PUBLIC HEALTH ASSESSMENT
MCCLELLAN AIR FORCE BASE
SACRAMENTO, SACRAMENTO COUNTY, CALIFORNIA
The tables in this section list contaminants of concern at the McAFB NPL site. ATSDR has evaluated those contaminants in the subsequent sections of the public health assessment in order to determine whether exposure to them has public health significance. In this section ATSDR selects and discusses the contaminants using the following information: concentrations of contaminants on and off the site; field and laboratory data quality and sample design; comparison of on- and off-site contaminant concentrations with background concentrations, if available; comparison of on- and off-site contaminant concentrations with ATSDR health comparison values for 1) noncancerous outcomes and 2) cancer; and community health concerns.
In the data tables in the On-site Contamination and Off-site Contamination sections, listing of a contaminant does not mean that adverse health effects will result from exposures. Rather, the list indicates contaminants that will be evaluated further in this public health assessment. When selected as a contaminant of concern in one medium, the presence or absence of that contaminant in all media will be discussed.
ATSDR health comparison values are contaminant concentrations in specific media used to select contaminants for further evaluation. Those values include environmental media evaluation guides (EMEGs), which are based on ATSDR minimal risk levels (MRLs) and factor in body weight and ingestion rates (Appendix C); cancer risk evaluation guides (CREGs), and other relevant guidelines. CREGs are estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors. The RfDC are media concentrations calculated from EPA's Oral Reference Dose (RfD). The RfD is an estimate of the daily exposure to a contaminant over a lifetime that is unlikely to result in adverse health effects. EPA's drinking water health goals include the maximum contaminant level goal (MCLG) and the proposed maximum contaminant level goal (PMCLG). Maximum contaminant levels (MCLs) are contaminant concentrations that EPA deems protective of public health (considering the availability and economics of water treatment technology) over a lifetime (70 years) at an exposure rate of 2 liters water per day. As stated previously, these health comparison values are used only to determine contaminants that need further evaluation. Issues related to exposures and health effects are discussed elsewhere in the public health assessment.
ASTDR conducted a search of the Toxic Chemical Release Inventory (TRI) database for the site by facility name and zip code. The database reported no chemical releases from McAFB. Releases of methylene chloride, arsenic products, PCE, and 1,1,1-trichloroethane (TCA) were reported from other industrial locations in the Sacramento area. Those chemicals are contaminants of concern at McAFB.
Groundwater contamination at McAFB was discovered in the late 1970s. Because of that early detection of contaminated groundwater at and emanating from McAFB, it was the first environmental medium studied. Remedial efforts, which concentrated on identifying and treating the groundwater, included extensive construction of monitoring wells and frequent sampling schedules (2). The groundwater sampling and analysis plan has defined the types of contaminants and contaminant levels in, and geographic ranges of, the existing plumes. A remedial investigation of the groundwater OU has further defined the hydrogeology of the site (10).
Adequate characterization of the contaminants and their concentrations in the other media (soil, surface soil, surface water, sediments, air, soil gases, and biota) will be available during the RI/FS documentation for each of the OUs. The limited information available on those media will be addressed in this section, but data gaps prevent a complete assessment at this time.
Groundwater, Production Wells
Much of the early data for production wells at McAFB focused on the TCE levels because that was the indicator chemical studied by the Groundwater Task Force.
Table 1-A shows TCE levels found in the base wells (BW) closed in 1979-80 (11). During the time period indicated, sampling and analysis of the wells continued after the wells were taken off line (removed from potable use). This was done for monitoring purposes. Later BW 1, 2, and 12 were decommissioned. BW-18, the major supply well for the base, was brought back on line in 1985 after an activated carbon filter treatment system was added to remove VOCs in the groundwater. The carbon filter system is carefully monitored and replaced when needed.
|Base Well #, OU||Concentration µg/L||Date||Action|
|# 18, OU B||4||Aug, '79|
|140||May, '81||taken off line|
|# 1, OU A||trace||Nov, '79||taken off line|
|trace||Jan, '80||placed on line|
|1.3 - 716||Mar, '80||taken off line|
|1300 - 2000||July, '81||monitored|
|# 2, OU A||trace||Nov, '79||taken off line|
|# 12, OU A||8||Apr, '80|
|35||Aug, '80||taken off line|
McAFB began monitoring the base potable water supply system for VOCs in November 1979. Because of TCE contamination in the base production wells, potable water samples were collected at various distribution areas around the base. McAFB established a routine monitoring program at seven distribution points in January 1980. TCE concentrations at those distribution points were used to determine whether or not to close base wells (12).
|Distribution Area ID||Monthly Average TCE Concentration, µg/L|
|Bldg # 368 (OU A)||2.1||22.5||0.9||7.0||15.8||3.5|
|Bldg # 431 (OU A)||0.9||8.1||3.5||2.3||3.5||3.2|
|Rafferty Dr. (OU G)||0.7||1.7||0.9||9.2||6.8||1.3|
|Bldg # 628 (OU B)||3.2||2.3||4.4||2.7||6.5||0.5|
|Bldg # 783 (OU C)||3.6||3.1||2.5||4.8||2.1||0.4|
|Bldg # 1074 (OU G)||0.6||22.2||1.6||14.9||12.7||3.6|
Average TCE concentrations for November 28, 1979, through December 18, 1980, (number of samples collected from each area varied from 48-54) ranged from 2.8 ppb to 6.4 ppb TCE. More significant, however, were the monthly averages that identified supply well contamination. High monthly averages (shaded in Table 1-B) prompted removal of the responsible BW from the system (Table 1-A lists the responsible BWs removed from service in March and August, 1980). Table 1-B shows data for the two peak TCE contaminant periods (March and July-August) for the seven distribution areas. The majority of the distribution points during those months had TCE concentrations in the base potable water greater than the health comparison level, CREG = 3.2 ppb.
In addition to TCE, other VOCs and semivolatiles analyses were completed on the all base well water samples during that time. Data for those BWs closed included the following: BW #2, 1,1-DCE at 140-700 ppb (9 of 15 samples collected between Jan - Aug '80); BW #18, one sample with 10 ppb PCE and one with 3.6 methylene chloride (out of 70 samples collected between Jan '80 - Jul '81); BW #1, one sample with 0.3 ppb PCE (out of nine samples collected between Jan - Mar '80); and BW #12, one sample with 0.6 ppb 1,2-DCA (out of 29 samples collected Jan '80 - Jul '81) (12a).
