Perchlorate reconnaissance sampling in streams and groundwater in the Central and Southwestern U.S.
The objectives of this study are (1) to collect data to determine the occurrence of perchlorate over a gradient of agricultural land-use intensity in areas of the Midwestern and North Central United States and (2) to collect data to determine if varying annual precipitation across the middle and western parts of the United States affects the occurrence of perchlorate in rivers and streams.
Water samples were collected from streams and groundwater along a gradient of decreasing agricultural intensity beginning in Minnesota and Iowa and extending southwest through Nebraska to central Colorado. Stream and river sites at the mouth of agricultural and undisturbed watersheds, used as part of the U.S. Geological Survey's NAWQA program, were sampled in Minnesota, Iowa, Nebraska, and Colorado during late summer or early fall in 2004. Also, small third-order streams that drain primarily agricultural areas in the Midwestern cornbelt were selected to determine if groundwater flowing to streams contained perchlorate. One hundred and ten sites in 10 Midwestern corn-belt States were sampled in the summer and early fall of 2004.Rivers and stream were sample at sites from California to Texas during the same period Sites were selected in areas of southern and southwestern U.S. where annual precipitation ranges from more than 60 inches per year to less than 10 inches per year.