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SP4 IL SEATTLE (FAX) 206 283 8036 TACOMA ,E PORTLANDSTOCry OCT 3 2002 RENO KTON l' Ta IDLRICHMOND OSANGEIES y i E TIME OIL tC,10o ENVIRONMENT HEALTH K s f E RV46��- 7 n s 2737 WEST COMMODORE WAY SEATTLE WA 98199 1233 PRooucrs P O BOX 24447 SEATTLE WA 98124-0447 TIME TESTES '* E October 28, 2002 Mr Harlin Knoll San Joaquin County Public Health Services Environmental Health Division P O Box 2009 Stockton, California 95201 RE Submittal of"Quarterly Monitoring Report, July-September 2002"for Jackpot Food Mart, 14000 E Highway 88, Lockeford, California (Property No 04-049) Dear Mr Knoll, An environmental investigation was implemented at the subject site in December 1994 to evaluate the extent of hydrocarbon-impacted soils and to determine whether or not groundwater had been impacted Four monitoring wells were installed during this investigation In July 1996, six additional monitoring wells were installed on and off of the subject site to assist in defining the extent of groundwater impacts, and quarterly monitoring was implemented in August and September 1999, SECOR installed a vapor extraction/arr sparging system at the subject site to remediate hydrocarbon-impacted soils and groundwater System operation began December 13, 1999 • Please find enclosed SECOR's "Quarterly Monitoring Report, July - September 2002" dated October 21, 2002 This document presents analytical results and field observations collected during Third Quarter 2002 groundwater sampling, and discusses the efficiency of the remediation system currently in operation Third Quarter 2002 Groundwater Sampling Results On July 25, 2002, groundwater samples were collected from MW-2 through MW-4 and MW-6 through MW- 10 at the subject site by a representative of SECOR MW-5 was not sampled as it was dry and MW-1 was not sampled due to the presence of a small amount of free product Prior to purging, the depth to water in all wells was measured to evaluate elevation, flow direction, and gradient As noted in the attached report, groundwater with a southwesterly flow direction and a gradient of 0 02 ft/ft was encountered in the wells at depths of 7100 feet to 84 80 feet below ground surface A small amount of free product was encountered in MW-1 (0 01 feet) The locations of the wells are identified on Figure 2 of the attached report Since the May 2002 sampling event, groundwater elevation decreased in each of the wells by 0 26 feet to 6 25 feet, resulting in an overall average decrease in grourKWater elevation of 1 27 feet across the site Changes in groundwater elevation are most likely a result of seasonal vanatton and operation of the remediation system Groundwater gradient and flow direction remained consistent with previously collected data Table 1 in the attached report summarizes historical groundwater elevation data Residual concentrations of hydrocarbons were identified in the sample collected from MW-6 (0 5 ppb ethyibenzene and 0 8 ppb xylenes) TPH-g and BTEX were not identified in the groundwater samples submitted from MW-2, MW-3, MW-4, MW-7, MW-8, MW-9 and MW-10 Analyses identified low concentrations of MTBE in the samples collected from MW-4 (1 5 ppb), MW-7 (1 8 ppb), MW-9 (0 6 ppb), and MW-10 (2 2 ppb), however, none of the other samples contained detectable concentrations of MTBE Table 2, Table 3, and Figure 3 in the attached report summarize groundwater analytical data and laboratory reports are included as Attachment 2 The highest concentrations of hydrocarbons appear to remain onsite in the vicinity of the pump islands (MW- 1) When compared to the May 2002 sampling event, hydrocarbon concentrations increased in MW-1 while they remained relatively unchanged in the remainder of the wells Since the initiation of remediation efforts, hydrocarbon concentrations across the site have substantially decreased