Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
Contact Us:
  • Centers for Disease Control and Prevention
    1600 Clifton Rd
    Atlanta, GA 30333
  • 800-CDC-INFO
    TTY: (888) 232-6348
    24 Hours/Every Day

Public Health Assessment
Drinking Water Supplies and Groundwater Pathway Evaluation,
Isla de Vieques Bombing Range,
Vieques, Puerto Rico

To print this report, please select the "Print Friendly View" option in left hand menu and use your browsers print function or the "Print Page" option on the right side of the page. You may also print individual sections of the report by navigating to a section using the left hand menu and following the same steps above.

October 16, 2001
Prepared by:

Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry


Appendix F: Responses to Public Comments

The Agency for Toxic Substances and Disease Registry (ATSDR) received the following comments during the public comment period (February 20 to May 4, 2001) for the Petitioned Isla de Vieques (Vieques) Public Health Assessment (PHA) (February 2001). For comments that questioned the validity of statements made in the PHA, ATSDR verified or corrected the statements. The list of comments does not include editorial comments concerning such things as word spelling or sentence syntax.

Pathways Other Than Consumption of Contaminated Water
  1. Comment: Three commentators note that the PHA did not evaluate all the potential exposure pathways that they were concerned about, such as the inhalation of contaminated air and dust, the consumption of contaminated foods, and the drinking of contaminated rainwater. One of these commentators argues that the PHA's analysis of drinking waters is incomplete because it does not consider the effects of air and dust pollution on the waters.

    Response: The public health assessment process may be lengthy, especially when addressing complex environmental issues. To be most responsive to the petitioner and the people of Vieques, ATSDR is addressing each exposure pathway in a different document, called a focused public health assessment. Each focused PHA examines environmental exposure through a different media (e.g., water, air, soil, and food chain). This focused PHA only addresses the public health implications of exposure through drinking water from public and private groundwater wells and the public water supply system. Within the PHA, ATSDR acknowledges that we cannot address public health issues pertaining to drinking water from rainfall catchment basins because no sampling or use data currently exist.

    ATSDR is preparing a focused PHA pertaining to inhalation of air and dust and focused PHAs on soil and consumption of fish and shellfish.

    Within the Pathway An sectalysision of the PHA, ATSDR explains that hydrogeologically there is no connection between groundwater at the Live Impact Area (LIA) and groundwater of the central portion of Vieques; therefore, the only way that groundwater in the residential section of the island could be impacted by operations at the LIA is "through air transport, deposition, and later movement of contaminants through the soil into the underground aquifers." Further, ATSDR recognizes that until the air pathway evaluation is completed, we do not know if "any measurable amount of chemical residue has traveled through the air to these areas." Despite not having the results of the air evaluation, this PHA's evaluation is still complete because ATSDR based the public health conclusions on data from the point of exposure (i.e., drinking water), which would be the same regardless of the source of the contamination.

  2. Comment: One commentator suggests that ATSDR investigate potential exposure pathways involving consumption of waterfowl, shellfish, and land crabs. The commentator notes that no data on contaminant levels in these organisms currently exist.

    Response: In July 2001, Environmental Response Team (ERT), a division of the U.S. Environmental Protection Agency (EPA), in cooperation with ATSDR sampled fish and shellfish from the coastal waters surrounding Vieques and land crabs from the LIA. ATSDR will evaluate the data once it becomes available and anticipates releasing a focused PHA addressing the consumption of fish and shellfish.

  3. Comment: Two commentators register their concern about airborne pollution resulting from Naval operations at the LIA. They are concerned about the chemicals contained in explosives, the chemicals generated by explosions, and the rock and pulverized metal dust kicked into the air after an explosion. The commentators note that prevailing winds generally blow from east to west and are concerned about the transport of airborne pollutants from the LIA to settled areas west of there. One commentator notes that many of the particles generated at the LIA may be so small they would travel a long distance before settling to the ground. The other commentator is also concerned that these dusts might transport heavy metals, radioactive materials, and organic compounds as they travel.

    Response: ATSDR is aware of the prevailing wind pattern that could blow airborne contaminants from the LIA to the residential area of the island. This specific concern will be evaluated in the focused PHA that addresses air contamination.

  4. Comment: One commentator suggests that ATSDR has been credulous in accepting that African dust storms are a significant source of dust in Vieques. The commentator explains ATSDR's willingness to believe this theory with the assertion that ATSDR holds preconceived ideas about the public health risks of Navy operations at Vieques.

    Response: Credible research conducted by the U.S. Geological Survey (USGS) and others, supports the validity of the African dust phenomenon. ATSDR is in the process of conducting a systematic evaluation of the potential pathways of human exposure to contaminants that may have been released during, or as a result of Navy training activities on Vieques. Our objective public health evaluations will be based upon the findings of those studies.

  5. Comment: One commentator expresses displeasure that ATSDR's Public Health Action Plan contains no reference to noise pollution. The commentator asserts that this issue is within ATSDR's purview and demands that the Agency either conduct a study of the effects of noise pollution on Vieques or state its reasons for declining to do so.

    Response: ATSDR is researching whether noises from the Navy bombing exercises cause the outer lining of the heart tissue among Vieques fishermen to thicken, as reported by a recent study (Torres et al.). In July 2001, ATSDR, the Ponce School of Medicine, and the Centers for Disease Control and Prevention co-sponsored an expert panel to review a study conducted by the Ponce School of Medicine. The findings of the review panel will be published separately.

  6. Comment: One commentator notes that the sediments at the Cerro Matías shooting range and other similar Navy sites are extremely sensitive to erosion. The commentator explains that these sediments are only sparsely covered by vegetation and are readily pulverized by the detonation of explosives and other human activities there. Once disturbed, these sediments may be easily transported from place to place. The commentator suggests that contaminated sediments might move in such a fashion as to concentrate contaminants in local areas.

    Response: ATSDR realizes that sediments from the LIA may be transported through the air or wash into the ocean. The transportation of sediments from the LIA through the air will be addressed in the focused PHA concerning the air pathway. The issue of sediments carrying contaminants into the ocean will be indirectly addressed in the focused PHA concerning fish and shellfish consumption in so far as it is one of the possible ways the marine biota could be impacted by the bombing activities at the LIA.

    Any movement of sediments at the LIA is not expected to directly impact the groundwater quality in residential areas because the geology and topography of the island prevents groundwater from moving in that direction. Indirectly, the groundwater could be influenced by aerial deposition of sediments from the LIA, however sampling indicates that the water is not contaminated to levels of health concern, with the exception of nitrate plus nitrite levels in Well 3-7. Additionally, recent groundwater sampling did not detect explosives or their residues in any groundwater on the island.

    Please read the response to the next comment for an answer concerning the possibility of sediment being transported via sea water.

Possible Routes of Water Contamination Not Adequately Examined
  1. Comment: One commentator asserts that past studies of marine biota demonstrate that the sea waters surrounding the LIA have been contaminated with heavy metals from the Navy's operations. The commentator suggests that pollutants may be transported from the LIA to Vieques' alluvial groundwater supplies via the movement of contaminated sea water.

    Response: There is no evidence that this route of movement would contribute substantially to the contaminant levels in the alluvial aquifers. First, any metals that wash into the ocean from the LIA would be greatly diluted in the ocean and second, they would have to travel a very specific route to reach the alluvial aquifers. Even if some of the metals reached the alluvial aquifer, it would be highly unexpected that the saltwater which contains the metals would mix with the fresh water that is being used because of the difference in densities between the two media. ATSDR is evaluating potential bioaccumulation of metals in marine biota.

  2. Comment: Two commentators suggest that ATSDR has not adequately addressed the possibility that water supplies in Vieques have been contaminated by dusts blown from the LIA. One commentator cites a 1978 study performed by the Navy. This study is asserted to reveal the presence of explosive residues in drinking water tanks holding water piped from mainland Puerto Rico.

    Response: ATSDR acknowledges in the Pathway Analysis section of the PHA that groundwater in the residential section of the island could be impacted by operations at the LIA "through air transport, deposition, and later movement of contaminants through the soil into the underground aquifers." By evaluating the available sampling data (i.e., the point of exposure), ATSDR was able to conclude whether drinking the water was of health concern, regardless of how the chemicals got there. The public water supply tanks do no have contaminant levels of health concern.

    ATSDR addressed the findings of the 1978 study performed by the Navy (Hoffsommer and Glover 1978; Lai 1978) in Appendix E of the PHA. Please read Appendix E for details pertaining to ATSDR's conclusions from this report.

  3. Comment: Three commentators urge ATSDR to evaluate the public health risks involved in consuming drinking water collected from rainfall. One commentator contends that ATSDR is unaware of how contaminated this water might be and how many rainfall collection systems are in use. Therefore, the commentator concludes, the PHA's statements reassurances that drinking water on Vieques is safe are inadequately grounded. Another commentator suggests that the connection between contaminant level in rainwater and the use of ammunition on the LIA be "recreated." for the sake of reconstructing past exposures.

    Response: ATSDR acknowledges in Question 3 of the Evaluation of the Drinking Water Quality section of the PHA that we are unable to evaluate the public health risks involved in drinking water from rainfall catchment basins due to the lack of use and sampling data. ATSDR recommends in the Public Health Action Plan that the Puerto Rico Department of Health (PRDOH) or the Puerto Rico Environmental Quality Board (PREQB) identify where collection systems are being used and perform sampling to evaluate if these systems deliver tap water that is safe to drink. Further, if the storage tanks associated with these collection systems contain bottom sediments, it is recommended that those sediments be sampled to provide an indication of potential past water quality.

