PUBLIC HEALTH ASSESSMENT
MATHER AIR FORCE BASE
MATHER, SACRAMENTO COUNTY, CALIFORNIA
|Site Description/Waste Disposal History||Investigation Results/Environmental Monitoring Results||Corrective Activities and/or Current Status||Evaluation of Public Health Hazard|
|Landfill Operable Unit|
|Landfill Sites 1 to 6
(LF01 to LF06)
|LF01 to LF05 are located in the northeast corner of the base. LF06 is located in the southeast corner of the base. LF01 was used for general refuse disposal until 1942. Investigations have found no waste at LF01; waste was likely removed in the 1950s during airfield construction. LF02 to LF06 served as base disposal areas consecutively from 1942 through 1974. In addition to general refuse, each of these landfills may have also received petroleum, oil, and lubricant (POL) wastes, solvents, waste paint and thinners, discarded pesticide containers, and hospital wastes.||Groundwater: Dichloroethylene (DCE) (35 part per
billion [ppb]), trichloroethylene (TCE) (7.5 ppb), tetrachloroethylene (PCE)
(35 ppb), benzene (1.3 ppb), benzyl chloride (0.5 ppb), and lead (85 ppb)
were detected above comparison values (CVs). Oil and grease (5,000 ppb)
and diesel fuel (1,330 ppb) were also detected, but no CVs are available
for these contaminants. In a sample from the perched water at LF03, DCE
(25 ppb) and vinyl chloride (140 ppb) were detected above CVs.
Surface Soil: Only benzo(a)pyrene at LF03 was detected above CVs. Oil and grease, gasoline, and diesel were also detected.
Surface Water/Sediment: No contaminants were detected above CVs. Gasoline and diesel were detected in both media.
Landfill Gas: Methane gas migration in excess of regulatory limits (5% of air by volume) is occurring at LF04.
|Remedial actions for each of the landfill sites were selected in a July 1995 Record of Decision (ROD). No remedial actions have been conducted at LF01 because waste was removed during airfield construction and no contamination was detected. Under a time-critical removal action, refuse at LF02 was excavated and disposed of at LF04 in 1996. No ongoing monitoring is planned at LF02, because no groundwater contamination has been detected. In 1996, the contents of LF05 and LF06 were excavated and disposed of at LF04. Groundwater monitoring is ongoing, but may end soon because contaminants have only been detected at low levels. LF03 and LF04 were capped and gas venting was implemented in 1996. Access and use restrictions are in place. Gas and groundwater monitoring are ongoing.||No public health hazards were identified at LF01 because
no waste has been located at this site. Waste was likely removed during
No apparent public health hazards are associated with the remaining landfill sites. Past access to these sites by the public was restricted. Past workers were likely exposed only infrequently and for short periods. Workers are also assumed to have worn personal protective equipment to prevent exposures. Removals and landfill capping has been conducted to prevent current and future exposures. Groundwater treatment systems operate at the base and well testing and monitoring is conducted to address contamination in groundwater.
Aircraft Control and Warning (AC&W) Operable Unit
|AC&W Groundwater Plume and Disposal Site 12
|The AC&W site, located in the eastern portion of the base, supports a radar station operated by the Federal Aviation Administration. From 1958 to 1966, an estimated 1,200 gallons of TCE and 1,400 gallons of transformer oil were used at the AC&W site. Waste TCE was reportedly disposed of in a pipe at this site. This disposal location was designated Installation Restoration Program (IRP) site WP12.||Groundwater: Investigations did not locate the
pipe that reportedly received site wastes. A plume of TCE, however, was
identified in the upper 60 feet of the water table unit of the upper aquifer.
This plume extends approximately 1 mile toward the southwest. TCE levels
were found at concentrations up to 800 ppb.
Water Supply Well: Between 1979 and 1980, TCE was found above its CV in 15 of 19 samples (3.6 to 112 ppb) collected from the facility's water supply well.
Soil: Samples collected from the suspected pipe location were analyzed for TCE and polychlorinated biphenyls (PCBs), which were not detected.
|A ROD detailing groundwater remediation was signed in December 1993. A pump and treat system was installed at the site and began operation in January 1995. Originally, treated groundwater was reinjected to the aquifer. Beginning in 1997, treated groundwater has been discharged to Mather Lake as authorized by an Explanation of Significant Difference. Treated water discharged to Mather Lake has a TCE concentration less than 0.5 ppb, which is below the Agency for Toxic Substances and Disease Registry's (ATSDR) cancer risk evaluation guide and the U.S. Environmental Protection Agency's (USEPA) maximum contaminant level (MCL).||No apparent public health hazards were found during ATSDR's evaluation of exposure to TCE in the AC&W site supply well. ATSDR used conservative assumptions about exposure concentrations, frequency, and duration and identified no potential adverse health effects. This well was no longer used as a potable water supply after 1979 and destroyed in 1990.|
|Underground Storage Tank (UST) Sites 25, 30, and 47
(ST25, ST30, and ST47)
|ST25, ST30, and ST47 are former UST sites where either spills or leaks occurred. The 550-gallon and 8,000-gallon USTs at ST25 and ST30, respectively, were used to store diesel fuel. The 4,000-gallon UST at ST47 was used to store gasoline. Leaks from these USTs resulted in subsurface soil contamination.||Surface Soil: No contaminants were detected above
Subsurface Soil: Investigations found lead (0.8 parts per million [ppm]), xylenes (2 ppb), and TCE (5 ppb) below their CVs after UST and soil removals were completed.
|The USTs at ST25 and ST30 and contaminated soils were removed in 1987. Sampling confirmed that no contamination remains. The UST at ST47 and contaminated soil was removed in January 1993. Because the USTs and contaminated soil were removed, no further remedial actions are planned at these sites, as discussed in the ROD signed in December 1993.||No public health hazards were identified because no contaminants were found above CVs in surface soil and contaminants in subsurface soil are inaccessible to the public.|
Soil Operable Unit
|Disposal Site 7 and Fire Training Area 11
(WP07 and FT11)
|WP07 and FT11 are located in the southwestern portion of the base. WP07 was a gravel borrow pit that was used as a disposal area for POL wastes from 1953 until approximately 1966. The POL wastes may have included solvents, waste paint and thinners, and oil containing PCBs. Soil excavated from other IRP sites has also been disposed of here. Waste fuels were burned at FT11, which was used for fire training exercises from 1958 until 1993. In the mid-1980s, however, training exercises were conducted in a lined and monitored fire training pit built near FT11.||Groundwater: WP07 is the source of the Site 7 groundwater
plume discussed below.
Surface Soil:. The maximum detected concentration of dioxins and furans, expressed as the 2,3,7,8-TCDD equivalent, was 19 parts per trillion (ppt). This is below the screening level of 1,000 ppt.
Subsurface Soil: Thallium was detected above its CV in subsurface soil at WP07. Oil and grease (29,000 ppm), diesel (190,000 ppm), and gasoline (9 ppm) were also detected, however, there are no CVs for these contaminants.
|Soil vapor extraction (SVE) systems were installed at WP07 and FT11 in 1998 to remove volatile fuel components from the soil above the water table. WP07 will be capped under applicable landfill closure regulations.||Contaminants in soil at WP07 and FT11 pose no apparent public health hazards. These sites are located in a remote area of the base. Any exposures to workers are expected to be infrequent and of short duration. Ongoing remediation is being conducted to prevent current and future exposures. Potential health hazards from exposure to contaminants in groundwater are evaluated under the Site 7 groundwater plume discussed below.|
|Fire Training Area Sites 9 and 10
(FT09 and FT10)
|FT09, located northwest of the airfield, was used for fire training from 1945 to 1947. FT10, located under the Strategic Air Command (SAC) refueling tanker loading apron southwest of the airfield, was reportedly used from 1947 to 1958. Approximately 50 to 500 gallons of POL wastes, which may have contained solvents, were used during training exercises.||No sampling has been conducted at FT09 because this site
has not been located on historic aerial photographs and no evidence of the
site has been found during investigations.
