Summary

The 2010 Bethpage groundwater-flow model (ARCADIS, 2010) was based on a steady state assumption. Although it is widely acknowledged that significant water-level changes have occurred in the past, the reviewed model does not represent changing water levels. The steady state approach limits the effectiveness of the following:

1. identification of sources of contamination,

2. analysis of model accuracy,

3. model calibration, and

4. simulations of future scenarios.

Future plume movement was simulated in an incomplete manner through an unchanging groundwater-flow field. Available time-series information on temporal variation of factors affecting groundwater-flow dynamics includes:

1. public-supply pumping,

2. groundwater discharges from systems remediating volatile organic compound (VOC) plumes,

3. recharge and precipitation rates, and

4. water levels and streamflows.

Transient phenomena that might be useful in future hypothetical simulations include pumping variations, redirection of containment-system waters for industrial use, and climate-change scenarios. Public-domain computer programs, U.S. Geological Survey guidance reports on transient-state calibration and uncertainty methods (Doherty and Hunt, 2010), and additional local and regional datasets are available to provide additional confidence in model evaluations and allow better evaluation of
their limitations.

First posted June 13, 2011