Groundwater Resources Investigations and Permitting Studies 

Solar Power Project Near the Colorado River

On behalf of a large solar power developer, JJ&A managed groundwater resources investigations and permitting studies for a proposed 500 MW solar thermal power project near the Colorado River. Work performed included project development planning efforts as well as the project’s Application for Certification (AFC) with the California Energy Commission (CEC).

Assessment of Available Groundwater Resources
The initial phase of the project involved preparing an Existing Conditions Report. This included compilation and review of available groundwater resources data to assess the availability of a suitable groundwater supply, investigating the quality and sustainability of the available supply, developing a project strategy to address water rights and permitting issues, and identifying potential data gaps. The availability and suitability of alternative water supplies (surface water, irrigation return water, and reclaimed wastewater) was also evaluated. The groundwater assessment was based on compilation and review of publicly available maps, published reports and research papers, and development of a well and water quality database from available state and federal on-line databases and information maintained by the local irrigation district and the Bureau of Reclamation. The basin was characterized in terms of its geology, groundwater flow, groundwater levels, aquifer characteristics, and groundwater quality. In addition, the basin water balance was established based on information about inflow from adjacent basins, recharge from precipitation, deep percolation of irrigation water, groundwater pumping, surface water interaction, and evapo-transpiration. Finally, an evaluation of the existing regulatory and water rights setting was conducted, including assessment of whether the basin is in overdraft, adjudicated, or subject to management under a special district. This latter evaluation specifically addressed whether the project was likely to draw water levels down below the proposed Colorado River Accounting Surface, which, if adopted by the Bureau of Reclamation, could require that the project obtain an entitlement to pump Colorado River water.

Groundwater Resources Impact Assessment
Based on the Existing Conditions report, a conceptual model of the basin was developed and final locations and pumping rates were selected for the project water supply wells. These inputs served as the basis to construct a three-dimensional, numerical groundwater flow model using USGS Modflow 2000 code and the Groundwater Vistas® platform. The model included simulation of underflow into and out of adjacent basins, mountain front and aerial recharge, deep percolation from irrigation, interaction with the Colorado River, recharge from wastewater disposal, and supply well pumping. Model parameters were estimated from a prior model of the area, geologic data, published studies and the results of aquifer tests, and were refined during model calibration to historical data. Predictive modeling was then conducted to assess potential project impacts in terms of induced drawdown, well interference, surface water depletion, water balance changes, and water quality effects. The potential for subsidence impacts and for adverse effects to groundwater-dependent vegetation was also assessed. A Groundwater Impact Assessment Report was prepared and appended to the AFC for the project.

Regulatory Support
After submittal of the AFC, JJ&A coordinated the project responses to CEC Data Requests and the Preliminary Staff Assessment, and participated in several informational workshops and meetings with CEC water resources staff. A mutually acceptable means to evaluate potential impacts to the Colorado River was negotiated, and an updated version of the model was prepared and accepted by CEC staff. In addition, JJ&A assisted in the negotiation of appropriate mitigation measures that were accepted by CEC staff.