United States Government Accountability Office

GAO Report to the Chairman, Committee on 

Environment and Public Works, U.S. 

Senate 

SECURING 

WASTEWATER 

FACILITIES 

Costs of Vulnerability 

Assessments, Risk 

Management Plans, 

and Alternative 

Disinfection Methods 

Vary Widely 

March 2007 

 

GAO-07-480 
What GAO Found

United States Government Accountability Office

Why GAO Did This Study

Highlights

Accountability Integrity Reliability

March 2007

SECURING WASTEWATER FACILITIES

Costs of Vulnerability Assessments, Risk 

Management Plans, and Alternative 

Disinfection Methods Vary Widely 

Highlights of GAO-07-480, a report to the 

Chairman, Committee on Environment 

and Public Works, U.S. Senate 

Wastewater facilities provide the

essential service of collecting and 

treating wastewater, and 

discharging treated effluent into

receiving waters. Since September 

11, 2001, the nation’s water 

infrastructure has received greater 

attention, including the risk of 

terrorist attacks at wastewater

facilities that store hazardous 

chlorine gas for disinfection. 

In 2006, GAO reported that many

large wastewater facilities have

responded to this risk by 

voluntarily conducting vulnerability

assessments and converting from

chlorine gas to other disinfection

methods. The Clean Air Act 

requires all wastewater facilities 

that use threshold quantities of 

chlorine gas to prepare and

implement risk management plans 

to prevent accidental releases and

reduce the severity of any releases. 

In this study, GAO was asked to

provide information on (1) the

range of costs large wastewater

treatment facilities incurred in 

preparing vulnerability 

assessments and risk management

plans, and (2) the costs large 

wastewater treatment facilities 

incurred in converting from

chlorine gas to alternative

disinfection processes. To answer 

these questions, GAO conducted 

structured telephone interviews 

with a number of facilities 

surveyed for the 2006 report. The

Environmental Protection Agency

(EPA) agreed with the report and

provided several technical changes 

and clarifications. 

Among the large wastewater facilities GAO examined, the costs reported to 

prepare vulnerability assessments ranged from $1,000 to $175,000, while 

costs to prepare risk management plans ranged from less than $1,000 to over 

$31,000. Whether the documents were prepared in-house or contracted to 

third parties such as engineering firms was a factor in cost differences. 

Despite higher costs, some facilities preferred to use contractors due to their 

expertise and independence. According to one wastewater security official,

these attributes can give contractor findings and recommendations greater 

credibility with utility governing boards that determine spending priorities. 

One facility that used a contractor to complete a vulnerability assessment in 

2002 did so because, at the time, vulnerability assessment software and 

training were not widely available. Since that time, EPA has increased 

funding for the development and dissemination of risk assessment software 

and related training. Overall, cost estimates for vulnerability assessments 

and risk management plans did not relate to facility size, as measured by 

millions of gallons of wastewater treated per day. 

For the large wastewater facilities GAO examined, reports of actual and 

projected capital costs to convert from chlorine gas to alternative 

disinfection methods range from about $650,000 to just over $13 million. 

Most facilities converted, or planned to convert, to delivered sodium 

hypochlorite (essentially a concentrated form of household bleach shipped 

in bulk to the facility). Managers of these facilities told GAO they 

considered other options, but chose delivered sodium hypochlorite because 

its capital conversion costs were lower than those associated with other 

alternatives, such as generating sodium hypochlorite on-site or using 

ultraviolet light. Overall, the primary factors associated with facilities’

conversion costs included the type of alternative disinfection method chosen 

and the size of the facility. Other cost factors facility managers cited 

included (1) whether existing buildings and related infrastructure could be 

used in the conversion, (2) labor and building supply costs, which varied 

considerably among locations, (3) the cost of sodium hypochlorite relative to 

chlorine gas, and (4) the extent to which training, labor, and regulatory 

compliance costs were reduced for utilities that no longer had to rely on 

chlorine gas. 

www.gao.gov/cgi-bin/getrpt?GAO-07-480.

To view the full product, including the scope 

and methodology, click on the link above. 

For more information, contact John

Stephenson at (202) 512-3841 or

stephensonj@gao.gov. 
Contents 

Letter 1

Results in Brief 4

Background 5

Costs of Preparing Vulnerability Assessments and Risk 

Management Plans among Large Wastewater Facilities Vary 

Widely 8

Costs of Converting to Alternative Disinfection Methods at Large 

Wastewater Facilities Depend on the Method Used and Other 

Factors 13

Agency Comments and Our Evaluation 20 

Appendix I Scope and Methodology 22 

Appendix II Comments from the Environmental Protection Agency 24 

Appendix III GAO Contact and Staff Acknowledgments 25 

 

Table 

Table 1: Reported and Planned Disinfection Conversion Costs for 

Large Wastewater Treatment Facilities 14 

Abbreviations 

AWWARF American Water Works Association Research Foundation 

DHS Department of Homeland Security 

EPA Environmental Protection Agency 

NACWA National Association of Clean Water Agencies 

OSHA Occupational Safety and Health Administration 

POTW publicly owned treatment works 

RAM-W Risk Assessment Methodology for Water Utilities 

VSAT Vulnerability Self Assessment Tool 

WEF Water Environment Federation 

Page i GAO-07-480 Wastewater Facility Security
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Page ii GAO-07-480 Wastewater Facility Security
United States Government Accountability Office

Washington, DC 20548 

March 30, 2007 

The Honorable Barbara Boxer 

Chairman 

Committee on Environment and Public Works 

United States Senate 

Dear Madam Chairman: 

Wastewater facilities in the United States provide essential services to 

residential, commercial, and industrial users by collecting and treating 

wastewater and discharging treated effluent into receiving waters. The 

Centers for Disease Control and Prevention cited sewage disposal and 

water treatment as important contributors to the control of infectious 

diseases, which it considers 1 of the 10 greatest achievements in public 

health of the 20th century. Wastewater disinfection, a key component of 

the wastewater treatment process, reduces the risk that disease will be 

transmitted through wastewater effluents. Historically, chlorination has 

been the most commonly used method of wastewater disinfection because 

it destroys a variety of pathogens and microorganisms. 

Since the events of September 11, 2001, the security of the nation’s water 

infrastructure against terrorist threats has received greater attention, 

including the potential for terrorist attacks at wastewater facilities that 

store large amounts of chlorine gas. If released, chlorine gas may threaten 

utility employees and the public near the affected facilities. The gas can be 

deadly if inhaled and, at lower doses, can burn the eyes and skin and 

inflame the lungs. In a 2004 report, the White House Homeland Security 

Council determined that a terrorist attack on an urban chemical facility 

that resulted in the rupture of a chlorine gas rail car could kill up to 17,500 

individuals and hospitalize as many as 100,000. 

