Little Lake is a highly utilized residential and recreational surface water body that has recently experienced declining water levels due to a relatively dry period. Residents and recreational users are concerned over related negative impacts, e.g., lower real estate values, poor boat navigation, etc. A lake augmentation well – which will pump groundwater from a deep aquifer (Aquifer B) directly into Little Lake – has been suggested as a way to restore lake levels. A thin aquitard layer exists between Aquifer B and the shallow aquifer (Aquifer A), but well production tests near the lake suggest a small break in the layer exists at some unknown distance from the far side of the lake (see Figure 1). The high-flow, deeply incised Grand River is situated approximately 2000m from the lake / proposed augmentation well location.

Develop a simple numerical model using MAGNET to evaluate the feasibility of the proposed solution. The analysis should determine the potential sources of water to the augmentation well and probe the impact of the distance to the break in aquitard from the augmentation well.

Figure 1: Plan view (top) and cross-section (bottom) view of the site of interest.

Prior information available from a preliminary field investigation includes (also see Figure 1):

• Average land surface elevation: 3 m
• Present-day water level in Little Lake: 1 m
• Present-day water level in Grand River: 0 m
• Recent average recharge: 6 in./yr
• Average thickness of Aquifer A, B_A = 65 ft
• Average thickness of Aquifer B, B_B = 75 ft
• Average thickness of the Aquitard Layer, B_z = 30 ft
  

Additional Hint/Suggestions:

• Place the side boundaries (parallel to the regional flow direction) sufficiently far from the lake and augmentation well so that flow near the boundaries is not impacted by the pumping.
• Use a large grid size (NX=100) to resolve the drawdown near the well.
• You may assume the Grand River is well-connected to Aquifers A and B. You may futher assume that Little Lake is well-connected to Aquifer A.
• To simplify your analysis, assume that the Little Lake water level does not change quickly, i.e., evaluate the water balance right when pumping begins, but the lake level has not changed yet.
• First, assume a distance x of the break in the aquitard layer and simulate under pumping conditions. Analyze the water balances of the two aquifers to determine the source of water to the pumping well.
• Then, analyze the water balance under different values of x to evaluate the sensitivity of your results under different pumping scenarios.
• See the MAGNET Tutorials for help developing multiple aquifer layer models, adding pumping wells or prescribed head sinks/source, etc.