Although larger well spacing slows remediation, ISTD is so fast that wider well spacing is favored, because the cost of constructing the site is reduced with the square of the well spacing. Figure 2 Temperature after 80 Days Figure 2 shows the temperature that will be achieved in the project after 80 days of heating. There are four major classes of destruction reactions. The reactions in ISTD are analogous to those that take place during in situ combustion or pyrolysis of petroleum. Combustion does not actually occur in ISTD because the concentration of fuel is not high where the flux of air is significant, e.g., at the heater-vacuum well.
Most decomposition takes place throughout the heated soil matrix and in the very hot vapors.
Other reactions that occur are similar to pyrolysis, coking and steam reforming reactions, which are used in chemical plants and refineries to form olefins, coke and carbon oxides. The steam reforming reactions that form carbon oxides are the same reactions used to make town gas at the site. Figure 3 Mole Fractions in ISTD Figure 3 compares the mole fractions of steam, air and PAHs that are predicted to be produced. Moreover, water is being removed from the site. This steam bank prevents air infiltration into the site.