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September 22, 2004


The Agency for Toxic Substances and Disease Registry (ATSDR) is an agency of the U.S. Public Health Service. It was established by Congress in 1980 under the Comprehensive Environmental Response, Compensation, and Liability Act, also known as the Superfund law. This law set up a fund to identify and clean up our country's hazardous waste sites. The U.S. Environmental Protection Agency (EPA) and the individual states regulate the investigation and cleanup of the sites.

Since 1986, ATSDR has been required by law to conduct a public health assessment at each of the sites on the EPA National Priorities List. The aim of these evaluations is to find out if people are being exposed to hazardous substances and, if so, whether that exposure is harmful and should be stopped or reduced. (The legal definition of a health assessment is included on the inside front cover.) If appropriate, ATSDR also conducts public health assessments when petitioned by concerned individuals. Public health assessments are carried out by environmental and health scientists from ATSDR and from the states with which ATSDR has cooperative agreements. The public health assessment program allows the scientists flexibility in the format or structure of their response to the public health issues at hazardous waste sites. For example, a public health assessment could be one document or it could be a compilation of several health consultations-the structure may vary from site to site. Nevertheless, the public health assessment process is not considered complete until the public health issues at the site are addressed.

Exposure: As the first step in the evaluation, ATSDR scientists review environmental data to see how much contamination is at a site, where it is, and how people might come into contact with it. Generally, ATSDR does not collect its own environmental sampling data but reviews information provided by EPA, other government agencies, businesses, and the public. When there is not enough environmental information available, the report will indicate what further sampling data are needed.

Health Effects: If the review of the environmental data shows that people have or could come into contact with hazardous substances, ATSDR scientists then evaluate whether these contacts may result in harmful effects. As a policy, unless data are available to suggest otherwise, ATSDR considers children to be more sensitive and vulnerable to hazardous substances. Thus, the health impact to the children is considered first when evaluating the health threat to a community. The health impacts to other high-risk groups within the community (such as the elderly, chronically ill, and people engaging in high-risk practices) also receive special attention during the evaluation.

ATSDR uses existing scientific information, which can include the results of medical, toxicologic, and epidemiologic studies and the data collected in disease registries, to determine the health effects that may result from exposures. The science of environmental health is still developing, and sometimes scientific information on the health effects of certain substances is not available. When this is so, the report will suggest what further public health actions are needed.

Conclusions: The report presents conclusions about the public health threat, if any, posed by a site. When health threats have been determined for high-risk groups (such as children, elderly people, chronically ill people, and people engaging in high-risk practices), they will be summarized in the "Conclusions" section of the report. Ways to stop or reduce exposure will then be recommended in the public health action plan.

ATSDR is primarily an advisory agency, so usually these reports identify what actions are appropriate to be undertaken by EPA, other responsible parties, or the research or education divisions of ATSDR. If there is an urgent health threat, though, ATSDR can issue a public health advisory warning people of the danger. ATSDR can also authorize health education or pilot studies of health effects, full-scale epidemiology studies, disease registries, surveillance studies, or research on specific hazardous substances.

Interactive Process: The health assessment is an interactive process. ATSDR solicits and evaluates information from numerous city, state, and federal agencies; the companies responsible for cleaning up the site; and the community. It then shares its conclusions with them. Agencies are asked to respond to an early version of the report to make sure that the data they have provided are accurate and current. When informed of ATSDR's conclusions and recommendations, the agencies sometimes begin to act on them before the final release of the report.

Community: ATSDR also needs to learn what people in the area know about the site and what concerns they may have about its impact on their health. Consequently, throughout the evaluation process, ATSDR actively gathers information and comments from the people who live or work near a site, including residents of the area, civic leaders, health professionals, and community groups. To ensure that the report responds to the community's health concerns, an early version is also distributed to the public for their comments. All the comments received from the public are responded to in the final version of the report.

