Oil and Natural Gas Sector: Definitions of Low Pressure Gas Well and Storage Vessel

40 CFR Part 60 , Subpart OOOO

Response to Public Comments on

P roposed Rule ( 80 FR 15180 ; March 23, 2015 )

U

. S

. Environmental Protection Agency Office of Air Quality Planning and Standards Sector Policies and Programs Division Research Triangle Park, NC 27711

July 20151 

### Table of Contents

1.0 Summary

................................ ................................ ................................ ................................ ... 2

1.1 Background

................................ ................................ ................................ ........................... 2

2.0 Response to Comments Regarding Subpart OOOO

................................ ................................ . 5

2.1 Definition of Low Pressure Gas Well

................................ ................................ ................... 5

2.1.1 Support for the Alternative Definition

................................ ................................ ........... 5

2.1.2 Revisions to the Alternate Definition

................................ ................................ ............ 7

2.1.3 Relationship of Low Pressure Wells with the Stages of Flowback

............................... 9

2.1.4 Accuracy of the Turner Equation

................................ ................................ ................. 10

2.2 Storage Vessel Definition and Requirements for Storage Vessels in Parallel

.................... 14

2.2.1 Support for the Proposed Changes to the Storage Vessel Definition and Requirements
for Storage Vessels Installed or Connected in Parallel

................................ ......................... 14

2.2.2 Support for Retaining the Requirements for Storage Vessels in Parallel

.................... 14

2.2.3 The EPA Should Grant a Stay of Final Provisions for Storage Vessels in Parallel

..... 15

2.2.4 Clarification of Whether the Storage Vessels in Parallel Provisions were in Effect

... 16

2.2.5 The EPA Must Propose New Requirements

................................ ................................ 18

2.2.6 The EPA Should Clarify the Storage Vessel Requirements I nstead of Removing Them

................................ ................................ ................................ ................................ ............... 19

2.2.7 The EPA Should Extend the Final Requirements to All Tank Batteries

..................... 19

2.2.8 Add Exclusion for Storage Vessels Used Primarily in Water Recycling Processes

.... 202 Acronyms and Abbreviations

CDPHE Colorado Department of Public Hea l th and Environment

CFR Code of Federal Regulations

EPA Environmental Protection Agency

GPA Gas Processors Association

HAP Hazardous Air Pollutant

IPAA Independent Petroleum Association of America

PTE Potential to Emit

PTE Potential to Emit

REC Reduced Emissions Completion

TPY Tons per Year

TVD True Vertical Depth

VOC Volatile Organic Compounds



### 1.0 Summary

1.1 Backgroun d

On July 17, 2014, the Environmental Protection Agency (EPA) published proposed amendments to the new source performance standards (NSPS) for the Oil and Natural Gas Sector. One of the issues addressed in the proposed amendments was the EPA’s proposed

de finition of “ low pressure gas well. ” A petitioner’s timely submitted comment on the proposed amendments concerning the definition was, inadvertently, not made part of the record in the rulemaking docket and was, therefore, not available to be considered by the EPA when the agency finalized t he definition of “ low pressure gas well ” in its December 19, 2014, final amendments to the NSPS. To correct the above mentioned procedural defect, in a not i ce published March 23, 2015, the EPA re

- propos ed its definition of “ low pressure gas well ” for

notic e and comment (see 80 FR 15180)

. In that action, w e also propos ed to amend the NSPS to remove provisions concerning storage vessels connected or installed in parallel and to revise the

definition of “ storage vessel. ”

This document presents a summary of the public comments rece ived regarding specific issues and topics related to March 23, 2015 proposed amendment and the EPA’s responses to

those comments. Table 1 provides the list of comments received by docket document ID, the

commenter and their affiliat ion. The last 4 digits of the docket document ID are used to identify comments summarized and responded to in this document.3

Table 1

. List of Commenters on the Oil and Natural Gas Sector: Definitions of Low Pressure Gas Well and

Storage Vessel; P roposed Rule (80 FR 15180; March 23 , 201 5)

Document ID Name and Affiliation Date Received

EPA

- HQ

- OAR

- 2010

- 0505

- 4752 James Elliott, Spilman Thomas &

Battle, PLLC, on behalf of
Independent Petroleum Association

of America et al. 8/18/2015

EPA

- HQ

- OAR

- 2010

- 0505

- 4755 Urban O’ Brien, Vice President,

Governme n t Affairs, Apache
Corporation 4/2 0 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4756 David Stuart, Vice President, Fluids
Conditioning, Rockwater Energy

Solutions, Inc. 4/2 2 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4757 Steven Fleming, Co

- Chair,
Regulatory Practices Committee,

Permian Basin Petroleum

Association 4 / 22 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4758 Thure Cannon, President, Texas
Pipeline Association 4 / 22/2015

EPA

- HQ

- OAR

- 2010

- 0505

- 4 760 Gretchen Kern, Senior Regulatory

and Environmental Policy Advisor,
Sustainable Development, Pioneer

Natural Resources USA, Inc. 4 /2 2 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4761 Cory Pomeroy, General Counsel,

Texas Oil and Gas Association 4 /2 2 /201 5

EPA

- HQ

- OA R

- 2010

- 0505

- 4762 Matthew Todd, Regulatory and

Scientific Affairs, American

Petroleum Institute 4 /2 3 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4763 V. Bruce Thompson, P r esident,
American Exploration and

Production Council 4 /2 3 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4764 Kathleen Sgamma, Vice President,

Government and Public Affairs,
Western Energy Alliance 4 /2 3 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4765 Darin Schroeder, Clean Air Task

