GE Comments to the Modeling Peer Review Panel

on EPA’s Model Framework Design

Lenox, MA

April 25, 2001

April 25, 2001 2

GE’s Role in the Modeling Effort

Goal of the Modeling

– Develop a scientifically supportable mathematical representation of the system

– Objectively evaluate risk reduction associated with alternative remedial actions

GE’s Modeling-Related Responsibilities under the Consent Decree (CD) – GE will perform the Corrective Measures Study (CMS) for the Rest of River – GE will apply the EPA models to evaluate remedial alternatives

Introduction

April 25, 2001 3

GE’s Role in the Modeling Effort

Interactions with the EPA Modeling Team – Cooperative arrangement established in the CD to provide a forum to:

• share insights on the system • establish and maintain a common database • identify and fill important data gaps • provide comments on EPA work products

– EPA responsible for model development, calibration, and validation

GE Is Actively Engaged in Modeling the System – Effort initiated prior to signing the CD – Effort continues to provide insights into mechanisms controlling PCB

fate within the System – GE’s modeling efforts have informed GE’s comments on EPA’s MFD

Introduction

April 25, 2001 4

GE’s Major Concerns with EPA Modeling Approach

Model Domain Should Be Expanded to Include – Upper 2 mile reach, including plant site area – Downstream of Woods Pond into CT

EPA Modeling Approach Is Overly Complex Without Supporting Data – Focused on fine-scale phenomena

• not necessarily important at scale of remedial decision • poorly understood and not feasible to simulate

– Model linkages complicated by model incompatibilities • models not simulating same parameters (e.g. solids) • models not simulating same processes consistently

– Insufficient data to constrain some model complexities • lateral variations in sediment/PCB transport processes • changes in ecosystem parameters (e.g., fish biomass) • could lead to erroneous predictions

Additional Data Are Needed to Simulate Potentially Important Processes – Sediment bed load – PCB partitioning

Overview

April 25, 2001 5

Model Domain Should Be Expanded

Model Domain Should Include the Upper 2 Mile Reach

– Understanding of PCB loading from 2 mile reach important to understanding Rest of River PCB dynamics

• Approx. 20% of low flow water column load • 20 to 60% of high flow water column load

– Explicit modeling will provide data-based mass balance constraints on loadings originating from this reach of the River

• provides a means to estimate bed load – Active remediation is on-going or planned for this reach of the River

• work in upper ½ mile has found both PCB and coal-tar DNAPLs – Data collected after upstream remediation will allow evaluation of the

impacts of this remediation on Rest of River

Charge Question 3

April 25, 2001 6

Upper ½ Mile DNAPL Seeps

March 27, 2001 – DNAPL in Excavation Cell F3 Aroclor 1260 – 438,000 ppm

Charge Question 3

April 25, 2001 7

Model Domain Should be Expanded

Model Domain Should Include the Upper 2 Mile Reach

– EPA should take advantage of this unique calibration opportunity • models will be used to project the effects of remedial alternatives

for Rest of River • should apply them to simulate the observed impacts of actual

remediation in upper 2 miles – Comparison of model simulation of this post-remediation period with

actual post-remediation data would represent a robust test of the model

Charge Question 3

April 25, 2001 8

Model Domain Should be Expanded

Model Domain Should Include Reaches Downstream of WP – Biota consumption advisories in MA and CT – Expansion of model domain will allow objective downstream

predictions of the impact of: • natural recovery • rare floods • upstream remediation activities

– Extensive CT biota data • could provide a robust data set for model calibration

Charge Question 3

April 25, 2001 9

Cornwall, CT Fish PCB Concentrations

Charge Question 3

April 25, 2001 10

Housatonic River Is a Complex System

Variety of Hydrodynamic Regimes – main channel and backwaters – floodplains – impoundments

Diversity of Sediment Transport Processes – cohesive sediment transport – non-cohesive sediment transport – bed load – floodplain sediment deposition – bank erosion

PCB Fate – potential “third phase” – partitioning onto autochthonous solids – bed load PCB transport

