Remediation of TCE-Contaminated Groundwater in a Sandy Aquifer Using Pulsed Air Sparging: Laboratory and Numerical Studies

The objective of this study was to investigate, through laboratory and numerical investigations, the effectiveness of a pulsed air sparging system for remediation of groundwater contaminated with trichloroethylene (TCE) in a sandy aquifer. In laboratory experiments, air was pulsed into TCE source zone on a daily basis in order to remediate TCE-contaminated groundwater. Most dissolved TCE was removed at the end of experiments although its concentrations fluctuated due to the air pulsing. The measured gaseous phase TCE concentration increased whereas the aqueous phase TCE concentration decreased during air sparging pulses. Experimental data were assessed by using a numerical code STOMP (subsurface transport over multiphases) with some modification based on the TCE dissolution kinetics. The unmeasured residual TCE mass was predicted through numerical simulations. Results show that aqueous concentrations for TCE are still much higher than the maximum contaminant level in spite of successful removal of 95% of residual TCE. It may imply that it would be more appropriate to apply air sparging combined with other remediation technologies such as bioremediation for remediation of TCE-contaminated groundwater.     

Factors Affecting Effectiveness and Efficiency of DNAPL Destruction Using Potassium Permanganate and Catalyzed Hydrogen Peroxide

This paper describes laboratory studies conducted to evaluate the impact of varying environmental conditions (dense nonaqueous phase liquid (DNAPL) type and mass, and properties of the subsurface porous media) and design features (oxidant type and load) on the effectiveness and efficiency of in situ chemical oxidation (ISCO) for destruction of DNAPL contaminants. Porous media in 160?mL zero-headspace reactors were employed to examine the destruction of trichloroethylene and perchloroethylene by the oxidants potassium permanganate and catalyzed hydrogen peroxide. Measures of oxidation effectiveness and efficiency include (1) media demand (mg-oxidant/kg-porous media), (2) oxidant demand (mol-oxidant/mol-DNAPL), (3) reaction rate constants for oxidant and DNAPL depletion (min?1), (4) the percent (%) DNAPL destroyed, and (5) the relative treatment efficiency, i.e., the rate of oxidant depletion versus rate of DNAPL destruction. While an obvious goal of ISCO for DNAPL treatment is high effectiveness (i.e., extensive contaminant destruction), it is also important to focus on oxidation efficiency, or to what extent the oxidant is utilized for contaminant destruction instead of competing side reactions, for improved cost effectiveness and/or treatment times. Results indicate that DNAPL contaminants can be treated both effectively and efficiently under many environmental and design conditions. In some cases, DNAPL treatment was more effective and efficient than dissolved/sorbed phase treatment. In these experiments, permanganate was a more effective oxidant, however catalyzed hydrogen peroxide treated contaminants more efficiently (e.g., less oxidant required per mass contaminant treated). Results also indicate that oxidation treatment goals can be dictated by environmental conditions, and that specific treatment goals can dictate remediation design parameters (e.g., faster contaminant destruction was realized in catalyzed hydrogen peroxide systems, whereas greater contaminant destruction occurred in permanganate systems).     

Estimation of Aquifer Parameters from Pumping Test Data by Genetic Algorithm Optimization Technique

