Sewage Irrigation As Practiced in the Western States '
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TECHNICAL BULLETIN NO. 675 MARCH 1939 UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. SEWAGE IRRIGATION AS PRACTICED IN THE WESTERN STATES ' By WELLS A. HUTCHINS, Irrigation economist^ Division of Irrigation, Bureau of Agricultural Engineering CONTENTS Page Page Introduction Safeguards and regulations of public-health Doflnitions of terms _ authorities—continued. C haraoter of the problem State poUcies concerning sewage irrigation - 28 Sewage as a source of irrigation water supply_. _ Sanitary and acsthciic basis of high stand- Differentiation between uses of sewaiîc be- ards - 30 töre and after discharge into stream Possibility of polluting ground waters by channels sewage irrigation 34 Extent of current uses .__ __. Sanitary considerations in the use of Reasons for adopting or discontinuing sludge - 37 sewage irrigation Character of public regulation 37 Potential uses Salts in sewage effluents 39 Use of water Boron 40 Supply and demand-- Effluents in southern California 40 Irrigated acreages Possible effect of chlorination upon chemi- Present uses by individuals primarily sup- cal quality of effluent for irrigation. 41 plemental Sewage water rights 43 Methods of distributing and applying Economic feasibility of sewage irrigation 44 water Effect and value of past and present prac- Irrigable lands tices -- _ *45 Character and use of lands Economic aspects of extending present Ownership of lands., .- practices 4C IVlunicipal sewage farms Ability of farm lands to pay for sewage 49 Crops Returns from municipal sewage farms 52 Experimental data Use and sale of sludge 53 Crops irrigated with sewage in western Summary 64 areas Literature ci ted 56 Safeguards and regulations of public-health Appendix 06 authorities - List of areas included in siudy in which W hat the public welfare requires _ sewage was being used for crop irriga- Character of sewage used in current irriga- tionin 1934 or 1937 or both 60 tion practices - - - INTRODUCTION Many western communities, in the face of limited supplies of irriga- tion water, have resorted to the use of sewage as a supplemental sup- ply. Because many cities in the West are surrounded by farm lands inadequately supplied with water, it is to be expected that the trend toward tliis practice will increase. There is small probability that this will enlarge irrigated areas, since in most of the localities now using sewage for this purpose it is used on farms that have too meager supplies of water and the need for better supplies is evident in most 1 Sul>mitted for publication April 4, 1938. n;in72°—39 1 2 TECHNICAL BUI.LKTIN 675, U. S. DEPT. OF AGRICULTURE places where usable supplies would be available. Eepeated droughts in recent years have emphasized the need and, as a result, there has been much careful canvassing of potential sources of supplemental water supply. Sewage irrigation is not new, not even in this country, but it pre- sents problems which differ in important respects from those involved in the use of water from streams and from ground-water sources. There are decided conflicts in thought as to some of these problems. Much has been written on various phases of the general subject, but comprehensive discussions, based upon field investigations and ap- proached from the primary standpoint of agriculture, are lacking. The first purpose of sewage disposal, of course, is protection of the public health, but if after the health factors have been amply safe- guarded to the satisfaction of the State and local authorities the water can still be made available for supplemental irrigation use, it is natural in the West to look upon it as an economic asset. So far the economic aspects of this use have not been much explored either by the cities themselves or by other users of this water, although many cities irri- gate witli sewage or sell it or give it to Irrigators. The question of economic feasibility is discussed in a special section. The present inquiry was undertaken to gather information on what constitutes adequate safeguards, according to the standards of public- health officials, the actual safeguards now applied through State and local laws and regulations, and present practices as to use of sewage for supplemental irrigation of crops in the West for the use of respon- sible public officers, landowners, and users who wish to determine the safety and economic effects of using sewage as a supplemental supply of water for irrigation. To this end a survey was made in the Western States in 1934 and 1935 and largely rechecked in 1937. Studies were made of 125 locali- ties in 15 States; sewage irrigation of crops is practiced in 113 of these places,^ and was formerly practiced and discontinued or reduced to a fraction of an acre in the remaining 12. Several other areas were included in which there were prospects for sewage irrigation, or in which sewage was applied to uncropped land, or where sludge was used for fertilizer. Nearly all examinations included personal visits. In addition, literature in the field of sanitary engineering bearing directly upon the irrigation factors, was examined and the implica- tions were weighed carefully. As a result of this study, the present bulletin has been prepared to report (1) what is now being done in the utilization of sewage in agriculture, (2) what authorities in the public sanitation field recommend by way of precautions, and what State and local laws and regulations prescribe, and (3) the economic effects of the present practices and the probable effects of their exten- sion so far as it is safe.