    The potential for contaminants from the LIA to travel through the air and be deposited in rain water catchment systems is being assessed and will be discussed in the focused air pathway document.

  4. Comment: Two commentators criticized the PHA for failing to take into consideration potential sources of water pollution from the Naval Ammunition Support Division (NASD) at the western end of Vieques. One commentator expressed particular frustration that this land has been transferred to Vieques Municipality subject to the restriction that no wells (including monitoring wells) may be established upon it. The commentator asserts that ammunition was burned and exploded on the NASD and cites a study performed by CH2MHILL as evidence that regions of the NASD are polluted above federal standards. The commentator acknowledges that CH2MHILL dismissed its findings for being below background levels for Vieques, but draws ATSDR's attention to the fact that CH2MHILL now admits that those background levels may need to be reevaluated. The commentator recognizes that ATSDR made a deliberate, disclaimed decision to confine the PHA to a discussion of potential contamination from the LIA and t hus to exclude the NASD from consideration. At the same time, however, the commentator states that ATSDR draws overly general conclusions about the safety of Vieques' drinking water from this restricted report.

    Response: ATSDR did review contaminant data collected on the former NASD. There is no evidence that the localized groundwater contaminants of that area have, or can migrate to areas of potential human exposure.

  5. Comment: One commentator criticized the PHA for failing to take into consideration potential sources of water pollution from the Atlantic Fleet Weapons Training Facility (AFWTF).

    Response: The LIA is part of AFWTF. As with the LIA there is also no hydrogeologic connectivity between the alluvial aquifers on AFWTF and those on the residential section of the island. Groundwater at AFWTF does not migrate to the west towards aquifers in the residential area for the same hydrogeologic and topographic reasons that the groundwater cannot move from the LIA towards the west. Groundwater at AFWTF, like the LIA, flows downhill north and south into the ocean or into isolated alluvial aquifers near Ensenada Honda.

    Several groundwater monitoring wells were drilled in the EMA near the residential area. Analyses of samples collected from those wells did not detect the presence of contaminants.

  6. Comment: One commentator criticized the PHA for failing to take into consideration potential sources of water pollution from the Eastern Maneuver Area (EMA), which is closer to populated areas of Vieques than the LIA. The commentator asserts that ammunition was stored and discharged there and that Agent Orange was used there as part of training exercises.

    Response: Potential sources of contamination from the EMA were considered for their influence on the nearby aquifers. The only drinking water source (former) in the EMA is the Navy Well 14. Two monitoring wells are also located in the EMA alluvial deposits. These three wells were tested for components of Agent Orange (2,4,5-T and 2,4-D, see Herbicides in Appendix C). No detections were found (see Table 3). These negative findings and the hydrogeology of the area which shows that groundwater does not flow in the direction of the communities indicate that groundwater wells are safe drinking water sources with respect to potential past use of the EMA for Agent Orange.

Contaminants of Concern
  1. Comment: One commentator argues that since most of the bombs used by the Navy were non-explosive, ATSDR should concentrate more on looking for residues of rocket fuels and propellants. In particular, the commentator suggests that further testing be done for ammonium perchlorate. The commentator notes that only one of the four sets of laboratory tests cited in Appendix C of the PHA checked for this chemical.

    Response: Rockets are designed to burn the propellants they contain, leaving very trace amounts of residual chemicals. Therefore, it is not expected that propellant residues would accumulate in large amounts. The Navy provided compositional information on the two kinds of rockets that are used on Vieques. The propellants mainly contain nitrocellulose and nitroglycerin (89.6% and 87.24% combined). Ammonium perchlorate is used in air to surface rockets.

    • Nitrocellulose was not sampled in any of the water wells or tanks. However, it is not a chemical expected to cause harmful health effects if found in the water because the available studies indicate that ingestion of nitrocellulose does not result in adverse health effects unless ingested in enormous quantities (e.g., ingestion of 10% nitrocellulose of the total diet caused animals to die from intestinal obstruction; EPA 1992).
    • In August 1999, nitroglycerin was sampled in water from 11 monitoring wells along EMA's western border, a former drinking water well in Camp Garcia (Navy Well 14), a former supply well in the NASD (Navy Well 17), and the NASD tank. It was never detected.
    • Ammonium perchlorate has been detected (at 0.123 ppb) in only one of 37 surface soil samples on or near the on the LIA in the soils. It is not known, but is not likely that ammonium perchlorate is in the groundwater directly below the LIA. It was, as noted by the commentator, tested for in one of the rounds of groundwater testing. It was not detected in any of the wells in the EMA. In addition, as stated before, groundwater does not flow from the LIA or EMA to groundwater wells in the communities.
  2. Comment: One commentator faults ATSDR for failing to furnish a complete list of the chemicals used for Naval ammunition at Vieques. Furnishing an example of a substance that ATSDR has not taken into consideration, the commentator asserts that in 1992 the Navy used napalm at Vieques. The commentator presses ATSDR to either provide a new list of chemicals that can be certified as complete or clearly state that it was unable to generate a complete list of the chemicals used as ammunition at Vieques.

    Response: Several factors were taken into consideration in assessing the drinking water issues on Vieques. The multitude of individual chemicals of various chemical classes (see Appendix C) for which water samples were tested and the low levels and low numbers of detections that were found show that excessive contamination has not reached the groundwater (see Tables 4 and 5). The explosive compounds tested for cover a large range of munition types. ATSDR considers the list of explosive compounds that were used for the majority of training exercises to be adequate for assessing the groundwater issues at Vieques.

    ATSDR is aware of napalm use on the LIA in 1992. Napalm is basically a mixture of gelled gasoline that burns and leaves little specifically traceable residue. One group of residues that might be left by the burning of napalm are polynuclear aromatic hydrocarbons (PAHs), which are listed under Semi-volatile Organic Compounds in Appendix C. The presence of PAHs could be from many sources, including a residue of burned napalm; however, PAHs were not detected in any of the groundwater supplies tested.

Multiple Chemical/Multiple Pathway Exposure
  1. Comment: Two commentators criticize ATSDR's practice of separately analyzing human health risks from different exposure pathways. The commentators are concerned about an imagined scenario in which ATSDR would find that human exposures to a particular chemical were within safe levels for individual pathways but would fail to notice that combined exposure from all pathways exceeded safe levels.

    Response: The entire public health assessment process is lengthy, especially when addressing complex environmental issues. ATSDR is evaluating each exposure pathway separately to be most responsive to the petitioner and the people of Vieques.

    After all the individual focused PHAs are completed, ATSDR will prepare a short summary of all health issues we have evaluated at Vieques. This summary will consider whether overall exposures to environmental contaminants pose a public health hazard, rather than focusing on exposures through just one medium.

  2. Comment: Two commentators are concerned that ATSDR would not take into account the combined or even synergistic effects of different chemicals that residents of Vieques might be exposed to. The commentators are concerned about an imagined scenario in which ATSDR would find that human exposures to individual chemicals were all within the safe levels established for those chemicals but would fail to notice that the additive or synergistic effect of all those chemicals was hazardous.

    Response: Most of the literature on the effects of mixtures focuses on relatively HIGH exposures that may produce results such as synergism and non-competitive inhibition. However, concentrations far in excess of typical environmental concentrations are generally required to produce such effects.

    Several studies conducted under the auspices of the National Toxicology Program (NTP) in the U.S. and the TNO Nutrition and Food Research Institute in the Netherlands, among others (For reviews, see Seed et al. 1995; Feron et al. 1993.) generally support the conclusion that exposure to a mixture of chemicals is unlikely to produce any adverse health effects as long as the components of that mixture are present at levels well below their respective No-Observed-Adverse-Effect-Levels (NOAELs; i.e., at concentrations that would have produced no adverse effects in animals separately treated with the component chemicals individually). This observation appears to hold whether the component chemicals affect the same or different target organ(s) via different mechanisms (i.e., the situations that generally pertain to typical environmental mixtures). Even chemicals with the same or similar modes of action apparently exhibit neither synergism nor additivity, as long as the levels of exposure are well below the r espective NOAELs of the component chemicals. This scenario fits the levels of chemicals found in drinking water and groundwater on Vieques.

Sampling Issues
  1. Comment: Five commentators expressed the opinion that ATSDR is remiss in failing to generate its own data to supplement those which it collected from published sources. One commentator suggested that ATSDR should have sampled water from the actual wells that are used in emergency circumstances. Another commentator suggested that ATSDR has unduly restricted the scope of its data selection process and argued that it must supplement its research with additional new data in order to construct meaningful conclusions. One of these commentators acknowledged that this state of affairs is not the result of any conscious decision by ATSDR officials, but rather of their lack of power and legislative authority.

    Response: ATSDR reviews all existing environmental data and exposure information that is available when drawing its conclusions and making its recommendations about public health. ATSDR considers the quality and extent of the existing information about the groundwater, the public drinking water system, and the hydrogeological findings, to be sufficient to support the public health decisions discussed in the document.

  2. Comment: Two commentators scoffed at ATSDR's request that the Navy conduct soil sampling for a future evaluation air exposure pathways. One commentator assured ATSDR that the people of Vieques will not trust data generated under the Navy's auspices. Another wonders why ATSDR didn't chose a neutral party to conduct the sampling.

