay with Sand (CL) 131 100 31

Soil 3: Sandy Silt (ML) / Lean Clay (CL) 109 0 31

Soil 4: Lean Clay with Sand (CL) 131 100 31

Soil 5: Well-Graded Sand with Silt and Gravel (SW-SM) 124 0 32

Ash: Fly Ash 85 0 25

4.2 CRITICAL CROSS SECTION SELECTION

Slope stability analyses were available from Stantec Consulting Services Inc. (2013) and Dames and Moore (1971). One primary cross section labeled A-A’ was previously analyzed. This cross section was selected for evaluation by Stantec in 2013 and is considered to be the most susceptible to structural failure based on engineering considerations per §257.73(e)(1). Figure 2 provides a plan view of the cross section A-A’ location.

Figure 2 Plan View of Cross Section A-A’ (Stantec 2013)




From Stantec Consulting Services Inc. (2013), the Ash Pond embankment is approximately 29 feet tall at cross section A-A’. The cross section reflects the geometry subsurface conditions of the Northern Dike, separating the Ash Pond from the Ohio River bank. The slope geometry used in 2013 is consistent with the current LIDAR survey data received in 2016. Slope stability analyses were initially performed during the Ash Pond design by Dames and Moore (1972).

A summary of the historic slope stability analyses results are listed in Table 4.

Table 4: Historic Slope Stability Analyses Results for Cross Section A-A’

Loading Condition Factor of

Safety Pool Elevations Reference Long Term Maximum

Storage Pool 1.7

Ash Pond Pool: 525.6’ Ohio River Pool: 484.5’

Stantec Consulting Services Inc. (2013)

Seismic 1.2 Ash Pond Pool: 525.6’ Ohio River Pool: 484.5’


Liquefaction 1.4 Ash Pond Pool: 525.6’ Ohio River Pool: 484.5’


Long Term Maximum Storage Pool

1.512 Ash Pond Pool: 525.0’ Ohio River Pool: 484.0’

Dames and Moore (1972)

Seismic 1.242 Ash Pond Pool: 525.0’ Ohio River Pool: 484.0’

Dames and Moore (1972)

4.3 WATER LEVELS

The water elevation for the Spurlock Ash Pond was recorded at 525.6 feet and the Ohio River elevation was recorded at 484.5 feet (Stantec Consulting Services, 2013). The water elevations were applied to the long-term maximum storage pool loading criteria for the EPA Final CCR Rule. Under the EPA Final CCR Rule, the inflow design flood for a low hazard potential CCR surface impoundment is the 100-year flood (§257.82(a)(3)(ii)). However, for the purpose of this evaluation, the maximum surcharge pool elevation is conservatively assumed to correspond to the top of the Ash Pond perimeter dike system. The pond elevations proposed for the slope analyses are summarized in Table 5: Spurlock Ash Pond Water Elevations for Stability Modeling

CCR Rule Criteria Spurlock Ash Pond

Elevation (feet, NGVD29) Ohio River Elevation

(feet, NGVD29)

Long-Term Maximum Storage Pool 525.6 484.5

Maximum Surcharge Pool 528.7 484.5

Seismic 525.6 484.5

Liquefaction 525.6 484.5




The Ash Pond water elevation was modeled at the recorded elevation of 525.6 feet for long-term analyses. During the long term and pseudo static analyses, the tailwater elevation was maintained at the recorded Ohio River elevation of 484.5 feet.

4.4 ANALYSIS METHODOLOGY

Global slope stability calculations were performed using the GeoStudio 2012, Version 8.12.3.7901 software package developed by GEO-SLOPE International, Ltd. Of Calgary, Alberta, Canada (GEO-SLOPE International, Ltd, 2012). This package includes the SLOPE/W module for slope stability analysis. SLOPE/W is a special-purpose computer code designed to analyze the stability of earth slopes using the following two-dimensional, limit equilibrium methods:

The analyses were performed in accordance with recommendations and criteria outlined in the USACE Design Manuals EM 110-2-1902 “Slope Stability” (United States Army Corps of Engineers, 2003).

4.4.1 Long-Term Maximum Storage Pool

A drained, effective stress analysis was used for this load case to evaluate incipient motions in the downstream direction. The headwater level is the “long-term maximum storage pool” level of 525.6 feet. The tailwater level is the Ohio River level of 484.5 feet.

