4.3. SR 10-18-1993 - Laserfiche WebLink

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. Ms. Amy Hadiaris Minnesota Pollution Control Agency September 28, 1993 Page 3 geologic cross sections depicting the waste fill in relation to till and outwash units must be constructed. In construction of these cross sections, till and outwash contact points, as presented in the CAIR, may have to be modified. Attached to this letter, as Attachment A, are errors and inconsistencies that BAL determined were made while interpreting monitoring well boring and gamma logs for construction of soil boring cross sections. These errors were found on soil boring cross sections presented in the CAIR. The errata information in Attachment A should be used in redrawing waste/fill cross sections. The hydrogeological discussion should more specifically define velocity direction and magnitude in three dimensions over the area of study. These velocities would be calculated using a sufficient variance of horizontal and vertical hydraulic conductivity values to effectively characterize the heterogeneous hydraulic conditions found at the site. e The contaminant migration discussion should contain an analysis of the types of contaminants detected at the site including their physical/chemical properties and their degradational and migrational characteristics, i.e. dispersive, diffusive and sorptive behaviors of individual chemicals. Using this information, as well as geological and hydrogeological interpretations, potential contaminant migration scenarios should be discussed as a precursor to identifying feasible remedial alternatives. 6. The CAIR addendum should also propose a residential well monitoring program. Included in this program should be those wells that have the potential of being impacted by off-site migration of contaminated groundwater based upon contaminant migration study. 7. At this juncture two options are being considered for remedial approach. o The City's consultant BAL is of the opinion that some interim groundwater corrective actions should be pursued within a short time frame. MPCA groundwater intervention limits have been continually exceeded for the past five years. Exceedance of intervention limits at this site warrants the timely implementation of corrective action. This has not occurred. e BAL proposes that ERL implement a groundwater pump and treat system in the area of highest contaminant concentration immediately adjacent to the waste fill boundary. An interim groundwater withdrawal and treatment system will have the following beneficial effects: