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2020-09-09 CC Packet
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2020-09-09 CC Packet
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PART 2. ASSESSMENT OF DATA ELEMENTS USED TO DELINEATE THE WELLHEAD <br />PROTECTION AREA <br />A. Use of the Wells – The wells shown in Table 1 serve as the primary drinking water source for <br />residents of the City of Centerville who are connected to the City’s water supply system. Well <br />2 is the primary well and Well 1 serves as an emergency backup. The City also maintains an <br />interconnection with the City of Lino Lakes that is capable of supplying 2000gpm. This <br />interconnection is only used during emergencies or periods when the City’s wells are <br />unavailable for pumping. <br /> Table 2 shows a comparison of the usage of the City of Centerville wells for the past five <br />years versus a projected pumping rate 5 years into the future. The greatest amount of pumping <br />from any of these years is used to represent the pumping rate for that well in the groundwater <br />model. This is done for the purpose of developing a delineation that is conservative and takes <br />into account the potential volume each well may be pumped in the near future. <br /> Other high capacity wells being included within the model, but not being delineated in the <br />plan, are modeled using an average pumping rate taken from a 5-year period. This is <br />explained in greater detail in the Metropolitan Council’s 2014 technical report for the <br />Metropolitan Model. High capacity wells within two miles of the Centerville wells are shown <br />in Table 3. These wells were modeled based on an average rate from the years 2012-2016. <br />These pumping volumes modify the volumes originally modeled by the Metropolitan Council. <br />B. Wellhead Protection Area Delineation Criteria <br />1.Time of travel – The minimum time-of-travel for porous-flow aquifer delineations is 10- <br />years, which is what was used for the Prairie du Chien aquifer. For the fracture-flow <br />delineation, a 5-year fixed radius with a 5-year upgradient extension is used to represent <br />an approximate 10-year capture zone for flow within the fractured Prairie du Chien <br />aquifer. A 1-year-year time-of-travel zone was also delineated for both porous-flow and <br />fracture-flow systems and represents the Emergency Response Area. <br />2.Hydrologic flow boundaries – The St. Croix River and Mississippi River represents the <br />major flow boundaries for the Prairie du Chien aquifer in the northeast metropolitan area. <br />Hydrologic flow boundaries included in the groundwater model are documented in greater <br />detail in the technical report for the Metropolitan Model (Metropolitan Council, 2014). <br />3.Daily volume – Projected annual pumping volumes for the Centerville wells are shown in <br />Table 2. The maximum projected annual pumping volumes were converted to cubic <br />meters per day in order to be applied to the groundwater model. <br />4.Groundwater flow field – The groundwater flow field was calculated by the groundwater <br />flow model. Original model calibration and ambient flow-field simulation results are <br />described in the technical report for the Metropolitan Model (Metropolitan Council, <br />2009). Model calibration remains relatively unchanged, since the only significant updates <br />to the model are updates to the wells and their pumping rates, and small-scale changes to <br />hydraulic conductivity and aquifer thickness near the Centerville well field. These <br />changes were not enough to significantly impact calibration results. <br />5.Aquifer transmissivity – Aquifer transmissivity for regional model was established by <br />the Metropolitan Council’s calculations for the 2014 update to the Metropolitan Model. <br />To refine transmissivity for the Centerville area, the aquifer pumping test from Centerville <br />Well 2 was utilized. This test was conducted by the MDH in March 1998 for the purposes <br />of wellhead protection planning. Transmissivity for the Prairie du Chien aquifer was <br />calculated based on a 24-hour aquifer pumping and recovery test. The results of the test <br />7 <br /> <br />
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