John J. Sansalone

Heavy Metal Contamination in Soils of Urban Highways Comparison Between Runoff and Soil Concentrations at Cincinnati, Ohio

Rainfall runoff from urban roadways oftencontains elevated amounts of heavy metals in both particulate anddissolved forms (Sansalone and Buchberger, 1997). Because metalsdo not degrade naturally, high concentrations of them in runoffcan result in accumulation in the roadside soil at levels thatare toxic to organisms in surrounding environments. This studyinvestigated the accumulation of metals in roadside soils at asite for which extensive runoff data were also available.For this study, 58 soil samples, collected from I-75 nearCincinnati, Ohio, were examined using X-ray fluorescence, C-Sanalyzer, inductively coupled plasma spectroscopy, atomicabsorption spectrometry and X-ray diffraction. The resultsdemonstrated that heavy metal contamination in the top 15 cm ofthe soil samples is very high compared to local backgroundlevels. The maximum measured amount for Pb is 1980 ppm (at 10–15 cm depth) and for Zn is 1430 ppm (at 0–1 cm depth). Metal content in the soil falls off rapidly with depth, and metalcontent decreases as organic C decreases. The correlation toorganic C is stronger than the correlation to depth. The resultsof sequential soil extraction, however, showed lower amounts ofPb and Zn associated with organic matter than was expected basedon the correlation of metals to % organic C in the whole soil.Measurement of organic C in the residues of the sequentialextraction steps revealed that much of the carbon was not removedand hence is of a more refractory nature than is usual inuncontaminated soils. Cluster analysis of the heavy metal datashowed that Pb, Zn and Cu are closely associated to one another,but that Ni and Cr do not show an association with each other orwith either organic C or depth. ICP spectroscopy of exchanged cations showed that only 4.5%of Pb, 8.3% of Zn, 6.9% of Cu and 3.7% of Cr in the soil isexchangeable. Combined with the small amounts of metals bound tosoluble organic matter, this result shows that it is unlikelythat these contaminants can be remobilized into water. At thissite, clays are not an important agent in holding the metals inplace because of low amounts of swelling clays. Instead, insoluble organic matter is more important. Mass balancecalculations for Pb in soil showed that most of the Pb came fromexhausts of vehicles when leaded gasoline was in use, and thatabout 40% of this Pb is retained in the soil.This study shows that, highway environments being a relativelyconstant source of anthropogenic organic matter as well as heavymetals, heavy metals will continue to remain bound to organicmatter in-situ unless they are re-mobilized mechanically. Removalof these heavy metals as wind-blown dust is the most likelymechanism. Another possibility is surface run-off carrying themetals into surface drainages, bypassing the soil. This studyalso shows that for those countries still using leaded gasoline,important reductions in Pb contamination of soils can be achievedby restricting the use of Pb additives.

Adsorptive infiltration of metals in urban drainage--media characteristics

Urban pavement drainage often contains significant quantities of anthropogenic metal elements, including Cd, Cu, Pb and Zn that exceed surface water discharge standards. In many urban areas low rainfall pH, results in predominately dissolved metal element mass. Such partitioning has critical implications for the selection of in-situ treatment. One such category of treatment is engineered infiltration systems. To be effective, such systems must adsorb dissolved metal elements to their fixed media while also acting as filters for particulate-bound fractions. One such strategy is called a partial exfiltration trench (PET). The PET contains oxide-coated sand (OCS); an amphoteric media of high surface area (5-15 m2/g) as compared to uncoated silica sand (0.01-0.05 m2/g). OCS was generated through heating a mixture of silica sand and ferric nitrate solution to dryness. This paper presents results of both media characterization and bench scale PET simulations. Media tested were OCS and plain silica sand. Media testing was carried out until capacity was exhausted, using both synthetic and actual stormwater loadings. Testing was conducted for pH levels of 6.5 and 8.0. Results indicated that OCS had greater capacity than silica sand for all dissolved fractions. As the pH was raised from 6.5 to 8.0, OCS capacity was improved. A PET configuration with porous pavement resulted in the highest in-situ treatment capacity for metal element bearing storm water.

A Granulometry-Based Selection Methodology for Separation of Traffic-Generated Particles in Urban Highway Snowmelt Runoff

Traffic activities generate a wide gradation of anthropogenic particulate matter that is entrained in highway snow and snowmelt. Granulometric-based analyses of this particulate mattercan provide guidance for selection and design for snowmelt solid/liquid separation processes. This study presents a granulometry-based analysis of snow melt particles from 10 highway shoulder sites in urban Cincinnati (State of Ohio, U.S.A.) generated from a 46 cm, 48 hr snowfall with a highwayshoulder residence time of 102 hr. Each site was exposed totraffic and maintenance activities (plowing and de-icing saltsonly). Despite variations in gradations and particle indices, measured lnv-Nt (number-volume mean size-particle counts) values for all sites were closely modeled using a two-parameter power law model. The model exponent, β, ranged from 2.22 to 2.64 indicating that a significant fractionof surface area is associated with the coarser gradation of particles. Modeled results support previous experimental data indicating the predominance of surface area and heavy metal mass is associatedwith the coarser fraction of particles. Results indicated a statistically significant difference in densities for coarse (2.86 gm cm-3) and fine particles (2.75 gm cm-3) (P < 10-11).A methodology is presented in the form of a process selection diagram to evaluate mechanisms of particle separation. It was determined that sedimentation could remove 90% of particles, bymass, within 2 hr for a typical roadway drainage design. The influence of particle specific gravity on sedimentation efficiency is illustrated for a range of specific gravities from 1.1 to 4.0. Although the very high concentrations of particulate matter in highway snow melt do not make it amenableto straining or direct filtration, such processes may be feasible as a secondary treatment for snowmelt or storm water effluent discharges to receiving waters.

