Contra Costa County is an active issuer of tax-exempt multifamily mortgage revenue bonds. Proceeds of the Series 2015A Bonds will be used to (1) pay the costs of certain transportation projects,.Principal of the Bonds is payable on February 1, 2021 with respect to the Taxable Series 2020 Bonds, and on. Expected to reduce GHG emissions in the unincorporated areas of Contra Costa County without the County taking additional action.