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II II II II II I II I II II II II II I I II I I II ENVIRONMENT At SETIING The Main Ditch is a manmade drainage ditch that flows along tile nortbcrn and eastern border of the city of Pipestone toward the northwest to Wmnewissa Falls, the Pipestone National Monument, and Pipestone Creek. County Ditch A flows into the Main Ditch approximately one-half of a mile east of the city. Main Ditch has a drainage area of 9 square miles just upstream of its confluence with County Ditch A (FEMA, 1991). According to the Minnesota Department of Natural Resources (DNR), this relatively small watershed is intensely drained and fanned. County Ditch A has a drainage area of 20.7 square miles. The total drainage area of Pipestone Creek at Winnewissa Falls is 52.3 square miles (FEMA. 1991). The topography in the study area is generally flat with elevations on tile order of I720i feet mean sea level (m.s.I.) National Geodetic Vertica1 Datum of 1929 (NGVD. 1929). Sioux quartzite underlies glacial till and loess in the project area. The quartzite bedrock crops out in the National Monument. Soils in the area are of the Estelline- Lamoure Association. These soils are formed of parent material of glacial origin. These mainly level soils range from being well drained to poorly drained, and were formed by wind- and water-deposited silty materials on steam terraces and bottom lands. The Main Ditch is shown on the National Wetland Inventory (NWI) map as a riverine system and may be considered ajmisdictional ditch. The National Park Service (NPS). in coordination with the Pipestone Soil and Water Conservation District, conducted water quality tests along the Main Ditch upstream from Wmnewissa Falls. Tests were conducted in the years 1993 and 1994 and were not related to 800d events. Iron, nitrates. and fecal coliform levels were found to be very high. Following the 1993 flood events, mercury and volatile organic compounds were detected at levels below acceptable limits. 7