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Draft Preliminary Site Evaluation
Santa Susana Field Laboratory (SSFL)
Ventura County, California


Exposure Pathways Analyses

A release of a chemical or radionuclide into the environment does not always result in humanexposure. People may be exposed by eating, breathing, or contacting these substances when theyare present in environmental media such as air, drinking water, or soil. Unlike chemicals,radionuclides that are present at high enough concentrations in the environment can result inirradiation exposures to persons who are sufficiently close to the material.

For exposure to occur, an exposure pathway must exist. The following section discusses thevarious pathways of exposure to persons in the community surrounding the SSFL site. The fiveelements of an exposure pathway are (1) a source of chemical or radiological contamination,

(2) an environmental medium (e.g., ground water, surface water, or air) through which the contaminants are transported from the site to the community, (3) a place or process where human exposure is likely to occur, (4) a route of human exposure (e.g., eating, breathing, skin contact), and (5) an exposed population in the surrounding community. Figure 5 illustrates the necessary components of an exposure pathway.

Figure 5:

Figure 5. Potential Exposure Pathways from the SSFL   to Man.

For example, chemicals or radionuclides may be released from a facility onto the ground (soil) during routine operations or an accident (the contaminant source). These substances may then dissolve in rainwater that percolates down through the soil to the underlying ground water (the environmental media). If the contaminated ground water is used as a drinking water source (the point of exposure), then people (the exposed population) may be drinking and bathing (the routes of exposure) in water that contains these substances. All elements of the pathway must be present before the pathway is complete.

With regard to chemicals and radionuclides, not all exposures result in adverse health effects. Several factors determine whether exposure to a chemical or radionuclide has the potential to cause harm. These factors include the contaminant concentration, the exposure duration and frequency, the route of exposure, the toxicity or radioactivity of the substances, and the way the substance is handled by the body following exposure. In addition, factors related to a person's overall health and nutritional status, as well as genetic and lifestyle factors (e.g., smoking and alcohol consumption, diet, level of physical activity), may affect whether exposure to a chemical or radionuclide results in adverse health effects. Therefore, ATSDR evaluates exposure pathways, and considers community concerns and population characteristics, when determining whether adverse health effects are likely to occur in a community.

Special Consideration of Women and Children


Women and children may sometimes be affected differently from the general population bycontaminants in the environment. Both are smaller than the population average and are affected bysmaller quantities of the contaminants. The effect of hormonal variations, pregnancy, and lactationcan change the way a woman's body responds to some substances. Exposure during pregnancyand lactation can expose the fetus or infant if contaminants cross the placenta or get into themother's milk. Depending upon the stage of pregnancy, exposure of the fetus could result in death(miscarriage or stillbirth) or birth defects. If the mother is exposed during lactation, her milk mayconcentrate certain contaminants, increasing the exposure to her infant.

ATSDR's Child Health Initiative recognizes that unique vulnerabilities are inherent in thedeveloping young, whether fetus, infant, or child. For example, some exposures would affectchildren more than adults because of their reduced body weight and higher ingestion rate,resulting in an increased dose or amount taken into the body compared to their body weight. Achild's shorter height results in a breathing zone closer to the ground; thus, closer to soilcontaminants and low-lying layers in the air. Children's behavioral characteristics include morehand-to-mouth behavior, increasing the ingestion of soil or dust contaminants.

In addition to physical and behavioral differences, children's metabolic pathways, especially in thefirst months after birth, are less developed than those of adults which can affect the uptake ortoxicological response to hazardous substances. In some instances, children's bodies are betterable to deal with environmental toxins, but in others, they are less able and more vulnerable.Some chemicals that are not toxic to adults are highly toxic to infants.

Children are rapidly growing and developing in the first months and years of life. Some organsystems, especially the nervous and respiratory systems, may experience permanent damage ifexposed to high concentrations of certain contaminants during this period. Because of rapidgrowth and development, a child's genetic material (DNA) is more likely to be exposed than laterin life making it more vulnerable to damage.

Children have more future years than adults, giving more time for the development of illnesses that require many years to progress from the earliest initiation to the manifestation of the disease. Finally, young children have less ability to avoid hazards because of their lack of knowledge and their dependence on adults for decisions.

In the following sections of this report, we will indicate whether people, including women and children, were, are, or may be exposed to contaminants of concern and discuss the possible health concerns related to these exposures.

Air Pathway


Process operations and waste disposal activities at SSFL have resulted in the airborne release ofnumerous chemicals and radionuclides. This section reviews the meteorological conditions at thesite, identifies the release processes, and discusses the information available or needed forestimating or documenting those releases. Finally, within the limitations of the availablemeteorological and environmental data, we discuss the potential for human exposure to chemicalsand radionuclides from the SSFL.

The Los Angeles basin is a semi-arid region with the climate controlled primarily by the semi-permanent Pacific high pressure cell. Changes in the position of this cell control seasonal weather patterns. During the summer months, the high pressure cell covers the Los Angeles area which results in mostly clear skies with little precipitation. During the winter months, the high pressure cell is displaced southward which allows Pacific frontal systems to move into the area producing light to moderate precipitation [Rutherford, 1999].

During the summer, a shallow inversion layer covers most of the Los Angeles basin. The base and top of this inversion are lower than the elevation of the SSFL site [Rutherford, 1999]. Air releases from SSFL during the summer are likely to disperse above the inversion layer before diffusing downward into the Simi or San Fernando Valleys. In the winter season, surface airflow is dominated by easterly moving fronts accompanied by rainfall. Generally, a light southwesterly wind precedes the storms producing an onshore flow of marine air and an unstable vertical profile. Wind speeds increase as the frontal systems approach. Average wind speeds range from 0 to 9.8 mph [Rutherford, 1999].

A meteorology station has been in intermittent operation at SSFL. ATSDR has received hourly meteorological data for the years 1994-97, summary data for 1960-61, and hourly data for the first 10 months of 1999 [PEC, 1999]. Rocketdyne has indicated that the 1994-97 data set was collected or recorded in error, however, they have provided documentation of the correction factors [PEC, 1999]. The general wind direction pattern from these data sets is predominantly diurnal with north-northwest winds blowing from the ocean during the day, and reversing to the east-southeast during the night. A wind rose diagram for the years 1960-61 also indicates a strong bi-modal wind pattern with similar wind directions.

Local wind directions are strongly affected by the orientation of canyons and ridges such thatwind directions at the SSFL meteorological station are different than those of stations in the Simior San Fernando Valleys and may be different for specific areas within SSFL. It is imperative thata consistent and representative meteorological data set be compiled and used for evaluating thepotential emission source areas within the SSFL site.

There are several processes or operations at SSFL that release chemicals and radionuclides to the atmosphere. These include rocket engine testing, waste treatment and disposal, and accidental releases or spills.

