Drinking water can come from either groundwater sources, via wells, or from surface water sources, such as rivers, lakes, and streams. All sources of drinking water contain some naturally occurring contaminants. As water flows in streams, sits in lakes, and filters thorough layers of soil and rock in the ground, it dissolves or absorbs the substances that it touches. Some of these contaminants are harmless, but others can pose a threat to drinking water, such as improperly disposed-of chemicals, pesticides, and certain naturally occurring substances. Likewise, drinking water that is not properly treated or disinfected, or which travels through an improperly maintained water system, may pose a health risk. However, the presence of contaminants does not necessarily indicate that water poses a health risk—all drinking water may reasonably be expected to contain at least small amounts of some contaminants. As of July 2006, EPA had set standards for approximately 90 contaminants in drinking water that may pose a risk to human health. According to EPA, water that contains small amounts of these contaminants, as long as they are below EPA’s standards, is safe to drink. However, EPA notes that people with severely compromised immune systems and children may be more vulnerable to contaminants in drinking water than the general population. Camp Lejeune covers approximately 233 square miles in Onslow County, North Carolina, and includes training schools for infantry, engineers, service support, and medical support, as well as a Naval Hospital and Naval Dental Center. The base has nine family housing areas, and families live in base housing for an average of 2 years. Base housing at Camp Lejeune consists of enlisted family housing, officer family housing, and bachelor housing (barracks for unmarried service personnel). Additionally, schools, day care centers, and administrative offices are located on the base. Approximately 54,000 people currently live and work at Camp Lejeune, including about 43,000 active duty personnel and 11,000 military dependents and civilian employees. In the 1980s, Camp Lejeune obtained its drinking water from as many as eight water systems, which were fed by more than 100 individual wells that pumped water from a freshwater aquifer located approximately 180 feet below the ground. Each of Camp Lejeune’s water systems included wells, a water treatment plant, reservoirs, elevated storage tanks, and distribution lines to provide the treated water to the systems’ respective service areas. Drinking water at Camp Lejeune has been created by combining and treating groundwater from multiple individual wells that are rotated on and off, so that not all wells are providing water to the system at any given time. Water is treated in order to remove minerals and particles and to protect against microbial contamination. (See fig. 1 for a description of how a Camp Lejeune water system operates.) From the 1970s through 1987, Hadnot Point, Tarawa Terrace, and Holcomb Boulevard water systems provided drinking water to most of Camp Lejeune’s housing areas. The water treatment plants for the Hadnot Point and Tarawa Terrace water systems were constructed during the 1940s and 1950s. The water treatment plant for the Holcomb Boulevard water system began operating at Camp Lejeune in 1972; prior to this time, the Hadnot Point water system provided water to the Holcomb Boulevard service area. In the 1980s, each of these three systems had between 8 and 35 wells that could provide water to their respective service areas. In 1987 the Tarawa Terrace water treatment plant was shut down and the Holcomb Boulevard water distribution system was expanded to include the Tarawa Terrace water service area. Generally, housing units served by the Tarawa Terrace and Holcomb Boulevard water systems consisted of family housing, which included single- and multifamily homes and housing in trailer parks. Housing units served by the Hadnot Point water system included mainly bachelor housing with limited family housing. Based on available housing data for the late 1970s and the 1980s, the estimated annual averages of the number of people living in family housing units served by these water systems at that time were: 5,814 people in units served by the Tarawa Terrace water system, 6,347 people in units served by the Holcomb Boulevard water system, and 71 people in units served by the Hadnot Point water system. In addition to serving housing units, all three water systems provided water to base administrative offices. The Tarawa Terrace, Holcomb Boulevard, and Hadnot Point water systems also served schools and other recreational areas. Additionally, the Hadnot Point water system also served an industrial area and the base hospital. Certain Navy entities provide support functions for Marine Corps bases such as Camp Lejeune. Two entities provide support for environmental issues: The Naval Facilities Engineering Command began providing environmental support for bases in the 1970s. The Naval Facilities Engineering Command, Atlantic Division (LANTDIV) provides environmental support for Navy and Marine Corps bases in the Atlantic and mid-Atlantic regions of the United States. For example, LANTDIV officials work with Camp Lejeune officials to establish environmental cleanup priorities and cost estimates and to allocate funding to ensure