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Mr.Michael Infurna,SJCEHD April 7,2006 <br /> Well Installation Work Plan <br /> Palisades Station No. 835, Stockton,CA <br /> Page 7 <br /> monitoring well was never installed in this area. Stratus proposes to complete shallow <br /> screened monitoring wells MW-11 and MW-20 in this area. <br /> Stratus proposes to install conductor cased wells MW-12, MW-13, and MW-21 in the <br /> vicinity of borings CPT-2, CPT-1, and CPT-3, respectively, to enable monitoring of <br /> dissolved MTBE and TBA concentrations below first encountered groundwater. The wells <br /> will be screened across sandy strata that appear to be laterally continuous in the eastern <br /> portion of the site. <br /> Based on historical groundwater analytical data, the lateral extent of petroleum <br /> hydrocarbon impact to groundwater is not fully characterized southeast (generally <br /> downgradient) of monitoring well MW-8. Stratus proposes to install wells MW-15 and <br /> MW-16 to enable further evaluation of dissolved hydrocarbon concentrations in this area. <br /> The installation of monitoring well MW 17 will be completed south of boring CPT-2, to <br /> more fully assess dissolved hydrocarbon concentrations in this area. <br /> Although the groundwater flow direction below first encountered groundwater has not <br /> been evaluated, Stratus anticipates similar groundwater flow patterns in shallow and <br /> deeper water bearing strata, based on our experience monitoring other UST sites in the <br /> Stockton area. The non-detectable levels of MTBE and TBA in samples collected below <br /> 30 feet bgs in the three CPT borings situated in the western portion of the site are also <br /> suggestive that groundwater flow direction below first encountered groundwater may be <br /> similar to shallow groundwater flow. Given these assumptions, Stratus will direct the <br /> installation of conductor cased wells MW-18 and MW-19 east-southeast of the site to <br /> characterize the lateral extent of dissolved TBA and MTBE impact off-site below first <br /> encountered groundwater. The screening intervals of wells MW-18 and MW-19 will <br /> target similar strata as wells MW 12, MW-13, and MW-21- <br /> Groundwater <br /> W21.Groundwater samples collected between 21 and 28 feet bgs in borings CPT 5 and CPT 6 <br /> were impacted with TBA, at concentrations ranging from 23 gg/L to 1,400 µg/L. Stratus <br /> has previously interpreted (in the SCM) that impact in this area of the site likely <br /> originated from 7-11 facility #14117. Stratus will direct the installation of well MW-14 <br /> to monitor potential migration of petroleum hydrocarbons from the 7-11 site towards the <br /> Palisades property. Well MW-14 will be screened from approximately 20 to 30 feet bgs, <br /> across sandy soils that may represent a pathway for lateral migration of dissolved <br /> hydrocarbons. <br /> The proposed scope of work has been subdivided into tasks 1 through 4. Details are <br /> provided for the activities associated with each task. All geologic work will be conducted <br /> under the direct supervision of a State of California Registered Geologist or Civil <br /> Engineer and will be conducted in accordance with standards established by the <br /> California Regional Water Quality Control Board (RWQCB, Recommendations for <br /> KAUSA Gasoline\0835\Work PlanApalisades835 workplan2006.doc STRATUS <br />