While federal law does not require wastewater systems to take security 

measures to protect specifically against a terrorist attack, it does require 

certain wastewater facilities to take security precautions that could 

mitigate the consequences of such an attack. For example, the Clean Air

Act1

 requires wastewater facilities that use threshold quantities of certain 

 1

Pub. L. No. 101-549 (1990). 

Page 1 GAO-07-480 Wastewater Facility Security
hazardous substances, such as chlorine gas, to prepare and implement a 

risk management plan designed to prevent accidental releases of regulated 

substances and reduce the severity of those releases that do occur.2

As we reported in March 2006,3 many of the nation’s large wastewater 

facilities have improved security since September 11, 2001. For instance, a 

substantial number of facilities reported improving security fences, 

increasing security lighting, and implementing improved employee and 

visitor identification systems, among other security enhancements. In 

addition, though not required, many large wastewater facilities reported 

that they conducted vulnerability assessments4

 to identify risks to key 

process components such as the use, storage, and handling of chlorine 

gas. Finally, many facilities reported that they recently stopped or plan to 

stop using chlorine gas in favor of alternate disinfection methods. 

Commonly used alternatives include sodium hypochlorite, essentially a 

concentrated form of household bleach, and ultraviolet light, which breaks 

down disease-causing microorganisms. 

For wastewater facility managers, the costs of preparing vulnerability 

assessments and risk management plans and converting to alternate 

disinfection methods must compete for available resources with other 

infrastructure needs. For instance, in 2003, in its most recent Clean Water

Needs Survey, the Environmental Protection Agency (EPA) estimated that, 

nationwide, wastewater systems faced $181.2 billion in costs to upgrade 

treatment systems and sewer lines, reduce the incidences of combined 

sewer overflows, which result in the discharge of untreated wastewater 

into receiving waters, and meet other pollution control requirements. 

Major U.S. cities, including Washington, D.C., and Cincinnati, Ohio, are 

facing costs between $1 billion and $2 billion to implement necessary 

capital improvements. 

 2

EPA requires that any facility storing at least 2,500 pounds of chlorine gas submit a risk 

management plan. 

3

GAO, Securing Wastewater Facilities: Utilities Have Made Important Upgrades but 

Further Improvements to Key System Components May Be Limited by Costs and Other

Constraints, GAO-06-390 (Washington, D.C.: Mar. 31, 2006).

4

According to the Environmental Protection Agency (EPA), vulnerability assessments 

performed by water sector utilities address not only utility vulnerabilities, but also utility 

threats and consequences. 

Page 2 GAO-07-480 Wastewater Facility Security
This report provides information on (1) the range of costs large 

wastewater treatment facilities incurred in preparing vulnerability 

assessments and risk management plans, and (2) the costs large 

wastewater treatment facilities incurred in converting from chlorine gas to

alternative disinfection processes. 

To identify the costs of preparing vulnerability assessments and risk 

management plans, we conducted structured telephone interviews with a 

select sample of large wastewater facilities identified as having completed 

these assessments in our March 2006 report.5

 Our March report identified 

106 large facilities that prepared vulnerability assessments or had one 

underway and 85 facilities that were required to prepare risk management 

plans because they currently used chlorine gas as a disinfectant. From this 

universe, we chose a nonprobability sample of facilities based largely on 

geographic representation and size.6

To identify the costs incurred by wastewater treatment facilities in 

converting from gaseous chlorine to alternative disinfection processes, we 

conducted structured telephone interviews with most of the 38 large 

facilities identified in the March report as having converted recently from 

chlorine gas or indicating that they planned to do so. We also conducted 

site visits with some of the facilities. Where available, we gathered 

documentation, such as capital plans, from these facilities in order to 

document conversion costs. We supplemented the cost information we 

gathered at individual wastewater facilities with information obtained at

EPA, the Department of Homeland Security (DHS), and nongovernmental

organizations. Reported costs for preparing vulnerability assessments, risk 

management plans, and conversion from gaseous chlorine include both 

actual and estimated costs. For estimated costs, we asked facility 

managers to explain how they arrived at these estimates. Reported costs 

were not adjusted for inflation. We determined that reported cost data 

were sufficiently reliable to provide useful information about the costs for 

preparing vulnerability assessments, risk management plans, and 

conversion from gaseous chlorine and the factors that affect these costs. 

We conducted our work between August 2006 and March 2007 in 

 5

We defined large wastewater facilities as those publicly owned treatment works (POTW)

that serve residential populations of 100,000 or greater. 

6

Results from nonprobability samples cannot be used to make inferences about a

population, because in a nonprobability sample some elements of the population being

studied have no chance or an unknown chance of being selected as part of the sample. 

Page 3 GAO-07-480 Wastewater Facility Security
accordance with generally accepted government auditing standards. A 

more detailed discussion of our scope and methodology is included in 

appendix I. 

The expenses large wastewater facilities reported to prepare vulnerability 

assessments and risk management plans varied widely among the facilities 

we interviewed, costing less than $1,000 in some cases to $175,000 in 

others. The cost differences were related to whether the documents were 

prepared in-house or contracted to third parties such as engineering firms. 

Despite higher costs, some facilities preferred to use contractors due to 

their expertise and independence. According to one wastewater security 

official, these attributes can give contractor findings and 

recommendations greater credibility with utility governing boards that 

determine spending priorities. Overall, cost estimates of the facilities we 

interviewed did not relate to facility size, as measured by millions of 

gallons of wastewater treated per day. 

Results in Brief 

Large wastewater facilities that converted or plan to convert from chlorine

gas disinfection to alternative disinfection processes also report widely 

varying costs, ranging from about $650,000 to just over $13 million. Key 

factors associated with these costs included the type of alternative 

disinfection method chosen and the size of the facility. The majority of the 

facilities we examined converted or plan to convert to sodium 

hypochlorite (either delivered in bulk to the facility or generated on-site), 

which has lower capital costs than converting to ultraviolet light. For 

example, managers of a treatment facility in Virginia told us they spent 

about $1.2 million in 2004 converting to bulk sodium hypochlorite 

disinfection, while managers of a comparably sized facility in Maryland 

told us they plan to spend an estimated $4 million converting to ultraviolet 

light disinfection by the end of this year. Managers of the Maryland facility 

indicated that one reason they chose the more expensive ultraviolet 

treatment option over bulk deliveries of sodium hypochlorite was to 

reduce risk to local traffic that could result from additional deliveries to 

the plant. In addition, using ultraviolet light eliminates the need for 

wastewater treatment plants to handle and store significant amounts of 

hazardous or corrosive chemicals. Other than the disinfection method and 

facility size, key cost factors wastewater facilities cited included 

(1) whether existing buildings could be used in the conversion, 

(2) building costs, which varied considerably from location to location, 

(3) the higher cost of sodium hypochlorite relative to chlorine gas, and 

(4) the extent to which training, labor, and regulatory compliance costs 

were lower at plants that no longer had to rely on chlorine gas. 

