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1 <br /> Ellet® <br /> iMr James L Barton <br /> 1 December 2, 2004 <br /> Page 4 <br />' and the RIW, sediments consist of anastomosing silts and clays with minor sand to a depth of <br /> approximately 50 feet bgs Below 50 feet, sand generally predominates with minor silt and clay <br /> Groundwater Depths and Flow Directions <br /> Site stratigraphy is generally segregated into four hydro-stratigraphic units The shallowest <br /> wells are screened across the hydro-stratigraphic unit designated as Unit A and the deepest <br />' wells are screened across the hydro-stratigraphic unit designated as Unit D Although four <br /> groundwater zoites have been designated by EAI, the water table elevation data and <br /> subsurface lithology reported on boring logs do not appear to support the existence of more <br />' than one distinct hydro-stratigraphic unit <br /> The approximate depth intervals corresponding to the hydro-stratigraphic units, as defined by <br /> EAI are as follows <br /> Hydro-Strati graphic Unit Depth Interval feet b s <br /> A 30-50 <br /> B 50-70 <br /> C 85-90 <br />'• D 97-103 <br /> The direction of groundwater flow beneath the site has been monitored since 1993 Data from <br /> these monitoring events indicates that groundwater flow is predominantly to the east <br /> Groundwater elevation at the site has typically ranged from approximately 33 to 38 feet below <br /> I ground surface (bgs) Groundwater contour maps produced with data from the fourth quarter <br /> 2004 Groundwater measurements recorded on July 12, 2004 from wells screened in zone B <br /> Indicate that the flow direction was to the east with an approximate hydraulic gradient of <br /> 0 006 feet per foot (fUft) <br /> Contaminants of Concern <br /> The primary contaminants of concern (CDCs) are total petroleum hydrocarbons as gasoline <br /> (TPHg) and benzene, ethyl-benzene, toluene, and xylenes (BTEX) Groundwater is monitored via <br /> forty monitoring wells screened at various depths across the aquifer The locations of the <br /> monitoring wells are depicted in Figure 2 <br /> Historical Contaminant Concentrations <br /> iHistorically, the aquifer at this site has been divided vertically into four zones which are designated <br /> A through D That majority of contaminants are confined in zone B, which is screened <br /> approximately 50-70 feet bgs The highest concentrations appear to be centered in an area under <br /> Robinhood Drive between MW-11 and MW-3 extending southwards to MW-2 Concentrations of <br /> TPHg and benzene detected during the fourth quarter 2004 groundwater monitoring and sampling <br /> I1DcsacramentolproiectslProiects10694015098-293TinanReports15098 RSE Results Report doc <br />