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Testimony: 

Before the Subcommittee on Environment and Hazardous Materials, House 
Committee on Energy and Commerce: 

United States Government Accountability Office: 

GAO: 

For Release on Delivery Expected at 10:00 a.m. EDT: 

Wednesday, April 25, 2007: 

Perchlorate: 

EPA Does Not Systematically Track Incidents of Contamination: 

Statement of John B. Stephenson, Director: 
Natural Resources and Environment: 

GAO-07-797T: 

GAO Highlights: 

Highlights of GAO-07-797T, a testimony before the Subcommittee on 
Environment and Hazardous Materials, House Committee on Energy and 
Commerce 

Why GAO Did This Study: 

Perchlorate has been used for decades by the Department of Defense, the 
National Aeronautics and Space Administration, and the defense industry 
in manufacturing, testing, and firing missiles and rockets. Other uses 
include fireworks, fertilizers, and explosives. Perchlorate is readily 
dissolved and transported in water and has been found in groundwater, 
surface water, and soil across the country. Perchlorate emerged as a 
contaminant of concern because health studies have shown that it can 
affect the thyroid gland, which helps regulate the body’s metabolism, 
and may cause developmental impairment in fetuses of pregnant women. In 
2005, EPA set a reference dose of 24.5 parts per billion (ppb)—the 
exposure level not expected to cause adverse effect in humans. 

Today’s testimony updates GAO’s May 2005 report, Perchlorate: A System 
to Track Sampling and Cleanup Results is Needed, GAO-05-462. It 
summarizes GAO’s (1) compilation of the extent of perchlorate 
contamination in the U.S. and (2) review of peer-reviewed studies about 
perchlorate’s health risks. GAO’s 2005 report recommended that EPA work 
to track and monitor perchlorate detections and cleanup efforts. In 
December 2006, EPA reiterated its disagreement with this 
recommendation. GAO continues to believe such a system would better 
inform the public and others about perchlorate’s presence in their 
communities. 

What GAO Found: 

Perchlorate has been found at 395 sites in the U.S.—including 153 
public drinking water systems—in concentrations ranging from 4 ppb to 
more than 3.7 million ppb. More than half the sites are in California 
and Texas, with the highest concentrations found in Arkansas, 
California, Texas, Nevada, and Utah. About 28 percent of sites were 
contaminated by defense and aerospace activities related to propellant 
manufacturing, rocket motor research and test firing, or explosives 
disposal. Federal and state agencies are not required to routinely 
report perchlorate findings to EPA, which does not track or monitor 
perchlorate detections or cleanup status. EPA recently decided not to 
regulate perchlorate in drinking water supplies pending further study. 

GAO reviewed 90 studies of health risks from perchlorate published from 
1998 to 2005, and one-quarter indicated that perchlorate had an adverse 
effect on human health, and thyroid function in particular. In January 
2005, the National Academy of Sciences also reviewed several studies 
and concluded that they did not support a clear link between 
perchlorate exposure and changes in the thyroid function. The academy 
did not recommend a drinking water standard but recommended additional 
research into the effect of perchlorate exposure on children and 
pregnant women. More recently, a large study by CDC scientists has 
identified adverse thyroid effects from perchlorate in women with low 
iodine levels that are found in about 36 percent of U.S. women. 

Figure: Number of Sites and Maximum Perchlorate Concentrations, by 
State: 

[See PDF for Image] 

[End of figure] 

[Hyperlink, http://www.gao.gov/cgi-bin/getrpt?GAO-07-797T]. 

To view the full product, including the scope and methodology, click on 
the link above. For more information, contact John Stephenson at (202) 
512-3841 or stephensonj@gao.gov. 

[End of section] 

Mr. Chairman and Members of the Subcommittee: 

I am pleased to be here today to discuss our work on perchlorate, a 
chemical most commonly used in rocket fuel. A combination of human 
activity and natural sources has led to the widespread presence of 
perchlorate in the environment. Perchlorate has been used for decades 
by the Department of Defense (DOD), the National Aeronautics and Space 
Administration (NASA), and the defense industry in the manufacturing, 
testing, and firing of missiles and rockets. According to the 
Environmental Protection Agency's (EPA) estimates, 90 percent of the 
perchlorate produced in the United States is manufactured for use by 
the military and NASA, with total typical production quantities 
averaging several million pounds per year. Private industry also has 
used perchlorate to manufacture automobile airbags, fireworks, flares, 
and commercial explosives. Natural sources include certain atmospheric 
processes and Chilean nitrate salts (saltpeter) that have been mined 
and refined to produce commercial fertilizers for use in the U.S. 
Perchlorate forms salts that are readily dissolved and transported in 
water and that have been found in groundwater, surface water, and soil 
across the country. People are exposed to the perchlorate primarily by 
ingesting it in drinking water and food, or by working to manufacture 
products that contain the chemical. Health studies have shown that 
exposure to perchlorate can affect the thyroid gland, which helps 
regulate the body's metabolism, and may cause neurodevelopmental 
impairment in fetuses of pregnant women. 

