Six years after unveiling plans to build a 320-foot high dam and reservoir at Pacheco Pass in southern Santa Clara County, the largest water district in Silicon Valley still hasn’t found any other water agencies willing to help fund the project. But this week, an unusual potential partner came to light: China. The revelation of interest from one of the United States’ most contentious rivals is the latest twist in the project’s shaky history: The price tag has tripled to $2.8 billion since 2018 due to unstable geology found in the area. The Santa Clara Valley Water District, which is pursuing the plan, has delayed groundbreaking by at least three years, to 2027, instead of 2024 as announced five years ago. And environmentalists won a lawsuit this summer that will require more study of how ongoing geological work will affect endangered plants and animals.