             Environmental Protection Agency (EPA): Draft Guidance
        Control Techniques Guideline for the Oil and Natural Gas Sector
                                 RIN 2060-ZA22
General Comments

  1) Reviewer recommends making any conforming changes to the CTGs that come about based on comments on the Oil and Gas NSPS rulemaking. 
  EPA Response:
     We are making any appropriate conforming changes to the CTG that came about based on comments on the Oil and Gas NSPS.
     
  2) Reviewer recommends providing clarity in relation to how the CTGs and the voluntary EPA programs are consistent and that companies that take voluntary actions that comply with EPA's programs will not be required to take additional action that would be counter to the voluntary program. 

     EPA Response:
     We are soliciting comment on this. 
     
  3) Reviewer recommends that RACT technologies explicitly include flexibility to include technologies in addition to OGI -- especially as new technologies emerge that provide similar or increased performance at reduced cost--e.g. infrared absorption based technologies, continuous monitoring systems, and unmanned sensing systems.  Suggested language could be: "...OGI and other sufficiently tested monitoring technologies that demonstrate equivalency or superiority to the technical capabilities of current OGI technologies." This language (or similar) should accompany all specifications of OGI technologies. 
     
     EPA RESPONSE:
     The draft guidelines provide recommendations for air agencies to consider in determining RACT. Air agencies can use the recommendations in this guideline to inform their own determination as to what constitutes RACT in their particular nonattainment areas. We are aware of several types of technologies that may be appropriate for fugitive emissions monitoring.  In the preamble to the NSPS, we are requesting comment on whether there are other fugitive emission detection technologies for fugitive emissions monitoring and details related to these technologies. However, we cannot recommend or allow the use of these emerging technologies until we have evaluated detailed information on topics such as detection capability; an equivalent fugitive emission repair threshold to what is required in the proposed rule for OGI; the frequency at which the fugitive emissions monitoring surveys should be performed and how this frequency ensures appropriate levels of fugitive emissions detection; whether the technology can be used as a stand-alone technique or whether it must be used in conjunction with a less frequent (and how frequent) OGI monitoring survey; the type of restrictions necessary for optimal use; and the information that is important for inclusion in a monitoring plan for these technologies.
     
  4) Reviewer recommends that EPA should propose allowing flexibility to enable the use of continuous emissions monitoring systems and mass flow rate thresholds for compliance.  Reviewer notes that a mass flow rate (scfh) is preferable to a concentration measurement (ppm), which is a less accurate measurement of leaks since it does not consider the impact of atmospheric conditions, such as wind or background methane. 
  
  EPA RESPONSE: 
     The CEMS technology is not used to determine the presence of fugitive emissions nor does EPA believe that CEMS are appropriate to be used in this case. Fugitive emissions are inconsistent by nature and come from various emissions points. CEMS are typically used on a source emission stack (e.g. boiler).  
     
  5) Reviewer recommends that EPA consider alternative approaches to conducting leak surveys that are more akin to approaches taken by Colorado and Wyoming.  Concerns with the proposed approach include:
      a. Many studies have shown a skewed distribution for emissions related to leaks and that the occurrence of such leaks is often random and difficult to predict, which suggests that more frequent surveys may be necessary to identify and repair the largest leaks. 
      b. The proposed structure for determining the frequency of surveys may create a disincentive for companies to find leaks because not detecting a leak for two consecutive surveys would reduce the frequency (and costs) of future surveys.
      EPA Response:
      a. We are soliciting comment, in the NSPS, on the use of Method 21, which is one of the options that Colorado allows in Rule 7; however, we are concerned with the ambiguity of the "other Division approved instrument based on monitoring device or method" provision.  There are no operational requirements to ensure that leaks can consistently be found during monitoring with such an instrument.  In addition to Method 21, we are soliciting comment on other potential leak detection approaches. In the NSPS, we are also soliciting comments on the use of other emerging technology for fugitive emissions monitoring. 
      b. EPA shares these concerns. In effort to ensure that fugitive emissions will be found when using OGI, we are proposing that all OGI operators develop fugitive emission monitoring plans. This plan includes daily instrument checks, determination of maximum wind speed during monitoring along with other specific parameters that ensure that leaks will be found. The monitoring plan would also require proof of inspection (i.e. still images of components during monitoring survey). The plan would require record keeping and reporting requirements to ensure compliance. We therefore believe that the methodology for surveying, repairing, and reporting fugitives is sufficient and that the OGI is optimized if all the parameters are met.  Appendix I. of the model rule provides details of the monitoring plan requirements.
Specific Comments

   1) Reviewer recommends changing the assumed price for natural gas from $3.50/ mcf to $4.00/mcf in Table 4-3.  A market price for natural gas of $3.5/mcf is inconsistent with the market price assumed on page 5-13 of this document and with the proposed NSPS, which assumes $4/mcf.  
   EPA Response:
   We have corrected the price for natural gas in Table 4-3.
   2) Reviewer requests clarification regarding the following text on page 5-6:
            "Although we have additional data available on fugitive emission from compressor stations, including data from the Measurement of Methane Emissions from Natural Gas Gathering Facilities and Processing Plants: Measurement Results study published in 2015, the data sets for gathering and boosting facilities had skewed distributions. In the study data set, 30 percent of gathering facilities contributed 80 percent of the total emissions, and gathering facilities emitted, on average, yielded higher emission than would be calculated with the factor used in this analysis. Therefore, for gathering and boosting station reciprocating compressors, we used the same methane emission factor used in the 2011 NSPS TSD."
Reviewer notes that the logic underlying this statement is unclear (there also seems to be grammatical problems with the second sentence). The text seems to be saying that recent research indicates that the distribution of emissions is skewed and greater than previously thought.  Yet, a decision is made to use an emissions factor based on less current information.  Is EPA trying to make the point that their estimated benefits of the rule are conservative?  Please clarify.

EPA Response:
For gathering and boosting station reciprocating compressors, we used the methane emission factor used in the 2011 NSPS TSD because factors for this source are not available in the GHG Inventory.

The above language will be replaced with:
      For gathering and boosting station reciprocating compressors, the 2011 NSPS TSD emissions factors were used because they are considered to be the best representative emissions factors at this time. 

