Journal of Environmental Engineering

A one‐dimensional, pseudo unsteady state, water quality model (SNOAP) was developed to simultaneously solve both nitrogen and dissolved oxygen mass balance equations. Expressions are derived to estimate ammonia‐N exsolution, bacterial ammonia‐N uptake, and aquatic plant ammonia‐N assimilation in terms of standard water quality indices. The SNOAP model calculates hourly values for all nitrogen species reaction rates (including nitrification and denitrification) based on observed in‐stream variation of organic‐N, ammonia‐N, nitrite‐N, nitrate‐N, dissolved oxygen, temperature, and pH. An iterative solution algorithm is required to simultaneously solve the nitrogen and dissolved oxygen mass balance equations. This iterative approach is stable and results in relatively quick convergence. Erroneous values of observed nitrogen species or dissolved oxygen variation, or both, may result in an impossible situation for simultaneous nitrogen and dissolved oxygen mass balance solution. This nonconvergence feature is a significant attribute, in that it allows for a systematic screening of measured water quality data.

The Stream Nitrogen and Oxygen Analysis Program (SNOAP) is a one‐dimensional, pseudo unsteady state, water quality model, which simultaneously solves both nitrogen and dissolved oxygen mass balance equations. The SNOAP model was successfully calibrated and verified for three, independent, data intensive water quality surveys. The modeled stream system was unsteady due to significant upstream impact from wastewater treatment plant effluent discharges. Denitrification was found to be the dominant total nitrogen sink. Average denitrification rates calculated by the SNOAP model range from $22.0-43.6\mathrm{mg}‐N/m^2/\mathrm{hr}\text{.}$ The computed values compare quite favorably with measured laboratory sediment denitrification rates which ranged from $28.2-39.2\mathrm{mg}‐N/m^2/\mathrm{hr}\text{.}$ In addition, the rate of ammonia‐N decay was found to be the most accurate nitrogen species estimator of in‐stream nitrification rates.

In the San Francisco Bay Region, the Regional Water Quality Control Board is now regulating approximately 140 sites where toxic chemicals have contaminated groundwater. Many of these were located through the Board's Underground Tank Leak Detection Program, which required subsurface investigations at sites with underground solvent tanks. New ordinances and state laws are expected to result in the discovery of hundreds more contamination sites in the next few years. The Regional Board is developing a ranking methodology to assign priorities among cases and a set of guidelines for establishment of clean‐up objectives on a site‐by‐site basis. Appropriate regulatory mechanisms have been selected to enforce the necessary investigation and cleanup activities.

Sand blasting residue containing cadmium and lead was used as an admixture for concrete. Concrete mixes with up to 15% waste added were found to retain the heavy metals such that none was detected following the EP Toxicity extraction procedure. Degradation of concrete strength as a function of amount of waste material added was observed. Results were correlated to determine the amount of additional cement needed to add along with the waste to maintain design strength.

The differential response of the two commonly used measures of light penetration in water, Secchi disc transparency $\left(\mathrm{SD}\text{,}m\right)$ and the attenuation coefficient for downwelling irradiance $\left(K_d\text{,}{m}^{-1}\right)\text{,}$ to the light attenuating processes of absorption and scattering is described. It is demonstrated that the commonly invoked constancy in the product $K_d\cdot \mathrm{SD}$ should only be expected when the relative contributions of scattering and absorption to $K_d$ remains uniform. A number of scenarios and documented phenomena are presented for which preferential effects on scattering or absorption, and therefore variable values of $K_d\cdot \mathrm{SD}\text{,}$ are expected. Measurement errors also contribute to variability in $K_d\cdot \mathrm{SD}\text{,}$ particularly at low $\left(<1.5m\right)$ SD values. Paired observations of $K_d$ and SD presented from four different systems, representing a wide range of $K_d$ and SD values, demonstrate the variability of the magnitude of $K_d\cdot \mathrm{SD}$ within individual systems. Secchi disc transparency is probably not a reliable indicator of $K_d$ in many systems. It is recommended that the uncertainty associated with invoking the constancy of $K_d\cdot \mathrm{SD}$ in various ecological modeling efforts, in which $K_d$ measurements are missing or are temporally limited, be accommodated.