No contamination has been found at FT10. However, site FT10C, located north of the refueling apron, is thought to be the actual location of the fire training area based on 1994 site investigations. FT10C is discussed under the Basewide Operable Unit.
|Under a ROD signed in June 1996, no further action was selected at FT09 and FT10. The presence of FT09 has not been confirmed and no contamination was detected at FT10.||No contaminants have been detected at either FT09 or FT10, therefore, these sites pose no public health hazards.|
|Drainage Ditch Sites 13 to 15
(SD13 to SD15)
|These ditches receive surface water drainage from the airfield and facilities north of the airfield. SD13 also includes an oil-water separator from the aircraft wash rack and a soil depression. Waste oils, jet fuel (JP-4), and solvents may have been discharged to these ditches through direct disposal or from oil water separators.||Site investigations at SD14 found no contaminants of concern.
The following contaminants were found at SD13 and SD15.
Surface Soil: Oil and grease (2,720 ppm) and diesel (11,900 ppm) were detected, but have no CVs. Polycyclic aromatic hydrocarbons (PAHs), Aroclor-1260, pesticides, arsenic (11 ppm), cadmium (10.2 ppm), and lead (515 ppm) were found above CVs.
Subsurface Soil: Oil and grease (446 ppm) and diesel (28 ppm) were detected, but have no CVs. No other contaminants were found above CVs.
Surface water: Bis(2-ethylhexyl)phthalate (5 ppb), arsenic (3.6 ppb), lead (106 ppb), and manganese (399 ppb) were detected above CVs.
Sediment: PAHs, PCBs, arsenic (17 ppm), cadmium (29 ppm), and chromium (260 ppm) were detected above CVs. Oil and grease (22,500 ppm), diesel (1,500 ppm), and gasoline (920 ppm), which have no CVs, were also detected.
|No further action is planned at SD14 because no contaminants of concern have been detected. Remedial actions at SD13 and SD15 included removing and treating surface water, excavating 6,200 cubic yards (cy) of contaminated soil (SD13 only) and sediment, and monitoring surface water and groundwater. Soil and sediment were treated by ex-situ bioremediation and disposed of at WP07. A Closure Report for SD13 was completed in July 1998 and no further action is planned at this site. A Draft Closure Report for SD15 was released in March 1999. No further action is expected at SD15.||No apparent public health hazards are associated with SD13 and SD15. These sites are located along the runways and in operational areas of Mather, therefore, past exposure to the public was unlikely because of access restrictions. Any contact by past on-base employees would have been infrequent. The drainage ditches comprising SD13 and SD15 have not been used for recreation and activities at these sites would have been limited. The U.S. Air Force (USAF) has conducted remedial actions at both sites to prevent current and future exposures.|
|Electron Tube Burial Site 16
|RW16 is located in the SAC area under the former Building 8170, which has been demolished. In the late 1950s, approximately 60 low-level radioactive electron tubes were reportedly buried in a 15-foot hole at the site. The tubes were placed in gallon containers and encased in concrete prior to disposal.||Investigations have revealed no increase in radiation levels at the surface of the site or in a nearby groundwater monitoring well.||No further action was selected at the site. The USAF, however, will notify future landowners or lessees about the presence of these tubes and the precautions needed for excavation.||No public health hazards were identified because no increase in radiation over background levels has been identified at this site.|
|Asphalt Rubble Storage Sites 21 and 22
(OT21 and OT22)
|OT21 and OT22 consisted of two sites in the southwestern corner of the base that were used to store asphalt and concrete rubble. No hazardous wastes were reportedly disposed of at these sites.||No samples of site media have been collected. A review of known disposal practices and visual site inspections found no evidence that hazardous materials were stored or disposed of at these sites.||No further action was selected at OT21 and OT22, as detailed in the ROD signed June 1996.||There is no evidence that hazardous materials have been stored, disposed, or released at this site. No public health hazards, therefore, were identified.|
|Spill Site 24
|ST24 is located on the aircraft refueling apron located along the southwestern edge of the airfield. In 1983, approximately 8,000 gallons of JP-4 were spilled on the concrete loading area.||Site investigations have found no contaminants of concern at the site.||No further action was selected at ST24, as detailed in the ROD signed in June 1996.||No public health hazards were identified at this site. No contaminants at levels of concern were detected during site investigations.|
|Spill Sites 26 to 28; 31 to 33; 38; 40 to 46; 48 to 53;
70; and 72 to 77
(ST26 to ST28; ST31 to ST33; ST38; ST40 to ST46; ST48 to ST53; ST70; and ST72 to ST77)
|These sites include releases from USTs located throughout the base. The UST at ST44 was a concrete tank that stored oil and water. Ammonia was stored in the UST at ST45. Other USTs were associated with on-base buildings. Gasoline (both leaded and unleaded), aviation fuel, diesel fuel, mineral spirits, lube oil, waste oil, fuel oil, and alcohols were released to the environment from leaks or spills.||Site sampling after UST removals found no contaminants of concern except at ST31 and ST33. Subsurface soil contamination with petroleum products remains at ST31 and ST33.||Between 1988 and 1993, USAF removed USTs, associated piping, and contaminated soil at each of these sites, except ST31 and ST33. No further action was selected. At ST31 and ST33, subsurface soil contamination remains. The USAF is planning to remove the soil at ST31. Excavation of contaminated soil at ST33 would threaten the stability of the nearby building, however, soil will be removed if needed to protect human health under future uses. Clean closure under Sacramento County regulations has been recommended or completed at each of these sites.||Contamination associated with USTs is restricted to the subsurface, which is inaccessible to the public. As such, no public health hazards were identified because no exposures have occurred.|
|Spill Sites 29, 32, 34 to 36, 50, and 71
(ST29, ST32, ST34 to ST36, ST50, and ST71)
|These sites include releases from USTs located throughout the base. USTs at ST29 were associated with a POL yard used as an on-base service station. USTs at ST32 and ST34 were associated with on-base service stations. ST50 is actually the same site as ST34. At sites ST35 and ST36, USTs were associated with adjacent buildings. USTs at these sites were used to store gasoline, waste oil, and fuel. ST71 consisted of five USTs used to store diesel fuel, gasoline, and waste oils from vehicle air aircraft maintenance.||Subsurface Soil: Gasoline (1,110 ppm) and diesel fuel (440 ppm) were detected, however, there are no CVs for these fuels. Benzene (240 ppm) and toluene (1,530 ppm) were detected above CVs.||These USTs sites are considered petroleum only releases and will be remediated and closed under regulations other than the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Between 1988 and 1993, the USAF removed the USTs from each site. Ongoing remediation at each site, except ST32, includes SVE systems and/or bioventing. At ST32 contaminated soils were excavated and the site was closed by the Regional Water Quality Control Board in 1997.||No exposure occurred and, therefore, no public health hazards were identified. Contaminants are located in subsurface soil which is inaccessible to the public. Past and ongoing remediation efforts prevent future exposures by removing contaminants.|
|Spill Site 37 and 39 and Hazardous Waste Accumulation
Yard Site 54
(ST37, ST39, and SS54)
|These three sites are located in the northern portion of the base. At ST37, USTs associated with a vehicle engine maintenance shop were used to store PCBs, alkalies, cyanides, and lead-acid batteries. ST39 and SS54 were part of the central storage facility and 90-day holding yard for hazardous materials and wastes. Hazardous material at ST39 included PCBs, alkalies, and cyanides. Wastes stored at SS54 included waste hydraulic fluids and solvents.||Surface Soil: Diesel (430 ppm), which has no CV,
was identified as a contaminant of concern at ST39. No other contaminants
were detected above CVs in surface soil at these sites.
