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An analytical model was developed for estimating the distribution and recovery of light nonaqueous phase liquids (LNAPL) in heterogeneous aquifers. Various scenarios of LNAPL recovery may be simulated using LDRM for LNAPL recovery systems such as skimmer wells, water-enhanced wells, air-enhanced wells, and trenches from heterogeneous aquifers. LDRM uses multiple horizontal soil layers to model a heterogeneous aquifer. Up to three soil layers may be configured with unique soil properties for each layer. Simulation results suggest that LNAPL distribution and its recovery volume are highly affected by soil properties. In sandy soils LNAPL can be highly mobile and the recovery efficiency can be high. In contrast, even at high LNAPL saturations, LNAPL mobility is typically low in fine-grained soils. This characteristic of LNAPL with respect to soil texture has to be carefully accounted for in the model to better predict the recovery of LNAPL from heterogeneous soils. The impact of vertical hydraulic gradient in fine grain zone was assessed. A sensitivity analysis suggests that the formation LNAPL volume can be significantly affected by a downward vertical hydraulic gradient if the magnitude is near a critical amount (= ρ r − 1). Sensitivity of input parameters with respect to LNAPL formation in soils and LNAPL recovery volume were identified through a sensitivity analysis. The performance of LDRM on predicting the distribution and recovery of LNAP was reasonably accurate for a short-term analysis as demonstrated in a case study. However, further validation is needed to ascertain the model's performance in long-term simulations.

To evaluate sediment removal in dry detention basins, one of the most frequently used Best Management Practices (BMPs), a particle pathline model using plug flow assumption was proposed in a previous study. The model requires numerical integration, thus it may not be convenient for quick evaluation and design of detention basins. To overcome the difficulty a simpler continuous stirring tank reactor (CSTR) model is proposed and used to compare outflow Suspended Sediment Concentrations (SSCs) from different size storms using a nondimensionalized time scale. The CSTR model satisfactorily predicts sediment removal and outflow SSC measured using a physical model. The paper presents the time nondimensionalization and CSTR model application processes and discusses the critical characteristics of the proposed models.

Porous pavements are gaining popularity in urban settings on highways based on their water quality benefits, noise reduction characteristics, and the reduced splash and spray they yield in wet weather. Over time, porous pavements can become clogged with sediment, resulting in a decrease in porosity and hydraulic conductivity as well as a loss of drainage benefits. This article provides an overview of water quality benefits and methodology for measuring hydraulic conductivity specifically for permeable friction course (PFC). PFC is a layer of porous asphalt ranging from 2.5 to 5.0 cm thick placed as an overlay on conventional impervious roadways. Research studies show a reduction in total suspended solids and total metals in runoff from PFC surfaces compared to runoff from conventional pavements. Monitoring results were mixed for nutrient removal from PFC. Porosity and hydraulic conductivity data collected over multiple years from different roadways in Austin, TX, are presented. The porosity values of PFC specimens ranged from 0.12 to 0.23. The non-linear flow relationship observed during hydraulic testing requires analysis of the Forchheimer equation, as opposed to the typical Darcy9s law. Hydraulic conductivity values ranged from 0.02 to 3.0 cm/s with significant variability. Furthermore, hydraulic modeling of PFC is useful for design purposes and determines when the layer becomes saturated and surface runoff is expected. Flow through PFC is modeled as an unconfined aquifer with an underlying sloping impervious boundary. The use of porous pavements in an urban environment not only improves driving conditions but also helps reduce the adverse impacts of urbanization on surface water and groundwater quality.

Permeable friction course (PFC) is a porous asphalt pavement placed on top of a regular impermeable roadway. Under small rainfall intensities, drainage is contained within the PFC layer; but under higher rainfall intensities, drainage occurs both within and on top of the porous pavement. A computer model—the permeable friction course drainage code (Perfcode)—is developed to study this two-dimensional unsteady drainage process. Given a hyetograph, geometric information regarding the roadway layout, and hydraulic properties of the PFC media, the model predicts the variation of water depth within and on top of the PFC layer through time. The porous layer is treated as an unconfined aquifer using Darcy’s law and the Dupuit-Forchheimer assumptions. Surface flow is modeled using the diffusion wave approximation to the Saint-Venant equations. A mass balance approach is used to couple surface and subsurface phases. Straight and curved roadway geometries are accommodated via a curvilinear grid. The model is valida...

