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Underground systems help wineries, builders in difficult, dry areas

ST. HELENA -- Some wineries and rural homeowners are turning to the underground sibling of drip irrigation for a solution -- albeit an expensive one -- to conditions in which conventional or other alternative septic systems fail or are unusable.

Napa County approved subsurface drip dispersion as an alternative system last April. Sonoma County has allowed it for several years on a limited basis -- 10 per year and limited to 480 gallons per day -- as part of its experimental system agreement with the North Coast water board. The county won’t have formal guidelines for the system for at least another year, according to the county’s onsite septic system supervisor Bob Herr.

Marin County has a pending update to its septic-system policy that would add subsurface drip to its list of allowed alternative systems.

Since April, Napa County has approved some 50 subsurface drip systems, with more than half installed so far, according to Sheldon Sapoznik, who oversees septic systems for the county Environmental Management Department.

“The majority of plan submittals for alternative systems have disposal to subsurface drip,” he said. “It’s a big shift. We had a half-dozen submitted with one site plan resubmitted so they would have subsurface drip.”

Many of the Napa County projects are rural homes, but some are wineries. For example, a subsurface drip system was designed to handle process wastewater from Whitehall Lane Winery near St. Helena. In the parched Pope Valley area east of Napa Valley, the Brown family proposes to irrigate 17.5 acres of vines with process wastewater aerated in above-ground tanks, then fed to subsurface drip zones.

Subsurface drip dispersion, also called subsurface drip irrigation, takes the tubing-and-emitter design of drip irrigation underground to dispose of treated wastewater six or more inches below ground or surface fill, rather than a few feet down with a traditional leech field. Though the shallow depth can allow for installation by hand on steep slopes, subsurface drip systems still are required to be at least a couple of feet above the highest groundwater level, and some counties require redundant installed or available drip fields.

The technology has been around since the 1950s, but only recently have local water-quality regulators allowed it as an alternative to a traditional septic leech field. Technologies that have helped subsurface drip make a comeback in recent years are controllers for releasing measured amounts of wastewater intermittently and a self-flushing system, developed by Corte Madera-based Geoflow, which has drip emitters resistant to clogging by roots.

Napa-based civil engineering firm Riechers Spence & Associates has been involved with 10 projects with subsurface drip. The firm usually recommends wineries use subsurface drip for treated sanitary wastewater in limited-soil conditions. Winery process wastewater is typically treated and reused for above-ground vine irrigation.

“We’re seeing a lot of these systems because many sites do not have six to seven feet of suitable soil above rocks or clays, but rather only two to three feet of soil, so the options are limited for septic systems,” said principal engineer Hugh Linn, who runs the firm’s environmental division. “It’s not that people necessarily want to use these systems, but in many cases, they have no choice.”

Subsurface drip is among the most expensive onsite treatment options, largely for the pretreatment system required before wastewater enters the drip tubing, according to Mr. Linn. With requirements for various floats, valves, backwash cycles and pumps involved -- not to mention maintenance of the advanced pretreatment systems -- subsurface drip systems can cost 30 percent to 40 percent more than other dispersion systems.

However, at the Vintners Inn just north of Santa Rosa, subsurface drip was the only option that would allow expansion from 44 rooms to 80 and double the number of seats in the John Ash & Company restaurant to 200, according to Bill Moon. Mr. Moon is the maintenance manager for the hotel and also Don Carano’s Ferrari-Carano winery near Healdsburg.

The water table is so high in that part of Russian River Valley that the existing mound-type wastewater disposal system wasn’t performing correctly, Mr. Moon noted. Questra Engineering of Point Richmond designed what was to become a model for Sonoma County’s gelling policy for subsurface drip.

A system of mounds, tanks, filters and large holding ponds treats and holds a year’s worth of wastewater for discharge over three of the driest weeks of the year via measured dosing in a subsurface drip system installed among 50 acres of vines.

Veteran sewage system contractor Leeroy Ress Jr. of Sebastopol installs about a couple dozen subsurface drip systems in the North Bay annually and says underground drip systems in vine rows can be problematic unless cover crops and weeds are mowed instead of disced.

Besides the potential for damage to barely buried drip tubing, regulators prohibit significant discing or ripping of soil above the drip zones because the filtration characteristics of the soil are changed.