Subsurface Soil: Oil and grease (16,000 ppm), diesel (1,400 ppm), and gasoline (5,900 ppm) were identified as contaminants of concern in subsurface soil, but have no CVs.
|Remedial actions selected in the ROD signed in June 1996 included excavation and on-site treatment of surface soil and installation of an in-situ bioremediation and SVE system to treat subsurface soil. The SVE system began operation in December 1998.||No apparent public health hazards were identified from potential exposures to contaminants in soil. These sites were located in the operations area of the base, northwest of the runways. Only infrequent and short duration exposures to workers at these sites was expected. Ongoing remedial actions are designed to prevent current and future exposures.|
|Oil-Water Separator Sites 55 to 66
(SD55 to SD66)
|Oil-water separators were located throughout the base and received waste water from various industrial operations, including maintenance shops, aircraft and vehicle wash facilities, and equipment testing facilities. SD63 also includes two USTs which held waste oil. Antifreeze, solvents, waste oils, grease, painter strippers, hydraulic fluid, fuels, and cleaning fluids may have been discharged to the oil-water separators.||No contaminants of concern were detected at SD55, SD58,
SD61, SD63, SD64, and SD66. The following contaminants of concern were detected
at SD56, SD57, SD59, SD60, SD62, and SD65.
Surface Soil: Benzo(a)pyrene (14 ppm), benzo(a)anthracene (4.2 ppm), benzo(b)fluoranthene (8.8 ppm), arsenic (16.8 ppm), cadmium (16.2 ppm), chromium (3,140 ppm), and lead (12,100 ppm) were detected above CVs. Oil and grease (5,040 ppm) and total petroleum hydrocarbons (TPH) (3,710 ppm), which have no CVs, were also detected.
Subsurface Soil: Benzo(a)pyrene (0.37 ppm) was detected above its CV. Diesel fuel (6,010 ppm) and gasoline (7,350 ppm) were detected, but have no CVs.
|No further action is proposed at sites SD55, SD58, SD61, SD63, SD64, and SD66. At SD60, SD62, and SD65, the oil-water separators and contaminated soil were excavated. Contaminated soil was treated on base by ex-situ bioremediation and disposed of at WP07. SVE systems were installed at sites with remaining soil contamination, including SD56, SD57, and SD59. A Closure Report was completed for SD62 and SD65 in 1997. A plume of TCE was detected in soil gas at SD57, therefore, remedial actions included installing a SVE system, which began operation in October 1997.||No apparent public health hazards are associated with these oil-water separators. No contaminants were found at some sites. Other sites are inaccessible to the public and worker exposure would be infrequent and of short duration. Contaminated soils have been excavated and treated on base to prevent current and future exposures.|
|Open Burn/Open Detonation Site 69
|OT69 was used from the 1950s until 1993 for destruction of unwanted small ordnance, aircraft parts, and other materials. Fuel oil used to burn materials and hazardous components of the destroyed materials may have resulted in site contamination.||Surface Soil: Dioxins and furans found at trace concentrations were identified as contaminants of concern.||Remedial actions selected under the ROD signed in June 1996 included removing surface water, excavating contaminated soil and sediment, and disposing soil and sediment at LF04. Sediment excavation was completed in 1999. After removal is complete, no further actions are expected.||Contaminants in surface soil at OT69 pose no apparent public health hazards. The site is located in the remote southeast corner of the base and access by the public during operation was not expected. Workers would have worn protective equipment and exposures are expected to have been infrequent and of short duration. Remedial actions have been conducted to prevent current and future exposures.|
|Groundwater Operable Unit|
|Main Base and SAC Industrial Area Groundwater Plume||The Main Base and SAC Industrial Area groundwater plume consists of several plumes commingled in the aquifer underlying the northwestern portion of the base. This plume migrated beyond base boundaries to the west and has impacted public and private drinking water supply wells. Sources of these plumes include dry cleaning, industrial activities, equipment maintenance, and waste disposal activities conducted in the north central and northwestern portions of the base between 1918 and 1993.||Groundwater: Contaminants detected above CVs in
monitoring wells include benzene (5 ppb), carbon tetrachloride (12 ppb),
chloromethane (6.8 ppb), 1,2-dichloroethane (1,2-DCA) (6.7 ppb), 1,1-DCE
(180 ppb), methylene chloride (41 ppb) PCE (1,100 ppb), TCE (1,100 ppb),
and lead (47.4 ppb). TPH (5,600 ppb) was also detected, but no CVs is available
for this contaminant.
Water Supply Wells and Private Wells: Drinking water wells that may have been impacted by this plume contained benzene (2 ppb), carbon tetrachloride (12 ppb), chloroform (10 ppb), 1,2-DCA (2.9 ppb), 1,1-DCE (9 ppb), 1,1-dichloropropane (4.3 ppb), and PCE (18.4 ppb) above CVs while the wells were active.
|The ROD signed in June 1996 selected groundwater treatment
as the most appropriate remedial action. Treatment consists of operating
several groundwater extraction wells and air strippers and reinjection of
the treated water. The treatment system will be installed in four phases.
Phase I (1999) treats on-base hot spots. Phase II (1999) treats off-base
hot spots and Phase III (1999) augments Phase I capture zones. Phase IV
(2001) augments off-base capture.
Contaminants were first detected in public supply wells in 1996 and 1997. Private well contamination was discovered between 1979 and 1987. Actions were immediately implemented to prevent exposures above action levels.
|No apparent public health hazards were found during ATSDR's evaluation of exposure to contaminants in drinking water supply wells. Using conservative assumptions about past use of public and private supply wells, ATSDR found no instances of potential adverse health effects. Contaminated wells have been closed or treatment systems installed. The USAF provided bottled water to homes with private wells and later connected these homes to public supplies. The USAF and public water suppliers collect samples from wells quarterly and analyze samples for VOCs and/or perchlorate to ensure that they are free of contamination.|
|Site 7 Groundwater Plume||The Site 7 groundwater plume originates at the WP07 waste disposal pit site in the southwestern portion of the base and extends approximately 1 mile off base to the southwest.||Groundwater: 1,2-DCA (14 ppb), 1,1-DCE (3.2 ppb),
PCE (35 ppb), and TCE (180 ppb) have been detected in monitoring wells above
CVs. TPH (990 ppb), which has no CV, has also been detected. Beginning in
July 1996, vinyl chloride (19 ppb) has also been detected in monitoring
wells above its CV.
Water Supply and Private Wells: No public or private drinking water wells have been impacted by this plume.
|The ROD signed in June 1996 called for installation of a groundwater treatment system consisting of extraction wells, several air strippers, and reinjection wells. Remediation began in December 1998 with one extraction well. Additional extraction wells will be installed in 2000 after gravel mining to the south is complete.||No public health hazards are associated with contaminants in the Site 7 groundwater plume. People are not exposed to these contaminants because no drinking water wells have been impacted by plume contaminants.|
|Northeast Groundwater Plume||The Northeast groundwater plume apparently originates from sources within LF04 and potentially LF05. This plume flows west-southwest and, in the north-central portion of the base, converges with the Main Base and SAC Industrial Area plume, which flows off base to the west.||Groundwater: Contaminants of concern detected above
CVs in monitoring wells include carbon tetrachloride (4.7 ppb), 1,2-DCA
(1.1 ppb), methylene chloride (14 ppb), PCE (17 ppb), TCE (8.5 ppb), 1,1,2,2-tetrachloroethane
(0.56 ppb), and vanadium (30.1 ppb). Although there is no CV for TPH, it
was detected to 120 ppb.