In 2003, EPA, DOD, NASA, and the Department of Energy asked the 
National Academy of Sciences to review the risks of exposure to 
perchlorate. In January 2005, the Academy recommended a reference dose 
of 0.0007 milligrams of perchlorate per kilogram of body weight per 
day, an estimated daily exposure level that is not expected to cause 
adverse effects in the children and pregnant women--the most sensitive 
human populations. This reference dose equates to a drinking water 
equivalent level of 24.5 parts per billion.[Footnote 1] In February 
2005, EPA adopted the Academy's reference dose for perchlorate, but it 
has not established a national federal standard for perchlorate in 
drinking water or other regulatory requirements to clean up perchlorate 
in groundwater, surface water, or soil, citing the need for additional 
study about the health effects of perchlorate exposure. 

My testimony today is based largely on our 2005 report for this 
Committee and summarizes (1) our analysis of the estimated extent of 
perchlorate found in the United States and (2) the results of our 
review of published studies on the health effects of 
perchlorate.[Footnote 2] In the 2005 report, we recommended that EPA 
develop a tracking system for perchlorate releases and cleanup efforts 
across the federal government and state agencies. This statement also 
includes information from my February 2007 testimony about EPA's recent 
response to our recommendation.[Footnote 3] 

To provide an estimate of the extent of perchlorate found in the United 
States, we compiled and analyzed data on perchlorate detections from 
EPA, DOD, the U.S. Geological Survey, and state agencies. To identify 
studies of the potential health risks from perchlorate, who conducted 
them, and what methodologies were used, we conducted a literature 
search for studies of perchlorate health risks published since 1998, 
interviewed DOD and EPA officials on what studies they considered 
important in assessing perchlorate health risks, and examined the 
references of each study for other studies we had not obtained. We 
identified 125 studies on perchlorate and the thyroid, of which we 
reviewed 90 that were relevant to our review. A more detailed 
description of our scope and methodology is presented in appendix I of 
our 2005 report. 

In summary, we found the following: 

* As of our May 2005 review, perchlorate had been found by federal and 
state agencies in groundwater, surface water, soil, or public drinking 
water systems at almost 400 sites across the country in concentrations 
that ranged from 4 parts per billion (ppb) to more than 3.7 million 
ppb. However, there is not a standardized approach to reporting 
perchlorate data nationwide, therefore there may be more contaminated 
sites than we identified. These sites are located across 37 states and 
U.S. territories, but more than half were found in California and 
Texas. The sources of perchlorate at the sites vary, but the greatest 
known source is defense and aerospace activities such as propellant 
manufacturing, rocket motor research and test firing, or explosives 
disposal. More than one-third of the sites were public drinking water 
systems, where perchlorate concentrations ranged from 4 to 420 ppb. 
Fourteen of these 153 public water systems had concentration levels 
above 24.5 parts per billion, the drinking water equivalent of EPA's 
perchlorate reference dose. EPA and state officials told us they had 
not cleaned up contaminated public drinking water systems, principally 
because there was no federal drinking water standard or specific 
federal requirement to clean up perchlorate. Further, it is difficult 
to determine the extent of perchlorate in the United States or the 
status of any cleanup actions because EPA does not centrally track or 
monitor perchlorate detections, environmental releases, or cleanup 
activities. 

