Geotechnical Frontiers 2017: Waste Containment, Barriers, Remediation, and Sustainable Geoengineering

Blended polyolefin (BPE) is a proprietary blend of polyolefin. There is little independent data on the potential long-term performance of this polymer resin to compare with that of high-density polyethylene and linear low density polyethylene under the same exposure conditions. This paper examines the performance of a BPE geomembrane immersed in incubation solutions relevant to its potential use in heap leach pads, Bayer process, municipal solid waste landfills, water lagoons, and potable water reservoirs. Results presented provide preliminary insight regarding antioxidant depletion as measured by Std-OIT in the immersion fluids and hence with respect to the first stage of the service life of BPE GMBs in these different applications.

The purpose of this study was to evaluate the suitability of thermally fusing GCL panels to prevent their separation when left under an exposed geomembrane undergoing cyclic wetting and drying. Small-scale tests were conducted to compare GCL seam shear strength with GCL panel shrinkage forces. GCL shear seam strength was evaluated for seams prepared with a propane torch and specimen widths of 100 mm and 200 mm. A bench-scale test setup was developed to measure shrinkage forces of a GCL sample during wetting and drying cycles. The shrinkage specimen was 300 x 600 mm (CD x MD) and clamped around its perimeter. The 200-mm wide seam strength specimens showed the smallest variability. After 32 cycles, the GCL shrinkage force in the roll cross-machine direction was approximately only 11% of the weakest average measured seam shear strength, suggesting that thermally fusing GCL panels might be a feasible solution to panel separation.

Polyethylene geomembranes typically have poor behavior when exposed to high temperature. Polyethylene materials soften as the temperature increases and lose their strength completely near 120C. Other research with landfill liners has shown that increasing the service temperature of a polyethylene geomembrane to 85C can reduce the service life of the liner to as little as 3 years through the rapid depletion of antioxidants. In this paper, the performance of a high temperature resistant geomembrane material was evaluated over a year-long period and compared to other geomembrane materials. The samples were exposed to three different service temperatures and then periodically evaluated for antioxidant retention. An Arrhenius-model was used to project antioxidant depletion. The projected service life of HDPE geomembranes exposed to high temperatures in these conditions was estimated considering antioxidant depletion as the end-of-life criteria.

The fabrication of geotextiles and geomembranes offers advantages in deployment speed and quality over field-installed materials. Traditional fabrication methods have joined one strip of material at a time to create extended panels. Recently, the authors have completed the development of a new fabrication machine that joins five strips of material at a time to create fabricated panels for large projects. The new machine is capable of both welding geomembranes and sewing of high strength geotextiles. This machine was specifically designed to address the problems of scale that need to be dealt with in oil sands tailings ponds. This paper will outline the development of this unique machine and present two case histories; one using high strength sewn geotextile, and one using welded geomembrane. The paper also highlights some exciting new equipment technology and innovation developed specifically for meeting the containment needs of larger scale projects.

This paper presents a unique comparison of single and multi-layer interface shear strength tests for a recently constructed landfill liner system. The comparison includes peak and large displacement combination strength envelopes from single- and multi-layer interface direct shear tests for the same geomembrane (GM)/ drainage geocomposite (GC), geosynthetic clay liner (GCL)/geomembrane, and soil/GCL interfaces. This comparison shows excellent agreement between strength envelopes and critical interfaces derived from single- and multi-layer interface tests for the materials tested. Based on this comparison, it is recommended that multi-layer interface tests be used for composite liner system design and if there is an anomaly with the multi-layer interface test results, single interface tests can be conducted to verify the weakest interface and to clarify the test results. Alternatively, the liner system can be designed using single interface tests and multi-layer interface tests can be used to verify the combination strength envelope derived from the single interface tests as was done in this case.

The dynamic coupled hydraulic, biodegradation and mechanical processes in conventional and bioreactor landfills significantly affect the in-plane shear response of the composite bottom and side liner system. Moreover, it is critical to investigate the in-plane shear behavior of the composite liner to maintain the integrity and serviceability of the liner systems. Previous studies on the shear response of composite liner systems have shown the shear response and importance of interface properties by considering only the influence of overburden stresses induced by waste mass in landfills. Till date, there is no study on the interface shear response of composite liner system that incorporates the effects of biodegradation of waste in landfills. In this study, a coupled hydro-bio-mechanical framework was formulated to investigate the in-plane shear response of the composite liner system in both conventional and bioreactor landfills as the MSW degradation progresses. The shear response of composite liner system was analysed both spatially and temporally in terms of the evolution of shear stresses and shear displacement along the liner interface. It was observed that the changes in the shear strength and stiffness of MSW due to biodegradation had a significant impact on the in-plane shear behavior of the composite liner system considered. In addition, the rate of biodegradation had considerable influence on the induced shear stresses and shear displacements along the liner interface. Overall, this study demonstrates the importance of assessing the in-plane shear response in identifying the stability of composite liner systems considering the influence of coupled processes in MSW landfills.

Geomembranes are often used in civil engineering applications to create a hydraulic barrier. With nearly all protection-layer systems, deformations occur in the geomembrane which need to be quantitatively assessed by reference to the indentations. The geomembranes basic function is to remain impervious over the entire design life of the project. However, mechanical stresses induced by confined materials could produce a deformation of the membrane and in critical situations, could ultimately puncture it. A protection geosynthetic needs to be designed in consideration of the specified geomembrane and its thickness as well as in consideration of the soil material (typically mineral drainage layer) and the surcharge placed above. Inappropriate selection of the protection geotextile can result in a failure, e.g., puncture of the lining material. Several methods of determining puncture protection are described in different standards. This paper will describe the design-related approach for protection layers and explain the concept of one specific test. Overall this paper will give a closer insight of this design-oriented test method.

To develop an economically viable method to close a large industrial wastewater sludge lagoon and reduce the amount of leachate generation, one of the following approaches is typically taken: solidify the sludge and install a low permeability cap system; solidification and offsite disposal of the sludge; if a sludge cannot be solidified, using a reasonable amendment mix ratio, then capping or offsite disposal may become difficult and costly for lagoon closures. A floating geosynthetic cover system may be an economic alternative for lagoon closure and leachate minimization. A floating geosynthetic cover consisting of geogrids, a floating modular layer, and a low permeability geomembrane was utilized to close a 4.86-hectare lagoon. This system allowed crews and equipment access to the lagoon surface for installation of the cover system. This design can be applied to hazardous and non-hazardous lagoons where in-situ solidification/sludge handling is not the preferred remedy.

