Envlron. Sci. Technol. 1984, 18, 953-961
Occurrence and Distribution of Organic Chemicals in Two Landfill Leachate Plumes Martln Relnhard' and Naoml L. Goodman
Department of Civil Engineering, Stanford University, Stanford, California 94305 James F. Barker
Earth Sciences Department, University of Waterloo, Waterloo, Ontario, N2L 3G1 Canada
w The spatial distribution of trace organic compounds in leachate plumes of two sanitary landfills was established by using multilevel sampling devices. The majority of the compounds originated from decomposing plant material and included aliphatic and aromatic acids, phenols, and terpene compounds. Minor constituents, including chlorinated and non-chlorinated hydrocarbons, nitrogen-containing compounds, alkylphenol polyethoxylates,and alkyl phosphates, were of industrial and of commercial origin. Vertical concentration profiles indicated accumulation of chlorinated solvents beneath the leachate plume. Lateral distribution profiles indicated that the sorptive capacity of the sandy aquifer was apparently too low to prevent migration of aromatic hydrocarbons with a log Km0, water of less than 3-4. The distribution of trace organics a i the two sites was much more complex than that of inorganics commonly used to map leachate plumes. This indicates that extensive monitoring will be required to predict future impacts.
Introduction Landfilling has long been the major disposal method for both domestic and industrial wastes. Unfortunately, many of the thousands of landfills, active or abandoned, have been operated with little regard for the dangers of groundwater contamination. In recent years, the number of sites in which landfill leachate is known to contaminate the underlying aquifer has been increasing, but only a few cases have been studied in detail with regard to geochemical processes (1-6). Likewise, few studies have addressed the occurrence of potentially hazardous organic chemicals in leachates of sanitary landfills (7,8). To assess the impact on water quality at a given site, several questions must be asked (i) What are the potentially h m f u l constituents in the leachate? (ii) What are the local hydrogeologic conditions? (iii) What is the significance of attenuating factors such as biological and/or chemical degradation, adsorption, ion exchange, precipitation, and hydrodynamic dispersion? These questions are difficult to answer, mainly because of the cost and complications involved in obtaining hydrogeological data and representative samples of groundwater, as well as a paucity of data on degradation and sorption constants. The objective of this study was to characterize the organic constituents in landfill leachate plumes and to identify geochemical, physical, and biological processes that affect their distribution in the subsurface environment. The Groundwater Research Institute at the University of Waterloo has furnished several landfill sites with observation wells and piezometers and has established the extent of the leachate plumes (3,4,9). The sites studied here are located near North Bay and Waterloo, Ontario, Canada, on sandy, relatively permeable deposits. Their hydrogeological characteristics have been under investigation, and the principal features of the leachate plumes, i.e., the distribution of the major reactive and nonreactive leachate 0013-936X/84/0918-0953$01.50/0
components, have been established (3,9). Reactive components of leachates include sorbable and degradable organic compounds, and nonreactive components include conservatively behaving anions such as chloride (Cl-). In this study the behavior of the reactive trace organics has been evaluated by using the Cl- distribution as a reference. The findings discussed here should be useful for the design of more detailed studies on groundwater contamination by landfills and for selection of protocols for groundwater monitoring in similar hydrogeologic settings.
Summary of Site Descriptions Woolwich. The Woolwich landfill is located in the northwestern part of the Regional Municipality of Waterloo, Ontario. I t is situated on a deposit of glaciofluvial sand which is generally about 30 m thick and overlies a deposit of relatively impervious clayey till. The landfill occupies approximately 3.5 ha, 75% of which has been filled since operation began in the mid-1960s. The site has received rural and municipal as well as some industrial wastes. Rain and snow melts infiltrated the sand-covered refuse, and after migrating through the unsaturated zone, contaminated waters dispersed into the underlying groundwater located 10-15 m below the refuse. The monitoring well network included 62 bundle piezometers (IO), each having eight to nine individual piezometers screened over short intervals (
