DESIGN HWA ALTERNATIVES

DESIGN HWA ALTERNATIVES

From 6-21-2006 Meeting Between DWQ and NC Pretreatment Consortium

Presented at 6-29-2006 NC-PC Meeting

DWQ Folks at the 6-21 Meeting

Matt Matthews-New Head of NPDES Section [Poupart’s new boss]

Mike Templeton-NPDES Unit Jeff Poupart – PERCS Jon Risgaard – PERCS (leaving PERCS

but staying on workgroup) Iswar Devkota-Construction Grants

Plan Review

NC Pretreatment Consortium Folks at the 6-21 Meeting

Sherry Bagwell – Winston Salem Leon Holt - Cary Martie Groome - Greensboro

“Old Business”

What is rule/regulation that is being violated?

143-215.67 (per Jeff) Context of Rule is not clear Jeff will check with DWQ General Counsel

(Mary Payne Thompson) to get legal ruling How does this rule apply with 80/90 rule?

“Old Business”

DWQ Pretreatment folks have not yet reviewed City of Charlotte design criteria study for Charlotte POTWs Dawn Submitted to DWQ at 4-18-06

meeting Reports were prepared by engineering

firm at cost of $10,000 each (done for 3 POTWs)

Study “re-rated” POTWs design capacity

“Old Business”

How many POTWs have potential to be impacted by this?

148 POTWs in North Carolina who are part of a PT Program 11 POTWs don’t have industries at all 7 Have no industries but want to keep

program Leaves us with 130 POTWs

potentially affected by this

6-21 Meeting Agreements Will limit discussion to BOD/TSS at this point

Nutrients [ammonia, TN and TP will be addressed eventually, but will be more complex Some BOD/TSS alternate options may also work

for nutrients Consortium members will review alternate

options/”practice” with them and comment Would like to have resolution on BOD and

TSS by conference in September NEXT MEETING WED: 8-23-2006

1. Maximum or Ceiling Removal Rate

Description: Develop a maximum removal rate usable in the headworks analysis (HWA), thus limiting the calculated pass through MAHL. For example, no POTW could use

anything higher than 98% removal on TSS even if their site specific data resulted in a value of 99.1%

You would use 98% or your specific value whichever was LOWER

1. Maximum/Ceiling Removal Rate Advantages:

Simple, and easy to implement Decreases the likelihood of the resulting Pass through

MAHL being extremely high May better lend itself to TSS

Disadvantages: Does not work well for WWTF with low limits that

already require a high removal rate to meet limits Appropriate maximum or ceiling removal rate will be

specific to different WWTF and may be highly variable.

Does not necessarily result in an MAHL that is a good representation of the WWTF

2. Design Criteria Multiplier

Description: Develop a multiplier that Towns can multiply by the design criteria to establish new MAHL For example:

Multiply Design lbs by 1.25 Multiply Design lbs by 1.5 Multiply Design lbs by 2.0

2. Design Criteria Multiplier Advantages:

Simple, and easy to implement. Results in a MAHL greater then the design

criteria. Disadvantages:

Multiplier is difficult to calculate Appropriate multiplier will be specific to different

WWTF and may be highly variable Risk using up built in design safety factor needed

for providing treatment under variable conditions.

3. Maximum Average Monthly load (in pounds)

Description: Use historical WWTF data to find the maximum average monthly load (lbs) treated without any effluent violations and use that month to determine the MAHL

3. Maximum Average Monthly load (in pounds)

Advantages: Simple, and easy to implement. Relies on proven plant performance to

calculate the pass through MAHL Disadvantages:

Historic data may not show values greater than the design MAHL

Will not work for POTWs that are currently underloaded

4. Re-rating of WWTF

Description: WWTF is re-rated by a certified engineer to determine design capacity. This would result in a different “design”

capacity than currently published in a POTW’s O and M manual

4. Re-rating of WWTF

Advantages: Results are stamped and certified by a

professional engineer. Site-specific determination

Disadvantages: May be cost prohibitive (~$60,000/POTW) Criteria on the required depth of study

has not been determined.

5. Require use of Detection Level instead of ½ DL

In calculating the WWTF removal rate, the Town would use the detection level instead of ½ of the detection level when the sampling results are reported as less than detect

5. Require use of Detection Level instead of ½ DL

Advantages: Simple, and easy to implement. Will decrease the calculated removal rate and

resulting pass though MAHL Disadvantages:

Does not necessarily result in an MAHL that is a good representation of the WWTF ability.

Will only affect WWTF that produce effluent less than the detection level.

