SITE INFORMATION AND CORRESPONDENCE

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Public Notification—Generforder No. R5-20034044 w • Mountain House Creek Restoration Project, Mountain House, California July 6,2004 According to construction plans provided by Trimark Communities(Trimark), Byron Road will be reconstructed into a six-lane throughfare and railroad line with a bridge crossing over a widened Mountain House Creek. The proposed bridge crossing will require spread footings to an approximate depth of 23 feet below ground surface(bgs)that span the width of the proposed Byron Road ROW and Union Pacific Railroad ROW. As part of Trimark's development plans, the proposed Mountain House Creek will be widened into a greenbelt area to an approximate width of 300 feet and deepened to an approximate depth of 15 feet bgs. Due to Trimark's development plans, SAIC on behalf of ChevronTexaco conducted a soil and groundwater investigation of the proposed excavation areas. Petroleum-affected soil and separate-phase oil (SPO)were encountered in the vicinity of the existing Mountain House Creek at depths ranging between approximately 6 and 40 feet bgs. Thus it is likely that during the proposed excavation of the bridge footings and dewatering of the subsurface, SPO and petroleum-affected soil and groundwater will be encountered. Therefore, on behalf of ChevronTexaco, SAIC designed a groundwater treatment system for this project. SAIC in conjunction with Calgon Carbon Corporation (Calgon)of Richmond, California,will provide, operate,and maintain the groundwater treatment system. The groundwater extraction, treatment, and disposal system for the Mountain House Creek Restoration Project and bridge construction will consist of three separate processes. Teichert Construction (Teichert), on behalf of Trimark Communities, LLC, will be responsible for the dewatering well construction and extraction,transferring the groundwater to the treatment system and conveying the treated groundwater for disposal by land application. Disposal of treated groundwater will be in accordance with the requirements of Order No. R5-2003-0044, General Order for Land Disposal of Groundwater or Surface Water from Cleanup of Petroleum Pollution, California Regional Water Quality Control Board, Central Valley Region (the Order). Teichert will install up to 18 groundwater extraction wells to a total depth of approximately 40 feet bgs in the general vicinity of the proposed road and bridge construction activities. Submersible pumps, capable of withdrawing groundwater at a rate of 25 gallons per minute (gpm), will be installed in the dewatering wells to facilitate the dewatering activities and to lift the water to the treatment system. The number of groundwater extraction wells may decrease over the life of the project as the site subsurface is dewatered and the project progresses. The groundwater treatment system consists of six 20,000-gallon open-top holding tanks that have the ability to be plumbed in series or parallel depending on the quantity of SPO that is encountered. The SPO will be removed from the process stream using disposable absorbent booms and pads installed in the holding tanks. The absorbent will be replaced as needed during treatment operations. The holding tanks will also be used as settling basins to remove the suspended solids from the process stream. Groundwater will then be transferred between holding tanks using piping installed near the bottoms of the tanks. This underflow piping will assist in minimizing SPO from entering the treatment train. Groundwater influent samples will also be collected for chemical analyses at the final holding tank. Groundwater will be transferred from the final holding tank for treatment using a 500-gpm diesel-powered transfer pump. A trailer-mounted duplex cartridge filter pre-treatment system is located downstream of the transfer pump. The cartridge filter system consists of eight 10-micron mesh filter units, and will be used to remove any remaining suspended solids from entering the granular activated carbon (GAC)treatment system. The filter cartridges will be replaced as needed during system operation and maintenance activities. Suspended solids removed by filtering or settling will be disposed of in accordance with Section D of the Order. A mechanical flow indicator and totalizer is located downstream of the cartridge filter system and upstream of the GAC treatment system.