ATSDR health comparison values (HCVs) for those chemicals are 0.06 ppb [CREG] for 1,1-DCE, 0.4 ppb [CREG] for 1,2-DCA, 0.7 ppb [CREG] for PCE, and 4.7 ppb [CREG] for methylene chloride. The concentrations of 1,1-DCE (BW #2) occurred after the well was removed from service. One BW #18 sample had PCE levels higher than the HCV at the well, but actual contaminant levels at the point of ingestion are not known. Blending and mixing of water from the various wells in use would have lowered the levels received at the tap.
McAFB has continued to sample and monitor the base drinking water wells. Current active base production wells are BWs #10, 18, and 29. Active wells are sampled for VOCs every two weeks, except BW #18 which is sampled weekly (and has the filter treatment system). Distribution points are sampled monthly. The base also samples each BW and the beginning point in the distribution system annually for metals, inorganics and a wide range of synthetic organic compounds. Review of VOC analyses results for BW #10 and 29 from 1981-1993 did not indicate any contaminant concentrations above health concern levels (12a).
Groundwater, Monitoring Wells
Monitoring well (MW) construction began at McAFB in 1980 at OU D. The base has approximately 300 active MWs; approximately 100 are sampled quarterly. Some wells, with screening at shallow depths, are now inoperable because of drought drawdown conditions in the region during the past few years. Previous and ongoing construction and placement of the MWs appear to be adequate for determining plume dimensions and site hydrogeology. McAFB's decisions about which MWs will be sampled and for which analytes depends partly on well location, contaminant history, and ongoing projects. All samples are field-filtered, a procedure that removes any particulate-sorbed metals and colloidal chemicals, and may introduce contaminants from filter materials. Thus, metal results are for dissolved metals only, resulting in variable, low-metal concentrations (13). ATSDR does not consider the filtered samples adequate for comparison with EPA drinking water standards, which are based on unfiltered samples. However, due to MW construction, groundwater pumped from those wells may have too much suspended, colloidal material for unfiltered samples.
Table 2 lists the highest concentration reported for each contaminant of concern. Data are presented for both the historical maximum concentration detected, and for maximum concentrations in 1989 (17). Comparison to the historical and 1989 data indicates a trend of decreasing levels of contamination in the groundwater.
|Contaminant||Historical Maximum Concentration||1989 Data Maximum Concentrations †||Comparison Value µg/L|
|1,1-dichloroethene (DCE)||OU D||63,000||'82||14||OU D||20,000||.06 (CREG)|
|TCE||OU C||52,000||'87||15||OU C||26,000||3.2 (CREG)|
|methylene chloride (MC)||OU D||5,000||'82||14||OU D||1200||4.7 (CREG)|
|benzene||OU D||680||'82||14||OU D||0||1.2 (CREG)|
|tetrachloroethene (PCE)||OU D||2,480||'85||15||OU D||270||0.7 (CREG)|
|vinyl chloride (VC)||OU D||2,230||'85||15||OU D||1300||.02 (CREG)|
|1,2-dichloroethane (DCA)||OU D||2,790||'85||15||OU D||5900||.4 (CREG)|
|chromium (total) *||OU B||2,200||N/A||16||OU C||55||50 (RfDC)|
|lead *||OU D||90||'82||14||OU D||0||0 (MCLG)|
|cadmium *||OU C||120||N/A||16||OU B||33||5 (RfDC)|
|arsenic *||OU C||240||N/A||16||OU C||0||0.02 (CREG)|
|mercury *||OU C||2||'87||15||OU C||0 (**)||2 (MCL)|
|thallium *||OU A||1||N/A||16||OU C||68||0.5 (MCLG)|
* monitoring well samples were field-filtered; assays are for
** data for 1988
N/A = not available
† Ref (17)
MWs are on and off base at positions defining current or potential areas of groundwater contamination. The wells are screened in four defined zones (shallow, middle, deep A, and deep B) to study hydrogeology and extent of contamination. Contamination movement will be further discussed in the Pathways Analysis section of this public health assessment.
On-base subsurface soil has been sampled during numerous projects within OUs A, B, C and D, and to a limited extent in other areas. The data presented in Table 3 represent the maximum concentrations detected for the contaminants of concern at the location noted (16,18). Sampling at the OUs listed and at certain other locations (e.g., around UST removals) has been ongoing since the early 1980s.
|Contaminant||Site/ Location||Date||Depth (feet)||Maximum Concentration mg/kg||Comparison Value mg/kg *|
|1,1-DCE||T/ OU D||'84||10-13||4.5||1.2 (CREG)|
|TCE||4/ OU D||'80||N/A||350||64 (CREG)|
|MC||4/ OU D||'80||N/A||27.5||93.3 (CREG)|
|benzene||4/ OU D||'80||N/A||50||24 (CREG)|
|PCE||47/ OU B||'83||N/A||130||13.7 (CREG)|
|VC||2/ OU D||'80||5-55||15||0.4 (CREG)|
|1,2-DCA||42/ OU C||'84/85||3-84||0.36||7.7 (CREG)|
|PCB, 1260||10/ OU C||'84/85||6-70||150||0.1 (CREG)|
|chromium (total)||5/ OU D||N/A||10-50||33,000||3000 (EMEG)|
|lead||4/ OU D||'80||N/A||4500||NONE|
|cadmium||5/ OU D||N/A||10-50||2100||350 (EMEG)|
|arsenic||40/ OU A||N/A||3-70||520||0.4 (CREG)|
|mercury||14/ OU C||'84/85||N/A||29||210 (RfDC)|
|thallium||B360/OUA||N/A||N/A||114||63 (RfDC) **|
* EMEG and RfD comparison values are calculated for adults
with an ingestion rate of 100 mg/day
** comparison value for thallium based on Rfd for the nitrate, acetate and selenite soluble salts
N/A = not available
Most soil samples were collected during the base site-characterization program in 1985-1986. Approximately 1500 soil borings were performed in 56 identified areas in OUs A, B, C, and D and other areas on base (16). The borings were sampled for volatile and semivolatile organic compounds, pesticides, PCBs, heavy metals, inorganic compounds, and oil and grease. However, additional soil sampling in OU D sites began in 1980. Contaminants were identified earlier in that area because the area was used for waste disposal for many years (1940s through the late '70s), and because private wells adjacent to the sites had confirmed contamination levels above health comparison values. Because of the high concentrations of several VOCs and metals at site #4 (an open sludge pit) 20,000 cubic yards of soil and sludge were removed from the site in 1984. Other sites at OU D did not have removal actions, but the entire area was capped (construction in 1985-1987). Table 3 indicates the highest levels found for each contaminant; the compounds found at site #4 have been remediated.
