Journal of Irrigation and Drainage Engineering

One aspect of integrated watershed management evaluates the impact of development on the local hydrologic cycle and, in particular, drinking water, wastewater, and storm-water infrastructure. Sustainable storm-water management focuses on selecting storm-water controls based on an understanding of the problems in local receiving waters that result from runoff discharges. For example, long-term problems associated with accumulations of pollutants in water bodies include sedimentation in conveyance systems and receiving waters, nuisance algal growths, inedible fish, undrinkable water, and shifts to less sensitive aquatic organisms. Short-term problems associated with high pollutant concentrations or frequent high flows (event-related) include swimming beach closures, water quality violations, property damage from increased flooding, and habitat destruction. A wide variety of individual storm-water controls usually must be combined to form a comprehensive wet weather management strategy. Unfortunately, combinations of controls are difficult to analyze. This will require new modeling techniques that can effectively evaluate a wide variety of control practices and land uses, while at the same time ensure that the flood-control objectives also are met. The results of these new models and novel techniques used for storm-water control then can be incorporated into an evaluation of the urban water cycle for a specific service area to determine whether storm-water controls can provide additional benefits such as reduction of potable water use and reduction of sanitary sewer overflow events.

This paper explores the performance and relative pollutant removal of several common best management practices (BMPs) using data contained in the International Stormwater BMP Database. These BMPs include retention (wet) ponds, extended detention basins, vegetated swales, and sand filters. Although the database contains numerous studies with varying amounts of detail, this comparison is based on the performance of only those sites with reported basic design characteristics and water quality data (event mean concentrations) so that constituent concentrations can be accurately determined and related to the design of the individual BMP. The use of selected BMPs has a number of advantages. Some of the variability in performance observed for facilities of a specific type can be explained by differences in design and/or watershed characteristics; consequently, the expected performance for a given set of conditions can be predicted more accurately. In addition, the differences in performance among BMP types for a given set of conditions can also be established with a higher degree of certainty. The principle measure for comparing the performance between the selected BMPs is their discharge quality, which was found to be a function of the influent concentrations for many constituents. A comparison of the discharge quality as a function of the concentration in untreated runoff demonstrates substantial differences in performance among these BMPs for many constituents.

Fifty-three years of historical precipitation data were applied to the U.S. Environmental Protection Agency Storm Water Management Model (SWMM) to conduct hydrologic and hydraulic simulations, generating continuous stream flow hydrographs in the receiving stream channels. On-site BMP and regional detention criteria were selected to allow postdevelopment replication of predevelopment peak flow frequency exceedance curves and the critical portions of shear stress duration curves. Instream continuous stage data generated by SWMM were used to examine erosion potential through the use of an erosion potential index. Coarse stream bed material were found to be less sensitive to changes in erosion potential due to urbanization, and extended detention ponds designed for flood control and water quality treatment were effective in reducing erosion potential. These controls were less effective in reducing erosion potential of fine loam bed material, indicating reductions of runoff volumes are required to minimize increases in channel erosion. Findings indicate that regional analysis based on local hydrologic and geomorphic characteristics are necessary to identify appropriate storm-water control requirements.

Microbial indicator organisms make up the greatest number of reported receiving water impairments, resulting in many questions on the fate of indicator bacteria passing through storm-water best management practices (BMPs). Storm-water BMPs are often considered effective tools to mitigate the effects of urbanization on receiving waters. The USEPA’s, Office of Research and Development investigated the processes occurring within two commonly used BMPs, constructed wetlands and retention ponds. This research focused on creating pilot-scale systems to determine the environmental mechanisms that affect effluent indicator bacteria concentrations and to provide better information for the prediction of bacterial indicators for models when developing and meeting total maximum daily loads. Research results indicate water temperature, light, and a combination of other environmental factors influence bacteria indicator concentrations. Results from this research suggest that both constructed wetlands and retention ponds lower microbial concentrations in urban storm-water runoff. Bacteria inactivation generally followed the first-order, ${\mathrm{KC}}^{*}$ model, which includes irreducible or background concentrations of a stressor. Sediment analyses indicate bacteria accumulated in sediments which may maintain background concentrations could be reintroduced into the effluent of these BMPs by turbulent flow causing resuspension or by accumulation through lack of maintenance. First-order models that do not consider irreducible concentrations may underestimate actual bacterial concentrations. The relationship between turbidity and bacteria suggests storm-water management practices that substantially reduce turbidity may also provide the greatest improvement in reducing concentrations of bacteria in storm-water runoff.

