15. BENEFITS FROM AVOIDING GROUNDWATER CONTAMINATION
While the extent of groundwater contamination is not accurately known, the problem is thought to be widespread and is the focus of much public apprehension. Contaminants in groundwater range across an enormous list of chemical substances, and usually no thorough checks for contamination are made until there is reason to suspect a problem.
Even at extremely low concentrations, many toxic chemicals pose serious, irreversible, health risks. In many of the cases checked, well water has been found to contain concentrations above, and often several orders of magnitude higher than, those commonly encountered in raw or treated drinking water drawn from contaminated surface sources.
Thus, while water from most wells is no doubt safe, the widespread nature of the contamination and its potential seriousness merit the public attention the problem is getting. The intent of the case study in this chapter is to develop methods for estimating benefits from preventing contamination of groundwater-based drinking water supplies. This, so far as I know, is the first study to attempt to quantify such benefits. As in the studies discussed in other chapters, the quantitative results reported here must be regarded as largely experimental, but the numbers turn out to be impressively large.
For any chemical source, the extent of groundwater contamination is determined by the characteristics of the underground storage medium--called an aquifer. Groundwater in shallow, alluvial aquifers typically moves less than a foot per day. That flow is governed by recharge and discharge rates from the aquifer, and by the aquifer's permeability. Contaminants are transported by diffusion together with the slow underground flow of groundwater. In that oxygen-poor environment, chemical or physical processes of contaminant degradation proceed very slowly. Thus the contaminant plume may move great distances, with hardly a change in toxicity levels, and may therefore reach drinking water wells.
Among the principal sources of groundwater contamination are waste disposal landfills and impoundments, accidental spills of chemical substances, and abandoned oil and gas wells. Most groundwater contamination can be traced to chemicals leaching into the aquifer from poorly constructed and managed industrial or municipal landfills, surface impoundments, or outright illegal dumps. Contamination from such sources has often been in process for years, and sometimes for decades. To date, most groundwater contamination incidents have been discovered only after a drinking water source has been affected. By the time suspected aquifer contamination is verified in samples drawn from drinking water wells, the problem may be irreversible. Stricter regulation of the disposal of potential contaminants in other environmental media, particularly air and surface waters, and the consequent rising cost of such disposal, is likely to increase the flow of wastes to land disposal and aggravate the threat to groundwater.
Benefit analysis of controlling groundwater contamination requires, as usual, quantification of several linkages between sources and receptors. One must know the location and strength of actual or potential sources of contamination. One must be able to model the spread of the contaminant plume in the aquifer. One must know the numbers of persons exposed to contaminated groundwater and the extent and timing of their exposures. One must know the "dose-response relationship," the nature and extent of health effects on the population at risk. And finally, one needs a way of converting health effects into monetary, or dollar values.
This is a very tall order, and we are far from being able to quantify these linkages with precision. In each case, there is a need for substantially improved methods and data. With these cautions in mind, let us proceed to the case study. It involves the situation associated with Price's landfill near Atlantic City, New Jersey.
Actually, while it is referred to as a landfill, this is rather euphemistic--dump would be a better word, but I shall stick with the conventional usage. Price's landfill occupies approximately twenty-two acres extending across the boundary of Egg Harbor Township and the town of Pleasantville, New Jersey. Until 1967, it functioned as a sand and gravel quarry. During 1968, when the pit was excavated to within approximately two feet of the water table, people from the surrounding area began to dump trash into it with the permission of the owner, Charles Price. In 1969, Price began commercial operations which continued until the landfill was closed in 1976.
In 1970, Price applied to the New Jersey Department of Environmental Protection for a license to conduct a sanitary landfill operation. The application listed the materials that Price intended to accept at the landfill, and specifically excluded "Chemicals (Liquid or Solid)." He was issued a certificate authorizing operation of a solid waste disposal facility.
In July 1972, authorities inspected the landfill, citing Price for accepting chemical wastes and formally advising him of the violation. Nonetheless, Price continued accepting significant quantities of chemical wastes until November 1972. After that date, no chemical wastes were disposed of at the landfill, although it continued in operation. In 1976, Price terminated the landfill operation and covered the site with fill material. The site has not been used since then.
But during the period May 1971 to November 1972, Price accepted approximately 9 million gallons of the toxic and flammable chemical and liquid wastes, either in drums or directly into the ground. These included (to name just a few) acids (glycolic, nitric, and sulfuric), caustics and spent caustic wastes, cesspool waste, chemical resins and other waste chemicals, chloroform, and cleaning solvents.
Price's Landfill is situated over the Cohansey aquifer, the principal source of Atlantic City's water supply, and the separation between landfill and aquifer is a relatively permeable layer. Waste from the landfill is free to leach into the aquifer; the direction of flow in the aquifer is eastward, which is toward Atlantic City's wells. Chemicals in the leachate can therefore be carried into the private and public water supply wells, and people can be exposed to those chemicals in drinking water. Test wells drilled near the landfill by EPA show that groundwater in the aquifer is contaminated and that the plume of contamination is indeed moving toward Atlantic City's wells.
