2.7.2.1. Ground Water Remedial Alternative No. 1 (The Selected Alternative)
- Ground Water Extraction Plan for Remedial Alternative No. 1-Complete Capture and Source Area Extraction
- Treatment Options for Ground Water Remedial Alternative No. 1
2.7.2.1.1. Ground Water Extraction Plan for Remedial Alternative No.
1--Complete Capture and Source Area Extraction
Under this plan, extraction wells would be strategically placed near
contaminant margins to intercept and hydraulically control all ground water
originating from LLNL with VOC concentrations exceeding MCLs. In addition,
ground water would be extracted from source areas (defined here as those areas
with concentrations above about 100 ppb in ground water) to expedite cleanup.
This plan would utilize 18 initial extraction locations and about 7 treatment
facilities shown conceptually on Figure 7. A plot of the predicted ground
water flow patterns using these locations is shown in Figure 8. The flow lines
(with arrows on Fig. 8) converge on extraction locations and show the areas
hydraulically captured by the extraction wells. The total rate of ground water
removal for this extraction plan is estimated to be about 350 gallons per
minute (gpm). Where VOCs and tritium occur together in ground water, the
extraction systems will be designed and monitored to minimize tritium migration
and to prevent the water influent to any treatment systems from containing
tritium in concentrations above the MCL. Therefore, no tritium will be
released from treatment systems in concentrations above the MCL.
The 350-gpm sitewide extraction rate is a preliminary estimate used to estimate
capture areas, cleanup times and costs relative to other alternatives presented
in the PRAP and ROD. This extraction rate and the estimated treatment facility
capacities will be analyzed and further refined in the Remedial Design and as
part of ongoing work to decrease cleanup times and optimize extraction and
recharge rates.
It is estimated that it would take about 50 years to reduce contaminant
concentrations to MCLs if only the 18 initial extraction locations are
employed. LLNL plans to implement the selected cleanup plan in phases, and
evaluate each phase with field data. Additional extraction locations may be
used to ensure full hydraulic capture of the plume, and/or to expedite cleanup.
If technologically feasible, and if funding permits, LLNL will attempt to
achieve cleanup in less than the predicted 50 years. It is estimated that all
extraction and treatment facilities under Alternative 1 would be operational in
the 1993-94 timeframe, depending on congressional funding. LLNL will make
every effort to obtain sufficient funding to fully support the selected cleanup
plan. This alternative will comply with all ARARs.
Ground Water Containing VOCs (Proposed Treatment Facilities A, B, C, E, and G)
(Fig.7). Treatment Facility E could potentially receive ground water
containing tritium as well as VOCs.
- Treatment Option 1. Granular-Activated Carbon. (GAC)
- Ground water pumped by
extraction wells would pass through beds of activated carbon where VOCs would
be removed by GAC. The operating costs of this treatment option are high.
- Treatment Option 2. Air Stripping with GAC Treatment of the Vapor.
- Ground water pumped by extraction wells would pass through an air stripper where VOCs
would be removed by transferring them from the water to the air. The vapors
from the stripper would pass through GAC to completely remove contaminants.
This treatment option is the most economical for ground water containing VOCs.
- Treatment Option 3. UV/Oxidation Plus Air Stripping with GAC Filtering of the
Vapor.
- Extracted ground water would be blended with small amounts of hydrogen
peroxide and exposed to strong ultraviolet (UV) light, destroying most of the
contaminants. LLNL pilot studies have shown that some compounds require
secondary treatment by air stripping, which would be added to treat water after
it passed through the UV/oxidation unit. The vapors from air stripping would
pass through GAC to remove contaminants. This option reduces the amount of
waste requiring further treatment or disposal, especially where the majority of
the contaminants are readily oxidized by the UV/oxidation process. Costs for
this option are moderately high.
Treatment Option 2 or 3 is preferred for Treatment Facilities A, B, C, E, and
G, depending on the concentrations and types of the compounds, and the flow
rate influent to each treatment facility.
Ground Water Containing VOCs and Chromium (Proposed Treatment Facility D) (Fig.7)
- Treatment Option 1. GAC Plus Ion Exchange.
- Ground water pumped by extraction
wells would pass through GAC beds, which would remove the VOCs. The VOC-free
water would then be fed through an ion-exchange resin to extract chromium. The
operating costs of this treatment option are high.
- Treatment Option 2. Air Stripping with GAC Filtering of the Vapor Phase Plus
Ion Exchange.
- Extracted ground water would pass through an air stripper to
remove VOCs. The vapors from the stripper would pass through GAC to remove
VOCs from the air. The VOC-free water would flow through an ion-exchange resin
to extract chromium. This treatment option is preferred because the higher
concentrations of TCE, carbon tetrachloride, chloroform, and
Freon 113 make this treatment option more economical.
- Treatment Option 3. UV/Oxidation Plus Air Stripping and Ion Exchange with GAC
Treatment of the Vapor.
- Extracted ground water would be treated by
UV/oxidation, destroying most of the VOCs. Remaining VOCs would be removed
from the water by air stripping. The
vapors from the air stripper would pass through GAC to completely remove VOCs.
The VOC-free water would then flow through an ion-exchange resin to extract
chromium. The operating costs of this treatment option are high.
Ground Water Containing FHCs, VOCs, and Lead (Proposed Treatment Facility F)
(Fig. 7)
- Treatment Option 1. GAC Treatment.
- Ground water pumped by extraction wells
would pass through GAC beds, which remove the FHCs, VOCs, and lead. The
operating costs of this treatment option are high.
- Treatment Option 2. Air Stripping with GAC Treatment of Both the Vapor and
Liquid Phases.
- Extracted ground water would pass through an air stripper to
remove FHCs and VOCs. The vapors from the stripper would pass through GAC to
completely remove FHCs and VOCs. The water would then pass through GAC to
extract lead and any remaining FHCs or VOCs. This treatment option is not
preferred because the high concentration of FHCs would require frequent carbon
regeneration that increases the operating costs of this treatment option
substantially.
- Treatment Option 3. UV/Oxidation Plus GAC.
- Extracted ground water would be
treated by UV/oxidation, destroying most contaminants. The water would then
pass through GAC beds to remove lead and any remaining FHCs or VOCs. This
treatment technology is preferred because it can handle the high concentrations
of FHCs. It is also the most economical of the treatment options.
- Treatment Option 4. Subsurface Bioremediation.
- Biological treatment would
utilize the metabolic destruction of organic compounds by microbes that convert
the organic compounds in the ground water to less toxic compounds.
Bioremediation of the FHCs in the Gasoline Spill Area is potentially viable.
However, the relatively great depth of FHCs at LLNL, which makes providing the
correct physical and chemical conditions for the microbes difficult, and the
sensitivity of microorganisms to subsurface conditions that are difficult to
control, make applicability of subsurface bioremediation at LLNL uncertain. In
addition, bioremediation has not yet been proven successful for chlorinated
VOCs. Therefore, this treatment option was not considered as an initial
remedial action.
2.7.2.2. Ground Water Remedial Alternative No. 2
UCRL-AR-109105
