Proposed General NPDES Permit for Industrial/Municipal Wastewaters Dischargers that Meet Objectives/Criteria at the Point of Discharge

1. What kind of discharge or facility would be eligible for coverage under the General NPDES Permit?

   Treatment facilities that treat domestic wastewater and meet water quality objectives/criteria at the point of discharge or “end‐of‐pipe.”

2. What does “at the point of discharge” mean?

   Point of discharge means the point just prior to where the facility effluent discharge meets the receiving water. Under this General Permit, facilities are required to meet all of their effluent limits prior to discharge to the receiving water – or “at the point of discharge.”

3. What are the potential advantages of having coverage under the General NPDES Permit vs. an Individual NPDES Permit?

   The following is a list of some of the advantages being covered under the General NPDES Permit vs. an Individual NPDES Permit:

   • Streamlined application
   • Streamlined permitting process (three to six months shorter duration)
   • Simple reenrollment under subsequent General NPDES Permit
4. How would I apply for the General NPDES Permit?

   The application will consist of the submittal of a Notice of Intent (NOI), discussed in the response to Question 5.

5. What is NOI?

   NOI includes information regarding the owner/operator/authorized representative and facility (e.g. Form). Additional data and/or information that the discharger would like the Regional Board to take into consideration can also be provided.

6. What is the Notice of Applicability (NOA)?

   NOA is the official document signed by the Executive Officer granting regulatory coverage under the General NPDES Permit to the discharger for the NPDES discharge. The NOA will include at minimum: facility description and applicable final effluent limitations, effluent and receiving water monitoring requirements, beneficial uses, pretreatment program requirements, and minor land discharge specifications.

7. What would the approval process be to get coverage under the General NPDES Permit?

   After the submittal of the NOI, Regional Board staff would review the application and perform a reasonable potential analysis of the data. Staff may request additional information in order to determine eligibility for coverage under the General NPDES Permit. Staff will develop the NOA for approval by the Executive Officer. The subject discharge would have regulatory coverage under the General NPDES Permit after the Executive Officer issues the NOA.

8. Will the discharger have an opportunity to review a draft of the NOA?

   Yes. The draft NOA will be provided to the discharger for review prior to the NOA being considered for approval by the Executive Officer.

9. Will there be public review of the NOA before the NOA is approved?

   No. The public review process will be completed during the development and approval process for the General NPDES Permit. The public will be notified by the posting of a Notice of Public Hearing and will have the opportunity to submit written comments and recommendations concerning the tentative General NPDES Permit. The Central Valley Water Board will consider all timely comments received from the public at a public hearing. At the public hearing, the Central Valley Water Board will consider testimony and whether to adopt the proposed General NPDES Permit. If the Central Valley Water Board adopts the General NPDES Permit, the Executive Officer will be authorized to issue individual NOAs to specific NPDES discharges that fall under the coverage of the General NPDES Permit.

10. How long would the application and approval process take?

    Since this would be a new General NPDES Permit, the complete process time is undetermined. However, staff estimates the process will take approximately three to four months from the time the applicant submits a complete NOI through issuance of the NOA.

11. What is the term of coverage under the General NPDES Permit?

    The General NPDES Permit would be effective for a five‐year term. Whenever a new discharge is issued an NOA and enrolled for coverage under the General NPDES Permit, that coverage will expire when the General NPDES Permit expires. When the General NPDES Permit is renewed, the coverage for existing enrollees will be automatically renewed for the next five‐year term of the renewed General NPDES Permit, as long as the terms and conditions of the NOA are still applicable.

12. Would this Permit apply to discharges that are effluent dominated?

    Yes. The General NPDES Permit can be used for both effluent and not‐effluent dominated situations.

13. How long is the information in an engineering study valid?

    As long as the information in the engineering study applies to the existing operations and conditions at the treatment facility, and it is useful to staff in the analysis of determining eligibility of the discharge, then the engineering study should be valid.

14. Would a discharge that has dilution credits be eligible for the General NPDES Permit?

    No. If dilution credits are needed to meet effluent limitations, then the discharge would not be eligible for coverage under the General NPDES Permit.

15. We do not currently meet end‐of‐pipe limits but are making upgrades to our facility that will enable compliance at the point of discharge – could we apply for the General NPDES Permit now or do we have to wait for the upgrades to be completed?

    A discharger whose facility upgrades are underway and will be able to meet applicable effluent limits at the point of discharge when the upgrades are complete may apply for the General NPDES Permit once it is adopted by the Central Valley Water Board. Regional Board staff would review the NOI as it is received and will develop an NOA for approval by the Executive Officer as appropriate. The existing compliance schedule would be amended to reflect that an NOA authorizes the facility's discharge is under the General NPDES Permit.

16. Has USEPA been involved with the development of the General NPDES Permit?

    Yes. Staff will continue to request input from the USEPA during the development process.

17. How will the General NPDES Permit work for site‐specific constituents that are dependent upon hardness, pH, or temperature?

    The basis for calculating the criterion and the effluent limitations for each constituent would be described in the General NPDES Permit. The applicable site‐specific details and applicable final effluent limitations for a particular facility would be contained in the NOA.

18. If the monitoring data for hardness changes, would the corresponding effluent limits change (i.e. will floating limits be issued)?

    No, floating limits will not be issued. The General NPDES Permit would include the procedures for determining site specific limitations and the final effluent limit applicable to the discharger would be included in the NOA.

