Improving the Conceptual Site Model with Mass Flux and Mass Discharge Calculations

Chlorinated ethenes and minerals spirits were released from underground storage tanks at a former paint factory north of New York City. The release was first noticed when an oily sheen was observed seeping into a river 300 feet downgradient of the factory in the 1990s. CDM Smith conducted a remedial investigation and feasibility study at the site. A key element of the remedial investigation was development of a robust conceptual site model (CSM) to support development of remedial alternatives in the feasibility study.

Due to the presence of a commuter railroad located between the facility and the river, groundwater characterization was limited to two transects of monitoring wells—one along the building and another along the river bank. Despite these limitations, the monitoring well configuration was sufficient to calculate mass discharge and mass flux of contaminants between the two transects. The calculations were used to clarify the CSM in three ways:  bound the uncertainty of contaminant mass under the railroad tracks, estimate the fate of contaminants in the plume between the source and the river, and estimate the mass of contaminants discharging to the river.

This presentation will discuss the design of the monitoring well transects at the source and the river bank, and the mass flux and mass discharge calculation methodology. The results and associated uncertainty of the analysis will be interpreted, focusing on how the results informed the CSM. The presentation will conclude with a discussion of how mass flux and mass discharge can be useful for the development of measurable and achievable remedial action objectives.