Natural Attenuation: A Feasible Approach to Remediation of Ground Water Pollution at Landfills?

Remediation of ground water pollution at old landfills with no engineered leachate collection system is a demanding and costly operation. It requires control of the landfill body, since the majority of the pollutants are still present in the landfilled waste for decades after the site has been closed. However removing the source is an attractive approach to managing leachate plumes. Natural attenuation has been implemented for petroleum hydrocarbon plumes and chorinated solvent plumes, primarily in the United States. Natural attenuation has not yet gained a foothold with respect to leachate plumes, however. Based on the experience gained from 10 years of research on two Danish landfills, it is suggested that natural attenuation is a feasible approach but is more complicated and demanding than in the case of petroleum hydrocarbons and chlorinated solvent.     

Statistical Comparison of Leachate from Hazardous, Codisposal, and Municipal Solid Waste Landfills

There has been considerable debate regarding the chemical characterization of landfill leachate in general and the comparison of various types of landfill leachate (e.g., hazardous, codisposal, and municipal) in particular. For example, the preamble to the U.S. EPA Subtitle D regulation (40 CFR Parts 257 and 258) suggests that there are no significant differences between the number and concentration of toxic constituents in hazardous versus municipal solid waste landfill leachate. The purpose of this paper is to statistically test this hypothesis in a large leachate database comprising 1490 leachate samples from 283 sample points (i.e., monitoring location such as a leachate sump) in 93 landfill waste cells (i.e., a section of a facility that took a specific waste slream or collection of similar waste streams) from 48 sites with municipal, codisposal, or hazardous waste site histories. Results of the analysis reveal clear differention between landfill leachate types, both in terms of constituents detected and their concentrations. The result of the analysis is a classification function that can estimate the probability that new leachate or ground water sample was produced by the disposal of municipal, codisposal, or hazardous waste. This type of computation is illustrated, and applications of the model to Superfund cost-allocation problems are discussed.     

The Geochemistry of Boron in a Landfill Monitoring Program

Ground water monitoring data collected during the past eight years at a permitted municipal solid waste (MSW) disposal facility located in the midwestern United States indicated fluctuations in typical leachate indicator parameter concentrations. Apparent trends in the data inferred leachate outbreak, generating suspicion as to the integrity of the landfill liner. Eight ground water monitoring wells were installed in three distinct geologic units at the landfill facility, including glacial drift, silurian dolomite, and a post-glacial peat fen, which is downgradient from the landfill. Piezometer nests were used to define ground water gradients at the site. Using boron as an indicator, the occurrence of analytes of concern in the downgradient monitoring wells were shown to be indicative of the natural geochemistry of site ground water. This work emphasizes the importance of understanding site hydrogeology during the interpretation of ground water quality data.     

A Method for Predicting Chloride Concentrations in Leachate at Natural Attenuation Landfills in the Precambrian Shield Regions of Ontario, Canada

Natural attenuation landfill sites continue to be the preferred method of domestic waste disposal in the Precambrian Shield regions of Ontario due to economic factors. The main challenge in siting these landfills is ensuring that there will be no adverse impact on off-site water resources. Impact risk assessments are generally based on estimated volumes and strengths of chloride in the leachate. While volumes can be estimated using simple water balances, peak chloride concentration predictions are based on judgment and are quite variable. Since design chloride strengths dictate the size of the required attenuation zone, overestimating concentrations will typically make it impossible to find a suitable site, while underestimating concentrations increases the potential for adverse off-site impacts occurring.
Hydrogeological data from active and closed landfills in the Precambrian Shield region were collected to help develop a reliable method of predicting peak chloride concentrations in leachate. This study focused on 21 sites located on relatively permeable sandy soils since landfills underlain by low permeability clayey soils retain leachate similar to lined facilities.
Linear regression analyses were conducted to determine if source chloride concentrations at the "sand" sites are significantly influenced by waste thickness, fill area, waste volume, waste deposition rate, hydraulic conductivity, upgradient flow length, depth to the water table, and moisture surplus.
A strong relationship (R = 0.957) was found to exist between source chloride concentrations and waste volume. This empirical volume versus chloride regression equation can be used as the basis for establishing design chloride concentrations at new natural attenuation landfills developed over sandy soils in the Precambrian Shield regions of Ontario. An alternative risk assessment approach is required for sites developed over clay soils.     