19. When can I submit the NOI application?

    Staff will begin accepting NOIs after the Central Valley Water Board has adopted the General NPDES Permit.

20. Where can I get information regarding what is required with the NOI?

    An application checklist will be developed listing all the necessary information for a complete NOI. Once available, the checklist will be included in the General NPDES Permit and will be posted on the Regional Board's website.

21. If the General NPDES Permit does not work for me, can I obtain an Individual NPDES Permit?

    A discharger authorized by the General NPDES may request exclusion from the General NPDES Permit by submitting a Report of Waste Discharge for an individual permit and reasons supporting the request. If the reasons for the individual permit are adequate to support the request, an individual permit will be prepared (see also Question 27).

22. Have groups or individuals other than dischargers been notified to take part in the development process for the General NPDES Permit?

    Yes. All NPDES permit holders and interested parties including individuals, stakeholders, and nongovernmental organizations that have expressed interest in the Central Valley Regional Water Board's NPDES program have been notified.

23. Are the enrollees grouped under the General NPDES Permit, such as by region?

    The General NPDES Permit will only be available to dischargers in the Central Valley Region. There is no grouping of certain types of projects within the Region.

24. Our treatment plant upgrades will not be completed before the General NPDES Permit is available. Will we miss the application window?

    No. You will not miss the application window. Please see Questions/Answers 15 and 19. You may apply for coverage under the General NPDES Permit at any time while the Order is effective.

25. How prescriptive will the General NPDES Permit be for the operation of the UV system?

    The General NPDES Permit would include the Regional Board's standard UV specifications, which are based on the National Water Research Institute guidelines. However, just like Individual Permits, the General Permit would allow site‐specific UV specifications to be included in the NOA if detailed UV specifications are contained in a Title 22 Engineering Report approved by the Division of Drinking Water.

26. Other general orders contain more restrictive monitoring than in our Individual NPDES Permit. Will this General NPDES Permit contain restrictive monitoring?

    The goal is not to include more restrictive monitoring than what is currently included in individual orders. However, the General NPDES Permit will be developed to apply to multiple discharges, so the monitoring may be different than what is in your current Individual NPDES Permit.

27. Will dischargers be able to choose between the General NPDES Permit and an Individual NPDES Permit for coverage of their discharge?

    Dischargers that are eligible for coverage under the General NPDES Permit have the option to be covered under the General NPDES Permit or an Individual NPDES Permit; however, the terms and conditions in the Individual NPDES Permit will likely be similar to those in the General Permit.

28. My Individual NPDES Permit does not expire for more than 180 days. When will I be required to apply for the General NPDES Permit?

    As soon as the General NPDES Permit becomes available, you may apply for coverage for your discharge. However, you may wait to submit your application until no later than 180 days prior to the expiration date of your existing NPDES Permit, in accordance with title 23 of the California Code of Regulations.

29. Does this General NPDES Permit apply to my facility?

    The Central Valley Water Board has identified 25 facilities that appear to be immediately eligible for the General NPDES Permit. However, there is no intent to guarantee coverage under the General NPDES Permit to the facilities on the list of 25, nor is it the intent to exclude any facility not on the list of 25 from applying for coverage under the General NPDES Permit.

30. If a discharger has more than one discharge point, can the discharger obtain regulatory coverage under the General NPDES Permit and under an Individual NPDES Permit for the separate discharges?

    Yes. The discharger can obtain regulatory coverage under the General NPDES Permit for discharges deemed eligible for coverage and obtain regulatory coverage under an Individual NPDES Permit for discharges that are not eligible for the General NPDES Permit.

31. Will discharges to land be covered under the General NPDES Permit?

    The General NPDES Permit will include standard land discharge specifications (e.g. no objectionable odors, no public contact, etc.). If the land discharge requires more complex or site‐specific specifications to ensure the protection of water quality, the discharger may need to obtain regulatory coverage for the land discharge under a separate permit.

32. Who is responsible for making the determination about whether a discharge of pollutants from a surface discharging system will enter waters of the United States?

    Following is a response from the response to comments document that addresses this question and also provides additional information on waters of the United States. The response indicates that the homeowner is responsible for making the determination. EPA expects that the homeowner will make the decision based on the information provided by the person who conducts the soil investigation. The response from the response to comments document is as follows:

    • Congress, in Section 502 of the CWA, defined “navigable waters” broadly as encompassing all “waters of the United States.” EPA has issued a regulatory definition of the term “waters of the United States” at 40 CFR § 122.2. EPA's definition includes, among other things, traditional navigable waters, tributaries of traditional navigable waters, and wetlands that are adjacent to traditional navigable waters or their tributaries. The Supreme Court has determined the scope of Congress' intent to regulate “waters of the United States” in several opinions of the Court, most recently in the case of Rapanos v. United States, 126 S. Ct. 2208 (2006).
    • EPA has provided guidance to individuals and companies impacted by the Rapanos decision; that guidance and other materials are set forth at http://water.epa.gov/lawsregs/guidance/wetlands/CWAwaters.cfm. This guidance discusses EPA's jurisdiction over traditional navigable waters, relatively permanent non‐navigable streams, non‐navigable streams that are not relatively permanent, and wetlands adjacent to those waters to help EPA and the Corps of Engineers, as well as citizens, identify whether particular surface waters are “waters of the United States.”
    • It is the responsibility of the potential discharger to determine whether or not his or her system might discharge to a water of the United States. EPA realizes, though, that the Rapanos guidance may be difficult for the average person to apply. As a common sense way of evaluating whether you are required to be covered by a permit, if you were to install a new or replacement surface discharging system on your land, would effluent or pollutants (even diluted ones) from your system end up in a water of the United States or a conveyance, such as a ditch, drainage pipe, channel, tunnel, conduit, discrete fissure or other means that leads to a water of the United States? In evaluating this question, consider that rain water, irrigation activities, lawn sprinkling systems and any other ways that water can carry pollutants to waters of the United States. If so, even though pollutants would not be carried to waters of the United States unless your area experienced an exceptionally wet season, you are still required to obtain coverage under a permit. Only if you are sure that your system would not discharge pollutants to a water of the United States or a conveyance that leads to a water of the United States should you forego obtaining a permit for a surface discharging system. If you do not obtain a permit, but actually discharge, you may be subject to an enforcement action under the CWA.
33. If a complaint is received by a local health department on an existing surface discharging system, does EPA get involved in the complaint investigation process?

