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Work Plan—Byron Road, Tracy, California June 16,2003 06-6102-00-2931-030 Page 2 polyvinyl chloride (PVC) well casing with 20-feet of slotted screen. The annular space was backfilled to near surface grade with gravel. The purpose of the dewatering wells is to lower the water table to facilitate the excavation. During dewatering well installation, Geomatrix Consultants, Inc. (Geomatrix) and Viking Drilling, Inc. (Viking), observed and logged the advancement of the well borings. Regional and Local Geology The study area lies along the western margin of the Great Valley Geomorphic Province at the northem end of the San Joaquin Valley. This province consists of a northwest trending, elongated lowland between the Sierra Nevada Range and the Coast Range, and is underlain by older marine sediments, younger fluvial and alluvial flood plain and delta deposits with a combined thick-ness greater than 10,000 feet. Locally, the study area is situated at an approximate elevation of 35 feet above mean sea level, underlain by silts, clays, and sands. Groundwater beneath the study area has been encountered between 5 and 22 feet bgs and flows in a northerly direction. Previous Environmental Investigations of Properties within Study Area Several private properties have undergone soil and groundwater investigations to facilitate development adjacent to the Byron Road corridor and the former pipelines. Previous property investigations are summarized below. McCormack Property According to a Geomatrix report entitled Summary of Soil and Groundwater Assessment and Recommendation for Site Closure, dated December 5, 1996; RESNA Industries (RESNA) performed a soil and groundwater investigation in September 1993. RESNA observed the advancement of seven soil borings near the northern site boundary that ranged in depth between 5 and 10 feet bgs. Soil samples were collected from five of the seven borings at depths ranging from 5 to 6.5 feet bgs. No soil samples were collected from two of the borings due to what RESNA called "obvious soil contamination." Soil samples were submitted for analyses of Total Oil and Grease(TOG)by Environmental Protection Agency (EPA) Method Standard Method 5520 E&F and benzene, toluene, ethylbenzene, and total xylenes (BTEX)by EPA Method 8020. One grab groundwater sample was collected from an area of non-affected soil and analyzed for the above constituents. Benzene was not detected in any of the soil samples analyzed. TOG was detected in two of the five soil samples analyzed at a maximum concentration of 730 milligrams per kilogram (mg/kg). Petroleum hydrocarbons were not detected in the grab groundwater sample analyzed. In July 1995, Ground Zero Analysis, Inc., (GZA) conducted a soil and groundwater investigation to explore previously documented affected soil near the northern boundary of the site. GZA supervised the advancement of two soil borings. One soil boring was drilled as a pilot hole to determine depth to groundwater(approximately 6.5 feet bgs) and a second was drilled to collect an unsaturated soil sample and grab groundwater sample. The soil sample was collected from approximately six feet bgs and the grab groundwater sample was collected from approximately l l feet bgs. Soil and grab groundwater samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg), as kerosene (TPHk), as diesel (TPHd), and as weathered crude (TPHc) by EPA Method 8015 Modified, for Total Recoverable Petroleum Hydrocarbons (TRPH) by EPA Method 418.1, and polycyclic aromatic hydrocarbons (PAHs) K:CVX-OVP\ROW_SITES\westsidechannelWmftworkplan.doc