Wastewater Treatment Plant Returns to Compliance

7/19/20

The discharge to the Columbia River from the City of The Dalles Wastewater Treatment Plant has returned to compliance with permit limits for E. coli as of July 19, 2020 at 5:18 a.m. The average of five samples taken throughout the day on July 18, 2020 at the City discharge point to the river were within limits. The delay in reading out the test results is due to the 24-hour incubation time that the test requires.

Recent Columbia River samples show that E. coli levels at the sample locations were well below bacterial criteria set by the Oregon Department of Environmental Quality for freshwater recreation.

Signs which were placed at locations of public river access on the Oregon shore of the Columbia River, to warn of contaminated water, were taken down this morning.

The Department is in communication with the Oregon Department of Environmental Quality and local health department officials to coordinate demobilization. Questions can be directed to the Public Works Department office at (541) 296-5401.

7/17/20

Operations at the City of The Dalles Wastewater Treatment Plant are improving but are not yet back in compliance after a recent plant upset that resulted in discharge to the Columbia River of treated wastewater exceeding the plant’s limit for E. coli.

A problem with the aeration system has been identified. Changes to the system have resulted in improvement. The City has added several loads of healthy biological process liquor to boost the treatment process. These measures are expected to restore the biological balance so that the plant can quickly return to normal operations.

The ultraviolet disinfection process remains ramped up to maximum capacity in an attempt to compensate for partially treated effluent due to the upset. Staff has increased the frequency of effluent sampling until E. coli counts are back within permit limits.

 On Wednesday July 15, 2020 samples were taken at pre-arranged locations in the Columbia River to determine the effect of the discharge on water quality in the river. Tests on five samples taken between River Mile 186.5 (Rocky Island, to the west of the Columbia Gorge Discovery Center) and 189.5 (City of The Dalles wastewater treatment plant outfall) show that E. coli levels at the sample locations were well below bacterial criteria set by the Oregon Department of Environmental Quality for freshwater recreation.

As a precaution, signs will remain in place at locations of public river access until the discharge from the wastewater treatment plant returns to compliance. Signs are posted on the Oregon shore of the Columbia River, from The Dalles Riverfront Park to West Mayer Park boat launch. The signs say: “Warning – Contaminated Water – No water contact” and give phone numbers to call for information.

The Department is in communication with the Oregon Department of Environmental Quality and local health department officials to coordinate response. Questions can be directed to the Public Works Department office at (541) 296-5401.

7/16/20

Operations at the City of The Dalles Wastewater Treatment Plant are not yet back in compliance after a recent plant upset that resulted in discharge to the Columbia River of treated wastewater exceeding the plant’s limit for E. coli. Wastewater treatment staff is working hard to restore the biological balance so that the plant can quickly return to normal operations.

The ultraviolet disinfection process has been ramped up to maximum capacity in an attempt to compensate for partially treated effluent due to the upset. Staff has increased the frequency of effluent sampling until E. coli counts are back within permit limits.

On Wednesday July 15, 2020 samples were taken at pre-arranged locations from the Columbia River to determine the effect of the discharge on water quality in the river. Five samples were collected between River Mile 186.5 (Rocky Island, to the west of the Columbia Gorge Discovery Center) and 189.5 (City of The Dalles wastewater treatment plant outfall). Processing of samples takes 24 hours. Therefore, test results will be available on Thursday July 16, 2020.  

As a precaution, signs will remain in place at locations of public river access until the discharge from the wastewater treatment plant returns to compliance. Signs are posted on the Oregon shore of the Columbia River, from The Dalles Riverfront Park to West Mayer Park boat launch. The signs say: “Warning – Contaminated Water – No water contact” and give phone numbers to call for information.

The Department is in communication with the Oregon Department of Environmental Quality and local health department officials to coordinate response. Questions can be directed to the Public Works Department office at (541) 296-5401.

7/15/20

The City of The Dalles Wastewater Treatment Plant has discharged effluent that exceeds the plant’s limit for E. coli due to incomplete disinfection. Sample test results read on the morning of July 13, 2020 indicated an E. coli exceedance. Several resamples in the following 24 hour period confirmed that the treatment process is not under control. The cause of the exceedance is an upset in biological processes. Rigorous water quality monitoring is ongoing.

The ultraviolet disinfection process has been ramped up to maximum capacity in an attempt to compensate for partially treated effluent due to the upset. Wastewater treatment staff is working hard to restore the biological balance so that the plant can quickly return to normal operations.

Staff has increased frequency of sampling until E. coli counts are back within permit limits. Samples will also be taken at pre-arranged locations in the river to provide data on the effect of the discharge on water quality in the river.

Signs will be placed at locations of public river access on the Oregon shore of the Columbia River, from The Dalles Riverfront Park to West Mayer Park boat launch. The signs say: “Warning – Contaminated Water – No water contact” and give phone numbers to call for information.

The Department is in communication with the Oregon Department of Environmental Quality and local health department officials to coordinate response. Questions can be directed to the Public Works Department office at (541) 296-5401.

For updates go to the City website thedalles.org

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