Calculation and Use of First-Order Rate Constants for Monitored ...

Bulk Attenuation Rate (k) as a Function of Longitudinal Dispersivity (α α x)The figures below show the calculation of k for different dispersivity values as well as a resulting plot of bulk attenuation rate as afunction of longitudinal dispersivity. The transverse dispersivity (α y) was set to 10% of the longitudinal dispersivity (α x), the verticaldispersivity (α z) was set to 10% of the transverse dispersivity (α y), and t = 30 years. The slopes of the concentration vs. distance plotswere multiplied by the contaminant velocity to obtain bulk attenuation rates. This type of calculation assumes that the plume is atsteady-state. The figures below suggest that the bulk attenuation rate (k) increases as dispersivity increases.10 x = 3 ft, y = 10.2 e -0.00058xConcentration (mg/L)5 x = 10 ft, y = 8.7 e -0.0011x x = 30 ft, y = 6.6 e -0.0014x x = 100 ft, y = 4.7 e -0.0020x00 200 400 600 800 1000 1200Distance from Source (ft)0.25Bulk rate ( k per year)0.20.150.10.0500 20 40 60 80 100 120 xfeet16