Page 4 GAO-07-480 Wastewater Facility Security
A majority of the nation’s wastewater is treated by publicly owned 

treatment works that serve a variety of customers, including private 

homes, businesses, hospitals, and industry. These publicly owned 

treatment works are regulated by the Clean Water Act. Wastewater 

treatment includes a collection system (the underground network of 

sewers) and a treatment facility. Wastewater enters the treatment facility 

through the collection system, where it undergoes an initial stage called

primary treatment, during which screens remove coarse solids, and grit 

chambers and sedimentation tanks allow solids to gradually sink. Next, 

wastewater enters secondary treatment, where bacteria consume most of 

the organic matter in the wastewater. After these processes, wastewater is 

disinfected to eliminate remaining pathogens and other harmful 

microorganisms. 

Background 

Wastewater facilities typically use both chemical and physical disinfection 

methods, including the following: 

• Chlorine gas. Injecting chlorine gas into a waste stream has been the 

traditional method of disinfecting wastewater. Chlorine gas is a 

powerful oxidizing agent, is relatively inexpensive, and can be stored 

for an extended period of time as a liquefied gas under high pressure. 

Also, the residual chlorine that remains in the wastewater effluent can

prolong disinfection after initial treatment. However, chlorine gas is 

extremely volatile and hazardous, and it requires specific precautions 

for its safe transport, storage, and use. Because it is stored and 

transported as a liquefied gas under pressure, if accidentally released, 

chlorine gas can quickly turn into a potentially lethal gas. EPA requires, 

among other things, that any facility storing at least 2,500 pounds of 

chlorine gas prepare a risk management plan that lays out accident 

prevention and emergency response activities. At certain 

concentrations, the residual chlorine that remains in wastewater 

effluent is toxic to aquatic life, so wastewater facilities that use 

chlorine compounds may also need to dechlorinate the treatment 

stream before discharging it to receiving waters.7

 Chlorine can also 

oxidize certain types of organic matter in wastewater, creating 

hazardous chemical byproducts, such as trihalomethanes. Our March 

2006 report found that many large wastewater facilities have 

discontinued, or are planning to discontinue using chlorine gas as a 

disinfectant in favor of alternative disinfection methods such as sodium 

 7

Sulfur dioxide, often used for dechlorination by wastewater facilities, is also covered by 

risk management plan rules when used or stored in threshold amounts. 

Page 5 GAO-07-480 Wastewater Facility Security
hypochlorite delivered in bulk to the facility. Of the 206 large 

wastewater facilities responding to our survey, only 85 facilities 

indicated they currently use chlorine gas, and 20 of these facilities plan 

to switch from the gas to another disinfectant. 

• Sodium hypochlorite. Injecting sodium hypochlorite—essentially a 

concentrated form of household bleach—into a waste stream is 

another chlorination method of disinfecting wastewater. Sodium 

hypochlorite is safer than chlorine gas because, if spilled, it remains 

liquid and can be contained and recovered. For this reason, it is not 

subject to EPA’s risk management planning requirements. However, 

sodium hypochlorite is more expensive than chlorine gas, and it 

degrades quickly if it is exposed to sunlight or is not kept at proper 

temperatures. For this reason, properly storing delivered sodium 

hypochlorite in the concentration necessary to disinfect wastewater 

may require an on-site building with environmental controls. Sodium 

hypochlorite can also be generated on-site at a wastewater facility 

using an “electrochlorination system” that produces sodium 

hypochlorite through an electrical reaction with high-purity salt and 

softened water. Facilities choosing this method of disinfection reduce 

chemical costs, but face increased electrical costs from the generation 

equipment. Because it is a chlorine compound, wastewater facilities 

using sodium hypochlorite must also be concerned with residual 

chlorine and hazardous chemical byproducts, such as trihalomethanes. 

• Ultraviolet light. This disinfection method uses ultraviolet lamps to 

break down disease-causing microorganisms in wastewater. 

Wastewater passes through an open channel with lamps submerged 

below the water level. The lamps transfer electromagnetic energy to an

organism’s genetic material destroying the ability of its cells to

reproduce. Because ultraviolet light is a physical process rather than a 

chemical disinfectant, it eliminates the need to generate, handle, 

transport, or store hazardous and corrosive chemicals. In addition, 

there are no harmful residual effects to humans or aquatic life. 

However, ultraviolet light disinfection may not be effective given the 

turbidity of some wastewater streams. Wastewater facilities using 

ultraviolet instead of chlorine gas or delivered sodium hypochlorite for 

disinfection will face additional costs to maintain lamps and increased 

electrical costs. 

• Ozone. This disinfection method feeds ozone generated on-site from 

oxygen exposed to a high-voltage current into a contact chamber 

containing wastewater. According to EPA, ozone is very effective at 

destroying viruses and bacteria, but it is the least used disinfection 

Page 6 GAO-07-480 Wastewater Facility Security
method in the United States largely because of its high capital and 

maintenance costs compared to available alternatives. 

According to EPA, vulnerability assessments help water systems evaluate

susceptibility to potential threats such as vandalism or terrorism and 

identify corrective actions that can reduce or mitigate the risk of serious 

consequences. The Public Health Security and Bioterrorism Preparedness

and Response Act of 2002 (the Bioterrorism Act)8

 required drinking water 

utilities serving populations greater than 3,300 to complete vulnerability 

assessments by June 2004.9

 Wastewater facilities are not required by law to

complete vulnerability assessments. Congress has considered bills that 

would have encouraged or required wastewater treatment plants to assess 

vulnerabilities, but no such requirement has become law. 

In our March 2006 report on wastewater facility security efforts, we found 

that many large wastewater facilities have either completed a vulnerability 

assessment or had one underway. Of the 206 large wastewater facilities 

that responded to our survey, 106 facilities—or 51 percent—reported that

they had completed a vulnerability assessment or were currently 

conducting one. Several other facilities indicated they had conducted or 

planned to conduct other types of security assessments. Facilities cited 

several reasons for completing a vulnerability assessment or some other 

type of security assessment, but most—roughly 77 percent—reported 

doing so on their own initiative. Many facilities indicated they were 

combined systems—facilities that manage both drinking water and 

wastewater treatment. As such, 37 percent of facilities reported that they 

did some type of security assessment in conjunction with the required 

assessment for their drinking water facility. 

The Clean Air Act requires wastewater facilities that use or store more 

than 2,500 pounds of chlorine gas to submit to EPA a risk management 

plan that lays out accident prevention and emergency response activities.

 8

Pub. L. No. 107-188 (2002). 

9

The Bioterrorism Act required the assessments to include, but not be limited to, a review 

of six components: (1) pipes and constructed conveyances; (2) physical barriers; (3) water 

collection, pretreatment, treatment, storage, and distribution facilities; (4) electronic, 

computer, or other automated systems that are utilized by the water system; (5) the use, 

storage, or handling of various chemicals; and (6) the operation and maintenance of such 

systems. The act further required systems to prepare or revise an emergency response plan

incorporating the results of the vulnerability assessment within 6 months after completing 

the assessment.