* Recent research indicates that low-level perchlorate exposure may 
adversely affect the thyroid and increase the risk of 
neurodevelopmental impairment in fetuses of pregnant women. In our May 
2005 review, we identified and summarized 90 peer-reviewed studies 
published from 1998 to 2005 on the health effects of perchlorate. The 
findings of 26 of these studies indicated that perchlorate had an 
adverse effect on thyroid function and human health. Most studies on 
adult populations were unable to determine whether the thyroid was 
adversely affected, because adverse effects of perchlorate on the adult 
thyroid, such as cancer, may happen over longer time periods than are 
generally observed in a research study. In contrast, the adverse 
effects of perchlorate on human development can be more easily studied 
and measured within study time frames, and 18 studies found adverse 
effects on development resulting from maternal exposure to perchlorate. 
We also found that some studies considered the same perchlorate dose 
but found different effects. The precise cause of the different results 
may be attributed to the studies' designs or to the physical 
conditions--such as sex, age, and blood iodine levels--of studies' 
subjects. Such unresolved questions were one of the bases for the 
differing conclusions among EPA, DOD, and other researchers on 
perchlorate doses and human health effects. In its January 2005 report, 
the National Academy of Sciences called for additional research on 
perchlorate exposure to help resolve questions about its effect on 
children and pregnant women. More recently, an October 2006 CDC study 
found that, for women with lower iodine levels, perchlorate reduced the 
thyroid hormone that helps regulate metabolism and that plays a part in 
central nervous system development in the fetus. 

We concluded in our report that EPA needed more reliable information on 
the extent of sites contaminated with perchlorate and the status of 
cleanup efforts, and recommended that EPA work with the Department of 
Defense and the states to establish a formal structure for tracking 
perchlorate information. In December 2006, EPA reiterated its 
disagreement with the recommendation stating that perchlorate 
information already exists from a variety of other sources. However, we 
continue to believe that the inconsistency and omissions in available 
data that we found during the course of our study underscore the need 
for a more structured and formal tracking system. 

Background: 

According to EPA, perchlorate can interfere with the normal functioning 
of the thyroid gland by competitively inhibiting the transport of 
iodide into the thyroid, which can then affect production of thyroid 
hormones. The fetus depends on an adequate supply of maternal thyroid 
hormone for its central nervous system development during the first 
trimester of pregnancy. The National Academy of Sciences reported that 
inhibition of iodide uptake from low-level perchlorate exposure may 
increase the risk of neurodevelopmental impairment in fetuses of high- 
risk mothers--pregnant women who might have iodine deficiency or 
hypothyroidism (reduced thyroid functioning). The Academy recognized 
the differences in sensitivity to perchlorate exposure between the 
healthy adults used in some studies and the most sensitive population 
and the fetuses of these high-risk mothers. Consequently, the Academy 
included a 10-fold uncertainty factor in its recommended reference dose 
to protect these sensitive populations. The Academy also called for 
additional research to help determine what effects low-level 
perchlorate exposure may have on children and pregnant women. 

EPA has issued drinking water regulations for more than 90 
contaminants. The Safe Drinking Water Act, as amended in 1996, requires 
EPA to make regulatory determinations on at least five unregulated 
contaminants and decide whether to regulate these contaminants with a 
national primary drinking water regulation. The act requires that these 
determinations be made every five years. The unregulated contaminants 
are typically chosen from a list known as the Contaminant Candidate 
List (CCL), which the act also requires EPA to publish every five 
years. EPA published the second CCL on February 24, 2005. On April 11, 
2007, EPA announced its preliminary determination not to regulate 11 of 
the contaminants on this list. The agency also announced that it was 
not making a regulatory determination for perchlorate because EPA 
believed that additional information may be needed to more fully 
characterize perchlorate exposure and determine whether regulating 
perchlorate in drinking water presents a meaningful opportunity for 
health risk reduction. 

Several federal environmental laws provide EPA and states authorized by 
EPA with broad authorities to respond to actual or threatened releases 
of substances that may endanger public health or the environment. For 
example, the Comprehensive Environmental Response, Compensation, and 
Liability Act of 1980 (CERCLA), as amended, authorizes EPA to 
investigate the release of any hazardous substance, pollutant, or 
contaminant. The Resource Conservation and Recovery Act of 1976 (RCRA) 
gives EPA authority to order a cleanup of hazardous waste when there is 
an imminent and substantial endangerment to public health or the 
environment, and one federal court has ruled that perchlorate is a 
hazardous waste under RCRA.[Footnote 4] The Clean Water Act's National 
Pollutant Discharge Elimination System (NPDES) provisions authorize 
EPA, which may, in turn, authorize states, to regulate the discharge of 
pollutants into waters of the United States. These pollutants may 
include contaminants such as perchlorate. The Safe Drinking Water Act 
authorizes EPA to respond to actual or threatened releases of 
contaminants into public water systems or underground sources of 
drinking water, regardless of whether the contaminant is regulated or 
unregulated, where there is an imminent and substantial endangerment to 
health and the appropriate state and local governments have not taken 
appropriate actions. Under certain environmental laws such as RCRA, EPA 
can authorize states to implement the requirements as long as the state 
programs are at least equivalent to the federal program and provide for 
adequate enforcement. 

