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PUBLIC HEALTH ASSESSMENT

MOFFETT NAVAL AIR STATION
(a/k/a MOFFETT FEDERAL AIRFIELD)
MOUNTAIN VIEW, SANTA CLARA COUNTY, CALIFORNIA


SUMMARY

Moffett Federal Airfield (MFA) is a former Navy base currently operated by the National Aeronautics and Space Administration (NASA). Located in Santa Clara County, California, MFA encompasses approximately 2,200 acres.

MFA was originally commissioned as Naval Air Station (NAS) Sunnyvale in 1933 to serve as a base for the West Coast dirigibles of the Navy's lighter-than-air program. After a brief period under Army control, the base was renamed NAS Moffett Field in 1942 and became a major naval air transport base. A large portion of the MFA property is dedicated to runways, taxiways, and hangars. The base was closed and transferred to NASA in 1994. Currently, NASA is continuing to operate MFA as a restricted federal airfield, but is also considering various other uses of the property that will support its mission.

Unit-level and intermediate-level aircraft maintenance was performed at NAS Moffett Field, as well as other activities related to the support of a military base. Contamination of groundwater, soil, surface water, and sediment at MFA has resulted from the handling and disposal of various fuels, solvents, and other chemicals used at the base. Sources and sites of contamination include landfills, wastewater holding ponds, drainage ditches, leaking underground storage tanks and sumps, fuel spills, and fire-fighting training areas. MFA is also affected by a plume of groundwater contamination originating at a nearby Superfund site.

There is little or no potential for public exposure to contamination at MFA. There are no water supply wells at MFA which draw from the contaminated aquifers, and groundwater contamination originating at MFA has not migrated offsite. Public access to MFA is restricted by base security measures, greatly limiting possible public exposures to soils, surface water, and sediment. Levels of contamination present do not present a public health hazard from any limited and infrequent exposures that would be likely to occur. Remediation of many sites is complete. Removal of contaminated sediments and soil will further decrease the possibility of exposure. Groundwater remediation and monitoring are ongoing. Contamination is well characterized, and will be taken into consideration during future use planning for the site. For these reasons, the public health assessment evaluation concludes that there are No Apparent Public Health Hazards relating to environmental contamination at MFA. This finding assumes that any proposed changes in land or water use at MFA will be evaluated to ensure that they will not result in contaminant migration or in public exposure to harmful levels of contamination.


BACKGROUND

Site Description and History

Moffett Federal Airfield (MFA), formerly Naval Air Station (NAS) Moffett Field, is currently operated by the National Aeronautics and Space Administration (NASA). Located in Santa Clara County, California, near the southern tip of San Francisco Bay, MFA encompasses approximately 2,200 acres. (Figure 1 shows MFA's regional location.) It is bordered on the north by salt evaporation ponds which are adjacent to San Francisco Bay, on the west by Stevens Creek and NASA's Ames Research Facility, on the south by Highway 101, and on the east by the Lockheed Aerospace Center (PRC, 1996b). MFA is surrounded by a security fence, and access is limited to personnel, residents, and authorized visitors. (Although the NASA-Ames property is distinct from the Moffett Federal Airfield property, NASA-Ames is located within the Moffett Field perimeter security fence.) The cities of Sunnyvale and Mountain View surround Moffett Field (IT, 1991).

MFA was originally commissioned as NAS Sunnyvale in 1933 to serve as a base for the West Coast dirigibles of the Navy's lighter-than-air program. Soon after the airship Macon was lost in a storm in 1935, the base was transferred to the Army Air Corps. In 1942, the base was transferred back to the Navy and renamed NAS Moffett Field. During the 1950s and 1960s, NAS Moffett Field served as a major naval air transport base. After a station reorganization in 1973, the mission of NAS Moffett Field was to support antisubmarine warfare training and patrol squadrons. During this mission, only unit-level and intermediate-level aircraft maintenance was performed. In 1992, the base was designated for closure under the Department of Defense Base Realignment and Closure (BRAC) program. In July 1994, NASA, which owns the adjacent Ames Research Center, assumed control of the NAS Moffett Field facility and changed its name to Moffett Federal Airfield. NASA has continued the tenant program begun by the Navy, hosting several other organizations at MFA including the Naval Reserve, the California Air National Guard, and Onizuka Air Force Base. Control of on-base and off-base housing was transferred to Onizuka Air Force Base (PRC, 1996b). Currently, NASA is continuing to operate MFA as a restricted federal airfield, but is also considering various other uses of the property that will support its mission (Staab, 1998).

Contamination at MFA has resulted from the handling and disposal of various fuels, solvents, and other chemicals used at the base. Sources and sites of contamination include landfills, wastewater holding ponds, drainage ditches, leaking underground storage tanks and sumps, fuel spills, and fire-fighting training areas. MFA is also affected by a regional plume of groundwater contamination originating at a nearby Superfund site (PRC, 1996b). Contaminated media include groundwater, soil, surface water and sediment.

