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t Off-Site Groundwater Investigation Work Plan Page 4 <br /> Rainwater Car Wash, Manteca, California 95336 <br /> May 30,2012 <br /> ' water was discharged directly to the City of Manteca sewer system,,located approximately 25 feet south of the <br /> groundwater system. <br /> ' 3.2.7 AGE, Multi-Level Monitoring Well Installation Report— Fourth Quarter 2002, April <br /> 13, 2003 <br /> ' AGE advanced soil borings MW7 through MW 12 at the site to determine the petroleum hydrocarbon content in <br /> the deeper water zones previously identified. The monitoring wells were installed as multi-level screening <br /> intervals and manufactured from polyethylene. Generally,each multi-level well consists of six screened intervals <br /> ' located at depths between 30 and 35 feet bgs(A),60 and 65 feet bgs(B), 85 and 90 feet bgs(C), 115 and 120 feet <br /> bgs(D), 140 and 145 feet bgs(E),and 165 and 170 feet bgs(F).Each chamber has a 0.5-inch diameter.No soil or <br /> groundwater samples were collected during this investigation. <br /> 3.2.8 AGE, Groundwater Extraction Well Installation Report— First Quarter 2010, <br /> February 17, 2010 <br /> ' AGE advanced soil borings EW2 and EW3 to 47 and 42 feet bgs, respectively, between January 14 and 15,2010 <br /> to enhance the remedial action at the site.EW2 and EWs were single-completed as 6-inch-diameter groundwater <br /> extraction wells with screened intervals between 20 and 45 and 15 and 40 feet bgs,respectively.No soil or <br /> ' groundwater samples were collected during this investigation. <br /> 3.2.9 AGE, Groundwater Remediation Report- First Quarter 2010, May 18, 2010 <br /> ' AGE operated the groundwater remediation system from December 15,2009 to March 23,2010. During this <br /> remedial event, approximately 646,824 gallons of treated groundwater were discharged into the City of Manteca <br /> ' sanitary sewer system and 1.24 pounds of MTBE were removed. <br /> 3.3 Groundwater Monitoring <br /> ' Groundwater monitoring has been ongoing since July 2000.AA&A conducted the most recent groundwater <br /> monitoring event on April 10,2012. Significant concentrations of petroleum hydrocarbons contamination were <br /> detected in groundwater samples collected from off-site,down-gradient monitoring wells. The TPHg and MTBE <br /> ' contaminant plumes were undefined in the northwest direction. The TPHg concentration contours in groundwater <br /> and the groundwater flow rose diagram and are shown on Figure 3. <br /> 1 4. ENVIRONMENTAL SETTING <br /> 4.1 Regional and Local Geology <br /> According to the Geologic Map of California published in 1966 by the California Department of Conservation <br /> Division of Mines and Geology,the site area is within the Great Valley Geomorphic Province(GVGP)of <br /> ' California,a large,elongated,northwest-trending structural trough. The GVGP is subdivided into two major areas <br /> designated the Sacramento and San Joaquin Valleys,which have been filled to the present elevation with thick <br /> sequences of sediment ranging in age from Jurassic to present day,creating a nearly flat alluvial plain extending <br /> from the Tehachapi Mountains in the south to the Klamath Mountains in the north. The western and eastern <br /> ' boundaries of this province consist of the California Coast Range and the Sierra Nevada Mountains,respectively. <br /> Based on a General Soil Map from the San Joaquin County Soil Survey,published by the United States <br /> ' Department of Agriculture Soil Conservation Service in 1992,the site area is described as being within the Delhi <br /> an,i A <br /> ' �i&Associri7tes.4rer., <br />