Geosynthetic clay liners (GCLs) have been used as a composite barrier material for almost three decades, and the design and practices of GCLs were advanced with our enhanced understanding of their physical and hydraulic performance. Although the primary application of GCLs is to serve as a hydraulic barrier, recently their applications in geo-engineering has been expanded as they were also applied to barriers, capping systems and transportation facilities targeted for different permeant fluids. This paper focused on understanding the behavior of GCL with organobentonite amendment: specifically, the goals are (1) to quantify the impact of organobentonite amendment on the conductivity for water and other permeants. The conductivity/permittivity for variable fluids in conventional GCL, GCL with organobentonite amendment was conducted in 1D permeameter, (2) to investigate the chemical sorption of organic contaminants onto the organobentonite amendment and retarded transport of organic contaminants due to sorption. Obtained results suggests that a small fraction of organobentonite amendment can slightly decrease the permeability for low polarity fluids and enhance the contaminants retention capacity of GCL.

Past estimates of geomembrane longevity have typically focused on the degradation of the polymer tensile properties with time, demonstrating that these materials exceed expectations for typical municipal solid waste (MSW) facilities. However, interest in the performance of geomembranes for the disposal of low-level (LLW) and intermediate-level (ILW) radioactive waste landfills poses additional challenges. Many of these facilities use probabilistic models of long-term performance in terms of contaminant transport and exposure to make design decisions. However, current models have relatively little information quantifying the potential for leakage through the geomembrane that directly consider the change in material properties with time. Studies of the various mechanical modes of deformation and rupture for polyethylene sheet allow for this quantification. An example of this approach illustrates how the consideration of crack development in final cover geomembranes can be adapted for use in simulations of long-term landfill system performance suitable for LLW/ILW facility performance assessments.

Nanocomposites give an innovative method to increase the mechanical, thermal, and barrier performance of geomembranes. However, all this can only be achieved if the nanoparticles are properly dispersed in the polymer matrix. For that purpose, nanoclay particles are functionalized with organic groups for instance. Polar compatibilizing agents are also often included in the nanocomposite formulation to improve the dispersion. Still, the optimal conditions for a perfect dispersion of nanoparticles in the polymer matrix that will lead to maximal performance of the nanocomposite geomembrane are yet to be identified. To help answer this question, this paper analyses the relative importance of different parameters that affect the dispersion of nanoparticles in a polymer matrix. The effectiveness of the approach is tested with data involving high density and linear low density polyethylene, various percentages of organically-modified nanoclay, and different compatibilizing agents.

Geosynthetic clay liners (also called GCLs or geosynthetic clay barriers - GBR-C according to ASTM, resp. ISO terminology) can be a replacement element for the mineral sealing layer in many sealing applications, such as landfill capping systems. Due to the thin thickness and the high sensitivity of bentonite to changes in the water content, GCLs are a sensitive structural geo-engineering element. To investigate the long-term sealing behavior of GCLs, six lysimeters were built in Lemfoerde, Germany, and were equipped with different cover systems in order to obtain further knowledge of the GCLs performance. GCLs with granular and powder bentonite filling have been investigated since 1998 and were rebuilt in the year 2010. After the first 10 years of performance, the GCL with the granular core showed an increase of the permeation through the GCL. This paper will show the results of the field study and the differences in sealing behavior of powder and granular filled GCLs.

Waste storage facilities located near Sydney, Nova Scotia, Canada, were reclaimed with engineered cover systems. Similar alternative cover systems were utilized, each comprised of a geomembrane and overlying growth medium layer; however, a drainage layer above the geomembrane was not included in all instances. The monitored field performance of the alternate cover systems highlighted the detrimental impact that ponding of water above the geomembrane will have on performance. Empirical relationships for leakage through the geomembrane as a function of ponding pressure heads highlights that the performance of a low permeable layer is enhanced if adequate lateral drainage capacity is provided to eliminate sustained periods of water ponding. The field performance of the Hamburg-Georgswerder Landfill in Germany and the Monterey Peninsula Landfill in the United States are re-evaluated based on this finding. These case studies support the finding that the inclusion of a drainage layer mitigates risk associated with leakage attributed to geomembrane defects. However, the relative value of including lateral drainage capacity is also a function of site specific climatic conditions. Of particular importance in this regard is the intrannual and interannual variability in precipitation relative to evapotranspiration which will control the transient nature of the ponded conditions.

A most frequently asked question regarding all types of geomembranes is, “How long will they last?” This paper answers the question for exposed geomembranes assuming that they were properly designed and installed. Ultraviolet radiation, elevated temperature and full oxygen are available which shortens the service lifetime of a geomembrane. Ultraviolet fluorescent tube weathering devices per ASTM D7238 were used for incubation purposes. Five different geomembranes were evaluated. Each material was incubated at 80, 70, and 60°C until 50% reduction of strength and elongation occurred. The data was then extrapolated down to 20°C for laboratory halflife values and for comparison with the nonexposed condition. Results for geomembranes vary from 47 to 97 years with high density polyethylene (HDPE) being the highest.

Three different lining systems are reviewed for their interesting performances and test results: (1) an high density polyethylene pond liner that suffered random groups of stress cracks in two spring times only 6 and 18 months after installation and for which cross roll direction elongation at break did not meet the manufacturer’s specification, (2) an internal polypropylene liner in a 100 mm steel pipe containing 35% hydrochloric acid that failed and when heated for butt fusion repairs generated bubbles in the weld zone, and (3) a 5 mm high density polyethylene sump box with flanges around the tops of three sides that leaked at the two top corners as a result of poor welding. While the causes of the failures vary from complex to simple all show the importance of manufacturing and construction quality control and quality assurance.

The focus of this study was to evaluate hydrologic performance of mixed mine tailings and waste rock in water balance cover systems via one-dimensional numerical modeling. Comparisons were developed between an actual water balance cover and the following theoretical scenarios: (1) cover systems with storage layers composed of (i) copper, (ii) gold, (iii) coal, and (iv) oil sand tailings; (2) constant thickness mine tailings storage layers with waste rock inclusions; and (3) re-designed storage layer thickness composed of tailings and waste rock to yield comparable percolation rate to covers with no waste rock. Percolation rates ranged between 0.0 and 3.2 mm/yr for pure tailings water balance covers, which was comparable to predictions for the actual earthen cover. Addition of waste rock increased percolation in all cases due to reduced storage capacity. Re-designed covers composed of tailings and waste rock yielded thicker storage layers, but comparable percolation rates to water balance covers with no waste rock inclusions.

Composite landfill cover systems can have a variety of components and configurations. One common configuration consists of a cover soil layer, a geocomposite drainage layer (GDL), and a geosynthetic barrier layer. When properly designed and constructed, the GDL is expected to provide sufficient drainage to limit water build-up above the geosynthetic barrier layer and therefore, protect the cover system from a potential seepage-induced veneer slope failure. However, the field performance of the cover system may be impacted by changed drainage conditions, such as clogging, construction-induced wrinkling, and inadequate daylighting of the GDL. This paper presents a study in which a combined transient seepage and slope stability analysis has been performed to numerically evaluate the impact of GDL drainage conditions on veneer slope stability. The analysis results indicated that the factor of safety varies with time and can decrease significantly under certain drainage conditions. The numerical modeling framework presented in this paper can be used to improve engineering design approaches and to perform forensic evaluations of the post construction system performance.

