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PHONE 2?6 2400 CABLE ADORESS T 101L SEATTLE TE I FAX) 206 283 8036 TACOMA v PORTLAND STOCKTON RENOT •LOS ANOGELES Q{ TIME I M G C O I L CO . 4 5 2737 WEST COMMODORE WAY SEATTLE WA"199 1233 PAoou_T, P O BOX 24447 SEATTLE WA 98124 0447 TIME TESTED 'E February 5, 2003 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, October- December 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 (MW-1 through MW-4) 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 (MW-5 through MW-10), and quarterly monitoring was implemented In August and September 1999, SECOR installed a vapor extraction/air sparging system at the subject site to remediate hydrocarbon- impacted soils and groundwater System operation began December 13, 1999 •i Please find enclosed SECOR's "Quarterly Monitoring Report, October - December 2002" dated January 30, 2003 This document presents analytical results and field observations collected during Fourth Quarter 2002 groundwater sampling, and discusses the efficiency of the remediation system currently in operation Fourth Quarter 2002 Groundwater Samplinq Results On November 12, 2002, groundwater samples were collected from MW-1 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 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 south-southwesterly flow direction and a gradient of 0 02 ft/ft was encountered in the wells at depths of 71 68 feet to 85 55 feet below ground surface Free product was not encountered in any of the wells The locations of the wells are identified on Figure 2 of the attached report Since the July 2002 sampling event, groundwater elevation decreased in each of the wells by 0 32 feet to 2 4 feet, resulting in an overall average decrease in groundwater elevation of 0 86 feet across the site Changes in groundwater elevation are most likely a result of seasonal variation 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 Hydrocarbons were identified in the sample collected from MW-1 (20,000 ug/1 TPH-g, 19 ugll benzene, 47 ugA ethylbenzene, and 2,040 ug/1 xylenes) TPH-g and BTEX were not identrfied in the groundwater samples submitted from MW-2, MW-3, MW-4, MW-6, MW-7, MW-B, MW-9 and MW-10 Analyses cdentrfied low concentrations of MTBE in the sample collected from MW-9 (0 6 ug/1), however, none of the other samples contained detectable concentrations of MTBE Other fuel oxygenates (TBA, DIPS, ETRE, and TAME)were not present at detectable concentrations in any of the samples 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 July 2002 sampling data, hydrocarbon concentrations decreased in MWA while they remained essentially "non-detect' in the remainder of the wells Since the initiation of remediation efforts,hydrocarbon concentrations across the site have substantially decreased