Comments: If, after reading this report, you have questions or comments, we encourage you to send them to us. Letters should be addressed as follows:

Attention: Chief, Program Evaluation, Records, and Information Services Branch
Agency for Toxic Substances and Disease Registry
1600 Clifton Road (E-56)
Atlanta, GA 30333


Built in 1949, the Agana Power Plant (APP) was once operated by the U.S. Navy. APP previously provided electricity not only to the Navy-particularly Naval Air Station (NAS) Agana-but also to the government of Guam and customers throughout the central and northern parts of the island. In the past, APP used polychlorinated biphenyls (PCBs) as cooling oils for its electrical transformers and switching-gears. By 1989, most transformers and related equipment either were removed or had their oils replaced with non-PCB coolants. The Navy Public Works Center and Guam Utilities Department, which formerly operated the plant, stopped generating power after NAS Agana's closure in 1995. After the Navy discontinued its power-generating activities, the Guam Power Authority began using the power plant as a substation, and the plant continues to operate as such. Since Navy power production ceased, PCBs, dioxins, and polycyclic aromatic hydrocarbons (PAHs) have been detected in soils and biota at or near APP. The Navy is currently characterizing and cleaning up the contaminated areas.

In May 2000, the Agency for Toxic Substances and Disease Registry (ATSDR) conducted an initial site visit and met with community members. In September 2000, ATSDR released a health consultation outlining various exposure issues and community concerns. In September 2002, ATSDR released for public comment a public health assessment (PHA) for APP addressing three past and present issues. This second PHA evaluates two other possible exposure situations associated with PCBs and other chemical contaminants primarily from APP in Guam. These issues are (1) breathing contaminants from past APP stack discharges and (2) drinking water from municipal or private wells and Agana Spring. This document also addresses the following community concerns: people eating foods raised locally, breathing PCBs that might evaporate from the Agana Swamp, breathing dusts from roads near the former APP, breathing smoke from fires in the Agana Swamp, unearthing buried wastes from various sources, past occupational exposures, and exposures to chlordane in the Mongmong area.

The Navy sampling data used in this evaluation focused on locations and chemicals that were likely to have been released by power plant operations. Other chemicals (such as heavy metals and pesticides) may be present throughout the swamp, but they are beyond the scope of this health assessment: the sources of these chemicals may be from trash piles, landfills, sewage overflows, septic tank releases, and sewage-amended soils. ATSDR has determined that none of the chemicals detected at the locations that were sampled indicates that exposures pose a public health hazard. Exposures to chemicals including PCBs have been reduced, to the extent practical, through remedial action. Community members can also reduce exposure to PCBs by eating a variety of food, including a variety of fish and seafood, and using food preparation and cooking techniques that remove fat and PCBs from the food they eat.

Breathing in Contaminants From Stack Discharges From the Former APP

Guam residents asked ATSDR to evaluate whether past stack discharges from the former APP caused local air pollution to reach levels of health concern. ATSDR considered two approaches when evaluating this issue: we evaluated measurements of air pollution collected on Guam, and we assessed the available data for use in a computer model to estimate potential air quality impacts from the former APP's emissions. The available ambient air monitoring data suggest that sulfur dioxide and particulate levels in neighborhoods downwind from the former APP did not reach levels of health concern. However, specific information about power plant operations are insufficient for an evaluation of past emissions.

Groundwater and Drinking Water

ATSDR evaluated groundwater contamination at APP and any potential for contaminants to migrate to the principle aquifer used for drinking water. PCBs and other site-related contaminants were not detected above ATSDR's screening level in on-site groundwater samples. ATSDR continues to evaluate additional information pertaining to groundwater underneath APP with characterization still ongoing. Guam EPA has recommended and the Navy has agreed to install two additional monitoring wells down gradient of APP to better measure any past migration of site-related contaminants. Sampling data from these additional down gradient monitoring wells will help the Navy and GEPA identify whether any existing groundwater or indoor air contamination is present.

