Design considerations of constructed wetlands to reduce landfill leachate contamination in tropical regions

In tropical regions, landfill leachate contamination at municipal solid waste disposal sites is a critical issue because of the large volume of highly contaminated leachate formed during the rainy season. We evaluated the efficacy of constructed wetlands (CWs) with the ability to reduce the water volume and pollutant levels to reduce leachate contamination compared to the most commonly used treatment system, stabilization ponds, based on parameters obtained in a field experiment in Thailand. The simulation indicated that CWs had a higher potential to reduce the water volume than stabilization ponds over the course of a year. Scenario evaluations under varying initial water depths, system depths, and area sizes indicated that the CWs could reduce the treatment area to prevent overflow and leachate pollution. In addition, the CWs were estimated to reduce the leachate amount and pollution by 83–100% and 92–99%, respectively. When there is limited land available, deeper CWs can be used to sustainably prevent contamination from leachate overflow. Effectively designed CW systems may be valuable for both reducing the required area and the contamination; therefore, CWs are a promising option for sustainable landfill leachate treatment systems in developing tropical regions.     

The performance of a natural treatment system for landfill leachate with special emphasis on the fate of organic pollutants.

A natural treatment system for the treatment of leachate was studied at Moskogen landfill in southern Sweden. This facility consists of three consecutive ponds and a soil-plant (SP)-system. A test area, receiving water from the third pond with the same hydraulic load as the SP-system, was used for estimation of the latter system. Quality parameters including biochemical oxygen demand, total organic carbon, ammonium, nitrate, orthophosphate, and total suspended solids along the treatment line were determined as well as soluble metals (Cu, Cd, Zn, Cr, Ni, and Pb). In addition a thorough investigation along the treatment line has also been performed concerning volatile organic compounds and semi-volatile organic compounds. Non-polar organic compounds were investigated using gas chromatography-mass spectrometry. Quantification was based on the assumption of equal response for the compounds found in comparison with the chosen marker substances. For polar, water-soluble compounds the measurements were restricted to phenolic compounds using high-performance liquid chromatography. Several different types of organic compounds were found in the raw leachate including aromatics, benzene-sulfonamides, biphenyls, naphthalene, organic phosphates, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phenols and phthalates. The treatment system efficiently reduced organic pollutants, heavy metals, and nitrogen/phosphorous compounds. Most metals and organic compounds in the leachate were already significantly reduced to a low level in the treatment ponds and ammonium-N was efficiently transformed to nitrate-N in the SP-system.     

Cost‐Effective Sediment Dredge Disposal Options for Small Craft Harbors in Canada

Sediment dredge disposal options were reviewed to improve cost‐effectiveness and environmental safety for dredging of coastal sediments at the Department of Fisheries and Oceans Small Craft Harbours (DFO‐SCH) program in Canada. Historically, contaminated dredge sediments exceeding federal guidelines were disposed of in nearby landfills. Recent federal regulatory changes in sediment quality guidelines adopted by provincial regulators in Canada has resulted in updates to guidelines for disposal of contaminated solids in landfills. Updates now require specific and general disposal options for contaminated dredge material destined for land‐based disposal, resulting in more expensive disposal in containment cells (if contaminated sediments exceed federal guidelines). However, as part of this study, a leachate testing method was applied to contaminated sediments to simulate migration of potential contaminants in groundwater. Using this approach, leachate quality was compared to federal freshwater criteria and drinking water quality guidelines for compliance with new regulations. Leachate testing performed on the highest sediment contaminant concentrations triggered less than 2 percent potable water exceedances, meaning that most dredge spoils could be disposed of in privately owned or provincially operated landfill sites, providing less expensive disposal options compared to containment cell disposal. Current dredge disposal practices were reviewed at 35 harbor sites across Nova Scotia and their limitations identified in a gap analysis. Improved site management was developed following this review and consultation with interested marine stakeholders. New disposal options and chemical analyses were proposed, along with improvements to cost efficiencies for management of dredged marine sediments in Atlantic Canada. © 2013 Wiley Periodicals, Inc.     

