2016 INSPECTION REPORT
BOTTOM ASH POND COMPLEX – ID # 05108 MITCHELL PLANT
MARSHALL COUNTY, WEST VIRGINIA
PREPARED FOR:
AMERICAN ELECTRIC POWER SERVICE CORPORATION CIVIL ENGINEERING & GEOTECHNICAL SERVICES
1 RIVERSIDE PLAZA COLUMBUS, OHIO 43215
PREPARED BY:
SCHNABEL ENGINEERING, LLC 3502 OVERLOOK CIRCLE
KNOXVILLE, TENNESSEE 37909
DECEMBER 20, 2016
ANNUAL DIKE INSPECTION REPORT BOTTOM ASH COMPLEX
REVISIONS PAGE FILE 15055011.00
Revision Date Description 0 December 20, 2016 Initial Release
2016 INSPECTION REPORT MITCHELL PLANT BOTTOM ASH COMPLEX
TABLE OF CONTENTS
INTRODUCTION ...........................................................................................................................1
SUMMARY OF VISUAL OBSERVATIONS ................................................................................1
Terms ...................................................................................................................................1
Site Description ....................................................................................................................2
Bottom Ash Pond Inspections ..............................................................................................4
Clear Water Pond Inspections ..............................................................................................5
ASSESSMENT OF INSTRUMENTATION DATA.......................................................................6
CONCLUSIONS AND RECOMMENDATIONS ..........................................................................6
Conclusions ..........................................................................................................................6
Recommendations - Remedial Actions and Repair .............................................................7
Recommendations - General Maintenance and Monitoring ................................................7
FIGURES
LOCATION PLAN .......................................................................................................... FIGURE 1
APPENDICES
INSPECTION PHOTOGRAPHS ............................................................................... APPENDIX I
PLAN VIEW DRAWING WITH PIEZOMETER LOCATIONS ............................ APPENDIX II
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INTRODUCTION The American Electric Power Service Corporation (AEPSC), Civil Engineering Department’s (CED) Geotechnical Engineering Services Section (GES) administers the Dam Inspection and Maintenance Program (DIMP) at AEP facilities. To satisfy DIMP inspection protocol, GES coordinated with Schnabel Engineering, LLC (Schnabel) to prepare the 2016 Inspection Report for the Mitchell Plant Bottom Ash Complex. Specifically, the inspection and reporting were performed by Mr. Seth W. Frank, P.E. (Schnabel). Kentucky Power Company (KPC) operates the Bottom Ash Complex. The facility inspection for the 2016 Inspection Report was conducted by Seth W. Frank, P.E.; Mohammad A Ajlouni, Ph.D., P.E. (AEPSC); and Dennis Henderson (KPC – Mitchell Plant) on October 12, 2016. Mr. Henderson was the facility contact for the inspection. During the October 12, 2016 inspection, the weather was clear and sunny with temperatures in the low 70’s. AEPSC Civil Engineering & Geotechnical Services coordinated the inspection, in part, to fulfill requirements of the West Virginia Department of Environmental Protection, Division of Water and Waste Management, EE/Dam Safety Section; in part to fulfill the requirements of the Environmental Protection Agency’s CCR Rules (40 CFR Parts 257 and 261); and in part to provide the plant with an evaluation of the facility to aid in the prioritization of maintenance activities. This report presents a summary of the inspection along with conclusions and recommendations. Photographs identifying typical conditions, problem areas, or items that need additional monitoring or correction are provided in Appendix I of this report.
SUMMARY OF VISUAL OBSERVATIONS
Terms The terms used for visual observations to describe the general appearance or conditions of an observed item, activity, or structure are listed below. The definitions of terms are presented below: Good: A condition or activity that is generally better or slightly better than what is
minimally expected or anticipated from a design or maintenance point of view.
Fair/Satisfactory: A condition or activity that generally meets what is minimally expected or
anticipated from a design or maintenance point of view.
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Poor: A condition or activity that is generally below what is minimally expected or anticipated from a design or maintenance point of view.
Minor: A reference to an observed item (e.g., erosion, seepage, vegetation, etc.)
where the current maintenance condition is below what is normal or desired, but which is not currently causing concern from a structure safety or stability point of view.
