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hood 1.0 INTRODUCTION This Workplan was prepared by GHD Inc. (GHD) on behalf of the State of California Department of General Services, Real Estate Services Division (DGS-RESD), under Contract No. 3152182, Amendment 12 for the Siebold Construction (site) located at 820 S. American Street, Stockton, California (Figure 1). The work will be implemented under the State Water Resources Control Board's (SWRCB's) Emergency, Abandonment, and Recalcitrant(EAR)Account. The scope of work described in this document was developed with the Central Valley Regional Water Quality Control Board (CVRWQCB)to delineate impacted groundwater associated with the documented petroleum hydrocarbon release resulting from the previous operations of underground storage tanks (LISTS) at the site. This Workplan will be subsequent to a previous subsurface investigation to determine the lateral extent of petroleum hydrocarbon impacted soil and groundwater. The proposed scope of work will include the installation, development, and sampling of three (3) monitoring wells; development of the newly installed monitoring wells; sample collection and handling; and coordination with GHD's California State licensed land surveyor to survey the locations and elevations of the new monitoring wells. 1.1 OBJECTIVE The objective of the proposed work is to investigate and define the lateral extent of petroleum hydrocarbon impacts to groundwater resulting from the previous operations of the USTs. 1.2 SITE DESCRIPTION The topography at the site is relatively flat and the property is surrounded by mixed commercial and residential properties. The three former LISTS were located in the central and western portions of the property. The former dispensers were located to the north of the former LISTS (approximate locations shown on Figure 2). Groundwater was previously encountered at approximately 36 feet below ground surface (bgs) as reported in historical subsurface investigation reports by other consultants. Based on the surrounding topography and groundwater data from nearby facilities, regional groundwater flow was inferred to be westerly, but was calculated to be northerly during this well installation report. 1.3 SITE HISTORY Based on the file review of the available historical data, the site contains residual soil impacts from gasoline components and, to a minor extent, from diesel fuel, primarily beneath and adjacent to the former 2,000-gallon gasoline UST. The three former USTs have been reportedly removed from the site in 1989 and 1990, which included one 2,000-gallon gasoline UST, one 8,000-gallon gasoline UST, and one 1,000-gallon diesel UST. Soil samples collected within the immediate vicinity of the former LISTS have been reported to contain: total petroleum hydrocarbons as gasoline(TPH-G) up to 4,600 milligrams per kilogram (mg/kg), benzene, toluene, ethyl benzene, and xylenes (BTEX) constituents up to 48 mg/kg, and total petroleum hydrocarbons as diesel (TPH-D) up to 66 mg/kg. The soil data is from a subsurface investigation performed in 1993. Limited over-excavation of impacted soil was performed around the 8,000-gallon gasoline UST, tank dispenser, and the 1,000-gallon diesel UST. It is unknown at this time as to the extent of the over-excavation or the exact location of the former 8,000-gallon UST. One groundwater monitoring well was installed in 1997 located in the sidewalk immediately to the west of the former 2,000-gallon gasoline UST. Groundwater samples collected after the monitoring well was installed were reported to contain TPH-G at 52,000 parts per billion as reported in the September 20, 2007 letter by the CVRWQCB. Monitoring well MW-1 has since been destroyed. 03009-10017-37110 1 of 6 March 2014