Hydraulic conductivity and swell index tests were conducted on a commercially available geosynthetic clay liner (GCL) containing a dry-blended bentonite-polymer (B-P) mixture using solutions with a single monovalent cation (Na⁺) and varying anion ratio, R, defined as the molar concentration ratio of Cl^- to SO₄^2-. Na⁺ solutions with pure Cl^- or SO₄^2- and with anion ratios of 5 and 20 were used as permeant liquids. Swell index of the B-P in 300 mM Na⁺ solutions was independent of anion ratio (SI ≈ 22.5 mL/2 g for all solutions). However, hydraulic conductivity of the B-P GCL permeated with NaCl was approximately three orders of magnitude greater than the hydraulic conductivity to Na₂SO₄. Comparative tests were conducted on a conventional GCL with sodium-bentonite (Na-B) with 100 and 300 mM Na⁺ solutions with pure SO₄^2- and pure Cl^- as anions. Hydraulic conductivity of the Na-B GCL was unaffected by anion species (1.5 x 10^-11 m/s for 100 mM NaCl, 2.1 x 10^-11 m/s for 50 mM Na₂SO₄). Sensitivity of the B-P GCL to anion species is attributed to collapse of the polymer as the Cl^- concentration increases, which opens intergranular pores and results in higher hydraulic conductivity.

The compatibility of phosphate-amended bentonite soil backfill with coal combustion residual impacted groundwater is investigated in this study. A series of laboratory experiments including free swell, liquid limit, flexible wall permeability, and consolidation tests using deionized/tap water or coal combustion residual impacted groundwater are conducted to explore chemical compatibility of the amended soil-bentonite backfill. The results indicate that the contaminated groundwater has different impacts on various engineering properties of the backfill materials. For example, free swell index of the amended bentonite and liquid limit of the backfill materials tested with contaminated groundwater are 29% and 3% lower than those tested with deionized water. The CCR groundwater has little effects on hydraulic conductivity, and the hydraulic conductivities obtained from both tap water and CCR groundwater are lower than 10^-9 m/s. The compression and swell indices for backfill in contaminated groundwater are 17% and 47% lower than those in the tap water scenario.

Sodium bentonite (Na-bentonite) commonly is used in chemical containment barriers to limit transport of contaminants into the environment. The potential for decreased performance of Na-bentonite barriers due to cation exchange with multivalent species (chemical incompatibility) has led to the development of chemically modified bentonites (CMBs), such as polymer-modified bentonites, for improved chemical resistance. Results of experimental research to date generally indicate that CMBs may maintain values of hydraulic conductivity, k, less than 10^-9 m/s, even when permeated with solutions with high ionic strength and concentrations of multivalent species (e.g., 500 mM calcium chloride (CaCl₂)). However, there is limited data available regarding diffusion through CMBs, even though diffusion has been shown to be a significant to dominant contaminant transport mechanism in clays when k is less than 10^-9 m/s. In this paper, results are presented for diffusion of chloride (Cl^-) through a bentonite-polymer composite (BPC) for source concentrations of CaCl₂ ranging from 0.005 M to 0.1 M. Effective diffusion coefficients (D^*) for Cl^- through BPC were measured using a multistage through-diffusion method as well as a single-stage, dialysis-leaching test (DLT) method. The values of D^* for Cl^- increased from 3.3 x 10^-11 m²/s to 3.5 x 10^-10 m²/s as the average Cl^- concentration in the BPC increased from 0.005 M to 0.173 M. In addition, there generally was good agreement between the results of the two test methods over the range of C_ave evaluated, despite significant differences in the procedures and test durations (e.g., > 2 months for through-diffusion test, ≤ 2 days for DLT). The results of the study are compared with available literature for diffusion in Na-bentonite and other CMBs, and recommendations for future research are provided.

Water vapor sorption was investigated as an alternative screening test for chemical compatibility of geosynthetic clay liners (GCLs) exposed to aggressive leachates. Water vapor sorption isotherms for sodium bentonite (Na-B) and a bentonite-polymer (B-P) mixture sampled from commercially available GCLs were measured before and after exposing the materials to synthetic coal combustion product (CCP) leachates and other solutions. Differences in the isotherms were quantified using the Freundlich isotherm (C) parameter. Systematic relationships were observed between the C parameter and hydraulic conductivity of the GCLs to the leachates, suggesting that water vapor sorption has potential application as rapid screening method for assessing chemical compatibility of GCLs contacted with aggressive solutions. Water vapor sorption testing was also shown to have potential application for quantitatively estimating polymer content of B-P GCLs.

Interface shear strength was investigated between a bentonite-polymer (B-P) geosynthetic clay liner (GCL) and a 1.5-mm textured high-density polyethylene (HDPE) geomembrane (GM). Comparative tests were conducted with a conventional GCL containing sodium bentonite. All tests were conducted to a maximum displacement of 50 mm under normal stresses of 20, 100, 250, and 400 kPa. Interfaces with the B-P GCL had lower peak shear strength than interfaces with the conventional GCL under the same normal stress. The interface strength envelope for the B-P GCL was highly non-linear with lower shear strengths occurring at 400 kPa relative to those at 250 kPa, suggesting that the mechanism controlling shear strength changes with normal stress. Extrusion of polymer hydrogel into the GCL-GM interface was identified as the likely cause for lower interface shear strength and the non-linear strength envelope for interfaces with the B-P GCL.

The sensitivity of laboratory measured hydraulic conductivity, k, to backpressure saturation is investigated for a fiber reinforced GCL containing natural sodium bentonite (Na-B GCL) and a non-reinforced GCL containing a polymer modified bentonite. Hydraulic conductivity tests were performed using a synthetic soil pore water (ionic strength, I = 4 mM, ratio of monovalent-to-divalent cations, RMD, = 0.22 mM^1/2), and a synthetic gold pregnant leach solution (PLS; I = 42 mM, RMD = 11 mM^1/2). Both GCLs were permeated by two methods under matching average effective stresses (27.6 kPa) and hydraulic gradients (160-200) following the ASTM D6766-12 default method (average pore water pressure = 524 kPa) and following ASTM D6766-12 but without backpressure saturation (average pore-water pressure = 6.9 kPa) or permeant interface devices. Both methods resulted in complete saturation of the GCL specimens by the termination of permeation, i.e., backpressure saturation was not necessary to attain saturation. Measured values of k were similar for both test methods for the GCL containing polymer-modified bentonite, but resulted in 50 to 100 times higher k for the Na-B GCL permeated without backpressure saturation relative to the ASTM D6766-12 default method. Flow through Na-B GCLs permeated without backpressure saturation (i.e., Na-B GCLs with higher k) was visually observed to occur through needle-punching fiber bundles.

