A state audit released on Tuesday has found Assonet-based Crystal Springs, a nonprofit that works with children and adults with developmental disabilities, incurred more than $500,000 in questionable costs over a two-year period. A large portion of those costs involved payment to Assonet-based Thermo Mechanical Systems Corp., which was frequently used to provide equipment and services without either a contract or a competitive bidding process. Crystal Springs stated in a press release that it will implement a new policy to bid competitively any purchase in excess of $2,500.