Journal of Environmental Engineering

Soils contaminated with lead and copper from three industrial-waste sites were characterized for particle-size distribution, heavy metal (Pb, Cu) content by particle size, sequential extraction for metal speciation, scanning electron microscopy for morphology, and energy dispersive X-ray microanalysis (SEM/EDX) for chemical composition. High concentrations of Pb and Cu were found in all size fractions of the test soils. Pb was observed to be associated primarily with the carbonate and the Fe-Mn oxide phases of the soil samples. Cu was associated with carbonate, Fe-Mn oxide, and organic fractions of the soils. In one of the test soils (Soil A), SEM/EDX analyses showed the presence of roughly spherical isolated Pb-enriched particles. In addition, a few irregularly shaped Cu-enriched particles were detected. Such particles were observed to increase with decreasing soil-particle size. The presence of small Pb particles or precipitates adhering to larger soil particles also was observed.

Results of field studies conducted downstream of five reservoirs are used to develop an improved understanding of the disappearance of reduced manganese in tailwaters. A first-order removal formulation accurately describes the removal of dissolved manganese versus travel time downstream. Results support the theory that adsorption to the stream bottom is the primary removal mechanism. The first-order removal rate, which varied by an order of magnitude from 0.30 to 4.45 day ⁻¹ , is found to be highly correlated to the stream slope, which affects shear velocity. Using observed removal rates, a formulation based on the ratio of the stream-bottom mass-transfer velocity, which depends on bottom-shear velocity, and stream depth is developed for computing the removal-rate coefficient. The formulation also depends on substrate type (i.e., cobble or fine-grain sediments). Dissolved manganese concentrations computed with the developed mathematical model show good agreement with observations. Some questions still remain, such as whether there is an annual acclimation time for manganese removal.

A predictive mathematical model was employed to examine trends in Chesapeake Bay eutrophication from 1959 to 1988. The model provided details of processes and substances for which no record existed. The simulation indicated the volume of anoxic water was largest in the decade 1969–78. Since then, anoxic volume has declined. The decline was largely due to hydrodynamic effects. In 1969–78, high runoff caused the Bay to be highly stratified and inhibited oxygen transport to bottom waters. Less runoff in the years 1979–88 diminished stratification and allowed enhanced oxygen transport to bottom waters. When only years of similar stratification were compared, an increase in anoxic volume was noted from the 1959–68 decade to the 1979–88 decade. The increase was associated with increasing nitrogen concentration in runoff from two major tributaries and with increasing chlorophyll concentration in the mainstem Bay.

A kinetic model is developed for the inactivation of viruses that exhibit a range of initial aggregate sizes. Aggregates are assumed to be more resistant to inactivation than single virions because (1) all virions within an aggregate must be inactivated before the aggregate as a whole is considered inactive; and (2) undamaged components of inactive virions within an aggregate may recombine to cause host-cell infection (multiplicity reactivation). Survival curves calculated from the model compare well with inactivation data published in a previous study. The analysis presented in this report provides an approach for estimating the contact time (or disinfection concentration) required to inactivate viral aggregates, and a framework for predicting virus survival in water-treatment systems and natural environments.

The object of this study is to investigate the data needs for accurate estimation of particle collision efficiencies (α). Batch flocculation and vertical flocculent settling studies were conducted on aquatic sediment particles in the size range of 2–80 μm in diameter. Dynamic particle-size distribution data sets were generated using a 256-category binary-collision-based flocculent settling model and subsequently compressed into 128, 64, 32, 16, 8, and 4 logarithmically varying particle-diameter categories. A previously developed parameter-estimation framework was used to estimate α values from the compressed data sets. Variability in the α estimates indicates that it is not an artifact of the experimental data. The residual function value after 20 estimation iterations increased with the discretization levels, indicating shallower residual function slopes. Parameter estimation accuracy was unaffected by the levels of data sparsity considered. Increased random noise resulted in consistently lower estimated collision efficiencies. Rate of convergence was unaffected by random noise but decreased with data sparsity levels. Particle water column residence times were significantly overestimated using four category distributions.

The concept of slowing the distributor speed to flush excess biofilm from rock media was discovered by English investigators in the late 1940s. In the 1980s, German investigators quantified the hydraulic effect of average flow and distributor speed in terms of instantaneous or flushing intensity ( SK ), in mm/pass of an arm. Studies and analysis conducted in recent years have found that the use of slowed distributor speed was effective in improving performance, but that optimum speed was much higher than that required to flush the media. This information evolved into distributor control/drive arrangements that would automatically provide the optimum speed as a function of flow and loading. This concept has been retrofitted at several wastewater-treatment plants, and the Central Valley, Utah, design and initial results are presented. A number of sizing formulations are provided that have evolved from these experiences.

A key parameter in modeling soil-venting systems is relative air permeability, determined as a function of liquid saturation. The focus of the present study was to characterize the relationship of the relative air permeability as a function of air saturation in soil-venting systems. A new laboratory apparatus was used to simulate the soil venting and measure the air permeability of soil samples. Sand samples wetted with mixtures of water and gasoline at different ratios were used. It was revealed that the prediction of relative air permeability for moist noncohesive soil can be made in terms of intrinsic permeability and air-filled porosity alone, and not the type of liquid present in the pores. Comparisons of measured data with existing relations for relative air permeability as a function of total liquid saturation were made to determine the most accurate and practical forms for engineering applications. For the sand sample used, the evaluation revealed that compared to the existing relations, a derived second-order polynomial expression provides a good estimate of relative air permeability and does not require estimation of soil-water–retention curve parameters.

Air infiltration through highly permeable concrete blocks can allow entry of various serious indoor air pollutants. An easy approach to avoiding these pollutants is to select a less–air-permeable concrete block. Tests show that air permeability of concrete blocks can vary by a factor greater than 50 (0.63–35 standard L/min/m ² at 3 Pa). The surface texture of the blocks correlates well with air permeability; test results of smoother, closed-surface-texture blocks were usually less air-permeable. During construction, air infiltration can be minimized by capping walls and carefully sealing around openings for utilities or other penetrations. Structures with indoor air-quality problems due to soil-gas entry can be mitigated more effectively with less coating material if the blocks have a closed surface texture. All coatings evaluated—cementaceous block filler (which has the lowest applied cost and is more than 99.5% effective), surface bonding cement, water-based epoxy, polysulfide vinyl acrylic, and latex (three coats)—were highly effective (more than 98%) in reducing air permeability when adequately applied. Coating selection should be influenced by expected service life, considering surface condition and cost.