Journal of Sustainable Water in the Built Environment

Informal settlements known as colonias in the US often lack access to infrastructure services or receive subpar services. Existing literature has focused on the dilapidated state of the physical infrastructure with less attention paid to how residents interact with their available systems while facing unreliable services. Using a survey carried out in 2018, this study explores the human–infrastructure interactions in residents of a non-border colonia in central Texas. Qualitative content analysis was used to explore how residents interact with their water and wastewater infrastructure within their household. Our study shows that residents’ perceptions of water safety influenced how residents used their household’s water infrastructure. Residents preferred alternative drinking water sources, seeking out bottled water. They also modified their services received via filtering and boiled drinking water from the tap. Importantly, the household income level was significantly associated with how residents interacted with water infrastructure, raising equity and cost issues. Regarding wastewater infrastructure, operational problems with septic tanks were the most pressing problems for residents. Maintenance costs were found to represent a barrier for residents precluding the sustainable operation of septic tanks in the long-term. Understanding how colonia residents respond to infrastructure challenges can enable policymakers to develop more effective and efficient policies for built-environment interventions. These findings should also prompt policymakers to assess state and local institutions’ roles as providers and enforcers of Texas water and environmental quality.

Fecal contamination in stormwater runoff is a leading contributor of waterbody impairment in the US, and green infrastructure (GI) has demonstrated variable performance in its mitigation. Therefore, there is a need for studies that use robust sampling methods to quantify concentration and load reductions as well as evaluate export of fecal contamination with respect to other water quality constituents. The objective of this study was to characterize the performance of various types of GI systems in mitigating fecal contamination [measured as Escherichia coli (EC)] in highway stormwater runoff. This study was conducted at a field site on Lorton Road in Fairfax County, Virginia, where a bioretention, bioswale, compost-amended grass channel and a grass channel were instrumented for 2 years in all seasons for flow-weighted composite sampling and volume monitoring. The bioretention effectively reduced EC concentration and loading from a relatively high inflow concentration [1,120 most probable number (MPN)/100 mL]. The swales, however, consistently increased EC concentration from their relatively low average inflow concentration of $58\mathrm{MPN}/100\mathrm{mL}$ but had no significant impact on mass load. For all GI systems, outflow concentrations were regularly above recreational water quality standards. Regression analyses indicated that average daily temperature, dissolved organic carbon, total dissolved nitrogen, and chloride were significantly correlated with the log-transformed EC concentrations exiting the GI systems. We conclude that EC export is prevalent in varying degrees in the studied GI systems such that the bioretention reduces its presence, whereas the swales often increase its presence. This study provides insight into environmental factors and common stormwater quality constituents that are correlated with the export of fecal contamination from GI.

Abstract

Significant environmental impact can be caused by surface runoff when it transports excessive phosphorus (P) to downstream surface waters. Excessive P can cause uncontrolled aquatic plant growth, low dissolved oxygen, and increased fish mortality. Urban stormwater is composed of both dissolved and particulate P fractions in roughly equal proportions. Many stormwater management controls (SMCs) like biofiltration and bioswales can remove particulate P easily through sedimentation and filtration processes, but dissolved P is much harder to remove. These SMCs also contain compost, which is excellent for removing many other pollutants but can decompose and release P. This laboratory study systematically evaluated dissolved P removal efficiency of 40 different adsorptive materials through jar tests and adsorption isotherm kinetics, column tests that emulate biofiltration systems, and channel tests to emulate bioinfiltration swales. The jar tests yielded 12 materials for further testing using complete adsorption isotherms. Seven of these 12 materials were tested extensively in the column studies. The best materials for enhancing P removal in the columns were activated alumina, alum-based water treatment residuals (WTRs), layered double hydroxyl (LDH), and zero-valent iron (ZVI) aggregate, all exceeding 90% P removal. Based on performance, three were chosen for the channel study: activated alumina, alum-based WTR, and ZVI aggregate. Results showed that lower compost content could reduce P leaching but not eliminate it completely, while biochar mixes were highly variable. Replacing half of the compost with an adsorptive material in a conventional bioretention/bioswale system gave good P removal results. The alum-based WTR is recommended in this study because it ranked excellently for all tests performed, and as a waste material, it can be recycled at a low cost.

