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Stockton Charter Way Commingled Plume - 3 - 6 March 2025 <br /> address deeper MTBE in the area of the SMW-10 well group, either the submerged <br /> screen interval of ART-9 should be deeper, or an additional deeper ART well should be <br /> installed in the vicinity. By 5 May 2025, Staff requests that you submit a brief work plan <br /> addendum to augment the scope of work to address deeper impact near the SMW-10 <br /> well group. <br /> Graph 1: SMW-10-81 MTBE Concentrations Over Time <br /> (Concentrations in micrograms per liter [ug/L]) <br /> 300 <br /> J\ <br /> m <br /> 7 <br /> 200 <br /> C <br /> O <br /> 100 <br /> a� <br /> u <br /> c <br /> 0 <br /> v 0 <br /> off° 0,off° 1 1 off° Off° ° o0° 'ti off° off° off° off° off° off° off° off° off° off° off° off° off° off° <br /> 1 1 1 1 1 1 1 1 'ti 1 1 1 1 1 1 1 1 <br /> — —MTBE MTBE Trend <br /> Graph 2: SMW-10-117 MTBE Concentrations Over Time <br /> (Concentrations in ug/L) <br /> 300 <br /> J <br /> 3 <br /> c 200 <br /> O <br /> 100 <br /> u <br /> c <br /> 0 <br /> v <br /> 0 <br /> O�°�0 O�°1\O'O�°1\°O O�°1\~O O�°1\11 O�°1\~~O�°~\1�O�°�\1A O�°1\1y O�°1v,O�°1\~�O� <br /> '1 1 1 1 1 1 1 1 1 1 1 1 1 I <br /> MTBE MTBE Trend <br /> Per Staff's request, Stantec proposed ART-10 well in order to address the MTBE <br /> concentration in groundwater that exceeded LTCP Groundwater Criteria near <br /> monitoring well SMW-19-81. This proposed ART well is deeper than existing nearby <br /> ART wells. Stantec proposes ART-10 with a submerged screen interval between 70 and <br /> 90 feet below ground surface (bgs) near wells SMW-19-81 and SMW-19-120. As <br /> SMW-19-81 is screened between 71 and 81 feet below ground surface (bgs), and <br /> deeper well SMW-19-120 is minimally impacted, the proposed screened interval of <br /> ART-10 is appropriate. Staff concurs with the installation of well ART-10 as proposed. <br />