20 ENGINEERING GEOLOGY/Ground Water Monitoring at Solid Waste Landfills early autumn to winter By utilising in situ passive samplers, owners and regulatory agencies could realize several key benefits: Parameters Unique to MSWLFs – The Subtitle D parameter list has inherent problems Firstly, most of the heavy metals are not critical to MSWLFs; secondly, some are soluble under oxidising conditions and/or low pH, a situation not pertinent due to the strongly reducing and buffering nature of MSWLF leachate; thirdly, the list implicitly assumes leachate impact only and does not address impact from landfill gas Alternative parameters, such as those presented in this article, not only serve as better indications of groundwater impact but also will better delineate the means of impact, leachate, or landfill gas Continuous Monitoring of Ground Water – Rather than quarterly or semi-annual monitoring, in situ passive sampling can provide much more data that depicts temporal, seasonal, or long-term trends in groundwater quality Reduced Frequency of Sampling – Owners could reduce sampling frequency by using the data from in situ monitoring to determine if and when a sample should be taken By establishing confidence intervals or other statistical criteria, owners would take samples only when exceedences of such criteria occurred Cost Control – Reduction of groundwater monitoring costs, particularly post-closure accruals, would assist owners with small buckets, such as municipalities Error Reduction – Data is simply downloaded from a datalogger to a laptop computer, thereby reducing a significant source of error, manual transcription Better Public Relationship – Continuous monitoring could reduce public concern and increase confidence that a MSWLF is operated properly Conclusion This article presents options to traditional groundwater monitoring at MSWLFs By incorporating these options, owners can better delineate leachate versus gas impact; fingerprint definitive sources, and generate more and higher-quality groundwater data specific to MSWLFs In Situ passive sampling may provide several benefits that include sampling frequency reduction, understanding of temporal trends, cost control, transcription error reduction, and better public confidence See Also Engineering Geology: Natural and Anthropogenic Geohazards; Liquefaction; Made Ground Quarrying Further Reading Baedecker MJ and Back W (1979) Hydrogeological Pro cesses and Chemical Reactions at a Landfill Ground Water 17: 429 437 Barcelona Michael, et al (1990) Contamination of Ground Water: Prevention, Assessment, Restoration Park Ridge, New Jersey: Noyes Data Corporation Beluche R (1968) Degradation of Solid Substrate in a Sani tary landfill Ph.D Thesis, University of Southern Cali fornia, Los Angeles, California Birman J (1990) Handbook of Ground Water Development by Roscoe Moss Company New York: John Wiley and Sons Carothers WW and Kharaka YK (1980) Stable Carbon Isotopes Of HCO3 in Oil field Waters Implications for the Origin of CO2 Geochimica et Cosmochimica Acta 44: 323 332 Coleman DD, et al (1993) Identification of Landfill Methane using Carbon and Hydrogen Isotope Analysis Proceedings of 16th International Madison Waste Con ference, pp 303 314 University of Wisconsin Madison Drever JI (1982) The Geochemistry of Natural Waters Englewood Cliffs: NJ Prentice Hall Farquhar GJ and Rovers FA (1973) Gas Production During Refuse Decomposition, Water, Air and Soil Pollution Vol Matthess FPG and Brown RM (1976) Deuterium and oxygen 18 as indicators of Leachwater Movement from a Sanitary Landfill In: Interpretation of Environ mental Isotope and Hydrochemical Data in Ground water Hydrology Vienna International Atomic Energy Agency Games LM and Hayes JM (1977) Carbon Isotopic Study of the Fate of Landfill Leachate in Groundwater Journal of Water Pollution Control Federation 49: 668 677 Hackley KC, Liu CL, and Coleman DD (1996) Environ mental Isotope Characteristics of Landfill Leachates and Gases Ground Water 34(5): 827 834 Liu, et al (1992) Application of Environmental Isotopes to Characterize Landfill Gases and Leachate Geological Society of America Abstracts with Programs, Cincinnati, Ohio, p A35 Ludwig H (1967) Final report: In Situ Investigation of Gases Produced from Decomposing Refuse California State Water Quality Control Board Murata KJ, Friedman I, and Madsen BM (1969) Isotopic Composition of Diagenic Carbonates in marine Miocene Formations of California and Oregon US Geology Survey Professional Paper 614 B Oneacre JW (1992) Solid waste Principles and Practice in the United States International Conference on Environ mental Protection and Control Technology, Enserach, Kuala Lumpur, Malaysia, pp 661 674