### Geotechnical Environmental and

Water Resources Engineering



# Specific Site Assessment for Coal Combustion Waste Impoundments at Duke Energy Indiana (DEI) Gibson Generating Station Owensville, Indiana

Submitted to: U.S. Environmental Protection Agency Office of Resource Conservation and Recovery 5304P 1200 Pennsylvania Avenue NW Washington, DC 20460



### Submitted by: GEI Consultants, Inc. 4601 DTC Blvd., Suite 900 Denver, CO 80237

September 2010 Project 092880

Stephen G. Brown, P.E. Senior Project ManagerGEI Consultants, Inc. 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### i 

# Table of Contents

1.0 Introduction 1 1.1 Purpose 1 1.2 Scope of Work 1 1.3 Authorization 2 1.4 Project Personnel 2 1.5 Limitation of Liability 2 1.6 Project Datum 2 1.7 Prior Inspections 2
2.0 Description of Project Facilities 3 2.1 General 3 2.2 Impoundment Dams and Reservoirs 3 2.3 Spillways 4 2.4 Intakes and Outlet Works 4 2.5 Vicinity Map 4 2.6 Plan and Sectional Drawings 5 2.7 Standard Operational Procedures 5
3.0 Summary of Constructi on History and Operation 7

4.0 Hazard Potential Classification 8 4.1 Overview 8 4.2 East Ash Ponds and East Settling Basin 8 4.3 North Ash Pond and North Settling Basin 9
5.0 Hydrology and Hydraulics 10 5.1 Floods of Record 10 5.2 Inflow Design Floods 10 5.2.1 East Ash Ponds and East Settling Basin 10 5.2.2 North Ash Pond and North Settling Basin 11 5.2.3 Determination of the PMF 12 5.2.4 Freeboard Adequacy 12 5.2.5 Dam Break Analysis 12 5.3 Spillway Rating Curves 12 5.4 Evaluation 12
6.0 Geologic and Seismic Considerations 13

7.0 Field Assessment 14 7.1 General 14GEI Consultants, Inc. 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### ii 7.2 Embankment Dam 14 7.2.1 Dam Crest 14 7.2.2 Upstream Slope 14 7.2.3 Downstream Slope 15 7.3 Seepage and Stability 15 7.4 Appurtenant Structures 15 7.4.1 Overflow Structures 15 7.4.2 Pump Structures 15 7.4.3 Emergency Spillway 15 7.4.4 Water Surface Elevations and Reservoir Discharge 16
8.0 Structural Stability 17 8.1 Visual Observations 17 8.2 Field Investigations 17 8.3 Methods of Analysis 17 8.4 Discussion of Stability Analysis and Results 18 8.5 Seismic Stability - Liquefaction Potential 20 8.6 Summary of Results 20
9.0 Maintenance and Methods of Operation 21 9.1 Procedures 21 9.2 Maintenance of Impoundments 21 9.3 Surveillance 21

10.0 Conclusions 22 10.1 Assessment of Dams 22 10.1.1 Field Assessment 22 10.1.2 Adequacy of Structural Stability 22 10.1.3 Adequacy of Hydrologic/Hydraulic Safety 23 10.1.4 Adequacy of Instrumentation and Monitoring of Instrumentation 23 10.1.5 Adequacy of Maintenance and Surveillance 23 10.1.6 Adequacy of Projec t Operations 23

11.0 Recommendations 24 11.1 Corrective Measures and Analys es for the Structures 24 11.2 Corrective Measures Required for Instrumentation and Monitoring Procedures 25 11.3 Corrective Measures Required fo r Maintenance and Surveillance Procedures 25 11.4 Corrective Measures Required for t he Methods of Operation of the Project Works 25 11.5 Acknowledgement of Assessment 26

12.0 References 28GEI Consultants, Inc. 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### iii List of Tables

Table 2.1: Summary Information for Impoundment Dam Parameters Table 4.1: DEI Gibson Generating Station – Summary of East Impoundments Parameters Table 4.2: DEI Gibson Generating Station – Summary of North Impoundments Parameters Table 8.1: Stability Factors of Safety and Guidance Values



### List of Figures

Figure 1: Site Vicinity Map Figure 2: Site Aerial Map Figure 3: Typical Dam Sections


### List of Appendices

Appendix A: Inspection Checklists Appendix B: Inspection Photographs Appendix C: Reply to Request for Information Under Section 104(e)GEI Consultants, Inc. 1 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 1.0 Introduction

1.1 Purpose

This report presents the results of a specific s ite assessment of the dam safety of six coal combustion waste (CCW) impoundments at the Gibson Generating Station in Owensville, Indiana. The Gibson Generating Station is ope rated by Duke Energy Indiana, Inc. (DEI) and owned by DEI, Wabash Valley Power Associ ation, Inc. and Indiana Municipal Power Agency. The six impoundments are the Nort h Ash Pond, North Sett ling Basin, East Ash Ponds #1, #2, and #3, and the East Settling Ba sin. These six impoundments comprise the active coal combustion waste facility at the Gibson Gene rating Station. Other coal combustion waste impoundments at the Gibson Generating Station in clude the South Ash Pond and Basin, which have been closed under In diana Beneficial Use Statute IC-13-19-3-3. The specific site assessment was pe rformed on April 26 and 27 of 2010.
The specific site assessment was performe d with reference to Federal Emergency Management Agency (FEMA) guidelines for dam safety, which includes other federal agency guidelines and regulations (such as U.S. Army Corps of Engineers [USACE] and U.S. Bureau of Reclamation [USBR]) for specifi c issues, and defaults to state requirements were not specifically addressed by federal guid ance or if the state re quirements were more stringent. 

## 1.2 Scope of Work

The scope of work between GEI Consultants, Inc. (GEI) and the U.S. Environmental Protection Agency (EPA) for the specific site assessment is summarized in the following tasks:

1. Acquire and review existing reports and drawi ngs relating to the safety of the project provided by the EPA and Owners. 2. Conduct detailed physical inspections of the project facilities. Document observed conditions on Field Assessment Check List s provided by EPA for each management unit being assessed. 3. Review and evaluate stability analyses of the project’s coal combustion waste impoundment structures. 4. Review the appropriateness of the inflow design flood (IDF), and adequacy of ability to store or safely pass the inflow design flood, provision for any spillways, including considering the hazard potent ial in light of conditions obs erved during the inspections or to the downstream channel. 5. Review existing dam safety performa nce monitoring programs and recommend additional monitoring, if required.GEI Consultants, Inc. 2 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### 6. Review existing geologic asse ssments for the projects. 7. Submit draft and final reports.



## 1.3 Authorization

GEI performed the coal combustion waste impound ment assessment as a contractor to the EPA. This work was authorized by EP A under Delivery Order EP09W001698 between EPA and GEI, dated August 12, 2009. 

## 1.4 Project Personnel

The scope of work for this task order was completed by the following personnel from GEI:
Stephen G. Brown, P.E. Pr oject Manager/Task Leader Nicholas D. Miller, P.E. Project Engineer Bryan M. Scott, Ph.D., P.E. Project Geotechnical Engineer

The Program Manager for the EPA was Stephen Hoffman. 

## 1.5 Limitation of Liability

This report summarizes the assessment of da m safety of North Ash Pond, North Settling Basin, East Ash Ponds #1, #2, and #3, and the Ea st Settling Basin co al combustion waste impoundments at Gibson Generating Station, Owensville, Indiana. The purpose of each assessment is to evaluate the structural inte grity of the impoundments and provide summaries and recommendations based on the available info rmation and on engineering judgment. GEI used a professional standard of practice to review, analyze, and apply pertinent data. No warrantees, express or implied, ar e provided by GEI. Reuse of this report for any other purpose, in part or in whole, is at the sole risk of the user. 

## 1.6 Project Datum

The project datum was not identified on the documents reviewed by the assessment team. 

## 1.7 Prior Inspections

The embankment dams for the six CCW impoundments are inspected monthly by a DEI Gibson Generating Station engineer but no written records of the inspections are maintained. A third-party engineering firm performed an in formal visual inspection of the embankments in October 2008; however neither state nor fede ral regulatory official s have inspected the embankments within the last five years.GEI Consultants, Inc. 3 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 2.0 Description of Project Facilities

2.1 General

Gibson Generating Station is a co al-fired power plant consisting of five units that generate about 3,250 megawatts (MW) combined. The pow er plant is located in the town of Owensville, Gibson County, Indiana approximately 35 miles north of Evansville, Indiana; see Figure 1. Gibson Generating Station is a cl osed loop facility with no discharge of any process water to waters of the U.S. Storm wa ter impacted from remote industrial activities on haul roads is regulated by Indiana Departme nt of Environmental Management under Rule 6 National Pollutant Discharge Elimination Sy stem (NPDES) storm water permit. The six CCW impoundments are located ad jacent to and northeast of th e power plant (Figure 2). These six impoundments are the North Ash P ond, North Settling Basin, East Ash Ponds #1, #2, and #3, and the East Settling Basin. All units are operated by DEI, and co-owned by DEI, Wabash Valley Power Association, and In diana Municipal Power Agency. The first unit went online in 1972. 

## 2.2 Impoundment Dams and Reservoirs

The embankment dams of the six CCW im poundments have not been assigned a hazard potential by a state or federal agency. Based on the geometry of the impoundments and the facilities downstream, recommended hazard po tential classifications for the impoundments have been developed in Section 4.0 of this repor t. The basic dimensions and geometry of the six CCW impoundments are summarized in Ta ble 2.1. East Ash Ponds #1, #2, and #3, and the East Settling Basin are adjacent to each other. The North Ash Pond and North Settling Basin are adjacent to each other, but ar e separated from the East Ash Ponds.

East Ash Ponds #1, #2, and #3, and the North Ash Pond are used to store fly ash, bottom ash, boiler slag, flue gas emission control residuals and other waste. The East Settling Basin and the North Settling Basin store fl y ash and other waste. DEI has identified other waste as landfill leachate, water treatment , boiler blow down, stormwat er runoff, boiler chemical cleaning wastes, mill rejects, floor and labor atory drains, and drains from equipment cleaning.
The embankments are relatively homogeneous, and were constructed of onsite clayey material. The dam embankments have crests varying from 12 to 40 feet wide, downstream slopes of 3H:1V, and upstream slopes varying from 2H:1V to 3H:1V.GEI Consultants, Inc. 4 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station Table 2.1: Summary Information for Impoundment Dam Parameters
Parameter Value

Dam East Ash Pond

#1 East Ash Pond

#2 East Ash Pond

#3 East Settling Basin North Ash Pond North Settling Basin
Height (ft) 18.5 18.5 23 18.5 14 18
Estimated Perimeter Length (ft) 8,750 8,750 10,200 6,800 5,000 4,000
Crest Width (ft) 20 20 20 20 12 to 40 12 Crest Elevation (ft) 404. 5 404.5 412.0 404.5 405.0 405.0 Design Side Slopes (H: V) 2:1 to 3:1 2:1 to 3:1 2:1 to 3:1 2:1 to 3:1 3:1 3:1

Estimated Freeboard (ft) at time of site visit 5.0 5.0 3.0 7.0 5.0 7.0
Storage Capacity (ac-ft)* 1733 1733 3325 743 350 150

Surface Area (acres)* 105 105 133 45 25 10
* Storage capacity and area values provided by DEI 

## 2.3 Spillways

None of the six CCW impoundments have spillways.



## 2.4 Intakes and Outlet Works

The intake structures located in the East Ash Ponds #1, #2, and #3 and the North Ash Pond consists of a square concrete stop log weir st ructure approximately 9-f eet long by 9-feet wide and 16-feet tall, that discharg es through a 36-inch-diameter co nnecting pipe to an adjacent impoundment. Flow through the weir structur es is controlled by manually adding or removing concrete stop logs into the guides.
The outlet works for the East Settling Basin cons ists of a pump station, ultrasonic water level indicator and operator, visual alarm, and a pipe that discha rges to the Cooling Pond. The East Settling Basin pump station has an estimated maximum discharge capacity of 10,000 gallons per minute (gpm). The North Se ttling Basin has a similar pump station system that consists of two pumps, ultrasoni c water level indicator and operator, visual alarm, and a pipeline that discharges to th e Cooling Pond. The North Settling Basin pump station has an estimated maximum discharge capacity of 20,000 gpm. 

## 2.5 Vicinity Map

Gibson Generating Station is located in th e town of Owensville, Gibson County, Indiana approximately 35 miles north of Evansville, Indiana, as shown on Figure 1. The six CCW impoundments are located adjacent to, and northeast of, the station.GEI Consultants, Inc. 5 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

## 2.6 Plan and Sectional Drawings

Engineering drawings for the six CCW impound ments were prepared by Sargent & Lundy. Construction record drawi ngs were not prepared. 

