Town of Westborough Wastewater Treatment Plant - Executive Summary
EXECUTIVE SUMMARY |
Chlorine is used as a disinfectant in the water pollution control plant. The finished water is disinfected by chlorine before discharge.
Chlorine is delivered to the treatment plant in one-ton containers. A maximum of four one-ton containers of liquid chlorine is stored on site in the chlorine storage room.
1.3 PROCESS SAFETY MANAGEMENT (PSM) AT FACILITY
The Town of Westborough Wastewater Treatment Plant Risk Management Program (RMP) includes the following key elements to mitigate the effects of potential chlorine release hazards:
7Preventive maintenance program
7Process specific safety equipment
7Safe and effective standard operating procedures, written with operator participation
7Hazard review of equipment and procedures
7Auditing and inspection programs
7Comprehensive management program
Further, WWTP maintains an active environmental, health, and safety program with the following elements specifically suppo
rting the safe handling of chlorine and the chlorination process:
7Respiratory protection (SCBA) program
7Chemical right to know program
7Personal protective equipment program
1.4 DESCRIPTION OF THE FACILITY
AND THE REGULATED SUBSTANCES HANDLED
The Westborough Wastewater Treatment Plant is located at 238 Turnpike Road in Westborough, Massachusetts. The facility has been contracted operated by USFilter Operating Services (formerly, EOS) since 1990. The Service area includes the towns of Westborough, Shrewsbury, and Hopkinton in Worcester County. The service area covers approximately 50 square miles and has an e3stimated population of 40,000 people. The Westborough Wastewater Treatment Plant was designed to treat an average daily flow of 4.38 MGD in its initial year of operation and an average of 7.78 MGD in the design year, 2005. Design maximum peak flow to the facility is 16.06 MGD.
There are three levels of treatment employed by the Westborough Wastewater
Treatment facility to produce the high quality effluent required by the NPDES permit and to stabilize the wastewater biosolids for beneficial reuse. They are physical treatment, biological treatment and chemical treatment.
The physical treatment processes employed at the Westborough Wastewater Treatment Plant include:
Biological treatment processes include:
7Conventional Activated Sludge
7Activated Sludge with Nitrification
Chemical treatment processes include:
The chlorination process is designed to remove approximately 99.7% of the bacteria remaining in the water after the filtration process. Indicator organisms used to determine the level of disinfection are known as fecal coliforms. Fecal coliform counts in excess of permit limits (200/100m.l average, 400/100 ml daily maximum) are indicative of inadequate disinfection. A chlorine res
idual of 0.5 mg/L usually yields a compliant bacteria count. However, the facility then must dechlorinate to meet the NPDES permit limit for chlorine (0.0015 mg/L).
1.5 GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAM
AND CHEMICAL-SPECIFIC PREVENTION STEPS
The facility complies with EPA's accident prevention rule and all applicable state and local codes and regulations. The chlorine system is designed, installed, and maintained in accordance with applicable codes and state law. The treatment plant maintains a Self-Contained Breathing Apparatus (SCBA) and The Chlorine Institute's Emergency Kit "B" for one-ton containers. This equipment is stored in a room that is adjacent to the room that houses the ton containers. WWTP personnel receive training on the use of the breathing apparatus and the emergency kit. The kit contains the necessary tools and other equipment to contain valve leaks and to repair small holes in a ton container, and capping devices for the fusible plugs in the ton
containers. Ton containers are equipped with fusible metal pressure relief devices. Most ton containers have six fusible metal plugs, three in each end. The fusible metal is designed to melt between 1580F and 1650F to relieve pressure and prevent rupture of the container in case of fire or other exposure to high temperature.
Chlorine gas is heavier than air and will settle to the lowest elevation when released. The chlorine storage area is equipped with an exhaust fan that's intake is mounted near the floor. The fan can be activated by a switch located outside the building. Two exit doors are provided in the chlorine storage room.
1.6 FIVE-YEAR ACCIDENT HISTORY
WWTP has never had an accident involving chlorine that required hospitalization, or care by a physician, or that caused death, injury, property/environmental damage, evacuations, or shelterings-in-place.
1.7 EMERGENCY RESPONSE PROGRAM
The WWTP has a site-specific Chlorine Emergency Response Plan (ERP), which o
utlines employee procedures in the event of an emergency. The facility's ERP includes specific procedures for material handling, emergency planning, evacuation, contact for emergency response organizations, reporting, training, fire protection, and media relations.
1.8 PLANNED CHANGES TO IMPROVE SAFETY
No changes to the safety procedures currently in place at the facility are planned at this time.
1.9 OFF-SITE CONSEQUENCE ANALYSIS
The impact area of a potential release of chlorine was determined using EPA guidance documents. The worst case analysis is the potential release of chlorine from a single one ton container over a ten minute period. The alternative release is a more gradual release corresponding to a sixty minute period. The results of the analysis are detailed in the RMP and are summarized below:
Description Worst-Case Release Alternate Release
Radial Distance to Toxic Endpoint of 3 ppm
1.3 miles 0.1 miles
Quantity of Chlorine Released 2,000 pounds 1,260 pounds
Population in Release Area 3,832 17
Schools in Release Area 6 0
Hospitals in Release Area 0 0