^ ' These 113 locaUties are listed In the Appendix. 3 The field work was done by or under the direction of the author. The larger part of the Texas work was done by Harry G. Nlckle, assistant Irrigation engineer, and the New Mexico work by Harry P. Blaney, irrigation engineer. Karl Harris, associate agri- cultural engineer, assisted in Arizona. Informal cooperation was eflfected with the com- mittee on salvage of sewage, sanitary and irrigation divisions, American Society of Civil Engineers, and with the departments of sanitary engineering of the several Western states. SEWAGE IRRIGATION IN WESTERN STATES 3 DEFINITIONS OF TERMS Certain terms used frequently in this bulletin are defined as follows, the definitions being largely those adopted by the American Society of Civil Engineers and the American Public Health Association." Sewage.—The liquid wastes flowing in a sewer from residences, business build- ings, institutions, and industrial establishments, with such ground, surface, and storm water as may be admitted to or And its way into the sewers. Crude sewage or raw sewage.—Sewage that has received no treatment. Effluent or sewage effluent.—Sewage, partly or completely treated, flowing out of any sewage-treatment device. Disinfected sewage.—Oude sewage, or a sewage-plant effluent, that has been treated with a disinfecting agent, commonly chlorine or "bleach", resulting in the destruction of bacteria sufficiently to reduce materially the danger of in- fection. Stable effluent.—A treated sewage that contains enough oxygen to satisfy its oxygen demand. Stability.—The ability of any substance, such as sewage, effluent, or digested sludge, to resist putrefaction. (Antonym, putrescibility.) Relative stability.—The ratio, expressed in percentage, of available oxygen in waste waters, sewage, effluent, or diluted sewage to that required to provide complete biochemical oxidation of the organic matters contained therein. Sewage irrigation.—The application of untreated or treated sewage to land for irrigation and fertilization purposes in the raising of crops, as distinguished from sewage disposal on land. Sewage disposal on land.—Tlie application of sewage to uncropped land for the sole purpose of disposing of the sewage by absorption. Sewage farming.—The raising of crops where sewage is applied to the land for irrigation and fertilization purposes. Sewage farm.—A farm where sewage or sewage effluents are used in whole or in part for irrigation and fertilization purposes in the raising of crops. It should be noted, therefore, that the term "sewage" is used in this bulletin irrespective of the state of its treatment or disposal, and that "sewage irrigation" includes the use of both raw sewage and effluents. Where a differentiation between untreated and treated sewage is in- tended, the specific terms "raw sewage" and "effluent" are used. CHARACTER OF THE PROBLEM Sewage irrigation in the West is not to be confused with sewage disposal. The terms are not synonymous ; on the contrary, sewage ir- rigation is a corollary of sewage disposal. Several decades ago, it is true, irrigation was primarily a convenient and relatively inexpensive method of disposing of sewage, but times and standards have changed. Authorities consider that water not safe enough to discharge into stream channels is not safe for general irrigation use, where it may be applied promiscuously to crops and may become a health hazard. Therefore sewage for general irrigation use requires pretreatment, such as commonly given before returning it to streams, m which case < While these definitions are largely those published in (2),° there are important excep- tions : First, the definition oí "sewage" published in (2) is more detailed than required ior the purpose of the present discussion. Likewise, the term "broad irrigation" given in (2) implies only incidental benefit to crops, the primary purpose being the disposal of sewage, thus differing in this primary purpose from "sewage farming." As the present discussion deals with the possibility of using sewage as a supplemental water supply for crops, and not with methods of sewage disposal, the term "broad irrigation" is omitted and "sewage irrigation" is used regardless of its primary or incidental relationship to sewage disposal. To this end, a different definition of sewage irrigation is given, as well as a definition of sewage disposal on land. ^ Italic figures in parentheses refer to Literature Cited, p.