Rocket Testing

The test firing of rocket engines over the operating history of the facility routinely released particulates (soot) and by-products of propellent combustion into the atmosphere. As indicated previously, rocket engine tests at SSFL utilized a variety of fuels; however, the predominant fuels were combinations of kerosene and liquid oxygen. Solid fuel rocket engine testing occurred on a limited basis at the SSFL during the 1960s [CH2M Hill, 1993; Ogden, 1998b; Rocketdyne, 1999b].

Routine rocket engine testing at the SSFL released combustion products into the atmosphere (Figure 6). The majority of these releases were products of complete and partial combustion of hydrocarbon fuels, and include carbon dioxide, carbon monoxide, hydrogen gas, hydrogen chloride, nitrogen gas, nitrous oxide, chlorine, metallic oxide particulates (e.g., aluminum oxide), soot, and organic compounds (e.g., polyaromatic hydrocarbons, [PAHs], Volatile organic compounds, [VOCs]).

In addition to combustion products, air releases were likely to have occurred during routine operations, accidents, and spills of rocket propellants. Liquid fuels containing hydrazines may volatilize from, or sorb to, soils following release. Hydrazines degrade fairly rapidly in most environmental media, including air, water, or soil. Oxidation is the dominant fate, but biodegradation occurs in both water and soil. The half-life of hydrazine in air ranges from less than ten minutes to several hours, depending on atmospheric ozone and hydroxyl radical concentrations. The half-life in water and soil ranges from several minutes to several weeks, depending on several factors such as the presence of certain metal ions, ionic strength, pH buffer, temperature, presence of bacteria, and amount of dissolved oxygen [ATSDR, 1997a]. Oxidizers are reactive and have a very short half-life in air or soil; therefore, they would rapidly disappear from soil and sediment following an accidental spill or release.

After firing, the tested engines were cleaned with large volumes of liquid solvent trichloroethylene (TCE) that was allowed to volatilize into air or was burned from open retention and skim ponds that received surface runoff from the test engine stands. Spills and accidents involving TCE releases also have occurred during rocket testing operations at the SSFL [CH2M Hill, 1993; ICF Kaiser, 1993]. TCE readily volatilizes from soil or surface water into air. Therefore, concentrations of TCE in soil or surface water would rapidly diminish after an accidental release or spill.

Figure 6. Test firing of an Atlas Rocket Engine, September 7, 1999. Note that most of the exhaust plume is steam from evaporation of the quench water used to cool the test stand

Figure 6. Test firing of an Atlas Rocket Engine,   September 7, 1999.

Waste Treatment and Disposal

Chemicals and radionuclides may have been released to air during waste handling, storage, treatment, and disposal operations. Both excess rocket fuels and solvents (such as TCE) may have been burned from the skim ponds following test firings. Hydrocarbon disposal by open burning was prohibited by Ventura County Air Pollution Control District in 1969. Mixtures of fuels, solvents, water, and other materials were also routinely burned at the Area I Thermal Treatment Facility (TTF) [Rockwell International, 1992; GRC, 1993; Rocketdyne unpublished letters, various dates]. Incomplete disposal records indicate that the burning or venting of waste materials at the TTF was conducted by the SSFL fire department and that disposal protocols were developed and observed [Rocketdyne unpublished letters, various dates].

Accidental Releases and Spills

Accident reports indicate that tank ruptures of gaseous materials and spills of liquid materials have resulted in airborne emissions. Historical accident reports are maintained by Rocketdyne, however, with the exception of TCE releases [CH2M Hill, 1993] these records have not been compiled and no evaluation of concentrations or dispersion to offsite areas has been conducted to date [Lafflam, 1989; ICF Kaiser, 1993]. Releases of radionuclides also occurred during incidents that occurred in Area IV from 1959 to 1976 (Table 2) and are evaluated later in this section.

Environmental Data

There are very few quantitative measurements of airborne chemicals from SSFL operations. Some meteorological data for the period of operation are available, however, there does not appear to be a long-term consistent record of when or what types of meteorological data have been collected. Current air emissions are regulated through permits by the Ventura County Air Control Board. These permits are based on estimates of materials usage and do not require ongoing air monitoring. Emissions from rocket engine tests were measured over a six-month period to quantify releases from liquid fuel engine tests [ABB Environmental Services, 1992]. Results from these measurements, a three-dimensional model of exhaust plume characteristics [Melvold, 1992], and associated fuel consumption rates are used to produce annual emission estimates.

With respect to disposal of chemicals at the Area I Thermal Treatment Facility (TTF), Rocketdyne kept some records on the types and volumes of material that were burned. A partial list of chemicals burned includes hydrazine and hydrazine compounds, sodium, pentaborane, kerosene-based fuels (e.g., RP-1, JP-4), lithium powder, nitrogen tetroxide, waste oils, TCE, chlorine trifluoride, and alcohol mixtures [Rocketdyne unpublished letters, various dates; Rockwell International, 1992; GRC, 1993]. The TTF was operational from 1958 to 1990 for the destruction of explosive, reactive, and ignitable wastes by open burning.

Although no air monitoring information is available for the TTF, soil sampling data provide important information concerning the dispersion and deposition of airborne chemicals. This is especially true for chemicals such as polyaromatic hydrocarbons (PAHs) that are not rapidly degraded (and thus persist) in soil for long periods. Soil sampling was conducted at the TTF in 1981, 1982, 1990, and 1993 [reviewed by ICF Kaiser, 1993]. Analyses were conducted for a variety of organic chemicals, anions (fluoride, chloride, nitrate, and sulfate), and metals. Overall, there is no indication that any of the chemicals in soils and sediment at the TTF have migrated to offsite areas [Appendix A].


As mentioned previously, the categories of chemicals evaluated as airborne releases are rocketfuels, oxidizers, and solvents. The types and quantities of airborne releases from the SSFL havevaried over time. ATSDR does not have quantitative measurements of offsite concentrations ofthese substances. Although future monitoring data cannot recreate historic concentrations, airdispersion modeling could be used to estimate past concentrations.


Of all the radiological incidents that are known to have occurred at the SSFL (shown in Table 2), only the Sodium Reactor Experiment (SRE) Fuel Damage incident, commonly known as "The Meltdown," resulted in a measurable release of radioactive material into the environment [Oldenkamp and Mills, 1991]. The SRE was a graphite moderated, liquid sodium cooled, 20 MW power reactor. In the Summer of 1959 a coolant channel became clogged, which resulted in localized melting of 30% of the fuel elements. The fuel elements fell to the bottom of the primary sodium containment vessel and the reactor was shut down. Most of the radioactive fission products were trapped in the sodium coolant or attached to metal components. Only the noble gas fission products made it to the helium cover gas and were held for decay before being vented to the atmosphere [Hart, 1962].

