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