Laserfiche WebLink
ENVIRONidENTAL HEALTH 11EPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Donna K. Heran R.E.H.S. P <br /> 2,y 2 Unit Supervisors <br /> 304 East Weber Avenue,Third Floor Carl Bor man,R.E.H.S. <br /> m r. � Director Borg <br /> man, <br /> A. Cotulla, R.E.H.S. Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I. <br /> cq c Program Manager Telephone: (209)468-3420 Douglas W.Wilson, R.E.H.S. <br /> c f r o a d` Margaret Lagorio,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellon, R.E.H.S. <br /> Website:www.sjgov.org/ehd/ Jeff Carruesco, R.E.H.S. <br /> DENIS L BROWN JUL $1 M <br /> SHELL OIL PRODUCTS US <br /> 20945 SOUTH WILMINGTON AVENUE <br /> CARSON CA 90810 <br /> RE: Former Shell-branded Service Station <br /> 1160 West Yosemite Avenue <br /> Manteca, California 95337 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Site Conceptual <br /> Model dated December 15, 2005, and analytical results for groundwater samples collected <br /> during the first and second quarterly groundwater monitoring events for 2006 at the above- <br /> referenced site, as submitted by Cambria Environmental Technology, Inc. (Cambria) on your <br /> behalf. It is Cambria's opinion that the plume of total petroleum hydrocarbons as gasoline <br /> (TPH-g), and benzene, toluene, ethyl benzene, total xylenes (BTEX) is adequately defined <br /> (within site limitations) and stable, and therefore Cambria recommends consideration of case <br /> closure for this site. <br /> EHD met with the Central Valley Regional Water Quality Control Board (CVRWQCB) on <br /> July 19, 2006, to discuss this site's historical and current conditions. EHD and CVRWQB are <br /> in concurrence that we cannot support a recommendation for site closure consideration at this <br /> time for the following reasons. Groundwater data demonstrate significant increases in <br /> concentrations for gasoline and benzene in monitoring wells MW-1 and MW-3 for <br /> groundwater samples collected during the first and second quarters of 2006 and in MW-4 for <br /> groundwater samples collected during the second quarter of 2006. This indicates that the <br /> groundwater plume is not stable. Also, EHD does not believe that the vertical extent of <br /> impacted groundwater has been demonstrated for chemicals of concern: TPH-g, BTEX, 1,2- <br /> dichloroethane (1,2-DCA), and tertiary butyl alcohol (TBA), in the area between monitoring <br /> well MW-1 and MW-3. Both a stable plume and vertical delineation of groundwater are <br /> requirements for closure consideration. The soil lithology for MW-1 and MW-3 includes a <br /> sand layer at total depth of 35 feet below surface grade (bsg) based on submitted boring logs, <br /> and EHD is concerned the sand layer may present a potential pathway for chemicals of <br /> concern. EHD believes another borehole with the total depth of at least forty feet bsg is needed <br /> to vertically delineate the groundwater plume. <br /> In Site Conceptual Model, Cambria stated that groundwater flow direction is variable across <br /> the site. EHD is specifically concerned about the flow direction in the north/central region of <br /> this site. Please prepare a rose diagram that demonstrates historical groundwater flow <br /> directions in the area between MW-1 and MW-3. <br />