Site 47 (building 666), located in the southwestern portion of OU B near the intersection of Dudley and Folsum Streets, had further soils sampling during recent site characterization (sampling in 1991-1992). High levels of VOCs detected in the soils at site 47 determined that the site may be the source for the TCE/PCE groundwater contamination plumes located southwest of the base. Sample results included 140 ppm PCE and 3.6 ppm TCE (12a).
Surface soil sampling (0-6 inches) at McAFB will be performed at each OU during the RI/FS. Surface soil samples, defined by ATSDR as samples from the top three inches below the surface, have not yet been collected on base. McAFB staff are re-evaluating their definition of surface soils and will address the issue in future projects. Sampling and analysis will include tests for chemical and radionuclide (alpha and beta emitters) contaminants. The first OU scheduled for surface soil sampling is OU B; preliminary results during 1992 on some OU B sites indicate contamination.
Analysis of samples from SA 12, the Defense Reutilization and Marketing Office (DRMO) lot on the west side of OU B near Building 700, showed widespread PCB contamination in the surface soils with concentrations as high as 240,000 mg/kg (ppm) in the top six inches of soil (19). ATSDR health comparison value for PCBs in soils is 0.091 ppm (CREG). The site is now identified as OU B1 and is under an expedited remedial process. Locations with high PCB concentrations (>500 ppm) were identified as "hot spots." Although the contamination is primarily in the top foot of soil, in the "hot spots" contamination is found as deep as 10 feet below ground surface (9). Testing for dioxins and furans in the surface soils was reported as total TCDD equivalents (TCDD refers to the most toxic isomer of dioxin, 2,3,7,8-tetrachlorodibenzodioxin). The samples results ranged from 0.001 ppb - 0.08 ppb total TCDD in most portions of the yard; two samples in the "hot spots" area had TCDD equivalents reported at 3.0 and 1.9 ppb (12a). The ATSDR HCV for TCDD is 0.7 ppb for adults.
The lot has operated as a salvage yard since the 1950s; the public has access. In addition to the public, workers are in the area. The surface of the lot where PCBs were detected is unpaved; perforated steel planking covers the area. This planking, used for about 30 years, does decrease dust evolution in the area, but does not remove the contaminated dust/soil from human contact. Analysis of surface water grab samples collected after rain events in 1992, detected PCBs in the drainage ditches leaving OU B1. A public health evaluation of that information was discussed in a ATSDR health consultation dated May 1993 (see Appendix D).
When the PCB surface soil contamination was discovered, several restrictive measures were used to help prevent human contact with the soils. In March, 1992, areas with PCB soil levels at 100 ppm or greater were cordoned and access to the yard was further restricted from casual visitors. Workers and visitors were required to wear personal protective equipment (such as overboots). Then solid steel planking was installed over the more highly contaminated areas. After surface water runoff sampling results indicated migration of the PCBs, the solid steel planking was replaced with a plastic liner over, and trenched around, the "hot spots." Those restrictions will be used until the soil on the site is remediated. The ROD for OU B1 has been signed; the remediation chosen included a capping of the entire area with the option to implement an effective treatment process in the future (cap construction is scheduled to begin in April 1994).
In February, 1992, before the hot spots were covered, Air Force staff from BEE performed swipe samples on eight areas on the planking near those highly contaminated areas, on ten surfaces within the buildings, and on two workers' bootsoles. One interior surface had detectable levels of PCB (3.4 µg/100 cm²; EPA action level = 10 µg/100 cm²). All the swipes near the contaminated areas had detectable levels of PCBs (34.4 - 1609 µg/100 cm²; EPA action level = 100 µg/100 cm²). The bootsoles had PCB concentrations of 2.4 and 21.2 µg/100 cm² (9).
BEE performed air monitoring in March, 1992. Eight DRMO yard workers wore personnel air monitors for four hours each; results were nondetect for all the samples (detection limit = 0.005 mg/m³). Eight air stations were placed in the vicinity of the DRMO yard; results were nondetect (detection limit = 0.005 mg/m³). Swipe and air sampling performed by McAFB BEE staff was for the 1254 PCB congener. ATSDR has no health comparison value for PCB levels in air; the National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) is 0.001 mg/m³.
The base clinic staff did medical testing on a portion of the workers in the area. That data will be discussed in the Public Health Implications section of the public health assessment.
Because the results for OU B are not yet complete and the other OUs have not yet been sampled, there is a data gap in surface soil data. Without the sampling data, ATSDR cannot completely assess the potential human health implications of exposure through ingestion of, inhalation of, or dermal contact with contaminants in surface soils.
McAFB conducted a preliminary pathways assessment of sediment and surface water January 13-18, 1989 (20). Sediment samples were collected from Robla, Don Julio, and Magpie creeks, and from the southern and northern drainage ditches. Samples collected were surface scrapings or hand auger specimens from 0 to 1, 1 to 2, or 2 to 3 foot depths. Sediment scrapes were done when ditches were lined with concrete, preventing hand auger borings. Samples were collected where each stream enters and exits the base, as well as at specific locations along the streambed or drainage channel. Forty samples were collected from 20 locations. Background and upstream samples were not collected during this preliminary study.
All on base sediment samples contained metals, including chromium, zinc, lead, nickel, copper, cobalt, and vanadium. It should be noted that those metals occur naturally in the area, but background levels were not available for comparison. No metals were present at concentrations above health comparison values for soils (the only comparison values available for sediments). One sample in the southern drainage ditch contained 2.8 ppb TCE. Magpie Creek samples included 36 ppm dichlorodifluoromethane and 1100 ppm fluoranthene. Other sampling data for VOCs and semivolatile compounds did not meet all applicable quality control standards (contaminant found in the blank; high or low recovery of the sample spike; or the result was less than five times the detection limit for the assay). Certain analytes were not found downstream near the stream or ditch exit point from the base (20).