Water Supply and Private Wells: The northeast plume may have impacted on-base supply wells in the main base water system. PCE was detected in these wells to 0.97 ppb.
|Long-term groundwater monitoring and institutional controls were selected as the most appropriate remedial action in the ROD signed in June 1996. These remedial actions were selected because contaminant concentrations only slightly exceed enforceable drinking water standards, contaminant concentrations are expected to decrease over time, and source control measures are being implemented at LF04 and LF05.||No apparent public health hazards were identified from past use of on-base wells containing PCE. PCE was detected below USEPA's MCL (5 ppb) and only slightly above ATSDR's CV (0.7 ppb). In addition, PCE was detected in only two samples, one sample each from two supply wells. Sampling before and after these detections did not identify elevated levels of PCE. ATSDR's exposure evaluation found no adverse health effects from this level of PCE.|
Basewide Operable Unit
|Fire Training Area Site 8
|FT08, located along the north-central base boundary, was the original fire-training area at the base. Until 1945, POL wastes were used for weekly training exercises.||FT08 was located by historic aerial photographs, but site investigations found no evidence of a burn pit. No contaminants of concern were identified during site investigations.||No further action is proposed at FT08, as detailed in the ROD signed in September 1998.||No public health hazards were identified because no contaminants of concern were detected during site investigations.|
|Fire Training Area Site 10C and Fuel Transfer Station
(FT10C and ST68)
|FT10C and ST68 are located along the southwestern edge of the airfield. FT10C was used for fire training exercises from 1947 until 1958. ST68 is a fuel storage facility with multiple USTs to store JP-4. Contaminants may have been released to soil and groundwater during fire training exercises or UST leaks and spills.||Surface Soil: Arsenic (10.5 ppm), cadmium (66.4
ppm), and lead (2,600 ppm) were detected above CVs. Oil and grease (4,400
ppm) and diesel (660 ppm) were also detected, but there are no CVs for these
Subsurface Soil: Oil and grease (10,600 ppm), diesel (3,500 ppm), and gasoline (2,700 ppm), which have no CVs, were detected. Only lead (1,830 ppm) was detected above its CV.
|Surface debris was excavated and disposed at LF04 in 1996. The USAF began a pilot SVE test in 1997 to evaluate the extent of contamination and in-situ treatment options. The SVE system was shut down in December 1997. Under the ROD, signed in September 1998, in-situ treatment was selected to address subsurface soil contamination and protect groundwater. The in situ system operated as a bioventing system in 1998 and 1999, then reverted to a combined SVE and bioventing system in 1999.||No apparent public health hazards were identified from past site uses. FT10C and ST68 are located adjacent to the runways where worker exposure would have been infrequent and of short duration. Removal of surface debris and ongoing remediation are expected to prevent current and future exposures.|
|Weapons Storage Septic Tank Leach Field Site 17
|WP17 is located within the SAC Weapons Storage Area in the southeastern corner of the base. The septic tank was used for sewage disposal until 1978. Small amounts of solvents and petroleum products may have been disposed in the septic system.||Site investigations did not identify any contaminants of concern at this site.||The ROD signed in August 1998 selected no further action as the most appropriate remedial action.||No public health hazards have been identified because contamination is absent at this site.|
|Old Burial Site 18
|Located in the northwestern portion of the site, LF18 reportedly served as a burial site for general refuse, stock items, and containerized ethyl mercaptan. Investigations have not identified any debris. Contaminants found at the site may actually be the result of aircraft maintenance and storm water runoff.||Subsurface Soil: Iron (44,300 ppm) and thallium (111 ppm) were detected above CVs. Oil and grease (6,600 ppm), diesel (50 ppm), and gasoline (19 ppm) were also detected. These contaminants, however, have no CVs.||Under the ROD, signed in September 1998, in-situ treatment was selected to address subsurface soil contamination and protect groundwater.||Contaminants were only found above CVs in subsurface soil, which is inaccessible to the public. In addition, remediation actions are planned to remove these contaminants and prevent future exposures. No apparent public health hazards, therefore, have been identified.|
|Bulk Fuel Storage Facility Site 19
|WP19 is located in the northwest portion of the base. This site was composed of two above ground JP-4 storage tanks within a bermed area. Two above ground fuel storage tanks are still present at this site. Waste sludge from the tanks was reportedly buried here.||Subsurface Soil: Gasoline (260 ppm), which has no CV, was the only contaminant of concern detected in shallow subsurface soil. The gasoline release is associated with the storage tanks, not the reported waste disposal.||WP19 is considered a petroleum only release and will be remediated and closed under regulations other than CERCLA. Ongoing remediation consists of a bioventing and a SVE system.||No public health hazards are associated with this site. Subsurface soil, which contains the only contaminants above CVs, is inaccessible to the public and ongoing remediation actions will prevent possible future exposures.|
|Sewage Treatment Plant Site 20
|The Sewage Treatment Plant, located near the southwestern end of the airfield, contained a 150-gallon UST that leaked approximately 700 gallons of diesel fuel in 1982. Other contaminant sources include sludge drying beds and surrounding soil. Dried sewage may have contained metals from base shops.||Surface soil: Benzo(a)pyrene (0.49 ppm), benzo(b)-fluoranthene
(0.94 ppm), arsenic (13 ppm), cadmium (42.4 ppm), chromium (307 ppm), iron
(272,000 ppm), and lead (895 ppm) were found above CVs.
Subsurface Soil: Although there is no CV, diesel (1,400 ppm) was identified as a contaminant of concern.
|Approximately 1,050 cy of contaminated soils were excavated between September 1996 and January 1997, treated in the on-base bioremediation facility, and disposed at WP07 or off-base facilities. Groundwater monitoring for phthalates and diesel will continue through 2000. A Draft Closure Report was released in March 1999. No further remedial actions are expected.||No apparent public health hazards were identified. Past worker exposure was infrequent and of short duration. Workers are also expected to have worn personal protective equipment to prevent exposure. Remediation at the site has been completed to prevent current and future exposures.|
|Sanitary Sewer System Site 23
|OT23 includes the Main Base portion of the sewer system (approximately 13,000 feet of sewer line). The Main Base system received waste from shop areas, which may have included industrial wastes and solvents. Leaks in the sewer line could have resulted in releases to the subsurface.||Subsurface Soil: No contaminants were detected above CVs.||Based on soil gas sample results, four areas along the sewer line were identified as needing remediation. The remedial actions selected under the ROD signed in September 1998 include installing a SVE system, which is scheduled to occur in 1999. The system is scheduled to be complete and begin operation in March or April 2000.||No public health hazards are present at this site because no contaminants have been detected above CVs.|
|SAC Drainage System Site 67
|OT67 consists of storm drains, approximately 14,200 feet of sewer line, and a 1,200-foot long open ditch in the western portion of the base. Waste solvents, fuels, and oils generated at the SAC facilities may have been disposed of in the sewer system and released to the environment through leaks in the system.||Site investigations found no evidence that leaks in the drainage system were a source of soil or groundwater contamination. No contaminants were detected above CVs.||No further remedial actions are planned at this site as detailed in the ROD signed in September 1998.||Site sampling found no contaminants above CVs, therefore, no public health hazards were identified at this site.|
|Spill Sites 78 and 79
(ST78 and ST79)
|ST78 and ST79 consist of USTs used to store fuel for heating adjacent buildings.||Diesel fuel was identified as the contaminant of concern during site investigations.||USTs were scheduled for removal in 1997. These sites were closed under Sacramento County Regulations.||No apparent public health hazards were identified. Past exposures were likely infrequent and of short duration. UST removals were completed to prevent current and future exposures.|
|Sewage Oxidation Pond Site 81
|ST81 consists of sewage oxidation ponds located in the southern portion of the base. These ponds were constructed to provide additional retention time for wastes from the sewage treatment plant. Some of these ponds also served as overflow ponds during heavy rains. Contaminants in the treated water or overflow may have been released to the environment.||Surface Soil/Sediment: These media could not be distinguished. Only cadmium (22.7 ppm) was detected above its CV. Oil and grease (63,500 ppm) and diesel (1,300 ppm) were also detected, but have no CVs.||The ROD signed in September 1998 selected no further action as the most appropriate remedial action. TPH was detected below levels of concern and cadmium was detected in samples collected from only 25% of the total site area.||No apparent public health hazards were identified from exposure to contaminants in surface soil and sediment. Only cadmium was found above its CV and only in a small portion of the collected samples. Therefore, any exposure would have been infrequent and of short duration. Current and future site use will likely be limited as this site is part of the parcel transferred to the Sacramento County Airports.|
|Golf Course Maintenance Yard Site 82
|The golf course and MY82 are located in the eastern portion of the base. Past and current activities include equipment washing, pesticide mixing and storage, and fuel and oil refilling and storage.||Surface Soil: No contaminants were identified above
Subsurface Soil: Petroleum products (diesel to 93 ppm and gasoline to 2.3 ppm) were identified as contaminants of concern based on their potential to impact groundwater. These petroleum products, however, have no CVs.
