SITE INFORMATION AND CORRESPONDENCE FILE 1

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N ' ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY Unit Supervisors Q' .4 Donna K. Heron, R.E.H.S. Carl Bor man, R.E.H.S. Director 304 East Weber Avenue, Third Floor g " { Mike Huggins, R.E.H.S., R.D.I. Al Olsen, R E.H.S. Stockton, California 95202-2708 Douglas W. Wilson, R.EA S. cq FOQN c Program Manager Telephone: (209) 468-3420 Margaret Lagorio, R.E.H.S. Laurie A. Corolla, R.E.H.S, Robert McClellon, R.E.H.S. Program Manager Fax: (209) 464-013$ Mark Barcellos, R.E.H.S. i PAUL SUPPLE ATLANTIC RICHFIELD COMPANY OCT o 4 2002 € PO BOX 6549 MORAGA CA 94570 RE: Arco Station #2130 Site Code 1094 7906 N . EI Dorado St. RO#: 035 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 'downsince 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 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 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 .