## 2.7 Standard Operational Procedures

Gibson Generating Station is a coal-fired pow er plant composed of five 650 MW units producing a total combined capac ity of 3,250 MW. Coal is deliv ered to the power plant by train, where it is then combuste d to power the steam turbines. The burning of coal produces several gases which are vented from the boile r, and bottom ash, which is made of coarse fragments, falls to the bottom of the boiler, a nd is removed along with boiler slag. Currently, bottom ash and boiler slag from all five units are being wet sluiced to North Ash Pond where primary settling occurs. Fly ash from Units #1, #2, and #3 are also wet sluiced to the North Ash Pond where primary settling occurs. Fly as h from Units #4 and #5 are collected dry and managed in onsite landfills. According to DEI, Units 1 th rough 3 are scheduled to be converted to dry handling by the end of 2013. All process water generated at the Gibson Generating Station is managed within a closed -loop pond system with no discharge to waters of the United States.
The North Ash Pond is used for primary se ttling and for temporary storage for coal combustion waste that is wet sluiced from the bo ilers. Bottom ash and fly ash are physically segregated in the North Ash Pond by separating the wet sluice discha rge pipes within the North Ash Pond. The fly ash is discharged to the north side of th e pond and the bottom ash is discharged to the south end of the pond. The fly ash is removed from the pond by a hydraulic dredge with a booster pump that disc harges to the East Ash Pond system. The bottom ash is decanted, excavated and then dispos ed of into one of the two onsite landfills. The North Ash Pond discharges decant water into the North Settling Basin. The water level in the North Ash Pond is controlled by concrete stop logs in the primary overflow structure to the North Settling Basin. The North Ash Pond can also discharge to the North Settling Basin through a second overflow structure that has a set discharge elevati on of 397.57. The North Settling Basin provides secondary clarifying of solids before th e effluent is discharged by pumping to the Cooling Pond. The discharge fr om the North Settling Basin is controlled by two pumps that are operated by an ultrasonic water level control system that is equipped with an alarm that triggers a flashi ng light at the pump station.
The East Ash Pond system consists of EastAsh Ponds #1, #2, and #3 and the East Settling Basin. East Ash Ponds #1, #2, and #3 were de signed to receive and store hydraulically dredged coal combustion waste that consists primarily of fly ash and lesser amounts of bottom ash, boiler slag, flue gas emission cont rol residuals and a mi nor amount of process wastewater from the North Ash Pond. Water leve ls in the system are controlled by stop log overflow structures located in each cell. The decant water in the system was designed toGEI Consultants, Inc. 6 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### flow as follows: East Ash Pond #3 to East Ash Pond #2, East Ash Pond #2 to East Ash Pond #1, and East Ash Pond #1 to the East Settling Basin. However, East Ash Pond #3 of the system began closure in 2009 upon receipt of the Indiana Department of Environmental Management approved Closure/Post Clos ure Plans on March 7, 2009 and is no longer receiving the hydraulically dredged waste. Closure of this cell is expected to be completed by the end of 2012. East Ash Pond #1 is no long er receiving coal waste because it is near capacity, but a discharge channe l is maintained for decant water from East Ash Pond #2 to discharge into the East Settling Basin. East Ash Pond #2 is actively receiving the hydraulically dredged coal waste from the Nort h Ash Pond. The East Settling Basin provides secondary clarifying of solids before the efflue nt is discharged into the Cooling Pond. The discharge from the East Settli ng Basin is controlled by a pump that is operated by an ultrasonic water level control system that is e quipped with an alarm that triggers a flashing light at the pump station.GEI Consultants, Inc. 7 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 3.0 Summary of Construction History and Operation

The first unit at Gibson Generati ng Station went online in 1972. The final unit (Unit 5) was online by 1983. Coal combustion waste was orig inally placed in as h ponds that are now closed. The North Ash Pond and North Se ttling Basin were commissioned in 1974. The East Settling Basin and East Ash Pond #1 we re commissioned in 1991, East Ash Pond #2 in 1995, and East Ash Pond #3 in 1999. The two north impoundments were constructed ad jacent to each other such that a common interior embankment separates the ponds. The four east impoundments were also constructed adjacent to each ot her using common interi or dikes. As a result, some of the embankments are exterior dikes (similar to typical embankment dams) and some of the embankments are interior dikes (designed to separate one pond from another pond). The dikes were constructed of homogeneous f ill material, typically with riprap and/or geotextile armoring on the upstream slope to protect against wave erosion. Typical geometries of the dikes are shown in Table 2.1 and Figure 3. The southern dike for East Ash Pond #3 was constructed as a rais e of the northern dike for East Ash Ponds #1 and #2. This was completed as a “downstream raise,” in wh ich the raised East Ash Pond #3 embankment was constructed over the existing dikes and na tive ground. The raised embankment was not founded on the coal combustion waste contained in East Ash Ponds #1 and #2. Original design drawings for the ponds and their embankments were available; however design reports and construction records were not available. Foundation preparation for the embankments included removal of 1 foot of t opsoil. Clayey soil excavated from onsite borrow areas was utilized in the constructi on of the embankments. Evidence of prior releases, failures or patchwork construction were not observed during the site visit or disclosed by plant personnel during the site vi sit. However, DEI’s interpretation of their groundwater monitoring program led them to be lieve that the bottom portion of the liner system was more permeable than the original design for the East Ash Pond #3. This led, in part, to the decision to close East Ash Pond #3, and the closure is currently in progress. A fixated scrubber sludge (FSS) landfill was de signed in 1999 by Fuller, Mosbarger, Scott & May that consisted of a landfill to be constr ucted over a portion of the North Ash Pond. The coal combustion waste placed in the FSS landfill includes:

 Dewatered FGD solids (synthetic gypsum) a nd FGD wastewater tr eatment solids from units 1, 2, and 3.

 Fly ash, FGD solids (calcium sulf ite) and quicklime from Unit 4.

 Fly ash, FGD solids (synthetic gypsum) and quicklime from Unit 5. Placement of this material is ongoing.GEI Consultants, Inc. 8 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 4.0 Hazard Potential Classification

4.1 Overview

According to the Federal Guidelines for Dam Safety the hazard potenti al classification for the CCW impoundments is based on the possible adverse incremental consequences that result from release of stored contents due to failure of the dam or misoperation of the dam or appurtenances. Impoundments are classified as Low, Significant, or High hazard, depending on the potential for loss of human life and/or economic and environmental damages. The Federal Guidelines for Dam Safety hazard pote ntial classification categories are consistent with the Indiana Department of Natural R ecourses Division of Water hazard potential classification categories. 

## 4.2 East Ash Ponds and East Settling Basin

The East Ash Ponds and East Settling Basin are regulated by the Indiana Department of Natural Resources, Division of Water, Dams, and Levees. The East Ash Ponds and East Settling Basin are relatively small in size a nd storage capacity. Th e pond size and capacity of each unit provided by Duke Energy is summarized in Table 4.1.

Table 4.1: DEI Gibson Generating Station – Summary of East Impoundments Parameters

Pond Name Height (ft) Storage (ac-ft) Surface Area (acres) East Ash Pond #1 18.5 1,733 105 East Ash Pond #2 18.5 1,733 105 East Ash Pond #3 23 3,325 133 East Settling Basin 18.5 743 45



### Based on current pond heights and storage capacity shown in Table 4.1 th e size classification for the East Ash Ponds and East Settling Basi n is “Small” in accordance with the USACE Recommended Guidelines for Safety Insp ection of Dams ER 1110-2-106 criteria.

An uncontrolled release of the CCW impoundments contents due to a failure or misoperation is not considered to cause loss of human lif e and the economic and environmental damages would be relatively low based on our review. The flood extent and depth would be limited by the adjacent USACE levee on the Waba sh River and the very flat surrounding topography. Flood waters would lik ely be widespread with sh allow depths and gradually rising waters. Based on the pond height and vol ume, the majority of inundation would be limited to the undeveloped property owned by DE I to the south and east around the Cooling Pond and the surrounding wetlands. The county road adjacent to the west dike could potentially be flooded and temporarily interrupt local traffic in the event of a breach of theGEI Consultants, Inc. 9 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### west dike. However, the breach development ti me is expected to be relatively long and the associated flood depths and flow velocities w ould be relatively small and are not considered to pose a significant hazard to vehicles. Flood waters would eventually drain to the Wabash River at culverts through the USACE levee lo cated about 3 miles downstream. There are no habitable structures in the flow path be tween the ash ponds and the Wabash River. Consistent with the Federal Guidelines for Dam Safety and the Department of Natural Resources Division of Water (DNR), Indian a General Guidelines for New Dams and Improvements to Existing Dams in Indiana, we recommend the East Ash Ponds #1 and #2, and the East Settling Basin dams be classified as "Low" hazard structures. We recommend the East Ash Ponds #3 be classified as “Le ss Than Low” hazard structure because this pond is currently in the process of being closed and no longer receives hydraulically dredged coal combustion waste. 

## 4.3 North Ash Pond and North Settling Basin

The North Ash Ponds and North Settling Basin are regulated by the Indiana Department of Natural Resources, Division of Water, Dams, and Levees. The North Ash Pond and North Settling Basin are relatively small in size a nd storage capacity. Th e pond size and capacity of each unit provided by Duke Energy is summarized in Table 4.2.

Table 4.2: DEI Gibson Generating Station – Summary of North Impoundments Parameters

Pond Name Height (ft) Storage (Ac-ft) Surface Area (acres)
North Ash Pond 14 350 25 North Settling Basin 18 150 10



### Based on current pond heights and storage capacity shown in Table 4.2 th e size classification for the North Ash Pond and North Settling Basin is “Small” in accordance with the USACE Recommended Guidelines for Safety Insp ection of Dams ER 1110-2-106 criteria.

An uncontrolled release of the CCW impoundments contents due to a failure or misoperation is not considered to cause loss of human lif e and the economic and environmental damages would be relatively low based on our review. The flood extent and depth would be limited by the adjacent USACE levee on the Waba sh River and the very flat surrounding topography. Flood waters would lik ely be widespread with sh allow depths and gradually rising waters. Based on the pond height and vol ume, the majority of inundation would be limited to the undeveloped property owned by DE I to the south around the Cooling Pond and the surrounding wetlands. Flood waters would eventually drain to the Wabash River at culverts through the USACE levee located a bout 3 miles downstr eam. There are no habitable structures in the flow path be tween the ash ponds and the Wabash River. Consistent with the Federal Guidelines fo r Dam Safety and the DNR Indiana General Guidelines for New Dams and Improvements to Existing Dams in Indiana, we recommend the North Ash Pond and North Settling Basin dams be classified as "Low" hazard structures.GEI Consultants, Inc. 10 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 5.0 Hydrology and Hydraulics

5.1 Floods of Record

Floods of record have not been evaluated a nd documented for the six CCW impoundments at the Gibson Generating Station. Th e National Weather Service loca l rain gage data reportedly recorded maximum daily rainfall depths ranging from about 6.5 to 7.4 inches in the surrounding areas. Recently, in March of 2008, a ma ximum daily rainfall depth of 6.4 inches was reported at the Evansville Regional Airport ga ge. These rainfall events are not expected to result in overtopping of the dams unde r the current normal operating conditions. No documentation has been provided to verify the storm results. 

## 5.2 Inflow Design Floods

Currently there is no hazard classificati on for the six CCW impound ments at the Gibson Generating Station. Based on obs ervations during the field inspection, we recommend the six CCW impoundments be classified as “Low” hazard structures (Section 4). Based on the recommended “Low” hazard classification, the DNR General Guidelines for New Dams and Improvements to Existing Dams in Indiana sp ecifies “Low” hazard dams be capable of passing a flood event that ranges from the 100-year storm to the 50 percent probable maximum precipitation (PMP) without overtopping the dam. The USACE Recommended Guidelines for Safety Inspection of Da ms ER 1110-20106 recommends a small “Low” hazard dam be capable of passing the 50- to 100-year storm event without overtopping the dam. Considering the “Low” hazard rating, th e relatively low economic and environmental damages that could potentially occur upon failu re, and the recommended range of inflow design storms, it is reasonable to select the 100-year precipitati on event as the inflow design storm for the six CCW impoundments at the Gi bson Generating Station. According to the DNR Guidelines, the 6-hour 100- year precipitation event shou ld be used to analyze the inflow design floods for the ash ponds because the time of concentration for the basins is less than 6 hours. Accordingly, the 6-hour 100-year precipitation at the Gibson Generating Station is about 4.75 inches.
5.2.1 East Ash Ponds and East Settling Basin

The contributing drainage area to the East CCW impoundments is limited to the impoundments surface area (Table 2.1) because th e surrounding dikes eliminate the potential for surface water run-on. Based the East CCW impoundments facility layout, all rainfall over East Ash Ponds #1, #2 and #3 will be routed to the East Settling Basin through the decant structures located in each pond. Therefor e, the total contributing drainage area to the East Settling Basin is approximately 388 acres. The East Settling Basin is not provided with a spillway for maintaining the reservoir level or storm water discharg e; rather, the dam isGEI Consultants, Inc. 11 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### equipped with a pump station that discha rges excess water to the Cooling Pond upon reaching a specified pool elevation. Currentl y, the East Settling Basin water level is maintained at an elevation of about 398.0 feet, which provides about 7 feet of freeboard and approximately 310 acre-feet of additional st orage capacity. Based on the contributing drainage area and the 6-hour 100-year precipitation of 4.75 inches, the East Settling Basin would receive approximately 154 acre-feet of storm water, wh ich would result in a water level at about El. 401.5, providing about 3.5 feet of freeboard. Based on these results, the East Ash Ponds and East Settling Basin meets the regulatory requirement s for storage of the 6-hour 100-year inflow design flood without overtopping the dam.
5.2.2 North Ash Pond and North Settling Basin

The North Ash Pond has been significantly modified since the original design. The modifications have changed the site drainage. Currently, th e majority of the southeast portion of the North Ash Pond has been conve rted into a Fixated Scrubber Sludge (FSS) landfill and the northwest corner has been conve rted into parking areas. Considering the current modifications, the North Ash Pond contri buting drainage area was estimated to be approximately 230 acres, which includes runoff from the portions of the FSS landfill and the parking areas. The North Settling Basin surf ace area was estimated to be approximately 18 acres, which is nearly doubl e the information provided by Duke Energy. Based on these estimates, the total contribu ting drainage area to the North CCW impoundments is approximately 248 acres.
Under the current configuration, decant water in the North Ash Pond is routed to the North Settling Basin through the two deca nt structure located through th e interior separating dike. The North Settling Basin is not provided with a spillway for maintaining the reservoir level or storm water discharge; rather, the dam is equipped with a pump st ation that discharges excess water to the Cooling Pond upon reaching a specified pool elevation. Currently, the North Settling Basin water level is maintained at an elevation of about 398.0, which provides about 7 feet of freeboard and approximately 80 acre-feet of additional storage capacity. However, once the North Settling Basin water leve l reaches the elevation of the weir in the decant structure in the North Ash Pond, flow will begin to equalize and storage from both ponds will be utilized. During the field investig ation, the weir elevation was estimated to be at least 2 feet below the North Ash Pond dam crest. Due to the irregular topography and continually changing geometry of the North Ash Pond it is difficult to estimate the available storage above the weir wit hout conducting a detailed t opographic map and calculating volumes; however estimates provided by Duke Energy indicate approx imately 175 acre-feet of available storage.
Based on the contributing drainage area and th e 6-hour 100-year precipitation of 4.75 inches, the North Settling Basin would receive approxima tely 98 acre-feet of storm water, assuming no losses. Based on this inflow volume, storag e from both ponds would be utilized. It is difficult to estimate the resulting pond elev ation and freeboard due to the irregularGEI Consultants, Inc. 12 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### topography and continually changing geometry of the North Ash Pond. However, the storm volume is relatively small compared to the es timated combined available storage capacity of both ponds and would likely result in a water surf ace elevation slightly above the decant weir elevation in the North Ash Pond. Based on th ese results, the North Ash Pond and North Settling Basin are expected to meet the regul atory requirements for storage of the 6-hour 100-year inflow design flood w ithout overtopping the dam.