Physical and Chemical Characteristics of Urban Snow Residuals Generated from Traffic Activities

Urban transportation activities generate a wide gradation of anthropogenic solids with varying physical and chemical properties. These solids accumulatein urban highway snow and remain as residual deposition material after the melting and recession of the snow from the pavement shoulder. This study analyzed the physical characteristics of these residuals and the associatedheavy metals for 10 urban highway sites located throughout metropolitan Cincinnati. Results from the residuals analyses indicate that for all sites particle gradations ranged from greater than 5000-μm to less than 25-μm with a mean d50 of 1225-μm. Specific gravity (ρsg) of residual solids ranged from 2.5 to 3.2 as evaluated for intervals across thegradations, with the lower specific gravity associated with particles less than 100-μm. For each gradation, specific surface area (SSA) generally increased with decreasing particle size while the predominance of total surface area (SA) was associated with the coarser size fractions. Cumulativeanalysis for Pb, Cu, Cd and Zn associated with snow residuals indicated that more than 50% of the heavy metal mass was associated with particles greaterthan 250-μm and more than 80% was associated with particles greater than 50-μm. Results provide guidance for management of urban snow residuals and design of treatment strategies focused on these residuals.

Hazardous Wastes Disposal: Stabilization/Solidification of Tannery Residue in the Presence of Chromium

Disposal or reuse of hazardous waste is a major consideration in chemical manufacturing and processing. Waste residuals from the tannery industry can contain high levels of chromium. Considered as a hazardous waste by the Brazilian environmental laws, the chromium-containing waste requires treatment before final disposal. This paper proposes a solution for the disposal of tannery wastes, which are rich in chromium by solidification in a Portland cement matrix using combinations of sodium bentonite and organoclay admixtures. This research is part of a series of experimental studies where Brazilian sodium bentonite, and organoclay materials are used to adsorb both inorganic and organic chromium. The solidified matrix is formed by Type II Portland cement, in which the hydration process stabilizes the tannery waste. Wyoming sodium bentonite and a commercial organoclay are analyzed and compared with the Brazilian clays. X-ray Diffraction is used to characterize the samples and leaching tests are performed to analyze the chromium concentration in the extract solution. In terms of leachate tests, the stabilization by solidification with cement is a process that can be used in the treatment of tannery waste.

X-Ray Diffraction Study of Particulate Tannery Waste Solidified in Cement

The leather industry creates a large quantity of organic and inorganic waste containing chromium. This research examines stabilization of particulate tannery waste in type II Portland cement. Several clays, Brazilian polycationic smectite modified in laboratory and commercial clays were used as additives with the aim of optimizing chromium adsorption. Tannery waste was added in quantities of 10, 15 and 20% relative to cement mass. The solidification components were analyzed separately and in combination in the solidified mixes using X ray diffraction. The analysis showed that reactions between the waste and the cement occurred, and that the tannery waste modified the final compounds of the system. Calcium sulfate present in the waste increased ettringite formation. Chromium also reacted with cement, since compounds with chromium and calcium were identified. Substitution of aluminum and silicon by chromium was also observed.

Influence of Chemistry, Hydrology and Suspended Solids on Partitioning of Heavy Metals to Particles - Considerations for In-Situ Control of Urban Stormwater Quality

In-situ control and treatment of urban storm water at the upper end of the urban catchment poses unique challenges due to the unsteady nature of processes including rainfall runoff, mobilization and partitioning of heavy metals, changes in aqueous chemistry, residence time between rainfall and runoff and delivery of particulate mass. In this study heavy metal partitioning results are examined for a series of rainfall runoff events in light of the role of the unsteady chemistry, hydrology and entrained solids. Aqueous chemistry and residence time characteristics such as low alkalinity, low hardness and short pavement residence time (less than 30 minutes) can result in a majority of the heavy metal mass remaining in solution at the edge of the pavement with trends in partitioning only approaching equilibrium conditions towards the end of the event as heavy metals partition to entrained solids. There are two primary implications when considering the application of in-situ control strategies at the upper end of the urban catchment. The first implication is to utilize a stormwater control to detain runoff and produce sufficient residence time so that partitioning to the entrained solids occurs and these solids are then effectively separated and recovered or managed. The second implication is to utilize a storm water control or treatment practice such as an engineered infiltration system to provide surface complexation for dissolved metals and filtration mechanisms for the particulate bound metals. Unfortunately such controls are still evolving and there still are no simple solutions that exist for the removal of a heavy metal or particle once released in the urban environment. However, knowledge of the dynamic processes in stormwater can provide insights for the proper selection of unit operations and processes depending on the conditions at the urban site. Therefore as one follows the drainage pattern of stormwater through the urban and natural environment, partitioning will tend towards the particulate phase as residence times increase. Any treatment design should be based on the concept that such controls, to be effective, are essentially garbage cans for heavy metals and solids and as such must be emptied and cleaned periodically.

Evaluation of S/S Process of Tannery Waste in Cement by Structural and Mechanical Analysis

This paper presents a study of a stabilization/solidification (S/S) process of a tannery waste containing chromium. In this process a mixture of cement, water and the waste is solidified during hydration of the former. Stabilization occurs by the reaction of the chromium components of the waste with the calcium hydroxide formed during the process. A rigid block is obtained with low hazardous of contamination of soil and groundwater after its disposal into industrial landfill. Mixtures were prepared adding dried tannery waste in 10, 15 and 20% of the Portland cement mass. Sodium bentonite and organoclays in 5 % of cement mass were used as additives. Solidified specimens were analyzed after 28 days of hydration time by solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy and unconfined compressive strength analysis. The increase of tannery waste content and the presence of the additives reduce silica polymerization as well as the mechanical strength of the solidified bodies.