The Marin County Planning Commission this week unanimously approved a master plan amendment aimed at converting office spaces into 57 overnight guest rooms for clients at George Lucas’s Big Rock Ranch, despite concerns from residents of nearby Nicasio that the switch might further drain their drought-stricken water supply. The amendment awaits final approval from the Board of Supervisors.

In Nicasio, 65 properties rely on wells fed by groundwater from Nicasio Creek, according to a letter submitted to the county by the Nicasio Land Owners Association. That “conservative estimate” only includes homes along Lucas Valley road, said the association’s design review chair, Sue Kline, who noted that the latest hydrological study was conducted in 1996.

“Surely, conditions have greatly changed for the worse,” she said.

Referencing a water-use report submitted by Big Rock’s owner, Skywalker Properties, the association and others in Nicasio noted that overnight guests could consume over 2,000 gallons of water per day, all pumped from wells located in the upper watershed of Nicasio Creek. That added use—combined with the prospect of supervisors passing looser second-unit regulations that could boost Nicasio’s population—could hit residents hard if the drought continues, the association’s letter reads. 

Homeowners are already left in a tough spot when their wells run dry, since Marin Municipal Water District—which draws much of its water from the Nicasio Reservoir—neither services the town nor sells water exports to its residents. Instead, residents have to hire companies from Petaluma to truck water in at a high cost.

“For us, water is life,” said George Forman, a longtime local. “For Big Rock, it’s business. Until the county has established a safe and sustainable yield for the Nicasio Creek watershed, it would be irresponsible—at minimum—to allow the conversion of day-use office space into a 57-room hotel.”

But commissioners were swayed by Skywalker Properties’ pledge to install a $250,000 greywater recycling system projected to reduce Big Rock’s water consumption by 40 percent—thereby offsetting any extra consumption from overnight guests. 

That pledge, however, is no guarantee: commissioners declined to compel Skywalker Properties to follow through with the greywater system, which would also require a permit from the state’s Regional Water Quality Control Board.

Even so, Skywalker Property representatives said the septic system at Big Ranch—which is restricted in its master plan from hosting more than 300 clients at once—handles on average only half of what its 8,700-gallon daily maximum capacity allows. 

“Our water is capped by septic capacity,” said Tom Forster, a spokesman for Skywalker Properties.

Critically, commissioners directed staff to strengthen the amendment’s language to prevent Big Rock from being used for anything other than office-related employee activities, such as for conventions or similar large events that would increase water use. Many in Nicasio and Lucas Valley have pointed to expanded dining rooms and meeting rooms and a fitness center included in the amendment as proof that the facility could accommodate large water-sapping events or even become a permanent hotel under a future owner.

“We’re more than happy to talk with staff about that and hopefully arrive at language that is satisfactory for all,” Mr. Forster said.

Office day-use at the 1,061-acre Big Rock Ranch was opposed by a group of residents called the Save Our Countywide Plan Committee, who sued the county in 1996 shortly after supervisors approved a master plan that outlines uses for Big Rock and four other ranches owned by Mr. Lucas. That suit was dropped after a settlement was reached.

“I think the [amendment] is actually a pretty benign use compared to what is there,” said Don Dickenson, a current planning commissioner who was a member of Save Our Countywide Plan in 1996. 

Mr. Lucas also sought to build a production studio for his 1,039-acre Grady Ranch in 2012, but scrapped that effort after receiving pushback from neighbors. He is now seeking approval from the county to build 224 affordable housing units on the property.