Elements in Cottonwood Trees as an Indicator of Ground Water Contaminated by Landfill Leachate

Ground water at the Norman Landfill Research Site is contaminated by a leachate plume emanating from a closed, unlined landfill formerly operated by the city of Norman, Oklahoma, Ground water contaminated by the leachate plume is known to be elevated in the concentration of many, organic and inorganic constituents. Specific conductance, alkalinity, chloride, dissolved organic carbon, boron, sodium, strontium, and deuterium in ground water are considered to be indicators of the leachate plume at this site.
Leaf samples of broad-leafed cottonwood, Populus deltoides , were collected from 57 sites around the closed landfill. Cottonwood, a phreatophyte or "well plant," functions as a & surrogate well and serves as a ground water quality sampler. The leaf samples were combusted to ash and analyzed by instrumental neutron activation for 35 elements and by prompt-gamma instrumental neutron activation, for boron. A monitoring well was located within a few meters of a sampled cottonwood tree at 15 of the 57 sites, and ground water samples were collected from these monitoring wells simultaneously with a leaf sample. The chemical analyses of the ground water and leaf samples from these 15 sites indicated that boron, bromine, sodium, and strontium concentrations in leaves were significantly correlated with leachate indicator constituents in ground water. A point-plot map of selected percentiles indicated high concentrations of boron, bromine, and sodium in leaf ash from sites downgradient of the most recent landfill and from older landfills nearby.
Data from leaf analysis greatly extended the known areal extent of the leachate plume previously determined from a network of monitoring wells and geophysical surveys. This phytosgeochemical study provided a cost-effective method for assessing the extent of a leachate plume from an old landfill. Such a method may be useful as a preliminary sampling tool to guide the design of hydrogeochemical and geophysical studies.     

Pharmaceuticals and Other Organic Waste Water Contaminants Within a Leachate Plume Downgradient of a Municipal Landfill

Ground water samples collected from the Norman Landfill research site in central Oklahoma were analyzed as part of the U.S. Geological Survey (USGS) Toxic Substances Hydrology Program's national reconnaissance of pharmaceuticals and other organic waste water contaminants (OWCs) in ground water. Five sites, four of which are located downgradient of the landfill, were sampled in 2000 and analyzed for 76 OWCs using four research methods developed by the USGS. OWCs were detected in water samples from all of the sites sampled, with 22 of the 76 OWCs being detected at least once. Cholesterol (a plant and animal steroid), was detected at all five sites and was the only compound detected in a well upgradient of the landfill. N,N-diethyltoluamide (DEBT used in insect repellent) and tri(2-chloroethyl) phosphate (fire-retardant) were detected in water samples from all four sites located within the landfill-derived leachate plume. The sites closest to the landfill had more detections and greater concentrations of each of the detected compounds than sites located farther away. Detection of multiple OWCs occurred in the four sites located within the leachate plume, with a minimum of four and a maximum of 17 OWCs detected. Because the landfill was established in the 1920s and closed in 1985, many compounds detected in the leachate plume were likely disposed of decades ago. These results indicate the potential for long-term persistence and transport of some OWCs in ground water.     

Characterization and identification of na-cl sources in ground water

Elevated concentrations of sodium (Na+) and chloride (Cl-) in surface and ground water are common in the United States and other countries, and can serve as indicators of, or may constitute, a water quality problem. We have characterized the most prevalent natural and anthropogenic sources of Na+ and Cl- in ground water, primarily in Illinois, and explored techniques that could be used to identify their source. We considered seven potential sources that included agricultural chemicals, septic effluent, animal waste, municipal landfill leachate, sea water, basin brines, and road deicers. The halides Cl-, bromide (Br), and iodide (I) were useful indicators of the sources of Na+-Cl- contamination. Iodide enrichment (relative to Cl-) was greatest in precipitation, followed by uncontaminated soil water and ground water, and landfill leachate. The mass ratios of the halides among themselves, with total nitrogen (N), and with Na+ provided diagnostic methods for graphically distinguishing among sources of Na+ and Cl- in contaminated water. Cl/Br ratios relative to Cl- revealed a clear, although overlapping, separation of sample groups. Samples of landfill leachate and ground water known to be contaminated by leachate were enriched in I and Br; this provided an excellent fingerprint for identifying leachate contamination. In addition, total N, when plotted against Cl/Br ratios, successfully separated water contaminated by road salt from water contaminated by other sources.     

Assessment of the Relative Adequacy of Landfills as a Means of Solid Waste Disposal in Malaysia

This study examined the relative adequacy of active landfills between states in Malaysia. The percentages of closed landfills were determined. The accessibility and loading of the landfills were examined. The characteristics of each landfill studied were noted. The study involved the compilation and analyses of data on groundwater, stream water and current land use surrounding landfills. Results of the study showed that the number of active landfills was not adequate to handle solid waste disposal. The potential of alternative approaches was examined and discussed.     

