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A pipeline break last week near Montezuma Creek in Utah's southeast corner leaked a small amount of oil into the San Juan River.

A tumbling boulder, loosened by recent rains Thursday, ruptured a flow line serving a well in the aging Aneth oil field, operated by Denver-based Resolute Natural Resources, according to a report posted on the Utah Department of Environmental Quality's spill database.

The operator shut down the well, capable of producing 34 barrels a day, once the leak was discovered, but by then three to five barrels escaped into a wash, the report said.

A rainstorm flushed the oil two miles to the San Juan, said Walt Baker, director of the Utah Division of Water Quality.

The company deployed booms on the wash and captured oil before it reached the river, a major tributary to the Colorado and an important water source, according to David Ariotti, a DEQ district engineer.

"They had equipment on site and were already 60 percent done with the cleanup when I got there," Ariotti said. "I didn't observe any impact on the river or near the river."

As a precaution, company crews also used absorbents and a containment booms several miles downstream at Sand Island, but no oil was captured there, although the DEQ spill report said a "rainbow sheen" was observed on the water.

Ariotti gathered water samples from the river to test for the presence of hydrocarbon pollution. Those results are not yet back.

The day before the Montezuma Creek spill, Aug. 13, another pipeline rupture near Bluff discharged 200 barrels of oil about 1,000 feet from the river, according to an earlier report posted on the DEQ database. Running Horse Pipeline Co., a firm belonging to the Navajo Nation, operates the 16-inch line. Contractors vacuumed most of the crude, which migrated toward the San Juan, but did not enter the water, the report said.