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Public Health Assessment
Air Pathway Evaluation,
Isla de Vieques Bombing Range,
Vieques, Puerto Rico

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August 26, 2003
Prepared by:

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

Appendices

Appendix A: Comparison Values

Following are definitions of the various health-based comparison values that ATSDR used in this PHA to put the measured and modeled levels of environmental contamination into perspective:
CREG: Cancer Risk Evaluation Guide, a highly conservative value that would be expected to cause no more than one excess cancer in a million persons exposed over time.
EMEG: Environmental Media Evaluation Guide, a media-specific comparison value that is used to select contaminants of concern. Levels below the EMEG are not expected to cause adverse noncarcinogenic health effects. These have been developed for acute exposure scenarios (EMEG-a), intermediate exposure scenarios (EMEG-i), and chronic exposure scenarios (EMEG-c).
NAAQS: National Ambient Air Quality Standard, an ambient air concentration that EPA has established to characterize air quality. The standards are health-based and were designed to be protective of many sensitive populations, such as people with asthma and children. The standards have been developed only for a small subset of pollutants, and the averaging time and statistical interpretations of the standards vary among the regulated pollutants.
RBC: Risk-based Concentration, a contaminant concentration that is not expected to cause adverse health effects over long-term exposure. These have been developed for both cancer outcomes (RBC-C) and noncancer outcomes (RBC-N).
REL: Recommended Exposure Level, an air concentration that the National Institute for Occupational Safety and Health (NIOSH) recommends should not be exceeded. RELs are designed primarily for occupational settings and exposures. The RELs used in this PHA are all based on 8-hour time weighted average exposures.
RfC: Reference Concentration, an ambient air concentration developed by EPA that people, including sensitive subpopulations, likely can be exposed to continuously over a lifetime without developing adverse noncancer health effects. RfCs typically have uncertainty factors built into them to account for any perceived limitations in the data on which they are based.


Appendix B: ATSDR Glossary of Environmental Health Terms

Acute Exposure:
Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.


Adverse Health Effect:
A change in body function or the structures of cells that can lead to disease or health problems.


ATSDR:
The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.


Background Level:
An average or expected amount of a chemical in a specific environment. Or, amounts of chemicals that occur naturally in a specific-environment.


Biota:
Used in public health, things that humans would eat - including animals, fish and plants.


Chronic Exposure:
A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.


Completed Exposure Pathway:
See Exposure Pathway.


Comparison Value (CVs):
Concentrations or the amount of substances in air, water, food, and soil that are unlikely, upon exposure, to cause adverse health effects. Comparison values are used by health assessors to select which substances and environmental media (air, water, food and soil) need additional evaluation while health concerns or effects are investigated.


Concern:
A belief or worry that chemicals in the environment might cause harm to people.


Concentration:
How much or the amount of a substance present in a certain amount of soil, water, air, or food.


Contaminant:
See Environmental Contaminant.


Dose:
The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day."


Dose / Response:
The relationship between the amount of exposure (dose) and the change in body function or health that result.


Duration:
The amount of time (days, months, years) that a person is exposed to a chemical.


Environmental Contaminant:
A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than that found in Background Level, or what would be expected.


Environmental Media:
Usually refers to the air, water, and soil in which chemcials of interest are found. Sometimes refers to the plants and animals that are eaten by humans. Environmental Media is the second part of an Exposure Pathway.


Exposure:
Coming into contact with a chemical substance.(For the three ways people can come in contact with substances, see Route of Exposure.)


Exposure Pathway:
A description of the way that a chemical moves from its source (where it began) to where and how people can come into contact with (or get exposed to) the chemical.

ATSDR defines an exposure pathway as having 5 parts:

  1. Source of Contamination,
  2. Environmental Media and Transport Mechanism,
  3. Point of Exposure,
  4. Route of Exposure, and
  5. Receptor Population.

When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.


Frequency:
How often a person is exposed to a chemical over time; for example, every day, once a week, twice a month.


Health Effect:
ATSDR deals only with Adverse Health Effects (see definition in this Glossary).


