Groundwater Flow Modeling

Groundwater contaminant plumes are delineated in the Monahne River alluvial aquifer and in the underlying confined aquifer as shown in Figure 17.1. The two aquifers are separated by a low-permeable, discontinuous silty clay layer (see Figure 17.2). Hydrogeologic assessment indicates that the contamination from the upper, unconfined aquifer enters the lower aquifer through the ‘‘window’’ in the silty clay layer due to the difference in hydraulic heads in the two aquifers. Develop a groundwater modeling concept and a model that will be used in the design of a well extraction system for containment of the two plumes. Hydraulic conductiv- ities of the upper and lower aquifers, as determined from slug tests, are 2.6 104 and 3.4 103 m=s, respectively. Hydraulic conductivity of the confining silty clay layer, determined in the laboratory from Shelby tube samples, is 6.5 107 m=s. Average annual recharge rate in the alluvial aquifer is estimated at 2.5 109 m=s, which corresponds to 12% of the gross annual precipitation in the area (660 mm).