Page 7 GAO-07-480 Wastewater Facility Security
Under this act, EPA requires that about 15,000 facilities—including 

chemical, water, energy, and other sector facilities—that produce, use, or 

store more than threshold amounts of chemicals posing the greatest risk 

to human health and the environment take a number of steps to prevent 

and prepare for an accidental chemical release. EPA regulations 

implementing the Clean Air Act require that the owners and operators of 

chemical facilities include a facility hazard assessment, an accident 

prevention program, and an emergency response program as part of their 

risk management plans. The regulations required that a summary of each 

facility’s risk management plan be submitted to EPA by June 21, 1999. The 

plans are to be revised and resubmitted to EPA at least every 5 years, and 

EPA is to review them and require revisions, if necessary. 

Although accurate information on the costs of vulnerability assessments 

and risk management plans is limited, available estimates suggest that 

their costs vary considerably. A factor contributing to the cost differential 

was whether they were contracted to third parties (such as engineering 

consulting firms) or prepared in-house with existing staff. Despite higher 

costs, some facilities preferred using contractors because their expertise 

and independence lent credibility to their assessments, which may be 

useful in obtaining support for security-related upgrades. Costs generally

did not relate to facility size, as measured by million of gallons of 

wastewater treated per day.10

The reported cost of preparing vulnerability assessments at the 20 large 

wastewater facilities where we interviewed officials ranged from $1,000 to

$175,000. Whether the assessment was done in-house with existing staff or 

contracted to a third party was a factor contributing to the cost 

differences. Officials from several facilities told us they used contractors 

to complete vulnerability assessments in 2002. For example, staff at the 

Denver Metro Wastewater Reclamation District reported that a contractor

completed a vulnerability assessment in November 2002 for its Central 

Treatment Plant, which treats 130 million gallons of wastewater per day, at

Costs of Preparing 

Vulnerability 

Assessments and Risk 

Management Plans 

among Large 

Wastewater Facilities 

Vary Widely

Vulnerability Assessment 

Costs Depend Primarily on 

Whether a Contractor Is 

Used 

 10In our structured interviews we asked facility managers to provide estimates of their 

treatment facility’s “existing flow” in millions of gallons per day. “Existing flow” refers to 

the calculated average flow for a recent 12-month period, as defined by EPA in its Clean 

Water Needs Survey, and is a common measure of treatment facility size. When we note 

how many gallons per day a facility treats, we are referring to its reported “existing flow.”

Page 8 GAO-07-480 Wastewater Facility Security
an estimated cost of $175,000. Of this cost, $100,000 was for the 

contractor, and $75,000 was estimated for in-house staff time. 

Other large wastewater facilities that reported completing vulnerability 

assessments in 2002 were part of combined systems that provide both 

drinking water and wastewater services. These systemwide vulnerability 

assessments were done before the 2002 Bioterrorism Act required drinking 

water utilities serving populations greater than 3,300 to complete 

vulnerability assessments by June 2004. The combined systems that 

conducted systemwide vulnerability assessments include the following: 

• San Antonio Water System (San Antonio, Texas). According to 

system staff, a contractor completed a systemwide vulnerability 

assessment for all its drinking water, wastewater, and related 

infrastructure in August 2002 for $112,000. Staff did not provide an 

estimate of in-house costs related to the assessment, but prorated the 

wastewater treatment plants costs related to this contract at $37,000: 

$25,000 for its Dos Rios plant, which treats 70 million gallons per day; 

$5,000 each for its Leon Creek and Salado Creek plants, which treat 33

million gallons per day; and $2,000 for its Medio Creek plant, which 

treats 5 million gallons per day. 

• The Phoenix Water Services Department (Phoenix, Arizona). 

According to department staff, a contractor completed a systemwide 

vulnerability assessment for its five drinking water plants, three 

wastewater plants, and related infrastructure in November 2002 for 

$479,725. Staff did not provide an estimate of in-house cost related to 

the assessment, but estimated the contract costs related to its largest 

wastewater treatment plant, the 91st Avenue Sewage Treatment Plant, 

which treats 140 million gallons per day, to be $100,000. 

• Fort Worth Water Department (Fort Worth, Texas). According to 

department staff, a contractor completed a systemwide vulnerability 

assessment for its four drinking water plants and one wastewater 

treatment plant in December 2002 at a cost of $292,300. Staff did not 

provide an estimate of in-house cost related to the assessment, but 

estimated the contract costs related to its Village Creek Wastewater 

Treatment Plant, which treats 96 million gallons per day, at $73,075. 

Wastewater facility managers cited several reasons for using contractors 

to complete vulnerability assessments. Staff with the Phoenix Water 

Services Department told us they used contractors for their vulnerability 

assessment because a citywide policy required that contract services be 

used whenever possible. Staff at other wastewater facilities told us that, 

Page 9 GAO-07-480 Wastewater Facility Security
despite the higher costs, they preferred to use contractors because of their 

expertise. According to a wastewater security official, contractor expertise 

and independence can give contractor findings and recommendations 

greater credibility with utility governing boards that determine spending 

priorities. 

One manager told us that he used a contractor for a 2002 vulnerability 

assessment because risk management software and tools were not yet

available. After the events of September 11, 2001, EPA provided funding to

the Association of Metropolitan Sewerage Agencies11 to develop software, 

called the Vulnerability Self Assessment Tool (VSAT), for water utilities to 

use to develop vulnerability assessments. According to a Water 

Environment Federation (WEF) official, VSAT became available in June 

2002. This official also said that EPA provided funding to WEF to provide

training workshops to wastewater utilities on how to use VSAT to conduct 

vulnerability assessments beginning October 2002.12

According to interviews with wastewater facility managers, large 

wastewater facilities that prepared vulnerability assessments in-house 

with existing staff reported lower costs for preparing the document. These 

include the following: 

• City of Ventura Public Works Department (Ventura, California). 

According to facility staff, in-house staff completed a vulnerability 

assessment in March 2003 for the Ventura Water Reclamation Facility, 

which treats 9 million gallons per day, at a cost of roughly $1,000 in 

staff time. Facility staff participated in VSAT training sponsored by 

EPA and completed the assessment using this tool. 

 11Now the National Association of Clean Water Agencies (NACWA). 

12Prior to September 11, 2001, EPA worked to develop and disseminate risk assessment 

methodologies for water utilities. In 2000, EPA funded an initiative with the American 

Water Works Association Research Foundation (AWWARF) and the Sandia National 

Laboratories to apply risk assessment methodologies developed by the laboratories to 

water utilities. The methodology, called the Risk Assessment Methodology for Water 

Utilities (RAM-W), was designed to assist large water utilities and security professionals in 

assessing the risks from malevolent threats. Through an interagency agreement with EPA, 

Sandia National Laboratories provided training to selected firms in the RAM-W 

methodology so that these firms could then provide training and technical assistance to 

water utilities. 