Remedial and Regulatory History

In 1981, the Navy began developing a priority list of contaminated installations and facilities. As a result, the Navy initiated its environmental program - called the Installation Restoration Program (IRP) - at NAS Moffett Field in 1983. An initial assessment study, completed in 1984, identified nine potential hazardous waste sites at MFA. Subsequent studies in 1986 and 1987 identified ten additional sites. MFA was proposed for placement on the U.S. Environmental Protection Agency's (EPA) National Priorities List in 1985 and was listed in 1987 (IT, 1991).

The Remedial Investigation/Feasibility Study (RI/FS) process was coordinated through a Federal Facilities Agreement entered into by the Navy, EPA, and the California Environmental Protection Agency. Phase I of the RI was completed in 1990 and Phase II investigations (to obtain detailed site-specific data) were begun later that year. During Phase II, the RI/FS process was divided into the following six separate operable unit (OU) studies:

OU1 Sites 1 and 2 landfill soils
OU2 Sites 3 through 11, 13, 14, 16, 17, 18, and 19 soils
OU3 Sites 12 and 15 soils
OU4 West-side aquifers
OU5 East-side aquifers
OU6 Wetlands areas

In 1992, EPA determined that aquifers on the west side of MFA were affected by a plume of contaminated groundwater migrating from the Middlefield-Ellis-Whisman (MEW) Superfund site south of MFA. It was decided, therefore, that these aquifers and the overlying soil would be covered by remedial guidelines specified in the 1989 MEW Record of Decision (ROD). Consequently, OU4 (the west-side aquifers) was deleted from Phase II investigations. OU5 was modified to include all aquifers not part of the regional plume, with the exception of aquifers in the area of the OU1 landfills, which were added to OU1. OU2 was divided into OU2-West (sites overlying the regional plume: Sites 8, 9, 10 [Chase Park], 14, 16, 17, 18, and portions of 19) and OU2-East (Sites 3, 4, 5, 6, 7, 10 [runways], and the remainder of 19) (PRC, 1996b).

In 1993, regulatory agencies agreed to remove petroleum-contaminated sites from the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) process because CERCLA contains an exclusion for petroleum contamination. The Navy proposed that these sites be treated according to relevant state and federal regulations concerning underground storage tanks. For these reasons, the following sites were deferred to the IRP petroleum sites program: Sites 12 and 15 (all of OU3), and Sites 5, 9, 14, and 19 (PRC, 1996b). The Navy's plans for remediating these sites were described in the 1994 Corrective Action Plan (PRC, 1994b). When the California Regional Water Quality Control Board (RWQCB) issued new guidance, however, the Navy reformulated its approach to these sites, as detailed in the 1997 "Draft Basewide Petroleum Site Evaluation Methodology Technical Memorandum" (PRC, 1997). Under the new RWQCB guidance, petroleum sites at MFA are being evaluated using risk-based screening levels (RBSLs) for various possible receptor scenarios.

Subsequent investigations identified eight additional sites: Zook Road Fuel Spill (Site 20), Patrol Road Ditch (Site 21), Golf Course Landfill Number 2 (Site 22), Golf Course Landfill Number 3 (Site 23), Active Petroleum Sites (Site 24), the Weapons Storage Bunkers, the Industrial Wastewater Flux Ponds, and the Potential Runway Wetland. (Note: All numbered RI sites are shown in Figure 2.)

As a result of these modifications, MFA is now divided into the OUs and study areas listed below. RODs have been issued for OU1, OU2-East, and OU5. A Station-Wide ROD that will also cover OU6 is pending (PRC, 1996b).

OU1 Soils and groundwater at Sites 1 and 2
OU2-West Soils at Sites 8, 10 (Chase Park), 14-North, 16, 17, and 18
OU2-East Soils at Sites 3, 4, 6, 7, 10 (runways), 11, and 13
OU5 East side aquifers
OU6 Wetlands areas
Petroleum Sites Sites 5, 9, 12, 14-South, 15, and 19
Station-Wide Sites 20 to 24, and Weapons Storage Bunkers, Industrial Wastewater Flux Ponds, and Potential Runway Wetland

Contaminants found during the RI include: volatile organic compounds (VOCs) and petroleum compounds in groundwater; VOCs, semi-volatile organic compounds (SVOCs), polychlorinated biphenyls (PCBs), and petroleum compounds in soil; and PCBs, pesticides, and petroleum compounds in surface water and sediment. Metals were detected in soils, groundwater and sediments, but were determined to be unrelated to site activities (i.e., they are naturally occurring and/or reflect typical urban levels) (TetraTech, 1998c). Table 1 summarizes the waste disposal history, investigation results, current status, and evaluation of public health hazards at all of the sites investigated during the RI.

