Evaluation of the effectiveness of green infrastructure on hydrology and water quality in a combined sewer overflow community

https://doi.org/10.1016/j.scitotenv.2019.01.416Get rights and content

Highlights

  • The enhanced model evaluates GI practices effectiveness and their associated cost.

  • Combined implementation of GI practices performed better than individual application.

  • More investments did not necessarily result in significant additional reductions.

  • Similar cost-effectiveness scenarios did not necessarily achieve similar reductions.

Abstract

Evaluation of the effectiveness of green infrastructure (GI) practices on improving site hydrology and water quality and their associated cost could provide valuable information for decision makers when creating development/re-development strategies. In this study, a watershed scale rainfall-runoff model (the Long-Term Hydrologic Impact Analysis - Low Impact Development model, the L-THIA-LID 2.1 model) was enhanced to improve its simulation of urban water management practices including GI practices. The enhanced model (L-THIA-LID 2.2) is capable of: simulating in more detail impervious surfaces including sidewalks, roads, driveways, and parking lots; conducting cost calculations for converting these impervious surfaces to porous pavements; and, selecting suitable areas for bioretention in the study area. The effectiveness of GI practices on improving hydrology and water quality in a combined sewer overflow urban watershed—the Darst Sewershed in the City of Peoria, IL—was examined in eleven simulation scenarios using 8 practices. The total cost and the cost effectiveness for each scenario considering a 20-year practice lifetime were calculated. Results showed: combined implementation of GI practices performed better than applying individual practices alone; adoption levels and combinations of GI practices could potentially reduce runoff volume by 0.2–23.5%, TSS by 0.18–30.8%, TN by 0.2–27.9%, and TP by 0.2 to 28.1%; adding more practices did not necessarily achieve substantial runoff and pollutant reductions based on site characteristics; the most cost-effective scenario out of eleven considered had an associated cost of $9.21 to achieve 1 m3 runoff reduction per year and $119 to achieve 1 kg TSS reduction per year assuming residents' cooperation in implementing GI practices on their properties; adoption of GI practices on all possible areas could potentially achieve the greatest runoff and pollutant reduction, but would not be the most cost-effective option. This enhanced model can be applied to different locations to support assessing the beneficial uses of GI practices.

Introduction

Combined sewer systems are conduits designed to collect and transfer sanitary wastewater (domestic sewage from residential, industrial, and commercial wastewater, plus stormwater) through a single pipe to a wastewater treatment facility (USEPA, 2004). These are typically owned by states or municipalities (USEPA, 2004). Combined sewer systems were the earliest sewer systems built in the U.S. and were first introduced in 1855 (Tibbetts, 2005; USEPA, 2004). During dry weather, a combined sewer system carries all sewage to the wastewater treatment plant. However, during rain or snowmelt periods, the waste water treatment facility may not be able to handle the high flow rate, and, in this case, the combined sewer is designed to overflow directly into surface waters such as a river or lake. If the combined sewer system did not release the excess sewage through the combined sewer overflow (CSO), raw sewage would back up into basements and streets.

CSO and Sanitary Sewer Overflows (SSOs) are threats to human health and the environment, based on U. S. EPA's Report to Congress on Impacts and Control of CSOs and SSOs (USEPA, 2004). According to this report, there are 746 communities with combined sewer systems with 9348 associated CSO outfalls; EPA estimates that about 3.2 billion m3 (850 billion gallons) of untreated wastewater and stormwater are released by CSOs into surface waters each year in the U.S.; combined sewer systems are found in 32 states and primarily in the Northeast and Great Lakes regions. Among those 746 CSO communities, more than half are found in Illinois, Indiana, Ohio, Wisconsin, and Michigan (USEPA, 2008).

Increased precipitation typically results in more surface runoff. A U.S. EPA screening assessment of the potential impact of climate change on CSO in the Great Lakes suggested that projected long-term (2060–2099) changes in precipitation would increase the frequency and volume of overflow discharged to rivers or lakes if CSO mitigation efforts were designed based on historical precipitation data (USEPA, 2008). Urbanization also increases the frequency and volume of urban runoff (Chen, 2018; Chen et al., 2017, Chen et al., 2018; Guan et al., 2016; Li et al., 2019). The urban land area in the United States has expanded substantially in recent decades (USEPA, 2013). Increased urbanization can amplify the impacts of increased precipitation as well as offset the impacts of decreased precipitation (Chen et al., 2018; Wang and Kalin, 2018). DeWalle et al. (2000) estimated the potential effect of climate change and urbanization on mean annual streamflow for 39 urbanizing and 21 nearby rural basins in four regions in the U.S. These authors found that urbanization could significantly offset flow decreases or augment flow increases resulting from climate change.

