Experimental Permeable Pavement Parking Lot and Rain Garden for Stormwater Management

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Permeable Parking Lot Design and Construction
Rain Garden Design and Construction
Publications
- Technical Fact Sheets
- Journal Articles and Reports
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EPA’s Edison Environmental Center in Edison, NJ, needed a 110-vehicle-capacity parking lot for facility staff and visitors. EPA researchers took this opportunity to design a parking area using low impact development (LID) controls and conduct long-term stormwater management studies. They used permeable pavement and rain gardens, two types of LID green infrastructure practices. Scientists and engineers are evaluating the ability of these practices to reduce negative effects of stormwater runoff, including stream bank erosion, contamination of water sources, and harm to aquatic plant and animal life.

The goal is to demonstrate and document the performance and capabilities of three permeable pavement systems: porous asphalt, pervious concrete, and permeable interlocking concrete pavers. Rain gardens were added to capture any runoff from the impervious sections of the parking lot, as well as the sidewalk and nearby roof runoff. The parking lot is monitored for water quality performance; maintenance effects; parking behavior; and hydrologic performance, including the ability to accept, store, infiltrate, and evaporate stormwater.

Permeable Parking Lot Design and Construction

The project removed existing concrete from the nearly 300,000-square-foot parking area and graded the surface, reusing the crushed concrete as a sub-base material. The project installed three types of permeable pavement surfaces and conventional asphalt in a 1-acre parking lot. The design includes 28 parking stalls made of permeable interlocking concrete pavers, 41 parking stalls made of pervious concrete, and 28 parking stalls of porous asphalt. Thirteen conventional asphalt stalls were installed to serve as an experimental control. The 25-foot wide driving lanes have conventional asphalt. Runoff from this area drains onto the permeable pavement surfaces.

For each permeable pavement type, an impermeable liner was installed 16-inches below the permeable pavement surface in four, 15.6-ft by 38-ft sections. This water seeps into to below-grade tanks for collection, measurement, and sampling. This allows the researchers to test each material’s response to a variety of pollutants (e.g., chloride, nutrients, heavy metals, suspended solids, pH, and semi-volatile organic compounds). The collection tanks can capture up to 1.5 inches of water. To identify sources of pollutants, infiltrate samples are compared to rainwater samples and stormwater runoff samples taken from the conventional asphalt spaces that drain into the rain gardens on the southern-end of the parking lot.

Rain Garden Design and Construction

An illustration of a bird's eye view of the laboratory's rain garden design at the Edison lab. — An illustration of a bird's eye view of the laboratory's rain garden design. The rain gardens are represented by the green rectangles. The red arrows represent stormwater runoff.

The schematic diagram details the design of the rain gardens. The rain gardens consist of six separate cells represented by solid green rectangles, which are hydrologically isolated from each other. EPA researchers installed 3/8 inch-thick plastic sheeting to a depth of four feet (represented by yellow lines). The six cells receive stormwater runoff (represented by red arrows) from an impervious section of the parking lot and adjoining sidewalk through curb cuts at the south end of the parking lot. Stormwater runoff from the roof of the adjacent building is collected from multiple downspouts and moved beneath the sidewalk in an 8-inch diameter pipe (represented by a thick dashed blue line). A dedicated 4-inch diameter pipe (represented by thin dashed blue lines) distributes the roof runoff upward into each bio-infiltration unit just south of the curb cuts.

The drainage area to all six cells is roughly equal, about 6,100 square feet. However, because they are different sizes, the cells represent different percentages of their drainage areas. The smallest cells are about 4.5% of their drainage areas, the medium-sized cells 9%, and the largest cells 18%. Each cell size is duplicated for statistical purposes, and both cells of each size are planted with the same plants. All cells are equipped with instrumentation for measuring the occurrence and timing of the stormwater as it infiltrates through the rain gardens during and following storm events. EPA installed small observation wells at different depths in the center of each rain garden to quantify the subsurface accumulation of infiltrating water.

Three years after planting, EPA examined and documented the growth habits of shrubs spatially in relation to the source of runoff water. This research provided a more complete understanding of the effects of rain gardens on plant health.

