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Quantifying E. coli Discharge from Onsite Sewage Facilities in the Dickinson Bayou Watershed, Texas

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131620636,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Derek Wayne Morrison, Clyde Munster, Raghupathy Karthikeyan, John Jacob
Keywords:   E. coli Dickinson Bayou Texas Surface Runoff OSSF anaerobic aerobic

Abstract. Since 1996, the bacteria levels in Dickinson Bayou have been considerably higher than the state limit of 126 colony forming units (CFU) / 100 mL for recreational waters. One hypothesis is that failing onsite sewage facilities (OSSFs) in the nearby residential areas are causing an increase of Escherichia coli (E. coli) concentrations in Dickinson Bayou. There are two types of OSSFs in the watershed; anaerobic and aerobic systems. The anaerobic systems discharge partially treated effluent below the soil surface from gravel drainage trenches while the aerobic systems disperse treated effluent on the soil surface using spray nozzles. This project is designed to determine if either of the two types of OSSFs is contributing to the elevated E. coli concentrations in Dickinson Bayou. Two water quality monitoring stations were installed in Dickinson Bayou to quantify E. coli in surface runoff. One of the monitoring sites was placed in a neighborhood that uses OSSFs. The second monitoring station was a control site placed in a neighborhood that is connected to a municipal wastewater treatment plant with no OSSFs. Each monitoring site is equipped with a flow meter and an automatic water sampler. Rainfall – runoff relationships were established for each monitoring station. Water quality samples were obtained during runoff events at each monitoring station and analyzed for E. coli concentrations. Runoff events were characterized as wet, average, or dry antecedent moisture conditions. The rainfall-runoff relationships and the E. coli concentrations in the runoff will be presented in this paper.

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