|No further action is planned under CERCLA, as detailed in the ROD signed September 1998. Corrective actions, such as removal of contaminated soil, will be completed under Resource Conservation and Recovery Act (RCRA) and California state regulations.||No public health hazards were identified. Surface soil sampling found no contaminants above CVs. Subsurface soil is inaccessible to the public and corrective actions will be completed to prevent current and future exposures.|
|Helicopter Washrack Site 83
|WR83 is located in the southeastern corner of the base. Oils, fuels, and fluids from the helicopters were released to the ground during washing.||Subsurface Soil: Diesel (110 ppm) and gasoline (18 ppm) were detected in subsurface soil during storm drain repairs. There are no CVs available for diesel and gasoline.||No further action is planned under CERCLA, as detailed in the ROD signed September 1998. Corrective actions, including removal of contaminated soil, were completed under RCRA and California state regulations.||Contamination is limited to subsurface soil which is inaccessible to the public. In addition, remedial actions to remove this contamination were conducted. No public health hazards, therefore, were identified.|
|Sewer Line Site 84
|The approximately 4,200 feet sewer line associated with WL84 ran from the SAC area to the sewage treatment facility. Various chemicals disposed in the sewer line may have been released to the subsurface by leaks in the sewer line.||Investigations found no evidence that leaks or releases from the sewer line have occurred or have served as a source of soil or groundwater contamination. No contaminants of concern were detected.||The ROD signed September 1998 selected no further action as the most appropriate remedial action.||No public health hazards were identified because no contaminants of concern were detected at the site.|
|Firing Range Site 86
|Until 1993, a rifle and small arms firing range was operated in the southeastern corner of the base. Potential contaminants include lead, copper, and tin.||Surface Soil: Lead (1,660 ppm) was detected above its CV.||Contaminated soil was removed in 1998, processed to remove recoverable lead, and stabilized for disposal at WP07. A Draft Closure Report for FR86 was released in March 1999. No further action is expected.||No apparent public health hazards were identified. Exposures during recreational use of the site would have been infrequent and of short duration. Removal of contaminated soil prevents current and future exposures.|
|Skeet and Trap Range Site 87
|Located in the eastern portion of the base, the skeet and trap ranges were operated by a local shooting club. Morrison Creek flows through the site in front of the firing positions.||Surface Soil: Investigations found benzo(a)pyrene
(3.7 ppm), benzo(b)fluoranthene 92.8 ppb), dibenz(a,h)- anthracene (0.97
ppm), indeno(1,2,3-c,d)pyrene (2.5 ppm), and lead (1,330 ppm) above CVs.
Sediment: Only arsenic (52 ppm) and lead (6,800 ppm) were detected above CVs.
|Based on the remedy selected in the ROD signed September 1998, the contaminated soil and sediment were excavated in 1998, stabilized, and disposed of at WP07. A Draft Closure Report was released in March in 1999.||Surface soil and sediment contamination poses no apparent public health hazards. Past exposures during recreational use were likely infrequent and of short duration. Remedial actions have been completed and prevent current and future exposures.|
Supplemental Basewide Operable Unit
|Drainage Ditch Site 80
|SD80 consists of a drainage ditch located downstream of the on-base golf course in the eastern portion of the base.||Surface Soil: Arsenic (9.8 ppm) was detected above
Surface Water: Dieldrin (0.029 ppb) and arsenic (2.5 ppb) were detected above their CVs.
Sediment: Chlordane (1.56 ppm), dieldrin (0.055 ppm), and arsenic (10.3 ppm) were detected above CVs.
|Site investigations are ongoing. Appropriate remedial actions have not been selected, however, it is anticipated that this site will be cleaned to allow unrestricted use.||Recreational use of the drainage ditch at SD80 poses no apparent public health hazards. Past exposure would have been infrequent and of short duration. Surface water does not serve as a drinking water supply. Remedial actions will be conducted to prevent current and future exposures.|
|Drainage Ditch Site 85
|DD85 consists of the south drainage ditch, which flows southwesterly along the southeastern edge of the airfield. Drainage ditches designated SD13 and SD15 discharge into this drainage ditch.||Sediment: Sampling at two outfalls detected organic and inorganic contaminants. Benzo(a)pyrene (1.7 ppm), benzo(b)fluoranthene (3.6 ppm), dibenz(a,h)anthracene (0.5 ppm), indeno(1,2,3-c,d)pyrene (2.1 ppm), and lead (1,500 ppm) were detected above CVs.||Approximately 10,400 cy of contaminated sediments were excavated in October 1997 and fall 1998. The majority of the contaminated sediments were disposed of at WP07, and a small amount with elevated concentrations of oil and grease were treated on base. A Draft Closure Report was released in March 1999. No further actions are planned.||No apparent past, current, or future public health hazards are associated with contaminants in sediment at DD85. This site is located along the airfield, which is a restricted part of the base. Access by base workers or trespassers would have been infrequent and of short duration. Completed remediation prevents current and future exposures.|
|Golf Course Maintenance Area Ditch 88
|DD88 is located adjacent to the golf course in the eastern portion of the base. Surface water in this ditch is only present for part of the year.||Surface Water: Only manganese (147 ppb) was detected
above its CVs.
Sediment: Antimony (10,500 ppm) and arsenic (12.1 ppm) were detected above CVs.
|Site investigations are ongoing. Appropriate remedial actions have not been selected, however, it anticipated that this site will be cleaned to allow unrestricted use.||No apparent public health hazards are associated with surface water and sediment contamination. Past exposures during recreational use would have been infrequent and of short duration. Surface water does not serve as a drinking water supply. Remedial actions will prevent current and future exposures.|
|Historic Trap Range Site 89
|OT89 consists of a trap range that was used in the 1940s and 1950s. Investigations found that two sets of firing stations were removed in the 1950s and the shot fall area of one was covered with 8 to 10 feet of fill.||Surface Soil: Lead (458 ppm) was found above CVs.||Site investigations are ongoing and remedial actions have not yet been identified. Future use of this site is expected to be restricted and remedial actions are expected account for this restricted land use.||No apparent public health hazards have been identified from past and current exposures. Past exposures during recreational use would have been infrequent and of short duration. Current access to the site is restricted based on the site's location adjacent to the runways. The USAF will conduct necessary remedial actions to prevent future exposures.|
|AC&W||Air Craft and Warning|
|ATSDR||Agency for Toxic Substances and Disease Registry|
|IRP||Installation Restoration Program|
|JP-4||jet petroleum number 4|
|MCL||USEPA's maximum contaminant level|
|PAH||polycyclic aromatic hydrocarbons|
|POL||petroleum, oil, and lubrication|
|ppb||parts per billion|
|ppm||parts per million|
|ppt||parts per trillion|
|RCRA||Resource Conservation Recovery Act|
|ROD||record of decision|
|SAC||Strategic Air Command|
|TPH||total petroleum hydrocarbons|
|USAF||United States Air Force|
|USEPA||U.S. Environmental Protection Agency|
|UST||underground storage tank|
The Agency for Toxic Substances and Disease Registry (ATSDR) conducts public health assessments (PHA) to find out if people are being exposed to hazardous substances and, if so, whether that exposure is harmful. The process of evaluating exposures and determining if there are potential public health hazards involves several steps: identifying potentially exposed populations, reviewing site contamination data, and evaluating exposure doses against information about the toxicology of site contaminants. The following text provides a description of each of these steps and details the results of ATSDR's evaluation for Mather Air Force Base (Mather).