Page 10 GAO-07-480 Wastewater Facility Security
• City of Fort Wayne Utilities Division (Fort Wayne, Indiana). 

According to facility staff, in-house staff completed a vulnerability 

assessment in November 2005 for the Fort Wayne Water Pollution 

Control Plant, which treats 43 million gallons per day, at undetermined 

staff time. Facility staff participated in VSAT training and updated a 

previous risk assessment prepared for the facility by a contractor in 

2000 at a contracted cost of $10,000.

• City of Eugene Wastewater Division (Eugene, Oregon). According to 

facility staff, in-house staff completed a vulnerability assessment in 

October 2005 for the Eugene/Springfield Regional Water Pollution 

Control Facility, which treats 38 million gallons per day, for about 

$2,000 in staff time. 

• City of Cedar Rapids Department of Water Pollution Control (Cedar 

Rapids, Iowa). According to facility staff, in-house staff completed a 

vulnerability assessment in January 2007 for the Cedar Rapids

Wastewater Treatment Plant, which treats 35 million gallons per day, 

for about $5,000 in staff time. 

• Detroit Water and Sewerage Department (Detroit, Michigan).

According to department staff, in-house staff completed a vulnerability 

assessment in January 2005 for the Detroit Wastewater Treatment 

Plant, which treats 700 million gallons per day, for about $20,000 in 

staff time. 

Risk Management Plan 

Costs Also Influenced by 

Use of Contractors

Costs to prepare risk management plans ranged from less than $1,000 for 

facilities that completed the plan in-house to over $31,000 for facilities that 

used contractors. Costs to update risk management plans were generally 

less, ranging from less than $1,000 to $20,000 depending upon whether 

facilities used in-house staff or contractors. 

Costs were generally higher at facilities that used contractors. These 

include the following: 

• The Phoenix Water Services Department (Phoenix, Arizona). 

According to department staff, a contractor completed risk 

management plans for all the system’s drinking and wastewater 

facilities in 1999 for $230,086. Costs for the 91st Avenue Sewage 

Treatment Plant were prorated at $28,761. Department staff said a 

contractor updated the 91st Avenue plant’s risk management plan in 

2004 for $20,000. 

Page 11 GAO-07-480 Wastewater Facility Security
• Fort Worth Water Department (Fort Worth, Texas). According to 

department staff, a contractor completed risk management plans for all 

of the department’s drinking water and wastewater facilities in 1999 for 

$124,718. Costs related to the Village Creek Wastewater Treatment 

Plant’s risk management plan were prorated at $31,100. Department 

staff reported that the contractor later updated these risk management 

plans for $18,040 in 2004, $4,510 of which was for the Village Creek 

plant. 

• City of Fort Wayne Utilities Division (Fort Wayne, Indiana). 

According to facility staff, a contractor completed a risk management 

plan in 2001 for the Fort Wayne Water Pollution Control Plant for 

$16,000. Facility staff reported a contractor updated the plan in 2005 

for $6,000. 

• South Central Regional Wastewater Treatment and Disposal Board 

(Delray Beach, Florida). According to facility staff, a contractor 

completed a risk management plan in 1999 for the South Central 

Regional Wastewater Treatment and Disposal Plant, which treats 18 

million gallons per day, for $10,000. Facility staff reported a contractor 

updated it in 2006 for $2,000. 

• City of Portland Bureau of Environmental Services (Portland, 

Oregon). According to bureau staff, a contractor completed a risk 

management plan in 1999 for its Columbia Boulevard Wastewater 

Treatment Plant, which treats 143 million gallons per day, for $30,000.

Bureau staff reported they updated the plan using in-house staff in 2004 

for $10,000 in staff time. 

Other large wastewater facilities that prepared risk management plans inhouse with existing staff reported lower costs for preparing the 

documents. These include the following: 

• San Antonio Water System (San Antonio, Texas). According to 

system staff, in-house staff completed a risk management plan in 1999 

for the Dos Rios Wastewater Treatment Plant for between $5,000 and 

$10,000 in staff time. In-house staff updated the plan in 2004 for less 

than $1,000 in staff time. 

• City of Cedar Rapids Department of Water Pollution Control (Cedar 

Rapids, Iowa). According to facility staff, in-house staff completed a 

risk management plan in January 2000 for the Cedar Rapids 

Wastewater Treatment Plant for $5,000 in staff time. In-house staff 

updated the plan in 2004 for about $250 in staff time. 

Page 12 GAO-07-480 Wastewater Facility Security
• Denver Metro Wastewater Reclamation District (Denver, Colorado).

According to district staff, in-house staff completed a risk management 

plan in 1999 for $10,000 in staff time. In-house staff updated the plan in

2006 for about $1,000 in staff time. 

• City of Savannah Water and Sewer Bureau (Savannah, Georgia).

According to facility staff, in-house staff completed a risk management 

plan in 1999 for the President Street Water Pollution Control Plant, 

which treats 17 million gallons per day, at a cost of only $150 in staff 

time. In-house staff updated the plan in 2006 for about $130 in staff 

time. 

Large wastewater facilities that convert from chlorine gas disinfection to 

alternative disinfection processes incur widely varying capital costs, which 

generally depend on the alternative treatment chosen and facility size. 

Other factors that affect capital costs include the characteristics of 

individual facilities, such as whether existing structures can be used, and 

local factors, such as building costs. Alternative disinfection processes 

may also pose higher annual operating costs than chlorine gas. However, 

these costs may be offset, at least somewhat, by savings in training and 

labor costs, and regulatory burdens associated with the handling of 

chlorine gas. Some facilities even reported or projected net annual cost 

savings related to wastewater disinfection. 

The 23 large wastewater facilities that we interviewed reported capital

costs for chlorine conversion ranging from $646,922 to just over $13 

million. Table 1 identifies the 23 large wastewater facilities that recently 

converted or plan to convert from chlorine gas to another disinfection 

method and their reported and planned capital conversion cost. 

