8.3. SR 05-16-2013 - Laserfiche WebLink

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In the City's opinion, ERL's attempt to demonstrate that surface water as the sole receptor for groundwater in this portion of the Site is not conclusive. The City clearly communicated to ERL and MPCA what scope of additional investigation would be necessary to enable a conclusive determination concerning the groundwater and surface water connection. The City remains opposed to the use of surface water standards at this facility because ERL has not sufficiently demonstrated that surface water is the appropriate receptor for potentially contaminated groundwater from the waste deposit. The groundwater performance standards presented in the Limits Table may not be adequately protective of human health and the environment. The Limits Table does not include recently constructed wells P323L and P324L, while it does include wells 315- OWA, 316-OWA, 322-OWA, 323-OWA and 324-OWA, which no longer exist or are not proposed for sampling. At a minimum, the Limits Table should be modified to reclassify wells such P304C, (which has a well screen near the base of the confined outwash) to groundwater compliance boundary wells. Intervention Limits The 2012 Annual Water Quality Report identifies numerous instances where parameters have exceeded the intervention limits for the wells located down gradient of the waste deposit. VOC Parameters The data for newly installed monitoring well, P323L, in conjunction with increasing parameter trends for P313C and P314C indicate that this area is a major area of concern for impacted groundwater leaving the Site. The investigation work that has been undertaken in recent years has located the major pathway for contaminated groundwater migration from the Site. ERL needs to develop a proposal for further evaluating groundwater conditions in support of a plan for mitigating contaminated groundwater. Chloride Results In recent annual water quality reports, ERL's interpretation of the results for chloride suggests that it is not a good indicator of a leachate release due to the use of deicing agents along Highway 169. The levels of chloride for wells adjacent to Highway 169 do indeed show significantly elevated levels of chloride. The concentration of chloride for wells which are more than 2000 feet from Highway 169 would be expected to approach natural background concentrations based on a simplified dispersion model. This is evidenced by the chloride results for unimpacted wells P303C, P305C, P311C and 408-OWA located on the west side of the Site. These wells show average chloride concentrations which average less than 5 mg/l over the last ten years of monitoring. Another important consideration for background chloride levels is the change in concentration over time. Deicing operations for Highway 169 has occurred for at least 50 years and it is expected that the potentially elevated concentration of chloride would be at a roughly steady state condition and concentrations would not vary significant from year to year. This is true for wells that are not impacted by the landfill, as evidenced by the plot of concentration vs. time for P311C presented in Appendix D. In contrast, the plots for P302C, P304C, P313C and P314C show increasing chloride trends with time. From this data, it is apparent that those wells are impacted by landfill leachate. This is further supported by the occurrence of VOC detections which correlate with the high