This work examines the basic processes and functions behind urban storm-water pollution delivery into surface waters and develops a set of tools that allow the estimation of pollutant load dynamics on receiving waters. In particular, the group of expressions developed in this paper allows the calculation of runoff parameters (volume, discharge rate and pollutant load) on an event average basis for an unregulated catchment. Using Monte Carlo simulation techniques, the runoff pollutant concentration probability distribution (as event averages) are obtained. Merging these runoff statistics with the stream parameters allows the receiving water pollutant concentration characteristics to be obtained as well as the probability of exceeding threshold pollutant concentrations in the mixing zone of a stream. The simulation can be performed with allowance for different levels of complexity with respect to catchment hydrologic representation and pollutant load functions. As a result, the magnitude of influence of urban runoff on a surface water body can be determined, pollutants of concern can be identified, and certain remedial measures recommended.

The Cherry Creek Reservoir in the Denver Metropolitan area is subject to the Cherry Creek Reservoir Control Regulation (control regulation), which establishes a total maximum annual load for the reservoir of $\mathrm{6,473}\mathrm{kg}$ $\left(\mathrm{14,270}\mathrm{lb}\right)$ of phosphorus. The load is distributed among phosphorus sources including background, nonpoint, and regulated storm water, municipal and industrial wastewater facilities, individual sewage disposal systems, and industrial sources. As a part of the control regulation, the Cherry Creek Basin Water Quality Authority (CCBWQA) is authorized to implement and maintain a trading program that allows phosphorus trading and the sale of phosphorus (kg/lb) in the Cherry Creek watershed. The trading program allows dischargers seeking new or increased phosphorus waste load allocations to obtain additional kilograms/pounds of phosphorus by constructing nonpoint source projects meeting certain criteria to immobilize phosphorus. This paper provides an overview of the CCBWQA trading program guidelines and describes two Arapahoe County Water and Wastewater Authority (ACWWA) trade credit projects: Lone Tree Creek Pond L-3 and Windmill Creek Pond W-6/W-7. The Pond L-3 and Pond W-6/W-7 projects are unique because they are the first two (and only two to date) projects that have successfully obtained trade ratios and estimated trade credits under the CCBWQA trading program. This paper describes the administrative and technical process for determining trade ratios and estimating trade credits for nonpoint-source-to-point-source phosphorus trades in the Cherry Creek watershed. The process for going from an established trade ratio and estimated trade credits to actual trade credits applied to a point source discharge presents its own set of challenges. Actual trade credits must be demonstrated by monitoring, which can be very expensive. The monitoring results must be reviewed and approved by CCBWQA before trade credits are awarded, and the Colorado Department of Public Health and Environment Water Quality Control Division must amend the facility’s discharge permit before additional phosphorus can be discharged. Therefore, establishing a trade ratio and estimating trade credits for CCBWQA approval of a phosphorus trading project is only the first step in a potentially expensive and time-consuming process for actually discharging additional phosphorus through a nonpoint-source-to-point-source trade in the Cherry Creek watershed.

