Initial Inflow Design Flood Control System Plan

Transcription

1 Initial Inflow Design Flood Control System Plan Upper AQC Impoundment La Cygne Generating Station Kansas City Power & Light Company October 1, 216

2 Table of Contents Table of Contents 1 Introduction Purpose Regulatory Requirements Brief Description of Impoundment Design and Construction Inflow from Plant Operations and Stormwater Runoff Outlet Structures Plan Approach Hydrologic Analysis Design Storm Rainfall Data Runoff Computations Hydraulic Analyses Process Flows Storage Capacity Discharge Analysis Results Inflow Analysis (a)(1) Outflow Analysis (a)(2) Inflow Design Flood (a)() Discharge (b) Conclusions Limitations Certification Statement References October 1, 216 Page i

3 Table of Contents Tables Table 1-1 Table 4-1 Table 4-2 CCR Rule Cross Reference Table Summary of Hydrologic and Hydraulic Analysis Summary of Outlet Works Appendices Appendix A Figure 1 Location Map Figure 2 Watershed Area Map October 1, 216 Page ii

4 Introduction 1 Introduction 1.1 Purpose The purpose of this is to document that the requirements specified in 4 CFR of the Coal Combustion Residual (CCR) Rule 1 have been met for the Upper AQC Impoundment at Kansas City Power & Light Company s (KCP&L) La Cygne Generating Station. The Upper AQC Impoundment is an existing CCR surface impoundment as defined by 4 CFR Regulatory Requirements In accordance with the CCR Rule, this plan documents how the inflow design flood control system has been designed and constructed to meet the requirements of 4 CFR referenced below and is supported by appropriate engineering calculations. This shall be completed no later than October 17, 216. Periodic inflow design flood control system plans shall be prepared every five years. The date of completing the initial plan is the basis for establishing the deadline to complete the first periodic plan. This plan shall be amended whenever there is a change in conditions that would substantially affect the written plan in effect. Regulatory Citation: 4 CFR (a); Design, construct, operate, and maintain an inflow design flood control system as specified: (1) Inflow design flood control system must adequately manage flow into the CCR unit during and following the peak discharge of the inflows design flood specified in paragraph (); (2) The inflow design flood control system must adequately manage flow from the CCR unit to collect and control the peak discharge resulting from the inflow design flood specified in paragraph (); () The inflow design flood is: (i) For a high hazard potential CCR surface impoundment, the probable maximum flood; (ii) For a significant hazard potential CCR surface impoundment, the 1,-year flood; (iii) For a low hazard potential CCR surface impoundment, the 1-year flood; or (iv) For an incised CCR surface impoundment, the 25-year flood. Regulatory Citation: 4 CFR (b); Discharge from the CCR unit must be handled in accordance with the surface water requirements under: Brief Description of Impoundment The La Cygne Generating Station is a coal-fired power plant located near La Cygne in Linn County, Kansas. The Station is located approximately 6.25 miles east of the city of La Cygne and is bordered to the west by La Cygnes Lake. The Upper AQC Impoundment is located on plant property. A site Location Map showing the area surrounding the station is in Figure 1 of Appendix A Design and Construction The original construction of the Upper AQC Impoundment was substantially completed in The Impoundment was constructed with embankments having an approximately maximum height of 5 feet and a crest elevation of 89 ft 2. The embankments have 2.5 horizontal to 1. vertical side slopes. The impoundment currently has a water surface area of approximately 88 acres at a conservatively high operating level of feet October 1, 216 Page 1-1

