A couple of birdies tell us that the recent nomination of Assistant U.S. Attorney Charles "Ben'' Burch to Contra Costa County's Superior Court bench came just as Burch's prosecution team was about to call a potentially key witness before a grand jury investigating state Senate leader Don Perata's political and business dealings. The witness, according to our sources, is Sandra Polka, a former Democratic legislative staffer who was hired by BART to provide political outreach for seismic bond measures in 2002 and 2004. Among the others who landed BART consulting contracts on those bond measures were a public relations firm...