    Response: ATSDR requested that the Navy sample soil on the LIA to aid in the air exposure pathway evaluation because it is the Navy's land and responsibility, the Navy is most equipped to safely obtain samples considering the safety issues of unexploded ordnance, and the time frame between training exercises was short. ATSDR was fully involved in designing the sampling plan. The sampling plan was designed using the number of samples, sample locations, and types of chemical analyses that ATSDR requested.

  3. Comment: Two commentators criticized ATSDR for failing to cite environmental research conducted by certain Puerto Rican researchers. One commentator suggested that ATSDR invite Puerto Rican scientists to assist in developing the PHAs.

    Response: ATSDR makes every attempt to evaluate relevant environmental research whenever possible. Much of the data evaluated in this document was provided by Puerto Rican agencies including PRDOH and PREQB. We have requested reports, documents and other relevant information from many sources. ATSDR spent several days in Puerto Rican libraries to obtain the most relevant reports that may not have been in general circulation.

  1. Comment: One commentator asserted that the groundwater around Vieques has never had an adequate test for explosives. The commentator was perplexed that one of the PHA's "actions planned" is to sample the Sun Bay wells before these wells are used in an emergency. The commentator reminded ATSDR that an emergency could necessitate the immediate use of these wells at any time--there would be no time for the sampling that ATSDR recommends. If one admits that the wells should be sampled before use, and one recognizes that the wells could be required at any moment, one is driven to the conclusion that they should be sampled immediately, not in the indefinite future.

    Response: After evaluating specific drinking water data as well as data from nearby monitoring wells, ATSDR believes that the emergency wells are safe for use in the case of emergencies. Many issues must be considered when a closed well is used for emergency supply. Wells that are not routinely used should be pumped out before water is used. Appropriate local authorities should be involved before emergency supplies are used. In addition, since time has passed from the last testing, ATSDR feels that a prudent public health action would be to evaluate the wells for water quality before use. As an advisory agency, ATSDR works with and provides recommendations to other responsible parties or agencies to ensure that measures protective of public health, such as testing, are taken. However, because ATSDR works in a non-regulatory capacity, we lack the authority to enforce these actions.

  2. Comment: One commentator inquired after the specific standards that were used for explosives. The commentator also noted that although EPA has standards for several explosives, it does not have an approved laboratory method for sampling.

    Response: The health guidance values (i.e., standards) used to compare calculated doses are ATSDR's minimal risk levels and EPA Region III's Reference Doses. EPA Region III's cancer slope factors were used to estimate whether carcinogenic explosives were detected at levels of health concern.

    Explosive compounds were analyzed by an EPA contract laboratory using SW-846, method 8330 "Nitroaromatics and Nitroamines by High Performance Liquid Chromatography." This method is approved under EPA's Hazardous Waste Program in the Office of Solid Waste.

  3. Comment: One commentator inquired after the results of PRDOH's 1999 sampling for explosives and asked if explosives had ever been detected since 1978.

    Response: In June 1999, PRDOH sampled for explosives in four public water supply tanks and one tap connected to the public water supply (PRDOH 1999). All of the results were below detection limits. Explosives have not been detected in any of the water samples taken since 1978.

  4. Comment: One commentator wondered about the objectives of the agencies conducting the various tests and whether they were consistent with each other.

    Response: The following describes the various objectives of the agencies who conducted sampling on Vieques, if the objectives were stated in the referenced reports:

    • In 1995, PRDOH conducted groundwater sampling at the Sun Bay wells and B wells (PRDOH 1995a, 1995b). No objectives for this sampling are noted.
    • USGS sampled five wells in the NASD during rehabilitation activities in 1996, to acquire a representative groundwater sample of the Resolucion aquifer (USGS 1997).
    • PRDOH sampled for explosive residues in supply and distribution tanks and a local tap in 1999 because they were aware of a study by Rafael Cruz Perez, Contamination Produced by Explosions and Explosive Residues in Vieques, Puerto Rico, that mentioned the possibility of explosive contamination and knew that explosive residues were not regulated in potable water (PRDOH 1999).
    • The Navy's contractor installed and sampled monitoring wells along EMA's western boundary in 1999, to determine if the groundwater contains explosive compounds, assess if there is a potential for the compounds to migrate off-site, evaluate the groundwater flow direction in this area, and assess the risk posed to potential receptors if explosives were found (CH2MHILL and Baker 1999).
    • In 1999, EPA and the Navy's contractor performed split sampling at the NASD distribution tank, a former supply well in the NASD, and a former drinking water well in Camp Garcia as part of the groundwater sampling efforts (Baker 1999). No objectives for this sampling are noted.
    • EPA sampled potable water supply and distribution tanks, the Sun Bay wells, and private and public wells in 1999, to determine the overall quality of the water and the level of certain contaminants because various parties raised concerns that explosive residuals were potentially contaminating the water supply (EPA 1999b). They re-sampled in 2000, because the explosives data from the 1999 sampling was determined by EPA to be unusable (EPA 2000).

    Although the various sets of data may have been collected by the individual agencies with slightly different objectives in mind, the overall data set provides appropriate information for ATSDR's public health evaluation.

Water Use
  1. Comment: One commentator noted that the Water Authority of Puerto Rico plans to construct a reservoir from the mainland river that supplies Vieques' water. This improvement would improve the piped water supply on Vieques and ensure that well water would only be needed during severe drought or emergencies.

    Response: Thank you for the information. ATSDR understands that the reliability of the public water supply is of concern to the residents of Vieques. This advancement should greatly improve the dependability of the public water system.

  2. Comment: One commentator noted that he never saw a rainfall collection system in use. He also notes that between 1965 and 1967, most potable water in Camp Garcia came from the NASD on the west end of the island.

    Response: Thank you for the information.

  3. Comment: One commentator warned that if the water supply from Puerto Rico were disrupted, the water in the transmission pipe would be exhausted in about 5 days and it could take months more to restore water flow.

    Response: Compania de Aquas, a company hired by the Puerto Rico Aqueduct and Sewer Authority (PRASA) to maintain and operate the pubic water supply system, is responsible for distributing drinking water to the residents of Vieques. Any concerns surrounding the operation of the public water supply system should be brought to their attention.

Sun Bay Wells
  1. Comment: Two commentators denied that ATSDR has addressed the concern of the original petitioner, Gordon Rumore Ferris, that the wells in the Sun Bay area may be contaminated. Both commentators insisted that the only acceptable way to address this question is to directly measure the quality of the water in those wells. They furthermore noted that no reliable sampling for explosive residues has taken place at these wells. They argue that for public health purposes, it is unacceptable to rely on conclusions about these wells that were made indirectly--that is, by extrapolating from observations made elsewhere. One commentator urged ATSDR to retract its statement that the wells do not pose a health hazard and arrange to have the Sun Bay wells tested immediately for explosive contamination.

    Response: The Sun Bay wells have been extensively sampled by PRDOH and EPA. In May 1995, PRDOH directly measured the quality of the water for inorganics, metals, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), pesticides, herbicides, and polychlorinated biphenyls (PCBs) [PRDOH 1995a]. In addition, EPA tested water from the Sun Bay wells in September 1999, for inorganics, metals, VOCs, SVOCs, and explosive residues; however, the explosives data were later determined by EPA to be unusable(1) (EPA 1999b). When EPA returned to Vieques in January 2000 to re-sample the Sun Bay wells for explosive residues, they were unable to "because they had been closed by PRASA" (EPA 2000). None of the chemicals reported to be present in the Sun Bay wells were detected at levels of health concern.

    Despite the lack of valid explosive residue data for the Sun Bay wells, ATSDR can make justifiable health decisions concerning the use of the Sun Bay wells in the event of an emergency. ATSDR does not expect explosive compounds to be detected at levels of health concern in the Sun Bay wells for the following reasons:

    • Explosives are designed to be consumed by the explosion and; therefore, are not expected to be released in large quantities.
    • There is no hydrogeologic connectivity between the Sun Bay wells and the groundwater at the LIA.
    • The sampling data establishes that there is no indication that explosive residues would be detected in any of the wells on Vieques. Explosive residues were sampled in water from fifteen wells (11 monitoring wells along EMA's western border, Well 2-3 in Martineau, and Well 3-7 in Proyecto Barracon, Navy Well 17 in the NASD, and Navy Well 14 in Camp Garcia) on Vieques, three of which are located in the same aquifer as the Sun Bay wells. Explosive residues were not detected in any of these wells.
  2. Comment: Two commentators found the circumstances surrounding EPA's September 1999 sampling of the Sun Bay wells to be mysterious. One commentator was baffled by the absence of any explanation in the PHA of why EPA suppressed its own results as unusable. Another commentator suggested that it was an extremely suspicious coincidence that the wells were closed (precluding further testing) shortly after these suppressed testing results. This commentator further asserts that the report of the September 1999 testing indicates that it underestimated explosive concentrations..

    Response: After EPA received and reviewed the complete data package from the contract laboratory, they determined that the explosive residue data were unusable because ten of the 15 samples tested for explosive residues did not meet the surrogate recovery specifications (e.g, the surrogate recoveries were below the 50% quality control criteria). In addition, an eleventh sample exceeded the allowable seven day holding time (EPA 1999c).

    Because exceedances of the surrogate recovery specifications indicate an increased potential for low bias, EPA re-sampled for explosive residues in January 2000 (except the Sun Bay wells could not be re-sampled, see comment 27 above). This data were determined to be usable and no explosive residues were detected.