5 Introduction and a main Upper AQC Impoundment surface area of approximately 98 acres at the zero freeboard elevation of Inflow from Plant Operations and Stormwater Runoff The Upper AQC Impoundment is primarily used as a holding basin for formerly sluiced CCR water and materials from the La Cygne Generating Station and storm water management. The watershed for the Upper AQC Impoundment includes the access road around the perimeter of the embankment as well as the entirety of the area within the embankment. There is no watershed area outside of the limits of the Upper AQC Impoundment. 1.. Outlet Structures The principle spillway for the Upper AQC Impoundment is located at the south side of the impoundment and consists of a 6 foot wide by 9 foot long by 22 feet high concrete riser fitted with stop logs. Stop logs are added or removed to manage operational water levels in the impoundment. The concrete riser is connected to a -inch corrugated metal pipe (CMP) that discharges to the Lower AQC Impoundment to the south. The impoundment also has an auxiliary spillway. The auxiliary spillway is a 5 ft. wide riprap lined channel that extends over the crest of the embankment and along the downstream slope and discharges into a drainage swale. The design plans show that the opening for the spillway is ft. lower than the top of embankment and has a 1 ft. thick, 66 ft. wide, 4 ft. deep seepage cut off wall at the inside crest. The auxiliary spillway does not discharge into the Lower AQC Impoundment, but rather discharges into a drainage swale that slopes downward to the west and discharges into La Cygnes Lake. The auxiliary spillway is functioning; however, to be conservative, the auxiliary spillway was not considered when analyzing the outlet from the Upper AQC Impoundment. 1.4 Plan Approach Analyses and calculations completed for the hydrologic and hydraulic assessments of the Upper AQC Impoundment are described in this plan. Data and analyses results are based on information shown on design drawings, topographic surveys, information about operational and maintenance procedures provided by KCP&L, and field observations by AECOM. The analysis approach and results of the hydrologic and hydraulic analyses are presented in the following sections. The results of this analysis will be used by AECOM to confirm that the Upper AQC Impoundment meets the hydrologic and hydraulic capacity requirements of the rules referenced above for CCR surface impoundments. Table 1-1 cross references the Plan sections to the applicable CCR Rule requirements. Table 1-1 CCR Rule Cross Reference Table Plan Section Title CCR Rule Reference 4.1 Inflow Analysis (a)(1) 4.2 Outflow Analysis (a)(2) 4. Inflow Design Flood (a)() 4.4 Discharge handled in accordance with (b) October 1, 216 Page 1-2

6 Hydrologic Analysis 2 Hydrologic Analysis 2.1 Design Storm The La Cygne Upper AQC Impoundment has been categorized by others 8 as a Low Hazard Potential CCR Impoundment, which indicates that the inflow design flood is the 1-year return frequency design storm event. 2.2 Rainfall Data The rainfall information used in the analysis was based on the National Oceanic and Atmospheric Administration (NOAA) Atlas 14, Volume 8, Version 2 4 which provides rainfall data for storm events with average recurrence intervals ranging from 1 to 1, years and durations ranging from 5 minutes to 6 days. The design storm rainfall depth, obtained from the NOAA website, is 8.6 inches for the 24-hour, 1-year storm The Soil Conservation Service (SCS) Type II rainfall distribution used by AECOM is appropriate to use for storms up to the 1,-year flood at the project site. 2. Runoff Computations The watershed areas for the Upper AQC Impoundment were determined using a computer-aided design (CAD) analysis of the Topographic Survey by Tukuh Technologies, LLC dated July 21, with corresponding aerial photography. The total watershed area to the impoundment is approximately 28. acres and is subdivided into nine sub-watersheds. Sub-dividing the Upper AQC Impoundment into sub-watersheds takes full advantage of upstream storage capacity in the various enhanced evaporation areas and provides a more accurate peak inflow to the main Upper AQC storage area. See Figure 2 in Appendix A for the Watershed Map. Runoff was calculated using the SCS Curve Number Method, where curve numbers (CN) were assigned to each sub-catchment based on the type of land cover and soil type present. Using the USDA Natural Resources Conservation Service (NRCS) Web Soil Survey 6, the soil type of the site was determined to be almost exclusively hydrologic soil group D. CN values for the land cover were selected from the SCS NRCS Technical Release-55 publication 7. Gravel roads and Water Surface land covers that are located on site were determined to have a CN value of 89 and 98, respectively. A majority of land cover for the Upper AQC Impoundment watershed consists of CCR. Based on past project experience, a curve number of was selected for the CCR area. A composite CN was calculated for each sub-catchment area by summing the products of each CN multiplied by its percentage of the total area. Calculations for the weighted runoff curve numbers for each sub-watershed were performed in XPSWMM. The time of concentration is commonly defined as the time required for runoff to travel from the most hydrologically distant point to the point of collection. Calculations for the time of concentration for each subwatershed were performed in XPSWMM. Stormwater runoff from the 1-year event into the southernmost node of the Upper AQC Impoundment has a peak runoff inflow of 289 cfs and total runoff inflow volume of 21 acre-feet. October 1, 216 Page 2-1

