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Deep Dive: Leaking sewage lagoon in McCall prompts questions on algae blooms. But water managers say it isn’t the cause


For more than a decade, the McCall water storage facility off of Deinhard Ln. has been leaking.

Treated effluent is making its way into the Payette River, upstream from the Cascade Reservoir. But water managers say the leak isn’t a direct cause of a harmful algae bloom on the reservoir this summer – or in years past.

A history of failed tests

The Payette Lakes Recreation Water and Sewer District has owned and operated the water storage facility for the past five years following a 2017 election that resulted in the City of McCall sewer systems being annexed into the district.

Water Quality Engineering Manager Valerie Greear, who works for the Idaho Department of Environmental Quality, says the storage pond repeatedly failed the leakage test well before it was acquired by PLRWSD.

The facility was first installed in 2003 and according to DEQ rules, wastewater lagoons must be tested when the system is first installed and every ten years. DEQ says the lagoon did not pass its initial test in 2003. This resulted in yearly testing, which the lagoon failed each year through 2011. The maximum allowed leakage is 0.125 inches per day or an eighth of an inch.

“The storage facility has been tested for leaks routinely and has failed to comply with the maximum allowable leakage rates,” an Environmental Monitoring Report from 2017 said.

After the regular failed tests, the operators of the storage pond asked DEQ if a different testing route could be explored. This led to an agreement between DEQ and the city to conduct environmental monitoring and study the effects of any leak on surface and groundwater. 

“So in about 2013, they asked if they could stop doing this every year and take a different approach,” Greear said. “And that’s kind of the path we’ve been on ever since of trying to figure out whether this leaking has an impact on the environment.”

BoiseDev had multiple people reach out inquiring about the leak and questioning whether it was related to the harmful algae blooms in the Cascade Reservoir.

Where is the leak? 

Because of the leak in the storage pond, water collected in the underdrain discharges to a drainage swale that DEQ says creates “wetland-like conditions,” which could then overflow to the North Fork Payette.

An underdrain is a drainage system that is installed under a road that collects, then transports subsurface water. This water also eventually makes its way to the Cascade Reservoir.

“The water collected in the underdrains includes leakage from the winter storage pond and groundwater. Cascade Reservoir is the “basin” of the watershed, catching the contributions of all the tributaries. So yes, that is where this water ultimately flows,” Greear said in an email. “The water also seeps into groundwater, and those impacts were also part of the focus of the 2017 Environmental Monitoring Report. Water stored in the winter storage pond has been treated and is beneficially used for irrigation under a Recycled Water Reuse Permit.”

Is the leak a cause for concern?

What are the ramifications of this leak? Greear says it’s important to understand that the leak is fully treated wastewater, not sewage. This means the wastewater has been through a treatment process to remove contaminants and converted into an effluent that can go back into the water cycle. In this case, the water is moved to the storage pond. Greear said farmers then use this water to irrigate land in the area. 

 “I think that it might be helpful, perhaps for people to understand that this isn’t like people are flushing their toilets and it’s going (straight) into this lagoon,” she said.

“A big point for us is this is not raw sewage,” Dani Terhaar, a Water Quality Analyst at DEQ, said. “We understand that the lagoon is leaking and we are actively working on this situation. We’re monitoring it. They are monitoring it. This is an active effort on behalf of us and the sewer district… (It’s) not a large volume and it’s treated water. It meets a reuse permit requirement before it ever reaches the river.”

While the water is treated, Greear says the leak is contributing phosphorus to the Cascade Reservoir, which can increase algae growth.

“Cascade Reservoir has been identified as impaired because it doesn’t achieve the environmental standards for dissolved oxygen, temperature, and pH, which primarily impacts fish. Phosphorus directly contributes to these issues, as well as harmful algae blooms (HABs,)” she said in an email.

Harmful Alge Blooms were detected in Cascade Reservoir earlier this June. But Greear says, even though the phosphorous from the leak can contribute to algae, it’s not the cause of the HABs, as some Valley Co. residents suggested in online posts.

