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k'% KLEINFELDER An employee owned company File No. 20-1129-30 :v' `rJ September 23, 1997 Sfib ;,Jv Mr. Tony Lopes .lye Siegfried Engineering 4045 Coronado Street Stockton, California 95204 Subject: ADDENDUM NO. 1 I,IMTTFD PHASE 11 ASSESSMENT WEBER POINT P SEAWALL ARCO SITE STOCKTON, CALIFORNIA Dear Mr. Lopes: Presented in this letter is a summary of additional tests and field explorations performed at the ARCO Service Station located at 205 North Center Street in Stockton, California. Reference is made to our Limited Phase II Assessment for this project dated July 14, 1997. At the time our environmental report was completed, access was not available to the ARCO property. One test boring, B-2, was located immediately adjacent to the ARCO property and the soil and groundwater in this boring were tested for hydrocarbons by Sequoia Laboratories. Identifiable hydrocarbons were not detected in these samples. On August 23, 1997, an 843 Bobcat with 8-inch diameter auger was used to explore the backfill soils behind the existing seawall at the ARCO site. The existing seawall at this location will be sloped down to the west similar to the seawall on the south bank. It is also tentatively planned not to remove the backfill soils as is currently proposed west of the ARCO site, For this reason, it was considered appropriate to explore only approximately 4 feet below existing grade. Unfortunately, the Bobcat drilling equipment encountered refusal at approximately 12 locations within the planter area on what appeared to be a concrete slab located 1 to Th feet below the surface. The general soil conditions encountered to these depths included 0 to 12 inches of light brown silty sand in a loose condition; 12 to 18 inches aggregate base rock; 18 to 21 inches brown sand; 21 to 25 inches dark brown moist clay, and 25 to 27 inches asphalt concrete. We note that PID readings taken in these shallow probes did not indicate the presence of hydrocarbons. At one location, a 1-inch diameter drill was used to evaluate the thickness of the concrete and the underlying soil conditions. The concrete measured approximately 6 inches in thickness, and was underlain by very loose soil that appeared to contain voids to the depth of 48 inches. 20-1129-30/1017R492 Page 1 oft © 1997,Kleinfelder, Inc. September 23, 1997 KLEINFELDER 2825 East%Ivrtle Street, Stockton,CA 95205-4794 (209)948-1345 (209)948-0621 fax