Groundwater modeling refers to the process of using computers to numerically simulate (or model) the flow of water beneath the ground surface. Like the way meteorologists use computer models to forecast the weather, and sometimes plumes of smoke, spreading through the atmosphere, hydrogeologists use computer models to forecast the movement of groundwater, and sometimes plumes of contamination, spreading through the lithosphere (the soil, sediments, and bedrock beneath us).
These forecasts are important because groundwater is the source of much of our drinking water, is used for irrigation, and discharges into rivers and streams. If the groundwater is contaminated, it can harm these features and the humans and ecosystems that interact with it. Contaminants present in groundwater can also produce vapors that intrude into the breathing space of our buildings.
Hydrogeologists work to safeguard the quantity and quality of groundwater, and are concerned with topics such as groundwater yield, hydraulic conductivity, and transmissivity; monitoring and protection; changing water table levels, effects of groundwater withdrawals on streams, and saltwater intrusion, among others.
Developing a Groundwater Model
An early and critical step in groundwater modeling is the development of a conceptual model of the groundwater flow system (hereafter aquifer). The conceptual model is a 3-dimensional representation of the sediments, bedrock, and zones of saturation in the aquifer. It is critical that the conceptual model accurately reflects the aquifer’s parameters because this information informs the development of the numerical model, and, in turn, influences its reliability.
To this end, our team integrates a wide range of geologic, hydraulic, climate, soils, vegetation, tectonic, potentiometric (i.e., hydraulic pressure), and geographic information into each conceptual model we develop. We also use a variety of geophysical techniques including seismic, ground-penetrating radar, electromagnetic induction, and electrical resistivity surveys where they cost-effectively strengthen the characterization of the aquifer.
Using this comprehensive suite of information helps improve the effectiveness and reliability of our numerical models; it also helps us design and implement more-cost-effective strategies for obtaining specific physical and chemical information from the actual aquifer. This specific information is obtained from borings drilled into the subsurface geology, the core and various measurements obtained from these borings, and water samples and hydraulic parameters obtained from wells constructed in these borings.
After the conceptual model is reviewed for consistency with the geologic history and processes that have acted in the region surrounding the aquifer, information from the conceptual model is translated into the numerical model. The numerical model can be thought of as a 3-dimensional block of cells that encompass and incorporate the geology and hydraulics represented by the conceptual model (yes, like The Matrix). Each cell (generally cube shaped) is programmed to exhibit the characteristics of the rock type (e.g., hydraulic conductivity), degree of saturation, and hydraulic potential (akin to pressure) in a manner that is representative of that respective place (horizontal and vertical position) in the aquifer.
This combination of hydraulic conductivity, saturation, and hydraulic potential controls the directions and rates of groundwater flow in each cell. In turn, the collective of cells simulates the directions and rates of groundwater flow through the whole aquifer.
At this point the representativeness of the numerical model is often further advanced by stressing the actual aquifer in various places and ways (e.g., pumping, or injecting water), and then monitoring the nature of response(s) elsewhere in the aquifer. Then the numerical model can be stressed in the same way, and its parameters can be calibrated to elicit the responses that are more representative of the real aquifer.
After the numerical model accurately reflects the real-world aquifer, various contaminants can be introduced at identified or suspected source locations in the numerical model, and the fate and transport behavior of these contaminants can be programmed in the model to further refine source locations and responsible parties, and to determine contamination migration pathways, timeframes, potential exposure scenarios, and anticipated responses to various remediation technologies/approaches.
Using Groundwater Models
Defensible groundwater models are strengthened by expertise in deterministic and stochastic numerical flow modeling, solute transport, and geostatistics; and how public-domain and proprietary software addresses specific project requirements and state and federal regulatory standards. We use modeling software including MODFLOW, MODPATH, and MT3D to:
- Evaluate source areas, identify Prinicpal Responsible Parties, support litigation, and apportion remediations costs.
- Assess exposure pathways, receptor impacts, corresponding risk, and groundwater cleanup levels.
- Select and design remediation systems that most effectively reduce risk and cost. We have expertise in a range of remedial techniques and technologies including natural attenuation, bioremediation, in situ chemical oxidation (ISCO), air sparging/soil vapor extraction (AS/SVE), barrier and reactive walls, pump and treat systems, infiltration galleries, and reinjection
- Assess groundwater yield, aquifer dewatering, and potential and actual impacts to surface waters and other aquifer uses and users.
