James H. Clarke

Soil Clean Up by in-situ Aeration. I. Mathematical Modeling

Abstract Mathematical models are developed suitable for use in evaluating the feasibility of in-situ vapor stripping approaches for selected chemicals and site-specific environments. These models simulate the operation of both laboratory soil stripping columns and field-scale vacuum extraction wells (vent pipes). The effect of an anisotropic Darcys constant is examined and the compressibility of the extracting gas is taken into account. The models incorporate the assumption of local equilibrium for the volatile compounds between the condensed and vapor phases. These models may use Henrys law or more complex isotherms for this equilibrium. A method is developed for calculating Henrys constant from field analytical data, and it is noted that use of Henrys constants calculated from laboratory data on solutions of volatile solutes in pure water can lead to very serious errors. It is shown that evacuation wells should be screened only down near the impermeable layer beneath the zone of stripping (unsaturat...

Electrical Aspects of Adsorbing Colloid Flotation. VIII. Specific Adsorption of Ions by Flocs

Abstract A Gouy-Chapman model of the solid-water interface with specific adsorption of ions is used to calculate surface and zeta potentials. The effects of sign and magnitude of ionic charge and surface charge density, ionic strength, specific binding energy, and temperature are examined. Experimental data on foam flotation of ferric hydroxide with sodium lauryl sulfate in the presence of a variety of anions support the model.

Soil Clean Up by in-situ Aeration. II. Effects of Impermeable Caps, Soil Permeability, and Evaporative Cooling

Abstract The clean up of soils contaminated by volatile compounds by in-situ vapor stripping was recently modeled by Wilson, Clarke, and Clarke. Their approach is modified to include the effects of a gas-impervious cap on the velocity field of the moving soil gas. Calculations indicate that such caps reduce the excessive flow of gas in the vicinity of the axis of the cylindrical volume of influence of a vent pipe, and they increase gas velocities near the periphery of the volume of influence. One thus expects use of impervious caps to improve the efficiency of in-situ soil vapor stripping: modeling of contaminant removal with such modified gas flow fields shows that this is indeed the case. Modeling of gas flow around buried obstacles indicates that these are not likely to interfere seriously with soil vapor stripping; some strategies are suggested to reduce their effects. The soil vapor stripping model is used to show that low soil permeabilities can be compensated for by increasing the radius of the str...

Information needs for siting new, and evaluating current, nuclear facilities: ecology, fate and transport, and human health.

The USA is entering an era of energy diversity, and increasing nuclear capacity and concerns focus on accidents, security, waste, and pollution. Physical buffers that separate outsiders from nuclear facilities often support important natural ecosystems but may contain contaminants. The US Nuclear Regulatory Commission (NRC) licenses nuclear reactors; the applicant provides environmental assessments that serve as the basis for Environmental Impact Statements developed by NRC. We provide a template for the types of information needed for safe siting of nuclear facilities with buffers in three categories: ecological, fate and transport, and human health information that can be used for risk evaluations. Each item on the lists is an indicator for evaluation, and individual indicators can be selected for specific region. Ecological information needs include biodiversity (species, populations, communities) and structure and functioning of ecosystems, habitats, and landscapes, in addition to common, abundant, and unique species and endangered and rare ones. The key variables of fate and transport are sources of release for radionuclides and other chemicals, nature of releases (atmospheric vapors, subsurface liquids), features, and properties of environmental media (wind speed, direction and atmospheric stability, hydraulic gradient, hydraulic conductivity, groundwater chemistry). Human health aspects include receptor populations (demography, density, dispersion, and distance), potential pathways (drinking water sources, gardening, fishing), and exposure opportunities (lifestyle activities). For each of the three types of information needs, we expect that only a few of the indicators will be applicable to a particular site and that stakeholders should agree on a site-specific suite.

Theory of Clarifier Operation. I. Quiescent-Hindered Settling of Flocculating Slurries

Abstract The operation of quiescent (batch) clarifiers operating in the Class III mode (hindered settling) with flocculating slurries is modeled by means of a set of nonlinear partial differential equations, the continuity equations for the individual species of particles. Disintegration of the larger particles by viscous drag forces is assumed to be first-order. The equations are integrated numerically for the case of batch settling (such as is used in jar tests), and the dependence of settling characteristics on the parameters of the model is studied.

