Andrea L. Welker

Fines accumulation and distribution in a storm-water rain garden nine years postconstruction.

Storm water control measures (SCMs), also known as best management practices (BMPs), such as rain gardens, are designed to infiltrate storm-water runoff and reduce pollutant transport to surface waters. The life span of these SCMs may be limited depending on the composition of sediments in runoff water. Settling of fine sediments may clog soil pore spaces, reducing the infiltration capacity of the soil and reducing the potential benefits of this SCM. A study was conducted on a Villanova campus rain garden that accepts runoff from an adjacent parking lot to determine if there was a relationship between the accumulation of fine sediments over time and the infiltration capacity. The soil textural profile within the rain garden was characterized prior to SCM installation (2001), after installation, after five years, and after seven years of receiving storm-water runoff. Infiltration data were collected by the single-ring infiltrometer method in 2006 and 2009. Differences in soil texture were found between loc...

Quantifying Evaporation from Pervious Concrete Systems: Methodology and Hydrologic Perspective

AbstractPermeable pavements underlain by infiltration beds have been used as storm-water control measures (SCMs) for several decades. As a design practice, runoff volume reduction in those systems is attributed exclusively to subsurface infiltration. Neglecting evaporation in the hydrologic cycle of permeable pavement systems is based on the perceived insignificance of this factor rather than on scientific evidence. This paper presents research designed to fill the knowledge gap in the evaporation behavior of pervious concrete SCMs. A laboratory simulation was conducted to identify parameters affecting evaporation from pervious concrete systems and to obtain the evaporation rates typical for summer months in the Philadelphia area. Considerations used in the experiment design, methodology, the experimental program, and the results are presented here. The depth to water surface and the time since rainfall event were both found to be significant terms in predicting the evaporation rate. The concept of influe...

Multiyear Performance of a Pervious Concrete Infiltration Basin BMP

The use of infiltration storm-water best management practices (BMPs) has become a more commonly used approach as a means of reducing postdevelopment runoff volumes in many areas throughout the United States. Although studies regarding the performance of infiltration BMPs are emerging, much remains to be learned about their design, construction, and operation. The increase in knowledge will improve the performance and longevity of these BMPs. The performance of one such infiltration basin over a 2-year cycle is presented in this paper. The study site is a pervious concrete infiltration basin BMP built in 2002 in a courtyard common area at Villanova University. The system consists of three linked infiltration beds lined with geotextile filter fabric, filled with coarse aggregate, and overlaid with pervious concrete. The natural soil beneath the infiltration BMP is a silty sand. The BMP is extensively instrumented to facilitate water quantity and quality research. Both water-quantity and -quality results are presented. The water-quantity analysis showed that the performance of the basin was directly related to its infiltration characteristics. The infiltration rate of the silty sand is cyclic, with higher rates during warmer periods and lower rates during colder periods. The water quality analysis investigated the pollutant reduction for chloride, copper, nitrogen, and phosphorus from the inlet to the surface-water outlet of the structure, as well as differences in pollutant concentration levels between the basin, surrounding ground, and varying soil layer elevations beneath the basin. In general, the pollutant reduction to the surface waters was greater than 90% from inlet to outlet, primarily influenced by the infiltration of the storm water into the natural soils below the BMP. The pollutant concentration of the infiltrating runoff was found to be higher than expected in the area adjacent to the bed when compared to concentration levels found at a similar depth beneath the infiltration bed. Comparison of pollutant concentration levels, as the water moved from within the storage bed to the soil beneath the bed, were shown to vary, with statistical differences found for mean concentration levels of both pH and copper levels; and no statistical differences were found for conductivity, total phosphorous, and chloride at each elevation.

Feasibility Study of As-Received and Modified (Dried/Baked) Water Treatment Plant Residuals for Use in Storm-Water Control Measures

AbstractUse of water treatment plant residuals (WTRs) in storm-water control measures (SCMs) is a sustainable alternative to landfill disposal of WTRs. However, research is needed to determine how effective WTR-amended SCMs would be in field-scale applications and what modifications can be implemented to improve performance. The modifications examined in this study were oven-drying (105°C) and baking (1,000°C) of the WTRs. Results showed that both modifications increase the hydraulic conductivity by two orders of magnitude. Dried WTRs showed no loss of phosphate removal potential compared to the as-received WTRs. Baking the WTRs lowered the phosphate removal potential but prevented manganese resuspension. The as-received WTRs, as well as both modifications, removed copper, lead, and zinc from storm-water runoff to below detection. Taken together, these results suggest that amending SCMs with modified WTRs has the potential to enhance the water quality improvement processes of SCMs while maintaining the in...

