Water quality standards and numeric criteria are developed to protect and define when waterbodies support their designated uses. Recreation is a common use type that most waterbodies are required to support. This use category includes swimming, wading by children, boating, water skiing, whitewater sports, and other recreational activities. Routinely, uses in this category are divided into primary and secondary contact relative to the likelihood that water ingestion may occur during the activity. Long-term geometric mean concentrations of fecal indicator bacteria from all flow conditions provide the basis for assessments to determine designated use support. This paper evaluates the effect of implementing an alternative water quality standards approach for contact recreation based on flow condition (safe vs. unsafe) and the type and volume of use. This effectively separates water quality samples based on hydrologic conditions for assessment purposes. Using this approach, high-flow event data considered in some assessments can be assessed differently without jeopardizing public health.
A case study performed on the Navasota River in Central Texas, USA evaluated data collected over a two-year period and separated it by flow condition to test for significant differences in median fecal indicator bacteria (Escherichia coli) concentrations between conditions. A maximum flow threshold for safe recreation (swimming, children wading) was established at 2.12 m3/s based on average depth and velocity at the monitored location. Statistical analysis using nonparametric tests suggests that significant differences in median E. coli concentrations exist between safe and unsafe flow categories but not between safe and all flows. This suggests that an alternative water quality standard that allows exclusion or re-categorizing E. coli concentrations above established thresholds may produce a different assessment outcome. Under the current assessment scheme where all flows are considered, the geometric mean of assessed data is 150.1 cfu/100 mL; however, re-categorizing and excluding high-flow data from the assessment yields a geometric mean of 106.4 cfu/100mL. This value meets the current standard of 126 cfu/100mL. Using this approach in other waterbodies may result in currently impaired waters meeting water quality standards.
Adopting this approach requires a shift from current water quality policy. Contact recreation standards are currently applied to all hydrologic conditions. Logic suggests that this is not appropriate since all types of contact recreation should not occur in streams during unsafe flow conditions. Water quality concerns are secondary to physical safety concerns and the increased risk of drowning. Persons engaging in contact recreation during unsafe hydrologic conditions assume increased risks inherent to the activity. This should also apply to water quality conditions. However, extreme sport enthusiasts have successfully argued that unsafe flow conditions should not be exempted from applicable water quality standards. As a result, numerous waterbodies are considered impaired because of E. coli data collected during unsafe hydrologic conditions. Implementing an alternative approach to water quality standards for contact recreation assessments can still protect human health while also minimizing the costs taxpayers incur to restore impaired waterbodies.