Selected Case Studies in Groundwater Modeling
Below are five key case studies where groundwater flow and transport models were used to cost-effectively address environmental contamination in these critical areas at highly impacted sites.
Petroleum Hydrocarbon Refinery, Large Contaminant Plume Study, Roxana, IL
Cameron-Cole provided expert witness testimony for two groundwater litigation cases resulting from 100 years of separate-phase petroleum hydrocarbon (SPH) releases at a large-scale refinery. Primary components of the subsurface contamination included residual separate-phase hydrocarbons (SPH) in the soil matrix and dissolved-phase benzene in groundwater. Our Hydrogeologic Expert and Rebuttal Reports showed that historical releases from the refinery and off-site pipelines generated the dissolved benzene and SPH plume extending off-site. These findings supported a class-action settlement involving $6 million in awarded damages.
Regional PFOS-PFOA Plume Groundwater Modeling Analysis, Pensacola, FL
Cameron-Cole completed a regional numerical groundwater model that supported analysis of two polyfluoroalkyl substance (PFAS) plumes and the design of a corresponding groundwater monitoring program. Aqueous film-forming foams (AFFF) were historically used to extinguish petroleum hydrocarbon fires at the site. The PFAS compounds in these foams (e.g., perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)) impacted groundwater in the underlying, regional sand and gravel aquifer. Our numerical groundwater flow and transport model showed the origin and extent of these plumes, and supported our design of an optimized groundwater monitoring well network that saved the client over $250,000.
Petroleum Hydrocarbon and Chlorinated Solvent Plume Reconstruction and Responsiblity Assessment, Kettle Falls, WA
Cameron-Cole developed a groundwater flow and solute transport model that was used to evaluate the release scenario of separate petroleum hydrocarbon and chlorinated solvent plumes beneath a railyard. The petroleum hydrocarbons consisted primarily of diesel range organics (DRO) comingled with trichloroethene (TCE). The model demonstrated a multi-decade origin for both the TCE and DRO plumes, and that our client was responsible for only 15% of the DRO impacts and none of the TCE impacts, resulting in a cost savings of more than $3 million in site investigation and remediation costs.
Hydrocarbon and Solvent Recycling Facility, Oklahoma. Confidential Waste Management Client
Cameron-Cole prepared a corrective measure study, completed groundwater flow/solute transport modeling, performed limited soil excavation, and installed an innovative groundwater recovery trench and 30-well in-situ biological reactor (ISBR) remediation system to mitigate risk posed by petroleum hydrocarbons (including BTEX), and chlorinated solvents (including BTEX, TCE, and PCE). More than 500 pounds of volatile organic carbon (VOC) mass has been removed, concentrations in all wells have decreased by three orders of magnitude, and the contaminant plume is now contained on-site. The model was used to negotiate reductions in contaminants of concern, volume of soils requiring remediation, and the scope of the monitoring program. Conservative estimates indicate that several years will be removed from the remediation effort, saving more than $500,000 in O&M costs.
Superfund Site Regional Groundwater Contaminant Plume Study, Pensacola, FL
Cameron Cole developed a groundwater flow and transport model that provided the basis for our expert witness testimony in a major, multimillion dollar groundwater trespass case. This Superfund site had releases of radium and other constituents of concern between 1890 to 1975. Our multi-layer groundwater flow and solute transport model was used to evaluate impacts within a 3-mile radius of the site and to quantitatively predict the fate and transport of these constituents in the aquifer over time. Groundwater pumping from downgradient municipal groundwater wells was shown to have accelerated transport of the contaminants 2 miles southeast of the site. This resulted in a class action lawsuit levied by homeowners claiming diminution in home values, and a $10,000,000 settlement.
Accessing Groundwater Modeling Expertise
Cameron Cole hydrogeologists and numerical modelers are devoted to thoroughly understanding your groundwater challenge, and then engaging our expertise and process to deliver uniquely-high-value. Whether you need litigation support, remediation strategy and design, water resilience or sustainability advice, we are interested to listen to your challenge and discuss how we can help.