ATSDR Involvement

The Agency for Toxic Substances and Disease Registry (ATSDR) released a preliminary public health assessment (PHA) for NAS Moffett Field in April 1989, based on the limited sampling data and exposure information available at that time. ATSDR recommended further investigations to characterize the extent of contamination and the potential for public contact with on-site contaminants. The RI/FS process has fulfilled this recommendation. ATSDR conducted a site visit and met with representatives from the Navy and California Department of Health in June 1991 to obtain updated information about the site. During this visit, ATSDR also met with representatives of the League of Women Voters and the Silicon Valley Toxics Coalition to assess community concerns, which focused primarily on the possibility of drinking contaminated groundwater. In January 1998, ATSDR conducted another site visit. ATSDR met with representatives of the Navy and attended a Restoration Advisory Board (RAB) meeting, where community members expressed their concerns about ecological issues and the need for community understanding of how cleanup levels were determined for the facility. In October 1998, ATSDR returned to present the Public Comment Release of the Public Health Assessment to the RAB. At that meeting, RAB members expressed further comments and concerns, which have been addressed in this final version of the PHA. ATSDR has requested that NASA keep ATSDR informed of any changes in land and water use at MFA so that ATSDR can evaluate the public health implications of those changes (see Appendix C).

Demographics

Prior to its closure, Naval Air Station Moffett Field employed more than 5,500 military, 1,500 civilian, and 1,000 reservist personnel (IT, 1991). Currently, MFA employs about 1,000 federal employees, 780 military personnel, 2,200 reservists, and 250 contractors (Olliges, 1998). At the time of the 1990 U.S. Census, 1,649 persons were housed at NAS Moffett Field; 61% of these were housed in group housing (military barracks) and the remainder in rented family housing. The neighboring towns of Mountain View and Sunnyvale had populations of 67,460 and 117, 229, respectively. The percentage of children under the age of 10 in the population was between 11 and 12 percent for the two cities and the base (Census of Population and Housing, 1990). (See Tables 2 and 3 for more detailed demographic information.)

Land Use and Natural Resources

MFA is located within the Santa Clara Valley groundwater basin, a large, northwest-trending valley which is bordered by the Santa Cruz Mountains on the west and the Diablo Range on the east. MFA itself is situated on nearly flat interfluvial basin deposits and fill, with elevations ranging from 36 feet above mean sea level (msl) to 2 feet below msl. The northern half of MFA, much of which was at one time submerged or marsh lands, is prone to flooding during exceptionally high tides (IT, 1991).

MFA is divided in half by the runway system which extends almost the length of the property. Most of the aircraft and flight training operations take place on the east side of the runway and administrative activities and base housing are located on the west side. Land use in the vicinity of MFA is urban/suburban; the cities of Mountain View and Sunnyvale are home to numerous industries including electronics, high tech, and aerospace firms. This area is part of the well-known "Silicon Valley" (IT, 1991).

Although MFA is bounded on the west by the intermittent-flowing Stevens Creek, most surface runoff at the base is collected in a network of subsurface storm drains. Runoff from the northern third of MFA is collected by storm drains which channel water to the pump station at Building 191. This station pumps the water into the Northern Channel, which also receives runoff from the eastern half of the base. The Northern Channel carries water to Guadalupe Slough, which drains into San Francisco Bay. Storm water from the western portion of the base collects in two stormwater retention ponds, from which overflow can be pumped into Stevens Creek if necessary. Additional surface water features in the immediate vicinity of MFA include wetlands in the northwestern portion of the base and diked water bodies (commercial evaporative salt ponds and the former Jagel Slough) bordering MFA to the north (PRC, 1996a).

Groundwater beneath MFA is divided into a shallow-aquifer sequence and a deeper, confined aquifer. Drinking water for Moffett Field was obtained from the deeper aquifer in the past; however, it is presently obtained from the Hetch-Hetchy dam project via the San Francisco Water Company (PRC, 1996b; Olliges, 1998). There are currently no active water supply wells on the MFA property. Drinking water for the towns of Mountain View and Sunnyvale is primarily obtained from surface water sources (Iwamura, 1998).

Quality Assurance and Quality Control

In preparing this PHA, ATSDR relied upon the information provided in the referenced documents. The environmental data presented in this PHA are from RI/FS documents produced by the Navy and its contractors as part of the CERCLA process. The limits of these data have been identified in the associated reports.


EVALUATION OF ENVIRONMENTAL CONTAMINATION, EXPOSURE PATHWAYS, AND PUBLIC HEALTH IMPLICATIONS

Introduction

ATSDR's public health assessments are driven by exposure to (contact with) contaminated media. Although chemical contaminants disposed of or released into the environment at MFA have the potential to cause adverse health effects, a release does not always result in exposure. People are exposed to a chemical only if they actually come in contact with the chemical. People may be exposed by breathing, eating, or drinking a substance containing the contaminant or by skin (dermal) contact with a substance containing the contaminant.

Exposure does not always result in adverse health effects. The type and severity of health effects that may occur in an individual from contact with a contaminant depend on the exposure concentration (how much), the frequency and duration of exposure (how long), the route or pathway of exposure (breathing, eating, drinking, or skin contact), and the multiplicity of exposure (combination of contaminants). Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, lifestyle, and health status of the exposed individual influence how the individual absorbs, distributes, metabolizes, and excretes the contaminant. These factors and characteristics determine the health effects that may occur as a result of exposure to a contaminant.

