The definition of contaminant source release is a necessary element of contaminant mass transport simulation in the saturated zone. At many sites the release history is unknown, and there has been a significant body of research to develop inverse models to define finite release histories. Instead of rigorously defining the source history, a mass balance-based approach is tested to explicitly account for uncertainty in rectangular pulse release variables. The approach has been incorporated into a spreadsheet model which uses a one-dimensional solution to the advection dispersion equation, which readily lends itself to Monte Carlo applications. After the model was tested with synthetic data sets, the model was calibrated and verified using a concentration data set collected at a Superfund site. Model calibration with synthetic and actual data resulted in a reasonable domain of source history parameters and the model provided reasonable results when the mass of contaminant in the aquifer was assumed to be random.
In this paper some of the practical issues involved in the development and application of an extraction-photodegradation remediation technology for polychlorinated biphenyl (PCB) impacted weathered soils are addressed. The extraction of PCBs from weathered soils was investigated using the conventional Soxhlet extraction and by shake extraction using different solvents. The shake extraction has the potential for up-scaling to a field technology. The photodegradation of the extracted PCBs was investigated under direct ultraviolet light at 254 nm wavelength as well as under photosensitized light at 350 nm. The production of biphenyl, a by-product of the dechlorination of PCBs was investigated and it was found to degrade in the same ultraviolet system.
Groundwater contaminated with the high explosive Demolition eXplosive, or hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) may also contain the nitroso-RDX metabolites hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX). Although adsorption to activated carbon effectively removes RDX from contaminated water, the treatability of the nitroso-RDX compounds by adsorption has not been previously reported. Single-component isotherms were completed and the Freundlich parameters (K and 1/n) were calculated for adsorption of these compounds to Calgon F400 from unbuffered high purity water under aerobic and anoxic (<1 mg/L dissolved oxygen) conditions. Under both conditions, MNX was the most adsorbable, followed by RDX, DNX, and TNX. The presence of dissolved oxygen slightly increased the Freundlich parameters for all compounds except TNX. Under aerobic conditions, Freundlich capacity parameters (K) ranged from 46.4 (mg/g)(L/mg)1/n for TNX to 164.2 (mg/g)(L/mg)1/n for MNX, while under anoxic conditions, K ranged from 47.1 (mg/g)(L/mg)1/n for TNX to 133.6 (mg/g)(L/mg)1/n for MNX. Additional testing showed that 7 days were sufficient for adsorption equilibration in most cases. Simplified granular activated carbon (GAC) column modeling demonstrated that the presence of these compounds in groundwater can reduce GAC service life.
Models describing adsorption equilibrium have not been derived for the sorption onto the biosorbents including both virgin and immobilized biomasses. Biosorption involves interaction of biopolymer-based surfaces with different types of pollutants which may be different for virgin and immobilized biosorbents. In the present study, 16 different isotherm models have been studied using equilibrium data obtained from biosorbents. Biosorbents, both virgin (prepared from two types of macrofungus biomass) and immobilized forms have been used. Results show that in general the accuracy of models to fit experimental data improves with the degree of freedom. Most widely used isotherm models, i.e., Langmuir and Freundlich, could be used to describe the sorption equilibrium of biosorptive processes for both virgin and immobilized biomasses. Comprehensive equilibrium analysis has assisted in understanding the mechanistic aspects associated with different types of sorbate-sorbent interactions.
Wind tunnel experiments were conducted to evaluate the effectiveness of two commercially available fixatives in controlling the mobility of soil particles on soil mounds when exposed to wind forces. The fixatives tested included two commercially available materials: (1) RoadMaster which consists of 38% calcium chloride solution and (2) DuraSoil which consists of a solution of alkanes and alkylated saturated compounds. Soil samples were placed in an open-loop low-speed wind tunnel and exposed to wind forces ranging from 10 to 30 mi per hour (mi/h). The amount of soil loss/displaced and particulate matter (PM10) generated were monitored in relation to soil moisture content and application rate of selected fixatives. The results showed that increase in soil moisture and amount of fixative used had a significant effect in controlling the particulate matter (PM10) concentrations and the amount of soil displaced by the wind forces. The calcium chloride solution was applied by spraying onto the soil samples. However, DuraSoil mixture was applied by pouring the fixative using pipettes due to its high viscosity.
