Laserfiche WebLink
50 INVESTIGATION RESULTS AND FIELD OBSERVATIONS <br /> Geophysical data and soil and groundwater analytical results are discussed below along with <br />' observations made in the field <br /> 5.1 Site Soil and Groundwater Conditions <br />' The subsurface site soils encountered during this limited site investigation generally consisted of a <br /> layer of fill overlying alluvium The log from the CPT boring indicated that the Site is underlain by a <br />' thinly interbedded sequence of silty clays, clayey silts, and stiff fine grained material The fill <br /> thickness in the monitoring well boring was about I meter (3 feet) and generally consisted of <br /> medium dense, silty gravel (0 6 to 1 2-centimeter in diameter) and moderate yellowish brown silt <br /> with some clay Alluvium, consisting of interbedded silty sand and clay, was observed underlying the <br /> fill to the maximum depth investigated of approximately 18 2 meters (60 feet) bgs A copy of the <br /> boring log is presented in Appendix B <br />' Based on the November 20, 2001 depth to groundwater measurement, the groundwater depth beneath <br /> the Site was approximately 15 30 meters (50 19 feet) <br /> 52 Geophysical Survey Results <br /> In order to calibrate the GPR data for depth, either the dielectric constant of the soil on the Site must be <br /> known, or the depth to a particular interface or object must be known Information was not readily <br /> available giving the depth to a particular interface or object on the Site The GSSI SIR System 8 manual <br /> states that an "average soil' has a dielectric constant of approximately 12 The standard formula for <br />' calculating depth based on the dielectric constant is as follows <br /> D — ) — 2(12 50 — 2 2 meters <br /> 2( <br /> r ' � <br />' 112 <br /> Where <br /> D=depth <br />' C=velocity of light of 3 x 10'meters per second=0 3 meters per nanosecond <br /> t=pulse travel time in nanoseconds=50 nanoseconds <br /> ET=relative dielectric constant on the material= 12 <br /> Using the standard formula for calculating depth based on the dielectric constant, 50 nanoseconds <br /> ' represent approximately 2 2 meters(7 2 feet)of depth <br /> The geophysical survey was inconclusive with regards to the location of MW-14 Interference from <br /> rebar in the concrete lining the drainage swale along the north edge of the area of investigation <br /> interfered with identification of GPR anomalies beneath it The concrete patch in the center of the area <br /> Project No S8475-06-02 -10- December 26,2001 <br />