This paper describes a method for incorporating the hydraulics of various bridge rail geometries on a bridge structure to determine the impacts on the surrounding floodplain during extreme flood events. Typical floodplain analysis either does not include the geometry of the bridge rails or simply increases the thickness of the bridge roadway deck to account for the bridge rails. These methods either underpredict or overpredict, respectively, the impact of the bridge rails and do not account for open space in the rails. The use of a previously developed rail rating curve and submergence model can be incorporated in floodplain mapping software such as HEC-RAS. The rail rating curve model can be used to determine the upstream specific energy as a function of the flow rate passing over the rail. Floodplain analysis software typically models flow over bridge structures using the weir equation. Therefore, the weir coefficient is altered such that the weir equation and rail rating curve model result in the same upstream specific energy. This method results in an iterative approach for incorporating the hydraulics of various bridge railing systems into floodplain analysis software. The method is outlined and a simple single bridge example is provided.

On a curved section of highway, the cross slope of the road is often designed to be superelevated to balance the centrifugal force and gravity applied on vehicles. The accumulation of storm-water runoff (sheet flow) near superelevation transitions may significantly increase due to the extended flow path and converging flow lines. A two-dimensional finite-volume-based diffusion wave model is developed to simulate the sheet flow on these geometrically complex surfaces. Both Dirichlet- and Neumann-type boundary conditions are developed for open boundaries based on kinematic wave theory. Results show that the distribution of sheet flow is closely related to the cross slope, longitudinal slope, rainfall intensity, and the width of the road. The analysis of sheet flow characteristics on superelevation transition areas suggests that the optimal longitudinal slope in the range of 0.3–0.4% minimizes the depth of storm-water runoff on the road surface.

Treatment of storm-water runoff may be necessary before discharge to surface waters. In urban areas, space constraints limit selection of conventional treatment systems, and alternative systems are needed. This research program involves design and laboratory testing of a small footprint nonproprietary detention basin which consists of pipes and box culvert sections with a specialized inlet and outlet system. This system can be placed below grade near the roadway section as part of the conventional drainage system and does not require additional right-of-way. A mathematical model, based entirely on hydraulic principles, is developed to estimate particle removal efficiency of the rectangular detention basin for the treatment of storm-water runoff by extending ideal horizontal tank theory under the condition in which water level is varied. A physical model was built in 1/5 scale to measure particle removal performance and validates the conceptual model. Experiments were performed for steady inflow conditions with different inflow rates, durations, and suspended sediment concentrations. Measured time series outflow suspended sediment concentrations and particle removal efficiency compare well with calculated results from the conceptual model. The outflow particle-size distribution can also be estimated using the conceptual model.

This paper presents results from an extensive experimental study of sheet flow on rough impervious surfaces that are used to represent highway pavement. Experiments were performed on three surfaces under no-rainfall and simulated rainfall conditions, and with slopes of 1, 2, and 3%. Measurements include flow depth and unit discharge. Turbulent boundary layer theory for a rough surface is used to describe the depth-discharge relationship, resulting in a model with a single parameter directly related to the surface roughness. Comparisons are made with Manning’s equation, and the variability of the Manning coefficient is assessed. Hydraulic effects of rainfall are generally found to be small compared to other factors.

This paper describes a three-parameter model used for determining the hydraulic performance of bridge rails during extreme flood events as well as two submergence models. Typically the geometry of the bridge rails is not considered when conducting floodplain analysis. The use of certain bridge rails with large height or minimal open space may adversely impact the surrounding floodplain. Therefore, a mathematical model used to characterize the hydraulic performance of bridge rails has been developed in order to understand how different bridge rail systems may impact a floodplain. Physical modeling experiments are conducted in order to determine rating curves for various rail geometries that describe the upstream specific energy as a function of the flow rate passing over the rail. In addition, the effects of the submergence of bridge rails by an increase in downstream water surface elevation are also evaluated, as well as the submergence effects of two bridge rails in series. Two different mathematical models are used to approximate and characterize the effects of rail submergence.

This paper presents a versatile two-parameter model describing the hydraulic performance of highway culverts operating under inlet control for both unsubmerged and submerged conditions. Applications show that the model can accurately represent the Federal Highway Administration (FHwA) performance curves (which use four parameters) for a range of culvert types and materials. Laboratory data from an investigation of the hydraulic performance of single- and multiple-barrel low-headwater box culverts are also used, and the resulting model predicts a smaller culvert size as compared with the FHwA equations for a given design discharge. Design recommendations are presented for low-headwater box culverts.