Publications

Technical Fact Sheets

Journal Articles and Reports

Quantifying Evaporation in a Permeable Pavement System. Green infrastructure (GI) stormwater control measures are often installed to satisfy stormwater regulations requiring water quality treatment and runoff reduction. This research quantifies evaporation for a larger field application by measuring the water balance from lined permeable pavement sections.
Chloride Released from Three Permeable Pavement Surfaces after Winter Salt Application. This study measured chloride present in the infiltrate from the three permeable pavement surfaces and in runoff from conventional asphalt immediately following winter salt application and for the remainder of the year. It compares the attenuation of chloride by the three permeable pavement materials and conventional asphalt.
Evaluation of Surface Infiltration Testing Procedures in Permeable Pavement Systems. This study evaluates surface infiltration rates of the three permeable pavement surfaces during the first three years of use without maintenance. The paper also evaluates the ASTM method (ASTM C1701C) for conducting surface infiltration tests on permeable pavement.
Assessment of Clogging Dynamics in Permeable Pavement Systems with Time Domain Reflectometers. This study used time domain reflectometers (TDRs) to measure spatial infiltration and assess clogging dynamics of permeable pavement systems in Edison, New Jersey, and Louisville, Kentucky.
Novel Use of Time Domain Reflectometry in Infiltration-based Low Impact Development Practices. This study describes initial bench-scale tests to employ time domain reflectometers (TDRs) in the gravel aggregate present beneath permeable pavement. The paper also includes responses measured by the sensors placed in the permeable pavement storage gallery, rain garden media, and underlying native soils during the first six months after installation.
Surface Infiltration Rates of Permeable Surfaces: Six-Month Update (November 2009 through April 2010). This document outlines the methods and results of the surface infiltration monitoring of the permeable parking surfaces during the first six months of operation.

Edison Environmental Center Publications

Rainwater Collection and Management from Roofs at the Edison Environmental Center. This paper discusses the water quality of the roof runoff directed to the rain gardens and the reductions in usage of potable water due to a rainwater capture system. Approximately 3.6 x 106 L (9.0 x 105 gal) of rainwater is being diverted from the existing stormwater sewer system annually.
Evaluation of Surface and Subsurface Processes in Permeable Pavement Infiltration Trenches. As infiltration and exfiltration are the primary functional mechanisms for green infrastructure (GI) stormwater control measures (SCMs), the objective of this study was to evaluate placement of pressure transducers in 2.47-m (8.1-ft) wide permeable pavement strips and develop data analysis techniques to determine when there is a significant change in hydrologic performance to signal a need for maintenance or replacement.
Modeling the Hydrologic Processes of a Permeable Pavement System. In this study, EPA developed a unit process model for evaluating the hydrologic processes of a permeable pavement system.
Factorial study of rain garden design for nitrogen removal. This study explores nutrient treatment in eight outdoor, unvegetated rain gardens based on the following factors: hydraulic loading (two sizes and two flow rates), presence of a subsurface saturated zone, and presence of an introduced carbon source.
Hydraulic Test of a Bioretention Media Carbon Amendment. A bench-scale experiment was conducted to test the drainage capability of media containing shredded newspaper layers as a carbon amendment. Stormwater was introduced at low and high rates to bins containing zero, one, and two layers of newspaper at varying depths.
Application of Time Domain Reflectometers in Urban Settings. Time domain reflectometers (TDRs) are sensors that measure the volumetric water content of soils and porous media. This study demonstrates the use of TDRs for quantifying drainage properties in low impact development (LID) stormwater controls, specifically permeable pavement and rain garden systems.
Environmental Effects of Pervious Pavement as a Low Impact Development Installation in Urban Regions - Chapter 13 (In Effects of Urbanization on Groundwater: An Engineering Case-based Approach for Sustainable Development). Pervious pavement systems can be used to reduce stormwater runoff volume and are efficient at removing solids from runoff; however, the pollutant removal efficiency for nutrients, metals, and organic contaminants is yet to be determined due to either a lack of data or inconsistent results. Every site is different and care should be taken to examine site conditions, underlying soil characteristics, and local climate prior to determining if the installation of pervious pavement would be an appropriate best management practice for stormwater management at a particular location.
Promoting Nitrate Removal in Rain Gardens. This research project investigates the performance of rain gardens in removing pollutants, and whether currently-accepted design standards can be adjusted to improve nitrate removal capabilities.