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3.0 Findings <br /> 3.1 H dro eolo <br /> Y g 9Y <br /> 3.1.1 Lithologic Descriptions <br /> A lithologic description for soil collected by Geoprobe° in boring DP-9 on March 30, 2006 is <br /> attached in Appendix E For comparison, Shaw' description of soils in boring MW-4-RD, made <br /> in March 2003, is also attached in Appendix E <br /> In boring DP-9 (made in 2006) the dominant lithology was brown to grey silt to 40 feet bgs, with <br /> a poorly graded sand layer at 18 5-21 feet bgs Sands were present from 40 feet to 60 feet bgs <br /> Silty sand was present from 65 feet to approximately 66 feet and grayish silt was present from <br /> 70 feet bgs, where the boring was terminated Trace amounts of caliche, oxidized wood <br /> fragments and roots up to 0 04 inch (1 mm) diameter were found from 60 feet bgs to 70 feet <br />' Results from the deepest and highest quality previously logged boring, made in 2003 (boring <br /> MW-4R) are generally similar <br /> Iridescent fuel sheen was observed in soil from two intervals beneath the water table in DR-9 <br /> from 47 5 to 48 feet bgs and from 52 5 feet to approximately 54 feet bgs The presence of fuel <br />� sheen indicates the presence of separate-phase hydrocarbons which significantly effects the <br /> selection of remedial options for site groundwater <br /> 3.1.2 Inferences from Conductivity Logging <br /> The MIP probe measured the total conductivity of the formation at a vertical resolution of less <br /> than 1 foot during advance The total conductivity is the response of the formation proximal to <br /> the probe head to an electrical signal The following responses are typical of subsurface <br /> conductivity <br />' o In the unsutured zone (i e , above the water table), conductivity is low <br /> a Conductivity in the saturated zone is higher than in the unsaturated zone in nearly all <br /> conditions <br /> o Conductivity is higher in clayey and silty formations than in sands and gravels This <br /> is because waters within clays and silts typically contain more cations (such as Na , <br /> K+, Ca+2, etc) and therefore are more conductive than waters in sands and gravels, <br />' which contain fewer cations The presence of cations facilitates electrical conduction <br /> o Conductivity is lower in zones where pore space is occupied by separate-phase <br /> hydrocarbons (SPH) <br /> ) <br /> ' &,DP.N IT&OPLM12W21 Do Rpdgm RptSVS1MSOM 2"SIR(A4"l dX <br /> 3-1 <br /> 82306 <br />