This effective response to drought conditions has led to a paradoxical situation:
- The reduction in water use has increased temperatures and the disinfectant residence time within PCWA’s water storage tank systems causing the levels of disinfection byproduct, specifically total trihalomethanes (TTHM), formation to approach, and in some cases exceed, the primary Maximum Contaminant Level (MCL) of 0.080 mg/L.
- In order to maintain water quality, PCWA has no alternative but to drain and refill the tanks on a monthly basis leading to a loss of 696 acre feet of water per year.
To reduce the TTHM levels in the water supply storage tanks and to conserve water, the project includes the installation of a tank mixer and ventilation system at seven tanks in PCWA’s service area – specifically in the Auburn/Bowman and Colfax distribution systems. Installing a tank mixer and ventilation system provides a mixed condition in which the mixture of older and newer aged water has a higher blended disinfectant residual, which improves control of microbial re-growth, and minimizes disinfection byproduct formation by eliminating stratification.
The project entails installing tank mixers and ventilation systems in the seven tanks listed below, at locations throughout PCWA’s service area where TTHMs are reaching unacceptable concentrations and are in service areas identified as Disadvantaged Communities (DAC):
- Colfax Clearwell Tank (1 MG).
- Ball Park Tank (0.6 MG).
- Colfax Clearwell Tank (0.3 MG).
- Bowman Clearwell Tank (10 MG).
- Bell Road Tank (1 MG).
- Channel Hill Tank (1 MG).
- Electric Street Tank (5 MG).
The proposed project offers a long-term solution to drought-induced water quality challenges while promoting water conservation and achieving long-term reduction in water use. The tank mixer and ventilations systems are a water conscious approach to addressing unacceptable TTHM concentrations – which are a direct result of on-going drought conditions. Without this project, PCWA would waste large volumes of water draining and filling tanks to control TTHM levels. The project offers a long-term solution and provides PCWA with more flexibility in handling variable water quality conditions and enduring future droughts. By implementing this project, PCWA will be able to promote continued water conservation measures by providing high quality water even during the operational challenges associated with drought conditions as well as setting a good example of the importance of water conservation for PCWA’s water users.
Current Status: December 2016
Tank mixers and Ventilation systems have been successfully installed at the Colfax Clearwell Tank (1MG), Ball Park Tank (0.6 MG) and Colfax Clearwell Tank (0.3 MG). Work on remaining tanks is about to start.
Placer County Water Agency
Aaron Sullivan, Associate Engineer, 530-823-2033, firstname.lastname@example.org
Measurable Physical Benefits
Water Supply, Water Quality