III. Pathway Analysis

This section of the PHA addresses the potential for human exposure to contamination. Figure 3 describes ATSDR's exposure evaluation process. ATSDR identifies and evaluates exposure pathways by considering how people might come into contact with, or be exposed to, a contaminant. For a public health hazard to exist people must come into contact with areas of potential contamination, contamination must be present, and the amount of contamination must be sufficient to affect people's health.

For the purpose of evaluating the public health impact of chemical releases into the environment, it is critical to determine if any people come into contact with the chemicals. If no one comes into contact with a chemical, then there is no exposure; therefore, no health effects could occur. Often the general public does not have access to the source area of the environmental release; this lack of access makes it more important to determine whether the chemicals are moving through the environment to where people may come into contact with them. The route of movement of chemicals is the pathway. An exposure pathway may involve air, surface water, groundwater, soil, dust, or even plants and animals.

Completed Pathways:

A completed pathway exists when the five elements of a pathway connect a source of contamination to a receptor population. If contaminants migrate from a source area to a point where people can contact them, a completed pathway of exposure could exist. In addition, completed pathways are likely to occur when people enter source areas. For example, anyone entering the LIA or the OB/OD area could potentially come into contact with chemical residue from the detonation of explosives in soil and water at the site. Additionally, there is a risk of disturbing UXO and detonating it, with obvious related health effects.

Navy personnel or their contractors routinely spend no more than eight to ten weeks per year cleaning the LIA's targets during the semi-annual refurbishment efforts. Therefore, the population potentially exposed for the greatest length of time were the protestors who occupied the LIA from April 1999 until May 2000. Soil samples are needed from these areas in order to permit exact definition of which chemicals are in the soil, so that a health evaluation can be completed. At the request of ATSDR, the Navy collected surface samples on the LIA and recorded sample locations. Evaluation of these samples will be addressed in a future PHA.

Potential Pathways:

A potential pathway exists when information for one of the five elements is unknown or missing. There are several potential pathways that may exist on Vieques. For example, if the wind carries potential contaminants 7.9 miles from the LIA to the residential section of Vieques, people could be potentially exposed through the air, through dust as it settles, or through the food chain. In addition, contaminated soils may be washed into the sea from the LIA. People could be potentially exposed if those contaminants migrated to populated areas or entered the food chain.

Data do not yet exist to permit direct assessment of these potential pathways. ATSDR will continue to work with other agencies to collect relevant data and, where necessary, to model the movement of chemicals in the environment.

This PHA, Drinking Water Supplies and Groundwater Pathway Evaluation, evaluates only those pathways that potentially impact drinking water supplies on the island. Other pathways are not assessed in this PHA, but will be addressed by ATSDR in the future as more data become available and the public health implications of the data are assessed. The pathways evaluated in this PHA are summarized in Table 1. The following questions regarding the safety of the drinking water supplies on Vieques are addressed in this PHA:

1. Is the current public water supply safe to drink?
2. Is the groundwater on Vieques safe to drink?
3. Is the water from rainfall collection systems safe to drink?

Future PHAs will address the remaining issues related to completed or potential pathways from the LIA to the residents of Vieques. The issues being evaluated by ATSDR at this time include:

1. The potential for contaminants to travel from the LIA to populated areas of the island through the air will be addressed in a future focused PHA. It will address potential exposures through the air, including the impact of any air transport of chemicals on dust, soil, and water. A further discussion of rainfall collection systems will also be included.
2. The potential for contaminants to travel from the LIA and deposit in residential areas of Vieques will be addressed in a focused PHA concerning exposures to soil on Vieques. This document will address exposures that the residential population might typically experience as well as exposures that individuals who lived on the LIA between April 1999 and May 2000 might have experienced.
3. The potential for residents to be exposed to contaminants through consumption of fish and shellfish collected in the nearby waters will be addressed in a future focused PHA.

As ATSDR's investigations proceed, additional issues and concerns may be identified and, if so, they will be evaluated.

The Groundwater Pathway:

The petitioner and other residents of Vieques have voiced a concern that contaminated groundwater may move from beneath the LIA and the OB/OD area to the populated areas of Vieques. However, the geology and topography of the island prevents groundwater from moving in that direction.

Any groundwater that might exist in the marine sediments and sand deposits at the LIA and the OB/OD area will move slowly downhill, under the influence of gravity, toward lagoons and the ocean that surround the LIA on most sides. Any movement of groundwater westward would be intercepted by the sea and lagoons on either side of the isthmus, or else would be prevented from further migration by the rising bedrock and topography of the island, west of the isthmus. Therefore, groundwater cannot move uphill from the LIA westward--there is no connection between groundwater at the LIA and groundwater of the central portion of the island. Neither the Esperanza aquifer, nor the shallow groundwater around Isabel Segunda and other populated areas of the island is directly impacted by groundwater beneath the LIA or the OB/OD area.

The only way the Esperanza aquifer or other groundwater in the center of the island could be impacted by operations at the LIA and the OB/OD area is through air transport, deposition, and later movement of contaminants through the soil into the underground aquifers. ATSDR does not know yet if any measurable amount of chemical residue has traveled through the air to these areas. However, recent groundwater sampling did not detect explosives or their residues in any groundwater on the island. Since the point of exposure, usable water, has been sampled and no ordnance-related contaminants found, the groundwater route is an incomplete pathway.