Mountain Lake, part of San Francisco’s Golden Gate National Park, was contaminated from highway storm water runoff over the last few decades. The dredge contractor for the project elected to use a suction dredge and dewatering bags to remove the contaminated sediments. The heavy sediments were removed using bags and then the leachate was captured and treated before returning the water to the lake under an Individual NPDES permit.
The treatment was designed for pH, turbidity, metals, and hydrocarbons. Treatment components included open top weir tanks, a control module for water quality monitoring and chemical addition, a sand filter system and a hydrocarbon removal system. Limits for pH were 6.5 to 9.0 S.U. with continuous monitoring. The turbidity limit was <20 NTU’s. Clear Creek provided on-site installation, periodic maintenance, and operation of the treatment system with successful discharge under the permit.