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,- - <br /> h _ T . <br /> •�,� k <br /> 2.2 VAOOSE INVESTIGATION <br /> Hydrocarbons have been confirmed in near-surface soils over an area about 50 x <br /> 85 feet. IT proposes initially to determine the vertical and lateral extent of <br /> vadose zone hydrocarbons, as follows: <br /> r Drilling three holes for groundwater monitoring wells. An average of <br /> three soil samples would be analyzed from each well bare in order to <br /> estimate hydrocarbon extent and concentration. <br /> _.: Brill two holes for vadose monitoring wells. Three soil samples <br /> would be analyzed from each well bore to estimate hydrocarbon extent <br /> and distribution. <br /> w Figure 3 diagrams the placement of subsurface sampling points. Methods for <br /> dril'.ing:and soil sampling are discussed in Section 3.1. <br /> 2.3 SOIL VAPOR COLLECTION SYSTEM <br /> IT believes it is important to prepare for in situ soil remediation while <br /> continuing the site investigation. Field observations indicate that a soil <br /> vapor collection system would probably be suitable at the site. Although <br /> �- -. native material is fine grained and apparently of low permeability (Section <br /> 1.2), rootlet holes up to one mm diameter were observed in many of the intact <br /> pieces of soil excavated from the site in February. These holes would likely <br /> is enhance permeability by several orders of magnitude, making soil vapor <br /> extraction feasible. <br /> L.: <br /> IT proposes the following to facilitate testing the feasibility of and <br /> facilitating completion of a soil vapor collection and treatment system: <br /> • Complete the two 30-Foot soil borings as vadose monitoring wells <br /> (Section 3.2). - <br /> '� Maintain the three remaining, existing groundwater monitoring wells <br /> as vadose zone monitoring wells and possible future vapor extraction <br /> points. <br /> • Place slotted pipe within the gasoline UST area as it is backfilled, <br /> to be utilized to extract sail vapor (Section 3.6). <br /> • Place closed pipe, running from the slotted pipe to an extraction and <br /> treatment area at the northwest corner of the site, in a trench, to <br /> _transport_sol l_vapor--(Sect i on-3.6).__ _-_ <br /> - 4 <br /> _IA:ENG:9205/031291 <br />