Indeterminate Public Health Hazard:
The category is used in Public Health Assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.


Inhalation:
Breathing. It is a way a chemical can enter your body (See Route of Exposure).


No Apparent Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where exposure to site-related chemicals may have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.


No Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.


PHA:
Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.


Plume:
A line or column of air or water containing chemicals moving from the source to areas further away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water (such as lakes, ponds and streams).


Point of Exposure:
The place where someone can come into contact with a contaminated environmental medium (air, water, food or soil). For examples:
the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, the location where fruits or vegetables are grown in contaminated soil, or the backyard area where someone might breathe contaminated air.


Public Health Hazard:
The category is used in PHAs for sites that have certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.


Public Health Hazard Criteria:
PHA categories given to a site which tell whether people could be harmed by conditions present at the site. Each are defined in the Glossary. The categories are:
  1. Urgent Public Health Hazard
  2. Public Health Hazard
  3. Indeterminate Public Health Hazard
  4. No Apparent Public Health Hazard
  5. No Public Health Hazard

Route of Exposure:
The way a chemical can get into a person's body. There are three exposure routes:
- breathing (also called inhalation),
- eating or drinking (also called ingestion), and
- or getting something on the skin (also called dermal contact).

Source (of Contamination):
The place where a chemical comes from, such as a landfill, pond, creek, incinerator, tank, or drum. Contaminant source is the first part of an Exposure Pathway.


Urgent Public Health Hazard:
This category is used in ATSDR's Public Health Assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.

Appendix C: Review of Air Sampling Studies

Air sampling results are measurements of the levels of air contamination that people might actually breathe. These are critical elements to this PHA, because they are direct measures of exposure point concentrations and do not involve the inherent uncertainties of modeling studies. ATSDR invested considerable effort in obtaining all ambient air monitoring data that might be relevant to air quality issues in Vieques.

This appendix presents ATSDR's review of all air sampling studies identified for this site. The reviews that follow present key information on the studies, such as number and locations of sampling stations, sampling frequencies, number of samples collected, pollutants measured, and comparisons of measured concentrations to health-based comparison values. Section V of this PHA indicates how ATSDR interpreted the air sampling data when reaching its conclusions for this site.

C.1 Review of PREQB's 2000-2001 Ambient Air Monitoring Data

Starting in July, 2000, PREQB has been collecting ambient air samples every sixth day at two locations on Vieques, and daily sampling has occurred during some of the Navy's past military training exercises. According to EPA's Aerometric Information Retrieval System (AIRS), the sampling location listed as "Ed. Defensa Civil Isabel II" (in Isabel Segunda) collected data through March 2002 and the other sampling location listed as "Esc. Juanita Rivera Albert La Esperanza" (in Esperanza) collected data through December 2002, and possibly continues to do so. These locations are shown in Figure 6.

Both sampling locations are equipped with two hi-vol gravimetric sampling devices, one to collect 24-hour average PM10 samples, the other to collect 24-hour average TSP samples. PREQB is using an EPA Reference Method to measure the concentrations of PM10. These methods have been shown to generate highly accurate and precise data when operated according to the specifications outlined in the EPA Reference Method and the manufacturer's user manual. All data that PREQB has collected at these stations are reviewed for quality before being submitted to EPA's AIRS database. ATSDR has learned from verbal communications with PREQB that the air samples have also been analyzed for concentrations of metals. ATSDR has requested access to PREQB's sampling results for metals (ATSDR 2001d), but has not yet received copies of the data.

For several reasons, ATSDR believes the data collected by PREQB are of a known and high quality. First, the PM10 measurements were made using EPA-approved reference method sampling devices, and the TSP measurements were made using widely-used methods. Second, PREQB's monitoring network throughout the Commonwealth follows a quality assurance plan and EPA's reference method, which includes requirements for periodic flow and calibration checks. Finally, all data collected by PREQB must be reviewed for quality before being submitted to AIRS. ATSDR has visited both of PREQB's monitoring stations on Vieques and did not identify any circumstances that would cause the devices to measure concentrations much lower than actual ambient conditions (e.g., the devices were not under the drip lines of trees).

