The company backed by Silicon Valley billionaires that for years stealthily snapped up more than $800 million worth of rural land for a new walkable, affordable and green city between San Francisco and Sacramento now needs voters to embrace the idea. Jan Sramek, the former Goldman Sachs trader spearheading the effort, spoke Wednesday to journalists and supporters about his vision for building a community on what’s now mostly farmland. His California Forever company needs approval from Solano County voters in November to bypass protections put in place in 1984 to keep agricultural land from being turned into urban space. … Beyond its agricultural use, the land California Forever is targeting is in the heart of the Sacramento-San Joaquin River Delta, a sensitive estuary home to many fish and wildlife species. The Delta is also the center of California’s already over-taxed water supply system. Critics of the project worry adding more development will further harm the already threatened ecosystem.