2011 Ground Water Summit and 2011 Ground Water Protection Council Spring Meeting

Groundwater Flow Modeling to Support Remediation of Riverbed Sediments

Monday, May 2, 2011: 2:30 p.m.
Constellation D (Hyatt Regency Baltimore on the Inner Harbor)
Loren North, PG, ARCADIS;
Gaston Leone, PE, ARCADIS U.S. Inc.;
David S. Lipson, Ph.D., PG, ARCADIS U.S. Inc.;

Phase I of the Lower Passaic River Removal Project requires removal of 40,000 cubic yards of dioxin-impacted sediment from an area of the tidally influenced Passaic River located immediately adjacent to the Diamond Alkali Superfund Site (DASS). The DASS has a remedy installed consisting of pumping and treating shallow groundwater inside a containment unit consisting of a cap, a floodwall, and slurry wall surrounding the site. The impacted riverbed sediments adjacent to the site are targeted for removal, with excavation of the sediments isolated inside a sheet pile wall enclosure.

 A groundwater flow model was developed to support the remedy implementation including providing a better understanding the potential impacts of the proposed temporary sheet pile wall enclosure on the upland site and groundwater extraction system, and estimating the water needed to be added to maintain the enclosure operating elevation. The groundwater flow model consisted of five layers and simulated the river adjacent to the site, the extraction system, the slurry wall, and existing floodwall. Data collection efforts to support the flow model construction and calibration consisted of a tidal study, monitoring site water levels while the pump and treat system was shut down and restarted, and short-duration single well pumping tests. These data were analyzed and used to estimate hydraulic parameters and for model calibration.

 This case study illustrates the advantages of collecting high frequency data and multiple types of hydraulic information to improve the site conceptual model. It also outlines an approach for considering these data in the model building and calibration process. Results from this model were useful in supporting design team decisions regarding installation of an additional sheet pile wall as part of the enclosure as well as other pertinent design features related to the groundwater-surface water interactions anticipated during the sediment excavation.