A completely mixed, expanded‐bed, anaerobic granular activated carbon reactor was operated continuously on synthetic wastewaters in which acetate was the only organic carbon source. Steady‐state performance was achieved for four influent acetate concentrations, namely: 800, 1,600, 3,200, and 6,400 mg/L. Steady‐state removal efficiencies of acetate, COD and DOC exceeded 98, 97 and 98%, respectively. Biological utilization was the major removal mechanism for acetate in the anaerobic filter. This process was demonstrated to be capable of purifying low strength wastewaters down to levels that are acceptable for final discharge.

Effluent dilutions predicted by near‐field models do not realistically reflect near‐field conditions in tidally influenced coastal waters since they neglect the advection of the pollutant cloud over the source. A theoretical solution has been developed for the case in which a conservative pollutant is released from a line source into a uniform unsteady flowing ambient where diffusion is only significant in the cross‐stream direction. Considering the case of a sinusoidal variation of velocity along the streamwise principal axis, it has been shown that the expected concentration at a source located in a typical flow field may increase by as much as 15% per cycle over that predicted by the near‐field model. A hypothetical outfall was analyzed using real data and a dispersion model which accounts for the near‐, as well as far‐field mixing. The near‐field model was found to underestimate the average dilution at the source by about 21%. Extreme values were also underestimated. The results of this study indicate that a complete dispersion model should be used in predicting dilutions in outfall mixing zones of coastal regions.

A comparative study was conducted on the adsorption/desorption of organic vapors (toluene and para‐xylene) on a synthetic resin (XAD4) and activated carbon using a gravimetric method involving the use of a quartz spring expansion. While the two sorbents can effectively remove the organic vapors, it was observed that activated carbon adsorbs more organic vapor than synthetic resin at low concentrations; but at higher industrial level concentrations, the resin adsorbs more organic vapor. The rate of adsorption is higher than that of desorption for the two organic vapors regardless of the sorbent. However, the resin showed higher reversible adsorption. The effective intraparticle diffusion coefficients ($D_c$) were observed to be strongly dependent on the solute concentration. As such, rate studies ought to be conducted around the expected concentration range that is expected during application. Pore diffusion dominated the adsorption/desorption of both organic vapors on the XAD4 resin. For the carbon system, pore diffusion dominated the adsorption but surface diffusion contributed to the desorption process. This is believed to be due to higher interaction of the solutes with activated carbon.

Synthetic organic polyelectrolytes can be used to condition sludges to enhance their dewaterability. When conditioning biological sludges, the charge on the polymer has a significant impact on the effectiveness of the polymer as a conditioner. The objectives of this investigation were to determine the most effective type of polymer product for conditioning anaerobically digested sludge prior to dewatering, and to investigate how the chemical characteristics of the polymer influence the way it interacts with the sludge particles. Capillary suction time and particle electrophoretic mobility measurements were employed to achieve this objective. The results indicate that cationic polymers with molecular weights in excess of ${10}^6$ appear to be required for effective conditioning. However, effective sludge conditioning can be achieved with either high or low charge density cationic polymers and that dosing to achieve charge neutralization of the sludge particles is not a prerequisite for effective sludge conditioning.

Granular activated carbon (GAC) adsorption is extremely effective for the removal of radon from water supplies. A high removal efficiency is achieved through an adsorption/decay steady state that can result in near‐background radon levels with currently available commercial GAC units. An adsorption/decay steady state analysis based upon secular equilibrium shows that the life of the GAC will be in terms of decades with respect to radon. A variety of GAC products were evaluated for radon removal and laboratory and field data are presented to document the steady state performance for water supplies ranging in concentration from 1,500–750,000 pCi/L. Because radon and its daughters build to steady state levels corresponding to the influent mass loading, the GAC bed becomes a source of low level gamma radiation. An empirical relationship is presented to estimate the maximum activity of the bed as a function of the influent radon concentration. This relation and other field measurements show that the low level activity of a GAC bed does not present a problem for the vast majority of high radon wells.

A novel landfill leachate liner design consisting of a series of vshaped contiguous elements constructed from an impervious membrane, a boxed soil layer saturated with clean water, and a gravel layer is proposed. Certain idealized boundary conditions are stipulated and an analytical solution is given for the diffusional mass transport of leachate through the saturated layer. This is used to assess the maximum value and time‐of‐occurrence of leachate concentration at the impervious membrane. It is shown that these two important quantities are sensitive to the diffusion coefficient and the thickness of the saturated layer. A method is formulated for the estimation of the diffusion coefficient, accounting for the type of contaminant, the effect of the porous medium, and the possibility of contaminant adsorption on the soil matrix. The overall procedure would be valuable in estimating the potential of destruction of the impervious membrane from the chemicals contained in the leachate.