The phreatic surface and steady-state pore pressures are based on a static piezometric line interpolated from the dam at this pool level to 2013 piezometer levels at the toe of the slope and the Ohio River tailwater elevation. The required minimum factor of safety corresponds to the entry for “long-term maximum storage pool” in Table 6. Piezometer levels obtained in 2016 correlated well with the previously used 2013 piezometer levels.




4.4.2 Maximum Surcharge Pool

The maximum surcharge pool load condition considers drained stability following a rapid rise in the pool following a 100-year, 6-hour rainfall event. However, the maximum pool surcharge load is conservatively assumed to correspond to the top of the perimeter dike system at elevation 528.7 feet. The surcharge pool is assumed to create a thrust on the slope face without saturating impervious materials above the phreatic surface that developed during the “long-term maximum storage pool” condition. Surcharge pressures are discussed further in Section 5.0.

A drained, effective stress analysis was used for this load case. Incipient motion in the downstream direction is evaluated. The headwater level is the “long-term maximum surcharge pool” level provided in Table 4. The tailwater level is the Ohio River level of 484.5 feet.

The required minimum factor of safety corresponds to the entry for “long-term maximum surcharge pool” in Table 6.

4.4.3 Seismic Factor of Safety

A pseudo-static method was used to evaluate the seismic stability of section A-A’. In this method the effects of an earthquake are applied as a constant horizontal load via the use of dimensionless coefficient kh equal to the peak ground acceleration (PGA) of the earthquake return period being considered. If a factor of safety greater than 1.0 for this loading is determined, it is considered that deformation does not take place. Should a factor of safety less than 1.0 be obtained, it is likely that the embankment will undergo deformation and more rigorous analyses are required.

As required by the EPA Final CCR Rule, a PGA value of 0.086 was obtained from the USGS Geohazards website (http://www.geohazards.usgs.gov) using a two percent probability of exceedance in 50 years.

The conventional guidelines for pseudo-static analysis utilize a horizontal coefficient (kh) equal to one-half of the PGA. However, this study utilized the full PGA as a measure of conservatism.

The pseudo-static evaluation used the same configuration and phreatic surface as the long-term maximum storage pool condition.

4.4.4 Liquefaction Potential

Liquefaction of soils is a phenomenon that may occur during seismic loading when a loose, saturated soil deposit experiences loss of shear strength. The short duration, cyclic loading induced by an earthquake increases the pore water pressure in the soil skeleton, which, in turn, decreases the effective stress resulting in a decrease in the soil's shear strength. If the pore water




pressure becomes equal to the total stress acting on the soil, the effective stress becomes zero and liquefaction occurs. Factors that affect the liquefaction susceptibility of a soil deposit are listed below:

• Soil Structure

• Grain Characteristics

• Relative Density

• Confining Pressure

• Maximum Ground Acceleration

• Duration of Earthquake

The previous liquefaction analysis (Stantec Consulting Services Inc., 2013) was re-evaluated to be in conformance with the EPA Final CCR Rule. Although clay-like soils will most likely not liquefy, they can soften and cause failure modes similar to liquefaction. The potential for liquefaction of clay-like soils was re-evaluated by reviewing natural moisture content determinations and Atterberg limits testing performed during the 2013 Stantec geotechnical investigation. Based on the evaluation of the laboratory data, Soil 3 was deemed susceptible to liquefaction, and per standard engineering practice, the shear strength of all the soils were reduced by twenty percent in the stability analysis.

A factor of safety of 1.4 was obtained from the GeoStudio stability analysis using the reduced soil shear strengths, thereby meeting the acceptable criteria required by the EPA Final CCR Rule. It was determined that a more detailed study to evaluate the potential for liquefaction is not warranted.

4.5 ACCEPTANCE CRITERIA

The following summary is taken from the EPA’s Final CCR Rule §257.73(e). The factor of safety assessment criteria are explicitly outlined in Table 6.

Table 6: EPA Final CCR Rule Factor of Safety Criteria

CCR Rule Criteria CCR Rule Required

Minimum FOS CCR Rule Reference

Long-term maximum storage pool loading condition

1.5 §257.73(e)(1)(i)


1.4 §257.73(e)(1)(ii)

Seismic condition 1.0 §257.73(e)(1)(iii)

Liquefaction 1.2 §257.73(e)(1)(iv)


Analysis Assumptions February 12, 2016


5.0 ANALYSIS ASSUMPTIONS

In an analysis for a surcharge case, the rising pool generates an increasing surcharge pressure on the submerged face of the dam and foundation. Where the surficial soil is assumed to be an undrained material for this condition, the surcharge pressure must be separately computed and inserted into the SLOPE/W analysis, as described herein.

