WQCD E. coli proposal for the Basic Standards Rulemaking Hearing - - PowerPoint PPT Presentation

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)

Recreational use classification

• E. coli standard (# CFU/100

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

126 205

• E. coli and illness rates

Problem with current standard

• Lack of averaging period
• Standard represents central tendency of E. coli
• ver 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): – 10+ datapoints pretty unrealistic for two-month period – May be appropriate for entire dataset

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)

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 points 7 7 13 9 4 7

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?