Written Closure Plan. Pawnee Station - Active CCR Landfill Public Service Company of Colorado Denver Colorado. October 17, 2016

Transcription

1 Written Closure Plan Pawnee Station - Active CCR Landfill Public Service Company of Colorado Denver Colorado October 17, 2016

2 Table of Contents 1.0 General Information Description of Closure Plan 40 CFR (b)(1)(i-iii) Inventory Estimate 40 CFR (b)(1)(iv) Area Requiring Final Cover 40 CFR (b)1(v) Schedule of Closure Activities 40 CFR (b)1(vi) Qualified Professional Engineer Certification 40 CFR (b)(4) and (d)(3)... 5 List of Tables Table 1. Schedule of Closure Activities... 4 List of Figures Figure 1. Pawnee Power Station CCR Landfill Location Map... 2 i

3 Table of Abbreviations and Acronyms Abbreviation ADF amsl CCR CFR cm/sec PSCo Definition Ash Disposal Facility above mean sea level Coal Combustion Residuals Code of Federal Regulations Centimeters per Second Public Service Company of Colorado ii

4 1.0 General Information On April 17, 2015 the U.S. Environmental Protection Agency (EPA) published the Disposal of Coal Combustion Residuals (CCR) from Electric Utilities; Final Rule (40 CFR 257 and 261) (Federal CCR Rule). The rule defines a set of requirements for the disposal and handling of CCR within CCR units. The requirements include preparation of a Closure Plan for all existing and new CCR landfills. The Pawnee Station Power Plant, operated by the Public Service Company of Colorado (PSCo), an Xcel Energy company, is located at Morgan County Road 24, Brush, Colorado, approximately 4 miles southwest of Brush, Colorado. Pawnee Station operates a CCR) landfill located on the plant property approximately one-half mile southwest of the main power plant building. The Pawnee Station CCR landfill is subject to the CCR rule. The Morgan County Commissioners approved construction and operation of the landfill for ash and raw water treatment solids in 1976 as part of the Special Use Permit issued for construction of Pawnee Station. The landfill has been in continuous use since 1981 when the plant started operations, with ash disposal in the northern half and lime sludge disposal in the southern half. The landfill is operated under an Engineering Design and Operations Pan developed pursuant to Colorado Department of Public Health and Environment Solid Waste Regulations. The CCR landfill subject to the CCR Rule is limited to the northern portion of the landfill, and encompasses an area of approximately 22 acres. A location map of the CCR landfill is provided on Figure 1. In accordance with 40 CFR 257 Disposal of Coal Combustion Residuals From Electrical Utilities (b), owners of CCR disposal units are required to publish a written closure plan that, describes the steps necessary to close the CCR unit at any point during the active life of the CCR unit consistent with recognized and generally accepted good engineering practices. This closure plan fulfills the requirements of 40 CFR (b). 1

5 Figure 1. Pawnee Power Station CCR Landfill Location Map 2

6 2.0 Description of Closure Plan (b)(1)(i-iii) According to 40 CFR (d) - Closure performance standard when leaving CCR in place the final cover system designed to have a permeability less than or equal to any bottom liner system or natural subsoils present, or a permeability no greater than 1x10-5 centimeters per second (cm/sec). The landfill was constructed with the base cut into native Pierre Shale bedrock, which is approximately 5,000 feet thick in this area. The bedrock has a permeability of approximately 1x10-8 cm/sec, and acts as a natural barrier to potential seepage. Therefore, no engineered liner was constructed. The current closure plan includes installation of a cover with a maximum permeability of 1x10-8 cm/sec. The cover may be constructed of on-site soils which can achieve a maximum permeability of 1 x 10-8 cm/sec, or on-site soils amended with bentonite, soils imported from off-site, or a composite synthetic cover system. Regardless of which type of cover is installed, a soil layer will be installed, tracked and seeded. Vegetative cover is an important part of the final cover system as it provides long-term stabilization of the slopes, limits erosion due to stormwater run-off, and reduces the potential for wind blown nuisance dust. The final cover will be vegetated with plants of native and hybrid seeds commonly used in the semi-arid western mountain states. The landfill will require approximately 70,000 cubic yards of soil for final cover and closure, if the final cover design does not include a geomembrane component. This material will be borrowed from the existing borrow area immediately west of the landfill or imported as needed. The final cover will have a grade that promotes surface water run-off and minimizes erosion. The slope of the final cover on the top of the landfill will be no less than 5% and the final cover side slopes will be no greater than 25% (4 horizontal feet to 1 vertical foot). A 5% slope will be sufficient to convey any precipitation runoff from the top of the landfill to downchute conveyance structures located at the perimeter of the landfill. Small swales along the tops and sidewalls of the landfill will direct precipitation runoff to the downchute conveyance structures. PSCo will initiate closure activities when the landfill reaches final grades. The facility will utilize a final cover design meeting the requirements of 40 CFR Inventory Estimate (b)(1)(iv) In accordance with (b)(1)(iv), an estimate of the maximum inventory of CCR ever on site over the active life of the CCR Landfill must be provided. Pawnee Station began operations in 1981 and generated approximately 65,000 cubic yards of CCR per year through 2013, resulting in approximately 2.1 million cubic yards of CCR generated over this time period. However, from about 1996 through 2013, the majority of CCR was sold for beneficial use. Therefore, the estimated inventory of CCR in the landfill at the end of 2013 was approximately 975,000 cubic yards. Sale of CCR for beneficial use ceased in 2014, and all CCR since 2014 has been disposed in the landfill. The estimated remaining air space in the CCR landfill at the end of 2013 was approximately 600,000 cubic yards. Therefore, the final inventory of CCR in the landfill at closure is estimated to be 1,575,000 cubic yards. 3

7 4.0 Area Requiring Final Cover (b)1(v) In accordance with 40 CFR (b)(1)(v), an estimate of the largest area of the CCR unit ever requiring a final cover must be provided. PSCo will install the final cover system as areas reach final capacity using a cap-as-you-go methodology. At any given time, the largest area containing CCR that will require a final cover is estimated to be approximately 22 acres. 5.0 Schedule of Closure Activities (b)1(vi) Table 1. Schedule of Closure Activities Task Start Date Finish Date (Initiation of Cell Closure) Written Closure Plan October 17, 2016 October 17, 2016 Written Post-Closure Plan October 17, 2016 October 17, 2016 Last Receipt of CCR On-going Year 2018 Landfill Closure Year 2018 Year 2018 Annual Inspections Annually Year 2018 Fugitive Dust Plan Updates Annually Year 2018 Post Closure Maintenance Year 2018 Year 2048 (minimum) 4

8 6.0 Qualified Professional Engineer Certification (b)(4) and (d)(3) In accordance with 40 CFR (b)(4), the owner or operator of the CCR unit must obtain a written certification from a qualified professional engineer that the initial and any amendment of the written closure plan meets the requirements of this section. In accordance with 40 CFR (d)(3), the owner or operator of the CCR unit must obtain a written certification from a qualified professional engineer that the design of the final cover system meets the requirements of this section. I, Douglas T. DeCesare, being a registered Professional Engineer, in accordance with the Colorado State Board of Licensure for Architects, Professional Engineers, and Professional Land Surveyors, do hereby certify to the best of my knowledge, information, and belief, that the information contained in this written Closure Plan dated October 17, 2016, was conducted in accordance with the requirements of 40 CFR (b) and (d), is true and correct, and was prepared in accordance with recognized and generally accepted good engineering practices. SIGNATURE: Colorado PE DATE: October 14,