5.2.3 Determination of the PMF

Not applicable.
5.2.4 Freeboard Adequacy

Freeboard is adequate at all facilities.
5.2.5 Dam Break Analysis

No dam break analysis has been performed for the six CCW impoundments at the Gibson Generating Station. However, the dam break analysis and inundation mapping developed for the Gibson Generating Station C ooling Pond was provided as reference information and was used to evaluate the areal extent of inundation and flow direction. 

## 5.3 Spillway Rating Curves

Not applicable.


## 5.4 Evaluation

Based on the current facility operations and inflow design floods documents, the six CCW impoundments at the Gibson Generati ng Station appear to have ad equate capacity to store the regulatory design floods wit hout overtopping the dams base d on the recommended hazard classifications for the dams.GEI Consultants, Inc. 13 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 6.0 Geologic and Seismic Considerations

Based on the Sargent & Lundy Gibson Pond Examination Report (2008):

The site is located in the Wabash Lowl and Physiographic Unit. Glacial outwash sediments consisting of sands and gravels ex ist in the Wabash River Valley. These unconsolidated sediments vary in thickness fr om 50 to 150 feet in this area. Windblown soils and river alluvium sediments cover the glacial deposits. The glacial deposits are underlain by Pennsylvanian ag e shales and sandstones.
Post-Pennsylvanian faults are present in th e area. They trend north-northeast and are parallel to faults in Kentucky and Illinois. The stability analysis for the dikes included a horizontal seismic acceleration coefficient of 0.13g at the time of the original construction.
The seismic coefficient of 0.13g corresponds to a peak ground acceleration of 0.26g. This value is lower than an acceleration of approximately 0.32g as shown on the 2008 United States Geological Survey (USGS) probabilistic seismic hazard map for 2 percent Probability of Exceedance within 50 years (recurrence inte rval of approximately 2,500 years), but higher than an acceleration of approximately 0.19g as shown on the hazard map for 5 percent Probability of Exceedance in 50 years (recurren ce interval of approximately 1,000 years). Application of a pseudo-static seismic coeffi cient of 0.13g in the facility design would be greater than the 1,000-year earthquake, which is within the appropriate range for application to low hazard classification impoundments ba sed on federal dam safety guidance.GEI Consultants, Inc. 14 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 7.0 Field Assessment

7.1 General

A site visit to assess the condition of the six CCW impoundments at the Gibson Generating Station was performed on April 26 and 27 of 201 0, by Stephen G. Brown, P.E., and Nicholas D. Miller, P.E., of GEI. Jim Meiers, Kevin Olivey, Ron Ehlers, Adam Deller, and Rebecca Sparks of Duke Energy assisted in the assessment
The weather during the site visit (April 26–27, 2010) was gene rally partly cloudy to sunny, with temperatures around 60 degrees Fahre nheit. The week preceding the inspection, a considerable amount of rainfall occurred at the site; however the majority of the ground was dry at the time of the site visit, ex cept for the perennial wetland areas.
At the time of inspection, GEI completed an EPA inspection checklist which is provided in Appendix A and photographs are provided in Ap pendix B. Field assessment of the six CCW impoundments included a site walk to observe the dam crest, upstream slope, downstream slope, intake structures and pu mp structures. We saw no obvious signs of settlement or displacement or adverse seepage that would adversely affect th e dam safety of the six CCW impoundments at the Gibson Generating Station.



## 7.2 Embankment Dam

7.2.1 Dam Crest

The dam crest of the six CCW impoundments app eared to be in good condition. No signs of cracking, settlement, movement, erosion or deterioration were observed during the assessment. The dam crest surface is generally co mposed of road base material that traverses the length of the dam for vehicle access.
7.2.2 Upstream Slope

The upstream slope of the six CCW impoundments is protected by either riprap or grassy vegetation. The upstream slope protection appeared to be in satisfactory condition. No scarps, sloughs, depressions or ot her indications of slope instabil ity or signs of erosion were observed during the inspection of the six CC W impoundments. Several small trees were observed on the upstream slopes of the interi or dikes at the Ea st CCW impoundments.GEI Consultants, Inc. 15 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### 7.2.3 Downstream Slope

The downstream slopes of the six CCW impoundments have well-establishe d stands of grass, which provides some erosion protection. No sc arps, sloughs, depressions or other indications of slope instability or signs of erosion were observed during the inspection of the six CCW impoundments. There were isolat ed areas at the East Settling Basin where minor transverse ruts were observed on the slope; however this likely resulted from the wheeled tractor that mowed the grass. Several large trees (2-foot-diame ter or greater) were observed at the toe of the downstream slope of the north dike of the No rth Ash Pond. These trees appear to be part of the pre-existing wetlands that is adjacent to the North Ash Pond. A few small trees (about 3-inch-diameter) were also observed at the to e of the downstream slope of the south and east dike of the East CCW impoundments. 

## 7.3 Seepage and Stability

No evidence of ongoing seepage was observed at the six impoundment embankments. No evidence of slumps, sloughs, settlement associated with slope instabilit y. DEI reported that seepage from Ash Pond #3 had occurred in th e past based on groundwater monitoring well data. The seepage was not through the embankme nt. This seepage was a contributing factor in the decision to close Ash Pond #3. 

## 7.4 Appurtenant Structures

7.4.1 Overflow Structures

The overflow structures located in the Ea st Ash Ponds #1, #2, #3, and the North Ash Pond appeared to be in fair to good condition. The structures were observed to be working properly, discharging decant water to the downs tream facility. The outlet conduits were not visible and could not be inspected. The outle t conduits consist of galvanized corrugated metal pipe (CMP), which is susceptible to corrosion and have a reduced service life compared to more robust pipe materials.
7.4.2 Pump Structures

The pump structures and equipment located at th e North and East Settling Basins appeared to be in fair to good condition. Oper ations tests were not performe d at the time of inspection; therefore, capacity and func tionality of the pump systems could not be confirmed.
7.4.3 Emergency Spillway

No emergency spillways are presen t at the six CCW impoundments.GEI Consultants, Inc. 16 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### 7.4.4 Water Surface Elevations and Reservoir Discharge

The reservoir water surface elevations at the time of inspection for the six CCW impoundments were not provided by Duke Ener gy. The reservoir water surface elevations for the North and East Settling Basins are gene rally maintained at an elevation of 398.0, or about 7 feet of freeboard. The North Ash P ond and East Ash Ponds #1, and #2 are generally maintained at an elevation of 400.0, or about 5 feet of freeboard. Discharge through the overflow structures located in the North Ash Pond and East Ash Ponds #1, and #2 was observed at the time of inspection. Flow depths over the stop logs in the overflow structure were estimated to range from 0.1 to 0.3 feet . The East Ash Pond #3 is currently in the process of being closed and no l ong receives hydraulical ly dredged waste material, as a result it contains negligible amount of stored water. However, the elevation of coal combustion waste material contained in East Ash Pond #3 is approximately at elevation 409.0, or about 3 feet of freeboard. No discharge through the ove rflow structure located in the East Ash Pond #3 was observed at the time of inspection.GEI Consultants, Inc. 17 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 8.0 Structural Stability

8.1 Visual Observations

The assessment team saw no visible signs of in stability associated with the interior or exterior dikes of the six impoundments dur ing the April 26–27, 2010 site assessment. 

## 8.2 Field Investigations

No subsurface investigation reports were provi ded for the North Settling Basin, East Ash Ponds #1 and #2, or the East Settling Basin. Based on the design drawings and specifications, the following subsurface inves tigations were performed at the site:

 Six borings to investigate the subsur face conditions below the eastern portion of the North Ash Pond. These borings were completed as part of a larger program for the original design of the generating station. Standard Penetration Tests (SPT) were performed as part of the investigation, with borings extending to depths of 30 feet to 81.5 feet. The logs of these borings are included in the original Gibson Ge nerating Station drawings prepared by Sargent & Lundy in 1971.

 In 1989 and 1990, Bennett, Williams & Blattert performed a subsurface investigation at the loca tion of the proposed East Ash Ponds. This program consisted of 45 borings within the footpr int of the East Ash Ponds and Settling Basin. Most borings were completed to a depth of 31.5 feet, but several were extended up to 71.5 feet. The logs of th ese borings appear in the construction specifications for the East Ash Ponds. The locations of these borings are shown on the East Ash Pond design drawings. A subsurface investigation report (Patriot Engineering and Environmental Co., LLC [Patriot], 1999) was provided for East Ash Pond # 3. This investigation included:

 10 borings around the perimeter of East Ash Pond #3 including Standard Penetration Testing. Limited laboratory tests were performed including Proctor compaction, unconfined compression tests, and a pair of consolidated undrained triaxial tests.


## 8.3 Methods of Analysis

The stability calculations for the Gibson Lake Cooling Pond were consid ered by the owner to be applicable to the design of the North As h Pond, North Settling Basin, East Ash Ponds #1 and #2, and the East Settling Basin. The method s of structural stability analysis for theGEI Consultants, Inc. 18 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### cooling pond are described in a letter from Sa rgent and Lundy to PSI Energy dated February 11, 1980. The methods of analysis for East Ash Pond #3 are presented in Report of Geotechnical Engineering Inve stigation Slope Stability Analysis of Proposed Ash Pond Addition Phase III (Patriot, 1999).
The description of the original analyses indicat es that a generalized section was evaluated. This section included a height of 25 feet, 3H :1V slopes both upstream and downstream, and a crest width of 40 feet. A gene ralized subsurface profile and soil parameters were used. Analyses considered long-term (steady-state) and pseudo-static load ing cases for both the upstream and downstream slopes. The steady-st ate analyses were conducted using Sargent and Lundy’s proprietary analysis software “BISHOP” using the Bishop method, and the pseudo-static analyses used the computer software “Ices Slopes” provided by McDonnell Douglas Automation Company using the Morgenstern and Price method. A seismic coefficient of 0.13g was used in the pseudo-static analyses.
The analyses for East Ash Pond #3 conducted by Patriot considered a generalized dike 21 feet high, with 3H:1V downstream slope a nd 2H:1V upstream slope, and a crest width of 20 feet. A generalized subsurf ace profile was considered. Analyses considered the upstream and downstream slopes, and considered long-te rm, short-term, and ps eudo-static loading cases. Each of these analyses was conducte d using the computer program STABL. The simplified Bishop method was used for these an alyses. A seismic coefficient of 0.10g was used in the pseudo-static analyses. 

## 8.4 Discussion of Stability Analysis and Results

The detailed results of the stability analyses co mpleted as part of the original design are not included in the Sargent and Lundy letter in 1980 describing the analyses. The letter states that “the results showed that the minimum factor of safety against slope failure for steady state condition is in exce ss of 1.5.” The letter adds that fo r the pseudo-static analysis, “the results indicated that the minimum factor of safety against slope failure is in excess of 1.1.” The material properties used for slope stabil ity indicate a cohesion for the embankment of 1316 pounds per square foot (psf) and a friction angle of 25 degrees. This cohesion appears unconservative for an applica tion to a long-term steady seep age analysis. The stability analysis documented in the complete Sargen t and Lundy letter in 1980 was not considered relevant and applicable to the design of th e East Ash Pond, North Ash Pond, and the settling basins.
A detailed presentation of resu lts is included in the Patrio t (1999) report. The minimum factors of safety for each load case are s hown in Table 8.1. The Patriot pseudo-static analyses considered a seismic coefficient of 0.10g.
It is typical to apply a seismic coefficient eq ual to one-half of the peak acceleration in the stability analysis. The peak acceleration for an earthquake with an approximate return periodGEI Consultants, Inc. 19 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### of 1,000 years is 0.19g as described in Section 6.0. Therefore, use of a seismic coefficient of 0.10g is considered equivalent to an earthqu ake with an approxima te return period of 1,000 years, which is within the appropriate range for application to a low hazard classification impoundment.
The material properties used in the Patriot st ability analyses included a cohesion of 300 psf and a friction angle of 18 degrees for the em bankment. These parameters are considered consistent with drained parameters for a clayey material.
The results of the Patriot (1999) stability analyses are consider ed appropriate for application to the six CCW impoundment embankments. GEI reviewed the computed factors of safety for the embankment stability analyses comple ted. We compared the reported calculated factors of safety (FOS) to minimum required f actors of safety as required by FERC. Table 8.1 presents the calculated factors of sa fety and the required factors of safety.

Table 8.1: Stability Factors of Safety and Guidance Values

Loading Condition Min. Calculated FOS* Min. Required FOS (FERC)
End of Construction 2.67 1.3 Full Reservoir – Steady-st ate Seepage 1.58 1.5 Full Reservoir – Steady-state Seepage - Seismic 1.14 1.0 * Patriot, 1999



### As indicated in Table 8.1, the calculated factor s of safety for all cases are greater than the guidance values.
Stability analyses for the FSS landfill placed on top of part of the North Ash Pond were completed by Fuller, Mosbarger, Scott & May (1999). These analyses included strength parameters considered consistent with the ma terials being modeled. Two stability sections were analyzed using the UTEXAS computer program and Spencer’s method for both static and pseudo-static loads. Based on the report:

 Along the ash pond section, static factor of safety ranged from 2.2 to 4.4 and dynamic factors of safety ranged from 1.3 to 2.2.

