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' GENERAL DYNAMICS Additional Investigation —Roo 3; SWMU21 Workplan, Revised NovennW003 ' TECHNICAL WORKPLAN ' ADDITIONAL INVESTIGATION ROUND 3 WORKPLAN ' - GENERAL DYNAMICS OTS TRACY TEST FACILITY 32727 Corral Hollow Road Tracy, California ' This workplan (WP), prepared by Chow Engineering, Inc. (CE), for submittal to the Department of Toxic Substances Control (DTSC) on behalf of General Dynamics OTS (California), Inc. (GD), presents the scope of work for additional assessment of Total petroleum hydrocarbons (TPH) in soil and groundwater at solid waste management unit number 21 (SWMU 21) at the former GD Tracy Test Site (TTS) located at 32727 Corral Hollow Road, approximately 3.5-miles south of Tracy, California (site). The location of ' the site is presented on Figure 1. A map of the site is presented as Figure 2. ' 1.0 INTRODUCTION The additional investigation of TPHd and O&G in soil and groundwater has been ' requested by the DTSC based on the analytical results of groundwater samples collected during the implementation of the Additional Investigation Workplan at SWMU21 in March 2003 and soil sampling results from earlier sampling events in 2001 ' and 2002. The March 2003 soil sampling results taken together with previous sampling events have defined the lateral extent of TPH in soil below the investigative goal of 1,000 mg/kg TPHd and O&G. This limited area of TPH in soil extends radially away ' from the southeast wall of the SWMU21 tank wall to a maximum distance of approximately 50 feet. The vertical extent of TPHd and O&G contaminants has been defined within the soil clean up goal of 1,000 mg/kg with the exception of the S-26 t boring location where TPHd and O&G exceeded 1,000 mg/kg at the deepest sampling location (40' bgs). In March of 2003 soil samples were proposed for collection at S-32 approximately 100' east of SWMU 21 just down gradient of the storm drain at depths of ' 1', 3', 5' and 10' bgs. Bedrock was encountered at 3' bgs preventing the collection of samples at the 5' and 10' depths. ' Groundwater sampling results collected from monitoring well S-33, approximately 19' south of SWMU21, in March of 2003 confirmed TPHd at a concentration of 30 mg/I. ' This work plan proposes the installation of three additional groundwater monitoring wells, to allow water sample collection in order to better define the extent of TPH in the ' groundwater, and to determine the direction and rate of groundwater flow below and surrounding SWMU21. Collection of soil samples are also proposed east of S-32 at the storm drain outfall at depths of 5' and 10' bgs or until refusal, and at 5' intervals during ' the installation of the monitoring well S-37, which is south of boring S-26. These soil CHOW ENGINEERING, INC. 1