The general cleanup goals were reasonable, and this
group encourages expedient action to prevent further spreading
of the contaminant plume. Comments on some aspects of the cleanup
plan are itemized below.
Pathways of Concern
No mention was made of inhalation risk from the remediation
scheme itself. The report itemized the minimal risk of inhalation
of VOCs as the material worked its way up through the soil and
into buildings via cracks in the foundations. This was deemed
of little risk. But no mention was made of the prior risk of air
stripping of 3200 pounds of VOCs from groundwater nor the potential
future risk of additional air stripping. This risk would be for
on-site workers and local residents. This risk should be considered
in conjunction with the TSA and the TGA/Cascade remediation plans
for air stripping.
The Columbia Slough
Section 7 (Interim Corrective Measures to Date) showed
that treated groundwater is discharged under a discharge permit
issued by Oregon DEQ to Storm Drain Creek which empties into the
Columbia Slough. In Section 9 (Description of the Proposed Corrective
Measures) the effluent from the new pump-and-treat wells will
ultimately be discharged to the Columbia Slough after air-stripping.
The groundwater already is high in the nutrient phosphorus (P).
Concentrations of dissolved P in the groundwater are about 0.1
mg/l. In the past Aqua-Mag, a phosphate based anti-fouling agent
was added to the groundwater prior to air-stripping. This resulted
in an increased load of P above the background level being discharged
to the Columbia Slough.
Based on current Oregon DEQ's assessment of the Columbia
Slough as water quality limited, no new sources of nutrients (such
as P) may be allowed to be discharged to the Slough. Coordination
with the Oregon DEQ surface water group is necessary to assure
that the remediation plan, as proposed, can proceed.
Proposed Cleanup Plan
The clean up time and cost estimate are valid only
if the contaminants are perfectly soluble and the TGA is perfectly
homogeneous. This is a huge "if" since there is evidence
that the site is extremely heterogeneous and NAPL and DLAPL may
exist in the TGA, especially near the source.
The heterogeneity of the TGA controls the removal
of the VOCs because of low flow areas in the contaminated zone.
The main mechanism for removal of these contaminants (even if
they are soluble) from these areas is diffusion, whether they
are low clay lenses or light fractures. Lenses that are relatively
small can still leak out of these areas for years. In any case,
where diffusion controls the removal of VOCs from the TGA, cleanup
time will be enormous.
Even if the aquifer is perfectly homogeneous, the
DNAPL sitting at the top of the aquitard would be moved by a pump
and treat system at a rate limited by the compound solubility
in water.
Contaminant concentration at typical pump and treat
sites often shows initial quick decline and then levels off to
an asymptotic limiting value. It is the mean transmissivity and
the pumping rate that control the time scale of initial concentration
decline, and it is 1) the heterogeneity, 2)amount of NAPL and
DNAPL present, and 3) distance from the source of contamination
that dictate the asymptotic concentration that can be realistically
achieved. At most of the pump and treat sites nationwide, unfortunately,
this asymptotic concentration is often much larger than the targeted
concentration or MCL due to heterogeneity and presence of DLAPL.
The estimated clean up time at the Boeing site seems to reflect
only the time scale of initial concentration drop.
Pump and Treat System
A pump-and-treat system when used for hydraulic containment
cannot control the potential spreading of DNAPL that may accumulate
at the top of the sloping CU1. DNAPLs tend to move down slope,
independent of the direction of groundwater flow. This should
be recognized since one of the remediation objectives is to control
contamination spreading.
Performance Compliance
The time frame for meeting the remediation objectives
was between 10 and 20 years. In Section 9 (Description of the
Proposed Corrective Measures) under Performance Monitoring, performance
monitoring of the groundwater and extraction wells was to "assess
the progress towards achieving the target cleanup levels for the
TGA." But very little information was given as to how the
progress of remediation would be assessed or what would trigger
additional remediation measures by the responsible parties. Questions
that require further explanation would be
Another aspect of performance monitoring is the proposed
evaluation of DNAPLs. What additional remediation measures and
what criteria will be used to determine if DNAPLs are present
at levels high enough that further remediation measures need to
be undertaken ? Has a removal program been evaluated for DNAPLs?
A proposed course of action should be addressed which more clearly
explains the options for DNAPL removal.
Chemicals of Concern
The chemicals of concern identified at the Boeing
site include several degradation products of PCE and TCE. Previous
sampling at similar and related sites has shown the presence of
vinyl chloride, one of the last degradation products of TCE and
PCE. Vinyl chloride is a known carcinogen, and cleanup levels
in the aquifer should address levels of vinyl chloride since they
will likely be produced from continued degradation. Concentrations
of the contaminating solvents are high, and there is a good probability
that vinyl chloride will be produced during degradation in the
subsurface. The assessment should also address the rate of degradation
of the contaminants in the Slough and the potential for completing
exposure pathways for vinyl chloride in this environment.