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' GEOMATRIX WORK PLAN FOR ADDITIONAL GROUNDWATER INVESTIGATION Former Agricultural Chemical Distribution Facility 1904 West Charter Way, Stockton, California 1.0 INTRODUCTION ' On behalf of Glenn Springs Holdings, Inc. (GSHI), a subsidiary of Occidental Chemical Corporation (OCC), Geomatrix Consultants, Inc. (Geomatrix) has prepared this work plan for additional ' groundwater investigation at and in the vicinity of the former agricultural distribution facility located at 1904 West Charter Way, Stockton, California(the Facility). The Facility has been occupied by various agricultural chemical companies since 1955. The results of previous investigations indicate that soil and groundwater beneath and adjacent to the Facility contain various pesticides, herbicides, and solvents. The California Regional Water Quality Control Board—Central Valley Region (RWQCB) has reviewed historical data for the Facility, and in a 30 April 1998 letter to GSHI, requested that a background groundwater investigation be performed at the Facility and its vicinity to further evaluate the vertical and lateral extent of groundwater containing chemicals believed to be associated with the Facility. Specifically, the RWQCB requested a plan to: (1) evaluate background groundwater condi- tions, (2)further define the lateral extent of chemicals in groundwater in the shallow and intermediate zones, and (3)evaluate whether contaminants have migrated into deeper water-bearing zone(s) beneath the Facility and vicinity. ' This work plan describes additional groundwater investigation activities to be conducted at the Facility ' in response to the RWQCB's requests. These activities are designed to further evaluate the vertical and lateral extent of groundwater containing chemicals upgradient, beneath, and downgradient of the Facility, establish background groundwater conditions for the Facility, and further characterize the ' hydrogeologic conditions beneath the Facility and vicinity. Section 2.0 of the work plan describes background information pertinent to the proposed characterization activities, Section 3.0 presents a ' description of the proposed groundwater characterization methods, Section 4.0 presents a preliminary schedule for the proposed characterization, and Section 5.0 presents references used in developing this ' characterization program and in preparing the work plan. The work plan is based on published regional studies and on reports of previous Facility assessments by TreaTek-CRA,Inc. (TreaTek)and others. ' 2.0 BACKGROUND This section provides a description of the setting, history, and hydrogeologic conditions beneath the Facility and vicinity. t ' bPROlECT08f9,p000FffIT)Bf9d]Ett 1