Adequate and reliable estimates of aquifer parameters are of utmost importance for proper management of vital groundwater resources. The pumping (aquifer) test is the standard technique for estimating various hydraulic properties of aquifer systems, viz., transmissivity (T), hydraulic conductivity (K), storage coefficient (S), and leakance (L), for which the graphical method is widely used. In the present study, the efficacy of the genetic algorithm (GA) optimization technique is assessed in estimating aquifer parameters from the time-drawdown pumping test data. Computer codes were developed to optimize various aquifer parameters under different hydrogeologic conditions by using the GA technique. Applicability, adequacy, and robustness of the developed codes were tested using 12 sets of the published and unpublished aquifer test data. The aquifer parameters were also estimated by the graphical method using AquiferTest software, and were compared with those obtained by the GA technique. The GA technique yielded significantly low values of the sum of square errors (SSE) for almost all the datasets under study. The results revealed that the GA technique is an efficient and reliable method for estimating various aquifer parameters, especially in the situation when the graphical matching is poor. Also, it was found that because of its inherent characteristics, GA avoids the subjectivity, long computation time and ill-posedness often associated with conventional optimization techniques. Furthermore, the performance evaluation of the developed GA-based computer codes showed that the fitness value (SSE) of the best point in a population reduces with increasing generation number and population size. The analysis of the sensitivity of the parameters during the performance of GA indicated that a unique set of aquifer parameters was obtained for all three aquifer systems. The GA-based computer programs with interactive windows developed in this study are user-friendly and can serve as a teaching and research tool, which could also be useful for practicing hydrologists and hydrogeologists.     

Chemistry of Modified Fenton’s Reagent (Catalyzed H2O2 Propagations–CHP) for In Situ Soil and Groundwater Remediation

The use of modified Fenton’s reagent, or catalyzed H2O2 propagations (CHP), has become increasingly popular for the in situ and ex situ treatment of surface soils and the in situ remediation of the subsurface. The process is based on the catalyzed decomposition of hydrogen peroxide by soluble iron, iron chelates, or iron minerals to generate the strong oxidant hydroxyl radical as well as other reactive oxygen species. Some of these species function as reductants and nucleophiles and may be responsible for the enhanced treatment of sorbed and nonaqueous phase liquid (NAPL) contaminants that is sometimes observed in the field. This paper serves as a review of the process chemistry of CHP; the goal is to provide researchers and practitioners with fundamental concepts that will aid in applying the CHP process to soil and groundwater contamination. Although the importance of well placement and the method of reagent injection must be considered in CHP remediation, understanding and promoting the most effective process chemistry is essential to successful soil and groundwater remediation.     

Evaluating Ozone as a Remedial Treatment for Removing RDX from Unsaturated Soils

Years of wastewater discharge at the Department of Energy’s Pantex Plant have contaminated the vadose zone and underlying perched aquifer with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Because the vadose zone is acting as a continual source of groundwater contamination, removing RDX from the unsaturated zone is paramount to prevent further contamination. We determined the efficacy of ozone to degrade and mineralize RDX. Solution experiments showed that ozone (27?mg?L?1; 150?mL?min?1) was effective in mineralizing 80% of the RDX (30?mg?RDX?L?1) provided that some Pantex soil was present to buffer the solution pH. Soil columns treated with ozone produced 50% RDX mineralization within 1 day and >80% within 7 day. Experiments designed to evaluate aerobic biodegradation following partial ozonation of a RDX solution showed that ozone-generated RDX products were much more biodegradable than untreated controls in aerobic microcosms (35 versus <0.3% cumulative mineralization). These results support the use of ozone as a remedial treatment for the contaminated vadose zone at the Pantex facility.     

Enhancement of Remediation of NAPL Contaminated Fractured Permeable Formations—Modeling Study

This study has been originated and motivated by a series of discussions, concerning the containment and use of polluted groundwater of a comparatively wide part of the Coastal Plain Aquifer (CPA) in Israel that has been polluted by kerosene [light nonaqueous phase liquid (LNAPL)]. A variety of types of information have indicated that hydraulic barriers should be employed. However, such an operation should be subject to optimize the aquifer remediation, which is also obtained due to the hydraulic barrier operation. The particular part of the CPA is comprised of “fractured permeable formation” namely sandstone interbedded with sandy clay lenses. Therefore, in this study a simplified conceptual model is applied to represent the formation and implement the pump-and-treat remediation procedure, whose major objective is cost effective containment of the polluted area. Three physical measures, aimed at the remediation process enhancement, have been analyzed: (1) changing the pumping-injection discharge, (2) use of surfactant additives (or other types of solubilizing agents), and (3) use of controlled means to increase the aperture size and density of fracture segments. Possibly, an appropriate combination of such means is most feasible and should be determined. However, the present study evaluates the separate possible effects of each one of such measures on major parameters of the remediation process (time and volume of water that should be treated). It is shown that a particular set of parameters can be applied to evaluate the optimal design and adequate combination of such physical measures aimed at remediation enhancement.     