Characterization of a dismissed landfill via electrical resistivity tomography and mise-à-la-masse method

Electrical resistivity methods are widely used for environmental applications, and they are particularly useful for the characterization and monitoring of sites where the presence of contamination requires a thorough understanding of the location and movement of water, that can act as a carrier of solutes. One such application is landfill studies, where the strong electrical contrasts between waste, leachate and surrounding formations make electrical methods a nearly ideal tool for investigation. In spite of the advantages, however, electrical investigation of landfills poses also challenges, both logistical and interpretational. This paper presents the results of a study conducted on a dismissed landfill, close to the city of Corigliano d'Otranto, in the Apulia region (Southern Italy). The landfill is located in an abandoned quarry, that was subsequently re-utilized about thirty years ago as a site for urban waste disposal. The waste was thought to be more than 20 m thick, and the landfill bottom was expected to be confined with an HDPE (high-density poli-ethylene) liner. During the digging operations performed to build a nearby new landfill, leachate was found, triggering an in-depth investigation including also non-invasive methods. The principal goal was to verify whether the leachate is indeed confined, and to what extent, by the HDPE liner. We performed both surface electrical resistivity tomography (ERT) and mise-à-la-masse (MALM) surveys, facing the severe challenges posed by the rugged terrain of the abandoned quarry complex. A conductive body, probably associated with leachate, was found as deep as 40 m below the current landfill surface i.e. at a depth much larger than the expected 20 m thickness of waste. Given the logistical difficulties that limit the geometry of acquisition, we utilized synthetic forward modeling in order to confirm/dismiss interpretational hypotheses emerging from the ERT and MALM results. This integration between measurements and modeling helped narrow the alternative interpretations and strengthened the confidence in results, confirming the effectiveness of non-invasive methods in landfill investigation and the importance of modeling in the interpretation of geophysical results.     

Bioattenuation in groundwater impacted by landfill leachate traced with δ13C

The impact on groundwater imparted by the infiltration of high dissolved organic carbon (DOC) leachate from capped, unlined landfills can be attenuated by biogeochemical reactions beyond the waste source, although such reactive loss in the aquifer is difficult to distinguish from conservative advective dispersion. Compound-specific measurement of δ(13)C in carbon species, including CH(4), dissolved inorganic carbon (DIC), and the major DOC compounds (acetate, humic acid, and fulvic acid) provides a constraint in this assessment that can assist in exercises of modeling and prediction of leachate transport. The Trail Road municipal landfill near Ottawa, Ontario, Canada, hosts an unlined sector which produces a highly enriched leachate (DOC >4500 mg/L) that provides a good site to examine reactive attenuation within the receptor aquifer. Acetate, a sentinel component of leachate DOC (~1000 mg C/L), is absent in impacted groundwater. Mass balance calculations together with reaction modeling suggest continued acetate fermentation with calcite control on DIC and δ(13)C(DIC) evolution. In groundwater within 50 m of the landfill, methane concentrations are elevated (~10 mg/L), consistent with acetate fermentation, whereas δ(13)C(CH4) measurements in deeper groundwater range down to -51‰ compared with -60‰ in the landfill demonstrating oxidative loss. DOC in the deep aquifer is remarkably depleted to values less than -40‰ suggesting methanotrophic bacteria selectively consume isotopically light CH(4) to fix carbon. Continued reaction of leachate DOC in groundwater is demonstrated by evolution away from conservative mixing lines on diagrams of δ(13)C vs. concentrations of DIC and DOC.     

Nitrogen Removal from Landfill Leachate Using an Infiltration Bed Coupled with a Denitrification Barrier

Treatment of nitrogen in landfill leachate has received considerable attention recently because of the relatively low levels at which some nitrogen species (i.e., NH3) can be toxic to aquatic life forms. This study reports on the results of a three-year, pilot-scale field trial demonstrating the use of infiltration bed and nitrate barrier technology to achieve nitrogen removal in landfill leachate. The infiltration bed comprises an unsaturated sand layer overlying a saturated layer of waste cellulose solids (sawdust), which acts as a carbon source for heterotrophic denitrification. When loaded at a rate of 1 to 3 cm/day, the infiltration bed was successful at lowering leachate inorganic nitrogen (NH₄⁺+ NO₃^-) levels averaging 24.8 mg/L N by 89%, including 96% in the third year of operation. The surface water discharge criteria for un-ionized ammonia (NH3) were met on all occasions in the treated leachate during the second and third years of operation. Nitrogen attenuation is presumed to occur by a two-step process in which leachate NH₄⁺ is first oxidized to NO₃^- in the unsaturated sand layer and then is converted to nitrogen gas (N₂) by denitrification occurring in the underlying sawdust layer. Mass balance calculations suggest that the sawdust layer has sufficient carbon to allow denitrification to proceed for long periods (1.0 to 30 years) without replenishment. Because this technology is simple to construct and is relatively maintenance free, it should be attractive for use at smaller landfills where the installation of conventional treatment plants may not be feasible.     

