SITE INFORMATION AND CORRESPONDENCE_FILE 2

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ENVIROl�MENTAL HEALTH DEPARTMENT PQ�,N SAN JOAQUIN COUNTY Pro ran: Coordinators Donna K. Heran, R.E.H.S. g 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. �•,..F..o..R•� Margaret Lagorio, R.E.H.S.P Assistant Director Telephone: (209)468-3420 Robert McClellon, R.E.H.S. Fax: (209)464-0138 Jeff Carruesco, R.E.H.S. Website:www.sjgov.org/ehd/ Kasey Foley, R.E.H.S. MR RUSSEL CHAPIN FEB 2 3 2007 CHAPIN BROTHERS, INC 1203 N CARLTON AVE STOCKTON CA 95203 RE: CHAPIN BROTHERS Site Code: 0850 1766 MONTE DIABLO AVENUE STOCKTON, CA The San Joaquin County Environmental Health Department (EHD) has received and reviewed Ground Water Extraction - Work Plan Addendum (WPA), dated 15 December 2006, prepared by Advanced GeoEnviron mental, Inc. (AGE). The WPA was prepared in partial response to the EHD directive letter dated 19 October 2006. The EHD letter directed submittal of technical justifications, feasibility analyses and work plan(s) addressing installation of additional groundwater extraction wells, testing dual- phase extraction (DPE) on the site, installation of additional borings to assess soil, soil gas and groundwater along the eastern and southern property boundaries, and collection of soil gas samples beneath the building currently on-site. WPA addresses only installation of additional groundwater extraction wells. The EHD is concerned that the additional site assessment issue, especially the vapor intrusion evaluation was not addressed in this work plan. The Central Valley Regional Water Quality Control Board (CVRWQCB) has identified vapor intrusion into structures from underground storage tank (UST) system releases to be a significant concern. Your site, with a known large contaminant mass in the shallow subsurface and shallow groundwater with residences nearby should be evaluated to safeguard the health of the nearby residents and other structure occupants. Submit either a technically sound vapor intrusion evaluation based on currently known site data or a work plan to evaluate the vapor intrusion issue to this office no later than 16 April 2007. The WPA amends Remedial Action Work Plan Addendum (WP) dated 28 June 2001 and utilizes the well design specifications with the exception that the newly proposed wells are to have 4-inch diameter casings. The purpose for installing the proposed wells near the current wells utilized for groundwater extraction (GWE), as discussed with your consultant on 21 February 2007, was to replace the wells designed for groundwater monitoring and soil vapor extraction with the proposed wells designed for groundwater extraction to improve the GWE system effectiveness. Total depths of the proposed wells are to be 30 feet below surface grade (bsg) with screen intervals between 10 and 30 feet bsg to intercept a sand unit generally between 20 and 30 feet bsg.