Skip to main content

Frequency-Based Impairment Determinations: Modeling Ambient Bacteria Dynamics to Demonstrate Compliance with Water Quality Standards

Buy Article:

$9.50 plus tax (Refund Policy)

Or sign up for a free trial

EPA guidance defines an exceedance in water quality standards as an inconsistency between ambient conditions and the combined three elements of numeric water quality criteria: magnitude, duration and frequency. A single sample exceeding a numeric criterion is defined as a digression and an average exceeding a criterion an excursion. EPA guidance also states that digressions and excursions alone are not impairment. To constitute impairment, the frequency of digressions or excursions must be greater than the frequency criterion. Given the variable nature of ambient waters, most monitoring programs do not generate enough data to assess compliance with bacteria water quality standards with statistical confidence. Even fewer programs generate enough data to meaningfully assess the frequency of digressions or excursions. Small data sets can magnify the impact of bad, biased or wet weather influenced samples and create the potential for 303(d) impaired water listing of a water body when comprehensive daily monitoring would show that the water body is, in fact, in compliance with bacteria standards.

Consistent with EPA guidance and under peer review by the Water Environment Research Foundation (WERF), comprehensive wet and dry weather bacteria monitoring and representative water quality modeling were performed over a nine-year period to support TMDL Implementation Planning for the Middle Chattahoochee River at Columbus, GA. The calibrated model indicates that when considering bacteria loads in daily mass flux over the entire period, the frequency of maximum value digressions and geometric mean excursions are less than 1%. This is in contrast to compliance analysis using limited, State scheduled, grab sampling data which suggests that over the same period the water body exceeds the State's 10% frequency criterion.
No Reference information available - sign in for access.
No Citation information available - sign in for access.
No Supplementary Data.
No Article Media
No Metrics

Keywords: AMBIENT BACTERIA; IMPAIRED WATERS; MODELING; TMDL; WET WEATHER

Document Type: Research Article

Publication date: 2007-10-01

More about this publication?
  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

    A subscription to the Proceedings of the Water Environment Federation includes access to most papers presented at the annual WEF Technical Exhibition and Conference (WEFTEC) and other conferences held since 2000. Subscription access begins 12 months after the event and is valid for 12 months from month of purchase. A subscription to the Proceedings of the Water Environment Federation is included in Water Environment Federation (WEF) membership.

    WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access. Access begins 12 months after the conference or event
  • Subscribe to this Title
  • Membership Information
  • About WEF Proceedings
  • WEFTEC Conference Information
  • Learn about the many other WEF member benefits and join today
  • Ingenta Connect is not responsible for the content or availability of external websites
  • Access Key
  • Free content
  • Partial Free content
  • New content
  • Open access content
  • Partial Open access content
  • Subscribed content
  • Partial Subscribed content
  • Free trial content
Cookie Policy
X
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more