ENR California Best Projects 2018 Water/Environment: Machado Lake Ecosystem Rehab
Machado Lake Ecosystem Rehabilitation
Owner: City of Los Angeles, Bureau of Engineering
Lead Design Firm/Civil/Structural/MEP Engineer: CDM Smith, in Association With Parsons
General Contractor: OHL USA
Dredging Subcontractor: JND Thomas Co.
Geotechnical: Ninyo and Moore
After a nearly 10-year effort, the Machado Lake Ecosystem Rehabilitation Project rehabilitated the historic Los Angeles lake, improving water quality, restoring habitat and enhancing water conservation. The lake was identified by the regional Water Quality Control Board as an impaired water body for trash, nutrients and toxics.
The $100-million project, which included three years of design and construction, consisted of hydraulically dredging approximately 240,000 cu yd of contaminated sediment from Machado Lake and applying a bio-layer to cap the remaining contaminants from migrating into the water.
The lake water is treated naturally through a constructed wetland as well as a super-oxygenation system. The project team installed five hydrodynamic separators at the major stormwater inlets, along with additional water conservation improvements including the installation irrigation pipes to capture reclaimed water from the Terminal Island Water Reclamation Plant.
The team had to obtain five environmental and regulatory clearances prior to construction, each with its own set of restrictions. Environmental compliance required a full-time biologist during construction to monitor effects on habitat and native species found on site. During nesting season, the team established no work buffer zones around bird nests, which became an issue when migrating marsh birds began nesting on the shores of the lake, preventing dredging activities in those locations.
Crews removed more than 15,000 truckloads of lake sediment, which was then tested and treated for water content and contamination. Even after being processed through the dewatering plant, the sediment was not dry enough to be accepted by the disposal sites. Workers put the sediment in 1,000-cu-yd stockpiles to dry out. Available space on site quickly filled up so the team needed to carefully balance production from the dredger and storage space.
Machado Lake’s recreational features include one mile of refurbished pathways, four observation piers, two observation zones, two pedestrian bridges, 622 new park trees and more than 50,000 new plants. This project site is one of the largest remaining coastal wetland ecosystems in Southern California.