Laserfiche WebLink
San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> 600 East Main Street Donna Heran, REHS <br /> Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Robert McClellon,REHS <br /> Jeff Carruesco,RENS, RDI <br /> Website: www.sjgov.org/ehd Kasey Foley, REHS <br /> Phone: (209)468-3420 <br /> Fax: (209) 464-0138 <br /> April 9, 2010 <br /> Terry Grayson <br /> ConocoPhillips <br /> Risk Management & Remediation <br /> 76 Broadway <br /> Sacramento, CA 95818 <br /> Subject: Former UNOCAL#6981 <br /> 4707 Pacific Avenue <br /> Stockton, CA <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed <br /> Quarterly Status Summary Report — First Quarter 2010 and Request for Low-Risk Case <br /> Closure (Report) dated March 5, 2010, and Results of Hydrogeologic Modeling (Model), <br /> dated December 18, 2009, both prepared and submitted on your behalf by Stantec <br /> Consulting Corporation (Stantec) and has the following comments. <br /> This contaminated underground storage tank (UST) site has been undergoing <br /> investigation of its unauthorized release of petroleum hydrocarbons since 1988 In <br /> addition to some over-excavation of soil conducted during site upgrades, two phases of <br /> remediation, soil vapor extraction (SVE) and ozone sparging, have been conducted. <br /> The submitted Model, which reported the results of using the FLOWPATH II groundwater <br /> flow and transport model, estimates that total petroleum hydrocarbon as gasoline (TPHg) <br /> concentrations currently reported in the groundwater in well VW-7 will degrade to <100 <br /> micrograms per liter (Ng/1) onsite and <50 N9/1 offsite by May 2018, and will have migrated <br /> approximately 100 feet downgradient offsite, under Pacific Avenue. <br /> In the Report Stantec recommends the site should be considered for low-risk closure <br /> based on a stable and declining plume and the lack of sensitive receptors downgradient of <br /> the plume. The EHD agrees with those two points, but is concerned with the lack of <br /> post-remedial soil data to confirm the effectiveness of the SVE remediation. Very high <br /> concentrations of contaminant were reported in soil samples collected from the borings for <br /> VW-2, VW-5 and VW-7. <br /> Review of the groundwater analytical data tables indicates that well VW-2 is most <br /> frequently noted as being 'dry'. This needs to be verified because VW-2 was built to total <br /> depth of 55 feet below surface grade (bsg) and has a screen interval from 25-50 feet bsg. <br /> Unless the well has been damaged or blocked in some way, there should be plenty of <br /> water to sample as current depth to groundwater is approximately 33 feet bsg. Located <br /> very near VW-2, VW-5 was built to 31 feet total depth. The EHD has discussed with <br /> Stantec the possibility that the identification of these two wells has been inadvertently <br />