 Along the access road section, the minimum fact ors of safety for static conditions for two potentially critical failure modes were 2.1 and 2.4. For dynamic conditions the minimum factors of safety for the same two modes were both 1.3.
These calculated factors of safety ar e greater than the guidance values.GEI Consultants, Inc. 20 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

## 8.5 Seismic Stability - Liquefaction Potential

The liquefaction potential at the six CCW impou ndments has not been previously evaluated based on review of the available documents . Certain conditions are necessary for liquefaction, including saturated, loose, granular soils and an earthquake of sufficient magnitude and duration to cause significant stre ngth loss in the soil. The water table is relatively shallow based on information from the borings completed within the footprints of the impoundments. The borings at the North Ash Pond encountered granular soils in the dike foundation that are likely below th e water table that are descri bed as very loose with SPT N-values as low as 2. The borings at the East Ash Ponds and Settling Basin encountered granular soils in the dike founda tion that are below the water tabl e that are described as very loose with N-values as low as 1. The loose to very loose, saturated, granular foundation soils may be susceptible to liquefac tion. However, the clayey soil s used for construction of the dikes are not likely susceptible to signifi cant strength loss during strong shaking. 

## 8.6 Summary of Results

Based on the Patriot (1999) analyses, the stabilit y analyses that have been performed for the embankments appear to adequately address the mo st critical sections. These analyses include use of appropriate material properties and loading conditions and the results exceed the minimum required factors of safety.
The liquefaction potential of th e foundation soils has not been an alyzed, and may be a critical loading condition. The loose to very loose, saturated, granular f oundation soils foundation soils encountered in the borings are poten tially susceptible to liquefaction.GEI Consultants, Inc. 21 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 9.0 Maintenance and Methods of Operation

9.1 Procedures

DEI’s experience with management of the co al combustion waste management system has resulted in the development of standard opera tional procedures to inspect, maintain, and operate the system. To the knowledge of the assessment team, these procedures have not been formally documented in an Operation a nd Maintenance Manual. The power plant is manned 24 hours a day, seven days a week. Monthl y inspections are perf ormed for the entire ash pond facilities by operations staff to obser ve the general condition of structures and embankments. Written inspection records are not currently maintained. 

## 9.2 Maintenance of Impoundments

Maintenance of the six CCW im poundments is performed by DE I staff under the guidance of DEI managers and engineers. Inspections of the East and No rth Ash Ponds and both settling basins are made every two years by an i ndependent engineering firm. Dam safety inspections have not previously been required or performed by state or federal agencies. However, the independent engineering firm’s in spection reports are subm itted to the Indiana Department of Natural Resources Division of Water, Dams, and Levees (IDNR) every two years.


## 9.3 Surveillance

The ash ponds and settling basins are checked fo r fugitive dust issues once per shift by DEI operations personnel. Plant personnel are avai lable at the power plan t and on 24-hour call for emergencies that may arise. There is a visu al automatic alarm system at the impoundments, but it does not transmit alarm information to the power statio n control room.GEI Consultants, Inc. 22 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 10.0 Conclusions

10.1 Assessment of Dams

10.1.1 Field Assessment

The dams and outlet works facilities associated with the six CCW impoundments at the Gibson Generating Station were generally found to be in FAIR condition. Issues of potential concern for the six CCW impoundments were identified from our field assessment as follows:

 The North Ash Pond dam have several large diameter trees (2-foot or greater) and vegetation located at the downstream toe of the north dike of the North Ash Pond. These trees appear to be part of the pre-existing wetlands that is adjacent to the North Ash Pond dam.

 The East CCW impoundments have several small diameter trees and vegetation located on the upstream and downstream slope s of the inner dikes. Additionally, there are several small diameter trees near the downstream toe of the south and east dikes.

 Isolated areas on the downstream slope of the East Settling Basin south dike were observed to have minor transverse ruts. The ruts are likely due to the wheeled tractor mowing the grass during wet or saturated soil conditions.

 A small excavated drain or sump pit was observed near the downstream toe of the west dike of East Ash Pond #2 (Photo 30). The excavated pit was previously used to drain the water from the dredge line out -of-service. The excavated pit could potentially initiate a seepage path through the foundation of th e west dike if the area is not repaired.
10.1.2 Adequacy of St ructural Stability

The factors of safety for the six CCW impound ments at the Gibson Ge nerating Station meet stability criteria using assumptions and met hods of analysis currently accepted by FERC Guidelines, with exception of li quefaction analysis, which has not been performed. The dike foundations include loose, satura ted, granular soil, which may be susceptible to significant strength loss or settlement under th e anticipated earthquake loading.GEI Consultants, Inc. 23 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### 10.1.3 Adequacy of Hydrol ogic/Hydraulic Safety

The six CCW impoundments at the Gibson Gene rating Station currently have adequate freeboard and storage capacity to safely st ore the 6-hour 100-year in flow design flood.
10.1.4 Adequacy of Instrumentation and Monitoring of Instrumentation

Instrumentation and monitoring programs are cons idered inadequate for the current facility operations. Daily water levels are being measured at the North and East Settling Basins but not at the North or East Ash P onds. No piezometers or settleme nt monuments are installed at any of the ash pond or settling basin dams. Several groundwater quality observation wells and a monitoring program are in place at the East CCW impoundments.
10.1.5 Adequacy of Maintenance and Surveillance

The six CCW impoundments at the Gibson Genera ting Station have fair maintenance and surveillance programs. The f acilities are adequately main tained and routine monthly surveillance is performed by Duke Energy staff. However, there is no formal inspection of the six CCW impoundments at the Gibson Generati ng Station. An informal visual inspection of the ash impoundment structures is performed biennially in conjunction with the formal inspection of the Cooling Pond Dam.
10.1.6 Adequacy of Pr oject Operations

Operating personnel are knowledgeab le and are well trained in th e operation of the project. The current operations of the facilities are satisfactory.GEI Consultants, Inc. 24 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 11.0 Recommendations

11.1 Corrective Measures and An alyses for the Structures

1. Several large diameter trees (2-foot or gr eater) and vegetation were observed at the downstream toe of the North Ash Pond dam. Th ese trees appear to be part of the preexisting wetlands that is adjacent to the North Ash Pond dam. Because the trees are well-established with considerable root systems and are part of the wetland, removal of the trees and root ball may cause further damage to the downstream slope of the dike and, is not recommended at this time. Duke Energy should continue to monitor the downstream slope for noticeable signs of seepage or transportation of embankment materials and obtain guidance fr om their engineers as to options and strategy for dealing with the trees. If cutting the trees is not possible due to the wetland status, one approach to address the concern of the trees would be to increase the structural stability of the dam (i.e. wi dening the dam in the upstream direction). Currently, DEI is in the process of widening this dike. This is one of the last original sections of the dike that remains; all others have been increased in width to accommodate other structures. This work is expected to be completed in 2010.
2. Several small diameter trees and vegeta tion were observed on the upstream and downstream slopes of the inner dikes at th e East CCW impoundme nts. The trees on the inner dikes should be removed within the next year. If these trees are not removed, they could potentially initiate seep age paths or affect the stability of the slope. All vegetation on the inner dikes shoul d be maintained to a level that does not obstruct visual dam safety inspec tions of the dam embankment.
3. Several small trees were observed near the downstream slope of the East CCW impoundments south and east dikes. A mini mum of about 25 feet of clear spacing should be provided at the downstream toe. The trees within this area should be removed within the next year.
4. Isolated areas on the downstream slope of the East Settling Basi n south dike were observed to have minor transverse ruts formi ng. The ruts are likely due to the wheeled tractor mowing the grass during wet or satura ted soil conditions. Pr eventative measure should be taken not to mow the embankment when wet or modify and vary the mowing operations so as not to create ruts perpendicular to the embankment slope.
5. A small excavated drain or sump pit was observed near the downstream toe of the west dike of the East Ash Pond #2 (Photo 30). The excavated pit could potentially initiate a seepage path through the west di ke if the area is not repaired. It is recommended that the excavation be backfilled with compacted clay.GEI Consultants, Inc. 25 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### 6. A liquefaction susceptibility analysis should be conducted for the embankments. Based on the results of this analysis, addi tional corrective measures may be required.

7. Currently the six CCW impoundments have ad equate freeboard and storage capacity to safely store the 6-hour 100-year infl ow design flood. However, the storage capacity and water level of the ash pond units can vary depending on operations. Due to this variability, it is recommended that Duke Energy maintain the six CCW impoundments at a level that ensures suffici ent storage capacity within the units to accept the inflow design storm volume without overtopping the dam.


## 11.2 Corrective Measures Required for Instrumentation and Monitoring Procedures

Daily water levels are measured at the North and East Settling Basins but not at the North and East Ash Ponds. No piezometers or sett lement monuments are in stalled at the ash pond or settling basin dams. It is recommended that a more thorough instrumentation and monitoring program be developed and implem ented that would include, at a minimum, piezometers and settlement monuments in stalled along the perimeter dikes of any impoundments that will continue to receive wet coal combusti on waste. Additionally it is recommended that an additional alarm for the water level control system for the North and East Settling Basins be co-located with central plant operations. 

## 11.3 Corrective Measures Required for Maintenance and Surveillance Procedures

Currently, the six CCW impoundments are visually inspected monthly by Duke Energy staff, and inspected by a third-party engineer biennial ly in conjunction with the formal inspection of the Cooling Pond Dam. It is recomme nded that Duke Energy develop and document formal inspections of the ash ponds and settling basins, at a minimum annually by plant staff and quinquennially by a third part y. It is also recommende d that a brief daily check inspection be conducted by DEI personnel and that a written record be maintained for the monthly inspections being conducted by DEI. 

## 11.4 Corrective Measures Required for the Methods of Operation of the Project Works

None.

## 11.5 Acknowledgement of Assessment

I acknowledge that the management unit(s) referenced herein was personally inspected by me and was found to be in the following condition (select one only):
SATISFACTORY



# ~ POOR
UNSATISFACTORY



### SATISFACTORY No existing or potential management unit safety deficiencies are recognized. Acceptable performance is expected under all applicable loading conditions (static, hydrologic, seismic) in accordance with the applicable criteria. Minor maintenance items may be required.



### FAIR Acceptable performance is expected under all required loading conditions (static, hydrologic, seismic) in accordance with the applicable safety regulatory criteria. Minor deficiencies may exist that require remedial action and/or secondary studies or investigations



### POOR A management unit safety deficiency is recognized for any required loading condition (static, hydrologic, seismic) in accordance with the applicable dam safety regulatory criteria. Remedial action is necessary. POOR also applies when further critical studies or investigations are needed to identify any potential dam safety deficiencies.



### UNSATISFACTORY Considered unsafe. A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution. Reservoir restrictions may be necessary.

I acknowledge that the management unit referenced herein:

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### Has been assessed on

Signature :

List ofParticipants:
Stephen G. Brown, P.E., Nicholas D. Miller, P.E., Jim Meiers, Kevin Olivey,

GEl Consultants, Inc. 

### April 26--27, 2010 (date)

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26 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating StationGEI Consultants, Inc. 27 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

### Ron Ehlers, Senior Engineer, Duke Energy Adam Deller, Civil EngineerDuke Energy Rebecca Sparks, Environmental Coordinator,Duke Energy Bill Goedde, Engineering Manager, Duke EnergyGEI Consultants, Inc. 28 092880 Coal Ash Impoundment SSA Report Duke Energy Indiana Gibson Generating Station 

# 12.0 References

Bennett, Williams, & Blattert, Inc. (1990). Boring Logs for East Ash Ponds, January, presented in Project Specifications for Ash Pond Phase I & Settling Basin.

Fuller, Mosbarger, Scott & May (1999). “R eport of Geotechnical Analysis and Seepage Design, Gibson, Station FGD Landfill E xpansion,” prepared for PSI Energy, December 13.

Indiana Department of Natural Resources Division of Water (DNR) (2001). General Guidelines for New Dams and Improvements to Existing Dams in Indiana. January.

Patriot Engineering and Envir onmental Co., LLC (Patriot) (1999) . “Report of Geotechnical Engineering Investigation Slope Stability Analysis of Proposed Ash Pond Addition Phase III,” prepared for Cinergy Corporation, April 19.

Sargent & Lundy (1971). Design drawings for Gi bson Station including Revisions, prepared for Public Service Indiana. Revisions dated later.

Sargent & Lundy (1980). “Response to Request fo r Lake Design Information,” prepared for Public Service Indi ana, February 11.

Sargent & Lundy (2008). “Gibson Generati ng Station 2008 Pond Examination, SL-009728”, prepared for Duke Energy Indiana, November 21.

U.S. Army Corps of Engineers (1979). “Recomm ended Guidelines for Safety Inspections of Dams. (ER 1110-2-106).” September.

