A resident of Vieques requested (petitioned) the Agency for Toxic Substances and Disease Registry (ATSDR) to determine if hazardous substances from the detonation of munitions at the Navy's bombing range pose a public health threat. A hazardous substance can affect human health only if people come into contact with the substance at the source or if the substance is transported to the public through a pathway (e.g., air, groundwater, soil, or biota). This public health assessment specifically focuses on the drinking water pathway with particular emphasis on explosive-related contamination. In the future, ATSDR will publish additional focused public health assessments that will address specific questions about the air, soil, and biota pathways as the data become available.

Historically, rainwater and groundwater have been used to supply the residents of Vieques with drinking water. Because of maintenance and salt water intrusion problems, the primary resource of groundwater, the Esperanza valley well field, was shut down in 1978. In 1977, an underwater drinking water pipeline from the mainland was built. Most residents receive their drinking water supply from Puerto Rico mainland through this pipeline. This water is stored in aboveground tanks prior to distribution. A few public and private groundwater wells still exist on the island and are occasionally used when the public water supply is interrupted. The number and current use of rainfall collection systems are unknown.

The United States Environmental Protection Agency (EPA), the Puerto Rico Department of Health (PRDOH), and an environmental firm hired by the Navy sampled public water supply tanks and groundwater wells on Vieques to characterize drinking water supplies. ATSDR also reviewed data collected by the Puerto Rico Environmental Quality Board (PREQB) and the US Geological Survey (USGS) from monitoring wells (not used for drinking water supply) or other inactive or closed wells. After evaluating the findings of those investigations of groundwater and drinkingwater sources and comparing detected levels of contamination to health-based guidelines known to be protective of public health, ATSDR determined that only nitrate plus nitrite levels in Well 3-7, a shallow, private drinking water well, were a public health hazard.

ATSDR concluded the following about the drinking water pathway:

The public water supply system is safe to drink. People who drink the water provided by Compania de Aguas from the mainland are not being exposed to harmful levels of contaminants.

Drinking the groundwater from the three Sun Bay wells, the four B wells, and Well 2-3 does not pose a public health hazard. The levels and types of chemicals detected are naturally occurring and are not expected to cause adverse health effects if or when these wells are used for drinking water supply when the public water supply is interrupted.

The concentration of nitrate plus nitrite, most likely resulting from agricultural pollution, in Well 3-7, a private drinking water well, was detected at levels higher than those that are considered safe for children. Because of elevated concentrations, ATSDR has determined that a public health hazard exists for people, especially children, who drink water from Well 3-7.

At this time, ATSDR does not have any use of sampling data for the rainfall collection systems that are being used as a source of drinking water. ATSDR will revisit this potential pathway when new information or data become available on the occasional or continuous use of rainfall collection systems for the supply of drinking water.

Very low levels of explosives and potential products of explosive combustion were reported in drinking water data from 1978, however, the validity and utility of the data is uncertain. None of the data provided any evidence which would lead agency scientists to conclude that the water sampled posed a past public health hazard on the island. Even assuming the validity of the data and the presence of the compounds, the reported concentrations were well below levels considered harmful to human health.