Reduction of storm-water volumes through infiltration is becoming a commonly applied practice in the effort to mitigate the negative hydrologic impacts commonly associated with land development. The hydrologic impacts generally include increases in both the volume and peak flow rate of runoff along with an associated decrease in groundwater recharge. Infiltration best management practices (BMPs) are the foundation of many low impact development and Green infrastructure practices. As the movement to volume reduction is a relatively recent concept, there remains a lack of detailed long-term monitoring data to support the implementation of storm-water infiltration BMPs. Two storm-water infiltration BMPs on the campus of Villanova University located in Southeastern Pennsylvania have been continuously monitored to determine the long-term and seasonal variation related to the engineered infiltration of storm-water runoff. The analysis of continuous monitoring data indicates that both BMPs show considerable seasonal variation but exhibit no evidence of a systematic decrease in performance to date. The seasonal variation of the BMPs is explained primarily by the temperature dependency of the viscosity of water.

A small storm-water retention pond is primarily designed to reduce the peak rate of surface runoff. From a water quality standpoint, that same pond may be irregular in shape and trap suspended sediment carried by the surface runoff generated upstream of the site. Considering different pond inlet locations, the writer’s numerical model is used to investigate the change in peak concentration of sediment discharge at the pond outlet. It has been found that the various hydraulic conditions can have a significant impact on sediment discharge. Three different cases are presented to show the flexibility of modeling changes in boundary conditions. The results may help designers evaluate sediment discharge to determine the most effective pond inlet locations.

Thirty well-established 240L bioretention mesocosms were used to investigate retention of dissolved nutrients by bioretention systems. Ten mesocosms were comprised of $80\mathrm{cm}$ sandy loam, ten of $80\mathrm{cm}$ loamy sand, and ten of pea gravel with $20\mathrm{cm}$ of loamy sand. Half were vegetated with shrubs/grasses, while the other half had no vegetation (barren). In the first part of our study, the loam and sand mesocosms were dosed with synthetic storm water comprising $0.8\mathrm{mg}{\mathrm{L}}^{-1}$ total phosphorus (TP) and $4.8\mathrm{mg}{\mathrm{L}}^{-1}$ total nitrogen (TN). TP retention in the vegetated loam was 91% compared to 73% in the barren, and TN retention was 81% compared to 41% in the barren loam. TP retention was 86–88% in the sand treatments, while TN retention in the vegetated sand was 64%, compared to 30% in the barren. In the second part of our study, all 30 mesocosms were loaded weekly with $45\mathrm{cm}$ of tertiary effluent with high nutrient loads ( $22.3\mathrm{m}{\mathrm{year}}^{-1}$ hydraulic load at a flow-weighted average of $4.5\mathrm{mg}{\mathrm{L}}^{-1}$ TP and $4.8\mathrm{mg}{\mathrm{L}}^{-1}$ TN, or $\mathrm{1,012}\mathrm{kg}{\mathrm{ha}}^{-1}{\mathrm{year}}^{-1}$ TP and $\mathrm{1,073}\mathrm{kg}{\mathrm{ha}}^{-1}{\mathrm{year}}^{-1}$ TN). After 50 weeks of loading, cumulative TP retention was 92% in the vegetated loam, 67% in the sand, and 44% in the vegetated gravel. However, TP retention by barren media was 56% in the loam, 39% in the sand, and 14% in the gravel. Cumulative TN retention was 76% in the vegetated loam, 51% in the sand, and 40% in the vegetated gravel. In contrast, maximum TN removal by barren media was 18% in the loam. The increase in TP retention by vegetated systems substantially exceeds phosphorus uptake rates for plants, suggesting that other processes are involved. The increase in TN retention by vegetated systems also exceeds nitrogen uptake rates for plants, suggesting that denitrification is involved.

