A Report of Water Pollution in the South Platte River Basin February 1953

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waters polluted by sewage to such an extent as to be inadmissible in the prior groups, but containing numbers of coliform bacteria, averaging not more than 5,000 coliforms (h.P.N >) per 100 ml. of sample in any one month and exceeding this ntunber in not more than 20 percent of the samples ex- amined in any one month, should be provided complete rapid sand filtration treatment or its equivalent, together with continuous postchlorinationo Waters which meet the requirements of the previous statement with respect to the limiting monthly average coliform numbers but showing numbers of coliforms exceeding 5,000 M.P.N. per 100 ml. in more than 20 percent of the samples examined during any one month and not exceeding 20,000 per 100 ml. in more than 5 percent of the samples examined during any month, should be provided auxiliary treatment in addition to filtration and postchlorination. Auxiliary treatment as used here is presedimentation or prechlorination or their equivalents either separately or combined as may be necessary. Long time storage for periods of 30 days or more repre- sents a permanent and reliable safeguard which, in many cases, would pro- vide something more than an effective substitute for one or both of the two other methods indicated. Maters which do not meet, the requirements cited are considered unsuitable for use as sources of water supply unless they can be brought into conformance with the requirements by means of prolonged preliminary storage or some other measure of equal permanence and reliability, as heavy prechlorination, preliminary coagulation, and sedimentation. In addition to the recommended bacterial requirements, waters for public supply should not contain toxic, taste - producing, or otherwise harmful substances, or organisms not readily and completely removed by the water treatment processes cited, and should be free of excessive amounts of acid, microscopic organisms, and organic matters causing any interference with the normal operation and efficiency of the water treat- ment processes. Whether or not upstream domestic and industrial waste is treated often determines the acceptability of a stream as a source of domestic or industrial supply. Standards adopted by the Public Health Service for Drinking and Culinary Water Supplied by Common Carriers in Interstate commerce pre- scribe limiting maximum concentrations of certain chemical substances inimical to public health, including the following: Substance Le,id Fluoride Arsenic Selenium Hexavalent chromium Copper f,iax.imum concentration in -parts Per million 010 1050 Oo 05 0.05 C� 05 3000 These standards have received official approval by the American Water Works Association and general acceptance by official health agencies and water works authorities and are widely used as one of the guides for administration of water pollution control programs. 35