And regulators and stakeholders in Washington State have recently endorsed its full-scale use. Support through OST's Subsurface Contaminants Focus Area has helped fund ISRM's development by Pacific Northwest National Laboratory , resolve stakeholder and regulator concerns that threatened to delay the technology's use, and finance its first full-scale deployment at Hanford. As applied at Hanford's 100-D Area, ISRM is the injection of sodium dithionite into an underground aquifer to create a permeable, in situ treatment zone, through which groundwater passes as it feeds into the Columbia River. By controlling the redox state of chromium, sodium dithionite is lessening the mobility of chromium ions by causing them to sorb to neighboring soils and sediments, instead of being transported along with the groundwater. When chromium and other contaminants such as uranium and technetium emerge as wastes from various industrial processes, they are in an oxidized state.
Oxidized ions have a more positive valence resulting from the loss of electrons.
These ions with higher valences are dangerous because they are more toxic and more readily dissolved in and spread by migrating groundwater. At Hanford's 100-D Area, the introduction of the chemical sodium dithionite causes iron that is indigenous to the aquifer to become reduced, thereby producing more valence electrons. These ions with lower valences are much less toxic and sorb to nearby soils and are therefore less available to pollute the groundwater. During initial field testing of the technology at Hanford in 1997 and 1998, PNNL researchers placed five groundwater wells about 500 feet from the Columbia River to inject sodium dithionite into a well for approximately 10 hours. On reaching groundwater, the sodium dithionite reacted with iron in the ground and spread into a circle approximately 50 feet in diameter.