When a surcharge pool load case is modeled in an analysis, the pore pressures are computed for the lower (normal) pool. In this case, SLOPE/W will assume water pressures acting on the ground surface that correspond to the lower normal pool, not the elevated pool being analyzed for undrained stability. The rising pool creates a surcharge pressure that must be added to the ground surface, wherever undrained soils exist at the submerged ground line. In the maximum surcharge model, this is reflected by the difference in the elevation between the surcharge pool and the maximum storage pool being modelled as a surcharge load applied on the ground surface. Note that the additional surcharge pressure is not needed where the surficial soil is fully drained because the pore pressures will be computed using a specified piezometric line that corresponds to the elevated pool condition.

On the graphical output from SLOPE/W, a water surface appears at the level of the lower, normal pool. This corresponds to the conditions for the undrained soils. The added pressure of the flood pool is depicted as a surcharge pressure along the submerged ground line, but is applied only to slow draining soil regions.

When the soils at the head of a slip surface are assigned cohesive strength (c > 0) in a slope stability analysis, tensile stresses are often computed along the base of the slices in that area. In the field, tensile stress results in the opening of a tension crack, reducing the lateral stresses to zero. Because tension results in a stabilizing force at the head of the slide mass, it is unconservative to have tensile stresses between the slices in a slope stability analysis. This problem is discussed by Duncan and Wright (2005).

When tensile stresses are reported in the stability calculation, a vertical tension crack is introduced into the analysis at the ground surface. The crack depth is increased until tensile stresses (negative normal stresses on the base of a slice) are no longer indicated. The depth of the tension crack (dcrack) should not exceed this theoretical maximum value:

(𝑑𝑑𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐)𝑚𝑚𝑐𝑐𝑚𝑚 =2 𝑐𝑐𝑑𝑑

𝛾𝛾𝑚𝑚 tan (45 − 0.5𝜙𝜙𝑑𝑑)

Here, γm is the moist unit weight, and cd and ϕd are the developed shear strength parameters (cd = c / FSslope, tanϕd = tanϕ / FSslope), for the upper soil layer at the head of the slip surface.

For earthquake load cases, tension cracks are assumed to be dry. For all other load cases, an incipient failure may coincide with rain and surface runoff, which would fill a tension crack with water and create an additional lateral force on the slide mass. Tensions cracks are thus assumed to be full of water for these load cases.


Analysis Results February 12, 2016


6.0 ANALYSIS RESULTS

The slope stability assessments presented in this report are focused on the potential for slope failures of significant mass, which could directly impact potential release of water and CCR materials from the Spurlock Ash Pond. The search for a critical slip surface in the slope stability assessments is thus restricted to consider only potential surfaces where the depth (measured at the base of at least one slice) is more than ten feet vertically below the ground surface. A summary of the safety factor evaluation results at the critical cross section of the Spurlock Ash Pond is summarized in Table 7.

Table 7: Initial Safety Factor Assessment Results for Spurlock Ash Pond

Plant Facility Cross

Section EPA Criteria

Calculated Factor of

Safety (FOS)

EKPC Spurlock Ash Pond

A-A’

Static FOS Under Long-Term Maximum Storage Pool Loading

1.8

Static FOS Under Maximum Surcharge Pool Loading

1.8

Seismic Factor of Safety 1.3

Liquefaction Factor of Safety 1.4


Conclusions February 12, 2016


7.0 CONCLUSIONS

This report documents the safety factor evaluation of the Spurlock Ash Pond. The evaluation was performed in accordance with section §257.73(e) of the EPA Final CCR Rule.

Based on the analyses performed for the four evaluated load cases (long term maximum storage pool, long term maximum surcharge pool, pseudo static, and liquefaction), the resulting factors of safety meet the criteria required by the EPA Final CCR Rule.


References February 12, 2016


8.0 REFERENCES

Dames and Moore (1972). “Subsurface Exploration Program – First Unit Spurlock Station” Prepared for East Kentucky Power Cooperative. Maysville, KY. 1972.

