Journal of Environmental Engineering

A risk-based approach is used to evaluate potential human health risks associated with a discharge from an ash disposal site into a small stream. The RIVRISK model was used to estimate downstream concentrations and corresponding risks. The modeling and risk analyses focus on boron, the constituent of greatest potential concern to public health at the site investigated, in Riddle Run, Pennsylvania. Prior to performing the risk assessment, the model is validated by comparing observed and predicted results. The comparison is good and an uncertainty analysis is provided to explain the comparison. The hazard quotient (HQ) for boron is predicted to be greater than 1 at presently regulated compliance points over a range of flow rates. The reference dose (RfD) currently recommended by the United States Environmental Protection Agency (U.S. EPA) was used for the analyses. However, the toxicity of boron as expressed by the RfD is now under review by both the U.S. EPA and the World Health Organization. Alternative reference doses being examined would produce predicted boron hazard quotients of less than 1 at nearly all flow conditions.

A multicomponent reactive solute-transport model was used to study the migration of dissolved heavy metals (Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺) in a clay barrier subject to two leachates having different pH values. This solute-transport model is capable of simulating simultaneous processes of water flow, advective-dispersive-solute transport, and chemical reactions. The migration of these metals was simulated in a kaolinite landfill liner, which was assigned realistic physical and chemical properties and boundary conditions to model one-dimensional contaminant transport. The leachate input properties to the model were those of an actual leachate containing the four heavy metals. The numerical simulations were focused on the concentration profiles of these metals in the simulated clay barrier and leachate pH affects their mobilities. The numerical results indicate that with a nearly neutral leachate, the heavy metals mobility follows: Cd²⁺ < Pb²⁺ < Cu²⁺ < Zn²⁺. With an acidic leachate, the order changes to Pb²⁺ < Cu²⁺ < Zn²⁺ < Cd²⁺. Leachate pH has a significant effect on Cd²⁺ and Pb²⁺ mobility and a small effect on Cu²⁺ and Zn²⁺.

The waterborne pathogen Cryptosporidium has been identified in surface drinking water supplies. Suspected sources of this pathogen include sewage and the feces of animals, particularly dairy calves. There are many dairy cattle and significant sewage effluent discharges in the Catskill-Delaware watershed that is part of the New York City water supply system. This water supply serves 8,000,000 customers with 5.8 × 10⁹ L (1.5 billion gal. of water daily). This paper is concerned with the movement and fate of pathogens from wastewater and dairy sources and the resulting raw water quality for New York City. Manure and Cryptosporidium oocysts are modeled as surface pollutants and assumed to move in response to runoff events in the six watershed-reservoir systems within the Catskill-Delaware watershed. Oocyst degradation in manure and in water is modeled with first-order kinetics. Rudimentary stream routing and reservoir modeling with a first-order decay function complete the fate and transport modeling of oocysts in the watercourse. Reported effluent discharge rates and oocyst concentrations in secondary treated sewage allow estimation of wastewater-derived oocyst contributions. This research highlights the importance of wastewater-derived oocysts, the need for expanded research into oocyst fate in streams and reservoirs, and the concentration of oocysts in sewage effluent.

A unitary environmental classification of water- and excreta-related communicable diseases is presented, which comprises seven categories: Feco-oral waterborne and water-washed diseases; non-feco-oral water-washed (skin and eye) diseases; geohelminthiases; taeniases; water-based diseases (bacterial and fungal, as well as helminthic); insect-vector diseases; and rodent-vector diseases. The global burden of some of these diseases in 1990 is reviewed. Water- and excreta-related diseases were responsible for 2,700,000 deaths in that year (5.3% of all deaths) and for the loss of 93,200,000 disability-adjusted life years (6.8% of all DALYs). Almost all these deaths and loss of DALYs occurred in developing countries (99.9 and 99.8%, respectively).

This work investigated the effects of cationic polymer flocculation on the continuous moisture distributions of two sludges by means of combined thermal gravitational analysis and differential thermal analysis tests. At a specific moisture content, the solid-water bond strength first decreases with increasing polymer dose, after it reaches a charge neutralization point, and then increases in the overdose regime. Effects of polymer conditioning on the moisture distribution in sludge, as well as the correlation with the bound water data measured by expression and drying, were discussed.

Shagawa Lake, Minn., received direct discharges of municipal wastewater for nearly 80 years and attained annual average total phosphorus concentrations of 30–60 μg/L. A tertiary wastewater-treatment facility was constructed in 1973 that removed 80% of the external total phosphorus loading to the lake. The subsequent recovery of the lake was less than expected because of internal loading of phosphorus associated with accumulated lake sediments. Therefore, it is necessary to consider the effects of sediment phosphorus release to predict accurately the dynamics of phosphorus in Shagawa Lake. Measurements of the sediment characteristics have been used to estimate mass transfer coefficients that describe the release of phosphorus from the sediments. Three alternative mass-balance models were developed to determine the significance of the water sediment interactions. Recent field measurements were used to gauge the performance of the models. It was found, even more than 20 years after the reduction of the external loading, that sediment feedback of phosphorus has a significant influence on the dynamics of total phosphorus in the lake. Continued monitoring and data analysis of the sediment are necessary to refine the models and to predict accurately the ultimate fate of the lake.

