Running BIOSCREEN and BUSTR-Screen Data in AT123D

SEVIEW can now be used to run BIOSCREEN and BUSTR-Screen simulations in AT123D. Although these models use almost identical input parameters the resulting groundwater concentrations typically differ by one to three orders of magnitude. This means that you can significantly reduce your remediation costs just by using AT123D.

This doesn't mean that BIOSCREEN and BUSTR-Screen are the more conservative models. Although BIOSCREEN and BUSTR-Screen produce higher downgradient concentrations it often takes significantly longer to reach them. For example according to BIOSCREEN it would take MTBE in a silty aquifer 245 years to reach the maximum concentration at a point 350 feet downgradient. While AT123D predicts it would take only 94 years. There are several reasons for this but, the principal reasons are associated with contaminant load and the processes used to simulate contaminant transport.

Groundwater contamination typically exists as a three dimensional plume consisting of a width, breadth, and depth. However, BIOSCREEN and BUSTR-Screen only use the depth and width perpendicular to groundwater flow. The third dimension along the x-axis is assumed to be infinite (Figure 1). This was not done because it is difficult to establish the x-axis distance in the field. Nor was it done because it is conservative. Instead it was done to improve computational speed. Contaminant load in AT123D is established in all three dimensions.

BIOSCREEN and BUSTR-Screen

AT123D

Analytical models like AT123D, BIOSCREEN and BUSTR-Screen use mathematical equations to simulate transport and fate processes. Common transport and fate processes include advection, dispersion, diffusion, adsorption and biological decay. Diffusion is the process by which contamination migrates from areas of higher concentration to areas of lower concentration even if there is no groundwater flow (Figure 2). Although not considered an important transport process in sand and gravel aquifers it can become the dominant process in silts and clays. However, BIOSCREEN and BUSTR-Screen do not simulate the diffusion process. This process was not left out because it is conservative to do so. In fact leaving it out actually reduces the rate of contaminant migration. Nor was it left out because it is difficult to find chemical diffusion values. It was left out simply to improve performance.

Figure 2
Chemical Diffusion

The BIOSCREEN and BUSTR-Screen programs simplified modeling to the point where anyone could do it, however the speed and ease of use came at a price. BIOSCREEN was released in 1996 and was designed to run on a PC unlike traditional models which were designed to run on mainframe computers. Of course by the mid 90's PC versions of AT123D and other mainframe models were available. Still these models were not as easy as BIOSCREEN to use and often took hours or days to run on a PC.

Today's powerful computers have improved the performance of AT123D to the point where it often takes only a few seconds to run. However, it was still difficult to setup. SEVIEW provides the next step by using the familiar BIOSCREEN and BUSTR-Screen interfaces to run AT123D. Finally making AT123D just as easy to setup and run. Using AT123D provides greater confidence in the results as the model was designed to be used over a wider range of conditions.

Simply download and install SEVIEW, then open BIOSCREEN or BUSTR-Screen and run AT123D. All you need to do is enter the x-axis coordinate of the release and the water diffusion coefficient. You can locate the water diffusion coefficient in the SEVIEW chemical database or even have SEVIEW look it up for you. Remember don't be surprised if the AT123D results are orders of magnitude different.