# EPA On-line Tools for Site Assessment Calculation

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#### Second lets use the plume diving calculator

The OnSite plume diving calculator simulates flow in a one-dimensional uniform aquifer. These are pretty restrictive assumptions, but the solution can give some idea of how much diving to expect from recharge. Knowledge of site stratigraphy is important to see how much diving might be caused by the geology. The calculator can help tell us how much to expect from recharge alone.

 Let's try the plume diving calculator and see what the predicted depth is at 450 feet based on recharge. The calculator provides three segments to allow different values for hydraulic conductivity and rates of recharge. First lets set the hydraulic conductivity to 215 ft/day for all three segments. Since there is vacant open land between the source and the first residence we'll set the first segment length to 100 feet with a recharge of 21 inches per year. The remainder of the site is a residential area with well maintained lawns. We'll set the length for the next two segments to 300 feet each and increase the recharge by 15 inches to account for lawn irrigation. We now have to specify the thickness of the saturated zone, the water table gradient and the location of our observation point. We know that the aquifer is about 65 feet thick so we'll set the Upgradient head at 65 feet. To calculate the head at the downgradient location simply multiply the combined length of the segments by the water table gradient and subtract from the upgradient head (65-(700 x 0.00194)) = 63.64. Now set the well location at 450 feet to show the depth of the plume at the distance of the second transect.

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