7 Hydraulic Analyses Hydraulic Analyses.1 Process Flows CCR sluicing operations to the Upper AQC Impoundment have been discontinued. Thus there are no inflows to the impoundment other than precipitation..2 Storage Capacity The storage volumes for the Upper AQC Impoundment were determined using a CAD analysis of the 216 Topographic Survey by Tukuh 5. The calculated volume of the Upper AQC Impoundment is approximately 194. acre-feet of available storage measured from the conservatively high operating pool elevation of feet to the zero freeboard elevation of 889. feet.. Discharge Analysis A hydraulic model was created in XPSWMM 216 to assess the capacity of the impoundment to store and convey the stormwater flows. XPSWMM has the capability to evaluate each storage area within the network, to respond to variable tailwater, dual drainage paths, and reversing flows. This dynamic interconnected impoundment routing makes the XPSWMM program an efficient tool for this evaluation. The analyzed scenario assumes the starting water surface elevation of the Upper AQC Impoundment is feet, the water surface elevation at the time of the 216 Topographic Survey. The invert elevation stop logs in the principle outlet structure was assumed to be at elevation assuming there is zero discharge at the start of the simulation. The IDF inflow is stored in the Upper AQC Impoundment and then discharged through the primary spillway into the Lower AQC Impoundment. October 1, 216 Page -1

8 Results 4 Results The hydrologic and hydraulic conditions of the Upper AQC Impoundment were modeled with the peak discharge of the 1-year storm event. 4.1 Inflow Analysis (a)(1) Adequately manage flow into the CCR unit during and following the peak discharge of the inflow design flood. Background and Assessment Using the XPSWMM model, the total inflow was stored and routed through the various swales, culverts, and dike openings of the Upper AQC Impoundment to determine the peak water surface elevations. Table 4-1 summarizes the water surface elevations of the Upper AQC Impoundment prior to and after the inflow design flood. Table Summary of Hydrologic and Hydraulic Analysis CCR Unit Upper AQC Impoundment 1-Year, 24-Hour Storm Notes: * WSE = Water Surface Elevation Beginning WSE* (feet) Peak WSE (feet) Min. Crest Elevation 5 (feet) Freeboard Above Peak WSE (feet) Conclusion and Recommendation As there is adequate storage within the Upper AQC Impoundment to manage the inflow design flood, there is no anticipated overtopping of the embankments, which meets the requirements in (a)(1). 4.2 Outflow Analysis (a)(2) Adequately manage flow from the CCR unit to collect and control the peak discharge resulting from the inflow design flood. Background and Assessment Using the XPSWMM model, the total inflow due to rainfall runoff was stored and routed to the outlet riser at the south end of the Upper AQC Impoundment to determine the peak water surface elevations. October 1, 216 Page 4-1

9 Results Table 4-2 summarizes the peak flow rates and velocities through the outlet. Table Summary of Outlet Works Invert Elevation Peak Flowrate Velocity at Peak Flowrate Storm Event (feet) (cfs) (fps) 1-Year, 24-Hour Conclusion and Recommendation As the Upper AQC Impoundment outlet manages the discharge of the inflow design flood without the peak water surface elevation overtopping the embankment, the impoundment meets the requirements in (a)(2). 4. Inflow Design Flood (a)() Required Inflow design flood for Low Hazard Surface Impoundments. Background and Assessment The calculations for the inflow design flood are based on the hazard potential of the impoundment. The different classifications of the impoundment hazard potential are high, significant, and low. Conclusion and Recommendation As the impoundment hazard potential category is Low 8, the 1-year design storm was utilized in the analysis, which meets the requirements in (a)(). 4.4 Discharge (b) Discharge from the CCR unit handled in accordance with the surface water requirements under: Background and Assessment The discharge from the Upper AQC Impoundment outlet riser enters a discharge pipe that leads to the Lower AQC Impoundment. The discharge must meet the requirements of the NDPES under Section of the Clean Water Act to meet the above requirement of the CCR rule. Conclusion and Recommendation Discharge from The Upper AQC Impoundment flows to the Lower AQC Impoundment which is a zero discharge site under normal operating conditions, but is allowed to discharge following significant events under a NPDES permit. Therefore, the facility does not cause a discharge of pollutants into waters of the United States that is in violation of the requirements of the NPDES under Section of the Clean Water Act, and thereby meets the requirements in (b). October 1, 216 Page 4-2

