4.2.3. Modeling

The CALFED Delta Drinking Water Council recommended a multi-faceted assessment program that included preliminary establishment of baseline Delta water quality conditions [93]. A workgroup was formed in 1999 and tasked with developing a model simulation of historical water quality conditions in the Delta [94] to (i) develop confidence in a previously developed hydrodynamic and water quality model of the Delta to establish baseline conditions for salt and organic carbon transport and (ii) establish error bounds for future simulation results. The model in question was the Delta Simulation Model version 2 (referred to as DSM2) [95]. CDWR [96] documents a DSM2 model validation study conducted in support of this CALFED effort. The validation study simulated transport of DOC and UV-254 from October 1990 through December 1997 and employed an approach documented in Jung [94] to characterize Delta island return water quality; this approach built upon earlier work documented in CDWR [64].

CDWR's Delta Modeling Section, acting as a program partner to the MWQI program, continued DSM2 model development for simulating DBP organic precursor transport throughout the CALFED years. Model development activities included formulating planning-level precursor boundary conditions [97] and implementing an algorithm to simulate the transfer of DOC from peat soils to Delta channels (due to leaching and microbial decay) when Delta islands are flooded [98,99]. This algorithm was used for evaluation of the proposed Delta Wetlands project, a project to store water on two Delta islands [100] and a major levee break in 2004 on the Jones Tract in the Delta [101].

Following the MWQI program's early success implementing real time monitoring in the Delta, proof-of-concept efforts were launched to utilize available modeling tools to forecast drinking water quality constituents of concern, notably bromide and DOC [102–104]. To support water quality forecasting capabilities beyond the Delta region, the DSM2 modeling platform was used for initial development of a water quality transport model of the California Aqueduct, South Bay Aqueduct, and Delta-Mendota Canal systems [105,106]. These nascent efforts ushered in a new MWQI program focus on providing decision support for SWP operation, as described in Section 4.3.