In the last two decades there has been an increased awareness of the contamination of groundwater due to the presence of denser-than-water nonaqueous phase liquids (DNAPLs). Numerous theoretical, experimental and numerical investigations have been conducted to study the various processes that impact aquifer contamination. These studies have provided us with greater insight into the individual processes and the complex nature of the problem. In spite of this progress, there still exists a need within the environmental community for a simple tool that will allow us to analyze a DNAPL contamination scenario from free-product release to transport of soluble constituents to downgradient receptor wells. Such a model may be useful in source term characterization for DNAPL releases to groundwater. The objective of this manuscript is to present the conceptual model and formulate the equations and modules which are utilized in this screening model. Three hypothetical releases are simulated and the results discussed to demonstrate the application and usefulness of this model. Due to its simplicity and ease of use, this screening model will be useful to industry, regulatory agencies and educators for estimating the impact of a DNAPL release on an aquifer.

Accidental release of petroleum hydrocarbons to the subsurface may occur through spills around refineries, leaking pipelines, storage tanks, or other sources. If the spill is large, the hydrocarbon liquids may eventually reach a water table and spread laterally in a pancake-like lens. Hydrocarbons that exist as a separate phase are termed light nonaqueous phase liquids (LNAPLs). The portion of the LNAPL that is mobile, not entrapped as residual saturation, is termed “free product.” This paper presents new analytical solutions for the design of long-term free-product recovery from aquifers with skimmer, single- and dual-pump wells. The solutions are for steady-state flow, based on the assumption of vertical equilibrium, and include the effect of coning of LNAPL, air, and water on flow. The solutions are valid for soils of large hydraulic conductivity where the effect of capillary pressure on coning is small. The results show how to estimate the maximum rate of inflow of LNAPL for skimmer wells, i.e., wells in which LNAPL is recovered with little or no water production. The paper also shows how to calculate the increase in LNAPL recovery when water is pumped by single- or dual-pump wells. A simple equation is given that can be used to adjust the water rate to avoid smearing of the LNAPL below the water table.

The dilution attenuation factor (DAF) is a quantity used to relate the concentration of leachate leaving a source zone (e.g., landfill, impoundment, or contaminated soils) to its impact on down-gradient ground water quality. The DAF is of importance because it plays a key role in U.S. Environmental Protection Agency (EPA)'s methodologies for developing soil cleanup goals and for managing hazardous wastes. In this work, a simplistic graphically-based approach for determining site-specific and generic DAFs was developed. In this case the DAF is based on time-and vertically-averaged concentrations along the plume centerline, and the mathematical framework employs well-known analytical and semianalytical solutions for dissolved contaminant transport. Finite sources with a range of decay characteristics are allowed for. One unique feature of this work is that the graphical approach allows for varying levels of sitespecificity, and thus can be used when one has a little, or a lot, of site-specific information. The graphs visually indicate the sensitivity to various parameters, which is valuable information not easily gleaned from most numerical software simulators. This approach is, however, not applicable to very complex hydrogeologic settings (e.g., fractured geology), or to ground water flows that cannot be reasonably approximated as one-dimensional.

Recovery wells remain the principle technology for removal of free-product hydrocarbon liquids from the subsurface. This paper presents simple models for estimating hydrocarbon recovery rates using wells and vacuum-enhanced systems. Use of LNAPL volume balance between LNAPL recovery rate and formation free-product volume leads to development of algebraic equations that can be used to estimate recovery times. Selection of model parameters is discussed, model comparisons are made, and applications are presented for design and analysis of recovery systems using wells. Model validation is also discussed.

Forced-gradient groundwater tracer tests may be conducted using a variety of hydraulic schemes, so it is useful to have simple semi-analytic models available that can examine various injection/withdrawal scenarios. Models for radially convergent tracer tests are formulated here as transfer functions, which allow complex tracer test designs to be simulated by a series of simple mathematical expressions. These mathematical expressions are given in Laplace space, so that transfer functions may be placed in series by simple multiplication. Predicted breakthrough is found by numerically inverting the composite transfer function to the time-domain, using traditional computer programs or commercial mathematical software. Transport is assumed to be dictated by a radially convergent or uniform flow field, and is based upon an exact first-passage-time solution of the backward Fokker–Planck equation. These methods are demonstrated by simulating a weak-dipole tracer test conducted in a fractured granite formation, where mixing in the injection borehole is non-ideal.

