| The assessment of any site requires an investigation into the hydrology of the area. The hydrology will dictate how the assessment will proceed, and identify potential areas of contamination. The Piedmont area of the southeastern U.S. and the glaciated terrain of the northeastern U.S. consist of small localized watersheds, and do not include a regional groundwater system. Hydrological evaluations of these watersheds should include the identification of recharge/discharge areas, and the identification of all aquifers, their properties and relationships. A hydrological evaluation of a contaminated site near Danielsville, Georgia indicates that it lies on a ridge that is a recharge zone for the underlying fractured bedrock. The saprolite and bedrock lithologies are hydraulically connected, and respond to stress as a single aquifer. Small streams near the site are not flow/transport boundaries or discharge points, but a large creek further downgradient is a groundwater discharge point/contaminant transport boundary. Many properties of the fractures such as orientation, direction, aperture, and tortuosity were not known, therefore the area was modeled using an equivalent porous media approach (EPM) with average values for the fractured bedrock parameters. The extent of contaminant migration was underestimated, and the model was a poor predictor of future contaminant conditions. The EPM approach to modeling of fractured systems should not be used to determine extent of contaminant migration, but to determine cleanup goals, or the effects of a remediation system on hydrodynamic control of the plume. The contaminant values used in the modeling were collected using the micropurge method of groundwater sampling. This method results in low cost of purge water disposal because of low volumes, and low amounts of colloid material in the samples. The method assumes horizontal water flow from the formation into the well with minimal mixing of casing water. Packers should be used for long screened wells or fractured bedrock wells where screened intervals or open boreholes may span multiple zones of hydraulic conductivity (Puls et al., 1996). Comparison of the micropurge method and the packer method of groundwater sampling, indicate that formation water was not sampled when using the micropurge method. |
