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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 2
April l, 2014
Robert Law, Ph.D.
demaximls, inc.
186 Center Street, Suite 290
Clinton, New Jersey 08809
290 BROAOWA Y NEW YORK, NY 10007-1866
Re: Response to CPG's November 22, 2013 model letter - Lower Passaic River Study Area (LPRSA)
Administrative Agreement and Order on Consent for Remedial Investigation I Feasibility Study (RI/FS) -
CERCLA Docket No. 02-2007-2009
Dear Dr. Law,
Thank you for your letter dated November 22, 2013, submitted on behalf of the Cooperating Parties Group
(CPG) to respond to EPA's model clarification letter dated October 23, 2014.
While it may be a matter of semantics, EPA does not agree with the CPG's assertion that there is "one
model." Rather, EPA stands by our conclusion that while the basic framework of the FFS, 17 mile RI/FS
and target remedy models is the same, the CPG has made modifications to the model utilized to develop
its targeted remedy outside the model Work Plan developed by EPA and outside the 17 mile RI/FS
oversight process.
Further, EPA would like to address some of the statements in your letter on which we do not share the
CPG's view.
1. Sediment transport modeling
The CPG correctly notes that EPA's modeling team provided oversight to the development of t he sediment
transport model supporting the RI/FS. Based on our review of the Sediment Transport Technical memo
submitted by the CPG on January 2013, EPA made recommendations and provided direction for additional
sensitivity analyses and modifications to the model. The CPG modeling team has been responding to the
comments made by EPA; some responses were presented at the modeling meeting of March 13 2014 and
are still being evaluated by EPA.
Your letter states that uno further communication" has occurred since AprilS, 2013. The current status is
that EPA is awaiting submission by the CPG of its latest version of h diment transport model code to
EPA for review.
2. Organic Carbon Simplification
In September 2011, EPA approved the approach for the simplification to the Organic Carbon Model
proposed by t he CPG. However, we note that the CPG did not use the approved approach for the model
results presented to EPA' s Office of Solid Waste and Emergency Response on July 2013, as part of its
presentation of its "targeted remedy". The results presented to support the targeted remedy used a more
simplistic approach with a constant Fraction Organic Carbon (FOC). The CPG has not provided carbon or
contaminant model results generated using the EPA approved approach.
Internet Address (URL) • http://wv.w.epa.gov Recycled/Recyclable •Printed with Vegetable Oil Based Inks on 100% Postconsumer, Process Chlorine Free Recycled Paper
The CPG's letter states that it is awaiting EPA approval of the Organic Carbon simplification code. EPA has
not approved the Organic Carbon Simplification code because our modeling team has not been able to
run it with the provided inputs. We expect to work in the near future with the CPG either demonstrating how the code works or discussing plans for getting it to work, so that we can evaluate and approve the
code, if appropriate.
3. COPC mapping
The CPG has presented their proposed COPC mapping and morphologic grouping approaches to EPA.
Given the variability of the contaminant data in the lower Passaic, the Thiessen polygon interpolation
method is not appropriate to establish a remedial footprint although it may be sufficient to establish
initial conditions for the chemical fate and transport model when averaged to the model grid.
The Thiessen polygon method assigns too much certainty to each data point assuming that that point can
represent conditions up to half a mile or a mile away.
As noted in the CPG letter, the CPG presented its mapping approach to EPA on September 26, 2013. The EPA team pointed out the following weaknesses in the technical analysis presented at the September 26,
2013 meeting:
• Kriging median concentrations should not be compared to Thiessen polygons mean concentrations
• The observation that the contaminant distribution derived from the Thiessen polygons
matches the distribution of the data cannot be used to describe the method as superior.
The method itself guarantees that.
• Cross validation statistics were not presented for all methods, particularly for the chosen
method of Thiessen polygons.
• The subdivision of the morphologic Group 3a and 3b is uncertain. The CPG should look at
more recent bathymetric surveys to define Group 3a and Group 3b better and include
uncertainty and variability in the location of areas of potential erosion.
4. Contaminant Fate and Transport Model
While this is not addressed in your November 22, 2103 letter1 the CPG's representation of the exchange
of contaminants between the sediment bed and the water column used for the targeted remedy is
different than what the CPG plans to implement for the RI/FS model. The CPG has introduced a quick fix
to control exchange of contaminants between the sediment bed and the water column to
generate results for the targeted remedy. While the fluff layer may limit the rate of contaminant
transport between the bed sediments and the water column, the empirical relationship used in the
targeted remedy model is not spatially representative of current conditions, and would be inappropriate
under future conditions.
EPA does not find the "kludge~~ approach to be defensible and is awaiting receipt of an alternate approach
to contaminant fate and transport.
5. Model Framework Issues
The CPG has brought to EPA's attention issues related to differences in sedimentation rates and bulk
density computations between the sediment transport, organic carbon and contaminant fate model.
EPA has pointed out that the primary cause of the differences described is due to running the
Hydrodynamics and Sediment Transport models decoupled from each other, and the approximation of
the bulk density used in the carbon and contaminant models. The approximate bulk density was used to
reduce both the complexity and quantity of information passed forward to the carbon and contaminant
models.
Based on the information provided at the March 13, 2014 modeling meeting, we understand that the
CPG has resolved the decoupled model issues, and reduced the differences in the approximations of the
bulk density information transferred from one model to another. The CPG is working on additional
modifications to further reduce the difference in these approximations. We are willing to discuss this
issue further. However, EPA will likely require the CPG to improve the representation of the time variable
changes in bed evaluation for remedies that include substantial changes In bathymetry, and bed
composition for remedies that include capping or backfill.
In summary:
• The modeling approach for the CPG's targeted remedy does not follow the modeling Work Plan
developed by EPA (e.g., in terms of the Organic Carbon Modeling approach, and the exchange of
contaminants between the sediment bed and the water column in the Contaminant Fate and Transport
modeling).
• EPA is awaiting submission by the CPG of its latest version of the sediment transport model code
to EPA for review.
• Additional discussion of the Organic Carbon simplification code is required before EPA can
approve this.
• Given the variability of the data, the Thiessen polygon method is not appropriate to establish a
remedial footprint.
• The implementation of a quick fix ("kludge") that controls the exchange of contaminants between
the sediment bed and the water column in the contaminant fate and transport model is not acceptable.
• Additional discussion of the representation of the time variable changes in bed evaluation for
remedies that include substantial changes in bathymetry, and bed composition for remedies that include
capping or backfill, is needed and improvements are likely to be required.
Please contact me with any questions, or call Jennifer laPoma, Remedial Project Manager for the 17-mile
RI/FS, at 212-637 4328
Sincerely,
Raymond Basso
Passaic River Project Director
cc:
Eugenia Naranjo, EPA Region 2 Jennifer laPoma, EPA Region 2 Alice Veh, EPA Region 2 Pat Hick, EPA Region 2 Sarah Flanagan, EPA Region 2