Electrical Aspects of Adsorbing Colloid Flotation. IV. Stripping Column Operation

Abstract The operation of a continuous flow foam flotation column in the stripping mode is analyzed under steady-state conditions. The effects of diffusive mixing, nonlinear adsorption isotherms, and finite rate of mass transport between the surface and bulk phases are taken into account in the differential equations from which column efficiencies are calculated. Adsorption isotherms are calculated by means of statistical mechanics for systems having coulombic interactions.

Methodology for analyzing environmental quality indicators in a dynamic operating room environment.

HighlightsThis study tests air quality indicators in a dynamic operating room environment.A mock surgical procedure led by a board‐certified surgeon was used to simulate actual conditions in an operating room to provide realistic data.Levels of airborne contaminants in a health care setting can be accurately quantified using this testing protocol.Environmental quality indicators, such as number of particles, microbial contaminant load, air velocity, and temperature, provide insight to the effectiveness of heating, ventilation, and air conditioning systems. Background: Sufficient quantities of quality air and controlled, unidirectional flow are important elements in providing a safe building environment for operating rooms. Methods: To make dynamic assessments of an operating room environment, a validated method of testing the multiple factors influencing the air quality in health care settings needed to be constructed. These include the following: temperature, humidity, particle load, number of microbial contaminants, pressurization, air velocity, and air distribution. The team developed the name environmental quality indicators (EQIs) to describe the overall air quality based on the actual measurements of these properties taken during the mock surgical procedures. These indicators were measured at 3 different hospitals during mock surgical procedures to simulate actual operating room conditions. EQIs included microbial assessments at the operating table and the back instrument table and real‐time analysis of particle counts at 9 different defined locations in the operating suites. Air velocities were measured at the face of the supply diffusers, at the sterile field, at the back table, and at a return grille. Results: The testing protocol provided consistent and comparable measurements of air quality indicators between institutions. At 20 air changes per hour (ACH), and an average temperature of 66.3°F, the median of the microbial contaminants for the 3 operating room sites ranged from 3‐22 colony forming units (CFU)/m3 at the sterile field and 5‐27 CFU/m3 at the back table. At 20 ACH, the median levels of the 0.5‐&mgr;m particles at the 3 sites were 85,079, 85,325, and 912,232 in particles per cubic meter, with a predictable increase in particle load in the non–high‐efficiency particulate air‐filtered operating room site. Using a comparison with cleanroom standards, the microbial and particle counts in all 3 operating rooms were equivalent to International Organization for Standardization classifications 7 and 8 during the mock surgical procedures. Conclusions: The EQI protocol was measurable and repeatable and therefore can be safely used to evaluate air quality within the health care environment to provide guidance for operational practices and regulatory requirements.

Lead levels in fresh water mollusk shells. [Corbicula manillensis]

Abstract The possibility of using the shells of various fresh water mollusks as indicators of lead levels has been investigated. Shells of Corbicula manillensis (Asiatic clam) were found to be reliable and readily available indicators of lead levels. Samples collected at a relatively clean site were found to yield a mean lead concentration of 0.6 ppm with a range of .1 ‐ 1.3 ppm. The sample means from other sites were increased by factors between 2 and 3. Also, the shells from very young (less than one year old) C. manillensis contained unusually high concentrations of lead.

Inter- and intra-laboratory comparison of protocols for the congener-specific analysis of polychlorinated dibenzofurans and polychlorinated dibenzodioxins in residues and sediments

Abstract Based on inter-/intra-laboratory comparisons of protocols for PCDF/PCDD analysis of residues/sediments, a 16 hr Soxhlet extraction with enhanced low resolution GC/MS was selected as a scientifically meritorious and time/cost effective procedure.

Theory of Clarifier Operation. III. Sludge Blanket and Upflow Reactor-Clarifiers

Abstract The operation of three designs of axially symmetric continuous-flow upflow clarifiers is modeled by means of the continuity equations. Class III operation (hindered settling) with flocculating slurries is considered, and the larger particles are permitted to disintegrate under the influence of viscous drag forces by a first-order process. The equations are integrated numerically, and the dependence of clarifier performance on clarifier type and hydraulic loadings is explored. A number of applications to clarifier design are suggested.