naughton power plant south ash pond initial closure … · 2018. 10. 31. · salt lake city, ut...

CCR Rule – Closure and Post-Closure Care §257.102(b) – Written Closure Plan

Naughton Power Plant South Ash Pond

Prepared by:

Prepared for:

Naughton Power Plant

October 2020

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§257.102(b) – Written Closure PlanNaughton Power Plant South Ash Pond

TABLE OF CONTENTS

1 Introduction ........................................................................................................................ 1

2 Closure Narrative Summary ................................................................................................ 1

3 Closure Tasks ..................................................................................................................... 2

3.1 Background ................................................................................................................. 2

3.2 Dewatering .................................................................................................................. 2

3.3 Consolidation of CCR Waste ....................................................................................... 3

3.4 Soil Sampling ............................................................................................................... 3

3.5 Cover System .............................................................................................................. 4

3.6 Stormwater Management ............................................................................................ 5

4 Groundwater Monitoring ..................................................................................................... 5

5 Schedule ............................................................................................................................. 5

6 Professional Engineer Certification ..................................................................................... 7

List of Figures Figure 1. South Ash Pond Existing Site Figure 2. South Ash Pond Site Plan Figure 3. South Ash Pond Soil Sampling Locations

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§257.102(b) – Written Closure PlanNaughton Power Plant Ash Pond

1 INTRODUCTION This Closure Plan presents the strategy for closure of the South Ash Pond (SAP), a Coal Combustion Residuals (CCR) unit at the Naughton Power Plant (NPP) in Kemmerer, Wyoming to comply with the Code of Federal Regulations (CFR) § 257 (CCR Rule), specifically with section 102(b). The SAP is an unlined impoundment with a permitted boundary of approximately 136-acres that receives sluiced bottom and fly ash from the two coal-fired boilers at the NPP. The NPP plans to cease the operation of its coal-fired boilers by December 31, 2025. The SAP will cease receiving CCR waste no later than September 30, 2026 and begin closure within 30 days after final receipt of waste. Closure activities will be completed in the shortest amount of time consistent with recognized and generally accepted good engineering practices. At the latest, as specified in CFR § 257.103 (f)(2) closure activities will be complete by October 17, 2028. The Ash Pond will be closed by leaving the CCR in place and installing a final cover system as set forth in CFR § 257.102(d).

2 CLOSURE NARRATIVE SUMMARY In order to close the SAP in accordance with the CCR Rule, it will cease receiving sluiced bottom and fly ash from the power plant by December 31, 2025 when the coal fired boilers cease operation. From January through September 2026 residual CCR material in the plant site will be removed and placed in the SAP. Following removal of all the residual CCR material from the plant site, SAP will begin closure. Figures 1 and 2 show the existing site infrastructure and proposed closure area. The closure activities will consist of the following:

• Initial dewatering of SAP and reduction of flow to the SAP• Cessation of flows to the pond• Dewatering of the ash in the pond via evaporation and mechanical dewatering• Consolidation of the ash in containment area• Sampling of the pond floor to identify the extent of ash deposits, and further consolidation

as needed• Construction of a final cover over consolidated CCR materials• Construction of additional stormwater control measures

Initial dewatering activities and flow reduction measures have started and continue to be implemented. Since 2020, NPP has been actively re-routing the majority of non-CCR flows, which has resulted in a reduction of flow to the SAP. Starting on April 11, 2021, non-CCR waste streams will no longer be placed in the SAP. Sluiced ash to the SAP will cease December 31, 2025 and all CCR material will cease in September 2026. The first phase after closure consists of completely dewatering the pond via decanting and allowing the ash deposits and pond bottom with residual water, to dry out. Once sufficiently dry, ash and visibly impacted soils in the pond will be consolidated in a containment area in the northern portion of the SAP. The next closure phase consists of sampling the subgrade to determine if any impacted soils are remaining within the pond footprint. If any impacted soils are present within the pond footprint. Impacted soils will be excavated and moved to the ash containment area. The containment area will then be capped with a sloped (minimum 1%) 24-inch soil cover, consisting of an 18-inch infiltration layer and 6-inch erosion layer. Soil materials for the cover will be obtained from collapsing the SAP

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§257.102(b) – Written Closure Plan Naughton Power Plant Ash Pond

pond embankments, and if necessary, a nearby borrow area. The cap will be revegetated to minimize erosion and maximize evapotranspiration. The pond footprint outside of the containment area will be tilled and revegetated. Stormwater control measures are in place to divert the majority of run-on into the SAP. A sediment pond will be constructed to capture surface water runoff from the pond footprint while vegetation is established.

