Water Quality

A report by the Illinois State Board of Health in 1901 reveals increases in chlorine and organic matter at a sampling point just south of Peoria, at Wesley, due to the pollution contributed by Peoria and Pekin. The Board of Health further reports that “purification continues throughout the extent of the river.” This is to due in part to the dilution of the sewage with a flow of from 300,000 to 600,000 cubic feet per of water per minute. The State Board of Health believes that the river will be “self-purifying” due to the increased flow diluting the sewage as well as the increased sedimentation and the absorption of contaminants. Their report states, “That river water grossly befouled by sewage in its higher reaches, becomes a few miles lower down so pure, from a chemical point of view, as to be certified by the most eminent analysts to be fitted for all domesticated purposes...”. Others at the time do not support this view.

The Illinois State Board of Health report shows continued decreases in organic matter from Joliet to the Peoria narrows and again from the Wesley sampling point to Grafton. The conditions in 1899 are better in Pearl and Grafton than at and above Peoria, but this changes in 1900 when the condition above Peoria is as good, if not better, than that of Grafton. This is due to the greater dilution of the Chicago sewage, and the increased amount of sewage contributed by Peoria, Pekin, and the Sangamon River. (Table 3)

Table 3: Comparison of Illinois River Water in 1899 and 1890 Prior to and After the Opening of the Chicago Drainage Canal (Illinois State Board of Health 1901)

The improvement in water quality shown by the Illinois State Board of Health in 1901 does not continue. Stephen A. Forbes and Robert E. Richardson (1919) provide documentation regarding the decline in water quality after the canal opens in 1900. The chlorine content is the best measure of the degree of contamination by sewage because chlorine passes downstream without the changes that occur to nitrogen, which is transformed and then consumed by plants. An examination of the amounts of chlorine passing Averyville, just above Peoria, before 1900 and in 1914 show an increase of 2.25 times as much per second for the latter period. The chlorine average at Averyville in 1897-1899 is 7.69 kilograms per second, whereas, in 1914 it is 17.31 kilograms per second.

There are several reasons for this change. Forbes and Richardson examine nitrogen and conclude that, since 1899, nitrogen-consuming organisms have not increased in quantity as fast as their food supplies. They note that between 1899 and 1914,

“the total nitrogen in a given quantity of the river water was increased by about one-fourth in spring and by six-tenths in summer, while the total for the entire flow of the stream in a given time was, in spring 3.5 times as great in 1914 as in 1899, and in summer 4.8 times as great. The nitrates, on the other hand, at the mouth of the river were, in parts per million, as 1 in 1899 and 1.48 in 1914.”

This is due in part to the increased volume and rate of flow of the river. About half the time is needed for water to flow the length of the stream in 1914 than it took before the opening of the canal in 1900. This has consequences. Decomposition and assimilation processes extend further downstream and those which formerly were completed at the mouth of the stream may now only be half finished at this point. Also, plankton has much less time to multiply, thus reducing its effectiveness in absorbing contaminants.

A second factor is the increase in sewage load of the river since 1899 as the population of Chicago grows as well as other towns along the river, particularly Peoria and Pekin.

In 1925, R.E. Greenfield examines a range of chemical and bacteriological factors as it relates to the water quality of the state’s waters. One issue he examines is the sewerage systems in towns. This includes the town’s population, the stream in which the sewage is discharged, and the type of sewerage system:

1. Discharged unpurified sewage into streams;
2. Treated the sewage with some sort of settling tanks; or
3. Treated the sewage with settling tanks and some additional treatment.

A total of 265 cities and towns are examined. Of these, 136 or 51.3% discharge unpurified sewage directly into the state’s streams. Another 27.2% treat sewage with settling tanks, and 21.5% use treatment in addition to settling tanks.

Along the Illinois River, no cities or towns in this study use settling tanks or additional treatments. Six communities are identified as discharging unpurified sewage directly into the Illinois River: Averyville, Beardstown, East Peoria, Havana, Pekin, and Peoria.