Tuesday, April 21, 2009: 4:10 p.m.
Joshua Tree (Hilton Tucson El Conquistador Golf & Tennis Resort )
Assessing risk of contamination to proposed public supply wells in heavily developed urban areas is a difficult and complicated task, particularly if the wells are screened hundreds of feet below the water table and the flow field has varied over time. Under these conditions, the recharge area to each proposed supply well may span a large area, encompassing hundreds of potential sources of contamination to the groundwater. Depending on the details of each source, public supply wells sited in seemingly equivalent locations, with respect to predicted water quality, may yield vastly different water quality. A modeling methodology has been developed to guide the site selection process for new supply wells, predict water quality at each well, and provide input to sizing and selection of treatment units.
For a client looking to site more than ten new public supply wells in a vast, developed urban area, a groundwater model was used to determine which potential sites were most likely to yield good water quality. Simulated transient flow fields (both historic and projected) were used with GIS coverages of documented potential sources (100s) of contamination to the groundwater to determine which sources posed the most significant risk (10s) to each proposed well by advection only. Each of these sources was then queried for more information regarding on-site concentrations, remedial activity, etc., and simulated again, yielding predicted concentrations of multiple constituents at each proposed well site. Risk scores, which incorporated the simulated potency of the sources impacting each well and the quality of data received regarding each source were assigned to each well/site. This methodology was necessary to efficiently parse the immense number of potential sources, account for the temporal variations in groundwater flow and contaminant movement over time, and determine the level of treatment needed for multiple iterations of future pumping options.
For a client looking to site more than ten new public supply wells in a vast, developed urban area, a groundwater model was used to determine which potential sites were most likely to yield good water quality. Simulated transient flow fields (both historic and projected) were used with GIS coverages of documented potential sources (100s) of contamination to the groundwater to determine which sources posed the most significant risk (10s) to each proposed well by advection only. Each of these sources was then queried for more information regarding on-site concentrations, remedial activity, etc., and simulated again, yielding predicted concentrations of multiple constituents at each proposed well site. Risk scores, which incorporated the simulated potency of the sources impacting each well and the quality of data received regarding each source were assigned to each well/site. This methodology was necessary to efficiently parse the immense number of potential sources, account for the temporal variations in groundwater flow and contaminant movement over time, and determine the level of treatment needed for multiple iterations of future pumping options.