McAFB, as part of the base remedial investigation, has scheduled sediment sampling in streams and wetlands areas for background data collection. Also, some data were collected during the evaluation of PCBs migration from OU B1 into drainage ditches. The contaminant was present near the DRMO yard (500 ppm); levels decreased with distance from the source and were not detectable about 1000 feet down the drainage system (prior to Magpie Creek) (20a).
Surface water samples from the on-base drainage system were collected January 6-12, 1989 (20). Twenty locations were sampled at Magpie, Robla, and Don Julio creeks, the two holding ponds for treated industrial wastewater (OU C), the two aeration lagoons west of the industrial waste water treatment plant (OU C), and other drainage ditches. The samples were analyzed for VOCs, semivolatile compounds, metals, and oil and grease. No direct health comparison values are available for surface water; therefore, drinking water comparison values are used.
No VOCs were above detection limits. The following semivolatile organic compounds were detected: 7.8 ppb pentachlorophenol in Robla Creek; 1.8 ppb phenol and 7.9 ppb 4-nitrophenol in the storm drainage north ditch; and 7.8 ppb 4-nitrophenol (lifetime health advisory = 60 ppb) in Magpie Creek. Cadmium, arsenic, mercury, and thallium were not detected. Lead was detected in several samples at low concentrations; the data were suspect either because of reagent blank contamination or spike recovery problems. The highest lead level reported (57 ppb) was in a surface water sample taken from the ditch on the southwestern base boundary, which flows into Magpie Creek (PMCL = 5 ppb). Lead concentrations in Magpie Creek at base entry and exit points were identical, 4 ppb.
The resulting data may not adequately document the extent of contamination. Because surface water was only sampled once (in January, 1989), which is the wet season at McAFB, the resulting data may not adequately document the extent of contamination. Additional samples taken over time and upstream will be necessary to completely evaluate surface water contamination.
Since 1984, the base has collected and analyzed influent and effluent samples for Magpie Creek on a monthly basis and submitted written reports to CRWQCB. McAFB is required to monitor on that schedule to meet its National Pollutant Discharge Elimination System (NPDES) permit requirements for discharge from McClellan's Ground Water Treatment Plant (GWTP) and storm water runoff. Base effluents are also monitored under NPDES permits for discharges into Arcade and Don Julio creeks. CRWQCB reported that contaminant concentrations in the effluent do not exceed those in the influent to the base and that the base now plans to sample both upstream and downstream in Magpie Creek, and at several industrial discharge points into the creek on base during three dry events and three wet events per year (21).
In December 1987, an environmental consultant for McAFB sampled 13 on-base, inactive landfills (22). Testing was performed according to the California Calderon Landfill Law, which requires analyses for 10 air contaminant compounds, plus methane. In addition, nine soil gas MWs on the perimeter of OU D and 14 gas vents on the OU D cap were sampled for VOCs. No ambient air samples were collected. To determine the gas generation potential of each landfill, up to five probes per site were installed to a depth of eight feet, then sampled. Perimeter samples were collected to define gas migration.
The sites sampled were #7, #8, #10, #11, #12, #13, #14, #22, #42, #43, and #69 in OU C, and #24 and #38 in OU A. Table 4 data include the maximum concentrations for the contaminants of concern from the landfills samples.
|Location||Comparison Value *
|TCE||8,000||#12/ OU C||0.11 (CREG)|
|MC||9,000||#7/ OU C||0.61 (CREG)|
|PCE||7,000||#8/ OU C||0.28 (CREG)|
|VC||120,000||#8/ OU C||0.004 (CREG)|
|benzene||32,000||#12/ OU C||0.04 (CREG)|
ND = not detected
NA = not analyzed
ppbv = parts per billion, volume/volume
* ambient air comparison values used; soil gas levels are indicators for potential ambient air contaminants
The soil gas MWs for OU D were in clusters of three; two sets were on base (Fig. 5). Screening levels (feet below ground surface) for the soil gas MWs are: 11-15 feet for MW-3 and MW-6; 34-44 feet for MW-2 and MW-5; and 60-79 feet for MW-1 and MW-4. Sampling and analysis of the OU D soil gas MWs and vent riser system on the OU D cap were performed again in March and April, 1991 (23). Additional sampling of the OU D soil gas MWs occurred in June, 1992 (24). Results of those studies for OU D are listed in Table 5. The maximum concentrations of contaminants of concern are listed for each sampling regimen. Soil gas results for the off-base MWs are presented in the Off-site Contaminants section of this public health assessment.
|Contaminant||1987 Results (ppbv)||1991 Results (ppbv)||1992 Results (ppbv)†||Comparison Value
|TCE||800 (5)||2000||0.17||182 (2)||215||0.75||1300 (4)||0.11 (CREG)|
|MC||ND||ND||24||150 (1)||ND||0.75||ND||0.61 (CREG)|
|PCE||2 (4)||9||0.14||1.1 (4)||34.2||0.75||ND||0.28 (CREG)|
|benzene||ND||100||13||2.3 (2)||1.0||0.75||ND||0.04 (CREG)|
|1,1-DCE||NA||NA||--||2688 (1)||870||0.75||9000 (1)||0.005 (CREG)|
ND = not detected
* DL = detection limits; detections limits are averages during the sampling period
NA = not analyzed
# = soil gas MW number (identifier)
† = detection limits ranged from 5.2 - 412
Detection limits, and the allowable VOC levels, for the 1991 analyses were considerably lower than those used in the 1987 study for some VOCs (Table 5), but were not as low as the CREGs. Because of high concentrations of certain VOCs detected during the June, 1992, sampling round, sample dilutions resulted in detection limits ranging from 5.2 to 412 ppbv.
Preliminary soil gas sampling in OU B show some areas with high VOC concentrations in the surface (top six feet) soil gas samples. Xylenes were detected up to 800 ppmv in the Mat K area. Other VOCs detected include TCE, PCE, toluene, and TCA (25). Shallow soil gas samples (upper 6 ft) in the western ditch in PRL S-13 (the hazardous waste area for the DRMO lot) had VOC levels at 2,000 ppb (19). Maximum soil gas sampling results for site 47 (B 666), samples collected from 20 - 80 feet below ground surface, were: 6,900,000 ppbv PCE and 2,100,000 ppbv for TCE (12a).