Drinking water from municipal supply wells located in the Mongmong area poses no past or current hazards from chemical contamination. ATSDR's evaluation shows that the drinking water supply is monitored routinely and results of past monitoring have consistently met all Guam and federal safe drinking water standards. Some very low concentrations of volatile organic compounds and pesticides were detected during routine monitoring, but at levels well below their respective maximum contaminant levels for drinking water. Monitoring of supply wells in the Mongmong area has periodically detected bacterial contaminants at levels that exceed Guam and federal safe drinking water standards. Continuing frequent bacteriological sampling, continuing standard operating procedures that include "boil water advisories" during catastrophic events including typhoons, and detecting sewer system leaks and promoting septic tank upgrades will help provide a safer water supply.

Other issues raised by the community are discussed in the "Community Concerns" section of this document.


In September 2000, after reviewing documents and meeting with villagers and staff of local government agencies, business people, village elders, and clergy during an initial site visit, ATSDR released a health consultation for Agana Power Plant (APP). The documents reviewed by ATSDR, combined with the evaluation of site conditions during visits to the village and the power plant, identified numerous potential sources of environmental contamination. In a focused public health assessment (PHA) released for public comment in September 2002, ATSDR addressed the following past and present issues: (1) people eating foods from Agana Swamp, including fish, eels, snails, fruits, and vegetables raised, harvested, or caught in the swamp; (2) village children playing in the dirt (soil), water, and sediment in ditches, as well as coming into contact with soil through family members' gardening; and (3) people swimming and wading in Agana Swamp and River.

This is ATSDR's second PHA for APP. It evaluates two other possible exposure situations associated with polychlorinated biphenyls (PCBs) and other chemical contaminants primarily from APP in Guam. These issues are (1) breathing contaminants from past APP stack discharges and (2) drinking water from municipal or private wells and Agana Spring. In addition, this document addresses the following community concerns: people eating foods raised locally, breathing PCBs that might evaporate from the Agana Swamp, breathing dusts from roads near the former APP, breathing smoke from fires in the Agana Swamp, unearthing buried wastes from various sources, past occupational exposures, and exposures to chlordane in the Mongmong area.

During ATSDR's site visits to Guam and during subsequent follow-up with various community members and government of Guam representatives, residents in the Mongmong area were concerned about a number of environmental issues. Some of these issues were directly related to contaminants released during APP's operation and others were associated with multiple sources of contamination, which may or may not be related to APP.


Site Description and History

What Are PCBs?

PCBs are a mixture of synthetic organic chemicals containing up to 209 individual chemical compounds, referred to as congeners. Because PCBs insulate well and do not burn easily, they were widely used as coolants for electrical equipment such as electrical transformers and capacitors.

The marketing and distribution of PCBs increased markedly around 1929. The major U.S. producer from 1930 to 1977 was Monsanto Corporation, which manufactured PCBs almost exclusively under the trade name Aroclor (ATSDR 2000c).

There are no known natural sources of PCBs in the environment; however, because PCBs were used worldwide, they are now detected in most areas of the world-air, water, soil and food (ATSDR 2000c). In 1977, PCBs were banned from both production and new uses in the United States because studies of laboratory, wildlife, and some worker populations showed that PCBs were toxic. Most other countries have stopped production and new uses of PCBs as well.

APP is located in the village of Mongmong in central Guam. Part of the Pacific Ocean's Micronesian Islands, Guam is the largest and most southern island of the Mariana Archipelago. The island has a total land mass of 212 square miles, excluding reef formations. APP comprises roughly 3 acres (approximately 0.05 square miles) of land north of Roy T. Damian Road, half a mile south of Agana Bay, Guam. The APP site is roughly 2,000 feet southwest of the southwestern corner of the former Naval Air Station (NAS) Agana (Tiyan) and approximately 325 feet north of the Agana Swamp (Figures 1 and 9) (Earth Tech 2000).

APP was constructed in 1949 to provide electricity to NAS Agana and government of Guam customers in the central and northern portion of the island (Earth Tech 2002). PCBs were reportedly used in cooling oils for transformers and other electrical distribution equipment at APP prior to 1988. PCBs may also have been used offsite for non-APP-related activities. PCBs have a very low solubility in water and readily adsorb to soil particles. These properties cause them to accumulate in soil deposited by stormwater runoff (Earth Tech 1999a).

