Fort Pierce Wastewater Treatment Plant - Executive Summary
Executive Summary |
Introduction and Background
The Ft. Pierce Utility Authority (FPUA) is committed to delivering quality drinking water and responsive service to its customers, and strives to be good a neighbor to the people who live near its treatment plants. This document is the FPUA Wastewater Treatment Plant (WWTP) Risk Management Program/Process Safety Management Plan (RMP/PSMP), which details the prevention programs that have been implemented at the WWTP to prevent and minimize the emergency release of chlorine gas.
Because the WWTP stores chlorine gas above the threshold quantity shown in Table ES-1, the FPUA is required to develop a plan to prevent and minimize emergency releases of chlorine gas to the atmosphere in quantities that could potentially affect the public beyond the facility's boundaries. The RMP regulations are from the in U.S. Environmental Protection Agency's (EPA) Clean Air Act Amendments of 1990, which are detailed and codified in 40 CFR Part 68. The PSMP regu
lation is from the Occupational Safety and Health Act (OSHA) Standards, which are detailed in OSHA 29 CFR 1910.119.
RMP/PSMP Threshold Quantity for Chlorine Gas
Chemical Name Location Used or Stored Chemical Abstract Service Number EPA RMP
(pounds) OSHA PSMP
(pounds) Maximum Quantity on Site
Chlorine Chlorine Storage Area 7782-50-5 2,500 1,500 24,000
The chlorination process at the WWTP is subject to the most stringent of the three RMP programs, Program 3, which has three major requirements. The first requirement is a Hazard Assessment, in which the effects that a release of a regulated substance could have on the public are determined. The Hazard Assessment for the WWTP has been completed and can be found in the document titled "Offsite Hazard Assessment for the Ft. Pierce Wastewater Treatment Plant". This report can be found in the Control Room of the WWTP. The second requirement is a Prevention Program, which consists
of 12 ele-ments designed to improve the system safety and decrease the likelihood of a release. The third requirement is an Emergency Response Program, which requires development of a plan for dealing with a release in the unlikely event that one would occur. The second and third requirements have also been satisfied and are detailed in this document, which will also be located in the Control Room of the WWTP.
Because the RMP and PSM regulations are very similar, the Prevention Program and the Emergency Response Program of the RMP also serve as the OSHA PSMPSMP; therefore, this document is referred to as the RMP/PSMP. This RMP/PSMP is divided into 13 sections, each representing a paragraph of requirements from the OSHA PSM Standard.
A Hazard Assessment was performed for the FPUA WWTP to determine the effects a chlorine gas release would have on the public. In this assessment, the distance a set endpoint concentration (3 mg/L) of chlorine gas would travel was estimate
d. In addition, an estimate of the population that could be affected by a release of chlorine gas was determined and sensitive receptors, such as hospitals, schools, and nursing homes, were identified. The Hazard Assessment considers two release scenarios-a "worst-case" and an "alternative case."
The RMP regulations require the development of a worst-case release scenario based on conservative assumptions. For example, it is required to assume in the Hazard Assessment that the entire contents of the largest single container of chlorine would be released over 10 minutes. This is unlikely to occur since the properties of chlorine would cause a freeze and thaw cycle to occur at the leak, which would slow the release. In addition only "passive" mitigation methods, such as buildings or dikes, can be considered when deter-mining the distance a release could travel. Active mitigation such as the vacuum regulators automatic shutoff used at the WWTP was assumed to be non-fu
nctional. In many scenarios mitigating the release by isolating the process could reduce the amount released. In addition, the worst-case scenario requires that conservative atmospheric conditions be assumed, which results in a large area of potential impact.
The Hazard Assessment also requires that the "toxic endpoint," or distance from the point of release to a location at which the chlorine concentration equals or exceeds a 3 mg/L, be determined. That concentration is defined as the maximum airborne concentration below which individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects, or symptoms that could impair an individual's ability to take protective action. Because the cloud from a chlorine leak will disperse rela-tively quickly, an individual at a toxic endpoint would be exposed to the exposure limit concentration for much less than the 1 hour assumed by the limit. In addition, the exposure limit concentratio
ns result in relatively minor health effects. Therefore, an individual at the toxic endpoint would be affected less than the results of the worst-case scenario may imply.