# Figures and Exhibits

### Assessment of Dam Safety of 

### Coal Combustion 

## Waste Impoundments at INDIANA



### SITE VICINITY MAP 

## DEl Gibson Generating Station 

# G E I**~~------E-nv-iro** 

## __**n_m_e-nta--1-Pro--ted--io~n~Ag-e_n_cy------~~~---c~o~nsu~lt~an~tsr-------------------~** 

## Washington, DC p 092880 May 2010 

## Figure 1

### Asaeaamant of 

### Dam Sarvty of 

### Coal Combustion SITE AERIAL MAP Wasta at 

### DEl Gibson Stallon

DC 

### 2TOEOFSHOWNONPLANS('1_ii20'-o·TYPEARlP-RAPTOEOFDIKESHOWNONPLANS"----'--389'-0"--388'-0"EASTASHPONDS&BASIN·TYPICALSECTION0.....t',-:.-.............,*'u:::"iii4"TOPSOJLtNO"TE.A5£CT.A,-A.•G.i"ACEb:S.l'OioJe:.TNORTHASHPOND&BASIN·TYPICALSECTIONAssessmentofDamSafetyofCoalCombustionwWasteImpoundmentsatDElGibsonGeneratingStationG EIConsultantsTYPICALDAMSECTIONS9EnvironmentalProtectionAgencya.:Washington,DCPro"ect092880May2010Figure3

# Appendix A

Inspection Checklists
April 26–27, 2010Coal Combustion Dam Inspection Checklist Form



### 1EPAForm,Jan 09US Environmental Protection Agency



### Site Name: Duke Energy, Gibson County, IN Date: April 26, 2010

Unit Name: East Settling Basin Operator’s Name: Duke Energy

Unit ID: N/A Hazard Potential Classification: High Significant Low 

### (see P.3)
Inspector’s Name: Steve Brown/GEI Consultants, Nick Miller/GEI Consultants

Checktheappropriateboxbelow,Provideco mmentswhenappropriate.Ifnotapplicableor notavailable,record"N/A",Anyunusu alconditionsorconstructionpracticesthat shouldbenotedinthecomments section,Forlargedikedembankments,separatechecklists maybeusedfordiffe rentembankmentareas.Ifseparateformsareused,ide ntifyapproximateareathattheformappliestoincomments. Yes No Yes No

1. Frequency of Company’s Dam Inspections? 18. Sloughing or bulging on slopes? X 2. Pool elevation (operator records)? ~EL. 398.0 19. Major erosion or slope deterioration? X 3. Decant inlet elevation (operator records)? Pump Invt = 401.0 2 0. Decant Pipes 4. Open channel spillway elevation (operator records)? NA Is water entering inlet, but not exiting outlet? X

5. Lowest dam crest elevat ion (operator records)? EL. 405.0 Is water exiting outlet, but not entering inlet? X 6. If instrumentation is present, are readings

recorded (operator records)? X Is water exiting outlet flowing clear? NA

7. Is the embankment cu rrently under construction? X 21. Seepage (specify location, if seepage carries fines, and approximate seepage rate below): 8. Foundation preparation (remove vegetation, stumps,

topsoil in area where embankment fill will be placed)? X From underdrain? X 9. Trees growing on embankment? (If so, indicate

largest diameter below.) X At isolated points on embankment slopes? X
10. Cracks or scarps on crest? X At natural hillside in the embankment area? X 11. Is there significant settlement along the crest? X Over widespread areas? X 12. Are decant trashracks clear and in place? NONE From downstream foundation area? X 13. Depressions or sink holes in tailings surface or whirlpool in the pool area X “Boils” beneath stream or ponded water? X
14. Clogged spillways, groin or diversion ditches? X Around the outside of the decant pipe? X 15. Are spillway or ditch linings deteriorated? X 22. Surface movements in valley bottom or on hillside? X

16. Are outlets of decant or underdrains blocked? X 23. Water against downstream toe? X 17. Cracks or scarps on slopes X 24. Were Photos taken during the dam inspection? X Major adverse changes in these items could cause instability and should be reported for further evaluation. Adverse conditions noted in these items should normally be described (extent, location, volume, etc.) in the space below and on the back of this sheet.

### InspectionIssue# Comments

1

. No formal inspections of CCW impoundments. Informal visual inspections

performed biennially in conjuction with cooling pond inspection. 3. Pump invert is the highest invert of gravity discharge pipe in system. 6. Only reservoir water levels are measured. No piezometers or settlement monuments on dam. Groundwater quality wells installed

near downstream toe of dam. 9. Only on interior divider dikes; trees ~1" caliper. 20. Pump not active during site visit and discharge end submerged in cooling pond. 23. Adjacent wetland area on east side of facility.

### Monthly by Staff, Biennial 3rd Party

### 2EPAForm,J an 09 

### Coal Combustion Waste (CCW) Impoundment Inspection

Impoundment NPDES Permit # N/A INSPECTOR Steve Brown/GEI

Date April 26, 201 0
Impoundment Name East Settling Basin, Duke Energy, Gibson County , IN
Impoundment Company Duke Energy
EPA Region 5
State Agency (Field Office) Address Indiana Dep W of 1DWXUDO5HVRXUFHV'LYRI:DWHU'DPV	/HYHHV 402 West Washington St, Room W264, Indianapolis, IN 46204
Name of Impoundment East Settling Basin (Report each impoundment on a separate form under the same Impoundment NPDES Permit number)
New X Update

Yes No
Is impoundment currently under construction? X Is water or ccw currently being pumped into the impoundment? X

IMPOUNDMENT FUNCTION: Decant Water Storage

Nearest Downstream Town: Name Grayville, I N Distance from the impoundment 35 miles Impoundment Location:

Does a state agency regulate this impoundment? YES X NO

If So Which Sate Agency? Indiana Dept RI1DWXUDO5HVRXUFHV'LYRI:DWHU'DPV	/HYHHV Longitude 8 7 Degrees 44 Minutes 27 Seconds W Latitude 38 Degrees 2 2 Minutes 18 Seconds N State I N C ounty Gibson

### 3EPAForm,Jan09

### HAZARD POTENTIAL (In the event the impoundment should fail, the following would occur):

LESS THAN LOW HAZARD POTENTIAL: Failure or misoperation of the dam results in no probable loss of human life or economic or environmental losses.

LOW HAZARD POTENTIAL: Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.

SIGNIFICANT HAZARD POTENTIAL: Dams assigned the significant hazard potential classification are those dams where failure or misoperation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

HIGH HAZARD POTENTIAL: Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life.

DESCRIBE REASONING FOR HAZARD RATING CHOSEN: An uncontrolled release of the structure's contents due to a failure or misoperation is not considered to cause loss of human life and the economic and environmental damages would be relatively low. The flood extext would be limited by the adjacent USACE levee on the Wabash River and the very flat surrounding topography. Flood waters would likely be widespread with shallow depths and gradually rising waters. Based on the pond height and volume, the majority of inundation would be limited to Company property to the south and east around the cooling pond and the surrounding wetlands. The county road adjacent to the we st dike could potentially be flooded and temporarily interrupt local traffic. However, the flood depths and flow velocities would be relatively small and are not considered to pose a significant hazard to vehicles. Flood waters would eventually drain to the Wabash River at culverts through the USACE levee located about 3 miles downstream. Consistent with the Federal Guidelines for Dam Safety, the dam should be classified as a "Low" hazard structure. X

### 4EPAForm,Jan09

### CONFIGURATION:

Cross-Valley Side-Hill Diked Incised (form completion optional) Combination Incised/Diked Embankment Height 15 feet Embankment Material Compacted fill Pool Area 45 acres Liner Unlined Current Freeboard 7 ft Liner Permeability NA X

### 5EPAForm,Jan09

### TYPE OF OUTLET (Mark all that apply)

None Open Channel Spillway Trapezoidal Triangular Triangular
Depth Bottom (or average) width Top width

Outlet

inside diameter

Material corrugated metal welded steel concrete plastic (hdpe, pvc, etc.) other (specify

Is water flowing through the outlet? YES NO X - Pump was not active.

No Outlet –

Other Type of Outlet (Specify)

The Impoundment was Designed By Sargent and Lundy Engineers, Chicago, IL for Public Service Indiana (PSI) at the time. Original construction completed in 1991.



### X

24"

X

### 6EPAForm,Jan09

### Has there ever been a failure at this site? YES NO X

If So When?

If So Please Describe:

### 7EPAForm,Jan09

### Has there ever been significant seepages at this site? YES NO X

If So When?

If So Please Describe:

### 8EPAForm,Jan09

### Has there ever been any measures undertaken to monitor/lower Phreatic water table levels based on past seepages or breaches at this site? YES NO X

If So which method (e.g., piezometers, gw pumping, ...)?

If So Please Describe:Coal Combustion Dam Inspection Checklist Form



### 1EPAForm,Jan 09US Environmental Protection Agency



### Site Name: Duke Energy, Gibson County, IN Date: April 26, 2010

Unit Name: East P ond #1 Operator’s Name: Duke Energy

Unit ID: N/A Hazard Potential Classification: High Significant Low 

### (see P.3)
Inspector’s Name: Steve Brown/GEI Consultants, Nick Miller/GEI Consultants

Checktheappropriateboxbelow,Provideco mmentswhenappropriate.Ifnotapplicableor notavailable,record"N/A",Anyunusu alconditionsorconstructionpracticesthat shouldbenotedinthecomments section,Forlargedikedembankments,separatechecklists maybeusedfordiffe rentembankmentareas.Ifseparateformsareused,ide ntifyapproximateareathattheformappliestoincomments. Yes No Yes No

1. Frequency of Company’s Dam Inspections? 18. Sloughing or bulging on slopes? X 2. Pool elevation (operator records)? ~EL. 400.1 19. Major erosion or slope deterioration? X 3. Decant inlet elevation (operator records)? EL. 40 0.0 20. Decant Pipes 4. Open channel spillway elevation (operator records)? NA Is water entering inlet, but not exiting outlet? X

5. Lowest dam crest elevat ion (operator records)? EL. 405.0 Is water exiting outlet, but not entering inlet? X 6. If instrumentation is present, are readings

recorded (operator records)? X Is water exiting outlet flowing clear? X

7. Is the embankment cu rrently under construction? X 21. Seepage (specify location, if seepage carries fines, and approximate seepage rate below): 8. Foundation preparation (remove vegetation, stumps,

topsoil in area where embankment fill will be placed)? X From underdrain? X 9. Trees growing on embankment? (If so, indicate

largest diameter below.) X At isolated points on embankment slopes? X
10. Cracks or scarps on crest? X At natural hillside in the embankment area? X 11. Is there significant settlement along the crest? X Over widespread areas? X 12. Are decant trashracks clear and in place? X From downstream foundation area? X 13. Depressions or sink holes in tailings surface or whirlpool in the pool area X “Boils” beneath stream or ponded water? X
14. Clogged spillways, groin or diversion ditches? X Around the outside of the decant pipe? X 15. Are spillway or ditch linings deteriorated? X 22. Surface movements in valley bottom or on hillside? X

16. Are outlets of decant or underdrains blocked? X 23. Water against downstream toe? X 17. Cracks or scarps on slopes X 24. Were Photos taken during the dam inspection? X Major adverse changes in these items could cause instability and should be reported for further evaluation. Adverse conditions noted in these items should normally be described (extent, location, volume, etc.) in the space below and on the back of this sheet.

### InspectionIssue# Comments

1

. No formal inspections of CCW impoundments. Informal visual inspections

performed biennially in conjuction with cooling pond inspection. 6. Groundwater quality wells installed near downstream toe of dam.
9. Only on interior divider dikes; trees ~1" caliper.
23. Adjacent wetland area on east side of facility.

### Monthly by Staff, Biennial 3rd Party

### 2EPAForm,J an 09 

### Coal Combustion Waste (CCW) Impoundment Inspection

Impoundment NPDES Permit # N/A INSPECTOR Steve Brown/GEI

Date April 26, 201 0
Impoundment Name East Pond #1, Duke Energy, Gibson County , IN
Impoundment Company Duke Energy
EPA Region 5
State Agency (Field Office) Address Indiana Dept RI1DWXUDO5HVRXUFHV'LYRI:DWHU'DPV	/HYHHV
402 West Washington St, Room W264, Indianapolis, IN 46204
Name of Impoundment East Pond #1 (Report each impoundment on a separate form under the same Impoundment NPDES Permit number)

New X Update

Yes No
Is impoundment currently under construction? X Is water or ccw currently being pumped into the impoundment? X

IMPOUNDMENT FUNCTION: CCW and Decant Water Storage

Nearest Downstream Town: Name Grayville, I N Distance from the impoundment 35 miles Impoundment Location:

Does a state agency regulate this impoundment? YES X NO

If So Which Sate Agency? Indiana Dept RI1DWXUDO5HVRXUFHV'LYRI:DWHU'DPV	/HYHHV Longitude 8 7 Degrees 44 Minutes 14 Seconds W Latitude 38 Degrees 2 2 Minutes 36 Seconds N State I N C ounty Gibson

### 3EPAForm,Jan09

### HAZARD POTENTIAL (In the event the impoundment should fail, the following would occur):

LESS THAN LOW HAZARD POTENTIAL: Failure or misoperation of the dam results in no probable loss of human life or economic or environmental losses.

LOW HAZARD POTENTIAL: Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.

SIGNIFICANT HAZARD POTENTIAL: Dams assigned the significant hazard potential classification are those dams where failure or misoperation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

HIGH HAZARD POTENTIAL: Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life.

DESCRIBE REASONING FOR HAZARD RATING CHOSEN: An uncontrolled release of the structure's contents due to a failure or misoperation is not considered to cause loss of human life and the economic and environmental damages would be relatively low. The flood extent would be limited by the adjacent USACE levee on the Wabash River and the very flat surrounding topography. Flood waters would likely be widespread with shallow depths and gradually rising waters. Based on the pond height and volume, the majority of inundation would be limited to Company property to the south and east around the cooling pond and the surrounding wetlands. Flood waters would eventually drain to the Wabash River at culverts through the USACE levee located about 3 miles downstream. Consistent with the Federal Guidelines for Dam Safety, the dam should be classified as a "Low" hazard

structure. X

### 4EPAForm,Jan09

### CONFIGURATION:

Cross-Valley Side-Hill Diked Incised (form completion optional) Combination Incised/Diked Embankment Height 15 feet Embankment Material Compacted fill Pool Area 105 acres Liner Unlined Current Freeboard 5 ft Liner Permeability NA X

### 5EPAForm,Jan09

### TYPE OF OUTLET (Mark all that apply)

Open Channel Spillway Trapezoidal Triangular Triangular
Depth Bottom (or average) width Top width

Outlet

inside diameter

Material corrugated metal welded steel concrete plastic (hdpe, pvc, etc.) other (specify

Is water flowing through the outlet? YES X NO

No Outlet

Other Type of Outlet (Specify)

The Impoundment was Designed By Sargent and Lundy Engineers, Chicago, IL for Public Service Indiana (PSI) at the time. Original construction completed in 1991. 

### X

36"

X None

### 6EPAForm,Jan09

### Has there ever been a failure at this site? YES NO X

If So When?

If So Please Describe:

### 7EPAForm,Jan09

### Has there ever been significant seepages at this site? YES NO X

If So When?

If So Please Describe:

### 8EPAForm,Jan09

### Has there ever been any measures undertaken to monitor/lower Phreatic water table levels based on past seepages or breaches at this site? YES NO X

If So which method (e.g., piezometers, gw pumping, ...)?

