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San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> Donna Heran,REHS <br /> 600 East Main Street <br /> U): Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> .. <br /> Robert McClellon, REHS <br /> -�.• Jeff Carruesco,REHS, RDI <br /> q�/FO•R�\ Website: www.sjgov.org/ehd Kasey Foley,REHS <br /> Phone: (209)468-3420 <br /> Fax: (209)464-0138 <br /> April 7, 2010 <br /> Terrence Fox <br /> Cal Trans District 6 <br /> 2015 East Shields Avenue, Suite 100 <br /> Fresno, CA 93726 <br /> Subject: Stockton Yard Maintenance Station <br /> 1604 B Street <br /> Stockton, CA 95201 <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Site <br /> Investigation and Air Sparging Pilot Test Work Plan (Work Plan) dated March 19, 2010, <br /> submitted on your behalf by AMEC Geomatrix (AMEC) and has the following comments. <br /> In the Work Plan, AMEC proposes the installation of four Cone Penetrometor Test (CPT) <br /> borings utilizing Membrane Interface Probe (MIP) technology to more tightly define the source <br /> area soil contamination, the installation of one air sparge well and three discretely screened <br /> observation wells, and conducting an air sparging pilot test. <br /> After discussion with Cal Trans, the EHD approves the proposed scope of work with the <br /> understanding that the proposed CPT/MIP work is intended to assure characterization of all <br /> likely areas of continuing source to the groundwater contamination. The location and specific <br /> depth of the air sparge well screen interval will be determined based on the results of the <br /> CPT/MIP investigation. The EHD notes that the proposed depths of the observation wells, two <br /> feet below the water table and screened in clayey silt, may be too shallow to detect the effects <br /> of the sparging and helium tracer if the air sparge well is screened in the silty sand/sand which <br /> underlies the clayey silt at approximately 50 feet below surface grade (bsg) on the provided <br /> cross-sectional diagrams. The EHD recommends using the vapor wells on site and possibly <br /> MWA and MW-3 as observation wells, as they are screened in the silty sand/sand below <br /> 50 feet bsg. <br /> If you have any questions please contact Lori Duncan at (209) 468-0337, or by email at <br /> Iduncan@sjcehd.com. <br /> Sincerely, <br /> Lori Duncan, REHS Nuel C. Henderson, Jr., PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> c: James Barton, CVRWQCB, 11020 Sun Center Drive #200, Rancho Cordova CA 95670 <br /> Eileen Gower, AMEC Geomatrix, 10670 White Rock Road, #100 Rancho Cordova CA 95670 <br />