Cumulative changes in impervious surfaces pose a number of potentially significant threats to Santa Clara County watersheds, particularly to water quality and potential erosion. Because Santa Clara County has water bodies that are already considered “impaired,” cumulative impacts present serious concerns.

Although data on impervious surface changes could be easily compiled for each new development, local governments do not currently require this information from new developments. Without anadequate analysis of impervious surface changes, the local governments cannot verify that theyhave avoided significant environmental impacts. New requirements under the Clean Water Actand Porter-Cologne Act address some impacts of impervious surfaces; however, these new requirements do not address all the potentially significant cumulative impacts, as is required underthe California Environmental Quality Act. Changes in CEQA Guidelines require this cumulativeimpact analysis.

Committee for Green Foothills has prepared a report: Controlling Cumulative Impacts from Impervious Surfaces: Analysis and Recommendations for Santa Clara County. Committee for Green Foothills gratefully acknowledges the Santa Clara Valley Water District, whose financial support made this report possible.

In addition, the author of this report, CGF Santa Clara County Legislative Advocate Brian Schmidt, has prepared a three-minute and a ten-minute PowerPoint presentation addressing the impervious surfaces issue.