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y <br /> ATC Associates Inc. <br /> (: <br /> V9%TC <br /> 1117 Lone Palm Avenue,Suite 201 <br /> Modesto,California 95351 <br /> 209-579-2221 <br /> fax:209-579-2225 <br /> ASS O C I ATE S I N C. <br /> field screened with a Photo Ionization Detector (PID) or similar instrument. Groundwater is <br /> assumed to be encountered at approximately 7 feet bgs. ATC estimates that approximately three <br /> to four soil samples will be collected for chemical analyses from each boring location. a <br /> Investigative derived wastes will be stored on-site in 55-gallon containers pending laboratory <br /> results. <br /> Groundwater Zone A Delineation <br /> The proposed scope of work described in this workplan is intended to evaluate the lateral and <br /> vertical extent of dissolved phase petroleum hydrocarbons. The lateral extent of the petroleum <br /> hydrocarbon plume in shallow groundwater (Zone A) is generally defined to the south in the <br /> vicinity of MW-2 and MW-3, but is not well defined to the north and west. <br /> The existing groundwater monitoring well network includes eight wells (MW-1 through MW-8) <br /> screened within shallow groundwater Zone A. Two additional groundwater monitoring wells are <br /> proposed to be installed in this zone. One off-site to the west across Holly Drive and the other <br /> will be on-site near the northwestern corner of the property. These groundwater monitoring <br /> wells will be used to evaluate and/or delineate the lateal extent of the petroleum hydrocarbon <br /> impacted groundwater plume within the A water bearing zone to the west and northwest of the <br /> identified source area. <br /> The proposed groundwater Zone A monitoring wells will be installed to approximately 25fee <br /> bgs collecting soil samples continuously. An estimated three soil samples will be collected for <br /> laboratory analyses from each boring, one from vadose zone soil above the capillary fringe, one <br /> from the capillary fringe, and one from the saturated zone. A reasonable effort will be made to <br /> collect soil samples representative of the vadose zone. Soil collected within the saturated zone or <br /> capillary fringe may not accurately represent adsorbed-phase petroleum concentrations, if <br /> present, due to the water component of the sample. <br /> The proposed groundwater monitoring wells will be constructed of 2-inch inside diameter, <br /> Schedule 40 PVC casing with approximately 20 feet of 0.010-inch slotted screen. A sand pack <br /> will be placed in the annulus of each well extending from the bottom of the well screen to <br /> approximately one foot above the top of the screen. Approximately one to two feet of bentonite <br /> will be placed on top of the sand pack and hydrated with potable water. The remaining annulus <br /> will be completed to surface with a neat cement grout slurry mix. To protect the integrity of the <br /> wells, locking, watertight well plugs will be installed on each well and a watertight wellhead <br /> labeled "monitoring well" will be set in concrete over each well. The proposed monitoring well <br /> locations are shown on Figure 3. Well construction diagrams associated with the A groundwater <br /> zone are provided as Attachment 1. <br /> hVW 7(V <br /> SAEnvironmenta1\25847\37 Tracy\Reports\wkp-addendum 2009.doc 5 <br />