ATSDR-PHA-HC-Sierra Army Depot, Herlong, Lassen County, California

HEALTH CONSULTATION

Air Pathway Evaluation

SIERRA ARMY DEPOT
HERLONG, LASSEN COUNTY, CALIFORNIA

VI. EVALUATION OF CANCER CASES

To determine whether SIAD's air emissions cause cancer among nearby residents, ATSDR not only evaluated potential air exposures (see Section V), but we also critically reviewed data on the number of people near SIAD who have been diagnosed with cancer. Our Division of Health Studies reviewed trends among the cancer statistics to answer a fundamental question: Are there more cases of cancer near SIAD than expected?

We also evaluated whether the cancer registries use acceptable methods to identify and interpret all reported cancer cases. This evaluation considered two concerns expressed specifically for the area surrounding SIAD: whether cancer cases are adequately tracked for California residents who seek medical care in Nevada, and vice versa; and how the cancer registries interpret cases for which residential addresses are not reported.

The remainder of this section documents our findings. This section first presents basic facts on cancer (Section VI.A), and then gives a general summary of how we interpreted the cancer data compiled by the California (Section VI.B) and Nevada (Section VI.C) cancer registries. Sections VI.D and VI.E present our comments on data limitations and data quality, respectively. Recommendations are provided in Section X.

A. Introduction

"Cancer" is a group of many different diseases that cause cells to grow and multiply at abnormal rates. Different cancers are caused by different risk factors. Cancer is the second leading cause of death in the United States, currently causing approximately one out of every four deaths nationwide (CDC 2002). Furthermore, roughly two out of every five Americans will be diagnosed with cancer at some time in their lives (NCI 2002).

There are numerous causes of cancer, many of which are not fully understood. Researchers often group factors that cause cancer into two broad categories–heredity and the environment (NCI 2001). Hereditary factors are genetic and therefore are present at birth. Environmental factors include a wide array of behavioral and lifestyle causes (e.g., smoking, exposure to sunlight), including exposures to cancer-causing chemicals. Although many individual causes of cancer have been identified, scientists are still learning how these various factors interact to cause different kinds of cancer. For instance, because some people may be potentially exposed to trace amounts of cancer-causing chemicals at their jobs, in their diets, and from the environment, the exact cause of a person's cancer is often not known. Furthermore, ten or more years may pass between the time that a cancer-causing exposure occurs and the time that the cancer is eventually diagnosed (ACS 2002), which complicates efforts to understand exactly which exposures may have potentially contributed to the cancer.

The community has expressed concerns about a perceived excess of cancer in the communities around the SIAD site. ATSDR's evaluation of perceived elevated types of cancer within a community involves the review of available environmental data to identify potential pathways of human exposure and the presence or absence of contaminants at or above levels of public health concern. In addition, a review of available health outcome data is also performed. In this health consultation, the health outcome data available for review consisted of descriptive data from a population-based cancer registry which was collected for purposes of cancer surveillance.

To determine whether SIAD's air emissions might be related to a perceived excess of cancer cases among nearby residents, ATSDR not only evaluated potential air exposures (see Section V), but also reviewed available health outcome data on cancer incidence within communities near the SIAD. Our evaluation is based largely on data reported to the California Cancer Registry (CCR). Information from the Nevada Central Cancer Registry (NCCR) specific to the communities around the SIAD was not available for this consultation. The purpose of this cancer data review is to evaluate available cancer incidence data to determine whether cancer incidence in the communities around SIAD is statistically significantly elevated.

B. Evaluation of Cancer Cases in California

The Cancer Registry of Northern California (CRNC), Region 6 of the California Cancer Registry (CCR), routinely calculates cancer incidence rates for the sixteen counties of the greater Northern California area, including Lassen County. Regional cancer incidence data is available at the county level; however, the data for Lassen County is combined with that of Plumas and Modoc counties which have smaller populations (CRNC 2000). In order to evaluate cancer incidence in the communities around the SIAD, ATSDR's review of CRNC/CCR's data is limited to descriptive analyses conducted by CRNC/CCR specific to the communities located near the SIAD site.

For this consultation, ATSDR reviewed three small area assessments for census tracts around the SIAD. Each of these assessments was performed by the CRNC/CCR. Each of the small area assessments had been conducted by the CRNC/CCR in response to community concerns about the possible health effects to Lassen County residents from potentially hazardous emissions from the combustion of surplus munitions at the SIAD site. It should be further noted that the CRNC/CCR assessments had been performed prior to the initiation of the environmental monitoring described in this health consultation. Therefore, no potential exposure pathways or potential contaminants of concern had been evaluated or identified for the SIAD site at the time that these small area assessments were performed. In addition, the first two assessments had been performed prior to ATSDR's involvement with the SIAD site.

Each of the three assessments evaluated cancer incidence for four census tracts in Lassen County, California: 040300 (Susanville), 040400 (Litchfield and Standish), 040500 (Janesville), and 040600 (Wendel, Herlong, Doyle, Patton Village, and Milford). These census tracts correspond to areas surrounding the SIAD facility and encompass the populated areas south of Eagle Lake, including Susanville, southeast to Herlong and Doyle and the California/Nevada border. The purpose of each of the three assessments was to evaluate whether the communities around the SIAD site had statistically significant excesses of (1) childhood cancers among persons ages 0 through 19 years of age; and (2) cancers selected by CRNC/CCR which had sometimes been associated with chemical exposures in occupational settings and which might serve as potential sentinels of possible ambient environmental exposures. The cancers selected by CRNC/CCR as being sometimes associated with occupational settings included: brain and nervous system tumors, Non-Hodgkin's lymphoma, leukemia (all types), lymphocytic leukemias, and granulocytic/myelocytic leukemias. As noted previously, the small area assessments were performed prior to the environmental monitoring discussed in this health consultation and no potential exposure pathways or potential contaminants of concern had been evaluated or identified for the SIAD site at the time.

CRNC/CCR calculated the number of observed and expected cancer cases and calculated a 99% confidence interval (range) around the number of observed cases. To estimate the number of cancer cases expected, 1988-1992 annual average sex-, race-, and age-specific rates of invasive cancers for all sites combined for the CRNC/CCR area were applied to the corresponding population residing in that area at the time of the 1990 Census. Exact number of cases were not presented by CRNC/CCR when small numbers were involved. This was done to maintain the confidentially of persons reported to the CCR. The confidentiality of persons whose cancers are reported to the CCR is mandated by law and is given the highest priority of registry operations (DHS 2000).

