Hydrogeologic Investigations
ENW’s Hydrogeologic Investigation Division has successfully completed highly visible water supply and water resource work. This broad-based experience in both water supply and contamination investigations is available to our clients in both the private and public sectors including:
· Environmental investigation and remediation
· Solid waste facility siting, design and cleanup
· Water supply for domestic and commercial developments
· Studies for preservation of anadromous fish runs and hatchery design
· Level 1 and 2 Critical Aquifer Recharge Area (CARA) Assessments
· Geothermal energy resource assessment and utilization
· Golf course design and resource development
· Dam and hydropower facility design and impact assessment
· Tunneling studies
· Watershed planning
· Stream bank restoration
PROMINENT PROJECTS
Lake Umatilla Columbia River, Oregon and Washington
When the US Corps of Engineers considered lowering the water level of Lake Umatilla, the body of water impounded by John Day Dam on the Columbia River, on a yearly schedule to encourage migration of threatened anadromous fish species, Mr. Woller was requested to evaluate the effects of lowering the lake level on water wells in the surrounding areas. The study included recommendations and cost estimates for mitigation of lost well production for five common well types found in the lake basin.
Indian Reservation Tribal Hatchery, Washington
When declining well production and spring flow hampered the operation of this hatchery, Mr. Woller’s well evaluation indicated that over-pumping caused plugging of the well screen and cavitation, which lowered the well's specific capacity. Mr. Woller explored options for rehabilitating the well to original condition, and also sited and designed additional wells.
City Water Station Clark County, Washington
When a city in Washington identified trichloroethylene (TCE) contamination in some of their municipal water wells, Neil Woller was the Hydrogeologist on the team selected to identify the contamination source, define the contaminant plume, evaluate hydraulic parameters of the pathways from the source area to the well field, and make recommendations for remedial actions. A thorough historical investigation was made, which included review of available well records, discussions with long-time residents, and careful following of leads. The major contaminant source was identified, and contaminant concentration contours were prepared.
Groundwater Modeling
Modeling is the process of using computer simulation techniques to reproduce the hydrogeologic and environmental conditions at a site. In groundwater modeling, the processes of groundwater flow in response to natural and imposed hydraulic head differences, advection, diffusion, dispersion, chemical equilibrium, absorption and chemical decay, leakage, withdrawal, and recharge can all be described with the mathematical language of the computer program and applied to a simplified two- or three-dimensional representation of subsurface conditions. Once the simulation is considered reasonably accurate, the model can be used to test hypothetical scenarios.
ENW applies groundwater models effectively for Prediction, Aquifer Characterization, Risk Assessment, and Remediation.
Prediction
Models are used for describing groundwater flow patterns and assessing impacts to aquifers and water resources under different groundwater resource stress scenarios. Predictive models can also address future migration, expansion, and attenuation of contaminant plumes. The predictive function facilitates resource planning. ENW utilizes Groundwater Modeling System (GMS) as a base for most intricate modeling projects. GMS is the most advanced and comprehensive groundwater modeling front-end package (i.e., graphical user interface) available. The program was developed under the direction of the U.S. Army Corps of Engineers and involves support from the Department of Defense, the Department of Energy, and the Environmental Protection Agency.
Aquifer Characterization
ENW uses a variety of computer programs for analysis of aquifer parameters and well-field performance. These include AQTESOLV (a program that performs curve-fitting analysis to a wide range of aquifer test solutions and variable head test solutions), THCVFIT (which fits drawdown data to the Theis equation), THEISFIT (a statistical best-fit program for fitting drawdown data to the Theis equation), VARQ (a variable discharge pump test analysis package), and OPTP/PTEST (uses variable discharge pump test data to determine optimum pumping discharge).
When ENW prefers to analyze aquifer characteristics outside of the constraints of prepared programs, our hydrogeologists use Microsoft Excel, a spreadsheet program with excellent graphic capabilities, which can also export data to and from other formats.
ENW is experienced with using sophisticated electronic pressure transducer systems (made by In Situ) to acquire and record high-quality data during pump test and down-hole testing procedures.
Risk Assessment
Modeling of impacted hydrogeologic systems can assist in matters of public policy, planning, and response. ENW has used modeling to assess the risk to water well owners, public water supplies, surface waters, and industrial-agricultural users.
Remediation
ENW staff have been frequently called upon to remediate sites where groundwater has already been impacted. In attempting to remediate a groundwater contamination site, several alternative technologies may be considered. Groundwater modeling is used to test the configuration of various arrays of extraction wells to determine the most efficient capture scenario for an expanding, migrating plume. Cost-efficiency and time-efficient performance frequently are the deciding factors among the various alternatives.