ATSDR evaluates environmental data by comparing contaminant concentrations to health-based comparison values (CVs). Comparison values are calculated by ATSDR toxicologists, using scientific literature available on exposure and health effects. These values, which are derived for each of the different media, reflect the estimated contaminant concentration for a given chemical that is not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight for specified periods of time. Contaminants detected above the CVs do not automatically present a public health hazard. If contaminant concentrations are above comparison values, ATSDR further analyzes exposure and the toxicology of the contaminant to determine whether a public health hazard could occur. For more information about ATSDR's comparison values, see Appendix B. For more detailed information about individual chemicals, consult ATSDR's toxicological profiles. Fact sheets based on these profiles, as well as further information about ATSDR, are available on ATSDR's home page:

http://www.atsdr.cdc.gov/

In the following section we evaluate the possible pathways of exposure to contamination at MFA. ATSDR examined the possible exposure situations to determine whether people in the community are, or have been, or will be exposed to contamination. ATSDR reviewed the available data compiled on all designated IRP sites (see Table 1) to ensure a thorough evaluation of all potential or completed pathways of human exposure to contaminants.

As a result of our site visit observations and based on the evaluation of available data, ATSDR concluded that there are no plausible exposure situations that could pose a public health hazard. Although hazardous chemical contaminants have been found in groundwater, soil, sediment, and surface water at MFA, there was little past potential, and there is little current or future potential, even in the worst case, for the public to be exposed to these contaminants. Any contact that has occurred is likely to have been only incidental, i.e. infrequent and of short duration. ATSDR assumes remedial activities will continue, and that precautionary measures will be taken to ensure that exposure does not occur in the future as a result of any changes in land or water use. ATSDR has requested inclusion in the decision process regarding future use changes, in order to provide the appropriate public health evaluation. Table 4 summarizes our evaluation.

Groundwater

MFA Hydrogeology

MFA is located within the Santa Clara Valley groundwater basin. Aquifers under MFA were divided for the purposes of the RI into zones A1, A2, B2, B3, and C, with A1 representing the shallowest aquifer and C the deepest. The A1 and A2 aquifers lie between approximately 10 and 60 feet below land surface (bls). The A2/B2 aquitard occurs at about 45 to 60 feet bls. The B2 and B3 aquifers range from 60 to 105 feet bls and 110 to 125 feet bls, respectively. An extensive aquitard separates these shallower aquifers from the deep C aquifer, which primarily lies between 155 and 500 or more feet bls. Recharge to the shallower A and B aquifers is primarily from upgradient infiltration by percolation of rainfall, streamflow, and excess irrigation water. Recharge to the deep, confined C aquifer is from percolation on upgradient alluvial fans (IT, 1991).

Groundwater flow in the A1 and A2 aquifers is predominantly north or northeast (i.e., towards San Francisco Bay) throughout the station. The drainage pumping station in the northern part of MFA, however, creates a localized depression, diverting groundwater flow in the immediate vicinity toward the pumping station (IT, 1991).

Groundwater Use

Historically, MFA used water from the C aquifer for irrigation and drinking water (IT, 1993). MFA now receives its drinking water from surface water supplies. No wells are currently active on the MFA property; one well at NASA-Ames, screened in the C aquifer, is used sporadically for irrigation (Olliges, 1998). Surface-water sources in the mountains supply most water to local communities; however, both Mountain View and Sunnyvale have municipal wells screened in the C aquifer. These wells are used for 15% or less of the total water supply (Hammons, 1998; Iwamura, 1998; HAZWRAP, 1989). The closest municipal well is upgradient and is located approximately one mile from MFA (EPA, 1989); there are private wells upgradient of the station just outside the perimeter fence (K/J/C 1988). These upgradient wells are not subject to contamination from the existing plume, as groundwater flow is from the direction of these wells toward the source of contamination.

Nature and Extent of Groundwater Contamination

For the purposes of the RI, groundwater under MFA was divided into the "west-side aquifers" and the "east-side aquifers." The dividing line between the west and east sides is roughly the eastern edge of the MFA runways. Contamination in each of the two areas is discussed below; see Table 1 for specific contaminant concentrations.

The west-side aquifers are affected by contamination resulting from Navy activities and by a regional plume of contaminants emanating from the MEW Superfund site to the south of MFA. The regional plume contains mostly trichloroethylene (TCE), with lower amounts of tetrachloroethylene (PCE) and dichloroethylene (DCE). MFA's releases of PCE and TCE in the vicinity of the MFA Dry Cleaner's sump have also apparently contributed to this plume. Maximum detections of TCE are 12,000 parts per billion (ppb) in the A1 aquifer and 18,000 parts per billion in the A2 aquifer; these concentrations are well above comparison values. Maximum concentrations of PCE and DCE are lower, but still above comparison values. In addition, three isolated petroleum plumes emanating from sources at MFA are found in the west-side aquifers. The west-side aquifer contamination is generally limited to the shallow (A1/A2) aquifers, with minor amounts of contaminants present in the B2 and B3 aquifer zone. Testing in 1997 detected vinyl chloride in a single monitoring well at 0.5 ppb (the California MCL for vinyl chloride is 0.5 ppb). Verification sampling and analysis will be conducted at the request of the EPA. The C aquifer zone is not contaminated (IT, 1992b).

