Registered Nurses who work at John Muir Mount Diablo Hospital in Concord have reached a tentative agreement on a new three-year contract that nurses say will provide for additional patient care improvements as well as securing nurses’ health coverage. The settlement, reached Wednesday, covers more than 700 RNs who are members of the California Nurses Association/National Nurses United. The settlement will go before RNs for ratification in membership meetings scheduled for October 1.