A nationwide need for information characterizing hydrologic conditions in mined and potential mine areas has become paramount with the enactment of the Surface Mining Control and Reclamation Act of 1977. This report is designed to be useful to the mine owners, operators, and others by presenting information about the existing hydrologic conditions and by identifying sources of hydrologic information. General hydrologic information is presented using a brief text with an accompanying map, chart, graph, or other illustration for each of a series of water-resources-related topics. The summation of the topical discussions provides a description of the hydrology of the area.

Coal has been mined for 130 years in Area 38, but large reserves remain. Production peaked in 1917 when Iowa produced 9 million tons and Missouri produced 6 million tons. Underground mining has been replaced by surface mining in Area 38. Not all past surface-mined lands are subject to reclamation under recently enacted reclamation laws.

The surface-water monitoring network in Area 38 consists of 183 stations. Streamflow varies seasonally and from year to year. Water-quality data are available for 49 stations in the study area. Measurements of specific conductance, dissolved solids, pH, alkalinity, sulfate, iron, manganese, trace metals and other constituents are available for 36 stations operated between 1978 and 1981 expressly for the collection of water-quality data within basins containing coal mines.

A cumulative impact of coal mining on the mineralization of surface water is evident from specific-conductance data for stations downstream from mining activities. Alkalinity in streams in Area 38 averaged greater than 118 milligrams per liter, providing the capability to neutralize acid-mine drainage to some extent. Sulfate concentrations in streamflow averaged 88 milligrams per liter at stations upstream from coal mines and 269 milligrams per liter at stations downstream from coal mines. Significant relationships exist between totalrecoverable-iron concentrations and suspendedsediment concentrations. Manganese concentrations are larger in streams draining mined areas. Streamflow at 5 of the 36 coal-hydrology stations in Area 38, all located downstream from coal mines, exceeded acid-mine-drainage criteria at one time or another.

In Area 38 dissolved-solids concentrations in water from the Cambrian-Ordovician aquifer range from 300 to 15,000 milligrams per liter; in southcentral Iowa and where the aquifer underlies the Missouri River alluvium, as in Boone County, Missouri, dissolved-solids concentrations are less than 1,000 milligrams per liter. In these areas the Cambrian-Ordovician aquifer is suitable for domestic and other uses. Chemical quality of water from Quaternary aquifers generally is suitable for domestic uses and other uses, dissolved-solids concentrations averaged less than 1,000 milligrams per liter. Iron, manganese and nitrate are excessive in some instances. Chemical quality of water from Mississippian and Pennsylvanian aquifers is unsuitable for domestic use and may be unsuitable for other uses. The Pennsylvanian and Misissippian aquifers have average sulfate concentrations in excess of 1,000 milligrams per liter.