CRNC/CCR performed the first small area assessment in April 1999 in response to community concern about the possible health effects to Lassen County residents from potentially hazardous emissions from the combustion of surplus munitions at SIAD. In this assessment, CRNC/CCR evaluated cancers which had been diagnosed in the years 1988 through 1996 and the years 1992 though 1996. The year 1988 represents the year in which regional population-based cancer registries in California began reporting to the CCR and 1996 was the most recent year of cancer incidence data available at the time of the assessment. The years 1992-1996 represent the most recent (at that time) five year period in which data were available. For the 9-year period, 1988-1996, CRNC/CCR identified 11 new primary, invasive cancers initially diagnosed among residents 0-19 years of age whose residential address at the time of diagnosis was in census tracts 040300-040600. For this period (1988-1996) ten cases of childhood cancer were expected. However, the slightly elevated number of childhood cancers observed was not statistically significantly elevated (observed cases=11, expected cases=10; 99% CI: 4-23 cases). It should be noted that this analysis involved childhood cancers for all cancer sites combined and not for specific childhood cancers sites because of small numbers of cases of specific cancer types among children 0-19 years of age. When CRNC/CCR evaluated cancers which had sometimes been associated with exposures in occupational settings, brain and nervous system tumors, leukemias (all types combined) and lymphocytic leukemias were slightly higher than expected, but none was statistically significantly elevated in the four combined census tracts.

CRNC/CCR's second assessment (dated February 2000) evaluated cancers reported to the registry which had been diagnosed during the 10-year period 1988 through 1997 and within the most recent (as of February 2000) 5-year period, 1993 through 1997. As a result of continued community concern and to remain as responsive as possible to the community, CRNC/CCR performed this assessment which re-analyzed the cancer registry data with new unvalidated information on potential cancer cases. Prior to February 2000, the last official interstate case share of cancer data from the Nevada Central Cancer Registry had been received by CCR in 1997 and consisted of reports of cancer cases diagnosed between the years 1988 through 1995. The February 2000 small area assessment identified a total of 14 new primary, invasive cancers among residents ages 0-19 years of age who lived at the time of diagnosis within the four census tracts during the 10-year period 1988 through 1997. For this period (1988-1997), ten cases of childhood cancer were expected; however, the slight elevation in observed cancer cases for this age group and time period was not statistically significantly elevated (observed cases=14, expected cases=10; 99% CI: 6-27 cases). The wide confidence interval reflects the small number of cases within the census tracts. Also, in this assessment, the review of cancers sometimes associated with exposures in occupational settings did not suggest any statistically significant excess of cancers for the 10-year period 1988-1997 or for the 5-year period 1993-1997.

The third small area assessment (dated July 2000) for the census tracts around the SIAD was performed by CRNC/CCR after CCR received an official electronic interstate case share of cancer cases from the Nevada Central Cancer Registry. These cases represented California residents who received a cancer diagnosis in the state of Nevada. The community, CCR and ATSDR were concerned and interested in knowing whether the additional cancer cases from Nevada might possibly reveal elevated types of cancers among California residents living in the census tracts surrounding SIAD. With the third assessment, CRNC/CCR was more confident that most, if not all, cases from the census tracts evaluated who might have been diagnosed in Nevada were included in the assessment. Comparison of the July 2000 assessment with the February 2000 assessment suggested, however, that there was no increase in the number of primary invasive childhood cancers within the census tracts evaluated for the years 1988 through 1997 (observed cases=14, expected cases=10.2; 99% CI: 6.0-26.6 cases). In addition, there were no statistically significant elevations in childhood cancers in this assessment for census tract 040300 (Susanville) or in the combined census tracts (040400-040600) in analyses which included or excluded untracted cases. Untracted cases are cases for which a Post Office Box or non-United States Postal Service address was reported as the residential address at the time of diagnosis. An untracted address cannot be accurately assigned to a specific census tract and thus increases the uncertainty of the analysis. In addition, census tracts (040400-040600) were combined in some analyses due to small numbers of cases within the separate census tracts. In the evaluation of cancers sometimes associated with exposures in occupational settings, the July 2000 assessment found the incidence of leukemias-all types combined (for all ages) for the Susanville census tract (040300) during the years 1988 through 1997 was statistically significantly elevated (observed cases=22, cases expected=11.5; 99% CI: 11.6-37.0 cases). However, it should be noted that this statistically significant excess did not remain when the six cases with untracted addresses were excluded from the analysis. Since the category of leukemias (all types) consists of many forms of leukemia, CRNC/CCR further evaluated the finding to determine what types of leukemia were driving the result. They found that no leukemia subset of the analysis was statistically significantly higher than expected for all four census tracts combined or for individual census tracts with or without the untracted cases. They found that lymphocytic leukemias seemed to contribute the majority of the excess cases observed in the Susanville census tract for the years 1988-1997, with acute and chronic lymphocytic leukemia accounting for the difference. However, they also found that no difference was significantly higher than expected in either the Susanville census tract or in the combined census tracts for acute or chronic lymphocytic, all lymphocytic, or all granulocytic leukemias for the periods 1988-1997 or 1993-1997.

C. Evaluation of Cancer Cases in Nevada

Noting that prevailing winds near SIAD blow the OB/OD air emissions toward the state of Nevada, ATSDR also evaluated data provided by the Nevada State Health Division (NSHD) on cancer cases east of SIAD. The most detailed information that ATSDR has examined is NSHD's recent statewide report on cancer (NSHD 2001). This report presents a wide range of cancer statistics, but spatial analyses are only offered at the county level. In addition, it should be noted that this data is limited by the fact that for the years 1995 through 1999, Nevada hospitals were the sole source of new (incident) cancer cases reported to the Nevada Central Cancer Registry (Bureau of Health Planning and Statistics 2001); therefore, some cancer types may have been under-reported. In addition, the possibility exists that a small number of cancers diagnosed outside a hospital setting may not have been reported to the Nevada Central Cancer Registry in order to be counted in either the Nevada or California cancer registries. Although air emissions from SIAD clearly blow into parts of Washoe County, cancer statistics for this entire county are a poor metric for the areas downwind from SIAD. As evidence of this, ATSDR notes that the population of Washoe County is 339,486 (US Bureau of the Census 2000), but fewer than 200 residents live in parts of the county that are within 20 miles of SIAD. Therefore, the county-wide cancer statistics are heavily skewed by the more populated areas of Washoe County (the Reno metropolitan area) and offer no meaningful insights for this health consultation.

