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9 + <br /> San Joaquin County DIRECTOR <br /> o N Donna Heran, REHS <br /> Environmental Health Department�. .—.�-s� .O I) ASSISTANT DIRECTOR <br /> r ± 600 East Main Street Laurie Cotulla,REHS <br /> �mIIIP 7 < i Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> lel? Carl Borgman,REHS <br /> Mike Huggins,REHS,RDI <br /> 54/FORS\ Website: www.sjgov.org/ehd Margaret Lagorio, REHS <br /> Phone: (209)468-3420 Robert McClellon, REHS <br /> Fax: (209)464-0138 Jeff Carruesco,REHS, RDI <br /> Kasey Foley,REHS <br /> October 23, 2008 <br /> Stephanie Furgal <br /> Chevron Environmental Management Company <br /> 6111 Bollinger Canyon Road Room 3652 <br /> San Ramon CA 94583 <br /> Subject: Former Unocal #0187 <br /> 437 E. Miner Street <br /> Stockton„CA <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed the "Work Plan <br /> for Additional Assessment' (Work Plan) dated October 10, 2008, prepared by ARCADIS for the <br /> above subject site and provides the following comments. <br /> In October and November 2006 soil vapor probes were installed and sampled at this site. <br /> Seven of the vapor probes were installed to a depth of five feet below surface grade (bsg) and <br /> seven of the vapor probes were installed to a depth of ten feet bsg. The concentrations of total <br /> petroleum hydrocarbons as gasoline in the vapor samples collected exceeded the San <br /> Francisco Bay Regional Water Quality Control Board Environmental Screening Levels. There <br /> was discussion that the tracer gas may have caused false positives. Those vapor probes are <br /> still in place at this site. The Work Plan provides no explanation for not using the vapor probes <br /> that are still in place. If these probes are no longer of use, they are to be destroyed under <br /> permit and inspection of the EHD. <br /> The Work Plan proposes to install eight shallow vapor probes to a depth of five feet bsg and <br /> eight deep vapor probes to a depth of 20 feet bsg. The Work Plan states the soil probe <br /> locations are based on previous site features, previous vapor assessment data and adjacent <br /> buildings. There is no technical justification for installation of vapor probes at 20 feet bsg. If the <br /> intent is to investigate vapor migration from the groundwater contamination, the placement of <br /> the deep probes should be limited to the southeast area of the site by U3, NP1, UV1, UV2 and <br /> UV3 which is also the area where the historical soil analytical results document soil <br /> contamination. <br /> Three of the probes are located closer to adjacent property buildings than the existing probes <br /> and shallow probes close to the buildings are necessary. The locations shown should be <br /> moved closer to the buildings. <br /> The Work Plan states that soil samples will be collected continuously from ground surface to the <br /> total depth of the borehole, but does not explain how this will be accomplished nor does-it-clarify <br /> whether this will be done on both the shallow and deep boreholes. The Work Plan states that <br /> the shallow boreholes are to be hand augered and the deep boreholes are to be drilled using <br />