CONVICT LABOR FOR ROAD WORK. 71 
the rock, as stated under the topic of camp sanitation; and, as it is 
usually impracticable to find and correct the source, springs in such 
formations always should be regarded with suspicion. 
Wells. 
Wells are of two general classes, shallow and deep. As a rule 
shallow wells are dug from 3 to 6 feet in diameter to a depth of from 
20 to 50 feet, while deep wells are bored or driven to depths of 100 
feet and more, often well down into the underlying rock. 
Both shallow and deep wells are subject to pollution from sur- 
face sources and by subsurface leachings from privies, cesspools, and 
other sources, as described in the foregoing treatment of springs. 
However, deep bored or driven wells are less liable to pollution 
than shallow dug or bored wells, as the former usually are incased 
in metal pipes and the surface water, to enter the well, must filter 
through the soil to the depth of the well, while in the case of shallow 
wells, even when tightly lined, the surface water has a comparatively 
short distance to filter before entering at the bottom of the well. 
About one-fourth of the camps investigated were using well-water 
supplies, and in general the surroundings of the wells were very 
unsanitary. Usually the wells were shallow ones 3 to 4 feet in diam- 
eter and from 12 to 30 feet deep. The main camp structures were 
generally from 35 to 50 feet away, with a privy of the hole-in- the- 
ground type not more than 100 feet distant and frequently at a some- 
what higher elevation than the well. Stables and hogpens were in 
close proximity and chickens and pigs were allowed to roam about 
the camp. Laundering usually was done within a hundred feet of 
the well and the laundry wastes were thrown almost invariably upon 
the surface of the ground, while faces and hands frequently were 
washed almost immediately at the well, the dirty water being wasted 
on the ground. Such conditions as these almost certainly must 
result in the contamination of the water supply. The soil surround- 
ing the well may remove the polluting substances at first by filtra- 
tion but it soon becomes overburdened with organic filth, and finally, 
unable to perform its purifying function, allows the contaminating 
water to enter the well practically unchanged. 
Wells in limestone regions are subject to the same danger of pollu- 
tion as springs in such sections, and always should be regarded as 
of doubtful purity. When it is necessary to use a well in a lime- 
stone country, frequent tests of the water should be made to ascer- 
tain that no contaminating matter is being introduced. 
Local pollution may best be prevented (1) by placing privies, 
stables, and all other possible sources of pollution at a safe distance 
from the well — never less than 200 feet — and on a slope below the 
well; (2) by keeping the surface of the ground about the entire camp 