Groundwater Impacts on Surface Water and Sediment—Gowanus Canal,Brooklyn, New York

The Gowanus Canal Superfund Site in Brooklyn, New York, is an approximately 1.5‐mile (1.61‐km) long estuary that was historically converted into a canal for industrial and commercial purposes. Three manufactured gas plants (MGPs) were formerly located on the Gowanus Canal and discharged waste into it. Surface sediments remain highly contaminated with polycyclic aromatic hydrocarbons (PAHs) long after the MGPs were razed. A hydrogeologic assessment indicates that groundwater passes through the deeper coal tar–contaminated sediment prior to discharging to the canal. This study was undertaken to investigate if groundwater passing through coal tar–contaminated sediment could be responsible for the ongoing contamination of both surface sediments and surface water in the canal. PAH compound distributions in surface water samples collected from the tidal canal at low tide were compared with PAH compounds found in adjacent groundwater‐monitoring wells, point sources (combined sewer overflows [CSOs]), and surface sediments. The results indicate a strong correlation between PAH contaminant distributions in groundwater, sediment, and surface water, indicating that contaminated groundwater passing through the deeper coal tar–contaminated sediments is the primary mechanism contributing to the contamination of both surface sediment and surface water in the canal. Therefore, any sediment remediation efforts in the Gowanus Canal that fail to evaluate and control the upward transport processes have a high chance of failure due to recontamination from below.  ©2016 Wiley Periodicals, Inc.     

A survey on characteristics of leachate pond in an offshore municipal solid waste disposal site

Leachate from a landfill is collected and flowed in leachate accumulation pond, and sent to treatment facility. However, leachate in the pond can be a source of complaints from residents due to off coloration or odor, particularly near heavily populated urban areas. In this study, for the purpose of appropriate control of leachate pond, pond water and sediment were sampled in an offshore municipal solid waste disposal site 2 years after the disposal site was closed, and analyzed some parameters to estimate their properties. The pond water had high alkalinity due to the disposal of incineration residues, and EC and COD_Mn were also high. On the other hand, Cr, Mn, Fe, Cu, Zn, Cd, and Pb did not exceed the Japanese effluent water standards. Total sulfide was detected from all sediment samples during the sampling period, and values in the summer were slightly higher than at other times. To investigate the stabilization of targeted disposal site, the relationships among cumulative liquid/solid ratio (L/S) with pH and Cl^? elution after closing the site were examined. Both parameters showed a direct relationship with cumulative L/S ratio, which can be anticipated to continue increasing in the future.     

Microbial nitrogen transformation potential in surface run-off leachate from a tropical landfill

Ammonium is one of the major toxic compounds and a critical long-term pollutant in landfill leachate. Leachate from the Jatibarang landfill in Semarang, Indonesia, contains ammonium in concentrations ranging from 376 to 929 mg N L⁻¹. The objective of this study was to determine seasonal variation in the potential for organic nitrogen ammonification, aerobic nitrification, anaerobic nitrate reduction and anaerobic ammonium oxidation (anammox) at this landfilling site. Seasonal samples from leachate collection treatment ponds were used as an inoculum to feed synthetic media to determine potential rates of nitrogen transformations. Aerobic ammonium oxidation potential (<0.06 mg N L⁻¹ h⁻¹) was more than a hundred times lower than the anaerobic nitrogen transformation processes and organic nitrogen ammonification, which were of the same order of magnitude. Anaerobic nitrate oxidation did not proceed beyond nitrite; isolates grown with nitrate as electron acceptor did not degrade nitrite further. Effects of season were only observed for aerobic nitrification and anammox, and were relatively minor: rates were up to three times higher in the dry season. To completely remove the excess ammonium from the leachate, we propose a two-stage treatment system to be implemented. Aeration in the first leachate pond would strongly contribute to aerobic ammonium oxidation to nitrate by providing the currently missing oxygen in the anaerobic leachate and allowing for the growth of ammonium oxidisers. In the second pond the remaining ammonium and produced nitrate can be converted by a combination of nitrate reduction to nitrite and anammox. Such optimization of microbial nitrogen transformations can contribute to alleviating the ammonium discharge to surface water draining the landfill.     

Hazardous chemical site remediation through capping: Problems with long-term protection

The capping of waste management units and contaminated soils is receiving increasing attention as a low-cost method for hazardous chemical site remediation. Capping is used to prevent further groundwater pollution by existing waste management units and contaminated soils through limiting the moisture that enters the wastes. In principle, for wastes located above the water table, the construction of an impermeable cap can prevent leaching of the wastes (leachate generation) and groundwater pollution. In practice, appropriately designed and constructed RCRA caps can provide for only short-term prevention of groundwater pollution. Alternative approaches are available for capping of wastes that can be effective in preventing moisture from entering the wastes and concomitant groundwater pollution. These approaches recognize the inability of the typical RCRA cap to keep wastes dry for as long as waste constituents will be a threat and, most importantly, provide the necessary funds to effectively address all plausible worst-case scenario failures that could occur at a capped waste management unit or contaminated soil area.     