    EPA's involvement depends upon the definition of an existing surface discharging system. EPA considers existing surface discharging systems to be those surface discharging systems that were installed and operational prior to the 10 February 2014 effective date of EPA's NPDES general permit for new and replacement surface discharging systems in Illinois. Therefore, to the extent that a local health department receives a complaint for an existing surface discharging system as described above, those particular systems are not covered by EPA's permit, and, thus, EPA would not get involved in a complaint investigation process.

    If the complaint is for a system covered under EPA's general permit, then EPA will only get involved in a complaint investigation process to the extent that the complaint involves alleged noncompliance with the NPDES general permit. If NPDES permit noncompliance is alleged, EPA would welcome the local health department's sharing of all information that it has regarding the complaint and any information the department has as the result of its own investigation.

34. If a property is so limited in area (due to well setback, space consumed by the building and driveways) that it is not physically possible to install any subsurface system, will a soils evaluation still be required? This could also apply to a site which is completely in a floodway. In such cases, I believe that the site evaluator could attest that there is no value to a soils evaluation being done, and therefore a soils evaluation should be waived.

    The final general permit requires that any NOI submitted include a technical feasibility analysis which is comprised of both the site evaluation and soil analysis. Even though there may be situations as described where there is limited area, a technical feasibility determination, which includes a soil analysis, is required for anyone seeking coverage under the general permit.

35. Does EPA see any difference between treated effluent discharged from an NSF Standard 40 treatment plant and an NSF Standard 350 treatment plant as far as NPDES requirements or monitoring?

    The general permit has effluent limitations that Dischargers must achieve regardless of what technology is used. Therefore, all permit requirements and monitoring are the same regardless of whether the effluent is discharged from an NSF Standard 40 treatment plant, NSF 350 treatment plant, or any other type of treatment system.

36. If a site contains only fill material, is a soil‐based system exempted from such a site, or is the suitability totally based on the soil classifier's report?

    The general permit would allow the use of a soil‐based system at a site containing fill material only. As at all sites, the site containing fill material would have to be evaluated to determine whether it can support various soil‐based alternatives through completing the technical feasibility analysis (soil analysis and site evaluation).

37. With regard to the 30‐day wait period, if the applicant does not hear anything from the EPA, then the applicant knows that he or she can install a surface discharging system, and the local county health department can issue a construction/installation permit. Will the EPA call a local health department once EPA has made a decision whether to grant or deny coverage if that decision is made prior to 30 days upon EPA's receipt of the NOI?

    Although it is not specified in the permit, and the final permit does not require it, EPA will send a coverage letter to the applicant and copy the applicable local county health department. EPA will notify both the applicant and the applicable county health department by telephone and/or email, and follow up with a formal letter regarding the decision. Should EPA reach a decision prior to 30 calendar days following receipt of an NOI, EPA will notify the applicant and applicable county health department upon reaching its decision.

38. Some properties in our county are very small and the only choice is to install an aeration unit. In these particular instances, why is it necessary to go through the Notice of Intent process?

    It is the applicant's decision whether or not to apply for coverage under the general permit, but if the applicant chooses the general permit, he or she must comply with the established application/NOI process. EPA's NPDES General Permit does not allow for an abbreviated application process for instances when particular sites, upon cursory inspection, appear to be inadequate to support an alternative to a surface discharging system. An abbreviated process could result in a premature decision ruling out a site's ability to support an alternative to a surface discharging system. Requiring everyone who applies for coverage under the general permit to submit a notice of intent and the required supplemental information ensures that each site, regardless of size, soil type, or other restrictive features are consistently evaluated based upon the technical and economic criteria established in the final permit.

USEPA Prevention of Significant Deterioration Permit

1. What is PSD?

   PSD is an acronym for Prevention of Significant Deterioration rules. These rules need to be addressed when a company is adding a new source or modifying an existing source in an attainment area. The PSD rules need to be addressed for the pollutants for which the area is classified as attainment with the National Ambient Air Quality Standards (NAAQS). PSD rules are designed to keep an area with “good” air in compliance with the NAAQS. The strategy with PSD rules assumes that minor new sources and minor modifications do not significantly affect the air quality. The distinctive requirements of PSD are Best Available Control Technology (BACT), air quality analysis–modeling (allowable increments), and analysis of impacts of the project on visibility, vegetation, and soils. Under PSD, if a source is classified as a major source for any one pollutant, then a significant increase in any pollutant (even one that the source is not major for) triggers PSD review.