Six adjacent research ponds were constructed in 1990 using different formulations and thicknesses of PVC geomembranes liners. The ponds were 1.8 m deep with slopes of three horizontal to one vertical. The ponds were located in Mancelona, MI, USA, and fully exposed to the envionment. They contained water but were exposed above the waterline. The site is situated in northwest lower Michigan, approximately on the 45th parallel. Ambient temperatures range from +30 to -30°C. An assessment of the six different PVC geomembranes after 25 years of service is provided herein. Results are based on physical, mechanical and endurance test results.

In 2015 the authors undertook to refurbish a 16.3 km (10.1 mile) elevated wood and metal flume that was owned by a private hydroelectric company near Mount Rainier, Washington. The hydroelectric facility was originally built in the early 1900s. Water is diverted from the Puyallup River at an intake diversion and carried by a wood flume structure downstream to the hydroelectric generating plant. The flume is supported by approximately 6,200 beams of which approximately 1,200 are wooden. In many areas of the flume, the wood floors and walls were badly decayed and leaking. The plant had an operating capacity of 26 megawatts (MW) however as a result of the structural decay the flume was experiencing significant water leakage resulting in the plant only operating at 8 MW. The project started with 165,000 m² of a high strength geotextile that was installed below the geomembrane to help structurally reinforce the deteriorating wood flume walls and flooring. The water proofing of the flume required a total of 140,000 m² of 2.5 mm and 2.0 mm HDPE liner material to be installed. The project faced many challenges as a result of poor access and tight space constraints. There was no roadway or vehicle access other than three staging areas. All project related materials and equipment needed to be deployed using a small rail car and track built into the top of the flume structure. Crews had to deploy, weld and mechanically attach geomembrane while working in a very confined working space.

Exposed geomembrane covers (EGCs) have been used on landfills in place of more traditional soil-covered geomembranes. The design details and economic benefits of not using a soil cover have been well documented. This presentation focuses on the benefits of installing an EGC instead of intermediate soil cover. While an EGC for this application adds additional cost, it provides improved landfill gas capture, reduces the amount of storm water that infiltrates the landfill to create leachate, and reduces potential erosion. The capture of more gas can reduce odor and greenhouse gas emissions, while at the same time provide more methane for use in renewable fuel projects. The reduction in leachate has a direct impact on leachate treatment and disposal cost, which is becoming more expensive as options are becoming more limited. The enhanced soil erosion protection saves valuable soil from washing away while also protecting surface water. A case study details the benefits that operators may achieve.

Carbon black is often added to polyethylene geomembranes to improve their ultraviolet resistance. The black color, on the other hand, absorbs most of the solar energy reaching the surface of the geomembrane. The resulting temperature rise induced in the geomembrane is the source of numerous problems in the field. A fine white layer may be added on the exposed surface of the geomembrane to reflect the solar radiation and reduce the geomembrane temperature. This study is aimed at quantifying the difference in heat generation under solar irradiation associated to the presence of this white surface layer. Black and white-surfaced geomembrane specimens were exposed to various laboratory-controlled solar irradiances, using a Xenon-arc chamber modified for the purpose of this project. Temperature was found to be significantly lower in the white-surfaced geomembranes, compared to the black ones, with differences in the range of 10 to 20°C depending on the laboratory controlled solar irradiance.

The optimum performance of a bioreactor landfill operation will minimize the operational cost and maximize the benefit to a landfill owner. Performance of bioreactor landfill operation can be evaluated through monitoring several indicators such as moisture distribution, leachate generation, gas production, and landfill settlement. The current study is focused to investigate the performance of a bioreactor landfill operation by assessing performance indicators. The study was conducted at the City of Denton Landfill, Texas, USA. Electrical resistivity imaging (ERI) technique was utilized as a tool to monitor moisture distribution within the landfill. The ERI results indicated that the moisture content rebounds back to its pre-existing state after 2 weeks (14 days) of leachate recirculation. The variation from base line to 14 days is due to moisture movement (horizontal and vertical), leachate generation, and waste decomposition with time. In addition, the water balance simulation model visual HELP is conducted which indicated that the actual leachate generation in the field was approximately 55% lower than the HELP model results. The added water/leachate being used in gas production and may resulted the lower leachate return from the landfill. Hence, an increase in gas generation was observed and it increased from 543.6 m³/h (320 scfm) in 2010-2011 to 1087.3 m³/h (640 scfm) in 2014-2015. Moreover, landfill settlement was determined through surveying and a total of 1.524 m (5 ft.) maximum settlement was observed in some locations of the landfill cell between in year 2014-2015 of bioreactor operation which leads to additional space gain in the landfill. Therefore, based on the preliminary results, it can be summarized that the bioreactor landfill operation is performing effectively with time.

In the design and construction of landfill leachate collection and detection systems, it is important to maintain adequate drainage in order to minimize the hydraulic head on both primary and secondary liner systems. This is reflected in minimizing the leakage through the liner system. The situation is heightened when wet (also called bioreactor) landfilling is practiced in order to have rapid degradation of the organics as opposed to traditional dry landfilling. Concern has been expressed over such aggressive liquid management practices in bioreactor landfilling in regard to the long term clogging of geocomposites in either the leachate collection or leak detection systems of double lined municipal solid waste (MSW) landfills. In order to evaluate different geocomposite drainage systems we tested several per the GRI-GC1 Standard, “Test Method for Soil-Filter Core Combined Flow Test”. These experiments were conducted for three years in a field laboratory at a major MSW landfill in the U.S.A. The investigation was conducted until system permeability reached equilibrium. It was found that the tubular geocomposite performed well over time. Good performance was predicated on proper geotextile filter selection with this particular leachate and set of environmental conditions. Conclusions and recommendations as to various possible drainage geocomposites and their behavior are presented.

There have been reports of landfills in North America that are experiencing elevated temperatures that are resulting in challenging issues for landfill management. The objective of this study is to develop a box model to describe the generation, consumption and release of heat in landfills and subsequently to predict temperature profiles. Initially, a box model was developed that treats the landfill as a completely mixed system in which all relevant reactions are described. This model will make it possible to identify processes and reactions that are most significant. The model is based on thermodynamic principles and accounts for all significant heat sources and sinks in landfills. Heat sources include energy from biotic and abiotic reactions and condensation. Heat removal processes include convection of methane and carbon dioxide, infiltration, leachate collection and evaporation. The model was used to evaluate the heat generation performance of aerobic and anaerobic biodegradation of waste with and without the presence of ash (from coal or municipal solid waste). The model analysis showed that the hydration of ash can increase landfill temperature above that predicted for the disposal of municipal solid waste alone.

