IOWA ACADEMY OF SCIENCE 
9 
Alluvial gravely soil and clay. 31 ft. 
Limestone 6 ft. 
Shale, blue 27 ft. 
Limestone 6 ft. 
Sandstone 42 ft. (tunnel in this formation.) 
There are only about 20 feet of gravel, alluvial soil and clay from the 
bottom of the river to the first layer of limestone. Through this the 
water from the river and surrounding soil will probably pass quite 
readily and without efficient filtration. It then comes to a layer of 
limestone which is known to contain many fissures, through which water 
may readily enter the shaft. Beneath the limestone is a layer of blue 
shale, 27 feet in thickness. This is relatively impermeable to water, 
hence tends to keep the water from passing directly downward and so 
hastens the passage of water laterally along the limestone fissures — in 
the direction of drainage — namely, toward the shaft. Previous to the 
construction of the tunnel the seepage into the shaft was at the rate of 
about 55 gallons per minute. This was increased to 80 gallons per 
minute by the construction of the tunnel. This would seem to indicate 
that the water which enters the shaft is of recent surface origin. That 
the water must have come principally through such fissures in the rocks 
is indicated by the fact that when the shaft was constructed, but little 
water appeared until after the limestone layer with its fissures had 
been entered. 
That the water which comes from the shaft is polluted with sewage 
material has been shown repeatedly by chemical and bacteriological exam- 
inations. When the first artesian well was drilled (Well No. 1) it was 
started from the bottom of the above mentioned shaft. The casing of 
this well extends through the shaft and projects at the top several 
feet above the level of the water in the shaft. The water flowing from 
the artesian well fell into the shaft which became filled with water to 
the top of the discharge pipe. In this manner the water from the 
artesian well and the seepage water from the shaft and tunnel were 
mixed. Soon after the completion of this artesian well, a sample of this 
water was sent to us for examination. We expected to find either no 
bacteria or only a very few. We found, however, that the bacterial 
count went up to 42 per cubic centimeter with 2 colonies of colon 
bacilli. Chemical examination likewise showed evidence of contamina- 
tion with sewage material. The reason for this was not explained until 
after a personal inspection and subsequent examinations showed that the 
contamination occurred in the large shaft with water from the shaft and 
