Goose Creek Wastewater Treatment Plant - Executive Summary

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Located in southeastern Pennsylvania, the Borough of West Chester is the county seat of Chester County and is an industrial and commercial center with approximately 18,000 residents.  The Borough of West Chester covers an area of approximately 1.9 square miles and lies across two watersheds: Goose Creek, a tributary of the Chester Creek, and Taylor Run, a tributary of the East Branch of the Brandywine Creek. 
The Borough of West Chester maintains two wastewater treatment plants (WWTPs), one serving each watershed.  The Goose Creek WWTP was built in originally built in the 1920's and rebuilt in 1988.  The Goose Creek WWTP is capable of treating 1.86 million gallons per day to the level required by the Pennsylvania Department of Environmental Protection (PADEP) and the Environmental Protection Agency (EPA).  Most of the industrial and commercial establishments lie in the Goose Creek watershed. 
The primary purpose of a WWTP is to protect public waterways from environme 
ntal harm and to promote the recreational, commercial, and/or industrial use of these waterways.  The WWTP helps to achieve and maintain water quality goals by achieving a high degree of treatment of all incoming wastewater, including industrial, prior to discharge to Goose Creek. 
All incoming wastewater is disinfected by using chlorine to kill any pathogenic organisms before discharging the water.  Excess chlorine, which itself can harm aquatic life, is removed prior to discharge utilizing sulfur dioxide.  A maximum of 6 one-ton containers (12,000 pounds) of chlorine and 6 one-ton containers (12,000 pounds) of sulfur dioxide may be stored onsite at any time, with 2 chlorine containers and 1 sulfur dioxide container in use at any given time.  Containers that are connected in the process are located in brick buildings designed specifically and solely for the safe movement, storage and use of these regulated chemicals. 
Goose Creek WWTP's accidental release prevention program is designe 
d to ensure that the facility operates in compliance with the RMP Rule and with industry standards of performance, such as the guidance documents written by the Chlorine Institute.  The prevention program is based on the following key elements: 
* High level of training of the operators 
* Preventive maintenance program 
* Use of state-of-the-art process and safety equipment 
* Use of accurate and effective standard operating procedures, written with the participation of the operators 
* Performance of a hazard review of equipment and procedures 
* Implementation of an auditing and inspection program 
Preventive maintenance is regularly scheduled and performed.  Trained, experienced vendors clean, service and replace pipes, valves, chlorinators, rotameters and other equipment, as needed. 
Chemical-specific prevention steps include the availability of self-contained breathing apparatus (SCBA), worn by operators during connection/disconnection of chlorine and sulfur dioxide supply, awareness  
of the hazardous and toxic properties of chlorine and sulfur dioxide, and the presence of chlorine and sulfur dioxide detectors. 
Chlorine gas and sulfur dioxide gas are fed into the wastewater with vacuum operated equipment, which offer the safest operation for low capacities.  Piping and connections are kept to a minimum for safety.  The piping was designed to be the shortest necessary length, and is properly supported and protected from risks of excessive heat or fire. 
Goose Creek WWTP is not required to maintain a site-specific emergency response program, as defined by OSHA and EPA.  However, it does have an Emergency Plan which has been coordinated with the LEPC, which gives specific details regarding emergency contacts, potentially affected areas, evacuation routes, and other information regarding the WWTP.  The WWTP would contact the local fire department and the Chester County Local Emergency Planning Committee (LEPC) in the event of an accidental release, since it does not tr 
ain its employees to handle such an emergency. 
The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case release" and "alternative scenario".  The first scenario is defined by EPA, which states that "the owner or operator shall assume that the ... maximum quantity in the largest vessel ... is released as a gas over 10 minutes," due to an unspecified failure.  EPA also requires the assumption of worst-case atmospheric dispersion modeling conditions in order to be conservative and ensure public safety.  The alternative scenario is defined as "more likely to occur than the worst-case release scenario". 
The worst-case scenario for an accidental release of chlorine (and/or sulfur dioxide, since the modeling and risk calculations are almost identical for both) is the catastrophic failure of a one-ton container.  The toxic endpoint selected by EPA for chlorine is 3 parts per million (ppm), which is defined by the American Industrial 
Hygiene Association (AIHA) as the "maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action".  This is the Emergency Response Planning Guideline Level 2 (ERPG-2).  The residential population within a circle with a radius corresponding to the toxic endpoint distance has to be defined "to estimate the population potentially affected". 
When atmospheric dispersion modeling for the worst case scenario was performed using the EPA assumptions, a distance to toxic endpoint of 1.3 miles and an estimated residential population potentially affected of 11,000 was obtained.  The building housing the containers was not considered as a passive mitigation system to reduce the potential risk for the worst-case scenario since some containers are stored outside the building. 
alternate-case release scenario is identified as a major leak caused by a bad valve, a poor connection, or a piping failure.  This scenario was selected as "a more likely to occur than the worst-case release scenario" based on the past history of chlorine releases at this facility and at other WWTPs that are similarly designed. 
When atmospheric dispersion modeling for the alternate scenario was performed, a distance to toxic endpoint of 0.2 miles and an estimated residential population potentially affected of 10 was obtained.  In addition to being enclosed in a building (passive mitigation) when the containers are in use, active mitigation measures in place to prevent and minimize releases include ambient chlorine and sulfur dioxide monitors and a remote vacuum piping system, which would significantly reduce the amount of chlorine or sulfur dioxide released in the case of a leak. 
EPA's innovative "Community Right-to-Know" software tool Landview III, along with database extracts of 19 
90 Census information and other sources were used to analyze the estimated residential population for the worst-case scenario.  An aerial photograph and onsite personnel's knowledge of nearby residents were used to confirm the estimated residential population in the alternate case scenario. 
There have been no accidental releases of chlorine or sulfur dioxide in the past five years. 
Based on the hazard evaluation, the compliance audit, and other actions taken to prepare this RMP, a few areas were identified for improvement and changes were made to improve safety at the facility.  This included the following: 
* Updating the Material Safety Data Sheets for chlorine and sulfur dioxide; 
* Writing a standard operating procedure for connecting and disconnecting containers; 
* A more formal documentation system for employee training; 
* Revising the preventive maintenance procedures; 
* Developing an Emergency Action Plan.
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