ENGINEER S CERTIFICATION OF AQUIFER SEPARATION DEMONSTRATION (40 CFR )

Transcription

1 PLATTE RIVER POWER AUTHORITY RAWHIDE ENERGY STATION BOTTOM ASH TRANSFER (BAT) IMPOUNDMENTS LARIMER COUNTY, CO ENGINEER S CERTIFICATION OF AQUIFER SEPARATION DEMONSTRATION (40 CFR ) FOR COAL COMBUSTION RESIDUALS (CCR) EXISTING SURFACE IMPOUNDMENTS Prepared for Platte River Power Authority Platte River Power Authority 2700 East County Road 82 Wellington, CO October 16, 2018 Prepared by

2 Rawhide Energy Station Page i TABLE OF CONTENTS 1.0 INTRODUCTION Objective Rule Requirements Site Background DESKTOP REVIEW/ASSESSMENT Groundwater Data Unit Base Data CONCLUSIONS REFERENCES... 4 FIGURES Figure 1: Site Location Map Figure 2: CCR Unit Site Overview Figure 3: Groundwater Potentiometric Map Figure 4: BAT Impoundments Base Elevation Map Appendices Appendix A Engineer s Certification

3 Rawhide Energy Station Page INTRODUCTION 1.1 OBJECTIVE The purpose of this demonstration is to document compliance with 40 CFR of the Environmental Protection Agency Final Coal Combustion Residual Rule (EPA Final CCR Rule). This Aquifer Separation Demonstration is based on existing documentation such as construction drawings, record drawings, groundwater potentiometric maps developed based on measured water levels, and any other pertinent data and/or investigations to support historical conditions and operations at the at the Rawhide Energy Station. 1.2 RULE REQUIREMENTS Pursuant to 40 C.F.R (a), new CCR landfills, existing and new CCR surface impoundments, and all lateral expansions of CCR units must be constructed with a base that is located no less than 1.52 meters (five feet) above the upper limit of the uppermost aquifer, or must demonstrate that there will not be an intermittent, recurring, or sustained hydraulic connection between any portion of the base of the CCR unit and the uppermost aquifer due to normal fluctuations in groundwater elevations (including the seasonal high water table). Pursuant to 40 C.F.R (b) and (c)(1), for an existing CCR surface impoundment, the owner or operator must obtain a certification from a qualified professional engineer stating that the owner or operator has demonstrated that the CCR unit meets the requirements for placement above the uppermost aquifer no later than October 17, Pursuant to 40 C.F.R (c)(4), an owner or operator of an existing CCR surface impoundment who fails to demonstrate compliance with the requirements of paragraph (a) of this section by the date specified in paragraph (c)(1) of this section is subject to the requirements of (b)(1). 2.0 SITE BACKGROUND Rawhide Energy Station (Rawhide) is a 4,560 acre facility located at 2700 East County Road 82 in Wellington, CO. Construction of Rawhide began in 1979 and it has operated as a coal-fired power plant since. The primary land use on the Rawhide property is related to utility service electric generation. Power generation at Rawhide produces coal combustion residuals (CCR). Rawhide places these residuals in the Solid Waste Management Facility (the Monofill), located in the northwest corner of the Rawhide site. The BAT Impoundments are located northwest of the main plant and north of the Cooling Pond. A site location plan of the Rawhide Energy Station is depicted on Figure 1. An overview of the impoundments is presented in Figure 2. Bottom ash is produced during the coal combustion process and is hydraulically sluiced from the boiler to one of the two incised BAT impoundments. These impoundments also receive resin filter backwash water from the demineralizer at the wastewater treatment plant. The impoundments were constructed in the early 1980s by excavating below grade into the underlying Pierre Shale and then lining the

4 Rawhide Energy Station Page 2 bottom with 18 inches of compacted clay. Each of the two impoundments measure approximately 725 feet by 225 feet at the surface (approximately 7.5 acres total) with a bottom elevation of 5,660 feet above mean sea level (amsl), a normal water elevation of 5,674 feet amsl, and a top of berm elevation of between 5,678 and 5,679 feet amsl. It takes approximately one to two years to fill one of the ponds. Once the ponds are filled, the solids are excavated by an outside contractor and disposed in the on-site monofill. The bottom clay liner has been surveyed during the cleanout. The ponds are cleaned out approximately every three years. A plant shutdown event at the Rawhide facility is planned to occur during Fall The existing BAT impoundments will be permanently taken out of service following this shutdown event.

