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n <br /> ERI 227903 w01 Former Unocal Service Staaon 5498 Stockton Cahfom1a November 12 1998 <br /> Task 2-Evaluation of Dissolved Hydrocarbons <br /> Observe the drilling of three shallow soil borings (MW 10A, MW 14A, and MW 18) utilizing a <br /> hollow-stem auger drilling rig and constructing single casing groundwater monitoring wells in <br /> these borings The borings will be advanced to approximately 50 feet below grade (10 to 15 <br /> feet below anticipated first encountered groundwater) The screened interval will be across the <br /> existing groundwater surface ERI expects groundwater to be encountered approximately 36 <br /> feet below ground surface The locations of the proposed wells are shown on Plate 2 <br /> • Observe the drilling of four deep soil borings (MW 19D, MW20D, MW21 D, MW22D) <br /> utilizing a hollow-stem auger drilling rig and constructing groundwater monitoring wells in <br /> these borings The borings will be advanced to approximately 75 feet below grade (35 to 40 <br /> feet below anticipated first encountered groundwater) The locations of the proposed wells are <br /> shown on Plate 2 <br /> • Soil samples for lithologic evaluation will be collected at the surface and every five feet <br /> thereafter using a split-spoon sampler Samples will also be collected at noticeable interrupted <br /> changes in lithology as noted by the driller or field geologist during time of drilling Samples <br /> will be described using standard procedures (i e the unified soil classification system) <br /> • After the drilling and completion of each of the deep ground water monitoring wells noted <br /> . above, an adjacent shallow groundwater monitoring well will be drilled and completed The <br /> purpose of the adjacent shallow groundwater monitoring well is to have a discrete screened <br /> groundwater monitoring well with the well screen above and below the groundwater table as <br /> encountered during the time of drilling These four groundwater monitoring wells will be <br /> drilled within 5 feet (lateral distance) of each of the deep groundwater monitoring wells and <br /> will be designated MW19S, MW20S, MW21S, MW22S Wells will be drilled utilizing a <br /> hollow-stem auger drilling rig and constructing single casing groundwater monitoring wells in <br /> these borings The borings will be advanced to approximately 50 feet below grade (10 to 15 <br /> feet below anticipated first encountered groundwater) The screened interval will be across the <br /> existing groundwater surface ERI expects groundwater to be encountered approximately 36 <br /> feet below the ground surface <br /> • Develop newly installed shallow wells and deep wells and collect groundwater samples from <br /> each casing The discreetly screened deep casings will be sampled utilizing a low flow <br /> submersible pump <br /> • Submit groundwater samples to Sequoia Analytical Laboratories (Hazardous Waste <br /> Certification No 1210) for analysis of TPPHg using Environmental Protection Agency (EPA) <br /> Method 50301 8015 (modified), and benzene, toluene, ethylbenzene, total xylene isomers <br /> (BTEX) Detection limits for the tests requested and concentrations present will be stated on <br /> the laboratory reports Analytical methods and detection limits will conform to guidelines <br /> specified in the latest edition of the Tri-Regional Recommendations — <br />