“It contributes some small amount of phosphorus to an already impaired reservoir, and there are many other sources that also contribute,” Greear said. “Phosphorus added to the reservoir plays a big part in creating the conditions for a bloom to occur, but other factors need to be there as well…Some cyanobacteria are nitrogen “fixers” meaning they can take nitrogen freely from the atmosphere, so this does not limit them as much as phosphorus.”

The Idaho Department of Health and Welfare said that cyanobacteria blooms have been found in the reservoir as far back as 1975.

In 1996, a plan was put in place to monitor the sources of contaiminants in the lake.

“In 1993, dense mats of cyanobacteria caused 23 cattle deaths after ingesting cyanotoxins, and a substantial fish kill occurred in 1994,” Greear said. “These events spurred the development of the Cascade Reservoir TMDLs (then called Watershed Management Plan), finalized in 1996, with several updates since. The TMDLs address the many sources of phosphorus that impact the lake, including wastewater treatment facilities, stormwater, agriculture, forestry, recreation, septic tanks, and natural sources.” 

Overall, Greear said that the amount of phosphorus leaking into the reservoir is not high enough to cause harm to humans or animals.

“…The flow of leak water into the North Fork Payette River comprises less than 0.1% of the river’s flow, and the storage lagoon water captured by the underdrain (i.e. the leak water) is treated to a quality for use for irrigation of crops and safety of livestock grazing,” Greear said in an email. 

The 2017 report 

As far as the potential effects the leak has on surface water, or any water above ground, that’s still unclear. An Environmental Monitoring Report from 2017, in which a year’s worth of data was collected, attempted to asses that but the results were inconclusive.

“(The report) concluded that the precise impact of the leak on surface water could not conclusively be determined,” Greear wrote. 

The data collected was representative of five monitoring wells in the water quality samples of the groundwater, flow of underdrain water to the drainage swales, the winter storage pond water, underdrain water, and the North Fork of the Payette. The study found that phosphorus was being discharged but they were unable to determine the impacts the leak had on surface water.

“Taken together, data indicate that the underdrains create a localized depression in groundwater, and therefore capture leaked water so groundwater quality is likely not impacted,” she wrote. “The data indicate that water leaks from the winter storage pond primarily when water levels in the pond are high (mid-winter to mid-summer). Data collected in the river did not yield many measurable results, so the report calculated estimates of the underdrain flow attributed to pond leakage.”

DEQ does not currently have a plan to require another seepage test on the storage pond, though the sewer district is monitoring the flow and entire concentration of the underdrain quarterly. 

The report also showed that the leak is at its highest during irrigation season, starting in the warmer months and usually concluding in early fall. This is because there is more water in the pond during this season.

“From late fall through early summer, water is added but not removed, so the water level increases during those months and is at its highest before irrigation season begins, which is the beginning of warm months,” Greear said. “Water level then begins to decrease, and a low water level in the storage pond is reached at the end of the irrigation season (fall).”

Through an email response, PRWLDS said that they are working on a master plan that looks at the entire system collection, treatment, and re-use system. They also said the leak was not causing any issues and there are many reasons for Harmful Alge Blooms in the reservoir that cannot be pinned to one cause. 

DEQ stated that the City of McCall and the Payette Lake Recreational Water and Sewer District are in good standing and are complying with DEQ-issued permits and agreements.

“The Wastewater Planning Grant Letter of Interest that the district submitted for grant funding, which includes monies available through the American Rescue Plan Act, states: “This Master Plan will be the first full system plan that will cover the District sewer system, annexed sewer system, [wastewater treatment facility], and reuse system in one document. The plan will also include the open compliance agreement regarding the recycled water storage facility liner, which has been found to leak.”

Autum Robertson - BoiseDev Reporter
Autum Robertson - BoiseDev Reporter
Autum Robertson is a BoiseDev reporter focused on Meridian and McCall. Contact her at [email protected].

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