    ATSDR does not know the rationale PRASA used for closing the Sun Bay wells.

  3. Comment: Two commentators expressed guarded skepticism that EPA exercised due diligence in its January 2000 attempts to re-sample the closed Sun Bay wells. One commentator noted that the well covers can be easily removed for purposes of either sampling the water or (in emergencies) consuming it. The other commentator noted that the PHA makes no statement of the level of effort with which EPA sought to gain access to the closed wells.

    Response: EPA explained that PRASA had planned on closing the Sun Bay wells prior to EPA's 1999 sampling. Under EPA's urging, PRASA did not close the wells until after EPA sampled. Neither agency expected that the Sun Bay wells would need to be re-sampled and when EPA returned in 2000, PRASA had already closed the wells (EPA Life Scientist; personal communication; October 9, 2001).

  4. Comment: One commentator insisted that both the 1978 and the September 1999 EPA sampling data indicate that the Esperanza groundwater supply is contaminated. The commentator cites a January 2000 statement made by EPA (in RCRA-02-2000-7301) that a human exposure pathway may exist via the emergency use of public wells.

    Response: Groundwater in the Esperanza valley was not sampled in 1978; therefore, this sampling event cannot indicate that the Esperanza groundwater supply is contaminated. In 1999, EPA sampled water from the three Sun Bay wells, which are located in the Esperanza valley aquifer (EPA 1999b). None of the chemicals were detected at a level of health concern.

    Even if a human exposure pathway exists for drinking water from public wells, exposure does not always result in harmful health effects. The type and severity of health effects that occur in an individual from contact with a contaminant depend on the exposure concentration (how much) and the frequency and/or duration of exposure (how long). ATSDR accounts for these parameters, using high-end exposure level estimates as the basis when evaluating whether harmful health effects are possible. Through a comprehensive evaluation, ATSDR concludes that the levels of chemicals detected in the Sun Bay wells were too low to be of health concern and are therefore, safe to use in emergency situations.

Other Wells
  1. Comment: One commentator (EPA Region 2) states that neither the Peterson (Well 3-7) nor the Martineau well (Well 2-3) should be used for drinking water, even during emergencies. One of the commentator's concerns about these wells is that they are inadequately protected from surface runoff. Therefore, they risk contamination with bacteria, nitrites, and nitrates. EPA recommends that they be permanently closed. EPA inquires whether the PHA's "Well 2-3" is the same as EPA's "Martineau Well." If the two labels are one and the same, then EPA strongly disagrees with ATSDR's conclusion that the well is safe to drink from.

    Response: ATSDR focused the public health evaluation on the chemistry of the water in Peterson and Martineau wells, rather than on the wells' construction. Thank you for bringing the condition of the wells to our attention. ATSDR was unaware of EPA's recommendation to permanently close Peterson and Martineau wells. In light of EPA's concerns, ATSDR agrees that the construction of the wells may be inadequate to protect the water from future surface contamination.

    Well 2-3 is USGS's well identification for the Martineau well.

  2. Comment: Two commentators disagreed with the PHA's conclusion that the elevated "nitrate+nitrite" levels in Well 3-7 are a result of runoff from agricultural pollution. The commentators denied that the PHA provided any real justification for this conclusion and believed that it was made arbitrarily. One commentator stated that 7,000 pounds of "drone fuel" (a mixture of nitric acid and mixed amine fuel #4) were disposed of near Building 422 of the NASD. The commentator stated that the PHA ignores the existence of drone fuel contamination, suggesting that a fuel spill, perhaps, is responsible for the contamination of Well 3-7.

    Response: ATSDR concluded that the elevated levels of nitrate plus nitrite in Well 3-7 are most likely the result of agricultural pollution because of the following reasons:

    • Hydrogeologically, the groundwater from the LIA cannot migrate west into Well 3-7; therefore, the bombing at the LIA cannot be the source of the contamination via the groundwater pathway.
    • Finding elevated levels of nitrate plus nitrite in Well 3-7 only and not in any of the other 14 wells that were sampled indicates a localized source of contamination (e.g., agriculture) rather than a source that would contaminate all the wells (e.g., aerial deposition from bombing at the LIA).
    • Well 3-7 is located in the weathered bedrock on the eastern side of the residential area (see Figure 5). Any groundwater contaminated from a fuel spill in the NASD cannot migrate several miles east from the NASD into Well 3-7 because of the hydrogeology and topography of the island.
  3. Comment: One commentator stated the following:

    In September 1999, di(2-ethylhexyl)phthalate was found at levels above federal standards at the Peterson well. This chemical is commonly found in plastics but can also come from explosive compounds. EPA assumes the chemical was not actually present in the well but, rather, was introduced into the sample over course of lab handling. It is true that phthalates are often accidentally introduced into samples being tested for semi-volatile organics. However, if the sample was to be tested for phthalates themselves, the laboratory protocols would have specified strict precautions to avoid contamination.

    In November 9, 1999, a report of EPA's Drinking Water Section recommended retesting to settle the question of whether the phthalates detected were present in the well or were introduced in the lab. However, no mention of this recommendation is made in EPA's January 20, 2000 summary report for the testing. A new, "reviewed" version of the original lab report was issued that eliminates all discussion of di(2-ethylhexyl) phthalate. EPA made an arbitrary and unjustified decision to discard the testing results for this compound.

    Response: EPA did not re-sample for di(2-ethylhexyl)phthalate because the low levels that were detected were not at a level of concern; therefore, EPA decided that di(2-ethylhexyl)phthalate did not need to be re-tested (EPA Life Scientist; personal communication; October 9, 2001).

  4. Comment: One commentator noticed that the PHA admits that water from small, unnamed alluvial deposits is being used. The commentator was concerned that no testing has been done to verify that these alluvial deposits are not harboring pockets of contamination.

    Response: In 1995, USGS identified 73 wells on Vieques; only one of which is located in the small, unnamed alluvial deposits (Cherry and Ramos 1995). It is a hand-dug well in Camp Garcia that is no longer in use; therefore, no one is drinking water from these unnamed alluvial deposits. As a reminder, ATSDR's PHAs are exposure (i.e., contact) driven. A release of a contaminant in the groundwater does not always result in harmful human exposure. If no one comes into contact with any potential contamination present, then there is no exposure and no health effects could occur.

  5. Comment: One commentator was dismayed that the PHA states that drinking water from the four B wells poses no public health hazard, given that none of these wells have been sampled for explosive compounds.

    Response: The B wells are located in the same aquifer and in close proximity to the Sun Bay wells. In May 1995, PRDOH sampled the water from the B wells for inorganics, metals, VOCs, SVOCs, pesticides, herbicides, and PCBs (PRDOH 1995b). Despite the lack of valid explosive residue data from the B wells, ATSDR can still make justifiable health decisions concerning the use of the wells in the event of an emergency. ATSDR does not expect explosive compounds to be detected at levels of health concern in the B wells for the same reasons we do not expect explosive compounds to be detected at levels of health concern in the Sun Bay wells (see comment 27).

Agree With Conclusions
  1. Comment: One commentator felt that the PHA accurately conveyed the fact that the Navy's activities do not hurt Vieques' drinking water supplies and/or groundwater.

    Response: Thank you for your acknowledgment.

  2. Comment: One commentator (PRDOH) indicated that, except as specifically noted elsewhere, the data cited in the PHA agrees with the data that the commentator has on record.
  3. Response: Thank you for your acknowledgment.

  4. Comment: One commentator downplayed the notion that the Navy's military operations has had an adverse effect on the civilian population of Vieques. The commentator admitted that Camp Garcia periodically spilled fuels (e.g., "AV Gas, Mogas, JP. 4") but he did not believe that these spills took place at a magnitude sufficient to contaminate local groundwater. The commentator cautioned, however, that unexploded ordnance on the bombing/firing range is a serious hazard for protesters.

    Response: ATSDR agrees with your concern about unexploded ordnance on the bombing/firing range and the safety of anyone entering the LIA. Fortunately, no accidents involving unexploded ordnance have been reported.

Disagree With Conclusions
  1. Comment: One commentator did not believe that ATSDR made a serious effort at fulfilling its legally mandated responsibility to protect public health.

    Response: As discussed in the PHA, ATSDR's primary goal in the health assessment process is to put possible exposure to environmental contaminants into meaningful perspective for the public. In doing so, ATSDR strives to explain whether people are being exposed to harmful substances and, if so, whether the exposure may cause harm. For a more detailed discussion on ATSDR's mandate please see the "Foreword" of the PHA.

  2. Comment: One commentator found it impossible to accept the notion that the dust kicked up on the LIA could not have contaminated wells. If the wells were safe, the commentator reasoned, the residents of Vieques would not have been forbidden to use the public wells when their regular water supply failed for a week in mid-February, 2001.

    Response: ATSDR was able to conclude whether drinking the public water or the groundwater was of health concern based on an examination of sampling data at the point of exposure. The sampling data do not indicate that bombing at the LIA has contaminated groundwater wells. To complement the drinking water supplies and groundwater pathway evaluation, ATSDR is addressing the transport of wind-blown dust generated from bombing at the LIA in a focused PHA pertaining to inhalation of air and dust.

  3. Comment: One commentator believed the PHA's conclusion is incorrect and that contaminants are migrating from the LIA to the populated center of the island. The commentator also criticized the PHA for failing to follow the scientific method.

