SITE INFORMATION AND CORRESPONDENCE

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USA#110 • - 2 - • September 2012 Claim No. 6098 ATTACHMENT SUMMARY OF BASIC SITE INFORMATION (Conceptual Site Model) Site Location/ History • The Site is located at 2132 East Mariposa Road in Stockton, California and is an active retail gasoline station. • The Site is bounded by Farmington Road to the north, East Mariposa Road to the southwest and a parking lot to the east. The surrounding land use is mixed residential and commercial. • In March 1987, soil contamination was identified during an environmental investigation. • To date, 17 active monitoring wells have been installed and monitored regularly. • A Site map showing the location of the current USTs, monitoring wells and groundwater level contours is provided at the end of this five year summary. Pollutant Source • Nature of Contaminants of Concern: Petroleum hydrocarbons only. • Source, Date reported, and Status of Release: UST system, 23 March 1987, USTs removed. • Free Phase Hydrocarbons: None reported. Geology/ Hydrogeology • Stratigraphy: The Site is underlain by interbedded and intermixed sand, silt and clay. • Maximum Sample Depth: 92 feet below ground surface (bgs). • Minimum Groundwater Depth: 45.82 feet bgs at monitoring well MW-17. • Maximum Groundwater Depth: 66.10 feet bgs at monitoring well MW-4P. • Current Average Depth to Groundwater: 46 feet bgs. • Saturated Zones(s) Studied: 45 to 92 bgs. • Groundwater Flow Direction: Northeast at between 0.002 to 0.007 feet per foot. Groundwater Trends: • There are more than 10 years of groundwater monitoring data for this Site. MTBE trends are shown below in source area well S-1 and down gradient well MW-17. METHYL-TERT-BUTYL ETHER (MTBE) Results for S-1 25000 20000 ,s000 10000 s000 _—__.,,,,.,�in •, _—�— i__ _..._—_ S' a` METKYL-TERT-BUTYL ETHER(MTBE) --- Trend ii