Effects of Groundwater Velocity and Permanganate Concentration on DNAPL Mass Depletion Rates during In Situ Oxidation

In situ chemical oxidation (ISCO) using permanganate has been increasingly applied to deplete mass from dense nonaqueous-phase liquid (DNAPL) source zones. However, uncertainty in the performance of ISCO on DNAPL contaminants is partially attributable to a limited understanding of interactions between the oxidant, subsurface hydrology, and DNAPL mass transfer, resulting in failure to optimize ISCO applications. To investigate these interactions, a factorial design experiment was conducted using one-dimensional flow through tube reactors to determine how groundwater velocity, permanganate concentration, and DNAPL type affected DNAPL mass depletion rates. DNAPL mass depletion rates were found to increase with increasing groundwater velocity, or increasing oxidant concentration. An interaction occurred between the two factors, where high oxidant concentrations had little impact on mass depletion rates at high velocities. High oxidant concentration systems experienced gas generation. Mass depletion rates were fastest at high velocities, but required additional oxidant mass and pore volume addition to achieve complete mass depletion. Lower-velocity systems were more efficient with respect to oxidant mass and pore volume requirements, but mass depletion rates were reduced.     

Remediation of RDX-Contaminated Water Using Alkaline Hydrolysis

The objective of this study was to assess the effectiveness of alkaline hydrolysis as an alternative ex situ technology for remediating groundwater contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Treatment in both batch reactor and continuous stirred tank reactor (CSTR) was investigated. RDX reactivity was strongly dependent on the reaction pH investigated (11–13). The batch system achieved pseudo-first-order RDX reaction rates in the range of (0.8–27.7)×10?3?min?1, corresponding to half-life periods of 17.9?to?0.5?h, respectively. In the CSTR system operated at the initial RDX concentration of 4.5×10?3?mM, 99% RDX removal was achieved with the hydraulic retention time of 2?days and the reaction pH of 11.9. Formate and nitrite were produced as the major hydrolysates in the CSTR system, indicating a simultaneous reaction mechanism involving RDX ring cleavage and elimination of the ring nitrogen. The net OH? demand used only for RDX removal in the CSTR was found to be 1.5, 390, and 130?M OH?/M RDXremoved at pH values of 11.9, 11.5, and 11.0, respectively. A conceptual cost analysis indicated that the expense of alkaline treatment may be comparable to the expense of granular activated carbon treatment for long treatment periods (30?years or more), due to the potentially lower annual operational cost of alkali treatment.     

Genesis and Effects of Particles Produced during In Situ Chemical Oxidation Using Permanganate

