4.1. ERMUSR 01-08-2013 - Laserfiche WebLink

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needed to address deficiencies in either the quality or the amount of data are included in the plan of action (Chapter 9). Chapter 3 - Delineation of the Wellhead Protection Area, Drinking Water Supply Management Area and Vulnerability Assessments A detailed description of the process used for 1) delineating the WHPA and the DWSMA, and 2) preparing the vulnerability assessments of the ERMU water supply well(s) and DWSMA is presented in Part 1 ERMU WHP Plan, Appendix 1. The Public work was performed by a geoscientist licensed by the State of Minnesota and employed by Bolton & Menk Engineering. 3.1 WHPA and DWSMA Delineation — Figure 1 shows the boundaries of the WHPA and the DWSMA. The WHPA was delineated by using computer simulations of groundwater movement to generate the underground capture zones for ERMU eight wells. The DWSMA boundaries were designated using the following criteria — • Center-lines of highways, streets, roads, or railroad rights-of-ways; • Public Land Survey coordinates; • Property or fence lines; 3.2 Well Vulnerability Assessment - The construction and water quality obtained from the wells that are used by the Public Water Supplier is included in the assessment of well vulnerability. All ERMU public water supplies are completed in the Mt. Simon-Hinckley formation and seems to exhibit confined aquifer conditions in most of the Elk River area. Tritium tests were performed on all ERMU wells, and only samples from Well 5 showed an indication of younger (post-1953) groundwater and is classified as vulnerable. It is hypothesized that either the Eau Claire Formation is thinner at the Well 5 location and potentially absent east of the well where buried bedrock valley is present. Or, it is possible that the integrity of the well casing itself has been compromised to allow infiltration of water from the upper aquifers into the water from the well. 3.3 DWSMA Vulnerability Assessment- The vulnerability of the DWSMA (Figure 1) was determined using geologic, soils, and groundwater chemistry information. Vulnerability is variable (moderate and low) in the area. While there is good protection provided over the Mt. Simon aquifer in the area of the ERMU DWSMA by the shale-rich, low-permeability Eau Claire formation, there is speculation that in the vicinity of Well 5 the protective shale Eau Claire layer may thin out and allow the infiltration of water from more shallow aquifers. Therefore, the recharge area around Well 5 is vulnerable (moderate), while the remaining portion of the DWSMA for all other wells is not vulnerable. 4