ATSDR has periodically consulted with representatives of NSHD about the availability of more detailed cancer registry records for subsets of Washoe County. In our final communication with NSHD prior to release of this health consultation, ATSDR learned that NSHD continues to work on expanding the utility of the cancer registry for Washoe County (e.g., attempting to incorporate data from the Pyramid Lake Indian Reservation), but has not yet compiled data that would allow ATSDR to examine cancer incidence among people who live in the parts of Washoe County that are downwind from SIAD.

In summary, the cancer incidence data ATSDR has reviewed to date do not support a meaningful analysis of cancer cases among Nevada residents who live downwind from SIAD. ATSDR will complete its cancer evaluation for these Nevada residents if NSHD can provide data that will support such an assessment.

D. Data Limitations

It should be noted that there are many limitations of using the descriptive data from a population-based registry. This type of health outcome data provides important information about the amount and distribution of disease within a population by person, place, and time; however, it cannot be used to identify an association between an exposure and a health outcome. In order to fully examine potential causes of cancer, more powerful analytic studies which include information on potential exposures and individual risk factors would have to be applied.

The cancer registry data was collected as a means of monitoring trends in cancer incidence, treatment and prevention and for generating research hypotheses (CRNC 2000). The cancer registry also evaluates its incidence data to help determine whether a perceived excess of cancer may be a public health concern or whether the perceived excess may be due to chance (CRNC 2000). The descriptive data do not include information on important confounding factors related to cancer such as whether a person smoked or consumed alcoholic beverages. Information about these and other individual risk factors are not available and therefore any interpretation of the data are subject to biases related to confounding and may not provide a true indication of risk in a community.

Also, the patient's address recorded in the cancer registry data base is the address where the patient lived at the time of cancer diagnosis. The data does not include information about how long the person has lived at the reported address. Since the latency of various types of cancer can range from approximately 10 years to a few decades, it is possible that persons may have been potentially exposed to substances from other residential (or occupational) locations.

In some instances, the address recorded in the cancer registry data base may not have been the patient's actual physical address at their time of diagnosis, but instead a post office box or non-United States Postal Service (USPS) address. These are known as untracted addresses. Untracted addresses cannot accurately be linked to a specific census tract. CCR reporting requirements urge those who submit registry data to provide street addresses (CCR 2001), but a small percentage of records in the registry contain a post office box or non-USPS address. While untracted entries in cancer registries limit the utility of spatial analyses, it should be noted that CRNC/CCR did conduct and present separate analyses including and excluding the untracted entries of the data in at least the February 2000 assessment to demonstrate the potential for uncertainty attributable to the untracted cases.

Another very important issue concerns the population estimates used in the evaluation of cancer in communities. Population estimates are used to generate the number of expected cancer cases in a specific geographic area over a specified time period. An evaluation of cancer incidence in a community includes the comparison of the observed and expected numbers of cancer cases over a certain time period. The population estimates used in the small area analyses reviewed are based on the 1988-1992 annual average sex-, race-, and age-specific rates of invasive cancers for all sites combined for the CRNC/CCR area which were applied to the corresponding population residing in that area at the time of the 1990 Census (obtained by the CCR from the California Department of Finance (DOF)). Expected numbers of cancer cases are based on the age and sex composition of the population; therefore, sufficient changes in the population structure over time can potentially result in either an over- or under-estimate of cancer incidence within a specific community over a specific time period. It is very important to note that CRNC/CCR clearly stated in their analysis that Lassen County estimates from the DOF indicated that between the years 1988-1997, the overall population of Lassen County increased by more than 20% with variation by race, sex and age. In the July 2000 assessment (CCR 2000b), CRNC/CCR noted that during this period, Lassen County experienced a 7% increase of residents 0-19 years of age; a 33% increase of persons 20-59 years of age and a 24% increase of persons 60 years of age and above. They further noted that among persons 20-59 years of age, the largest increases were among black (134% increase) and Hispanic (113% increase) males, compared to white males (14% increase).

Another issue that should be noted concerns the small number of cases within census tracts. The small numbers may have been due to small populations or short time periods evaluated, which could fluctuate and be influenced by chance. The small area assessments reviewed for this consultation include small numbers of cancer cases in small geographic areas and as such have wide confidence intervals associated with them.

Another potential limitation of cancer registry data relates to the race and ethnicity of the patient. A person's race or ethnicity recorded in the cancer registry is based on information from the patient's medical record which may not have necessarily been provided by the patient. In some instances, information on race or ethnicity may have been provided by hospital personnel on the assumption of a person's race based on their last name or an assumed race or ethnicity of parents (CRNC 2000). Race and ethnicity are important types of information because many types of cancers vary by race or ethnicity and misclassification of individuals by these factors can potentially bias results. In addition, it is also important to keep in mind that variations in cancer incidence reported by cancer registry data may possibly be the result of differences in cancer screening and registration practices as well as factors related to access to medical care or lifestyle or environmental factors. Finally, the development of cancer may also be the result of chance occurrences.

E. Community Concerns About Data Quality

This evaluation also considered a concern expressed specifically for the area surrounding SIAD: whether cancer cases among California and Nevada residents are appropriately reported to cancers registries within their respective state.

CRNC, Region 6 of the CCR, covers the 16 most northern California counties including Lassen County, and therefore has the responsibility for gathering, reviewing, and interpreting cancer data for the area near SIAD. The data in this cancer registry are constantly being updated and evaluated as new cancer data are reported.

Since 1988, CCR has gathered and managed data on cancer cases diagnosed and treated at medical facilities throughout California. CCR's reporting system standards require medical facilities to submit reports that contain at least the following information on the individual with cancer: name, age, sex, type of cancer, diagnosis date, and address (CCR 2001). Several measures are in place to ensure that the information provided is kept confidential. Before adding new cancer cases into the registry, CCR personnel review new records for accuracy and verify that they are not duplicates of existing records. These and many other quality control procedures help ensure the accuracy of CCR's data.

Community members expressed concern that the CCR does not account for cancer cases in California residents who are diagnosed or treated by Nevada health providers. ATSDR was informed by CRNC/CCR that some residents who live near SIAD receive medical care in Nevada health facilities because there are no oncology related services available in Lassen County or in nearby Modoc or Plumas counties. It should be noted, however, that California and Nevada have a written agreement to share cancer data (CCR/SCR 1994). Although this agreement does not specify how often the states share records, it is our understanding that records have been exchanged at least twice in the last 5 years. Before entering data provided by Nevada into California's registry, CCR officials first carefully review the records to ensure they are not duplicates of existing registry entries and apply other relevant quality control procedures. ATSDR is satisfied that these procedures are sufficient for tracking reported cancer cases among California residents, including those that are diagnosed or treated in Nevada. However, it should be noted that for the years 1995 through 1999, Nevada hospitals were the sole source of new (incident) cancer cases reported to the Nevada Central Cancer Registry (Bureau of Health Planning and Statistics 2001); therefore, the possibility exists that some cancers diagnosed outside a hospital setting may not have been reported to the Nevada Central Cancer Registry in order to be counted in either the California or Nevada cancer registries. Overall, ATSDR found that the methods CCR used to collect and interpret cancer data are adequate for evaluating cancer incidence.

