Nationwide, more than 16,000 POTWs serve more than 200 million people, or about 70 percent of the nation’s total population. The remaining population is served by privately-owned utilities or by on-site systems, such as septic tanks. A relative handful of large wastewater systems serve the great majority of people, as about 500 large public wastewater systems provide service to 62 percent of the population connected to a sewer system. In addition to serving residential populations, approximately 27,000 commercial and industrial facilities rely on wastewater treatment facilities to treat their wastewater. POTWs discharge treated effluent into receiving waters and are regulated under the Clean Water Act. Wastewater systems vary by size and other factors, but all include a collection system and a treatment facility. The collection system is the underground network of sewers including both sanitary and storm water collection lines. Collection systems tend to be dispersed geographically and have multiple access points, including drains, catch basins, and manholes. Lines may range from 4 inches to greater than 20 feet in diameter, and access is usually conducted through manholes that are typically 300 feet apart. Many collection systems rely on gravity to maintain the flow of sewage through the pipes toward the treatment plant. However, collection systems may also depend on pumping stations to propel the flow when gravity alone is insufficient. Nationwide, there are approximately 800,000 miles of sewer lines and 100,000 major pumping stations. The wastewater treatment facility receives wastewater from the collection system and begins the treatment process which typically involves several stages before treated effluent is released into receiving waters. Primary treatment includes removal of larger objects through a screening device or a grit removal system, and the removal of solids through sedimentation. Secondary stage treatment includes a biological process that consumes pollutants, as well as final sedimentation. Some facilities also use tertiary treatment to remove nutrients and other matter even further. Following these treatments, the wastewater is disinfected to destroy harmful bacteria and viruses. Disinfection is often accomplished with chlorine, which is stored in gaseous or liquid form on-site at the wastewater treatment plant. The collection system and treatment process is typically monitored and controlled by a Supervisory Control and Data Acquisition (SCADA) system, which allows utilities to control such things as the amount of chlorine needed for disinfection. Wastewater treatment facilities may possess certain characteristics that terrorists could exploit either to impair the wastewater treatment process or to damage surrounding communities and infrastructure. For example, the numerous storm drains, manholes, and sewers that make up a community’s wastewater collection system’s network of sewers could be used to covertly place explosives beneath a major population center or to introduce substances that may damage a wastewater treatment plant’s process. Damage to (or destruction of) tanks that hold large amounts of gaseous chlorine used to disinfect wastewater could release the potentially lethal gas into the atmosphere. Such events could result in loss of life, destruction of property, and harm to the environment. Documented accidents and intentional acts highlight the destruction that could arise from an attack on a wastewater system. In June 1977 in Akron, Ohio, an intentional release of naptha, a cleaning solvent, and alcohol into a sewer by vandals at a rubber manufacturing plant caused explosions 3.5 miles away from the plant, damaging about 5,400 feet of sewer line and resulting in more than $10 million in damage. In 1981 in Louisville, Kentucky, thousands of gallons of a highly flammable solvent, hexane, spilled into the sewer lines from a local processing plant. Fumes from the solvent ignited, and the resulting explosions collapsed a 12-foot diameter pipe and damaged more than 2 miles of streets. No one was seriously injured, but sewer line repairs took 20 months, followed by several more months to repair the streets. In 1992 in Guadalajara, Mexico, a gasoline leak into a sewer caused explosions that killed 215 people, injured 1,500 others, damaged 1,600 buildings, and destroyed 1.25 miles of sewer. In 2002 in Hagerstown, Maryland, chemicals from an unknown source entered the wastewater treatment plant and destroyed the facility’s biological treatment process. The event resulted in the discharge of millions of gallons of partially treated sewage into a major tributary of the Potomac River, less than 100 miles from a water supply intake for the Washington, D.C., metropolitan area. In January 2005, we reported the views of 50 nationally recognized experts on key issues concerning wastewater security. Our panel of experts identified five key wastewater assets as most vulnerable to terrorist attacks: the collection systems’ network of sewers (42 of 50 experts), treatment chemicals (32 of 50 experts), key components of the treatment plant (29 of 50 experts), control systems (18 of 50 experts), and pumping stations (16 of 50 experts). When asked to identify and set priorities for the security-enhancing activities most deserving of federal