Fort Morgan officials are investigating mysterious surges of some sort of contaminant in the city's wastewater treatment plant.

Water Resources Director Gary Dreessen told the Fort Morgan City Council on Tuesday about the episodes, providing a chart of one such incident on Sunday night that showed "a huge spike in the total suspended solids" in the effluent from the treatment plant.

The TSS is essentially a measurement of the "dirt" remaining in the treated wastewater after it passes through the plant, Dreessen said.

While the city's limit for TSS is 30 milligrams per liter, and the plant's discharge is normally well below 10, the spike on Sunday night reached more than 100 mg/l, Dreessen said in an interview Wednesday.

The surges have been happening periodically over the last couple of months, usually at night, he said.

City officials are trying to determine what is in the wastewater stream and where it's coming from.

Dreessen said he has contacted the city's wastewater consultant and state officials, and both believe that "we're being hit by something," he said - meaning that someone is putting a large amount of an unknown substance into the sewer system.

"It's probably not residential," he said. "It must be a pretty big volume or very potent, whatever it is - we're not sure."

The city has been placing samplers into the system at various points in an effort to isolate the location of the source of the contaminant.

"We do that by eliminating sections of town, and just working up the ladder," he said. "Once we find it, we'll take a sample and then we'll test it. It's intermittent, so that's why it's so hard to track down. The plant will go good for a couple of days, then all of a sudden, bam."

The extent of the city sewer system also makes it hard to determine when the substance is actually being put into the system, Dreessen said.

Something entering the sewer from the farthest reaches of the system could take five or six hours to reach the treatment plant, he said, and Log Lane Village is also on the system and even farther away. Also, the spikes are being seen in the plant's "final clarifier," he said, and something entering the plant at a given time may not show up there until 24 hours later.

The spikes have caused the city treatment plant to violate its discharge permit in several areas, Dreessen said, and if it violates what is known as a "WET" test - a quarterly test measuring "whole effluent toxicity" and costing $850 per test - the problem could quickly get expensive.

"If you fail that, you have to go through a bunch of tests to prove the toxic substance is gone," he said. "If we have to do a bunch of tests at $850 each, that runs into a significant amount of money in a hurry."

Those costs, Dreessen pointed out, are borne by all users of the city sewer service.

"This costs everybody - everybody has to pay for it," he said. "The wastewater fund is an enterprise fund, so if our costs go up it gets passed to the ratepayers."

Dreessen said all treatment plants experience fluctuations, but the unusual things about these is how quickly they go up and come back down.

"It skyrockets and then drops like a rock - it's not normal," he said. "When a plant goes bad or operators are screwing up, it'll go up ... and stay there for few days while you adjust. This goes straight up and straight down. It's like you getting sick - you don't get sick all at once and then all of a sudden you get better."

Dreessen told the council Tuesday that he was bringing up the matter to request that whoever is causing the problem stop whatever they're doing.

"If somebody has doubts, if they don't know whether they're causing it, call us - we'll work with them, we just want to find it," he said. "But if we catch you then we're going to work with you, too."

Dreessen also told the council that a leak has been found in the water pipeline from the city's water source at Carter Lake to Fort Morgan, and the line will be shut down on March 16-17 for repairs to the leak near Longmont.

The city has been filling its storage tanks in preparation for the shutdown, he said, so there should be no impact on city water service.