Significant: A reference to an observed item (e.g., erosion, seepage, vegetation, cracks,
concrete surface, etc.) where the current maintenance program has neglected to improve the condition. These are usually conditions that have been identified in previous inspections, but have not been corrected.
Excessive: A reference to an observed item (e.g., erosion, seepage, vegetation, cracks,
concrete surface, etc.) where the current maintenance condition is above or worse than what is normal or desired, and which may have affected the ability of the observer to properly evaluate the structure or particular area being observed or which may be a concern from a structure safety or stability point of view.
Site Description The Bottom Ash Complex at the Mitchell Plant consists of a clear water pond and a bottom ash pond. The bottom ash pond area of the complex is partitioned into two main areas by an interior, north to south trending splitter dike. The eastern area of the pond is the primary settling area and receives the sluiced bottom ash at the northeast end. This area is typically maintained above the normal operating pool level and does not impound a significant volume of water, and the bottom ash is routinely excavated from this area for construction purposes. The western area of the bottom ash pond is hydraulically connected to the eastern area through a culvert pipe located in the splitter dike. Process water also flows into the western area. The western area of the bottom ash pond has a number of small internal dikes to provide a longer flow path in an effort to further promote settlement of suspended solids and provide a means for chemical treatment. The internal dikes in the western area also facilitate equipment access for periodic cleaning of the pond without lowering the water level. Flow from the bottom ash pond is routed through the principal spillway structure located at the western end of the south dike. The south dike of the bottom ash pond divides the bottom ash pond from the clear water pond. The clear water pond provides additional retention time for the sluiced water prior to discharging into the Ohio River. Additionally, there is a secondary containment basin that abuts the bottom ash pond west dike exterior slope. The secondary containment is a lined basin and provides protection from
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unexpected leakage from an infrequently used metal cleaning waste tank. The facility arrangement is shown in Figure 1. The embankments of the facility are considered small (i.e., ≤ 40 ft. in height) with interior and exterior slopes of approximately 3:1 (3H to 1V). A summary of relevant storage information for the Bottom Ash and Clear Water Ponds is provided in Table 1.
Table 1. Summary of Relevant Storage Information (257.83(b)(2)(iii, iv, v))
Bottom Ash Pond
Approximate Minimum Depth / Elevation of Impounded Water 5.6 feet / 675.60 feet, NAVD
Approximate Maximum Depth / Elevation of Impounded Water 8.83 feet / 678.83 feet, NAVD
Approximate Depth / Elevation of Impounded Water on Oct. 26, 2016 6.4 feet / 676.4 feet, NAVD
Approximate Minimum Depth / Elevation of CCR(2) < 10 feet / 670 feet, NAVD
Approximate Maximum Depth / Elevation of CCR(2) > 30 feet / 690 feet, NAVD
Approximate Depth / Elevation of CCR on Oct. 26, 2016 ≈ 30 feet / 690 feet, NAVD
Volume of Impounded Water / CCR and Sediment Oct. 26, 2016 55,400 / 130,400 cubic yards
Available Storage Volume on Oct. 26, 2016 145,700 cubic yards
Clear Water Pond
Approximate Minimum Depth / Elevation of Impounded Water 6.6 feet / 661.60 feet, NAVD
Approximate Maximum Depth / Elevation of Impounded Water 7.85 feet / 662.85 feet, NAVD
Approximate Depth / Elevation of Impounded Water on Oct. 26, 2016 6.9 feet / 661.9 feet, NAVD
Approximate Minimum Depth / Elevation of CCR(3) ≤ 10 feet / 655 feet, NAVD
Approximate Maximum Depth / Elevation of CCR(3) ≤ 10 feet / 655 feet, NAVD
Approximate Depth / Elevation of CCR and Sediment on Oct. 26, 2016 ≈ 10 feet / 655 feet, NAVD
Volume of Impounded Water / CCR and Sediment Oct. 26, 2016 17,650 / 19,900 cubic yards
Available Storage Volume on Oct. 26, 2016 54,400 cubic yards
Note: 1. Maximum and minimum levels pertain to the monitoring period from September 21, 2015, to October 26, 2016.