At the time this report was written, sampling results from PREQB's monitors are available from July 2000 to December 2002. This time frame includes several military training exercises that involved use of practice bombs. Overall, 51 valid samples were collected during these exercises. Table C-1 summarizes the sampling results for both PM10 and TSP concentrations. The table indicates that the average and maximum ambient air concentrations of PM10 are lower than EPA's current health-based National Ambient Air Quality Standard (NAAQS) and the average and maximum ambient air concentrations of TSP are lower than EPA's former NAAQS for this pollutant.

C.2 Review of ATSDR's 2001 Vieques Air Monitoring Program

In late May, 2001, the Navy officially announced plans to conduct military training exercises on Vieques starting on June 18, 2001. Given the residents' health concerns about exposures to air contaminants during bombing exercises and the fact that no metals sampling had ever been conducted during such exercises, ATSDR coordinated an air sampling project that lasted throughout much of the scheduled exercises. Due to the limited time available to plan for this project and the fact that no previous sampling had occurred for the contaminants being considered (i.e., metals and explosives), the sampling program was designed to be an initial survey of air quality impacts that might result from the use of practice bombs.

The "Vieques Air Monitoring Program" involved contributions from ATSDR, the Navy, and contractors to both parties (ERG 2001). In general, contractors to the Navy were responsible for collecting samples, and contractors to ATSDR were responsible for analyzing them in the laboratory. All sampling took place during the military training exercises the Navy conducted in June, 2001. This program was conducted to characterize air concentrations of three classes of contaminants: PM10 (through both continuous and integrated measures), metals, and explosives and selected decomposition products. Key findings from the four different types of sampling that took place follow:

  • Continuous PM10 sampling. Continuous PM10 sampling devices were operated at two locations during the VAMP. One device malfunctioned during the program, and the other reported an average PM10 concentration of 26.0 µg/m3 over roughly 1 week of operation. The continuous measurements were made with a field surveying tool.
  • Hi-Vol PM10 sampling. 24-hour average integrated PM10 samples were collected using General Metal Works Model 1200 PM10 Samplers at six locations on and near Vieques (see Figure 6). The measured PM10 concentrations from the 49 samples ranged from 13.9 to 176.9 µg/m3, with the highest concentration occurring at a sampling location upwind (on a boat) from the Navy's bombing range. These measurements were found to be of questionable quality for several reasons. Though sampling was intended to follow specifications in EPA's reference method, site conditions prevented the field sampling team from adhering to some critical aspects of the method, particularly with regard to siting and sample duration. The deviations from the reference method, combined with poor precision of collocated samples and extremely poor agreement with the collocated continuous PM10 measurements, strongly suggest that the Hi-Vol PM10 sampling data from this program were of questionable quality. Placement of the sampling devices on dirt surfaces may have contributed to a positive bias in the measurements.
  • Metals data. Every filter collected using the Hi-Vol PM10 sampling devices was analyzed for 18 metals. Most metals were detected in every sample. The metals detected at highest levels were magnesium, sodium, and aluminum. The quality of the measured metals concentrations depends both on the quality of the laboratory analysis and the quality of the field sampling. Multiple data quality indicators compiled by the analytical laboratory suggest that the filter analyses were both highly accurate and precise. As stated above, the Hi-Vol PM10 devices were not operated according to the EPA reference method. Because inaccuracy or imprecision in the Hi-Vol PM10 measurements also affects the accuracy and precision of the metals measurements, the metals sampling data from this program were also of questionable quality.
  • Explosives and decomposition product data. Field sampling personnel collected four samples for explosives using sorbent cartridges. They returned the cartridges for analysis, but discarded, instead of returning to the laboratory, the sampling filters that collect particulate-bound contaminants. As a result, all measurements of explosives represent estimates of vapor-phase explosives only and do not characterize amounts of airborne particulate-bound explosives. Several data quality indicators suggested that the laboratory analyses of explosives samples were of a known and high quality. Of the 13 analytes considered, eight were not detected in any sample. Four analytes were detected at trace levels less than twice those found in blank samples; detections at these levels therefore cannot be considered significant. One analyte, nitrobenzene, was detected at trace levels (0.0019-0.0024 ppb) in three of the four samples. Additional sampling is needed to verify the presence of nitrobenzene and to characterize the total ambient air concentrations of particulate-phase and gas-phase explosive compounds.