Potential for Human Exposure

ATSDR reviewed the available environmental data and site-specific information to evaluatepotential human exposure to chemicals and radionuclides in the community surrounding theSSFL. There are very few quantitative measurements of airborne chemicals and radionuclidesoffsite of the SSFL. Available information indicates that these substances were released onsiteduring rocket engine testing, waste treatment and disposal, and accidental releases or spills. Releases were probably much higher in the past than at present, due to increased awareness aboutenvironmental processes (release, transport, fate) and more stringent environmental regulations. Several factors must be considered when evaluating the potential for any onsite releases to migrateoffsite and be a potential source of exposure to nearby communities.

First, many of the active areas at the SSFL are located within valleys surrounded by rugged, hillyterrain that separates the active areas from nearby communities. Airborne releases from SSFLsources would be dispersed during transport over these hills to offsite areas. The nearest offsiteresidences are currently located more than one half mile from any of the facility sources. Giventhe distance of the nearby populations to the source areas, it is likely that airborne contaminantconcentrations would be substantially reduced before reaching offsite communities. During thepeak operations at the facility in the 1950s and 1960s, very few residents lived near the SSFL.Although air releases may have been higher in the past, the potentially exposed population wasquite distant from the source areas. In addition to the dispersion of air pollutants that occursduring transport, the oxidizers used at SSFL have a very short half-life in the atmosphere andwould be degraded to non-toxic compounds and elements before reaching offsite areas.

Second, a shallow inversion layer covers most of the Los Angeles basin during the summer months [Rutherford, 1999]. Because of this inversion, any airborne emissions from the SSFL are released above the inversion layer and are dispersed in the atmosphere high above ground level where human exposure could not occur. This means that during the summer months, there is no direct way for airborne releases from the SSFL to be transported to nearby communities before being substantially reduced by dispersion and degradation.

Finally, although there are no wind direction data for specific release incidents, the prevailingwind directions at SSFL blow from the source release areas towards uninhabited areas aroundSSFL. The residences nearest to the site boundaries are not downwind for the strongly prevailingwind directions. Thus, during prevailing wind conditions that have occurred for more than 70% ofthe recorded hourly wind measurements, the closest potentially exposed populations are more thanone mile from the nearest source areas.

ATSDR used the available environmental data, incident reports, and computer modeling toestimate possible radionuclide exposures to the offsite community from the SRE meltdownincident that occurred in 1959. Making a conservative assumption that all of the radioactive noblegases were released instantaneously in the incident, ATSDR used CAP88-PC, a software packagefrom the U.S. Environmental Protection Agency, to estimate doses from air release of radiologicalmaterial. We estimated that the maximally exposed individual could receive up to 0.005millirem. The current exposure limit for members of the public is 100 millirem in one year. Dueto residential locations and meteorological conditions, it is unlikely that anyone received themaximum estimated dose of 0.005 millirem dose.

Based on the distance from the onsite release sources to offsite residential areas, the predominantwind directions, the meteorological conditions at the site, and the rapid dispersion and degradationof oxidants in air, it is unlikely that offsite residents have been, or currently are being exposed tochemicals and radionuclides at concentrations that would result in adverse human health effects.However, because there has been no monitoring of past airborne releases, air dispersion modelingof past releases using site-specific meteorological data would improve the current assessment ofpotential past exposures.

Groundwater and Surface Water Pathway


Ground water in the SSFL area occurs within two distinct hydrogeological units. These units are identified as the Shallow Zone and the Chatsworth Formation. The Shallow Zone occurs within the thin (0 to 20 ft.), discontinuous surficial alluvium found along canyon drainages and in isolated level areas. The principal ground water aquifer occurs within the Chatsworth Formation, which is composed of fractured sandstones with siltstone and claystone interbeds. Almost all water flow occurs within fractures and the unfractured portions are virtually impermeable [GRC, 1999].

Because of the overall low precipitation in this area, there are no continuous streams draining thesite. However, ground water elevations under the SSFL site are significantly higher than Simi andSan Fernando Valleys such that ground water emerges at a number of springs and seeps in thecanyons leading from the site into the valleys. Similarly, surface water impoundments within thesite boundary directly recharge the ground water flow system. Because of these linkages betweenthe surface water and ground water flow systems, and the intermittent nature of surface waterflows, the ground water and surface water system will be evaluated as an integrated exposurepathway.

Ground water beneath the SSFL was found to be contaminated with trichloroethylene (TCE) in the early 1980's [GRC, 1999]. The presumed source for most of the TCE contamination was downward flow from the series of surface water impoundments that drain the rocket engine test areas of the site. Historically, TCE was used to wash the rocket engines between tests [CH2M Hill, 1993]. Following the discovery of TCE in ground water, the facility installed a network of 214 monitor wells to define the distribution of the contaminants. These 214 monitor wells, plus 13 facility supply wells and 16 private wells and springs are sampled quarterly or annually for more than 100 different chemicals, radioactive isotopes, or trace metals.

Plumes of TCE-contaminated ground water have migrated offsite along the northeast and northwest boundaries of SSFL (Figure 7). The facility purchased the property overlying the northwest TCE plume from the Brandeis-Bardin Institute such that this area is now onsite and comprises the northwest buffer area.

Since 1987, the SSFL has operated a network of ground water remediation and treatment wells and eight contaminant treatment systems. More than 1.4 billion gallons of contaminated water have been treated since initiation of the treatment system. The treatment system includes six packed tower aeration systems, and two ultraviolet/hydrogen peroxide units with air emissions regulated by permit from the Ventura County Air Control Board [GRC, 1999].

Water level data from the monitor, remediation, and supply wells indicates that long term water levels underlying SSFL have declined as much as 200 feet [GRC, 1999]. This decline in water elevations creates ground water flows towards the central portion of the SSFL facility and has likely reduced offsite migration of ground water contaminants.

Figure 7. Location of TCE ground water plumes, NPDES sampling stations and surface water drainages.

Figure 7. Location of TCE ground water   plumes, NPDES sampling stations and surface water drainages.
(Click on Thumbnail for larger view)

Environmental Data

Groundwater Resource Consultants has provided ATSDR with a comprehensive data base containing most of the monitoring data collected (electronic data sets listed in Appendix C). This data base has records for 256 locations, with more than 120 different analytes (including volatile organic compounds, metals, acid and base/neutral organics, and common ions). Perchlorate and radionuclide analyses were provided to ATSDR in separate data bases and tables. ATSDR also reviewed written documentation and reports on ground water investigations conducted at the site (shown in Appendix B). Overall, the available data provides good documentation of the distribution of chemicals and radionuclides underlying the SSFL facility, and areas surrounding the site that are most likely to be affected by site releases. However, the possibility of deep fracture flow presents the potential for substances in ground water to migrate long distances and emerge at springs and seeps along the margins of Simi Valley.

Surface flow at the SSFL drains to the north, northeast, south, or east and is very intermittent. Surface water drainages are regularly monitored as National Pollutant Discharge Elimination System (NPDES) outfalls at seven locations (Figure 7), five in Meier Canyon (in the northwestern portion of the site), and two in Bell Canyon (in the southwestern portion of the site). An additional station, located in Woolsey Canyon, has been measured only once due to infrequent surface water flow and the lack of source areas within that drainage system.

