Using an appropriate bedrock investigation procedure for a coal tar-impacted fractured bedrock aquifer

Andrew Jay Coleman

Abstract

Traditional conventional isoplethic groundwater modelling approaches for manufactured gas plant sites tend to use finite-difference or finite-element models such as MODFLOW©, which can be expensive and somewhat unreliable in modelling groundwater in bedrock (Leake 1997). More innovative models that better address boundary conditions have been developed using a more sophisticated and multi-tiered modelling approach involving 3-dimensional flow, fractured bedrock flow, heterogeneous formation determination, and multi-layer stratified flow (FracMan© Software). Using a finite-element transport model coupled with an analytical element flow model, one can employ regional-scale modelling to provide a higher reliability than most traditional modelling approaches (Bradbury and Rothschild 1985; Risser and Barton 1995; Gburek 1999; Leake 2003; Mack 2003). Commonly, regional groundwater flow modelling is often perceived as impractical when using traditional numerical groundwater flow modelling software, due to the computer memory limitations and complexities in defining large, regional models. By further studying geological features of the bed-rock, biodegradation parameters, aquifer characteristics and chemicals of concern (COC), coupled with conventional transport information; the prediction of the flow of dense non-aqueous phase liquids in bedrock may be made possible (Shapiro 1989). By combining a regional flow model with some conventional conceptual modelling, a defensible argument to define a source area in bedrock can be established (McDonald and Harbaugh 1988; Risser and Powers 1995).

Key words:bedrock, coal tar, fracture analysis, groundwater modelling, MGP

© 2007 EPP Publications Ltd

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Article code 737