Vegetative storm water controls include grassed swales and vegetated filter strips. The effectiveness of these controls for removing pollutants found in runoff from highways and other urban areas has not been demonstrated to the satisfaction of regulatory agencies; therefore, these technologies have been limited to applications as pretreatment devices for other structural runoff controls. Many highways in Texas and other areas discharge storm water to grassy medians and shoulder areas, which act as both filter strips and grassed swales. The runoff flows overland down the sides of the median as in a filter strip and then parallel to the highway as in a grassed swale. This study investigated the capability of vegetated highway medians for treating storm water runoff in the Austin, Tex. area. Two medians on major highways were monitored to document pollutant removal efficiencies. The medians were designed solely for storm water conveyance and differed in slope and vegetation type. In addition, the highways a...

This paper investigates a number of methods that can be used to generate constituent concentrations for use in stormwater modeling. These include the use of event mean concentrations (EMCs) and pollutant buildup and washoff formulations. Suspended solids data collected in the Austin, Texas, area from single-land-use watersheds were used to evaluate the usefulness of these methods. Use of a single EMC for all urban land uses was shown to provide a reasonable estimate of solids loads. This suggests that increases in total suspended solids loads resulting from development will be primarily a function of the increase in runoff volume, which in turn may be related to increased impervious cover. Water quality data did not indicate a strong correlation between initial pollutant load on the watershed and length of the antecedent dry period; however, the concentration of suspended solids in stormwater runoff does follow a simple washoff model.

Storm-water data collected from an expressway in the Austin, Tex. area were used to develop regression models for predicting loads for a number of constituents commonly found in highway runoff. The goal of the model development was to identify the processes that affect the quality of highway runoff. Linear regression was selected as the most appropriate technique for analyzing the data because of its ability to identify constituent specific causal variables. The regression equations indicate that the majority of variations observed in highway storm-water loading can be explained by causal variables measured during the rainstorm event, the antecedent dry period, and the previous rainstorm event. Loads for each of the constituents were dependent upon a unique subset of the identified variables, indicating that processes responsible for the generation, accumulation, and washoff of storm-water pollutants are constituent specific. Loads of some constituents, such as total suspended solids, were dependent on th...

The performance of geotextiles for sediment control was evaluated in the field and laboratory. Runoff samples collected in the field indicated that essentially no sediment removal was attributable to filtration by the fabric. Silt fences also had little influence on the turbidity of the discharged runoff. Total suspended solids removals of 68 to 90% were found in flume tests in which silt fences were installed. The removal efficiency was correlated with the average detention time of the impounded runoff behind the fence. Flow rates through the fences under field conditions were two orders of magnitude less than would be calculated using standard ASTM index characteristics of the fabrics. This discrepancy resulted from clogging of the fabric with sediment and from the turbulent flow through the fabric openings at the hydraulic heads on the fabrics when used as silt fences. The Center for Research in Water Resources, The Center for Research in Water Resources, The University of Texas at Austin.

Water quality of highway runoff in the Austin, Texas, area was determined by monitoring runoff at three locations on the MoPac Expressway. Daily traffic volumes, surrounding land uses, and highway drainage system types were different at each site. The concentrations of constituents in runoff at all sites were similar to median values compiled in a nationwide study of highway runoff quality. A grassy swale at one site was effective in reducing the concentrations of most constituents in runoff. The lower runoff coefficient at this site is attributable to infiltration of runoff into the grassy swale. The pollutant loads discharged from the pipe draining the swale were lower than those observed at the sites where runoff drained directly from the pavement. A first flush effect (i.e., higher pollutant concentrations at the beginning of an event) was evident during selected events, but was generally limited to a small volume. The overall effect was negligible when all monitored events were considered.