Dewberry and Davis, LLC (2011). “Coal Combustion Residue Impoundment, Round 9 – Dam Assessment Report.” H.L. Spurlock Power Station, Spurlock Ash Pond. Prepared for East Kentucky Power Cooperative. Maysville, KY. 2011.

Environmental Protection Agency (2015). “Final Rule: Disposal of Coal Combustion Residuals from Electric Utilities”, Federal Register, April 17.

GEO-SLOPE International, Ltd (2012). GeoStudio 2012, Version 8.12.3.7901. Calgary, Alberta, Canada. <www.geo-slope.com>.

Stantec Consulting Services Inc. (2013). “EKPC Spurlock Ash Impoundment Structural Analysis, Geotechnical Investigation and Engineering Report.” Prepared for East Kentucky Power Cooperative, July 9, 2013.

LIDAR Data received from East Kentucky Power Cooperative on January 12, 2016.

Duncan, J. M. and Wright, S. G. (2005). Soil Strength and Slope Stability. New Jersey: John Wiley & Sons, Inc. 2005.

APPENDIX A SLOPE STABILITY ANALYSIS

Soil 1

Soil 2

Soil 3Soil 4

Soil 5

Fly Ash

1.8

Factor of Safety: 1.8

2/12/2016 4:09:48 PM

Initial Safety Factor Assessment Spurlock Ash Pond EPA Final CCR RuleEast Kentucky Power Cooperative H.L. Spurlock StationMaysville, Kentucky

Static Slope Stability AnalysisExisting Geometry Long Term - Maximum Storage Pool LoadingEffective Strength Analysis; Drained Strengths

Ash PondNorth PerimeterDike

Material

Soil 1 Soil 2 Soil 3 Soil 4 Soil 5 Fly Ash

Unit Weight(pcf)132 131 109 131 124 85

Ohio River

Cohesion(psf)200 100 0 100 0 0

Phi(deg.)27 31 31 31 32 25

Distance-75 -50 -25 0 25 50 75 100 125 150 175 200 225 250

Ele

vatio

n

460

470

480

490

500

510

520

530

540

Ele

vatio

n

460

470

480

490

500

510

520

530

540

Soil 1

Soil 2

Soil 3Soil 4

Soil 5

Fly Ash

1.8


2/12/2016 4:43:25 PM


Static Slope Stability AnalysisExisting Geometry Long Term - Maximum Surcharge Pool LoadingEffective Strength Analysis; Drained Strengths

Ash PondNorth PerimeterDike

Material


Unit Weight(pcf)132 131 109 131 124 85

Ohio River

Cohesion(psf)200 100 0 100 0 0

Phi(deg.)27 31 31 31 32 25

Distance-75 -50 -25 0 25 50 75 100 125 150 175 200 225 250

Ele

vatio

n

460

470

480

490

500

510

520

530

540

Ele

vatio

n

460

470

480

490

500

510

520

530

540

Soil 1

Soil 2

Soil 3 Soil 4

Soil 5

Fly Ash

1.3

Ohio River

Initial Safety Factor Assessment Spurlock Ash Pond EPA Final CCR RuleEast Kentucky Power Cooperative H.L. Spurlock StationMaysville, KentuckyStatic Slope Stability AnalysisExisting Geometry Long Term - Psuedo Static LoadingEffective Strength Analysis; Drained Strengths

Unit Weight(pcf)132 131 109 131 124 85

Cohesion(psf)200 100 0 100 0 0

F of S: 1.3

Phi(deg.)27 31 31 31 32 25

Material


2/12/2016 4:39:12 PM

North Perimeter Dike

PGA: 0.086 (USGS)

Ash Pond

Distance-75 -50 -25 0 25 50 75 100 125 150 175 200 225 250

Ele

vatio

n

460

470

480

490

500

510

520

530

540

Ele

vatio

n

460

470

480

490

500

510

520

530

540

Soil 1

Soil 2

Soil 3 Soil 4

Soil 5

Fly Ash

1.4

Ohio River

NOTE: Based on laboratory test data for Soil 3, the soil was deemed succeptible to liquefaction failure. For this reason, the strength parameters of all clay-like soils were reduced to 80 percent of the total value per standard engineering practice.

