Graph of observed and simulated groundwater levels
Observed and simulated groundwater levels after model calibration

Key Issue

  • Optimize recharge and recovery operations at the Upper VDC Ponds and RF

Solutions

  • Refine the regional groundwater flow model to provide better local-scale simulations
  • Provide rigorous calibrations for reliable optimization predictions

Optimizing Recharge and Recovery in the Pauba Valley

Riverside County, California

Numerical groundwater flow modeling and particle tracking were conducted to assess operational scenarios to optimize pond recharge and recovery.

Rancho California Water District (District) operates a series of groundwater recharge percolation ponds, referred to as the Valle de los Caballos Recharge (Upper and Lower VDC Ponds) to provide a sustainable groundwater supply for the greater Temecula and Murrieta area. Artificial recharge of imported water during the winter allows for subsequent recovery during peak demand periods.

Since 1999, the District has recharged an average of about 15,000 acre-feet per year (AFY) in the Upper VDC ponds, which were the focus of this study. The Upper VDC Recovery Facility (RF) production occurs with numerous recovery wells sited adjacent to and downgradient of the five ponds. Unrecovered groundwater that travels beyond the RF is recovered by both shallow and deep production wells located throughout the groundwater basin underlying Pauba Valley.

Aerial photograph showing location of project sites
Significant project site locations

Numerous operational scenarios were evaluated by Todd Groundwater including increased recharge in certain ponds or sub-portions of ponds, use of recovery wells adjacent to the ponds to control groundwater mounding, and selective operation of key downgradient recovery wells to increase extraction of the recharged water.

A telescopic grid mesh and layer refinement of the regional basin-wide model was conducted and numerical groundwater modeling and particle tracking were used to determine the fate of the recharged water. A five-layer MODFLOW/MODPATH model was applied to the analysis. Calibration included transient simulations of water level responses to variable recharge rates and production well pumping rates for the period of January 1997 through June 2010, which represents a period of metered recharge events at the Upper VDC Ponds and RF.

Aerial photograph showing simulated groundwater flowpaths
Simulated groundwater flowpaths under current operational conditions

Optimization Results

  • Established relationship between total groundwater production (recovery) and recharge capacity
  • Identified optimal distribution of recharge within individual ponds and pond sub-areas
  • Simulations indicated augmented recovery well system could increase total recharge to 45,000 AFY
  • Determined new recovery well locations and pumping schedules