Impact Analysis of Infrastructure Development on Groundwater-fed Wetlands
(ADVANCED – Multi-week, integrated groundwater modeling project)
Background
The potential construction consists of two sites for housing missile silos and associated support facilities. Although details are not known about the proposed facilities at this time, preliminary information indicates that each potential site will modify a maximum of approximately 1.7 square miles. This will likely cause a significant portion of this area to experience a change from the current forest/wetland natural land cover to an ‘institutional’-type land cover with more impervious surfaces and man-made facilities. By the nature of the proposed facility, a portion of it will be dedicated to a sub-surface silo structure that houses the missile. As such, there will be certain amount of sub-surface changes, including consolidation (and lowered hydraulic conductivity) over the development area and obstructions due to the facilities themselves.
Topology of the Fort Custer Training Center and the surrounding area
Objectives
Conduct a hydrological assessment of the Fort Custer Training Center with a specific emphasis on the prairie fen wetland ecologies / habitats that are present. In particular, develop a site-specific, process-based groundwater model to assess the current hydrologic conditions (i.e., pre-development analysis) and estimate the impacts that the proposed facilities will have on the groundwater-related hydrology including streams, lakes, wetlands, and the prairie fens (post-development analysis). A regional model has been previously developed and will be used to provide boundary conditions to your local model.
Specific questions to address:
- What are the dominant processes and features – including those both within the FCTC and outside – that control the groundwater flow patterns and the water balance conditions at the FCTC?
- What are the water sources for the on-site creeks, wetlands, and fens (e.g. direct precipitation, surface runoff, or groundwater)? What are the travel times for recharge from the sources to their related surface features? (pre-development)
- How will the hydrologic conditions at the FCTC site change after construction is completed (post-development). More specifically, what are the potential impacts on groundwater flow patterns and groundwater dependent surface features? (Consider both seepage areas and water fluxes into wetland areas and groundwater-fed streams.)
Regional Hydrogeology
A previous study summarized the regional hydrogeology around the site. The FCTC is in the Kalamazoo River Watershed and consists primarily of forest / wetland natural land cover with some transportation and institutional land uses. The site is drained by three first-order streams (with two flowing off-site to Eagle Lake and the other through New Lake and then to Jackson Hole Lake off-site). The highest elevations occur along the southern boundary near I-94 and the regional watershed boundary.
The glacial geology at the site (see below) is primarily ‘ice-contact’ outwash (dark pink) with small amounts of ‘pro-glacial’ outwash (light pink) – both of which have high hydraulic conductivities. The high permeability of the soils means that the groundwater recharge rates are very high across much of the site. ‘Coldwater shale’ – the confining bedrock layer – underlies the entire site. Shown below is a cross-sectional view of the glacial and bedrock geology along the red line indicated in the plan view. Within approximately two miles to the east, the bedrock layer becomes ‘Marshall sandstone’ which is highly fractured and has very high transmissivity which supports high capacity well production.
Surficial geology and surface features at the site.
Cross-sectional view of the glacial and bedrock geology along the red line indicated in the plan view
Because the glacial outwash layer is relatively thin in the area and the Coldwater shale underneath is relatively impermeable, the water table at the site is shallow and actually intersects the ground surface in a number of locations, resulting in surface seepage that creates the site’s wetlands. In addition, the groundwater likely contributes significant flow to the site’s streams.
The overall pattern of groundwater flow at and around the site is similar to that of the overland flow: moving towards the Kalamazoo River – the regional sink – from the higher elevation boundary areas.
Available Data/Models/Tools:
Further Instructions/Suggestions:
- Assume two site locations somewhere within the Fort Custer Recreational area. When choosing your sites, consider: how to minimize potential impacts on groundwater flow patterns and discharge to wetlands/streams; access and supporting infrastructure
- Assume approximate depths of subsurface structures. Multiple model (computational) layers will be needed to resolve the subsurface structures
- Use particle tracking applications on your local flow patterns to determine source water contribution areas to the groundwater-fed streams and wetlands i) before construction; and ii) after construction
- Your model should reflect changes in recharge and hydraulic conductivity expected at the site areas
- Prepare a 1-2-page memo that summarizes your approach and findings. You should also provide final model inputs and calibration parameters and detailed model results in an appendix to allows following your analysis and the basis for your conclusions.