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=i'S•L"i " rk `_ YA' .3.x3' a , w "Yr <br /> i <br /> 6 <br /> .y <br /> Mr.H.C. Winsor <br /> February 23, 1988 <br /> page 1p <br /> i <br /> M BTX concentrations in Wells W-2 and W-3 have decreased between July and November <br /> 1987• Factors that may have influenced this change in BTX concentrations include removal <br /> of free product, seasonal water level changes, and natural chemical and biological <br /> degradation. BTX concentrations in Well W-1 increased between July and November 1987• <br /> ... This may be due to Iateral dissemination of these constituents in the direction of Well <br /> W-1. Although Well W-1 iz: upgradient of the hydrocarbon source, the relatively flat <br /> gradient could allow for hydrocarbons toof in an u <br /> po pgradient direction toward Well W-1. <br /> Minor amounts of BTX have been detectcd in Well W-5, the off-site monitoring weU most <br /> Proximal to ARCO Station 434. Minor amounts of BTX were detected in Well W-4 in the <br /> ' August 23, 1987, and November 13, 1987, groundwater samples. BTX constituents were <br /> �- nondetectable in groundwater samples from Well W-4 on February 2, 1988, <br /> is shown ARCO has approved BC's design for a remedial system at Station 434. BC's remedial plan <br /> possible m Appendix 3. ARCO intends to implement the remedial system as soon as <br /> E BC recornmendsrformin <br /> g a geologic study of the area. Regional and site-specific <br /> geologic information, including existing well logs and geologic cross sections, should be <br /> obtained and reviewed. <br /> i <br /> BC also recommends the installation of an extraction well located in proximity to Well W-2. <br /> This, in addition to the eight existing on- and off-site monitoring wells, will be suffi <br /> to document the planned groundwater cleanup. cient <br /> J F BC j recommends performing an-� g aqu;fer test and groundwater modeling to determine the <br /> hydraulic communication between the shallow and dee <br /> " communication will be important <br /> returned to service. .for remediation, and for ppri aquifers.g when Well 12 can be <br /> It will also help to determine whether or not maintenance pumpin of <br /> u Well 12 will degrade the quality of the deeper <br /> recommendations are addressed in BC's work plan of additional Sco e of work A details of BC's <br /> ' pe (Appendix 4). <br /> 1 In addition, BC recommends that the City continue to hold Muttici al Wel <br /> service until the degree of hydraulic p 1 12 out of <br /> k aquifer has been determined. <br /> y odic communication between the shallow and the deep <br /> .. <br /> r <br /> , E tit <br /> S <br /> i <br /> C BROWN AND CALDWELL <br /> 72ASSIREET <br /> r - -ACAAMENT6.CA 55Bti• 97513940173 - - <br /> - -- - <br />