- U.S. EPA Office of Water,Office of Science and Technology,Washington, DC
- U.S. EPA Region I, Boston, MA
- Weston Solutions, Inc., West Chester, PA
Since 1998, AQUA TERRA's principals and staff have been involved in a
modeling study of PCB contamination in the Housatonic River in western
Massachusetts. Initial work efforts focused on the development of a
modeling framework to represent the fate, transport, and
bioaccumulation of polychlorinated biphenyls (PCBs) within the river
system. PCBs historically were released to the Housatonic River from
the General Electric facility in Pittsfield, MA. Over a period of
decades, starting in the 1930s, these compounds have accumulated in the
river's bed and floodplain sediments and impoundments both in
Massachusetts and further downstream in Connecticut. As part of a
comprehensive agreement among the various governmental agencies and GE,
signed in 1998, EPA is conducting detailed modeling of PCB fate,
transport, and bioaccumulation to support both human health and
ecological risk assessments from PCB exposures in the area.
AQUA TERRA supported EPA's efforts in this investigation by
developing the integrated modeling framework to address both current
conditions and projected impacts of alternative future conditions,
including a 'no-action' alternative and various remediation measures.
Since the study is designed to support EPA's regulatory decision-making
related to a major remediation effort, the production of
scientifically-defensible results is mandated.
The primary study area (PSA) extends from the confluence of the East
and West Branches of the River below Pittsfield, MA to the Woods Pond
Dam, a distance of approximately 10 miles; the contributing watershed
area extends an additional 24 miles downstream to the USGS gage at
Great Barrington, MA, with a total drainage area of 282 square miles. A
modeling framework was needed because no single model is capable of
representing all the physical, chemical, and biological processes
critical to PCB fate, transport, and bioaccumulation over the wide
range of spatial and temporal scales needed to address the
contamination issue. To support the exposure and risk assessment
efforts, the PCB modeling involves Total PCBs, and selected congeners.
AQUA TERRA Consultants directed the development of the initial
modeling framework design (MFD) involving three separate, but linked,
component models to represent the watershed loadings, hydrodynamics,
sediment transport, water quality and bioaccumulation processes needed
to analyze the historical and current PCB contamination in the
Housatonic River system. A team of modeling experts in these
disciplines was assembled to meet the challenges of the study. The
watershed analysis is being performed by AQUA TERRA using the U. S EPA
Hydrological Simulation Program - FORTRAN (HSPF); the results obtained
from using HSPF quantify the hydrologic and sediment source loadings
from the contributing watershed to the river segment. HydroQual will
perform instream modeling of sediment and PCB fate and transport using
the Environmental Fluid Dynamics Code (EFDC), and EVS Environmental
will use the outputs of the HSPF and EFDC models to simulate PCB
bioaccumulation and uptake using an aquatic food chain model FCM.
The project has demonstrated several innovative software tools and
capabilities designed and/or used by AQUA TERRA Consultants to
facilitate watershed modeling. Development of the watershed model
involved the use of the following modern computational techniques:
model segmentation, land use, soils-related parameters, and
precipitation patterns were developed \ characterized from a Geographic
Information System; the hydrology calibration was performed using an
"Expert Advisor" program designed for HSPF by the U.S. Geological
Survey and Visual Basic scripts to automate calibration output; The
Housatonic watershed model is operated by an interactive graphical
interface ("Scenario Generator") that facilitates simulation of the
calibrated model to represent a range of scenarios. The interface
includes a map of the basin and capabilities to modify the model
inputs, execute the model, and display graphical and statistical
results.
A pilot application on a test reach located in the primary study area was
performed to develop and test the model linkage components between and
among HSPF, EFDC and FCM. The pilot application produced a sound
methodology for linking the models. Concurrent with the hydrology and
sediment calibration for the entire watershed, AQUA TERRA is working
jointly with the other modeling groups to fully implement the linkage
of HSPF with the EFDC and FCM models. The linked modeling system will
be used to calibrate to current/historical conditions, assess
historical PCB accumulation over time, and project impacts of
alternative future conditions, including remediation needs and plans.
