Projects: Groundwater Modeling
Tennessee Hollow Watershed Project, The Presidio of San Francisco
Working as part of a multi-disciplinary team, CGC developed a conceptual model and three-dimensional numerical model of the Tennessee Hollow Watershed at the Presidio of San Francisco. A detailed conceptual model was initially created to guide numerical model development. The numerical model was built using MODFLOW and MODFLOW-SURFACT. The three-dimensional model simulates groundwater flow in both unconsolidated alluvial sediments and underlying fractured bedrock. Complete water balance components of both groundwater flow and surface water flow were calculated during conceptual model development and subsequently used in the numerical model. The interaction between groundwater and surface water was simulated and calibrated to existing conditions. The model will be used as the primary tool in evaluating the feasibility of proposed project alternatives.
Unsaturated/Saturated Zone Modeling of Irrigation and Pipeline Leakage
CGC performed numerical modeling to estimate the impact of precipitation and irrigation on groundwater recharge and groundwater elevations for a landslide area in southern California. Groundwater flow through both the saturated and unsaturated zones was explicitly simulated in the model. Detailed climate and irrigation data were first used to estimate groundwater recharge using the EPA HELP model. Groundwater recharge results were then used as input to the finite element unsaturated/saturated zone model SEEP/W to evaluate the impact of recharge on local and regional groundwater elevations.
Natural Attenuation and Degradation Modeling
CGC developed a two-dimensional fate and transport model using the EPA BIOCHLOR code to simulate the lateral migration and sequential degradation of chlorinated solvents at a Superfund site in the Seattle, Washington area. The model was used to estimate the average and peak concentrations reaching a nearby tidal waterway and to estimate dilution-attenuation factors for risk assessment. Sequential degradation of solvents was simulated using decay constants calculated from site-specific natural attenuation data.
Superfund Cost Allocation Modeling
Developed an analytic computer model to assess the contribution of VOCs from individual PRPs to the Puente Valley Operable Unit of the San Gabriel Basin in southern California. Contaminant flux to groundwater from overlying soil was estimated using SESOIL, a vadose-zone leaching model. The SESOIL release rate was input to WinTran, an analytic flow model containing an embedded finite-element simulator, to estimate individual plume dimensions. Plume dimensions for individual PRPs were used as a key component of a cost allocation formula to divide remediation costs among all PRPs in the valley.
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