SESSION I-6. BIOSCREEN MODEL
BIOSCREEN is an EXCEL spreadsheet model which simulates the migration of a dissolved contaminant plume as it moves down-gradient from a defined source area. The model is public domain software, developed for the Air Force Center for Environmental Excellence (AFCEE) Technology Transfer Division at Brooks Air Force Base by Groundwater Services, Inc. Houston TX. It can be downloaded directly from http://www.epa.gov/ada/csmos/models/bioscrn.html
As you will see the BIOSCREEN model incorporates many concepts presented in previous Module I sessions including NAPL dissolution in the source zone, advection, dispersion, retardation and biodegradation of dissolved organic contaminants as the migrate down gradient from the source area. BIOSCREEN is ideally suited for evaluating Monitored Natural Attenuation as a potential remediation strategy.
It is important to note that the flow field in the BIOSCREEN model is one-dimensional (i.e. ground water flow velocity is one dimensional). However the contaminant plume, which emanates from a source zone of fixed dimensions, is actually modeled in three dimensions by considering dispersion in the longitudinal, transverse and vertical directions.
Reading Assignment. Refer to page 367 (Wiedemeier) to section 8.3 titled Governing Equations for Contaminant Fate and Transport. Examine Equations 8.1 –8.6. Note that the analytical solution for Equation 8.4 is the basis for the BIOCREEN model. Look at the definition of the variables and parameters in Equation 8.4 and note that the terms in the equation include the transport processes of advection, dispersion (three dimensional), sorption and biodegradation (first order).
To further prepare to use the BIOSCREEN Model refer to page 380. Read the section on Three Dimensional Analytical Models. This section discusses the Domenico, 1987 solution to Equation 8.4 (note misprint in Wiedemeier says Equation 8.5). Equation 8.4 is the three-dimensional partial differential equation describing transient solute (dissolved contaminant) transport with advection, dispersion, sorption and first-order biodegradation in saturated ground water flow. The analytical solutions for transient and steady state conditions are given by Equations 8.23 and 8.24. Continue reading page 382-385 to gain further insight into the features of BIOSCREEN. A good summary is given by Figure 8.4. Finally please carefully read the section entitled “Decaying Source term”, pg 383 – 386. This will be very helpful in understanding how BIOSCREEN handles the initial concentration of dissolved contaminant emanating from the source zone.
The material on pages 387 – 394 provides background for the BIOSCREEN model which will become more useful after you have become familiar with the model. In particular, the discussion of “Instantaneous reaction kinetics” can be skipped over for now. We will take this topic up in module II. For now please concentrate on the BIOSCREEN Example discussed below.
BIOSCREEN Example. Refer to pages 395-402 for a detailed example of applying the BIOSCREEN Model to a BTEX release at Keesler Air Force Base. At this point it will be helpful to load you version of the BIOSCREEN which will display the Keesler Air Force Base data file by default. Please take some time here and look over the BIOSCREEN Users manual Version 1.3, provided on your course CD. Familiarize yourself with the Table of Contents and note that detailed sections are provided for BIOSCREEN Data Entry, Analyzing BIOSCREEN Output, and BIOSCREEN Trouble Shooting
Written Assignment: Questions I-29 through I-31.