A research effort was undertaken to investigate the genesis of particles produced during in situ chemical oxidation (ISCO) of trichloroethene (TCE) with permanganate (MnO4?) and to explore the effects of those particles on system permeability and metal mobility. The experimental approach included characterization of soil and groundwater samples from an ISCO field site, batch experiments with a replicated 25 factorial design, and flow-through column experiments. Analyses of intact soil cores from an ISCO field site revealed that MnO2 solids were present in the subsurface near an injection well for NaMnO4 but at low levels (2.3–2.5 mg/g dry wt media) calculated to fill <1% v/v of the aquifer porosity. Batch tests revealed that the mass of filterable solids (>0.45 μm) produced during chemical oxidation with MnO4? was increased at higher TCE concentrations (54 versus 7 mg/L) and in the presence of ambient silt/clay-sized particles in the groundwater (750 versus 7.5 mg/L). Under otherwise comparable conditions, increasing the MnO4? dose markedly increases the oxidant consumption and also increases the solids production. The oxidant form (NaMnO4 versus KMnO4) or reaction time (15 versus 300 min) had little effect on oxidant consumption or filterable solids production. During MnO4? oxidation of higher levels of TCE in a groundwater with ambient silt/clay particles present, there can be substantial increases in filterable solids generated, which are <1 μm in size and consist of MnO2, commingled with other mineral matter. Conceivably, low volumetric fillings of these solids could cause permeability loss. Flow-through column experiments revealed that permeability loss was possible during ISCO but only under conditions with very high MnO2 solids production. On the positive side, the MnO2 solids produced can increase the sorption potential for metals such as cadmium and can represent a mode of immobilization. This research demonstrated that ISCO with permanganate has the potential to yield system permeability loss under some conditions as well as to affect metal mobility. The magnitude of these effects is related to the subsurface conditions, target organic chemical mass, and permanganate dose and delivery method. The production of solids during ISCO needs to be carefully considered during process design and operation to avoid solids-related performance problems while exploiting potential benefits.     

Hydrodechlorination of Chlorinated Ethanes by Nanoscale Pd/Fe Bimetallic Particles

Chlorinated ethanes are contaminants commonly found in soil and groundwater. The potential of nanoscale bimetallic (Fe/Pd) particles for the hydrodechlorination of seven chlorinated ethanes (C2H6?xClx) was evaluated in batch experiments. Hexachloroethane (HCA) (C2Cl6), pentachloroethane (PCA) (C2HCl5), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA, C2H2Cl4), and 1,1,1,2-tetrachlorethane (1,1,1,2-TeCA, C2H2Cl4) were rapidly hydrodechlorinated (9–28 min half-lives) at a nanoparticle loading of 5 g/L. End products were ethane (61–87%) and ethylene (6–16%). Only one chlorinated intermediate, a corresponding β-elimination product, appeared temporarily during the reactions. Reductive dechlorination of 1,1,1-trichloroethane (1,1,1-TCA, C2H3Cl3) to ethane was completed at a relatively slower rate with half-life at 44.9 min. Little reduction of dichloroethane (C2H4Cl2) was observed within 24 h. The Pd/Fe bimetallic nanoparticles generally exhibit much higher reactivity when compared with conventional micro- and millimeter scale iron powders. The hydrodechlorination reactions are more complete, with a much higher yield of ethane and lower yield of chlorinated byproducts. A kinetic model incorporating a transition state species was proposed. Results from this work suggest that the Pd/Fe bimetallic nanoparticles may represent a treatment alternative for in situ remediation of chlorinated ethanes.     

Field Monitoring of a Permeable Reactive Barrier for Removal of Chlorinated Organics

The application of zero-valent iron (Fe0) in the funnel-and-gate permeable reactive barrier (PRB) installed at the Vapokon site, Denmark, was conducted in 1999 to remediate the groundwater contaminated by chlorinated aliphatic hydrocarbons (CAHs). Over the past 4?years, except in September 2002 and January 2003, about 92.4–97.5% CAH removal could be achieved with the PRB. Although there was a continuous decrease in total alkalinity (90.3%), calcium (81.7%), and sulfate (69.2%) ions in the groundwater crossing the PRB, probably caused by mineral precipitation and resulting in 0.88% porosity loss per year, no noticeable deterioration of the barrier’s performance was observed between March 2000, and August 2003. Instead, climatic variation in the barrier’s performance on CAH dechlorination was examined. The dechlorination rates in the cold season (January 2003 and March 2000) were generally smaller than those in the hot season (August 2003, September 2000, and September 2001). Besides, 1,2-dichloroethane and dichloromethane, which were proven to be not treatable by Fe0, could also be removed with the PRB, thereby suggesting enhancement from Fe0 adsorption or microbial degradation.     

