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APR. -28' 99 (WED) 15: 11 UNOCAL '- NORTH RE TE1,:510 v+ 3781 _ P. 005 <br /> APR-26-1999 09=85 SaCB/CLFAN QATER­Ma�!9S 916 227 4349 P-03/04 <br /> collected from the bbft- :aid-matiO= p16i _sub> 9uen#ly con eaW film the well <br /> constructed at the loeatioel of the 6013118{Wt O,screened from 50 to 60 feet), it is <br /> obvious that the 77 ppb.M7'9 so-"-tive." <br /> 4, tJSTs arc not the only sourc'e"deMT'ft ii.dyetnvironment. It is true that MTBE is <br /> not detecmcd in W site wens but it is also.true.that the detections have beer, somewhat <br /> random and in wells upgtadiertt as*a as down.gradient of the site. This line of logic <br /> enema to presume that"back g vu '`ci�iii�t�atians of&-particular constituent should <br /> be uniform within the hydro$ e'er lfii°�Drt t:. As the data show variability in <br /> ba*49t'ound carrxxntratioits 6 '>flprgailu = Rue:m Amoss the site, variability in <br /> bu*vound eoneentrstioitia of oig ic`ransttltucnv can be expected to be even greater, <br /> 5. While Y don't know what the groirndweter.dernands in the Swdcton area wwo prior to <br /> 1993, it would be safe to.asamhe thattjj�'ci#� e- emand is equal or Bruer today. <br /> When viewing the dynamics.of the byidrulogio,aysWn involved, the rising water level <br /> at the site is a response to gremw-tim Hort W rainfall but am to a reduction in <br /> canaumpti..a use. The probable•tIelarlprtship'b�the deeper aquifers that <br /> production well pump:f DrO arid,tbi�iellp""." uridwatar matritarod at:he site is one <br /> of leakage through the:ir�tervQiuttg sa i. i laycy strata In this respect the shallow <br /> Broundwatcr arcd dcepbr. giyfera it e'ii ur=Faak'summadr pumping► the head <br /> di$enntial between tlu dceper.aqui .Md:shsllow groundwater may approach 50 <br /> lea or more though ftappasrt�t vpii �raxiimt.im the ynterval monitored ax the site <br /> would likdy approach 0.01. However, a dimi; comectich, ie., one were shadow <br /> groundwater flow is directly iatluenee&by pumping its the deeper aquifers, is not the <br /> case. The recommendation for a deep downgradient monitor well to detsrinine the <br /> magnitride and extant of impacts serggcsta that Ma staff have not Lhorcugtaly evaluated <br /> all data and than developed-a sound-c n=ptuapmodol for the site and its surroundings. <br />