But estimation of actual or potential human exposures requires either considerable information on, or heroic assumptions about, the mechanism by which toxins are transported from the source of contamination to the water supply wells. This is the second linkage mentioned earlier. It will be clear shortly why discussion of this linkage logically precedes the first quantification of the source of the contamination.
Efforts to understand and model the source to receptor links, called groundwater solute transport, are relatively recent. While there has been considerable earlier work on salinity transport, study of the more difficult cases of chemically reactive toxic groundwater contaminants is less advanced. Improvements in our ability to model these phenomena must be a prime objective for future research.
For purposes of analyzing the Price's Landfill situation, the researchers chose and estimated numerically a technique called the Wilson-Miller solute transport model. This relatively simple model was chosen because of limitations of time and funding for the research. The model chosen does appear to fit the Price's Landfill situation relatively well and was judged adequate for conducting this experiment. Future research should check to see if more complex models yield substantially different results.
But to apply any solute transport model, it is necessary to have so-called source-term information: the amounts of materials entering groundwater and their distribution over time. This is the first linkage mentioned earlier. Much of the activity at Price's landfill was illegal. It therefore seems unlikely, to say the least, that careful records of what went into the pit were kept. Indeed there is no information at all about the amounts of the large number of chemical substances dumped there. Where such records exist, or if leaching rates are known or can be calculated, deliveries of pollutants to the aquifer can be estimated directly. In the Price landfill type of situation, typical of many existing groundwater contamination situations, there is only one way to estimate the quantity of the source. Since we have information on what is already present in test wells drilled by EPA, the solute transport model can be run "backwards," so to speak, and used to infer what the amount of the source had to be to produce the existing groundwater concentrations. This is why, logically, discussion of the transport model precedes discussion of the source term.
The reader should be cautioned that this estimate, while necessary, is based on many assumptions and involves great uncertainty. Just to give one example, the procedure assumes that releases occur at a constant rate. This may not be true for some pollutants, and "slugs" may be released which cause transients of pollution in much higher concentrations than would be predicted by the model.
But given the computed source term, the model can be run "forward," so to speak, to compute concentrations, at any well drawing on the aquifer--the production wells of Atlantic City, for example--and for any time after some contaminant enters the aquifer. Those concentrations and the times at which they are projected to occur were computed for the wells from which the Atlantic City Municipal Water Authority pumps its water. Assuming that no mitigating action is taken, this provides the link that specifies the exposure of the population to contamination from Price's landfill.
To take the next step, one must have dose-response information--that is, the actual health risk stemming from the contamination. To make this link, information published by EPA was used. There is a section of the Clean Water Act that requires EPA to estimate excess cancer risks for 129 chemicals called "Priority Pollutants." Many of these "Priority Pollutants" are ones leaching from Price's landfill into the Cohansey aquifer. Using this information, the probability of excess mortality from cancer was estimated for the population of Atlantic City. While this procedure is the best available based on existing information, the reader should be aware that, for this purpose, the risk factors provided by EPA are both incomplete and very uncertain. For example, there are many pollutants that have been identified in groundwater that are not on the EPA list, and extrapolations from animal toxicity tests to human risks are quite uncertain. In addition, it is assumed that each chemical risk is independent of each other chemical risk so that risks can simply be added up across chemical categories. It is well known that "synergism" can occur which make the combined toxicity of two chemicals greater than the sum of the effects of each one taken independently.
Again, with all these cautions in mind, I turn to the next, and final step, monetary evaluation of damages. The value of risk the researchers chose to use is a range that reflects the underlying uncertainty and reasonably well spans the range of values discussed in chapter 4. The range chosen was from one hundred thousand dollars to one million dollars per death. These values were then multiplied by the mortality numbers calculated in the risk analysis to get a total benefit from averting the damage which would otherwise emanate from Price's landfill. The range turns out to be from 180 million dollars to 1.8 billion dollars.
Those are large figures, and one must be clear about what they mean. Say that, at some site like the Price's landfill site, there is a comparable release of contaminants into a similar aquifer, and that the release goes unnoticed for two decades. Then there will be human exposures through drinking water, and incremental mortality risks f aced by the exposed population over their remaining lifetimes. Valuing this incremental mortality risk produced the above numbers. At a site at which groundwater contamination has already occurred, those figures represent the damages that might be avoided by measures taken to prevent future exposures, either by restricting access to, or by cleansing, the aquifer. Needless to say, those figures are impressively large. But the limited information there is indicates that the costs of cleansing aquifers are always large and the cost of obtaining an alternate water supply may be large. This analysis, shaky as the numbers necessarily are, suggests that in the case of groundwater contamination affecting drinking water supplies, prevention is the best cure.