Journal of Environmental Engineering

Modelers of contaminant fate and transport in surface waters typically rely on literature values when selecting parameter values for mechanistic models. While the expert judgment with which these selections are made is valuable, the information contained in contaminant concentration measurements should not be ignored. In this full-scale Bayesian analysis of polychlorinated biphenyl (PCB) contamination in the upper Hudson River, these two sources of information are combined using Bayes' theorem. A simulation model for the fate and transport of the PCBs in the upper Hudson River forms the basis of the likelihood function while the prior density is developed from literature values. The method provides estimates for the anaerobic biodegradation half-life, aerobic biodegradation plus volatilization half-life, contaminated sediment depth, and resuspension velocity of 4,400 d, 3.2 d, 0.32 m, and 0.02 m/yr, respectively. These are significantly different than values obtained with more traditional methods, and are shown to produce better predictions than those methods when used in a cross-validation study.

In 1981 the Minnesota Pollution Control Agency completed a wasteload allocation study of the Metropolitan Wastewater Treatment Plant's [11 m ³ /s (250 mgd)] impact on dissolved oxygen levels in Pool 2 of the Upper Mississippi River, using the water quality model AESOP. Subsequently, a low flow water quality survey was conducted in the summer of 1988 to monitor the improvement in the river following the treatment upgrade at the plant. In this postaudit study, the AESOP model was checked using the 1988 data set. The significance of the postaudit analysis is that the model kinetic coefficients remain unchanged, except the biochemical oxygen demand deoxygenation rate and the algal growth rate, from the 1981 wasteload allocation study. The carbonaceous biochemical oxygen demand (CBOD) deoxygenation rate dropped after treatment upgrade, and the algal growth rate is within the range of values used in previous calibrations of the AESOP model. CBOD and ammonia loads from the Metro Plant now contribute a small dissolved-oxygen deficit in the receiving water.

A methodology for ocean outfall mixing zone analysis is presented. It is based on a combination of four deterministic models for predicting hydrodynamic mixing behaviors of the discharged effluent, a continuous time domain simulation method, and an exceedance probability field concept. The approach provides a framework for evaluating mixing zones in compliance with receiving water criteria that are set in statistical terms. The approach was applied to the Hollywood outfall located off the east coast of South Florida. An exceedance probability field for effluent at a specified relative concentration of 0.021 was created. This field was applicable for determining the exceedance probability-based concentrations of any conservative pollutant at the regulatory mixing zone edge. A comparison of the probabilistic approach with the worst-case approach was made. The use of the worst-case approach was found to be too conservative for the subject outfall.

This paper describes the results of a study conducted to determine the fate of bacterial aerosol emissions from aeration tanks of an activated sludge treatment plant relative to the height above the liquid surface. Bacterial aerosols were collected using Andersen six-stage viable samplers positioned at heights ranging from 7.6 to 318 cm above the aeration tank liquid surface. Samples were analyzed for heterotrophic plate count (HPC), total coliform (TC), fecal coliform (FC), and fecal streptococci (FS). A statistical analysis of the data indicates that HPC and TC concentrations decreased exponentially with height above the aeration tank liquid surface. Fecal coliform and FS concentrations were low or below detection limits ( <4 cfu/m ³ ) in the collected samples and showed no decrease with height. This study demonstrates that a significant decline in number of aerosolized bacteria (leaving the surface of an aeration tank) occurs within the air column directly above the aeration tank liquid surface. Also, bacteria of potential public health concern, such as FC and FS, often reach nondetectable levels ( <4 cfu/m ³ ) within one meter above the liquid surface of these aeration tanks.