10 Conclusions 5 Conclusions The hazard classification assessments conducted by others concluded that the Hazard Potential category of the impoundment is Low 8. The inflow design flood control system of the Upper AQC Impoundment adequately manages flow into the CCR unit during and following the peak discharge of the 1-year, 24-hour frequency storm event inflow design flood. The inflow design flood control system of the Upper AQC Impoundment adequately manages flow from the CCR unit to collect and control the peak discharge resulting from the 1-year, 24-hour frequency storm event inflow design flood. Discharge from the Upper AQC Impoundment is handled in accordance with the surface water requirements of 257. during the 1-year, 24-hour flood event. Therefore, the Upper AQC Impoundment meets the requirements for certification. The contents of this plan, specifically Sections 1 through 5, represent the Initial Inflow Design Flood Control System Plan for this unit. October 1, 216 Page 5-1

11 Limitations 6 Limitations Background information, design basis, and other data have been furnished to AECOM by KCP&L, which AECOM has used in preparing this plan. AECOM has relied on this information as furnished, and is not responsible for the accuracy of this information. Our recommendations are based on available information from previous and current investigations. These recommendations may be updated as future investigations are performed. The conclusions presented in this plan are intended only for the purpose, site location, and project indicated. The recommendations presented in this plan should not be used for other projects or purposes. Conclusions or recommendations made from these data by others are their responsibility. The conclusions and recommendations are based on AECOM s understanding of current plant operations, maintenance, stormwater handling, and ash handling procedures at the station, as provided by KCP&L. Changes in any of these operations or procedures may invalidate the findings in this plan until AECOM has had the opportunity to review the findings, and revise the plan if necessary. This hydrologic and hydraulic analysis was performed in accordance with the standard of care commonly used as state-of-practice in our profession. Specifically, our services have been performed in accordance with accepted principles and practices of the hydrologic and hydraulic engineering profession. The conclusions presented in this plan are professional opinions based on the indicated project criteria and data available at the time this plan was prepared. Our services were provided in a manner consistent with the level of care and skill ordinarily exercised by other professional consultants under similar circumstances. No other representation is intended. October 1, 216 Page 6-1

12 AECOM Certification Statement 7 Certification Statement CCR Unit: KCP&L La Cygne Generating Station, Upper AQC Impoundment I, Brian D. Linnan, being a Registered Professional Engineer in good standing in the State of Kansas, do hereby certify, to the best of my knowledge, information, and belief that the information contained in this certification has been prepared in accordance with the accepted practice of engineering. I certify, for the above referenced CCR Unit, that the dated October 1, 216, which includes all pages in Sections 1 through 5, meets the requirements of 4 CFR Brian D. Linnan Printed Name October 1, 216 Date Brian D. Linnan Digitally signed by Brian D. Linnan Date: :6:5-5'' AECOM 28 McGee Street, Suite 2 Kansas City, Missouri October 1, 216 Page 7-1

13 References 8 References 1. U.S. Environmental Protection Agency, Standards for the Disposal of Coal Combustion Residuals in Landfills and Surface Impoundments, 4 CFR 257. Federal Register 8, Subpart D, April 17, AECOM, History of Construction Report, Upper AQC Impoundment, La Cygne Generating Station, Kansas City Power & Light Company, dated October AECOM, Hydrologic and Hydraulic Support Calculations,, Upper AQC Impoundment, La Cygne Generating Station, Kansas City Power & Light Company, dated October 1, National Oceanic and Atmospheric Administration, NOAA Atlas 14 Point Precipitation Frequency Estimates, Volume 8, Version 2, dated Tukuh Technologies, LLC, Topographic Survey Plans for the La Cygne Generating Station dated July 21, USDA Natural Resources Conservation Service, Web Soil Survey, dated USDA Natural Resources Conservation Service, Technical Release 55, dated June SCS Engineers, Initial Hazard Potential Classification Assessment Report, Upper AQC Impoundment, Kansas City Power & Light Company, La Cygne Generating Station, dated October 7, 216. October 1, 216 Page 8-1

