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M. Scott Mansholt • - 3 - • 4 May 2007 <br /> Mountain House Site #2 <br /> According to the Water Quality Control Plan for the Sacramento and San Joaquin River Basins <br /> (Basin Plan), groundwater is considered a potential source of drinking water provided the TDS <br /> is less than or equal to 3,000 mg/I and yield of greater than 200 gallons per day. As stated in <br /> SAIC's report, since the site is located within the Byron Road right-of-way, it is unlikely that the <br /> shallow groundwater and/or the site will be developed for future residential or commercial use. <br /> CHARACTERIZATION SUMMARY <br /> Regional Water Board staff concurred in our 14 July 2005 response that the affected soil and <br /> groundwater had been adequately delineated. The area of affected soil is limited with <br /> approximate dimensions of 75-feet by 100-feet; affected groundwater generally coincides with <br /> the outline of affected soil, although slightly larger. <br /> The affected portion of the site is located beneath Byron Road and within the Byron Road <br /> right-of-way, and it is very unlikely that future commercial/industrial or residential development <br /> will occur on this site. Historical DWR records indicate that water supply wells in the area <br /> commonly are deeper with sanitary seals of 35 to 50-feet, generally extending below the <br /> vertical depth of affected soil and/or groundwater. <br /> HEALTH RISK EVALUATION <br /> The laboratory analysis as described in the January 2005 report used conservative method <br /> detection limits for shallow soil samples to support a future Human Health Screening <br /> Evaluation (HHSE). Samples for HHSE purposes were obtained from a depth of two feet and <br /> six to ten feet; lateral and vertical characterization samples were obtained at depths between <br /> 27 and 44-feet. <br /> Current land use for the site adjacent to Byron Road and within the Byron Road right-of-way <br /> will remain unchanged and continue for use by the roadway, ingress/egress needs, and <br /> possibly for active pipelines. Other than maintenance related to these features, additional <br /> future site development will likely not occur and it is very unlikely that residential and/or <br /> commercial use exposure to affected soil or groundwater will occur. <br /> Groundwater use does not exist at or in close proximity to the site and it is unlikely <br /> domestic/commercial use of shallow groundwater will occur in the future. Consequently, <br /> provided groundwater wells are not installed, exposure pathways to potential receptors should <br /> not occur. SAIC's report stated that no surface water habitat is present within the area of <br /> affected soil and/or groundwater and thus, surface water receptor scenarios are not <br /> applicable. <br /> Consequently, given the permanent features within the right-of-way, and anticipated future <br /> land use, the applicable human health risk scenario consideration will be for <br /> construction/trench worker exposure to affected soil and/or groundwater. <br /> SAIC compared soil and groundwater analytical results of previous investigations to the <br /> Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater <br />