The Leary Weber Ditch Basin is nested within the Sugar Creek Basin in central Indiana. These basins make up one of the five study sites in the Nation selected for the Agricultural Chemicals: Sources, Transport, and Fate topical study, a part of the U.S. Geological Survey’s National Water-Quality Assessment Program. In this topical study, identifying the natural factors and human influences affecting water quality in the Leary Weber Ditch and Sugar Creek Basins are the focus of the assessment. A detailed comparison between the environmental settings of these basins is presented. Specifics of the topical study design as implemented in the Leary Weber Ditch and Sugar Creek Basins are described.

The Leary Weber Ditch and Sugar Creek Basins have moderate temperatures with well-defined winter and summer seasons. The mean annual precipitation is 39.5 inches, with the majority of rainfall in spring and early summer and the lowest amount of precipitation in winter. Yearly, an average of 25 inches of moisture moves into the atmosphere as a result of evapotranspiration.

Physiographically, both basins are contained completely within the New Castle Till Plains and Drainageways. The gradients of the valleys of Leary Weber Ditch and Sugar Creek differ substantially. Most of the Sugar Creek Basin and the entire Leary Weber Ditch Basin overlie a combination of Devonian limestone and dolomite bedrock. Unconsolidated materials (sand and gravel) overlie much of the bedrock in the basins. Soils are either loam or silt loam, generally deep, poorly drained, medium textured, and nearly level. The potential for surface erosion is negligible because runoff is slow. Available water capacity is high. Natural fertility and organic matter are moderate. Soils are naturally suited to row crops.

Agriculture is the principal land use in the Leary Weber Ditch and Sugar Creek Basins. Respectively, 87 percent and 75 percent of the total land area in these basins are used for row crops. The cropped areas within the basins are divided nearly equally between corn and soybeans. Farming practices in the area employ a wide range of tools to promote growth and inhibit vegetative competition; these include the use of fertilizers, herbicides, and pesticides. Tile drains are used extensively to improve yields and make the soils farmable. Irrigation and manure application in the study area are minimal.

Most of the study area is in Hancock County, Indiana. The county population is approximately 61,000. There are no large cities in either basin; most residents live in small communities or rural areas. Water use in Hancock County totalled 6.37 million gallons per day during 2002. Drinking water comes entirely from ground water.

The U.S. Geological Survey operates streamflow-gaging stations at Sugar Creek at New Palestine and at Leary Weber Ditch at Mohawk within the study area. Mean daily streamflow for Sugar Creek is higher than streamflow at Leary Weber Ditch. Through most of its length, Sugar Creek is a gaining stream and base flow is supported by ground-water sources. At Leary Weber Ditch, there is little to no streamflow when tile drains are dry. Modifications to the natural hydrology of the study area include a large system of tile drains, the intersection of Sugar Creek by several major roads, and outflows from nearby wastewater-treatment plants. Leary Weber Ditch is affected only by tile drains.