El Paso Natural Gas Waha Gas Plant - Executive Summary
ACCIDENTAL RELEASE PREVENTION AND RESPONSE POLICIES |
The Waha Gas Plant (WGP) has a long-standing commitment to workers and public safety. This commitment is demonstrated by the resources invested in accident prevention, such as training personnel and considering safety in the design, installation, operation, and maintenance of the facility's processes. The El Paso policy is to implement reasonable controls to prevent foreseeable releases of substances. However, if a release does occur, gas plant trained personnel will respond to control and contain the release.
DESCRIPTION OF THE STATIONARY SOURCE AND REGULATED SUBSTANCES
EPNG operates the WGP located in Reeves County, Texas. The WGP is designed for compressing, transporting natural gas, and removing H2S, CO2 and water from sour gas prior to transport. As evidence in the ensuring text and based on criteria outlined in the Accidental Release Prevention Program (ARP), the WGP is a Program 1 process. The Certification Statement a
ddressed in 40 CFR 69.185 (a), and required for each Program 1 process has been completed and submitted.
The WGP was evaluated to determine if any regulated flammable or toxic substances were present in the process and if they exceeded the threshold quantity. The North and South Amine Contactors are considered to be co-located; consequently, for the purposes of the ARP Program. These vessels are being considered a part of a single process. Because of the location of these vessels, with their combined capacity, the threshold quantities for a regulated flammable would be exceeded them making this process subject to threshold determination for offsite consequence analysis.
EPNG identified one regulated flammable substance (flammable gas mixture) and zero regulated toxic substances along with the largest vessel quantity stored. It was determined that the North and South Amine Contactor vessels containing the flammable gas mixture exceeded the 10,000 lb. threshold quantity for regulat
ed flammable substances. The identification of this exceedance indicates that WGP is a covered process with a regulated substance subject to threshold determination for offsite consequence analysis.
OFF-SITE CONSEQUENCE ANALYSIS RESULTS
WORST-CASE SCENARIOS (WCS)
The Environmental Protection Agency (EPA) has defined a worst-case release as "the release of the largest quantity of a regulated substance from a vessel or process line failure that results in the greatest distance to a specified endpoint." A WCS analysis is required for each toxic substance in a covered process while only one WCS analysis is required for regulated flammable substances as a class. WCSs are assumed to occur at ground level with meteorological conditions defined as atmospheric stability class F (stable atmosphere), wind speed of 1.0 meters per second (2.2 miles per hour), and an ambient air temperature of 25:C (770F). Topography for WCSs are distinguished between rural and urban.
egulated flammable substances or mixtures containing flammable substances include both gases and volatile liquids. The WCS assumes that the total quantity of a vapor cloud is released and detonates. The endpoint for a WCS involving a regulated flammable substance or mixture is an overpressure of 1 pound per square inch (psi). For a regulated flammable substance, consequence distance determination is based on its heat of combustion. For regulated flammable mixtures, the component with the highest heat of combustion can be used for consequence distance determination or, if preferred, directly calculated using equation C-1 of the Offsite Consequence Analysis Guidance Document (OCAGD). The quantity of a regulated substance/mixture used to determine distance to endpoint is the largest quantity of a regulated substance/mixture in a single vessel.
The flammable gas mixture evaluated at the WGP is a mixture of methane,
ethane, propane, butanes, and pentanes, contained in pressurized storage vessels in gaseous form. The North and South Contactor vessels together contain 10,026 pounds of the flammable gas mixture. Using the criteria outlined in the ARP rule, this mixture represents the facility's WCS for flammables.
The distance to endpoint of 1 psi overpressure for the flammable gas mixture using OCAGD equations is presented in Table 2. Methane was identified as having the highest heat of combustion (50,029 kjoule/kg) and is the major component (95.7%) of the gas mixture. It was determined that if the WCS calculations were made assuming a 100% methane composition it would provide a more conservative consequence distance. The distance to the endpoint of 1 psi overpressure for the worst-case release of the flammable gas mixture was calculated and determined to be 0.18 miles. The distance to endpoint is less than the distance to any public receptors- - a mandatory criterion for all Program 1 proc
TOXIC LIQUIDS AND GASES
Toxic gases include all regulated toxic substances that are gases at ambient temperature (temperature 25: C, 770F), even if they are stored as liquids under pressure or refrigeration. For the consequence analysis, a gaseous release of the total quantity is assumed to occur in 10 minutes, regardless of storage conditions. For toxic liquids, the total quantity in a vessel is assumed to be spilled onto a flat, non-absorbing surface. For toxic liquids carried in pipelines, the quantity that might be released from the pipeline is assumed to form a pool. Passive mitigation systems may be taken into account in consequence analysis for both toxic gases and liquids. The endpoint for air dispersion modeling to estimate the consequence distance for a release of a toxic gas and liquid is presented for each regulated toxic gas and liquid in Appendix B of the OCAGD in Exhibits B-1 and B-2, respectively.
The WGP does not have any toxic substances present above
the threshold quantity. Analysis of one worst-case release scenario for all regulated toxic substances is, therefore, not required.
ALTERNATIVE RELEASE SCENARIOS (ARS)
An ARS describes an incident that is more likely to occur than those cited for a WCS. One ARS analysis is required for each listed toxic substance in a Program 2 or 3 process that exceeds threshold quantity while only one ARS analysis is required for all flammable substances as a class in a Program 2 or 3 process. For ARSs, both active and passive mitigation systems can be considered.
Alternative release scenarios for flammable substances should have the potential to cause substantial damage, including on-site damage. Alternative release scenarios for toxic substances should be those that lead to concentrations above the toxic endpoint beyond the process fenceline. Those releases that have the potential to reach the public are of the greatest concern.
WGP ALTERNATIVE RELEASE SCENARIO FOR REGULATED FLAMMABLES
The WGP is a Program 1 process and is, therefore, not required to complete an ARS for regulated flammables.
WGP ALTERNATIVE RELEASE SCENARIO FOR REGULATED TOXICS
The WGP does not have any toxic substances held above the threshold quantity and, in addition, is a Program 1 process. Analysis of each regulated toxic substance is, therefore, not required.
FIVE YEAR ACCIDENT HISTORY
WGP has not had any accidental releases during the past five years which meet the criteria for an accidental release as discussed in 40 CFR 68.42.
LOCAL EMERGENCY RESPONSE COORDINATION
The WGP has coordinated its emergency response activities with the local emergency planning and response agencies as required in 40 CFR 68.12(b)(3).