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0 0 <br /> 3) Maximize the cement well seal - especially in wells located within disposal <br /> fields. <br /> Well construction plans have been modified to increase the cement well seal 3 to <br /> 5 feet, corresponding to a final seal thickness of 8 to 10 feet thick. Actual well <br /> seal thickness shall be determined on a site-by-site basis employing one or a <br /> combination of the following: shortening the sand filter pack above the well <br /> screen (original proposed thickness of 3-feet); shortening the well screen <br /> (original proposed length of 10-feet); and shortening the well sump (original <br /> proposed length of 2-feet). The actual design modifications shall consider water <br /> table depth and historical seasonal variations in groundwater levels. <br /> 4) Increase horizontal survey accuracy of monitoring well locations. <br /> Based on our discussion with MacKay & Somps, the horizontal coordinates for <br /> monitoring wells in the Mossdale Subarea can be surveyed with an accuracy less <br /> than one-foot. We therefore plan to survey the horizontal coordinates for the <br /> monitoring wells at an accuracy of one-foot or less. <br /> 5) Locate and appropriately destroy previously installed monitoring wells not <br /> planned for future data collection activities. <br /> The attached Table 1 identifies all known pre-existing monitoring wells and <br /> piezometers located in the Mossdale and River Islands subareas. Some of these <br /> monitoring wells are presumed damaged or destroyed (the shaded well names in <br /> Table 1). To the extent possible, monitoring wells presumed damaged or <br /> destroyed shall be located, the well-casings removed, and the boreholes sealed <br /> as appropriate. The Monitoring Well Installation Workplan identifies some pre- <br /> existing wells to be destroyed or replaced; wells slated for destruction shall have <br /> their casings removed and the boreholes sealed as appropriate. The remaining <br /> pre-existing monitoring wells, whose locations and status have been confirmed, <br /> shall be incorporated into the Mossdale and River Islands subarea groundwater <br /> monitoring network, or continue to be utilized by developer consultants for data <br /> collection activities. <br /> If you have questions, please call John Fio at (707) 678-6458. <br /> Sincerely, <br /> John L. Fio <br /> Hydrologist <br />