Passive biological filtration for nitrate removal from storm-water drainage is challenged by highly transient mass loadings, the need to adequately supply an electron donor, and potential inhibition by dissolved oxygen (DO). An approach to optimizing nitrate removal is to employ a filter medium containing a mixture of ion exchange and electron donor particles, where the former serve to retain nitrate at high loadings and enable biological denitrification to be more effective. Bench scale filtration experiments were conducted using a 50:50 volume mixture of expanded clay particles (Filtralite P) and elemental sulfur pastille. Nitrate reduction was 98% under steady flowrate operation at $30\min$ residence time and $2.1\mathrm{mg}∕\mathrm{L}$ influent $\mathrm{N}{\mathrm{O}}_3–\mathrm{N}$ . Step increases in flowrate by factors of 5.2, 11, and 25 resulted in maximum effluent $\mathrm{N}{\mathrm{O}}_3–\mathrm{N}$ of 0.93, 1.54, and $1.87\mathrm{mg}∕\mathrm{L}$ , respectively. Substantial nitrate breakthrough occurred even when effluent DO remained close to zero. The results suggest methods by which mixed media denitrification filters can be more effectively designed and operated.

The highway deicing agent groundwater plume from an infiltration basin in the Plymouth-Carver Aquifer near State Route 25 in southeastern Massachusetts is modeled and measured in order to assess the impact of the basin on groundwater transport processes. The advective transport model superimposes the existing steady models of axisymmetric basin hydraulics of Zlotnik and Ledder in 1992 and the two-dimensional ambient flow of Gelhar and Wilson in 1974. The basin component incorporates a surface source of finite-radius into a Hankel transform model for unconfined aquifers, whereas the ambient component varies linearly in the horizontal and vertical directions. Contaminant streamlines describe the resulting groundwater plume, and highway deicing agent constituents provide useful tracers. A simple vertical dispersion model quantifies the spread of contaminants across the bottom of the plume. Deicing agent constituent data calibrate a $17\mathrm{m}$ basin radius, a $45\mathrm{m}$ plume width, a bottom streamline $6–10\mathrm{m}$ below the water table, and a vertical dispersivity of $34\mathrm{cm}$ . The latter value is comparable to the amplitude of vertical excursions caused by storm scale fluctuations of hydraulic head, as measured by Ostendorf et al. in 2007. Infiltration basins alter ambient advection by displacing streamlines downward and augment vertical mixing by imposing aperiodic vertical fluctuations on the ambient flow field.

Development in sensitive watersheds continues to pose environmental problems for receiving waters. One contributor to this long-term pollution is building and other construction materials. However, the long-term effect of many building materials on the environment has not been quantified due to limited testing of these materials prior to sales and installation. Laboratory “leach” testing of commercially available roofing materials by this research group indicated that the potential for release (primarily nutrients, lighter hydrocarbons, pesticides, and metals) is substantial. Testing of metals’ release from aged roofing panels also has shown that the potential for pollutant release still exists after $60\text{years}$ . The data missing from a complete evaluation of many roofing materials is behavior over the lifespan of the material, including the critical period of initial exposure. The $2\text{years}$ of runoff data from a pilot-scale testing of these materials indicated substantial concerns regarding zinc from uncoated galvanized metals and copper from treated woods in this early part of the materials’ lifespan, plus the potential for long-term nutrient releases in the runoff from several roofing types.

This project documents the impact of a porous asphalt overlay on the quality and quantity of highway storm-water runoff. A permeable friction course, also known as open graded friction course, is a layer of porous asphalt approximately $50\mathrm{mm}$ thick, which is often applied on top of conventional asphalt or concrete highways to enhance safety and reduce noise. Storm-water runoff from a four-lane divided highway in the Austin, Texas area was monitored at two sites before and after the installation of a PFC. Observed concentrations of total suspended solids and pollutants associated with particulate material were much lower in the runoff from the PFC than that derived from the conventional asphalt surface. Concentration reductions were observed for total suspended solids, total lead, total copper, and total zinc at both monitoring locations. In addition to the above-mentioned constituents, concentrations of chemical oxygen demand and total Kjeldahl nitrogen were also lower in the runoff from the PFC at a site collecting paired samples from both pavement types. Concentrations of dissolved constituents were not significantly different and concentrations of polycyclic aromatic hydrocarbons were below the detection limit for both pavement types. The runoff coefficient for the PFC appears to be higher than for conventional pavements.