The east-side aquifers are affected by a chlorinated VOC plume and isolated petroleum plumes resulting from Navy activities. The contaminants in the VOC plume were used at Hangars 2 and 3 (Site 7) and were also discharged with wastewater to the former wastewater holding ponds at Site 4. Petroleum hydrocarbons (chiefly JP-5) originate from Sites 5, 19, and 24. Again, contamination is limited to the shallow (A1/A2) aquifers, with minor amounts of contaminants present in the B2 aquifer zone. Small amounts of contamination found during one round of sampling of the C aquifer were not confirmed with subsequent sampling (IT, 1993).

Shallow groundwater discharges into the base drainage system where it is collected before flowing into the bay. NASA monitors discharges from the base drainage system under the system's National Pollutant Discharge Elimination System (NPDES) permit (Navy/EPA, 1996). Low levels of VOCs have been detected in recent monitoring of the discharge from the pumping station (Moudy, 1998). The levels detected are not sufficient to present a public health hazard. In addition, VOCs have a short residence time in surface water (ATSDR, 1997a, b). That is, they will volatilize without reaching concentrations that would be a public health hazard, even in the unlikely event that people were to be exposed to them.

Metals were found in the east- and west-side aquifers, but statistical and spatial analyses of metals concentrations did not find them to be elevated above background levels. In addition, there are no known sources of metals contamination at MFA (PRC, 1996). Thus, metals found in groundwater were determined to be naturally occurring.

Evaluation of Potential Public Health Hazards

ATSDR found no evidence that anyone has been or will be exposed to the contamination present in the shallow aquifers at MFA, for the following reasons:

  • Water from the A and B aquifers is not used at MFA for any purpose and is unlikely to be used in the future.
  • No contaminants were found in the C aquifer, in which an irrigation well at NASA-Ames is screened.
  • Because the vertical hydraulic gradient is upward from the C aquifer to the B aquifer, contaminants are unlikely to migrate to the C aquifer.
  • Contaminants from MFA have not migrated offsite.
  • Contaminated groundwater is unlikely to affect San Francisco Bay. The regional plume appears to have stopped migrating (Chao, 1998). Low levels of VOCs discharged at the pumping station are not expected to pose a threat to public health, as there is no public contact with surface water near the discharge and VOCs will volatilize rapidly from surface water.
  • The Navy plans to conduct long-term monitoring of groundwater to assess any migration of the plumes, and, if contaminants are detected at harmful levels in areas that could be impacting human or ecological receptors, treatment will be undertaken (Navy/EPA, 1996).

At this time, groundwater contamination at MFA does not present a public health hazard. Significant contamination from onsite has not migrated offsite, and is unlikely to do so, as the plume appears to have stopped migrating. Residents and workers at MFA are not affected by contamination from onsite or from the regional groundwater plume, as water from the contaminated aquifers is not used for any purpose at MFA except monitoring. If, in the future, water from the C aquifer is used for domestic purposes (such as drinking or bathing) at MFA, or if the amount pumped in the vicinity of MFA is increased significantly, monitoring should be conducted to ensure that contaminants do not migrate from the shallow aquifers to the C aquifer.

Soil

Nature and Extent of Soil Contamination

Contamination by VOCs, SVOCs, PCBs, and pesticides was detected in surface and subsurface soils at MFA; however, levels were below ATSDR health-based comparison values in almost all cases. See Table 1 for detailed site-by-site information.

Metals were found in soils at MFA, but, as was the case with groundwater, statistical and spatial analyses of metals concentrations did not find concentrations to be elevated above ambient (background) levels. In addition, there are no appreciable sources of metals contamination at MFA (PRC, 1996). Thus, metals found in soils were determined to be unrelated to site contamination (Tetra Tech, 1998c).

Evaluation of Potential Public Health Hazards

Public access to the MFA is minimal because of security measures. In addition, contamination is located in restricted and/or infrequently accessed areas. As a result, public and onsite worker exposure to contaminated soils is expected to be infrequent and of short duration. Further, remediation has been completed at many sites, reducing contamination to levels that do not present a possible public health hazard. Consequently, ATSDR believes that any human exposure that might occur to soil contamination will be limited. For these reasons, no apparent public health hazard is associated with exposure to soil contamination at MFA at this time. If, in the future, land use changes at MFA, further evaluation should be conducted to ensure that any areas that may be accessed by the public or workers do not contain unsafe levels of contaminants.

Surface Water and Sediment

Nature and Extent of Contamination

The RI for OU6 included characterization of all surface water bodies at MFA; these water bodies are drainage channels, stormwater retention ponds, or wetlands. Both surface water and sediment were tested for the presence of contamination. Some pesticides and PCBs were detected above comparison values in sediments; one PCB (Aroclor-1254) was detected above its comparison value in surface water (PRC, 1996a). See Table 1 for detailed information.

Metals were found in sediments at MFA, but, again, statistical and spatial analyses of metals concentrations did not find concentrations to be elevated above ambient (background) levels. In addition, there are no appreciable sources of metals contamination at MFA (PRC, 1996). Thus, metals found in soils were determined to be unrelated to site contamination (Tetra Tech, 1998c).