If So Please Describe:Coal Combustion Dam Inspection Checklist Form



### 1EPAForm,Jan 09US Environmental Protection Agency



### Site Name: Duke Energy, Gibson County, IN Date: April 26, 2010

Unit Name: East P ond #2 Operator’s Name: Duke Energy

Unit ID: N/A Hazard Potential Classification: High Significant Low 

### (see P.3)
Inspector’s Name: Steve Brown/GEI Consultants, Nick Miller/GEI Consultants

Checktheappropriateboxbelow,Provideco mmentswhenappropriate.Ifnotapplicableor notavailable,record"N/A",Anyunusu alconditionsorconstructionpracticesthat shouldbenotedinthecomments section,Forlargedikedembankments,separatechecklists maybeusedfordiffe rentembankmentareas.Ifseparateformsareused,ide ntifyapproximateareathattheformappliestoincomments. Yes No Yes No

1. Frequency of Company’s Dam Inspections? 18. Sloughing or bulging on slopes? X 2. Pool elevation (operator records)? ~EL. 400.2 19. Major erosion or slope deterioration? X 3. Decant inlet elevation (operator records)? EL. 40 0.0 20. Decant Pipes 4. Open channel spillway elevation (operator records)? NA Is water entering inlet, but not exiting outlet? X

5. Lowest dam crest elevat ion (operator records)? EL. 405.0 Is water exiting outlet, but not entering inlet? X 6. If instrumentation is present, are readings

recorded (operator records)? X Is water exiting outlet flowing clear? X

7. Is the embankment cu rrently under construction? X 21. Seepage (specify location, if seepage carries fines, and approximate seepage rate below): 8. Foundation preparation (remove vegetation, stumps,

topsoil in area where embankment fill will be placed)? X From underdrain? X 9. Trees growing on embankment? (If so, indicate

largest diameter below.) X At isolated points on embankment slopes? X
10. Cracks or scarps on crest? X At natural hillside in the embankment area? X 11. Is there significant settlement along the crest? X Over widespread areas? X 12. Are decant trashracks clear and in place? X From downstream foundation area? X 13. Depressions or sink holes in tailings surface or whirlpool in the pool area X “Boils” beneath stream or ponded water? X
14. Clogged spillways, groin or diversion ditches? X Around the outside of the decant pipe? X 15. Are spillway or ditch linings deteriorated? X 22. Surface movements in valley bottom or on hillside? X

16. Are outlets of decant or underdrains blocked? X 23. Water against downstream toe? X 17. Cracks or scarps on slopes X 24. Were Photos taken during the dam inspection? X Major adverse changes in these items could cause instability and should be reported for further evaluation. Adverse conditions noted in these items should normally be described (extent, location, volume, etc.) in the space below and on the back of this sheet.

### InspectionIssue# Comments
1

. No formal inspections of CCW impoundments. Informal visual inspections

performed biennially in conjuction with cooling pond inspection.
6. Groundwater quality wells installed near downstream toe of dam.
9. Only on interior divider dikes; trees ~1" caliper.

### Monthly by Staff, Biennial 3rd Party

### 2EPAForm,J an 09 

### Coal Combustion Waste (CCW) Impoundment Inspection

Impoundment NPDES Permit # N/A INSPECTOR Steve Brown/GEI

Date April 26, 201 0
Impoundment Name East Pond #2, Duke Energy, Gibson County , IN
Impoundment Company Duke Energy
EPA Region 5
State Agency (Field Office) Address Indiana Dept  of 1DWXUDO5HVRXUFHV'LYRI:DWHU'DPV	/HYHHV

 402 West Washington St, Room W264, Indianapolis, IN 46204
Name of Impoundment East Pond #2 (Report each impoundment on a separate form under the same Impoundment NPDES Permit number)

New X Update

Yes No
Is impoundment currently under construction? X Is water or ccw currently being pumped into the impoundment? X

IMPOUNDMENT FUNCTION: CCW and Decant Water Storage

Nearest Downstream Town: Name Grayville, I N Distance from the impoundment 35 miles Impoundment Location:

Does a state agency regulate this impoundment? YES X NO

If So Which Sate Agency? ,QGLDQD'HSWRI1DWXUDO5HVRXUFHV'LYRI:DWHU'DPV	/HYHHV Longitude 8 7 Degrees 44 Minutes 34 Seconds W Latitude 38 Degrees 2 2 Minutes 36 Seconds N State I N C ounty Gibson

### 3EPAForm,Jan09

### HAZARD POTENTIAL (In the event the impoundment should fail, the following would occur):

LESS THAN LOW HAZARD POTENTIAL: Failure or misoperation of the dam results in no probable loss of human life or economic or environmental losses.

LOW HAZARD POTENTIAL: Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.

SIGNIFICANT HAZARD POTENTIAL: Dams assigned the significant hazard potential classification are those dams where failure or misoperation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

HIGH HAZARD POTENTIAL: Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life.

DESCRIBE REASONING FOR HAZARD RATING CHOSEN: An uncontrolled release of the structure's contents due to a failure or misoperation is not considered to cause loss of human life and the economic and environmental damages would be relatively low. The flood extent would be limited by the adjacent USACE levee on the Wabash River and the very flat surrounding topography. Flood waters would likely be widespread with shallow depths and gradually rising waters. Based on the pond height and volume, the majority of inundation would be limited to Company property to the south and east around the cooling pond and the surrounding wetlands. The county road adjacent to the we st dike could potentially be flooded and temporarily interrupt local traffic. However, the flood depths and flow velocities would be relatively small and are not considered to pose a significant hazard to vehicles. Flood waters would eventually drain to the Wabash River at culverts through the USACE levee located about 3 miles downstream. Consistent with the Federal Guidelines for Dam Safety, the dam should be classified as a "Low" hazard structure. X

### 4EPAForm,Jan09

### CONFIGURATION:

Cross-Valley Side-Hill Diked Incised (form completion optional) Combination Incised/Diked Embankment Height 15 feet Embankment Material Compacted fill Pool Area 105 acres Liner Unlined Current Freeboard 5 ft Liner Permeability NA X

### 5EPAForm,Jan09

### TYPE OF OUTLET (Mark all that apply)

Open Channel Spillway Trapezoidal Triangular Triangular
Depth Bottom (or average) width Top width

Outlet

inside diameter

Material corrugated metal welded steel concrete plastic (hdpe, pvc, etc.) other (specify )

Is water flowing through the outlet? YES X NO

No Outlet

Other Type of Outlet (Specify)

The Impoundment was Designed By Sargent and Lundy Engineers, Chicago, IL for Public Service Indiana (PSI) at the time. Original construction completed in 1995. 

### X

### 6EPAForm,Jan09

### Has there ever been a failure at this site? YES NO X

If So When?

If So Please Describe:

### 7EPAForm,Jan09

### Has there ever been significant seepages at this site? YES NO X

If So When?

If So Please Describe:

### 8EPAForm,Jan09

### Has there ever been any measures undertaken to monitor/lower Phreatic water table levels based on past seepages or breaches at this site? YES NO X

If So which method (e.g., piezometers, gw pumping, ...)?

If So Please Describe:Coal Combustion Dam Inspection Checklist Form



### 1EPAForm,Jan 09US Environmental Protection Agency



### Site Name: Duke Energy, Gibson County, IN Date: April 26, 2010

Unit Name: East P ond #3 Operator’s Name: Duke Energy

Unit ID: N/A Hazard Potential Classification: High Significant Low 

### (see P.3)
Inspector’s Name: Steve Brown/GEI Consultants, Nick Miller/GEI Consultants

Checktheappropriateboxbelow,Provideco mmentswhenappropriate.Ifnotapplicableor notavailable,record"N/A",Anyunusu alconditionsorconstructionpracticesthat shouldbenotedinthecomments section,Forlargedikedembankments,separatechecklists maybeusedfordiffe rentembankmentareas.Ifseparateformsareused,ide ntifyapproximateareathattheformappliestoincomments. Yes No Yes No

1. Frequency of Company’s Dam Inspections? 18. Sloughing or bulging on slopes? X 2. Pool elevation (operator records)? ~EL. 409.1 19. Major erosion or slope deterioration? X 3. Decant inlet elevation (operator records)? EL. 40 9.0 20. Decant Pipes 4. Open channel spillway elevation (operator records)? NA Is water entering inlet, but not exiting outlet? X

5. Lowest dam crest elevat ion (operator records)? EL. 412.0 Is water exiting outlet, but not entering inlet? X 6. If instrumentation is present, are readings

recorded (operator records)? X Is water exiting outlet flowing clear? X

7. Is the embankment cu rrently under construction? X 21. Seepage (specify location, if seepage carries fines, and approximate seepage rate below): 8. Foundation preparation (remove vegetation, stumps,

topsoil in area where embankment fill will be placed)? X From underdrain? X 9. Trees growing on embankment? (If so, indicate

largest diameter below.) X At isolated points on embankment slopes? X
10. Cracks or scarps on crest? X At natural hillside in the embankment area? X 11. Is there significant settlement along the crest? X Over widespread areas? X 12. Are decant trashracks clear and in place? X From downstream foundation area? X 13. Depressions or sink holes in tailings surface or whirlpool in the pool area X “Boils” beneath stream or ponded water? X
14. Clogged spillways, groin or diversion ditches? X Around the outside of the decant pipe? X 15. Are spillway or ditch linings deteriorated? X 22. Surface movements in valley bottom or on hillside? X

16. Are outlets of decant or underdrains blocked? X 23. Water against downstream toe? X 17. Cracks or scarps on slopes X 24. Were Photos taken during the dam inspection? X Major adverse changes in these items could cause instability and should be reported for further evaluation. Adverse conditions noted in these items should normally be described (extent, location, volume, etc.) in the space below and on the back of this sheet.

### InspectionIssue# Comments
1

. No formal inspections of CCW impoundments. Informal visual inspections

performed biennially in conjuction with cooling pond inspection. 2. Elevation varies, western portion of pond being capped for closure through IDEM. Cap elevation is about 7-feet higher than partially

dewatered pond. Pond 3 is reported as 95% full of CCW. 6. Groundwater quality wells installed near downstream toe of dam. 9. Only on interior divider dikes; trees ~1" caliper. 23. Adjacent wetland area on east side of facility

.

### Monthly by Staff, Biennial 3rd Party

### 2EPAForm,J an 09 

### Coal Combustion Waste (CCW) Impoundment Inspection

Impoundment NPDES Permit # N/A INSPECTOR Steve Brown/GEI

Date April 26, 201 0
Impoundment Name East Pond #3, Duke Energy, Gibson County , IN
Impoundment Company Duke Energy
EPA Region 5
State Agency (Field Office) Address Indiana Dept. of Natural Resources Div. of Water, Dams & Levees
402 West Washington St, Room W264, Indianapolis, IN 46204
Name of Impoundment East Pond #3 (Report each impoundment on a separate form under the same Impoundment NPDES Permit number)

New X Update

Yes No
Is impoundment currently under construction? X Is water or ccw currently being pumped into the impoundment? X

IMPOUNDMENT FUNCTION: CCW and Decant Water Storage

Nearest Downstream Town: Name Grayville, I N Distance from the impoundment 35 miles Impoundment Location:

Does a state agency regulate this impoundment? YES X NO

If So Which Sate Agency? Indiana Dept. of Natural Resources Div. of Water, Dams & Levees Longitude 8 7 Degrees 44 Minutes 23 Seconds W Latitude 38 Degrees 2 2 Minutes 57 Seconds N State I N C ounty Gibson

### 3EPAForm,Jan09

### HAZARD POTENTIAL (In the event the impoundment should fail, the following would occur):

LESS THAN LOW HAZARD POTENTIAL: Failure or misoperation of the dam results in no probable loss of human life or economic or environmental losses.

LOW HAZARD POTENTIAL: Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.

SIGNIFICANT HAZARD POTENTIAL: Dams assigned the significant hazard potential classification are those dams where failure or misoperation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

HIGH HAZARD POTENTIAL: Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life.

DESCRIBE REASONING FOR HAZARD RATING CHOSEN: East Pond #3 is currently in a closure status and there is negligible amount of free standing water in East Pond #3 . Consistent with the Federal Guidelines for Dam Safety, the dam should be classified as a " Less Than Low" hazard structure.

### 4EPAForm,Jan09

### CONFIGURATION:

Cross-Valley Side-Hill Diked Incised (form completion optional) Combination Incised/Diked Embankment Height 22 feet Embankment Material Compacted fill Pool Area 133 acres Liner Unlined Current Freeboard 3 ft Liner Permeability NA (Note: Freeboard estimate is for the uncapped eastern portion of the pond only.) 

### X

### 5EPAForm,Jan09

### TYPE OF OUTLET (Mark all that apply)

Open Channel Spillway Trapezoidal Triangular Triangular
Depth Bottom (or average) width Top width

Outlet

inside diameter

Material corrugated metal welded steel concrete plastic (hdpe, pvc, etc.) other (specify

Is water flowing through the outlet? YES X NO

No Outlet

Other Type of Outlet (Specify)

The Impoundment was Designed By Sargent and Lundy Engineers, Chicago, IL for Public Service Indiana (PSI) at the time. Original construction completed in 1999. 

### X

3 0 "

X None

### 6EPAForm,Jan09

### Has there ever been a failure at this site? YES NO X

If So When?

If So Please Describe:

### 7EPAForm,Jan09

### Has there ever been significant seepages at this site? YES NO X

If So When?

If So Please Describe:

### 8EPAForm,Jan09

### Has there ever been any measures undertaken to monitor/lower Phreatic water table levels based on past seepages or breaches at this site? YES NO X

If So which method (e.g., piezometers, gw pumping, ...)?

