FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

i 9.0 REMEDIAL DESIGN SPECIFICATIONS This section provides practical information to be used in the conceptual design of the Central Area wellfield, including well locations, discharge and injection rates, and recommendations for screened intervals. ICE well effluent concentration data is also provided for use in the design of the Central Area water treatment system. Construction design specifications (e.g. well materials, discharge piping locations, etc.) and injection well design specifications are not provided in this document. The proposed Central Area well-field design is based on the Optimal Design Scenario presented in Section 8.4.5. Minor adjustments to extraction/injection rates and/or additional wells may be required based on the results of model sensitivity analyses and operating experience. 9.1 Well Locations Figure 9-1 shows the locations of 11 proposed Central Area extraction wells and nine injection wells. Model results indicate the injection of treated water will require two additional wells in the North Balloon Area in order to maintain adequate capture and optimal removal efficiency. These wells are also identified on Figure 9-1. If injection of treated water is not included in the final design, these additional North Balloon wells will not be necessary. The proposed Central Area extraction well design will function without injection of treated water. Model results show that the injection of treated water does not adversely affect plume containment or substantially increase the rate of ICE removal from the Central Area. The proposed locations of extraction wells in Figure 9-1 correspond to locations of existing monitoring wells (with the exception of well CB-1), and will be completed as new installations with a unique well name (extraction well names are not proposed in this document). Model results suggest that existing monitoring wells are well positioned to allow containment and efficient removal of ICE. The designation of existing well locations as extraction well locations • allows flexibility in extraction well design. New extraction wells may be installed immediately adjacent to existing well locations, and existing monitor wells may be used as "back-up" wells in the event of extraction well failure or other design modifications. Model results suggest that removal efficiency and containment are nearly identical regardless of whether new or existing — monitoring wells are used (increased pumping rates of new extraction wells due to increased well efficiency and full penetration provides no significant improvement in TCE removal efficiency or containment). The two new extraction wells located at well cluster 453 and at well 460-AB may be completed as single extraction wells which are screened across the transmissive portions of the A and B zones. Combining well 453-A and 453-B into a single extraction well explains the apparent discrepancy between the number of wells simulated in the Optimal Design Scenario (12) and the number proposed in this design (11)). Well 460-AB is located in an area where a discernible aquitard is not present between the A- and B-zones; therefore, the separate screening of the A- and B-intervals at this location is academic. Any significant aquitards encountered during the . � O � 9 - 1