Agenda - Council - 06/23/1981 - Laserfiche WebLink

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Honorable Mayor and City Council City of Ramsey June 18, 1981 Page Two Rock wells draw water from the deeper bedrock formations which underlie the glacial drift. The Twin Cities metropolitan area has several sandstone formations which can provide water in quantities suitable for municipal supply. A large number of wells serving suburban communities are completed in these sandstone formations. These deep wells generally provide high quality water which requires no treatment before use, although softening and/or iron and manganese removal is sometimes done to reduce the relatively high levels of dissolved minerals. A rock well is constructed by installing steel casings through the entire glacial drift. The casing may also be extended into the upper bedrock layers, until the top of-the water bearing formation is reached. The casing is then grouted in place, to prevent drift water from flowing down the outside of the casing to the bedrock aquifer. An open hole is then drilled to the bottom o~ the aquifer. Well development, using dynamite and compressed air, may be done to enlarge the open hole. Finally, the well is test pumped to determine the rate of water production available without pumping an excessive amount of sand. Several sources of information were used during the study of water well feasibility for municipal water supply in Ramsey. The Minnesota Geological Survey maintains records of all wells drilled in the state, including municipal, irrigation, and private residential wells. Staff personnel at the Geological Survey are also available for consultation on geologic conditions and for interpretation of well logs in a particular area. The United States Geological Survey {U.S.G.S.) pub- lishes hydrologic investigations for major river watersheds which include infor- mation on geology and groundwater hydrology. The U.S.G.S. publication for the Rum River and for the Mississippi and Sauk Rivers in Central Minnesota were con- ,sulted during the course of this study. Finally, we have discussed groundwater and well questions with a local well driller who is familiar with the area. Drift wells do not appear to be a viable source of municipal water supply in 'Ramsey. The glacial drift in most of Ramsey is relatively impermeable, con- taining substantial amounts of silt and clay. Large deposits of coarse sand and gravel, which supply water to some metropolitan area communities, are not present in Ramsey or exist only in small, isolated areas. This conclusion is borne out by an examination of logs on existing residential wells in Ramsey. Of the nearly 80 well logs examined, only three were completed in the glacial drift. The remainder draw water from the upper sandstone formations. Since residential wells requiring only a few gallons per minute cannot utilize the glacial drift, it is clear that the probability of developing a 5DO gpm to 1000 gpm municipal well is slight. The best chance of developing a drift well is probably along the Rum River, but this chance is considered small. As is the case with the glacial drift, the sandstone bedrock formations are some- what variable in terms of their location, depth, thickness, and permeability.