Elevated temperatures in municipal solid waste landfills can produce obnoxious odors, toxic gases, and aggressive leachates, as well as damage gas extraction, leachate collection, interim cover, and composite liner systems. They also can result in expensive remedial measures and warrant permanent closure of the facility. Several factors can lead to elevated landfill temperatures, including air ingress, partially extinguished surface fires, reactive wastes, and spontaneous oxidation. Landfills typically experience changes to gas composition and flow, leachate chemistry and volume generation, and surface movement. Based on observed management, operation, and maintenance of elevated temperature facilities, various operational techniques are proposed for isolating and containing the elevated temperatures in a landfill.

For reasons that are not entirely clear, incidents of elevated temperatures in landfills are occurring at increasing frequency in the U.S. A Florida landfill has experienced temperatures that well exceed the tolerable range for microorganisms and permit standards set by the Florida Department of Environmental Protection. The landfill has experienced elevated temperatures in gas wells on the west side of the active cell. These wells were installed in 2010 in an area that received biosolids treated with incinerator fly and bottom ash. These biosolids may have caused an exothermic reaction that has interrupted methane generation. In addition to elevated temperatures (as high as 175°F), smoke, odors, hydrogen in the landfill gas, leachate color darkening, and decreased leachate generation have been observed. However, abnormal settlement has not been observed in the landfill. Preliminary data analysis of gas temperatures suggests that 20% of the wells at the landfill are impacted. Waste samples have been collected and are being analyzed. Results of waste characterization support the presence of ash in areas of elevated temperature.

Partition and diffusion coefficients for phenol, methylene chloride, toluene, and TCE for a co-extruded geomembrane (inner EVOH layer, HDPE outer layer) were measured using batch tests at 23°C (room temperature), 38°C (intermediate temperature), and 75°C (high temperature). The partition coefficients for EVOH increased by as much as 36% as the temperature increased from 23 to 35°C and 79% for 23 to 75°C. The diffusion coefficients increased by as much as 82% and 200% over the same ranges of temperature. However, for HDPE, the increase in the partition and diffusion coefficients with increase in temperature was less than half that observed for the EVOH. For HDPE, the partition coefficient increased by as much as 18% and 46% for temperature increases from 23 to 35°C and 23 to 75°C, respectively. The diffusion coefficients increased by as much as 22% and 53% over the same ranges of temperature. Thus, temperature sensitivity of partition and diffusion coefficients for EVOH is significantly higher than for HDPE.

Data from a municipal solid waste (MSW) landfill with elevated temperatures are evaluated to assess how characteristics of landfill gas and leachate evolved as the landfill temperature increased from ranges typically associated with methanogenic decomposition (40 – 50°C) to more than 100°C. The MSW landfill was deep (~ 100 m), unlined, and most of the waste was saturated and below the water table. Temporal trends in landfill gas temperature measured at the wellhead indicate that the gas temperatures increased abruptly and systematically following a shutdown to address a concern about the potential for subsurface combustion. Temperature profiles collected subsequently indicated that the highest temperatures were substantially below the leachate level, making combustion an unlikely mechanism for the elevated temperatures. Temporal trend analysis indicated that the primary gas ratio (CH₄:CO₂) decreased systematically and substantially when the gas temperature increased abruptly. Leachate chemistry also changed significantly after the gas temperature increased abruptly, with BOD, COD, and the BOD:COD ratio increasing rapidly, pH dropping more than one unit, and total suspended solids increasing more than two orders of magnitude.

A conventional landfill cover system composed of a geomembrane and low permeability soil is the typical minimum requirement for landfill covers as required by the Resource Conservation and Recovery Act (RCRA). More recently, alternate cover systems have been used to reduce costs and still meet the regulatory objectives. Evapotranspiration (ET) cover systems have gained popularity over the years due to their low cost and ability to meet the performance objectives when designed properly. The purpose of this paper is to evaluate alternate landfill cover systems and to provide a sustainability assessment by evaluating the carbon footprint and the life cycle assessments of three commonly used landfill covers. The findings suggest that while an ET cover system is the most sustainable alternative in most cases, hauling soils greater distances can result in an ET cover being less sustainable and likely costlier due to the increased transportation.

The demands for pollution-free and recyclable engineering materials have increased as energy cost and environmental concern have risen. Moving toward green materials and design are approaches for better environmental quality and sustainable civil infrastructures. Pavement construction is one of the largest consumers of raw materials. Beneficial utilization of recycled materials in the pavement can result in an extraordinary opportunity to save mining, natural resources, energy, and landfill spaces. This study evaluates the structural and environmental-economical benefit performance of hot mix asphalt (HMA) by substituting virgin materials with one or a combination of two recycled materials. The two used recycled materials are recycled asphalt shingle (RAS) and municipal solid waste incineration bottom ash (MSWI-BA). This research introduces a sustainable HMA that potentially reduces the necessity of virgin fine aggregate and asphalt binder to 20% and 19%, respectively. In terms of environmental and economic impacts, in comparison with the regular HMA, it generates 15.5% less greenhouse gas emission, and for a period of 20 years, the cost of construction and maintenance would be 46% less.

This study evaluates the environmental and economic impacts of five ground improvement methods for the possible redevelopment of Treasure Island in San Francisco, California. Each method is required to meet a deterministic performance criterion to minimize susceptibility to liquefaction triggering, defined as a normalized standard penetration test (SPT) blow count of 15 or greater. For each improvement method, the study quantifies the resources and emissions flows over the entire life cycle from raw material extraction through the end of construction operations and evaluates the primary energy, global warming potential, acidification potential, smog formation potential, raw project cost, and social cost of carbon. Sensitivity analysis was performed to evaluate assumptions regarding materials selection and transport distances, and a scenario analysis was conducted to compare multiple improvement scenarios for the Treasure Island redevelopment project. The study concludes that the most environmentally preferable combination of improvement methods does not include deep soil mixing.

Landfills that receive municipal solid waste represent a critical component of solid waste infrastructure in the U.S. and are a leading source of greenhouse gas emissions. Thus, it is critical to understand the factors that control the environmental performance of landfills. Life-cycle modeling of landfills is complex, as landfills constantly change over time. The objective of this research was to develop a life-cycle model of an average ton of municipal solid waste disposed in a “national average” landfill. The framework considers critical factors relating to the temporal changes in landfill gas generation, collection, beneficial use, and oxidation. The model calculates temporally averaged landfill gas collection efficiencies for individual waste components in consideration of the aforementioned factors. The results indicate that for mixed waste, 12 to 41% of the generated methane becomes fugitive emissions. The results also show the significant potential benefits of earlier landfill gas collection.

