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TreadwelFb MEMORANDUM TO: Vicki McCartney, REHS FROM: David Dixon DATE: 10 December 2004 PROJECT: Former County Motor Pool Site 130 North Hunter Street, Stockton SUBJECT: Addendum to 4 November 2004 Workplan This addendum to our 4 November 2004 soil and groundwater investigation workplan for the Former County Motor Pool Site at 130 North Hunter Street in Stockton, presents modifications to the soil boring program on the basis ofrecommendations in your 9 November 2004 conditional approval letter for our Workplan, and the results of our 12 November 2004 sampling at the site. This addendum also includes a description ofthe proposed groundwater monitoring well sampling procedures. The work will be conducted on 14 and 15 December, 2004. The following summarizes the proposed work: Soil Boring and Sampling 1 . Two borings, SB• 1 and SB-2, will be advanced to 60 feet below ground surface (bgs) in the parking lane of North Hunter St., 4- feet off of the curb (Figure 1 ). During our 12 November investigation we had USA mark street utilities, and a private utility locator see if we could place these borings further away from the curb, however, due the presence of utilities, borings would have to be placed near the other side of the street. As this would be approximately 50- feet upgradient, we do not believe that it would provide useful data. 2. Two soil borings, SB-3 and SB-5B will be advanced to 60 feet below ground surface (bgs) in the building (Figure 1). Boring S13-3 will provide data in the previously uncharacterized northeasterly direction, which data from boring S134 indicates could be impacted. Boring SB-5B will be advanced adjacent to boring SB-5, where a deep groundwater sample was not previously obtained. 3 . Two groundwater samples will be collected from boring SB- 1 , SB-2 and SB-3 ; one at fust encountered groundwater at approximately 30- feet bgs, and the second at approximately 55- feet bgs. Only a 55- foot deep groundwater sample will be collected from boring SB-513. Due to the low yield clays previously encountered at 55-feet, boring casing will be left in place overnight for borings completed on 14 December, if no groundwater is recovered that day. Open borings will be protected to prevent intrusion of water and covered with steel plates to restrict access. Cones and/or barricades will be used over the borings. Treadwell R Rollo, Inc. Environmental & Geotechnical Consultants 555 Montgomery Street, Suite 1300, San Francisco, CA 94111 Telephone (415) 955-9040 Facsimile (415) 955-9041 �C f