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Knowles Gas Station <br /> 202/799-5027.02 <br /> w July 21, 1988 <br /> E . <br /> aa+ <br /> I Two general hydrogeologic divisions are recognized <br /> underlying this site which include consolidated to semicon- <br /> solidated units containing saline connate water, and the <br /> � F <br /> overlying unconsolidated fresh water-bearing units. The <br /> • consolidated to semiconsolidated rock units are composed of the <br /> Mehrten and the Valley Spring Formations. These formations are <br /> Eof volcanic origin and contain andesitic and rhyolitic breccia, <br /> fluffand ash. The groundwater wi`-hin these two formations-is <br /> saline and is hydraulically separated from the overlying fresh <br /> W! water-bearing units by an impermeable bed within the upper <br /> f*a <br /> Nlehrten Formation which impedes hydraulic communication between <br /> 9 f <br /> the aquifers. <br /> f <br /> The unconsolidated units consist of alluvial sediments of <br /> the Victor Formation, Arroyo Seco Gravel, and the Laguna Forma- <br /> tion. These formations are composed of detrital sediments which 't <br /> have a total thickness of approximately 1000 feet. Goad quality <br /> E groundwater is present in these units, under generally .unconfined <br /> conditions although locally confined aquifers exist.. <br /> ' eImp As evidenced by the drill logs (Appendix. I) the sites <br /> underlain by clay, silt, and sand with a clayey to silty sand <br /> 4' ( increasing with depth. The topography in the vicinity of the <br /> �+ site is relatively flat. Site elevation is approximately 13 feet <br /> i (mean sea level datum) . Intermittent channelized creeks comprise <br /> . the majority of the surface water in the area. Groundwater was <br /> encountered at a depth of approximately 49 feet within predomi- <br /> ;� nantly sandy soils. <br /> Groundwater monitoring performed at the site on June. 24, <br /> # �' 1988 revealed depths to groundwater. of 50.88, 51.29 and .49.89 <br /> Z <br /> i <br /> E yN <br /> r� <br /> t "' <br />