Overall, the Vieques Air Monitoring Program had several unforeseen difficulties, which resulted in the organizers of the program concluding that all measurements are of questionable quality. Accordingly, ATSDR believes the utility of the sampling results is limited, and they should be viewed only as very rough indicators of air quality during a military training exercise using practice bombs. Given the data quality concerns, ATSDR did not consider these sampling results when evaluating air quality issues at Vieques. Nonetheless, ATSDR still recognizes the need for having high quality air sampling results during military training exercises involving practice bombs and has made a recommendation in this PHA (see Section IX) to ensure that this data gap is filled.

C.3 Review of Other Air Sampling Results Downloaded from EPA's AIRS Database

In the interest of being thorough, ATSDR not only downloaded ambient air monitoring data collected in Vieques from EPA's AIRS database, but also downloaded data collected from sampling stations near the east coast of the main island of Puerto Rico. ATSDR briefly reviewed these data to identify evidence of any potential regional air quality problems (i.e., elevated levels of air pollution that might exist throughout the area).

This query on AIRS identified two particulate sampling stations on the eastern shore of Puerto Rico, one in Fajardo and the other in Ceiba. Between the two stations, 1,780 particulate sampling observations were recorded, including concentrations of TSP, PM10, and PM2.5. However, none of the 24-hour average sampling results for these stations, or the corresponding annual averages that ATSDR computed, exceeded EPA's current or former health-based air quality standards. Moreover, ATSDR found no evidence suggesting that concentrations of particulate matter at these locations might be traced to a single source.

ATSDR realizes that the sampling results from Fajardo and Ceiba are of limited utility in this PHA, because the sampling locations in these cities are approximately 20 miles away from the residential areas of Vieques. The only conclusion that ATSDR draws from these results is that particulate emissions from the Navy bombing range do not appear to present health hazards at locations on the main island of Puerto Rico. This finding, however, provides no insights into levels of air pollution in the residential areas of Vieques.

C.4 1972 PREQB Air Sampling Study

Over the last 2 years, ATSDR has identified two documents indicating that PREQB conducted air sampling on Vieques in 1972 (Cruz Pérez 2000; TAMS 1979), but original documentation for this sampling effort apparently cannot be located. The two secondary references of this sampling project are reasonably consistent, implying that the information presented in these documents is correct. The following bulleted items summarize the information presented in the individual secondary references, after which ATSDR presents its interpretation of the sampling project.

  • Information documented in "Cruz Pérez 2000." This reference is an article that is published in a magazine published by the College of Engineers and Surveyors of Puerto Rico. According to the article, the 1972 PREQB sampling project included placement of sampling devices at two locations, one in Isabel Segunda and the other in Esperanza. Sampling results presented in the article follow:
    Sampling results presented
    Pollutant Range of Concentrations Measured
    Hydrocarbons (aldehydes) 2.74-40.00 µg/m3
    Nitrogen dioxide Not detected-35.8 µg/m3
    Ozone Not detected-29.0 µg/m3
    Particulate matter 13.9-98.98 µg/m3
    Sulfur dioxide Not detected in any sample

    The article does not provide critical information ATSDR typically reviews when interpreting sampling results, such as the time (in what months) samples were collected, how many samples were collected, the averaging time of the samples, the exact locations of sampling stations, and the methods used to collect and analyze samples. Moreover, the article does not mention whether sampling took place during military training exercises. The article cited the following report as the original reference for the sampling data: "Vieques 1972, Survey of Natural Resources, EQB, 1972-1973." ATSDR has contacted several agencies in attempts to obtain this report, but none has been able to locate a copy.