    Response: ATSDR based its conclusions on defendable hydrogeologic and topographic information that show that contaminants cannot migrate from the LIA to the residential section of the island through the groundwater pathway. ATSDR's assessment of potential contamination of groundwater and drinking water supplies in Vieques is based on information presented in environmental investigation documents by USGS and the Navy's contractor in addition to other sampling data by EPA, PRDOH, USGS, and the Navy's contractor. Collectively, the environmental information indicates that the extent of migration is limited because of the hydrogeology and topography of Vieques. In addition, the sampling data indicate that contamination has not migrated with groundwater beyond the Navy's border. Together, these factors provide compelling evidence that contamination has not reached the residential areas.

  4. Comment: One commentator states that she/he would like to be able to tell the citizens of Vieques that their water is uncontaminated, but unfortunately the available data support the opposite conclusion.

    Response: ATSDR disagrees that the available data support a conclusion opposite to the ones we established in the PHA.

  5. Comment: One commentator accuses ATSDR of purposefully failing to draw obvious logical connections between the presence of certain contaminants in well water and their presence on Navy land. As evidence that there is some transport of contaminants from eastern Vieques to the Resolucion aquifer, the commentator reminds ATSDR that the PHA noted the presence of trace quantities of benzene and toluene in Navy Well 17 (in the Resolucion aquifer). Even if these chemicals are present only at small levels, the commentator concluded, they still provide evidence that the LIA is not completely chemically separated from the rest of Vieques.

    Response: Benzene and toluene were detected in a former supply well in the Resolucion aquifer (Navy Well 17); however, neither was detected in the other 14 wells which were also tested for VOCs. This lack of detection elsewhere indicates that a localized source (perhaps a fuel spill) contaminated this well rather than a source that would contaminate all the wells.

Incomplete Evaluation
  1. Comment: Three commentators were outraged that ATSDR felt confident in offering paternalistic reassurances about the safety of Vieques' drinking water while simultaneously issuing disclaimers that in some respects their data might be incomplete. "If adequate scientific evidence was not available," wrote one commentator, "the conclusions should have been postponed." It seemed to one commentator as if ATSDR had started with the presumption that the community's health was not at risk until proven otherwise. This perceived stance came across as an insulting bias--as, perhaps, a sign of deliberate scorn for the people of Vieques.

    Response: When evaluating public health hazards, ATSDR prefers to use as much information as possible when assessing environmental exposures. However, sometimes data are limited, particularly for past exposure scenarios. With limited data, ATSDR uses the available information about site conditions and our best professional judgement to draw conclusions and make appropriate recommendations. Following this approach, we had sufficient information to address the central question of whether residents of Vieques are being exposed to harmful levels of contaminants in their drinking water and groundwater supplies.

    ATSDR wants to reassure the reader that we based our public health decisions on the best available scientific evidence, and with great consideration to the concerns voiced by the people of Vieques. ATSDR's primary goal is to identify possible site-specific exposures to environmental contaminants and determine their probable implication for the Vieques' community. Because our public health assessments are exposure driven, we first identify whether residents of the island have contacted or could come into contact with harmful substances. Part of the challenge we face in doing this is explaining to the community that while contaminants may exist in the environment, exposures are only possible if people actually come in contact with contaminated media. If you have specific concerns that prompted these comments, ATSDR is available to further explain the basis of its public health conclusions.

  2. Comment: One commentator acknowledged that the PHA was completed under time pressure and that it is tightly focused. Nevertheless, the commentator felt that the PHA fell short of its goals. It inspires little confidence in the reader when it states the obvious: that water piped in from Puerto Rico is safe to drink. When confronted with potentially contaminated water, ATSDR either:

    a) says it is safe without adequate justification;
    b) says it is polluted but assumes, without justification, that its pollution is unrelated to explosives (Well 3-7); or
    c) ignores the question of whether or not it is safe because of a lack of data (rainfall collection systems).

    Response: The public water supply system was evaluated by ATSDR because there were concerns that the bombing at the LIA could potentially affect this system. In 1978, an environmental consultant hired by the Government of Puerto Rico demonstrated that air was being sucked into the public water storage tanks (EPA 1999a). In addition, EPA sampled potable water supply and distribution tanks in 1999 because various parties raised concerns that explosive residuals were potentially contaminating the water supply (EPA 1999b). Therefore, to dismiss these concerns without a full evaluation because it seems obvious that water piped in from Puerto Rico is safe to drink, would not have met ATSDR's goal of addressing the environmental health concerns of the residents.

    ATSDR strongly affirms that adequate justification for the conclusions we draw are presented in the PHA.

    Specific issues in this comment are addressed throughout the responses to comments.

  3. Comment: One commentator said that the PHA needs to distinguish which conclusions can be drawn and, more importantly, which conclusions cannot be drawn from the information presented. Right now, people might be misled into concluding, from reading the PHA, that their water supplies are not affected by explosive-related contamination. Considering that the Sun Bay wells have not been tested for explosives, this is an unjustified conclusion.

    Response: Based upon a thorough evaluation of the available sampling data, there is no evidence that water supplies are being affected by explosive-related contamination. In addition, the hydrogeologic and topographic information indicates that contaminants cannot migrate from the LIA to the residential section of the island through the groundwater pathway.

    Despite the lack of valid explosive residue data for the Sun Bay wells, ATSDR can make justifiable health decisions concerning the use of the Sun Bay wells in the event of an emergency. ATSDR does not expect explosive compounds to be detected at levels of health concern in the Sun Bay wells for the reasons outlined in the response to comment 27.

  4. Comment: One commentator criticized the PHA for extrapolating the results of tested wells to untested wells. The commentator stated that the PHA was based on only a limited sample of the wells on Vieques (only 18 out of 73 were tested). Furthermore, there is no reason to believe that those 18 are representative of the rest. A 1991 USGS survey stated that 4 wells on Vieques were then being used for drinking water. EPA analyzed only one of these. How can ATSDR generalize from one to the other three?

    Response: It is true that 73 wells have been identified on Vieques (Cherry and Ramos 1995). However, according to the report, only seven of these wells were in use: one was used agriculturally to water livestock (Well 2-2), four were used for drinking water and other domestic purposes (Wells 3-4, 3-5, 3-7, and 10-2), and two were used to supply public water to Camp Garcia personnel (Wells 11-14 and 11-17). The remaining wells were listed as not in use. Therefore, even though 73 wells may exist, no one is drinking water from the majority of them and, consequently, are not being exposed to any potential contamination.

    ATSDR focuses our public health evaluation on contamination of private wells that supply drinking water to the residents of Vieques. Therefore, the discussion in the PHA is centered on Wells 3-4, 3-5, 3-7, and 10-2. Of the four wells, Well 3-7 has been sampled and conclusions were drawn based upon the data.

    Wells 3-4, 3-5, and 10-2 are located in weathered bedrock to the west of the EMA. The only way for any contamination from the LIA to reach this area of the island is through aerial deposition; not groundwater flow. A PHA will be released to deal specifically with the air pathway; however, ATSDR based some of the conclusions in this PHA on the basic principle that aerial deposition will not have significant spatial variations at locations approximately 7-10 miles from the source (i.e., the amount of material falling from the air is expected to be relatively consistent across the residential area).

    To evaluate the likelihood that Wells 3-4, 3-5, and 10-2 are being contaminated by activities at the LIA, we looked at other wells located in the weathered bedrock. Nine monitoring wells, located in the weathered bedrock along EMA's western boundary, were sampled for explosives. Wells 2-3 and 3-7, also located in the weathered bedrock, were sampled for VOCs, SVOCs, inorganics, metals, and explosives. Of all of these chemicals sampled from these 11 wells, only nitrate plus nitrite was detected at a hazardous level in Well 3-7.

    Since we attribute the nitrate plus nitrite levels in Well 3-7 to local agricultural sources rather than bombing at the LIA (because of the reasons listed the response to comment 27) we would not automatically expect these levels to be in all the wells. Local sources might potentially contaminate any well. Therefore, ATSDR previously recommended that, when shallow drinking water wells are found in use, PRDOH or PREQB should sample the wells to assure that the water is safe to drink.

Geology and Hydrogeology
  1. Comment: One commentator remarked that the PHA claims that the Esperanza aquifer is not of high quality because it is contaminated with metals and total dissolved solids. While the PHA attributes this fact to circumstances of natural geography, the commentator attributes it to Naval activities on Vieques.

    Response: ATSDR believes that metals and total dissolved solids found in the groundwater are attributable to the natural geology and geography of Vieques. The groundwater evaluation conclusively indicates that groundwater at the LIA cannot travel west (upgradient and past a geologic barrier) into the residential area. Of more importance to ATSDR, and users of the drinking water wells, is that while metals and total dissolved solids were detected in the groundwater, the concentrations that are present were not at levels of health concern (except nitrate plus nitrite in Well 3-7).

  2. Comment: One commentator cited the fact that ATSDR omitted discussion of a CH2MHILL report that presents pollution in western Vieques in the PHA as evidence that ATSDR personnel lack the necessary expertise to competently evaluate public health at Vieques..

    Response: ATSDR reviewed evidence of groundwater contamination in the former NASD area (Navy 2000). Although information presented for that area does not fully characterize the extent of this contamination, there is not now and has not been in the past a potential pathway of human exposure to those contaminants.