Reactive transport modeling of remedial scenarios to predict cadmium,copper, and zinc in north fork of Clear Creek,Colorado

The North Fork of Clear Creek (NFCC), Colorado, is an acid‐mine‐drainage‐impacted stream typical of many mountain surface waters affected by historic metal mining in the western United States. The stream is devoid of fish primarily because of high metal concentrations in the water (e.g., copper and zinc) and has large amounts of settled iron oxyhydroxide solids that coat the streambed. The NFCC is part of the Central City/Clear Creek Superfund site, and remediation plans are being implemented that include treatment of three of the main point‐source inputs and cleanup of some tailings and waste rock piles. This article examines dissolved (0.45‐μm filterable) concentrations of cadmium, copper, and zinc following several potential remediation scenarios, simulated using a reactive transport model (WASP4/META4). Results from modeling indicate that for cadmium, remediation of the primary point‐source adit discharges should be sufficient to achieve acute and chronic water‐quality standards under both high‐ and low‐flow conditions. To achieve standards for copper and zinc, however, the modeling scenarios suggest that it may be necessary to treat or remove contaminated streambed sediments in downstream reaches, as well as identify and treat nonpoint sources of metals. Recommendations for improvements to the model for metal transport in acid‐mine drainage impacted streams are made. These recommendations are being implemented by the U.S. Environmental Protection Agency. © 2009 Wiley Periodicals, Inc.     

Case study: On-site remediation of soil and groundwater for a michigan town's water supply

In 1993 environmental consultants, working in concert with the State of Michigan, discovered groundwater contamination that threatened the drinking water supply of the town of Big Rapids. The contamination originated from leaking underground storage tanks and gasoline lines, which were removed. A pilot study indicated the contaminated area extended to 240′ x 180′ and affected soil as well as groundwater. A remediation plan was designed by and implemented by Continental Remediation Systems, Inc., a Natick, Massachusetts, firm. The remediation plan is ongoing and includes an interceptor trench to stop gasoline from flowing into the creek, as well as air sparging to vent and treat the contaminated soil. It is anticipated that the remediation project will take six months to complete. The chief advantage of on-site remediation is that it avoids the costs and liabilities associated with landfill disposal and no materials need leave the site.     

Treatment technology for remediation of wood preserving sites: Overview

This is the first in a series of five articles describing the applicability, performance, and cost of technologies for the remediation of contaminated soil and water at wood preserving sites. Site‐specific treatability studies conducted under the supervision of the United States Environmental Protection Agency (US EPA), National Risk Management Research Laboratory (NRMRL), from 1995 through 1997 constitute much of the basis for the evaluations presented, although data from other treatability studies, literature sources, and actual site remediations have also been included to provide a more comprehensive evaluation of remediation technologies. This article provides an overview of the wood preserving sites studied, including contaminant levels, and a summary of the performance of the technologies evaluated. The subsequent articles discuss the performance of each technology in more detail. Three articles discuss technologies for the treatment of soils, including solidification/stabilization, biological treatment, solvent extraction and soil washing. One article discusses technologies for the treatment of liquids, water and nonaqueous phase liquids (NAPLS), including biological treatment, carbon adsorption, photolytic oxidation, and hydraulic containment. The reader should be aware that other technologies including, but not limited to, incineration, thermal desorption, and base catalyzed dehalogenation, also have application for treating contaminants on wood preserving sites. They are not discussed in these five articles since the focus was to evaluate lesser known and hopefully lower cost approaches. However, the reader should include consideration of these other technologies as part of any evaluation or screening of technologies applicable to remediation of wood preserving sites.     

In Situ Solidification (ISS) of River Sediments: Pilot Demonstration and Discussion of ISS as a Remedial Alternative to Dredging and Capping

In situ solidification (ISS) is a proven technology for remediation of upland site soils, but has not been thoroughly demonstrated for use in impacted underwater sediments. This article describes the first successful use of ISS techniques to solidify underwater sediments containing manufactured gas plant non‐aqueous‐phase liquid (NAPL). The techniques consisted of mixing cementitious grout with the sediments in situ to create a monolith that immobilized the contaminants, significantly decreased the hydraulic conductivity, and also vastly decreased contaminant leaching potential of the sediments. The success of this pilot demonstration project suggests that ISS may be a viable alternative for: sites requiring deep dredging; large volume projects on urban waterways where staging and amending areas are limited; sites with NAPL impacts that cannot be controlled during dredging; and sites where eventual NAPL breakthrough is anticipated if reactive caps are employed. The potential economic, environmental, and operational benefits of this technology will be discussed. This article focuses on the primary objectives of the pilot demonstration: to meet quantitative performance criteria for strength and hydraulic conductivity; to assess the leach performance of the solidified sediments; and to satisfy water quality parameters for turbidity, pH, and sheen. Approach/activities: The pilot study utilized a customized marine platform (modular floats, tug boats, etc.) and full‐scale ISS equipment (auger rig, silos, etc.) and varied operational parameters to provide a range of data to assist in evaluating the feasibility and efficacy of the technology for use in similar environments and in planning future ISS projects on the water. Water quality controls and monitoring were implemented during the operation, and the study documented and evaluated the environmental disruption (short‐term impacts) and costs of the application of the ISS process to contaminated aquatic sediments. ©2016 Wiley Periodicals, Inc.     