Application of a Monitoring Plan for Storm-Water Control Measures in the Philadelphia Region

AbstractStorm-water control measures (SCMs), also known as storm-water best management practices (BMPs), are increasingly being used to mitigate the impacts of development and restore the hydrologic cycle. This paper presents a three-tiered monitoring plan that can be used to determine the effectiveness of structural, nonproprietary SCMs in the Northeast United States. The monitoring plan offers three levels of monitoring: high, medium, and low. This 1-2-3 approach is common in environmental monitoring. The monitoring protocol integrates hydrologic, water quality, and ecological factors and recommendations for equipment with the level of monitoring. The monitoring plan is then applied to a rain garden on Villanova University’s campus in Villanova, Pennsylvania, and a cost analysis of the different monitoring levels is provided.

Continuous Modeling of Bioinfiltration Storm-Water Control Measures Using Green and Ampt

AbstractContinuous simulation of storm-water control measures (SCM) requires consideration of the variable environmental and site factors that affect infiltration. This article reviews the theory of the Green and Ampt infiltration model and presents a unit process approach to how it can be applied to a bioinfiltration SCM. The paper discusses how to vary the soil moisture parameters using the soil water characteristic curve, how to modify the Green and Ampt equation for different basin cross-sections, and how to model or bound the infiltration rate when soil media layers are added. Both the standard Green and Ampt parameters and alternative moisture conditions were compared with data from a bioinfiltration SCM; these results confirm that the standard parameter tables often used to select Green and Ampt parameters represent conservative, wet conditions, and that a single value for the parameters will not be able to reproduce the range of infiltration rates observed in the field. When using variable soil mo...

Evapotranspiration in Rain Gardens Using Weighing Lysimeters

AbstractQuantification of evapotranspiration (ET) and infiltration from vegetated stormwater control measures (SCMs), such as rain gardens, is necessary to properly assess their volume reduction po...

Evaluation of Soil Class Proxies for Hydrologic Performance of In Situ Bioinfiltration Systems

AbstractThe hydrologic performance of in situ bioinfiltration systems (bioretention systems with no fill media or underdrain) is quantified and soil classes are evaluated as proxies for design requirements. A one-dimensional (1D) Richard’s equation model of a bioinfiltration system is used in combination with a dataset of soil hydraulic properties to conduct a Monte Carlo analysis of the effect of soil hydraulic properties; the results are summarized both by soil textural class and by hydrologic soil group (HSG), showing that textural class is generally a poor proxy for estimating the infiltration performance of in situ bioinfiltration cells (R2=0.40). Because infiltration measurements are required to estimate the HSG, they are a better proxy for bioinfiltration performance (R2=0.89). It is found that soil proxies do provide certain reliable guidelines: HSG-D soils always require engineered fill media with an underdrain; whereas underdrains are not necessary for sand, loamy sand, HSG-A, and HSG-B native s...

Evapotranspiration and Infiltration in Rain Garden Systems

Quantification of evapotranspiration (ET) and infiltration from vegetated stormwater control measures (SCMs), such as rain gardens, is necessary to properly assess their volume reduction potential. Weighing lysimeters at Villanova University mimic three bioretention rain garden designs and measure water budget parameters to determine how design elements impact ET and infiltration (percolation). The designs compare two soil medias: a loamy sand (72% sand, 12% silt, 1% clay) and sand (96% sand, 4% silt, 0% clay), and different drainage systems: a controlled valve and internal water storage (IWS) outflow. The controlled valve outflow allows a user defined flow rate. The IWS outflow maintains a storage volume within the media. A custom distribution system was built to simulate excess rain delivered to a rain garden during natural storm events. In Pennsylvania, SCMs are often sized to control a multiple (typically 5:1 for rain gardens) of a selected rain event. Trials were performed in April and August 2014 for half open controlled valve configurations. Both loamy sand and sand soils with a controlled valve configuration showed an average ET of 3.1 mm per day for 7 days after simulated 5:1 events. Sand soil with an IWS showed an average of 6.0 mm per day for 7 days after simulated 5:1 events. Simulated storm events produced larger ET rates, on average, than that of a 1:1 ratio. Comparisons of predictive equations show the ASCE Penman-Monteith (uncorrected for water stress or crop type) under-predicting and Hargreaves (corrected for water availability) over-predicting observed ET, but follows the trend of each lysimeter.

Predicting Ecological Effects of Watershed-Wide Rain Garden Implementation Using a Low-Cost Methodology

AbstractStormwater control measures (SCMs) have been employed to mitigate peak flows and pollutants associated with watershed urbanization. Downstream ecological effects caused by the implementation of SCMs are largely unknown, especially at the watershed scale. Knowledge of these effects could help with setting goals for and targeting locations of local restoration efforts. Unfortunately, studies such as these typically require a high level of time and effort for the investigating party, of which resources are often limited. This study proposes a low-cost investigation method for the prediction of ecological effects on the watershed scale with the implementation of rain garden systems by using publicly available data and software. For demonstration purposes, a typical urban watershed was modeled using Storm Water Management Model (SWMM) 5.0. Forty-five models were developed in which the percent impervious area was varied 3 to 80%, and the fraction of rain gardens implemented with respect to the number of...