Experience of the State of Illinois with Shallow Wells*
Very few Illinois cities obtain their municipal water supplies from shallow wells. Many people in cities, either from necessity or preference, use shallow well water for drinking purposes. Oftentimes the city mains are not extended to new sections. Oftentimes in old sections the houses are not connected with the mains, making the use of a shallow well necessary. Oftentimes the city water furnished has unpleasant physical characteristics like taste, color or turbidity, causing people to prefer the clear, shallow well water. In a great measure the relative use of shallow wells in different sections of the State is dependent upon the source and character of the municipal water supplies. In the northern part of the State of Illinois the majority of the city water supplies are obtained from deep rock wells. In the cast central portion of the State the water supplies are obtained from deep drift wells, in the west central and southern parts of the State from streams. It is possible to have deep rock wells in the northern part of the State because the St. Peter and Potsdam sandstones which outcrop in the central and northern part of Wisconsin dip to the southward, so that they are from a few hundred to two thousand feet below the surface in the northern third of Illinois, or rather north of a line drawn from Quincy to Chicago. Because the height above sea level in Illinois is less than in Wisconsin, wells which enter these two strata are free flowing or can be easily pumped. Such wells furnish an ideal water for a municipal water supply. As the water lies in the water-bearing strata, it is absolutely free from contamination. Proper measures must be taken to prevent contamination during delivery to the consumer from defective casing, from contaminated reservoirs or from faulty connections with river supplies. In deep rock wells along or south of a line drawn from Quincy to Chicago there is a strong probability that the water will be very highly mineralized. It is, therefore, necessary in the central and southern parts of the State to obtain water supplies from sources other than deep wells in the rock. In the eastern part of the central area the glacial drift is deep enough and contains gravel coarse enough to furnish a satisfactory water-bearing stratum. We therefore find many of the cities in this area obtaining their water supplies from wells from 100 to 200 feet in depth. These waters arc also perfectly free from contamination in the water-bearing strata, and if properly cared for furnish a perfectly hygienic supply. In the western part of this area and to the south of a line drawn from St. Louis to Danville, the drift is not deep enough to furnish sufficient reservoir capacity, and it is necessary to rely on surface waters for municipal supplies. Very few of the surface water supplies in this section of the State have been filtered. The unfiltered water supplies are not only unattractive for drinking but they may be contaminated, or even infected. With unattractive municipal supplies the citizens in this section use water from shallow wells which may be impure. Under such conditions we expect a higher typhoid fever death rate in the southern part of the State than in the east central and northern parts. A study of the statistics collected by the State Board of Health from 1904 to 1911† shows this to be the case. Dividing the State into two parts (sec map), 51 counties to the north and the same number to the south, we find in the northern part of the State but two counties with a rate exceeding 30 per 100,000, and not one county with a typhoid fever death rate of 40 per 100,000. Sixteen of these northern counties had a rate below 10 per 100,000. In the southern part of the State there were five counties with a typhoid fever rate of more than 40 per 100,000 and 12 more with a typhoid fever death rate of more than 30, and but one with a rate below 10 per 100,000. It is gratifying to note that the average for the eight years, 1904-11 is better than the average for the five years 1904-8. Another reason for southern part of the State is the fact that 32 per cent, of the towns of more than 1,000 inhabitants have no water supply, whereas, in the northern part only 10 per cent. are without a water supply. Shallow wells are, of course, used where there are no water supplies, and it is certain that the use of shallow well waters is influential in spreading typhoid fever. We have carefully classified all well waters sent to the survey for examination during the years 1907-12.
The waters received have been classified according to depth as follows: Less than 25 feet, 25-50 feet, 50-100 feet, over 100 feet, and unknown. The variation in the quality of each class from year to year is but slight as indicated on the diagram. The average number condemned decreases with the depth of the well. The wells are condemned because the analysis, considered in conjunction with the source of the water and its surroundings, indicates contamination. The condemnation docs not indicate the presence of disease germs, but the presence of filth and the possibility of infection. Of these less than 25 feet in depth. 70 per cent. were condemned; of those 25 to 50 feet, 63 per cent. were condemned; of those from 50 to 100 feet. 32 per cent. wore condemned; of those 100 feet in depth, only 15 per cent. were condemned: and many of the deepest were condemned because of the excess of the mineral content, and not because of the contamination. Of those of unknown origin. 45 per cent. were condemned. Of all the well waters received during the six years. 47 per cent. were condemned. It is gratifying to note an improvement in the character of the water (see diagram 1) and a decrease in typhoid fever during the latter part of the period.
Without doubt, the above does not give the true idea of the actual condition of the water obtained from wells throughout the State. As a matter of fact, a majority of samples scut to the water survey for examination is sent because of typhoid fever among those using the water. A truer estimate of the actual character of the waters of the State can be obtained from a study of waters collected by representatives of the survey from typical farm wells.‡ The number of samples examined is comparatively small. (See table 2.) While 73 per cent. of those less than 25 feet were condemned, only 54 per cent. of those front 25 to 50 feet, 13 per cent. of those from 50 to 100 feet, and none of those over 100 feet in depth were condemned. Diagram 2 shows the relation between the character of samples analyzed by request of citizens and of those analyzed on the initiative of the water survey. Those collected by the survey are of better quality. The results of the examination of the water from shallow wells showed three-fourths of them to be contaminated and possibly dangerous. An ideal remedy would be to abolish all shallow dug wells, but the ideal cannot be attained in this as in many other matters. As indicated in the discussion of the sources of municipal water supplies in the State, it is impossible in some parts of the State to obtain a satisfactory water from deep wells, so that the shallow well is a necessity. Whenevcr the water-hearing stratum is porous enough to allow free flow, a driven or bored well less than 50 feet deep should furnish a satisfactory water. In many cases, however, the flow through the water-bearing stratum is so small that it is necessary to make a reservoir into which the water may slowly percolate and from which it can be drawn as needed. Hence the shallow dug well is a necessity. Granting that it is a necessity, great care must be taken to protect the water The character of the strata which it penetrates must be taken into consideration. Strata of clay or other material through which water may flow in crevices or cracks may allow pollution to be carried considerable distances.
*Paper read at the recent convention of the Indiana Water Supply Association by Edward Bartow, Director of the State Water Survey.
†Proceedings Illinois Water Supply Association Vil. II, pp. 151-164.
‡University of Illinois Bulletin, Water survey Series, No. 7, pp. 78-97.
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Experience of the State of Illinois with Shallow Wells
(Continued from page 241.)
Samples collected by the survey, and should represent average conditions:
Wells should be located on a higher level than cesspools, privies or barnyards, and these must be built at a distance from the well. The immediate surroundings of the well must be carefully protected. A surface water should not be allowed to pass through the casing within at least 4 feet from the top. The cover should nc tight, so that water from the pump may not flow back into the well, carrying with it dirt and filth from the well cover. If typhoid fever does break out, we wish to emphasize the fact that about the last thing to do is to send water for examination. Typhoid fever infection has taken place from 10 days to two weeks before the symptoms are recognized. There arc other sources of typhoid fever, and even if the water were the cause, during the time between infection and the outbreak of the disease the water in the well may have lost its infection. Rather should the patient be so cared for that he may not again infect the well or infect others by contact. The water may be analyzed, but it will require from one week to 10 days to obtain the results of an analysis, and in the meantime infection may have spread through other means. It is the wisest course to protect the well so that infection cannot enter, making the water safe at all times.