Total diversion of treatment plant effluents is sometimes possible, but is subject to the same objections that apply to total diversion of untreated sewage—possible pollution of the receiving water (such as Chesapeake Bay or the lower Potomac estuary, both of which have been suggested and considered for Washington's effluent) and the alteration of hydrological and ecological conditions. Modified forms of effluent diversion, however, may offer more promise.
Effluents from maximum standard treatment processes, for instance, can be injected into underground strata as recharge water for aquifers—a process mentioned earlier as one alternative in the emerging package of water supply techniques—or may be spread over the surface of large areas of rural land where they serve as irrigation water and fertilizer combined, as well as soaking down into underlying aquifers. For large scale, sustained use, both of these practices still offer some technical difficulties—algae buildups that interfere with percolation, odor problems, limited aquifer capacities, the large amounts of land required for spreading, the effect of rain and freezing weather, and such things. And where the aquifers in question do not feed the original source stream system, a big subtraction is again involved. But for certain conditions in certain places these problems are undoubtedly going to be worked out.
A more modest but highly useful modification of effluent diversion is the spacing of treatment plant outfalls at intervals for a long distance downstream from a treatment plant. If nutrient and organic loads are not tremendously heavy in relation to the size of the receiving stream, this procedure can help to assure that no one stretch gets too strong a dose of them. It is likely to find good use in the Potomac and elsewhere, though only as an adjunct to the best available treatment.
"Advanced treatment" and "tertiary treatment" are becoming common terms nowadays. They refer to any of a considerable array of additional or intensified processes aimed at attaining levels of purification that would have cost an impossible price a few years ago. Most of them are still experimental and often still expensive, and they involve everything from filtration through powdered coal to flash distillation, with still others in prospect. Some bypass conventional treatment and deal with whole raw wastes. More build on conventional treatment and are designed to remove nutrients and residual organic material from its effluents. Of these latter approaches, at least one, involving lime precipitation and other processes to remove nearly all phosphorus and most remaining organic material, is nearing a stage of development and economy that may warrant important use. It will be applied first at the new Piscataway treatment plant of the Washington Suburban Sanitary Commission in Prince Georges County, Maryland, which will also incorporate research and demonstration projects in nitrogen stripping and other things.
In the long run such advances offer the main hope of clean water for a superpopulated future America, where volumes of wastes are going to be enormous and first-rate off-stream treatment is going to have to be the main way of handling them. Even where wastes can be collected easily for treatment, however, as in industry or in sewered populated areas, it may take a good many years to work out varied forms of advanced treatment adaptable to different sets of circumstances, at prices that communities can afford to pay—and a willingness to pay what can be paid is going to have to be a part of the long clean-up job ahead. Undoubtedly continuing research will work out such forms of treatment, but the research itself may be quite costly and no one can predict its pace.
Where waste sources are too diffuse to be channeled into collection systems—as along many agricultural streams heavily polluted through land runoff and drainage, and also in some urban situation—present tools are extremely limited. Soil conservation practices aimed at cutting down erosion—to be discussed within a few pages—tend to keep not only silt but nutrients and other substances on the land to some extent. Concentrated sources of animal manure such as dairies, poultry operations, and feed lots can be brought under some control by fencing stock off from streams and by techniques of lagooning and later field spreading, which need much wider use in the Potomac Basin. But even if these approaches were applied fully throughout the region within a shorter time than appears likely or even possible, land runoff would still be a heavy source of water degradation.
Hence it is probable that flow augmentation—sometimes called "flow dilution" or included in the broader term "flow regulation"—through the release of stored water, will be an important auxiliary tool in water quality management for a good while to come. This is not a form of flushing wastes downstream from their source and out of sight, as some opponents continue to insist, but a means of helping streams to oxygenate and decompose excess wastes by the same processes they have always used on natural and normal loads. On the other hand, neither is flow augmentation the end-all cure for pollution that enthusiasts of a few years ago claimed it to be. Its effect on slow masses of water is uncertain and probably minimal, and too much dependence on it even for flowing streams would obviously encourage neglect of the practical and moral need to keep filth and troublesome substances from getting into the streams in the first place. Furthermore, such dependence would lead rapidly to a point of diminishing returns, like the flood-plain development and protection cycle examined in the preceding chapter. Increases in populations and pollution would lead to a necessity to provide more and more augmentation of flows, with storage space in reservoirs becoming more and more expensive precisely as flood protection does. Flow augmentation is no substitute for good treatment, but a valuable adjunct.
In the record drought summer of 1966 the South Fork of the Shenandoah, heavily polluted with municipal and industrial wastes near Waynesboro, and with fertilizer, manure, and other substances in drainage from the rich and intensively utilized farm country through which it flows, ran very low for months. In many places it was slimy and unpleasant, and aquatic life suffered to some extent, but the picture was not nearly so dismal as it would have been if the river had not been helped out more or less by accident. The source of this help was some 2000 gallons of water per minute that the Merck plant at Elkton and the Dupont plant near Waynesboro were releasing after having pumped it out of deep aquifers and used it for cooling. If all sources of pollution had been receiving adequate treatment, this minimal dilution might not have been so badly needed to avoid the fish kills and algal stagnation and other results that would have ensured without it. But "all sources" include the problematic agricultural drainage, and for that matter the definition of "adequate treatment" is going to have to go up and up in our expansive future.