Strategies that can be used to reduce the negative impacts that urbanization can have on hydrology and water quality typically involve reducing stormwater runoff rates and volumes. Sustainable urban development or re-development solutions include green infrastructure (GI) practices as on-site stormwater management approaches that increase infiltration and storage, delay runoff peaks, reduce runoff rates and volumes, and control the movement of pollutants (Benedict and McMahon, 2012; Gill et al., 2007; Tiwary and Kumar, 2014; Tzoulas et al., 2007). Large-scale GI practices, also known as best management practices (BMPs), include retention ponds and detention basins that are space-intensive and usually collect and treat runoff at drainage outlets (U.S. Environmental Protection Agency (EPA), 1999a, U.S. Environmental Protection Agency (EPA), 2009). Small-scale GI practices, also termed low impact development (LID) practices, include porous pavements, green roofs, and bioretention systems, seek to control the timing and volume of stormwater from impervious surfaces (Di Vittorio and Ahiablame, 2015; PGCo, 1999; USEPA, 2004).

Communities with CSOs are usually located in densely developed areas, where large-scale GI practices are not always suitable. Small scale GI practices or LIDs have shown promise in these areas, increasing the infiltration and storage of stormwater and contributing to inflow control to the sewer systems (USEPA, 2004). Porous pavements, for example, are special types of pavement forming an infiltration system that allows runoff to pass through and filter some pollutants from a site and surrounding areas (USEPA, 1999b). Typically, areas most suitable for porous pavements have high soil permeability and low traffic volume; some common suitable implementation places include street parking lanes, driveways, parking lots, and sidewalks (USEPA, 2004). By using plants and underlying soil to intercept stormwater, green roofs can postpone runoff peaks, and decrease runoff rates and volume (USEPA, 2004). Green roofs can be designed for many areas, including single/multi-family homes, industrial facilities, commercial buildings, and garages; however, factors, such as roof deck load bearing capacity, the roof membrane resistance for the moisture and root penetration, wind shear, roof shape and slope, and hydraulics, must be considered before implementation (USEPA, 2004). Bioretention areas can collect, filter and infiltrate runoff from impervious areas (streets, parking lots, rooftops, etc.) and thus reduce runoff rates and volumes (USEPA, 1999c). They are constructed to imitate natural vegetated areas and can be implemented in new development or be retrofitted into developed areas. Heavily urbanized areas, including street median strips, parking lots, traffic islands, sidewalks, and other impervious areas, are suitable for bioretention (USEPA, 2004).

Representation of GI practices through hydrological models can help to effectively evaluate GI practices performance. Computer-based hydrological models can perform temporal and spatial simulations of the effects of hydrologic processes and management activities on hydrology and water quality (Moriasi et al., 2007). The Long-Term Hydrologic Impact Assessment (L-THIA) model is a user-oriented tool that requires only data on hydrologic soil groups (HSG), land use, and long-term precipitation (typically 30 years or more) to estimate surface runoff changes (Bhaduri et al., 2001; Harbor, 1994; Grove et al., 2001; Tang et al., 2005). The L-THIA-Low Impact Development (L-THIA-LID) model integrates LID design practices into L-THIA and has been successfully used to assess the impacts of BMPs/LID practices on surface hydrology and water quality (Ahiablame et al., 2012, Ahiablame et al., 2013; Engel and Ahiablame, 2011; Hunter et al., 2010; Liu et al., 2015a, Liu et al., 2015b, Liu et al., 2016a, Liu et al., 2016b; Martin et al., 2015; Wright et al., 2016). For example, Ahiablame et al. (2013) simulated six scenarios of porous pavements and rain barrels/cisterns in two highly urbanized watersheds to find their effectiveness in reducing runoff and pollutant loads using the L-THIA-LID model. These authors found reductions ranging from 2% to 12% associated with the implementation of LID scenarios. Liu et al. (2015b) evaluated 12 BMPs/LID practices for their impacts on water quantity and water quality in the Crooked Creek watershed using 16 scenarios and found that the various implementation levels and combinations of BMPs/LID practices reduced runoff volume by 0 to 26.5%, total suspended solids (TSS) by 0.3 to 53.6%, total nitrogen (TN) by 0.3 to 34.2%, and total phosphorus (TP) by 0.3 to 47.4%. The adoption of grass strips in the 25% of the watershed where this practice could be applied was found to be the most cost-efficient scenario (Liu et al., 2015b). Wright et al. (2016) examined the impacts of LID practices on surface runoff using the L-THIA-LID model in four neighborhoods in Lafayette, Indiana and found that 10%–70% runoff volume reductions could be achieved depending on the LID practices and adoption level.