Force et al. 4 /2 3 /201 54 Document ID Name and Affiliation Date Received

EPA

- HQ

- OAR

- 2010

- 0505

- 4766 Theresa Pugh, Vice President,

Environment and Construction,

Interstate Natural Gas Association of

America 4 /2 3 /201 5

EPA

- HQ

- OAR

- 2010

- 0505

- 4767 James Elliott, Spilman Thomas &

Battle, PLLC, on behalf of
Independent Petroleum Association

of America et al. 4/22/20155 

### 2.0 Response to Comments Regarding Subpart OOOO

2.1 Definition of Low Pressure Gas Well

2.1.1 Support for the Alternat iv e Definition

Comment: Several commenters ( 4752, 4761, 4762, 4764, 4767 ) express support for the alternative definition of “low pressure gas well” provided by IPAA as being more representative of current industry practice of defining these wells.

According to one commenter (4761) the alternative definition is based on the fresh water gradient, is widely used in industry and appropriately describes the well conditions where

installation of reduced emissions completion ( REC ) equipment is impractical. The commenter

state d that the fresh water gradient (i.e., 0.433 psi/ft or 8.33 lbs/gal x 0.052 x True Vertical Depth (TVD)) represents normally pressured wells based on the hydrostatic overhead pressure of fresh water that increases linearly with true vertical depth. If reservoir pressure is less than the hydrostatic pressure of water, the well will not flow on its own because of the overhead pressure

of f racture fluids in the wellbore that will be higher than the reservoir pressure which may make REC equipment impractical. The commenter added that whether a well’s productive reservoir pressure is above or below the water gradient may be readily confirmed b y reading offset reservoir pressure data in the development field or by evaluating certain wireline well logs that may be run after drilling a well before well completion begins.

Another commenter (4767) state d that the EPA’s current definition is does no t accurately define what industry has historically defined and recognized as a low pressure well. According to

the commenter , because EPA's definition does not accurately delineate low pressure wells, the current definition of low pressure well will subjec t a subset of wells to RECs where the operation of a separator is not physically possible thereby making the wells uneconomical as a result of being subject to REC requirements. The commenter included a table showing the values calculated using the EPA’s d efinition for various well depths and flowline pressure s. According to the commenter, the alternate definition would classify all of the values in the table as a low pressure well, while the EPA’s definition would only consider about a quarter of the wells as low

pressure.

The commenter further state d that the permeability of the reservoir and other reservoir characteristics play a critical role in determining when a well is a low pressure well or under

pressured. In addition to overcoming the hydrostatic pressure and sale s line pressure, the separator necessary for the REC adds to the pressure which must be overcome for gas to flow

from the reservoir. The commenter stated that the separator pressure is arguably the controlling parameter on when a REC is f easible versus the sales line pressure. Unlike the sales line pressure, which is easily known, the commenter contend ed that the separator pressure can vary greatly depending on gas and liquid rates, liquid composition and equipment limitations. The commenter point ed out that the EPA's definition does not take separator pressure into account thereby making the definition overly conservative. The commenter admits that the alternative definitions does not contain an adjustment for separator pressure eit her, but the definition is more

accurate and is inclusive of wells recognized by the industry as "low pressure. ”6

In addition to the pressure associated with the separator, the commenter state d that in order for a separator to function, there must be a suff icient volume of gas (at appropriate pressure) to lift the associated liquids and overcome the pressure of the separator. The

commente r add ed that i f that gas rate is not achieved, the well will load up and a REC will not be possible. According to the comm enter, t he gas rate necessary for a REC varies based on reservoir pressure and casing/tubing diameter. The commenter provided a graph of Coleman curves to illustrate this point, which illustrates that a s the pressure and casing diameter increase, so must

t he gas rate.

Response: The EPA believes that the alternative definition of low pressure well

, based only on fresh water gradient

, may not adequately account for the parameters that must be taken

into account when determining whether a REC would be feasible for a given hydraulically fractured gas well. We believe that, to determine whether the flowback gas has sufficient

pressure to flow into a flow line, it is necessary to account for reservoir pressure, well depth, flow line pressure , and surface ( i.e. REC) equipment . In addition, it is important for any such

determination to take into account pressure losses in the surface equipment used to perform the

REC. The EPA’s definition in the rule was developed to account for these factors.

The EPA agrees that there must be a sufficient volumetric flow of gas (caused by adequate reservoir pressure) to lift the associated liquids and overcome the pressure of the separator, enabling the gas to be collected (i.e., enter the flow line). However, t he EPA disagrees

that the current definition , which we re

- proposed for notice and comment, does not take into account the additional backpressure caused by REC equipment. The model uses an energy balance to determine the pressure drop based on the calcula ted velocity, and then the model accounts for pressure losses caused by REC equipment, including the separator. The result of

the model is a prediction of the pressure of the flowback gas immediately before it enters the

flow line. The result can be compared to the actual flow line pressure available to the well. For

wells with insufficient predicted pressure to produce into the flow line, as predicted using the

EPA equation, combustion must be used to control emissions . For wells with sufficient pres sure to produce into the flow line, gas capture in combination with combustion must be used to

control emissions

.

