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Interim Emergency Remedial Action/Monitoring Well Installation Work Plan Page 6 <br /> Former Union Facility,-Cutter Lumber <br /> Project No 102 2 <br /> May 20, 1997 <br /> 1 <br /> 2.2 Proposed Free Product Extraction Well Installation <br /> A free product extraction well (EW-1) will be installed through the back-filled excavation <br /> for the purpose of skimming free product off of the water table The following sections <br /> discuss the construction of the well, the well sampling plan as well as the free product <br /> skimmer installation <br /> 2.2.1 Extraction Well Installation and Construction <br /> A soil boring will be installed to a total depth of 40-45 feet below ground surface through <br /> the back-filled excavation In order to increase the effective well diameter, we propose to <br /> drill the well using a bucket auger type drilling rig The diameter of the bore will be from <br /> 36 to 48 inches in diameter One soil sample will be collected from the boring at the <br /> capillary fringe for analysis (see section 3 1 2 for details on soil sample analysis) <br />' The well will be constructed using 4" Schedule 40 PVC flush threaded casing from 0 to <br /> 20 feet below ground surface The well will be slotted from 20 to 45 feet below grade <br /> using 040 inch slotted casing The annulus between the slotted 4 inch well casing and <br /> the borehole will be filled with pea gravel from the total depth of the boring to t18 feet <br /> below grade, i e , 2 feet above the screened interval A two foot thick bentonite transition <br /> seal will then be installed followed by clean sand compacted in lifts to 2 to 3 feet below <br /> I ground surface The uppermost 2 to 3 feet of the annulus will be filled with concrete to <br /> act as a surface seal A locking water tight cap enclosed in a traffic rated well box will be <br /> installed in two feet of concrete at ground surface to protect the well (See Figure 4 for a <br /> schematic of the free product extraction well) <br /> Due the very clay-rich, impermeable nature of the soil, it is our opinion that a standard 12 <br />' inch diameter borehole may not yield sufficient surface exposure between the filter pack <br /> material and native soil to facilitate rapid free product removal Using a 36 to 48 inch <br /> diameter auger will have the effect of increasing the effective area of the well bore from <br />' 0 79 square feet in the case of a 12 inch diameter bore, to 7 1 square feet for a 36 inch <br /> bore or 12 6 square feet for a 48 inch diameter bore The exposed circumference of the <br /> I well bore will be increased from about 3 1 feet to 9 4 feet in the case of the 36 inch bore <br /> to 12 6 feet in the case of the 48 inch boring This increased annular exposure to the <br /> native material expected to make the removal of free product to proceed at a much more <br />' expeditious rate than would be the case for a narrow diameter bore hole <br /> 2937 Veneman Ave ,#13240 Geo-Phase Environmental Inc Phone(209) 569-0293 <br /> Modesto,CA 95356 Fax (209) 569-0295 <br /> I <br />