Groundwater monitoring Accurate assessment and reasonable economy are achievable
J. W.Kwhn G. € Stankn, I. Jr. Shell Development Company Houston. TX n om Groundwater is a vitally important natural resource. It is the only source of drinking water in many locales. With the heightened awareness of groundwater contamination has come the burden of sampling and analyzing an increasing number of monitoring wells. The number of analyses and comsponding costs have been expanding. Regulatory agencies have not been consistent in the number of parameters they require for each well. Often a shotgun approach to sampling and analysis is used, without thorough planning or scientific necessity. This report describes such an approach toward groundwater monitoring and presents a more d i t i c and cost effective perspective.
Groundwater monitoring There are many valid reasons monitoring programs must be initiated and maintained. However, the goal of a program must be kept in sharp focus. The objectives are to warn of, identify, assess, and monitor a contamination episode. If the extent and duration of a program is not properly defined, both in number of wells and the list of analytes, then a massive economic burden might be generated withont producing a constructive outcome. Over the years Congress has enacted laws defining and regulating discharge and disposal of a wide variety of chemicals. The lists of chemicals and the mechanisms controlling releases into the environment have been re6ned as the potential impact on human health is better understood. Along with the chemical lists, but sometimes independently, series of analytical methods have been developed for use in analyzing particular matrices. For organics, 1262 Envimn. Sci.Technol., W. 22, NO. 11,198B
the EPA 600 series methods (I) are required when analyzing wastewaters regulated under the National Pollution Discharge Elimination System of the Clean Water Act (2). The 500 series methods are for analyzing water intended for drinking (SafeDrinking Water Act) (3). The SW-846 8000 series methods apply to groundwater and solid matrices associated with Resource Conservation and Recovery Act (RCRA) and Comprehensive Environmental Response, Compensation, and Liability Act regulations (4). Using these methods the government has moved toward defining a comprehensive list of chemicals that encompasses all known hazards. The recently promnlgated Appendix M list represents the latest effort to define analytes for groundwater monitoring that can be
(3.
Of all the chemicals that are listed in Appendix M and for which established analytical methods exist, the volatile organics the most interesting. They are generally the most water soluble of the organic compounds, and cons& quently they exhibit the greatest mobility with water flow. This is particularly important when considering the great extent of both permitted and illegal surface and underground disposal of organic chemicals that has occurred over the years. In addition, leaking underground pipes and tanks have contributed to the contamination of groundwater. To date, Congress and regulatory agencies have successfully identified a reasonable list of analytes (Appendix IX) for groundwater monitoring and have provided appropriate methodology (SW-846) for the analysis of these hazardous chemicals. In addition,there is a growing body of knowledge about the mobility and fate of these chemicals in groundwater. However, an issue that is not well-defined or controlled, but which can have as great a long-range environmental impact as groundwater contamination itself, is the economics of identifying and correcting real and potential groundwater contamination. Increasingly, regulators are requiring that wells be sampled and analyzed for the entire Appendix M list of chemicals. This l i t of 232 chemicals covers a range of volatile and semivolatile organics, pesticides, herbicides, dioxins and furans, metals, and anions. Although some parameters are measured by relatively quick, inexpensive techniques such as titrimetry and colorimetry, all organics are measured using gas chromatography (GC)with mass spectrometry ( M S ) or other conventional detectors. The cost for a complete A p pendix IX analysis runs about $2500. Currently, there are no screening methods approved for initial groundwater investigations. For those instances (e.g., RCRA disposal units) where Appendix IX is necessary, the
001~938W88/0922-1262$01.50100 1988 American Chemical Society
law requires analysis of all of the Appendix M analytes. In many cases, however, this is really not necessary from a technical point of view. When the list of contaminants has been established for a given well, continuing to analyze subsequent samples for the entire list of Appendix IX analytes does not provide information beyond that available through judicious selection of specific methods for monitoring the target analytes. Continuing to analyze each sample for the entire Appendix IX list is expensive and ties up limited analytical resources. Numerous environmental situations do not require a complete Appendix M investigation. For instance, when the initial analysis for Appendix IX analytes in a well reveals no evidence of contamination, subsequent analyses for organics should be restricted to the most common class of pollutants, the volatiles. Analyzing samples for A p pendix IX volatiles using Method 8240, “Gas Chromatography/Mass Spectrometry for Volatile Organics” (4) or its equivalent would be appropriate. Another example would be if an Appendix M investigation revealed the presence of specific chemicals. In this case, an appropriate cost effective a p proach would be to focus subsequent analyses on these particular contaminants. Fuel hydracarbons A good example of the focused approach, which is fairly common, is that of groundwater contaminated by fuel hydrocarbons. When one measures a real or potential contamination at an oil refinery, a fuel distribution terminal, or a service station, the major concern is potential groundwater contamination from hydrocarbons. Crude oil and refined products contain no halocarbons, dioxins or furans, very few metals (in unleaded gasoline), and very few sulfur and nitrogen compounds. Therefore many of the analyses required for A p pendix IX analytes are essentially wasted when monitoring for fuel hydrocarbons. Because the water solubility of most hydrocarbons is very low, the compounds seen primarily in conjunction with fuel contamination of groundwater are the light mononuclear aromatics [benzene, toluene, ethyl benzene, and the xylenes (BTEX)]. These compounds have the greatest water solubility of the common fuel components and hence exhibit the greatest degree of mobility with the movement of groundwater. An analytical technique commonly used to measure these aromatic chemicals in water is purge-and-trap to isolate and concentrate the organics, GC to separate, and photoionization detection
