City of Danbury Water Pollution Control 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. Sulfur dioxide is added to remove excess chlorine.
Chlorine and sulfur dioxide is delivered to the treatment plant in one-ton containers. A maximum of ten one-ton containers of liquid chlorine is stored on site in the chlorine storage room. A maximum of six one-ton containers of sulfur dioxide is stored on site in the sulfur dioxide storage room.
1.3 PROCESS SAFETY MANAGEMENT (PSM) AT FACILITY
The Danbury Water Pollution Control Plant Risk Management Program (RMP) includes the following key elements to mitigate the effects of potential chlorine/sulfur dioxide release hazards.
. Operator training
. Preventive maintenance program
. Process specific safety equipment
. Safe and effective standard operating procedures, written with operator participation
. Hazard review of equipment and procedures
Auditing and inspection programs
. Comprehensive management program
Further, DWPCP maintains an active environmental, health, and safety program with the following elements specifically supporting the safe handling of chlorine/sulfur dioxide and the chlorination process.
. Respiratory protection (SCBA) program
. Chlorine/Sulfur Dioxide detectors
. Chemical right to know program
. Personal protective equipment program
1.4 DESCRIPTION OF THE FACILITY AND THE REGULATED SUBSTANCES HANDLED
The DWPCP has the design capacity to handle 15.5 million gallon per day. The plant is a secondary treatment plant that includes trickling filters. Wastewater is received in the headworks and processed through three primary settling tanks. The discharge from the primary settling tanks is sprayed onto circular stone beds where contact is made with biological growth. The discharge from the trickling filters is processed through intermediate settling tanks and is then passed through aeration tanks an
d final settling tanks. Liquid chlorine is taken from one ton containers and injected into the treated sewage flowing through the chlorine contact tank and, when necessary, into the raw sewage at the head of the plant. Disinfection is accomplished in the contact tank. Sulfur dioxide is added to removal residual chlorine. Chlorine and sulfur dioxide are the only substances handled at the facility that is regulated by 40 CFR Part 68 Accidential Release Prevention Requirements. Risk Management Program under Clean Air Act Section 112(r) (7).
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/Sulfur Dioxide 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/Sulfur Dioxide 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. DWPCP 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/sulfur dioxide gas is heavier than air and will settle to the lowest elevation when released. The chlorine/sulfur dioxide storage area is equipped with an exhaust fan that's intake is mounted near the floor. The fan can be activated by a swi
tch located outside the building. Two exit doors are provided in the chlorine/sulfur dioxide storage room.
1.6 FIVE-YEAR ACCIDENT HISTORY
DWPCP has never had an accident involving chlorine/sulfur dioxide 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 DWPCP has a site-specific Chlorine/Sulfur Dioxide Emergency Response Plan (ERP), revised May 17, 1996, which outlines 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. A plant layout has also been given to the fire department.
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 CONSEQUE
The impact area of a potential release of chlorine or sulfur dioxide was determined using EPA guidance documents. The worst case analysis is the potential release of chlorine or sulfur dioxide 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/Sulfur Dioxide Released 2,000 pounds 1,260 pounds
Population in Release Area 11,518 46
Schools in Release Area 3 0