Although numerous modeling studies have been conducted to evaluate the effectiveness of GI practices on water quantity and quality (Eckart et al., 2017; Zhang and Chui, 2018), few studies to date have focused on evaluating the possible impacts of GI practices at watershed scales considering different implementation levels and combinations of GI practices in series. In addition, research related to estimation of associated costs of GI implementation at watershed scales are scarce, despite the fact that cost-benefit analyses are critical for decision making. In this study, we provide a case study of a sewershed - the Darst Sewershed in the City of Peoria, IL - to evaluate the costs and impacts of GI practices on water quantity and quality at a watershed scale. We first enhanced the L-THIA-LID 2.1 model to simulate more detailed impervious surfaces including sidewalks, roads, driveways, and parking lots and to represent the actual suitable area for bioretention in the model. Secondly, the long-term effectiveness of GI practices on hydrology and water quality at the Darst Sewershed was evaluated with the L-THIA-LID 2.2 model (enhanced version) for eleven scenarios with different implementation levels and combinations of GI practices. Finally, we analyzed the total cost, cost effectiveness and performance of each scenario, and identified the most cost-effective scenario.

Section snippets

City of Peoria

The City of Peoria is the largest city on the Illinois River and was the seventh most populated city (population of 115,007) in Illinois as of the 2011 census (U.S. Census Bureau, 2011). Water quality is of great importance since the Illinois River has rich economic, social and cultural connections with the City of Peoria. The City has maintained a system of combined sewers and overflows for >100 years, and with the developing economy, increasing urbanization, and increasing population, the CSO

Model background

The L-THIA-LID 2.1 model (Liu et al., 2015b) is designed to evaluate BMP and LID perfomance at the watershed scales (Liu et al., 2015b; Liu et al., 2016a; Liu et al., 2016b). The input data needed include long-term daily precipitation (typically 30 years or more), HSG, and land use types, consistent with other versions of L-THIA and L-THIA-LID models (Harbor, 1994; Engel et al., 2003; Ahiablame et al., 2012; Liu et al., 2015a). A total of 12 B.P. or LIDs are represented in this model, including

Pilot test of the L-THIA-LID 2.2 model

A pilot test was conducted for porous sidewalks and porous parking lots in a single HRU in a densely developed sewershed (Fulton sewershed) in the City of Peoria. Land use in this sewershed is solely commercial and the land cover consists of building roofs (50%), roads (15%), sidewalks (7%), parking lots (19%), and vegetation (9%). The purpose of this pilot study was to test the L-THIA-LID 2.2 model before applying it to much larger areas. The model set up is detailed in Section 4.3. Four

Suitable locations for implementing GI practices in the Darst sewershed

Based on the site suitability criteria (Table 1), suitable locations for GI practices in the Darst Sewershed are as shown in Fig. 2. Areas that were not suitable for GI practices covered 437 ha (light yellow in Fig. 2), which accounted for 69% of the total study area. The rain barrels/cisterns could be applied to eligible roof tops in the residential areas covering a total area of 75 ha, as shown in dark green (Fig. 2). These accounted for 12% of the total area in the Darst Sewershed. Green

Conclusions

This work enhanced the L-THIA-LID 2.1 model to: simulate impervious surfaces including sidewalks, roads, driveways, and parking lots in greater detail; conduct cost calculations for these more detailed impervious surfaces; and consider the actual suitable areas for bioretention in the model. The effectiveness of eight GI practices - including rain barrels/cisterns, bioretention, green roofs, green roofs plus rain barrels/cisterns, porous roads, porous parking lots, porous sidewalks, and porous

Acknowledgements

Special thanks to Peoria County IT Services-GIS Division for providing GIS data, Jane Gerdes for providing documents regarding the Peoria CSO Long-Term Control Plan, and Katy Shackelford for arranging a tour of the City of Peoria. This research was funded by USDA National Institute of Food and Agriculture (Project No. IND010639R).

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