5 Rawhide Energy Station Page 3 Figure 1: Site Location Map Figure 2: CCR Unit Site Location 3.0 DESKTOP REVIEW/ASSESSMENT AECOM reviewed readily available for the BAT Impoundments to determine the uppermost aquifer limits as on groundwater elevations and the base grade elevations of the bottom of the CCR Units. 3.1 GROUNDWATER ELEVATION DATA A review of a groundwater potentiometric map (Figure 3, attached) from the Sitewide Monitoring Plan (AECOM 2018) indicates the groundwater elevation beneath the BAT Impoundments is approximately 5,677 feet above mean sea level (ft msl). This map was developed based on groundwater elevation measurements taken at the impoundment monitoring wells. 3.2 CCR UNIT BASE ELEVATION DATA The elevation of the base of the BAT Impoundments is approximately 5,660 ft msl as shown on Figure 4 (attached) from the Surface Impoundment Closure Plan Revision 6 (AECOM 2018). For this demonstration, AECOM assumes the bottom of ash elevations are the base of each unit. Comparison of the base impoundment elevation (5,660 ft msl) with the groundwater elevation beneath the impoundments (5,677 ft msl) indicates that the impoundment bottom elevations are approximately 17 feet below the water table.

6 Rawhide Energy Station Page CONCLUSIONS Based upon a review of the information presented above, it is concluded the Rawhide Station BAT Impoundments (CCR Surface Impoundments) does not meet the required minimum 1.52 meters (five feet) separation of the base of the CCR unit and the upper limit of the uppermost aquifer per the EPA Final CCR Rule Pursuant to 40 C.F.R (c)(1), for an existing surface impoundment, the owner or operator must complete the demonstration no later than October 17, Certification by a qualified professional engineer is included in Appendix A. 5.0 REFERENCES AECOM Appendix N Sitewide Monitoring Plan Revision 2, Engineering Design and Operations Plan (EDOP) for Type B Surface Impoundments Revision 2, Rawhide Energy Station, Platte River Power Authority, Fort Collins, Colorado. September. AECOM Appendix O Surface Impoundments Closure Plan Revision 6, Engineering Design and Operations Plan (EDOP) for Type B Surface Impoundments Revision 2, Rawhide Energy Station, Platte River Power Authority, Fort Collins, Colorado. September.

7 Rawhide Energy Station FIGURES

8 BAT-09!? BAT-08!? BAT-01 BAT-02 BAT-03!?!?!? Bottom Ash Transfer Ponds Path: M:\DCS\Resources\ENV\GIS\LD\GIS\Projects\ _PRPA_Hydro_Assessme\7.0_CAD_GIS\7.2 GIS\Mxds\Figure_3_BAT_Potentiometric_Map_2017.mxd Hamilton Legend!? Existing Monitoring Well 5673 BAT-06!? Reservoir (Cooling Pond) Groundwater Elevation Contour (ft msl) Bottom Ash Transfer Ponds BAT-05!? Scale in Feet BAT-04R!? Copyright: 2013 National Geographic Society, i-cubed, Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community Coal Combution Residuals (CCR) BAT Impoundments Aquifer Separation Demonstration, Platte River Power Authority Rawhide Station, Wellington, CO Project: Date: Rawhide Energy Station BAT Impoundments Groundwater Potentiometric Map October 2017 Figure 3

9 5680 ANSI B 11" x 17" Last saved by: SCHWARTZE( ) Last Plotted: Project Management Initials: Designer: Checked: Approved: Filename: \\USFCO4FP001\DATA2\WORKING\PLATTE RIVER POWER AUTHORITY\900-CAD\06-FIGURES\RES-COAL COMBUST RES_4_LOCATION MAP.DWG BAT-06 BAT COOLING POND LEGEND MONITORING WELL ABANDONED MONITORING WELL EXISTING SURFACE CONTOUR (CONTOUR INTERVAL = 2') BAT-08 BAT BAT-06 SLUICE WATER RECYCLE (RECLAIM) POND 5700 GATE VALVE (NORMALLY CLOSED) NORTH BAT IMPOUNDMENT HIGH WATER CONCRETE GATE OVERFLOW (ELEV. 5674) SOUTH BAT IMPOUNDMENT STORMWATER RETENTION POND BAT BAT-05 BAT BAT-03 BAT-04R 5682 BAT-04 NOTES: 1. DESIGN CONTOURS OF PONDS PROVIDED BY PLATTE RIVER POWER AUTHORITY. OTHER SURFACE CONTOURS FROM USGS DIGITAL ELEVATION MODEL N "=120' BOTTOM ASH TRANSFER (BAT) IMPOUNDMENTS BOTTOM ELEVATIONS Coal Combustion Residuals (CCR) BAT Impoundments Aquifer Separation Demonstration Platte River Power Authority Rawhide Station, Wellington CO Figure: 4 Date: 10/10/18 Project No.:

10 Rawhide Energy Station APPENDIX A ENGINEER S CERTIFICATION

11