Practical Applications

High phosphorus concentrations in the surface waters act as a fertilizer, exacerbating the growth of aquatic plants and algae and harming the ecosystem. One source of phosphorus to surface waters is stormwater runoff from urban lawns and impervious surfaces. Treatment of stormwater using biofiltration media can reduce the problem if the treatment removes the dissolved phosphorus. In this project, 40 different adsorptive materials were tested for phosphorus removal and screened using batch adsorption experiments, column studies, and channel studies. This process identified an outstanding material, i.e., alum sludge, that works excellently and is essentially free. Alum sludge is the residual sludge material from drinking water treatment plants that use alum for turbidity removal. Biofiltration media with the addition of alum sludge can remove phosphorus up to 89%, copper up to 87%, and zinc up to 98%. The sludge also does not leach any aluminum. Globally, millions of tons of alum sludge are produced by water treatment plants daily. The addition of the alum sludge to the traditional biofiltration media is not only a cost-effective way of removing stormwater phosphorus but could also be a way of sustainably recycling huge volumes of water treatment plant residuals.

Abstract

As part of the reconstruction of Interstate-95 in Philadelphia, a series of vegetated stormwater infiltration basins (bioswales) have been installed to manage highway runoff. To assess these bioswales, we used simulated runoff tests (SRTs), where the bioswale is flooded from a fire hydrant to simulate a major storm event. SRT monitoring relies on point measurements of inflow, outflow, and soil moisture to determine the volume of stormwater the bioswale can handle and the time to recovery. To provide better spatial coverage for site assessment, we tested the use of time-lapse electrical resistivity tomography (ERT) during a SRT. Using an onsite geophysical monitoring station, we performed ERT surveys every 4 h before, during, and after the SRT test. Inflow and outflow measurements taken during the SRT found that a majority of the water did not exit the bioswale via the outlet box. The time-lapse inversion results indicated that runoff uniformly spread throughout the basin before infiltrating into the heterogeneous urban soil below. The ERT demonstrated that the underlying native soil contributed to the overall performance of the bioswale, a contribution which was previously assumed to be minimal. Recovery to pretest soil moisture levels took roughly 2–3 days, according to both soil moisture sensors and time-lapse geophysical data. The SRT results were consistent with natural storm events recorded by our geophysical monitoring station, which have been monitored continuously for over a year. Use of ERT during SRTs characterize the pattern of infiltration and recovery rate of the soil beneath a stormwater control. Additionally, the heterogeneous infiltration observed during the SRT suggested that ERT surveys preconstruction may improve future planning of stormwater controls by guiding the location of infiltration measurements.

Practical Applications

To assess green infrastructure performance, we conducted a simulated runoff test by flooding a bioswale designed to accept highway runoff with water from a nearby fire hydrant to simulate a major storm. It is common during simulated runoff tests to monitor soil moisture using buried sensors, but point measurements provide limited spatial coverage. We tested an alternative method for tracking changes in soil moisture, namely time-lapse electrical resistivity, to see whether the continuous spatial coverage provided by resistivity cross sections would improve bioswale performance assessment. Resistivity decreases with increasing soil water content; hence, we saw a significant decrease in resistivity during the test. Our main finding was that water infiltrated past the bioswale fill and into the urban soil below. The bioswale was designed assuming that the urban soil would impede infiltration, but our results showed the bioswale was larger than necessary. We suggest conducting more infiltration tests on the native soil before green infrastructure is constructed because this could lead to smaller, less costly designs. For existing green infrastructure, using time-lapse resistivity imaging during simulated runoff test can provide better spatial coverage within and beneath the fill material than soil sensors alone.

Abstract

Bioretention units were constructed at the US Environmental Protection Agency’s Edison Environmental Center to evaluate drainage-to-surface runoff ratio for sizing of bioretention stormwater controls. Three sizes of hydraulically isolated bioretention units were tested in duplicate with changes in aspect ratio of length from inlet wall by doubling successive length from smallest (3.7 m) to largest (14.9 m) while width remained the same (7.1 m). The watershed areas were nominally the same, resulting in watershed-to-surface area ratios of $5.5:1$ for largest duplicate units, $11:1$ for the middle units, and $22:1$ for the smallest. Each unit was instrumented for continuous monitoring with water content reflectometers (WCRs) and thermistors with data collected since November 2009. The bioretention units were filled with planting media initially comprising 90% sand and 10% sphagnum peat moss by volume and approximately 99% and 1%, respectively, by weight. These units were then planted between May and November of 2010 with a variety of native grasses, perennials, shrubs, and trees that were tolerant to inundation, drought and salt. In late 2012, a survey of the shrubs planted in these bioretention units was performed. The published results of the combined analyses of moisture content, rainfall, and size of shrubs indicated that the smaller units had superior shrub growth due to the more frequent saturation of the root zone as measured by WCR, while the plants in the largest units, particularly away from front wall where runoff entered, potentially relied on direct rainfall only. Starting in 2017, additional monitoring was performed in these units, including chemistry analysis by loss on ignition and total phosphorus of the engineered planting media and an additional survey of the plants. As in the previous study, plants did better in the medium ($11:1$) and small ($22:1$) bioretention units than in the largest units ($5.5:1$), and there was greater buildup of organic matter and phosphorus in the smaller units. One species of grass that dominated the two largest bioretention units away from the inlet was drought tolerant, which indicated that plants in these units relied on rainfall rather than stormwater runoff. Oversized units did not completely use the stromwater control volume, and many of the other original plantings grew slower or were less widespread in comparison to plantings in that smaller units that flooded more frequently and achieved greater growth.

