SITE INFORMATION AND CORRESPONDENCE

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M. S[ott Mansholt - 3 - 26 March 2007 Mountain House Site #1 0 0 Department of Water Resources (DWR) well completion records report three private wells within one-half mile of the site were completed with a minimum sanitary surface seal of 35-feet to 50-feet. Considering the depths of the sanitary seals coupled with the distance from the project site, dissolved petroleum constituents likely will not affect these domestic wells. Groundwater samples obtained during the investigation were submitted for total dissolved solids (TDS) determination with values ranging from 712 milligrams per liter (mgll) to 1,350 mg/l. According to the Water Qualify Control Plan for the Sacramento River Basin and the San Joaquin River Basin (Basin Plan), groundwater is considered a potential source of drinking water provided the TDS is less than or equal to 3,000 mg/l and yield of greater than 200 gallons per day. CHARACTERIZATION SUMMARY Regional Water Board staff concurred in our 8 March 2005 response that the affected soil and groundwater had been adequately delineated. The area of affected soil is limited with approximate dimensions of 150-feet by 200-feet; affected groundwater generally coincides with the outline of affected soil. The affected portion of the site is located within the Byron Road and UPRR right-of-way, and it is very unlikely that future commercial/industrial or residential development will occur on this site. Historical DWR records indicate that water supply wells in the area commonly are deeper and the sanitary seals extend below the vertical extent of affected soil and/or groundwater. HEALTH RISK EVALUATION The laboratory analysis as described in the January 2005 report, used conservative method detection limits for shallow soil samples, to support a future Human Health Screening Evaluation (HHSE). Samples for HHSE purposes were obtained from a depth of two feet and six to ten feet; lateral and vertical characterization samples were obtained at depths of up to 48 feet. Current land use for the site within the right-of-way will remain unchanged and will continue for the Byron Road roadway, ingress/egress needs, the UPRR railroad tracks, and for the other pipelines. Other than these features, additional development will not occur and it is very unlikely that residential and/or commercial use exposure to affected soil or groundwater will occur. Groundwater use does not exist at or in close proximity to the site and it is unlikely domestic/commercial use of the shallow groundwater will occur in the future. Consequently, provided groundwater wells are not installed, exposure pathways to potential receptors should not occur. However, given the permanent features at the site within the right-of-way, and anticipated future land use, the applicable human health risk scenario consideration will be for construction/trench worker exposure to affected soil and/or groundwater.