VII. COMMUNITY HEALTH CONCERNS

Senator Reid's original petitions asked CDC to evaluate concerns regarding health effects that might be related to air emissions from SIAD's waste treatment operations. CDC referred these petitions to ATSDR for action and follow up. The two primary community health concerns, and ATSDR's response to these concerns, follow:

Concern:

Community members asked if residents in the vicinity of SIAD, both in California and Nevada, are inhaling unhealthy levels of air contaminants released from the SIAD's waste treatment operations.

ATSDR Response:

Linking observed health effects with low-level environmental exposures is extremely difficult, especially in cases where relevant data are limited or missing. In the case of SIAD, however, a recent air monitoring study collected more than 200 valid air samples to characterize air quality during typical waste treatment operations. Moreover, extensive modeling analyses have been conducted to characterize air quality in locations where samples were not collected and for pollutants that were not measured. ATSDR believes the available sampling and modeling results provide an adequate basis for evaluating potential health concerns.

ATSDR thoroughly reviewed the sampling and modeling data for this site and carefully examined whether short-term or long-term exposures to the air pollutants reach levels of public health concern. Using standard health consultation approaches, we found no evidence that residents are exposed to site-related contaminants at levels that would be associated with adverse health effects.

ATSDR notes, however, that evaluating the potential effects of environmental contaminants on humans involves some uncertainty. For instance, the health effects that might result from exposure to complex mixtures of chemicals are largely not understood. Moreover, detailed dose-response data are not available for every health condition of concern and contaminant released from SIAD. Additionally, this health consultation does not consider residents' other risk factors (e.g., smoking, family history of disease, and past exposures) as possible contributing factors for their reported health concerns. Though these uncertainties undoubtedly exist, ATSDR's approach to evaluating the health implications of chemical exposures is generally conservative, and this conservative evaluation compensates for some of the inherent uncertainties associated with establishing links between exposure and adverse health outcomes.

Concern:

Community members asked if there are more cases of cancer in the areas around the SIAD, both in California and Nevada, than are to be expected.

ATSDR Response:

Both California and Nevada maintain cancer registries that are continually updated with information on new cancer cases, and the states share their data to ensure that the registries properly account for residents who receive medical care in another state. However, it should be noted that, for the years 1995 through 1999, Nevada hospitals were the sole source of new (incident) cancer cases reported to the Nevada Central Cancer Registry (Bureau of Health Planning and Statistics 2001); therefore, some cancers types may have been under-reported. In addition, the possibility exists that a small number of cancers diagnosed outside a hospital setting may not have been reported to the Nevada Central Cancer Registry in order to be counted in either the Nevada or California cancer registries. The cancer data for California communities near SIAD have been analyzed several times in recent years. Only the July 2000 assessment found a statistically significant finding-elevated leukemia in the Susanville census tract, a finding that did not remain when untracted cases were removed from the analyses. We do not believe anyone in Susanville is exposed to air emissions from SIAD that would cause adverse health effects, including cancer. This conclusion is based on three observations: Susanville is upwind from SIAD; during the infrequent times when winds blow from SIAD toward Susanville, air emissions would disperse to immeasurably low levels over the more than 30 miles that separate these locations; and levels of particulate matter in Susanville do not appear to be influenced by air emissions from SIAD (see Appendix C.2). It is ATSDR's opinion that the evaluations conducted thus far have shown no evidence of excess cancer among the cancers evaluated in the California communities around SIAD, with the exception of the Susanville finding. This opinion is however based on the review of descriptive cancer data collected for the purposes of cancer surveillance. The data currently available to ATSDR for Nevada does not contain enough information on where people live to support a detailed analysis of cancer cases among Nevada residents who live downwind from SIAD. ATSDR will evaluate cancer data for this part of Nevada, once adequate data for the areas east of SIAD are provided. However, we emphasize that our environmental evaluations found no evidence that residents of Nevada are exposed to cancer-causing chemicals at levels of health concern.

VIII. CHILD HEALTH CONSIDERATIONS

Because children often are at greater risk than adults for being exposed to toxic chemicals, and because 6% of the population within 20 miles of SIAD are children (age 6 and under), ATSDR's exposure and public health evaluations specifically consider children's health issues. In general, children are more likely than adults to suffer from adverse health effects due to environmental exposure for several reasons, such as:

Children's developing bodies can be particularly sensitive to toxic exposure during certain critical growth stages, especially when children are exposed to chemicals known to cause developmental effects (e.g., lead).

Children weigh less than adults. As a result, when children and adults inhale the same amount of chemicals, children receive a greater dose (on a pound of contaminant per pound of body weight basis) than adults. For many chemicals, this higher dose causes a greater likelihood for developing adverse health effects.

Because children play outdoors more than adults, they are often more likely to inhale greater amounts of airborne pollutants.

For these reasons, ATSDR specifically considered children's health issues in two critical steps of the public health consultation process. First, when comparing levels of air pollution to health-based comparison values (see Section V), ATSDR identified comparison values that are protective of children's exposures and of health conditions more common in children (e.g., asthma), to the extent they are available. For instance, ATSDR used EPA's National Ambient Air Quality Standards for particulate matter and lead when evaluating the air sampling data for SIAD. These standards were developed to protect the health of sensitive populations, including children. Second, when evaluating the cancer registry data for California, ATSDR evaluated CRNC/CCR's small area assessments which analyzed childhood cancers in Lassen County census tracts around SIAD.

Therefore, ATSDR carefully evaluated the available data to identify specific children's health issues at SIAD. Although we found that children who live near SIAD were exposed to site-related environmental contamination, the trace amounts of contaminants that children inhaled were far below levels associated with adverse health effects. In short, ATSDR's evaluations found no evidence that chemicals released from the SIAD's waste treatment operations pose any health hazards for children in the area. Section X of this report includes recommendations to ensure that no health hazards occur in the future, should waste treatment operations resume at SIAD.