compliance with state and federal environmental regulations. The Navy Environmental Health Center (NEHC) has provided environmental and public health consultation services for Navy and Marine Corps environmental cleanup sites since 1991. NEHC is also designated as the technical liaison between Navy and Marine Corps installations and ATSDR and, as a part of this responsibility, reviews and comments on all ATSDR reports written for Navy and Marine Corps sites prior to publication. Prior to 1991, no agency was designated to provide public health consultation services for Navy and Marine Corps sites. In 1980, the Department of the Navy established the Navy Assessment and Control of Installation Pollutants (NACIP) program to identify, assess, and control environmental contamination from past hazardous material storage, transfer, processing, and disposal operations. Under the NACIP program, initial assessment studies were conducted to determine the potential for environmental contamination at Navy and Marines Corps bases. If, as a result of the study, contamination was suspected, a follow- up confirmation study and corrective measures were initiated. In 1986 the Navy replaced its NACIP program with the Installation Restoration Program. The purpose of the Installation Restoration Program is to reduce, in a cost-effective manner, the risk to human health and the environment from past waste disposal operations and hazardous material spills at Navy and Marine Corps bases. Cleanup is done in partnership with EPA, state regulatory agencies, and members of the community. Congress passed the Safe Drinking Water Act in 1974 to protect the public’s health by regulating the nation’s public drinking water supply. The Safe Drinking Water Act, as amended, is the key federal law protecting public water supplies from harmful contaminants. For example, the act requires that all public water systems conduct routine tests of treated water to ensure that the water is safe to drink. Required water testing frequencies vary and range from weekly testing for some contaminants to testing every 3 years for other contaminants. The act also established a federal-state arrangement in which states may be delegated primary implementation and enforcement authority for the drinking water program. For contaminants that are known or anticipated to occur in public water systems and that EPA determines may have an adverse impact on health, the act requires EPA to set a nonenforceable maximum contaminant level goal, at which no known or anticipated adverse health effects occur and that allows an adequate margin of safety. Once the maximum contaminant level goal is established, EPA sets an enforceable standard for water as it leaves the treatment plant, the maximum contaminant level. A maximum contaminant level is the maximum permissible level of a contaminant in water delivered to any user of a public water system. The maximum contaminant level must be set as close to the goal as is feasible using the best technology or other means available, taking costs into consideration. The North Carolina Department of Environment and Natural Resources and its predecessors have had primary responsibility for implementation of the Safe Drinking Water Act in North Carolina since 1980. In 1979, EPA promulgated final regulations applicable to certain community water systems establishing the maximum contaminant levels for the control of TTHMs, which are a type of VOC that are formed when disinfectants—used to control disease-causing contaminants in drinking water—react with naturally occurring organic matter in water. The regulations required that water systems that served more than 10,000 people and that added a disinfectant as part of the drinking water treatment process begin mandatory water testing for TTHMs by November 1982 and comply with the maximum contaminant level by November 1983. TCE and PCE were not among the contaminants included in these regulations. In 1979 and 1980, EPA issued nonenforceable guidance establishing “suggested no adverse response levels” for TCE and PCE in drinking water and in 1980 issued “suggested action guidance” for PCE in drinking water. Suggested no adverse response levels provided EPA’s estimate of the short- and long-term exposure to TCE and PCE in drinking water for which no adverse response would be observed and described the known information about possible health risks for these chemicals. Suggested action guidance recommended remedial actions within certain time periods when concentrations of contaminants exceeded specific levels. Suggested action guidance was issued for PCE related to drinking water contamination from coated asbestos-cement pipes, which were used in water distribution lines. The initial regulation of TCE and PCE under the Safe Drinking Water Act began in 1989 and 1992, respectively, when maximum contaminant levels became effective for these contaminants. (See table 1 for the suggested no adverse response levels, suggested action guidance, and maximum contaminant level regulations for TCE and PCE.) The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980 established what is known as the Superfund program to clean up highly contaminated waste sites and address the threats that these sites pose to human health and the environment, and assigned responsibility to EPA for administering the program.