14 Appendix A Figures October 1, 216

15 BOICOURT QUADRANGLE U.S. DEPARTMENT OF THE INTERIOR KANSAS-LINN CO. 7.5-MINUTE SERIES U.S. GEOLOGICAL SURVEY y Va' " 5 49 E LM D R LO OP Upper AQC Impoundment 1 VALLEY RD Cr MA I N SHOWALTER RD 1 ULLERY RD 9 8 FEET E 22 5 TH R D 47 E 2275TH RD ' " 94 7' " 2 FEET WOO DCU T DR SPRUCE DR 56 9 VD BL 9 Y 55 LE le 4' 54 F 9 5 ^ HOLIDAY DR E 2 5 TH RD 9 NEWBERRY DR 52 L VA Linn Valley Midd 48mN R R D N DR CA PE DE A A LV EL X BO S LINN VALLEY DR NN DR R MA LI 51 48mE 9 R O S E M A RI E D R 94 45' 8 22' " La Cygnes Lake 9 46 La Cygne 1 Ninety Six Cem! " # E MARKET ST «F ROBERTSON RD 152 «E MARKET ST La Cygne Generating Station E 8 8 N S ug ar C r 8 Cr Middle 2' E 21TH RD 8 69 E 21 RD E 21TH RD VAIL RD UMPHREY RD E 2TH RD E 2 RD East Mount Zion Cem E 2TH RD! " # 8 TAY L O R R D E 2TH RD SHOWALTER RD YANCEY RD ' " YANCEY RD 8 52 « KILOMETERS METERS Expressway KANSAS 6 FEET U.S. National Grid CONTOUR INTERVAL 1 FEET NORTH AMERICAN VERTICAL DATUM OF 1988 UC Grid Zone Designation 7 This map was produced to conform with the National Geospatial Program US Topo Product Standard, 211. A metadata file associated with this product is draft version Local Connector Local Road Secondary Hwy Ramp 1 UTM GRID AND 215 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET 1,-m Square ID 94 7' " X W Interstate Route 1 QUADRANGLE LOCATION ADJOINING QUADRANGLES Fontana New Lancaster Drexel La Cygne Amoret Mound City Pleasanton Worland 4WD. / US Route H State Route BOICOURT, KS 215 Figure 1 - Location Map NSN. NGA REF NO. U S G S X 2 4 K ' 57mE ROAD CLASSIFICATION * * MILS 56 SCALE 1:24 MILES 15S WAKEFIELD RD 6mN Ù GN 7 E 17TH RD 9 AL MI NE HA UL RD PR RD - O LD CO E 1 9 TH R D This map is not a legal document. Boundaries may be generalized for this map scale. Private lands within government reservations may not be shown. Obtain permission before entering private lands. Imagery...NAIP, July 214 Roads... U.S. Census Bureau, Names...GNIS, 215 Hydrography...National Hydrography Dataset, 214 Contours...National Elevation Dataset, 214 Boundaries...Multiple sources; see metadata file Public Land Survey System...BLM, 215 Wetlands...FWS National Wetlands Inventory «MN 1 19 MILS 41 Cr e dl 8 ve r s Ri id gne M Cy es sd 9 North American Datum of 198 (NAD8) World Geodetic System of 1984 (WGS84). Projection and 1 -meter grid: Universal Transverse Mercator, Zone 15S 1 -foot ticks: Kansas Coordinate System of 198 (south zone) ^ Produced by the United States Geological Survey 8 ai ar M 8 8 E 1TH RD E 1 RD E 19 5 T H R D N S ug ar C r ' " 8 8 Sway Back Cem E 18TH RD RD E 18 E 18TH RD! " # 9 8 C r 8 r uga NS FEET E RD E 17TH 17 RD Boicourt 7 8 BIOCOURT RD 52 RD EY LL VA Boicourt 6 Lake ar 9 M 9 69 Trading Cem Post! " # ' FEET ' '" 4' d id 8 M le C r TREGO RD 8 TUBBSLN ai s de sc y g ne sr i ve r VA I L R D VALLEY RD E 25TH RD WAKEFIELD RD 8 VALLEY RD TAYLOR RD 8 RD 8 44 TH 8 8 E 22TH RD E 215TH RD 9 2'

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