IX. CONCLUSIONS

This health consultation evaluates potential inhalation exposures to air contaminants released from waste treatment operations at SIAD. After thoroughly evaluating environmental contamination and cancer registry data, ATSDR has reached the following conclusions. Refer to the Glossary (Appendix B) for our agency's definitions of the hazard categories, which are shown in bold lettering below.

Evaluation of environmental data. Emissions from SIAD blow primarily in the prevailing wind direction, which is toward the east. Therefore, SIAD's air emissions rarely affect air quality in upwind communities far from the installation, like Susanville. For the downwind communities, modeling studies and a recent sampling study indicate that the contaminants released by SIAD disperse greatly over the distance that separates the installation from residential areas. Moreover, these studies suggest that residents who live near SIAD did not breathe air contamination at levels associated with adverse health effects. For almost every contaminant, the estimated air quality impacts are more than 100 times lower than levels of public health concern. Though the modeling studies involve inherent uncertainties, ATSDR believes the modeling analyses likely overestimated exposure concentrations; the monitoring measurements did not show any contaminants at levels of health concern where people live.

Evaluation of cancer cases. Our review of environmental data concluded that SIAD's emissions of cancer-causing chemicals were not of public health concern. Overall, the descriptive cancer registry did not suggest evidence of excess cancers based on the cancer types analyzed in small area assessments for census tracts surrounding SIAD. However, the exception to this finding was a slight excess of leukemias (all types combined) in the Susanville area for the period 1988 through 1997a finding that did not remain statistically significant when persons with post office boxes or other non-U.S. Postal Service addresses were removed from the analysis. Because Susanville is more than 30 miles upwind from SIAD, it is extremely unlikely that cancers among Susanville residents are caused by exposure to SIAD's air emissions. The data currently available from the state of Nevada do not allow for a meaningful analysis of cancer cases among Nevada residents who live downwind from SIAD. ATSDR does, however, acknowledge the uncertainties and limitations of population-based cancer registry data.

When completing health consultations, ATSDR assigns one of five "hazard categories" to the site based on the findings of our technical analyses. ATSDR assigns inhalation exposures to emissions from SIAD to be no apparent public health hazard, which is the hazard category we use when community members are exposed to site-related contamination, but the exposures are not at levels expected to cause adverse health effects.

The Public Health Action Plan (Section XI) outlines past and future actions that various agencies will take to evaluate environmental health issues related to SIAD.

X. RECOMMENDATIONS

ATSDR recommends the following future actions:

Environmental data. Because SIAD's major waste treatment operations no longer occur, ATSDR does not believe any further action will reduce uncertainty in our analysis. Should OB/OD operations resume at SIAD, however, ATSDR recommends that the Army conduct routine air sampling for particulate matter in at least one residential area downwind from the installation. Such sampling is needed for greater confidence that short-term peaks in particulate matter levels do not exceed levels of health concern. This recommendation is made as a prudent public health measure; ATSDR has no knowledge of whether OB/OD operations will resume at SIAD.

Cancer registries. When reviewing the cancer incidence data, the one statistically significant finding was the excess of leukemias (all types combined) in the Susanville area for the period 1988 through 1997a finding that did not remain statistically significant when persons with post office boxes or other non-U.S. Postal Service addresses were removed from the analysis.

XI. PUBLIC HEALTH ACTION PLAN

The Public Health Action Plan for SIAD describes specific actions that have been taken or should be taken by parties involved with the site, including ATSDR, the Army, and the state cancer registries. The purpose of this Public Health Action Plan is to ensure that this health consultation produces a plan of action to mitigate and prevent harmful health effects that may be resulting from exposure to hazardous substances in the environment. The following list identifies the public health actions that have been completed, that are ongoing, and that ATSDR recommends take place:

Actions Completed:

Contractors to the Army have collected air samples during typical OB/OD waste treatment operations and modeled the air quality impacts from SIAD's air emissions.

ATSDR has toured SIAD, met with local agencies and community members, and gathered available environmental and cancer incidence data.

The California Cancer Registry has analyzed cancer incidence in California communities near SIAD on several occasions. They also produced annual regional reports on cancer incidence. The Nevada State Health Division has published an annual report on cancer incidence, which includes county-level data for Washoe County.

Actions Ongoing:

The California and Nevada cancer registries continue to share information on cancer cases for residents who receive medical care in medical facilities across state lines.

Recommendations for Further Action:

Should OB/OD waste treatment operations resume at SIAD, ATSDR recommends that the Army conduct routine air sampling for particulate matter in at least one residential location downwind from the installation.

The California and Nevada cancer registries should conduct periodic monitoring of cancer incidence in communities in the vicinity of SIAD.

XII. PREPARERS OF REPORT

Gary Campbell, Ph.D.
Environmental Health Scientist, Section Chief
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation

Jeffrey Kellam, MS
Environmental Health Scientist
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation

W. Mark Weber, Ph.D.
Geologist
ERG

Patricia Price-Green
Epidemiologist
Epidemiology and Surveillance Branch
Division of Health Studies

John Wilhelmi, MS
Senior Chemical Engineer
Eastern Research Group, Inc.

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Bjorklund et al. 1998. Open Burn/Open Detonation Dispersion Model (OBODM) User's Guide. J.R. Bjorklund, J.F. Bowers, G.C. Dodd, J.M. White. Prepared for the U.S. Army Dugway Proving Ground. February 1998.

BLM 1995. BLM Manual: Interim Management Policy for Lands Under Wilderness Review. Release 8-67. Bureau of Land Management. July 5, 1995.

BLM 1997. Recreation Guide for Northeastern California and Northwestern Nevada (map). Bureau of Land Management. 1997.

Brown and Root Environmental 1995. SIAD Meteorological Monitoring Plan. Prepared by Brown and Root Environmental for the U.S. Army Environmental Center. November 1995.

Brown and Root Environmental 1996a. Health Risk Assessment for Military Munitions Treatment Facilities at Sierra Army Depot, Herlong, California. Prepared by Brown and Root Environmental for the U.S. Army Environmental Center. September 12, 1996.

Brown and Root Environmental 1996b. Resource Conservation and Recovery Act Ecological Risk Assessment at Sierra Army Depot, Herlong, California. Prepared by Brown and Root Environmental for the U.S. Army Environmental Center. April 1996.

Bureau of Health Planning and Statistics 2001. M. Hemmings and W. Yang. Nevada Report on Cancer, 1995-1999. 2001.

CARB 2000. California Ambient Air Quality Data: 1980-1999. California Air Resources Board. CD Number PTSD-00-013-CD. November 2000.

