ENVS 2256 Lecture Notes - Lecture 26: New Source Performance Standard, Clean Water Act, Long Term Ecological Research Network

You are working for the Utah DEQ, Division of Water Quality, and you have been asked to check two preliminary calculations to estimate a Stream Standard effluent limit for a WWTP discharge, and to determine the size of an Interceptor sewer needed to carry a community's WW to their lagoons that they are planning to install in the near future. They currently ship their waste to a regional treatment plant that is quickly running out of capacity, and they plan to stop flow to the regional plant and treat their own waste in lagoons that are currently under design. You have the following design information to work with: Wastewater: Temp-27°C, BOD5-2 (TO Be Determined), Qae-1.2 MGD, DO ?(To Be Selected, use Initial 4.5 mg/L to 95% of Cs). Qmax hourly/Qave-2.6; Qmin/Qave-0.65, k1 = 0.23 @ 20°C Natural Stream: Temp 15°C, BOD5 2 mg/L, Qave 1.07 MGD, DO 6.0 mg/L, Stream Classification 3B, Warm Water Fishery; k2 = 0.9/d @ 20°C. 1. Calculate the impact of this WWTP's discharge on the stream, if its effluent has a BOD5 of 25 mg/L and a DO of 4.5 mg/L. Compare the resultant minimum DO (at the critical deficit Dc to that for the 3B stream classification for a 30-day, 7-day, and 1-day average minimum DO that would be allowable for that stream use. If this DO is not adequate to maintain the designated use for the stream, determine what the permit for the treatment plant should require for effluent BOD5 and DO. (Effluent temperature cannot be changed, so the only variables that can actually be modified in the plant are effluent DO to 95% Cs through aeration and BOD5). Show all of your work and justify your decision. (50 pts) 2. Check the requisite collector sewer size calculations if the land surface slope from the collection system to the lagoon influent is 0.0010 ft/ft. The flows given above include infiltration. Size the pipe using the guidelines in the Utah Rules, R317-3 for Interceptors, and using the flow data estimated for the city as given above. Also, determine the depth of flow and velocity in the Interceptor line that would occur when the Interceptor is put into place if the current flow is only 60% of the design flows given above for the Wastewater. Show all of your work, and make recommendations for maintenance of this Interceptor line if necessary to meet the standards of R317-3. (50 pts)