URBAN INDICATOR BACTERIA TMDL DEVELOPMENT

Buffalo and Whiteoak Bayous frequently exceed water quality criteria for contact recreation. This urban bacterial contamination is unique due to the extreme nature of the urban contamination as well as the particular flow regimes of Houston bayous.The watersheds for Buffalo and Whiteoak Bayous are highly developed urban watersheds. These bayous are located in Houston, Texas, the nation's fourth largest city. High-density urban and residential land uses dominate the majority of land area. Historical data show that fecal contamination of both bayous is extensive, with all water quality monitoring stations having geometric means significantly above the contact recreation criterion of 200 colony forming units (cfu)/100 mL.Identified sources of the fecal contamination in the bayous include point sources and dryweather storm water flows, in addition to sediments, wildlife, and upstream discharges from the Addicks and Barker reservoirs. This paper will present the results of efforts aimed at quantifying the relative contribution of these sources to the observed fecal levels in the bayous. The paper will also present modeling results aimed at developing Total Maximum Daily Loads (TMDLs) and load allocation scenarios for the two watersheds.In dry weather, the majority of the flow to both bayous is theoretically from point source discharges. Monitoring of wastewater effluent from 76 plants in Buffalo and Whiteoak Bayous during the summer of 2001 indicated that less than 10% of the facilities were exceeding the water quality standard. Other potential dry-weather sources such as illegal discharges and sewer leaks were also evaluated. Monitoring of dry weather storm sewer discharges within the Buffalo and Whiteoak watersheds indicated that over half of the discharging sewers had relatively high fecal coliform levels, in excess of the 200 cfu/100 mL standard.Since Houston typically receives about 50 inches of rainfall annually, it was important to determine whether bayou fecal levels can be correlated to typical, relatively small, but frequent, rainfall events. Results from summer 2001 monitoring for two such storm events show a direct correlation between in-stream bayou flow and Escherichia coli concentrations. In-situ studies conducted to assess the rates of bacterial regrowth in chlorinated wastewater effluent, sediment resupply and die-off as influenced by light intensity, sediment concentrations, organic strength and isolation from sediment indicate that sediment resupply may be a significant reservoir and source of bacteria to bayou waters.The Hydrological Simulation Program – FORTRAN (HSPF) was used to model the various bacterial point and non-point sources in the bayous. The model used both historical data as well as the monitoring data discussed above as inputs. Model calibration and verification was undertaken prior to development of load allocation scenarios.