The facility monitors various parameters at the NPDES outfalls, including physical parameters(e.g., rainfall, flow, temperature), common ions (e.g., nitrate and nitrite, chlorine, fluoride, sulfate,boron), oil and grease, radioactive parameters (e.g., gross alpha and beta, radium 226/228, tritium,and strontium-90), heavy metals (e.g., arsenic, beryllium, chromium, lead), and other substancesrelated to site operations. Several stations are also monitored for organic compounds, includingpolychlorinated biphenyls (PCBs), ethylbenzene, toluene, and xylenes. Volatile organiccompounds (VOCs) such as trichloroethylene (TCE) and its degradation products are monitoredonly at the two NPDES outfalls (01 and 02) located in Bell Canyon. These substances are notmonitored at other NPDES stations because the substances are no longer being used at the site. With the exception of the OS-14 station located in the undeveloped area of the SSFL facility asdescribed below, existing monitoring of surface water runoff appears adequate for detection andmonitoring of surface water contaminants from current facility operations.


Table 6 lists the offsite surface water and ground water sampling stations that may be impacted bychemicals and radionuclides migrating in ground water and surface water from the SSFL. Thetable also includes the sampling points or wells where these substances were found.

Chemical concentrations in surface water samples routinely collected at the NPDES outfalls havegenerally been below regulatory limits. Two VOCs, chloroform and TCE, have been detected atotal of three times in samples collected at the outfalls; the concentrations did not exceedregulatory limits. Chloroform was detected on two occasions at concentrations of 4 µg/L (in 1992)and 1.6 µg/L (in 1995); TCE was found on one occasion at a concentration of 4.3 µg/L (at outfall#02, in 1995).

Metals, such as cadmium, chromium, nickel, lead, and zinc have frequently been detected atNPDES outfalls but levels are similar to background concentrations in most samples. Chromiumwas measured at outfall #02 at a concentration of 75 µg/L (in 1993), which exceeded theregulatory limit of 50 µg/L. Zinc was detected at outfalls #03, #04, and #06 on several occasions;the maximum concentration detected was 640 µg/L, which is well below the NPDES regulatorylimit of 5000 µg/L. PCB (Aroclor 1254) was detected at outfalls #05 and #06 on several occasionsat a maximum concentration of 120 µg/L in 1994.

Sample location OS-14 is located in the undeveloped southern buffer zone of the SSFL facilityand is in the drainage leading to Bell Creek. This station was sampled on only one occasion in1985. The contaminants detected were: TCE (100 ug/l), vinyl chloride (8 µg/l), and trans-1,2-dichloroethylene (1,2-DCE; 230 µg/L). Although NPDES outfalls are downstream of the OS-14location, and have routinely been found to contain low or non-detectable concentrations of VOCs,the finding of chemical contamination at OS-14 suggests possible migration of chemicals infracture flow from the SSFL. Additional sampling at OS-14 is warranted to better characterizeoffsite concentrations and possible migration of chemicals in deep fracture flow from the SSFL.

Table 7 lists the chemicals that were commonly detected in onsite ground water wells. Of thetwenty-one chemicals listed in Table 7, eighteen were detected in offsite wells or springs, and fiveof the these were detected on only one to three occasions. The only routinely occurring chemicalsin offsite ground water samples are TCE and its degradation products, 1,1-dichloroethylene (1.1-DCE) and 1,2-dichloroethylene (1,2-DCE). TCE was found at a maximum offsite concentration of670 µg/L at well RD-38A (in 1994). Maximum TCE concentrations currently found offsite havedecreased to 330 µg/L (in 1999). Well RD-56A, which was previously considered an offsitesample location but is currently part of the onsite property (within the northern buffer area), had amaximum TCE concentration of 810 µg/L (in 1999).

Two other offsite wells located within the boundaries of the eastern TCE plume have shown significant decreases in concentrations of TCE, and its degradation products, over time. Forexample, TCE concentrations in Well RD-36B decreased from 320 µg/L (in 1994) to 24 µg/L (in1999); concentrations in well RD-36C decreased from 310 µg/L to 78 µg/L during this same timeperiod. The declining concentrations of TCE and its degradation products over time indicate theeffectiveness of the ongoing ground water remediation program at the SSFL. No chemicals havebeen detected in the two offsite wells known to be used as drinking water sources.

Perchlorate has been detected in only one of the offsite monitor wells routinely sampled by the SSFL facility (Table 7). It was also detected at a concentration or 4.6 µg/L in a ground water well that discharges into the storm drains in the City of Simi Valley [CDHS, 1999]. This concentration is below public health standards proposed by the U.S. Environmental Protection Agency and the State of California [EPA, 1998, 1999; CDHS, 1999]. In addition, this well is located more than three miles northwest of the SSFL. Ground water in this area is currently not being used as a drinking water supply. Although perchlorate has been found in soil and water samples collected from SSFL Area I, ATSDR has no information indicating that the perchlorate found in this discharge well is related to the SSFL. However, the potential for deep fracture flow from the SSFL exists and has not been fully characterized.

Perchlorate contamination has been detected in a number of water sources throughout much of California and the United States, indicating that there may be other sources of perchlorate contamination for the Simi Valley well [CDHS, 1999]. Additional perchlorate characterization and monitoring of ground water in Simi Valley is warranted to identify possible sources of contamination and to better characterize deep fracture flow from the SSFL.

Table 6. Surface Water and Ground Water Sampling Stations Offsite of the SSFL Facility

DirectionNWNNE, E, SES, SW



Santa Monica



Private Lands

Woolsey, DaytonCanyons

Bell Canyon Area
Ground water wellsOS-1 to10







OS-15-17, 19, 20, 27

RD-32, 43

Surface Water StationsNPDES 03- 07


no surfacewater drainageinto this area NPDES NearWell 13,

OS-12, 13

Bell Creek

NPDES # 01,02


Note: Wells OS-17 and OS-27 are drinking water supply wells. No contaminants have been detected in those wells.

Table 7. Offsite Distribution of Chemicals Commonly Found in SSFL Monitoring Wells

ContaminantNumber ofOffsiteDetectionsNumber ofOffsite



µg/L or ppb

Location ofMax. Conc.(Well ID)Date ofMaximumConc.
Carbon Tetrachloride28954.5RD-59A02/95
Methylene chloride168606OS-806/92
Vinyl Chloride889564RD-56A*03/94

1,1-DCA = 1,1,-dichloroethane; 1,2-DCA = 1,2-dichloroethane; 1,1-DCE = 1,1-dichloroethylene; cis-1,2-DCE andtrans-1,2-DCE = cis/trans-1,2-dichloroethylene; PCE = tetrachloroethylene; 1,1,1-TCA = 1,1,1-trichloroethane; TCE= trichloroethylene.

ND = not detected above analytical reporting limits

Note: Wells OS-17 and OS-27 are used for drinking water supply. No contaminants have been detected in thesewells.

