The Relationship Between Monitoring Well and Aquifer Solute Concentrations

Disparities between organic solute concentration in the aquifer and that in monitoring wells have been observed; an order of magnitude disparity had been recorded in some cases. Therefore, it is important to be able to relate concentrations between the two media for design of remediation systems. More significantly, to assess the impact of leachate from a landfill on a downgradient drinking water well, it is important to correlate aquifer concentration with that in a drinking water well such that the true risk is properly estimated. A three‐dimensional finite‐difference flow and transport model has been applied to demonstrate that the disparity between aquifer and well concentrations results primarily from advective flow phenomena and can be quantified. The modeling shows that the concentration in the well is a function of the initial vertical concentration profile in the aquifer, the volumetric flow rate from below the partially penetrated well, the penetration fraction, and the amount of water purged before sampling. Under steady‐state conditions, the dilution of concentrations in monitoring wells may be expressed as a simple analytic function of the above parameters. The result from this analytic function agrees well with numerical solutions and field sampling data.