Evaluation of Potential Public Health Hazards

Observations made during the RI found that many areas of OU6 are remote and are infrequently or never used by humans. All contamination found above ATSDR comparison values was located in these areas, with the exception of Lindbergh Avenue Ditch which has been remediated by NASA and which was accessed only for maintenance prior to remediation (PRC, 1996a). Remediation reduced contamination to levels that do not present a public health hazard for the limited, infrequent contacts that might occur. For these reasons, no apparent public health hazard is associated with exposure to surface water and sediment contamination at MFA at this time. If, in the future, land or water use changes at MFA, further evaluation should be done to ensure that any areas that will be accessed by the public or workers do not contain unsafe levels of contaminants.


REUSE EVALUATION

NASA-Ames is currently working to create research, development, and educational partnerships with academia, private industry, and nonprofit organizations in support of its mission. Some of these entities are expected to be located onsite (Staab, 1998). It is possible that these plans could involve changes in land or water use at MFA. Any land-use changes would, by law, be handled through the National Environmental Protection Act (NEPA) review process, which includes public review and comment. In addition, ATSDR has asked to be apprised of any plans for changes in land or water use at MFA, so that it can evaluate the public health implications of any such changes (see Appendix C).


COMMUNITY HEALTH CONCERNS

ATSDR identified the community health concerns through RAB meetings, contact with officials, and review of site documents, including RODs and the Community Relations Plan prepared by the Navy (HAZWRAP, 1989). The concerns received are answered in this section. Additionally, technical comments provided by reviewers for the Public Comment Release have been incorporated throughout the document.

Will groundwater contamination at MFA affect my drinking water?

It is highly unlikely that groundwater contamination at MFA will affect drinking water. There are no drinking water wells at MFA and contamination originating at MFA has not migrated offsite and most likely will not in the future. Groundwater flow is predominantly to the north at MFA. Because the terrain to the north of MFA, between the airfield and the bay, consists of stormwater retention ponds, wetlands, and salt evaporation ponds, it is unlikely that water wells would be constructed downgradient from the contaminant plume. Further, most drinking water for MFA and surrounding communities is supplied by surface water sources in the mountains.

Will groundwater or surface water contamination at MFA affect San Francisco Bay?

It is highly unlikely that groundwater or surface water contamination at MFA will affect San Francisco Bay. Little surface water contamination was found, and what contamination does exist would be greatly diluted upon reaching the bay. Further, most of the surface water on the property (e.g., water in the stormwater retention ponds) evaporates rather than flowing into the bay (TetraTech, 1998b). State and federal regulators require the Navy to conduct long-term monitoring of groundwater to assess any migration of the plumes; and to take action if the plumes migrate to areas in which they could pose a hazard (Navy/EPA, 1996). Groundwater under most of MFA flows into the NASA/MFA drainage system before flowing into the bay. NASA monitors discharges from the drainage system under a NPDES permit (Navy/EPA, 1996). The San Francisco Bay Regional Water Quality Control Board reviews the NPDES monitoring data, and would work with NASA to remedy any potential problem if it determined that NASA's discharge posed a threat to water quality. The VOCs present in groundwater volatilize very rapidly upon being exposed to air, and would not be expected to remain in surface water long enough to affect the bay (ATSDR, 1997a,b).

Did groundwater contamination at MFA in the past, when groundwater was used as a drinking water supply, represent a past public health hazard?

According to Navy records, the water supply for MFA came from the deeper C aquifer. Groundwater sample analyses have not detected contamination that would present a hazard. It is not likely that contaminants such as the solvents that are the contaminants of concern would have been present in the past and would not have been detected in the sampling that has occurred at MFA. Groundwater contamination does not present any apparent health hazard from past use of the C aquifer.

Are the "cleanup levels" established for remediation of contamination (and protection of public health) at MFA adequately protective of public health?

In selecting its remedial actions, the Navy has used the assumption that people are going to live on formerly contaminated areas and drink the groundwater in the shallow aquifers. Because neither of these scenarios is likely to occur, this remedial approach is very conservative and protective of human health.

What are the public health implications of possible future use scenarios at MFA?

ATSDR prepares public health assessments that evaluate the potential for past, present or likely future exposures. Future exposures examined would be those that might occur with use consistent with past or present use. ATSDR does not make judgments about the public health implications of hypothetical future scenarios. Currently, NASA has no formal plans to significantly modify use of the MFA properties. ATSDR has asked that NASA notify ATSDR of any changes in land and water use at MFA (see Appendix C). As ATSDR receives any such information, we will evaluate the public health implications of the future use plans.

How does ATSDR determine whether levels of contamination pose a public health hazard?

ATSDR compares contaminant concentrations to health-based comparison values. These values are calculated based on scientific literature concerning exposure and health effects; they are conservative screening levels that contain a large margin of safety. If contaminant concentrations are below these values, the contaminants do not pose a health hazard. If concentrations exceed these values, the contaminants do not necessarily pose a health hazard; the potential hazard depends on to what extent people are actually exposed to the contaminants and the toxicity of the individual chemicals. ATSDR examines past, present, and likely future exposures to determine whether people have been, are, or are likely to be exposed to the contaminants, and what the frequency and duration of the exposure are. If there is significant exposure, ATSDR calculates exposure doses and evaluates possible health effects. For MFA, ATSDR did not find any situations in which people were exposed more than incidentally (i.e. infrequently and for short periods of time) to levels of contamination exceeding comparison values. The site-by-site evaluation of whether contaminant levels exceeded comparison values can be found in Table 1.

