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i 1 �Y r I Project No, 034-98081 Page No. 3 4.0 PURPOSE OF THE ASSESSMENT , The purpose of the proposed assessment is to complete the definition of the lateral and vertical extent of PHCs in subject site soils and groundwater and define site specific groundwater gradient through k advancement and sampling of Geoprobe® soil borings. 5.0 BACKGROUND INFORMATION/PREVIOUS INVESTIGATIONS j A Phase I Preliminary Hazardous Materials Site Assessment was prepared for the subject site by Telic Engineering Corporation, dated October 4, 1993. The Phase I Site Assessment indicates that a 1,000- gallon underground storage tank (UST) and related piping were removed from the subject site in 1987. Evidently, a soil sample was obtained from a depth of approximately seven feet below;,ground surface during UST removal operations. Analytica[ testing of this sample detected minor concentrations of { i petroleum hydrocarbons (7.2 parts per million total petroleum hydrocarbons). It is reported that the removed UST did not show any signs if leakage, and excavated soils were replaced within the UST .. removal excavation following aeration activities (spreading and mixing soils on asphalt pavement surface). 5.1 January/February 1998 Soil Assessment j i. Based oii the due diligence requirements presented by Union Bank of California in an Interoffice i Correspondence dated December 23, 1997, H&H Engineering Construction, the current site owner and tenant, retained Krazan to conduct a Limited Subsurface Investigation on the subject site. The results of the subsurface investigation are summarized below and were presented in Krazan's February 16, 1998 report prepared for H&H. Engineering Subsurface Investigation, Former Underground Storage Tank Area, H&H Engineering Property, 212 Industrial Drive, Stockton, California. On January 14, 1998, two exploratory borings were advanced with a truck mounted drill rig utilizing eight-inch diameter hollow augers within the general area of the former UST on the subject site (see Site �fMap, Figure 2). Boring la was located in an area of significant asphaltic concrete cracking (area of possible excavation backfill settlement). However, native soils were encountered within this boring within a depth of three feet and this boring was abandoned since it did not appear that1l`this boring was i KRAZAN& ASSOCIATES,INC. �I Offices Serving the Western United States 1! 3498081.WP