Steel slag, a byproduct of steel industry and approximately 15% of original steel input, has favorable engineering properties. However, the tendency of the material to expand due to free lime and magnesia within the elemental composition impedes its use in highways, where large volumes of the slag can be utilized, hence a pretreatment is required. For this purpose, water treatment residual (WTR), an aluminum rich by-product of drinking water plants, and a sandy borrow material provided by Maryland State Highway Administration are used as dry mixing additives by different percentages. In order to evaluate the swelling behavior of three steel slag materials with different aging properties upon the two treatment techniques, accelerated swell tests (ASTM D-4792) are performed. The results indicate that both treatment methods decrease the ultimate swelling ratio significantly. Using treated steel slag in highways results in reduction in waste disposal costs and in consumption of natural resources.

Geotextile tubes have been used extensively to contain and dewater high water content materials. Geotextile tubes are typically manufactured from polypropylene (PP), a high embodied energy polymer, because of their relatively high tensile and seam strength properties that are often necessary to withstand the stresses that can develop in a geotextile tube during filling, and to maintain geotextile tube shape after filling. There are applications where lower-strength jute geotextiles could be used to manufacture smaller, more sustainable geotextile tubes for use in sensitive environmental applications, such as in wetland or shoreline rehabilitation applications. This paper presents the results of a laboratory study that compares the filtration performance of PP versus jute geotextiles for use as geotextile tubes, demonstrating the potential use of jute in geotextile tubes. Second, the paper presents a life cycle analysis that compares commercially available PP geotextile tubes to jute geotextile tubes. Overall, jute shows great promise for use in geotextile tubes.

Recently passed federal environmental regulations require electrical and industrial utilities to evaluate and address final environmental closure for coal ash storage areas. In many cases, the plans for closing these storage facilities are complicated by aggressive deadlines, absence of soil materials necessary for traditional closure methods, state and local regulatory uncertainty, and heightened public scrutiny. Additionally, many of these facilities are impoundments containing saturated waste, which introduces technical challenges that compound the difficulties of meeting the project objectives. This paper examines a final closure project where an alternative closure method was successfully deployed and satisfied all of the criteria described above; namely regulatory requirements, community approval, geotechnical instability, project schedule, and soil conservation. The alternative closure method presented utilizes a unique tufted geosynthetic material, a structured geomembrane and a specified infill material that is laid within the tufts of the geosynthetic material.

In the present study an attempt has been made to use pond ash collected from Talcher, India as a filling material. Two dimensional domain of pond ash having relative density 50% and 65% have been developed to analyze its response under the excitation of North East India (Mw-7.5) and Bhuj (Mw-7.7) earthquakes. The responses have been presented in terms of peak ground acceleration (PGA); peak ground displacements (PGD); shear stress; effective stress; pore water pressure, acceleration and displacement time history; and liquefaction susceptibility. From the results, PGA and PGD vary from 1.593 m/s² to 3.812 m/s² and 0.119 m to 6.498 m respectively for the above stated excitations. Also, the pond ash deposits are not susceptible to liquefaction as the excess pore pressure ratio observed are less than unity. Hence, these pond ashes can be effectively used as a filling material for various geotechnical applications.

Coal has been used for electrical power generation for decades. While the use of coal as a fuel for power generation has decreased during the last 15 years primarily due to the increased use of natural gas, there are several hundred unlined coal ash ponds and landfills in the U.S. The new federal regulations for disposal of coal ash combustion residuals have spurred an immediate need to classify the environmental risk from the existing unlined coal ash ponds or landfills. Percolation of leachate from these ponds is a vital input to the groundwater flow models used for assessing the risk. This project entails simulating water balance of coal ash ponds for a location in the southeastern U.S. and evaluating uncapped scenario to simulate long-term percolation of leachate. The numerical model UNSAT-H was used for simulating water balance. The model predictions indicate that long-term percolation from coal ash ponds containing predominantly fly ash will be about 700 gallons per acre per day for the humid southeastern region of the United States.

The handling and disposal strategies of coal combustion residuals (CCRs) such as fly ash, bottom ash, and gypsum in the U.S. are undergoing a paradigm shift from wet sloughing in a basin to dry disposal in an engineered landfill. This shift is motivated in part due to recently implemented regulations by the U.S. Environmental Protection Agency. As part of these new approaches of handling and disposal it will be important to investigate compaction characteristics as well as water infiltration behavior of CCRs. This paper presents results of an ongoing study where 7 different CCRs materials from different utilities in the U.S. have been characterized. Specifically, the paper presents geotechnical index properties, compaction curves, X-ray fluorescence, X-ray diffraction, and water retention characteristics of compacted CCRs samples. Also discussed is the relevance of these results towards alternative capping systems that would involve compacted CCRs materials treated with organosilane chemicals to render the cap essentially hydrophobic.

pH values significantly affect leachability of stabilized/solidified heavy metals contaminated soils. The diffusion coefficient (D_e) and the retardation factor (R_d) are essential for quantitative assessment of the impact of stabilized/solidified contaminated soils on surrounding environment. Diffusion of Cd leached from a new binder stabilized/solidified Cd-contaminated soil are investigated in this research. A series of tests including desorption test and semi-dynamic leaching test conduct to determine the obvious diffusion coefficient (D^obs) and the R_d, respectively. Desorption test results show that leached concentrations of Cd increase with the increase of its initial concentrations and a desorption curve fit well in the Freundlich desorption/adsorption model. The semi-dynamic leaching test results show that the accumulated heavy metal mass has a linear-relationship with time on a logarithmic scale. The results demonstrate that the D^obs of Cd calculated at 2.11×10^-12, the retardant factor of Cd determined as 109.7 and the D_e is therefore determined as 2.32×10^-10 m²/s.

“Tunable” clay-polymer composites are designed to be modifiable in-situ through controlled manipulation of interparticle/interlayer spacings via the surrounding fluid chemistry. This study explores the one-dimensional consolidation behavior of “tunable” clay-polymer composites in low and high ionic concentration solutions. Both low and high ionic concentrations were selected to promote polymer molecule expanded and coiled conformation, respectively. Oedometer tests were carried out on pre-consolidated specimens derived from slurries (both composite and pure clay). Also, bender elements were employed to measure shear wave velocities during consolidation. A comparison between the resulting compression curves and shear wave results indicate that as ionic concentration increases, the coefficient of consolidation, compression index, swell index, and shear wave velocity of the composite increase compared to pure clay. These results are consistent with coiled conformation of the responsive polymer.

In this study soils were sampled from three different locations which were at high risk for contamination having different categories of hazardous wastes such as steel plant, automobile and batteries work unit and municipal dumpsite near Bangalore City, India. These soils were artificially spiked with high concentration of cadmium (Cd²⁺) to the tune of 3,000 mg/L. The leaching behaviour of cadmium (Cd²⁺) with these soils and soils amended with nano calcium silicate (NCS) were studied with four different leaching methods viz. ASTM D3987, toxicity characteristics leaching procedure (TCLP), extended TCLP, and caged TCLP. In order to understand the type of sorption taking place in the soil matrices, sequential extraction in five stages was performed on these Cd²⁺ spiked soils. It was found that soils treated with nano calcium silicate sorb cadmium effectively and as per ASTM D3987. The retention of Cd²⁺ was permanent over long term and TCLP tests proved sorption was 90% better with NCS treated soils and the leaching rate for treated soils was found to be less than 1cm/yr. Sequential extraction confirmed that encapsulation of Cd²⁺ as a dominant mechanism in immobilizing it in the matrices of soil and NCS.

