2020-09-09 CC Packet - Laserfiche WebLink

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3.0 VULNERABILITYASSESSMENT Two separate assessments were undertaken to determine the vulnerability of the City's water supply. The firstconsisted of an assessment of the vulnerability of the Prairie du Chien-Jordan aquifer to contamination within the identified DWSMA. This assessment was completed according to MDH guidelines and recommended methodology. The second assessment was a wellvulnerability assessment for the City’s wells. The well vulnerability assessment was also completed using MDH guidelines. A description of the two assessments is presented in City of CentervilleWellhead Protection Plan, Part 1 (Amendment), prepared by Stantec (December 2018). The result of the analysis is that the Prairie du Chien-Jordan aquifer in the vicinity of the DWSMA has “moderate” vulnerability. Moderate vulnerability indicates that while protective geologic layers appear to be present that could offer protection to the aquifers that supply the City’s wells, there is information to suggest that some younger water is still infiltrating to the aquifers from the land surface. This was determined by the presence of tritium in City Well No. 2, which is an isotope of hydrogen that indicates the water was in contact with the atmosphere within the last 60 years. This determination of moderate vulnerability was used to establish the types of potential contaminant sources that were tobe inventoried and managed as part of this plan. A more detailed discussion of potential contamination sources is presented in Chapter 5. 9 193803358 Stantec Consulting Services, Inc.