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Regulatory Alert - RA 06-02

Member Pipeline - Regulatory - Alert (RA 06-02)

To: Members & Affiliates, Air Quality Committee
From: National Office
Date: May 30, 2006
Subject: NACWA IDENTIFIES PROBLEMS WITH EPA EMISSIONS MODEL; SEEKS MEMBER INPUT ON WATER9
Reference: RA 06-02

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Action Please By:
June 23, 2006

NACWA’s Air Quality Committee has recently completed work on a Targeted Action Fund (TAF) evaluation of several commonly used air emissions models and has identified several issues NACWA members should be aware of when using certain models to estimate air emissions from their systems. The project was initiated to specifically evaluate the U.S. Environmental Protection Agency’s (EPA’s) WATER9 model, which the Association believed might significantly overestimate hazardous air pollutant (HAP) emissions. Earlier versions of the WATER9 model (WATER7 and WATER8) were used by EPA to estimate HAP emissions from wastewater treatment plants during the publicly owned treatment works (POTW) maximum achievable control technology (MACT) regulatory development process. These earlier versions significantly overestimated HAP emissions leading EPA to conclude that POTWs with an average daily flow of 50 million gallons per day or higher were major sources of HAPs.

NACWA’s primary concern was that WATER9’s inclusion of volatile organic compound (VOC) and HAP emissions from wastewater collection systems, and treatment plants, combined with the conservative assumptions from earlier model versions, would result in even more POTWs being identified as major sources of HAPs. Based on its evaluation, NACWA has concluded that the results generated by WATER9 are significantly different than field-measured data and the results from the other two models that were investigated, INTERCEPTOR and TOXCHEM+. In addition, NACWA found that how the WATER9 model was set up and executed could affect the resulting emission estimates.

This Regulatory Alert outlines some of the problems NACWA identified and solicits information from any NACWA member who may have used WATER9 (or earlier versions). NACWA will use this information to develop next steps and in discussions with EPA as the Air Quality Committee works to have EPA correct the identified problems. NACWA members are asked to respond to the questions below by June 23, 2006, via email to Chris Hornback, NACWA’s Director of Regulatory Affairs, at chornback@nacwa.org.

NACWA Notes Flaws in WATER9 Emissions Model
NACWA’s evaluation of the emissions models focused on predicting emissions from two wastewater collection system components, gravity flow reaches and drop structures. For the drop structure analysis, two distinct approaches were suggested by EPA for using WATER9. Results using both approaches were determined to be significantly different than either the INTERCEPTOR or TOXCHEM+ models. Additionally, the two approaches to using WATER9 produced results that were significantly different from each other, meaning that understanding how to correctly set up and execute WATER9 is critical.

While NACWA believes that more study using municipal-specific data to validate the algorithms in the WATER9 model is necessary, NACWA believes that the largest obstacle to the use of WATER9 as a fully-functional emissions tool is in the setup and execution of the model. It is especially troubling that the results from two different modelers performing model runs on the same scenarios with seemingly the same input data yielded different results. A source of at least some of the confusion may be the use of nomenclature that is not commonly used by municipal wastewater treatment agencies to describe components of their collection systems.

NACWA is preparing to send a letter to EPA’s air office to alert them to the problems identified during its evaluation and to suggest the following improvements at a minimum:

  1. Improved documentation on model component selection, e.g., how to represent gravity-flow sewers in the model;
     
  2. Improved documentation on model setup and execution; and
     
  3. Improved documentation on algorithms used, thereby allowing for independent evaluation of model results.

NACWA is also trying to determine the extent to which the WATER9 model (or earlier versions) is being used by POTWs or is being required by regulatory agencies and requests that members provides responses to the questions below to assist the Air Quality Committee in determining the extent of the model’s use.

NACWA Seeks Member Input on Use of EPA’s WATER9 Model
NACWA’s Air Quality Committee would like to hear from members who have used EPA’s WATER9 model (and earlier versions) to estimate air emissions from their treatment plant(s) or collection system. NACWA will use this information to assess next steps and in discussions with EPA, but will keep utility-specific information confidential. Again, NACWA members are asked to respond to the questions below by June 23, 2006, via email to Chris Hornback, NACWA’s Director of Regulatory Affairs, at chornback@nacwa.org.