Laserfiche WebLink
PUBLI HEALTH SER1ICES <br /> SAN JOAQUIN COUNTY ' ?, <br /> a: < <br /> JOG]KHANNA M.D.,M.P.H. <br /> Health Officer <br /> P.O. Box 2009 • (1601 East Hazelton Avenue) • Stockton, Califomia 95201 �4t(coaMsr <br /> (209) 468-3400 <br /> DAVE CAMILLE <br /> UNOCAL PORATION <br /> 2000 CROW PLACE COPY <br /> SUITE 400 <br /> SAN RAMON CA 94583 'JUN O 11993 <br /> RE: Unocal Service Station #6981 SITE CODE: 1217-123 <br /> 4707 Pacific Avenue <br /> Stockton CA <br /> San Joaquin County Public Health Services,Environmental Health Division (PHS/EHD)has <br /> completed review of the 'Remedial Action Plan" dated May 4, 1993 and prepared by <br /> RESNA. PHS/EHD has the following comments for your consideration. <br /> The Remedial Action Plan (RAP) proposed installation and operation of a soil vapor <br /> extraction remediation system to address the hydrocarbon contamination of soil. The RAP <br /> also proposed the installation of two additional vapor extraction wells screened between 5 <br /> and 30 feet to address shallower soil contamination. The existing vapor extraction wells, <br /> VW1 - VW4, are screened between 25 and 50 feet. RESNA recommended that <br /> groundwater extraction and treatment be postponed until the soil has been sufficiently <br /> remediated to no longer be a source of contamination to groundwater. <br /> The results of vapor extraction testing indicated that an effective radius of influence of <br /> approximately 50 feet could be acheived per vapor extraction well. The installation of two <br /> shallow vapor extraction wells should provide sufficient vacuum to remediate the <br /> contamination documented between 15 and 25 feet. The existing vapor extraction wells <br /> which are screen between 25 and 50 feet should provide sufficient vacuum to remediate the <br /> contamination documented between 30 and 40 feet; however contamination documented <br /> between 45 and 56 feet may require additional wells to provide the vacuum necessary to <br /> remediate soil contamination at these depths. The use of currently dry monitoring wells, <br /> MW1 - MW5, as vapor extraction wells should be evaluated. <br /> PHS/EHD grants an extension on installation and operation of a groundwater remediation <br /> system, until levels of soil contamination no longer pose a threat to groundwater. The extent <br /> of groundwater contamination is well defined. However, the direction of groundwater flow <br /> which is to the northeast and contaminant levels observed in MW7 indicate that <br /> contamination has migrated off site beneath Pacific Ave. Should MW12 or MW13 ever <br /> detect groundwater contamination, groundwater extraction would be requested to control <br /> plume migration. <br /> A Division of fan Jnaqum(-ounm Heakh C: c`mccs C <br />