1. Regulation Requirements (a)(2)

Transcription

1 16644 West Bernardo Drive, Suite 31 San Diego, CA Phone: Fax: HAZARD POTENTIAL CLASSIFICATION ASSESSMENT ASH POND 2 JOLIET 29 STATION OCTOBER 216 This initia hazard potentia cassification assessment (HPCA) addresses the requirements of (a)(2) of the Coa Combustion Residuas (CCR) reguations, Code of Federa Reguations Tite 4, Part 257 for Ash Pond 2 at the Joiet 29 Station (Site) in Joiet, Iinois. The CCR reguations were pubished in the Federa Register on 17 Apri 215 and became effective as of 19 October 215. The Site is currenty a gas-fired power station, owned and operated by Midwest Generation, LLC (Midwest Generation). The Station previousy operated as a coa-fired power station through March 216. Ms. Jane Soue, P.E., of Geosyntec, prepared this HPCA in accordance with (a)(2). Mr. Robert White reviewed this report in accordance with Geosyntec s peer review poicy. Summary Based on the resuts of the anaysis provided in this report, Ash Pond 2 is cassified as a significant hazard potentia CCR surface impoundments because a faiure woud not resut in probabe oss of ife, but coud resut in economic and environmenta osses. 1. Reguation Requirements (a)(2) Accorng to the Preambe of the CCR reguations (page 21377), a hazard potentia cassification provides an incation of the potentia for danger to ife, deveopment, or the environment in the event of a reease of CCR from a surface impoundment. This cassification is not an assessment of the ikeihood of a reease or faiure, but rather an evauation of the potentia impacts if one were to occur. Per (a)(2), the owner or operator must document the hazard potentia of each CCR unit as either a high hazard potentia CCR surface impoundment, a significant hazard potentia CCR surface impoundment or a ow hazard potentia surface impoundment. The assessment must incude certification from a quaified professiona engineer stating that the initia hazard potentia cassification (and each subsequent perioc cassification) was conducted in accordance with these requirements. Section provides the foowing definitions for hazard potentia cassifications: A high hazard potentia CCR surface impoundment means a ked surface impoundment where faiure or mis-operation wi probaby cause oss of human ife; SW JOLIET HPCA.F.DOCX 1

2 Ash Pond 2, Joiet 29 Station Hazard Potentia Cassification Assessment October 216 A significant hazard potentia CCR surface impoundment means a ked surface impoundment where faiure or mis-operation resuts in no probabe oss of human ife, but can cause economic oss, environmenta damage, sruption of ifeine faciities, or impact other concerns; and A ow hazard potentia CCR surface impoundment means a ked surface impoundment where faiure or mis-operation resuts in no probabe oss of human ife and ow economic and/or environmenta osses. Losses are principay imited to the surface impoundment owner s property. Based on the definitions contained in , a demonstration that an impoundment does not quaify for either a ow or high hazard potentia cassification resuts in a hazard cassification of significant by defaut. 2. Site Pan The Site is bounded on the north by U.S. Route 6 and on the south by the Des Paines River. Because of geographic constraints, the watershed area for the Site is imited. A Site Pan identifying the Pond and key Site eements, incung buings and other surface waters, is shown in Figure 1. Ash Pond 2 is east of the main powerbock buing and approximatey 4 feet north of the Site s intake cana which connects to the Des Paines River. Pond 1 is ocated west of Ash Pond 2 and has embankment crest eevations consistent with those of Ash Pond 2 (approximatey 535 feet Mean Sea Leve [MSL]). A surface water coection pond is ocated south of Ash Pond 2. The Site sopes southward from a maximum eevation of approximatey 54 feet MSL aong the northern perimeter to eevations of approximatey 58 to 514 feet MSL aong the banks of the inet cana to the south. Based on site observations and a review of avaiabe construction documents, Ash Pond 2 was constructed with eevated embankments on the south, east, and west perimeters. There are no embankments on the north side of the pond where existing ground eevations generay increase to the north and a 5-foot high, non-structura berm exists between Ash Pond 2 and US route 6. Due to these topographic constraints, run-on to the Pond is generay imited to the embankment crests and access road aong the north of the embankment. The Pond capacity and embankment height are shown in Tabe 1 beow. Tabe 1: Estimated Capacity and Maximum Height Estimated Capacity Estimated Maximum Embankment Height 45. acre-feet 19 feet SW JOLIET HPCA.F.DOCX 2