Practical Applications

Defining the size of stormwater controls can be difficult because there are often multiple objectives imposed on the final design of these structures, including safety and flooding. Results presented here would indicate that if the objective is to create a bioretention area with healthy vegetation, undersized controls may be acceptable because undersized infiltrating controls will have healthier plantings and infiltrate throughout the storm. For municipalities, this means that rights of way previously thought to be too small to use for infiltrative stormwater controls may be converted to such a purpose. This does not free municipalities from stormwater systems that address flooding and safety design objectives, but demonstrates that increasing plantings in the municipal right of way could help to address stormwater as well as other objectives, like greenhouse gas emissions, urban heat island reduction, and clean air. Distributed bioretention controls that capture part or all the runoff of the smaller, most frequent rainfall events should be incorporated throughout municipalities and into their overall stormwater control systems. If clogging by runoff is a concern, roof runoff may be more appropriate for bioretention, or other measures such as sediment capture or increased maintenance may need to be performed.

This paper presents an ensemble of methods for determining the variations in the efficiency of a common small curb inlet that directs runoff to green stormwater infrastructure due to changes in longitudinal and crossroad slopes and runoff rate. A physical model of a curb inlet with a lateral curb inlet opening size of 0.46 m was built and its efficiencies were measured. Two computational models, HEC-RAS 6.3 and Ansys Fluent 18.1, were developed and compared with measured data. The measurements showed that an increase in longitudinal slope and runoff rate reduced the curb inlet efficiency, whereas an increase in crossroad slope increased the efficiency. Both computational models captured the variations and trends in curb inlet efficiencies. The HEC-RAS error varied from $-21\%$ to 12% with a mean absolute error of 8.8%, whereas for the Ansys Fluent, the error varied from $-37\%$ to 7% with a mean absolute error of 32%.

To evaluate the effectiveness of dispersed stormwater control measures (SCMs), it is important to consider groundwater–surface water interactions and their consequences for stream hydrologic responses relevant to channel geomorphic stability and ecology. This study aimed to evaluate the effectiveness of different SCM design scenarios and implementation alternatives on exceedance levels and volumes of streamflow at the watershed scale. For this purpose, a process-based block-connector model of Sligo Creek, an urban watershed ($29{\mathrm{km}}^2$) in the suburbs of Washington, DC, was used to study the effects of SCM system design on the stream hydrograph. The watershed has 34% impervious area (IA), which was discretized into 14 similar-sized subwatersheds, each consisting of pervious and impervious surface areas. Each subwatershed was compartmentalized with the representative overland flow, unsaturated flow, groundwater blocks, and links to main channel segments. The model was calibrated and validated to existing conditions using a 3-year time series of observed flow data. Afterward, a predevelopment simulation was configured. Three SCM unit designs and IA diversions through the SCM retrofit system were simulated. The three unit design scenarios represented a simple pond with surface storage and overflow or SCMs that infiltrate with an engineered soil layer and with or without an underdrain pipe. Differences among the model simulations were evaluated using flow exceedance probability curves. The area of the SCM system was modeled as 5% of the IA retrofit. Three implementation levels, including 10%, 50%, and 90% of the IA diverted through SCMs, were considered for each SCM unit design. The results showed that at least a 50% retrofit of runoff from IA watershedwide would be needed to achieve similar predevelopment base flows and peak flows. Intermediate flows could not be matched but were closest for the infiltration with the underdrain pipe design scenario. It was also found that concentrating the SCMs in the lower portion of the watershed resulted in more effectively achieving the predeveloped exceedance curves than uniform SCM implementation. The results are relevant to planning-level decisions that depend on effectiveness predictions of different SCM unit designs and implementation alternatives in developed watersheds.

