TOXIC CHEMICALS AND DRINKING WATER

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WASTE TREATMENT PLANTS: As we've already suggested, the "cleaned" output from most municipal sewage plants is something less than potable. And during times of heavy rain, many of these facilities are forced to bypass raw sewage because of inadequate storm sewers. This foul outflow may be picked up by a water supply plant for treatment (which may or may not remove any offending compounds), or it may recharge the ground-water supplies.

STORAGE LAGOONS. Those who have to dispose of nasty, hard-to-treat materials (and are not too sure how to do so) often choose to dig a hole and fill it with the liquefied product. Common contents for such lagoons include the brine that's a by-product of petroleum production (in theory, this sodium-laden liquid is supposed to evaporate ... which it may do to some extent in very dry climates) and various toxic chemicals and elements (which typically fall to the bottom of settling ponds). Of the 76,000 impoundment sites pinpointed by the EPA (as of 1982), 70% had no lining to prevent the migration of the substances held in the "dumps" to ground water.

LANDFILLS: Many of the most serious well contamination incidents have been result of legal (or illegal) dumping of to wastes into "sanitary" landfills. But you may be surprised to know that even properly controlled facilities accept materials that can be hazardous if they're allowed to leach into ground water. In fact, it's been estimated that about half of the landfills in the U.S. contain dangerous amounts of hazardous wastes. (Used crankcase oil — which often has high concentrations of lead, cadmium, etc. — is one commonly found substance.)

AGRICULTURE: Excessive use of nitrogen fertilizer, as well as of pesticides and herbicides, can result in large quantities of these substances running off in heavy rains. The contamination of surface water is immediate, and studies indicate that much of this waste is beginning to find its way into ground water, too. Also, in and areas where irrigation is extensive, the problems appear to be growing particularly severe. (Large feedlots are another recognized source of pollution, since so much nitrogen is deposited on the ground by the packed-together livestock in such facilities.)

INJECTION WELLS. As we already mentioned, wells are sometimes used to dispose of wastes. The majority of these are found in oil fields, where brine is often injected into formations from which oil is being removed. (This is also a method of recovering a greater quantity of petroleum from a rock bed.) Problems with injection wells usually result from leaks either in the well casings themselves or between aquifers at points where the casings pass through impermeable layers. (Since oil deposits are generally found at considerable distances below the surface these days, direct contamination is seldom a problem.)

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