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HEALTH DEPARTMENT <br /> ENVIRONMENTAL HEAL <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Carl Borgman,R.E H.S. <br /> { ',.; `' Director 304 East Weber Avenue, Third Floor Mike Huggins,R.E.H.S.,R.D.I. <br /> 1 n Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Robert McClellan,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. <br /> KAREN PETRYNA DEC 2 3 2003 <br /> EQUIVA SERVICES LLC <br /> PO BOX 7869 <br /> BURBANK CA 91501-7869 <br /> RE: Shell Service Station SITE CODE: 1223 <br /> 6131 Pacific Avenue <br /> Stockton CA 95207 <br /> San Joaquin County Environmental Health Department (SJC/EHD) has reviewed "Site <br /> Conceptual Model/Site Investigation Work Plan"dated October 3, 2003 that was <br /> submitted on your behalf by Cambria Environmental Technology, Inc. (Cambria) and has <br /> the following comments. <br /> SJC/EHD's review of the Site Conceptual Model (SCM) found that there was no <br /> discussion of the adsorbed and/or dissolved contaminant masses. Please prepare and <br /> submit to SJC/EHD estimates of the masses. Also, there was no discussion of <br /> contaminant migration pathways in the subsurface below the utility trenches. <br /> SJC/EHD's analysis of the data suggests that there are three sand-rich intervals currently <br /> identified that may act as conduits for lateral migration of contaminants: <br /> 1. Thin sand at approximately 40 feet below surface grade (bsg)with sand described <br /> in 40% of the samples recovered at that depth. The distribution of sand at this <br /> depth, interspersed with fine-grained soil samples may be due to thin sand <br /> interval(s) intercalated with fine-grained intervals. <br /> 2. A potentially thicker sand interval encountered at 55 feet and 60 feet bsg. Eighty <br /> percent of the soil samples recovered at these depths were sand. <br /> 3. A thicker sand, possibly a channel deposit, encountered between 71 feet and 78.5 <br /> feet bsg in SB-5 and between 74.5 feet and 80 feet bsg in SB-6. SJC/EHD <br /> believes that potentially this sand could be a significant lateral migration pathway <br /> and should be monitored by discretely screened wells. <br /> Review of the CPT log for boring SB-6 and its apparent disconnect from surrounding <br /> lithology as encountered in soil samples and in the SB-5 log suggests to SJC/EHD that <br /> the CPT point may have broken into the annular space of a long abandoned well at 46 <br /> feet bsg to 74 feet bsg. The long sequence of sensitive fines, fairly unique for the <br /> Stockton area, may represent uncompacted fines in the suspected well bore. If true, the <br /> old boring could serve as a vertical conduit. SJC/EHD believes it would be prudent to <br /> install discretely screened monitoring wells in the 75-80 foot sand interval to assess and <br /> monitor groundwater in this unit. <br />