The county and the San Geronimo Valley Planning Group are using two different kinds of technology to conduct coordinated tests of the valley’s watershed that have the potential to shed more light on the sources and strengths of contaminants.
The planning group has pushed for creek testing because of its concerns about a proposed community wastewater system for Woodacre and San Geronimo, arguing there is no proof that the primary pollutant is human waste.
But the county frames the testing differently: as another piece of information in a long line of evidence that failing septic systems are problematic in the area—a problem that the county believes a community wastewater system could help solve.
An initial study of the proposed system and its alternatives is expected to be released within weeks, said Lorene Jackson, with the county’s Environmental Health Services. Scoping for an environmental review of the proposal could begin in February.
The planning group is utilizing a relatively new and sophisticated technology called the PhyloChip. The small chip, with a surface bearing 1.1 million different stretches of DNA sequences, can identify 60,000 types of microbes found in the guts of animals.
That translates into about 30 species the chip can identify, said Gary Anderson, head of the ecology department at the Lawrence Berkeley National Laboratory, where the PhyloChip is processed.
The chip reveals whether a particular animal’s fecal presence in the creek is major or minor, he said.
“The main goal of this testing is to confirm whether, in fact, human contaminants, from septic, are found year-round in our watershed,” Brian Staley, the chair of the San Geronimo Valley Planning Group, wrote in an email. “Since we will be looking for every biological contaminant testable, we will either have clear evidence of human sources of pollution or not.”
The planning group is paying the lab $3,000 for the tests out of its own pocket, about a 50 percent discount, though Mr. Staley said it’s possible a donor will ultimately cover the cost.
The county, on the other hand, is using microbial source tracking, which utilizes one representative microbe per animal to determine whether waste from a given species is present in the water. The San Francisco Regional Water Quality Control Board is allowing the county access to a lab in San Francisco free of charge for the tests.
The county, working with an employee of the Marin Municipal Water District, is collecting four sets of three samples taken between December and this summer, thereby covering the wet and dry seasons.
The county and planning group coordinated their December tests, taking water from the same areas at the same times. But though the planning group hopes to test a large area in the valley—the extent and sites have not been finalized, Mr. Staley said—the county’s tests will be limited to the areas covered by the proposed wastewater system.
“Our focus, with our limited resources, is the project area,” Ms. Jackson said.
The results will not determine the fate of the project, she said, but will be used as background information in the environmental review. “We’ve been studying [the watershed] for quite a while. This gives us two more tools to clarify what’s going on,” she said.
Lagunitas Creek, the main stem in the watershed, is designated as a federal impaired waterway for pathogens and nitrogen.
A 2008 report commissioned by the county that provided free and anonymous septic evaluations found that, in Woodacre, a significant portion of the systems evaluated were inadequate or failing.
A community wastewater system could allow up to 300 people in the flats of Woodacre and San Geronimo to leave behind their septic systems and hook up to a community pond that could also provide recycled water to the San Geronimo Golf Course.
Community members advocating for the system have contributed over $20,000 to fund the environmental impact report, which will cost a total of about $225,000. Supporters say the project would provide a group solution for residences with failing systems in the flats, an area they say is not ideal for septics, given the clay soil and high groundwater.
But the planning group has lodged a number of complaints about the proposal, including that it does not cover the entire valley, that it does not prioritize hooking up homeowners with failing systems, that it could lead to more development—and that specific testing should be done to pinpoint the source of pollution in the watershed.
Last April, Marin Municipal Water District authorized a $50,000 grant to help fund the environmental review, but the planning group successfully lobbied to make that funding contingent on water source testing. Microbial source tracking identifies the cause of pollution, but Mr. Staley called the PhyloChip a more sophisticated and reliable test.
“With hundreds of markers, we can confidently identify [sources],” Mr. Anderson, of the Berkeley lab, said, providing high-level information “to make better management decisions.”
The recent extreme rains, Mr. Anderson added, mean the group can use the chip to test three different conditions: dry, wet and extremely wet. “Which could be really interesting… You’re flushing massive amounts [of microbes during a big storm], which could be different than with lesser amounts of rain. That could help with risk assessment.”
The county has used the PhyloChip before. A wide-ranging testing program of county beaches in 2012, for instance, used it to determine the source of contaminants in places like Tomales Bay and Muir Beach.
Ms. Jackson said that initially the county envisioned undertaking both source tracking and Phylochip testing, but a donor who was going to cover the latter ultimately decided not to.