According to some of the comme n ters, the EPA’s definition of low pressure gas well should be revised because it does not comport with what t he industry has historically considered to be a low pressure gas well. W e are not making a determination on the similarity of the two

definitions because we do not believe that the two must be the same for purposes of the oil and gas NSPS. The EPA has pro vided a definition of “low pressure gas well” in the NSPS in order to designate a class of wells where a REC is not technically feasible. Our definition of “ low pressure gas well ” in the NSPS is for a singular purpose

– to identify the wells that cannot

i mplement a REC because of a lack of necessary reservoir pressure to flow gas at rates appropriate for the transportation of solids and liquids from a hydraulically fractured gas well during flowback against additional backpressure which would be caused by the REC equipment

, thereby making a REC infeasible . (80 FR 15182) To the extent that the industry definition is different from the EPA definition, the industry likely defines a particular well as being low7

pressure for a variety of reasons. 1 As such, i t is not clear that REC is not technically infeasible

for all of the wells that the industry has historically considered to be “low pressure wells.”

2.1.2 Revisions to the Alternate Definition

Comment: One commenter (4761) state d that t he alternativ e definition should also be clarified to state “where field reservoir pressure is less than 0.433 times the true vertical depth of

the reservoir.” According to the commenter, r eferring to reservoir pressure adds clarity and true vertical depth is a well

- kn own standard term in the industry to differentiate from “measured depth

, ” where measured depth is the length of the well. T he commenters stated that t his is an important distinction, especially for directional or horizontal wells, that should be clarified in the low pressure well definition.

Another commenter (4762) similarly suggested that instead of defining the term “low pressure gas well” in terms of the “vertical depth” of the deepest target reservoir, it should

instead b e defined in terms of the “true vertical depth.” The commenter cited to the Schlumberger online Oil Field Glossary, which defines “true vertical depth” as follows :

The vertical distance from a point in the well (usually the current or final depth) to a

p oint at the surface, usually the elevation of the rotary kelly bushing (RKB). This is one of two primary depth measurements used by the drillers, the other being measured depth. TVD is important in determining bottomhole pressures, which are caused in part by the hydrostatic head of fluid in the wellbore. For this calculation, measured depth is irrelevant and TVD must be used. For most other operations, the driller is interested in the length of the hole or how much pipe will fit into the hole. For those me asurements, measured depth, not TVD, is used. While the drilling crew should be careful to designate which measurement they are referring to, if no designation is used, they are usually referring to measured depth. Note that measured depth, due to intentio nal or unintentional curves in the wellbore, is always longer than true vertical depth.

The commenter stated that i t would be better to use “true vertical depth” because the measured vertical depth can overstate actual vertical depth because well bores m ay not be absolutely vertical. Thus, measured vertical depth often exceeds the true vertical depth of a well

bore.

One commenter (4752) state d that the IPAA’s proposed definition for "low pressure

well" was based on the weight of fresh water (8.33 lbs /gal) which is stacked on top of itself, and is known as hydrostatic pressure. Converting the density of fresh water to a pressure gradient results in 8.33 lb/gal being equal to 0.433 psi/ft. Therefore, the pressure of fresh water in the well

bore is 0.433 psi/ft times the vertical well depth.

1 “USEPA's proposed low pressure well definition forces controls on a segment of the industry that have no or minimal beneficial impact on the environment while imposing significant additional costs that will make drilling and operating such wells uneconomical.” ( James Elliott, Spilman Thomas & Battle, PLLC, on behalf of Independent Petroleum Association of America et al. , 8/8/2014)8

The commenter add ed that i n reality, the fluid flowing to the surface could be fresh

water, re

- used hydraulic fracturing water, re

- used, produced water, or a mixture. Additionally, in the beginning of the operation, the commenter state d that initial fluids flowing to the surface are essentially the fracturing fluids put down hole. At the end of the operation, the fluids flowing to the surface will mainly consist of reservoir fluids, and the water will be more of a br ine water

and not fresh water. The commenter add ed that b rine water has a greater density, and more reservoir pressure will be required to lift the fluid to the surface. The commenter contends that

the use of a fresh water gradient of 0.433 psi/ft should b e used to keep the definition conservative and simple.

As an alternative

, or in addition

, to a fresh water gradient, the commenter recommend ed

that the density of brine water influenced by sand or proppant should be used to more accurately reflect the pressure of the water column in the well bore. The commenter pointed out that the EPA appears to have utilized a gradient of 0.4645 psi/ft in the "Lessons Learned from Natural Gas STAR Partners; Reduced Emissi ons Completions for Hydraulically Fractured Natural Gas Wells" paper developed as a part of the EPA's Natural Gas STAR Program. T he commenter

stated that t his is evidenced by the gradients listed in Exhibit 5 of the paper. Additionally, to perform a REC, t he commenter contend ed that the downhole reservoir pressure must be sufficient enough to lift the hydraulic fracturing fluid to the surface and through the separation equipment and piping, with the resulting gas still having enough back pressure for it to get into the natural gas gathering line. According to the commenter, t o combust flowback emissions the downhole reservoir pressure must be sufficient enough to lift the hydraulic fracturing fluid to the surface and through the separation equipment and pipi ng, with the resulting gas still having enough back pressure to flow to a flare or enclosed combustion device.

To reflect these realities, the commenter propose d that no emission control be required when the following scenario exists:

"A well where the reservoir pressure is less than 0.4645 times the vertical depth of the deepest target reservoir."

At reservoir pressures below this value, the commenter contend ed that insufficient pressure exists for any gas to flow to a flare, enclosed combustion devic e or the process. Consequently, the commenter propose d that combustion through a flare or enclosed combustion

device be required when the following scenario exists:

"A well where the reservoir pressure is less than 0.4645 times the vertical depth of the deepest target reservoir plus the gathering or sales line pressure."