Organic surfactant modified zeolites (SMZs) are a group of organo-aluminosilicates that have enhanced sorption capacity for organic compounds. They have various engineering applications in wastewater treatment, groundwater remediation, and waste containment. Previous research indicated that naturally occurring zeolites are capable of removing nutrients and heavy metals from groundwater in the permeable reactive barriers. However, their retention capacity for organic pollutants is relatively limited. In this study, the natural zeolite was modified by organic surfactant to synthesize a zeolite-surfactant hybrid, and the interaction between the synthesized zeolite and benzene were quantified. Packed soil columns were used to evaluate the hydraulic performance of sand/organo-zeolite mixtures. Additionally, the breakthrough of benzene in the soil column was examined. The objectives of this study were: to provide an understanding of the interaction between organo-zeolite and organic contaminants as a function of surfactant loading; to evaluate the applicability of organo-zeolites as a potential media for the groundwater treatment in permeable reactive barriers.

Acid mine drainage (AMD) generated during mining operations is characteristically acidic and contains metals at concentrations that are toxic to aquatic ecosystems. This study, through laboratory testing and analysis, evaluated the low-cost construction waste product, recycled concrete aggregate (RCA) as a remediation material for AMD. Column leach tests (CLTs) were conducted to determine the effects of the four different RCAs on pH, electrical conductivity, iron (Fe), copper (Cu), and zinc (Zn) in AMD. Results of the CLTs suggest RCAs can effectively raise pH of the AMD and reduce concentrations of Cr, Cu, and Fe in AMD. The pH of AMD prior to treatment ranged from 2 to 4, and after treatment with the RCAs the pH of the AMD increased to above 11. Following RCA treatment, Cr concentrations in the AMD decreased by 22 to 62%, Cr concentrations reduced average of 85%, and Fe concentrations declined by over 98%.

The aim of this study is to investigate low cost, easily available, and sustainable solutions to remove heavy metal ions from the effluent from geotextile tubes and wastewater. Three soils and three cellulosic materials have been used to study their effectiveness in adsorbing as well as retaining heavy metal ions when mixed in contaminated aqueous solutions. The effect of different particle sizes, physical and chemical properties of soils in adsorption has been studied by performing a batch adsorption test in 15% concentration (sediment: heavy metal solution) slurry. Similarly, batch adsorption tests were also conducted on cellulosic materials (peanut hulls, jute fibers, kraft pulp) mixed with heavy metal solution. The studied heavy metal ions are lead (Pb), copper (Cu), cadmium (Cd), and zinc (Zn). The samples collected from batch adsorption tests were tested for heavy metal ions using inductively coupled plasma optical emission spectrometry (ICP-OES). It was observed that the removal efficiency for all heavy metals was higher with tully soils compared to kaolinite. In case cellulose adsorbents, one correlation could be established between the dosage of jute fibers and amount of Pb adsorbed. However, the adsorption of Pb from the solution into peanut hulls and kraft pulp increased linearly with their dosage. Kraft pulp had the highest adsorption capacity of Cu and Cd compared to other cellulose adsorbents.

The influence of mix water hardness and salinity on bentonite-water slurry used in soil-bentonite cutoff walls was investigated. Slurries prepared by blending 5-12% sodium bentonite with aqueous solutions containing CaCl₂ and/or NaCl were tested for Marsh viscosity, filtrate loss, and bleed. Slurries containing 5% bentonite exhibited acceptable bleed, filtrate loss (≤ 25 mL), and viscosity (32-45 s) when mixed with solutions containing ≤5 mM CaCl₂ (hardness ≤ 500 mg/L) and ≤ 50 mM NaCl (salinity ≤ 2,900 mg/L). Increasing the CaCl₂ concentration to 10 mM or the NaCl concentration to ≥ 100 mM yielded inadequate viscosity and excessive filtrate loss, but these properties were improved by increasing the bentonite content to 6 or 7 %. Slurries prepared with water containing 25 mM CaCl₂ (hardness ≈ 2,500 mg/L) required 12 % bentonite to exhibit acceptable viscosity, filtrate loss, and bleed. Overall, hardness had a greater impact on the slurries relative to salinity.

The present study investigates in the field the potential of switchgrass to survive in the harsh high pH slag disposal area at big marsh and phytoremediate existing polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BaP) and heavy metals such as lead (Pb) and arsenic (As). Test plots were prepared by adding compost and tilling the fill material. Switchgrass was planted and monitored. Soil was sampled before, after preparing the test plots, and after the second and third growing seasons, together with plant root and shoot samples. PAHs and total metals were analyzed, and the fractionation of metals in the soil was determined by sequential extraction. A decrease of PAHs concentrations in the soil was observed, while the concentration of heavy metals remained constant. Additionally, concentrations of PAHs and heavy metals in shoots were undetectable, demonstrating insignificant uptake of contaminants by the plants.

Landfill gas (LFG) needs to be efficiently and effectively extracted from active and closed landfills to comply with air quality regulations as well as to fuel beneficial uses. LFG extraction is performed by applying a vacuum onto vertical wells or horizontal collection trenches. LFG collection trenches are commonly constructed by excavating into the waste mass and backfilling the trench with aggregate and a perforated high-density polyethylene (HDPE) pipe. While LFG collection trenches are an important component to a well-operated landfill, the costs associated with constructing trenches and relocating waste are significant. This paper presents a review of tubular drainage geocomposite used for more than 5 years in replacement of traditional pipes and aggregates LFG trenches. The use of this geocomposite improves the zone of influence (ZOI) of the “trench” without reducing the collected flow, as well as reduces dramatically the costs and the Greenhouse gas (GHG) emissions.

Soil-bentonite slurry-trench cutoff walls are used extensively as vertical engineered barriers for groundwater pollution control. The workability of soil-bentonite backfills used for these walls is an important design and construction consideration. In this study, a systematic analysis of extensive database reported in previous studies is made. It is found that bentonite content required to achieve workability in bentonite-water slurry decreases with increasing liquid limit of bentonite and then it remains constant at ~5% for bentonite with liquid limit of 400 to 600%. The water contents of backfills required to achieve target slump (-ΔH = 100 to 150 mm) can be estimated by an empirical equation established based on an apparent liquid limit of backfill calculated based on the proportions and liquid limits of individual constituents of the backfill. The results of this study are useful for preliminary estimation of the required bentonite content in the bentonite-water slurry and backfill water content to yield the target slump (workability).