Using Continuum Approach to Quantify the Remediation of Nonaqueous Phase Liquid Contaminated Fractured Permeable Formations

This study addresses the feasibility of using a continuum modeling approach to simulate pump-and-treat remediation of nonaqueous phase liquid (NAPL) contaminated fractured permeable formations. A simplified discrete fracture model, which incorporates permeable blocks with embedded parallel equidistant constant aperture fractures, was used to simulate the NAPL dissolution in an idealized fractured permeable formation. The applicability of this model is defined by the ranges of a dimensionless mobility number and interphase mass transfer coefficient. A continuum based model able to simulate phenomena predicted by the discrete fracture model has also been used. Three dimensionless parameters referring to organic solute advection and dispersion, and the continuum interphase mass transfer coefficient govern the performance of the continuum model. The nonlinear relationships between the discrete fracture and continuum model have been identified and formulated. However, the simplified conceptual models of this study may be inapplicable to many types of fractured formations. Ranges of possible use of the continuum modeling were determined in terms of dimensionless parameters. The discrete fracture and continuum approaches of this study can be useful for the preliminary evaluation of ideas concerning optimization of the remediation of NAPL contaminated fractured permeable formations.     

Chemical Oxygen Demand and the Mechanism of Excess Sludge Reduction in an Oxic-Settling-Anaerobic Activated Sludge Process

A modified activated sludge process, called the oxic-settling-anaerobic (OSA) process, achieved effective reduction in excess sludge production. Its key feature is the insertion of a sludge holding tank in the sludge return circuit to provide an anaerobic sludge zone. Our previous studies suggested that such excess sludge reduction might be associated with an increased sludge decay rate and the effective consumption of organic substrates generated during the retention of the thickened sludge in the sludge holding tank under a low oxidation-reduction potential (ORP) at ?250?mV. To confirm this suggestion, we analyzed the chemical oxygen demand (COD) balance in the sludge holding tank through batch experiments to simulate the sludge concentration, ORP level, and retention time in the sludge holding tank. The COD generated from the sludge reduction in the tank was utilized by organic gas (mainly CH4) production, denitrification, sulfate reduction, and phosphorus release, among which the gas production accounted for 50% of the COD utilization. We confirmed that the mechanism of the excess sludge reduction in the OSA process is through enhancement of the sludge decay rate in the anaerobic sludge zone, which increases the soluble COD level, which in turn is mainly transformed into methane gas and carbon dioxide during denitrification.     

工业废水中化学耗氧量（COD）催化快速法测定研究

研究了采用催化快速法测定工业废水中化学耗氧量（COD）的含量。该方法检出限范围为45～1000mg/L,COD含量与吸光度成线性关系,相对标准偏差为2.5%,该方法适用于监测工业外排废水。     

化学需氧量两种测定方法的比对研究

分别用重铬酸钾法、光电比色法测定水样中的化学需氧量,比较这两种监测方法的监测结果之间的差异性及优劣。结果表明：光电比色法具有简便、快速、试剂用量少、对环境产生的二次污染小等特点。     

Destruction of a Carbon Tetrachloride Dense Nonaqueous Phase Liquid by Modified Fenton’s Reagent

Destruction of a dense nonaqueous phase liquid (DNAPL) by soluble iron (III)-catalyzed and pyrolusite (β-MnO2)-catalyzed Fenton’s reactions (hydrogen peroxide and transition metal catalysts) was investigated using carbon tetrachloride (CT) as a model contaminant. In the system amended with 5 mM soluble iron (III), 24% of the CT DNAPL was destroyed after 3 h while CT dissolution in parallel fill-and-draw systems was minimal, indicating that CT was degraded more rapidly than it dissolved into the aqueous phase. Fenton’s reactions catalyzed by the naturally occurring manganese oxide pyrolusite were even more effective in destroying CT DNAPLs, with 53% degradation after 3 h. Although Fenton’s reactions are characterized by hydroxyl radical generation, carbon tetrachloride is unreactive with hydroxyl radicals; therefore, a transient oxygen species other than hydroxyl radicals formed through Fenton’s propagation reactions was likely responsible for CT destruction. These results demonstrate that Fenton-like reactions in which nonhydroxyl radical species are generated may provide an effective method for the in situ treatment of DNAPLs.     