Soil infiltration is a critical component of most urban runoff models. However, it has been well documented that, during urbanization, soils are greatly modified, especially in relation to soil density. Increased soil compaction results in soils that do not behave in a manner predicted by traditional infiltration models. Laboratory and field tests were conducted to investigate detailed infiltration behavior of disturbed urban soils for a variety of soil textures and levels of compaction. The results from traditional permeability tests on several soil groups showed that, as expected, the degree of compaction greatly affected the steady-state infiltration rate. The field tests highlighted the importance of compaction on the infiltration rate of sandy soils, with minimal effect seen from antecedent moisture conditions. For the clayey soils, however, both the compaction level and antecedent moisture conditions were important in determining the steady-state infiltration rate.

This paper presents the Cantabrian portable infiltrometer (CP infiltrometer), a specially designed device based on rainfall simulation for the assessment of the infiltration capacity of all types of urban pavements. Several pervious and impervious surfaces were tested with the LCS permeameter, an existing infiltration test based on the use of a column of water, and the CP Infiltrometer, simulating rain intensities with return periods of 10, 50, and 500 years and $5\min$ duration. The discussion of the results indicates that the CP infiltrometer could be used successfully to identify different levels of infiltration capacity and to assess the correct performance of pervious surfaces on which design, construction, and maintenance decisions are based.

Permeable pavement, specifically cementitious permeable pavement (CPP), is a passive structural low impact development material and green infrastructure system for rainfall-runoff control. Multifunctional engineered CPP can fulfill requirements as a load-transmitting surface while serving as a more environmentally conscious infrastructure material that functions to restore the in situ hydrology while also functioning as a passive treatment unit operation and process. As an infrastructure material; CPP reduces runoff, filters, and treats infiltrating runoff, reduces thermal pollution and temperature, provides the load-carrying capacity of conventional rigid concrete pavement, and leaches environmentally beneficial Ca and alkalinity, as compared to flexible asphalt. In this study, pore characteristics of CPP, including effective porosity $\left({\varphi }_e\right)$ , pore size distribution and tortuosity $\left(\tau \right)$ are examined using x-ray tomography and gravimetric-geometric methods. Total porosity $\left({\varphi }_t\right)$ is measured and utilized as a comparative index. Results provide insight when modeling CPP as an infiltration and evaporation interface, a conveyance/storage medium for liquid and gas, and with admixtures or coatings an adsorptive-filtration medium for pollutants such as phosphorus and metals. Results indicate that high particle separation and significant hydraulic conductivities can be achieved with CPP. The effectiveness of CPP for particle removal also requires that these particle deposits are managed on a periodic basis through practices such as pavement cleaning.

Storm-water management strategies increasingly focus on the implementation of infiltration-based best management practices (BMPs) such as swales, bioretention basins, and rain gardens. The surface vegetation and underlying soil in these BMPs remove a variety of pollutants including heavy metals and nutrients from urban storm-water runoff. The successful attenuation of these storm-water stressors is largely influenced by the physical and chemical properties of the soils used in these systems. Controlled-condition research is being conducted using pilot-scale swales and rain gardens at U.S. EPA’s Urban Watershed Research Facility in Edison, N.J. to evaluate their performance and collect data that would help in understanding the engineering design. The first phase of this research was to evaluate and select the most appropriate soil media for use in infiltration-based BMPs for the efficient removal of heavy metals and nutrients. The objective of this laboratory incubation study was to determine how the acidic pH of an engineered infield soil media could be improved to the target pH range $(5.5–7.0)$ suitable for heavy metals adsorption using dolomitic limestone amendments $\left({\mathrm{CaCO}}_{3.}{\mathrm{MgCO}}_3\right)$ . Lime additions to the acidic infield mix resulted in neutral or slightly basic soil conditions after only $48\mathrm{h}$ of incubation. The soil response to various lime additions appeared to stabilize after more than $100\mathrm{h}$ of incubation. These results could potentially be applied to bioretention facilities to improve the sorption characteristics of the soil media.