Detection of Contaminant Plumes by Borehole Geophysical Logging

Two borehole geophysical methods—electromagnetic induction and natural gamma radiation logs—were used to vertically delineate landfill leachate plumes in a glacial aquifer. Geophysical logs of monitoring wells near two land-fills in a glacial aquifer in west-central Vermont show that borehole geophysical methods can aid in interpretation of geologic logs and placement of monitoring well screens to sample landfill leachate plumes.
Zones of high electrical conductance were delineated from the electromagnetic log in wells near two landfills. Some of these zones were found to correlate with silt and clay units on the basis of drilling and gamma logs. Monitoring wells were screened specifically in zones of high electrical conductivity that did not correlate to a silt or clay unit. Zones of high electrical conductivity that did not correlate to a silt or clay unit were caused by the presence of ground water with a high specific conductance, generally from 1000 to 2370 μS/cm (microsiemens per centimeter at 25 degrees Celsius). Ambient ground water in the study area has a specific conductance of approximately 200 to 400 μS/cm. Landfill leachate plumes were found to be approximately 5 to 20 feet thick and to be near the water table surface.     

Utilizing Natural Liner Materials for Heavy Metal Removal in Simulated Landfill Conditions

Inorganic industrial waste landfills have the potential to contaminate subsurface groundwater supplies through migration of leachates down to the water table and into groundwater aquifers, despite the use of compacted low permeability clay or polyethene liners. This paper aims the removal of Cu²⁺ and Zn²⁺ in the leachate from an industrial waste landfill using natural materials (natural zeolite, expanded vermiculite, pumice, illite, kaolinite, and bentonite) as a liner material. Cu²⁺ and Zn²⁺ concentrations for all treatments decreased during the process. Of all the different natural materials, natural zeolite, expanded vermiculite and pumice, with bentonite, were effective in removing Cu²⁺ and Zn²⁺ present in the leachate. However, the use of illite and kaolinite with bentonite as liner materials could be of disadvantage in Cu²⁺ and Zn²⁺ removal from leachate. The adsorption kinetic models were also tested for the validity. The second order kinetics with the high correlation coefficients best described adsorption kinetic data.     

西安北动车段垃圾填埋场地基处理措施研究

随着城市化进程的加快,建筑用地日趋紧张,将垃圾填埋场作为工程场址愈发寻常。为探讨垃圾填埋场各类土的物理力学性质及其作为地基时所应采取的必要处理措施,在西安北动车段垃圾填埋场的地基处理及施工中,采用室内试验及现场原位测试,定量分析杂填土地基的工程特性,提出合理的地基处理方案。工程实践证明,采用挖除换填和强夯处理后地基各参数均满足设计要求,达到预期效果,且创新性地采取掺入生石灰的方法对场区固体废物进行处理,避免二次污染的产生。研究成果可供类似条件下其他垃圾填埋场的地基处理参考和借鉴。     

Options for the Treatment and Management of Municipal Landfill Leachate: Common and Specific Issues

This paper aims to explore information from the literature for emphasizing the state‐of‐the art and progress in landfill leachate generation, fate and migration, and treatment. Leachate composition is discussed in terms of types of waste disposed and the processes occurring within landfill. The focus is also on potential pathways of environmental contamination by leachate, which may increase environmental and human health risk. The analysis addresses the opportunity and support for decision making concerning alternatives for leachate management and treatment. Advantages and limitations of treatment methods and processes are discussed considering leachate transfer, physico‐chemical methods, biodegradation, and combined methods.     

