Assimilative Capacity of Small Streams

A rational basis for modeling small streams to determine assimilative capacity in order to assign waste-load allocations to meet the requirements of Public Law 92-500 is necessary. This paper summarizes the results of waste-load assimilation analyses of Coleman Creek at Boydton and Flat Creek near South Hill, Va. and the possible impact on these communities. The assimilative capacity of each stream was analyzed by using modified Streeter-Phelps methodology, a water quality model for self-purification of small streams. Based on the results of these studies, it became apparent that very stringent effluent limits, overtaxing the financial capabilities of these communities, would be needed to maintain the existing stream DO standards. Accordingly, to prevent undue economic hardship to these communities, the concept of issuing a tiered permit was considered in order that a seasonally-controlled system of waste treatment could be utilized, i.e., a higher and more expensive treatment step may be required only during periods of low flow. These strategies will decrease the capital costs of the plants and will significantly lower the operating and maintenance costs.