support, the expert panel identified 11 key actions, but ranked three as deserving highest priority—replacing gaseous chemicals used in the wastewater treatment process; improving local, state, and regional efforts to coordinate responses in advance of a potential terrorist threat; and completing vulnerability assessments for individual wastewater systems. Federal law does not address wastewater security as comprehensively as it does drinking water security. In particular, wastewater facilities are not required by law to complete vulnerability assessments. The Clean Air Act does require wastewater facilities using certain amounts of hazardous substances, such as chlorine gas, to submit to EPA a risk management plan that lays out accident prevention and emergency response activities. Also, under EPA guidance, the Clean Water State Revolving Fund can be used in many instances for certain wastewater system security enhancements. While federal law governing wastewater security is limited, in December 2003, the president issued HSPD-7. The directive designated EPA as the lead agency to oversee the security of the water sector, including both drinking water and wastewater critical infrastructures. In 2002, Congress passed the Bioterrorism Act, which amended various laws, including the Safe Drinking Water Act. The Bioterrorism Act required drinking water systems serving more than 3,300 people to complete vulnerability assessments of their facilities by June 2004 and to prepare or update an existing emergency response plan. 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 which are utilized by the public water system; (5) the use, storage, or handling of various chemicals; and (6) the operation and maintenance of such systems. Under the act, the emergency response plans were to include plans, procedures, and identification of equipment to lessen the impact on public health and the drinking water supply of terrorist attacks or other intentional acts against drinking water systems. The act authorized $210 million for fiscal year 2002, mostly to assist drinking water systems in completing vulnerability assessments, preparing or updating response plans, and making needed security improvements. Drinking water systems are not required to implement any risk-reduction actions based on their vulnerability assessments or report to EPA on measures that have been implemented. In 2003, the Congress considered alternative bills that would have encouraged or required wastewater treatment plants to assess the vulnerability of wastewater facilities, make physical security improvements, and conduct research. However, the legislation did not become law and, consequently, no such requirement or specific funding exists for wastewater facilities. 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 1990 Clean Air Act amendments mandated EPA oversight of risk management planning at facilities that handle more than specified-threshold quantities of hazardous substances, including the gaseous chlorine often used as a disinfectant at wastewater facilities. Specifically, EPA regulations implementing the Clean Air Act require these facilities to prepare Risk Management Plans (RMPs) that summarize the potential threat of sudden, accidental, large releases of certain chemicals; including the results occurring off-site in a worst-case chemical accident, and the facility’s plan to prevent releases and mitigate any damage. RMPs are to be revised and resubmitted to EPA at least every 5 years, and EPA is required to review them and require revisions, if necessary. For a March 2003 report, EPA told us it believed the Clean Air Act could be interpreted to provide authority to address site security from terrorist attacks at RMP facilities, because the act imposes certain requirements on these facilities regarding “accidental releases.” The act defines an accidental release as an unanticipated emission of a regulated substance or other extremely hazardous substance into the air, so any chemical release caused by a terrorist attack could be considered “unanticipated” and covered under the Clean Air Act. Such an interpretation would provide EPA with authority under the act’s RMP provisions and general duty clause to require security measures or vulnerability assessments with regard to terrorism. However, EPA has not attempted to use these Clean Air Act provisions because it is concerned that such an interpretation would pose significant litigation risk and has concluded that chemical facility security would be more effectively addressed by passage of specific legislation. Wastewater facilities that store certain amounts of hazardous chemicals may also be subject to the Resource Conservation and Recovery Act. Under regulations implementing the act, facilities that house hazardous waste generally must take certain security actions, such as posting warning signs and using a 24-hour surveillance system, or surrounding the active portion of the facility with a barrier and controlled entry gates. However, according to EPA, these security measures are aimed at keeping out trespassers or wanderers, not intentional intruders. Other federal statutes impose safety requirements on certain wastewater facilities that may incidentally reduce the likelihood and mitigate the consequences of terrorist attacks.