Characterizing Contaminant Transport in a Dual Aquifer System with Intervening Vadose Zone for Remedy Selection

The hydrogeologic conditions at an EPA Superfund site involve both an overburden and bedrock aquifer impacted with VOCs. The overburden aquifer is a continuing source to the bedrock aquifer, which are separated by 30 to 40 feet of bedrock vadose zone. Fractured bedding plane partings extend above the saturated zone of bedrock aquifer to the base of the perched overburden aquifer. The understanding of the hydraulic relationship between the aquifers is paramount in developing an effective remedy.

A CSM was further developed by implementing a 72-hour pumping test. The objectives of the pumping test were to refine the existing bedrock hydrostratigraphic model, determine orientation and extent of pumping influences, identify the hydraulic connection between the bedrock and overburden aquifers, and define an appropriate remedy for the site.

Analysis of the pumping test data was performed through curve matching techniques in Aqtesolv, and visualization of head change over time. Further development of the CSM informed remedy design for commingled plumes from various stakeholders across this multiple property site. Validation of the new CSM included various communications with all stakeholders and modification to the regulatory framework, and will result in developing an appropriate groundwater remedy for both the bedrock and overburden aquifer.