Groundwater Modeling Helps Expand Water Supply
Groundwater was potentially a new water source for Iowa City as it has historically utilized the Iowa River for nearly 100 percent of its supply. The City needed help with recommendations for expanding its water source, treatment, distribution, and storage. Hydrogeologic investigation included a thorough review of all available ground-water sources to determine if some or all of the City’s future need of 16.7 MGD could be obtained from groundwater.
The key to the study was defining the interaction between surface water and groundwater because the high capacity of the wells is dependent upon induced recharge from the river. This was accomplished through the application of analytical groundwater modeling.
Among the recommendations provided by HR Green was the hydrogeologic evaluation and wellfield development within the alluvial deposits along the Iowa River. In particular, because bedrock was known to be shallow, a feasibility analysis for the installation of high-capacity radial collector wells was performed.
Investigating the Site
The Hydro Group performed the initial hydrogeologic evaluation at two potential locations to assess the potential for high-capacity radial collector wells. HR Green conducted drilling, pumping test, and hydrogeologic evaluation at a third location where the yield capacity of the aquifer was assessed. The contribution of recharge from the Iowa River was estimated by determining the infiltration rate of surface water through the riverbed, including the application of the Hantush-Papadopulos and Rorabaugh analytic groundwater models. Groundwater contribution from aquifer storage was estimated by calculating aquifer parameters transmissivity, hydraulic conductivity, and the coefficient of storage. A fourth location was subsequently evaluated by the well contractor, Reynolds.
The Wellfield Expansion
A recommendation for four (4) radial collector wells with a projected design capacity of 7.4 MGD for the entire wellfield was presented. Each well design recommended three or four standard orientation 150-foot long lateral screen sections, for a wellfield total of 1,800 to 2,400 feet of lateral screen. As constructed, the wellfield consists of four collector wells with a total of 2,490 feet of linear screen and a capacity greater than 7.4 MGD, depending upon river stage conditions.