Environmental effects from a 57-mile-long transmission line under the bay from the East Bay to San Francisco will not be "significant," according to an environmental impact report by URS Corp. More than five miles of the $300 million, 400 MW DC line is planned to be buried up to six feet below the San Francisco Bay. There is one exception to potential effects, however. The development plans to destroy some 1920s-era warehouses at a converter station site in San Francisco considered historically significant, according to the report. Mitigation measures by developer Babcock & Brown and Pittsburg Power Company - known as Trans Bay Cable - include plowing under the Bay's benthic layer during non-spawning season for salmon and steelhead. According to the report issued last week, dredging for the line is expected to have only "localized and minor" effects on marine life. The report warns of the potential for the construction to run into shipwrecks. Developers propose exploring the area to determine whether shipwrecks exist near the San Francisco end of the project. If significant archaeological structures are found, the project could be halted while they are evaluated. The project has the support of the California Independent System Operator. It is planned to go on line in 2009 (Circuit, Sept. 9, 2006).