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04/09/98 THU 07:57 FAX GROUNDWATER <br /> April 8,Igoe <br /> Fea,wrty Evekmmn for Umhd ex=40 n va 1"Mi Ren v soon Merlwds Pape 7 <br /> S,MWd 20304,455GrvM Line Road.TWY.CA. <br /> post.Excavation Groundwater Monitoring Well Construction and Installation <br /> One groundwater monitoring well will be installed near the current location of well GWE-3 atter completion of <br /> remedial excavation and pit area backfilling and compaction. The wall will be drilled to 15 feet below ggradea and <br /> soil samples will be collected for analysis at 5 feet below grade. The camp <br /> by EPA Method 6015M020 for TPHI,benzene,toluene,ethyibenzene,and total xylenes,and for meth <br /> depths of 10 and 1yl tertiary <br /> butyl ether by EPA Method 8280. <br /> The well will be constructed of 24nch casing,perforated from about 10 feet below grade to about 5 feet below <br /> grade. Seed titer packing will surround the well casing to about 4 feet below grade,overlain by bentonite pellets <br /> saturated in place as a seal. The bentontte seal will extend to about 2 feet below grade. From 2 feet below grade <br /> to ground surface,the well will be completed with concrete,and enclosed at ground surface with a Christy well <br /> box. <br /> Previous data Indicates that suit types at the site consist of clay and silt to about 10 fest below grade,underlain by <br /> higher-permeabliity sand from about 10-15 feet below grade. Although samples will be obtained from depths of <br /> more than 10 feet below grade,the well will be set within the lower-permeability soil types at the request of the <br /> SJCEHD to prevent vertical migration of any residual hydrocarbons to more permeable strata. After collection of <br /> the 15-foot-depth sample,the borehole will be backfilled with bentonite pellets to about 10 feet below grade. <br /> Approximately 4 inches of sand filter pack will be placed on top of the bentonite seal prior to setting the well,to <br /> reduce the possibility of bentonite clogging the well screen. <br /> Proposed Path to Closure <br /> Two quarters of post-excavation groundwater monitoring data will be collected to verify stabilization of d"molved <br /> hydrocarbon levels in the former location of the source areas. if substantiated by post remediation data,closure <br /> will be requested by the end of 1998, <br /> please call me at 510-370-3990,ext 350 if you have any questions or require further information. <br /> Cordially, <br /> FLUO ANIEL GT FLUOR DANIEL GTI <br /> c <br /> Shelby Lathrop Simonr <br /> Project Manager Senior Geologist <br /> cc_ The Southland Corporation <br /> Attachments, Figure <br /> General Remedial Alternative Feasibility Analysis and Cost Comparison <br /> FLUOR DAM99L GTI <br />