Power and Energy

Challenge. Determine impacts of additional groundwater withdrawals required to meet water needs of a large solar plant project in the Dry Harper Lake Basin

Solution. Water requirements for the proposed solar plant meant obtaining a permit for two new groundwater wells. INTERA personnel evaluated existing groundwater use in the basin and determined that the proposed new wells in combination with retiring the irrigation wells on the parcel of land to be used for the parabolic mirror field would actually reduce overall groundwater withdrawal in the basin. Our staff (Dr. Jack Wittman) testified before the California Energy Commission to explain how the addition of the new wells, and retirement of existing irrigation wells, would affect regional groundwater levels. Modeling showed that over decades water levels in the basin rebound from the decades of withdrawal for alfalfa irrigation. Despite the initial concerns of the regulators, testimony demonstrated how the system would recover over the life of the project. Additional scope included aquifer testing, collection of water quality samples, and the refinement of a published United States Geological Survey flow model to evaluate impacts on other water users and the ecosystems. As a result of our contributions, the permit was granted for two local wells as a source for deionized rinse in this arid adjudicated groundwater basin.

Challenge. Assessment of available water supplies, source water quality, and permitting requirements for siting of two power plants

Solution. INTERA applied expertise with the surface and groundwater characteristics at both sites in conjunction with our experience working with groundwater conservation districts to define the most suitable water sources, with respect to water quality, quantity, and permitting requirements, for each proposed power plant site. Surface water was not a viable option at either of the sites. The target raw water production rates were 2,500 gallons per minute (average) and 4,100 gallons per minute (peak) for each of the sites, which were located over two different aquifer systems. The Fannin County site overlies the Northern Trinity and Woodbine aquifers in north Texas, while the Neches County site overlies the Carrizo-Wilcox Aquifer—the more productive of the two aquifer systems. INTERA reviewed relevant literature regarding hydraulic properties of the aquifers and collected and analyzed pump test and specific capacity test data in the areas of the two proposed sites. Groundwater quality was assessed through groundwater samples and geophysical logs (gross quality). We provided guidance in obtaining the appropriate permits for the water supply wells and performed local-scale drawdown analyses with a multi-layer analytic element code (TTIM) that enabled us to evaluate drawdowns at both the water supply wells and other nearby wells that could potentially be impacted. After our assessment confirmed that adequate supplies exist at each site, we also provided optimal well layouts to establish the costs associated with developing the water supplies.

Challenge. In area with limited available hydrogeologic data, determine availability of water source to provide a minimum of 10 million gallons per day (MGD) required for operation of new power plant

Solution. Recognizing that the limited available data required an innovative analysis approach to provide the high level of confidence needed to project owners, regulators, and stakeholders, INTERA personnel used a set of specialized analytic element models to determine the likelihood that the required water was available near the proposed site. Our analysis showed that the water was available if pumped from the alluvial system with wells installed along the banks of the Sangamon River. The results included a complete description of the testing required during site characterization to design the wells and determine yield. Our innovative approach provided the assurances needed to satisfy regulators and help stakeholders consider the options for energy production in the area. This included a focused discussion on in-stream aquatic impacts and drought mitigation planning.