This paper describes the hydrologic system associated with the Barton Springs portion of the Edwards aquifer and presents a lumped parameter model capable of reproducing general historical trends for measured water levels and spring discharge. Recharge to the aquifer was calculated based on flow loss studies of the creeks crossing the recharge zone and on estimates of the rate of diffuse infiltration of rainfall. Flow measurements on each creek above and below the recharge zone were used to develop a relationship between flow above the recharge zone and the rate of recharge. The five-cell groundwater model, each cell corresponding to one of the watersheds of the five main creeks crossing the recharge zone, was developed to support the management objectives of the City of Austin. The model differs from previous models in that the aquifer properties within cells are allowed to vary vertically. Each cell was treated as a tank with an apparent area and the water level of a single well in each cell was used to characterize the conditions in that cell. The simple representation of the hydrologic system produced results comparable to traditional groundwater models with fewer data requirements and calibration parameters. ©1997 Elsevier Science B.V.

Free-product hydrocarbon which floats on the water table may be recovered using single-pump and dual-pump systems. The factors that affect the long-term free-product recovery using dual-pump systems include the free-product thickness as measured in monitoring wells, the ground-water pumping rate, hydrocarbon density and viscosity, and the soil permeability. This paper presents a simple model for prediction of free-product recovery using dual-pump systems. The model predicts the long-term rather than short-term recovery rates, and lends itself to spreadsheet calculations on microcomputers. A particularly simple form arises for cases where the drawdown is small. An application for estimating recovery from a dual-pump system is presented, and limitations of the model are summarized.

This paper presents results from an extensive experimental study on hydraulic performance of new rectangular bridge deck drains developed by the Texas Department of Transportation (TxDOT) Bridge Division. It fits between the deck reinforcement with the top of the drain flush with the bridge surface and does not interfere with the structural connection of the bridge rail to the deck. Experiments have been performed by varying drain sizes, the number of open drains in series, approach discharges, cross slopes and longitudinal slopes. Measurements include a series of approach gutter flow depth and ponding width at different stations along the deck, and weir heights for capture and bypass discharges. An accurate prediction model has been developed for the captured discharge. The model reveals that the capture discharge is a function of the drain size, the number of open drains, the Manning’s roughness coefficient, the depth of approach flow, the longitudinal slope, and the cross slope. The rating curve for each individual drain in series is the same when the drain size is 10 cm by 20 cm; however, it decreases slightly along the flow direction when the drain size is 15 cm by 20 cm.

[1] This paper presents analytical solutions for the problem of steady one-dimensional Forchheimer flow in an unconfined layer. The study's motivation is the drainage behavior of a highway pavement called permeable friction course. Permeable friction course is a layer of porous asphalt placed on top of impermeable pavement. Porous overlays are growing in popularity because they reduce noise, mitigate the hazards of wet weather driving, and produce cleaner runoff. Several of these benefits occur because water drains within the pavement rather than on the road surface. Drainage from the friction course is essentially that of an unconfined aquifer and has been successfully modeled using Darcy's law and the Dupuit-Forchheimer assumptions. Under certain cases, drainage may occur outside of the range where Darcy's law applies. The purpose of this paper is to identify cases where the assumption of Darcy flow is violated, develop analytical solutions based on Forchheimer's equation, and compare the solutions with those obtained for the Darcy case. The principle assumptions used in this analysis are that the relationship between hydraulic gradient and specific discharge is quadratic in nature (Forchheimer's equation) and that the Dupuit-Forchheimer assumptions apply. Comparing the Darcy and Forchheimer solutions leads to a new criterion for assessing the applicability of Darcy's law termed the discharge ratio.

Linear sorption coefficients and first-order biotransformation rates for para-dichlorobenzene (pDCB) and naphthalene are fit to data from a three-well forced-gradient (injection-production) field test performed at the site of an abandoned creosoting facility in Conroe, Texas. The breakthrough curve of an injected inert tracer, chloride, is used to describe the hydraulics of the field test. Along each streamline, the movement of a reactive solute is described by a one-dimensional transport equation. The hydraulic and streamline transport models are coupled through a combination integral, the evaluation of which yields the effluent concentration (at the production well) of that reactive solute as a function of time. Transport parameters for the field site, sorption coefficients and biotransformation rates for pDCB and naphthalene, are obtained through inverse analysis of effluent data obtained at one of the production wells. The method is formulated such that no formal treatment of dispersion is required.

