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WASHINGTON rE PHONE(206)285-2400 OOAEGONNIA f �Z To FAX(206)283-8036 gWPAHO"EVADA 9 123 NE TIME OIL COO a 4 �T:WE 7 6 5 Tg2737 WEST COMMODORE WAY SEATTLE,WA 98199-1233 ODUCTS PO BOX 24447 SEATTLE,WA 98124-0447 TESTED E August 7, 2001 ¢ tr� i 0 Mr Harlin Knoll San Joaquin County Public Health Services .o Environmental Health Division P O Box 2009 Stockton, California 95201 RE Submittal of"Quarterly Monitoring Report, April-June 2001"for 01. 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 operation began December 13, 1999 Please find enclosed SECOR's "Quarterly Monitoring Report, April - June 2001" dated July 31, 2001 This document presents analytical results and field observations collected during Second Quarter 2001 groundwater sampling, and discusses the efficiency of the remediation system currently In operation Second Quarter 2001 Groundwater Sampling Results On April 27, 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 67 77 feet to 76 00 feet below ground surface Approximately 2 9 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 January 2001 sampling event, groundwater elevation decreased in MW-1 by 2 19 feet, MW-5 by 2 97 feet, and in MW-7 by 0 01 feet while it decreased In the remaining wells by 0 09 feet to 4 98 feet These changes resulted in an overall average Increase in groundwater elevation of 0 72 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 Analyses Identified trace concentrations of hydrocarbons in the samples collected from MW-4 (0 51 ppb benzene) and MW-9 (0 56 ppb benzene) TPH-g and BTEX were not Identified in the samples collected from MW-2, MW-3, MW-5, MW-6, MW-7, MW-8, or MW-10 Low concentrations of M-TBE were identified in the groundwater sample collected from MW-5 (0 9 ppb) MTBE was not Identified in the samples collected from MW-2, MW-3, MW-4, MW-6, MW-7, MW-8, and MW-10 No sample was collected from MWA, 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 January 2001 sampling event, hydrocarbon concentrations Increased in MWA