Location: Little Falls, New Jersey
Regulatory Program: Industrial Site Recovery Act (ISRA)
Duration: 1998 to 1999
Summary: Complex groundwater flow assessment in fractured rock
During previous employment, Mr. Peterson designed, implemented and managed a detailed investigation and natural attenuation applicability assessment for chlorinated solvent-impacted groundwater in the fractured basalt aquifer at this active metalworking facility.
At the inception of the project, the NJDEP case management team was insisting that deeper wells be installed in a chlorinated solvent “hot spot” area, to achieve vertical delineation. During a meeting and in subsequent correspondence, proposed Project Manager presented a conceptual site model which supported the conclusion that vertical migration had previously been exacerbated by well installation in the hot spot area. Based on this presentation, subsequent activities focused on evaluating vertical permeability contrasts and the vertical extent of the dissolved-phase plume at downgradient locations. Geologic characterization of the bedrock structure was completed via bedrock coring, with involvement of a geologist from the New Jersey Geological Survey.
Based on the geologic structure evaluation and demonstrated hydraulic properties of the bedrock unit, NJDEP agreed that delineation and natural attenuation monitoring would focus on the shallow bedrock zone, above a depth of 45 feet.
Another aspect of this project was the complexity of interpretation required in evaluating groundwater flow directions. Because a strong vertical hydraulic gradient component exists at the site, interpretation of the horizontal gradient component (for estimating flow direction) was strongly influenced by factors such as well completion depth, screen length and depth(s) of water-bearing fracture occurrence. The flow interpretation presented to NJDEP accounted for each of these influences and was accepted as the basis for selecting locations for offsite delineation and monitoring.