(PID) to measure their presence. Purge-and-trap GC can also be used with an MS detector. This latter use is common when measuring Appendix D( compounds by Method 8240, for example. However, PID is more sensitive for BTEX by more than one order of magnitude. In addition, it is easier to operate than a mass spectrometer and thus results in faster turnaround time for the samples at a lower cost. PID is specified when using Method 602, “Purgeable Aromatics” (I), or Method 8020, “Aromatic Volatile Compounds” (4). Note that Method 602 does not list the xylenes as parameters. However, PID shows very good response for these compounds and generates a classic output pattern or “fingerprint” for BTEX. To demonstrate the utility of the quicker, less expensive PID analysis, a comparison of analytical data resulting from the analyses of split samples using various options is summarized in Table 1. It should be noted that Table 1 includes interlaboratory variability because three different laboratories were used. One of the laboratories employed Method 602 and modified it to include the xylenes (I). A second laboratory analyzed the samples following Method 624, “Purgeables by GCIMS” (I). A third laboratory analyzed one of the three well samples for the entire Appendix M list of analytes. The expense of Appendix IX analysis precluded the analysis of a l l three wells. The data are similar for the three techniques for each compound in each well. The observed variability due to sampling and the use of three laboratories (with different instruments and analysts) is quite acceptable. The important point is that each of the techniques
detected and measured the pollutants in the samples. If a real or potential fuel hydrocarbon contamination is being monitored in groundwater, Method 602 with PID (modified to include additional compounds) is just as capable, if not more so, of measuring BTEX as is the GClMS Method 624 or of analyzing for the complete Appendix M analytes. Monitoring these chemicals was best carried out by applying the simplest, most straightforward analytical technique. This focusing of the analytical a p proach is not just an academic point to be argued. The data listed in Table 1 are from wells where pollutants were actually found. These three wells represent only 12% of the wells actually sampled and analyzed. For most of the wells monitored, no pollutants were detected. Figure 1 shows what happens to monitoring costs when the various techniques are used. For example, one year’s worth of quarterly measurements on 25 wells (100 analyses) will cost $250,000 if analysis for all Appendix M analytes is performed. The same information can be obtained for $10,500 using Method 602 or for $22,500 using Methods 624 or 8240. Analysis for the entire Appendix M list in this situation represents a huge expense and results in many cases of “not detected.”
Conclusion It is generally agreed that Appendix M represents a reasonable list of analytes for groundwater monitoring and that the Test Methods for Evaluating Solid ulrste (4)provides the necessary methodology for groundwater analysis. However, the cost of analyzing all groundwater samples for the entire
Envimn. Sci.Technol., MI.22, NO. 11. lseB 1283
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Appendix M list of analytes is prohibitive and not technically justified in many instances. Groundwater monitoring must be properly defined in the number of wells, the l i t of analytes, the correct methodology, and the duration of the program in order to wntsol the economic outlay and produce a constructive outcome. Perhaps initially defining a potential or real contamination by analyzing for the entire Appendix M list has merit, but it must be recognized that such a requirement is expensive and diverts limited analytical resources. Current experiences with reliable laboratories analyzing samples for Appendix M analytes show long turnaround times, and premium prices are often paid for turnaround times of three to four weeks. If groundwater contamination is known to result from petroleum hydrocarbons, then the optimum use of available resources is obtained by employing the analytical technique that identifies hydrocarbons most efficiently. As we have demonstrated, Method 602 (modified) is clearly capable of monitoring for select hydrocarbons at a fraction of the cost of GUMS analysis by Method 624 or of analysis of all Appendix IX analytes. For other situations, including refined hydrocarbons, a screening procedure based on the analysis of the most common class of groundwater pollutants, the Appendix M volatiles, should seriously be considered to reduce groundwater monitoring costs.
Acknowledgment This article has been reviewed for suitability as an ES&T feature by lay H. Lehr, National Water Well Association, Dublin, 1264 Envlmn. Sei. Technol.. Vol. 22. No. 11, 1988
OH 43017 and by Donald D. Runnells, University of Colorado, Boulder, CO 80309.
References (1) Code of Federal Regvlotions. Title 40,
Part 136 (40CFR136). (2) "Water Pollution Control Acl"; Public Law 92-500, 33 U.S.Code I251 et seq., and amendments, 1972. (3) "Safe Drinking Water Act.'; Public Law 93-523, 42 US. Code 300 et seq., and amendments. 1974. ~~~~~~~~~~~~, ~. (4) Est Methods for Evoluoring Solid Waste, 3rd ed.;SW-846: U. S. Environmental
(5)
Protection Agency. U.S. Government Printing Office: Washington, DC, 1986.
Fed. Regist. 1987, 52, 25942.
Jahn U! Kwhn (1) is an associate research chemist with Shell Development Company in Houston. He obtained an M.S. in chemistryfrom Sam Houston Stare University in 1983; he has experience in the sampling and analysis of groundwater and hazardous waste, and in the fields of drinkingwater preparation and wastewater treat-
ment. George H. SIadw, JI., (r) is a staff research chemist with Shell Development Company in Houston. He obtained a B.A. from Southern Illinois University in 1965 and has been working in the environmental fieldsince 1976. Hisprime interest is analysis of trace-level organicpollutants in water, wastewater, and groundwater to meet regulatory requirements.