As a result of NAS Agana's closure in 1995, the Navy Public Works Center and Guam Utilities Department stopped generating power from APP. The Guam Power Authority began using the power plant as a substation, and the plant continues to operate as such. Today, APP receives power from one or more power plants on the island and redistributes it to area residents, businesses, and municipalities. The Navy, however, still owns APP. The Guam Power Authority currently leases the facility from the Navy to operate an electrical substation at the site. Land use at APP is not anticipated to change in the near future, and use of the site is anticipated to remain industrial (Earth Tech 2002).

Remedial and Regulatory History

An environmental baseline survey was conducted in 1994 to assess potential impacts of hazardous materials originating at APP. Seven points of interest (POIs) were identified at APP and recommended for further investigation (Earth Tech 2002).
  • POI-1-Above Ground Storage Tank Fueling Area
  • POI-2-Drum Storage Area
  • POI-3-Generator Storage Area
  • POI-4-Guam Power Authority Substation Yards
  • POI-5-Former Mobile Substation
  • POI-6-Storm Water Outlets
  • POI-7-Battery Storage Area
In 1995, PCB contaminated soil was discovered in the vicinity of the APP. In 1998, as part of its standard procedures for the transfer of former industrial properties, the Navy tested for traces of chemicals that could be harmful to humans and the environment. PCBs, dioxins, and polycyclic aromatic hydrocarbons (PAHs) were detected in some soils and foods at or near APP. The Navy is currently characterizing and cleaning up the contaminated areas. Preliminary studies carried out by the Navy subsequently revealed PCBs in fish taken from the swamp and the adjacent river system. The source of the PCBs is uncertain, but concentrations found in fish and sediment samples from sites close to the power plant were lower than those taken at more distant locations such as the headwaters of the Agana River. This suggests that multiple PCB sources exist in the area.

The Navy is currently characterizing and cleaning up the contaminated areas. For detailed information on the Navy's continuing environmental investigation and remediation plans at APP and surrounding areas, refer to APP's documents located at the three public repositories:
  • Nieves M. Flores Public Library, Agana
  • Robert F. Kennedy Library, University of Guam
  • Micronesia Area Research Center, University of Guam
ATSDR's Involvement at the Agana Power Plant

On January 14, 2000, Guam Environmental Protection Agency (GEPA) requested that ATSDR conduct a PHA to determine the possible public health impact of PCB contamination at APP, and other contamination sources possibly impacting residents in the Mongmong community.

On February 29, 2000, the Department of the Navy, Pacific Division, Naval Facilities Engineering Command, asked ATSDR to expedite the PHA because the community surrounding the APP had many health concerns.

On May 8 through 12, 2000, ATSDR visited APP and began collecting information necessary to conduct the PHA. ATSDR reviewed available site-specific information and visually inspected the plant and other areas where hazardous substances might have been released to the environment.

On May 9 and 10, 2000, ATSDR and the Guam Department of Public Health and Social Services (GDPHSS) met with Mongmong residents to gather information about chemicals and human exposure-including PCBs-from APP. The public availability sessions were held to give individuals and families an opportunity to talk privately with the public health representatives about their health concerns, problems, or both.

In September 2000, ATSDR released a health consultation entitled Outlining Various Exposure Issues From Initial Site Visit-May 2000 to Mongmong and the Agana Power Plant, Mongmong, Guam. This document identified community health concerns and eight possible exposure issues. ATSDR concluded that no issues posed an immediate public health threat.

In January 2002, ATSDR released two fact sheets. The first, Community Questions and Answers on PCB Contamination and Health, was designed to give the people of Mongmong information about PCB contamination from APP. The second, Update on ATSDR's Public Health Assessment for Agana Power Plant, Guam, was jointly released with GEPA and GDPHSS.

From February 24 through March 1, 2002, ATSDR visited APP again. This visit featured a tour of the APP site and nearby sites in the Mongmong area. ATSDR representatives also met with the Congressman from Guam, the Mayor of Mongmong, and representatives from the GEPA, GDPHSS, the University of Guam, the Water and Environmental Research Institute of the Western Pacific (WERI), the U.S. Navy, and the Agana Restoration Advisory Board.

