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S E C ® R Conceptual Site Model March 24, 2004 Page 7 limits Soil located adjacent to the northwestern corner of the former dispenser island is delineated laterally and vertically Soil located to the northeast, east and south of the former dispenser islands is not delineated laterally and vertically i 4 12 3 UST and Pump Island Additional Over-Excavation Soil samples were collected from soil adjacent to the former dispenser islands (OX1 and OX2) at 11 feet bgs and 12 feet bgs, the former UST and former dispenser island excavation sidewalls (0XS1, OXS2, and OXS3) at depths ranging from 9 feet bgs to 16 5 feet bgs and, the formefeT and VM. r former dispenser island excavation bottom (OXB1 through OXB4) at depths ranging from et bgs � [ to 19 feet bgs Petroleum hydrocarbons were reported above laboratory reporting limits in all sod samples analyzed with the exception of OXS2 collected at 9 feet bgs and OXB3 collected at 8 5 feet bgs Sod samples collected along the western UST over-excavation were reported either below laboratory reporting limits or at low levels indicating that petroleum hydrocarbons are defined adjacent to the former dispenser islands conveyance piping Petroleum hydrocarbons do not appear to be defined in the vicinity of the southwest corner of the former UST excavation w 41 3 August 2000; Site Assessments During site assessment activities three soil samples were collected from SB-2 and submitted for chemical analysis CPT borings identified three discrete water bearing zones at approximately 35 feet bgs, 50 feet bgs, and 80 feet bgs Groundwater was gauged at approximately 19 feet bgs in 3000 Sod samples collected from SB-2 were analyzed for TPHg, BTEX and MtBE TPHg and ethyl-benzene was detected in the sod sample collected at 27 feet bgs Soil samples collected at 20 feet bgs and 82 feet bgs were reported below laboratory reporting limits 41 4 Petroleum Hydrocarbons Adsorbed In Soil The maximum historical concentrations of petroleum hydrocarbons in sod appear to be located in the vicinity of the former dispenser islands and former UST locations and may extend to a depth greater than 30 feet bgs Historical maximum concentrations of TPHg, TPHd, STEX, and MtBE are presented in sections 3 1 through 3 4 Historical soil analytical data is presented in Appendix B Historical detections of benzene and TPHg, in sod are presented on Figure 8 -For SB-1) 5 t3-Z M LJ-f MW-2— ark6l.rn WW'30Alti 4 14 1 Estimated Mass of Petroleum Hydrocarbons Remaining In Soil This mass calculation was based on historical data (Appendix B) For this estimate the following conservative assumptions were made The area of impacted soil at the site consists of one contiguous area, • Impacted soil in the area of the former dispense islands and UST pit was excavated to an approximate depth of 3 5 feet bgs and 15 feet bgs, respectively Impacted soil remaining on-site extends from 16 feet bgs to a depth of approximately-24-5-feet bgs or first encountered groundwater, 35 �m • Soil concentrations in the former dispenser island and UST areas-+s equal to maximum concentrations found in sod during dispenser islands and UST removal activities, I IC'ievron1920331REPORTSICSM\CSKA 92033(REV B) doc N