The two-year saga of the Mill Creek “mystery pipe” was finally put to rest Tuesday when test results of a water sample from the pipe showed dramatically decreased levels of E. coli.
In March, the city tested water from the mystery pipe and levels were so high — as they have been for nearly two years of measuring — that they exceeded the parameters of the test. It hit the test’s maximum level of 2,419 organisms per 100 milliliters.
Tuesday’s test came back at just 387 organisms per 100 milliliter, out of the acute range, said Steve Byers, wastewater collections manager for The Dalles Public Works Department.
“I was surprised it slowed down so fast,” Byers said. Just the week before, a contractor had relined with hard plastic the interior of some 700 feet of cracked sewer main along Wright Street and Wright Drive. The $40,000 emergency repair job was the latest, and final, move in the city’s lengthy effort to find the source of the E. coli coming from the “mystery pipe,” which juts into Mill Creek behind a home in the 2500 block of Wright Drive.
E. coli itself is often harmless but is an indicator of fecal contamination in water. The city earlier this year posted the creek as being unsafe for swimming.
The city will do more testing until the E. coli level drops further, Byers said. “We haven’t really picked a number to get down to,” he said. But he knows that zero is unrealistic, because the creek has several sources of E. coli, including cattle and wild animals. In fact, the mystery pipe was discovered in August 2012 by the Wasco County Soil & Water Conservation District, which was studying sources of E. coli in the creek.
“We will monitor it until we know there’s nothing else connected to it and we have a clean line,” he said.
By federal standards, a level over 126 organisms per milliliter is considered a chronic level of E. coli. An acute level is 406 organisms.
City officials developed a theory that the mystery pipe was meant to dewater a natural spring in order to build homes on the hillside, and sewage was leaking from a failed system somewhere and was coming into contact with the natural springs and then flowing out the mystery pipe.
Officials dye-tested numerous homes and used a variety of measures — including metal detectors, scoping cameras, smoke, water witching and digging holes in a yard, a bare lot and the street — to trace the mystery pipe to its origins. They discovered the pipe went east from the creek about 160 feet, going under a house and then turned south under Wright Drive. It continued at least another 90 feet on Wright before officials were unable to trace it further.
But that spot 90 feet away led them to a house they initially thought was the problem. It turned out it wasn’t, and the city started looking at the sewer main in front of the house. They found three cracks that went around the circumference of the 10-inch main. The section of sewer main that was sliplined, or lined with hard plastic, is about 215 feet as the crow flies from the outfall of the mystery pipe, Byers said.
Before the main was repaired, crews put green dye in it and the dye appeared about 20 minutes later in the mystery pipe. After the repair, dye was put in the main, and it never showed up in the pipe, showing the repair worked.
The pipe has a steady stream of clear water flowing from it, which is consistent with it draining a natural spring.
While the mystery of the source of the E. coli coming from the pipe is solved, the origins of the mystery pipe itself are still just that.
“I still don’t know where that mystery pipe goes,” Byers said.