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WASHINGTON TE PHONE(206)285-2400 N CALIFORNIA T FAX(206)283-8036 NEVAD.;IDAHOA q ' ' 23 OREGON E U I E (OIL C ® o B 4 IT 7 6 5 5 2737 WEST COM 1N({Y SEATTLE,WA 98199-1233 PR...23 TQM PO BOX 24447 Jv) $ I4TTLE,WA 96124-0447 nMe TesTeo E ��u 111��]}}L February 20, 2002 FEB 262002 Mr Harlin Knoll ENVIR ',,'- -N-1 HEALTH San Joaquin County Public Health Services PERMIT/SERVIGES Environmental Health Division P O Box 2009 Stockton, California 95201 RE Submittal Of"Quarterly Monitoring Report, October- December 2001"for Jackpot Food Mart, 14000 E Highway 88, Lockeford, California (Property No 04-049) Dear Mr Knoll, At the request of the San Joaquin County Public Health Services Environmental Health Division (PHS/EHD), 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 A total of 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/air . sparging system at the subject site to remediate hydrocarbon-impacted soils and groundwater System 1 operation began December 13, 1999 Please find enclosed SECOR's "Quarterly Monitoring Report, October- December 2001" dated February 11, 2002 This document presents analytical results and field observations collected during Fourth Quarter 2001 groundwater sampling, and discusses the efficiency of the remediation system currently in operation Fourth Quarter 2001 Groundwater Sampling Results On November 28, 2001, groundwater samples were collected from MW-2 through MW-10 at the subject site by a representative of SECOR Prior to purging, the depth to water in all wells (MW-1 through MW-10) 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 70 11 feet to 85 98 feet below ground surface Approximately 0 28 feet of free product was encountered in MW-1 The locations of the wells are identified on Figure 2 of the attached report Since the August 2001 sampling event, groundwater elevation decreased in each of the wells by 0 96 feet to 14 3 feet resulting in an overall average decrease In groundwater elevation of 2 68 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 TPH-g and BTEX were not Identified in the groundwater samples submitted from MW-2 thorough MW-10 Analyses identified 1 0 ppb MTBE in the sample collected from MW-4, however none of the other samples contained detectable concentrations of MTBE No sample was collected from MW-1, as it contained free product 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 August 2001 sampling event, hydrocarbon concentrations decreased in MW-1 (as shown by a decrease in free product thickness) while they remained "non-detect" in the remainder of the wells Since the initiation of remediation efforts, hydrocarbon concentrations across the site have substantially decreased