On March 1, 2002, ATSDR hosted a public meeting about APP to update the community on the follow-up visit and to give them an opportunity to provide additional information, comments, ask questions, and express concerns related to APP.

In September 2002, ATSDR released for public comment a focused PHA addressing three of the eight exposure issues outlined in the 2000 health consultation. A final report that responds to public comments was released in September 2003.

In May 2004, ATSDR visited the Mongmong-Toto-Maite community and held a public meeting on Tuesday, May 25 to present the findings of the Public Comment APP Focused PHA report on Air and Groundwater Pathways. During this visit ATSDR representatives met with the Navy, providing an out briefing and participating in Agana Power Plant related discussions. ATSDR also met with many representatives from different Guam Government agencies (e.g., Guam Department of Public Health and Social Services, Guam EPA, Guam Agriculture, and Guam Coastal Management). During the site visit ATSDR gathered additional community concerns and comments, which are compiled along with responses in Appendix I of this report.


ATSDR examines demographic data (i.e., population information) to determine the number of people potentially exposed to environmental chemicals. This information is also used to determine the presence of sensitive populations, such as women of childbearing age (15 to 44 years old), children (6 and younger), and the elderly (65 and older). Demographic data also provide details on population mobility, which in turn help ATSDR evaluate how long residents might have been exposed to environmental chemicals.

The population of Guam is estimated at approximately 155,000 persons (U.S. Bureau of the Census 2002). This includes both military and civilian populations. It also represents an increase of about 22,000 from the 1990 Census. The military personnel are largely concentrated in the northern portion of Guam, whereas the civilian population is mostly concentrated in Apra Harbor, Santa Rita, and villages in the coastal areas of Guam (ATSDR 2003).

The majority of Guam's resident population, approximately 81,000 persons (52%), was born on Guam. The native Chamorrans are the largest ethnic group, making up over 42% of the island's population (including 5% who are both Chamorran and members or another ethnic group). Of those not born on the island, a large number of Guam residents have emigrated from the Philippines (21.1%), the United States mainland (12.3%), and the Federated States of Micronesia (4.5%) (U.S. Bureau of the Census 2002).

Toto and Maite are the closest communities to Mongmong. The Mongmong-Toto-Maite district has a population of about 5,800, with Mongmong alone accounting for over half of this number (approximately 3,300 people). In this district, 45% of the population speaks a language other than English at home: 27% speak Chamorro and 13.5% speak Philippine languages (U.S. Bureau of the Census 2002). Approximately 35% of Guam's population is under the age of 14 and only about 6% of the population is 65 years or older. There are many child day care centers available on the island. However, a listing of day care and family day care centers licensed by the Department of Public Health and Social Services for 2003-2004 only identified one day care center in the immediate Mongmong-Toto-Maite district (Pacific Daily News 2003).

Land Use and Natural Resource Use

APP is a fenced site containing various buildings, storage tanks, and paved areas. The rest of the site is covered with turf grasses such as Bermuda grass (Cynodon dactylon) (Earth Tech 1999b). APP is situated on a plateau at 97 feet above mean sea level, overlooking the Agana Swamp, which is at an elevation between 0 and approximately 10 feet above mean sea level. The power plant was constructed on a site cut into a shallow hillside.

The Agana Swamp is a wetland area located south of APP. It is groundwater-fed and also receives surface runoff from the surrounding slopes of Sinajana to the southwest and Mongmong to the northeast. Water drains from the swamp into the marine waters via the Agana River. The swamp contains a rich diversity of flora and fauna and is a popular fishing ground for many local people.

The areas within approximately a mile of APP are primarily residential and include single-family homes as well as apartment buildings (Earth Tech 2000). Residents in the area use the Agana Swamp and Agana River for recreational purposes (e.g., fishing and swimming). Although residential and commercial growth has progressed steadily near APP, the hills on the southeast side of the swamp have remained largely undeveloped.

