It is overlain by glacial till consisting principally of clay with intermittent deposits of sand and gravel. The majority of wells are drilled into the limestone, and yields generally are adequate for domestic and farm water supplies. Although yields in excess of 1,000 gpm have been obtained in wells less than 300 feet deep, regional yields are less than 500 gpm. Farm and domestic supplies of 10 to 15 gpm can usually be developed in wells less than 80 feet deep. Because the minerals in limestone are water soluble, water from this formation may be excessively hard and mineralized, and may require treatment.
Many wells contain an excess of iron.
Wells drilled into the limestone often produce water that contains hydrogen sulfide. Objectionable amounts of hydrogen sulfide generally increase with the depth drilled. The aquifer for the extreme eastern portion of Marion County is shale, as illustrated as Area B. This type of sedimentary bedrock produces extremely small yields of water. Dry wells and cisterns are common. Wells drilled into shale often produce water charged with hydrogen sulfide.