CARB 2002. California Emission Inventory Data (last updated October 8, 2000). Emissions inventory data downloaded from the California Air Resources Board's Web page. Site last accessed August 9, 2002.

CCR 1999. Letter from Sharan Campleman (CCR Region 6) to local resident. Initial review of cancer data: 1988-1996. April 1999.

CCR 2000a. Letter from Sharan Campleman (CCR Region 6) to local resident. Review of cancer data for census tracts surrounding SIAD: 1988-1997 and 1993-1997. February 2000.

CCR 2000b. Letter from Sharan Campleman (CCR Region 6) to ATSDR. Review of cancer data for census tracts surrounding SIAD: 1988-1997 and 1993-1997. July 2000.

CCR 2001. Cancer Reporting in California: Abstracting and Coding Procedures for Hospitals. Volume One, Sixth Edition. California Cancer Registry. October, 2001.

CCR/SCR 1994. Inter-State Cancer Case-Sharing Agreement. California Cancer Registry and State of Nevada, Statewide Cancer Registry. January 1994.

CDC 2002. Preventing and Controlling Cancer: Addressing the Nation's Second Leading Cause of Death. Centers for Disease Control and Prevention. 2002.

CRNC 2000. Campleman SL, Dryden M. Cancer in Northern California, 1988-1997. Cancer Registry of Northern California, Chico, CA. June 2000.

DEIR 2000. Draft Environmental Impact Report: Off-Site Hazardous Waste Facility Permit Application. Prepared by the California Environmental Protection Agency Department of Toxic Substances Control, TetraTech NUS, and Hazardous Waste Remedial Action Program (HAZWRAP). August 2000.

DHS 2000. Morris CR, Cohen R, Perkins CI, Allen M, Schlag R, Wright WE. Cancer in California:1988-1997. Sacramento, CA: California Department of Health Services, Cancer Surveillance Section. June 2000.

EPA 1986. INPUFF 2.0 - A Multiple Source Gaussian Puff Dispersion Algorithm. User's Guide (abbreviated). U.S. Environmental Protection Agency. EPA/600/8-86/024. August 1986.

EPA 1987a. User's Guide to the Rough Terrain Diffusion Model (RTDM), Rev 3.20. U.S. Environmental Protection Agency. July 1987.

EPA 1987b. Health Advisory for Nitrocellulose. U.S. Environmental Protection Agency, Office of Drinking Water. 1987.

EPA 1992. Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, Revised. U.S. Environmental Protection Agency. Document number EPA-454/R-92-019. October 1992.

EPA 1998. Emission Factors for the Disposal of Energetic Materials by Open Burning and Open Detonation (OB/OD). U.S. Environmental Protection Agency. EPA/600/R-98/103. August 1998.

EPA 1996. AP-42 Compilation of Air Pollutant Emission Factors: Wildfires and Prescribed Burning. U.S. Environmental Protection Agency. October 1996.

EPA 1999. Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air. U.S. Environmental Protection Agency. EPA/625/R-96/010a. June 1999.

EPA 2001. 1999 Toxics Release Inventory, Public Data Release: State Fact Sheets. U.S. Environmental Protection Agency. EPA 260-F-01-001. April 2001.

EPA 2002a. Air emissions data accessed from the U.S. Environmental Protection Agency's Toxic Release Inventory database (www.epa.gov/tri). Data last queried on August 9, 2002.

EPA 2002b. Air emissions and ambient air monitoring data from the U.S. Environmental Protection Agency's Aerometric Information Retrieval System (www.epa.gov/air/data/index.html). Data last queried on August 9, 2002.

EPA 2002c. List of Designated Reference and Equivalent Methods. U.S. Environmental Protection Agency. July 1, 2002.

EPA 2002d. 2000 Toxics Release Inventory Data Release: Questions and Answers. U.S. Environmental Protection Agency. May 29, 2002.

EPA 2002e. Third External Review Draft of Air Quality Criteria for Particulate Matter (April, 2002). U.S. Environmental Protection Agency. EPA/600/P-99/002aC. April, 2002.

EPA, not dated. 1999 Toxic Release Inventory: California State Fact Sheet. U.S. Environmental Protection Agency. Publication date not specified on fact sheet; hard copies of fact sheet were reportedly available in 2001 (www.epa.gov/tri).

Holsey 2003. Written correspondence from David Holsey (Sierra Army Depot) to John Wilhelmi (Eastern Research Group, Inc.). October 8, 2003.

Long 2002. Written correspondence from Gene Long (Sierra Army Depot) to John Wilhelmi (Eastern Research Group, Inc.). April 9, 2002.

NCI 2001. Cancer Facts: Cancer Clusters. National Cancer Institute. November 19, 2001.

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NDEP 2001. Ambient Air Quality Trends: 1989-2000. State of Nevada Department of Conservation and Natural Resources, Division of Environmental Protection, Bureau of Air Quality. 2001.

Reno Gazette-Journal 2000. Army depot sometimes violates own rules on destroying ordnance. Frank X. Mullen Jr. Reno Gazette-Journal. February 21, 2000.

Reno Gazette-Journal 2001a. Depot burning blocked. Munitions: Lassen County officials reject Sierra Army Depot's air pollution exemption. Frank X. Mullen Jr. Reno Gazette-Journal. September 2001.

Reno Gazette-Journal 2001b. Study: Sierra Army Depot Is California's Top Polluter. Frank X. Mullen Jr. Reno Gazette-Journal. April 25, 2001.

Sacramento Bee 2001. Lassen base tops toxics list: The Army depot may face tougher pollution requirements to get state and federal permits. Jane Braxton Little. Sacramento Bee. April 23, 2001.

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TetraTech NUS 2001. Draft Final Ambient Air Monitoring Report: Open Burning/Open Detonation Treatment Facilities at Sierra Army Depot. TetraTech NUS, Inc., and Advanced Infrastructure Management Technology. April 2001.

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WCDHD 2002. 2001 Washoe County Air Quality Data. Washoe County District Health Department. Report downloaded from district's Web page, July 2002.

Zschiesche et al. 1992. Exposure to soluble barium compounds: an interventional study in arc welders. W. Zschiesche, KH Schaller, D Weltle. Int Arch Occup Environ Health 64(1):13-23.

