SIMULATIONS OF A NOVEL WELL DESIGN FOR REDUCING THE RISK OF ARSENIC CONTAMINATION

Arsenic in groundwater is a serious problem In New England , particularly in domestic wells drawing water from bedrock aquifers. The overlying glacial aquifers generally have low arsenic but are seldom used because they are more susceptible to water-level declines in dry periods and are more vulnerable to surface-sourced bacterial contamination. A new well system, specifically designed to be drought and bacteria resistant, could greatly reduce exposure to arsenic through drinking water. The well is installed horizontally in a trench within the glacial aquifer and has a large gravel pack. It is covered with low permeability material to prevent flow through disturbed material above the well. (Ayotte, 2015).

A series of hypothetical MODFLOW-NWT and MODPATH models were used to investigate the new well design and the potential exposure to arsenic while still providing an adequate water supply. The aquifer system was divided into two parts, an upper section representing the glacial aquifer and a lower section representing the bedrock aquifer. Multiple layers were used to simulate both sections. The location of the well, and a variety of hydraulic properties were systematically varied in a series of simulations. In each simulation, the number of flow paths passing through the bedrock aquifer and reaching the well was used to quantify the risk of arsenic contamination.

The greatest risk of arsenic contamination occurred when either there was natural upward flow from the bedrock aquifer because of the position of the well in the flow system or when there was a localized higher hydraulic conductivity in the bedrock near the well. Even in those cases, however, the risk of arsenic contamination was relatively small because less than 10% of the water entering the well passes through the bedrock aquifer.

Ayotte, J.D., 2015, Safe, directional, drought-resistant dug well (sddw), in United States Patent and Trademark Office: United States, no. 14/488,097.