A month after Mayor Tim Grayson returned campaign contributions linked to Lennar Urban, a competitor has raised troubling questions about the integrity of the selection process for the Concord Naval Weapons Station developer. In a strongly worded letter to City Manager Valerie Barone, the attorney for Catellus Development Corp. demanded that the city investigate whether Lennar and its associates had improperly lobbied the City Council in violation of the negotiating agreement both firms signed in May. Catellus also asked why staff failed to recommend a preferred master developer, as expected.