Integration of Physical Hydrogeologic Data to Enhance the Performance of an In Situ Denitrification System in a Heterogeneous Aquifer

Spatial and temporal variability in groundwater velocity and contaminant mass flux significantly influence the design and performance of in situ remedial strategies. In this paper, the efficacy of an acetate cross-injection system (CIS) designed to stimulate in situ denitrification in an aquifer servicing an urban community in southern Ontario is examined.  Core logging, grain size analysis, slug testing, borehole flowmeter testing, PVP velocity measurements, and tracer testing were used to quantify the physical properties of the target aquifer.  A conceptual model was used to integrate the various field data sets in order to develop a 3D numerical model of the site, calibrated with tracer tests, which provided insight into the performance characteristics of the denitrification system and informed monitoring protocols. The physical data indicated that the aquifer comprises a variably conductive multi-layered system, with hydraulic conductivity (K) values ranging over nearly four orders of magnitude.  The integrated data suggested that the aquifer could be reasonably described with 5 to 6 layers of varying K.  A strong qualitative correspondence between physical hydrogeology and denitrification intensity was observed at the site, with higher velocity zones exhibiting the highest apparent denitrification rates.  The enhanced understanding of variable groundwater velocity and contaminant mass flux permitted depth-selective acetate pulsing intervals to be identified, leading to a more effective remedial strategy for the site