Philadelphia Employees Retirement System is considering changing its three bond benchmarks to one, said Marc Bonavitacola, acting CIO for the $4.6 billion system. The fund uses the Lehman full- and intermediate-duration and international fixed-income indexes for benchmarks. Its looking to change to the core-plus Lehman aggregate, he said. "Were in the process of negotiating with managers, said Mr. Bonavitacola. The change is due to an asset allocation study the plan completed last year. It would affect the systems six active bond managers, he said. Philadelphia Municipal Employees current bond portfolio totals $1.4 billion.