After closure is complete, maintenance and monitoring will be on-going. In accordance with the CCR Rule, long term groundwater monitoring will continue until attainment of the GWPS and for 30 additional years of post-closure care.

Closure Tasks

2.1 BACKGROUND The SAP is separated from the South Clear Water Pond (SCWP) via an intermediate dike (Figure 1). The northern portion of the SCWP is the recycle pond. The main dike is located on the south and east sides of the SAP and along the east side of the SCWP (Figure 1). The three cells together are considered one CCR unit and are covered under this closure plan.

The SAP accepts bottom ash and fly ash, produced as part of power generation. The ash is hydraulically conveyed to the SAP through an open concrete ditch. Until 2020, water from flash tank blow down, process water (liquor) from boilers associated with Units 1 and 2, seal water, waste water from NaZ softeners, reverse osmosis system, and the capacitive deionization system and fire water system were conveyed to the SAP. These non-CCR wastewater streams have since been rerouted and are used at various other locations throughout the plant. The only non-CCR waste currently entering the SAP is from a vacuum truck which the NPP uses for various maintenance and cleaning activities, however this non-CCR waste stream will cease by April 11, 2021.

Once ash is removed in the SAP, clear water is discharged into the SCWP via a 24-inch concrete conveyance pipe that runs below the crest of the dike. The flow from the SAP to the SCWP is controlled by a drop decant tower located adjacent to and south of the intermediate dike.

A portion of the water from the SCWP flows into the recycle pond, from which it is then pumped back to the plant to be used for sluicing fly ash and bottom ash to the SAP.

No CCR wastes will be accepted by the SAP starting in September 30, 2026. Upon final receipt of CCR material into the pond, a notice of intent will be placed in the operating record and then onto the webpage. Closure of the pond will then begin.

2.2 DEWATERING In February 2020, the SAP CCR unit had an estimated water volume of 1864 acre-feet. To achieve the final dewatering date of May 2027 and meet the October 17, 2028 closure deadline, the majority of the free water will be removed prior to December 31, 2025. The following steps will be implemented starting in 2020 to reduce the volume of water in the SAP, SCWP and recycle pond prior to commencing official closure activities:

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• Prevention of the majority of stormwater run-on into the SAP via construction ofstormwater control measures on the upstream, western edge of the SAP;

• Re-routing of non-CCR wastewater streams;• Reconfiguring the plant’s scrubber system to operate on recycled ash water;• Using recycled water to sluice ash from the plant to the SAP;• Evaporating recycled ash water using the plant’s modified scrubber system;• Enhancing the existing sprinkler systems located within the SAP used for dust control

and increased evaporation.

After cessation of flows to the SAP, final dewatering of the ash and removal of residual groundwater is expected to begin in May 2026 and be complete by May 2027. The ash deposits and the pond bottom will be allowed to dry sufficiently until the pond can be entered by earth moving equipment during the next closure phase. The drying process may need to be enhanced using mechanical methods such as spreading out the ash materials to speed up drying, or construction of trenches in the pond bottom to facilitate pumping of residual water. Ash will need to dry sufficiently to support a final cover system without the potential for excessive setting and subsidence. The CCR will be considered dewatered when it meets the paint filter test for free liquid prior to depositing in the final consolidation area.

2.3 CONSOLIDATION OF CCR WASTE Once the ash is dewatered, visible ash deposits and stained soils will be excavated and consolidated in the northern portion of the SAP as shown Figure 2. This area overlaps with the depositional fan where sluiced ash is currently discharged and the majority of the ash historically settled upon entry into the SAP. The ash consolidation area and any excavated slopes during this consolidation phase will have maximum slopes of 3:1. The unsalvageable infrastructure (e.g. drop decant tower structure, culverts) will be disposed of in the plant’s Industrial landfill.

The SAP was constructed in 1974, and expanded in 1976, 1981, 1987 and 1994. By the time closure activities will start, the SAP is estimated to have a maximum CCR volume of approximately 3,000,000 cubic yards. The impacted soil volume will be determined based on the soil sampling results.