At reservoir pressures less than the sum of the water column pressure and the sales line

pressure, the commenter contend ed that the recovered gas will not naturally flow into the sales

line. The commenter state d that the proposed rule does not require compression of recovered gas

into the sales line. The commenter further states that the EPA has recognized this type of simpler approach in estimating the level of pressure necessary for re covered gas to flow into a gathering

or sales line in their Gas STAR document cited above . In this Gas STAR paper, a table (Exhibit9

5) is provided that shows the pressures necessary for various well depths. For instance, the commenter point ed out that the document indicates that the reservoir pressure necessary to flow recovered gas into a sales line for a 10,000

- foot well would be 4,645 psig plus the sales line

pressure.

Response: We agree with the commenters that “true vertical depth” is more accurate terminology that better represents our intent. Although we are not adopting the alternative definitions for the reasons presented above, we are amending the current definition of low pressure gas well to include “true vertical depth.”

2.1.3 Relationship of Low Pressure Wells with the Stages of Flowback

Comment: According to one commenter (4752), d uring the initial flowback stage the EPA has indicated that there is not enough gas to operate a separator. Gas generated during the initial flowback stage wou ld not be controlled under the proposal. The commenter states that the EPA acknowledges that during the separation flowback stage there may not be enough gas to operate a separator, with the gas either combusted or recovered depending on the well type. For certain lower pressure wells (that the commenter contends would most likely not meet the E PA ’s proposed definition of a low pressure well), the overall flowback period (all three stages) is so short that there is an insufficient amount of gas generated du ring the separation flowback stage to be able to operate or utilize a separator for a meaningful time period.

The commenter states that their proposed definition of a low pressure well that focused

on the "three day" flowback period attempted to recognize this point. According to the

commenter, t he dynamics of most vertical wells and energized wells are such that RECs or combustion by way of a separator is not feasible. The commenter request s that the EPA address

this issue in their final rule to acknowledge that not every well will have the three flowback stages clearly defined, and in certain instances, the separation flowback stage is so short that RECs are not feasible or required, i.e., that a well can essentially go from the initial flowback

sta g e to the production stage. The commenter states that t here is a subjective element to this evaluation, which the EPA has acknowledged, so the final rule should not prevent those drilling low pressure wells from continuing their ope rations. The commenter notes that the economic

incentive to undertake RECs exists. The EPA's proposed low pressure well definition forces controls on a segment of the industry that ha s no or minimal beneficial impact on the environment while imposing signi ficant additional costs that will make drilling and operating

such wells uneconomical. The commenter request s that the definition of a low pressure well be

revised or that the EPA acknowledge the separation flowback stage can be so short in duration

that RECs are not necessary.

Response: In the proposed rule we solicited comment on the alternative definition suggested by the petitioners and on specific concerns or questions we have with respect to the

alternative de finition. We received no comments that provided any data or other information that

would lead us to conclude that the alternative definition is sufficient to predict whether an REC would be infeasible for wells meeting the alternative definition. As explai ned in the proposal, we agree with the petitioners that this alternative definition is straightforward and easy to use.
However, we are concerned that it may be too simplistic and may not adequately account for the10

parameters that must be taken into accoun t when determining whether a REC would be feasible for a given hydraulically fractured gas well. According to the commenter, the 3

- day flowback

duration in the alternative definition is not an attempt to define technical feasibility of REC but

to exempt from the REC requirement well completions where a separator would not be used for

what the commenter considers a meaningful time period. Because the purpose of defining “low pressure well” is to define those wells for which REC is technically infeasible, we decline to adopt the 3 day flowback duration. Further, we question how an operator would know before

flowbac k begins that the flowback period would be less than 3 days in duration. We believe that,

to determine whether the flowback gas has sufficient pressure to flow into a flow line, it is

necessary to account for reservoir pressure, well depth and flow line pr essure. In addition, it is important for any such determination to take into account pressure losses in the surface equipment used to perform the REC. The EPA’s definition in the rule was developed to account
for these factors.

The commenter also appears to be questioning the current well completion requirements, in particular in relation to a separator. The se comments do not appear to address how to define wells for which REC is technically infeasible, which is the purpose of our re

- proposal of the

“low pressure well” definition. In that respect, we find the comments outside the scope of this rulemaking.

2.1. 4 Accuracy of the Turner Equation

Comment: One commenter (4752) cites a recent engineering doctoral dissertation at

Tulsa University that com pared several methods of calculating liquid loading in a well, which is relevant as it pertains to the equations used by the EPA to develop the definition of a low

pressure well. The dissertation was delivered by Dr. Shu Luo, a graduate student at Tulsa University, in 2013. [The commenter letter includes the abstract of the thesis, which is omitted in this summary for brevity.]

The commenter states that, i n relevant part, the thesis shows that the Turner equation typically under

- predicts the velocity ne cessary to unload the well. The commenter contends that

s ince the Turner equation under

- predicts velocity, the resulting EPA low pressure well formula

then also under

- predicts the pressure necessary for a well to flowback without assistance. For instance, to increase velocity in the well tubing, which has a fixed flow area, the flow rate of gas must be increased to carry the liquid up the tubing. To increase the flow rate within a given pipe size, the commenter contends that pressure must increase. The comm enter states that o perators
will sometimes install smaller tubing to decrease flow area, which also increases velocity. According to the commenter, t his is one example of where the EPA's derivation of a complex equation to define low pressure well is flawe d. The commenter believes that a more accurate low pressure well definition should rely on the liquid film reversal model rather than the Turner equation, which would result in a higher pressure threshold than currently proposed by the EPA. Again, the comm enter believes that the burden is on the EPA to justify its definition and not to simply question the alternative definition proposed by the commenter

. The commenter contends

that the E PA's reliance on an outdated equation not recognized or utilized by the industry is inappropriate.11

One commenter (4752) takes issues with the EPA’s statement that the commenter’s petition for reconsideration did not include any details on which of the EPA’s assumptions regarding the definition is questionable. The commenter contends that it is not their burden to justify the definition; that burden falls on the EPA. The commenter does not believe that the EPA adequately justified the basis of the definition.