2. The level of Bottom Ash (CCR) in the Bottom Ash Pond varies across the pond and based on excavation and removal schedules. The maximum, minimum, and current levels provided are visual estimates and may vary.
3. The maximum, minimum, and current levels of CCR / Sediment in the clear water pond are visual estimates. The CCR / Sediment levels change slowly over time, unless AEP dredges or dips the pond.
Per CFR 257.83(b)(1)(i), we reviewed available, pertinent information, including weekly site inspections. Other than routine maintenance items, no signs of potential structural weakness or adverse conditions were reported in AEP weekly site inspection reports. Additionally, based on a review the weekly site inspections, discussions with site personnel, and based on observations during the October 12, 2016, site inspection, no modifications have been made to the geometry of the Bottom Ash Pond Complex, since the 2015 annual inspection. The geometry of the impoundments has remained essentially unchanged (257.83(b)(2)(i)). Field inspection
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photographs for the Bottom Ash Complex are provided in Appendix I. Results of the visual inspection are summarized below.
Bottom Ash Pond Inspection Overall, the support structure for the ash inlet piping at the bottom ash pond appeared to be in satisfactory condition. Deterioration of the wooden support structure appeared to be about the same as that observed during prior inspections and did not appear to pose any immediate issues. See Photograph No. 1 for an overview showing the general condition.
For the most part, the exterior slopes at the bottom ash pond were in good condition. Vegetation appeared to be properly managed around the perimeter with areas having been recently cut. Photograph No. 16 provides an overview of the proximity of the dry fly ash pneumatic transport piping and supports along the length of the east dike. Animal burrows noted during previous inspections have been filled. Seepage was not observed at the time of the inspection and is not anticipated with the current mode of operation. The general conditions found at the exterior slopes of the north and west dikes comprising the bottom ash pond can be seen in Photograph Nos. 3 and 7. The interior slopes at the bottom ash pond were generally in good condition. Interior portions of the east dike, which in past inspections showed signs of erosion and exposed liner, have been repaired/graded. Aggregate placed along the west dike, lower slope – just above the normal operating pool level – was in good condition. Vegetation control was generally good. Photograph Nos. 2, 4, 6, and 8 provide overviews of the interior slopes of bottom ash pond dikes. Surface irregularities along the slopes appeared to be the same as observed in prior inspections.
The crest of the bottom ash pond serves as an access roadway around the perimeter. The crushed aggregate surfacing on the north, west, and south dike crests was graded to promote storm water runoff and is properly maintained. Further, the bituminous concrete surfacing on the crest of the east dike continues to perform well under the significant haul truck traffic. Both the crest and the crest surfacing appeared to be in good condition. Neither misalignment nor settlement was observed.
The decant structure and skimmer structure at the bottom ash pond appeared to be in fair condition and are functional. The decant pipes, at the time of the inspection were flowing freely; however, a filter sock was partially obstructing the inlet. See Photograph Nos. 8 and 9 for an overview of the decant structure and skimmer.
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The interior splitter and flow diversion dikes of the bottom ash pond appeared to be in stable and functional condition. In general the crest surfaces were well maintained for service access and the slope vegetation management was observed to be adequate. Photograph 5 shows the interior splitter dikes and culverts.
Clear Water Pond Inspection The interior slopes of the clear water pond were in good condition with no areas of recent slope instability. Vegetation control is considered good. Surface irregularities noted in past inspections were deemed to be essentially the same as previously observed. Photograph Nos. 10, 11, and 13 show the typical condition of the interior slopes.
