Groundwater Problems Caused by Irrigation with Sewage Effluent

Article excerpt

Abstract

Increasingly, sewage effluent will be used for urban and agricultural irrigation. The main concern is the potential for infectious diseases in farm workers and city dwellers exposed to the effluent, as well as in people who consume crops irrigated with effluent, especially when those crops are eaten raw or brought raw into the kitchen. Prevention requires adequate disinfection of the effluent. The effluent also must meet normal irrigation water requirements for parameters such as salt content, sodium adsorption ratio, trace elements, and so forth. Unfortunately, little or no attention is paid to long-term effects of sewage irrigation on underlying groundwater. Since most of the water applied for irrigation in dry climates evaporates, the concentrations of non-biodegradable chemicals in the drainage or deep-percolation water going down to the groundwater can be much higher than in the effluent itself (about five times higher for an irrigation efficiency of 80 percent). These chemicals comprise not only the sa lts, nitrates, and possible pesticide residues normally expected in irrigated agriculture, but also "sewage chemicals" like synthetic organic compounds, disinfection by-products, pharmaceuticals and pharmaceutically active chemicals like endocrine disrupters, and fulvic and humic acids. These acids are known precursors of disinfection by-products that are formed when the drainage water ends up in drinking-water supplies that are then chlorinated. Thus, groundwater below sewage-irrigated areas eventually may become unfit for drinking, which raises questions of liability. More research on long-term effects of sewage irrigation on groundwater is urgently needed.

Editor's note: Through NEHA's long-standing relationship with NSF International, NEHA was granted permission by NSF International to share with the Journal's readership various papers that were presented January 12-15, 2000, at the "NSF International Small Drinking Water and Wastewater Systems International Symposium and Technology Expo" in Phoenix, Arizona. This paper, "Groundwater Problems Caused by Irrigation with Sewage Effluent," is one of them.

It is important to note that these papers were screened by an NSF International advisory committee prior to their presentation at the conference, but they have not been peer reviewed by NEHA's Journal program for technical accuracy.

Because these papers contain useful and interesting ideas and information that may be either delayed or lost if the papers were sent through the Journal's normal peer review process, NEHA has decided to publish them as presented, with only minor editorial modifications.

We hope you look forward to more of these papers in future issues of the Journal!

Introduction

Global population growth will take place mostly in developing countries and in cities, giving rise to mega-cities with mega-water needs, mega-sewage flows, and mega-problems. Populations in countries with higher living standards will grow more slowly, except in the United States, where immigration can be expected to stay high. As growing populations continue to increase demands and competition for water, management of water resources must become increasingly integrated, taking into account all aspects of the problem and using holistic approaches to achieve optimum strategies and solutions. For example, water supply management must also include demand management that determines whether more economical solutions to water shortage problems can be achieved with conservation (more efficient use), water transfers to uses with higher economic returns or other benefits, water pricing, recycling and reuse, and similar measures. Integrated water management also involves water quality management, effective pollution con trol, economics, public health, environmental and ecological aspects, sociocultural aspects, water storage (including long-term storage or "banking'), conjunctive use of surface water and groundwater, public involvement, conflict resolution, the flexibility to cope with climatic changes (McClurg, 1998) or other changes in water supply, regional rather than local approaches, weather modification, use of the virtual water concept, sustainability, and so forth. …