Artificial Sweeteners Identify Spatial Patterns of Historic Landfill Contaminated Groundwater Discharge in an Urban Stream

Leachate-contaminated groundwater from historical municipal landfills, typically lacking engineered liners and leachate collection systems, poses a threat to nearby urban streams, particularly to benthic ecosystems. Effective monitoring and assessment of such sites requires understanding of the spatial patterns (i.e., two-dimensional footprint) of contaminated groundwater discharge and associated controlling factors. However, discharges from groundwater contaminated by modern wastewater can complicate site assessments. The objectives of this study were to (1) demonstrate the use of artificial sweeteners (AS): saccharin (SAC), cyclamate (CYC), acesulfame (ACE), and sucralose (SUC), to distinguish groundwater discharge areas influenced by historic landfill leachate (elevated SAC and sometimes CYC; low ACE and SUC concentrations) from those influenced by wastewater (high ACE and SUC concentrations), and (2) investigate contaminant discharge patterns for two gaining urban stream reaches adjacent historic landfills at base flows. Contaminant discharge patterns revealed by the AS were strongly controlled by hyporheic flow (low AS concentrations), particularly for the straight reach, and stream sinuosity, particularly for the meandering reach. These patterns were different and the contaminant footprint coverage (<25% of streambed area) much less than most past studies (typically >50% coverage), likely due to the homogeneous streambed-aquifer conditions and shallow, narrow landfill plume in this setting.     

Effects of local site conditions on the seismic response of municipal solid waste landfills

Over the last decade, the seismic response of landfills made of municipal solid waste has drawn attention mainly due to the environmental and public-health issues that could be raised in the event of a failure. Nevertheless, there are several associated technical issues that have not been adequately investigated. One of these is the impact of local site conditions on the earthquake-induced accelerations and, thereby, on the seismic design of a landfill. This study presents the results of a parametric numerical simulation that has been performed in order to examine the effects of local site conditions on the dynamic response of a typical landfill. Emphasis is given on the special characteristics of ground motion, while the material nonlinearity of both soil and waste is taken into account by an equivalent-linear procedure. Results indicate that local site conditions may play a significant role in the seismic response of a landfill. However, this role cannot be judged a priori as beneficial or detrimental, as it depends not only on soil conditions and seismic excitation, but also on the material and geometric characteristics of the landfill.     

Frequency Domain Electromagnetic Induction Sounding Surveys for Landfill Site Characterization Studies

A frequency domain electromagnetic induction sounding survey (FDEM) was conducted on a landfill in northern Illinois to determine the depth of fill, locate areas of drum disposal, and locate areas of heavy metal sludge disposal. Sketchy information obtained from interviews of the site personnel identified specific exploration targets and areas of concern. The results of the geophysical survey verified much of the reported disposal history and identified areas suspected to contain hazardous waste.
Based on the results of the survey, the thickness of fill was estimated and two areas with highly conductive fill were located. These areas could represent leachate pockets or sludge disposal areas. An area in which the fill appears to be thicker than expected was identified. This area is thought to represent industrial sludge disposal in trenches excavated into the existing fill and underlying soils. An area with several linear in-phase, quadrature, and conductivity highs was detected. A subsequent magnetometer survey detected linear magnetic anomalies that are believed to be caused by parallel trenches filled with steel drums. This area is believed to be a previously unreported hazardous waste drum disposal cell excavated into the native soil.
As of this writing, the results of this survey have not been verified by traditional intrusive methods. When these investigations begin, we expect that information provided by the FDEM survey will reduce project costs by directing subsequent investigations, thereby reducing the number of borings and test pits required to characterize the site. While there is an unavoidable margin of error and uncertainty in remote sensing methods, the subsurface coverage provided by this geophysical survey could not have been reproduced by traditional methods without substantial expense. This paper presents the results of the survey and discusses application of the FDEM method on landfills.     

The Detection of Naturally Occurring BTX During a Hydrogeologic Investigation

Benzene, toluene and xylenes (BTX) were detected in ground water during a contaminant hydrogeological investigation of a landfill site. The landfill site was situated on approximately 10m (33 ft) of clay and glacial till overburden soils, which were underlain by a shaly limestone bedrock. The top part of the bedrock was the regional aquifer in the study area. Initial thoughts were that the landfill was the source of the BTX. However, the BTX was detected in ground water a considerable distance from the known extent of the leachate plume. Subsequent detailed analysis of rock cores showed the BTX could be leached from bituminous layers of shale that were interbedded in limestone. Rock core testing included gas chromatograph (GC) analysis of organic free reagent water used for leaching tests, flame ionization detection on a solvent used for leaching tests and thermal desorption analysis of the solid rock. The naturally occurring BTX, along with the presence of brackish ground water in the shaly bedrock, made it difficult to identify ground water contamination emanating from the landfill. Thus, the presence of BTX should not be considered definitive evidence of ground water contamination in certain sedimentary rock aquifers.