Environmental Contaminated Sediment Remediation and Ecological Restoration, Little Menomonee River

Moss American Superfund Site, Wisconsin

Soils, river sediments, and groundwater were contaminated with polycyclic aromatic hydrocarbons (PAHs) as a result of past operations at a former 23-acre creosoting facility where railroad ties and other wood products were treated.  Working closely with local, state and federal agencies at this Superfund site, Weston Solutions, Inc. (WESTON^®)  is managing site remediation and the relocation, realignment, and restoration of a 5-mile-long impacted stretch of the Little Menomonee River.

At the start of the project, WESTON delineated the contamination for soils, river sediments, and groundwater. Comprehensive biological and risk assessments, wetland delineations, habitat assessments, and threatened and endangered species surveys were conducted to determine the appropriate removal, treatment, and disposal options for contaminated soils, sediment, and debris. Scientists and engineers performed river, floodplain, and watershed hydraulics modeling to assess realignment alternatives, minimize floodplain and habitat impacts, and establish appropriate parameters for remedial system operations, stream relocation, floodplain restoration, maintenance, and long-term monitoring.

Site Design and Planning

In preparation for river remediation, WESTON led the characterization of the Little Menomonee River corridor. Hydraulic and hydrologic studies were performed to further define the river and its floodplain. This information was used to evaluate the potential impacts of alternate river alignments during design.

In preparing the conceptual design, WESTON reviewed ten years of site information, including Platte surveys, legal property descriptions, and tax records. WESTON prepared excavation plans, earthwork quantities and volumes, and engineering opinions with estimated probable costs, and associated documents for infrastructure design. WESTON prepared a remedial alternatives analysis and innovative, low-cost groundwater containment and in situ treatment plans. These plans became part of the site’s administrative record, supporting a Record of Decision amendment. Remedial costs will be reduced by several million dollars as a result of WESTON's strategic project management.

River Diversion and Erosion Control

WESTON diverted parts of the Little Menomonee River to take sediment samples in the riverbed. Cost-effective on-site immuno-assay analysis was conducted on soil samples from the proposed new river alignment. Design improvements for river realignment include leveling existing berms and creating meanders to control river flow velocity and improve habitat. To control flooding, WESTON created channels to direct overflow from the river to existing wetlands to be absorbed during storms.

For the five-mile section of the river, WESTON created erosion control plans and designed and constructed modifications to existing stormwater infrastructure. WESTON evaluated stormwater outfalls, ditches, piping, and associated conveyances to gauge potential impacts from inflow and address infrastructure design requirements.

WESTON has returned completed portions of realigned river to levels within .1 foot of original elevations. This degree of accuracy will reduce the risk for flooding neighboring properties or inadvertent hydrologic drawdown in nearby wetlands.

Technology Drives Modeling and Data Solutions

WESTON performed hydrologic and hydraulic modeling, including Log Pearson Analysis of flow data for gauged watersheds, and HEC2 modeling, calibration, and verification. Modeling included use of WESTON-developed software to perform calculations and generate hydrologic parameters from land use and soils data using ARCINFO, Geographic Information System (GIS), and dBase.

WESTON developed site- and compound-specific laboratory and field analytical procedures, and managed and processed samples and electronic data deliverables from laboratory results by loading files into data management software, Enviro Data®.  WESTON used Enviro Data^® to generate analytical data tables to determine the necessary cleanup levels in the riverbed. Data was then exported for use in GIS applications. WESTON implemented a phased and targeted sampling plan that greatly decreased the number of samples collected and analyzed.