2.5. Site Characteristics
- VOCs
- Fuel Hydrocarbons
- Metals
- Tritium
Initial releases of hazardous materials occurred at the LLNL site in the mid-
to late 1940s when the site was the Livermore Naval Air Station (Thorpe et al.,
1990). There is also evidence that localized spills, leaking tanks and
impoundments, and landfills contributed VOCs, FHCs, lead, chromium, and tritium
to ground water and unsaturated sediment in the post-Navy era. A screening of
all environmental media showed that ground water and unsaturated sediment are
the only media that require remediation (Thorpe et al., 1990). The identified
compounds that exist in ground water at various locations beneath the site at
concentrations above drinking water standards are:
- The VOCs trichloroethylene (TCE), perchloroethylene (PCE),
1,1-dichloroethylene (1,1-DCE), 1,2-dichloroethylene (1,2-DCE),
1,1-dichloroethane (1,1-DCA), 1,2-dichloroethane (1,2-DCA), carbon
tetrachloride, and the trihalomethane (THM) chloroform.
- FHCs (leaded gasoline), including benzene, ethylbenzene, toluene and
ethylene dibromide.
- Chromium and lead.
- Tritium.
The quality of data for these compounds was considered in the selection of the
remedies for the LLNL site in accordance with the LLNL Quality Assurance
Project Plan (QAPP, Rice, 1988).
The VOCs in ground water beneath LLNL occur in relatively low concentrations
that underlie about 85% of the LLNL site, over a total area of about 1.4 square
miles (Fig. 3). The calculated total volume of undiluted VOCs in ground water
is less than 200 gallons. The vertical thickness of the ground water VOC
plumes varies from about 30 to 100 feet, and VOCs are seldom found below a
depth of about 200 feet. VOCs are relatively mobile in ground water and
migrate at a rate of about half the velocity of ground water. TCE and PCE are
the predominant VOCs in the study area, and are currently present locally in
concentrations up to 4.8 and 1.1 parts per million (ppm) respectively (1992
data). However, the higher concentrations are localized, and total VOC
concentrations exceed 1 ppm in ground water from only 10 out of a total of
more than 300 wells. The distribution of VOCs in ground water exceeding MCLs
is shown in Figure 4. The VOCs and chromium in ground water in the vicinity of
the Patterson Pass-Vasco Road intersection appear to originate on private
property northwest of the LLNL site as discussed in Iovenitti et al. (1991)
and Hoffman (1991a). This offsite area will be investigated by the potentially
responsible parties under RWQCB order. If LLNL is found to be the source of
chromium in this area, LLNL will incorporate this area into the remedial
design.
Chemical data from boreholes drilled at the locations of suspected VOC releases
at LLNL indicate that generally low residual VOC concentrations (less than 100
parts per billion [ppb]) are present in unsaturated sediments. The calculated
total volume of undiluted VOCs in the unsaturated zone is less than 100
gallons. Computer modeling indicates that downward movement of VOCs above the
water table is not likely to result in ground water VOC concentrations
exceeding MCLs for drinking water, except at the Building 518 Area in the
southeast corner of the site (Isherwood et al., 1990). The Trailer 5475 Area
is also being evaluated for possible cleanup.
In the Building 518 Area, VOCs (predominantly TCE) reach a maximum
concentration of about 6 ppm at a depth of 20 feet. These VOCs are believed to
have originated from surface spills or leaking drums in the post-Navy era.
Recent investigation in the Trailer 5475 Area (also called the East Taxi Strip
Area) in eastern LLNL indicate that remediation may be necessary pending
additional subsurface investigations and modeling. Total VOC concentrations
(predominantly TCE) reach a maximum concentration in unsaturated soil of about
5 ppm in that area. These VOCs originate from former landfills and surface
impoundments.
FHCs occur almost exclusively where a leak of roughly 17,000 gallons of leaded
gasoline occurred from a U.S. Navy-era underground fuel tank in the southern
part of the site (Fig. 5). Although some gasoline constituents are relatively
mobile in ground water, FHCs in ground water have not migrated more than about
500 feet from the leak point due to the very slow ground water movement in the
area (Thorpe et al., 1990). Within this area, total FHC concentrations in
ground water range from 0.001 to 16 ppm, and benzene concentrations range from
less than 0.0001 to about 4 ppm. Ethylene dibromide has been detected in nine
Gasoline Spill Area monitor wells above the MCL in concentrations from 0.0001
to 1.3 ppm. FHCs are not present in ground water beneath a depth of about 150
feet.
