MBK Engineers has assisted Contra Costa Water District (CCWD) with CalSim II modeling support for Los Vaqueros Reservoir since 2009. MBK developed the Los Vaqueros Module (LVM) in CalSim II for modeling of existing CCWD operations and Los Vaqueros Expansion Alternatives. LVM was designed to function as a stand-alone model or as an integrated submodule to CalSim and includes complex algorithms for meeting CCWD water supply and water quality targets. MBK provided modeling support for the Los Vaqueros Reservoir Expansion (LVE) by simulating various LVE alternatives using CalSim II and evaluating operational impacts due to changed Delta diversions and use of the expanded reservoir. Impact metrics included water supply to SWP and CVP contractors and proposed Project partners, salinity of CCWD water supply, Delta outflow, X2, Old and Middle River flow, and CVP and SWP upstream storage. More recently, MBK has enhanced the LVM to add a power use and cost analysis component to the Los Vaqueros Module to allow CCWD staff to develop power cost minimization strategies for operation of the CCWD system. MBK also developed integrated reservoir operations logic to allow CCWD and East Bay Municipal Utilities District (EBMUD) staff to explore to possibility of an additional Los Vaqueros Expansion partnership. Integration of EBMUD imports and exports through the Mokelumne Intertie were coordinated with CCWD water supply and water quality operations. Model flexibility was maintained to allow CCWD and EBMUD staff to explore a wide range of alternatives.