The commenter states that o ne of the key assumptions to the E PA' s definition is its reliance on the Turner equation to calculate the minimum gas velocity needed to lift a droplet. This equation is used to predict the velocity needed to lift to the surface the proppant used to hydraulically fracture the well. The commenter contends that the Turner equation is from a 1969

article in the Oil and Gas Journal. The equation is based on a droplet reversal model. The

commenter is not aware of the oil and gas industry using the Turner equation for any practical applicatio ns (unlike the commenter’s proposed definition which the commenter contends relies on industry accepted calculations).

Response: The EPA disagrees with the commenter’s assertions with respect to the EPA’s use of the Turner equation in two critical ways. First, the EPA notes that in using certain data sets, the thesis cited by the commenter predicts the Turner equation to be effective and superior to other models on the velocity calculation evaluated in the thesis, which is contrary to the way the commenter characterizes the data underlying the Turner research.

Second, the EPA adapted the Turner research into the equation to define a low pressure well, but made specific provisions to adapt the Turne r liquid loading model into a model to predict the ability to execute a REC. The thesis referenced by the commenter deals with the determination of flow velocity of the liquids in the well and does not provide any methodology

to convert this into wellhead flowing pressure, which is required for designating wells as being low pressure. Unlike the EPA’s adapted model, the Turner equation used in the commenter’s cited thesis uses a constant natural gas density, meaning the velocity is determined throughout

th e entire length of the well at only one pressure condition. Additionally, to convert this into a wellhead pressure requires further steps which are not available in the thesis nor is an alternative method for this conversion proposed by the commenter.

Ho wever, in the adapted equation used in EPA’s composite analysis, the well is divided into 2,000 segments and the natural gas density is varied by pressure over each segment. The pressure at the end of each segment is subsequently used as the initial pressu re in the next segment, until the pressure at the wellhead is finally estimated. Considering the calculated velocity is dependent on the natural gas density, having this value reflect the condition for each segment accounts for the variation in pressure ov er the entire length of the well.

The liquid film reversal model proposed in the thesis also underperforms the Turner equation depending on conditions. The EPA is not aware of any composite model that approximates not only the liquid velocity, but also th e wellhead pressure using key factors that influence the calculation. Therefore, in the absence of a composite model to calculate wellhead

pressure, the EPA is retaining its model that applies to all wells across the country, and one that

is not limited t o certain well characteristics.12

The EPA notes that the commenter’s definition of a low pressure well being proposed as
an alternative is an approximation with no basis in the liquid film reversal model. The EPA also

notes that the Natural Gas STAR Program Lessons Learned document is meant to serve as
guidance only from a methane emissions calculations perspective and not as a definitive
methodology to establish low pressure wells.

Finally, the pressure gradient charts from the United States Geological Sur vey (USGS)

, shown below, indicate that using the commenter’s proposed definition, the pressure gradients for
a significant number of wells are inaccurately estimated. This is to say that the commenter
proposed definition will overestimat e the well tubing pressure necessary to overcome formation
pressure for a larg e n umber of wells. Therefore in the absence of any complete model that
estimates wellhead pressure, the EPA is retaining its previous approach

.13

Formation Pressure and Gas

- Flow Rates from Well Tests, Southwestern Wyoming

Province, Wyoming, Colorado, and Utah 2

Figure 2C. Pressure data from wells with drill

- stem tests in Jurassic and older Phosphoria

- sourced
units in the Southwestern Wyoming Province, Wyoming, Colorado, and Utah. Lines of constant
pressure gradient give ratio of pressure to depth in pounds per square inch per foot (psi/ft). Well
locations are shown in figure 2A [ figure 2A well locations not shown in EPA TSD . See a copy of the

full document in the docket ].

2 Nelson, Philip H., and Kibler , Joyce E. (2005). Formation Pressures and Gas

- Flow Rates from Well Tests, Southwestern Wyoming Province, Wyoming, Colorado, and Utah. In USGS Southwestern Wyoming Province Assessment Team, compilers, Petroleum Systems and Geologic Assessment of Oil and Ga s in the Southwestern Wyoming Provice, Wyoming, Colorado, and Utah. U.S. Geologic Survey Digital Data Series DDS

- 69

- D, Chapter

17

.14



### 2. 2 Stor age Vessel Definition and Requirements for Storage Vessels in Parallel

2.2.1 Support for the Proposed Changes to the Storage Vessel Definition and Requirements for Storage Vessels Installed or Connected in Parallel

Comment : Several commenters (4755, 4757, 4758, 4760, 4761 , 4762 , 4763, 4764 , 4766,

4767 ) express ed support for the proposed changes to the definition of storage vessel and removing requirements specific to storage vessels installed or connected in parallel. Most of these commenters agree d that the provisions related to storage vessels installed or connected in parallel are counter to the EPA’s often stated intent that a storage vessel affected facility is a single storage vessel. One commenter (4767 ) state d that the EPA has explained its concern and taken the steps necessary to forewarn industry that connecting storage vessels in parallel to

circumvent the 6 t py applicability threshold is not allowed under the NSPS

.

