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Mr Nuel Henderson, Jr, SJCPHS July 1,2003 Remedial Action Plan ARCO Station No 6100 Page 3 On June 5, 2000, Delta submitted a work plan for groundwater assessment The work plan was subsequently approved with comments by CRWQCB in a letter dated June 9, 2000 Delta contracted Water Development Corporation of Woodland, California, to drill and install monitoring well MW-1 in August 2000 The boring was drilled to a depth of 202 feet bgs and the monitoring well was completed to a depth of 115 feet bgs The screen interval is from 95 to 115 feet bgs Between August 29 and September 7, 2001, Delta oversaw Western Strata Exploration, Inc of West Sacramento (C-57 #552198) advance six onsite soil borings (B-33 through B-38) Eight 4-inch diameter PVC wells (MW-2 through MW-9) were installed in four clusters (two each adjacent to borings B-33 through B-36) The shallow well in each cluster was completed to a maximum depth of 65 feet bgs using 10 feet of 0 02-inch diameter well screen, and the deep well in each cluster was completed to a maximum depth of 95 feet bgs using 20 feet of 0 02-inch diameter well screen During first quarter 2002, the dispensers and product piping were replaced Delta collected compliance soil samples Based on analytical results of the soil samples, limited over-excavation was conducted in the vicinity of dispenser islands Stratus submitted a site conceptual model (SCM) dated October 3, 2002, recommending onsite remediation and further offsite assessment SJCPHS has yet to respond to the SCM - vl- SENSITIVE RECEPTOR SURVEY A water supply well is present onsite in the southwestern portion of the site This well is used to supply water for the ARCO facility Petroleum hydrocarbons have never been detected in this well The supply well is screened from 396 to 416 and from 496 to 536 feet bgs A well search conducted by Delta with Department of Water Resources (DWR) files identified eight additional water supply wells located within a 0 5 mile radius of the site A figure illustrating the locations of the wells is presented in Appendix C Locations or usage of the wells identified in the DWR records search could not be verified during a field reconnaissance The supply wells identified in DWR records are either cross gradient to the site or have been abandoned and hence do not pose a threat as a likely potential receptor The water supply well, identified approximately 2,000 feet southeast of the site, is down-gradient and a possible potential receptor An aqueduct used to transport water from the Sacramento-San Joaquin River delta to southern California is situated approximately 1,200 feet northeast of the ARCO facility Based on a dip of the strata beneath the ARCO facility, and assuming that the aqueduct is P 113p-Arco for URS161001Reports\Arco 6100 RAP doe