Aquila ( ILA), agreed to buy the Aries power plant in Pleasant Hill, Mo., from Calpine for $158.5 million. Aquila will use the 580-megawatt natural gas-fired facility as an intermediate-capacity power plant, one that will provide power over an extended period of time to supplement base load coal and nuclear power plants. Aquila will absorb all employees of Aries. The transaction is subject to approval by the Federal Energy Regulatory Commission and bankruptcy court approval. Other parties will also be bidding and if the court adopts the procedural schedule proposed by the parties, the transaction is expected to close in December of this year.