An analytic approach is developed for quantifying the distribution of fluid passage times in a heterogeneous porous medium. The basic methodology employed utilizes a diffusion theory description for the displacement of a purely advected fluid subject to a random field of hydraulic conductivity. Within this framework, a governing model is formed using the backward form of the statistical Kolmogorov equation, which yields the inverse Gaussian distribution as a solution to the fluid passage time problem. In proposing the methodology, a rationale is presented for quantifying the associated model parameters using a simple appli- cation of the mean and variance to Darcy's law, with subsequent comparisons being made to previous results obtained for perturbation solutions of the associated stochastic partial differential equations. In addition, the validity of the model is discussed within the bounds of a Markovian description for ground-water flow under a continuum-based modeling framework. Here, it is argued that acceptably accurate results may be achieved for a statistical Peclet number in excess of 70.

In this paper, a screening model for flow of a nonaqueous phase liquid (NAPL) and associated chemical transport in the vadose zone is developed. The model is based on kinematic approximation of the governing equations for both the NAPL and a partitionable chemical constituent. The resulting governing equation is a first-order, quasi-linear hyperbolic equation to which the generalized method of characteristics can be applied. This approach generally neglects the contribution to the NAPL flux from capillary pressure gradients. During infiltration under ponded conditions, or when the NAPL flux exceeds the maximum effective conductivity of the soil, the effect of capillary suction is included in the model through the usage of the Green-Ampt model. All of the resulting model equations are in the form of ordinary differential equations which are solved numerically by a variable time step Runge-Kutta technique. Results from a simple column experiment were used to evaluate the vadose zone flow model assumptions. Independently measured parameters allow simulation without calibration of the model results. The match of the model to the data suggests that the model captures the qualitative behavior of the experimental system and is capable of an acceptable degree of quantitative agreement.

Permeable Friction Course (PFC) is a layer of porous asphalt approximately 50 mm thick placed as an overlay on conventional impervious roadway surfaces. The use of PFC improves driver safety due to reduced splash/spray, improved visibility, and decrease in hydroplaning during rainfall events. In addition, PFC improves the stormwater runoff quality from the roadway and has recently been approved as a new stormwater best management practice (BMP) in the State of Texas. However, over time the pore space in the PFC can become clogged with trapped sediment, suggesting a decrease in driver safety and water quality benefits. Therefore, to ensure proper utilization of these benefits, accurate measurement of the drainage properties of PFC is required. In particular, measurement of the hydraulic conductivity is used to determine whether the drainage benefits of PFC are expected to persist. This paper discusses methods for measuring the porosity of core specimens and hydraulic conductivity under non-Darcy flow behavior characterized by the Forchheimer equation. Laboratory and field experimental results of four years of data (2007 to 2010) for three roadways around Austin, TX are presented. The accurate measurement of in-situ hydraulic conductivity using a new nondestructive field test is essential to maintain proper drainage of the PFC layer and to determine when the pore space has become clogged with sediment. In addition, an overview of numerical modeling results of nonlinear two-dimensional flow through PFC is outlined and results are presented in order to properly determine the hydraulic conductivity. Statistical analysis of porosity data show a decrease in porosity with time suggesting clogging of the pore space. Porosity values range from 12% to 23%. However, there has been no observed statistical decrease in hydraulic conductivity with time, suggesting the driver safety and water quality benefits of the PFC layer have persisted after six years of operation. Hydraulic conductivity values on PFC core specimens range from 0.02 cm/s to nearly 3 cm/s. Furthermore, no maintenance of the PFC layer has been conducted during that time.

A permeable friction course (PFC) is a 50 mm layer of porous asphalt placed on top of conventional, impermeable pavement. This paper describes a multi-year research effort on the water quality and hydraulic aspects of PFC. Water quality monitoring of three field sites near Austin, Texas showed a 90% reduction of total suspended solids (TSS) compared to conventional pavement. Significant reductions were also observed for total copper, total lead and total zinc, though concentrations of dissolved constituents were not significantly different. The hydraulic properties of PFC are of interest to assess the drainage capacity of the pavement and the effects of clogging. The properties investigated in this study were the porosity and the hydraulic conductivity. Porosity was measured from core specimens and found to range from 0.12 to 0.23. Hydraulic conductivity was also measured from core specimens and ranged from 0.1 to 3 cm/s. A new field method for measuring the in-situ hydraulic conductivity of PFC was developed and compared to the laboratory measurements. Predictions of the water depth on PFC roads are needed to assist designers in selecting a pavement thickness and to evaluate the effects of clogging. A Permeable Friction Course Drainage Code (PERFCODE) was developed to make these predictions. Measured porosities and hydraulic conductivities were used as inputs to PERFCODE. Outputs were the variation of water depth through a storm and the runoff hydrograph. The modeled hydrograph is compared to runoff hydrographs obtained by field measurement.