Soil gases indicate the potential for human exposure to the contaminants in the ambient air pathway. McAFB is actively identifying soil gas contamination and testing for releases of the soil gases into the air.
A simulation (computer model for emissions based upon quantities of chemicals used by McAFB) of the concentrations of contaminants in ambient air was conducted by the base to satisfy the California Air Toxics "Hot Spots" Information and Assessment Act of 1987 (26). The reported air emission inventory for the base in 1989 included gasoline vapors (25,000 pounds [lbs]), PCE (42,000 lbs), 1,1,1-TCA (45,000 lbs), MC (10,000 lbs), xylenes (19,000 lbs), chlorine (1,300 lbs), benzene (1,000 lbs), 1,1-DCE (180 lbs), TCE (120 lbs), hexavalent chromium (4.2 lbs), and cadmium (1.3 lbs). Additional contaminants were emitted in small amounts.
McAFB has monitored ambient air around the perimeter of OU D since 1987 (27). For about one year (1986-87), McAFB also monitored air at the Industrial Waste Water Treatment Plant (IWTP) to meet permit requirements. To gather data for comparison with the OU D air monitoring data, one air station was placed on base at OU B near Building 644. The prevailing wind direction at McAFB is to the northwest; therefore, air stations near OU D also monitor emissions from the IWTP. Before entering the Interagency Agreement with EPA, the McAFB EM division sent those results quarterly to the Sacramento County Air Pollution Board for review. Two stations are still being monitored on base near OU D. Background air monitoring data used for comparison with the 1987 McAFB data included results from air stations around the perimeter of the Aerojet NPL site, several miles east of McAFB. Table 6 reports data on VOCs of concern detected during the 1987 air monitoring program (28).
|Contaminant||Station #2, OU D
annual avg. 1987
|Station #5, OU B
4th quarter avg. 1987
annual ave. 1987, ppbv
|MC||1.38||7.52||0.092||not reported||0.61 (CREG)|
|VC||ND||ND||N/A||not reported||0.004 (CREG)|
|benzene||1.63 *||2.00||N/A||not reported||0.04 (CREG)|
* data average of 3rd and 4th quarters only
N/A = not available, ND = not detected
The air stations were designed to sample at the breathing zone (4-5 ft above ground surface). All of the carcinogens detected, except PCE, were at concentrations higher than health comparison values. Data from Aerojet were from 12 stations sampled approximately 25 times per quarter (n= 1,200 for the year).
The California Air Resources Board air monitoring station in Citrus Heights (located about 5 miles northeast of McAFB) reported VOC concentrations for several of the compounds listed in Table 6. The 1987 annual average results from that air station were: 0.03 ppbv TCE; 0.08 ppbv PCE; 0.5 ppbv MC; and 1.91 ppbv benzene (29). Benzene concentrations on base are comparable to the Sacramento air station, but levels of MC on base are higher than the background station. Contaminants in ambient air at station #5 (OU B) were at higher levels than station #2. Station #5 is in a more populated section of the base; the stations on the perimeter of OU D are near adjacent off-base housing.
McAFB EM provided 1992 air monitoring data for two air stations; air station #2 in OU D and an air station near the GWTP. Sampling was performed over three and one half days for each of the sampling regimens. Results for various VOCs are presented in Table 7 for sampling in the spring and fall, 1992 (30).
|Contaminant||Station #2, OU D
May / Oct
|GWTP Air Station
April / Oct
|TCE||ND/ 2.1||0.01/.087||0.002||0.11 (CREG)|
|PCE||0.04/ 4.64||0.05/ 0.29||0.001||0.28 (CREG)|
|1,1-DCE||ND/ 0.29||ND/ 1.73||0.03||0.005 (CREG)|
|MC||1.5/ 0.97||0.9/ 1.75||0.07||0.61 (CREG)|
|1,1,1-TCA||.18/ 18.04||0.21/ 4.4||0.001||300 (EMEG) *|
ND= not detected
NA = not analyzed
No background air monitoring data were available for the 1992 on base air monitoring. Results were not reported for VC and benzene. Air station #2 results were comparable with 1987 for some VOCs; TCA and PCE levels in October samples were higher than results for other sampling dates.
Mercury Contamination, Building 252 (PRL S-18, OU A)
Building 252 was used as an aircraft instrument maintenance shop for more than 20 years. In May 1990, during a remodeling project, high levels of mercury were discovered inside and adjacent to the building. The shop vacuum system, debris from the system, walls, floors, workbenches, and other surface areas were contaminated with inorganic mercury. Outside, near the dust hopper used in the vacuum system, was a break area workers used for picnicking. Air was sampled using portable direct-reading mercury analyzers in the breathing zone and in area air. Swipe samples were collected throughout the first floor of the building. Localized areas of contamination were identified in the break area between buildings 252 and 251 and in areas inside Building 252. In May, 1990, an environmental contractor for McAFB collected various types of samples from the identified areas and analyzed those samples for mercury. Table 8 lists the results of the sampling for mercury in this area (31,32,33).
|Sample Type/ Locations||Mercury Concentration||# detects/# samples||Comparison Value|
| AIR inside Bldg 252 breathing
|1-9 µg/m3||15/24||0.06 µg/m3 (EMEG)|
|AIR outside Bldg 252 near ground surface||2-60 µg/m3||N/A|
|AIR in dust hopper||19-21 µg/m3||2/2|
|SWIPE SAMPLES collected from surfaces throughout inside Bldg 252||0.21-3312 µg/100 cm²||21/21 *||NONE|
|GRAB sample dust from hopper||139 mg/kg||1/1||NONE|
|SWEEP samples outside building||1.8-160 mg/kg||NONE|
N/A = not available
* 13/21 swipe samples exceeded the calibration range
The initial surface sweep samples in the area between buildings 252 and 251 identified certain locations with elevated levels of mercury. Remediation of the highly contaminated areas included three removal processes. Those actions resulted in a decrease of the maximum mercury concentrations from 160 mg/kg to 52 mg/kg. In a December, 1990, report, air samples collected in the affected area did not have detectable levels of mercury; the report also stated that the area is fenced (34).
Groundwater, Residential Wells
In 1979, McAFB initiated the first sampling of base production wells and off-site municipal and residential wells for VOCs. Off-base wells west and south of McAFB, particularly those near OU D, were selected. Initially, the Sacramento County Health Department and CRWQCB conducted the program. In 1985, the Air Force contracted the operation of the program. Groundwater samples from the wells were sampled for priority volatile and semivolatile contaminants, and samples from a small subset of the identified residential wells were analyzed for metals.
