Indianapolis Water Company (IWC) needed hydrogeologic expertise to guide the construction, testing, and permitting of their White River North Well Field at a location selected by IWC. IWC considered the addition of this well field crucial for meeting projected water demands. The property available for well construction surrounded a water-filled former gravel pit, which created a concern of potential surface water influence. If present, surface water influence would significantly increase raw water transmission and treatment costs. Analysis of the subsurface geology revealed that the aquifer beneath the property was a buried valley that had once been a tributary to the White River. The walls of the buried valley sharply limited the extent of the aquifer supplying groundwater to the wells. Furthermore, the buried valley was also determined to be a source to another well field operated by a different water company. Each of these factors was recognized as likely limits to the long-term sustainable yield of the well field. Another challenge arose from the fact that the durations and rates of pumping anticipated to occur in actual operation significantly exceeded the limits of temporary pumps and water handling capacities available for performance testing.
Significant challenges to the project included:
- Define and map subsurface geologic characteristics to optimize well locations and well screen designs.
- Design well performance tests that would yield the quantitative information needed to predict long-term effects of potential surface water influence, well drawdown, well interference, and aquifer storage depletion from both pumping and seasonal recharge fluctuations.
- Design analytical methods to extract the needed information from the well performance tests, while taking into account subsurface boundaries (valley walls and nearby well field) and environmental effects from long-term, seasonal water level decline and short-term rainfall events.
- Simulate responses of the wells and aquifer storage under a variety of long-term operational pumping schemes.
- Develop and recommend alternative operational strategies, each having sustainable yield forecasts, for the well field.
- Prepare documentation of well field construction and testing and laboratory analyses required for permitting.
The Interdisciplinary Approach
The project team worked closely with the IWC project engineer to schedule and supervise the construction and testing of wells in the White River North Well Field. Chester’s work included siting and design of the wells, supervision of well drilling and construction, and design and supervision of well performance tests. All of this work required constant coordination and communications with the well drilling and testing subcontractor. Many aspects of the design of individual wells, including the well field layout depended on a solid understanding of constraints imposed by the subsurface geology. Visualization products, including maps, geologic cross sections, and perspective three-dimensional imagery were prepared to assist the project team and IWC in this effort. Similarly, the design of well performance tests and the selection of analytical methods depended on the capacity to forecast the various ways that subsurface geology, environmental effects, and well field interference might constrain the long-term operational capacity of the well field.
The Sustainable Result
The study provided the IWC with:
- A high-yield well field suitable for potable water supply.
- Documentation of the well field construction and testing required for permitting
- Recommendations of pump sizes and capacities and potential savings by recommending that a planned fourth well was not needed to fully realize the long-term capacity of the well field.
- Alternative optimization strategies, based on quantitative forecasting, for well field usage in long-term pumping and shorter-term (6-month) usage during periods of peak demand.