Groundwater quality monitoring network design is defined as the selection of sampling sites and temporal sampling frequency to determine physical, chemical, and biological properties of ground wate...

Characterization of the fate and transport of solutes through the vadose zone requires estimation of average water contents and travel times through the unsaturated profiles. This paper reviews a model for long-term simulation of the soil water content profile for a homogeneous bare soil using physically based parameters. For an arbitrary rainfall record, the model calculates the cumulative infiltration, runoff, evaporation, and recharge components, as well as the time average reduced saturation and its variance as a function of depth. The model is computationally efficient and easily allows long-term simulation for parameter sensitivity investigations.

[1] This paper describes solutions to the hydraulic equations that govern flow in permeable friction courses (PFC). PFC is a layer of porous asphalt approximately 50 mm thick that is placed as an overlay on top of an existing conventional concrete or asphalt road surface to help control splash and hydroplaning, reduce noise, and enhance quality of storm water runoff. The primary objective of this manuscript is to present an analytical system of equations that can be used in design and analysis of PFC systems. The primary assumptions used in this analysis are that the flow can be modeled as one-dimensional, steady state Darcy-type flow and that slopes are sufficiently small so that the Dupuit-Forchheimer assumptions apply. Solutions are derived for cases where storm water drainage is confined to the PFC bed and for conditions where the PFC drainage capacity is exceeded and ponded sheet flow occurs across the pavement surface. The mathematical solutions provide the drainage characteristics (depth and residence time) as a function of rainfall intensity, PFC hydraulic conductivity, pavement slope, and maximum drainage path length.

A comparison is conducted between Monte Carlo simulation and first‐order uncertainty analysis within the framework of an exposure assessment procedure. The modeled scenario consists of contaminated soil located directly above an aquifer and upgradient of a water supply well. For the exposure assessment procedure, the exposure point concentration is predicted by performing Monte Carlo simulation using a one‐dimensional vertical, soil‐water solute‐transport model coupled with a two‐dimensional, horizontal ground‐water fate and transport model. The result is expressed as a probability distribution of the contaminant concentration at the point of human exposure (water supply well). To complete the exposure assessment procedure, the concentration corresponding to a prespecified risk level (usually 5%) is evaluated against the appropriate and/or relevant health‐based standards for the site. First‐order uncertainty analysis is another probabilistic method that under certain circumstances may be applied in place ...

ALEX S. MAYER and S. MAJID HASSANIZADEH. American Geophysical Union (2005). This timely manuscript is Water Resources Monograph 17 in AGU's series of topical contributions to water resources management. It provides an introductory treatment of the subject of nonaqueous phase liquids (petroleum

In situ estimation of parameters in chemical models describing groundwater pollutant transport and fate is considered. During tracer tests, the observed breakthrough of a conservative species yields information characterizing the hydraulic behavior of a multiple-well system. A streamline advective solute transport model incorporating the chemical model of interest is scaled so that it applies to all streamlines in the flow system. The hydraulic and chemical data are coupled through a combination integral which calculates the production well effluent concentration of a reactive tracer as a function of time. This mathematical model is combined with the measured effluent data and a nonlinear estimation procedure to estimate the parameters in the chemical models. The procedure is tested in controlled laboratory experiments. A later paper will present a field application.

When water of one chemical composition is displaced by water of another, there is a change in composition at any point within the flow system which may occur more or less rapidly, depending on both the hydraulics and chemistry of the system. For many applications it is possible to decouple the hydraulic and chemical analyses, and later combine them for prediction of effluent compositions from well fields or concentration histories at observation wells. When an advection-reaction model is used, the displacement problem is described mathematically as a Riemann problem. In this paper the Riemann problem is solved for the ternary exchange system using the method of characteristics. The pattern of composition changes is found to follow the right eigenvector paths in composition space, and the eigenvalues provide composition-dependent retardation functions. The hydraulics is treated fairly generally and allows one to consider steady uniform or nonuniform flow fields or stochastic flow models. Both laboratory and field applictions are presented.