Brassfield Estate Vineyards – Water Budget Report & Groundwater Flow Model
Clearlake Oaks, CA

 For this project, EBA developed the transient three-dimensional calibrated High Valley Groundwater Basin (HVGB) Groundwater Flow Model (GFM) to build a better understanding of regional groundwater flow, develop an updated and more sophisticated water budget, and provide insight into cumulative aquifer storage trends over time for the site’s underlying aquifer complex that is comprised of two water-bearing formations. The GFM was executed on a monthly time-step for 864 stress periods and utilizes inputs of infiltration, pumping, and boundary conditions to model hydraulic heads and water budget values for the HVGB. The GFM was developed with United States Geologic Survey (USGS) finite-difference MODFLOW-NWT^® in conjunction Visual MODFLOW^® Flex (VMODFLEX), QGIS, AutoCAD® Civil3D^® (C3D) software information to develop a three-dimensional representation of the aquifer complex that includes groundwater elevations, flow regimes, and estimates of hydraulic conductivity specific storage for each of the two formations.

The MODFLOW-NWT^® model utilized the following USGS packages:

• WEL – Well package (to simulate groundwater pumping);
• RCH – Recharge Package (to simulate recharge from precipitation);
• CHD – Constant Head Boundary Package (to simulate constant hydraulic heads from adjacent hydrogeologic formations); and
• FHB – Flow and Head Boundary Package (to simulate transient inbound and outbound fluxes from adjacent hydrogeologic formations).

The Groundwater Flow Model (GFM) was calibrated to historical groundwater hydraulic head measurements dating back to the 1950s from six Department of Water Resources (DWR) monitoring wells located in High Valley. In addition, the impacts of inflows and outflows to adjacent hydrogeologic formations were incorporated into the model calibration process to provide additional insight into the dynamic character of the aquifer complex. Aquifer storage capacity was estimated monthly by adding water budget inflows and subtracting outflows from the cumulative aquifer storage from the previous month.

Furthermore, model uncertainty was characterized by calibrating the GFM using PEST v12.3 (Model- Independent Parameter Estimation and Uncertainty Analysis). Hydraulic conductivity and specific storage values were optimized using the PLPROC (parameter list processor) subprogram in a sum of the square residuals (best-of-fit) calibration routine to the available hydraulic head measurements and Well Completion Report (WCR) data. Model boundary conditions, i.e. constant head, flux, and precipitative recharge were also parameterized on manually to further move the calibration process forward.