[*RD-56AB, RD-34ABC, RD-57, and RD-33ABC are currently considered to be onsite but were considered part of the offsite area until Rocketdyne acquired the northern buffer area ]



Offsite areas have had limited sampling and radiological characterization of surface water because of the intermittent flow from the SSFL. Surface water sampling has been sufficient to find limited radionuclide migration. Sampling in the Bell Canyon area found only background concentrations of naturally occurring radionuclides. Multi-media sampling at the Brandeis-Bardin Institute and the Santa Monica Mountains Conservancy revealed that radionuclides have washed down from the Radioactive Material Disposal Facility (RMDF) at the SSFL onto what was part of the Brandeis-Bardin property, located north of Area IV [McLaren/Hart,1993; 1995]. This area has been purchased by Rocketdyne and is now part of the SSFL buffer zone. Strontium-90 and tritium were detected at concentrations slightly above background levels in these areas. Concentrations of radionuclides in ground water and surface water offsite of the SSFL are presented in Table 8 (below).

Table 8. Concentrations of Radionuclides in Ground Water and Surface Water Offsite of the SSFL

RadionuclideMaximum ConcentrationLocation
Cesium-137NDBrandeis-Bardin or

Bell Canyon

Iodine-131NDBell Canyon
Strontium-907.79 pCi/LRMDF Watershed on


Tritium1500 pCi/LRMDF Watershed on


Key : ND = not detected above analytical reporting limits

pCi/L = picocuries per liter

Potential for Human Exposure

Rocket testing operations and waste disposal activities at the SSFL have resulted in the contamination of ground water and surface water underlying and immediately adjacent to the SSFL facility (Figure 7). Well surveys conducted by Groundwater Resource Consultants indicate that there are 42 privately-owned water wells located within one mile of the SSFL [GRC, 1995; 1998]. Most of these wells are used for livestock watering; only seven of these wells are known to have been used, or are currently being used, for drinking water purposes. No contaminants have been detected in any of the wells used for drinking water.

There are dozens of other privately-owned water wells located more than one mile from the SSFL. Most of these wells are located in the Santa Susana Knolls community and the unincorporated areas outside the City of Simi Valley. Because well usage for most of these wells is not specified in the Off-Site Well Inventory [GRC, 1995], it is assumed that all of these wells are used for drinking water supply. Based on available information, ATSDR has no indication that privately-owned wells in the Santa Susana Knolls and Simi Valley areas have been affected by chemicals from the SSFL.

Available monitoring data indicates that there is limited offsite migration of chemicals in groundwater at the SSFL. It is likely that water level drawdowns created by SSFL water supply wellshave reduced ground water flow from the site and limited chemical migration to the surroundingcommunities.

There are no known municipal water supply wells located within two miles of the SSFL facility. Most of the municipal water provided to residents near the SSFL is supplied by various resellers of water imported by the Metropolitan Water District of Southern California [GRC, 1995]. Although several of the local water purveyors operate ground water wells to supplement imported water supplied to local residents, none of these wells are located within two miles of the SSFL boundary. ATSDR has no information indicating that any of these municipal wells has been contaminated by chemicals from the SSFL or any other source.

The SSFL has constructed 13 water supply wells onsite; however, these wells are currently beingused only for industrial supply. Several of these wells are routed through the site remediationfacilities for VOC extraction and treatment prior to any use. ATSDR has no information aboutwhether any of these wells were ever used for drinking water at the SSFL.

Based on our review of ground water monitoring data and well inventories, there is no indicationthat residents living near the SSFL have been exposed, or are currently being exposed tochemicals or radionuclides in ground water offsite of the SSFL. Chemicals in ground water at theSSFL have not migrated to offsite privately-owned wells or to municipal water supplies. As aresult of the ongoing ground water remediation at the SSFL site, it is unlikely that there will befuture exposure to contaminated ground water. However, because the potential for deep fractureflow from the site has not been adequately characterized, there is a potential for substances inground water to discharge at springs or downgradient water wells along the margins of SimiValley. Development of a regional hydrogeological flow model and additional monitoring atdowngradient springs or seeps in Simi Valley and Santa Susana Knolls would provide additionalcharacterization of potential future exposure via ground water and surface water pathways.

Surface water samples collected at the NPDES outfalls (located in the undeveloped area south ofthe SSFL) have been found to contain volatile organic compounds (chloroform, TCE), metals(chromium), and PCBs on a few isolated occasions. However, the concentrations detected aregenerally below regulatory discharge limits and are not at levels that would result in adversehuman effects if people came into contact with this surface water.

Surface water runoff from the SSFL is not used for drinking water purposes either at the SSFL orin nearby communities. These NPDES outfalls are located upstream of the residential area of BellCanyon (and Bell Creek) and have not been shown to be contain chemical contamination. Basedon the available data, there is no indication that chemicals and radionuclides have migrated, or arecurrently migrating in surface water from the SSFL to Bell Canyon. This is confirmed by the factthat these substances have not been detected in soil and sediment samples collected in BellCanyon and along Bell Creek. These data are discussed in the Soil and Sediment Pathway.

Based on our preliminary review of the available data, there is no indication that residents livingnear the SSFL have been exposed, or are currently being exposed to chemicals or radionuclidesin ground water or surface water at levels that would result in adverse human health effects. Based on the discontinuation of TCE use and the effectiveness of the ground water treatmentsystem, it is unlikely that future exposure to chemicals or radionuclides will occur. However, dueto the potential for deep fracture flow to offsite areas, additional monitoring of offsite springs andmodeling of regional ground water flow is recommended to improve the assessment of potentialfuture exposures.

Soil and Sediment Pathway Background

ATSDR reviewed the available environmental sampling data, information on the potential foroffsite migration of soil and sediment (e.g., surface water flow and wind patterns), and populationcharacteristics to determine whether chemical and radionuclide releases from the SSFL havemigrated, or are currently migrating to offsite areas where they may be a source of potentialhuman exposure. Soil and sediment at the SSFL site have been shown to be contaminated by avariety of chemicals and radionuclides. Migration to offsite areas may result from (1) release ofchemicals and radionuclides to air during rocket testing or waste storage, treatment, or disposal;transport in air; and then deposition onto surface soil and sediment in offsite areas, and(2)accidental spills and leaks of chemicals and radionuclides onto onsite soil and sediment withsubsequent resuspension and transport via surface water or air to offsite areas.

As discussed previously for the Air Pathway, air releases at the SSFL site are not likely to have impacted offsite areas. Therefore, the predominant pathway for chemicals and radionuclides to be transported offsite areas is via sediment resuspension and surface water flow. The SSFL site is located in hilly terrain that controls surface flow patterns at the site (Figure 2). Surface water flow onsite is directed through a series of surface impoundments that drain the active areas of the site and ultimately discharge through several NPDES permitted outfalls near the northern and southern site boundaries. Approximately 90% of the surface water flows from the site into Bell Creek through the Bell Canyon residential community located directly south of the SSFL property. These two onsite drainage channels join to form the headwaters of Bell Creek in the southern buffer zone of the SSFL. The remaining surface flow from the site (10%) discharges via drainage channels flowing in a northerly direction from Area 4 to Meier Canyon in Simi Valley [Rocketdyne, 1999a].

