Over the past few years water seepage through the gravel foundation of Twin Buttes Dam at San Angelo, Texas, has increased far beyond original expectations. The rate of loss is estimated to have reached 3 million gallons per day, endangering the quality of drinking water from Lake Nasworthy just downstream of the dam because of increased levels of dissolved salts. The U. S. Bureau of Reclamation has studied ways to seal the dam foundation, which is a porous conglomerate. The cemented but porous gravel layer lies on top of the formation rock. The Bureau decided on pressure grouting but emphasized the need for new approaches that are more effective and efficient. Test Drilling Service Company of Maryland Heights, Missouri, won the bid for the first of three section of the 8 mile long dam crest by planning to use new grouting methods and efficient drilling equipment. The company's bid was not only 33 percent lower than the Bureau of Reclamation's estimated cost but the projected time for job completion was 160 days versus the Bureau's figure of 260. The effectiveness of the grout curtain still remains to be determined. Changes are expected to become apparent in the water flow downstream of the dam- where the huge water loss had not only boosted the hardness of water in Lake Nasworthy but also raised a threat to San Angelo's Mathis Airport.