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5.1.7 <br />Figure 4 in Appendix D depict bedrock protection Geologic Sensitivityfor Anoka County. While <br />the majority of the bedrock aquifers exhibit a low geologic sensitivity some areas are depicted <br />with a high sensitivity_ The areas of high sensitivity do not appear to correspond to specific <br />bedrock geologic conditions. Instead, high sensitivity is more likely related to where confining <br />units have been removed and where coarse grained Quaternary sediment overlies the bedrock <br />surface. <br />Figure 5 in Appendix D depicts tritium samples taken within the City of Ramsey. Tritium is a <br />radioactive isotope of hydrogen that can be used to indicate water age. MDH classifies young <br />(post-1953) water, as indicated by the presence of 1 TU or greater in the well water. Tritium <br />results for these samples depict a mixed result This rnixed results reflects uncertainty about the <br />pathway for young water (containing tritium) to reach the deeper bedrock aquifers. Although the <br />presence of tritium may be the result of a compromised well casing allowing surface water <br />seepage, conservatively, it is assumed that some pathways may exist. <br />Well Spacing <br />Determining the proper spacing of wells in Artesian Aquifers is a balance of well drawdown, the <br />ability of the surrounding formation to recharge, and further economic considerations (USGS <br />1961). In general, the farther apart high capacity wells are from one another, the less mutual <br />interference will occur on the wells. Additionally, the economics of well spacing needs to be <br />weighed against the potential drawdown of the wells. <br />The USGS in 1961 developed a method utilizing the Theis equation for hydraulics to determine <br />expected well drawdown and the surrounding one of depression. Calculations using this <br />equation were completed to understand the hydrogeology of this aquifer system. <br />The following example depicts drawdown in well 8 over the course of 12 hour period while well 7 <br />was pumping at an Average of 800 GPM. <br />840 <br />835 <br />co <br />830 <br />w <br />825 <br />413 <br />co 820 <br />Figure 5 — Drawdown in Observation Well 8 <br />Drawdown in Observation Well 8 <br />—2400 feet from pumping well (Well 7) <br />October 19, 2019 <br />ED 10 LO ID 4.0 LO ES, CD. 13) la, WI VD ID W. CO k0 <br />e ezi tv itgb ED 1) e 44 cuzi FP ifk CD a <br />65 tii iii ii 47, 1 6 r"-: 6 6.1 6, dci 6 <br />6 3 a — <br />4-iLN g i- LO in .9-.. <br />.to T1/2- r ei 6 Q <br />04 <br />Titre <br />FEASIBILITY STUDY -DRAFT RAMS? 154354 <br />Page 20 <br />