Environmental Data

ATSDR evaluated environmental data from soil and sediment sampling conducted in three main areas surrounding the SSFL. These include (1) the Brandeis-Bardin Institute [McLaren/Hart, 1993; 1995], (2) the Santa Monica Mountains Conservancy (McLaren/Hart, 1993; 1995), and

(3) Bell Canyon, including Bell Canyon Creek [Ogden, 1998a]. These areas are downgradient of SSFL and therefore are most likely to be impacted by any chemicals and radionuclides migrating from the site [McLaren/Hart, 1993; 1995; Ogden, 1995]. In addition, ATSDR evaluated sampling data for the Former Sodium Disposal Facility located in Area IV (onsite) because chemicals from this source have migrated to nearby offsite areas. Samples from these all of these areas were analyzed for a variety of chemicals and radionuclides [ICF Kaiser, 1995; ITC, 1999].

The Area IV Radiological Characterization Survey, dated August 6, 1996, found limited cesium-137 contamination on the SSFL site [Rocketdyne, 1996]. The Environmental Protection Agency in Las Vegas, Nevada, identified problems with the sampling techniques used in the Area IV characterization survey. They identified specific problems related to survey instrument calibration procedures and too large of a grid spacing. They also suggested that using improper techniques used could have resulted in an under-reporting of possible contamination [Dempsey, 1997]. The DOE Oakland Office and EPA's Las Vegas Laboratory are currently negotiating an Interagency Agreement to conduct a revised radiological survey of the Area IV at SSFL.

Maximum concentrations of chemicals and radionculides found in samples at these offsite locations is presented in Tables 9 and 10 (chemicals) and Table 11 (radionuclides), below.


Bell Canyon

Soil and sediment samples were collected in areas of Bell Canyon that are most likely to be impacted by surface flow from the SSFL site. These areas include the surface drainages leading from SSFL to Bell Canyon, Bell Creek, and the yards of three residents who requested sampling [Ogden, 1998]. Background samples were collected in undeveloped portions of Bell Canyon representing areas that are not likely to be impacted by the SSFL.

Sample analyses were conducted for a wide range of chemicals and radionuclides. Because perchlorate and dioxin (and dioxin-like compounds) have been found in soil and sediment samples collected on the SSFL, analyses were also conducted for these analytes. There were no procedures established by the EPA for analyzing perchlorate in soil and sediment samples at the time that these analyses for Bell Canyon were conducted. Concentrations of dioxin and dioxin-like compounds were reported in units of TCDD-Total Equivalents (TCDD-TEQs) which reflects the sum of all dioxin and dioxin-like congeners in a sample [Ogden, 1998a].

As presented in Table 9, concentrations of total TCDD-TEQ and several metals (arsenic, barium, beryllium, chromium, and lead) were above analytical reporting limits in soil and sediment samples collected in Bell Canyon. However, the maximum concentrations in these samples were similar to levels in background samples. Two organic compounds, pyrene and N'-nitrosodiphenylamine were detected above analytical reporting limits (at a maximum concentration of 39 µg/kg and 36 µg/kg, respectively) only in background samples, and not in samples collected along drainage channels leading from the SSFL to Bell Canyon. Collectively, these data indicate that chemicals in soils and sediment at the SSFL are not migrating to Bell Canyon.

Brandeis-Bardin Institute and Santa Monica Mountains Conservancy

Soil and sediment samples were collected in the Brandeis-Bardin Institute and Santa Monica Mountains Conservancy. The areas sampled were ravines nearest the SSFL (and most likely to have received surface runoff from the site), and nearby playgrounds, campgrounds, and parking lots. Background samples were collected from areas 1.5 to 12.5 miles away from the SSFL representing areas that are not likely to be impacted by the SSFL [McLaren/Hart, 1993;1995].

Sample analyses were conducted for a wide range of chemicals and radionuclides. Maximum concentrations of chemicals in soil and sediment at the Brandeis-Bardin Institute and Santa Monica Mountains Conservancy are presented in Table 10. Two metals, mercury and lead, were found in samples from the Brandeis-Bardin Institute and Santa Monica Mountains Conservancy at concentrations significantly above background levels. Mercury was detected in a single sample (at a concentration of 0.35 mg/kg) collected along the drainage leading from the former Sodium Disposal Facility, located in Area IV, to the Brandeis-Bardin Institute. Contamination in this sample most likely resulted from past activities at the Sodium Disposal Facility because mercury was not found in background samples or in samples from other offsite locations. The SSFL facility has removed the mercury-contaminated soils from this area.

Lead was also found at concentrations significantly above background levels in a single sample atthe former Rocketdyne Shooting Range near the Santa Monica Mountains Conservancy. Othersamples collected in the Brandeis-Bardin Institute and Santa Monica Mountains Conservancy didnot have elevated lead concentrations. The isolated distribution of the soil lead at the formerShooting Range is due to lead ammunition used at the shooting range and does not indicate offsitemigration of SSFL contamination.

Several organic compounds, including bis(2-ethylhexyl)phthalate, 4,4'-DDE, 4-methylphenol, andmethylene chloride, were found in single samples collected in the Brandeis-Bardin Institute andnot in any background samples. Because these were single detections, there is no indication thatthere is widespread contamination at the Brandeis-Bardin Institute and the Santa MonicaMountains Conservancy. Methylene chloride and toluene were also detected in samples collectedat the Conservancy, and not in background samples.

Former Sodium Disposal Facility

ATSDR evaluated environmental data from several onsite areas where chemicals have been released into the environment and have the potential to migrate to offsite areas. These include the Area I Thermal Treatment Facility [Rockwell International, 1992; GRC, 1993], the Former Sodium Disposal Facility [ICF Kaiser, 1995; ITC, 1999], Sodium Burn Pit, and Happy Valley [Ogden, 1999]. ATSDR also evaluated environmental data pertaining to a number of accidental releases of chemicals and radionuclides to soil and sediment to determine whether these releases could have resulted in contamination of offsite areas [Lafflam, 1989; ICF Kaiser, 1993; Rockwell International, 1994].

Based on the information reviewed, chemicals from the Former Sodium Disposal Facility have migrated to offsite areas. The Disposal Facility is located on the western boundary of Area IV and is comprised primarily of an upper pond, lower pond, and adjacent areas. Approximately 12,000 cubic yards of soil have been removed from this area to an offsite landfill. Currently, up to six feet of overburden remains in the upper pond (Figure 8). In the lower pond, all soils have been removed down to bedrock [ITC, 1999].

Figure 8. Site of former Sodium Disposal Facility. The view is looking northwest towards Brandeis-Bardin Institute and Simi Valley. Figure   8. Site of former Sodium Disposal Facility.

