Little Road Water Treatment Plant - Executive Summary
a. The Pasco County Utility Services accidental release prevention policy combines sound operating procedures and management practices. The policy complies with all pertinent procedures of the U. S. Environmental Protection Agency (EPA) Accidental Release Prevention Program. The Pasco County emergency response policy involves the preparation of site specific response plans, taking into consideration the available emergency response services surrounding each facility. The emergency response policy is in accordance with the EPA Emergency Response Program requirements. |
b. The Little Road Water Treatment Plant (WTP) is located at 8215 Little Road in Pasco County. The WTP employs treatment processes to remove impurities from the water and disinfect it with chlorine. Disinfection of all public water supplies is necessary to prevent waterborne diseases such as cholera, typhoid, and dysentery. The WTP contains a chlorination room which houses two chlorinators and various proces
s piping; an outdoor, open, roofed chlorine storage area with up to sixteen "ton" chlorine containers; and assorted safety equipment. The operations room containing flow recorders, various electrical panels, and additional safety equipment is located approximately 50 feet away from the chlorination room. the facility is staffed 10 hours per day, seven days per week. The facility is equipped with an auto dialer to notify on-call personnel of a problem when the plant is not staffed. Tampa Bay Water also monitors the plant by computer 24 hours per day and notifies the on-call operators in the event of an alarm at the plant.
c. The offsite consequence analysis takes into consideration two chlorine release scenarios, specified as "worst-case release" and "alternative scenario". The "worst-case release" is defined by the EPA as "the release of the largest quantity of a regulated substance (chlorine gas) from a vessel or process line failure that results in the greatest distance to
a specified endpoint". The "alternative scenario" is defined as the "more probable" scenario of a failure, than is the "worst-case release".
Atmospheric models determine the distance from a point of release to the "toxic endpoint" where the chlorine concentration has decreased to three (3) ppm as selected by the EPA. The toxic endpoint selected by the EPA is based on Emergency Response Planning Guide 2 (ERPG-2) "toxic endpoint" which is defined by the American Industrial Hygiene Association 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 life-threatening health effects". The ERPG-2 for chlorine is 0.0087 mg/l or 3 ppm (40 CFR 68.22, Appendix A). The residential population found within the circle defined by the radius to the toxic endpoint for each scenario has been determined using the 1990 census data projections for 1997 from geographic information systems (GIS) s
oftware produced by Environmental Systems Research Institute (ESRI). For both the worst-case and the alternative scenario the percentage of each census tract inside the area defined by the toxic endpoint was estimated and multiplied by the total population for each affected tract to determine the residential population affected by an accidental release.
The worst-case release scenario at the Little Road WTP involves the release of one one-ton cylinder of chlorine (2,000 lbs.) outdoors. The offsite consequence analysis for this scenario is determined based on predefined conditions set by the EPA. The general conditions are as follows: the release of the entire contents from the cylinder as a gas in 10 minutes, an atmospheric stability class of F, wind speed of 1.5 m/s, ambient temperature of 25 degrees celsius, and a relative humidity of 50 percent. The conditions surrounding the Little Road WTP are defined as "urban" by the EPA. Based on exhibit 4-3 of the Risk Management Progr
am Guidance for Wastewater Treatment Plants (EPA 550-B-98-010 October 1998), the distance to the toxic endpoint for the worst-case release scenario is 1.3 miles. The distance closely corresponds to independent site specific modeling performed using the DEGADIS model.
The case study for the alternative release scenario involves the failure of a 5/16" gas valve to close. It is assumed that chlorine detectors alert the WWTP operators to the release. The amount of chlorine released is equal to 2,000 lbs., released at an average rate corresponding to the 5/16" hole, which equates to a release rate of 240 lb/min. The entire contents of the cylinder are released in 8.3 minutes. Exhibit 4-13 of the Risk Management Program Guidance for Wastewater Treatment Plants (EPA 550-B-98-010 October 1998), determines that the distance to the toxic endpoint is 0.3 miles.
d. The Pasco County Utility Services accidental release prevention program consists of the following elements:
e ongoing and continuous training of the operators.
- A preventative maintenance program that follows manufacturer's specifications and acceptable
- The Implementation of state-of-the-art process and safety equipment.
- Ongoing equipment and hazard reviews.
- The use of current operations and maintenance manuals.
- Continued equipment inspections.
The Pasco County Utility Services has also included the following chemical specific prevention steps:
- The use of chlorine dectectors.
- The use of self-contained breathing apparatuses (SCBA), when handling chlorine containers.
- All operators have been trained to be aware of the hazardous effects and toxic properties of
e. The Little Road WTP has experienced no accidental releases of chlorine over the past five (5) years.
f. The Little Road facility has an emergency response
plan that has been coordinated with the Local Emergency Planning Committe (LEPC). This plan consists of a chain of command and decision tree for the response to a release of chlorine. The plan coordinates local and regional organizations to combat the effects of the release.