Since last spring, Mountain Lake has looked a lot like a construction site as dredging equipment has sat on the surface, methodically removing sediment contaminated with lead and motor oil from the bottom of the lake.
In late 2011, a $13.5 million settlement was reached between the Presidio Trust and CALTRANS for cleanup of contaminated sediments that have run into Mountain Lake off of the Park Presidio roadway. The runoff has been occurring since the roadway opened 70 years ago.
The first phase of the project involved making adjustments to the roadway to avoid future runoff, including the installation of 400 stone columns into the ground along the northbound shoulder of the roadway west of Mountain Lake. Treatment devices were also installed in storm drains along the highway to prevent contaminants from entering the lake in the future.
Another part of the project involved removing all non-native species from the lake, including fish and turtles. All of the captured wildlife, including 42 red-eared slider turtles (photos), were taken to Sonoma County Reptile Rescue where they were relocated with breeders, pet stores, herpetological societies and local citizens.
One of the red-eared slider turtles that was removed from the lake and relocated
Dredging then got underway in Spring 2013. The dredged sediment from the bottom of the lake was transported via pipeline to a staging area north of the lake where it was dewatered and then pumped back into the lake. The dried, contaminated sediment was transported offsite and disposed of in a permitted, offsite landfill.
The last truckload of sediment left Mountain Lake in December, and all of the dredging equipment was removed from the lake. The remediation equipment in the staging area will also be removed soon, officially completing the remediation portion of the Mountain Lake project.
Crews plant new trees along the Park Presidio roadway in May 2013.
In the background, dredging barges can be seen on the lake. Photo: Presidio Trust
Up next is the beginning of the restoration phase, which is expected to last nearly three years. During that time, Biological Science Technician Jason Lisenby says they “will plant thousands and thousands of local plants into the newly cleaned-up areas.”
Planting will also take place in the lake itself, to ready it for the return of fish and act as a food source for wildlife:
Planting into Mountain Lake is expected to begin in March, and the first priority, Laskowski said, will be to introduce three of the lake’s most important plants: sago pondweed (Stuckenia pectinata), coontails (Ceratophyllum demersum) and water nymphs (Najas guadalupensis).
Those plants will play many roles, Young and Laskowski said. They will form a leafy canopy to shield microorganisms on the bottom from sunlight and provide a source of food for the lake’s dabbling ducks, as well as for the rare Western pond turtles that are being raised at the two zoos until they can be moved to the lake.
Once the plants are thriving, Young’s team will introduce hundreds of fish called three-spined sticklebacks, (Gasterosteus aculeates), a 2-inch species with a crucial role in the lake’s ecology. [SFGate]
CELEBRATION & VOLUNTEER PLANTING ON FEBRUARY 8
Next Saturday, the Presidio Trust will host a celebration of the end of the remediation phase that includes a volunteer planting day. Volunteer opportunities will run from 9am to 12noon, followed by guided walks and a talk about future plans for Mountain Lake by Michael Boland, Chief Planning, Projects & Programs Officer for the Presidio Trust.
This is an auspicious rebirth for Mountain Lake, which scientists estimate is 1,700 years old, and one of the few remaining natural lakes in San Francisco (the others are Lake Merced, Pine Lake west of Stern Grove and the semi-natural Chain of Lakes in Golden Gate Park).
The lake was also a valuable source of drinking water for the Ohlone Indians and for early European settlers like Juan Bautista de Anza, who camped along its shores in 1776.
For more information on the Mountain Lake remediation and enhancement project, visit the project website.
A view of Mountain Lake from 1899, looking west from the south shore (the side where Mountain Lake Park is today). The buildings in the background are the historic Marine Hospital, where the Presidio Landmark apartments are today. Photo: Presidio Trust