5.4. SR 05-17-2010 - Laserfiche WebLink

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Page5of6 Letter to Mr. Join Elks & Mr. Matt Ledvina RE: Revised SAA I~ydrogeologic Evaluation Report Eik River Landfill, Inc. A maximum spacing of 400 feet between downgradient compliance boundary monitoring wells has be used for the existing landfill, It is suggested that this maximum spacing be maintained for the landfill expansion. This implies that several additional upper outwash monitoring wells would be included in the monitoring network. The outwash unit consistutes the uppermost saturated groundwater flow pathway at the Site. Hydraulic head monitoring at the SDA indicates there is a downward hydraulic potential between the outwash and lower outwash units. Downward flow potential is not unusual for permeable units underlain blow-permeability deposits and it is not indicative of actual flow direction. The weight of the evidence suggests that flow in both outwash units is horizontal and that these units are not in direct hydra.L~ic connection. This evidence includes LIST~~er our meeting_ However, the potential does not ;however, downward migration of groundwater is not predicted due to the continuous till deposit at the Site. Dif~terent hydraulic gradients between units, uniformit~of the gtadients/flow field in each unit - if their were a si Z,~z ificant connection it would. he reflected in the gradients. Accordingly, WMI proposes routinely monitoring groundwater quality in the outwash unit. in-t~l-iir-...~~°~~* ° ~•°'°~°° ~° ~a°,,_,~±°,a_;K_ft,° .,t.., .,1., , .,;± ~.,h~-1 e--ice"„M°.,:~~d-tea T~~„~~~d-aooard~~gl3~It should also be noted that WMI will oontinue to monitor groundwater quality in residential wells west of the SDA on an annual basis. The 400 foot spacing interval on the downgradient side of the existing facility was largely based on the presence of the unlined, pre-subtitle D portion of the landfill. The spacing of the proposed monitoring points for the SDA is nearly 400 feet but takes into account the till highs that act as boundaries to groundwater flow along the west and southern property lines. S. Page 22, T~Vell bzstallation Schedule: The report states that the current network of monitoring wells is sufficient to monitor the expansion of the fill area through Cell 20. The southerly limit of fill of Cell 20 would correspond to plan station 246,100 based on available engineering plans for site development. From the Conceptual Hydrogeologic Model, Figure 17, a southwesterly component to groundwater flow from portions of the proposed fill area is apparent. There are no monitoring wells existing or planned within a reasonably close distance that would intercept these groundwater flow lines. The suitability of the existing network of wells to monitor the development of the site through Cell 20 is questionable. The expected life of the facility is mor°e than 19 years. The total remaining life of the existingpermitted landfill area and the expansion area is more than 28 years. The existing and proposed monitoring wells are located at the distance roughly 200 feet from the ultimate fill boundaries. The functionality of an early warning monitoring system during the operational life of the site with wells located in the proposed positions is questionable. The overall schedule for the placement of monitoring wells in relation to the site development needs to be further evaluated.