During periods of rainfall, surface flow from the Disposal Facility flows primarily in a northerly direction via two channels that ultimately discharge at NPDES-permitted outfalls at the northwest property boundary. In 1995, contractors for the SSFL facility collected soil and sediment samples along these surface drainages. The samples were analyzed for several types of organic compounds, including polychlorinated biphenyls (PCBs), dioxin and dioxin-like compounds (reported as TCDD-TEQs), volatile and semi-volatile organic compounds, and metals [ITC., 1999]. Sampling data indicate that PCBs, TCDD-TEQ, and mercury had migrated in drainages from the Disposal Facility to offsite areas. Maximum concentrations were found in offsite samples collected a short distance downstream of the upper and lower ponds; concentrations decreased with increasing distance from the ponds.

Offsite concentrations of PCBs ranged from 22 to 3800 µg/kg. The maximum concentration wasfound in a sample collected just north of the facility boundary; the lowest concentration was foundin a sample collected at a distance of 4000 feet from the Disposal Facility.

Offsite concentrations of TCDD-TEQ ranged from 0.00018 to 0.00672 µg/kg, which is equivalentto 0.18 to 6.72 parts per trillion (ppt) for TCDD -TEQs; concentrations of mercury ranged fromnot detected to 0.00052 µg/kg. The maximum concentration of TCDD-TEQ and mercury werefound in samples collected just north of the facility boundary. The lowest concentration of TCDD-TEQ was in a sample collected at a distance of 4000 feet from the Disposal Facility. Mercury wasnot detected in samples collected just offsite of the SSFL boundary; therefore additional samplingat more distant areas from the source was not conducted.


The U.S. Department of Energy's Remote Sensing Laboratory and EG & G Energy Measurement Group from Las Vegas performed aerial radiological surveys of all nuclear facilities in the late 1970s [EG&G, 1979]. In June and July of 1978, they performed surveys of the Rockwell International Facilities in Canoga Park and at the SSFL. The report states that radiation on the Rockwell properties could not be detected from the property boundary lines. The survey of SSFL detected no gamma emitters (e.g., cesium-137, cobalt-60) above background levels in drainage channels at the site.

Offsite areas have had limited sampling and radiological characterization, but sufficient to find limited radionuclide migration. The Bell Canyon sampling found only background concentrations of naturally-occurring radionuclides [Ogden, 1998a]. Multi-media sampling at the Brandeis-Bardin Institute and the Santa Monica Mountains Conservancy found that radionuclides have washed down from the Radioactive Material Disposal Facility (RMDF) onto what was part of the Brandeis-Bardin property, North of Area IV [McLaren/Hart, 1993;1995]. Cesium-137, strontium-90, and tritium were detected at levels above background.

Table 9. Maximum Contaminant Concentrations in Surface (0 to 0.5') and Subsurface

(0.5 - 1') Soil and Sediment Samples in and near Bell Canyon

ContaminantSurface Soil(SS)

Bell Canyon

µg/kg or ppb

Surface Soil(SS)

Backgroundµg/kg or ppb

SubsurfaceSoil (BS)

Bell Canyon

µg/kg or ppb

Subsurface Soil(BS)Background

µg/kg or ppb

PCBs<110-150(RL)<100-110 (RL)<120-160 (RL)<120 (RL)No samples abovereporting limits forAroclor 1016-1260
PAHs<32-46 (RL)<31(RL)-39<34-48 (RL)<36 (RL)Only 1 bkgrdBCSS09 with PAHconc. abovereporting limit, forpyrene (39 ppb)
Total TCDD-TEQ0-0.000130-0.0000460.00001-0.000550See text fordiscussion of TotalTCDD-TEQ
Perchlorate<43-260 (RL)<41-230 (RL)<46-210 (RL)<49 (RL)No samples abovereporting limits forperchlorate
N'-Nitrosodi-methylamine(NDMA)<2-3 (RL)<2 (RL)<2-3 (RL)<2 (RL)No samples abovereporting limits forNMDA
N'-Nitrosodi-phenylamine(NDPA)<32-46 (RL)<31-34 (RL)<34-48 (RL)<36No samples abovereporting limits forNDPA
As (ppm)<5(RL)-14<5(RL)-16<6(RL)-814  
Ba (ppm)31-17036-9722-63140  
Be (ppm)0.5(RL)-1.00.5(RL)-1.1NA1.1Analyses forberyllium wasconducted for 4 of15 samples (SS andBS) collected fromBell Canyon
Cr-total (ppm)5-309-266-1529  
Pb (ppm)6(RL)-277-266(RL)-929  


RL = Analytical Reporting Limits

ppb = parts per billion; ppm = parts per million

PCBs = polychlorinated biphenyls; PAHs = polyaromatic hydrocarbons; TCDD-TEQ = TCDD-toxicequivalency; As = arsenic, Ba = barium, Be = beryllium; Cr-total = total chromium; Pb = lead

[Source: Ogden, 1998]

Table 10. Maximum Contaminant Concentrations in Soil and Sediment at Brandeis-BardinInstitute and Santa Monica Mountains Conservancy from Sampling Conducted in 1992[McLaren/Hart, 1993; 1995]

Contaminant Background
Concentration (mg/kg or ppm) and sample with maximum concentration
Concentration at BBI
(mg/kg or ppm) and sample with maximum concentration
Concentration at SMMC
(mg/kg or ppm) and sample with maximum concentration
As14 (BG-03)24 (BB-18)8.2 (SM-01)  
Be1.00 (BG-03)0.99 (BB-13)1.20 (SM-01)  
Cd7.3 (BG-03)1.1 (BB-06)ND (<0.50) BB-06 detection reported by EPA
Cr-total96 (BG-03)27 (BB-09)24 (SM-01)  
Hg  0.35 (BB-18)   Only offsite sample with positive detection in drainage from the former Sodium Burn Pit; EPA split sample reported a concentration of 0.4 ppm; contaminated soils have been excavated from this area
Pb22.8 (BG-02)53 (BB-12)26 (SM-01);

280 (SM-03)

SM-03 is near the former Rocketdyne Employee Shooting Range
Zn 120 (BG-03)78 (BB-12)76 (SM-01)  
Bis(2-ethylhexyl)-phthalate8.5 (BB-07)Only offsite sample with positivedetection
4,4'-DDE---0.360 (BB-11)--- Only offsite sample with positive detection
4-Methylphenol---0.670 (BB-02)--- Only offsite sample with positive detection
Acetone0.012 (BG-02)0.030 (BB-19) ---
MethyleneChloride---0.017 (BB-15)0.007 (SM-01)  
Toluene------0.009 (SM-01)  

Key: BBI = Brandeis-Bardin Institute

SMMC = Santa Monica Mountains Conservancy

ND = Laboratory analysis indicating that the concentration is below specified reporting limit