Data presented in Table 9 are the highest concentrations recorded for each of the contaminants of concern (35,36). All residential well samples were field-filtered using same procedure as for monitoring wells. ATSDR considers the filtered samples inadequate for reporting concentrations of metals. Unfiltered groundwater samples from residential wells are necessary to permit adequate comparison with EPA drinking water standards. Without the proper sampling data, ATSDR cannot assess the potential public health implications of exposure to groundwater from residential wells.
|Contaminant||Maximum Concentration µg/L||Date||Comparison Value µg/L|
|chromium (total) *||19||'85||50 (RfDC)|
|lead *||ND||NA||0 (MCLG)|
|mercury *||1.1||'85||2 (MCL)|
|arsenic *||6||'85||0.02 (CREG)|
|cadmium *||42||'83||5 (RfDC)|
* groundwater well samples were field-filtered; assays are
for dissolved metals
NA = not analyzed
ND = not detected
Sampling and analysis of groundwater from residential wells stopped when residents were provided with municipal water in 1986-1987. Off site MWs are located in the area; some of those are screened at depths comparable to private wells, but samples collected are field-filtered. ATSDR review of the environmental contaminant data from past sampling (Table 9) of those off-site residential wells prompted an ATSDR health consultation (Appendix E). Metals concentrations detected in filtered groundwater samples from several of the wells were near or above health comparison values. Updated information on concentrations of heavy metal contaminants in the wells was required because some residents reported using their wells for watering gardens and livestock. It was also possible that some people were drinking well water. Unfiltered groundwater samples were needed to properly analyze for metals in order to assess the potential for adverse health effects.
Unfiltered groundwater samples were collected from six residential wells and four off base MWs between August 22 and September 26, 1991 (Fig. 7). Metal analyses for all wells and VOC analyses for the residential wells were conducted by a contractor; split sample analyses were performed on three samples by CDHS (37). Table 10 contains a summary of the data for the residential wells.
|Contaminant||Maximum Conc. µg/L||range of detects
|Detection Limit µg/L||Comparison Value µg/L|
|1,1-DCE||17||4.6-17 (2)||0.7||0.06 (CREG)|
|TCE||4.1||1.3-4.1 (2)||0.2||3.2 (CREG)|
|chromium (total)||15||9.8-15 (6) *||7.0||50 (RfDC)|
|chromium (hexavalent)||14||8.5-14 (3) *||7.8||50 (RfDC)|
|lead||6||3.7-6 (2) *||3.2||0 (MCLG)|
|arsenic||4.8||4.5-4.8 (2) *||4.2||0.02 (CREG)|
|cadmium||0.97||(1) *||0.5||5 (RfDC)|
* results are estimates
ND = not detected
Comparing the data in Tables 8 and 9 shows that contaminant concentrations have dropped considerably between 1985 and 1991. The comparison assumes the same set of wells were sampled; this was not entirely possible due to changes is well usage. Arsenic, lead, TCE and 1,1-DCE were detected in 1991 at concentrations above health comparison values.
In response to a request from ATSDR, the EM division of McAFB performed an off-base sampling of soils from properties adjacent to OU D. Fourteen surface soil samples (top 3 in of soil) were collected from residential areas west and northwest of OU D (Fig. 5). The samples were analyzed for volatile and semi-volatile organic compounds, pesticides, metals, and PCBs, and for polychlorinated dibenzodioxins and polychlorinated dibenzofurans (dioxins and furans). No PCBs, dioxins, furans, or semi-volatile contaminants were detected. PCE was found in one sample. Pesticides detected (dieldrin, DDT, DDD, DDE and endosulfan) were all at concentrations below health comparison values, and were at concentrations consistent with the agricultural use of the properties. Maximum concentrations of contaminants of concern are presented in Table 11 (38).
|chromium (total)||20.3||'91||14/14||50||10 (EMEG)|
|arsenic||110 ##||'91||13/14||5||0.4 (CREG)|
|thallium •||63.7||'91||14/14||0.1-0.4 ‡||0.2 (RfDC) **|
* EMEG and RfD comparison values are calculated for a pica child (ingestion rate of 5000 mg/day)
** comparison value for thallium based on RfD for the nitrate, acetate and selenite soluble salts
# The sample with high lead content was collected near a residence. It could be localized contamination from leaded gasoline. Other lead results ranged from 7.9 - 46.2 ppm, above background levels.
## The sample with high arsenic content was collected upstream of the base near a barn, suggesting local contamination (perhaps spilled arsenic insecticide). Other arsenic results ranged from 2.5 - 4.4 ppm, within background levels.
† Background levels calculated for McAFB, OU B (on and off site).
‡ Background levels for thallium from USGS, Western U.S.
• Thallium concentrations are qualified; results are defined as false positives; discussion in text below.
No other off-site soils had been sampled prior to the 1991 residential sampling. The high concentration of thallium in surface soil samples (range 19.8 - 63.7 ppm) is of concern compared with the western U.S. background range (39). ATSDR could find no other background data on thallium for the region; the United States Geological Survey (USGS) regional and headquarters offices, state geologists, and the United States Department of Agriculture, Soil Conservation Service were queried.
Review of the lab results for the 1991 thallium analyses indicated that the method used was not specific for thallium. Interference from iron present in the soils could result in false positives for thallium. Because of the potential for false positives, McAFB EM resampled the residential surface soils (at the same locations) in November, 1992. The lab method used in 1992 was very specific and selective for thallium, with a detection limit of 0.2 ppm (detection limit = RfDC). No thallium was detected in any of the 14 samples (40).
