The southern part of the Camp Ripley Military Reservation, in central Minnesota, includes an area of about 20 square miles. This investigation was conducted to assist the U.S. National Guard Bureau in locating adequate water supplies for expansion and standby needs.
Bedrock in the area consists of Precambrian phyllite which is equivalent to the Virginia slate. The area is covered largely by Pleistocene deposits in the form of moraines, ice-contact features, outwash plains, and the valley train of the Mississippi River. Almost all the surface deposits consist of outwash-plain and valley-train sediments that are generally permeable. Test drilling and an electrical-resistivity survey indicate that the post area, in the southeast part of the reservation, is underlain by about 50 to 115 feet of glacial drift. The west side of the post area is underlain by a bedrock valley filled in part by permeable glaciofluvial deposits in which there is a narrow, highly permeable channel deposit of sand and gravel. Aquifers of this type are probably the most important source of ground water in the area, although substantial quantities of water also may be obtained from other types of glacial aquifers. Properly constructed and developed wells tapping the channel deposits should yield 2,000 to 3,000 gallons per minute, or more.
Recharge to the aquifers in the reservation is derived from the downward percolation of local precipitation. Most recharge occurs during the spring breakup when accumulated winter snows melt and during the warmer months when the heaviest rains occur.
Sufficient water is stored in sands and gravels in the area to support substantial water-supply developments for several years, even without normal recharge.
The water is harder than is desirable for domestic uses, and it is relatively highly colored, probably owing to the presence of iron. Otherwise, the water is satisfactory for most domestic purposes as it contains only about 250 parts per million of dissolved solids.