2. What is PSD increment?

   PSD increments prevent the air quality in attainment areas from deteriorating to the level set by the NAAQS. A PSD increment is the maximum allowable increase in concentration that is allowed to occur above a baseline concentration for a pollutant. The ambient air quality evaluated is the ambient air quality in effect at the time the minor source baseline dates were established. An increment is defined as the maximum increase in ambient air quality that is allowed above the conditions that exist on the date the baseline dates are set. At the time increments were established, states were permitting new and modified stationary sources to consume 100% of the available NAAQS. Congress with the 1977 amendments to the federal CAA and EPA set increments at specific percentages of the NAAQS to define the maximum increment of deterioration from existing air quality. Increments limit the deterioration in the air quality and is more stringent than the NAAQS in limiting emissions increases. Exceeding (i.e. overconsuming) an increment does not result in the same requirements as exceeding a NAAQS in that it does not trigger nonattainment. Instead, upon finding an increment has been over consumed, the federal rules in 51.16(a) require the state to develop a plan to rectify the overconsumption of increment. The plan is a SIP amendment. The PSD increments are contained in 40 CFR 51.166(c) and 40 CFR 52.21(c). The federal CAA allows any increment other than an annual increment to be exceeded once per year and not trigger any requirements to address increment over consumption. The baseline concentration is defined for each pollutant and is the ambient concentration existing at the time that the first complete PSD permit application affecting the area is submitted. Significant deterioration is said to occur when the amount of new pollution would exceed the applicable PSD increment. It is important to note, however, that the air quality cannot deteriorate beyond the concentration allowed by the applicable NAAQS, even if not all of the PSD increment is consumed. Therefore, the NAAQS is the maximum allowable concentration “ceiling.”

3. What is a minor source baseline date?

   A minor source baseline date is the date when increment consumption/expansion by nonmajor sources begins. Minor source baseline dates are set for each air quality control region established by the state under requirements of the federal CAA (Section 107 – Planning areas). To set a minor source baseline date, the PSD application has to include the pollutant (NO_x, SO₂, PM₁₀, or PM_2.5) as

   • a pollutant which will be emitted at or above the major source threshold triggering the need for PSD permitting, or
   • a regulated pollutant which is emitted as a result of the project subject to PSD permitting at or above the significant emission rate, and
   • the PSD application is accepted as complete.

   The minor source baseline date denotes the date/calendar year that a state needs to track and retain an emission inventory for the air quality control region, where the baseline date has been set. According to the federal CAA, the baseline date denotes the baseline concentration of pollutants in the air as determined by ambient monitoring date acquired by EPA and the states. After the minor source baseline date, any increase in actual emissions from both major and minor sources consumes the PSD increment for that area.

4. What is the major source baseline date?

   The major source baseline dates for SO₂ and TSP/PM₁₀ were set by congress in the 1977 amendments to the federal CAA. As directed in the law, EPA established the dates for NO_x by rule in 1988 and for PM_2.5 by rule in 2010. EPA justified that PM_2.5 was a different pollutant than TSP/PM₁₀ in its rulemaking to establish the increment. Between the major source baseline date and the minor source baseline date, only major sources can consume or expand increment. After the minor source baseline date, permitting of major sources must determine how much increment has been consumed/released by the major source and how much increment remains in the area of the source.

5. Can a minor source consume or expand increment before the minor source baseline date is triggered?

   No. Minor source changes before the minor source baseline date has been triggered have no effect on the available increment.

6. Can a major source consume or expand increment before the minor source baseline date?

   Yes. Starting on the major source baseline date and ending on the minor source baseline date, only changes at major sources can consume or expand increment. Major sources also continue to consume and expand increment after the minor source baseline date.

7. Can a minor source consume or expand increment after the minor source baseline date is triggered?

   Yes. A minor source in existence on the date the minor source baseline date has been set can consume or expand increment. Minor sources coming into existence after the minor source baseline date consumes increment until it closes or implements more stringent emission controls.

8. What is a “netting exercise”?

   A netting exercise is a demonstration by the applicant which sums up emission changes which have occurred at a source over a contemporaneous time period. The resulting emission changes are then reviewed to determine if the proposed project must undergo PSD. Netting is used when a proposed project is significant by itself, but the applicant wants to avoid PSD rule applicability by taking into account other emission decreases which have occurred over the contemporaneous timeframe. The applicant must also account for other emission increases. Thus, when summing the net emissions decrease from other projects with the emissions increase from the proposed project, the overall net increase in emissions would not be significant.

   For PSD, netting is only required if the proposed project by itself has significant emissions. For example, a major source could have three unrelated projects of 20 tons of NO_x each; in an attainment area over a five‐year period whose accumulated emissions would be significant, but netting and hence PSD review is not required because the projects were not related. Note, however, that a deliberate decision to split an otherwise “significant” project into smaller projects to avoid PSD review would be viewed as circumvention. In determining if projects are related, you need to ask two basic questions:

   1. Were the projects proposed over a relatively short period of time?
   2. Could the changes be considered part of a single project or business decision?
9. What are contemporaneous emission decreases and when are they needed?

   The term emission decreases is most often used to refer to a decrease in emissions at a source which is used to counterbalance or compensate for an emissions increase in a netting exercise. For example, if a proposed project will result in an increase of 100 TPY of a pollutant, but three years earlier the source removed 80 TPY unit of the same pollutant, then 80 TPY of decreases are available such that the contemporaneous increase from the proposed project is only 20 TPY. Use of emission decreases in this manner is not “needed” but is an option available to the applicant under PSD.