The WWTP's worst-case scenario results indicated a distance of 1.6 miles to the toxic endpoint, affecting approximately 8,700 people. However, an actual release of chlorine gas would not result in chlorine travelling 1.6 miles in almost all cases because of the vacuum regulators automatic shutoff, which would shutoff the chlorine supply from the cylinders.
The RMP rule also requires that at least one alternative release scenario be evaluated for chlorine gas. The alternative scenarios reflect a type of release that is more likely to occur compared to the worst-case scenario. Unlike the worst-case scenario, the alternative release scenario may consider "active" mitigation such as the vacuum regulator automatic shutoff and a more realistic release quantity and release rate. Active mitigation is de
fined as requiring mechanical, electrical, or human input. Lastly, it assumes local, typical meteorology, which is more realistic than the conservative meteorological conditions that must be assumed for the worst-case scenario. These alternative release scenarios are considered to be more representative of the effects likely in the event of a chlorine gas release. The FPUA WWTP conducted two alternative release scenarios for chlorine.
Scenario 1 was a release of chemical through a connection failure at the auxiliary cylinder valve. No passive or active mitigation measures were considered for this scenario. The results indicate a distance of 0.36 miles to the toxic endpoint, affecting approximately 170 people. However, if a release occurred from a loose pipe fitting, the vacuum regulators automatic shutoff valves would stop the flow of chlorine gas.
Scenario 2 was a release of chemical through venting of the vacuum regulators. No passive or active mitigation measures were considered f
or this scenario. The results indicate a distance of 0.19 miles to the toxic endpoint, affecting approximately 65 people. Again, if a release occurred through the vent of the vacuum regulator the automatic shutoff valves would stop the flow of chlorine gas.
The Prevention Program, together with the Emergency Response Program, make up the core of the RMP/PSMP. The Prevention Program consists of 12 elements, listed below, which are designed to improve system safety and decrease the likelihood of a release. These elements were developed by the FPUA with the assistance of CH2M HILL.
7 Employee Participation
7 Process Hazard Analysis
7 Process Safety Information
7 Operating Procedures
7 Contractor Safety
7 Pre-Startup Review
7 Mechanical Integrity
7 Hot Works
7 Management of Change
7 Incident Investigation
7 Emergency Response Program
7 Compliance Audit
The participation of the FPUA WWTP staff in preparing the RMP/PSMP was critical to the program's successful
implementation. Employee participation is valuable because it increases the safety awareness of the staff and it allows the staff's experience in operating and maintaining the processes to be incorporated into the plan.
FPUA WWTP staff participated in the development of the Prevention Program through a series of meetings and workshops. They also participated in the development of the Process Hazard Analysis (PHA). The PHA was conducted on June 8, 1999. A list of recommended improvements to the chlorination system was developed in the PHA meeting.
Staff who operate and maintain the chlorine gas processes were trained in how to safely maintain and operate the chlorine gas processes on June 17, 1999. All other WWTP staff received RMP/PSMP awareness training on June 18, 1999, which detailed how the new requirements may impact their jobs.
The remaining elements of the Prevention Program were developed with the assistance of the Water Resources Superintendent and the Water/Wastewater Main
tenance Superintendent. These elements will go into affect by June 21, 1999.
To protect the welfare of the community, staff, and the environment, the City has taken many proactive steps over the last decade to minimize potential hazards related to chlorine gas. It has satisfied and exceeded the requirements of RMP/PSMP, and has a number of preventative measures in place to guard against the release of chlorine gas. Safety features implemented at the WWTP include:
7 Chlorine gas sensors to detect leaks and trigger safety systems.
7 Automatic valves and vacuum technologies that will stop the flow of chlorine gas if there is a break in the piping system.
7 Extensive training of all plant operators involved in the water treatment process on the use, hazards, handling, and safe operation of chlorine gas. Staff also have special emergency action training on how to respond to a chlorine gas leak.
7 Comprehensive planning and coordination with the St. Lucie County Fire Di
strict HAZMAT team in the unlikely event that a leak occurs.