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, <br /> t <br /> C <br /> Wnght Enwronrnentai Seances,Inc <br /> The majority of the contaminant mass appears directly under the site in the vadose zone and <br /> within the A-aquifer in the 45 to 60 foot depth A residual vadose zone contaminant area is as <br /> mapped previously by Ramage in the vicinity of the former tank pit and wells MW-2 and MW-3 <br /> Contaminants were observed in the B-aquifer in up gradient CPT-03, but not down gradient <br /> CPT-04 and CPT-05 Ramage reported 1,2-DCA in CPT-02 across Charter Way from the site <br /> An off-site source is contributing contaminants to the site TPHG was present in CPT-03 In the <br /> lower portions of the A-aquifer and B-aquifer 1,2-DCA is present at in up gradient CPT-03 <br /> and appears present in the A-aquifer on-sate and down gradient at CPT-05 The similar range <br /> of detections from 21 ugll up gradient to 12 ugll down gradient in the A-aquifer indicates some <br /> source up gradient contribution of 1,2-DCA generally in the A-aquifer TPHG, BTEX, MTBE <br /> and 1,2-DCA were not observed in the A-aquifer or B-aquifer at down gradient boring CPT-05 <br /> The detections for 1,2-DCA all exceed the current California Maximum Contaminant Level <br /> (MCL) <br /> 7.0 Proposed Additional Monitoring Well Placement, Depth and Slotted <br /> Intervals <br /> Six additional new discretely slotted monitoring wells are proposed to monitor this dissolved <br /> contaminant plume The wells will be two-inch diameter Sch 40 PVC cased wells with <br /> machine 0 020 inch slotted and sand packed intervals Well slotted intervals were selected <br /> using the site stratigraphy and interpreted hydrostratigraphy aquifer contact relationships <br /> Wnght has discussed the feasibility of using multi-level wells with short discrete intervals using <br /> a pre-sand packed intervals and small diameter tube extending to the surface, constructed in <br /> one borehole However the sampling equipment and techniques for sampling at these depths <br /> in multi-level well design approach might result in problems collecting the samples Wright's <br /> discussion with the subcontractor indicated that they do not have the appropriate equipment <br /> for these installations and may not be able to reliably sample at depths below 50 to 60 feet <br /> Consequently it is Wright's opinion that conventional well installations are appropriate for the <br /> site at this time for this work <br /> Proposed New A-aquifer Wells <br /> Three wells are proposed for this aquifer as shown on Figure 4 Two new wells will be <br /> clustered in the A-aquifer on the Sheba Liquors property adjacent to the CPT-04 boring <br /> These wells will be discretely slotted from 50-60 feet and one at 70-75 feet The well at 70-75 <br /> feet would be used to verify connection to the A-aquifer and monitor that pathway down <br /> gradient from the site One A-well will be installed across East Charter Way adjacent to boring <br /> CPT-05 and slotted from 47-57 feet <br /> Prosed New B-acguifer Wells <br /> At least three B-aquifer monitoring wells are needed to be able to plot groundwater flow <br /> direction One B-aquifer well will be installed adjacent to the new A-wells at CPT-04, with the <br /> B-well slotted from 115-120 feet One B-well will be installed on-site adjacent to the CPT-01 <br /> boring, slotted from 114-119 feet One 13-well will be installed adjacent to CPT-05 and slotted <br /> from 115-120 feet <br /> Stefano's—CPT Report <br /> Page 7 of 11 <br />