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Table 3-5 Bedrock geology characteristics <br />Glacial Drift <br />IVOOOOOOOOOOOIILIOOIOIOOIOOOOOOOOOOOOOOIIIIII IIIIIIIII IIII IIII I11O, <br />IIII0IIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII100 <br />IIIIIIII <br />oloolooloolooloolooloolooloolooloo 000 (IIIIIIIII IIIIIIII <br />100-250 <br />Till, sand, gravel, lake deposits <br />May yield small supplies for <br />domestic use <br />St. Lawrence <br />Formation <br />40-50 <br />Dolomitic siltstone and <br />sandstone <br />Confining bed with little yield <br />Tunnel City <br />Group <br />140-180 <br />Fine to very fine grain <br />May yield small supplies for <br />limited use <br />Wonewoc <br />Sandstone <br />50-60 <br />Fine to coarse grain, <br />moderately sorted sandstone <br />A significant aquifer within the <br />LRRWMO watershed <br />Eau Claire <br />Sandstone <br />75-80 <br />Fine grained sandstone, <br />siltstone and shale <br />Confining bed with little yield <br />Mount Simon <br />Sandstone <br />125-200 <br />Medium to coarse grain <br />A significant aquifer in the Twin <br />Cities metropolitan area <br />Source: Anoka County Geologic Atlas <br />More information about the bedrock geology of the LRRWMO is available from the Anoka County <br />Geologic Atlas at: tts://c <br />s rvo c <br />*/11 <br />/ <br />1111 <br />The glacial and bedrock deposits form layered sequence of aquifers and confining unit. An aquifer is a <br />geologic formation capable of supplying sufficient quantities of water to a well. A confining unit is a <br />geologic deposit that impedes the flow of water between aquifers (see also the Anoka County Geologic <br />Atlas (Setterholm, 2013)). <br />The uppermost aquifers in the LRRWMO are glacial deposits. Glacial aquifers (also known as surficial <br />aquifers) include the water table and buried glacial aquifers, which are primarily used for domestic <br />purposes. Glacial aquifers are variable in location and yield. Groundwater quality in glacial aquifers is often <br />correlated to the quality of the water that is infiltrating at the surface. The regional groundwater flow <br />within the surficial aquifers and glacial drift is generally to the south, except near the Rum River where <br />ground water tends to flow toward these surface waters. The Rum River is predominately a discharge area <br />for groundwater. Areas not near the Rum River are predominately groundwater recharge areas (see <br />Section 2.6.1). <br />Most high -capacity wells draw water from bedrock aquifers. The bedrock aquifers within the District <br />include the following: <br />• Tunnel City-Wonewoc Aquifer (formerly Franconia-Ironton-Galeville Aquifer) — This aquifer <br />includes three hydrogeologically connected layers. Groundwater flow in this aquifer is generally <br />from towards the Mississippi River. Within this aquifer, the hydraulic conductivity is variable. This <br />2-14 <br />