Remediation of Trapped Free‐Phase LNAPL

Free‐phase light nonaqueous phase liquids (LNAPLs) may be trapped in certain stratigraphic and structural features near or at contaminated sites due to seasonal or other variations in the water table elevation. The purpose of this article is to point out particular subsurface conditions that are conducive to trapping of free‐phase LNAPLs and to suggest approaches to remediating LNAPL‐contaminated sites exhibiting similar subsurface geometry and stratigraphy. To trap free‐phase LNAPL, a structure must have, in addition to closed contours, an upper boundary with pores small enough so that the LNAPL will not enter them. This boundary usually consists of clay‐rich sediments. The Lower Mississippi River Valley contains thousands of these potential traps associated with the geomorphic surfaces mapped as outwash or braided stream terraces, which are covered with thin layers of backswamp clays. These traps may have closure heights ranging from about 1 to 7.5 meters or more and have variable lateral extents. Based on surface geomorphic analysis, the potential LNAPL traps in the Lower Mississippi River Valley range in size from about 0.06 by 0.02 km to 4.19 by 0.69 km. The apparent best remediation strategy for LNAPL sites located on these geomorphic surfaces, which contain these trapping structures, is to first determine if free‐phase is present. If it is present, and is contained in one of the stratigraphic traps, the free‐phase can be removed through an extraction well or wells located at the trap apex. Geomorphic analysis and geophysical surveys may be necessary to accurately locate the trap apex. The remaining residual hydrocarbons might best be remediated using an air sparging system, although it may be necessary to install air vents through the clay cap by backfilling augured holes with washed sand. If it is determined that, due to geometry, the dissolved LNAPL plume cannot be adequately remediated using an air sparging system, then groundwater circulation wells or monitored natural attenuation may be alternative technologies. © 2002 Wiley Periodicals, Inc.     

Interactions of Natural Colloidal Material and Phenanthrene in the Aquatic Environment

Resuspension of contaminated aquatic sediments by natural and anthropogenic activities (i.e., dredging, boat activities, fish, wildlife, storms, runoff) increases the flux of natural colloidal material and colloidally bound contaminants into the overlying water column. Colloidal material extracted from lower Fox River sediments was analyzed for various physical and chemical characteristics and subjected to batch aggregation studies under controlled conditions of pH (～3–8) and colloid concentrations (5 and 9 mg L^?1 as TOC equivalents) in the presence of dissolved phenanthrene in solution. Under water chemistry conditions where pH and K⁺ concentration are typical of most natural waters (10^?2 M K⁺ and pH～8), the presence of phenanthrene in solution (average [phen] = 0.2–0.4 mg/L) prevents particle aggregation and decreases the settling rate of these particles. Ultimately, this increases the total concentration of colloidally bound contaminants in the water column. Dredging is the most popular remediation technique for removing contaminated sediments from the aquatic environment. However, this laboratory study suggests that for typical waters, dredging may potentially elevate the concentrations of contaminants found in the water column. © 2001 John Wiley & Sons, Inc.     

Hazardous Substance Research Centers program: An incubator for remediation research

The Hazardous Substance Research Center (HSRC) was established by the U.S. Environmental Protection Agency (EPA) to assist in the implementation of Superfund and to address major hazardous substance environmental problems at a regional level. Over the past 12 years, the HSRC program has produced more than 1,200 peer‐reviewed technical articles, 27 patents and licenses, 21 new technologies for the remediation marketplace, and provided technical assistance to more than 300 communities. Research, technology transfer, and training are conducted by five regional multi‐university centers, which focus on different aspects of hazardous substance management. Areas of focus include urban environments, contaminated sediments, natural remediation and restoration technologies, abandoned mine lands, and chlorinated solvents in groundwater. This article provides an overview of the five HSRC programs including current areas of research, field studies, and technology transfer Internet links to access research results and remediation technology information. © 2003 Wiley Periodicals, Inc.     

