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ENVIRONMENTAL HEALTHVEPARTMENT °P4u�N c� SAN JOAQUIN COUNTY Z-� Donna K. Heran, R.E.H.S. Program Coordinators " :.4 Director 304 East Weber Avenue,Third Floor Carl Borgman, R.E.H.S. -_ Laurie A. Cotulla, R.E.H.S. Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I. c4 •.:... `�P Margaret Lagorio, R.E.H.S. Assistant Director �rFpRN Telephone: (209)468-3420 Robert McClellon, R.E.H.S. Fax: (209) 464-0138 Jeff Carruesco, R.E.H.S. Website:www.sjgov.org/ehct/ Kasey Foley, R.E.H.S. AUG 31 2006 STEPHANIE FURGAL CHEVRON ENV MGMT COMPANY CHRISTINE CORONEO 6001 BOLLINGER CANYON RD SUTTER OFFICE CENTER ROOM K2240 2001 UNION STREET #300 SAN RAMON CA 94583 SAN FRANCISCO CA 94123 RE: Former Chevron Station 9-8227 Site Code: # 9327 Sutter Office Center 242 Sutter Street Stockton CA 95202 San Joaquin County Environmental Health Department (SJC/EHD) has reviewed Response to Comments — Work Plan Addendum dated August 24, 2006, submitted on your behalf by Blasland, Bouck & Lee, Inc. (BBL) and has the following comments. SJC/EHD had requested clarification of two issues presented in the July 26, 2006 Work Plan for Additional Site Assessment near MW-1. One issue was the need for a boring located northwest of MW-1; data exists in that area from Unocal monitoring well U-7. The U-7 boring log and a copy of the soil analytical data is attached; BBL can obtain additional information on this well when they complete their proposed file review. The second issue is the vertical definition of the soil contamination in the area of MW-1. Soil samples from CPT-1, located near MW-1, contained 4,800 milligrams per kilogram (mg/kg) total petroleum hydrocarbons (TPH) as gasoline at 78 feet below surface grade (bsg), but were non-detect at 55 feet bsg for both TPH as gasoline and diesel. BBL considers this to indicate that the contamination of the 500-gallon tanks thought to be closed in place near this location to be defined at 55 feet bsg. SJC/EHD considers it to be premature to call the soil contamination at this location defined when the actual location of the 500-gallon tanks has not been determined, and with no explanation for the contamination noted at the deeper sample. It is not unusual for contaminants to follow an irregular pathway while migrating downward. The following scope of work to obtain additional data necessary to prepare a feasibility study is approved for implementation: 1. One soil boring will be advanced at a location approximately 30 feet east of MW-1; this boring will be converted to shallow groundwater monitoring well MW-6 with a screen interval from 20-40 feet bsg. SJC/EHD recommends this boring be drilled to approximately 80 feet bsg to collect soil samples to verify the CPT soil sample results. If appropriate, an additional short screened monitoring well should be installed across the first sand unit underlying the proposed 20-40 foot screen interval, to monitor the sand which is a potential migration pathway at that depth. 2. All existing, and new, monitoring wells will be surveyed to an established benchmark for elevation.