2.4 SOIL SAMPLING After consolidation of visible ash deposits, the soil on the pond bottom will be sampled to delineate the extent of ash deposits or impacted soil outside the depositional fan. Subgrade soils will be tested on a systematic grid after the initial consolidation phase has been completed. A typical grid density is shown in Figure 3. A sampling and analysis plan will be developed as a stand-alone plan and will include the subgrade soil sampling plan and sampling grid density.

In order to determine if the soil has been impacted by contaminants of potential concern (COPC), it is necessary to determine a soil screening limit (SSL) for the COPC’s. The NPP will determine the appropriate SSL using either naturally occurring background concentrations or a combination of background concentrations and published soil leaching data or site specific leaching analysis. If these data show that the remaining concentration in soil will not cause an

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impact to groundwater, the information will be documented in a final report and additional excavation will not be necessary. The calculated SSL’s will ultimately determine if the soil is impacted and over-excavation depths beyond the current pond bottom are necessary.

The soil removal is expected to be completed in one year including soil sampling and excavation. The soil will be excavated and deposited on top of the ash in the consolidation area. The impacted soils removal may require several iterations of sampling, soil removal and resampling to verify impacted soil has been removed.

2.5 COVER SYSTEM As specified in 257.102(d)(3) the final cover system is designed to minimize infiltration and erosion. The permeability of the final cover system will be less than or equal to the natural subsoils present, or a permeability less than 10-5 cm/sec, whichever is less. The disruption of the integrity of the final cover system will be minimized through a design that accommodates settling and subsidence.

The ash deposits will be covered by an infiltration layer of at least 18 inches of earthen material. This infiltration layer will be covered by an erosion layer of at least six inches of earthen material that is capable of sustaining native plant growth. The 24-inch soil cover will be constructed with a minimum slope of 1% to reduce potential for long-term erosion. Design drawings for the final cover will be developed as part of the detailed design.

Soil from the collapsed SAP embankments will be used to construct the infiltration layer and erosion layer. Prior to collapsing the SAP embankments, 6 inches of topsoil will be stripped from the vegetated areas and stockpiled. Next, the SAP embankments will be excavated and soils will be transported to the ash consolidation area, to be used as general fill for the infiltration layer. If necessary, additional material will be obtained from a borrow source. The soils in the infiltration layer will be compacted to achieve a higher density to reduce the potential of settlement within the cover.

Once this layer has reached a thickness of at least 18 inches it will be covered by six inches of erosion layer. Topsoil stripped from the embankments will be used for this erosion layer, and if necessary additional material will be obtained from a borrow area in a location as close as practical. The erosion layer will be compacted to a lower density than the infiltration layer. To achieve a uniform slope throughout the soil cover, and limit compaction, the erosion layer will be placed using a low-pressure tracked dozer. Following tilling of the final cover and the remaining pond footprint (SAP, SCWP and recycle pond) the entire area will be seeded using a native seed mix. Seeding will occur in late fall or early spring. Reclamation seed mixtures and applicationrates will be specified in the detailed cover design.

The containment area is approximately 70 acres in size. The remaining pond footprint that will be revegetated is approximately 60 acres in size.

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2.6 STORMWATER MANAGEMENT Surface water flows towards the SAP from the upstream western edge. The majority of stormwater run-on is currently routed around the SAP and these structures will remain in place to provide stormwater management during the dewatering, ash consolidation, final cover construction and revegetation phases. During the revegetation phase, runoff from the final ash containment area cover and pond bottom will be captured in a sediment pond to be constructed in the southeast corner of the SAP. Sediment pond dimensions will be specified in the detailed design.

3 GROUNDWATER MONITORING PacifiCorp has completed long-term WDEQ and CCR monitoring at the pond. A corrective measures assessment was completed for SAP in 2019 and updated in 2020. It concluded that the exceedances of groundwater protection standards (GWPS) for Appendix IV constituents lithium, selenium only occurred in monitoring wells SAP-5 and SAP-6 with an SSI in monitoring well SAP-6 for cobalt are due to seepage from FGD Pond 2, another CCR unit located north and upgradient of the SAP. Closure activities at FGD Pond 2 started in 2016 and were completed in March 2020. Seepage from the SAP has resulted in elevated concentrations Appendix III constituents in the vicinity of monitoring well MW-9 and SAP-3. An inceptor trench south of the SAP is being evaluated to capture any impacted water from SAP in this area.

