Fifty years of defense production has resulted in significant subsurface contamination at the Department of Energy's Hanford Site. An estimated 450 billion galls of liquid waste, some containing radionuclides and hazardous chemicals, have been released to the ground at Hanford since 1944. Much of the contamination remains above the groundwater in the vadose zone, the region between the land surface and underlying groundwater, but some has reached Hanford's groundwater. The Richarland Operations Office estimated that 80 square miles of Hanford's ground water had contaminated levels greated than Federal and State drinking water standards. Although groundwater at Hanford is not a primary source of drinking water, it does eventually flow into the Columbia River, a major drinking water source for a significant section of the Northwest.