Garbage in, garbage out. Experience in, experience out. EarthFax has combined their field and digital expertise in a number of cases to predict future groundwater responses to various activities. Our experience with groundwater flow and contaminant transport modeling has included:
DEVELOPMENT OF AN UNSATURATED FLOW MONITORING PLAN. EarthFax developed a plan to monitor flow in unsaturated cover material at a low-activity radioactive waste disposal facility in western Utah. Following an evaluation of various instruments and a comparison of instrument ambient requirements with local conditions, we provided recommendations for installation, operation, and maintenance of time domain reflectometry instrumentation. This instrumentation measures the dielectric constant of the materials in the cell compared to that of water, allowing the volumetric moisture content of the cell to be determined.
GROUNDWATER FLOW MODELING OF A PETROLEUM REFINERY. To assist in evaluating future remedial-action alternatives, a numerical groundwater model was constructed for a petroleum refinery in Utah. Water-level and hydraulic data obtained from on-site monitoring wells, off-site monitoring and water-supply wells, and local rivers and canals were utilized to construct the model. The model was calibrated under steady-state conditions, with verification being performed using data collected from a recently-implemented groundwater remediation program. The hydraulic influence of various remedial-action alternatives was then evaluated as affected by proposed closure plans.
CONTAMINANT TRANSPORT MODELING OF A PETROLEUM REFINERY. A numerical contaminant transport model was developed and run to assist in making closure decisions at a petroleum refinery in northern Utah. Of particular concern were benzene and toluene concentrations in plumes which had developed from selected solid-waste management units at the site. Although still within the property boundaries, these plumes were migrating toward off-site areas and a river which could carry contaminated water to the Great Salt Lake. The groundwater-quality influence of various remedial-action alternatives was evaluated for the solid-waste management units and the need for active remediation of the groundwater plumes was determined. Based on the modeling effort and data obtained from groundwater monitoring, it was determined that continued migration of the plumes would cease once the source areas were remediated and that the contaminants would adequately degrade as a result of natural bioattenuation. Therefore, active remediation of the plumes was not required. Results of the modeling effort were used to design a groundwater monitoring program to verify the future occurrence of natural bioattenuation.
FLOW AND CONTAMINANT TRANSPORT MODELING OF OFF-SITE PLUMES. Plumes of groundwater contamination which had their source in a refinery tank farm in central Michigan had migrated into an adjacent residential area. Contaminated groundwater had also been intercepted by a storm drain in the neighborhood. To assist in evaluating various remedial-action alternatives for the area, a flow- and contaminant transport model was developed and run. Alternatives which were evaluated included barrier trenches, groundwater recovery systems (trenches, horizontal wells, and vertical well fields), the introduction of oxygen-releasing compounds, and air sparging. Recommendations, as well as estimated costs of installation and operation of remediation systems, were prepared for the client.
MODELING OF WELLFIELD IMPACTS ON AN ADJACENT GROUNDWATER CONTAMINATION PLUME. The potential impacts of industrial water use on an adjacent municipal wellfield in southwestern Michigan were numerically modeled using a finite-difference model with a multi-aquifer module. The primary concern to be addressed was the effect of the industrial wells on the potentiometric surface near sites suspected to be contaminated with organic chemicals. Both winter and summer conditions (i.e., low and high water usage) were modeled, using public and client data on local water use. The finite-difference grid consisted of over 10,000 cells for each of three aquifers being modeled. Included in the model were the affects of an adjacent river plus the effects of wells that were completed in multiple vertical zones.
STORM DRAIN DETENTION POND IMPACT MODELING. The potential impacts of leakage from a runoff storm drain detention pond on an adjacent municipal subdivision in Utah were numerically modeled. The primary concern was to determine if leakage from the detention pond produced a mound in the shallow groundwater table which resulted in the flooding of the subdivision facilities. The calibrated model was used to identify the source of the groundwater and to develop a drain system which would alleviate the flooding problems. The finite-difference grid consisted of a 100 by 100 grid for two aquifers being modeled. Included in the model were the affects of an adjacent river plus the effects of municipal wells that were completed in the underlying aquifer.
MODELING OF CONTAMINANT MIGRATION IN A FRACTURED AQUIFER. Contaminant migration in a fractured aquifer was analytically modeled to assist in design of a groundwater remediation program. Contamination originated in an unlined uranium-mill tailings impoundment. The location and orientation of fractures in the water-bearing sandstone were delineated using electromagnetic surface geophysical methods and long-term pumping tests. The physical properties of the fractures were then estimated from published data. The model was calibrated using site-specific concentration data for chloride. Time frames for interception of the downgradient edge of the plume were then estimated. Subsequent monitoring of the contaminated aquifer, following implementation of the remediation program, indicated that the model was an adequate predictive tool.
MODELING OF GROUNDWATER IMPACTS OF SURFACE MINING. The groundwater impacts of surface coal mining were modeled for two adjacent coal mines in eastern Wyoming with a combined production of approximately 16 million tons per year. The need for accuracy was increased by the fact that the coal seam being mined also served as a regional aquifer. Approximately 40 slug tests and 10 pumping tests were performed on existing monitoring wells to assess local groundwater conditions. Data from several monitoring wells and private water-supply wells were reviewed to determine the shape of the potentiometric surface in the overburden, coal, and underburden for an area of approximately 400 square miles around the mines. The impacts of mining were then determined three-dimensionally using a finite-difference numerical model. Sensitivity analyses were performed to assess the effects of varying model parameters on model output. The time required for water levels to recover following mining was also estimated using the model. Based on the model data and regional studies, the cumulative hydrologic impacts of mining in the region were estimated.
MODELING SOLVENT MIGRATION IN A GLACIAL-OUTWASH AQUIFER. A spill of trichloroethylene in western Michigan resulted in contamination of a shallow groundwater aquifer contained in unconsolidated glacial outwash. Remediation activities associated with the plume had been ongoing for approximately 7 years, with little change in the plume boundaries. As a result, concern was expressed by the client that the plume may have been only partially caused by the known spill, with the majority of the plume being the result of previous spills at the site prior to current ownership. EarthFax analytically modeled the known spill to determine if that event could create a plume of the extent and magnitude noted in the field. Hydraulic and chemical data collected from previous investigations were used, along with published values of selected model inputs. The investigation indicated that the plume could not have been caused solely by the known spill.
MODELING OF GROUNDWATER IMPACTS OF LAKE-LEVEL CONTROL. The rapidly rising level of the Great Salt Lake in the mid-1980s had prompted government agencies in Utah to consider several options for protecting public and private facilities adjacent to the lake. EarthFax personnel examined the groundwater impacts of these various options, including diking and pumping of the water to the adjacent desert areas. Representative areas to be affected by the control options were examined and numerically modeled. Regional hydrogeologic data were utilized to establish the hydraulic characteristics of the groundwater system. The impacts of each alternative were quantified.
GROUNDWATER MODELING OF A ROCKET-MOTOR MANUFACTURING FACILITY. A numerical groundwater model was developed for a rocket-motor manufacturing facility in northern Utah to assess the hydraulic effectiveness of future groundwater remediation alternatives. Water-level and aquifer-characteristics data obtained from over 80 monitoring wells on the facility were utilized to construct the model. In addition, data from logs of private water-supply wells in the downgradient areas were utilized to expand the area of the model. Once calibration of the model was complete, various remediation alternatives were modeled to assist in selecting the most appropriate alternative.