INCORPORATING HYDROLOGY IN DETERMINING TMDL ENDPOINTS AND ALLOCATIONS

Pollutant loading is a function of concentration and flow. Analysis of the prevailing flow conditions during periods of water quality impairment can lead to better understanding of the responsible sources contributing pollutant loads. This analysis, using the entire hydrologic spectrum seen on a stream can distinguish impairments from point sources from those of nonpoint sources, including background conditions. The endpoints to be achieved by TMDLs utilizing analysis of hydrology will be a more accurate assessment of the level of water quality to be attained upon implementation of the load allocations. The implications to point sources will reflect a more direct linkage of their impacts to the stream and the desired goals of the TMDLs under flow conditions which are a subset of the total flow regime occurring on the river.