Identifying Potentially Exposed Populations
ATSDR's PHAs are exposure, or contact, driven. A contaminant may be present in the environment, however, the contaminant only has the ability to cause adverse health effects if people are exposed to or come in contact with the contaminant. Exposure may occur by breathing, eating, or drinking a substance containing the contaminant or by skin contact with a substance containing the contaminant. To identify potentially exposed populations ATSDR considers land use, available natural resources, and locations of nearby populations.
Potentially Exposed Populations at Mather
Mather is a former U.S. Air Force Base (USAF) that supported USAF operations, provided housing for military personnel and their families, and contained areas for recreation, such as a golf course and firing ranges. Currently, Mather is undergoing redevelopment with future uses including a cargo airport, commercial businesses, residential housing, and parks and recreation areas. An on-base hospital and several elementary schools also operate at Mather and have remained in use through base closure and current redevelopment. Residential neighborhoods and commercial businesses are also located west and north of the base. Businesses and homes both on and off base depend on groundwater as their drinking water supply.
Based on past, current, and future land uses and development plans, ATSDR identified on-base workers, on-base residents, on-base recreational users, on-base hospital patients, off-base residents, and off-base workers as populations that could potentially be exposed to contaminants in surface soil, surface water, sediment, and groundwater.
Reviewing Site Contamination Data
ATSDR evaluates site contamination data by comparing the maximum detected contaminant concentrations found in site media (e.g., groundwater or soil) against ATSDR's comparison values. Comparison values are developed by ATSDR from scientific literature available on exposure and health effects. These comparison values are derived for each of the different media and reflect an estimated contaminant concentration that is not likely to cause adverse health effects for a given chemical, assuming a standard daily contact rate (e.g., amount of water or soil consumed) and body weight. Comparison values are not thresholds for adverse health effects. If contaminant concentrations are above comparison values, ATSDR further analyzes potential exposures.
Some of the comparison values used by ATSDR scientists include ATSDR's environmental media evaluation guides (EMEG), reference dose media guides (RMEG), and cancer risk evaluation guides (CREG) and EPA's maximum contaminant levels (MCL). MCLs are enforceable drinking water regulations developed to protect public health. CREGs, EMEGs, and RMEGs are non enforceable, health-based comparison values developed by ATSDR for screening environmental contamination for further evaluation.
Contaminants Found Above Comparison Values at Mather
ATSDR reviewed site contamination data for contaminants found in surface soil near residential and recreational areas, surface water and sediment near residential and recreational areas, and in groundwater plumes. On-base workers are expected to wear personal protective equipment, such as gloves, long pants, and work boots, to prevent exposures during their employment at Mather. At Mather, ATSDR found polyaromatic hydrocarbons, arsenic, and lead above comparison values in surface soil; dieldrin (a pesticide), arsenic, and manganese above comparison values in surface water; arsenic, antimony, and lead above comparison values in sediment; and volatile organic compounds (VOCs) and perchlorate above comparison values in drinking water supply systems.
Evaluating Exposure Doses
After identifying contaminants in site media above comparison values, ATSDR further evaluates exposures to these contaminants considering information about exposures combined with scientific information from the toxicological and epidemiological literature. If necessary, ATSDR estimates exposure doses, which are estimates of how much contaminant a person is exposed to on a daily basis. Variables considered when estimating exposure doses include the contaminant concentration, the exposure amount (how much), the exposure frequency (how often), and the exposure duration (how long).
The estimated exposure doses can be used to evaluate potential noncancer and cancer effects associated with contaminants detected in site media. When evaluating noncancer effects, ATSDR compares the estimated exposure dose to standard toxicity values, including ATSDR's minimal risk levels (MRLs) and the U.S. Environmental Protection Agency's reference doses (RfDs), to evaluate whether adverse effects may occur. The chronic MRLs and RfDs are estimates of daily human exposure to a substance that is likely to be without appreciable risk of adverse noncancer effects over a specified duration. The chronic MRLs and RfDs are conservative values, based on the levels of exposure reported in the literature that represent no-observed-adverse-effects levels (NOAEL) or lowest-observed-adverse-effects-levels (LOAEL) for the most sensitive outcome for a given route of exposure (e.g., dermal contact, ingestion). Uncertainty (safety) factors are applied to NOAELs or LOAELs to account for variation in the human population and uncertainty involved in extrapolating human health effects from animal studies. ATSDR also reviews the toxicological literature and epidemiology studies to evaluate the weight of evidence for adverse effects.
When evaluating the potential for cancer to occur, ATSDR uses cancer potency factors (CPF) that define the relationship between exposure doses and the likelihood of an increased risk of developing cancer over a lifetime. The CPFs are developed using data from animal or human studies and often require extrapolation from high exposure doses administered in animal studies to lower exposure levels typical of human exposure to environmental contaminants. The CPF represents the upper-bound estimate of the probability of developing cancer at a defined level of exposure; therefore, they tend to be very conservative (i.e., overestimate the actual risk) in order to account for a number of uncertainties in the data used in extrapolation. ATSDR also considers the cancer effect levels (CELs) reported in the literature. The CEL is the lowest dose of a chemical in a study, or group of studies, that was found to produce increased incidences of cancer (or tumors).
Exposure Doses for Potentially Exposed Populations at Mather
For exposures to surface soil, surface water, and sediment, ATSDR evaluated potential health effects considering contaminant concentrations, exposure frequency, and exposure duration and determined it was unnecessary to estimate an exposure dose. As described in the "Evaluation of Environmental Contamination and Exposure Situations" section of this PHA, exposures to surface soil, surface water, and sediment would be infrequent and of short duration. ATSDR concluded that these exposure pose no apparent public health hazards.
For exposures to groundwater, ATSDR estimated exposure doses for people consuming and using contaminated water from on-base water supply systems, off-base community supply systems, and off-base private wells. In estimating to what extent people might be exposed to contaminants, ATSDR used "conservative" assumptions about contaminant concentrations (e.g., the maximum detected concentration), as well as how much and how often people drank the contaminated water (e.g., an adult consumed 2 liters of water every day for 365 days each year). These assumptions allow ATSDR to estimate the highest possible exposure dose and determine the corresponding health effects. Although ATSDR expects that few people were exposed at this highest level, the "conservative" estimates are used to protect public health.
Using conservative exposure assumptions, ATSDR estimated doses for VOCs and perchlorate and compared these doses to the MRLs for each contaminant. ATSDR found that the exposure doses for only carbon tetrachloride in off-base private wells and perchlorate in the main base water supply wells exceeded their MRLs. Therefore, ATSDR further reviewed the scientific literature about the toxicity and potential health effects for these contaminants.
The MRL for carbon tetrachloride was derived from a laboratory study that found a NOAEL that is more then 250 times greater than ATSDR's dose estimated using conservative assumptions (ATSDR 1994). The provisional RfDs for perchlorate were derived from a study of Grave's disease patients dosed with perchlorate. The doses calculated by ATSDR for each exposed population were much lower than the NOAEL and the LOAEL found in this study (CDHS 1999). Appendix D provides more detail about the toxicology of perchlorate because only provisional RfDs are available and there is growing concern about perchlorate in drinking water. In addition, ATSDR conservatively assumed that people received all their drinking water from a well containing the maximum detected contaminant concentration. This is an overestimate of actual exposure because lower contaminant concentrations have been found in the effected wells and people ingest water from many sources (e.g. prepackaged juices or soda and water supplies at the workplace or school). Based on this information and the conservative assumptions ATSDR used to overestimate actual exposures, ATSDR concluded that consumption of groundwater has posed no apparent public health hazards.