Costs of Converting to 

Alternative 

Disinfection Methods 

at Large Wastewater 

Facilities Depend on 

the Method Used and 

Other Factors 

Disinfection Method 

Chosen, Facility Size and 

Characteristics, and Other 

Factors Determine Capital 

Conversion Costs 

Page 13 GAO-07-480 Wastewater Facility Security
Table 1: Reported and Planned Disinfection Conversion Costs for Large Wastewater Treatment Facilities 

Facility name Facility location 

Conversion

year 

Facility size (in 

millions of 

gallons treated

per day)a Disinfection method 

Reported or planned 

conversion costb

(in dollars)

Facilities that have completed conversion from chlorine gas 

 Chambers Creek University Place, Wash. 2002 19 Ultraviolet light $3,900,608

 Blue Plains Washington, D.C. 2003 307 Sodium hypochlorite 12,980,726

 Northeast Philadelphia, Pa. 2003 190 Sodium hypochlorite 2,600,000

 Back River Baltimore, Md. 2004 150 Sodium hypochlorite 3,300,000

 Essex and Union Elizabeth, N.J. 2004 65 Sodium hypochlorite 775,000

 Chesapeake-Elizabeth Virginia Beach, Va. 2004 21 Sodium hypochlorite 1,225,000

 Nansemond Suffolk, Va. 2004 17 Sodium hypochlorite 1,650,740

 Columbia Boulevard Portland, Ore. 2005 143 Sodium hypochlorite 4,660,490

 Valley Creek Bessemer, Ala. 2005 46 Ultraviolet light 3,561,272

 Dry Creek Fort Wright, Ky. 2005 36 Sodium hypochlorite 646,922

 Southern Regional Boynton Beach, Fla. 2005 22 Sodium hypochloritec2,592,800

 Burbank Burbank, Calif. 2005 9 Sodium hypochlorite 2,500,000

 Southeast Philadelphia, Pa. 2006 90 Sodium hypochlorite 1,920,000

 Papillon Omaha, Neb. 2006 62 Sodium hypochlorite 3,000,000

Facilities that plan to convert from chlorine gas 

 Metro Central Denver, Colo. 2007 130 Sodium hypochlorite 13,135,000

 Fort Wayne Fort Wayne, Ind. 2007 43 Sodium hypochlorite 1,791,417

 Everett Everett, Wash. 2007 18 Sodium hypochlorite 2,562,460

 South Central Delray Beach, Fla. 2007 18 Sodium hypochloritec2,454,700

 Mill Creek Cincinnati, Ohio 2008 120 Sodium hypochlorite 3,085,000

 Western Branch Laurel, Md. 2008 20 Ultraviolet light 4,000,000

 South Treatment Plant Renton, Wash. 2009 75 Sodium hypochlorite 2,575,000

 Hartford Hartford, Conn. 2009 51 Ultraviolet light 10,892,000

 Eugene-Springfield Eugene, Ore. 2009 38 Sodium hypochlorite 4,498,000

Source: GAO.

a

Plant size figures are figures for existing flow (a measure of average daily flow) reported by

wastewater facilities in our survey. 

b

Conversion costs were not adjusted for inflation. Figures do not reflect changes in annual costs, but 

are reported costs for construction, labor, and materials related to the disinfection conversion. 

Reported conversion costs include actual costs and estimates from facility managers. As such, these 

cost figures do not represent the present value of the life-cycle cost of conversion. Conversion costs 

include reported temporary and permanent conversion costs. 

c

These facilities will generate sodium hypochlorite on-site. All other facilities listed as converted or 

planning to convert to sodium hypochlorite are having the chemical delivered in bulk to the facility.

Page 14 GAO-07-480 Wastewater Facility Security
As shown in the table, 17 of the 23 facilities converted or plan to convert 

to sodium hypochlorite delivered in bulk to the facility. Officials with 

several of these facilities told us they considered ultraviolet disinfection, 

but chose delivered sodium hypochlorite because of its lower capital 

conversion costs. The remainder converted or plan to convert to sodium 

hypochlorite generated on-site or ultraviolet light. None of the facilities we 

contacted adopted ozone. 

Interview responses indicate that several factors affect the cost of 

conversion; among these are disinfection method chosen, facility size, key 

facility characteristics such as available buildings, and whether the 

conversion was permanent or temporary, as follows. 

Generally, conversion to delivered sodium hypochlorite has the lowest 

capital costs, followed by sodium hypochlorite generated on-site, and 

followed again by ultraviolet light.13 This observation is supported by cost 

estimates in the Chlorine Gas Decision Tool, a software program released 

by DHS in March 2006. The decision tool was designed to provide water 

and wastewater utilities with the means to conduct assessments of 

alternatives to chlorine gas disinfection. DHS cautions that the final costs 

of the disinfection systems will depend on project design details, actual 

labor and material costs, competitive market conditions, actual site 

conditions, final project scope, implementation schedule, continuity of 

personnel and engineering, and other variable factors.14 With these 

caveats, the decision tool estimates that for a wastewater facility with an 

average disinfection flow of 10 million gallons per day and a peak 

disinfection flow of 20 million gallons per day, capital costs for conversion 

to delivered sodium hypochlorite would amount to $533,000, on-site 

generation of sodium hypochlorite would total $1,238,000, and ultraviolet 

disinfection would reach $1,526,000.15

Disinfection Method 

 13Conversion to disinfection methods such as ozone and ultrafiltration can have higher

capital costs than ultraviolet light. 

14The decision tool provides cost estimates for disinfection conversion alternatives where 

there is limited site-specific engineering data. DHS notes that cost estimates were based on 

cost curves that were developed from a combination of the actual construction costs of

different-sized disinfection systems and cost estimates based on conceptual designs. 

15DHS notes that it is normally expected that an estimate of this type would be accurate

within +50 percent to -30 percent. 

Page 15 GAO-07-480 Wastewater Facility Security
Our interviews with wastewater facilities provide specific examples of 

conversion costs. For example, managers of the Chesapeake-Elizabeth 

Treatment Plant, which treats 21 million gallons per day and serves 

customers in Virginia Beach, Virginia, reported spending an estimated 

$1,225,000 in 2004 converting to bulk sodium hypochlorite disinfection. 

Managers of the comparably sized Western Branch Wastewater Treatment 

Plant, which treats 20 million gallons per day and serves customers in 

Laurel, Maryland, estimated that they will spend $4 million converting to 

ultraviolet light disinfection by January 1, 2008. Managers of the Western 

Branch plant indicated that one reason they chose the more expensive 

ultraviolet treatment option over bulk deliveries of sodium hypochlorite 

was to avoid the risk to local traffic that could result from additional 

deliveries to the plant. Plant managers indicated that because sodium 

hypochlorite degrades more quickly than chlorine gas, truck deliveries 

would increase under a disinfection system using sodium hypochlorite. 

They also noted that ultraviolet light disinfection would eliminate the need

for the facility to handle and store significant amounts of hazardous and 

corrosive chemicals. 

In addition to disinfection method chosen, facility size can also influence 

capital conversion costs. In general, larger facilities spend more 

converting to alternative disinfection methods. For example, because 

larger facilities process a greater flow of wastewater, converting to 

delivered sodium hypochlorite would require a larger sodium hypochlorite 

storage building or buildings relative to a smaller facility. It may also 

require additional pumps, instrumentation, and piping to deliver treatment

chemicals to a greater number of contact tanks. Importantly, the largest 

facilities also tend to serve high-cost urban areas, and their conversion 

costs reflect the higher costs for construction materials and contract labor 

in these markets. 

Facility Size

For example, the Blue Plains Wastewater Treatment Plant, which treats 

307 million gallons per day and serves over 2 million customers in the 

Washington, D.C., metropolitan area, converted from chlorine gas to 

delivered sodium hypochlorite in 2003 at a cost of almost $13 million. 