  3. Comment: One commentator asks ATSDR to incorporate into the PHA a discussion of how pumping wells may disrupt the normal flow of groundwater. The commentator suggests that the fact that salt water has intruded into heavily pumped freshwater aquifers is evidence that wells may significantly alter the natural movement of groundwater. Furthermore, the commentator argues that it is inadequate to simply study the groundwater patterns that exist at present. One must also study the groundwater patterns that existed in the past, when groundwater pumping was more prevalent.

    Response: Pumping groundwater from wells does influence the flow of groundwater in the near well area. A production well has a radius of influence, within which groundwater levels are drawn down due to pumping. The radius of influence is a function of the well's design, operation, and surrounding aquifer parameters and can range from a few feet to more than a mile. Perhaps more importantly, when wells pumping from an aquifer draw out more water than is recharged by rainfall and other sources, the level of the whole aquifer drops.

    The fact that saltwater intruded into heavily pumped freshwater aquifers is evidence of aquifer drawdown, and is independent of the groundwater flow direction. Because of excess pumpage, the hydraulic head of the freshwater over the saltwater was reduced, allowing the freshwater/saltwater interface to move inland (Torres-Gonzalez 1989).

    The lack of comprehensive historical groundwater elevation data makes discussion of past groundwater flow direction speculative, especially considering how important secondary porosity (water contained in bedrock fractures and joints, which is difficult to model or characterize without exhaustive sets of data) is to the groundwater regime on Vieques. The most common way to characterize past groundwater movement is through numerical modeling. The USGS created such a model in 1989 (Torres-Gonzalez 1989). However, they were only able to create a steady-state model (i.e., one that pertained to the 1989 data set). Calibrating a transient model (i.e., one that would extrapolate groundwater levels over time) was precluded by limited data (Torres-Gonzalez 1989).

    Beyond the zone of the well's influence, the regional patterns of groundwater flow are not altered. Thus, the pumping rate and history of the large public wells located in aquifers isolated from the sources of contamination are not factors that determine past pathways of contaminant migration.

  4. Comment: One commentator disputes the PHA's conclusion that a geological barrier prevents water movement between the groundwater near the LIA and groundwater in the Esperanza alluvial valley. The commentator cites CH2MHILL and Baker's 1999 study, which shows that water moves southwest (not south) from the region that ATSDR considers to be a barrier, potentially contaminating the Sun Bay wells west of Puerto Ferro.

    Response: CH2MHILL and Baker's study does show south and southwest moving groundwater flow originating from the southwest side of the groundwater barrier. Groundwater flow is also shown as heading northeast and east from the northeast side of the groundwater barrier. However, the LIA is over six miles east of this groundwater divide. As such, groundwater originating to the east of the groundwater divide will not flow upgradient to the west and; therefore, cannot flow towards any wells west of the divide (CH2MHILL and Baker 1999). Groundwater in unconfined aquifers does not flow uphill.

  5. Comment: One commentator notes that military debris at LIA is never removed from the site. Rather, it is simply bombed over or buried, creating a potential for groundwater contamination.

    Response: Despite any source of contamination, groundwater at the LIA is hydrogeologically isolated from aquifers in the residential area of the island and therefore, cannot affect the quality of the groundwater in the residential area (see also response to comment 51).

  6. Comment: One commentator disputes the adequacy of CH2MHILL and Baker's hydrogeology study, on a variety of grounds:

    • CH2MHILL and Baker gives no justification for their choice of the western boundary of the Eastern Maneuver Area as its focus of groundwater sampling.

    Response: CH2MHILL and Baker explain their choice of the western boundary of the EMA as its focus of groundwater sampling in Section 1.1 "Purpose and Objectives of the Field Investigations" and Section 3.2.1 "Groundwater Investigation - Investigation Rationale" (CH2MHILL and Baker 1999). The purpose was to determine whether explosive compounds were present and if they were moving off site from on-site sources of contamination. In other words, they were looking for contamination flowing over the boundary. Therefore, they needed to test for contaminants at the boundary and determine the flow direction at the boundary.

    • Soil samples were taken only of the first 6 inches of soil, well above the level of any aquifers. Water samples were only taken from the bottom of aquifers, well below the level at which contamination would likely be manifested. Instead of conducting such limited sampling, CH2MHILL and Baker should have systematically sampled water and soil, at different depths but at a geographic single location.

    Response: According to section 3.1.1 "Soils Investigation - Investigation Rationale," the goal of the surface soil investigation was to determine whether or not surface water runoff and transport through air dispersion was carrying contaminants off site (CH2MHILL and Baker 1999). Drilling of boreholes, and collecting and testing subsurface soil samples would not have addressed this goal. If surface soil has not been contaminated, then soil beneath it could not have been contaminated from a surface source.

    Wells installed in the bedrock were drilled to the depth at which water was first encountered. During well development at least three of the wells were bailed until dry. When groundwater elevations in some of these wells were later measured, they were much higher. However, when six of the wells were measured, the depth to water was within 15 feet of the top of the well screen. The sources of water for the bedrock wells were fractures and joints in the bedrock. Since these wells were installed in such a low-flow formation, all the water in the wells originated from a water bearing fracture. As such, the samples are not missing potentially contaminated water at a higher elevation. Additionally, two of the wells (NW-8 and RCRA-4) were specifically designed to allow sampling of the Esperanza Aquifer, where the groundwater elevation in both of the wells was measured within three feet of the top of the screen (CH2MHILL and Baker 1999).

    • Soil sampling was conducted in regions where there was no runoff from rain. It is unknown how the results from runoff areas may differ from these results.

    Response: Soil sampling was conducted near surface water runoff drains and monitoring wells (CH2MHILL and Baker 1999). These locations address two concerns--the presence of contaminants in surface water runoff and the connection of surface water infiltration to groundwater.

    • The operational wells constructed by PRASA had not been operating for a period exceeding 48 hours before they were tested by CH2MHILL and Baker. This lack of pre-operation means that the test results do not reflect the overall quality of the groundwater feeding each well but rather the quality of the groundwater which has colleted in immediate proximity to the well.

    Response: CH2MHILL and Baker did not collect any samples from PRASA wells (CH2MHILL and Baker 1999). Prior to collecting groundwater samples from its monitoring wells, CH2MHILL and Baker purged each well of at least three well volumes (except well NW-1, which had a low capacity, allowing only one well volume to be purged) to make certain that the water samples collected were representative of formation water, not stagnant water that had collected in the well casing.

    • CH2MHILL and Baker furnishes no evidence to assure residents that it has been comprehensive in its identification of all the different aquifers which may exist on Vieques.

    Response: CH2MHILL and Baker's approach of installing wells and testing along the EMA boundary addresses the question of whether or not groundwater contamination is migrating off site from an on-site source. CH2MHILL and Baker did not set out to identify all of the different aquifers on Vieques. The goal of the CH2MHILL and Baker investigation was to find out whether or not explosive-related chemical compounds were migrating from the Navy property off site towards the homes and wells of the residents of Vieques.

  7. Comment: One commentator argues that due to topologically variable patterns of dust fallout, rainfall, and soil permeability, contaminated dusts could generate highly localized pockets of chemical contamination. The commentator argues that this is a particularly serious problem because there are many small, discontinuous "micro-aquifers" on Vieques. Thus, the commentator implies, the chemical contamination of Vieques' groundwater may be so heterogenous that existing data are inadequate to support general statements about its safety.

    Response: While very complex scenarios cannot be completely ruled out, the public health assessment process protects against a wide range of potential threats using all the available information. Should new information become available that identifies locations of potential "micro-aquifer" contamination, the effect of that information on the current conclusions of the public health assessment can be evaluated. Additionally, the public health assessment for the air pathway will address the potential pathways associated with airborne dust.

Stop Bombing
  1. Comment: One commentator recommended that military exercises at Vieques be suspended pending a full and accurate health effects evaluation. The commentator reminded ATSDR that it is better to err on the side of caution than to err on the side of mediocrity and indifference.

    Response: During visits to Vieques and through a comprehensive evaluation of drinking water supplies and the groundwater pathway, ATSDR found no evidence of public health threats causing significant harm to the public's health that would require an immediate suspension of the bombing activities. If an acutely toxic situation were identified, ATSDR would have requested actions, including an immediate halt to the bombing, to protect public health. ATSDR is further evaluating other potential pathways of exposure (e.g., soil and air) through focused PHAs. If a harmful situation is identified in any of the pathways, ATSDR will request that the necessary steps be taken to protect public health.

Past Data Issues
  1. Comment: One commentator said that ATSDR overreaches itself when it makes claims to have evaluated the past impacts of Naval activities on public health. In fact, it has only gathered data about a portion of the period during which Navy has been at Vieques. Only one study, conducted in 1978, is available to represent conditions on Vieques prior to 1995. The commentator reminds ATSDR that the Navy took over Vieques property in 1941, targets were established in 1960, and Naval training exercises began in 1971. The commentator also reminds ATSDR that the 1978 study did find explosives in a drinking water well. Current data, the commentator argues, are insufficient to draw conclusions about the extent of past exposures. The current PHA cannot justifiably conclude that there have not been past exposures to explosive compounds in drinking water.

    Response: Prior to the late 1970s, little if any environmental monitoring occurred, owing largely to the absence of federal, state, or local environmental requirements. This problem is not specific to Vieques, but is a common concern at many sites throughout the world. One of the challenges we face is to evaluate public health hazards that may have occurred in the past, given the absence of adequate environmental monitoring. Where no historical data exist, we review available environmental and contaminant fate data and make assumptions about past exposure using our best professional judgement to draw conclusions regarding the likelihood of potential exposure to harmful levels of contaminants.

