Nevada City Wastewater Treatment Plant upgrades to avoid fine
The Nevada City Wastewater Treatment Plant has agreed to make $177,973 worth of upgrades in lieu of a $147,000 fine levied by the state water board after it found the plant committed around 50 violations from May 2018 to May 2019.
The Central Valley Regional Water Quality Control Board found the plant committed 49 violations in that time span that required mandatory minimum penalties. An additional two violations had no monetary penalties.
Out of the violations, nine were serious offenses where water discharged contained pollutants over 20% above the legal allowable limit for the most serious contaminants, or more than 40% above the limit for other contaminants.
According to Nevada City Engineer Bryan McAlister, the violations largely stem from unusually high volumes of rainfall last year in February and March which caused the plant to receive storm drain overflow.
“We have old pipes that we’re gradually trying to replace, but they have storm water that comes into the sewer system so the sewer plant gets inundated with excess flow. We had several violations that are due to those abnormal events,” McAlister said. “We’ve been working with the state water board on these notice of violations and we’ve come up with compliance projects. These projects are specifically designed to target the pollutants that are related to the violations.”
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Most of the violations came from emission levels above limits for total coliform, an indicator that while not harmful to humans is used to determine the possibility of other pathogens in drinking water and the adequacy of water treatment.
Total coliform levels are determined using the minimum number of viable bacterial cells present in 100 milliliters of sample cultures. The maximum number of viable cells allowed in a seven-day average sample is 2.2 per 100 mL, but Nevada City’s plant recorded 240 viable cells on Feb. 19, 2019, and 500 viable cells just three days later — more than 200 times the limit. It also twice recorded emissions at nearly 900 cells per 100 mL above monthly limits in February.
The plant received the second most violations for total suspended solids above regulation — a measure of solids remaining following filtration. In February 2019 the plant recorded a total suspended solids monthly average more than five times the limit and a daily maximum 18 times the limit. McAlister said increased sewer runoff brought more solids into the plant, overloading its filtering and drainage system that led to the violations.
Other violations included seven instances of higher than allowed levels of dichlorobromomethane, a by-product of chlorinated water that is “reasonably anticipated to be a human carcinogen,” according to the National Cancer Institute.
The plant has faced similar violations in the past. In June 2018 it entered into a compliance project agreement rather than pay a $54,000 fine resulting from 18 violations between January 2016 and March 2018. This included 12 serious violations stemming from dichlorobromomethane levels that exceed the effluent limitation by 20% or more. For that compliance agreement the plant repaired its sand filtration system and improved pump and plumbing repairs for about $68,000. Several violation in January and February 2017 were explained by unusually high water flows due to extreme rainfall as well.
The plant entered into an agreement with the water board to make repairs bringing them into compliance that cost at least as much as they would have to pay for their fine, $3,000 per violation.
“I think this has been good in a way, because it’s made us (focus) in certain areas that can make the plant have better capacity for storm events like this,” McAlister said.
In order to reach compliance the plant agreed to make five corrective actions. It will hire a consultant to review causes of the violations and recommend procedures for improvement; repair leaking aeration pipes; repair and upgrade its equalization system to better manage intake and prevent overloading filters during periods of high flow; install automatic cleaning mechanisms to minimize buildup that could overload filters; and add an additional sludge wasting day tank.
According to the compliance project description, the additional tank will have the highest potential impact by helping to maintain proper sludge settling, a mix of micro-organisms that feed on matter in waste, which officials said combined with high flows led to the most significant violations.
All projects must be completed by March 31, 2021. McAlister said the plant has implemented about half of the recommendations.
The city has hired consultant Dan Cortinovas, who for the last six months has already provided guidance on sludge processes and modified its treatment process. In that time the facility hasn’t had any significant violations, though the plant was out of compliance in 10 out of the last 12 quarters, including seven quarters with significant noncompliance violations. It had nine informal and two formal enforcement actions against it within the last five years.
According to Nevada City Manager Catrina Olson, the city is also looking into creating regulations for commercial waste discharge that could have impacts on the plant, such as pretreatment and timing of waste removal. The city sent letters to heavy commercial dischargers and will be collecting sample data throughout Nevada City to inform their next steps.
To contact Staff Writer John Orona, email email@example.com or call 530-477-4229.
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