According to facility managers, the facility temporarily converted from 

chlorine gas to delivered sodium hypochlorite in April 2002 at a cost of 

$500,000, primarily for storage tanks, pumps, piping, and related 

instrumentation. It completed the permanent conversion in October 2003 

at an added cost of about $12.5 million, which included the purchase of 

additional storage tanks, related pumps, piping and instrumentation, and 

the construction of storage facilities for sodium hypochlorite and sodium 

bisulfate (used for dechlorination). 

Page 16 GAO-07-480 Wastewater Facility Security
In addition to facility size, other physical characteristics related to 

individual facilities also play a large role in conversion costs. For instance, 

the availability of usable buildings on facility grounds will determine 

whether a facility needs to construct, expand, or update a building to 

properly house sodium hypochlorite and its associated metering 

equipment. In addition, the distance between the storage building and 

treatment tanks will determine the amount of piping needed to deliver 

stored sodium hypochlorite to the treatment tanks. An example comes 

from the Hampton Roads Sanitation District which provides wastewater 

treatment to approximately 1.6 million people in 17 cities and counties in 

southeast Virginia, including the cities of Newport News, Norfolk, Suffolk, 

Virginia Beach, and Williamsburg. In 2004, the sanitation district converted 

from chlorine gas to bulk sodium hypochlorite disinfection at two of its 

plants—the Nansemond Treatment Plant, which treats 17 million gallons 

per day for the city of Suffolk, and the previously mentioned ChesapeakeElizabeth plant, which treats 21 million gallons per day. The Nansemond 

plant conversion cost an estimated $1.65 million, while the slightly larger 

Chesapeake-Elizabeth plant conversion cost about $1.2 million. Costs 

were higher at the Nansemond plant because a building needed to be 

constructed for sodium hypochlorite storage, while the ChesapeakeElizabeth plant had an existing building that only needed to be upgraded

to properly store the chemical. 

Other Key Facility 

Characteristics 

Federal discharge permit requirements related to individual treatment 

facilities can also influence conversion costs. Certain wastewater facilities 

may be allowed higher chlorine residuals in treated effluent because they

discharge into less sensitive waters. Often, these facilities do not have to 

dechlorinate wastewater, saving the facility the cost of dechlorination 

chemicals, equipment, and storage. For example, the Philadelphia-area 

Southeast and Northeast Wastewater Treatment Plants, which treat 90 and 

190 million gallons per day, respectively, need only to chlorinate water 

prior to discharging into the Delaware River. Both plants were converted 

to delivered sodium hypochlorite—the Southeast plant in 2006 at an 

estimated cost of $1.9 million and the Northeast plant in 2003 at an 

estimated cost of $2.6 million. In contrast, the Baltimore-area Back River 

Wastewater Treatment Plant, which treats 150 million gallons per day and 

discharges into the ecologically sensitive Chesapeake Bay, must chlorinate 

and dechlorinate its wastewater before discharge. This facility converted 

to delivered sodium hypochlorite in 2004 at a reported cost of $3.3 million. 

Finally, some facilities have reduced conversion costs in the short term 

through temporary conversions. For example, the Metropolitan Sewer 

District of Greater Cincinnati decided to convert its Mill Creek Wastewater 

Temporary Conversions 

Page 17 GAO-07-480 Wastewater Facility Security
Treatment Plant, which treats 120 million gallons per day, from chlorine 

gas to sodium hypochlorite disinfection soon after September 11, 2001. 

According to the plant manager, by mid-October 2001, the facility had 

begun disinfecting with sodium hypochlorite by hooking up a rented 

sodium hypochlorite trailer to its disinfection system at a cost of $25,000. 

By May 2002, the facility had completed an interim conversion to sodium 

hypochlorite by purchasing and installing two 8,000 gallon outdoor storage 

tanks for sodium hypochlorite at a cost of $60,000. According to the plant

manager, this interim disinfection system is still in use today, though the 

plant intends to permanently convert to delivered sodium hypochlorite in

2008 or 2009 at an estimated cost of $3 million. The plant manager said the 

permanent conversion would include an unloading station for sodium 

hypochlorite deliveries and a new storage building for the chemical and 

related instrumentation. The plant manager said the new storage building 

was needed to reduce the decay of stored sodium hypochlorite. The plant 

manager added that the storage building and additional piping would 

improve plant safety because it would allow for central storage and 

delivery of sodium hypochlorite. Currently, sodium hypochlorite deliveries 

are made at several plant locations for odor control which, according to 

the plant manager, increase the odds the chemical may be mishandled and

accidentally mixed with other reactant chemicals used at the plant, such 

as ammonia. 

Similarly, the Eastern Water Reclamation Facility, which treats 16 million 

gallons per day and provides service to Orange County, Florida, converted 

from chlorine gas to sodium hypochlorite disinfection at a cost of $60,000

in November 2001 through the addition of outdoor storage tanks and 

related pumps. According to the plant manager, the facility may consider 

additional changes in the future, such as permanent sodium hypochlorite 

storage or on-site generation. 

Changes in Annual Costs 

Vary Widely, with Some 

Facilities Reporting 

Savings 

Changes in annual costs related to disinfection treatment conversions 

were hard to measure due to lack of data. Many facilities we interviewed 

were unable to provide complete information on annual costs related to 

disinfection before and after converting from chlorine gas. Available data 

show that annual chemical costs related to disinfection increased for 

facilities that converted to delivered sodium hypochlorite, because sodium 

Page 18 GAO-07-480 Wastewater Facility Security
hypochlorite costs more than chlorine gas.16 Available data also show that 

electrical costs related to disinfection increased for facilities that 

converted to on-site generation of sodium hypochlorite or ultraviolet light

treatment, however these facilities also saw large reductions in chemical 

costs. Available data also show that increases in annual costs related to 

disinfection were offset somewhat by savings in training and regulatory 

requirements, as several facilities that converted reported a reduced need

for staff time devoted to complying with the EPA risk management 

planning that was required when the plant used chlorine gas.

A few facilities were even able to report or project annual savings due to 

the disinfection conversion. For example, the wastewater treatment 

manager of the Columbia Boulevard Treatment Plant, which treats 143 

million gallons per day and provides wastewater service to Portland, 

Oregon, estimated that annual costs related to disinfection fell by over 

$100,000 after the plant completed a 2005 conversion from chlorine gas to

delivered sodium hypochlorite disinfection.17 According to the wastewater 

treatment manager, increases in disinfection chemical costs for the plant 

were more than offset by reductions in electrical, labor, and training costs. 