Research of indoor biocontamination is motivated by the potential for bioaerosols to cause human illness. Several methods have been used for sampling indoor bioaerosol levels. For screening or characterization purposes of indoor bioaerosol contamination, the Andersen viable (microbial) particle sizing sampler, the portable Reuter centrifugal sampler, and the gravitational collectors (agar-filled petri plates) are among the frequently used samplers. These conventional methods require an incubation period of about 2–7 d. An effort was undertaken to develop a measuring technique for screening purposes that would eliminate the incubation “wait time.” The filtration fluorescence direct counting method was developed, tested in the laboratory, and applied in a pilot field study. The filtration fluorescence direct counting method is a modified six-stage Andersen viable sampler that uses sterilized water instead of culture medium in each petri dish. After sampling, water is filtered and the filter is stained with acridine orange for direct counting of bioparticles under a fluorescent microscope. This technique for measuring bioaerosol eliminates the necessity for incubation and provides a measure of total bioaerosol concentration within an hour after sampling. The database generated by the new method compares favorably with data from side-by-side sampling using conventional methods. It is concluded that the method developed is an appropriate screening tool for evaluating the bioburden of indoor and outdoor environments.

Under a simplifying assumption of uncharged particles, the adhesion theory was used in conjunction with the boundary layer theory to derive an expression for the lower limit of velocity for the resuspension of fibrous particles from flat surfaces. The theory, albeit approximate, suggests that mineral fibers with diameters less than 9 μm diameter will not be resuspended by bulk air velocities less than 10 m/s. Since electrostatic forces, fiber orientation or high humidity will require a higher aerodynamic force to lift the fibers off a surface, this theoretical limit is conservative for environmental exposure considerations. The theoretical calculations were experimentally confirmed by observing the behavior of settled single fibers in turbulent air flow. The results of the theoretical analysis and the subsequent experimental confirmation suggests that the concerns about the aerodynamic resuspension of mineral fibers within a biologically significant size range are overstated.

Bioremediation can remove petroleum products from soil that has been contaminated by leaking underground storage tanks, but abiotic processes such as evaporation can contribute significantly to the overall removal process. The mathematical model described in this paper was developed to predict the evaporation rate of volatile liquids from petroleum-contaminated sand. The model is based on simple concepts relating to molecular diffusion embodied in the theory underlying the estimation of binary diffusivities using measurements made with an Arnold diffusion cell. The model in its simplified form indicates that the rate of evaporation for a particular volatile liquid is proportional to the square root of the product of diffusivity and partial pressure divided by the molecular weight of the liquid. This in part explains why evaporative losses from sand are so much higher for gasoline than for diesel fuel. The model also shows that the time for evaporation is directly proportional to the square of the depth dried out and inversely proportional to the vapor pressure of the volatile liquid. The model was tested using gravimetric measurements of the evaporation of n-heptane, unleaded gasoline, and diesel fuel from sand under laboratory conditions.

This paper describes in detail a new integrated risk model, SoilRisk, for low-levels of organic pollutants in soil. An analytical model of the fate and transport of organics in unsaturated soil is used where chemical losses from the unsaturated zone occur due to first-order degradation, volatilization at the soil surface, and leaching to the saturated zone. The unsaturated zone module is linked to air dilution/dispersion, saturated zone transport, and dust generation modules to allow estimation of long-term average air, groundwater, respirable dust, and soil contaminant concentrations. With SoilRisk, the carcinogenic risk resulting from a specified contaminant concentration in soil or the contaminant concentration in soil to meet a specified level of risk can be estimated. These model outputs can be evaluated as single values or as cumulative distribution functions, depending on whether the input parameters are specified deterministically or probabilistically. In a subsequent paper, the model is applied to evaluate the risk implications of establishing uniform, concentration-based soil remediation goals.

A method for economically based conceptual design of soil venting systems is described. The objective of this method is to provide a means of estimating the cost and schedule of site cleanup for the purposes of technology selection and for focusing detailed system design. Idealized treatments of contaminant volatilization and flow of gas in the soil are employed to obtain estimates of transient off-gas concentration and the vacuum required at the extraction vents for a given set of site and system design conditions. Capital and operating costs of blowers and emissions control devices are estimated using standard techniques, allowing comparison of the required processing cost for cleanup under various design strategies. The utility of this technique is illustrated for an example case of a 95,000-L (25,000-gal) JP-4 jet fuel spill. The results for this test case indicate that emissions control predictably increases cleanup cost, with carbon adsorption being more costly than catalytic oxidation. This treatment predicts than an optimum flow rate and system size exist for each design strategy at a particular site.

