REMEDIATION OF AQUIFERS WITH OXIDANT BEARING SODIUM SILICATE SOLUTIONS/GELS

Sodium silicate solutions are envisioned as a media for delivering oxidants into aquifers contaminated by TCE and PCE. There are two areas targeted for remediation: 1) contaminated clay rich lenses, which pose a problem for aquifer remediation because of slow re- diffusion of the contaminants back into the aquifer system, 2) large, deep, dilute contaminant plumes in the permeable zones of the aquifer. The sodium silicate solutions can gel after being injected into the targeted areas by lowering pH. Permanganate bearing silicate solutions can be injected into coarse grained media above clay lenses. When gelling is complete, contaminants in the targeted clay lenses are trapped and thus contaminants could be prevented from back-diffusion into the aquifer. Furthermore, permanganate diffuses out of the silicate solution/gel and into targeted areas, oxidizing the contaminants within the clay lenses. In order to target large, deep dilute plumes, sodium silicates can be injected into a coarser grained media. Due to differences in density permanganate mixes with the groundwater creating barriers of oxidants along the pathway followed by the plume. We performed a small flow tank experiment where we injected permanganate silicate solutions into the targeted areas. The experiment consisted of a small (39.5x8.0x19.5 in.) tank connected to a water pump creating ambient flow through the tank. A permeability structure was created composed of glass beads [ .65mm median size (coarse), .15 mm median size (fine)] and a clay lens at the bottom. The KMnO₄ bearing silicate solutions gelled within four hours above the clay lens, and in one hour within the coarse lens. Permanganate diffusion into the clay lenses and aquifer was observed. Injection into a coarse grained lens produced a barrier of permanganate that diffused from the lens into finer grained media. These large “fingers” of oxidants formed by differences in density proved to be an excellent mixing mechanism for oxidants with the contaminated porewater.