Las Vegas Water Pollution Control Facility - Executive Summary

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Executive Summary 
 
Introduction and Background 
 
The City of Las Vegas Water Pollution Control Facility (WPCF) operates a biosolids stabilization process commonly referred to as "digestion". The digestion process is carried out in digester tanks that are an integral part of the wastewater solids treatment process. Digester gas, which consists of primarily methane and carbon monoxide gases, is a byproduct of digestion. The WPCF stores methane (digester gas) in quantities above the regulatory thresholds that subject the WPCF to RMP, as well as OSHA Process Safety Management (PSM) Standards. The WPCF does not store or handle any other substances covered by the RMP regulations and have actually eliminated storage and handling facilities for chlorine and sulfur dioxide. 
 
The WPCF is undergoing expansion that will result in the addition of four digester tanks by end of year 2001. The existing digester gas system will be integrated with the new digester tanks. 
 
Digester Gas Quantity 
 
The quan 
tity of digester gas stored at the WPCF totals 11,500 pounds. This quantity includes digester gas present in eight digester tanks, one 100 psi storage sphere, and associated digester gas system piping. The WPCF exceeds the storage threshold of 10,000 pounds for RMP and PSM. 
 
Five-year Accident History 
 
The WPCF has not had any accidental releases of digester gas within the past 5 years that met the USEPA definition of an accidental release of a regulated substance per 40 CFR Part 68.10. 
 
Hazard Assessment 
 
A Hazard Assessment was performed using the methodology described in Appendix C of the USEPA's Offsite Consequence Analysis Guidance to calculate the distance to a 1-psi overpressure. Affects of "worst case" and "alternative case" release scenarios were carried out. 
 
The worst case scenario considered an explosion of the digester gas storage sphere, which is the largest digester gas storage vessel at the WPCF. The distance to the 1-psi overpressure was calculated to be 525 feet. The  
alternative case scenario considered an explosion of one digester tank. The distance to the 1-psi overpressure was calculated to be 310 feet. 
 
The closest receptor to the WPCF would not be affected by the impact of the explosion for either worst case or alternative case release scenarios. A future digester tank was used to map the 1-psi distance since this digester will be located closest to the WPCF property line than the other digester tanks. 
 
RMP Program Level 
 
Because a release of digester gas would not reach an offsite receptor, and because there has not been any accidental releases of digester gas in the past 5 years, both the existing WPCF and the WPCF following the expansion are eligible for Program 1. 
 
Emergency Response Program 
 
An Emergency Response Program was developed for dealing with a digester gas release as required by OSHA Process Safety Management regulation 29 CFR 1910.119(n) and EPA RMP regulation 40 CFR 68 Subpart E. The plan was also prepared in accordance with t 
he provisions of the Employee Emergency Plans (29 CFR 1910.38(a)) with consideration given to provisions of the OSHA hazardous waste and emergency response standard, 29 CFR 1910.120 (q). 
 
The Emergency Planning and Response plan provides specific emergency response procedures for accidental release of digester gas. The emergency response procedures cover a release from the initial alarm stage through either leak stoppage or hazmat assistance. As part of the emergency response procedures there are plans for victim rescue, leak investigation, and communication with additional support agencies. In addition, critical plant operations are identified to insure that, if possible, the critical WPCF functions are kept operational. The Emergency Planning and Response plan also indicates the level of training need to carryout the emergency response procedures. Only personnel trained at the First Responder Operative can attempt to stop a leak.  
The Emergency Planning and Response Plan provides pla 
nt evacuation procedures. It also addresses plant site communication, emergency response equipment, first aid and medical treatment, medical surveillance and consultation, and emergency response drills. 
 
The Emergency Planning and Response Plan has been submitted to and reviewed with the Clark County Fire Department. The Clark County Fire Department has agreed to provide emergency response support as included in the Emergency Planning and Response Plan.
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