  • Information documented in "TAMS 1979." This reference is an environmental impact statement that a Navy contractor prepared in 1979, and it also documents a PREQB air sampling project taking place on Vieques in 1972. The report provides much more detailed information on the sampling project, such as noting the exact locations of the two sampling stations: one at Duteil School in Isabel Segunda and the other at Puerto Rico Aqueduct and Sewer Authority Pump Station No. 1 in Esperanza. The report also presents a specific time frame for this sampling project: August 3 to August 22, 1972. Further, the report presents a data summary identical with the one listed above, and provides the additional insight that the concentrations listed are 24-hour average observations. Unfortunately, this report also fails to document critical information ATSDR typically reviews when evaluating data, such as the frequency of sampling, the number of samples collected, the methods used to collect samples, and whether samples were collected during military training exercises. This report cites the following document as the primary reference of the 1972 sampling results: "Ecology and Environment, Inc., 1978." A more detailed citation is not provided.
  • ATSDR's interpretation of these accounts. Given the similarity between the two accounts of the PREQB 1972 air sampling project, ATSDR assumes that this sampling did take place during August 1972 at the two locations specified in the TAMS report and that the concentrations listed above are the actual measurement results. ATSDR further assumes that the concentrations of "particulate matter" are actually concentrations of TSP. This assumption is based on the fact that EPA did not start regulating PM10 as a criteria pollutant until 1987 and the overwhelming majority of particulate sampling during the 1970s was for TSP, not PM10. Neither report specifies whether this sampling took place during military training exercises. Overall, ATSDR finds that the sampling results listed above are of unknown quality, because detailed information on the sampling methods and quality assurance is not available.

    ATSDR encourages any individual with access to the original documentation and data from the PREQB 1972 sampling project to provide copies to the agency for review. Though the two accounts of the 1972 sampling project are similar, ATSDR always prefers to base important public health conclusions on primary, rather than secondary, references of environmental sampling studies.

C.5 1978 Air Sampling Study

ATSDR has identified two references suggesting that another air sampling project took place on Vieques in 1978, starting on May 16 and continuing through July (Cruz Pérez 2000; EPA 1999). However, original documentation of this sampling project has not been located. In this project, 11 valid samples were taken, all of which were reportedly "particulate matter" samples collected with a hi-vol device. The sampling is said to have taken place at two locations near water tanks while the Navy intermittently fired 105 mm cannons over a time frame of 8 hours (EPA 1999). It is not clear, however, if this level of ordnance usage occurred on a single day of the program or on every day of the program. According to an interview between EPA and the manager of the sampling project, a PREQB laboratory weighed the particulate filters collected by the hi-vol devices (EPA 1999).

No detailed results from this 1978 sampling are presented in either reference ATSDR obtained, other than suggesting that the measured particulate concentrations fell within the range (13.9-98.98 µg/m3) observed during the 1972 sampling (Cruz Pérez 2000). Overall, the account of the 1978 sampling at Vieques is incomplete. Most notably, detailed information on sampling locations, sampling frequency, measured concentrations, and quality assurance are not provided. The article cites the following document, which cannot be retrieved, as a reference of the 1978 sampling data: "Muestreo Especial de Vieques: 3 de Julio del 1978, Memorial Interno, Ing. Edgardo Soto, Junta de Calidad Ambiental."

In summary, ATSDR assumes the project occurred during an 8-hour intermittent exercise involving shelling with 102 mm ordnance and measured particulate matter concentrations were within the range 14-99 µg/m3. ATSDR again assumes that these concentrations are TSP and not PM10, given the year in which this sampling project occurred. Because no quality assurance data are available, ATSDR finds that the 1978 sampling results are of unknown quality.