Does the "public" for which ATSDR evaluated health hazards include workers at MFA?

Occupational exposure to chemicals, safety for workers engaging in remedial activities, and other worker health and safety issues are evaluated or governed by the Occupational Safety and Health Administration, National Institute of Occupational Safety and Health, and various state agencies. ATSDR evaluates any type of exposure not falling under the purview of these agencies. ATSDR did include the general population of base workers in its consideration of exposure to the contamination at MFA.

What is the meaning of "incidental exposure"?

Incidental exposure is exposure that occurs infrequently and for a short duration. This type of exposure at MFA might be an occurrence such as a visitor gaining access to an area containing low levels of soil contamination, and being exposed by walking across the area. Another scenario might involve a worker or visitor accidentally coming in contact with drainage ditch sediment or water and being exposed dermally or via ingestion. Such exposure is only of health concern if the contamination exceeds an acute health-based guideline. There were no such exceedances of acute comparison values at MFA.

On what basis did ATSDR determine that shallow groundwater at MFA has not been used for any purpose other than monitoring and remediation?

ATSDR obtained this information from remedial investigation documents.

Could contaminants from groundwater volatilize through the soil into buildings and pose a health hazard in indoor air?

It is unlikely that this would occur. TCE is the main contaminant of concern in groundwater, and research has shown that it is unlikely to volatilize from groundwater through soil at levels that would pose a health hazard unless it is present in the uppermost aquifer at levels greater than 1% of its solubility in water (Tewari et al. 1982; EPA 1992; ATSDR 1997b). Maximum levels of TCE found in the A1 aquifer are below this level. In addition, soil gas monitoring during the remedial investigation did not reveal widespread elevated levels of gaseous TCE, as would be expected if TCE were volatilizing from groundwater.


HEALTH OUTCOME DATA

ATSDR did not evaluate health outcome databases because people have not been exposed to site contaminants at levels that would pose a health hazard.


ATSDR CHILD HEALTH INITIATIVE

ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of hazardous substances emitted from waste sites and emergency events. They are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. They are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children are also smaller, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.

ATSDR evaluated the likelihood for children living on-base or in the Mountain View and Sunnyvale communities to be exposed to base contaminants at levels of health concern. ATSDR did not identify any past, present, or future situations in which children were or would be likely to encounter chemical contaminants at MFA, other than incidental exposure. Although children reside on the base, contamination is located in restricted or not-accessed areas and in unused groundwater aquifers. ATSDR will evaluate future use changes that might occur for MFA to ensure that children will not be exposed to contamination as the result of any future activities at the site.


CONCLUSIONS

ATSDR has drawn the following conclusions from environmental data and information on Moffett Federal Airfield:

1. Contamination in soil, groundwater, surface water, and sediment presents No Apparent Public Health Hazard in the past, present, or future, because the potential for public exposure was and is low, and any exposure would have been, or would be, incidental.

2. This conclusion is based on the premise that, if land or water use at MFA changes from the current situation, precautions will be taken to ensure that the changes will not result in migration of contamination or public exposure to contamination at unsafe levels.


PUBLIC HEALTH ACTION PLAN

The Public Health Action Plan (PHAP) for Moffett Federal Airfield contains a description of actions taken and those planned by ATSDR, the Air Force, NASA, and other federal and state agencies at the site after the completion of this public health assessment. The purpose of the PHAP is to ensure that this public health assessment not only identifies public health hazards, but also provides a plan of action designed to mitigate and prevent adverse human health effects resulting from exposure to hazardous substances in the environment. The public health actions that are being implemented or are recommended by ATSDR are as follows:

Actions in Progress

1. The Navy, NASA, and other federal and state agencies are enacting remediation activities to decrease or eliminate onsite contamination in soil, surface water, sediment and groundwater, and to decrease or eliminate the potential for migration of groundwater contaminants offsite from the facility.

2. RODs to initiate remedial actions are scheduled for site 22 landfill and for the wetlands areas, to decrease or eliminate existing contamination.

3. The Navy and NASA will continue to monitor groundwater to ensure that contamination is not migrating offsite.

4. ATSDR has requested that it be apprised of any changes to land or water use at MFA.

Actions Recommended

1. If, at some time in the future, water from the deep aquifer at MFA is used for any purpose which may involve significant human contact, sampling and analysis should be conducted to ensure that contamination has not migrated to this aquifer.

2. If land or surface water use at MFA changes, evaluation should be undertaken to ensure that the changes will not result in migration of contamination or public exposure to harmful levels of contamination.


PREPARERS OF REPORT

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

Gwendolyn Eng
Regional Representative
ATSDR Region 9


REFERENCES

Agency for Toxic Substances and Disease Registry (ATSDR). 1997a. Toxicological profile for tetrachloroethylene. September 1997.

ATSDR. 1997b. Toxicological profile for trichloroethylene. September 1997.