10. Does one ever need to go beyond the contemporaneous time period to consider past emissions increases?

    Yes. One cannot relax restrictions placed on a project to avoid status as a major project without considering whether the project would then have been major when originally permitted. If the project would become major with a requested relaxation in limits, appropriate PSD must be imposed as part of the issuance of a revised permit.

11. What is a “Sham” permit?

    Sham is defined as counterfeit, untrue, or fake. A Sham permit is when a source pursues a permit limit on the potential to emit (PTE) for a proposed project in order to limit the source to minor source levels as a means of circumventing the requirements of PSD. Most often this term applies to construction situations when a company wants to expedite commencement of construction so they are willing to take what they consider temporary limits on PTE such that the proposed project is not required to undergo PSD. Therefore, the company can get their permit without any of the PSD associated delays. The company's intent in such cases would be to remove the limiting permit conditions prior to normal operation, or shortly thereafter (e.g. request a revision to the permit or appeal the permit). Another circumstance which may occur is when a major project is broken up into several smaller minor projects in order to avoid PSD requirements.

12. What is “debottlenecking”?

    When the output of a multistep process is limited by the capacity of one unit or activity, that unit or activity is a bottleneck. Debottlenecking this step in a process can increase the capacity of the other steps both upstream and downstream. Debottlenecked emissions increase must be counted as part of a project's emissions increase. For example, if a paper cutter at the end of the printing line is replaced and the new paper cutter can handle a larger volume of paper quicker such that more printing will be performed, and emissions will increase. The cutter itself has no emissions. However, by replacing the cutter, the entire process line has been debottlenecked, and the process line's emissions were increased.

13. What does “relied on” mean in regard to creditable emissions increases and decreases in a netting exercise and what are its implications?

    In PSD rules (40 CFR 52.21), it is stated that emissions increases and decreases are creditable to the extent that they were not previously relied on [40 CFR Part 52.21(b)(3)(iii)]. “Relied on” means that a permit was issued where the proposed project was actually required to meet PSD requirements and such decreases and increases were accounted for in any modeling or analysis of the use of available PSD increments. As per EPA guidance MEMO dated 29 December 1989, there are situations, such as when a source nets out of review, when the permitting authority does not rely on creditable emissions increases or decreases in issuing a PSD permit. For example, when a source nets out of review, no PSD permit is issued. As such, the reviewing authority has not relied on any creditable emissions increases or decreases in issuing a permit, so the emissions increases and decreases are still available for future applications.

14. What do the terms “synthetic minor” and “natural minor” generally mean?

    A person may mean the following when using these terms, although they are not specifically defined in any known PSD rules or literature. The term “synthetic minor” is generally used to describe a source that has permit conditions which limit its potential‐to‐emit (PTE) to less than major source levels, but whose PTE in the absence of any permit conditions would be above major source levels. The term “natural minor” is generally used to describe a source whose PTE is less than major source levels in the absence of any permit conditions.

15. What criteria do you use to determine if two facilities which are close by and related should be treated as the same source or separate sources for purposes of PSD?

    The PSD rules provide that facilities should be considered a single stationary source if they meet all of the following three criteria:

    1. Belong to the same SIC major (two‐digit) group. If the facilities could have separate SICs but a support relationship exists (e.g. 50% of the product of one is utilized by the other), then one facility is considered a support facility and this criterion shall be considered met.
    2. Are located on one or more contiguous or adjacent properties (in the same general area).
    3. Are under common ownership or control. If the applicant challenges the existence of common control, it may be necessary to look at the contractual agreement between the facilities to determine if they are under common control.

    In reviewing applications, one must check these factors carefully if the circumstances at the source are not straightforward. In particular, is a company trying to improperly separate a single source into multiple plants in order to avoid PSD applicability? Is a company trying to improperly claim contemporaneous decreases from another source to avoid PSD applicability?

16. An engine manufacturing plant sprays VOC contaminated wastewater into the air to dispose of VOC. Is the activity, if new, subject to PSD?

    If the source has non‐fugitive emissions greater than 250 TPY, the new emissions which are fugitive would count in determining PSD applicability. The only place fugitives are given special treatment is in determining if the source is subject to PSD review.

    Reference: 40 CFR §52.21(i)(4)(vii)

17. A major source makes a physical change which increases emissions by a “significant” amount. The project also has offsetting reductions elsewhere at the same time. In the past five years, however, there have been other increases such that the net emission increase result over five years is greater than the significant emission rate for at least one pollutant. Is the new physical change subject to PSD review?

    Yes. PSD review is triggered if

    1. the proposed change, by itself, without counting any offsetting reductions, will result in a significant emissions increase and
    2. when facility‐wide increases and decreases over the past five years are considered, a significant net emissions increase results.

    Emissions decreases are not counted in “Step 1” of the PSD applicability analysis.

    Reference: 40 CFR §52.21

18. A major source wishes to take two actions: (i) increase production at a previously PSD‐permitted emission unit and (ii) build a new emission unit whose emissions will be less than the SER. Emissions of fluorides from the two actions, when added together, are greater than the SER and occur within the contemporaneous time frame. Does the physical change (new unit) trigger PSD review because of the change in actual emissions at the previously permitted units being greater than the SER?

