The regional board or state board shall respond with a written notice to the department within 20 working days after receipt of the notice or information provided pursuant to Section 80590 indicating whether the regional board or a local oversight program agency under contract with the state board will oversee the response action pursuant to this article. If the regional board or state board does not provide this notice within that time period, the regional board or state board shall be deemed to have elected not to oversee the response action.