Amesbury Water Treatment Plant - Executive Summary

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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 
one time.   
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 
release scenario."  
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 
0.2 miles.   
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.
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