Lower Rapid Creek Watershed Assessment and TMDL Development

A team from the Civil and Environmental Engineering Department at South Dakota School of Mines and Technology is in the process of obtaining samples from the Lower Rapid Creek near Rapid City, South Dakota. The purpose of this study is to conduct a watershed assessment along the lower Rapid Creek, which will identify point and nonpoint source pollution. Eight stations on the lower Rapid Creek were chosen for sampling. The main purpose of such sampling is to provide information for quantification of present loads and calibration of future modeling efforts. The obtained data will be used to provide information to support evaluation of watershed management alternatives and development of the total maximum daily load (TMDL) for lower Rapid Creek. Further analysis using the QUAL2E model in conjunction with the Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) will be used to model the response of the stream. Sampling sites will be determined based on existing USGS and state Department of Environment and Natural Resources gauging stations. Samples will all be collected employing methods described in the Standard Operating Procedures for Field Samplers by the State of South Dakota Clean Lakes Program. The proposed frequency of sampling at the Rapid Creek sites will result in approximately 200 samples. The approximately 330 square mile study area is subject to wastewater treatment discharge, urban stormwater runoff, irrigation withdrawls and return flows, and runoff from agricultural areas. The sampling period in the study will include snowmelt runoff, the irrigation season, and low flow conditions. Preliminary sampling and analysis results for chemical loadings and Sediment Oxygen Demand will be presented.