3 Ash Pond 2, Joiet 29 Station Hazard Potentia Cassification Assessment October Pond Faiure Impact Evauation In order to cassify the hazard potentia of the Pond, impacts of a potentia faiure must be evauated. Due to the proximity of the Pond to the Site s inet cana, which is connected to the Des Paines River, potentia faiure of the southern embankment of the Pond coud resut in environmenta osses resuting from scharge of CCR and/or CCR-aden water to a water of the United States. This potentia impact excudes the Pond from a ow hazard cassification. The next step in cassification is to evauate the potentia for faiure or mis-operation to cause oss of human ife by modeing the most critica breach scenario. Figure 1 identifies the ocation of buings in the vicinity of the Pond, incung both occupied and unoccupied buings 1. Occupied buings, incung the main power bock, are ocated approximatey 3 feet to 8 feet south and west of the Pond; no occupied buings are ocated east of the Pond within the potentia impact area. Potentia faiure modes were evauated to determine the ocation of a breach with the greatest potentia impact on human ife. Faiure of the western embankment of Ash Pond 2 (recty adjacent to Pond 1) is not anticipated to instigate a faiure of the Pond 1 embankments, as the embankment crests for Pond 1 and Ash Pond 2 are at simiar eevations. Based on visua observation of site topographic contions and the ocation of nearby buings, a breach of the southern embankment of the Pond coud resut in a potentia impact on human ife. As such, the modeed embankment breach scenario assumes that the breach woud occur in the southern embankment. Detaied modeing, scussed beow, was used to assess the impact of a potentia faiure of the southern embankment. 3.1 Southern Embankment Faiure Modeing Breach modeing was performed for a scenario where the Pond is at fu capacity prior to embankment faiure and downstream depressions or other surface water coection ponds within the impact area are fu and not capabe of containing adtiona fow (food contions faiure scenario). As scussed in Section 2, run-on to the Pond is imited and infow is generay imited to rect precipitation. Therefore, modeing of the Probabe Maximum Precipitation (PMP) or other precipitation frequency event was not performed as the infow of the precipitation event is minima compared to the capacity of the Pond. 2 1 ng identification numbers used in this report were generated for reference purposes ony and may not correspond to identifications names or numbers utiized at the Site. ngs are assumed to be occupied if there is at east one human occupant for a minimum of 12 hours per day. 2 The tota voume of rect precipitation from PMP event during the estimated duration of the faiure (ess than 24 minutes) is minima compared with the voume that woud be reeased during a faiure. SW JOLIET HPCA.F.DOCX 3

4 Ash Pond 2, Joiet 29 Station Hazard Potentia Cassification Assessment October 216 HEC-HMS Version 4.1 (HEC-HMS, 213) modeing software was used to estimate the breach hydrographs which are pots of the rate of fow over time. A FLO-2D mode (FLO-2D, 29) was then used to estimate fow depth and veocity resuting from the seected hydrograph. The resuts of the modeing are described beow. Detais of the modeing methods and procedures are provided in Geosyntec (216). The cacuated maximum fow depth and maximum veocity from the Pond breach modeing are shown in Figures 2 and 3, respectivey. The resuts of the FLO-2D mode show that fow through the modeed breach traves from Ash Pond 2 toward the south, southeast, and southwest with a majority of the fow heang southwest. Fow from the Pond eventuay reaches the inet cana to the south. ngs impacted by Ash Pond 2 faiure incude ng 8, 9, 1 (occupied) and ngs 7, 11, and 12 (unoccupied). Tabe 2 beow summarizes the estimated water depths and veocities for the buing impacted by the Ash Pond 2 faiure. Tabe 2: Estimated Water Depths and Veocities near ngs ng Estimated Maximum Fow Depth (feet) Estimated Maximum Fow Veocity (f) ng 8 (Occupied) ng 9 (Occupied) ng 1 (Occupied) ng 7 (Unoccupied) ng 11 (Unoccupied) ng 12 (Unoccupied) Hazard Cassification Assessment A CCR surface impoundment is cassified as having a high hazard potentia if faiure or mis-operation wi probaby cause oss of human ife. Guideines for evauating potentia oss of ife during food contions are provided in USBR (1988). Figure 4, adapted from USBR (1988), presents a reationship between danger to human ife and food fow depth and veocity for a house-type structure. Figure 4 presents the modeed depth-veocity combinations for the occupied buings within the impact zone. As seen on Figure 4, the modeed resuts incate that the occupied buings are considered to be within the ow danger zone which corresponds to zero ives seriousy in danger from that particuar scenario (USBR, 1988). SW JOLIET HPCA.F.DOCX 4