In addition, some states have their own environmental and water quality 
laws that provide state and local agencies with the authority to 
monitor, sample, and require cleanup of various regulated and 
unregulated hazardous substances that pose an imminent and substantial 
danger to public health. For example, the California Water Code 
authorizes Regional Water Control Boards to require sampling of waste 
discharges and to direct cleanup and abatement, if necessary, of any 
threat to water, including the release of an unregulated contaminant 
such as perchlorate. Finally, according to EPA and state officials, at 
least 9 states have established nonregulatory action levels or 
perchlorate advisories, ranging from under 1 part per billion to 18 
parts per billion, under which responsible parties have been required 
to sample and clean up perchlorate. For example, according to 
California officials, the state of California has a public health goal 
for perchlorate of 6 parts per billion and has used the goal to require 
cleanup at one site. 

Perchlorate Has Been Found At 395 Sites Including 153 Public Drinking 
Water Systems: 

Because information on the extent of perchlorate contamination was not 
readily available, we thoroughly reviewed available perchlorate 
sampling reports and discussed them with federal and state 
environmental officials. We identified 395 sites in 35 states, the 
District of Columbia, and 2 commonwealths of the United States where 
perchlorate has been found in drinking water, groundwater, surface 
water, sediment, or soil. The perchlorate concentrations ranged from 
the minimum reporting level of 4 parts per billion to in more than 3.7 
million parts per billion--a level found in groundwater at one of the 
sites. Roughly one-half of the contaminated sites were found in Texas 
(118) and California (106), where both states conducted broad 
investigations to determine the extent of perchlorate contamination. As 
shown in figure 1, the highest perchlorate concentrations were found in 
five states--Arkansas, California, Nevada, Texas, and Utah--where, 
collectively, 11 sites had concentrations exceeding 500,000 parts per 
billion. However, most of the 395 sites did not have such high levels 
of contamination. We found 271 sites where the concentration was less 
than 24.5 parts per billion, the drinking water concentration 
equivalent calculated on the basis of EPA's reference dose. 

Figure 1: Number of Sites and Maximum Perchlorate Concentrations, by 
State: 

[See PDF for image] 

Sources: Environmental Protection Agency, Department of Defense, U.S. 
Geological Survey, and state environmental agencies. 

[End of figure] 

According to EPA and state agency officials, the greatest known source 
of contamination was defense and aerospace activities. As shown in 
figure 2, our analysis found that, at 110 of the 395 sites, the 
perchlorate source was related to propellant manufacturing, rocket 
motor testing firing, and explosives testing and disposal at DOD, NASA, 
and defense-related industries. Officials said the source of the 
contamination at another 58 sites was agriculture, a variety of other 
commercial activities such as fireworks and flare manufacturing, and 
perchlorate manufacturing and handling. At the remaining sites, state 
agency officials said the source of the perchlorate was either 
undetermined (122 sites) or naturally occurring (105 sites). Further, 
all 105 sites with naturally occurring perchlorate are located in the 
Texas high plains region where perchlorate concentrations range from 4 
to 59 parts per billion. 

Figure 2: Activities Linked to Perchlorate, by Site: 

[See PDF for image] 

Sources: Environmental Protection Agency, Department of Defense, U.S. 
Geological Survey, and state environmental agencies. 

[End of figure] 

Of the sites we identified, 153 were public drinking water systems. The 
Safe Drinking Water Act's Unregulated Contaminant Monitoring Regulation 
required sampling of public drinking water systems for a 12-month 
period between 2001 and 2003. . As of January 2005, 153 (about 4 
percent) of 3,722 systems that were sampled and reported reported 
finding perchlorate to EPA. Located across 26 states and 2 
commonwealths, these 153 sites accounted for more than one-third of the 
sites we identified where perchlorate concentrations reported ranged 
from 4 parts per billion to 420 parts per billion but averaged less 
than 10 parts per billion. Only 14 of the 153 public drinking water 
systems had concentration levels above 24.5 parts per billion, the 
drinking water equivalent calculated on the basis of EPA's revised 
perchlorate reference dose. California had the most public water 
systems with perchlorate, where 58 systems reported finding perchlorate 
in drinking water. The highest drinking water perchlorate concentration 
of 420 parts per billion was found in Puerto Rico in 2002. Subsequent 
sampling in Puerto Rico did not find any perchlorate, and officials 
said the source of the initial finding was undetermined. 

