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Site Background Information: Herman and Helens Marina <br /> Page 3 of 13 <br /> Soil types in the uppermost fine-grained interval (40 to 70 feet bmsg) include silty clay, <br /> clayey silt and gravelly clay; a brown, wet fat to lean clay that appears to be laterally <br /> continuous was encountered near the top of this interval at approximately 45 feet bmsg. <br /> Below 80 feet bmsg, the dominant soil type of the two fine-grained intervals, based on CPT <br /> soil behavior properties, was silt, with occasional presence of interbedded sandy silt. <br /> HYDROGEOLOGICAL MODEL <br /> Based on the results of site-assessment activities to date, AGE has developed a <br /> preliminary subsurface model of the hydrostratigraphy comprised of nine informal zones, <br /> a vadose (unsaturated) zone and eight hydrogeologic units. Hydrogeologic or <br /> hydrostratigraphic units (HUs) are defined as a body of rock or sediment that has <br /> hydrogeologic characteristics (i.e. hydraulic conductivity, pore pressure, etc.) that make it <br /> distinct from surrounding bodies of rock or sediment (Sanders, 1998), or a part of a body <br /> of rock that forms a distinct hydrologic unit with respect to the flow of ground water(Maxey, <br /> 1964). A 'flow unit' may be defined as a hydrogeologic unit and is characterized by <br /> significantly greater hydraulic conductivity values than overlying and underlying units; a flow <br /> unit is capable of serving as a preferred migration route, and could potentially allow <br /> migration of large contaminant masses over great distances. The model presented is <br /> interpretational and will be modified as more data is collected. The nine vertical zones, <br /> measured in depth below maximum surface grade (bmsg) at the top of the levee, are as <br /> follows (depths are approximate and can vary by several feet across the site): <br /> Vadose Zone, ranging in thickness on the levee from approximately 6 feet adjacent to the <br /> slough to approximately 20 feet at the eastern edge; in the flat land east of the levee, <br /> vadose-zone thickness is approximately 4 feet. This unit is comprised predominately of <br /> engineered fill material. <br /> Hydrostratigraphic Unit 1 (HU1), extends from the top of the current saturated zone (6 to <br /> 20 feet bmsg at the top of the levee) to approximately 30 feet bmsg. This interval is <br /> comprised primarily of peat, and is characterized by generally low pore-water pressures <br /> and low CPT-interpreted hydraulic conductivities;the hydraulic conductivities(10"8 cm/sec) <br /> were consistent with laboratory-derived values of 10` cm/sec. <br /> Hydrostratigraphic Unit 2 (HU2) extends from approximately 30 to 40 feet bmsg and <br /> consists dominantly of silty to fine sands. CPT-derived hydraulic conductivities in this <br /> interval ranged from 104 to 10-6cm/sec, which is generally higher than laboratory-derived <br /> hydraulic conductivity values of 10-7 cm/sec. However, pore-water pressures are low, and <br /> rapid recovery in two pore-pressure dissipation tests suggests that hydraulic conductivities <br /> can be much higher in this interval. <br /> Hydrostratigraphic Unit 3 (HU3) extends from approximately 40 feet to 75 feet bmsg, and <br /> consists predominantly of fine-grained, silty clay and clayey silt; a laterally continuous, fat <br /> Advanced CeoEnvironmental,Inc. <br />