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I. INTRODUCTION Haley&Aldrich, Inc. has prepared this Work Plan for a subsurface investigation at the Stockton Elevator facility on behalf of Huff&Huff, Inc. and its client, ContiGroup Companies,Inc. The Stockton Elevator is located at 1805 Harbor Street in Stockton, California. This work plan describes our proposal to conduct soil and groundwater sampling in order to fill data gaps and improve our understand of subsurface conditions.-This better understanding will—in turn be valuable as we develop-a remedial strategy for the site. This work plan has been prepared in response to a letter from San Joaquin County Environmental Health Department(EHD) dated 9 September 2002. In the September 2002 letter EHD requested that ContiGroup better delineate the northern extent of the soil j contamination and the vertical extent of the groundwater contamination at this site. This ' report presents our plan for conducting a subsurface investigation in accordance with EHD directives. 1.01 Previous Environmental Work Four underground storage tanks (USTs) were removed from the site in 1988. One former tank, a 10,000 gallon UST near the southern portion of the property, is reported to be the source of petroleum hydrocarbon releases to soil and groundwater(Figure 1). An environmental investigation was conducted in phases between 1997 and 2000. In 1997, Smith Environmental Technologies Corporation advanced seven soil borings, six of which were in the vicinity of the 10,000 gallon UST. In 1998, ATC Associates, Inc. installed three groundwater monitoring wells at the site. ATC Associates installed three additional monitoring wells in 2000. 1.02 Soil and Groundwater Impact Sail. Figure 1 provides Haley&Aldrich's interpretation of the distribution of total � petroleum hydrocarbons-gasoline range(TPHg) and total petroleum hydrocarbons-diesel range (TPHd) in soil. The geometry of the soil impact probably reflects the lateral spreading of contamination in the capillary fringe above the 1997 water table. By 2002, groundwater had risen approximately eight feet, submerging much of the contamination that had previously been in the vadose zone. Over the course of the investigation in the late 1990's, light nonaqueous-phase liquid (LNAPL)was reported in wells or during drilling at MW-2, MW-4, SB-2 and SB-3. In 2002, LNAPL is reported to occur only in monitoring well MW-2. Groundwater. Figure 2 provides Haley&Aldrich's interpretation of the distribution of dissolved TPHg and TPHd in groundwater at the site. We plotted concentration contours for the 1997/1998 time period as well as contours from the most recent available data (June 2002). A comparison of these maps shows that the extent of groundwater contamination has apparently declined over the last five years. This decline is probably due in part to biodegradation of petroleum hydrocarbons; however, it may also be affected by variations in groundwater levels during this period. Since quarterly monitoring began in 1998, MUM 1