Not all contaminants in the environment have the potential to cause cancer. Within the water supplies used at and around Mather, only the VOCs (benzene, carbon tetrachloride, chloroform, 1,2-dichloroethane, 1,1-dichloroethylene, 1,1-dichloropropane, trichloroethylene, and tetrachloroethylene) are considered carcinogens. Perchlorate is not considered a carcinogen. ATSDR, therefore, evaluated exposure to VOCs for their potential to result in increased cancer risks.
Using conservative exposure assumptions, ATSDR found that the levels of VOCs found in the drinking water supply systems do not pose a risk for excess cancer cases in the community at and surrounding Mather. ATSDR conservatively assumed that people were exposed to the maximum detected contaminant concentrations daily over the entire exposure period. However, samples collected at other times contained lower contaminant levels. ATSDR also assumed that people received all their drinking water from a single well over the entire exposure duration. This is an overestimate of actual exposure because people would also ingest water from other sources, such as prepackaged drinks and other water supplies. For these reasons, ATSDR does not expect any increase in cancer risk from past ingestion of drinking water containing VOCs.
Perchlorate is a contaminant that exists in the environment as part of other chemical compounds such as ammonium perchlorate. Ammonium perchlorate is manufactured as a component in solid fuel propellant for rockets, missiles and fireworks. Although perchlorate has been known as an environmental contaminant at some hazardous waste sites, no standardized methods exist for detecting perchlorate in water. Until recently, perchlorate could not be detected at concentrations below 400 parts per billion (ppb).
In 1997, Aerojet General Corporation (Aerojet)--located northeast of Mather--developed a new analytical method to detect perchlorate concentrations as low as 4 ppb. When Mather wells were sampled and analyzed using this new method in March 1997, perchlorate was found in three of the four wells in the main base water supply system. Detected concentrations ranged from 14 to 120 ppb. As a result of the improved analytical method and detections of perchlorate in drinking water, regulatory agencies, water purveyors, and the public is becoming more aware of perchlorate as a potential contaminant in drinking water and are especially interested in the potential health effects of this contaminant.
In 1992 and again in 1995, the U.S. Environmental Protection Agency (USEPA) evaluated the body of toxicological information on perchlorate and determined that, although there is considerable information about the health effects from short-term exposure to perchlorate, there is not enough information about the effects from long-term exposure (CDHS 1997).
At high levels, perchlorate can interfere with production of thyroid hormones and lead to below-normal levels of thyroid hormones in the blood. This condition, called hypothyroidism, can cause the body to increase its production of thyroid stimulating hormones. Increased levels of thyroid stimulating hormones may cause enlargement of the thyroid and a person to feel sluggish, depressed, cold, or tired. Because perchlorate can reduce the body's level of thyroid stimulating hormones, in the past doctors used high doses of potassium perchlorate (KClO4) as a drug treatment for people with hyperthyroidism, a condition in which the thyroid produces an above-normal amount of hormones (this condition is often caused by Grave's Disease). Perchlorate treatments were discontinued when some patients developed blood or immune system disorders, however, it is unknown if perchlorate caused these problems (CDHS 1997).
Based on toxicological studies of perchlorate, USEPA derived a provisional reference dose (RfD) for perchlorate. An RfD is a dose of chemical to which a person could be exposed over a long period of time without an increased risk of adverse, noncancer health effects. Using the available toxicological information, USEPA estimated that a perchlorate dose of 0.14 mg/kg/day (i.e., a milligram of perchlorate absorbed per kilogram of a person's body weight per day) would not be expected to adversely affect a person's thyroid. By applying a safety margin of 300 to 1,000 to this value to account for any uncertainties in the toxicological data, USEPA derived an RfD of 0.0001 to 0.0005 mg/kg/day.
Toxicological studies have also found that the lowest dose at which adverse effects to the thyroid occur is 1.4 mg/kg/day. This is 10 times more than the dose at which no adverse effects were observed and more than 2,500 times greater than the derived reference doses. Fatal bone marrow effects were observed in Grave's disease patients at perchlorate doses of 6 to 14 mg/kg/day (CDHS 1999).
As the interest in perchlorate contamination has grown, USEPA and other researchers have begun new studies on the toxicological effects of perchlorate. Currently, the USAF and Aerojet, a potential responsible party for the perchlorate contamination, are funding studies to assess potential health hazards posed by perchlorate exposure (Gutierrez-Palmenberg, Inc. 1999). USEPA's National Center for Environmental Assessment (NCEA) is in the process of reviewing current perchlorate data and has completed a draft toxicological assessment for perchlorate. The document is expected to be finalized in late 2000. The draft document proposes a revised RfD for perchlorate of 0.0009 mg/kg/day, nearly double the highest provisional RfD value (CDHS 1999; USEPA 1999).
Safe Drinking Water Levels
The California Department of Health Services (CDHS) used the upper limit of the provisional RfD range (0.0005 mg/kg/day) to determine a provisional drinking water standard (called an "action level") of 18 ppb for California. Because of the 300-fold margin of safety, this action level would translate to a perchlorate dose that is 300 times less than the lowest dose of perchlorate at which no adverse health effects have been observed. For example, although the action level is 18 ppb, an adult could drink 2 liters (approximately eight cups) of water contaminated with 120 ppb perchlorate (the maximum detected perchlorate found in a main base supply well) and still be ingesting 40 times less perchlorate than the lowest amount at which no health effect has been observed in toxicological studies.
A child could drink 1 liter of this water and still be ingesting 10 times less perchlorate than the lowest amount at which no health effect has been seen. To observe adverse thyroid effects, an adult would need to consume water with 49,000 ppb perchlorate based on observed thyroid effects at 1.4 mg/kg/day. Consumption of water containing 210,000 to 490,000 ppb of perchlorate would be required to observe fatal bone marrow effects, based on bone marrow effects seen at 6 to 14 mg/kg/day (CDHS 1999). The maximum detected perchlorate concentrations at Mather were much lower than any of these levels.
The California Environmental Protection Agency's Office of Environmental Health
Hazards Assessment is currently developing a public health goal for perchlorate
in drinking water based on existing toxicological data. The draft public health
goal is anticipated to be released for public comment in spring 2000. If regulators
develop action levels using the proposed NCEA RfD (0.0009 mg/kg/day), the drinking
water standard would be 32 ppb (CDHS 1999; USEPA 1999).
- How a chemical enters a person's blood after the chemical has been swallowed, has come into contact with the skin, or has been breathed in.
- Acute Exposure:
- Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.
- Adverse Health Effect:
- A change in body function or the structures of cells that can lead to disease or health problems.
- The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.
- Background Level:
- An average or expected amount of a chemical in a specific environment. Or, amounts of chemicals that occur naturally in a specific environment.
- A group of diseases which occur when cells in the body become abnormal and grow, or multiply, out of control.
- Any substance shown to cause tumors or cancer in experimental studies.
- See Comprehensive Environmental Response, Compensation, and Liability Act.
- Chronic Exposure:
- A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.
- Completed Exposure Pathway:
- See Exposure Pathway.
- Comparison Value (CVs):
- Concentrations or the amount of substances in air, water, food, and soil that are unlikely, upon exposure, to cause adverse health effects. Comparison values are used by health assessors to select which substances and environmental media (air, water, food and soil) need additional evaluation while health concerns or effects are investigated.
- Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA):
- CERCLA was put into place in 1980. It is also known as Superfund. This act concerns releases of hazardous substances into the environment, and the cleanup of these substances and hazardous waste sites. ATSDR was created by this act and is responsible for looking into the health issues related to hazardous waste sites.
- A belief or worry that chemicals in the environment might cause harm to people.
- How much or the amount of a substance present in a certain amount of soil, water, air, or food.
- See Environmental Contaminant.
- Dermal Contact:
- A chemical getting onto your skin. (see Route of Exposure).
- The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day".
- Dose / Response:
- The relationship between the amount of exposure (dose) and the change in body function or health that result.