One commenter (4758) state d that the requirements for storage vessels installed or connected in parallel for the first time treat these storage vessels as a single unit with aggregated

PTE. According to the commenter, t his was a departure from the initially promulgated s ubpart

rules and the rule as proposed for public comment, whereby affected facility status for storage

vessels was based on assessment of a storage vessel's individual PTE, with no mention of aggregation of vessels connected in parallel. Moreover, the commenter conten ds that removing the requirements for storage vessels installed or connected in parallel would have the benefit of eliminating the imposition of controls on low

- emitting storage vessels, which the EPA has already determined not to be cost effective.

The c ommenter add ed that the EPA is correct to recognize that the terms “connected in parallel” and “installed in parallel” inadvertently included storage vessels beyond those that it

intended to address in the December 2014 Rule. The commenter adds that the EP A indicated that it did not intend for the final rule to have the widespread impact currently in effect. The

commenter note d that, i n the preamble to the current reconsideration proposal, the EPA stated

that the breadth of the 2014 final rule's impact on s torage vessels was “inadvertent.” The

commenter state d that it can be expensive and time consuming to bring a storage vessel into compliance with subpart OOOO requirements, and those requirements should not be imposed on a storage vessel based on inadverte nt rulemaking actions by the EPA.

Response: The EPA thanks the commenters for their support.

2.2.2 Support for Retaining the Requirements for Storage Vessels in Parallel

Comment: One commenter (4765) acknowledged the EPA’s proposal to remove provisions relating to storage vessels “installed in parallel” or “connected in parallel” because these provisions “inadvertently” encompassed storage vessels the Agency did not intend to
address. However, the comm enter contend s that the EPA does not identify those vessels that it believes were inadvertently covered in the December 2014 rule, nor does it propose alternative regulatory language that would ensure adequate control measures for vessels connected or

inst alled in parallel that were intended to be covered under the December 2014 rule.15

Given that storage vessels, including those installed or connected in parallel, can be significant sources of emissions, the commenter opposed the EPA’s proposal to simply re move any provisions addressing these vessels. Instead of removing all provisions regarding vessels installed or connected in parallel, as the Agency proposed, the commenter urged the EPA to instead clarify its existing requirements for such vessels. The co mmenter suggested that the EPA could, for instance, clarify that pollution control measures apply to storage vessels operated in parallel in the relevant regulatory provisions addressing storage vessel affected facilities and the

definitions of “returned t o service” and “storage vessel.”

Response: The change to the definition of storage vessel was intended to preserve the original basis of the individual storage vessels to determine affected facility status, while addressing the potential situation where crude oil, condensate, intermediate hydrocarbon liquids or produced water is divided into two or more storage vessels operated in parallel (i.e. sharing the emissions at the correlated fraction of what a single tank would emit). Through comments

submitted on the March 2015 proposed rule, the public has informed us that many storage vessels that are configured in parallel may not be operated or constructed to divide their potential to emit continuously, if ever. The EPA has now reconsidered our attempt to include storage vessels connected in parallel to address the specific situation resulting in circumvention. We

believe that we do not have sufficient data to evaluate the scope of storage vessels that would fall

un der the definition and for which we did not intend to cover.

We believe that we have sufficient provisions under the General Provisions at 40 CFR 60.12 “Circumvention” to address the specific situation where storage ves sels are divided into

smaller t anks to avoid applicability of t h e rule and which was our intent with the previous amended definition. Therefore, we do not beli e ve that our reverting to the prior definition of “storage vessel” will affect our ability to ensure control of these storage vessel s. Consequently, as proposed, we are finalizing the removal of pr ovisions made in the 2014 amend m e n t relating to the storage vessels “installed in parallel” or “conn e cted in parallel.”

2.2.3 The EPA Should Grant a Stay of Final Provisions for Storage Vessels in Parallel

Comment: Several commenters (4758, 4760, 4761, 4762, 4763 ) believe that the EPA should stay the storage vessel requirements finalized in the December 3 1, 2014 Federal Register

notice

.

Two commenter s (4758 , 4761 ) recomme nd that the EPA stay the effectiveness of the

revised definition of “ storage vessel ” at 40 CFR §6 0.5430 and all other newly added language pertaining to vessels connected or installed “ in parallel ” while this reconsideration process goes

forward. The comme nter s contend that the Clean Air Act provides that that the EPA may grant a stay if the A gency has decided to reconsider a rule. 42 USC § 7607(d)(7)(B). According to one of the commenter s (4758)

, Congress imposed no additional criteria, standards, or condi tions concerning the EPA's authority to issue a stay under §7607(d)(7)(B) . The commenter adds that as long as a r econsideration proceeding is underway, granting of a stay is within the discretion of the Agency.16

On e commenter (4758) contends that a stay is warranted in the present case, because regulated entities are now confronted with “ inadvertent ” but important new regulatory provisions regarding vessels connected or operated “ in parallel, ” including a revised definition of “ storage
vessel ” that has a major impact on determining whether a vessel is an affected facility covered by

s ubpart OOOO. While some state agencies may act to alleviate the problem, for example by exercising enforcement discretion while the EPA acts to remedy the current confus ion, the

commenter contends that other state agencies may not do so. Th e commenter state d that the stay should take effect immediately and should continue until this reconsideration process has been completed and corrected rule language has been finalized.

Response: In this action, t he EPA has finalized the removal of the revision made in the

2014 amendment to the definition of “storage vessel

. ” T he definition at issue no longer exists and thus no longer in effect such that a stay would have any effect

.

2.2.4 Clarification of Whether the Storage Vessels in Parallel Provisions were in Effect

Comment: Several commenters (4758, 4760, 4761, 4762, 4763) believe that the EPA should provide guidance on precisely which storage vessels would be subject to the requirements and when they would be subject.

