[caption id="attachment_14187" align="alignleft" width="300" caption="Napa Sanitation District's water recycling facility is located on the east bank of the Napa River just south of the Butler Bridge. (Napa Sanitation District photo)"][/caption]

NAPA - As the number of wineries locating in southern Napa Valley business parks increases, Napa Sanitation District is studying whether it can offer a more financially attractive option for wineries to dispose of their process wastewater than to have it trucked roughly 35 miles to a large treatment facility in Oakland.

So far the district has tallied 43 winery-related facilities operating from industrial buildings within the service area, handling a total of about 70,000 tons of grapes annually and ranging in size from boutique producers with a few tons a year to 40,000-ton operations, according to General Manager Michael Abramson.

"Frankly, this is a new phenomenon for us," he said.

Some of these are casegoods warehouses and don't have high-strength wastewater.

Another 10 facilities have been approved or are proposed, adding 44,000 tons of grapes.

In the past several years, a number of small-scale vintners, custom-winemaking operations and large production and bottling facilities have started up or relocated to business parks and urban areas as regulatory requirements for setting up traffic- and wastewater-generating operations in rural areas have become costly.

A frequent challenge vintners have faced in moving to industrial parks is what to do with process wastewater and by-products such as grape skins as well as on-site treatment-system sludge and salty water-softener concentrate. Unlike other food processors, wineries produce most of their wastewater in a short period of time, mostly around harvest, to wash presses, tanks, barrels and other equipment.

That wastewater often has high concentrations of organic material such as skins and juice. For a single-family home, average biological oxygen demand, or BOD, one common measure of that concentration, is 175 milligrams per liter, while a winery's can be 5,000 to 30,000.

High flows of such highly concentrated wastewater in such a short period require treatment plants to use more energy and oxygenation to lower to levels that are considered safe to discharge for irrigation in summer or into the Napa River.

That extra treatment comes at a cost that district officials started hearing was too high for smaller vintners to pay, particularly since connection fees are based on peak flow and concentrations of BOD and suspended solids, according to Mr. Abramson.

Napa Sanitation connection fees for industrial users are $5,660 per equivalent dwelling unit, or EDU, or 210 gallons per day with strength concentrations for BOD of 175 milligrams per day and for suspended solids of 200 milligrams daily. So a winery or bottling plant with the equivalent of 50 times the wastewater production of a home would purchase 50 EDUs worth of capacity, costing $283,000.

That doesn't include ongoing service fees or overages. Exceeding flow or strength limits by more than 1.5 times in a given day could require the purchase of more capacity.

That cost has persuaded operators of urban wineries to take several approaches to wastewater. Some have spent tens of thousands of dollars to as much as $1 million to install an on-site pretreatment system to lower the sewer cost. Some use water recycled on site for irrigation of landscaping or vines, as long as the blended streams of wastewater aren't too salty from softening. Others use the hold-and-haul method of storing wastewater in tanks and contracting for it to be trucked to a lower-cost treatment facility for disposal. Many use a combination of methods to balance.

East Bay Municipal Utility District has been marketing to North Coast and Central Valley wineries to receive their wastewater at its Oakland plant, which can process 200 million gallons a day and has a dozen biological digesters that turn wastewater into methane to power 90 percent of the facility.

By comparison, Napa Sanitation has a daily capacity of 15.4 million gallons.

Some wineries have been exploring the potential of factoring in net greenhouse-gas emissions savings from biogas power production at the plant over the emissions from trucking the water there, according to Ben Horenstein, manager of East Bay MUD's environmental services division.

East Bay MUD treatment fees for winery wastewater start at 3 cents per gallon, but hauling costs can make that bill significantly higher, according to Hugh Linn, a principal at Napa-based civil engineering firm Riechers Spence & Associates.

Several North Bay civil engineering firms have been studying lower-cost options for on-site pretreatment.

"If water is really cheap, it makes sense to use it and blow through it and waste it," Mr. Linn said.

Napa Sanitation's winery wastewater production study, expected to be submitted to the district board in October, will be included in a 20-year district master plan to be completed late next year.

Solutions from this planning process could include segregating winery waste at the plant, installing pretreatment systems to "scalp" high-strength components of winery process water, building another biodigester and treatment ponds, and offering tiers of sewer fees for small wineries, according to Mr. Abramson.

Challenges for adding ponds to the Soscol plant include needed land and potential for odors.