Aquifer sediments contain a wide distribution of particle sizes, but only a single collector diameter ( d ) can be used in a filtration equation. To establish a method for selecting a characteristic d when media are composed of different sized particles, we measured bacterial retention in columns packed with either crushed quartz sand (separated into three different size ranges) or borosilicate glass beads. The best methods for choosing d were those that produced nearly constant collision efficiencies (α's). Characteristic diameters included: d₁₀ (10% of all particles were smaller), d₉₀ (90% of all particles were smaller), d _a (arithmetic mean), and d _g (geometric mean), where all diameters were calculated using number, area, and volume size distributions. Bacterial α's decreased in proportion to the distance traveled in the packed bed, and were scaled by the number of bacteria-sediment collisions using a dimensionless collision number (ξ). These comparisons indicated that characteristic diameters based on the smaller particles ( d _a and d _g using number distributions, and d₁₀ using a volume distribution) most accurately described bacterial transport in the different-sized porous media.

Alternative formulations of the analytical modeling for contaminant transport in nonisothermal fractured porous media are presented. Transient and steady heat flows are coupled with solute transport, either implicitly as natural convection incorporating the effect of thermal flux on the variation of concentration gradients, or explicitly as a “Soret effect,” where the divergence of the thermal flux acts as an additional source term affecting the change of solute concentration. The effect of solid deformation due to temperature changes and subsequent impact on the variation of solute concentrations are identified. The proposition of using function transformation within Laplace space may be of significance for numerical implementation in solving advection-dispersion equations. Two different dual-porosity conceptualizations of fractured porous media are proposed based on alternative assumptions of matrix flow. The concept of “matrix replenishment” in relation to the traditional “matrix diffusion” is presented, which may have practical significance in the evaluation of contaminant transport in fractured porous media. The solutions are applicable for modeling the process using thermal sweeping to remediate contaminated areas.

Toxicity of eightand 10-component mixtures of several organic chemicals to activated sludge (A/S) microorganisms was analyzed. The joint toxic effects of the tested chemicals were found to be simply additive. The quantitative structure activity relationship (QSAR) technique using molecular connectivity indices was used to develop single variable models to fit single chemical toxicity data. A QSAR-based approach is proposed to predict the concentrations of components in equitoxic mixtures that would jointly cause 50% inhibition of the A/S microorganisms. The validity of this predictive approach was demonstrated by comparing the predicted concentrations against those found experimentally.

Each year, American families are exposed to toxic substances brought home on the work clothes of other family members. Case studies show that illness and death have resulted and that small amounts of contamination can create an unsafe environment in the home. In this paper, the available data on the transport pathway for workplace chemicals into the home are reviewed. A model to describe contaminant accumulation in the home is proposed. The half-life for some contaminants in the home appears to be on the order of months instead of years.

In 1991, approximately 37%, by weight, of the materials going to landfills was paper. Landfill space in the United States is becoming a critical problem in certain areas. This mixed paper fraction does not have a good use in traditional recycling applications. Wastepaper dealers have an excess of mixed wastepaper. This project explored the possibility of producing a value added product that would consume large amounts of mixed waste. The product selected was to produce 5 × 10 × 20 cm paper blocks. These blocks could find applications in building structures. The blocks were molded using a heated platen press and an aluminum mold, fitted with porous brass plates on the top and bottom in order to ease water removal. The material produced was similar to synthetic wood. Unlike wood, it could be molded into different shapes if desired. The density and physical properties of tensile strength and modulus were determined and compared to wood. The water absorption properties were evaluated and found to be a potential problem. Various coatings were investigated in order to improve the water holdout properties. A manufacturing process was laid out and the cost of block production was estimated to be from $0.15 to $0.24 per block, which would make it competitive with other blocks.