If So Please Describe: Existing piezometers/monitoring wells were installed in the vicinity of Pond 3 as part of a groundwater quality monitoring program for Pond 3 closure under

IDEM and not directly in response to seepage events or breaches that pertain to dam safety issues with the containment dikes.Coal Combustion Dam Inspection Checklist Form



### 1EPAForm,Jan 09US Environmental Protection Agency



### Site Name: Duke Energy, Gibson County, IN Date: April 27, 2010

Unit Name: North Ash Pond Operator’s Name: Duke Energy

Unit ID: N/A Hazard Potential Classification: High Significant Low 

### (see P.3)
Inspector’s Name: Steve Brown/GEI Consultants, Nick Miller/GEI Consultants

Checktheappropriateboxbelow,Provideco mmentswhenappropriate.Ifnotapplicableor notavailable,record"N/A",Anyunusu alconditionsorconstructionpracticesthat shouldbenotedinthecomments section,Forlargedikedembankments,separatechecklists maybeusedfordiffe rentembankmentareas.Ifseparateformsareused,ide ntifyapproximateareathattheformappliestoincomments. Yes No Yes No

1. Frequency of Company’s Dam Inspections? 18. Sloughing or bulging on slopes? X 2. Pool elevation (operator records)? ~EL. 400. 1 19. Major erosion or slope deterioration? X 3. Decant inlet elevation (operator records)? EL. 400.0 20. Decant Pipes 4. Open channel spillway elevation (operator records)? NA Is water entering inlet, but not exiting outlet? X

5. Lowest dam crest elevat ion (operator records)? EL. 405.0 Is water exiting outlet, but not entering inlet? X 6. If instrumentation is present, are readings

recorded (operator records)? X Is water exiting outlet flowing clear? X

7. Is the embankment cu rrently under construction? X 21. Seepage (specify location, if seepage carries fines, and approximate seepage rate below): 8. Foundation preparation (remove vegetation, stumps,

topsoil in area where embankment fill will be placed)? X From underdrain? X 9. Trees growing on embankment? (If so, indicate

largest diameter below.) X At isolated points on embankment slopes? X
10. Cracks or scarps on crest? X At natural hillside in the embankment area? X 11. Is there significant settlement along the crest? X Over widespread areas? X 12. Are decant trashracks clear and in place? NONE From downstream foundation area? X 13. Depressions or sink holes in tailings surface or whirlpool in the pool area X “Boils” beneath stream or ponded water? X
14. Clogged spillways, groin or diversion ditches? X Around the outside of the decant pipe? X 15. Are spillway or ditch linings deteriorated? X 22. Surface movements in valley bottom or on hillside? X

16. Are outlets of decant or underdrains blocked? X 23. Water against downstream toe? X 17. Cracks or scarps on slopes X 24. Were Photos taken during the dam inspection? X Major adverse changes in these items could cause instability and should be reported for further evaluation. Adverse conditions noted in these items should normally be described (extent, location, volume, etc.) in the space below and on the back of this sheet.

### InspectionIssue# Comments
1

. No formal inspections of CCW impoundments. Informal visual inspections

performed biennially in conjuction with cooling pond inspection.
4. No open channel spillway.

6. No instrumentation. 9. Large trees located at downstream toe, 2-ft dia. Trees are part of the

wetland. 23. Adjacent pre-existing wetland area on north side of facility.

### Monthly by Staff, Biennial 3rd Party

### 2EPAForm,J an 09 

### Coal Combustion Waste (CCW) Impoundment Inspection

Impoundment NPDES Permit # N/A INSPECTOR Steve Brown/GEI

Date April 27, 201 0
Impoundment Name North Ash Pond, Duke Energy, Gibson County
, IN
Impoundment Company Duke Energy
EPA Region 5
State Agency (Field Office) Address Indiana Dept. of Natural Resources Div. of Water, Dams & Levees
402 West Washington St, Room W264, Indianapolis, IN 46204
Name of Impoundment North Ash Pond (Report each impoundment on a separate form under the same Impoundment NPDES Permit number)

New X Update

Yes No
Is impoundment currently under construction? X Is water or ccw currently being pumped into the impoundment? X

IMPOUNDMENT FUNCTION: CCW and Decant Water Storage

Nearest Downstream Town: Name Grayville, I N Distance from the impoundment 35 miles Impoundment Location:

Does a state agency regulate this impoundment? YES X NO

If So Which Sate Agency? Indiana Dept. of Natural Resources Div. of Water, Dams & Levees Longitude 8 7 Degrees 45 Minutes 29 Seconds W Latitude 38 Degrees 2 2 Minutes 38 Seconds N State I N C ounty Gibson

### 3EPAForm,Jan09

### HAZARD POTENTIAL (In the event the impoundment should fail, the following would occur):

LESS THAN LOW HAZARD POTENTIAL: Failure or misoperation of the dam results in no probable loss of human life or economic or environmental losses.

LOW HAZARD POTENTIAL: Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.

SIGNIFICANT HAZARD POTENTIAL: Dams assigned the significant hazard potential classification are those dams where failure or misoperation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

HIGH HAZARD POTENTIAL: Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life.

DESCRIBE REASONING FOR HAZARD RATING CHOSEN: An uncontrolled release of the structure's contents due to a failure or misoperation is not considered to cause loss of human life and the economic and environmental damages would be relatively low. The flood extent would be limited by the adjacent USACE levee on the Wabash River and the very flat surrounding topography. Flood waters would likely be widespread with shallow depths and gradually rising waters. Based on the pond height and volume, the majority of inundation would be limited to Company property to the southeast around the cooling pond and the surrounding wetlands. Flood waters would eventually drain to the Wabash River at culverts through the USACE levee located about 3 miles downstream. Consistent with the Federal Guidelines for Dam Safety, the dam should be classified as a "Low" hazard structure. X

### 4EPAForm,Jan09

### CONFIGURATION:

Cross-Valley Side-Hill Diked Incised (form completion optional) Combination Incised/Diked Embankment Height 15 feet Embankment Material Compacted fill Pool Area 25 acres Liner Unlined Current Freeboard 5 ft Liner Permeability NA X

### 5EPAForm,Jan09

### TYPE OF OUTLET (Mark all that apply)

Open Channel Spillway Trapezoidal Triangular Triangular
Depth Bottom (or average) width Top width

Outlet

inside diameter

Material corrugated metal welded steel concrete plastic (hdpe, pvc, etc.) other (specify

Is water flowing through the outlet? YES NO

No Outlet –

Other Type of Outlet (Specify)

The Impoundment was Designed By Sargent and Lundy Engineers, Chicago, IL for Public Service Indiana (PSI) at the time. Original construction completed in 1974. 

### X

24"

X

X None

### 6EPAForm,Jan09

### Has there ever been a failure at this site? YES NO X

If So When?

If So Please Describe:

### 7EPAForm,Jan09

### Has there ever been significant seepages at this site? YES NO X

If So When?

If So Please Describe:

### 8EPAForm,Jan09

### Has there ever been any measures undertaken to monitor/lower Phreatic water table levels based on past seepages or breaches at this site? YES NO X

If So which method (e.g., piezometers, gw pumping, ...)?

If So Please Describe:Coal Combustion Dam Inspection Checklist Form



### 1EPAForm,Jan 09US Environmental Protection Agency



### Site Name: Duke Energy, Gibson County, IN Date: April 27, 2010

Unit Name: North Settling Basin Operator’s Name: Duke Energy

Unit ID: N/A Hazard Potential Classification: High Significant Low 

### (see P.3)
Inspector’s Name: Steve Brown/GEI Consultants, Nick Miller/GEI Consultants

Checktheappropriateboxbelow,Provideco mmentswhenappropriate.Ifnotapplicableor notavailable,record"N/A",Anyunusu alconditionsorconstructionpracticesthat shouldbenotedinthecomments section,Forlargedikedembankments,separatechecklists maybeusedfordiffe rentembankmentareas.Ifseparateformsareused,ide ntifyapproximateareathattheformappliestoincomments. Yes No Yes No

1. Frequency of Company’s Dam Inspections? 18. Sloughing or bulging on slopes? X 2. Pool elevation (operator records)? ~EL. 397.3 19. Major erosion or slope deterioration? X 3. Decant inlet elevation (operator records)? NA (pump) 20. Decant Pipes 4. Open channel spillway elevation (operator records)? NA Is water entering inlet, but not exiting outlet? X

5. Lowest dam crest elevat ion (operator records)? EL. 405.0 Is water exiting outlet, but not entering inlet? X 6. If instrumentation is present, are readings

recorded (operator records)? X Is water exiting outlet flowing clear? NA

7. Is the embankment cu rrently under construction? X 21. Seepage (specify location, if seepage carries fines, and approximate seepage rate below): 8. Foundation preparation (remove vegetation, stumps,

topsoil in area where embankment fill will be placed)? X From underdrain? X 9. Trees growing on embankment? (If so, indicate

largest diameter below.) X At isolated points on embankment slopes? X
10. Cracks or scarps on crest? X At natural hillside in the embankment area? X 11. Is there significant settlement along the crest? X Over widespread areas? X 12. Are decant trashracks clear and in place? NONE From downstream foundation area? X 13. Depressions or sink holes in tailings surface or whirlpool in the pool area X “Boils” beneath stream or ponded water? X
14. Clogged spillways, groin or diversion ditches? X Around the outside of the decant pipe? X 15. Are spillway or ditch linings deteriorated? X 22. Surface movements in valley bottom or on hillside? X

16. Are outlets of decant or underdrains blocked? X 23. Water against downstream toe? X 17. Cracks or scarps on slopes X 24. Were Photos taken during the dam inspection? X Major adverse changes in these items could cause instability and should be reported for further evaluation. Adverse conditions noted in these items should normally be described (extent, location, volume, etc.) in the space below and on the back of this sheet.

### InspectionIssue# Comments
1

. No formal inspections of CCW impoundments. Informal visual inspections

performed biennially in conjunction with cooling pond inspection. 4. No open channel spillway. 6. Only reservoir water levels are measured. No piezometers or settlement monuments. 20. Discharge not flowing at time of inspection. Monthly by Staff, Biennial 3rd Party

### 2EPAForm,J an 09 

### Coal Combustion Waste (CCW) Impoundment Inspection

Impoundment NPDES Permit # N/A INSPECTOR Steve Brown/GEI

Date April 27, 201 0
Impoundment Name North Settling Basin, Duke Energy, Gibson County
, IN
Impoundment Company Duke Energy
EPA Region 5
State Agency (Field Office) Address Indiana Dept. of Natural Resources Div. of Water, Dams & Levees 402 West Washington St, Room W264, Indianapolis, IN 46204

Name of Impoundment North Settling Basin (Report each impoundment on a separate form under the same Impoundment NPDES Permit number)

New X Update

Yes No
Is impoundment currently under construction? X Is water or ccw currently being pumped into the impoundment? X

IMPOUNDMENT FUNCTION: Decant Water Stor age

Nearest Downstream Town: Name Grayville, I N Distance from the impoundment 35 miles Impoundment Location:

Does a state agency regulate this impoundment? YES X NO

If So Which Sate Agency? Indiana Dept. of Natural Resources Div. of Water, Dams & Levees Longitude 8 7 Degrees 45 Minutes 48 Seconds W Latitude 38 Degrees 2 2 Minutes 45 Seconds N State I N C ounty Gibson

### 3EPAForm,Jan09

### HAZARD POTENTIAL (In the event the impoundment should fail, the following would occur):

LESS THAN LOW HAZARD POTENTIAL: Failure or misoperation of the dam results in no probable loss of human life or economic or environmental losses.

LOW HAZARD POTENTIAL: Dams assigned the low hazard potential classification are those where failure or misoperation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.

SIGNIFICANT HAZARD POTENTIAL: Dams assigned the significant hazard potential classification are those dams where failure or misoperation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or can impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be located in areas with population and significant infrastructure.

HIGH HAZARD POTENTIAL: Dams assigned the high hazard potential classification are those where failure or misoperation will probably cause loss of human life.

DESCRIBE REASONING FOR HAZARD RATING CHOSEN: An uncontrolled release of the structure's contents due to a failure or misoperation is not considered to cause loss of human life and the economic and environmental damages would be relatively low. The flood extent would be limited by the adjacent USACE levee on the Wabash River and the very flat surrounding topography. Flood waters would likely be widespread with shallow depths and gradually rising waters. Based on the pond height and volume, the majority of inundation would be limited to Company property to the south east around the cooling pond and the surrounding wetlands. Flood waters would eventually drain to the Wabash River at culverts through the USACE levee located about 3 miles downstream. Consistent with the Federal Guidelines for Dam Safety, the dam should be classified as a "Low" hazard structure. X

### 4EPAForm,Jan09

### CONFIGURATION:

Cross-Valley Side-Hill Diked Incised (form completion optional) Combination Incised/Diked Embankment Height 15 feet Embankment Material Compacted fill Pool Area 10 acres Liner Unlined Current Freeboard 7.7 ft Liner Permeability NA X

### 5EPAForm,Jan09

### TYPE OF OUTLET (Mark all that apply)

Open Channel Spillway Trapezoidal Triangular Triangular
Depth Bottom (or average) width Top width

Outlet

inside diameter

Material corrugated metal welded steel concrete plastic (hdpe, pvc, etc.) other (specify

Is water flowing through the outlet? YES NO X - Pump was not active.



### No Outlet –

Other Type of Outlet (Specify)

The Impoundment was Designed By Sargent and Lundy Engineers, Chicago, IL for Public Service Indiana (PSI) at the time. Original construction completed in 1974. 

### None

X

24"

X

### 6EPAForm,Jan09

### Has there ever been a failure at this site? YES NO X

If So When?

If So Please Describe:

### 7EPAForm,Jan09

### Has there ever been significant seepages at this site? YES NO X

If So When?

If So Please Describe:

### 8EPAForm,Jan09

### Has there ever been any measures undertaken to monitor/lower Phreatic water table levels based on past seepages or breaches at this site? YES NO X

If So which method (e.g., piezometers, gw pumping, ...)?

If So Please Describe:

# Appendix B

Inspection Photographs
April 26-27, 2010

### Asaeaamant of 

### Dam Sarvty of 

### Coal Combustion Wasta at 

### DEl Gibson Stallon

DC EAST ASH PONDS & 

### SETTLING BASIN PHOTOGRAPH LOCATION MAP

### Asaeaamant of 

### Dam Sarvty of 

### Coal Combustion Wasta at 

### DEl Gibson Stallon

DC NORTH ASH POND & 

### SETTLING BASIN PHOTOGRAPH LOCATION MAPPhoto 1: East Settling Basin ‐ South dike upstream slope, looking east from south west corner.

Photo 2: East Settling Basin –Pump intake that discharges to the Cooling Pond, looking north.Photo 3: East Settling Basin

– West dike upstream slope, looking north.

Photo 4: East Settling Basin

– West dike downstream slope, looking north.Photo 5: East Settling Basin

– South dike upstream slope protection detail.

Photo 6: East Settling Basin

– Reservoir area from south dike, looking north.Photo 7: East Settling Basin

– South Dike downstream slope, looking west.

Photo 8: East Settling Basin

– East Dike upstream slope, looking north.Photo 9: East Settling Basin

– East and south dike downstream corner, looking south.

