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RISC User's Manual Version 4 0 i ay =a= , a= = ay (B-7) T� TZ where Tl and T2 are assumed to have a mean value of 3 and 87, respectively, based on field data If the user chooses to have RISC calculate the disperstvtties, then the values of Tp and T2 are assumed to be equal to 3 and 87 respectively 5B3�ESTIIAAMAG'THE CONCENTRATION K'THE WELD The concentration in the well is estimated by vertically averaging the estimated concentrations over the"screened interval" of the well The user specifies the distance downgradient from the downgradient edge of the source to the exposure point location (possibly a well screen) A distance off the centerline may also be entered To estimate the concentration on the centerline of the plume, this value should be left at zero The code will always predict the highest concentrations to be along the ccnterlme of the plume because it assumes a uniform flow field The depth to the top and bottom of the well screen measured from the water table (not ground surface) must be specified The code will calculate concentrations in the groundwater at the top and bottom of the well screen at a minimum The user may increase the number of points used to average the concentration across the well screen A minimum of two averaging points must be specified in the input, i e the output will be an average of the concentrations at the top and bottom of the well screen If more than two points are used, the averaging points are assumed to be located at equal intervals (= n-1 intervals, where n=number of points)with one point at the top of the well screen and one at the bottom The concentrations at the top and bottom of the well screen are weighted at 112 the value of the concentrations at the other points The maximum number of averaging points is ten Figure B-2 shows a schematic with three averaging points as an example i B-6