Low Flow Streams Conditions in Georgia
Nwogu, Peter C.
Burke, R.C. III
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In Georgia, there are low flow streams that receive high quality domestic treated wastewater due to the increasing urban development. Municipal and industrial water pollution control plants (WPCP) often request a waste load allocation (WLA) evaluation for a discharge of treated wastewater to low flow surface waters, under the National Pollutant Discharge Elimination Systems (NPDES) permit of the Clean Water Act1. A response to a WLA request requires an examination of whether or not there is enough water, in the context of 7Q10 and the physical, chemical and biological factors of the receiving stream. Other factors evaluated include the existing assimilative capacity, permitted upstream and downstream discharges, (305(b) and 303(d) lists, the overall headwater areas, critical temperature, total maximum daily loads issues, (TMDL) and the hydrology of the watershed. This paper discusses some of the considerations and challenges associated with determining whether a given stream, with low flow conditions, can assimilate the requested organic and nutrient waste loads. The significance of this discussion is to assist industries and municipalities in factoring in the physical and chemical instream constraints in their planning for urban development and sitting of point source discharges. Information to consider includes low flow streams conditions in the context of 7Q10, and temperature used in developing water quality models for waste load allocation. This presentation will show how the headwater 7Q10, and the critical temperatures vary in the physiographic river basin regions of the mountains, Piedmont, upper coastal and lower coastal plains. Low flow conditions in the coastal plains present greater modeling challenges than in the mountains and Piedmont regions in terms of allocating the amount of organic and nutrient loads in treated waste water discharges to low flow stream.