To run the applet, we recommend you have at least a Pentium 200 MHz with 32 MB RAM. You will also need to use a browser that will run Java. Alternatively, if you have Java on your own machine, the applet will run faster if you download the programs.
The applet on this web page can be used for NAPL invasion into either homogeneous or heterogeneous aquifers. For a homogeneous aquifer, choose a sticking probability between 0 and 1 or choose a range of sticking probabilities. If you choose a range, the model will select randomly from the range given. For a heterogeneous aquifer, you may "draw a medium", i.e., draw a soil profile consisting of lenses of different soils. Then choose a sticking probability for each "lens". The value of the sticking probability is a function of many factors but generally increases as the permeability increases for DNAPLs that are less viscous than water (see the worksheet to calculate sticking probabilities). As the sticking probability increases, the front becomes more ramified. As the sticking probability decreases, the front becomes more compact. Be forewarned that you will be waiting longer if you choose a low sticking probability because more particles must be released for each one that sticks. DLA has a sticking probability of 1. DLA models displacement of a viscous fluid by a nonviscous fluid in a hele-shaw model. Thus, invasion pathways for DLA are very fingered.
To get started, click on "run applet" and then click "demo" or try to duplicate one of the pictures above. For example, set the probability to 0.6 and you should get a very fingered front such as that shown in figure 1d(overview). Next try a heterogeneous example. Select "Draw Medium" and draw any number of boxes to represent different lenses. Then choose different sticking probabilities for each color. Don't choose a sticking probability less than about 0.02. Remember, the lower the sticking probability, the slower the program will run. Now press "start" and you will see the DNAPL invade the aquifer at the center top of the profile. When it reaches the bottom, the program will stop. Go back and draw another medium or try different sticking probabilities. After you have some experience with the program, go to the worksheet and calculate sticking probabilities for your NAPL and soil profile.
If you are interested in more of the background, see the linked paper by Trantham and Durnford, 1999. This web page is a work-in-progress, so if you find any problems, please email me at firstname.lastname@example.org.
To toggle the applet into draw mode, click the 'draw medium' button. This will empty the random fields. Once in draw mode, select a color and draw in the canvas. When the desired medium is complete, click start.