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.CLEAR`!hATER <br /> G R O U P, I' N" C. <br /> Soil generated during, this ,portion of, the_project will'_be sampled and profiled', in '. <br /> accordance with the requirements"of,the County and 'the selected disposal -facility: <br /> This soil; and that.-soil remaining from the'earlier tank removal, shall be removed <br /> following receipt of-analysis and County,approval.. " <br /> `5.2.Evaluation of the-Distribution of-Hydrocarbon Compounds <br /> Clearwater recommends that an additional phase 'of subsurface investigation be <br /> completed in'order' to determine the extent of "hydrocarbon migration in the vadose <br />' and water saturated zone. , This investigation should consist of the installation of <br /> additional'soil .borings, boh on and off-site. The- evaluation of the extent of the <br /> -intermediate.sand.layer should.be included in subsequent phases of.activity, as this <br />' layer may have acted_ as a zone " of ,,preferential hydrocarbon concentration 'or <br /> migration. <br />' Clearwater. anticipates. that this ,phase of site ..characterization will include the <br /> advancement.of a single deep (into groundwater) boring through the backfilled tank' • <br /> cavity, as well as several additional borings on and off site. The.deep. tank"cavity <br /> boring would be converted into a'4-inch diameter monitoring well, suitable for use <br /> as an extraction point during pumping tests or longer term remedial measures. The <br /> E other borings would_ be converted into 2-inch diameter monitoring wells as <br /> appropriate.' �It is proposed that all water samples be analyzed for concentrations of <br /> diesel-range compounds,.iri addition to gasoline-range compounds, because, diesel <br /> was detected in soil" samples collected during- the preliminary:phase of site <br /> investigation. -It is also, recommended that the drilling program be designed to <br /> facilitate the complete. definition of contaminants in soil and groundwater during <br /> this phase-of field investigation, eliminating the.need for further site study. <br /> Clearwater also recommends the installation of four additional soil.vapor extraction <br /> wells_beneath the former tank. excavation: , Two of these wells.would''be"screened <br /> from approximately 35 to-45 feet below grade, in,the more fine grained sediments <br /> below the-intermediate sand layer' -The other 'two would- be screened. from,27'to 35 ' <br /> Meet below rade, within the .intermediate sand layer. This discrete screening is " <br /> - g Y g - <br /> required in-order topreventr.event vapor "short circuiting" durin testiior lon e -term <br /> extraction,- thereby adequately 'addressing contaminants in ,the 'respective <br /> sedirhentologic units. <br /> D-105'PSA 7 May 25, 1995 <br />