Census of Population and Housing. 1990. Summary Tape File 1A (California) [machine-readable data files]. Prepared by the Bureau of the Census. Washington, DC: The Bureau [producer and distributor], 1991.

Chao. 1998. ATSDR record of activity for telephone communication with Stephen Chao, Remedial Project Manager, U.S. Navy, Engineering Field Activity West. April 1998.

EPA. See U.S. Environmental Protection Agency.

Hammons. 1998. ATSDR record of activity for telephone communication with Dan Hammons of the City of Sunnyvale. April 1998.

HAZWRAP Support Contractor Office, Martin Marietta Energy Systems, Inc. (HAZWRAP). 1989. Community Relations Plan for Remedial Investigation/Feasibility Studies at Naval Air Station Moffett Field. May 1989.

International Technology Corporation (IT). 1991. Phase I Characterization Report, Naval Air Station Moffett Field, Volume 1. April 1991.

IT. 1992a. Draft Final Remedial Investigation Report, Operable Unit 2, Naval Air Station Moffett Field, Volumes 1 and 2. August 1992.

IT. 1992b. Draft Final Remedial Investigation Report, Operable Unit 4, Naval Air Station Moffett Field, Volumes 1 and 2. August 1992.

IT. 1993. Remedial Investigation Report, Operable Unit 5, Naval Air Station Moffett Field, Volume 1. August 1993.

Iwamura. 1998. ATSDR record of activity for telephone communication with Tom Iwamura of the Santa Clara Valley Water District. March 1998.

Kennedy/Jenks/Chilton (K/J/C). 1988. Active Wells Report, Potential Conduits Investigation, Naval Air Station Moffett Field. November 1988.

Moudy. 1998. ATSDR record of activity for telephone communication with Jill Moudy of Science Applications International Corporation, a contractor to NASA. June 1998.

Navy/EPA. See U.S. Department of the Navy, Naval Facilities Engineering Command, Engineering Field Activity West, and U.S. Environmental Protection Agency, Region 9.

Olliges. 1998. ATSDR record of activity for telephone communication with Sandy Olliges of NASA. April 1998.

PRC Environmental Management, Inc. (PRC). 1993. West-Side Aquifer Long-Term Source Remediation Draft Final Remedial Design and Remedial Action Work Plan, Naval Air Station Moffett Field. October 1993.

PRC. 1994a. Revised Final IRP Petroleum Sites (and Wastewater Tanks and Sumps) Characterization Report, Naval Air Station Moffett Field. January 1994.

PRC. 1994b. Final Installation Restoration Program Petroleum Sites (and Wastewater Tanks and Sumps) Corrective Action Plan (CAP), Moffett Federal Airfield. December 1994.

PRC. 1995. Final Feasibility Study Report, Operable Unit 1, Moffett Federal Airfield. May 1995.

PRC. 1996a. Revised Final Operable Unit 6 Remedial Investigation, Moffett Federal Airfield, Volume 1. March 1996.

PRC. 1996b. Final Station-Wide Remedial Investigation Report, Moffett Federal Airfield, Volumes 1 and 2. May 1996.

PRC. 1997. Draft Basewide Petroleum Site Evaluation Methodology Technical Memorandum, Moffett Federal Airfield. January 1997.

Staab. 1998. ATSDR record of activity for telephone communication with Brian Staab of NASA. November 1998.

Tetra Tech EM Inc. (Tetra Tech). 1998a. Draft Site 22 Feasibility Study Report, Moffett Federal Airfield. January 1998.

Tetra Tech. 1998b. Revised Draft Final Station-Wide Feasibility Study Report, Moffett Federal Airfield. January 1998.

Tetra Tech. 1998c. Final Station-Wide Feasibility Study Report, Moffett Federal Airfield. October 1998.

Tewari YB, Miller MM, Wasik SP, Martire DE. 1982. Aqueous solubility and octanol/water partition coefficient of organic compounds at 25.0 degrees C. J Chem Eng Data 27: 451-454.

U.S. Department of the Navy, Naval Facilities Engineering Command, Engineering Field Activity West, and U.S. Environmental Protection Agency, Region 9 (Navy/EPA). 1994. Moffett Federal Airfield, Final Operable Unit 2-East Record of Decision. October 1994.

U.S. Department of the Navy, Naval Facilities Engineering Command, Engineering Field Activity West, and U.S. Environmental Protection Agency, Region 9 (Navy/EPA). 1996. Moffett Federal Airfield, Final Operable Unit 5 Record of Decision. June 1996.

U.S. Department of the Navy, Naval Facilities Engineering Command, Engineering Field Activity West, and U.S. Environmental Protection Agency, Region 9 (Navy/EPA). 1997. Moffett Federal Airfield, Final Operable Unit 1 Record of Decision. August 1997.

U.S. Environmental Protection Agency (EPA). 1989. Record of Decision, Fairchild, Intel, and Raytheon Sites, Middlefield/Ellis/Whisman (MEW) Study Area. May 1989.

U.S. Environmental Protection Agency (EPA). 1992. Estimating Potential for Occurrence of DNAPL at Superfund Sites. Office of Solid Waste and Emergency Response, Publication 9355.4-07FS. January 1992.

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