TABLES

Table 1. Contaminants with More than 10 Pounds of Air Emissions Per Year from SIAD's OB/OD Operations

Metals (and Inorganic Materials)
Aluminum Antimony Barium Chromium (trivalent) Chromium (hexavalanet)	Copper Fiberglass Hydrogen chloride Iron Lead	Manganese Nickel Particulate matter Zinc
Explosives, Propellants, and Fillers
2,4,6-Trinitrotoluene 2,4-Dinitrotoluene 2,6-Dinitrotoluene 2-Nitrodiphenylamine Cryolite Dibutyl phthalate	Diethyl phthalate Diphenylamine Ethyl centralite HMX^*Nitrocellulose Nitroglycerin	Nitroguanidine PETN^RDX^*Tetryl Triacetin
OB/OD Chemical Byproducts
1,3-Butadiene Methylene bisphenol^****2-Methylnaphthalene 2-Methylphenol 2-Nitrophenol 4-Nitrophenol ,-Dimethylphenethylamine Ammonia Mixed aromatic compounds Benzene Benzo(b)fluoranthene bis(2-ethylhexyl)phthalate	Butylbenzyl phthalate Carbon monoxide di-n-Octyl phthalate Dibenzofurans Ethylbenzene Fluoranthene Hexane Hydrogen cyanide Methane N-Nitrosodiphenylamine Naphthalene	Nitric oxide Nitrogen dioxide Mixed olefins Mixed paraffins Phenanthrene Phenol Pyrene Styrene Sulfur dioxide Toluene Xylenes

Notes:

Data source: Brown and Root Environmental 1996a.
^* HMX =cyclotetramethylenetetranitramine
^** PETN = pentaerythritol tetranitrate
^*** RDX = cyclotrimethylenetrinitramine
^**** The full chemical name for "methylene bisphenol" is 2,2'-methylene-bis-(4-methyl-6-t-butyl-phenol).

Table 2. Emissions Data SIAD Reported to EPA's Toxic Release Inventory

Chemical	Emissions (in pounds per year)
Chemical	SIAD's Original Submission for 1999	SIAD's Revised Submission for 1999	Submission for 2000
Aluminum (fume or dust)	4,120,000	22,283	24,407
Chromium	Not reported	5	5
Copper	1,042,000	7,887	2,913
Di-butyl phthalate	Not reported	250	250
Dinitrotoluene isomers	Not reported	250	250
Dioxin-like compounds	Not reported	Not reported	0.00080
Hydrogen cyanide	37,000	Not reported	Not reported
Lead	29,200	250	250
Manganese	Not reported	5	10
Nickel	16,400	0	Not reported
Nitroglycerin	Not reported	0	0
Styrene	14,000	Not reported	Not reported
Zinc (fume or dust)	131,639	255	255

Notes:

Data source: EPA 2002a.
TRI data are self-reported; the accuracy of SIAD's release data is not known.
For reporting year 1999, SIAD has certified that the revised data are representative of actual conditions, and the emissions data documented in the revised submission replaced the data reported in the original submission.
Releases of zero pounds suggest that SIAD manufactured, processed, or otherwise used the chemical in large enough quantities to trigger TRI reporting, but none (or less than 0.5 pounds per year) of the chemical was estimated as being released to the air.
"Not reported" means SIAD did not submit a reporting form for the year of interest. SIAD is not required to submit reporting forms for chemicals that do not meet reporting thresholds.

Table 3. Estimated Ambient Air Concentrations of Metals and Inorganic Compounds
(See footnotes at end of table for explanation of contents)

Contaminant	Estimated Annual Average Concentration for Maximally Impacted Residential Location in California (g/m³)	Estimated Annual Average Concentration for Maximally Impacted Residential Location in Nevada (g/m³)	Health-Based Comparison Value (g/m³)	Type of Comparison Value
Aluminum	2.8	1.4	3.7	RBC-n
Antimony	0.00055	0.00044	1.5	RBC-n
Arsenic	0.000000045	0.0000000052	0.0002	CREG
Barium	0.0066	0.0014	0.51	RBC-n
Beryllium	0.000000027	0.0000000031	0.0004	CREG
Cadmium	0.00000083	0.000000096	0.0006	CREG
Chromium (III)	0.000056	0.000046	5,500	RBC-n
Chromium (VI)	0.0000062	0.0000051	0.00008	CREG
Copper	0.31	0.25	150	RBC-n
Fiberglass	0.2	0.16	5,000	NIOSH-REL
Hydrogen chloride	3.3	0.56	20	RfC
Iron	3.4	2.8	1,100	RBC-n
Lead	0.082	0.0062	1.5	NAAQS
Manganese	0.016	0.013	0.04	EMEG (chronic)
Nickel	0.0023	0.0019	0.2	EMEG (chronic)
Selenium	0.00000015	0.000000017	18	RBC-n
Zinc	0.047	0.0039	1,100	RBC-n

Notes:

Source of estimated concentrations: Appendix 3-5 in Brown and Root Environmental 1996a.
The maximally impacted residential location in California and Nevada were Skedaddle Ranch and Flanigan, respectively.
Ambient air concentrations lower than their corresponding comparison values are generally considered to be safe and not expected to cause harmful health effects (see Section IV.B). The lowest, or most conservative, comparison value was selected for all contaminants, considering those published for cancer and non-cancer endpoints. Appendix A defines the abbreviations used in the "Type of Comparison Value" field.
Concentrations of metals listed in this table likely overstate actual ambient air concentrations, as Appendix D.1.1 describes.
The comparison value used for fiberglass is a Recommended Exposure Limit for total fibrous glass particulates published by the National Institute for Occupational Safety and Health in 1977.

Table 4. Estimated Ambient Air Concentrations of Explosives, Propellants, and Fillers
(See footnotes at end of table for explanation of contents)

Contaminant	Estimated Annual Average Concentration for Maximally Impacted Residential Location in California (g/m³)	Estimated Annual Average Concentration for Maximally Impacted Residential Location in Nevada (g/m³)	Health-Based Comparison Value (g/m³)	Type of Comparison Value
*Chemicals for which health-based comparison values are available*
2,4,6-Trinitrotoluene	0.00034	0.00019	0.21	RBC-c
2,4-Dinitrotoluene	0.00014	0.000077	7.3	RBC-n/PRG
2,6-Dinitrotoluene	0.00014	0.000077	3.7	RBC-n/PRG
Dibutyl phthalate	0.0013	0.00013	370	RBC-n/PRG
Diethyl phthalate	0.0003	0.0015	2,900	RBC-n/PRG
Diphenylamine	0.000071	0.000013	91	RBC-n/PRG
Hexachlorobenzene	0.000000094	0.0000011	0.002	CREG
HMX	0.00032	0.000086	180	RBC-n
Nitroglycerin	0.002	0.00023	0.45	RBC-c
Nitroguanadine	0.00099	0.000064	370	PRG
RDX	0.00043	0.0002	0.057	RBC-c
Tetryl	0.000032	0.00008	37	RBC-n/PRG
Chemicals for which no health-based comparison values are available
2-Nitrodiphenylamine	0.000065	0.0000046	NA	NA
Cryolite	0.000033	0.0000030	NA	NA
Ethyl centralite	0.000065	0.0000047	NA	NA
Nitrocellulose	0.0041	0.00096	NA	NA
PETN	0.000047	0.000057	NA	NA
Triacetin	0.00011	0.000019	NA	NA

