Flow & Transport Modeling Projects
Hill Air Force Base
INTERA developed and used a geosystem model to help evaluate remedial options, determine feasible remedial objectives, and develop an effective remedial plan for NAPL source zones at OU 1. This "geosystem" model describes the site-specific attributes and properties of the aquifer, groundwater, NAPL, and capillary barriers that define the system comprising the contamination. Ultimately, implementing the geosystem model in a three-dimensional numerical simulator provides a way to quantitatively assess and optimize decisions associated with remedial options. Once the character, migration, and behavior of OU 1 LNAPL were understood in the context of the site's hydrogeological setting, we developed a three-dimensional flow model and conducted feasibility simulations to assess remediation strategies at OU 1. Numerical simulations were performed at two scales. Three-dimensional groundwater flow simulations conducted at the scale of the on-base source zone at OU 1 (the "site scale") to evaluate the impact of existing de-watering trenches that were installed to contain groundwater in the source zones and recover NAPL. Multi-phase fluid flow simulations were also conducted at a local scale (one trench segment) to evaluate the removal of NAPL or NAPL constituents through groundwater pumping, soil vapor extraction (SVE), and surfactant flooding. The effect of operating these trenches on the distribution of NAPL, their effectiveness in recovering NAPL, and their potential for use in future enhanced LNAPL removal operations were also evaluated. The results of our modeling efforts were instrumental in guiding the subsequent remedial action process.
State Superfund Site
The North Railroad Avenue Plume (NRAP) State Superfund site has been impacted by chlorinated solvent releases from an old dry cleaning facility. The groundwater contaminant plume includes potential impacts to surface water and confirmed impacts to municipal water supply wells. INTERA developed the Feasibility Study (FS) report to evaluate a series of remedial alternatives. As part of the FS, we developed a three-dimensional groundwater flow and transport model to support the risk assessment and to assist in the subsequent remedial design.
Groundwater flow and transport modeling was conducted to provide a quantitative analysis of the contaminant migration and its potential to impact human and ecological receptors. The modeling was also designed to provide a means of evaluating the need for, and effectiveness of, various remedial alternatives. The various remedial alternatives used a zone of enhanced bio-remediation to create a 'bio-curtain' to degrade the dissolved phase PCE plume over a short lateral distance. In addition, given the importance of NAPL dissolution in the evolution and future behavior of the plume, the multi-phase, multi-component numerical code UTCHEM was used to simulate various multi-phase (water, NAPL) flow processes—specifically NAPL dissolution.
Savannah River Site
INTERA performed flow and transport modeling of three inorganic constituents (manganese, boron, and mercury) and one organic constituent (TCE) to support the TNX Area Operable Unit (OU) Feasibility Study and a Ground Water Mixing Zone (GWMZ) Application at the Savannah River Site. We developed a three-dimensional model that incorporated coastal plain sediments and alluvial fill in the Savannah River flood plain. Since previous studies at the TNX OU indicated that TCE naturally attenuates in the floodplain because of evapotranspiration, a significant portion of our modeling effort focused on developing a detailed model of the evapotranspiration process in the wetlands and calibrating the model to observed uptake as measured by tree cores and the enhanced groundwater concentration reduction downgradient. After constructing and calibrating the model, we used it to evaluate a number of remedial processes including phytoremediation, groundwater extraction through pumping wells and geosiphon systems, and advection and dispersion. The modeling report and GWMZ Application were submitted to US EPA Region IV and SCDHEC for review. Based on the thoroughness and quality of INTERA's modeling efforts, only minor comments were received from the regulators, and these were resolved without the need to conduct additional model simulations.
Petroleum Refinery
INTERA conducted modeling to predict travel paths and times from a client's property onto adjacent off-site property. The site data consisted of very little in the way of hydraulic aquifer test results but did have over 755 soil borings and wells with over 11,000 geologic lithologic descriptions. No geologic data control was available for the off-site region. To account for the uncertainty of geology, we used statistics to develop multiple geologic models that were consistent with the available site data.
Our methodology consisted of a four-step process consisting of indicator classification, variogram analysis for each indicator class, Sequential Indicator Simulations (SISIM) to develop conditional simulations of the hydrostratigraphy in the study domain, and stochastic flow modeling using each conditional simulation. For each stochastic MODFLOW simulation (2.1 million grid blocks each) result, MODPATH was used to particle track 250 particles from the site boundary to the off-site properties. This four-step process produced a geologic model that honored the available data and the observed spatial structure of the lithofacies and allowed a statistically consistent method for interpolating on-site and extrapolating off-site lithofacies. The methodology also allowed for the quantification of uncertainty in the performance measure of interest to our client (i.e., particle travel time/path). Two telescopic-mesh-refined models were also developed and hundreds of conditional simulations of the geology were simulated.
