Amesbury Water Treatment Plant - Executive Summary
Executive Summary |
The Amesbury Water Treatment Plant (WTP) accidental release prevention
policy involves a consolidated approach that integrates technologies,
procedures, and management practices. All applicable procedures of the U.S.
Environmental Protection Agency (EPA) Prevention Program are followed. The
WTP emergency response policy involves the preparation of response plans
that are tailored to each facility and to the emergency response services
available in the community, and meets the EPA Emergency
Response Program requirements.
The Amesbury WTP, located at Rings Corner, Newton Road, Amesbury, Massachusetts, uses
chlorine to obtain proper disinfection for both pre-treatment and
post-treatment practices. The WTP presently utilizes chlorine gas for
disinfection to meet water quality standards. Ten 150-lb containers of
pressurized liquid chlorine are connected to the treatment train, six
containers connected to the pre-treatment system and four containers
connected to the
post-treatment system. The amount of 150-lb chlorine containers in storage peaks at thirty, therefore a maximum of forty 150-lb containers may be at the Amesbury Water Treatment Plant at
Any facility which handles, manufactures, uses or stores any of the toxic
and flammable substances listed in 40 CFR Section 68.130 above the specified
threshold quantities in a process is required to develop and implement a
risk management plan. The 1990 Amendments to the Clean Air Act (CAA)
require the EPA to issue a rule specifying the type of actions to be taken
by facilities to prevent accidental releases of such hazardous chemicals
into the atmosphere and reduce their potential impact on the public and the
environment. Title 40 of the Code of Federal Regulations, Part 68 addresses
the specifications and guidelines for development of risk management
programs. If a facility is subject to part 68, it's risk management program
must be in compliance no later than June 21, 1999. The C
ity has contracted
with Camp Dresser & McKee Inc. to assist in the completion of a
comprehensive evaluation of the WTP including a risk management plan.
The offsite consequence analysis includes consideration of two release
scenarios, identified as "worst case release" and "alternative scenario."
EPA defines the first scenario, 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. The
alternative scenario is defined as "more likely to occur than the worst-case
Atmospheric dispersion modeling has to be performed to determine the
distance traveled by the chlorine released before its concentration
decreases to the "toxic endpoint" selected by EPA of 3 ppm (chlorine), which
is the Emergency Response Planning Guideline Level 2 (ERPG-2). The American
Industrial Hygiene Association (AIHA) defines this as the "maximum airborne
ion 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." The residential
population within a circle with a radius corresponding to the toxic endpoint
distance has to be defined, "to estimate the population potentially
The worst-case release scenario involves the catastrophic failure of a
150-lb chlorine cylinder outside the chlorine storage room. The offsite
consequence analysis for this scenario was predefined by the EPA. This
analysis assumed that the vessel would completely release all of its
contents in ten minutes. The toxic endpoint used was the one-hour average
ERPG-2. The population residing within a full circle with a radius
corresponding to the toxic endpoint distance was determined.
For the worst-case modeling analysis, the EPA-mandated meteorological
ons were used. These correspond to Stability F, wind speed of 1.5
m/s, highest daily temperature of 77oF and an average humidity of 50%.
From the modeling results, it was concluded that the radius which
corresponded to the toxic endpoint distance was 0.8 miles. Within the 0.8
miles, approximately 1,100 people would be affected by this EPA-specified
release and the corresponding conditions.
The alternative release scenario involves the release of chlorine from a 3/8
inch diameter whip connected to a 150-lb cylinder. In this case, however,
the release is inside a building. With the operating pressure of 120 psi,
the release rate was calculated as 22.2 lb/min. This rate would release the
entire contents of the 150-lb cylinder in approximately 7 minutes. Liquid
chlorine released from the ruptured whip would flash immediately to a vapor.
As required by EPA, the alternative release scenario was formatted as
meteorological conditions of Stability D, wind speed of 3.0 m/s, average air
temperature of 50oF, and average humidity of 50 percent. The fact that the
release happens in an enclosed building allows enclosures to be an act of
passive mitigation. Based on these conditions, the off-site impact extends
The general WTP accidental release prevention program is based on the
following critical elements:
High level of training of operators
Preventive maintenance program
Use of state-of-the-art process and safety equipment
Use of accurate and effective 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
Chemical-specific preventions steps include availability of self-contained
breathing apparatus (SCBA), worn by the operators during
connection/disconnection of chlorine supply, awareness of the hazardous and
toxic properties of chlorine, and presence of chlorine detectors.
No accidental releases of c
hlorine have occurred at this facility in the
past five years.
The facility has an emergency response program, which has been coordinated
with the Amesbury Fire Department. This program includes an emergency
coordination team, and a notification plan.