Evaluation of Granular Surfactant-Modified/Zeolite Zero Valent Iron Pellets As a Reactive Material for Perchloroethylene Reduction

The use of permeable reactive barriers (PRBs) for groundwater remediation is based on two distinct mechanisms: sorption and transformation. With sorption as the main mechanism, contaminants sorb on the PRB materials and are retarded. With transformation as the main mechanism, the contaminants react with the PRB materials and then converted to less toxic or innocuous substances. In this study, we tested surfactant-modified zeolite/zero valent iron (SMZ/ZVI) pellets as a PRB material to retard and degrade perchloroethylene (PCE), utilizing both sorption and transformation processes. Batch PCE kinetic studies showed instantaneous PCE removal from the aqueous phase due to sorption and subsequent removal with time due to reduction. The separation of sorption from reduction can be used to obtain both the PCE distribution coefficient (Kd) and the pseudofirst-order reduction rate constant (μobs) from a single batch experiment. The calculated Kd and μobs values are 3.0 and 0.5?L/kg and 0.14 and 0.05?h?1 for SMZ/ZVI and Z/ZVI pellets, respectively. Column experiments were performed at linear flow velocities of 0.07, 0.14, and 0.20?cm/min. The results were modeled using the one-dimensional advection–dispersion equation with linear sorption and first-order transformation. The Kd values were 2.3±0.4 and 0.5±0.1?L/kg for SMZ/ZVI and Z/ZVI pellets, respectively, in agreement with those of the batch study. The PCE transformation constants varied between 0.077 and 0.199?h?1 for the SMZ/ZVI pellets and between 0.037 and 0.144?h?1 for the Z/ZVI pellets, indicating that an enhanced transformation of PCE occurred with the sorbing SMZ/ZVI pellets. The PCE reduction rates were faster at slower flow rates, indicating that the reduction was not a mass-transfer-limited process.     

Simulation of Metals Total Maximum Daily Loads and Remediation in a Mining-Impacted Stream

Simulation of metals transport was performed to help develop metals total maximum daily loads (TMDLs) and evaluate remediation alternatives in a mountain stream in Montana impacted by hundreds of abandoned hardrock metal mines. These types of watersheds are widespread in Montana and many other areas of the western United States. Impacts from abandoned hardrock or metal mines include loadings of sediment, metals, and other pollutants causing impairment of multiple beneficial uses and exceedances of water quality standards. The United States Environmental Protection Agency (EPA) Water Quality Analysis Simulation Program (WASP) was used to model and evaluate TMDLs for several heavy metals in Tenmile Creek, a mountain stream supplying drinking water to the City of Helena, Mont. The model was calibrated for baseflow conditions and validated using data collected by the EPA and the United States Geological Survey, and used to assess existing metals loadings and losses, including interactions between metals in water and bed sediment, uncertainty, water quality standard exceedances, TMDLs, potential source areas, and required reductions in loadings. During baseflow conditions, adits and point sources contribute significant metals loadings to Tenmile Creek. Exceedances of standards are widespread throughout the stream under both baseflow and higher flow conditions. Adsorption and precipitation onto bed sediments play a primary role in losses from the water column in some areas. Modeling results indicate that some uncertainty exists in the metal partition coefficients associated with sediment, significance of precipitation reactions, and in locations of unidentified sources and losses of metals. TMDLs and loading reductions were calculated based on variations in flow, concentrations, loadings, and standards (which vary with hardness) along the mainstem. In most cases, considerable reductions in loadings are required to achieve TMDLs and water quality standards. Reductions in loadings from point sources, mine waste near watercourses, and streambed sediment can help improve water quality, but alteration of the water supply scheme and increasing baseflow will also be needed.     