Surface Water and Sediment
Surface and subsurface sediment samples were collected along Magpie Creek in April, 1992. A total of 16 sampling locations were selected; 11 were off base along the current Magpie Creek and the former creek channel. Samples were analyzed for metals, radionuclides, and organic compounds; results were compared to background surface soil contaminant concentrations defined during the ongoing OU B RI sampling and analysis for McAFB. ATSDR considers those background contaminant concentrations within ranges for the geographic area. Results of the few organic volatile compounds detected were qualified as laboratory contaminants, except for one TCE result. However, the TCE level detected was 0.002 mg/kg, much lower than the health comparison value (64 mg/kg, CREG). Radionuclides detected were within the background range for the area and were not of health concern. Certain metal contaminants of concern were present in the surface sediment samples. The preliminary data for those metals are listed in Table 12 (41).
|# detects/ # samples||
|Comparison Values *
|chromium||18 - 110||11 / 11||50||10 (RfDC for Cr VI)
2000 (RfDC for Cr III)
|cadmium||1 - 18||11 / 11||0.4||1 (EMEG)|
|arsenic||0 - 13||1 / 11 ***||5||0.4 (CREG)|
|lead||7 - 100||11 / 11||13||NONE **|
|mercury||0 - 0.4||6 / 11||0.2||0.6 (RfDC)|
† surface soil background levels determined for McAFB, OU B
(on and off site) Ref (41)
* EMEG and RfDC comparison values are calculated for a pica child (ingestion rate of 5000 mg/day)
** lead is listed as a B2 carcinogen; no comparison values available for ingestion
*** one arsenic detect - probably due to spot dumping of pesticide or other chemical
Subsurface sediment sampling (1-4 feet below ground surface) was also performed at the sampling locations. The metals listed in Table 12 were detected in the subsurface samples as follows: chromium (11/11 samples, 22-120 mg/kg); cadmium (9/11 samples, 0.44-12 mg/kg); arsenic (not detected); lead (10/11 samples, 6-110 mg/kg); and mercury (2/11 samples, 0.2-0.5 mg/kg). Subsurface contaminants are indicative of historical activities.
In March, 1993, McAFB collected shallow sediment samples at three of the locations listed in Table 12. Samples were tested for chromium and hexavalent chromium (Cr VI); results for Cr VI were all below the detection limit of 0.5 ppm, total chromium results ranged from 25-85 ppm (12a).
Off-site surface waters have not been sampled. However, McAFB discharge waters (or effluent) into Magpie, Arcade, and Don Julio Creeks are monitored through NPDES permits with the CRWQCB. The levels of contaminants in the effluents must be below standards for public drinking water and meet aquatic life criteria.
In 1986, nine soil gas MWs were constructed in groups of three, at various depths, (11-15 ft, 34-44 ft, and 69-79 ft screening levels). One off-base cluster is adjacent to and just west of OU D (Fig. 5). MW-7 is screened at 60-79 ft; MW-8 at 34-44 ft; and MW-9 at 11-15 ft below ground surface. Soil gas samples were collected in December 1987, and March-April 1991, from the MWs in conjunction with additional sampling of soil gases from the vent capping system in OU D (22,23); additional sampling of the MWs occurred in June, 1992 (24). The maximum concentrations from the three sampling regimens are listed in Table 13.
|Contaminant||1987 Results (ppbv)||1991 Results (ppbv)||1992 Results||Comparison Value
|TCE||6000 (7)||0.17||22,049 (7)||0.75||19,000 (7)||1100||0.11 (CREG)|
|MC||<90||24||385 (7)||0.75||ND||1100||0.61 (CREG)|
|PCE||90 (7)||0.14||256 (7)||0.75||ND||1100||0.28 (CREG)|
|VC||<300||18||ND||0.75||3000 (7)||1100||0.005 (CREG)|
|benzene||<100||13||512 (7)||0.75||ND||1100||0.04 (CREG)|
|1,1-DCE||NA||--||11,000 (8)||0.75||330,000 (7)||1100||0.005 (CREG)|
|1,2-DCA||<80||18||1,278 (7)||0.75||ND||1100||0.009 (CREG)|
ND = not detected
* detection limits are averages during the sampling period
NA = not analyzed
† 1992 detection limits high
# soil gas MW number
Contaminant levels for the off-site well cluster (MW-7,8, and 9) in 1991 were higher than those found in 1987. In this cluster, the highest contaminant concentrations were found in the deepest well (MW-7) and the lowest in the shallowest well (MW-9). Due to high concentrations of 1,1 DCE in the 1992 samples, dilutions were required that resulted in high detection limits for all the VOCs analyzed. Vinyl chloride was detected in 1992 in the deep screened well. Both VC and 1,1 DCE are byproducts of the anaerobic biodegradation of TCE and PCE.
Shallow soil gas sampling for OU D (on and off site) was performed in September, 1992. Samples were collected at depths of 4.5-10 feet below ground surface. Higher concentrations of VOCs were present in residential samples collected near the base boundary; VOC levels decreased with distance from the OU D capped area. In those shallow samples, the primary contaminant detected was 1,1-DCE (719-91,873 ppbv in samples located near the boundary). Other VOCs detected included TCE (2-641 ppbv), PCE (1-55 ppbv), TCA (2-114 ppbv), VC (in one sample at 78 ppbv), MC (in two samples, 3-35 ppbv), and benzene (3-19 ppbv; benzene results are qualified due to trip blank contamination) (42). The soil gas concentrations are indicative of the continuing presence of VOCs in the area.
Air was monitored in the crawl spaces under residences adjacent to OU D. CDHS collected samples in the crawl spaces and well heads (at depths of 10 and 40 ft) of residential wells at four properties adjoining the base boundary. Crawl space samples were obtained from 10 ft probe samplers. Sampling dates were October 12, 1984, December 19, 1984, and February 5, 1985. No background samples were reported, but CDHS selected ambient air values for rural Washington state for comparison levels. Table 14 reports data on maximum levels of VOCs detected (43).
|Crawl Space Data||Well Head Data||Ambient Air
WA State, ppbv
|MC||1.8 *||12.9||2/85||17.9||2/85||0.005||0.61 (CREG)|
|VC||0.03 *||ND||--||2.6||12/84||<0.005||0.005 (CREG)|
|1,1-DCE||2.5 *||3.8||10/85||4539||10/85||<0.005||0.005 (CREG)|
|1,2-DCA||0.9-12.3 *||ND||--||195.7||2/85||<0.005||0.009 (CREG)|
|1,1,1-TCA||0.2||0.85||2/85||120.9||10/84||0.1||300 (EMEG) **|
ND = not detected
* detection limit above the CREG for this contaminant
NA = not analyzed
** comparison level for acute exposure
McAFB EM sampled air in the crawl spaces of the same four homes on a quarterly basis for one year. Quarterly samples were collected on April 10, 1986, July 23, 1986, October 22, 1986, and January 22, 1987, using a low flow rate over three and a half days. Air samples were collected on jumbo carbon tubes in series, about 3-4 inches from the ground surface. The bubble meter, a primary standard, was used to calibrate each pump's flow rate. The same procedure was used to collect a background sample in an open field south and east of the homes. Table 15 reports data on maximum concentrations of the VOCs detected (44).
