Before you build a building .....
Before building the nature center, we needed to know some answers to the questions:
Can we dig deep enough for the foundation, or will we hit solid rock?
Will the soil be firm enough to support the weight of the building?
Is the soil porous enough for the septic system to work properly?
Do we have to design a building to resist earthquake damage?
How will we get water – drill a well, or is City water available?
In the Lake Elmo area, the upper layer of earth is generally loose material many feet thick that can be excavated with normal equipment. Luckily, during the digging process, we did not find a huge rock that would require special handling, or a hard layer of rock near the surface that would require blasting. Soil testing showed that a normal set of footings would support the weight of the building so it would not sink deeper into the earth. If the soil was very soft or very wet, special building methods would have been necessary. Testing also showed that the upper levels of the soil were porous enough so that we could install a septic system to allow for disposal of the waste from the rest rooms and the kitchen sink drain. The engineer took several soil samples using a hand-operated device called a core drill. Then water is poured in the holes and the time to drain is measured. These tests are called percolation tests. The report tells us the nature of the soil to a depth of about 4 feet. . And what about earthquakes? Earthquakes are not expected in the Twin Cities area, and there are no special building code requirements for earthquake resistance here. Minnesota has had very few earthquakes, mostly along a line running roughly from the border between North and South Dakota to the western tip of Lake Superior. The last one was in 1975! And for our water supply – our location is close to the water line that runs to the fire hydrant by the parking lot, and we were able to apply for a connection to the Lake Elmo City water system.
What was found during excavation?
We found lots of different kinds of rocks, and the students of Dr. Andrew Wickert at the University of Minnesota identified them for us. These rocks were shown to have been moved long distances to Lake Elmo from the locations of their original formation. This information correlates with what is known about glacier movements. In the upper layer of soil we found a deer skull, leg bones, and two beer cans of relatively recent origin – they have captive pop-tops. A vertical strip of soil from the open face of the excavation was treated with diluted Elmer’s Glue, then peeled off in sequence to show the nature of the soil as a function of depth.
The agate collection was not found here, but is a gift of the late Earle Kask, local agate expert who spent years gathering them and studying them. On our theater menu is a video of “Lunch with Earle the Agate Man” where you can hear his story in his own words.
Glacier Damage - How the Park got to be hilly
Between scraping out depressions for shallow lakes, pushing ice underground to eventually melt and form “kettle lakes”, and directing water flow to leave long gravel accumulations called “eskers”, the glaciers really did a job shaping our Park.
Deeper Underground
The placard to the left shows the depths and names of the strata (underground layers in the earth) below Sunfish Lake Park. Some are water-bearing, others are impervious, some are sandy and others are solidified rock.