T wo commenters (4758, 4760) believe that the EPA should state in its upcoming final rule that the “in parallel” provisions in the December 2014 rule were never effective because they were promulgated without notice and comment, in violation of the rulemaking procedures under the Clean Air Act. Two commenters (4758, 4761) believe that such a statement by the EPA would be appropriate, in light of federal case law holding that a rule promulgated without

notice an d comment is void ab initio. It would have the benefit, according to one of the commenters (4758), of removing the uncertainty, and the possibility of enforcement actions, created by the EPA's improper finalization of provisions in the December 2014 rule t hat suddenly and without notice altered the manner in which a storage vessel's affected facility status

was determined.

One commenter (4761) added that because there are multiple configurations for installation and because any given installation may be o perated in different configurations, the rule language has created significant confusion, potentially exposing companies to enforcement and leading to the need for case

- by

- case interpretations from the EPA and delegated state permitting authorities. The co mmenter states that their members have already encountered state regulators seeking to enforce the improperly promulgated new language for vessels not previously regulated under subpart OOOO, demonstrating that the rule language is having immediate impacts on regulated entities.

Even if the EPA grants a stay of the effectiveness of those provisions going forward as requested, one commenter (4758) points out that there would remain a period of time, beginning on December 31, 2014 and ending on the date suc h a stay begins, during which low

- emitting storage vessels connected to other storage vessels could be deemed by enforcement personnel to17

have been subject to subpart OOOO requirements, by virtue of the new PTE aggregation requirements for vessels connecte d in parallel. A clear statement by the EPA that those “in parallel” provisions were never effective would, according to the commenter, remove this possibility and would properly reflect federal case law holding that a rule promulgated without

notice and c omment is void from the outset.

One commenter (4761) add ed that should these provisions remain effective from December 31, 2014 through the date these proposed changes are finalized, which they should not, the Agency needs, at least, to clarify that to t he extent that these provisions were originally intended, at most they were only applicable to storage vessels returned to service and operated in parallel. The commenter believes that this would assist in clarifying that the EPA intended the added languag e to mean given that the Agency did not provide a definition of “in parallel.” The commenter contends that the preamble to the December 31, 2014 rule provides indication that this is the situation that the final action was trying to address

— storage vessels removed from and, subsequently, returned to service

— but it would be helpful to be clear on that point.

Another commenter (4762) contends that the December 31, 2014 rule is not sufficiently clear about when its amendments to subpart OOOO are effective. T he commenter note d that the EPA plainly states that the revisions are intended to be effective as of December 31, 2014, meaning that none of the revisions should be applied to conduct occurring prior to December 31, 2014. However, the commenter contends th at none of the specific rule text implementing the revisions includes an applicability date. Once the revisions are published in the U.S. Code, the commenter believes that will create the possibility that some of the revisions may be interpreted to apply t o conduct occurring prior to December 31, 2014. For example, t he commenter state d that §60.5420(c)(1)(A) includes new reporting requirements for gas well affected facilities. According to the commenter, nothing in the code will indicate that these new reporting requirements apply beginning on December 31, 2014. Thus, the commenter believes that for someone who looks just to the code and not to the underlying Federal Register final rule notice, that person easily could mistakenly interpret these new repo rting requirements to apply prior to December 31, 2014.

Further, the comment e r suggest ed that the effective date of the December 31, 2014 rule revisions that are unaffected by the March 23, 2015 proposed changes should be set at least 60

- days after publi cation of the final rule and not on the date of publication. The commenter believes that many of the new provisions could not be implemented immediately (such as the recordkeeping requirement referenced in § 60.5420(c)(1)(iii)(A), and a reasonable period o f time is needed for such provisions to be implemented.

Response: The EPA disagrees with the comment that the provisions in the December 2014 rule were never effective. Further, with respect to the commenter’s allegation of inadequate

notice and comment, the proper recourse is to petition the EPA for reconsideration

. (See Mexichem Specialty Resins, Inc. v. EPA, 2015 U.S. App. LEXIS 8903 (D.C. Cir. May 29, 2015) )

. The commenter also could have sought judicial stay of the rule. In any event, the EPA has appropriately addressed the issue through rulemaking.18

With respect to the comment suggesting that the effective date of the December 31, 2014 rule revisions that are unaffected by the March 23, 2015 proposed changes should be 60 days after public ation, the comment is outside the scope of this rulemaking.

With respect to the comment that multiple configurations for installation may result in

case

- by

- case interpretations, we agree with the commenter. Determining applicability for any specific sour ce is always case

- by

- case determination by definition; it will involve many factors, one of which may be storage tank configuration. As we discussed in the preamble to the December 2014 rule (79 FR 79027), we expect the situation where two or more storage vessels receive liquids in parallel such that the total throughput is shared between or among the parallel vessels and which causes the PTE of each vessel to be a fraction of the total PTE, to be a rare occurrence. However, these types of scenarios warra nt case

- by

- case analysis of applicability, especially under the circumvention requirements of the General Provisions. Regarding the comment about efforts by states to “enforce the improperly promulgated new language,” for the reasons previously discussed, we do not believe the language was “improperly promulgated.” Determinations of applicability made by a delegated state, which may or may not result in enforcement, should be taken up with the appropriate delegated state.

2.2. 5 The EPA Must Propose New Requirements

Comment: In response to the EPA’s request for suggestions on other approaches to discourage deliberate reductions in the potential to emit be installing multiple storage vessels, one commenter (4761) does not believe additional changes are ne cessary because they are not aware of an industry practice to install multiple smaller storage vessels in place of one larger vessel to unnecessarily reduce the PTE below the applicability threshold. Rather, according to the commenter, storage vessels are generally sized and installed based on the anticipated production of the gas well.

