SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt -2 - 18• March 2009 Mountain House Development A In addition, low concentrations of three polynuclear aromatic hydrocarbons (PAHs) were detected at concentrations between 0.2 and 14.6 mg/kg. Groundwater, encountered at approximate depths of between 8 and 17 feet bgs, was not sampled. SAIC conducted an investigation in 2005, advancing eight borings to depths of 32 to 46 feet bgs. Twenty-eight soil samples and five groundwater samples were collected for analysis. Soil boring MH5-1, completed to a depth of 44 feet bgs near the 2001 borings, reported TPHc in samples from depths of 1, 8, 10.5, and 23.5 feet bgs at concentrations of 320, 14, 32, and 1,100 mg/kg, respectively. Benzene, toluene, ethylbenzene, and xylenes (BTEX) were ND except for ethylbenzene and xylenes detected slightly over the method detection limits (MDLs). PAHs were ND and/or detected at low concentrations slightly over respective MDLs. No analytical result exceeded screening levels. Based on the findings, SAIC concluded the lateral extent of crude oil affected soil was defined with approximate dimensions of 60 by 75 feet, centered near two borings completed at the Site in 2001 . The vertical extent was defined by ND results for TPH constituents from i the sample taken at a depth of 32 feet bgs in boring MH5-1. The area of affected soil is delineated beneath and within the Byron Road ROW easement. Analysis of the five groundwater samples reported TPH as diesel (TPHd) at 350 and 670 micrograms per liter (pg/L). The results for BTEX were ND as were PAHs except for concentrations detected at or slightly exceeding the MDLs in one sample. Additionally, the other three samples were ND for TPHd. Depth to groundwater was observed at approximately 13 to 18 feet bgs and based on information from nearby Mountain House Development sites, the gradient is northeast. There are no groundwater monitoring wells at the Site. Based on the 2005 investigation, the downgradient extent of affected groundwater was not defined and additional borings for groundwater sampling were proposed northeast of the Site. In July 2007, three borings were drilled northeast of the Site to determine the downgradient extent of affected groundwater and to evaluate water quality conditions. Soil samples submitted for laboratory analysis were ND for TPH constituents. Additionally, the three groundwater samples submitted for analysis were also ND for TPH constituents and thus the downgradient extent of affected groundwater was adequately delineated. As a result, the area of affected groundwater is defined at slightly larger than the affected soil area having approximate dimensions of 75 by 125 feet. To evaluate groundwater quality at the Site, samples were collected and submitted for General Mineral's analyses. The analytical results were compared to Water Quality Objectives (WQOs) described in: Central Valley Regional Water Quality Control Board— Wafer Quality Control Plan (Basin Plan) for the Sacramento River Basin and the San Joaquin River Basin, 4th edition, revised August 2006. The analytical results from the investigations were compared to the WQOs to determine the Site groundwater quality parameters. Total dissolved solids (TDS) concentration for groundwater samples submitted for analysis were greater than 1,100 milligrams per liter (mg/L), which exceeds exceed the U.S. EPA Recommended Secondary Maximum Contaminant Level (MCL) of 500 mg/L. The General Minerals analytical results of several mineral constituents exceeded respective WQOs, which are based on aesthetic (taste and odor) and technical (staining and corrosion) characteristics. Analytical results reported for iron, boron, sodium, and sulfate exceeded WQOs; iron and manganese also exceeded the WQOs and/or MCLs. SAIC stated that installation of new