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ENVIRONMENTAL HEALTH DEPARTMENT SAN JOA UIN COUNTY P Unit Supervisors Donna K Heran,R> H S 304 East Weber Avenue, Third Floor Carl Borgman,R r-H S _ T Director Mike Huggins,R E H S ,R D I •. Al Olsen,R E N S Stockton, California 95202-2708 Douglas W Wilson,R E H s Program Manager Telephone (209) 468-3420 Margaret Lagono,R E H S pop Laurie A Cotulla,R E N S Program Manager Fax (209) 464-0138 Robert McClellon,R E H S Mark Barcellos,R E H S PAUL SUPPLE ATLANTIC RICHFIELD COMPANY OCT U 4 2002 1 PO BOX 6549 MORAGA CA 94570 RE Arco Station #2130 Site Code 1094 7906 N EI Dorado St RO# 035 1 Stockton, CA 95210 San Joaquin County Environmental Health Department (EHD) has reviewed the Quarterly Monitoring Report, (QMR) Second Quarter 2002 dated August 9, 2002 as submitted by your consultant Stratus Environmental on August 19, 2002 and has the following comments ARCO began active remediation of this site in 1994 and has continuously modified the approved remediation system to meet the changing situations at this active gas station EHD appreciates these efforts and as a result, has devoted little time to comment or to direct any additional changes In reviewing the latest QMR it has become apparent that rising groundwater depths over the years have caused the initially approved air sparge/soil vapor extraction (SVE/AS) to change substantially The soil vapor extraction system has been `down' since November 1997 and as the report has indicated, only 'air bubbling' Into the saturated zone is being conducted Most of the SVE wells are reported as `drowned' Petroleum concentrations in the groundwater samples collected from eight monitoring wells associated with this site indicate only low levels remain Unfortunately, these 1 monitoring wells were installed some time ago and constructed with the top of screened interval between 53 and approximately 60 feet below ground surface (' bgs) The depth to first groundwater at the last monitoring and sampling event, June 18, 2002, was 1 38 65' bgs in MW-1 Since none of the monitoring wells have screened intervals intersecting first water, investigation for contaminants in first water is not occurring Twelve SVE wells were installed at this site and currently six (VW-1, 3, 4, 8, 11, and VW- 12) have their screened Intervals completely submerged by groundwater('drowned') The remaining SVE wells have the current depth to water within their screened interval, and as such, are the closest thing ARCO has for providing valid wells for monitoring the current interface between the vadose and the saturated zone for this site Unfortunately, these SVE wells are not being sampled