    ATSDR has stated in the document that very low levels of cyclotrimethylene trinitramine (RDX), methyl-2,4,6-trinitrophenylnitramine (tetryl), ammonia, and nitrate plus nitrite may have been present in drinking water samples taken by the Navy in 1978. The validity and utility of the data are uncertain because of the small numbers of samples collected and the description of the location or media represented by the samples. Regardless, the concentrations of explosive compounds reported in drinking water in the past were well below levels considered harmful to human health and any potential past exposure to these compounds would not have posed a public health hazard. Although activities occurred at the LIA prior to 1978, ATSDR's review of historical activities did not find indications that conditions would have been such that a greater potential for contamination of the groundwater existed at that time.

1978 Data
  1. Comment: One commentator complained that ATSDR only provided details about four of the samples taken in the 1978 Naval Surface Weapons Center Water Sampling Data (Hoffsommer and Glover 1978; Lai 1978), presumably on grounds that only these four samples represent drinking water. The commentator stated that ATSDR should furnish all the data because they will all be useful in characterizing the effects of the LIA activities on the environment.

    Response: Regardless of the presence or extent of contamination detected in environmental samples from the site, exposures are only possible if people drink or otherwise come in contact with the groundwater. That is why whenever possible, ATSDR uses data collected directly from drinking water sources, rather than data from bomb craters or lagoons not being used to supply drinking water. As we discuss in the PHA, no one uses groundwater drawn from beneath or immediately near the LIA. ATSDR believes that the contaminant levels detected in the four drinking water samples discussed in the PHA more accurately represent the water component supplied to and used by Vieques residents.

  2. Comment: Two commentators asserted that the 1978 Navy study found that the concentrations of man-made explosive compounds (e.g., RDX) present in drinking water sources near Isabel Segunda and Esperanza were essentially the same as those found in puddles on LIA. This finding undermines the PHA's thesis that contamination cannot migrate from the LIA to residential area of the island. The commentator emphasizes that the overall magnitude of these concentrations is not the issue of importance. The issue of importance is that these data provide evidence of transport mechanisms linking contamination at the LIA contamination elsewhere on Vieques.

    Response: Finding RDX in a public drinking water supply tank does not undermine our conclusion that contamination cannot migrate through the groundwater pathway from the LIA into the residential section. First, the public water is supplied from a river on the mainland of Puerto Rico. Second, a careful analysis of the hydrogeology and topography of Vieques conclusively shows that groundwater at the LIA cannot travel upgradient, past the groundwater divide, and into residential wells to the west. Therefore, the RDX detected(2) in the Isabel Segunda and Esperanza tanks did not migrate there through the groundwater pathway. ATSDR is addressing the issue of contaminants traveling from the LIA into the residential section of Vieques through the air in another focused PHA

    Contrary to the commentator's opinion that the magnitude of the concentration is not the important issue, ATSDR asserts that the chemical's concentration is a highly important factor in the public health assessment process. Looking at exposure by itself will not address the issue of whether that exposure will result in harmful health effects. The type and severity of health effects that occur in an individual from contact with a contaminant depend on the exposure concentration, the frequency and duration of exposure, and how the contaminant is absorbed, distributed, metabolized, and excreted.

  3. Comment: One commentator found it outrageous that ATSDR suggested that the nitrate plus nitrite levels in water samples from bomb craters could have come from agricultural sources. The commentator suggested that unless ATSDR furnishes convincing evidence for a counter-theory, it should presume the more obvious conclusion that these levels are the result of explosions.

    Response: ATSDR apologizes for the lack of clarity related to this comment. The paragraph has been revised in the PHA to more accurately state the intended focus on the drinking water samples. While it is possible that nitrate plus nitrite that is detected in water from a crater on a bombing range may indicate a source of explosives or residual compounds, nitrate may be present in the environment from a wide variety of sources and mechanisms. It is true that NO2 gas is one emission resulting from detonation of high explosives. It is also true that NO2 gas is a major component of the atmosphere. The NO2 gas in the atmosphere, regardless of its source, can be converted through natural processes to nitrate. This is just one of many explanations available for the presence of nitrate in pond water. Thus, measured levels of nitrate (or nitrite) cannot be considered conclusive evidence of the presence of explosives or explosive, especially in the residential area. Nitrate plus nitrite can also indicate other sources of contamination such as agricultural fertilizers.

  4. Comment: One commentator denied the PHA's claim that the only groundwater samples in the Esperanza aquifer available to characterize the potential for explosives contamination are the Navy wells that were sampled in 1999. The commentator claimed that the Esperanza aquifer data from both the 1978 and the 1999 EPA studies provide evidence of explosive contamination. In 1978, for example, small levels of RDX were found in the Esperanza groundwater supply and there has been no subsequent retesting to confirm or refute these findings.

    Response: The water sample taken from Esperanza in 1978 was from a public water supply tank, not of the Esperanza aquifer (Hoffsommer and Glover 1978; Lai 1978); therefore, this sample cannot provide evidence of explosive contamination in the groundwater. In 1999, EPA sampled for explosives in wells located in the Esperanza aquifer, however, the data were determined to be unusable (EPA 1999b). This does not imply that there was evidence of explosive contamination; no conclusions can be drawn from unusable data. There are three wells (a former supply well in Camp Garcia and two monitoring wells) located in the Esperanza aquifer that have recently been sampled for explosive residues and have not shown any evidence of explosive contamination (Baker 1999; CH2MHILL and Baker 1999).

Depleted Uranium
  1. Comment: Two commentators were concerned about the possibility of air pollution resulting from the use of depleted uranium (DU) ammunition at the LIA. One commentator hypothesized that radioactive bullets lying on the ground might be pulverized into dust by subsequent explosions. Another commentator noted that vapors are created when a bullet hits its target.

    Response: As explained in the PHA, two U.S. Marine Corps aircrafts fired 263 rounds of ammunition armed with DU penetrator projectiles on the LIA in February 1999. The Nuclear Regulatory Commission (NRC) conducted an environmental survey on Vieques in June 2000 to address the community's concern that DU could be transported from the LIA to the residential area (NRC 2000a, 2000b). The inspectors performed independent direct measurements of radiation levels and collected and analyzed environmental samples both inside and outside the LIA. NRC concluded that DU from the firing of DU penetrators into the LIA had not spread to the environment outside the LIA. In addition, the Navy has committed to the recovery of all detectable DU rounds from the LIA and has recovered 116 equivalent units as of September 2001.

    The possibility that some DU would be volatile is a legitimate concern. However, DU, like uranium, is extremely dense and would rapidly settle to the ground. If the material were to migrate the 7.9 miles from the LIA to the residential areas of the island, the concentration expected would be well below levels of uranium known to cause adverse health effects. Also, if the DU remaining in the impact area were to be impacted by other inert weapons, there would be no significant DU vapors produced as there is no excessive heat generated. The amount of DU injected into the atmosphere by those impacts would also settle rapidly.

  2. Comment: One commentator complained that the NRC report on DU use contained significant errors and omissions. The commentator:

    • Challenged NRC to justify its decision to limit its sampling to soil 6 inches or less below the surface. The commentator stated that there is no reason for believing that there are not DU bullets buried deeper in the soil.

    Response: People can receive a dose of environmental DU through internal and external exposures. Internal exposures can occur from inhalation of particles, direct ingestion of soil, ingestion of produce that contains DU from the soil, and drinking water containing DU. External exposure is usually very small because DU is less radioactive than natural uranium. The radiation from DU in soil through many of the internal and external routes is important only for DU near the surface; therefore, when addressing health concerns it is appropriate to measure the DU near the surface.

    There are two methods of DU entering the body that may require knowledge of DU below the surface: (1) plant uptake of DU through the roots and (2) DU in the groundwater. The uptake of DU by plants is partially accounted for by the surface concentration. In addition, NRC investigated plant uptake by collecting plant samples, thereby making deeper soil sampling unnecessary. DU in groundwater beneath the LIA is not of health concern because no one is drinking the groundwater beneath the LIA and the groundwater is hydrogeologically isolated from the residential section of Vieques. Therefore, collecting surface soil samples is adequate for addressing health concerns.

    • Regretted NRC's sampling method, which apparently involved pooling five 1-kilogram samples from a single sampling area. The commentator suggested that actual levels of radioactivity in a sampling area may be quite heterogenous and that the act of pooling samples may obscure detection of localized areas of significant radioactivity.

    Response: NRC sampled to characterize the DU concentration distributions and estimate dose from the DU concentrations. Dose estimates are made from average concentrations per unit area and the concentration distribution. Pooling samples to obtain the average concentration per unit area is an acceptable and recommended process, following guidance in the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM). The pooling of samples gives an estimate of the average concentration for the pooled samples, but also allows estimating the upper bound for a single sample. If it is assumed that the entire DU came from a single sample then the upper bound concentration for the samples is 5 times the average. Dose is estimated from the average contribution from the area represented by the samples, so the estimated dose is the same regardless of the DU distribution within the area.

    • Argued that the laboratory commissioned by NRC to detect DU used the wrong analytical methods. The commentator contended that the laboratory used alpha and gamma spectroscopy to when it should have used a technique known as ICP-MS.

