ARCHIVED REPORTS_SITE CHARACTERIZATION WORK PLAN

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A Zone The A Zone typically extends from ground surface to approximately 20 to 25 feet below ground surface (bgs). The upper 10 to 15 feet of the A Zone consists of silt and clay with lesser amounts of interbedded sand. Sand units in the upper part of the A Zone are typically 1 foot to 2 feet thick, and are laterally discontinuous. The lower part of the A Zone consists of interbedded clay, silt, and sand. Sand units in the lower part of the A Zone are typically thicker than those of the upper A Zone (up to 10 feet in thickness) and can be correlated over greater lateral distance. The thickest A Zone sand sequences occur in the central part of the site, and thin to the east and west becoming laterally discontinuous. The basal portion of the A Zone and upper part of the B Zone typically consists of low-permeability silt and clay with minor interbedded sands. Over lateral distances of 100 to 200 feet, the thickness of lower permeability materials separating A Zone and B Zone sands may vary from 3 feet to greater than 10 feet. Depth to groundwater in the A Zone ranges from approximately 2 feet to 6 feet bgs. Groundwater levels typically fluctuate from 1 foot to three feet seasonally. Groundwater within the A Zone generally flows south to southeast with hydraulic gradients ranging from approximately 0.001 to 0.016 feet per foot(ft/ft). B Zone The upper part of the B Zone is encountered at approximately 20 to 25 feet bgs. The B Zone generally extends to depths of approximately 40 feet bgs; however basal portions of the B Zone have been defined down to depths of approximately 55 feet bgs. The B Zone tends to have a higher proportion of sand than the A Zone, and individual sands are more continuous. Low-permeability B Zone strata consist of silt and clay distributed through the upper part of the B Zone as described above, and are locally interbedded with B Zone sands. Groundwater within the B Zone generally flows east to southeast with hydraulic gradients ranging from approximately 0.001 to 0.015 ft/ft. The B Zone water levels also exhibit seasonal fluctuation. B/C Aquitard The B Zone is underlain by low-permeability silts and clays that comprise the B/C aquitard. The thickness of the B/C aquitard is highly variable. Variations in thickness are likely the result of localized scouring and deposition of overlying B Zone sands. The B/C aquitard is approximately 4 feet thick in the northwest part of the site, and thickens to the east and south where 10 to 20-foot thick low-permeability units are encountered. site Characterization Work Plan,Final, May 18,2012 1007-012.002 2-4