SITE INFORMATION AND CORRESPONDENCE_CASE 2

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CHRONOLOGY O OLOGY LATHROP GAS AND FOOD MART 14800 HIGHWAY 99,MANTECA 12/29/98 San Joaquin County. Environmental Health Department (EHD) issued a "No Further.Action Required" letter.for.this site after completion of the investigation of the underground storage tanks(USTs) that were removed in 1989.. 01/17/03 Eight soil samples were collected beneath the product piping and dispensers during system upgrades of the USTs installed in 1990. . Petroleum hydrocarbon concentrations were detected beneath dispenser D-1. for total petroleum hydrocarbons as gasoline (TPH-g) at 6,100. milligrams per kilogram (mg/kg), TPH as diesel (TPH-d) at 8,500 mg/kg, ethyl benzene at 11. mg/kg, and total xylenes at 137 mg/kg; and petroleum hydrocarbon concentrations were detected beneath D-4 for.TPH-d at 110 mg/kg, toluene at 0.005 mg/kg, and total xylenes at 0.006 mg/kg..Also, methyl tertiary-butyl ether(MTBE)was detected at 0.019 mg/kg and tertiary-butyl alcohol (TBA) was detected at 0.16 mg/kg in one stockpile sample, SP2A-213. . 05/27/03 EHD filed Notification of Hazardous Waste Discharge. 05/28/03 EHD.filed Unauthorized Release Form.#.03-Ul0. 09/03103. Site entered the.Local Oversight Program. 08/02-03/04 Three soil borings (B1, B2, and B3) were advanced, B1.to total depth of 40. feet below surface grade (bsg), B2 and B3 to total depths of 35. feet bsg. Hydrocarbon concentrations were found at 250 mg/kg for TPH-g, 190,mg/kg for TPH-d, and 0.51. mg/kg for total xylenes only at 15. feet bsg in B 1, located approximately two feet east of dispenser D 1. . Grab groundwatersamples were collected at each boring but only groundwater. collected from B 1 contained petroleum hydrocarbon contamination detected as THP-g at 2,100. micrograms per liter.(µg/Q, TPH-d at 7,200 gg/L., ethyl benzene at 7.9. µg/L, total xylenes at 63.µg/L,MTBE at 18 µg/L, and 1,2-dichloroethane(1,2-DCA)at 2.7 gg/L. 10/31/05. Date of Site Conceptual Model and request for. no further action for future. investigation at this site based on the following: • D1 was the source of contamination and the extent of contamination was localized because D1 was the only location where significant concentrations of petroleum hydrocarbons in soil were detected during underground storage tank (UST) system upgrades in 2003. Also, hydrocarbon contamination was found only in borehole Bl. located adjacent to D1. • Groundwater and soil samples collected from B 1, contained TPH-g that was identified as degraded gasoline by Cal Tech Environmental Laboratories,the laboratory that analyzed the samples..