-- = Laboratory analysis indicating that the concentration is below reporting limits

mg/kg = milligrams per kilogram; ppm = parts per million

As = arsenic; Be = beryllium; Cd = cadmium; Cr-total = total chromium; Hg = mercury, 4,4'-DDE = 4,4'-dichloro-bis(p-chlorophenyl)ethylene

EPA = Environmental Protection Agency

Table 11. Maximum Offsite Radionuclide Concentrations in Surface Soils and Sediments

RadionuclideMaximum ConcentrationSampling Location
Cesium-1370.60 pCi/gRMDF watershed on Brandeis-Bardin
Iodine-131NDBell Canyon
Plutonium-238NDBell Canyon
Potassium-4025 pCi/gBell Canyon
Radium-2261.5 pCi/gBell Canyon
Strontium-900.15 pCi/gOrange Grove on


Thorium-2281.8 pCi/gBell Canyon
Thorium-2301.4 pCi/gBell Canyon
Thorium-2321.5 pCi/gBell Canyon
Tritium0.36 pCi/gBell Canyon
Uranium-233/2341 pCi/gBell Canyon
Uranium-2350.07 pCi/gBell Canyon
Uranium-2381.1pCi/gBell Canyon

Potential for Human Exposure

ATSDR used the available sampling data and other information about the site and surroundingcommunity to determine whether persons in the community may have been exposed, or becurrently exposed, to chemicals or radionuclides released to soil and sediment from the SSFL.

Chemicals and radionuclides have migrated by sediment transport in surface water runoff from the SSFL to offsite areas. In general, maximum concentrations have been detected just outside the SSFL property boundary; concentrations decrease rapidly with increasing distance from the facility. The area surrounding the SSFL is rugged and hilly and not easily accessible to persons in the nearby community. There is a limited likelihood that persons in the community would come into contact with chemicals and radionuclides in soils and sediment just offsite of the SSFL. In addition, maximum concentrations of chemicals and radionuclides at these offsite areas are not at levels that would result in adverse human health effects if human exposure were to occur [DeRosa, 1997; ATSDR, 1997b, 1998]. Chemicals and radionuclides have not been found in samples collected in more distant residential or recreational areas surrounding the SSFL, including Bell Canyon, Brandeis-Bardin Institute, and Santa Monica Mountains Conservancy, at levels that would result in adverse human health effects if any human exposure were to occur in these offsite areas. As mentioned previously for Bell Canyon sampling data, there were no established procedures for analyzing perchlorate in soil and sediment samples at the time the Bell Canyon investigation was conducted. Therefore, ATSDR evaluated the potential for adverse health effects to occur if persons were exposed to soil and sediment containing perchlorate at the maximum reporting limit used for Bell Canyon, which was 260 µg/kg.

The U.S. EPA recently published a comprehensive review of toxicity data for perchlorate [EPA, 1998, 1999]. In this review, the EPA considers the most sensitive effect of perchlorate exposure to be developmental effects on the thyroid of newborn rats (exposed in the womb or in utero). Based on these animal studies, they reported that human exposure to perchlorate at a dose of 0.0009 mg/kg/day or less does not pose a health hazard for thyroid toxicity or cancer. We used this reference dose established by the EPA to determine whether potential exposure to persons in the Bell Canyon would pose a health hazard. To do this, we assumed that a small child living in Bell Canyon ingests contaminated soil (at a maximum concentration of 260 µg/kg for perchlorate) while playing. We assumed exposure to a small child because children are potentially more sensitive to the toxic effects of chemicals because of their immature and developing biological systems. We determined that even if a small child ingests 200 milligrams of soil containing 260 ppb of perchlorate daily for several years, adverse health effects on the thyroid are not likely. In fact, a small child would have to ingest more than 300 times this concentration in soil to exceed the dose that the EPA considers to be protective for thyroid toxicity. Therefore ATSDR considers the reporting limit used in the Bell Canyon sampling to be protective of public health.

Based on our preliminary review of the available data, ATSDR has no indication that persons inthe community surrounding the SSFL have been, or are currently being exposed to chemicals orradionuclides in soil or sediment from the SSFL at levels that would result in adverse humanhealth effects .

Public Health Implications

In this section, ATSDR considers the results of the exposure pathways analyses together with thecommunity concerns and available health studies to determine the potential for health impact tocommunities surrounding the SSFL.

The results of the exposure pathways analyses for air, surface water and ground water, and soiland sediment indicate that human exposure to chemicals and radionuclides from the SSFL is notlikely to have occurred, or be occurring, in the communities surrounding the SSFL at levels thatwould result in adverse human health effects. Chemicals and radionuclides have been released tothe environment at the SSFL site. Based on the available data, ATSDR has no indication thatsignificant concentrations of chemicals and radionuclides have migrated from the site to offsiteareas where human exposure could occur. Because we have no indication of human exposure atlevels of health concern in offsite communities, there is also no indication that adverse humanhealth effects are likely to occur in these communities.

The findings of the health studies for the SSFL area do not provide conclusive answers regardingwhether members of the community surrounding the SSFL site experienced adverse health effectsfrom potential exposure to chemicals and radionuclides released from the SSFL. While thecommunity expressed concern about potential exposure to radionuclides from the SSFL, thecommunity studies do not show any increase in cancers considered to be "very radiosensitive",such as leukemia.

Interpretation of the bladder and lung cancer findings for the community cancer registry studies isdifficult because the increases were not consistent across sex or the surrounding geographic area(Ventura vs. Los Angeles County). In addition, the studies provide no information about potentialenvironmental or lifestyle exposures that may have contributed to these observed increases. Forbladder cancer, there was no evidence of increased mortality among the SSFL workers; site-related exposures should have been higher for the SSFL workers than for the communitymembers, thus health effects of the exposures would more likely be found in the worker studies.The worker studies did show an increase in lung cancer mortality in workers with presumedexposure to external radiation or hydrazine, however confounding effects due to smoking, lifestylefactors, and other unmeasured chemical exposures, could not be ruled out. The uncontrolledconfounding effects can introduce either positive or negative bias into the expected mortalityfrequencies.

The community identified a number of specific health concerns in addition to the incidence ofbladder and lung cancers. In the absence of documented exposures to SSFL chemicals andradionuclides, it is very unlikely that the diseases underlying those health concerns are related toenvironmental releases from the SSFL. Specific community environmental concerns included thesafety of drinking water supplies, surface water runoff, radiation exposure, and the desire foradditional environmental sampling. Currently no drinking water supply wells have been affectedby SSFL-related contaminants. Due to water recycling processes at the SSFL and the aridconditions in this area there is very limited potential for surface water runoff. Surface watermonitoring indicates that chemicals and radionuclides are rarely detected and well below levels ofhealth concern. Extensive monitoring also indicates that radiation in areas of potential offsiteexposure has not been detected above background levels. Concerns related to additionalenvironmental sampling are addressed in the Exposure Pathways Analyses and Conclusions andRecommendations sections.

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