    No. Unless the production rate of the previously permitted unit was limited in the PSD permit. An increase in production is exempt from PSD review, unless the production rate is limited in the permit. Also, the PTE of the new unit by itself must be greater than the SER to trigger review. Unless the increase in emissions from the previously permitted emission unit was a result of the new emissions unit (i.e. debottlenecking).

    Reference: 40 CFR §52.21

19. Is an iron foundry one of the 28 PSD categories?

    Yes. It is a secondary metal production plant if it uses scrap metal to produce iron, even if the metal is poured into molds.

    Reference: 40 CFR §52.21(b)(1)(i)(a)

20. Is a whiskey distillery one of the 28 categories (chemical process plants) listed in 40 CFR §52.21(b)(1)(i)(a)?

    No. A chemical process plant is any establishment in Major Group 28 of the SIC Code. Beverage distilleries are in Major Group 20.

    Reference: 40 CFR §52.21(b)(1)(i)(a)

21. A major stationary source wishes to make a physical change resulting in a 15 TPY increase in particulate matter emissions. Less than five years ago, the source had a production increase (not subject to PSD permitting) resulting in a 50 TPY increase in SO₂. There were no increases in particulate matter emissions at the source over the past five years. Is the proposed increase subject to PSD permitting?

    No. The triggering increase must be of the same pollutant as the one for which a significant increase results. Also, the proposed physical change must be greater than the SER by itself. If the PM10 emissions is 15 TPY or PM2.5 emissions is 10 TPY or more, then PSD applies.

    Reference: 40 CFR §52.21

22. A boiler at a major stationary source has been shut down for 11 years. At the time of the shutdown, extensive efforts were made to keep the boiler from deteriorating. During the shutdown period, this maintenance has continued. A recent inspection by the manufacturer shows that very little effort would be required to return the boiler to service. The air‐operating permit has been allowed to expire. The owner maintains that the boiler was always intended to be used at some time in the future. Is the returning to service of the boiler subject to PSD review?

    No. Normally, a shutdown of greater than two years is considered permanent. If, however, the owner demonstrates that the shutdown was not intended to be permanent, the shutdown may be considered temporary. If the shutdown is considered temporary, a start‐up would not be subject to PSD review. The “acid test” is whether the shutdown is permanent. In any case, the increase would be considered an increase in actual emissions for any future net increase calculation and for increment consumption purposes.

23. A minor source which adds emissions of a pollutant in a major amount (100 TPY if one of the 28 listed source categories or 250 TPY if not listed) is subject to PSD review as a new major source, rather than as a modification. The netting concept is used only in the definition of major modification, and not in the definition of major stationary source. This seems to indicate that a minor source adding a major emission unit could not escape PSD review by considering previous decreases which cause the net increase to be less than the major source threshold. Is this the case?

    Yes. For example, suppose a minor source emitting 200 TPY had a decrease in actual emissions in 2010 of 50 TPY, leaving 150 TPY. In 2012, 260 TPY is proposed to be added. If the 50 TPY reduction could be used to offset the 260 TPY increase, the increase would be only 210 TPY and the source would escape review. The 50 TPY decrease cannot be used, however, so the 260 TPY increase is subject to review as a new major stationary source.

    Reference: 40 CFR §52.21(b)(1)

24. An existing source is major only because its SO₂emissions are 120 TPY. The source proposes to add 60 TPY of particulate emissions. At the same time, the source is willing to accept a new, federally enforceable limitation which lowers its SO₂emissions to 90 TPY. Is the proposed addition of 60 TPY of particulate subject to PSD review?

    No. Since the source will not be major after the change, the action is not subject to PSD review.

    Reference: 40 CFR §52.21(b)(2)(i)

25. The PSD baseline air quality is based on actual emissions from existing sources. Actual emissions are defined as the average emissions rate in TPY. How does Ecology interpret this in establishing short‐term (24‐hour, 3‐hour) baseline air quality levels when air quality modeling is used?

    Baselines for 3‐ and 24‐hour averages should be set using the maximum 3‐hour average or 24‐hour average emission rate of the existing source, respectively, which occurred during the period over which the annual emission rate was determined. For example, if a source's annual emission rate is determined to be 430 TPY by averaging 400 TPY in 1978 and 460 TPY in 1979, the 3‐hour baseline emission rate would be the maximum 3‐hour average emission rate which occurred during the period of 1978 and 1979.

    For short‐term PSD modeling, only the new and contemptuous equipment is modeled. Equipment with increase in utilization is not part of the short‐term modeling.

26. An ambient monitor was operated for one year (or shorter time, if representative of highest values) and then shut down. A proposed source wishes to use the data for its PSD application. Except for the time lapse, the data is representative of current air quality at the proposed site, is of good quality, and was gathered entirely in a time period less than three years before the source submits its application. Can the data be used, even though the monitor has been shut down?

    As long as all the data needed in the application are collected sequentially, and all the data are collected sometime in the previous three years, the timing requirement is satisfied. For example, suppose an agency operated an ozone monitor throughout a particular ozone season, which the agency determines to be April through September of 2010. The monitor is then shut down. This data could be used in a PSD application submitted any time before 1 April 2013, provided the data are still representative of current conditions, and all other requirements are met, such as quality assurance and monitor location.

    Reference: 40 CFR §52.21(m); 45 FR 52724

27. A minor source locates in a PSD area where the baseline has been triggered. In another nearby PSD area, the baseline is still not triggered after the minor source begins operation. The source's emissions impact this neighboring area. Do these emissions consume increment?