2/12/2016 4:44:28 PM

North Perimeter Dike

Ash Pond


Static Slope Stability AnalysisExisting Geometry Long Term - Liquefaction LoadingEffective Strength Analysis; Reduced Drained Strengths

Material


Unit Weight(pcf)132 131 109 131 124 85

Cohesion(psf)160 80 0 80 0 0

Phi(deg.)22.2 25.6 25.6 25.6 26.56 20.5


Distance-75 -50 -25 0 25 50 75 100 125 150 175 200 225 250

Ele

vatio

n

460

470

480

490

500

510

520

530

540

Ele

vatio

n

460

470

480

490

500

510

520

530

540

APPENDIX B LIQUEFACTION POTENTIAL ANALYSIS


Spurlock Ash Pond

EPA Final CCR Rule

East Kentucky Power Cooperative

H.L. Spurlock Station

Maysville, Kentucky

Liquefaction Susceptibility of Fine-Grained SoilsStantec Project Number:

Project Name:

Site/Structure Name:

Overall Judgement

based on 3 methods

(sand-like or clay-

like)

Overall Judgement based

on 2 methods

(susceptibility)

Meets

criteria for

sand-like

behavior

Meets

criteria for

clay-like

behavior

Meets

criteria for

sand-like

behavior

Meets criteria

for clay-like

behavior

Borderline

soils (treat as

sand-like)

Lab ID Boring Depth(s)Soil

Classification

NMC (wc)

(%)

% Passing

#200

% Passing

#40LL PI

LL in Zone

A (see

plot)

PI in Zone

A (see

plot)

LL in Zone

B (see

plot)

PI in Zone

B (see

plot)

LL in Zone

C (see

plot)

PI in Zone

C (see

plot)

PI < 7 PI >= 7 PI <= 7

P40>=35%,

P200>=20%,

and PI>=10

7 < PI < 10, or

does not meet

P40 or P200

LL PIwc/LL >=

0.85

PI <=

12

wc/LL <

0.80

PI >

18

Intermediate

wc/LL (see

plot)

Intermediate

PI (see plot)

54 B-1 10.0-11.5, 20.0-21.5, 30.0-31.5 CL 17.63333 80.9 99.5 31 13 -1 -1 31 13 -1 -1 -1 13 -1 13 -1 Clay-like -1 -1 -1.00 -1 0.57 13 -1.00 -1 Not Susceptible

69 B-1 42.5-44.0, 45.0-46.5 ML 23.8 65.2 99.9 22 19 -1 -1 22 19 -1 -1 -1 19 -1 19 -1 Clay-like 22 19 -1.00 -1 1.08 19 -1.00 -1 Susceptible

13 B-1 OFFSET 15.3-16.5, 16.5-16.9 CL 18.05 76.6 99.4 29 11 29 11 -1 -1 -1 -1 -1 11 -1 11 -1 Clay-like -1 -1 -1.00 -1 0.62 11 -1.00 -1 Not Susceptible

29 B-2 12.0-13.5, 16.5-18.0 CL 32.55 88 99.8 37 15 -1 -1 37 15 -1 -1 -1 15 -1 15 -1 Clay-like 37 15 -1.00 -1 -1.00 -1 0.88 15 Susceptible

37 B-2 35.0-36.5, 60.0-61.5 SW-SM 6.1 26.3 NP NP Sand-like

Sand-like versus Clay-like Behavior (-1 indicates result does not meet criteria, green shading indicates result does meet criteria, no results shown for

non-plastic material)

Meets criteria for sand-

like behavior

175563005 / 175665216

Spurlock Stability Analysis

EKPC Spurlock Ash Pond

Susceptibility of Clay-like Soils to Cyclic Softening (-1 indicates result does not meet criteria, green shading

indicates result does meet criteria, no results shown for Sand-like materials)

Using Criteria published by

Seed et al (2003)

Meets all criteria for B (clay-like

and potentially liquefiable, -2

indicates zone A but

susceptible, -3 indicates not

applicable due to fines content

Clay-like soil is

susceptible (must

meet both)

Clay-like soil is

not susceptible

(must meet

one or both)

Using Criteria published by Seed et al (2003) Using Criteria published by Bray and Sancio (2006)

Clay-like soil is moderately

susceptible

Using Criteria

published by Idriss and

Boulanger (2008)

Meets criteria for clay-like behaviorNote: NP = Non-Plastic

Using criteria published by MSHA (2010)

Fine_Grained_Liq_Screening1_Appendix B.xlsx Stantec Consulting Services Inc. 2/12/2016

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