Notes:

Source of estimated concentrations: Appendix 3-5 in Brown and Root Environmental 1996a.
The maximally impacted residential location in California and Nevada were Skedaddle Ranch and Flanigan, respectively.
Ambient air concentrations lower than their corresponding comparison values are generally considered to be safe and not expected to cause harmful health effects (see Section IV.B). The lowest, or most conservative, comparison value was selected for all contaminants, considering those published for cancer and non-cancer endpoints. Appendix A defines the abbreviations used in the "Type of Comparison Value" field.
The modeled concentrations of chemicals listed in this table likely overstate actual ambient air concentrations, as Appendix D.1.1 describes.

Table 5. Estimated Ambient Air Concentrations of OB/OD Chemical By-Products
(See footnotes at end of table for explanation of contents)

Contaminant	Estimated Annual Average Concentration for Maximally Impacted Residential Location in California (g/m³)	Estimated Annual Average Concentration for Maximally Impacted Residential Location in Nevada (g/m³)	Health-Based Comparison Value (g/m³)	Type of Comparison Value
*Chemicals for which health-based comparison values are available*
1,1,1-Trichloroethane	0.000000012	0.00000019	3,800	EMEG (intermediate)
1,3,5-Trinitrobenzene	0.0000011	0.00000089	110	RBC-n/PRG
1,3-Butadiene	0.00004	0.000033	0.004	CREG
1,4-Dichlorobenzene	0.00000078	0.00000063	600	EMEG (chronic)
2-Methylphenol	0.0000022	0.0000018	180	RBC-n/PRG
4-Nitrophenol	0.0000026	0.0000021	290	RBC-n
Acenaphthalene	0.0000012	0.00000097	220	RBC-n
Acetophenone	0.00000049	0.0000004	0.021	RBC-n
Ammonia	0.00088	0.0007	100	RfC
Anthracene	0.00000058	0.00000047	1,100	RBC-n/PRG
Benz(a)anthracene	0.00000021	0.00000017	0.0086	RBC-c
Benzene	0.0007	0.00056	0.1	CREG
Benzo(a)pyrene	0.000022	0.0000015	0.00092	PRG
Benzo(b)fluoranthene	0.0000017	0.0000014	0.0086	RBC-c
Benzo(k)fluoranthene	0.0000013	0.0000011	0.086	RBC-c
Benzyl alcohol	0.00000036	0.00000029	1,100	RBC-n/PRG
Bis(2-ethylhexyl)phthalate	0.0000074	0.000006	0.45	RBC-c
Butyl benzyl phthalate	0.0000024	0.0000028	730	RBC-n/PRG
Carbon monoxide	0.15	0.12	10,000	NAAQS
Carbon tetrachloride	0.000000025	0.00000052	0.07	CREG
Chlorobenzene	0.000000047	0.00000077	62	RBC-n/PRG
Chloroform	0.00000014	0.0000024	0.04	CREG
Chrysene	0.00000064	0.00000052	0.86	RBC-n
Di-n-octyl phthalate	0.0000093	0.0000076	73	RBC-n
Dibenz(a,h)anthracene	0.0000012	0.00000025	0.00086	RBC-c
Dibenzofurans	0.0000023	0.0000017	15	RBC-n/PRG
Dimethylphthalate	0.00000095	0.00000077	37,000	RBC-n/PRG
Dimethylphenethylamine	0.0000028	0.0000022	3.7	PRG
Ethylbenzene	0.000066	0.000054	4,300	EMEG (intermediate)
Fluoranthene	0.0000021	0.0000017	150	RBC-n/PRG
Fluorene	0.00000083	0.00000067	150	RBC-n{RG
Hexane	0.000052	0.000042	200	RfC
Hydrogen cyanide	0.0097	0.0079	3	RfC
Methylene chloride	0.000000085	0.0000014	3	CREG
N-Nitrosodiethylamine	0.00000033	0.00000027	0.00002	CREG
N-Nitrosodiphenylamine	0.000037	0.0000043	1.3	RBC-c
Naphthalene	0.000037	0.000033	3	RfC
Nitric oxide	0.17	0.02	370	RBC-n
Nitrogen dioxide	0.074	0.011	100	NAAQS
Phenol	0.00015	0.000046	2,200	RBC-n/PRG
Pyrene	0.0000018	0.0000016	110	RBC-n/PRG
Styrene	0.0029	0.0023	300	EMEG (chronic)
Sulfur dioxide	0.032	0.012	80	NAAQS
Tetrachloroethylene	0.000000012	0.00000019	270	EMEG (chronic)
Toluene	0.00043	0.00035	300	EMEG (chronic)
Trichloroethylene	0.00000021	0.0000034	40	RfC
Xylenes (mixed isomers)	0.00037	0.0003	400	EMEG (chronic)
*Chemicals for which no health-based comparison values are available*
1-Nitropyrene	0.00000058	0.00000012	NA	NA
Methylene bisphenol	0.000019	0.0000022	NA	NA
2-Methylnaphthalene	0.0000048	0.0000039	NA	NA
2-Nitronaphthalene	0.0000014	0.0000003	NA	NA
2-Nitrophenol	0.000036	0.0000019	NA	NA
Methane	0.2	0.018	NA	NA
Phenanthrene	0.000003	0.0000024	NA	NA
Picric acid	0.00000014	0.00000011	NA	NA

Notes:

Source of estimated concentrations: Appendix 3-5 in Brown and Root Environmental 1996a.
The maximally impacted residential location in California and Nevada were Skedaddle Ranch and Flanigan, respectively.
Ambient air concentrations lower than their corresponding comparison values are generally considered to be safe and not expected to cause harmful health effects (see Section IV.B). The lowest, or most conservative, comparison value was selected for all contaminants, considering those published for cancer and non-cancer endpoints. Appendix A defines the abbreviations used in the "Type of Comparison Value" field.
The modeled concentrations of chemicals listed in this table likely overstate actual ambient air concentrations, as Appendix D.1.1 describes.

FIGURES

Figure 1. Location of Sierra Army Depot