Citation:

Fan*, C, D Sullivan*, AND R Field*. ESTIMATING URBAN WET WEATHER POLLUTANT LOADING. Presented at Water Environment Federation TMDL 2003 Specialty Conference, Chicago, IL, November 16 - 18, 2003.

Impact/Purpose:

To inform the public

Description:

This paper presents procedures for estimating pollutant loads emanating from wet-weather flow discharge in urban watersheds. Equations are presented for: annual volume of litter and floatables; the quantity of sand from highway runoff; the quantity of dust-and-dirt accumulation on street surfaces during dry weather and their washoff rates during a storm event; and the amount of sediment and in-sewer solids deposition. In particular, this paper describes details of pollutant emissions associated with resuspension of in-sewer sediment.

During low-flow, dry-weather periods, sanitary wastewater solids deposited in combined sewers have significant adverse impacts on the integrity of sewerage system and receiving-water quality. In the US, estimates of dry weather flow deposition in combined sewers vary from 5 to 30% of the daily inputs of solids and pollutants. In Europe, average deposition rates have been measured at between 30 and 500 g/m/d. Even sewers that are supposedly designed to be 'self-cleansing' will have transient sediment deposits and part of the load in transport will move near the sewer invert.

Deposited organic matter contains high concentrations of sulfates that can be reduced to hydrogen sulfide under anoxic conditions often reached in a sewer. The hydrogen sulfide is then oxidized to sulfuric acid, a highly toxic and corrosive gas, by biochemical transformation. The concentration of BOD5, COD, and NH3-N in sewer sediments can be as high as 150,000 mg/L, 200,000 mg/L, and 300 mg/L, respectively. During a storm event, resuspended sediments are discharged directly into receiving waters. Thus, sewer sedimentation should be controlled.

Record Details: