Sewage Flows into River after Line Test Goes Awry by Mike Conway The Modesto Bee - July 28, 2000 A sewer line serving Yosemite National Park plugged up during a test and spilled sewage into the Merced River early Thursday. Downstream users of the river, from campers to the utility district that supplies Mariposa with some of its water, were advised to stay away from the waterway. The 16-inch pipe got clogged with sand and debris. Sewage gushed out of a manhole near the park's waste-water treatment plant in El Portal, according to park spokesman Scott Gediman. It is unknown how many gallons of sewage were dumped into the river. Gediman said popular swimming and camping spots along the river have been posted with warnings about staying out of the water. The posted area stretches from the plant to about four miles downstream. Gediman said officials expected the waste to be diluted to safe levels by today. "It was felt it was smart to keep people out of the river until enough time has passed that the impact of the spill was gone," said Dr. Charles Mosher, public health director for Mariposa County. "For the moment, any health risk has been taken care of. Now it's just a matter of figuring out how it happened and how to prevent it in the future." Mosher said the Mariposa Public Utility District wasn't pumping river water at the time of the spill. The Merced River is just one of the sources of drinking water for the community of Mariposa. "The initial calculations look like the water would be safe in eight to nine hours," Mosher said Thursday. "We'll be conservative and look at 24 hours before pumping again." The sewer line, which serves Yosemite Valley, runs along Highway 140 to a treatment plant on Foresta Road in El Portal. The line was rebuilt and completed earlier this year when crews reconstructed Highway 140 where it enters the park. Gediman said the line was tested beginning at 11 p.m. Wednesday until about 5:30 a.m. Thursday, when the sewage leak was discovered. During the test, approximately 300,000 gallons of sewage and water were pumped through to mimic a peak-flow situation. Gediman said most of the substance in the test was water, not sewage. "This was to test the integrity of the system and to see if it would perform at maximum use," Gediman said. "It did perform fine." After the clog was discovered, crews removed the debris and flushed the sewer line. The river water is being tested by park and state Regional Water Quality Control Board staff to measure bacteria levels and compare them with water samples upstream from the plant. "With the length of the river, it's felt the sewage will dissipate through natural processes," Gediman said. "As much as we hate to see this happen, there doesn't seem to be any long-term damage to the river," he said.