SUMMARY: Home owners from a beautiful lake community faced a water problem: their lake was ‘sick’ – it was losing water and lake levels were getting lower. An expert "fixed" the problem by pumping deep groundwater directly into the lake. But years layer, the same problems returned. A second expert says the plan never really worked in the first place. Determine if the lake augmentation project was doomed from the beginning. 

The lake, augmentation well, and other salient features of the site.

Background & Problems

In 2005, home owners from a beautiful lake community faced a water problem. Their lake was ‘sick’ – it was losing water; lake levels were getting lower. This was impacting the value of their homes, especially for those on the lake front. One lake front owner whose home value was particularly impacted had an idea: maybe we can pump water from underground and add it to the lake.

The community felt it was a good idea, so they hired a consultant to explore its feasibility. The consultant told the home owners association that – yes – it is possible, but it will require that the water is pumped from a source that is ‘external’ to the lake. In other words, he said, if you pump groundwater, you want to make sure you go deep enough, and hopefully you are getting water from a confined aquifer that is not hydraulically connected to lake.

The consultant suggested drilling a deep test well and pumping really hard to see what happens to the water levels in the shallow aquifer and wells surrounding the lake. He claimed, if the test results showed that the shallow wells around the lake do not respond to the pumping from this deep test well, it means the deep aquifer is disconnected or separated from the shallow aquifer and the lake. Otherwise, the pump-into-the-lake idea won’t work, as it will it cycle water from the lake/shallow aquifer to the deep pumping well in a connected system. The home owners thought this made perfect sense and agreed to give it a try. The consultant installed a test well, penetrating 200 ft deep into the ground and equipped with a high-capacity pump. He completed the test in collaboration with the home owners with water wells.

Here is the gist of the results: despite pumping 1000 GPM continuously for two weeks, there was no measurable responses observed in any of the shallow wells. In fact, there were no measurable responses even in the existing wells in the deep aquifer. So, the consultant concluded that the results were better than expected! He thought he had found a very good external source of water that was separate from all the various existing wells and lakes, and that the deep aquifer is not connected to the shallow aquifer. He recommended moving forward with the lake augmentation project.

The community was very happy to hear this! They decided to immediately move the proves forward and quickly build the necessary infrastructure. After a little time had passed, the community was pleased with the results: the lake responded to continuous augmentation pumping, although sometimes the lake behaved in a way they did not expect (occasional ups and downs). So the community declared the project a success.

But the success did not last. A few years later, the lake got sick again, especially during the time following the drought of 2012. The community waited another two years, and the lake seemed to remain sick. It even seemed to take longer to respond to the augmentation pumping.  So they hired a different expert. He gave the community a much different response after reviewing all of the information. He said the project never worked in the first place; it was all controlled by mother nature; it appeared to have worked because the years right after the installation coincided with a few wet years.

Objectives & Deliverable

You have been asked to determine if the lake augmentation project was doomed from the beginning, as claimed by the expert. You will develop a 3D groundwater model to assess the sources of water to the deep augmentation well that pumps water into the lake, and discuss the implications on lake level control.

In particular, you will evaluate the source of water to the wells for the case of (a) a continuous clay layer extending from east of the lake to the break near the River and Stream; and (b) a clay layer with a 2^nd small break (discontinuity) below the lake.

Prepare a 1-2 page report that summarizes your approach and findings. You should discuss your findings with regards to responsibility for the contamination. Include any detailed model results / graphics in support of your conclusions in an appendix. 

Given Information

Site Geology

Available borehole lithologic records from nearby and along the lake (see above) suggest that a thick layer of confining materials (clay, silts, etc.) separate sandy surficial deposits from deeper aquifer materials. This clay layer is expected to extend toward the deeply-incised (i.e., well-connected) River and Stream, where this is an abrupt break below the surface water. However, it is not clear from the available data if a similar break exists below the Lake (see below).

Conceptual cross-section of the groundwater-surface water system.

Field Data

The following information/data are available from a preliminary study:

• Average land surface elevation:                                               …230m
• Present-day water level in the Lake:                                       …227m          
• Present-day water level in the River:                                      …205m
• Average thickness of sandy surficial deposits                        …b_sand = 150m
• Hydraulic conductivity of sandy surficial deposits                …K_sand = 20 m/d
• Hydraulic conductivity of the River channel deposits           …K_channel = 33 m/d
• Average hydraulic conductivity of clay layer                        …K_clay = 0.01 m/d
• Hydraulic conductivity of the break in the clay                     …K_break = 10 m/d
• Average thickness of clay layer                                              …b_clay = 20m
• Average thickness of the deep aquifer                                    …b_deep = 50m 
• Average hydraulic conductivity of the deep aquifer              …b_deep =50m
• Proposed well withdrawal rate                                               …Q = 1000 GPM
• Average long-term recharge ε:                                               …15 in./yr.

MAGNET/Modeling Hints:

• Use ‘Synthetic mode’ in MAGNET to create a model domain with the same dimensions as shown in the map
• Overlay the provided SiteMap image file included in the problem description. Choose ‘Use Domain Extent’ to fit the image to the established domain size. 
• You may assume the River / Stream is perfectly-connected to shallow aquifer. You may further assume that the Lake is perfectly-connected to the surficial aquifer.
• To simplify your analysis, assume that the 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.
• Use zones features to assign hydraulic conductivities to the River channel deposits and the break in the clay layer
• Note that the River channel deposits extend down through the clay layer, so the zone feature should exist in both the first and 2^nd layer