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ENVIRONMENTAL HEALTH DEPARTMENT <br /> pUi�y <br /> > SAN JOAQUIN COUNTY <br /> "t Donna K Heran,R E H S <br /> Unit Supervisors <br /> N- 304 East Weber Avenue, Third Floor Carl Borgman,R F H S <br /> s Director H S,R D I <br /> E R, <br /> • A]Olsen,R E H S Stockton, California 95202-2708 Douglas W Mike Huggins, <br /> R E ,R E x s <br /> C, _ �P Program Manager Telephone (209) 468-3420 Margaret Lagono,R E H S <br /> LaurieCotR H S Fax (209) 464-0138 Robert McClellon,R E H S <br /> Program Man Managerr Mark Barcellos,R E H S <br /> PAUL SUPPLE <br /> ATLANTIC RICHFIELD COMPANY OCT 0 4 2002 <br /> PO BOX 6549 <br /> MORAGA CA 94570 <br /> RE Arco Station #2130 Site Code 1094 <br /> 7906 N EI Dorado St RO# 035 <br /> Stockton, CA 95210 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed the <br /> Quarterly Monitoring Report, (QMR) Second Quarter 2002 dated August 9, 2002 as <br /> submitted by your consultant Stratus Environmental on August 19, 2002 and has the <br /> following comments <br /> . ARCO began active remediation of this site in 1994 and has continuously modified the <br /> approved remediation system to meet the changing situations at this active gas station <br /> EHD appreciates these efforts and as a result, has devoted little time to comment or to <br /> direct any additional changes <br /> In reviewing the latest QMR it has become apparent that rising groundwater depths over <br /> the years have caused the initially approved air sparge/soil vapor extraction (SVE/AS) to <br /> change substantially The soil vapor extraction system has been 'down'since November <br /> 1997 and as the report has indicated, only 'air bubbling' into the saturated zone is being <br /> conducted Most of the SVE wells are reported as 'drowned' <br /> Petroleum concentrations in the groundwater samples collected from eight monitoring <br /> wells associated with this site indicate only low levels remain Unfortunately, these <br /> monitoring wells were installed some time ago and constructed with the top of screened <br /> interval between 53 and approximately 60 feet below ground surface (' bgs) The depth <br /> to first groundwater at the last monitoring and sampling event, June 18, 2002, was <br /> 38 65' bgs in MW-1 Since none of the monitoring wells have screened intervals <br /> intersecting first water, investigation for contaminants in first water is not occurring <br /> Twelve SVE wells were installed at this site and currently six (VW-1, 3, 4, 8, 11, and VW- <br /> 12) have their screened intervals completely submerged by groundwater('drowned') <br /> The remaining SVE wells have the current depth to water within their screened interval, <br /> and as such, are the closest thing ARCO has for providing valid wells for monitoring the <br /> current interface between the vadose and the saturated zone for this site Unfortunately, <br /> these SVE wells are not being sampled <br />