Laserfiche WebLink
1 _ <br /> AW <br /> . , C' <br /> LEAR�VATER <br /> G- R O U P, I' N C. . <br />' zone pilot testing., , As thepresence of the existing tank .cavity precludes' the . <br /> 'assessment or :testing of sediments. in this area, -Clearwater ,recommends the <br /> excavation be"properly backfilled and -paved. priory to the commencement -of <br />' additional investigative efforts. .Clearwater recommends that tasks associated`with <br /> these,activities be.completed during the next phase of the project. <br />' In order to adequately. investigative measures Clearwater recommends the <br /> preparation ,of a -project workplan. This workplan' should describe in- detail all- <br /> measures associated with excavation backfilling and proposed site characterization LL 'activities summarized in" the •,following subsections. ' The workplan would be <br /> submitted after receipt of PHS/EHO concurrence with- the following conceptual <br />' approach. <br /> 5.1'Backfill of 1xisting Tank Cavity <br />' Sediments beneath the former tank area were shown by analyses bf samples <br /> collected during.tank removal to .contain concentrations of fuel hydrocarbons. The <br /> presence of the currently open excavation makes the- evaluation of the interval <br />'. between the i floor.of the tankP it and the •to ,of the'water table difficult, if not A. <br /> P <br /> impossible. This'is primarily due to,the fact that the location of the service station <br /> ' building and adjacent streets elirninates the possibility of significant additional . <br />' excavation, and the angle of approach required for' s would make slanted soil borings_ g PP q g <br /> this type of sampling impracticable. Clearwater .therefore recommends that- the <br /> excavation be backfilled prior to the commencement of additional investigation in <br /> the vicinity of the former tankfield. <br /> Clearwater Irecommends that, if possible, the excavation be deepened to ,20-25 'feet , <br />' prior to proceeding with backfilling, in <br /> order to expose the surface, of the sand unit . <br /> encountered during drilling. The• exposure of this more permeable unit -will <br /> Ifacilitate hydrocarbon recovery from the vadose zone. 'Four samples of-the,floor of- <br /> the excavation shallbe collected following completion of soil removal. The samples <br /> shall be forwarded to'the project-lab for analysis of conceritrations of previously ; <br /> detected hydrocarbon compounds. <br /> -.The excavation shall be backfilled,'with pea gravel or .other acceptable backfill <br /> material,, and compacted in `accordancewith the requirements of the appropriate <br /> .agency. If practical,several PVC or cardboard cylindrical forms will be placed:within <br /> the 'excavation 'during 'filling. The'. forms' will be- ;seated on .the. flooi- of _the <br /> I excavation, and will serve as vertical conduits 'for subsequent drilling activities.. The <br /> forms will be capped to prevent-infiltration I of rainwater or debris. , The drilling, - <br /> described below; would occur immediately 'following' completion of backfill <br /> t ; activities, 'in order to prevent mis-handlingof the forms. The surface shall be-paved <br /> following the' compietion of drilling activities. <br /> "D-105 PSA 6- May 23, 1995 <br />