Pure Water Soquel Groundwater Model Simulation Results

This technical memorandum discusses model simulation groundwater levels, groundwater budget, and particle tracking results to support the Environmental Impact Report of the Pure Water Soquel project involving replenishment of advanced purified recycled water within Soquel Creek Water District’s (SqCWD’s) service area. Six model simulations have been run using the calibrated GSFLOW model for the Santa Cruz Mid- County Basin (the Basin) where SqCWD’s service area is located. These simulations have different pumping and active replenishment distributions, as follows:

• Two Projected Existing Conditions (No Project) simulations with SqCWD’spumping distribution reflecting future demand without additional replenishment at proposed recharge wells.
• Two Project simulations with SqCWD’s pumping distribution reflecting future demand and pumping re-distribution with the addition of replenishment at the Monterey and Cabrillo College Dr. sites (referred to as the Cabrillo-Monterey simulations). These simulations also represent potential replenishment at the Twin Lakes Church site instead of one of the two Cabrillo College Dr. sites. The Twin Lakes Church site is approximately 500-750 feet to the west of the Cabrillo College Dr. sites.
• Two Project simulations with the same pumping distribution as the Cabrillo- Monterey simulations, but with replenishment at the Monterey and Willowbrook sites (referred to as the Monterey-Willowbrook simulations).Simulation groundwater levels are evaluated for the following effects:
• • Comparison of groundwater levels at coastal monitoring wells to protective elevations estimated to prevent seawater intrusion from further occurring in groundwater supply aquifers.
  • Groundwater levels in the recharge wells to assess whether model results are consistent with estimated capacities for the well, recognizing that site specific testing will be needed to confirm recharge well capacities.
  • Groundwater levels at nearby wells to evaluate effects on operation of those municipal, private, and institutional wells.Simulation groundwater budgets are evaluated for following effects:

    • Flows entering and leaving the Basin, including flows to and from groundwater in storage and flows offshore to prevent seawater intrusion.

    • Flows between groundwater and surface water.

    This memo does not include results for a Cumulative simulation. Information from the City of Santa Cruz to define its Aquifer Storage and Recovery project to be cumulative with Pure Water Soquel is not available or developed at this time.

    This memo includes results from particle tracking based on the above simulations performed to support the Salt and Nutrient Anti-degradation Study and permitting of the recharge wells. This involves particle tracking of simulated purified, replenishment water to evaluate the fate of the water as it travels in subsurface aquifers. Particle tracking is also used to evaluate travel times of purified, replenishment water, which requires refined analysis near the recharge wells. A scope to superimpose analytic element solutions for recharge and nearby extraction wells onto GSFLOW results to facilitate travel time calculations was approved by SqCWD Board December 18, 2017 and results should be forthcoming in July 2018.