Electrical power costs fell because the plant no longer had to power 

chlorine gas evaporators, which heat and help convert the pressurized 

liquid into gas before it is injected into the waste stream. In contrast, 

sodium hypochlorite is fed into the waste stream via less energy-intensive 

pumps. Labor and training costs also fell because the plant no longer had

to meet the Occupational Safety and Health Administration’s (OSHA) 

Process Safety Management of Highly Hazardous Chemicals standard,18

and risk management and emergency response planning costs associated 

with the use of chlorine gas were eliminated. 

 16In addition, sodium bisulfate, the dechlorination chemical often used with sodium 

hypochlorite, costs more than sulfur dioxide, the dechlorination chemical often used with 

chlorine gas. 

17According to the wastewater treatment manager, annual costs related to disinfection fell 

from $411,531 for the operating year covering July 1, 2004, to June 30, 2005, to $302,998 for 

the operating year covering July 1, 2005, to June 30, 2006. The wastewater treatment 

manager reported the plant’s annual operations and maintenance budget at $12.4 million 

for the most recently completed operating year. 

18OSHA’s Process Safety Management of Highly Hazardous Chemicals standard (29 CFR 

1910.119) contains requirements for the management of hazards associated with processes 

using highly hazardous chemicals.

Page 19 GAO-07-480 Wastewater Facility Security
In another example, the South Central Regional Wastewater Treatment 

and Disposal Plant, which treats 18 million gallons per day for customers 

in the cities of Delray Beach and Boynton Beach, Florida, predicts that it 

too will achieve annual savings once it converts from chlorine gas to 

sodium hypochlorite generated on-site, which it anticipates completing in 

September 2007. According to the Executive Director of the South Central 

Regional Wastewater Treatment and Disposal Board, potential disruptions 

of sodium hypochlorite delivery during hurricane seasons motivated them 

to begin generating their disinfection chemicals on-site. The plant’s most 

recent fiscal year operating and maintenance budget for disinfection is 

estimated to be roughly $307,000 for chlorine gas and associated costs 

including equipment and maintenance, labor, and risk management 

planning. Postconversion annual operating and maintenance costs for 

disinfection are estimated to fall to $205,000 in the 2008 calendar year, 

primarily due to the suspension of chlorine gas purchases. 

We provided a draft of this report to EPA for review and comment. In its 

letter, reproduced in appendix II, EPA concurred with the results of the 

report. EPA’s Water Security Division in the Office of Ground Water and 

Drinking Water provided technical comments and clarifications that were 

incorporated, as appropriate. 

As agreed with your office, unless you publicly release the contents of this 

report earlier, we plan no further distribution until 30 days from the report 

date. At that time, we will send copies of this report to the appropriate 

congressional committees; interested Members of Congress; the 

Administrator, EPA; and other interested parties. We will also make copies

available to others on request. In addition, the report will be available at 

no charge on the GAO Web site at http://www.gao.gov. 

Agency Comments 

and Our Evaluation 

Page 20 GAO-07-480 Wastewater Facility Security
Should you or your staff need further information, please contact me at 

(202) 512-3841 or stephensonj@gao.gov. Contact points for our Offices of 

Congressional Relations and Public Affairs may be found on the last page 

of this report. GAO staff who made major contributions to this report are 

listed in appendix III. 

Sincerely yours, 

John B. Stephenson 

Director, Natural Resources 

 and Environment 

Page 21 GAO-07-480 Wastewater Facility Security
Appendix I: Scope and Methodology Appendix I: Scope and Methodology 

To identify the costs of preparing vulnerability assessments and risk 

management plans, we conducted structured telephone interviews with a 

select sample of large wastewater facilities identified as having completed 

these documents in our March 2006 report.1

 Our March report identified 

106 large facilities that reported they had prepared vulnerability 

assessments or had one underway, and 85 facilities that were required to 

prepare risk management plans because they currently used chlorine gas 

as a disinfectant. From these two groups, we identified 47 facilities that 

reported that they had prepared vulnerability assessments and currently 

use chlorine. Of this universe, we chose a nonprobability sample of 25 

facilities to assure geographic dispersion and adequate variation in size, 

since these factors were likely to influence their costs.2

 We completed 

structured interviews with 20 of the remaining 25 facilities. We sent an 

interview schedule in advance of each of the interviews. We completed the 

structured interviews between November 2006 and February 2007. 

Reported costs included both actual and estimated costs. For estimated 

costs, we asked facility managers to explain how they arrived at these 

estimates. Reported costs were not adjusted for inflation. 

To identify the costs incurred by wastewater facilities in converting from 

gaseous chlorine to an alternative disinfection process, we conducted 

structured telephone interviews with a nonprobability sample of 26 of the 

38 large facilities identified in the March report as having recently 

converted or planning to convert from chlorine gas to an alternative 

disinfection process. We sent an interview schedule in advance of each of 

the interviews. We completed the structured interviews between October 

2006 and February 2007. Reported costs included both actual and 

estimated costs. For estimated costs, we asked facility managers to 

explain how they arrived at these estimates. Reported costs were not 

adjusted for inflation. We also conducted site visits with some of the 

facilities. Where available, we gathered documentation, such as capital

plans, from these facilities in order to document conversion costs. We 

supplemented the cost information we gathered at individual wastewater 

 1

GAO, Securing Wastewater Facilities: Utilities Have Made Important Upgrades but 

Further Improvements to Key System Components May Be Limited by Costs and Other

Constraints, GAO-06-390 (Washington, D.C.: Mar. 31, 2006). We defined large wastewater 

facilities as those publicly owned treatment works (POTW) that serve residential 

populations of 100,000 or greater. 

2

Results from nonprobability samples cannot be used to make inferences about a

population, because in a nonprobability sample some elements of the population being

studied have no chance or an unknown chance of being selected as part of the sample. 

Page 22 GAO-07-480 Wastewater Facility Security
Appendix I: Scope and Methodology 

facilities with information obtained at the Environmental Protection 

Agency, the Department of Homeland Security, nongovernmental 

organizations, and industry representatives. We determined that reported

cost data were sufficiently reliable to provide useful information about the 

costs for preparing vulnerability assessments, risk management plans, and 

conversions from gaseous chlorine and the factors that affect these costs. 

We conducted our work between August 2006 and March 2007 in 

accordance with generally accepted government auditing standards. 

Page 23 GAO-07-480 Wastewater Facility Security
Appendix II: Comments from the Appendix II: Comments from the Environmental Protection Agency 

Environmental Protection Agency 

Page 24 GAO-07-480 Wastewater Facility Security
Appendix III: GAO

A

 Contact and Staff 

cknowledgments 

Page 25 GAO-07-480 

Appendix III: GAO Contact and Staff 

Acknowledgments 

John B. Stephenson, (202) 512-3841 or stephensonj@gao.gov

In addition to the contact named above, Jenny Chanley, Steve Elstein, 

Nicole Harris, Greg Marchand, Tim Minelli, Alison O’Neill, Daniel Semick, 

and Monica Wolford made key contributions to this report. 

Wastewater Facility Security

GAO Contact 

Acknowledgments 

(360738) 
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