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City of Pequot Lakes <br /> Geology and Groundwater Flow—The city of Pequot Lakes has two primary wells screened in a <br /> sand and gravel aquifer that is buried beneath a layer of day-rich sediment.Such aquifers are <br /> known generically as Quaternary Buried Artesian Aquifers(QBAA).The city's aquifer is between <br /> approximately 75 and 150 feet below the ground surface.Regionally,groundwater flow <br /> generally follows a similar pattern to that of surface water within this region and moves from <br /> upland areas towards major surface water features such as the Crow Wing and Mississippi <br /> rivers. Locally,groundwater flow is to the southwest. <br /> Well Vulnerability-The vulnerability of each well has been assessed based on 1)well <br /> construction details,especially conformance with standards required by the state well code, 2) <br /> the geologic sensitivity of the aquifer,and 3) past monitoring results. It is unknown if Well#3 <br /> (241514) meets construction standards, as drilling method and grouting information is <br /> unknown. Depending on the drilling method,if the well was not grouted,it has the potential for <br /> acting as a conduit for flow of surface water and contaminants into the buried aquifer.Well#3 <br /> and Well#4 are also considered vulnerable to contamination due to tritium being detected in <br /> the well water. Detectable tritium indicates the presence of young(post-1953)water.This is <br /> reinforced by the chloride concentration and chloride/bromide ratios observed at Well#3. <br /> Higher concentration or concentration ratios indicate recent recharge from the surface.Well#3 <br /> shows evidence of human impact from chloride sources,but Well#4 does not. <br /> DWSMA Vulnerability-The vulnerability of the city's aquifer throughout the DWSMA is based <br /> on the geologic sensitivity ratings of wells and their monitoring data. Based on this information <br /> MDH has assigned a moderate vulnerability to the DWSMA.This suggests that water and <br /> contaminants may travel from the land surface to the city's aquifer within a time span of years <br /> to decades. This rating reflects uncertainty about the pathway for young water reaching Wells 3 <br /> and 4.Although this may be the result of a well casing problem,for the time being it is assumed <br /> that the clay-rich sediments that overlie the city's aquifer are leaky. Moderately vulnerable <br /> aquifers are prone to a variety of contaminant threats,including chemical storage tanks and <br /> abandoned wells which can provide conduits for contaminants to quickly reach the city's <br /> aquifer. <br />