May not be over limiting for WWTF with low limits and low influent concentrations

6. Use Biowin Program (SASPRO, or other products)

Description: Allow for Towns to use the Biowin modeling program (or other approved modeling program) to essentially re-rate the WWTF Some NC-PC Consortium members

suggested buying this and having some members train on this software but there may be liabilities to this

6. Use Biowin Program (SASPRO, or other products)

Advantages: Approved model that is used by professional

engineers for the design of WWTF and therefore has the potential to produce technically based results.

Disadvantages: May be cost prohibitive. High probability for error if used by inadequately

trained individuals. Training to properly use the program may be

resource prohibitive.

7. WRRI Research Institute Study (UNC-Charlotte research projects)

Description: request that NC State or other research group investigate the issue for us. Charlotte is using UNC-C students

currently and would be willing to give this issue to some of those students

7. WRRI Research Institute Study (UNC-Charlotte research projects)

Advantages: Does not require upfront resources from

the State or Towns. Can be assumed that results will be

unbiased Disadvantages:

Will require an unknown amount of time No guarantee that results will be broadly

usable.

8. Develop RR based on Influent and NPDES Limit

Description: When calculating the removal rates, use the discharge limit instead of effluent sampling results to limit the removal rate, and thus limit the calculated pass through MAHL

8. Develop RR based on Influent and NPDES Limit

Advantages: Simple, and easy to implement.

Disadvantages: May not result in MAHL greater then

when using the design criteria. Does not necessarily result in an MAHL

that is a good representation of the WWTF ability.

9. 80% rule (or 70% rule, or 90% rule)

Description: Set criteria for when the design criteria can be re-evaluated similar to the flow moratorium requirements. When a WWTF receives less then the cut-off percentage of the design MAHL, the POTW must use the design MAHL. When a WWTF receives more then the cut-off percentage of design MAHL, and they POTW consistently meets their effluent limits, additional MAHL can be granted. (would need to review HWA on a more frequent basis)

9. 80% rule (or 70% rule, or 90% rule)

Advantages: Allows of case by case analysis of the WWTFs As the WWTF approaches capacity existing data

is a better representation of how the WWTF will operate into at or above design criteria.

Disadvantages: Criteria for allowing more MAHL not yet

established Appropriate cut off percentage criteria will be

difficult to establish. POTWs approaching but not meeting the cut-off

criteria may be constrained.

10. Ammonia Trading

Description: Allow WWTF with low ammonia design criteria to trade some of their BOD loading for ammonia loading based on known oxygen requirements for removing the different parameters. Thus increasing the ammonia MAHL

10. Ammonia Trading Advantages:

Fairly simple, and easy to implement. Results in a greater MAHL for ammonia.

Disadvantages: Oversimplified approach, as biodegradation and

nitrification are more complicated then just accounting for the available oxygen

Criteria are not established for how much trading is appropriate.

Only addresses ammonia issue

11. Flag Level adjustment to allocation table

Description: Develop method for being able to show more actual flow/concentration table in allocation table instead of limits developed with safety factor. Maybe allow for limits in permit as

normal but include “flag level” set at expected loading at which permit will be

12. Design Criteria

Use Design Criteria Calculations This may be appropriate for some

POTW situations

13. “Local Pollutant Allocations”

Description: Issue “Local Pollutant Allocations” and Limits to SIUs Local Pollutant Allocation goes into Allocation

Table but enforcement is not taken until SIU exceeds limit (which would be higher)

Local Pollutant Allocation does not have as large of a “buffer”.

Have one allocation table used by POTW another table for Dept of Commerce

Similar concept to #11

13. “Local Pollutant Allocations”

Advantages Eliminates “unused capacity” at POTW Gives truer picture to Dept of Commerce

Disadvantages Complicated Time Consuming Only solves “overallocation” situation-

does not truly solve design criteria issue

14. Hybrid of Several Options No action required until you get to 80% of

MAHL for a pollutant Recalculate BOD and TSS %RR and ACTUAL

INFLUENT loadings every calendar year and include in PAR

At the 80% point, POTW must choose an option(s) to reduce “on-paper” loading for that pollutant

Options can be different for different pollutants

Where Do We Go From Here?? Review/Discuss options Develop other options

Present to DWQ Contact other states to determine

how the MAHL for TSS and BOD are determined

Narrow the list of options to a workable number for further investigation and “testing”

Where Do We Go From Here? Take the viable options and use with site-

specific data from as many POTWs as possible Various loadings, treatment processes, NPDES

limits, etc.) Present DWQ with the Consortium options

“Wish List” Continue negotiations with DWQ Along with DWQ, write new guidance on

HWA Calculations for BOD and TSS Implement Guidance