A potential wastewater solution for the Woodacre and San Geronimo Flats has been scaled back. After years of planning, the county’s engineer has determined that the project should be confined to Woodacre and the treatment plant located at a newly selected site: the Dickson Ridge, above the eastern end of San Geronimo Valley Drive.
At a virtual meeting late last month, Questa Engineering updated residents on six alternatives that range from repairing individual septic systems to building an elaborate system that involves irrigating pastureland at Spirit Rock Meditation Center with recycled wastewater. Norman Hantzsche, the project’s engineer at Questa, which has helmed the project since 2017, underscored that the project is still in motion and subject to change.
A new feasibility study, scheduled to be published at the end of June, evaluates the six options—four of which depend on the use of roughly four acres of land between Fire Road and San Geronimo Valley Drive as a site for a community leach field.
Grace Tolson, co-owner of the Dickson Ranch and the ridge property, said she is optimistic that her land could be used for the project, but said that nothing is certain.
“We thought we might be able to help the valley by doing this,” Ms. Tolson said. “It’s on a piece of property that we don’t use, but we don’t know if we’d lease the land or what. I wasn’t totally against it because I realize the flats down in Woodacre—they really need some help. We’re doing everything we can to protect the creeks and every inch of our land has been walked [by Questa] already.”
Pooling groundwater and ephemeral streams carry sewage from leaky septic systems in the Woodacre and San Geronimo Flats. The idea for a community wastewater system to address the problem is at least 15 years old and was sparked in part by bacterial monitoring conducted in the watershed in 2004. Woodacre, with its high water table, clay soils and preponderance of 50-year-old redwood septic tanks, scored poorly for fecal indicator bacteria like E. coli.
When nine atmospheric rivers brought heavy rains to the Bay Area this winter, residents of the Woodacre and San Geronimo Flats were particularly afflicted. Christin Anderson, a member of the Woodacre and San Geronimo Flats Wastewater Group, which first pushed the county to pursue a community-wide solution, said that even though her septic system has been inspected by the county, it still flooded after the storms. While her septic system was being pumped, pooling groundwater was flowing back into it.
“I have a 1,200-gallon tank and as they were pumping it, within minutes it started filling up,” Ms. Anderson said. “I talked to all my neighbors about it and everybody was having the same issues. We’re all hopeful that this project is a solution to the issues that have impacted the creek and us residents.”
In 2017, the county commissioned an environmental impact report for a proposed wastewater treatment plant on the former San Geronimo Golf Course, but the county soon sold the property and the new owner, the Trust for Public Land, was not interested in hosting a treatment facility.
Then, last July, supervisors approved $120,000 for a new feasibility study, including a community leach field and treatment facility on the Dickson Ridge—a site included in the original list of possible sites, along with the golf course. More than 90 percent of the funds approved last year had been previously allotted for the 2017 environmental report.
“We’re looking at a lot of options here, but nothing has been finalized,” Mr. Hantzsche said at a community meeting in March. “When the golf course fell through last year, the county supported the community to fund going back to the local alternative.”
A new proposed map shows 4-inch gravity effluent sewers that run through the Woodacre Flats to a main lift station at the corner of Railroad Avenue and San Geronimo Valley Drive. A sublift station at the foot of Redwood Drive would feed water to the main lift station. The streets would require trenching to install the connective piping.
Kent Julin, an arborist and Woodacre resident, assessed the tree species at the proposed leach field site and their tolerance to construction impacts. He recommended tree protection measures, including avoiding sensitive root areas. His report found that the nutrients and water from the system would benefit tree health dramatically, and appropriate thinning would increase forest health and reduce wildlife hazards.
If a leach field were to be built at the Dickson Ridge property, the system could service up to 150 homes. Another option would expand the system with a secondary sand filter treatment system at the same site. That option would double the service size.
Another alternative would use the Dickson Ridge leach field in the winter and a site at Spirit Rock during the summer. Wastewater treated in the sand filter system would be pumped to the meditation center and used for pasture irrigation. This option could also service 300 or more homes. Mr. Hantzsche said that Questa has received positive feedback from Spirit Rock regarding sharing the costs and operation of the treatment system, which could benefit the center during drought.
A final community-wide alternative adds a third component, a tertiary water treatment system at the Dickson Ridge site that would expand the opportunities for the use of recycled wastewater. This option could also serve over 300 homes.
There are other options, too. The county could opt not to build a community leach field and instead upgrade individual septic systems on a case-by-case basis. Of the 270 parcels in the Woodacre Flats, just 12 have new septic systems. As many as 144 systems have no documentation, Mr. Hantzsche said. A county survey found that two-thirds of the village’s septic systems were in bad shape, and another study found that failing septics continued to be a source of contamination in Woodacre Creek. The 23 vacant parcels in the Woodacre Flats would not be included in the plan.
Questa hopes to complete a feasibility study by June 30, after which the county will engage the community in determining the preferred alternative. From there, Questa can undertake an environmental impact report before applying for grants. A governing district would need to be created, or the system could be governed by an existing district, such as Marin Water or Ross Valley Sanitary. The community would then vote on whether to build a system. The measure would need a majority of the vote.