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6 Ash Pond 2, Joiet 29 Station Hazard Potentia Cassification Assessment October References FLO-2D, 29. FLO-2D Basic, FLO-2D Software, Inc., Arizona 29. Geosyntec, 216. Ash Pond 2 Hazard Potentia Cassification Assessment Embankment Breach Anaysis, Joiet 29 Station, Joiet, Iinois, October. HEC-HMS, 213. HEC-HMS Hydroogic Modeing System User s Manua, Version 4., U.S. Army Cor of Engineers, Hydroogic Engineering Center (HEC), Davis, Caifornia, December 213. United States Department of the Interior, Bureau of Recamation (USBR), Downstream Hazard Cassification Guideines, ACER Technica Memorandum No. 11. Attachments Figure 1 Site Map Figure 2 Ash Pond 2 Food Contions Maximum Fow Depth Figure 3 Ash Pond 2 Food Contions Maximum Veocity Figure 4 Estimated Food Danger Leves SW JOLIET HPCA.F.DOCX 6

7 p ng 5 Ash Pond 2 ng 13 ng 4 ng 7 Pond 1 ng 3 ng 2 ng 12 ng 8 Cana e k Inta ng 6 Surface Water Coection Pond ng 1 ng 11 Path; author; dd-mmm-yyyy; ProjNum-Task-Phase; Document Number; etc. Main Powerbock ng ng 9 De ng 1 Legend Unoccupied es r Site Map Ash Pond 2 - Joiet 29 Midwest Generation, LLC Joiet, Iinois ngs Occupied n a i P s ve Ri Feet San Diego October 216 Figure 1

8 p ng13 Ash Pond 2 ng4 ng5 V 9. 1f Pond 1 ng7 ng3 ng8 ng2 Legend V 15. 3f ng12 3f ng6 e Intak ng9 Surf ac ew ater Co ec ti o npo nd V 2. 9f Co mp utati o nabo undary ng1 1 CCRPo nd ngs Occup i ed Path; author; dd-mmm-yyyy; ProjNum-Task-Phase; Document Number; etc. Cacuated Maximum f Main Powerbock ng Uno ccup i ed Fow Depth (feet) ng1 ng n a i P s es ve Ri r Joiet 29 - Ash Pond 2 Food Contions - Maximum Fow Depth Mi dw es tgenerati o n,llc J o i et,i i no i s >5. De 4f Cana Feet SanDi ego Octo ber 216 Fi gure 2

9 p ng13 Ash Pond 2 ng5 ng4 V 9. 1f Pond 1 ng7 ng3 ng8 ng2 V 15. 3f ng12 3f ng6 Legend e Intak ng9 ng1 1 CCRPo nd ngs Occ up i ed Path; author; dd-mmm-yyyy; ProjNum-Task-Phase; Document Number; etc. Cacuated Maximum Fow Veocity (f) 1-2 8f Main Powerbock ng Uno cc up i ed -1 ng1 ng1 n a i P s es ve Ri r Joiet 29 - Ash Pond 2 Food Contions - Maximum Veocity Mi dw es tgenerati o n,llc J o i et,i i no i s 3-4 >5 De 4f Surf ac ew ater Co ec ti o npo nd V 2. 9f Co mp utati o nabo undary Cana Feet SanDi ego Octo ber 216 Fi gure 3

10 = Prected maximum veocity and depth of water at occupied buings resuting from potentia faiure of Ash Pond 2. Estimated Food Danger Leves Ash Pond 2 - Joiet 29 Midwest Generation, LLC Wi County, Iinois Adapted from Figure 2, USBR (1988), for houses/buings buit on foundations. San Diego October 216 Figure 4