Project Specifics

An active rail yard in Grand Rapids, Michigan has been used as a rail car storage and maintenance facility for the last 100 years. Diesel fuel impacts entered the subsurface during this period, resulting in 7.8 acres of light non-aqueous phase liquid (LNAPL) up to seven feet in thickness. Years of active LNAPL recovery had not sufficiently addressed underlying risks to potential environmental and human health receptors.

Geosyntec Scope of Services

The client retained Geosyntec to develop and implement a new risk-based strategy to evaluate actual risks resulting from the remaining LNAPL and to bring the site to closure. A high-resolution, multifaceted characterization strategy was developed to assess current risks and exposure pathways. Investigation work included: LNAPL delineation and characterization; evaluation of risks to direct contact, vapor intrusion, drinking water, and discharge to groundwater-surface water interface (GSI) pathways; installation and monitoring of off-site wells; assessment in seasonal variation in groundwater elevations and apparent LNAPL thicknesses; and natural attenuation evaluation.

The results and Conceptual Site Model (CSM) have been presented and shared with stakeholders via a web-based interactive map tool customized for the project. The webmap allows non-technical users to view the Site data on desktop or mobile devices; navigate around the Site and select data and base map layers to view; click on Site features to view associated data, charts, photographs, and documents; and annotate the map to share printouts or images to facilitate team discussions and analysis. The webmap is particularly useful given the complex and interconnected nature of the site investigation, reducing the need to develop many different figures to show combinations of data layers.

Notable Accomplishments

Geosyntec completed characterization of saturational and compositional LNAPL risks in accordance with State and Interstate Technology and Regulatory Council (ITRC) guidance, successfully demonstrating to Michigan Department of Environmental Quality (MDEQ) that natural source zone depletion (NSZD) is a viable option for closure. GSI characterization activities, including an evaluation of potential storm water impacts within a large MS4 drain, have shown the pathway to be incomplete.

Sharing the webmap with stakeholders has allowed for faster and clearer communication of Site data and will reduce project costs by eliminating the need for interim reports. The webmap presentation approach was well received by the MDEQ and was glowingly reviewed by the client.

Concurence on the completeness of risk characterization and a path to restricted site closure under the state Part 201 Program has been reached with MDEQ.

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