C.6 Navy Air Sampling During the 1970s

The Navy's 1979 Environmental Impact Statement (EIS) for continued use of the bombing range documents results from a 2-month air sampling program (TAMS 1979). The EIS appears to be the primary reference for this sampling program, as the document does not cite other reports when presenting the program's results. According to the EIS, the sampling program started in July 1978 and ended 60 days later, in August 1978. Of these 60 days, 20 days of continuous sampling took place during military training exercises, and the remaining 40 days of sampling occurred when the bombing range was idle. This program involved three sampling locations, all within either the EMA or ATWTF. No information is provided on the sampling methods used or on data quality.

According to the EIS, the geometric mean TSP concentrations at the three sampling locations were 39.5 µg/m3, 40.2 µg/m3, and 35.4 µg/m3 (TAMS 1979). Moreover, the sampling program found that geometric mean TSP concentrations on days without bombing exercises were higher than the program-average geometric mean concentrations. The EIS infers from this trend that ". . . the effects of ordnance detonation have a negligible effect on 24-hour values of particulate levels" (TAMS 1979).

ATSDR has considered these sampling results in this PHA. However, ATSDR finds that the measured concentrations from this sampling effort are of an unknown quality, because no documentation can be found describing the sampling methods used or the quality assurance measures taken.

C.7 Reports that EPA Conducted Air Sampling on Vieques During the 1970s

ATSDR has identified two accounts of an EPA air sampling project that reportedly took place on Vieques in the 1970s (ViequesLibre 2001, ViequesWar 2001). According to one of these accounts, ". . .the US Environmental Protection Agency sampled Vieques' air and soil. After studying the samples, the EPA determined that the air has unhealthy levels of particulate matter and the ground has iron levels above normal" (ViequesLibre 2001). The account from the other source is nearly identical (ViequesWar 2001). However, neither account cites an EPA document where these findings are published or provides critical information ATSDR would need to interpret this sampling project, such as the number and locations of sampling stations, the sampling methods, and the measured air concentrations.

Given the implications of the quote cited above, ATSDR made several attempts to locate the primary sources of information on EPA's sampling. First, ATSDR downloaded all ambient air monitoring results for Vieques from EPA's Aerometric Information Retrieval System (AIRS)–an online clearinghouse of air sampling data. However, AIRS had no sampling records for Vieques from the 1970s. The absence of data from AIRS does not necessarily mean that samples were never collected, but EPA typically submits its sampling results for criteria pollutants to this system. Second, ATSDR contacted senior officials from EPA Region 2 and EPA's Caribbean Environmental Protection Division. Individuals from both offices had no knowledge of the agency ever conducting air sampling projects on Vieques. Third, ATSDR conducted a thorough review of the project files on the Vieques site at EPA Region 2, and found no information about past air sampling projects.

Therefore, based on the best information available, ATSDR has reason to believe that EPA never sampled air on Vieques in the 1970s. Because valid sampling data form the best basis for evaluating the public health implications of exposure to air pollution, ATSDR encourages any individuals with detailed information on past sampling projects to submit them to the agency for review.

Table C-1.

Summary of PREQB's 2000-2001 Sampling Results
Parameter Sampling Results, by Location
Esperanza Isabel Segunda
Summary Statistics for PM10 Sampling
Number of samples 130 91
Average concentration 34.1 µg/m3 23.5 µg/m3
Range of concentrations 14-79 µg/m3 10-94 µg/m3
Standard deviation 12.9 µg/m3 13.0 µg/m3
Summary Statistics for TSP Sampling
Number of samples 133 89
Average concentration 40.4 µg/m3 34.0 µg/m3
Range of concentrations 17-163 µg/m3 14-177 µg/m3
Standard deviation 20.3 µg/m3 21.3 µg/m3

Notes:
- Data downloaded from EPA's AIRS database.
- EPA's current health-based air quality standards for PM10 are: 150 µg/m3 for 24-hour average concentrations, and 50 µg/m3 for annual average concentrations. The maximum and average PM10 concentrations measured at both stations on Vieques are lower than their corresponding standards.
- EPA's former health-based air quality standards for TSP were: 260 µg/m3 for 24-hour average concentrations, and 75 µg/m3 for annual average concentrations. The maximum and average TSP concentrations measured at both stations on Vieques are lower than their corresponding standards.


 
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