[http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2012/01/23/MNMA1JSDB8.DTL]
It is a good thing that nobody attempts to swim in Mountain Lake.
The 4-acre pond on the southern boundary of the Presidio of San Francisco is sloppy with toxic gunk.
The mud at the bottom of the 8-foot-deep body of water is saturated with lead, pesticides and oil that has drained off Park Presidio Boulevard and the adjacent golf course and flowed into the lake through storm drains.
The Presidio Trust, which oversees the lake, has known about the hazard for more than a decade, but regulatory hassles delayed the cleanup. This week, a $9.5 million plan to clean the sludge will be presented to the public.
"It needs to be clean," said Dana Polk, a senior adviser and spokeswoman for the Presidio Trust. "It's impacting the aquatic health of the lake."
A panoply of complicated and expensive schemes is being considered to remove the tainted sediment, including draining the lake and scooping out the silt. Most experts favor traditional dredging, which is the trust's preferred option.
A two-hour community workshop will start at 6:30 p.m. Wednesday at the Golden Gate Club in the Presidio to discuss the various proposals.
Water for Indians -
Mountain Lake, which scientists say is 1,700 years old, is one of the few remaining natural lakes in San Francisco. The Ohlone Indians are believed to have used it as a source of freshwater. The earliest written record of the lake comes from the 1776 diary of Pedro Font, a padre on the famous expedition led by Juan Bautista de Anza.
"This place and its vicinity has abundant pasturage, plenty of firewood, and fine water," Font wrote. "Here and near the lake there are yerba buena and so many lilies that I almost had them inside my tent."
The fine water and fertile grounds were ripe for exploitation. The Spanish grazed their cattle in the area, and in 1853, a 3,500-foot-long tunnel was built next to the lake in a failed attempt to bring water to the developing city of San Francisco.
Invasive eucalyptus trees were planted everywhere, and in 1897, the U.S. Army began siphoning water out of the lake to, among other things, irrigate its newly built golf course.
The lake, which was once 30 feet deep, shrank by 40 percent when Park Presidio Boulevard was built through part of the lake bed in 1939. Dirt and excavation spoils were dumped into the basin.
Lead from car emissions seeped into the lake for decades until leaded gasoline was phased out beginning in the 1970s. It combined with petroleum hydrocarbons from motor oil and accumulated on the lake bed along with pesticides flowing in from the golf course.
The preferred cleanup plan, which will be helped along by a $5.5 million contribution from Caltrans, involves dredging about 4 feet, or 11,500 cubic yards, of sediment from a barge that would be either floating on the lake or sitting on the shoreline. The waste material would be dried and trucked to a landfill.
Michael Boland, the chief of planning, projects and programs for the Presidio Trust, said the dredging will serve the dual purpose of deepening the lake.
"It's now too shallow to stay healthy," Boland said. "The best thing about this restoration is that it will take out sediment, and we will be able to regrade the lake bed. Our goal is to get it to a minimum of 14 feet deep."
Public dumping ground -
There are other problems, Boland said. For decades, Mountain Lake has been a dumping ground for nonnative species, including goldfish, bullfrogs, turtles known as red-eared sliders and, in 1996, an alligator.
Former San Francisco Chronicle and Examiner Editor Phil Bronstein made headlines that year when he was prevented from entering the water and trying to wrestle the wayward reptile from the murky depths, which probably would have posed a bigger threat to his health than the alligator.
Shortly after that, one of the lake's two resident swans - affectionately named Daisy - died. A necropsy found high levels of lead in her liver. Hundreds of dead carp and catfish would die every summer during the 1990s when oxygen-sucking algae blooms formed on the lake.
The Presidio Trust has been working for a decade planting native grasses, cutting groves of litter-prone eucalyptus trees, and enhancing the surrounding habitat. Pesticides are no longer used on the golf course.
Catching runoff -
The plan now is to restore wetlands near the lake and build bio-swales, or basins, to catch the runoff from the surrounding highway and neighborhoods and allow it to percolate into the ground. Biologists would like to reintroduce native species, such as the pond turtle, to the lake.
"Our goal is to make this lake as natural as possible," Boland said. "Eventually we would like to restore some of the native fauna, but we will have to first educate some of the neighbors to not drop their former pets into the lake."
The draft remedial action plan for Mountain Lake is scheduled to be released for public comment in mid- to late March. Final approval by the California Department of Toxic Substances Control is planned for April, and the muck work is expected to begin in the spring or summer of 2013.
Learn more about tainted sediment
Public meeting: The Presidio Trust and the California Department of Toxic Substances Control will outline the options for cleaning up Mountain Lake at a community meeting from 6:30 to 8:30 p.m. Wednesday at the Golden Gate Club, 135 Fisher Loop, San Francisco.
Walking tour: The public is invited to walk with naturalists who will explain the Mountain Lake enhancement project. The tour will be begin at 4:30 p.m on Feb. 22 and at 10 a.m. on Feb. 25 at the south shore of the lake, near the playground.
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