Mountain Lake, a popular visitor destination, is a natural lake located in the southern Presidio between the Public Health Service District and Presidio Golf Course. A small portion of the lake is within the City of San Francisco. Highway 1, operated by Caltrans, runs along the lake to the west. The roadway was constructed in 1937.
Over several decades, sedimentation, run-off from Highway I and the Presidio Golf Course, and urbanization has degraded Mountain Lake's water quality and surrounding habitat, prompting an ongoing program of enhancement that is taking a major leap forward in 2012/2013.
Restoration: The First Decade
Restoration began in 2001. With community stewardship, native plants were reestablished, invasive eucalyptus were removed, and benches and a south shore overlook were installed. In that time, more than 14,000 native plants were planted and countless truckloads of weeds pulled and composted. This work was mostly performed by Presidio Park Stewards volunteers, school groups, corporate groups, and the neighboring Friends of Mountain Lake Park. In total, more than 15,000 hours from the community were donated to this effort. The area around the lake now supports a much richer habitat. Many wetland, riparian, scrub, and oak woodland species now thrive where before only a few could be seen. To date 3.5 acres of riparian, oak woodland, riparian scrub, and wetland habitats have been restored.
Remediation and Enhancement: Project Activities 2012/2013
In May 2012, the California Department of Toxic Substances Control (DTSC) approved a Final Feasibility Study/Remedial Action Plan (FS/RAP) for environmental cleanup of the Presidio's Mountain Lake. Excavation by dredging is the selected cleanup alternative. The Presidio Trust and the California Department of Transportation (Caltrans) is implementing the work through fall 2013.
Step 1: Caltrans Highway 1 Stabilization Work (July through November 2012)
Under a 2011 settlement between the Presidio Trust and Caltrans, Caltrans agreed to stabilize Highway 1 (Park Presidio Boulevard) prior to the start of lake dredging work. In 2012, Caltrans installed approximately 400 stone columns into the ground along the northbound shoulder of the roadway west of Mountain Lake. Caltrans will also install treatment devices in storm drains along the highway to prevent contaminants from entering the lake in the future.
Step 2: Site Preparations (Fall 2012 to Spring 2013)
September 2012 through April 2013, the Presidio Trust will be conducting site preparation work. The work will include mobilizing construction equipment to the site, erecting temporary construction fencing, removing submerged trees, partial clearing of tule reeds, installing dredging equipment in the lake, removing and relocating exotic species, and grading the staging area. The grading work will require several hundred truckloads of soil, concrete, and vegetative material be transferred in and out of the work areas. The section of Park Trail that runs through the golf course will be used as the primary haul route for this material.
To ensure public safety, portions of Park Trail and Mountain Lake Trail will be closed intermittently during truck hauling activity, and Mountain Lake Beach will be closed whenever work is occurring in the lake. The staging area north of the lake and the east shore access route will remain closed for the duration of the construction project.
Step 3: Dredging (Spring 2013 through Fall 2013)
The Presidio Trust will dredge sediment contaminated with lead and motor oil from the bottom of the lake. The sediment will be transported via pipeline to a staging area north of the lake where it will be dewatered. After dewatering, the water will be pumped back into the lake. Dried sediment will be transported offsite and disposed of in a permitted, offsite landfill.
The lake dredging work conducted by the Presidio Trust and overseen by DTSC is expected to begin in spring 2013 and continue through the fall. In support of and prior to dredging, the Presidio Trust will collect sediment and water samples from the lake and prepare staging areas. Sampling occurred in June and July 2012. Preparation of staging areas, which includes tree and brush removal, will continue through April. A work notice with more details of the dredging work will be distributed prior to the start of field work.
Step 4: East Arm Wetland Expansion and Lake Enhancement (2013 and Beyond)
The Presidio Trust, through a grant from the San Francisco International Airport, will begin work on the creation and enhancement of wetland in the East Arm of Mountain Lake. Beginning August 2013, work will include removal of sediment and eucalyptus from the bottom of the east arm to improve air movement, improve drainage, and expand wetland habitat.
Completed Work in 2012:
- Relocation of non-native turtle and fish population (summer 2012)
- Stabilization of Park Presidio Boulevard by Caltrans (July–November 2012)
- Archaeological coring of lake sediment (October 2012)
- Vegetation removals from west shore, east shore access route and staging area (August through December 2012)
- Brush clearing and archeological excavation in the East Arm (October - November 2012)
Current and Upcoming Work in 2013:
- Grading and preparation of east shore access route and staging area (January - April 2013)
- Storm water piping upgrades on Park Presidio Boulevard by Caltrans (January - April 2013)
- Restoration of west shore of lake (April - June 2013)
- Dredging of lake (May - December 2013)
- Cultivating SAV (July – December 2013)
- East Arm tree removals and wetland creation (August – October 2013)
- Re-contouring of lake bottom (September - October 2013)
- Restoration of east shore access route and staging area (November through December 2013)
- Occasional truck hauling on Mountain Lake trail (January 2013 through December 2013)
- Occasional trail closures (January 2013 through December 2013)
Future Enhancement Activities (2013-ongoing):
- Replanting of many thousands of local plants (December 2013 - March 2016).
- Hosting volunteer programs to steward Mountain Lake’s plant and animal communities (ongoing)
- Educational outreach to local schools and community groups (ongoing)
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