These 153 public drinking water systems that found perchlorate serve 
populated areas, and an EPA official estimated that as many as 10 
million people may have been exposed to the chemical. EPA officials 
told us they do not know the source of most of the contamination found 
in public drinking water systems, but that 32 systems in Arizona, 
California, and Nevada were likely due to previous perchlorate 
manufacturing at a Kerr McGee Chemical Company site in Henderson, 
Nevada. Regional EPA and state officials told us they did not plan to 
clean up perchlorate found at public drinking water sites until EPA 
establishes a drinking water standard for perchlorate. In some cases, 
officials did not plan to clean up because subsequent sampling was 
unable to confirm that perchlorate was present. 

EPA officials said the agency does not centrally track or monitor 
perchlorate detections or the status of cleanup activities. As a 
result, it is difficult to determine the extent of perchlorate 
contamination in the U.S. EPA maintains a list of sites where cleanup 
or other response actions are underway but the list does not include 
sites not reported to EPA. As a result, EPA officials said they did not 
always know whether other federal and state agencies found perchlorate 
because, as is generally the case with unregulated contaminants, there 
is no requirement for states or other federal agencies to routinely 
report perchlorate findings to EPA. 

For example, DOD is not required to report to EPA when perchlorate is 
found on active installations and facilities. Consequently, EPA region 
officials in California said they did not know the Navy found 
perchlorate at the Naval Air Weapons Station at China Lake because the 
Navy did not report the finding to EPA. Further, states are not 
required to routinely notify EPA about perchlorate contamination they 
discover. For example, EPA region officials in California said the 
Nevada state agency did not tell them perchlorate was found at 
Rocketdyne, an aerospace facility in Reno, or that it was being cleaned 
up. EPA only learned about the perchlorate contamination when the 
facility's RCRA permit was renewed. 

Recent Research Indicates that Perchlorate Exposure May be a Concern 
for Pregnant Women: 

In our May 2005 review, we conducted a literature search for studies of 
perchlorate health risks published from 1998 to 2005 and identified 125 
studies on perchlorate and the thyroid. After interviewing DOD and EPA 
officials about which studies they considered important in assessing 
perchlorate health risks, we reviewed 90 that were relevant to our 
work. The findings of 26 of these studies indicated that perchlorate 
had an adverse effect on thyroid function and human health. In January 
2005, the National Academy of Sciences considered many of these same 
studies and concluded that the studies did not support a clear link 
between perchlorate exposure and changes in the thyroid function or 
thyroid cancer in adults. Consequently, the Academy recommended 
additional research into the effect of perchlorate exposure on children 
and pregnant women but did not recommend a drinking water standard. 

DOD, EPA, and industry sponsored the majority of the 90 health studies 
we reviewed; the remaining studies were conducted by academic 
researchers and other federal agencies. Of these 90 studies, 49 were 
experiments that sought to determine the effects of perchlorate on 
humans, mammals, fish, and/or amphibians by exposing these groups to 
different doses of perchlorate over varied time periods and comparing 
the results with other groups that were not exposed. Twelve were field 
studies that compared humans, mammals, fish, and/or amphibians in areas 
known to be contaminated with the same groups in areas known to be 
uncontaminated. Both types of studies have limitations: the 
experimental studies were generally short in duration, and the field 
studies were generally limited by the researchers' inability to control 
whether, how much, or how long the population in the contaminated areas 
was exposed. For another 29 studies, researchers reviewed several 
publicly available human and animal studies and used data derived from 
these studies to determine the process by which perchlorate affects the 
human thyroid and the highest exposure levels that did not adversely 
affect humans. The 3 remaining studies used another 
methodology.[Footnote 5] Many of the studies we reviewed contained only 
research findings, rather than conclusions or observations on the 
health effects of perchlorate. Appendix III from our 2005 report 
provides data on these studies, including who sponsored them; what 
methodologies were used; and, where presented, the author's conclusions 
or findings on the effects of perchlorate. 