The island of Guam has relied on four main sources of fresh water for its drinking water supply: groundwater, springs, and two other surface-water bodies (the Fena Reservoir and the Ugum River). Approximately 74% of the drinking water distributed to residents on Guam is provided by the Guam Waterworks Authority (GWA). The remainder is distributed by the Air Force and Navy installations on Guam.

GWA's water sources are groundwater and surface water (the Ugum River). The Ugum River supplies drinking water to villages in the southeastern portion of the island. The Navy water source is a surface reservoir (the Fena reservoir) in the southern portion of the island (U.S. Department of the Interior 1999). The Fena reservoir is the largest source of potable surface water on the island. GWA purchases approximately 65% of the reservoir's output, or about 9.4 million gallons per day, for use as tap water and for other needs. GWA produces approximately 35 million gallons per day from its own water sources (Pieper 2002; Jenson and Jocson 1998).

Geology and Hydrogeology


The island of Guam has two distinct physiographic provinces: the Northern Limestone Plateau and the Southern Volcanics. APP lies at the southern edge of the Northern Limestone Plateau. The plateau is characterized by exposed rock, referred to as Mariana limestone. The Mariana limestone consists of a high percentage of clay and fragmented and worn rocks. Silty clays have generally been observed across APP down to approximately 6 feet below ground surface (bgs), although they have been observed down to 25 feet bgs at the eastern portion of the site. The topsoils (i.e., the upper 12 inches) are moderately permeable and consist of clay loam originating from the weathering and dissolution of the limestone bedrock below (Earth Tech 2002). Figure 2 shows the surface geology near APP and Figure 3 shows the soils in the same area.


Guam comprises two hydrogeologic provinces. In the southern half of the island, groundwater primarily occurs in volcanic rock of low permeability. There is very limited groundwater production in the unconfined aquifer underlying the southern half of the island. In northern Guam, groundwater is contained within the "Northern Guam Lens." This aquifer serves as the primary source of potable groundwater for the island (NRCS 1998) and is situated below densely populated areas of Guam and most of the agricultural activity on-island. Almost all agricultural irrigation is done with potable water from public mains (University of Guam 1999).

The groundwater underlying APP is part of the Northern Guam Lens and lies within a hydrologic sub-basin identified as Agana West. On average, the groundwater at the site is approximately 80 to 90 feet bgs. Original groundwater production well data and groundwater elevation data from monitoring wells installed in October 2000 indicated that groundwater flows northwest toward the Philippine Sea, away from the Agana Swamp. However, recent groundwater measurements from existing monitoring wells indicate that groundwater flow is toward the mouth of the Agana River, contrary to the idea that the groundwater flowed towards Agana Swamp. Additional groundwater flow characterization is ongoing. Heavy rains occur seasonally on Guam and can affect subsurface hydrogeologic conditions, causing variations in water quality and flow direction (Earth Tech 2000, 2002; GEPA 1998).

Surface Water

There are several surface-water features in close proximity to APP. The Agana Swamp, a marshy area, is a catchment area for the Agana River. Portions of the Agana Swamp are located between the Agana River and APP. The Agana Swamp is approximately 325 feet south of APP (Earth Tech 1999a). The Agana River, which originates from Agana Springs and runoff near the springs, is approximately 1,400 feet west of APP at its closest pass (see Figure 4). Runoff of surface water at the site is limited due to the fractured nature of the Mariana limestone in this region of Guam. Precipitation likely infiltrates quickly through the porous Mariana limestone. The fractures can also affect the flow paths for infiltrating surface water and the potential migration of subsurface soil contamination to groundwater (Earth Tech 2000).

There are two drainage areas close to the APP site. Site drainage is engineered to discharge at POI-6 East and POI-6 West on the perimeter. After leaving APP, stormwater runoff can enter the Agana Swamp and the Agana River (Earth Tech 1999a). Runoff from the eastern half of the site is collected in a concrete ditch system that discharges to an unlined swale in the southeastern corner of the site (POI-6 East). Runoff from private properties east of APP is prevented from entering APP by a run-on control swale and joins the onsite runoff in twin culverts at the southeast corner of the site. Site drainage from POI-6 East flows south in the twin culverts across Roy T. Damian Road into a Tangantangan scrub woodland, which is referred to as the APP Drainage Outfall Area. Runoff continues for approximately 250 feet until it reaches a steep slope that drops directly into an isolated bay, the Utan arm, on the northeastern end of the Agana Swamp (See Figure 4).

