WQCD E. coli proposal for the Basic Standards Rulemaking Hearing January 28, 2010 E. coli workgroup Photo credit: Joe Amon in Denver Post, June 2, 2009
Overview • Current standards • Proposed changes – For June 2010 Basic Standards Hearing – Notice published in Colorado Register 3/10/10 • Considerations beyond standards – Permitting – Assessment (listing methodology)
Current standards • All are geometric means • All are based upon recreational uses (even seasonal, site-specific standards) E. coli standard (# CFU/100 Recreational use classification mL) Existing primary contact (E) 126 Potential primary contact (P) 205 Not primary contact (N) 630 Undetermined (U) 126
Current standards • 1986 EPA criteria • Linear regression – Target illness rate of 8 in 1,000 swimmers – Geo mean of data over course of study (8 weeks) • Standard for Use E—directly based on EPA criteria • Standards for Uses P and N—based upon acceptance of higher risk level (illness rate)
Current standards E. coli and illness rates 126 205
Problem with current standard • Lack of averaging period • Standard represents central tendency of E. coli over a specific amount of time (8 weeks) – Without a comparable averaging period, we are unable to determine if the standard is being met – Long averaging periods may mask occurrence or magnitude of exceedance.
Proposed changes • Identify a two-month averaging period for existing standards in Footnote 7 to Table I. (7) E.coli criteria and resulting standards for individual water segments, are established as indicators of the potential presence of pathogenic organisms. In the 2005 rulemaking hearing, the Commission transitioned from reliance on both fecal coliform and E. coli standards. The Commission intends standards for individual water segments will be revised to the E. coli standards. Compliance with E. coli standards shall be based on the geometric mean of representative stream samples. Standards for E. coli are expressed as a two-month geometric mean. Site-specific or seasonal standards are also two-month geometric means unless otherwise specified.
Proposed changes • What else did we consider? – 30 days • EPA recommendation • Used by many other States • Exceedances observed with both 30-day and 2-month period – Recreation season • Difficult to define for entire State • More appropriately addressed as a use issue – Longer averaging periods (3-6 months) • Not comparable to basis for standard • Cannot be assumed to be protective
Considerations beyond standards Permitting – No direct changes – Permits for domestic WWTPs will continue to have 30-day limits. – Any changes to permit requirements for MS4s would be based upon a determination that the discharge has the potential to contribute to an exceedance. • Likely through a TMDL
Considerations beyond standards Listing Methodology – Sample minimum • Confidence – Protect use – Manage variability of E. coli • Reality of data availability – One sample every week is about 8 samples within 2 months – One sample every two weeks is about 4 samples within 2 months • Precedent – 5 is most common – 4, 3, 2 less common but used
Considerations beyond standards – Our current sample size requirements (2010 Listing methodology, page 28): Evidence of impairment based on… Result <3 datapoints M&E 4-10 datapoints M&E 4-10 datapoints + overwhelming evidence 303(d) 10+ datapoints 303(d) – 10+ datapoints pretty unrealistic for two-month period – May be appropriate for entire dataset
Considerations beyond standards – Interpretation of two-month averaging period • For seasonal, site-specific standards: as close to two months as possible • Rolling • Interval (example below) Year Jan/Feb Mar/Apr May/June Jul/Aug Sept/Oct Nov/Dec 2005 -- -- ee -- -- e 2006 e ee ee ee ee ee 2007 ee e eeee ee e e 2008 e ee ee eee -- e 2009 eee ee eee ee e ee # data 7 7 13 9 4 7 points
Considerations beyond standards • Rolling – Potentially more thorough (captures greater variety of conditions) – Data limitations more frequent • Interval – Enables assessment across multiple years • Data limitations less frequent • Retains seasonality • Potentially loses evaluation of conditions within a single year • Could be implemented with tiered approach – Use adequate data within a single year if available – If data within single year not available, look across multiple years
Considerations beyond standards Current thinking for listing methodology… Sample minimum: 4 How to balance confidence with reality of data availability for decision making? When to collect more data? Averaging period: interval approach Do benefits outweigh negatives?
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