Evaluation of Stream Sampling Methodologies For Fecal Coliform Bacteria

The agricultural community and its effect on surface water quality is coming underincreased public and regulatory scrutiny. One key component of water quality monitoring is theassessment of organisms that indicate the presence of fecal material and the possible presence of pathogenic organisms. Coliform bacteria and Escherichia coli are the two primary freshwaterindicator organisms monitored by regulatory agencies. Demonstration of compliance with surfacewater quality standards requires the development of sampling strategies that provide defensible andcost effective results. While sample handling and analysis have been addressed in detail, littleattention has been given to sample site selection and collection of representative samples. Thecurrent EPA recommendation is that, for compliance samples, a minimum of 5 single samples over a30-day period should be used. There is no guidance on sample site location. Concern has beenvoiced over the wide range and representativeness of the results using this approach. Researchwas conducted at four study areas within the Texas Panhandle to evaluate stream morphologybasedjudgmental sampling methodologies. Stream concentration estimates of the standardfreshwater indicator organism Escherichia coli, produced by various judgmental samplecombinations, were compared to average stream concentrations determined from randomly selectedsamples collect over the same stream stretch. Results from stream morphology-based sampleswere compared to statistically defensible stream sampling results to determine if a representative,defensible and cost effective sampling methodology could be developed. Results demonstrated thepossibility of obtaining a wide range of concentration estimates using the EPA approach and that ajudgmental, three-event mid-run sampling methodology may provide representative results.