    Response: Most laboratories can detect all uranium isotopes down to about 0.02 pCi per sample. This is usually sufficient to detect U-235 at the average natural background level. However, depleted uranium has much less U-235, so the accuracy of detection of additional U-235 would be poor. The interest is in concentrations of DU much higher than background levels. In depleted uranium the U-234 activity is about 10 times higher than U-235 activity. Therefore, alpha spectrometry is an adequate method to measure DU based on U-234 when U-235 is not well detected. ICP-MS can be used to differentiate the difference in the masses of the uranium. However, since we know DU was used, differential detection of the uranium isotopes is not required.

    • Stated that the NRC report lacks a section describing chain-of-custody or quality control procedures.

    Response: The cover letter for data transmittal from Dale Condra of ORISE to Jay Henson of NRC (August 24, 2000) states that all Quality Control procedures were followed for the analyses. The ORISE Quality Control requires completion of chain-of-custody. Since all Quality Control was completed at ORISE, by inference the chain-of-custody documentation was complete. The commentator should request chain-of-custody and sampling quality control from the NRC.

  3. Comment: One commentator denied that NRC report's hydrological observations were adequate to support the conclusions that ATSDR drew from them. The commentator stated that NRC presents no sampling data for groundwater or drinking water--only data for sediments and surface water. Furthermore, the commentator stated that none of the sediment and surface water sampling conducted took place at the LIA itself.

    Response: The NRC report establishes that DU has not migrated to the residential area through the air (NRC 2000a, 2000b). In addition, DU was not detected in the environment, except in the soil immediately surrounding the DU penetrator. This is not surprising since the density of DU is such that it is not expected to carry very far and will; therefore, settle close to its impact area. DU in the soil at the LIA could migrate into the groundwater at the LIA. However, groundwater at the LIA is isolated from the groundwater in the residential area; therefore, any potential DU contamination present could not affect the groundwater or drinking water on Vieques.

  4. Comment: One commentator suggested that ATSDR has been credulous in accepting that the only DU contamination at LIA is that which Navy has acknowledged was released in 1999. The commentator was puzzled that ATSDR does not take a more skeptical stance towards information provided by the Navy, at least until obtaining independent verification. The commentator asserted that the Navy erroneously supplied an entire aircraft carrier with DU ammunition and that DU contamination may therefore be greater than the Navy currently admits. Furthermore, the commentator claimed that Vieques residents are capable of distinguishing those bullet holes which are made by DU bullets and that residents started finding these special bullet holes in the LIA before 1999. The commentator denied that samples were taken from all of the "civil disobedience camps" present on the LIA.

    Response: NRC has regulatory authority over the use of DU on the LIA. The incident was reported to the NRC by the Navy and was investigated by the NRC. ATSDR reviewed the evaluations carried out by the NRC and believes that appropriate sampling methodology and analyses were carried out. If more widespread use of DU was carried out, evidence of it would have been discovered through the sampling efforts of the NRC.

Non-technical Comments
  1. Comment: Two commentators found the PHA to be well-written and informative. They offer their thanks to ATSDR for its efforts.

    Response: Thank you for your acknowledgment.

  2. Comment: Five commentators disparaged ATSDR and its PHA on a variety of grounds (unscientific, biased, inadequate, etc.). One commentator complained that the PHA was put together too hastily and did not involve any original research. Three commentators questioned whether ATSDR is capable of conducting an unbiased investigation of public health at Vieques. Two commentators expressed the opinion that ATSDR operates as a puppet of the Navy.

    Response: ATSDR is an independent public health agency in the Department of Health and Human Services. In evaluating potential public health hazards, ATSDR thoroughly reviews available environmental data. ATSDR reviews relevant material from a variety of sources for the exposure pathway of concern. For the drinking water supplies and groundwater evaluation, ATSDR based its conclusions and recommendations on available environmental data and exposure information provided by the Navy, EPA, PRDOH, and USGS. For a more detailed discussion on our process, please refer to the "Foreword "of our PHA. You may also review the Vieques documents cited in the "Reference" section of this PHA.

  3. Comment: One commentator was concerned that ATSDR might be conducting an epidemiological study of cancer risk in Vieques. The commentator feared that ATSDR would mishandle such a study.

    Response: Since the beginning of ATSDR's involvement on Vieques, many people have expressed serious concerns about cancer, citing reports that cancer rates on the island are significantly higher than on the mainland of Puerto Rico. In order to carry out a credible epidemiological study that might address the cause of a disease or a group of diseases, a clearly exposed group of people must be identified and compared with a non-exposed group of similar characteristics. Complete evaluation of exposure pathways is currently ongoing. The design of such an epidemiological study could be considered only after identification of exposed populations.

    The Puerto Rico Central Cancer Registry is being updated by PRDOH. Data for more recent years are not yet complete. The National Program of Cancer Registry standards suggest that data be at least 90% complete before statistics on new cases and deaths are published. A team of highly qualified scientists and physicians from The Centers for Disease Control and Prevention (CDC) is providing technical assistance to the Puerto Rico Central Cancer Registry staff to help achieve national standards.

  4. Comment: One commentator stated that ATSDR has a bad reputation among residents of Vieques. The commentator said that the community of Vieques has rejected ATSDR's conclusions and refused to participate in ATSDR's March 14, 2001 meeting.

    Response: At the outset, and as an integral part of the continuing public health process, ATSDR seeks to foster open dialogue with the community about health concerns. ATSDR has visited Vieques on many occasions and has had useful discussions with small groups of residents, political leaders, and health care providers. ATSDR took note of their health concerns. Although attendance at the March 14, 2001, meeting was small, the goal was to have ATSDR staff available in person to discuss with Vieques residents the findings of the evaluation of groundwater and drinking water. Local residents who have site-related concerns or who have questions about ATSDR's evaluations still have the opportunity to talk to staff directly and confidentially by calling the agency's toll free number, 1-888-42ATSDR.

  5. Comment: Two commentators complained that many of the documents upon which ATSDR's conclusions were founded were unavailable for them to review. They indicated that ATSDR has refused to directly furnish these documents and has referred them to the Navy instead. The commentators noted that some of the documents they seek can only be obtained from the Navy via a Freedom of Information Act (FOIA) request.

    Response: Many of the documents cited in the PHA are available to the public in document repositories on Vieques. The Freedom of Information Act is an appropriate mechanism to obtain documents from the federal agency that was the author of the document.

  6. Comment: Two commentators deplored the effects of the Navy's activities on the island of Vieques. One commentator noted that the Cerro Matías Impact Area looks hellish. Another commentator stated that Vieques is in the middle of an environmental crisis that requires immediate action. The commentator insisted that the Navy should immediately cease using land on Vieques.

    Response: Certainly the activities at a bombing range would impact the immediate environment. The evaluation of groundwater and drinking water by ATSDR focused on the potential impact on human health. Part of our challenge is explaining that while contaminants may exist in the environment or the character of the landscape may be changed from bombing practices, exposures are only possible if people come in contact with contaminants. Even though the LIA has been environmentally impacted by bombing target practices--ATSDR found no evidence in this drinking water evaluation that human exposures are occurring, or have occurred in the past, at levels of health concern.

  7. Comment: One commentator did not expect ATSDR to find evidence that the Navy is currently causing environment contamination. The commentator imagined that the Navy is now operating on its "best behavior" in response to the monitoring activities that are currently going on.

    Response: Improved conditions are largely a result of environmental legislation that has been enacted since the late 1970s. Prior to that time, little if any environmental monitoring occurred, owing largely to the absence of federal and local environmental requirements. The new laws, aimed at protecting land and public health, now provide guidance for identifying and cleaning up chemicals and hazardous substances released in the environment.

  8. Comment: Two commentators made sociological statements about the island of Vieques. One of these commentators felt that the people of Vieques have been neglected, in general, by the government of San Juan. The commentator viewed the construction of a piped water supply from the mainland as an exception to this larger pattern of neglect. The other commentator was not surprised that the people of Vieques are suspicious of the PHA because they have been an oppressed people for so long and they have only recently found their voice.

    Response: The comments are noted.

  9. Comment: One commentator applauds ATSDR's efforts to investigate additional exposure pathways, but doubts that any of these other pathways will be identified as potentially harmful.

    Response: Only a comprehensive evaluation of human exposure to contamination can adequately determine whether other pathways are potentially harmful. ATSDR will continue to identify and evaluate exposure pathways by considering how people might come into contact with areas of potential contamination, whether contamination is present, and whether the amount of contamination is sufficient to affect people's health.

  10. Comment: One commentator finds the PHA uninteresting because it focuses on an exposure pathway--consumption of water imported from mainland Puerto Rico--that the commentator would not have expected to be a significant public health risk.

    Response: ATSDR realizes that the water from the public water supply system originates from the mainland of Puerto Rico, is regulated by PREQB and PRDOH under EPA's Safe Drinking Water Act to be acceptable for human consumption, and therefore, is not likely to be a significant public health risk. However, this PHA not only addresses consumption of water from the mainland of Puerto Rico, but also consumption of water from public and private groundwater wells on Vieques.

1. It should be noted that only the explosive residue data were determined to be unusable; all the other data were acceptable.
2. There is some uncertainty that RDX and tetryl were truly detected in the samples. The authors of the study note that "a completely positive identification was not possible due to the extremely low concentrations found" (Hoffsommer and Glover 1978; Lai 1978). ATSDR discusses the limitation of the study in detail in Appendix E of the PHA.

top of page The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #