Todd Developing Salt Management Strategies for California Groundwater Basins

Temescal Subbasin and Salt Balance

Todd Engineers constructed groundwater basin "salt balance" models for the City of Corona, California to evaluate potential future groundwater Total Dissolved Solids (TDS) and nitrate concentrations in the Temescal Groundwater Basin. Groundwater volumetric inflows and outflows, along with TDS and nitrate concentrations for all key basin sources and sinks, were estimated for a future 20-year period.

The approach is consistent with and builds on the basin conceptual model, water balance, and numerical flow model developed by Todd Engineers for the City's Groundwater Management Plan adopted in 2008. A three-dimensional MODFLOW model incorporated assumptions for future pumping, imported water recharge, and wastewater discharge in the basin.

The initial volumes of groundwater and TDS and nitrate mass present in the basin were estimated to provide reference points for predicting groundwater water volume and chemical mass changes over time. A base case was compared to several scenarios of enhanced recharge in the basin using imported water. The analysis allowed the evaluation of changes to salt loading resulting from imported water recharge.

A sensitivity analysis was included to provide a range of possible future water quality conditions.

The base-case TDS mass balance indicates that future concentrations in the Temescal basin may increase, depending on inflow and outflow mass fluxes including future pumping. Nitrate concentrations in the groundwater basin are predicted to decrease. Simulations of future imported water recharge projects indicate that the addition of relatively higher-quality Colorado River or State Water Project water will help to at least maintain -- and more than likely improve -- overall TDS and nitrate concentrations in the future.