The overflow structure at the clear water pond appeared to be in a good condition. The steel landing and stairs that were installed to facilitate access to the lower part of the structure and to manage the normal operating pool were observed to be in good condition. Photograph No. 11 provides an overview of the overflow structure, elevated walkway, landing, and skimmer structure. Due to the lower than usual water level (the Mitchell Plant was temporarily idled) we were able to observe the skimmer structure (trough) in more detail. It appeared that water was entering below the skimmer structure at many locations along its length. The leaks are likely due to corrosion and generally correspond to locations where metal struts are attached to the skimmer structure. However, the skimmer structure has little bearing on the performance/stability of the overflow structure; therefore, this issue is raised as a maintenance/water quality issue. The clear water pond is generally incised with the exception of the southwestern end. Erosion caused by roadway runoff was observed at the toe of the south exterior slope near the facility fence and along the east exterior slope, but overall, the exterior slopes were in satisfactory condition and showed no signs of slope instability. Photograph No. 14 depicts the general conditions along the west slope. The crest of the clear water pond serves as a service road and appeared to be in good condition with no signs of settlement or misalignment. The roadway surface was found to be properly graded for storm water runoff and ponding was not observed. The effluent from the clear water pond discharges into the Ohio River through a series of buried, reinforced concrete and corrugated metal pipes. In the spring of 2015, a sinkhole was identified above the 36-inch diameter corrugated metal transport pipe, approximately 250 feet downstream of the toe of the west dike. The sinkhole was subsequently filled with grout. The grout surface appeared unchanged from last year’s inspection. Due to a train blocking the access road, we were unable to inspect the outlet end of the spillway pipe and riprap channel leading to the Ohio
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River. Mr. Dennis Henderson provided photographs of the spillway outlet and riprap channel on November 7, 2016. Based on those photographs (Photograph No. 17 and 18) the spillway and riprap channel appear unobstructed and functioning as intended.
ASSESSMENT OF RECENT INSTRUMENTATION DATA (257.83(b)(2)(ii)) Stand pipe piezometers were installed at the bottom ash complex in 2009. The piezometers became accessible for measurement purposes in 2010. Regular readings are made and recorded for each piezometer during the monthly inspections performed by plant personnel. Operating pool levels are also recorded on a monthly basis. Pool elevations listed on the October 26, 2016, 30-day Inspection Checklist were 676.42 feet, NAVD, and 661.85 feet, NAVD, for the bottom ash pond and clear water pond, respectively. The reported pool levels were compared with the piezometer readings. An assessment of those readings follows: 1. Reports during the past year continue to indicate piezometer B-2 at the north dike of the
bottom ash pond is very low to dry; 2. Piezometers B-3 and B-4 continue to exhibit minor fluctuations. Operating pool
information is available for comparison purposes, and it appears the levels generally follow trends in the pool;
3. Piezometer B-5 is located in the west dike of the clear water pond and generally follows the same trends as B-3 and B-4.
Table 2. Maximum Recorded Piezometer Levels during Monitoring Period
Piezometer Location Maximum Level
(ft, NAVD) Date of Reading
B-2 East Abutment 661.87 April 13, 2016
B-3 East Abutment 667.65 January 20, 2016
B-4 East Hillside 666.07 March 16, 2016
B-5 East Hillside 663.81 March 16, 2016
CONCLUSIONS AND RECOMENDATIONS Conclusions Based on the visual inspection, the Bottom Ash Complex is generally in good condition. Other than the minor maintenance issues discussed in the following list, no specific deficiencies or signs of structural weakness were observed at the time of the inspection (257.83(b)(2)(vi)).
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Routine inspection and monitoring activities, being performed by the plant and AEPSC Civil Engineering Geotechnical Services, should continue. Specific conclusions related to this inspection include: 1. The Bottom Ash Complex appears to be operating as designed and shows no signs of
distress (with exception to the clear water pond outlet works), slope instability, dike misalignment, or settlement.
2. Vegetation management for the facility is considered mostly good. Only minor erosion was observed during the inspection.
3. The bottom ash pond decant inlet was partially obstructed by a filter sock. 4. The piezometer covers located in the dike crests are in varying states of disrepair. 5. The piezometers show minor fluctuations; however, those fluctuations generally follow
seasonal/pool level changes. Following are remedial actions, general maintenance items, and monitoring requirements that are recommended as a result of the inspection. Assistance or guidance with the implementation of these items can be provided by AEPSC Civil Engineering & Geotechnical Services:
Remedial Actions and Repair 1. The potentially compromised portion of corrugated metal outlet pipe (from 2015 sinkhole)
should be assessed and slip lined/repaired as necessary. 2. Provide routine maintenance to fill/regrade erosion rills on the upstream and downstream
sides of the east dike. 3. The filter sock, located in the bottom ash pond decant inlet, should be removed.