Phytoremediation of landfill leachate

Leachate emissions from landfill sites are of concern, primarily due to their toxic impact when released unchecked into the environment, and the potential for landfill sites to generate leachate for many hundreds of years following closure. Consequently, economically and environmentally sustainable disposal options are a priority in waste management. One potential option is the use of soil-plant based remediation schemes. In many cases, using either trees (including short rotation coppice) or grassland, phytoremediation of leachate has been successful. However, there are a significant number of examples where phytoremediation has failed. Typically, this failure can be ascribed to excessive leachate application and poor management due to a fundamental lack of understanding of the plant-soil system. On balance, with careful management, phytoremediation can be viewed as a sustainable, cost effective and environmentally sound option which is capable of treating 250m(3)ha(-1)yr(-1). However, these schemes have a requirement for large land areas and must be capable of responding to changes in leachate quality and quantity, problems of scheme establishment and maintenance, continual environmental monitoring and seasonal patterns of plant growth. Although the fundamental underpinning science is well understood, further work is required to create long-term predictive remediation models, full environmental impact assessments, a complete life-cycle analysis and economic analyses for a wide range of landfill scenarios.     

Remediation of fly ash landfills through plantation

In India, a significant area of land is occupied by preexisting coal‐fired thermal power plants (TPPs) for the storage of fly ash slurry in ash ponds. However, the area available for storage of fly ash at these TPPs is limited. In addition, this type of fly ash disposal poses a problem due to restricted land availability and potential contamination issues. A viable alternative is the reclamation of fly ash ponds by plantation. A study at the Ramagundam Super Thermal Power Station (RSTPS) in Andhra Pradesh, India, on reclamation of a portion of an ash‐filled, low‐lying area has been performed. This article describes the characteristics of the RSTPS pond ash, ash leachates, and improvements in the fertility status of the reclaimed area over a three‐year period. Furthermore, morphometric observations of different planted species indicate that these types of ash‐filled, low‐lying areas can be suitably reclaimed and the nutrient‐rich leachate from ash‐filled areas potentially can be used for irrigation purposes. © 2008 Wiley Periodicals, Inc.     

Expediting remedial designs and assessments

A successful air-based remediation system, now frequently chosen for sites contaminated with VOCs, demands a thorough understanding of the nature and distribution of the VOCs and the soil air permeabilities. Considering likely remediation methods during the site investigation allows collection of all data needed for method selection and design within a single, highly efficient site visit. A case history illustrates how to integrate several data collection and testing activities into a single site visit.     

Hydrologic evaluation of landfill performance (HELP) modeling in bioreactor landfill design and permitting

The practice of operating municipal solid waste landfills as bioreactor landfills has become more common over the past decade. Because simulating moisture balance and flow is more critical in such landfills than in dry landfills, researchers have developed methods to address this problem using the hydrologic evaluation of landfill performance (HELP) model. This paper discusses three methods of applying the HELP model to simulate the percolation of liquids added to landfill waste: the leachate recirculation feature (LRF), the subsurface inflow (SSI) feature, and additional rainfall to mimic liquids addition. The LRF is simple to use but may not be able to bring the landfill to bioreactor conditions. The SSI feature provides a convenient user interface for modeling liquids addition to each layer. The additional rainfall feature provides flexibility to the model, allowing users to estimate the leachate generation rate and the leachate head on bottom liner associated with daily variation in the liquids addition rate. Additionally, this paper discusses several issues that may affect the HELP model, such as the time of model simulation, layers of liquids addition, and the limitations of the HELP model itself. Based on the simulation results, it is suggested that the HELP model should be run over an extended period of time after the cessation of liquids addition in order to capture the peak leachate generation rate and the head on the liner (HOL). From the perspectives of leachate generation and the HOL, there are few differences between single-layer injection and multiple-layer injection. This paper also discusses the limitations of using the HELP model for designing and permitting bioreactor landfills.     

Remediation and review: Developing groundwater strategy at the hanford site

The U.S. Department of Energy's (US DOE's) environmental challenges include remediation of the Hanford Site in Washington State. The site's legacy from nuclear weapons “production” activities includes approximately 80 square miles of contaminated groundwater, containing radioactive and other hazardous substances at levels above drinking water standards. In 1998, the U.S. General Accounting Office (US GAO), the auditing arm of Congress, concluded that groundwater remediation at Hanford should be integrated with a comprehensive understanding of the “vadose zone,” the soil region between the ground surface and groundwater. The US DOE's Richland Operations Office adjusted its program in response, and groundwater/vadose‐zone efforts at Hanford have continued to develop since that time. Hanford provides an example of how a federal remediation program can be influenced by reviews from the US GAO and other organizations, including the US DOE itself. © 2008 Wiley Periodicals, Inc.