    No. The baseline air quality is that which actually exists in the baseline area on the baseline date, minus contributions from new major sources. Therefore, at some future baseline date for the neighboring area, the baseline air quality must include the actual contribution from the minor source. Since the emissions are in the baseline for the area, they do not consume increment. If the situation is reversed (minor source locates in an area that has not been triggered, impacts a triggered area), emissions would consume increment in the neighboring area, but not in the area where the source locates.

D.5.1 Model Development Is Based upon Several Assumptions

Molecular diffusion is insignificant when compared to the dispersion produced by atmospheric turbulence in both convective and stable conditions in the layer of the atmosphere between the Earth surface and an upper boundary that lies between a few tens of meters above the surface and a few thousand meters depending of meteorological conditions. This layer is called the planetary boundary layer (PBL). The PBL may be either convective (CBL), dominated by turbulent plumes, or more quiescent (stable) with much smaller fluctuations in the vertical and crosswind directions (SBL).

Theory predicts and observations confirm that in the free atmosphere the vertical and horizontal concentration profiles have nearly Gaussian distributions about the plume centerline.

If the emission is visualized as a series of overlapping puffs, then equations for the growth of each puff are just the familiar Gaussian equation.

Let us begin with the familiar Gaussian distribution.

Convention is to set up a Cartesian coordinate system with the x‐axis extending downwind from the source, the z‐axis extends in the vertical, and the y‐axis in the crosswind direction (Figure D.1).

In the plume from a continuously emitting source, maximum concentration decreases, but the width of the plume increases as the plume moves downwind as shown in Figure D.2 (note: the vertical coordinate is concentration).

Observations

1. The rates of both the horizontal and vertical spreading depend on atmospheric conditions.
   1. Atmospheric conditions depend on
      1. incoming short wave radiation, e.g. sunlight
      2. outgoing long wave radiation, mainly affected by degree of cloudiness
      3. terrain surface roughness
      4. terrain surface moisture
      5. wind speed
2. Buoyancy affects the plume centerline to produce a change in the height depending on the difference in temperature between the plume and the surrounding atmosphere.

The idealized concentration at any point downwind of an elevated source at height H is given by “emission rate of pollutant, wind speed, distance, and plume standard deviations in the horizontal and vertical directions.”

However, permitting decisions are based on the concentration at breathing height which must consider the effect of the ground surface on the plume dispersion. Because the deposition velocity of gases and most particulates of concern are small compared with the vertical velocities of atmospheric turbulence, the Earth surface behaves as a reflecting surface which modifies the dispersion equation. This effect is modeled as a virtual (imaginary) source shown in Figure D.3.

Recalling that the Gaussian distribution may be defined by two parameters, its maximum value and a measure of its spread, we may calculate the concentration at any location by estimating them. Obviously, the maximum value is related to the emission rate and the spread depends on atmospheric parameters including time. Wikipedia has a good review: https://en.wikipedia.org/wiki/Outline_of_air_pollution_dispersion.

In addition to point sources (stacks) important sources of pollutants of concern look more like lines (e.g. roads), areas (e.g. settling ponds, unpaved parking lots), or volumes (pollutants are emitted within the influence of a large building). Equations for line and area sources are derived by integrating the previous equation in one or two dimensions. Volume sources have initial dimensions which affect the dispersion equation.

D.5.2 Information Required for Modeling the Dispersion of Emissions

• Characterize the type of source

  Point, line, area, volume

• Characterize the emissions temperature

  Vertically directed exit velocity

  Initial dimension, e.g. stack diameter

  Emission rate of pollutant of concern

• Characterize the immediate area around the source

  Isolated source|nearby buildings

  Flat|Significant nearby terrain

  Land use classification, e.g. agricultural, forest, desert

• Characterize the meteorology wind speed and wind direction

  Vertical temperature gradient, i.e., lapse rate

• Existing (background) ambient concentrations of the pollutant of concern
• Develop a plan for predicting the ground‐level concentrations produced by the source, often called a modeling protocol

  Obtain protocol approval from the appropriate entities

The currently accepted steady‐state dispersion model for evaluating the ground‐level concentrations in the United States is AERMOD. The following is taken from the AERMOD Model Formulation and Evaluation report, EPA‐454/ R‐17‐001, May 2017.

In the following AERMIC stands for the AMS/EPA Regulatory Model Improvement Committee comprised of American Meteorological Society (AMS) and US Environmental Protection Agency (EPA) scientists.

The AERMOD modeling system consists of two pre‐processors and the dispersion model. The AERMIC meteorological preprocessor (AERMET) provides AERMOD with the meteorological information it needs to characterize the PBL. The AERMIC terrain pre‐ processor (AERMAP) both characterizes the terrain, and generates receptor grids for the dispersion model (AERMOD).

AERMET uses meteorological data and surface characteristics to calculate boundary layer parameters (e.g. mixing height, friction velocity, etc.) needed by AERMOD. This data, whether measured off‐site or on‐site, must be representative of the meteorology in the modeling domain. AERMAP uses gridded terrain data for the modeling area to calculate a representative terrain‐influence height associated with each receptor location. The gridded data is supplied to AERMAP in the format of the Digital Elevation Model (DEM) data. The terrain preprocessor can also be used to compute elevations for both discrete receptors and receptor grids.

