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j Q ENVIRONMENTAL HEALTAEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> 2: L Unit Supervisors <br /> 0 ervenue, Floor <br /> Donna K Heran,R.E.H.S. 304 East WebAThird Fl <br /> Director Carl Borgman,R.E.H.S. <br /> AI Olsen,R.E.H.S. Stockton, California 95202-2708 Mike Huggins,R.E.H.S.,R.D.I. <br /> • r.. P. <br /> Douglas W.Wilson,R.E.H.S. <br /> Program Mana Manager Telephone: (209) 468-3420 <br /> Margaret Lagorio,R.E.H.S. <br /> Laurie A.Co R.E.H.S.H.S. <br /> Man Fax: (209) 464-0138 Robert McClelton,R.E.H.S. <br /> Program Manager Mark Barcellos,R.E.H.S. <br /> DENIS L BROWN MAY 1 7 2005 <br /> HSE ENVIRONMENTAL SERVICES <br /> 20945 S WILMINGTON AVENUE <br /> CARSON CA 90810 <br /> RE: Shell-branded Service Station SITE CODE: 1223 <br /> 6131 Pacific Avenue <br /> Stockton CA 95207 <br /> San Joaquin County Environmental Health Department (SJC/EHD) has reviewed Interim <br /> Remediation Report (Report) dated February 9, 2005, and Fourth Quarter 2004 <br /> Groundwater Monitoring Report dated March 7, 2005, submitted on your.behalf by <br /> Cambria Environmental Technology, Inc. (Cambria), and has the following comments. <br /> In Interim Remediation Work Plan Addendum dated February 12, 2004, Cambria <br /> proposed to perform interim remediation at this site by dual phase extraction (DPE) to <br /> reduce the residual source mass of contamination. Cambria made this proposal based <br /> on their review of a soil vapor extraction (SVE) test conducted by Aegis during late 1991 <br /> and early 1992 that indicated SVE was a feasible and effective remediation alternative <br /> for this site. As groundwater elevation has risen significantly since the SVE test was <br /> conducted, dual phase was added to SVE to dewater the current saturated zone and <br /> expose impacted soil in the 35 to 50 feet below surface grade interval in vapor extraction <br /> well VEW-2. SVE alone was conducted on VEW-1, which is a shallower well than <br /> VEW-2. SJC/EHD approved the interim remediation by DPE with the condition that DPE <br /> continue until analysis of extracted vapor indicated that DPE was no longer effective for <br /> removing the core of the remaining soil contamination. Cambria did not note this <br /> condition of the approval; DPE was conducted for only five days. With the exception of <br /> total petroleum hydrocarbon as gasoline (TPHg) in VEW-2, contaminant concentrations <br /> reported in vapor samples collected from each vapor well, at the conclusion of their <br /> respective events, were generally higher than they were at the beginning of the DPE. <br /> Also, the water sample collected from VEW-2 at the conclusion of the five days had <br /> contaminant concentrations higher than those reported in a water sample collected <br /> before the interim remediation began. <br /> Analytical data reported from soil and groundwater samples collected from two CPT <br /> borings advanced in May 2000, borings SB-5 and SB-6, indicated that the vertical extent <br /> of contamination in both soil and groundwater remains undefined. A deeper screened <br /> monitoring well, MW-13, was installed on the east side of the property in February 2004. <br /> Total depth of this well is 84 feet below surface grade, which is not the total depth of the <br /> CPT borings; it was built to intercept a sand interval noted in the log of CPT SB-6. <br /> During the four quarters of reported sampling events MW-13 has been consistently "non- <br /> detect" for most constituents; it does have 1,2-dichloroethane at low concentrations. <br />