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1.0 INTRODUCTION <br /> This Workplan was prepared by Winzler& Kelly on behalf of the State of California Department of <br /> General Services, Real Estate Services Division (DGS-RESD), under Contract No. 3152182. This <br /> scope of work was requested by the Central Valley Regional Water Quality Control Board <br /> (CVRWQCB)for the Siebold Construction (site) located at 820 S.American Street, Stockton, <br /> California (Figure 1). This Workplan has been prepared to initiate a subsurface investigation to <br /> determine if the soil and groundwater beneath the site have been impacted from the former <br /> underground storage tanks (USTs). The scope of work includes the installation of three monitoring <br /> wells and two soil gas monitoring points to determine the extent of on-site impacts. A 1,300-foot <br /> sensitive receptor survey will also be performed and the new monitoring wells will be used to <br /> implement a quarterly monitoring and sampling program. <br /> 1.1 OBJECTIVE <br /> The objective of the proposed work is to investigate the vertical and lateral extent of hydrocarbon <br /> impacted soil and groundwater in order to assist with moving the site towards environmental case <br /> closure. Based on previous investigations conducted at the site,hydrocarbon impacted soil is <br /> present beneath the former USTs. <br /> 1.2 SITE DESCRIPTION <br /> The topography at the site is relatively flat and the property is surrounded by mixed industrial / <br /> commercial and residential land uses. The three former USTs were located near the northwestern <br /> comer of the property, near S. American Street. The former dispensers were located to the north of <br /> the former USTs. Groundwater was previously encountered at approximately 36 feet below ground <br /> surface (bgs) as reported in historical subsurface investigation reports. Based on the surrounding <br /> topography and groundwater data from nearby facilities, groundwater flow is inferred to be <br /> westerly. <br /> 1.3 SITE HISTORY <br /> Winzler& Kelly has reviewed the available project files and reports. However, we have not verified <br /> the information; and therefore, Winzler& Kelly does not take responsibility for the accuracy of the <br /> data reported herein. <br /> Based on the file review of the available data, the site contains residual soil impact from gasoline <br /> components, and to a minor extent from diesel fuel,primarily beneath and adjacent to the former <br /> 2,000-gallon gasoline UST. The three former USTs have been reportedly removed from the site in <br /> 1989 and 1990, which included one 2,000-gallon gasoline UST, one 8,000-gallon gasoline UST, <br /> and one 1,000-gallon diesel UST. Soil samples collected within the immediate vicinity of the <br /> former USTs have been reported to contain: total petroleum hydrocarbons as gasoline (TPH-G) up <br /> to 4,600 milligrams per kilogram (mg/kg); benzene, toluene, ethyl benzene, and total xylenes <br /> (BTEX) constituents up to 48 mg/kg; and total petroleum hydrocarbons as diesel (TPH-D) up to 66 <br /> mg/kg. <br /> The soil data is from a subsurface investigation performed in 1993. Limited over-excavation of <br /> impacted soil was performed around the 8,000-gallon gasoline tank dispenser and the 1,000-gallon <br /> diesel UST. It is unknown at this time as to the extent of the over-excavation. One groundwater <br /> monitoring well was installed in 1997 immediately to the west of the former 2,000-gallon gasoline <br /> 03009.10017-37020 1 <br /> WINZLER&KELLY <br /> August 2011 <br />