A remedy selection report, as directed by CCR rules is being completed for FGD Pond 2. As an interim remedial measure, horizontal wells are scheduled to be installed beneath FGD Pond 2 in the Fall of 2020. These wells will remove mounded impacted groundwater beneath FGD Pond 2. The remedy is considered complete when groundwater standards are achieved at all points within the plume and when concentrations of Appendix IV constituents have not exceeded GWPS for three consecutive years. The estimated time to achieve groundwater standards downgradient from the FGD Pond 2 is 18 years after the installation the selected remedy. In accordance with the CCR Rule, long term groundwater monitoring will continue until attainment of the GWPS and for 30 additional years of post-closure care.

4 SCHEDULE Initial dewatering measures are on-going and will continue until closure of the coal fired boilers on December 31, 2025. Final dewatering is expected to be complete by May 2027. The consolidation of ash and excavation of visibly impacted soils is projected to take one year. The soil on the pond bottom will be sampled and, if required, moved to the ash containment area in 2027. The final closure phase, which includes collapsing of the embankments, removal of infrastructure from the pond footprint, construction of the final cover on the ash containment area, construction of a sediment pond to capture stormwater, as well as revegetation is scheduled for to start in May 2027 and be completed by September 30, 2028. The following Gantt chart summarizes the closure tasks and expected completion dates.

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Naughton SAP Closure Schedule 2020 2021 2022 2023Closure Task Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4Initial Pond DewateringEngineering / DesignPermittingCease Operation of Coal-Fired Boilers Final Dewatering Ash/Pond BottomAsh ConsolidationSoil Screening DeterminationImpacted Soil SamplingImpacted Soil RemovalCollapsing of EmbankmentsFinal Cover ConstructionSediment Pond ConstructionVegetating Cover and Pond BottomCCR Closure Deadline October 17, 2028

2024 20282025 2026 2027

December 31, 2025

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5 PROFESSIONAL ENGINEER CERTIFICATION I hereby certify, as a Professional Engineer in the State of Wyoming, that the information in this document was assembled under my direct supervisory control. This report is not intended or represented to be suitable for reuse by PacifiCorp or others without specific verification or adaptation by the Engineer.

I hereby certify as a Professional Engineer in the State of Wyoming that this report has been prepared in accordance with, and meets the requirements of, 40 Code of Federal Regulations §257.102(b) – Written Closure Plan.

________________________________ John Trudnowski, P.E.

10-14-2020

Date

§257.102(b) – Written Closure Plan Naughton Power Plant Ash Pond

Figures

Depositional Ash FanDepositional Ash Fan

intermediate Dike

Approximate Location of SAP/SCWP Discharge Structure

Main Dike

SWCP Discharge Structure

ConveyanceDitch

South ClearSouth ClearWater PondWater Pond

South Ash PondSouth Ash Pond FGD Pond 4FGD Pond 4

RecycleRecyclePondPond

South Ash Pond CCR Unit

0 250 500 750 1,000125Feet

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Job#: PERCM02

Date: 9/24/2020FIGURE 1

NAUGHTON POWER PLANTSouth Ash Pond

Existing Site

Path: M:\PERC_CCR\Naughton\2020\SV_maps\FIGURE1.mxd, Author: jleprowse

Background Map:Source: USDA NAIPResolution: 0.5 meterDate: 2019

Area to be used for Area to be used for ash consolidationash consolidation

Collapseintermediate Dike

RemoveSAP/SCWP Discharge Structure &existing culvert

CollapseMain Dike

Remove SWCP Discharge Structure

Remove SlurryConveyanceDitch

South ClearSouth ClearWater PondWater Pond

South Ash PondSouth Ash Pond FGD Pond 4FGD Pond 4

RecycleRecyclePondPond

Collapse Dike

ConstructSediment Pond

3:1 Slope

3:1 Slope

3:1 Slope

3:1 Slope

Area to be vegetated

Area to be vegetated

"T

0 200 400 600 800100Feet

.

Job#: PERCM02



Site Plan



0 125 250 375 50062.5Feet

. Job#: PERCM02



Sampling Locations



naughton power plant south ash pond initial closure … · 2018. 10. 31. · salt lake city, ut...

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