General Maintenance and Monitoring 1. Follow the recently approved Maintenance and Monitoring Plan. Including, but not limited
to:
Continuation of the monthly inspections at the plant level, and forwarding the associated inspection reports to AEPSC Civil Engineering;
Performance of weekly surveillance of the outfall structures and record observations; and
Continuation of the vegetation management program. 2. Fill animal burrows as they are observed and eliminate the burrowing animals by means
allowed through a catch and release program or by the means and methods allowed by the West Virginia Division of Natural Resources’ Hunting and Trapping regulations.
3. Ongoing erosion repair of the interior and exterior slopes for the bottom ash pond and the clear water pond.
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4. Sediment control/skimmer structures located at/around the decants for both the bottom ash pond and clear water pond should be routinely monitored and maintained to prevent them from interfering with performance of the decant structures.
If you have any questions about this report, please contact Seth W. Frank, P.E., at (865) 584-0344.
Respectfully Submitted, Schnabel Engineering, LLC Seth Frank, P.E. West Virginia R.P.E. No. 20574
FIGURE 1
Location Plan
APPENDIX I
Inspection Photographs
Photograph 1. Bottom Ash Complex Bottom Ash Pond – overview of influent line support structure looking north northeast from dry bottom ash loadout area. Structure is in satisfactory condition (10-12-16).
Photograph 2. Bottom Ash Complex Bottom Ash Pond – east interior slope looking north. Note the graded slopes (10-12-16).
Photograph 3. Bottom Ash Complex Bottom Ash Pond – north dike exterior slope looking west. Note vegetation management considered good (10-12-16).
Photograph 4. Bottom Ash Complex Bottom Ash Pond – north dike interior slope looking east from southeast corner of embankment (10-12-16).
Photograph 5. Bottom Ash Complex Bottom Ash Pond – view of internal splitter dike and culvert system. Photo taken from bottom ash loadout area facing approximately west (10-12-16).
Photograph 6. Bottom Ash Complex Bottom Ash Pond – West dike interior slope and internal splitter dikes looking south from the crest of the north dike. (10-12-16).
Photograph 7. Bottom Ash Complex Bottom Ash Pond – view of west dike crest and exterior slope looking south from west dike. Note vegetation management considered good (10-12-16).
Photograph 8. Bottom Ash Complex Bottom Ash Pond – view of west dike interior slope (foreground) and splitter dike and spillway structure, looking southeast from west dike. Note vegetation management considered good (10-12-16).
Photograph 9. Bottom Ash Complex Bottom Ash Pond – spillway structure inlet. Note the presence of filter sock in inlet. (10-12-16).
Photograph 10. Bottom Ash Complex Clear Water Pond – view of north dike (splitter dike between Clear Water Pond and Bottom Ash Pond) interior slope looking west (10-12-16).
Photograph 11. Bottom Ash Complex Clear Water Pond – view of west dike interior slope and overflow structure looking north from interior slope of south dike – note vegetation management considered good. Note leaks in skimmer structure (10-12-16).
Photograph 12. Bottom Ash Complex Clear Water Pond – view looking down into vertical overflow control structure (10-12-16).
Photograph 13. Bottom Ash Complex Clear Water Pond – view of south dike and west dike interior slopes looking west from interior slope of south dike – note vegetation management considered good (10-12-16).
Photograph 14. Bottom Ash Complex Clear Water Pond –view of downstream slope of west dike (10-12-16).
Photograph 15. Bottom Ash Complex Clear Water Pond – view of east dike crest. Note the minor erosion rills due to runoff from the crest (10-12-16).
Photograph 16. Bottom Ash Complex – Overview of the exterior slope of the east dike looking north (Clear Water Pond east dike in the foreground and Bottom Ash Pond east dike in the distance). Note the moderately sized erosion rills due to runoff from the crest (10-12-16).
Photograph 17. Bottom Ash Complex Outfall to the Ohio River – outlet end of a series of corrugated metal pipes to the riprap-lined outlet channel (11-7-16).
Photograph 18. Bottom Ash Complex Outfall to the Ohio River – overview of the outlet channel to the Ohio River. Channel unobstructed and flowing freely (11-7-16).
APPENDIX II
Plan View Drawing with Piezometer Locations