- The amount of time (days, months, years) that a person is exposed to a chemical.
- Environmental Contaminant:
- A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than that found in Background Level, or what would be expected.
- Environmental Media:
- Usually refers to the air, water, and soil in which chemcials of interest are found. Sometimes refers to the plants and animals that are eaten by humans. Environmental Media is the second part of an Exposure Pathway.
- U.S. Environmental Protection Agency (EPA):
- The federal agency that develops and enforces environmental laws to protect the environment and the public's health.
- The study of the different factors that determine how often, in how many people, and in which people will disease occur.
- Coming into contact with a chemical substance.(For the three ways people can come in contact with substances, see Route of Exposure.)
- Exposure Assessment:
- The process of finding the ways people come in contact with chemicals, how often and how long they come in contact with chemicals, and the amounts of chemicals with which they come in contact.
- Exposure Pathway:
- A description of the way that a chemical moves from its source (where it
began) to where and how people can come into contact with (or get
exposed to) the chemical.
ATSDR defines an exposure pathway as having 5 parts:
- Source of Contamination,
- Environmental Media and Transport Mechanism,
- Point of Exposure,
- Route of Exposure, and
- Receptor Population.
When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.
- How often a person is exposed to a chemical over time; for example, every day, once a week, twice a month.
- Hazardous Waste:
- Substances that have been released or thrown away into the environment and, under certain conditions, could be harmful to people who come into contact with them.
- Health Effect:
- ATSDR deals only with Adverse Health Effects (see definition in this Glossary).
- Indeterminate Public Health Hazard:
- The category is used in Public Health Assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.
- Swallowing something, as in eating or drinking. It is a way a chemical can enter your body (See Route of Exposure).
- Breathing. It is a way a chemical can enter your body (See Route of Exposure).
- Lowest Observed Adverse Effect Level. The lowest dose of a chemical in a study, or group of studies, that has caused harmful health effects in people or animals.
- Soil, water, air, plants, animals, or any other parts of the environment that can contain contaminants.
- The chemical process of digesting or breaking down food or contaminants.
- Minimal Risk Level. An estimate of daily human exposure - by a specified route and length of time -- to a dose of chemical that is likely to be without a measurable risk of adverse, noncancerous effects. An MRL should not be used as a predictor of adverse health effects.
- The National Priorities List. (Which is part of Superfund.) A list kept by the U.S. Environmental Protection Agency (EPA) of the most serious, uncontrolled or abandoned hazardous waste sites in the country. An NPL site needs to be cleaned up or is being looked at to see if people can be exposed to chemicals from the site.
- No Observed Adverse Effect Level. The highest dose of a chemical in a study, or group of studies, that did not cause harmful health effects in people or animals.
- No Apparent Public Health Hazard:
- The category is used in ATSDR's Public Health Assessment documents for sites where exposure to site-related chemicals may have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.
- No Public Health Hazard:
- The category is used in ATSDR's Public Health Assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.
- Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.
- A line or column of air or water containing chemicals moving from the source to areas further away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water (such as lakes, ponds and streams).
- Point of Exposure:
- The place where someone can come into contact with a contaminated
environmental medium (air, water, food or soil). For example:
the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, the location where fruits or vegetables are grown in contaminated soil, or the backyard area where someone might breathe contaminated air.
- A group of people living in a certain area; or the number of people in a certain area.
- Public Health Assessment(s):
- See PHA.
- Public Health Hazard:
- The category is used in PHAs for sites that have certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.
- Public Health Hazard Criteria:
- PHA categories given to a site which tell whether people could be harmed
by conditions present at the site. Each are defined in the Glossary. The
- Urgent Public Health Hazard
- Public Health Hazard
- Indeterminate Public Health Hazard
- No Apparent Public Health Hazard
- No Public Health Hazard
- Receptor Population:
- People who live or work in the path of one or more chemicals, and who could come into contact with them (See Exposure Pathway).
- Reference Dose (RfD):
- An estimate, with safety factors (see safety factor) built in, of the daily, life-time exposure of human populations to a possible hazard that is not likely to cause harm to the person.
- Route of Exposure:
- The way a chemical can get into a person's body. There are three exposure
- breathing (also called inhalation),
- eating or drinking (also called ingestion), and
- or getting something on the skin (also called dermal contact).
- Safety Factor:
- Also called Uncertainty Factor. When scientists don't have enough information to decide if an exposure will cause harm to people, they use "safety factors" and formulas in place of the information that is not known. These factors and formulas can help determine the amount of a chemical that is not likely to cause harm to people.
- The Superfund Amendments and Reauthorization Act in 1986 amended CERCLA and expanded the health-related responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health effects from chemical exposures at hazardous waste sites.
- Source (of Contamination):
- The place where a chemical comes from, such as a landfill, pond, creek, incinerator, tank, or drum. Contaminant source is the first part of an Exposure Pathway.
- Special Populations:
- People who may be more sensitive to chemical exposures because of certain factors such as age, a disease they already have, occupation, sex, or certain behaviors (like cigarette smoking). Children, pregnant women, and older people are often considered special populations.
- A branch of the math process of collecting, looking at, and summarizing data or information.
- Superfund Site:
- See NPL.
- A way to collect information or data from a group of people (population). Surveys can be done by phone, mail, or in person. ATSDR cannot do surveys of more than nine people without approval from the U.S. Department of Health and Human Services.
- Harmful. Any substance or chemical can be toxic at a certain dose (amount). The dose is what determines the potential harm of a chemical and whether it would cause someone to get sick.
- The study of the harmful effects of chemicals on humans or animals.
- Abnormal growth of tissue or cells that have formed a lump or mass.
- Uncertainty Factor:
- See Safety Factor.
- Urgent Public Health Hazard:
- This category is used in ATSDR's Public Health Assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.
The Agency for Toxic Substances and Disease Registry (ATSDR) received the following comments/questions during the public comment period (July 14 to August 28, 2000) for the Mather Air Force Base (Mather) Public Health Assessment (PHA) (July 14, 2000). For comments that questioned the validity of statements made in the PHA, ATSDR verified or corrected the statements. The list of comments does not include editorial comments concerning such things as word spelling or sentence syntax.
Comment: Page 8, Line 4. If Mather went on the National Priorities List (NPL) in November 1989, what was the reason for ATSDR to do a Preliminary PHA in April 1989.
Response: The Foreword to the April 1989 Preliminary PHA states that section 104(i)(7)(A) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) required ATSDR to prepare a PHA for Mather using available data. This section of CERCLA states that a PHA "shall include preliminary assessments of potential risks to human health posed by individual sites and facilities." The preliminary assessments should be based on the nature and extent of contamination, potential human exposure pathways, the size of the local community, and data from health studies.
At the time of the Preliminary PHA, the U.S. Air Force (USAF) had identified 32 areas of potential contamination. For some of these sites, not enough data were available to characterize the site. ATSDR, therefore, focused the Preliminary PHA on threes sites: the 7100 Disposal Area, the West Ditch, and the Aircraft Control and Warning (AC&W) Disposal Area.
Comment: Representatives from the USAF submitted a number of comments that provided additional or updated information about the status of site conditions at Mather. Additional information was provided about the peak employee population, the status of the housing being built as part of base redevelopment, remedial actions conducted at the landfill sites, the population served by community supply systems, the USAF groundwater monitoring and treatment program, and transfer of base water supply systems to Sacramento County.
Response: ATSDR updated this PHA to include additional information provided by the USAF. This information has been incorporated throughout the document as applicable.
Comment: Representatives from Aerojet provided additional information about the perchlorate groundwater plume, including the details about Aerojet's monthly monitoring program, potential sources of perchlorate, recent investigations, and planned remediation.
Response: ATSDR updated this PHA to include additional information about the perchlorate groundwater plume as provided by Aeroject. This information was added to the Exposure to Contaminants in Drinking Water section.