The commenter contends that e ven if the EPA were to consider additional regulations to address this issue, it must re

- propose this, and provide the exact regulatory language it is considering to avoid unintended consequences. Where multiple storage vessels are installed at a single location, the commenter states that industry may use several configurations to connect these vessels and may operate these vessels in several manners, including in

- series, in

- parallel, or with common vent lines. Due to the highly technical nature of these operations, t he commenter

believes that the EPA must solicit comment from industry to determine how to best achieve its stated goals without dramatically expanding the scope and costs of the regulation. A ccording to

the commenter a ny proposal by the Agency must careful ly consider the impacts of the rule on all possible vessel connections and operating scenarios and be carefully crafted to avoid expansion of the affected facility to storage vessels with PTE below the intended threshold.

Response: The EPA thanks the co mmenter for its information on industry practice with regard to installation of storage vessels. The EPA further agrees that should the Agency

consider additional regulation s to address the issue

, the EPA will do so through notice and comment rulemaking.19

2.2.6 The EPA Should Clarify the Storage Vessel Requirements Instead of Removing Them

Comment: One commenter (4765) state d that the EPA now proposes to remove provisions relating to storage vessels “installed in parallel” or “connected in parallel” in response to a petition for reconsideration filed by the Gas Processors Association (GPA). According to the commenter, the Agen cy explains that the terms “installed in parallel” and “connected in parallel” as they appeared in the regulatory text “inadvertently” encompassed storage vessels the Agency
did not intend to address. However, the commenter contends that the EPA does not i dentify those vessels that it believes were inadvertently covered in the December 2014 rule, nor does it propose alternative regulatory language that would ensure adequate control measures for vessels connected or installed in parallel that were intended t o be covered under the December 2014 rule.

Given that storage vessels, including those installed or connected in parallel, can be significant sources of emissions, the commenter opposes the EPA’s proposal to simply remove any provisions addressing these vessels. Instead of removing all provisions regarding vessels installed or connected in parallel, as the Agency proposes, the commenter urges the EPA to instead clarify its existing requirements for such vessels. The commenter suggest ed that the EPA could, for instance, clarify that pollution control measures apply to storage vessels operated in parallel in the relevant regulatory provisions addressing storage vessel affected facilities and the definitions of “returned to service” and “storage vessel.”

Re sponse: The change to the definition of storage vessel was intended to preserve the original basis on individual storage vessels to determine affected facility status, while addressing the potential situation where crude oil, condensate, intermediate hydro carbon liquids or produced water is divided into two or more tanks operated in parallel (i.e., sharing the emissions at the correlated fraction of what a single tank would emit). Through comments submitted on the March proposed rule, the public has informe d us that many storage vessels that are configured in parallel may not be operated or constructed to divide their potential to emit continuously, if ever. The EPA has now reconsidered our attempt to include storage vessels connected in parallel to

address the specific situation resulting in circumvention. We believe that we do not have sufficient data to evaluate the scope of storage vessels that would fall under the amended

definition and for which we did not intend to cover.

We believe that we have s ufficient provisions under the General Provisions at §60.12 “Circumvention” to address the specific situation where storage vessels are divided into smaller tanks to avoid applicability of the rule and which was our intent with the previous amended

definit ion. Therefore, we do not believe that our reverting to the prior definition of storage

vessels will affect our ability to ensure c ontrol of these storage vessels

.

2.2.7 The EPA S hould Extend the Final Requirements to A ll Tank Batteries

Comment: I n light of the increasingly common practice of manifolding storage vessels,

one commenter (4765) believes that the EPA should ensure that emission controls apply to all connected storage vessels that have aggregate throughput exceeding the applicability th resholds,20

regardless of whether they are currently being operated in parallel. Without these or similar protections, the commenter believes that loopholes for strategic parallel installation or connection would undermine the protective and comprehensive re gulation of these significant

sources of emissions.

Response: The change to the definition of storage vessel was intended to preserve the original basis on individual storage vessels to determine affected facility status, while addressing the potential si tuation where crude oil, condensate, intermediate hydrocarbon liquids or produced water is divided into two or more tanks operated in parallel (i.e., sharing the emissions at the correlated fraction of what a single tank would emit). Through comments submi tted on the March proposed rule, the public has informed us that many storage vessels that are configured in parallel may not be operated or constructed to divide their poten tial to emit continuously, if ever. The EPA has now reconsidered our attempt to i nclude storage vessels connected in parallel to address the specific situation resulting in circumvention. We believe that we do not have sufficient data to evaluate the scope of storage vessels that would fall under the amended

definition and for which w e did not intend to cover.

We believe that we have sufficient provisions under the General Provisions at §60.12 “Circumvention” to address the specific situation where storage vessels are divided into smaller tanks to avoid applicability of the rule and which was our intent with the previous amended definition. Therefore, we do not believe that our reverting to the prior definition of storage vessels will affect our ability to ensure control of these storage vessels .

2. 2.8 Add Exclusion for Storage Vessels Used Primarily in Water Recycling Processes

Comment: Several commenters (4755, 4756, 4757 ) propose that the EPA further amend the definition of “storage vessel” in § 60.5430 to exclude vessels used primarily in water recycling processes.

Response : The EPA thanks the commenter for its information on industry practice with regard storage vessels. Consideration of this issue is outside the scope of this rulemaking.

Should the Agency consider additional regulations to address the issue, EPA will do so through notice and comment rulemaking.