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The sources of selenium and sulfate are natural. The geology under the City contains large amounts of selenium and sulfate. This causes high selenium and sulfate concentrations in the groundwater that enter the Pueblo sewer system during precipitation events when the groundwater table is high.
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A water quality standards variance is a time limited designated use and condition (i.e., interim requirements) that is targeted to a specific pollutant(s), and/or waterbody segment(s) that highest attainable condition during the specified period. As such, a variance requires a public process, State, and EPA review and approval under the CWA 303(c). While the designated use and condition reflect what is ultimately attainable, the variance reflects the highest attainable condition for a specific timeframe and is therefore less stringent. Where the currently applicable designated use and condition are not being met, a water quality standards variance that reflects a less stringent, time limited designated use and condition allows the state and stakeholders additional time to implement adaptive management approaches to improve water quality, but still retain the currently applicable designated use as long term goal for the waterbody.
Water quality standards variances are useful to consider when there is a new or more stringent effluent limit if the City of Pueblo (City) can demonstrate that attaining the designated use and criterion is not feasible for the term of the variance but may be attainable in the longer term. The City’s variance is appropriate due to attaining the designated use and criterion is not feasible under the current conditions (e.g., water quality-based controls required to meet the numeric selenium and sulfate would result in substantial and widespread social and economic impact) but could be feasible should the circumstances related to the attainability determination change (e.g., development of less expensive pollution control technologies or change in the local economic conditions).
Selenium and sulfate are the two constituents that are covered by the variance.
The cost of treatment is about $200 million. The cost of treatment would cause the rates of the citizens of Pueblo to have very high bills and the treatment is still experimental.
The City has spent about $12 million to meet the variance requirements. The requirements in State of Colorado’s Code of Regulations, Regulation 32 for the City’s discharger specific variance are:
Pueblo will be required to spend $10 million to implement a comprehensive source control, sampling, analysis, and optimization adaptive management program to reduce selenium and sulfate concentrations in the effluent as much as feasible and to ensure that the discharge does not contribute to any lowering of the currently attained ambient water quality.
The City is continuing to work on completing the requirements.
The variance lasts for 10 years. The review this year in October is to review the progress the City of Pueblo has made in the last 5 years to control the amount of selenium and sulfate that enters the sewer system through infiltration of the ground water. The City of Pueblo has proposed that the current variance conditions be kept the same.
No, the discharge does not cause harm to the environment. The groundwater that infiltrates into the sanitary sewer system also flows into the Arkansas River. The wastewater plant removes about 50% of the selenium that comes into the plant, so the amount that is discharged is lower than what would naturally flow into the Arkansas River from the groundwater. The sulfate limit is based on how water tastes when used in a drinking water system.
No, the selenium and sulfate amounts that are discharged into the Arkansas River will not cause human health problems. The selenium standard is based aquatic life criteria, and the sulfate standard is based on water supply as sulfate causes issues with taste of the water. Studies have shown that the sulfate improves the tolerance for selenium in fish.
The Water Quality Control Commission will be reviewing whether the City of Pueblo has made progress in lowering the amount of selenium and sulfate in the discharge from the wastewater plant into the Arkansas River, and if the economic conditions have changed since 2018 when the discharger specific variance was adopted. The evaluation that was done for the hearing in October 2023 has shown a decrease in the amount of selenium coming into the treatment plant, so there is less going into the river. The economic conditions have not changed for the City of Pueblo since the variance was adopted in 2018.