Rainwater harvesting (RWH) systems have long been used to supply water for a variety of end uses. RWH systems, when used correctly, have proven to be effective at reducing runoff volumes and improving runoff quality at the site and catchment scales. Stormwater runoff from impervious surfaces in urban areas is thermally enriched, causing detrimental impacts to receiving waters. Research has begun to identify stormwater control measures (SCMs) that can offset this thermal loading by reducing total runoff amounts or storing the water in cooler locales. To the authors’ knowledge, no evidence exists in the literature to support whether RWH systems are sources or sinks of thermal pollution or to inform the thermal dynamics within the tanks. Monitoring was undertaken to compare the thermal dynamics of paired above- and below-ground RWH systems from three locations across the eastern United States (Ohio, Virginia-North Carolina, and Florida) over a three-year period. Below-ground RWH systems had lower minimum, mean, and maximum temperatures than their above-ground counterparts. The difference in temperatures between above- and below-ground RWH systems was greatest in late spring and summer months. Water temperatures in the above-ground systems exceeded thermal sensitivity thresholds for regionally important cold-water fish for 0.7%–60.3% of the time. Below-ground tanks exceeded these limits less than 1% of the time; variance in below-ground RWH system water temperatures were $2–3$ fold lower than for their above-ground counterparts. Both RWH system types formed a vertical thermal gradient with a temperature drop of $1.72°\mathrm{C}–5.6°\mathrm{C}$ from the top of the tank to the bottom. This thermal stratification suggests that RWH systems should be designed to overflow from the bottom of the tank in urbanizing watersheds that support cold-water fish species or are otherwise sensitive to spikes in receiving water temperature.

To date, the knowledge benefits that can result from the growing abundance of measured stormwater data have yet to be fully realized within the industry. Obstacles due to data format and storage, retrieval, and quality control have limited the size and impact of accessing known data, resulting in data that are often siloed by project or objective, which inhibits advancements in our understanding, as well as decision making and information sharing across municipalities. Consortium of Universities for the Advancement of Hydrologic Sciences, Inc. (CUAHSI)’s observations data model (ODM) is a relational data model designed to organize disparate types of data; however, it does not provide avenues for the storage of stormwater monitoring–specific metadata. To facilitate stormwater infrastructure data analysis, the Villanova stormwater infrastructure data model (SIDM), constructed comparably to ODM1, was created by adding and removing tables from the ODM1 structure, along with other modifications to enable efficient data access. The novel data model presented here facilitates a comprehensive spatiotemporal analysis specific to stormwater systems to overcome traditional stormwater data siloes and harness the benefits of stormwater data through efficient avenues. The data model structure of the SIDM enables stormwater-specific data to be managed efficiently not only to provide data regarding function and performance but to advance the science around stormwater planning and management, as well as knowledge sharing across researchers, utilities, and municipalities. In this paper, we describe the logic of the design, benefits of the data model, and applications to specific green stormwater infrastructure installations. This has the potential to not only provide novel insight but open the door for applications of modeling advancement in physics-based models and beyond to artificial intelligence, data analysis, and data-informed decision making in the planning, design, operation, and maintenance of stormwater systems.

Abstract

Huff rainfall temporal distributions published in Atlas 14 are contrasted with rainfall distributions with nested intensity-duration-frequency functions that are also derived from Atlas 14, and the role of Huff rainfall distributions in the design of stormwater-management systems is assessed. Results show that Huff distributions generally underestimate average rainfall intensities for shorter-duration time intervals, which makes them not acceptable for designs based on peak runoff rates. In the design of detention basins to control site discharge rates for a given return period, the results show that in many cases conventional detention-basin designs based on nested rainfall distributions will perform inadequately in response to the more realistic Huff rainfall distributions. Overall, the results indicate that Huff rainfall distributions should be incorporated in sizing detention basins to ensure that peak postdevelopment discharges do not exceed peak predevelopment discharges for given design return periods.

Practical Applications

Site development usually results in postdevelopment peak runoff rates exceeding predevelopment peak runoff rates for given return periods. Stormwater-management regulations and/or best professional practice generally require that peak offsite discharges not be increased by development, and onsite detention basins are commonly used to attenuate postdevelopment runoff rates. Analyses to effectuate this outcome are usually based on using synthetic extreme rainfall distributions derived from Atlas 14, while not considering the more realistic Huff rainfall distributions that are also available in Atlas 14. The results of this investigation show that the Huff rainfall distributions should be incorporated in sizing detention basins to ensure that, under realistic circumstances, peak postdevelopment discharges from a site do not exceed peak predevelopment discharges for a given return period.