Groundwater/Surface Water Interaction Model

The second major study to be initiated will develop a groundwater-surface water model for the Upper Santa Clara River Watershed. The study will determine the interaction between surface water and groundwater and its linkage to surface water quality and groundwater quality with respect to chloride and total dissolved solids (TDS). The model will assess the assimilative capacity of the surface water and groundwater system(s) in relation to existing Basin Plan water quality objectives for groundwater and surface water.

One goal of the model is to determine the dilution of WRP effluent with natural sources of flow (such as tributary runoff and rising groundwater). The model will be used to determine the concentration gradient between the Saugus and Valencia WRPs and key locations(s) where surface water is diverted for agricultural irrigation. Another objective for the model is to assess the extent of mixing, assimilation and attenuation of chloride/TDS from WRP effluents.

Because the model may potentially be used in a Basin Plan amendment, it will be developed to facilitate public review, both during the study process and during the comment phase of any regulatory action by the Regional Board. The public will be able to examine the model’s data files, replicate model results, and have access to model assumptions. The TWG and TAP will be involved throughout the study to validate the process used to develop the model.

In combination with the results of the other Chloride TMDL studies, the Groundwater-Surface Water Interaction Model may be used by the Regional Board to develop a site-specific chloride objective for the affected reaches of the Upper Santa Clara River Watershed.

Study Process