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• UNDERGROUND ENGINEERING& g ENVIRONMENTAL SOLUnON5 1 rj,,r � �fH EALIfi Haley&Aldrich,Inc. 03 JUL 2 j pM 1: 06 3 West Carrillo Street Suite 201 Santa Barbara,CA 93101-3283 Tel: 805.899.9224 Fax:805.899.8365 • ; 18 July 2003 www.HaleyAldrich.com File No. 29629-000 San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, California 95202 Attention: Jeffrey Wong J� 9 Subject: Groundwater Monitoring Plan Former ContiGroup Grain Elevator Cam Stockton, California Dear Mr. Wong: Haley&Aldrich, Inc. has prepared this proposed groundwater monitoring plan for the OFFICES underground storage tank(UST)project at the Stockton Elevator facility. We are submitting this plan on behalf of Huff&Huff, Inc. and their client, ContiGroup Companies, Inc. In a letter Boston dated 13 June 2003, San Joaquin County Environmental Health Department(EHD) informed Massachusetts ContiGroup of the need for quarterly groundwater monitoring. Also in the 13 June letter, EHD Cleveland offered to consider an alternative to quarterly monitoring of all wells "if in can be shown that a Ohio reduced sampling frequency will not result in a less effective monitoring program." We Dayton appreciate your willingness to consider alternative plans and feel we have developed an Ohio alternative that preserves the effectiveness of the monitoring program and makes the most Denver effective use of ContiGroup's environmental dollars. Colorado Detroit Groundwater Plume is Shrinking. In our December 2002 Site Investigation Work Plan, we Michigan presented an interpretation of subsurface conditions based on all available'soil and groundwater Hartford data,dating back to 1997. We showed that the zone of total petroleum hydrocarbon (TPH) Connecticut groundwater impact had declined dramatically between 1997 and 2002,presumably due to Los Angeles biodegradation, dispersion, volatilization and other natural attenuation processes. A copy of California Figure 2 from the Work Plan, which illustrates this observation, is included as an attachment to this letter. The USTs were removed from this site in 1988 so there is no known ongoing release Manchester New Hampshire of contamination(although migration from residual contamination in the vadose zone is likely to be supplying some mass to groundwater). Based on this strong body of evidence, we Newark conclude that the dissolved contaminant plume is stable in size or shrinking and there is not a New significant threat of rapid downgradient migration of the plume. Portlanandd Maine Biannual Monitoring Proposed.is ro d. Given the stable nature of the p groundwater plume, we Rochester propose to conduct biannual groundwater monitoring for MW-2, MW-3 and MW-4: these are New York the three wells in which TPH has been historically detected. We propose annual monitoring for San Diego MW-1, MW-5 and MW-6: these are wells that have never had detectable levels of TPH. Since California the groundwater plume has been consistently shrinking over the last four years, we believe this Tucson schedule is sufficient to a)provide a time-series data set of groundwater conditions and b) Arizona provide for early detection of changing groundwater conditions at the site. The Stockton site is Washington an active grain elevator facility and the operator occasionally stores grain in large piles on the District of Columbia P-fe o —Fled ywpa.