Abstract
The grain-size distribution of turbidity, water chemistry, and the size of fine particles associated with contaminants in turbid groundwater were investigated in existing monitoring wells. Groundwater monitoring wells are used in obtaining general information on groundwater quality and specific information on concentrations and specification of mobile contaminants in the vicinity of a monitoring well. This information is used in determining whether a given facility is currently in compliance with regulations. Turbidity (fine particles) are present in monitoring wells as a result of well installation in a stratum containing many fine particles (e.g., clay and silt) at a depth of less than GL-10m, well development, prior purging, sampling events, and natural colloidal transport and deposition over time. It is crucial that samples obtained from monitoring wells accurately reflect in situ mobile contaminant concentrations. The filtration of groundwater samples may remove both mobile fine particles/colloids and artifact particles. The most common groundwater purging method is to purge a monitoring well using bailers or pumps to remove 3 to 5 casing volumes to obtain formation water. In this paper, the concept and numerical formulas of a well-purging model are introduced and discussed. The calculation result shows that prepurging more than 3 casing volumes ensures a sampling of well water which is similar to formation water. The differences between filter pack and gravel pack (filter media #2 - #4) and the method of selecting the sizes of filter media were surveyed and discussed with the aim of installing a monitoring well in a stratum containing many fine particles.
