City Engineers to Conduct Dye Test in Colorado River; Color May be Visible

Test will advance the protection of recreational opportunities, water quality,
and aquatic species in our community

Diffuser2On Monday, March 11, if you notice a greenish color in the Colorado River, it is not an early St. Patrick’s Day prank, it is simply a test of a recently completed diffuser improvement project being conducted by the City of Grand Junction at the Persigo Wastewater Treatment Plant.

The test, which will be conducted at approximately 10:30 a.m., will involve pouring several gallons of environmentally friendly colored dye into the diffuser and observing how the effluent (the stream of treated water) mixes when it enters the Colorado River. A drone will fly over the dyed area to gather video evidence of proper mixing.

The colored dye does not pose a threat to the environment or public health, but it will be visible to the public for a short period and may briefly change the color of the Colorado River downstream of the Persigo Plant, which is located between Grand Junction and Fruita.


The test is required by the Colorado Department of Public Health and Environment (CDPHE) as part of the recent completion of the Diffuser Outfall Improvement Project, which has been underway since October 2018. The project, which was constructed by Grand Junction’s United Companies, was completed for $5,123,502 and was paid for by Persigo capital improvement funds.

In 2017, CDPHE implemented more stringent regulations related to the discharge of effluent from wastewater treatment facilities. Up to this time, the discharge point for treated wastewater from the Persigo Plant had always been the Persigo Wash. Under the new regulations, this discharge location would no longer be permitted. As a result, the City pursued the construction of a diffuser making it possible to discharge directly into the Colorado River to meet the new regulations.

The Persigo diffuser is a 67-foot long, 54-inch diameter pipe manifold with a series of 17 rubber valves that discharges the treated wastewater effluent from Persigo into the Colorado River providing instantaneous mixing with the river water.

Contact:  Sam Rainguet, Communications Manager   970-244-1507 or

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