Rea

ch 5

5A

5B

5C

WP

SackettBrook

RoaringBrook

West BranchConfluence

PittsfieldSTP

Charge Questions 1,2, and 3

April 25, 2001 11

EPA Modeling Approach Is Overly Complex

Impractical to Simultaneously Represent All the Following System Complexities – Floodplain interactions – Lateral gradients in current velocity and turbulent eddies in main

channel – Bank erosion – Bar and terrace formation and degradation

Lack of Sufficient Data to Constrain Some Processes

– Food web dynamics – Adding such complexity to model without supporting data will:

• increase uncertainty of model predictions • obscure model uncertainties • possibly lead to erroneous predictions

Charge Questions 1,2, and 3

April 25, 2001 12

EPA Modeling Approach Is Overly Complex

Need to Develop a Model at a Scale That – Is technically feasible given computational constraints – Is supported by available data – Possesses sufficient predictive capabilities to be applied to guide

remedial decisions

Charge Questions 1,2, and 3

April 25, 2001 13

Rea

ch 5

5A

5B

5C

WP

SackettBrook

RoaringBrook

West BranchConfluence

PittsfieldSTP

Model Grid Challenges

Narrow Meandering Channel Nested within Broad Floodplain

Complex Interactions between Main Channel and Floodplain during Floods (~1.5 yr return interval) – Complex flow routing – “Wetting and drying” of floodplains – Sediment and PCB transport

Charge Questions 1,2, and 3

April 25, 2001 14

Nested Curvilinear Grid Proposed by EPA

200 0 200 400 600 8001000 Feet

•Orthogonal curvilinear grid ambitious, but not practical for this system due to complex geometry

–extremely small elements –excessive computational burden

•Nested grid to represent floodplains is creative, but may not realistically represents channel/floodplain interactions

–momentum is not conserved –doesn’t represent sheet flow under high flow conditions

–sediment and PCB dynamics in flood plain and channel may not be realistically represented

Charge Questions 1,2, and 3

April 25, 2001 15

Model Grid Alternative

GE/QEA Has Simulated Hydrodynamics and Sediment Transport Using 20-meter Rectangular Grid Between Confluence and Woods Pond – 2,288 channel elements – 1,313 backwater elements – 8,981 floodplain elements

Similar Grid Envisioned for Upper 2 Miles, Including Plant Site,

While Coarser Grid Envisioned for Downstream to CT

Grid Attributes – Computationally feasible to perform 30 year projection runs – Should be sufficient to model remedial alternatives for the CMS

Charge Questions 1,2, and 3

April 25, 2001 16

Hydrodynamic Model Grid (20m x 20m)

Rea

ch 5

5A

5B

5C

WP

SackettBrook

RoaringBrook

West BranchConfluence

PittsfieldSTP

Charge Questions 1,2, and 3

April 25, 2001 17

Model Grid Alternative

A 20-meter Grid Necessitates Aggregation of Some Hydrodynamic and Sediment Transport Processes – Model cannot simulate lateral differences in bottom shear and sediment

transport – Individual point bar and terrace deposits not resolved

Small Scale Deposits Only Important If They Dominate PCB

Transport Process and Goal is to Remediate at That Scale – That is, if they contain higher PCB concentrations than surrounding

channel sediments such that aggregation of sediment transport processes misrepresents PCB transport

A 20-meter Grid Requires Appropriate Data to Constrain the Inherent Empiricisms of the Approach

Charge Questions 1,2, and 3

April 25, 2001 18

Sediment PCB Distribution

Charge Questions 1,2, and 3

April 25, 2001 19

Areal Distribution of Bar and Terrace Deposits

Source: BB&L 1994 Probing data

0

5000

10000

15000

20000

25000

30000

128129130131132133134135136137138River Mile

Are

a (m

2 )

0

5

10

15

20

Are

a (%

)

Bars and TerracesOther Channel Samples % Bars and Terraces

WBC PSTP

Charge Questions 1,2, and 3

April 25, 2001 20

Constraining the Inherent Empiricisms

Sediment Transport

– Data-based solids mass balance calculations during flood events • spatial patterns in erosion and deposition • generate understanding of system behavior