The western half of the site drains to a concrete-lined channel, which discharges at the west fence line towards POI-6 West. Water flows south in an unlined ditch to the drainage ditch on the north side of Roy T. Damian Road. At Route 7A, the flow enters a subsurface storm drain system that outfalls to the Agana River immediately north of the bridge.

Runoff from the southern portion of APP flows towards a retaining wall, which directs the runoff east and west, then south to an unlined ditch on the north side of Roy T. Damian Road. The drainage ditch then carries the runoff west, joining POI-6 West drainage (Earth Tech 1999b).

Climate and Meteorology

ATSDR researched weather conditions and prevailing wind patterns at Guam, because these factors largely determine how contaminants move through the air. Guam's climate is generally warm and humid, with temperature and humidity levels not varying considerably from one season to the next. Over the last 30 years, the average daily temperature has been 79.2 degrees Fahrenheit (26.2 degrees Celsius), with minimal fluctuations between months.

Unlike temperature and humidity, the rainfall and wind patterns at Guam exhibit strong seasonal effects. According to the National Weather Service, 15% (approximately 15 inches) of the annual rainfall at Guam occurs during the dry season, which runs from January through April. On the other hand, 55% of the annual rainfall typically occurs during the wet season, which runs from mid-July through mid-November (NCDC 2003). The central portion of Guam receives 103 inches of rainfall per year. Rainfall patterns are influenced by typhoons, which occasionally pass near or over Guam, typically during the months of July through November.

The wind patterns at Guam are dominated by trade winds blowing out of the east, but winds blowing from all directions have been observed at the island. The average wind speed recorded by the National Weather Service meteorological station at Guam International Airport is 7.4 miles per hour. Wind directions observed at the airport during a recent 5-year period were distributed as follows:

Wind Direction1 Percent of Time Winds Blow in This Direction
East to west 77%
North to south 11%
West to east 3%
South to north 9%

This table shows that the most common wind direction observed near the site of the former APP was from east to west. Such wind directions would have blown emissions from the site primarily toward communities in the municipalities of Mongmong, Agana, Agana Heights, and Asan. Emissions undoubtedly blew toward communities in other directions from the former APP, but far less frequently. Our conclusions regarding inhalation exposures (presented later in this PHA) are based, in part, on these observations of prevailing wind directions.

Meteorological data from the Guam International Airport are likely reasonably representative of conditions at the former APP because the two locations are approximately 1 mile apart with no significant terrain features between them. However, due to local influences on meteorology, such as land-sea breezes, landscape turbulence, and heat island effects, the meteorological data collected at the airport are not perfectly representative of conditions in the Mongmong area.

Quality Assurance and Quality Control

In preparing this PHA, ATSDR reviewed and evaluated environmental data provided in various reports prepared by the US Navy, Navy Contractors, and other parties. Documents prepared for the Navy's Baseline Realignment and Closure POI sites have Navy, GEPA, and US EPA oversight to verify that the data meets specific quality assurance and quality control measures for chain-of-custody procedures, laboratory procedures, and data reporting. These reports note any identified limitations to the sampling data. ATSDR's evaluation of the data included looking for inconsistencies and data gaps. The validity of analyses and conclusions drawn in this PHA are based on the reliability of the information referenced in reports related to APP. ATSDR believes that the quality of environmental data available in documents relating to APP is sufficient for public health findings and recommendations provided in this report.

1 In this tabulation, wind directions between 45 and 135 are considered to be from east to west, wind directions between 135 and 225 are considered to be from south to north, wind directions between 225 and 315 are considered to be from west to east, and all other wind directions are considered to be from north to south. Hours with variable wind directions are excluded from this tabulation.

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