Only 44 of the studies we reviewed had conclusions on whether 
perchlorate had an adverse effect. However, adverse effects of 
perchlorate on the adult thyroid are difficult to evaluate because they 
may happen over longer time periods than can be observed in a typical 
research study. Moreover, different studies used the same perchlorate 
dose amount but observed different effects, which were attributed to 
variables such as the study design type or age of the subjects. Such 
unresolved questions were one of the bases for the differing 
conclusions in EPA, DOD, and academic studies on perchlorate dose 
amounts and effects. 

The adverse effects of perchlorate on development can be more easily 
studied and measured within typical study time frames. Of the studies 
we reviewed, 29 evaluated the effect of perchlorate on development, and 
18 of these found adverse effects resulting from maternal exposure to 
perchlorate. According to EPA officials, the most sensitive population 
for perchlorate exposure is the fetus of a pregnant woman who is also 
nearly iodine-deficient. However, none of the 90 studies that we 
reviewed considered this population. Some studies reviewed the effect 
on the thyroid of pregnant rats, but we did not find any studies that 
considered perchlorate's effect on the thyroid of nearly iodine- 
deficient pregnant rats. 

In January 2005, the National Academy of Sciences issued its report on 
EPA's draft health assessment and the potential health effects of 
perchlorate. The Academy reported that although perchlorate affects 
thyroid functioning, there was not enough evidence to show that 
perchlorate causes adverse effects at the levels found in most 
environmental samples. Most of the studies that the Academy reviewed 
were field studies, the report said, which are limited because they 
cannot control whether, how much, or how long a population in a 
contaminated area is exposed. The Academy concluded that the studies 
did not support a clear link between perchlorate exposure and changes 
in the thyroid function in newborns and hypothyroidism or thyroid 
cancer in adults. In its report, the Academy noted that only 1 study 
examined the relationship between perchlorate exposure and adverse 
effects on children, and that no studies investigated the relationship 
between perchlorate exposure and adverse effects on vulnerable groups, 
such as low-birth-weight infants. The Academy concluded that an 
exposure level higher than initially recommended by EPA may not 
adversely affect a healthy adult. The Academy recommended that 
additional research be conducted on perchlorate exposure and its effect 
on children and pregnant women but did not recommend that EPA establish 
a drinking water standard. To address these issues, in October 2006, 
CDC researchers published the results of the first large study to 
examine the relationship between low-level perchlorate exposure and 
thyroid function in women with lower iodine levels. About 36 percent of 
U.S. women have these lower iodine levels. The study found decreases in 
a thyroid hormone that helps regulate the body's metabolism and is 
needed for proper fetal neural development in pregnant women. 

Mr. Chairman, this concludes my testimony. I would be pleased to answer 
any questions that you or other Members of the Subcommittee may have at 
this time. 

GAO Contacts and Staff Acknowledgments: 

For further information about this presentation, please contact me, 
John Stephenson, at (202) 512-3841 or stephensonj@gao.gov. Contact 
points for our Offices of Congressional Relations and Public Affairs 
may be found on the last page of this statement. Contributors to this 
testimony include Steven Elstein, Assistant Director, and Terrance 
Horner, Senior Analyst; Richard Johnson, Alison O'Neill, Kathleen 
Robertson, and Joe Thompson also made key contributions. 

FOOTNOTES 

[1] The drinking water equivalent level is based on a reference adult 
weighing 70 kilograms (or 154 pounds) drinking 2 liters of water per 
day, assuming that all perchlorate exposure comes from drinking water. 

[2] GAO, Perchlorate: A System to Track Sampling and Cleanup Results is 
Needed, GAO-05-462 (Washington, D.C.: May 20, 2005). 

[3] GAO, Environmental Information: EPA Actions Could Reduce the 
Availability of Environmental Information to the Public, GAO-07-464T 
(Washington, D.C.: February 6, 2007). 

[4] Castaic Lake Water Agency v. Whittaker Corp, 272 F. Supp. 2d 1053 
(C.D. Cal. 2003). The conclusion that perchlorate is a hazardous waste 
was the first step in the court's analysis of whether perchlorate is a 
hazardous substance under the Comprehensive Environmental Response, 
Compensation, and Liability Act (CERCLA). (The definition of hazardous 
substances under CERCLA includes hazardous waste under RCRA.) 

[5] The number of study types is greater than the total number of 
studies because 3 studies used a combination of experimental design and 
data analysis methodologies.

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