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John Yoakum [EH] From: Larry Witwer <larryw@amiadini.com> Sent: Friday,August 16, 2013 1:07 PM To: John Yoakum [EH] Subject: RE:420 W Yosemite, Manteca Attachments: Elder 2013-08-01 CVRWQCB_install new down-gradent wells.pdf; Elder triple-nested well construction diagram_Proposed_08-15-13.pdf, Elder_p01_GVA_WP_Figure01 _Proposed Wells-Revised-Triple Nested-08-2013.pdf John, We have some new developments on the subject case to report to you which are described below. We recently received the attached directive from the Oversight Agency (Central Valley RWQCB). Following our submittal of an MTBE Plume Travel Model (Fate and Transport Model) that was requested to estimate the fate and transport of the groundwater contaminant plume, the Agency responded as follows. The Agency concluded that the Model results do not support closure under the State Water Resources Control Board Low Threat Closure Policy (LTCP), which does not allow petroleum releases to impact water supply wells. The Agency further directed that the proposed off-site wells as we had permitted with your office now be installed, with a further condition that depth-discrete well clusters must be constructed to monitor at least the first three water-bearing zones down-gradient of MW-11. The wells we had previously proposed and permitted with your office included two separate split wells at four locations (MW14A, MW14B, MW15A, MW15B, MW16A, MW16B, MW17A, and MW17B), which will be located next to each other and each having a different screen interval and depth (one 2-inch well to a depth of 30 feet below ground surface (bgs) and one 2-inch well to a depth of 70 feet bgs.). The objective here was to monitor the first two water-bearing zones. We are now required by the Agency to provide an additional well in each location to monitor the third water- bearing zone, which is estimated to be at a depth range of 135 to 145 feet bgs. Installing three separate depth-discrete wells in clusters at each location would be a very expensive undertaking. We have thus looked into alternative well designs that may save on the costs. We arrived at a design that we would like to get your preliminary approval of. We are proposing to install a triple-nested well to a depth of 146 feet bgs at each of the four locations. Each of the three well casings would be 1 inch in diameter, and would be installed in an 8-inch diameter borehole utilizing a HSA-type drill rig. The well casings would be strapped together with cable ties at minimum of one (1) cable tie per ten (10) linear feet of casing during well installation to ensure the casings remain true to center and provide a minimum 2 inches of filter pack on every side. Attached is a well construction diagram which details this proposed well design and a site map depicting the four proposed well locations . Before we move forward with this design, we are asking for your input and preliminary approval of this well design in concept. Following that, once we have the Central Valley RWQCB approval of the design, we will submit new well permit applications to your office. Please note that the Agency is also requiring in the attached directive that existing monitoring wells MW-7 through MW-13 be abandoned. We are not asking for guidance on this task, and we will submit well abandonment permit applications to your office when the times comes to proceed. Thank you for your time and attention to this matter and we look forward to hearing from you. 1