AERMOD is a steady‐state plume model. In the stable boundary layer (SBL), it assumes the concentration distribution to be Gaussian in both the vertical and horizontal. In the convective boundary layer (CBL), the horizontal distribution is also assumed to be Gaussian, but the vertical distribution is described with a bi‐Gaussian probability density function (pdf). Additionally, in the CBL, AERMOD treats “plume lofting,” whereby a portion of plume mass, released from a buoyant source, rises to and remains near the top of the boundary layer before becoming mixed into the CBL. AERMOD also tracks any plume mass that penetrates into the elevated stable layer, and then allows it to re‐enter the boundary layer when and if appropriate. For sources in both the CBL and the SBL AERMOD treats the enhancement of lateral dispersion resulting from plume meander.

Using a relatively simple approach, AERMOD incorporates current concepts about flow and dispersion in complex terrain. Where appropriate, the plume is modeled as either impacting and/or following the terrain. This approach has been designed to be physically realistic and simple to implement while avoiding the need to distinguish among simple, intermediate and complex terrain, as required by other regulatory models. As a result, AERMOD removes the need for defining complex terrain regimes.

D.5.3 Screening Modeling

EPA's currently accepted screening dispersion model is AERSCREEN. In keeping with the screening approach of the past four decades, AERSCREEN calculates the expected maximum ground‐level concentration for multiple averaging periods (1‐hour to annual) for a single emission point. It uses the primary components of the AERMOD modeling system but uses an additional program, MAKEMET, to create the meteorological conditions that have been shown to produce the maximum ground‐level concentration from the source and land classification/land use characteristics. A quick round of screening modeling is often all that is required to demonstrate compliance with air quality standards.

The MAKEMET program has a long complex history, dating back over 10 years. Suffice it to say that the version of MAKEMET supplied with AERSCREEN operates in the following manner. As mentioned earlier, MAKEMET generates a matrix of meteorological conditions for application of AERMOD in a screening mode and output the results in the form of AERMOD‐ready surface and profile meteorological data files. The matrix is generated based on looping through a range of wind speeds, cloud covers, ambient temperatures, solar elevation angles, and convective velocity scales (w* for convective conditions only) for user‐specified surface characteristics (Z_o, B_o, r). For stable cases, the mechanical mixing height (Z_m) is calculated based on the friction velocity, u*. A loop through Z_m factors (multiplied times the initial value calculated form u*) is also included to account for smoothing of Z_m that occurs with refined AERMET data. Stable transition cases with solar angle greater than zero but less than the critical solar angle (ACRIT) are also included in the matrix.

AERSCREEN is an interactive wrapper for the AERMOD modeling system and computes input values according to user supplied values in response to prompts printed to the screen.

Before running AERSCREEN, users should consult and become familiar with the following:

• AERMOD User's Guide (USEPA 2016a)
• AERMAP User's Guide (USEPA 2016b)
• AERMET User's Guide (for surface characteristics tables) (USEPA 2016c)
• BPIPPRM User's Guide (USEPA 2004) – relates to building effects on dispersion
• AERSURFACE User's Guide (USEPA 2008)
• AERMOD Implementation Guide (USEPA 2016e)

Although the next two references are specific to the United States, there is useful information that may be important to dispersion modeling in general.

• Guideline on Air Quality Models (Appendix W) (USEPA 2016d)
• Screening Procedures for Estimating the Air Quality Impact of Stationary Sources (USEPA 1992)

A link to AERSCREEN (Version 16216) code including the latest MAKEMET code (Version 16216) is provided below along with documentation and test cases. The MAKEMET program interfaces with AERSCREEN to generate a site‐specific matrix of screening meteorological conditions based on user inputs for input into AERMOD.

• AERSCREEN code and executables (v16216) (ZIP)(759 K)
• MAKEMET code and executables (v16216) (ZIP)(355 K)

Please note that before using AERSCREEN, users must have the latest AERMOD executable (18081) as well as the AERMAP terrain preprocessor and BPIPPRM executables. These programs can be downloaded from the AERMOD Modeling System section.

D.5.4 AERSCREEN Examples

Figure D.4 was produced in response for an analysis of emissions from an anaerobic digester used to produce methane for power generation. Analysis showed that the methane also contained sulfur compounds. It provides an example of the effect of stack height on ground level concentration. It also demonstrates that a very small, 10 TPY source of SO₂ with a short stack may exceed the US standard to several thousand meters from the stack. The Air Quality Impact Analysis (AQIA) starts with preliminary modeling for each pollutant to determine whether an applicant can forego detailed analysis and preconstruction monitoring. If the projected ambient concentration increase for a given pollutant is below the PSD Significant Impact Levels (SILs) for each averaging period, no further analysis of the ambient impact is required for that pollutant. For those pollutants with averaging periods that have impacts greater than the SIL, a full impact analysis (taking into account other increment consuming sources) is used to demonstrate compliance with PSD increments and NAAQS (national ambient air quality standard). Many SO₂ sources emit thousands of tons but may have stacks as high as 300 m. AERSCREEN can quickly provide an estimate of the maximum ground‐level impact and distances of significant contribution to the ambient concentration. Note that the concentration axis is logarithmic.

Figure D.5 shows the effect that land use, e.g. water, forest, grassland, has on ground‐level concentration for the same 10 TPY source. It is also a good demonstration of the rule of thumb that the maximum ground‐level concentration occurs at approximately ten times the stack height from the source, e.g. for this 10 m stack height the maximum ground‐level concentrations occurs about 100 m downwind.