Laserfiche WebLink
Mr. Mike Desso -4- • 31 August 2011 <br /> improve the lateral characterization of COCs that have migrated from the former facility in the <br /> A or C Zones. <br /> City Water Supply Wells MW-8, MW-13, MW-16, and MW-18: City municipal water supply <br /> wells MW-8 (abandoned), -13, -16, and -18 are referenced but not shown on Figure 2 of each <br /> groundwater monitoring report. Nestle should include the locations of these wells on the <br /> figures of all future reports. <br /> Nestle Guard Wells for City Water Supply Well MW-10: Nestle has installed and currently <br /> monitors two guard well nests up-gradient of City water supply well MW-10: 1) the M-27 nest <br /> located approximately 1,960 feet east-southeast of the City well and 2) the M-29 nest located <br /> approximately 1,230 feet southeast of the City well. MW-10 pumps water from the C Zone <br /> and D Zone. The well is screened in the C Zone between 165 and 182 feet bgs. The purpose <br /> of the guard wells is to provide early warning of contaminant migration towards the City well by <br /> detecting COCs before they reach it. Well nest M-27 includes three monitoring wells: M-27A <br /> screened in the Lower A Zone 90 to 105 feet bgs, M27-C screened in the C Zone 122 to <br /> 142 feet bgs, and M-27D screened in the D Zone 200 to 210 feet bgs. Additional <br /> investigations must identify the current pathways that CDCs are migrating in and must <br /> evaluate the adequacy of the current guard well screen placements. <br /> Comment Summary <br /> The-following_list summarizes_Central Valley Water Board staff comments regarding <br /> necessary additional characterization work: <br /> 1) Additional investigation work is necessary to complete the lateral characterization of COCs <br /> in the A Zone near monitoring well nest M10. <br /> 2) Additional investigation soil borings drilled between CPT-23 and monitoring well nest M-13 <br /> are necessary to improve the lateral characterization of TCE migration from the former <br /> facility in the A and C Zones. <br /> 3) Nestle must resume quarterly monitoring and sampling of monitoring well M-13A because <br /> CDCs have recently migrated in this well and the concentrations are increasing. <br /> 4) Nestle should begin discussions with the City regarding recent detections of COCs in the <br /> guard well nest M-28 nest and in City municipal water supply well MW-3. <br /> 5) Nestle should begin discussions with the City regarding pumping rates at municipal water <br /> supply well MW-3, and any available information on its perforation intervals. <br /> 6) Additional investigation soil borings between CPT-30 and school water supply well RPS-1 <br /> are necessary to improve the lateral characterization of COCs that have migrated from the <br /> former facility in the A or C Zones. <br /> 7) Nestle must include the locations of all City municipal water supply wells, both existing and <br /> decommissioned. <br /> 8) Additional investigations must identify the pathways that COCs are migrating within and <br /> must evaluate whether or not current guard well screen placements are adequate to <br /> provide early warning of COC migration to City municipal supply well MW-10. <br /> Additional Investigation Requirements <br /> Nestle has made progress with the characterization of TCE and TCE-degradation products <br /> that have migrated from the former facility towards the northwest and west. The offsite CPT <br /> investigation conducted in 2010 has identified three sandy units within the A Zone in which the <br />