Oxygen Demand by a Sediment Bed of Finite Length

A model of sedimentary oxygen demand (SOD) for a sediment bed of finite length is presented. The responses of diffusive oxygen transfer in turbulent flow above the sediment surface and of microbial activity inside the sediment to a developing diffusive boundary layer are modeled numerically. The developing diffusive boundary layer above the sediment/water interface is modeled based on shear velocity and turbulent boundary layer concepts, and dissolved oxygen (DO) uptake inside the sediment is modeled as a function of the microbial growth rate. The model predicts that the diffusive boundary layer above the sediment/water interface thickens in flow direction, and that DO penetration depth into the sediment is practically constant over the length of the sediment bed. The effect of the developing diffusive boundary layer on SOD is minor, except at very low shear/flow velocities (shear velocity U*<0.01?cm/s) and/or high microbial density inside the sediment. The average SOD over the sediment bed therefore varies only slightly with its length. SOD varies somewhat in flow direction, i.e., SOD is largest near the leading edge (x = 0), decreases with distance, and finally, approaches a nearly constant value for fully developed boundary layer. Including microbial activity in the sediment makes the change of SOD in flow direction much smaller than is predicted by a pure vertical diffusive flux model. The diffusive boundary layer is nearly fully developed at a dimensionless distance x+ = 10,000, regardless of microbial activity inside the sediment. Longer sediment beds are required to eliminate the small leading edge effect on any measured average SOD value. SOD depends strongly on the diffusion coefficient of DO inside the sediment bed. This effect becomes more significant as shear/flow velocity is increased. Overall, SOD is found to be controlled principally by shear velocity of the water flowing above the sediment/water interface, microbial activity inside the sediment, and diffusion of DO inside the sediment. The length of the sediment bed is of lesser influence.     

Dissolved Oxygen Demand at the Sediment-Water Interface of a Stream: Near-Bed Turbulence and Pore Water Flow Effects

A microbial dissolved oxygen (DO) uptake model was developed for a stream bed, including the effect of turbulence in the flow over the bed and pore water flow in the porous bed. The fine-grained sediment bed has hydraulic conductivities 0.01 ≤ k ≤ 1??cm/s, i.e., sediment particle diameter 0.006 ≤ ds ≤ 0.06??cm. The pore water flow is driven by pressure fluctuations at the sediment-water interface, mostly attributable to near-bed coherent motions in the turbulent boundary layer above the sediment bed. An effective mass transfer coefficient (De) coupled to a pore water flow model was used in the DO transport and DO uptake model. DO flux across the sediment-water interface and into the sediment, i.e., sedimentary oxygen demand (SOD), was related to hydraulic conductivity and microbial oxygen uptake rate in the sediment and shear velocity at the sediment-water interface. Simulated SOD values were validated against experimental data. For hydraulic conductivities of the sediment bed up to k ≈ 0.01??cm/s, the pore water flow effect on SOD was found negligible. Above this threshold, the effective mass (DO) transfer coefficient in the sediment bed (De) becomes larger as the hydraulic conductivity (k) becomes larger as the interstitial flow velocities increase; consequently, DO penetration depth increases with larger hydraulic conductivity of the sediment bed (k), and SOD increases as well. The enhancement of vertical DO transport into the sediment bed is strongest near the sediment-water interface, and rapidly diminishes with depth into the sediment layer. An increase in shear velocity at the sediment-water interface also enhances DO transfer. Shear velocity increases at the sediment-water interface will raise SOD regardless of the maximum oxidation rate if the hydraulic conductivity is above the threshold of k ≈ 1??cm/s. The relationship is nearly linear when U*<0.8??cm/s. At shear velocity U* = 1.6??cm/s, SOD for oxidation rates μ = 1000 and 2000??mg?l-1?d-1 are almost five times larger than those with no pore water flow. When pore water transport of DO is not limiting, SOD is a linear function of oxygen demand rate μ in the sediment when 0 ≤ μ ≤ 200??mg?l-1?d-1.