Dissolved Oxygen Criteria Assessment (Chapter 5)

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Dissolved Oxygen Criteria Assessment (Chapter 5)

• Significant Comments and Recommended Resolutions

Rich Batiuk and Gary Shenk November 14-15, 2006
Chesapeake Bay Water Quality Steering Committee
Meeting
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Chapter 5-DO Attainment(Attachment M)

• Background
• Clarification of temporal periods for assessing
  dissolved oxygen attainment
• Clarification open-water criteria apply to
  shallow-waters
• Methodologies for assessing attainment of the
  7-day, 1-day, instantaneous minimum criteria
• Refinement of OW, DW reference curves
• Rationale for not publishing percent
  saturation-based dissolved oxygen criteria

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SIGNIFICANT COMMENTS

• Issue No. 1 Assessment period
• A concern has been raised regarding the summer
  criteria attainment assessment period.
• Recommendation
• Water Quality Steering Committee should agree to
  publish guidance recommending open-water and
  deep-water dissolved oxygen criteria continue to
  be assessed for June 1-September 30 for the
  summer period and open-water dissolved oxygen
  criteria continue to be assessed also during the
  non-summer October 1-May 31 period.

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SIGNIFICANT COMMENTS

• Issue No. 2 Allowable exceedances of
  instantaneous minimum criteria
• Conflicting comments were received expressing
  concern about the EPA recommendation that
• attainment assessment of the instantaneous
  minimum dissolved oxygen criteria be conducted
  strictly based on analysis of violations of the
  observed data within the appropriate designated
  use segment over the appropriate time of the year
  and three year assessment period without
  application of the CFD methodology and use a
  reference curve.

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Evaluation of Instantaneous Criteria

• Method 1 Direct evaluation of interpolated
  cruise data (same as 2006 deep channel 303d list)
• Method 2 Logistic Regression

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Evaluation of Instantaneous Criteria

• Method 1 Direct evaluation of interpolated
  cruise data (same as 2006 deep channel 303d list)

Note No reference curve is used in evaluation.
Each cruise is interpolated separately and used
as a point in the CFD. Any violation of the
criterion at any time during the 3-year period is
a failure
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Evaluation of Instantaneous Criteria

• Method 2 Logistic Regression. Determine the
  probability that an exceedence occurred in each
  month, given location, time, and observed DO.

Calculate probability that DO was below the
criterion given the observations that month.
Interpolate probabilities
Assign an acceptable probability
Apply CFD and reference curve
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Evaluation of Instantaneous Criteria

• Direct Estimation
• Estimate of space and time below criterion is
  unbiased
• No reference curve necessary
• Straightforward Procedure
• Estimate of pass/fail biased toward passing
• (reduced with more samples or application of
  reference curve)

• Logistic Regression
• Estimate of space and time below criterion bias
  not known
• Reference curve and/or acceptable failure rate
  necessary
• Complex Procedure
• Estimate of pass/fail bias unknown

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Open Water 30-day criterion more strict than
Instantaneous
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Open Water Direct Evaluation less strict than 10
Logistic and more strict than 50 Logistic
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Deep Water 30-day criterion consistent with
Instantaneous
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Deep Water Direct Evaluation consistent with
Logistic
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Deep Channel Direct Evaluation consistent with
Logistic
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Instantaneous Criteria
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SIGNIFICANT COMMENTS

• Issue No. 2 Allowable exceedances of
  instantaneous minimum criteria
• Recommendation
• Water Quality Steering Committee agreement on the
  method to be used in assessing attainment of the
  open-water and deep-water instantaneous minimum
  dissolved oxygen criteria OR give clear
  directions to the CAP Workgroup and the
  analytical team working on the two methodologies
  as to what to pursue and what to/not to focus on.

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SIGNIFICANT COMMENTS

• Issue No. 2 Allowable exceedances of
  instantaneous minimum criteria
• Recommendation (Continued)
• If work is not completed on a methodology in time
  for publication in this Bay criteria addendum,
  then proceed forward with assessing attainment of
  the instantaneous minimum dissolved oxygen
  criteria strictly based on analysis of violations
  of the observed data within the three year
  assessment period without application of the CFD
  methodology and use of a reference curve.

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SIGNIFICANT COMMENTS

• Issue No. 3 Assessing attainment of 1-day, 7-day
  mean criteria
• Recommendations and concerns were both expressed
  in response to proposed approaches to developing
  methods to assess attainment of the 1-day and
  7-day mean dissolved oxygen criteria.

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1-day and 7-day DO criteria

• Can not be measured, must use some type of model
• Directly use Bay Model
• Not based on data, not unbiased
• Years of simulation are not always the most
  current

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1-day and 7-day DO criteria

• Statistical Simulation Model
• Run many instances and sample it.
• Can be constructed if spatial and temporal
  structure of variance and distributions are known
• Buoys
• Continuous monitoring
• Water quality mapping
• Bay model

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SIGNIFICANT COMMENTS

• Issue No. 3 Assessing attainment of 1-day, 7-day
  mean criteria
• Recommendation
• Water Quality Steering Committee should charge
  the CAP Workgroup and the existing analytical
  team to complete their work on methodologies for
  assessing attainment of the 1-day and 7-day mean
  dissolved oxygen criteria in time to publish the
  recommended methodology in the final Bay criteria
  addendum.

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SIGNIFICANT COMMENTS

• Issue No. 4 Statistical evaluation of attainment
• Recommendations for proceeding forward with the
  STAC recommended development of statistical
  methods for assessing attainment.
• Recommendation
• Water Quality Steering Committee should support
  follow-up work in the next several years on the
  recommendations laid out in the STAC expert
  panels report.

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SIGNIFICANT COMMENTS

• Issue No. 5 Implication of new
  open-water/revised deep-water ref. curves
• Concerns were expressed about the new
  biologically-based open reference curve, the
  revised/updated deep-water reference curve and
  implications for future criteria attainment
  assessments.

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Non-Summer (Rest of Year)

• Open water to bottom everywhere
• Uses Jan 1 through May 31 and Oct 1 through Dec
  12 of same year.
• Uses default 10 reference curve
• Does not drive decisions

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Rest of Year Results for 2006 303d list

• 33 assessed areas passed OW summer and OW ROY
• 42 failed OW summer, but passed OW ROY
• 3 failed OW ROY, but passed OW summer
• CB3 and CB4 failed DW and DC
• SASOH passed OW, failed ROY by 1.6

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Rest of Year Results for 2006 303d list
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Updated Reference Curves

• Published reference curves were developed using
  old evaluation procedures and IBI locations that
  did not necessarily reflect the correct
  designated uses.
• New curves developed consistent with latest
  procedures

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Results of new curves little change
2 changes in attainment RDHMH Open Water now
passes YRKPH Deep Water now fails Both changes
less than 1
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Open Water DO 30-day Attainment
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Deep Water DO 30-day Attainment
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SIGNIFICANT COMMENTS

• Issue No. 5 Implication of new
  open-water/revised deep-water ref. curves
• Recommendation
• Water Quality Steering Committee should agree to
  the publication of the proposed
  biologically-based open-water dissolved oxygen
  criteria reference curve.