|Contaminant||Concentration ppbv||Date||Background ppbv, date||Comparison Value, ppbv||Detection Limit, ppbv|
|TCE||0.17||4/86||0.58, 4/86||0.11 (CREG)||0.011|
|MC||36.99||7/86||2.96, 7/86||0.61 (CREG)||0.604|
|PCE||1.31||7/86||0.18, 7/86||0.28 (CREG)||0.003|
|1,1,1-TCA||5.86||7/86||0.87, 7/86||300 (EMEG) *||0.006|
ND = not detected
NA = not analyzed
* comparison value is for acute exposure
The results from the two crawl space studies indicate several data gaps that should be addressed. All of the VOCs tested for in the two studies, except 1,1,1-TCA, are carcinogens. Background levels in the McAFB study exceeded health comparison levels, which could indicate contaminated ambient air in the area. The choice of an on-base location for the background air station is questionable. Detection limits are one to two orders of magnitude higher than CREGs for the carcinogens benzene, VC, 1,2-DCA, 1,1-DCE, and MC. Detection limits were also higher than the Washington state ambient air levels used in the CDHS study for background comparisons. Data gaps exist for both studies because of the detection limits; i.e., VC detected in well heads could be present in the crawl spaces, but not detected.
During the 1991 soil gas sampling of the OU D MWs and vents, two ambient air samples were collected on private property (residence involved in earlier crawl space studies) adjacent to the base boundary (33). VOCs detected were MC (4 ppbv) and 1,1-DCE (3 ppbv); both are carcinogens.
Crawl spaces at three of the residences were sampled again in January 1992. Sampling for VOCs took place over an eight-hour period on January 7. Results from that monitoring are provided in Table 16 (45). Benzene and MC were detected at concentrations above health comparison values; however, detection levels for several other contaminants of concern were higher than the health comparison values.
|Contaminant||Detection Limit ppbv||Crawl Space Data, ppbv||Comparison Value ppbv|
|Res #1||Res #2||Res #3|
|VC||0.8 *||ND||ND||ND||0.005 (CREG)|
|benzene||0.57 *||0.65||1.0||0.81||0.04 (CREG)|
|1,1-DCE||0.32 *||ND||ND||ND||0.005 (CREG)|
|1,2-DCA||1.19 *||ND||ND||ND||0.009 (CREG)|
ND = not detected
* detection limit above the CREG for this contaminant
NA = not analyzed
In June and September, 1992, additional crawl space sampling and ambient air monitoring in yards occurred using methods with lower detection limits (46,47). Results of those air samples are presented in Table 17.
|Contaminant||Crawl Space Data, ppbv
|Ambient Air Data, ppbv
| Bkgd †
|Res #1||Res #2||Res #3||Res #4||Res #1 *||Res #2||Res #3||Res #4|
|TCE||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||0.11 (CREG)|
|PCE||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||0.28 (CREG)|
|MC||.64/ ND||.3/ ND||.23/ ND||.21/ ND||ND/ ND||ND/ ND||.29/ ND||.31/ ND||.22/ .32||0.61 (CREG)|
|VC||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||0.004 (CREG)|
|benzene||.41/ .54||ND/ .44||.48/ .48||.42/ .42||ND/ .4||ND/ .43||.52/ .44||.46/ .49||.42/ .53||0.04 (CREG)|
|1,1-DCE||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||0.005 (CREG)|
|1,2-DCA||ND/ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||ND/ ND||0.005 (CREG)|
|1,1,1-TCA||57/ 3.8||.61/ .31||.59/ .28||.83/ 5.1||2600/ 17||160/ 13||1.1/ .24||.58/ 3.2||.39/ .27||300 (EMEG)**|
ND = not detected, Detection limit for VC = 0.1 ppbv; detection
limit for other VOCs = 0.2 ppbv
* during ambient air sampling the resident was spray cleaning structures on the property
** value is for acute inhalation EMEG (less than 14 days exposure)
background samples collected upgradient on residence #1
The residential air samples were collected over 24 hour time periods for each sampling round. Detection limits were 0.2 ppbv for each VOC except vinyl chloride; detection limit for VC was 0.1 ppbv. Methylene chloride and benzene were detected in most of the samples, as well as the background samples. Although not detected, the detection limits for TCE, VC, 1,1-DCE, and 1,2-DCA were higher than the health comparison values. The high concentration of TCA in one ambient air sample may have been caused by activities of the resident (reports indicate spray cleaning of fences during the sampling time period) (46).
Biota have not been sampled. The base and surrounding communities do not have surface water streams or lakes that support fish used for food. On the northern portion of the base there are regulated hunts for quail and partridge. Homes west of the base are large plots with livestock and gardens for residents' personal use (there is no commercial agriculture near the base). Produce grown in home gardens in the Sacramento area includes tomatoes, beans, squash, carrots, radishes, and melons, and apricot, peach, plum, pear, citrus, walnut, and almond trees. If any of the contaminants of concern bioaccumulate in vegetables, fruits, or livestock (chickens, sheep, goats, and cattle), and are present in irrigation water or garden soils, a potential public health concern by way of the food chain is possible. ATSDR considers the lack of biota data a potential data gap.
Notations have been made in the contaminants of concern section when the data provided are inadequate because of limited sampling, lack of background samples, or high proportion of the data outside of quality assurance standards. Data quality concerns include contamination of blanks, detection limits higher than health comparison values, groundwater results based on field-filtered samples, and an inconsistency in speciation of metal analyses.
McAFB EM staff informed ATSDR that groundwater and soil sampling and analysis before 1985 was not performed using the QA/QC standards currently followed during the CERCLA process. However, potable water data were subject to state standards, and the analyses were performed in state-certified labs, resulting in adequate data for that period.
McAFB is an active military installation; access to the entire facility is restricted (fenced and guarded entry gates). Most identified areas of environmental concern are in industrial parts of the base where access is even further restricted. Methane is typically found in municipal landfills and may be in soil gases emanating from landfills. If methane is in enclosed areas at McAFB, it could pose an explosive hazard.