Between the United States Environmental Protection Agency’s proposed Effluent Limitation Guidelines and the Storm Water Construction General Permit a better focus and accountability on standard erosion and sediment control is a necessity for all dischargers. Active treatment systems are required for sites that discharge storm water directly to a water body listed on the Clean Water Act Section 303(d) or permanent storm water drainage systems. Storm water may only be discharged if the storm water meets the chemical and sediment monitoring plans specified in the applicable permit.
ETIC’s engineering department has effectively worked with local, state, and federal oversight agencies to design and implement active treatment systems to reduce storm water turbidity for a major utility client. Two selected active treatment systems are described below:
ETIC designed a 1,000-gallon-per-minute surface active treatment system tailored to reduce turbidity, which included installing four 20,000-gallon storage tanks, a chitosan polymer flocculation metering/mixing system, sand and bag/cartridge filtration units, and multiple extraction and discharge pumps prior to discharge to the drainage channel. The premise of the treatment system consists of four collection pits within the substation area, which pumped collected storm water to the four 20,000-gallon storage tanks for treatment. The turbidity of the discharged water was consistently less than 20 Nephelometric Turbidity Units. The system was installed in late 2009 and was decommissioned in 2011.
The active treatment system was designed to treat turbid storm water impacted with suspended sediments and elevated pH (dissolved calcium). The active treatment system consisted of a collection impoundment, a pre-treatment unit, two 21,000gallon tanks, one submersible and one transfer pump, a control unit for automated measurement of active treatment system parameters, bag and cartridge filters, a sand filter, and piping. The design also included the use of chitosan for treating turbidity and carbon dioxide (CO2) or citric acid for adjusting the pH. The system was installed in 2012 and was decommissioned in 2013.
Client: Major Utility Company Governed By the California Public Utilities Commission