Settling and entrainment are the dominant processes governing noncohesive particle concentration throughout the water column of salt-wedge estuaries. Determination of the relative contribution of these transport processes is complicated by vertical gradients in turbulence and fluid density. A differential-turbulence column (DTC) was designed to simulate a vertical section of a natural water column. With satisfactory characterization of turbulence dissipation and saltwater entrainment, the DTC facilitates controlled studies of suspended particles under estuarine conditions. The vertical decay of turbulence in the DTC was found to obey standard scaling law relations when the characteristic length scale for turbulence in the apparatus was incorporated. The entrainment rate of a density interface also followed established grid-stirred turbulence scaling laws. These relations were used to model the change in concentration of noncohesive particles above a density interface. Model simulations and experimental data from the DTC were consistent over the range of conditions encountered in natural salt-wedge estuaries. Results suggest that when the ratio of entrainment rate to particle settling velocity is small, sedimentation is the dominant transport process, while entrainment becomes significant as the ratio increases.

The performance of a field study to determine whether any of the 14 New York City water pollution control plants are major sources of air pollution required sampling and the analysis of a large number of samples. To reduce the number of samples for analysis and address the associated storage concerns of the analytical laboratories, the experimental design called for compositing air and wastewater samples, and for investigating the stability of wastewater samples. This paper addresses the quality control issues associated with the compositing and stability components of the experimental design. The study tested the hypothesis that compositing techniques used for air and wastewater sampling lead to results that are not unlike those obtained by conventional grab sampling. The study also tested whether wastewater samples stored under proper laboratory conditions remain stable for a period longer than the conventionally accepted storage period of 2 weeks. Statistical analyses demonstrated that the hypotheses tested cannot be rejected and, consequently, compositing techniques employed in this study are equivalent to conventional grab sampling and the storage period of samples can be extended beyond the accepted 2 week period.

In the Mediterranean region, climatological factors make combined sewer overflows a major urban pollution problem that should be monitored and controlled. Some online management solutions require the use of real-time models to forecast flows at the most sensitive points of the combined sewer systems. These models need a very good time and spatial resolution of the rainfall field, which is not sufficiently reproduced by a conventional rain-gauge network. This paper presents a case study where the use of rainfall estimates from weather radar pictures is compared with the use of a rain-gauge network in terms of the ability to predict sewer flows in an urban basin in Barcelona, Spain. The results show that the use of radar data enables the combined sewer systems model to improve the reproduction of observed flows, and they provide support for the idea that the spatial description of rainfall is a key problem in modeling the events giving rise to combined sewer overflows.

The technical and economical feasibility of using water hyacinth ponds for the treatment of wastewater is well established. However, various purification mechanisms operative in a pond have not been understood fully. In the present work, an attempt has been made to study stratification in four laboratory scale models of different depths operated continuously over a period of 4 months. It was concluded from this study that stratification did not occur in ponds. An attempt also was made to study the possible reasons for it. First, dense water hyacinth canopy stops radiation in excess of 90%. This prevents the growth of algae and subsequent increase in dissolved oxygen. Second, based on temperature profiles, thermal and density stratification also were found to be absent. Third, the secondary circulation in the ponds, induced because of influent and effluent being at different levels, also assists in checking the stratification. All these effects make a water hyacinth pond unstratified, which helps in uniform treatment throughout the depth and maintenance of designed hydraulic detention time.

A conventional pressure cell may be inadequate for making the multiple capillary pressure–saturation relationships necessary to characterize waste sites because of its materials of construction and poor dynamic response. This paper outlines the design of a pressure cell apparatus that is constructed of chemically resistant materials and is capable of generating drainage and imbibition capillary relationships at both positive and negative capillary pressures for sandy porous media containing organic liquids and surface-active solutes over a range of pH values. Its rapid response is caused primarily by a highly conductive capillary barrier and the continuous visual display of degree of saturation. Because of the high conductivity of the capillary barrier, bubbles form under it, limiting the cell to 40 h of use at a capillary pressure head of 150 cm H₂O or 10 h at 200 cm H₂O. This range is sufficient, however, to allow the generation of the five capillary pressure relationships necessary to characterize wettability for many waste-site systems.

In most experimental studies concerning negatively buoyant water jets the buoyancy was produced by density differences due to salt while the temperature of the jet and the ambient fluid was identical. Another method to produce a negatively buoyant water jet is to use different temperatures between the jet and the ambient fluid. However, there are essential differences between thermal and saltwater buoyant jets. In this technical note a modified version of the integral Fan–Brooks model has been used to calculate the vertical penetration of inclined heated water jets discharged downward. The classical initial densimetric Froude number is replaced by an initial effective Froude number based on the thermal expansion coefficient of water. Using the above model, a new equation is derived that predicts the vertical penetration of the thermal jet at a given effective Froude number and discharge angle. This formula reduces to Turner's equation for vertical jets if the densimetric Froude number is substituted by the effective Froude number.