Charge Questions 1,2, and 3

April 25, 2001 21

Temporal Trends in TSS During May 1999 Flow Event

New Lenox Rd

Pror

ated

Col

tsvi

lle F

low

(c

fs)

TSS

(mg/

L)

Charge Questions 1,2, and 3

April 25, 2001 22

Constraining the Inherent Empiricisms

Solids Mass Balance Calculations – Develop hourly time series of TSS concentrations from data using

linear interpolation • upstream and downstream boundaries • tributaries

– Develop time series of flow rate from model inputs and predictions • inflows developed from upstream and tributary inputs • outflow determined from hydrodynamic model results

– Calculate hourly solids loads at inflow and outflow boundaries using TSS concentration and flow rate information

– Calculate sediment mass balances for different reaches of the River

Charge Questions 1,2, and 3

April 25, 2001 23

Sediment Mass Balance – POM – NLR Charge Questions 1,2, and 3

April 25, 2001 24

Sediment Mass Balance – NLR - WP Charge Questions 1,2, and 3

April 25, 2001 25

Constraining the Inherent Empiricisms

PCB Fate and Transport – Low flow

• diffusional processes • molecular, biologically enhanced

– High flow

• net effect of sediment erosion and deposition processes

Charge Questions 1,2, and 3

April 25, 2001 26

Examples of Water Column PCB Load Dynamics

0

100

200

300

400

500

600

PCB

Loa

d (g

/day

)

Flow Regime Low Flow High Flow

HeadwatersDam

Holmes Rd. Woods Pond

Effect of Flow Trapping in WP

Charge Questions 1,2, and 3

April 25, 2001 27

Comments on Specific Models Proposed by EPA

EPA Approach Complicated by Use of Two Models to Simulate PCB Transport and Fate – EFDC and AQUATOX

• different spatial and temporal domains and scales • different representations of PCBs (total vs. congener) • complex model linkages

– floodplain inundation – solids dynamics

– Complicates water, solids, and PCB mass balances

EPA Should Use Only EFDC to Simulate PCB Fate – AQUATOX incapable of effectively simulating floodplain PCBs

Charge Questions 2 and 4

April 25, 2001 28

Comments on Specific Models Proposed by EPA

AQUATOX Proposed to Simulate Ecosystem Dynamics – Simulating “population dynamics” in multiple species and trophic levels – Complex predator-prey relationships

Housatonic River Data Insufficient to Support the Development

and Calibration of Ecosystem Model – No data on biomass changes over time – Data from other sites inadequate

Artificial Ecosystem Dynamics Will Impact Fish Exposures and

PCB Bioaccumulation – Exposure related to prey population abundances – No constraints on prey population calculations

Charge Questions 1,2, and 4

April 25, 2001 29

Comments on Specific Models Proposed by EPA

AQUATOX Should Be Used Only to Simulate “Average” Fish

Exposure – Consider temporal trends in water column and sediment concentrations

predicted by EFDC – Bound the diet of each species based on site data, information from

other studies – Calibrate by adjusting diets within observed bounds

Charge Questions 1,2, and 4

April 25, 2001 30

Additional Data Required

Constrain Potentially Important Processes – Sediment bed load – PCB partitioning

EPA Recently Committed to Collecting New Data

– Water column partitioning data – Sediment pore water partition data – Sediment bed load measurements

Additional Data May Be Required to Further Constrain Inherent

Empiricisms of Approach – Finer longitudinal spacing in water column sampling program – Site-specific fish gut content survey

Charge Questions 5 and 6

April 25, 2001 31

Summary of GE Comments

EPA Should Expand Model Domain to Include – Upper 2 mile reach, including plant site area – Downstream into CT

EPA Should Modify Modeling Approach

– Hydrodynamics/sediment transport • develop model at a resolution that is computationally feasible and

realistically represents floodplain hydrodynamics – PCB fate

• conduct PCB fate modeling with a single code (i.e., EFDC) – PCB bioaccumulation

• abandon plans to simulate ecosystem dynamics

EPA Should Use Data Collected After 2 Mile Remediation to Calibrate the Models

EPA Should Collect Additional Data Required to Constrain

Empiricisms of Approach

Summary