Prior to withdrawal of fuel vapor by vacuum-induced venting as part of a
Gasoline Spill Area pilot study, up to 11,000 ppm total FHCs and 4,800 ppm
aromatic hydrocarbons were detected in the unsaturated sediments beneath the
former fuel tank. Virtually all FHCs in the unsaturated zone are about 50 feet
radially from the leak point.
Metals above MCLs are present in only a few locations. Chromium in ground
water exceeds the MCL in 16 wells scattered in the northwest, central, and
southwest parts of the study area and near Arroyo Seco (Fig. 6). The maximum
chromium concentration in ground water in the LLNL study area is 160 ppb, in
the northwestern corner of the site. Chromium in the LLNL area sediments and
ground water appears to have originated naturally and from some LLNL site
activities. At LLNL, chromate solutions were used in cooling towers as
corrosion inhibitors from approximately 1958 to 1970. Blowdown from the
cooling towers was released to the storm drain system, but neither the exact
quantity of releases nor the chromium content of the water are known.
According to anecdotal information, storm runoff caused the blowdown to flow
northerly before infiltrating into the ground near the West Traffic Circle. In
addition, naturally occurring chromium deposits have been mined in the hills
southeast of LLNL. As described in Section 2.5.1, chromium in ground water
northwest of LLNL appears to orginate on private property and will be
investigated by others (i.e., the potentially responsible parties).
Recent analyses indicate lead is above the 15 ppb remediation standard in only
two wells, both in the Gasoline Spill Area, at a maximum concentration of 38
ppb. Lead has a low potential for migration in both the saturated and
unsaturated zones because it binds strongly to sediment. This low migration
rate and limited extent, indicate that lead at LLNL does not pose a health
threat. If, however, lead is found in ground water above the remediation
standard, it will be remediated.
Tritium in ground water has historically exceeded its MCL (20,000 picocuries
per liter [pCi/L]) in only two wells, MW-206 and MW-363, both in the southeast
part of the LLNL site. Currently, water from only MW-206 exceeds the tritium
MCL (Fig. 6). This tritium was released to the subsurface in former, nearby
evaporation ponds, is localized and well defined, and the affected ground water
is not used for drinking water. Although tritium migrates at the same rate as
ground water, ground water modeling indicates that by the time the affected
ground water moves offsite in the absence of active remediation, tritium
concentrations would be reduced to concentrations below drinking water
standards by natural decay (tritium has a 12.3-year half-life). Therefore, no
pathway to humans exists for the observed tritium in ground water. The tritium
is effectively self-remediating via natural decay. Ground water will continue
to be monitored for tritium to track its distribution and concentrations over
the duration of the cleanup.
Recent investigations have identified additional areas where tritium
concentrations in unsaturated sediments at LLNL are significantly elevated.
These include the Building 514, Eastern Landing Mat Storage, West Traffic
Circle, Building 292, and Old Salvage Yard Areas. However, the tritium
activity in ground water in these areas is well below the 20,000 pCi/L MCL.
The only potentially significant transport pathways to human populations for
this tritium are inhalation and skin absorption of tritiated water from direct
soil evaporation or from water taken up by plants and released to the air by
transpiration from plant leaves. Most of the areas where tritium has been
detected are paved with asphalt, thereby limiting potential evaporation from
soil and further downward migration by infiltration of rainwater. Elevated
tritium levels in transpired water have been measured in isolated areas at
LLNL. Screening-level calculations have been performed by LLNL using the
standard EPA model AIRDOS-EPA and very conservative assumptions that maximize
the calculated dose. These calculations indicate that any potential dose from
the measured tritium in soil would not exceed 0.01% of the
10-millirem/year Federal dose standard (Macdonald et al., 1990). Additional
information regarding the distribution, concentration, toxicity, mobility,
potential routes of migration, and potential exposed populations of all LLNL
compounds of concern can be found in the RI, the Baseline Public Health
Assessment (BPHA) (Layton et al., 1990), and Sections 2.1 and 2.6 of this
ROD.
2.6. Summary of Unremediated Site Risks
UCRL-AR-109105