Photo 10: East Ash Pond #1

– Intake structure near southeast corner of EAP #1 that discharges to Settling Basin, looking west.Photo 11: East Ash Pond #1

– EAP #1 reservoir area, approximately 95% full of CCW, looking west.

Photo 12: East Ash Pond #1

– Interior dike crest between EAP #1 and Settling Basin, looking west, notice several small trees.Photo 13: East Ash Pond #1

– East Dike crest, road, and reservoir area, looking north from SE corner.

Photo 14: East Ash Pond #1

– East Dike crest and road, looking south from NE corner.Photo 15: East Ash Pond #1

– Drainage swell on north side of EAP #1 that discharges to EAP #2, looking west.

Photo 16: East Ash Pond #3

– Interior dike crest and road between EAP #1 and EAP #3, looking west.Photo 17: East Ash Pond #3

– EAP #3 reservoir area, about 95% full, in close out phase, looking northwest.

Photo 18: East Ash Pond #3

– EAP #3 Intake structure, looking north from interior dike between EAP #1 and EAP #3.Photo 19: East Ash Pond #3

– Interior dike between EAP #1 and EAP #3, looking west, notice trees along dike.

Photo 20: East Ash Pond #3

– East dike downstream slope, looking north from the corner of EAP #1 and EAP #3 interior dike.Photo 21: East Ash Pond #3

– North dike crest and reservoir area, looking northwest from northeast corner of EAP #3.

Photo 22: East Ash Pond #3

– EAP #3 capping construction, notice geofabric and geogrid, looking south from north dike.Photo 23: East Ash Pond #3

– North dike crest and capping material, looking east from northwest corner of EAP #3.

Photo 24: East Ash Pond #3

– West dike crest and road, looking south, notice county road to the west.\Photo 25: East Ash Pond #2

– CCW discharge line crossing Coon Creek, downstream of west dike, looking west.

Photo 26: East Ash Pond #2

– CCW discharge line crossing under county road, looking southwest from west dike.Photo 27: East Ash Pond #2

– CCW discharge line crossing west dike dam crest, looking north.

Photo 28: East Ash Pond #2

– EAP #2 west dike crest, looking south. 

### Discharge PipePhoto 29: East Settling Basin

– Interior dike crest between East Settling Basin and EAP #2, looking east.

Photo 30: East Ash Pond #2 ‐ EAP #2 downstream slope, abandoned discharge lines and drainage sump, looking northwest.Photo 31: North Ash Pond

– Downstream slope and crest of northeast dike, looking southeast.

Photo 32: North Ash Pond

– North Ash Pond reservoir area, looking south towards FSS landfill from northeast dike.Photo 33: North Ash Pond

– Downstream slope and crest of northeast dike, looking northwest.

Photo 34: North Ash Pond

– Downstream slope of northeast dike looking northeast at wetlands area from crest.Photo 35: North Ash Pond

– North dike downstream slope, looking southeast at northeast dike.

Photo 36: North Ash Pond

– North Ash Pond reservoir area and dredging equipment, looking southeast from north dike.Photo 37: North Ash Pond

– North Ash Pond reservoir area, looking east, notice upstream slope extended into reservoir.

Photo 38: North Ash Pond

– North dike downstream slope, looking west, notice large trees in wetland at toe of slope.Photo 39: North Ash Pond

– Wetlands area downstream of north dike, looking north from interior dike between NAP and NSB.

Photo 40: North Settling Basin

– USACE Levee, looking northeast from levee crest.Photo 41: North Settling Basin

– Pump intake structure that discharges to cooling pond, looking northeast.

Photo 42: North Settling Basin

– Reservoir area looking northeast from pump intake structure.Photo 43: North Settling Basin

– Discharge into settling basin, looking northwest from interior dike between NAP and NSB.

Photo 44: North Ash Pond

– Intake structure in NAP that discharges into NSB, looking southeast from interior dike.Photo 45: North Ash Pond

– Southeast dike upstream slope, crest and road, looking southeast from crest.

Photo 46: North Ash Pond

– Southeast dike downstream, crest and cooling pond reservoir area, looking southeast.

# Appendix C

Reply to Request for Information Under Section 104(e)

## A Dulce 

## [ff'Energy®

Via Certified Mail 7008 2810 0000 0830 9222

March 25, 2009

Mr. Richard Kinch US Environmental Protection Agency (5306P) 1200 Pennsylvania Avenue, NW Washington, DC 20460

Dear Mr. Kinch, DUKE ENERGY CORPORATION WP994 I 1000 East Main Street Plainfield, IN 46168-1782

RE: CERCLA 104(e) Request for Information Gibson Generating Station 1097 North 950 West Owensville, Indiana 47665

Duke Energy Indiana, Inc. (DEI) hereby responds to the request for information the EPA submitted to the Gibson Generating Station, letter dated March 9, 2009, under Section 104(e) of CERCLA, 42 USC§ 9604(e), relating to surface impoundments or similar diked 

### I bermed management units which receive liquid-borne material for storage or disposal of residuals or by-products from the combustion of coal DEI received this request on March 12, 2009, and today's response complies with the I 0-business day deadline.

The attached responses are full and complete and were developed under my supervision with assistance from Duke Energy's Engineering and Technical Services group. The following clarifications should be noted for the· attached responses.

• The responses in this submittal are for surface impoundments and the associated secondary I clarifying ponds used for temporary or permanent storage of flyash, bottom ash, boiler slag, and flue gas emission control residues at this station (hereinafter "coal combustion by-products").

o These ponds are also an integral part of the station's wastewater treatment system used to manage wastewater before discharge.

• The response to the questions does not include ponds that are retired 

### I closed and which no longer contain free liquids.

• The response to questions does not include landfill runoff collection ponds or any other miscellaneous ponds 

### I impoundments that are not designed to or do not regularly receive and
store coal combustion by-products.

• Where actual measurements could not be collected within the timeframe allotted by EPA, DEI has provided estimates, which are noted as such.

• The criteria that DEI used to identify any spills or unpermitted releases over the last 10 years in the response to Question #9 include the failure of physical pond or impoundment structures (i.e. berms, dikes, and discharge structures).



### I certify that the information contained in this response to EPA's request for information and the accompanying documents are true, accurate, and complete. As to the identified portions of this response for which I cannot personally verify their accuracy, I certify under penalty of law that this response and all attachments were prypared in accordance with a system designed to

assure that qualified personnel properly gather and evaluate the information submitted. Based on my inquiry of the person or persons who manage the system, those persons directly responsible for gathering the information, the information submitted is, to the best of my knowledge, true,

www. duke-energy. com

### accurate, and complete. I am aware that there are significant penalties for submitting false information, including the possibility of fines and imprisonment for knowing violations.

If you have any questions regarding today' s submittal please contact Richard Meiers at

our corporate offices at 317-838-1955.

Sincerely, Duke Energy Indiana, Inc.

Barry E. Pulskamp Senior Vice President Regulated Fleet Operations

Attachments (3)

Responses to Enclosure A Inspection Report Confidential Business Information

cc Thomas 

### J. Guthrie Gibson Generating Station Vice President Regulated Fossil Station Rebecca M. Sparks Sr. EHS Professional Richard J. Meiers Principal Environmental Scientist

# Attachment # 

# 1
Response to Questions in Enclosure A

Gibson Generating Station

March 24, 2009

1. Relative to the National Inventory of Dams criteria for High, Significant, Low, or Less than Low Hazard Potential, please provide the rating for each management unit and indicate which State or federal regulatory agency assigned that rating. If the unit·does not have a rating, please note that fact.

Duke Energy Indiana, Inc. (DEI) is not aware of any National Inventory of Dams criteria rating that has been assigned by a State or Federal Agency for the management units at the Gibson Generating Station of the management units listed in the response to Question #2 below.

2. What year was each management unit commissioned and expanded?



### North Ash Pond was commissioned in 1974.

North Settling Basin was commissioned in 1974.

East Ash Pond 

### # 1 was commissioned in 1991.

East Ash Pond #2 was commissioned in 1995.

East Ash Pond #3 was commissioned in 1999.

East Ash Pond Settling Basin was commissioned in 1991.

3. What materials are temporarily or permanently contained in the unit? Use the following categories to respond to this question: (1) fly ash; (2) bottom ash: (3) boiler slag; (4) flue gas emission control residuals; (5) other. If the management unit contains more than one type of material, please identify all that apply. Also, if you identify "other," please specify the other types of materials that are temporarily or permanently contained in the unit(s).

Management East Ash Pond #1 East Ash Pond #2 East Ash Pond #3 Unit Contents. 1,2,3,4,5* 1,2,3,4,5* 1,2,3,4,5*

Management East Ash Pond Settling North Ash Pond North Ash Pond Settling Unit Basin Basin Contents 1, 5* 1, 2, 3, 4, 5* 1, 5* 

## * "Other" includes landfill leachate, water treatment, boiler blow down, stormwater runoff, boiler chemical cleaning wastes, mill rejects, floor and laboratory drains and drains from equipment cleaning.4. Do you have a Professional Engineer's certification for the safety (structural integrity) of the management unit( s )? Please provide a copy if you have one. If you do not have such a certification, do
you have other documentation attesting to the safety (structural integrity) of the management unit(s)? If
so, please provide a copy of such documentation.

The safety (structural integrity) was certified through the design documents when the Gibson Generating Station management units were designed and constructed. The Engineering firm. responsible for the design was Sargent and Lundy Engineers. Copies of the design documents
may be available from our drawing archives. Due to the expediency of the requested reply, DEI is not submitting these documents as part of our response; however, we can research our archival information should there be a future need to submit original design documentation.

5. When did the company last assess or evaluate the safety (i.e., structural integrity) of the management unit(s)?

All management units listed in the response to question #2 were inspected in October 2008 by a third party firm.
Briefly describe the credentials of those conducting the structural integrity assessments/evaluations.

There have been both third party engineers with P.E.s and Duke Energy's Generation Department civil engineers involved with the inspections.
Identify actions taken or planned by facility personnel as a result of these assessments or evaluations.

See attached inspection reports (Attachment 2). The attached inspection reports identify findings, and corrective actions recommended and taken by facility personnel as a result of these inspections. Typical findings that require corrective actions are: Treat excess vegetation, clear ditch line of sediment and debris, re-seed sparsely vegetated and disturbed areas, and mow slopes in a diagonal pattern running transverse to existing rut lines. Other more site specific maintenance items are detailed in the reports.

If corrective actions were taken, briefly describe the credentials of those performing the corrective actions, whether they were company employees or contractors.

Duke Energy's Generation Engineering Department provides engineering oversight, review, and documentation of maintenance done and repairs made.

If the company plans an assessment or evaluation in the future, when is it expected to occur?

The next inspection is scheduled in the third quarter of2009.

6. When did a State or a Federal regulatory official last inspect or evaluate the safety (structural integrity) of the management unit(s)? If you are aware of a planned state or federal inspection or evaluation in the future, when is it expected to occur? Please identify the Federal or State regulatory agency or departmentwhich conducted or is planning the inspection or evaluation. Please provide a copy of the most recent official inspection report or evaluation.

The Gibson Generating Station has not had State or Federal regulatory officials performing ash pond dike inspections in the last five years. DEI is not aware of any federal or state agency inspection reports. The state regulatory agency governing dams would be the Indiana Department of Natural Resources (IDNR).

7. Have assessments or evaluations, or inspections conducted by State or Federal regulatory officials conducted within the past year uncovered a safety issue(s) with the management unit(s), and, if so, describe the actions that have been or are being taken to deal with the issue or issues. Please provide any documentation that you have for these actions.

DEI is not aware of any State or Federal regulatory officials conducting assessments, evaluations

or inspections at the Gibson Generating Station within the past year.

8. What is the surface area (acres) and total storage capacity of each of the management units? What is the volume of material currently stored in each ofthe management unit(s). Please provide the date that the volume measurement was taken.

The response to this question contains Confidential Business Information, which is of a competitive and commercial nature, pursuant to 40 C.P.R. Part 2. Our response is therefore provided in a separate attachment (Attachment 3), which has been labeled "CBI." DEI requests that EPA treat the information in Attachment 3 as CBI and safeguard it from inadvertent disclosure and contact DEI if EPA receives a request for this CBI.

9. Please provide a brief history of known spills or unpermitted releases from the unit within the last ten years, whether or not these were reported to State or federal regulatory agencies. For purposes of this question, please include only releases to surface water or to the land (do not include releases to groundwater).

There have been no spills or unpermitted releases from any of the management units listed in
response #2 over the past ten years.

10. Please identify all current legal owner(s) and operator(s) at the facility.

Duke Energy Indiana, Inc. is the operator of the facility.

Duke Energy Indiana Inc., Wabash Valley Power Association, Inc., and Indiana Municipal Power Agency are the legal owners of the facilities.

# Attachment #3

CBI

This attachment contains Confidential Business Information, which is of a competitive and commercial nature, pursuant to 40 C.F.R. Part 2. DEI requests that EPA treat the information in Attachment 3 as CBI and safeguard it from inadvertent disclosure and contact DEI if EPA receives a request for this CBI.



# Gibson Generating Station

Response to Question# 8

North Ash Pond was commissioned in 1974.

o 25 

### acres in total surface area with 350 

### acre/feet of total storage volume

o The station estimated in January 2009 

### that the pond was 50% 

### full.

North Settling Basin was commissioned in 1974.



### o 10 

### acres in total surface area with 150 

### acre/feet of total storage volume

o The station estimated in January 2009 

### that the pond was 30% 

### full

East Ash Pond #1 

### was commissioned in 1991.



### o 105 

### acres in total surface area with 1733 

### acre/feet of total storage volume

o The station estimated in January 2009 

### that the pond was 95% 

### full

East Ash Pond #2 

### was commissioned in 1995.



### o 105 

### acres in total surface area with 1733 

### acre/feet oftotal storage volume

o The station estimated in January 2009 

### that the pond was 50% 

### full

East Ash Pond #3 

### was commissioned in 1999.



### o 133 

### acres in total surface area with 3325 

### acre/feet of total storage volume

o The station estimated in January 2009 

### that the pond was 95% 

### full.

East Ash Pond Settling Basin was commissioned in 1991.



### o 45 

### acres in total surface area with 743 

### acre/feet of total storage volume

o The station estimated that the pond was 20% 

### full