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Mr. Mark Clardy <br /> ' Page 2 <br /> April 3,2006 <br /> • borings were advanced, and 329 soil samples and 42 groundwater samples were submitted for <br /> ' analysis. For reference,the analytical tables and soil and groundwater data presentation figures <br /> are reproduced in this workplan as Attachment 1. In a letter dated December 22,2005,the <br /> Regional Water Quality Control Board(RWQCB)requested additional delineation in a few <br /> ' areas. Clayton submitted a work plan for additional soil delineation in two areas, and additional <br /> groundwater delineation in five areas. As the further delineation is primarily focused on <br /> groundwater, and only minor additional soil delineation is planned, sufficient information exists <br /> ' to develop a soil remediation plan,and this plan is presented below. <br /> SITE CONCEPTUAL MODEL <br /> Development of remediation strategies depends on developing an understanding of the <br /> constituents present,the impacted media(soil and/or groundwater)and the sensitive receptors <br /> ' (i.e., groundwater, ecological,or human health-related issues). These factors are generally <br /> evaluated in a site conceptual model (SCM). SAIC has developed an SCM for the site to aid in <br /> understanding these issues. <br /> tSITE GEOLOGY <br /> Soil borings at the site indicate that the site is underlain by interbedded clays, silts,and sands. <br /> The uppermost 5 feet most commonly consists of a fine-grained unit,and this unit commonly <br /> extends to a depth of around 10 feet. Below 10 feet, sand, silt,and clay interbeds are common. <br /> Groundwater was typically encountered at around 19 to 20 feet, and stabilized at around 23 feet. <br /> SITE HYDROGEOLOGY <br /> ' Groundwater flow direction has not been specifically determined at the site. However,based on <br /> the regional topography and groundwater flow in other portions of the Mountain House <br /> development,groundwater flow is expected to be to the northeast. <br /> PRIMARY SOURCES <br /> Primary sources at the site would have consisted of the crude oil pipelines. Since the pipelines <br /> ' were deactivated in the 1960s and are no longer present at the site,no primary sources are <br /> present at the site. <br /> ' SECONDARY SOURCES <br /> Secondary sources may include impacted soils and separate-phase hydrocarbons(SPH)within <br /> the soil matrix. <br /> SPH in Soil <br /> ' SPH in soil was noted in areas B-2, B-3, and B-6,at depths ranging from 4 to 8 feet. <br /> 1 <br />