This study investigated a new and practical approach to remediate urban stormwater runoff contaminated by mixed pollutants. The study consisted of evaluation of different permeable filter medium in terms of the removal efficiencies when addressing typical urban mixed pollutants; and development of a feasible design and recommendations for an effective in-ground filtration system. Mixed pollution indicators used to assess stormwater quality included: heavy metals (As, Cr, Cd, Cu, Ni, Pb, and Zn), nutrients (nitrates and phosphates), polycyclic aromatic hydrocarbons (PAHs) (naphthalene, phenanthrene and benzo(a)pyrene) and bacterial contamination (E. coli abundances), all of which are contaminants commonly found in urban stormwater runoff. To determine removal efficiencies of targeted contaminants in different permeable medium, synthetic stormwater (SSW) representative of urban stormwater runoff was applied to packed columns with different permeable filter medium, and the contaminant concentrations in the resulting effluents were analyzed. Batch tests were also conducted to determine the maximum removal efficiency of each filter medium. Based on the batch and column studies, it was found that a mixed media, consisting of calcite, zeolite, iron filings and sand was effective with high removal efficiencies for nutrients, TSS, E. coli, heavy metals and PAHs. Large-scale laboratory test and field pilot-scale demonstrations were conducted to evaluate the performance of this permeable mixed media filter system.

Acidic groundwater resulting from the oxidation of pyrite in acid sulfate soil (ASS) is a major geo-environmental problem in low-lying coastal regions. While the pyrite submerged is relatively inert, if exposed to atmospheric oxygen, it will rapidly oxidise to form sulphuric acid. This poses a serious challenge for floodplain management due to the catastrophic consequences associated with agriculture and aquaculture productivity, environmental damage to river ecosystems and acid damage to steel and concrete infrastructure. This paper reports the results of different methodologies adopted in the Shoalhaven floodplain (NSW, Australia) over two decades for remediation of acidic groundwater. Different approaches implemented over the years are compared in terms of their efficiency in halting pyrite oxidation and neutralizing the acidic groundwater and removing heavy metals, mainly dissolved Al and Fe resulting from the oxidation of the pyrite in the local acid sulfate soils.

Carbonation of cement-treated soils results in physical and chemical transformations that can affect the long-term effectiveness of stabilization/solidification. In order to ensure safety of further utilization, it is necessary to investigate the effect of carbonation on the performance of cement-solidified contaminated soils. Artificial contaminated soils with different lead contents were solidified using cement, moisture content, density, pH value, strength, and microstructure of solidified samples before and after carbonation were tested. The experimental results show that carbonation decreases moisture content of samples, and increases dry density. Unconfined compressive strength of carbonated samples is 5-25% higher than that of non-carbonated samples. The pore solutions of non-carbonated samples are highly alkaline (pH=11-12), whereas those of carbonated samples exhibit lower pH values (pH=8-9). Thermogravimetric analysis test and scanning electron microscopy test results confirm the transformation of cement hydration products to calcium carbonate during the carbonation process.

This paper describes the laboratory investigation of hydraulic properties in filter media mixtures designed for use in bioslopes along roadways. The accumulation of pollutants on roadways can result in contaminated stormwater runoff that has a negative effect on receiving water quality, groundwater quality, and aquatic ecosystems. Additionally, roadways increase impervious surface area resulting in an increase in runoff volume and peak discharge intensity. Therefore, current requirements focus on retention of the first inch (2.54 cm) of highway stormwater runoff. Current Minnesota Department of Transportation (MnDOT) specifications were developed using mixtures of clean sand and organic compost. However, mixtures of locally available organic materials in rural areas have not been tested. While there are industry-accepted methods of measuring infiltration rates in situ (i.e., the double ring infiltrometer and the modified Phillip-Dunne infiltrometer (MPDI)), there is no current standard for testing new mixtures on a smaller scale prior to field implementation. This project compares filter media mixtures to material passing current MnDOT specifications using a laboratory testing program. Laboratory constant and falling head tests were used to determine steady-state infiltration rate on samples using different combinations of various locally available organic material with screened sand or taconite tailings. Data from new filter media mixtures are compared to filter material passing current MnDOT specifications. Alternative media mixtures of peat, muck and taconite tailings were found to match the hydraulic conductivity of compost-sand mixtures. These results indicate that alternative media mixtures are suitable for stormwater biofiltration applications, allowing the authors to select mixtures for larger-scale field testing. Applying this laboratory testing program to previously untested filter media mixtures will allow for better design of filter media mixtures.

Based on saturated sands contaminated by methyl tert-butyl ether (MTBE), one-dimensional laboratory column tests were performed, through which the removal ratio of common air sparging (CAS) and foam-based surfactant enhanced air sparging (FSAS) were systematically studied. The sands with particle size of 0.5-1.0 mm and 2.0-4.0 mm were used. Test results indicate that the concentration of VOC contaminant at the top layer of soil strata will first increase and then decrease during FSAS, and under the condition of bubble flow during CAS. The long-term remediation effect of FSAS is almost the same as that of CAS for homogeneous sands as in this research. Due to the special property of foam movement, FSAS is actually a kind of pulsed air sparging, which may resolve the traditional tailing problems. In addition, the effects of FSAS should be comprehensively considered under two- or three-dimensional conditions, and complex soil strata.

The addition of biochar to soil has been shown to improve soil quality for agronomic applications, demonstrating its usefulness in altering soil physical and chemical properties. While biochar has been suggested as an additive to stormwater treatment media, little is known about its impact on hydraulic properties, especially the saturated hydraulic conductivity (K_sat). In this research, K_sat of a stormwater bioretention media and a uniform sand amended with 4% by weight wood biochar prepared in three different sizes was measured. Based on the K_sat results and the physical properties of the biochar and biochar-amended media (i.e. d50, void ratio, etc.), the Kozeny-Carmen model was evaluated for its ability to predict the changes in K_sat due to biochar addition. The bioretention medium consisted of a mixture of sand, clay, and sawdust at 88%, 8%, and 4% (w/w), respectively. Addition of the biochar universally decreased dry bulk density and increased the porosity compared to the unamended medium, regardless of biochar particle size. K_sat increased for all bioretention media: small biochar caused less increase (67%), and unsieved and large biochar amendment resulted in greater increases (306% and 213%). The effect of biochar amendment was also investigated on a uniform sand. In contrast to the bioretention medium, all biochars decreased the K_sat of the uniform sand. The Kozeny-Carmen model predicted observed K_sat changes well for small biochar particle amendments, but it predicted K_sat would increase with large biochar amendment by 450-700% while experiments showed it decreased by 20-40%. This unexpected result when large biochar particles were mixed with a uniform sand is postulated to be caused by changes in tortuosity of the pore space by the generally more irregularly large biochar particles, effects that are not accounted for in the Kozeny-Carmen model.