7/30/2019 Retzlaff Et Al 2009 Water Quality

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Green roof storm water runoff is not heavy

(with metals)W. Retzlaff1, S. Ebbs2, L. Battaglia2, S. Alsup2, S. Morgan1, and K. Luckett3

1Southern Illinois University Edwardsville, 2Southern Illinois University Carbondale, and3Green Roof Blocks

Abstract

With increased interest in green roof systems, concerns regarding their

influence on water quality have been raised. Green roofs can be complex systemswith many components and the degree to which water quality might be affected

may be related to green roof design, the underlaying roof itself, the componentsutilized, and the contaminants in the precipitation that falls on the green roof. Toaddress questions regarding green roof influence on metal contaminants in storm

water runoff, runoff water samples were collected from experimental green roofsystems and evaluated to investigate potential impacts these systems may have on

downstream water quality with respect to heavy metals and some micronutrients.Overall, results obtained for Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations

observed in leachate collected from the evaluated green roof systems do notindicate that green roofs are a significant source of heavy metal and micronutrient

contaminants in urban storm water runoff. Further, modular green roof systemsevaluated in this study release less or the same metal concentrations as built-in-

place green roof systems. Concentrations quantified in green roof storm waterrunoff were compared to IEPA effluent standards to assess whether or not there

may be any negative impacts on water quality. With the exception of excess Znlevels in collected runoff from green roof systems in October (with 10 cm of growth

media) and in February (with 5 cm of growth media), metal concentrations in runoff

from green roof systems were below IEPA effluent standards.

Materials and Methods

Green roof models were set up at the SIUE Environmental Sciences FieldSite in a completely randomized experimental design (CRD), with four replications

of various depths (5cm, 10cm, 15cm, and 20cm) (Forrester 2008). There are fourcontrol roofs with black EPDM membrane surfaces only and four commercial Green

Roof Blocks included in the thirty-six total green roof models. At each depth thereare representative models with plants and models without plants (growing medium

only). Models were planted with Sedum hybridum immergrauch in September 2005,and we have monitored storm water runoff since planting. A covered gutter

connected to a water collection system is present at each of the 36 individual greenroof models.

When possible (either most or all units had sufficient leachate), using 500 mL

Nalgene collection bottles, at least 250 mL of leachate was collected andtransported to the lab for filtration. Collection dates assessed were June 27th 2007,

Oct 18th 2007, Feb 8th 2008, and April 8th 2008. Nalgene collection bottles werepretreated by acid washing overnight and rinsing with Millipore water. To remove

any biomatter present in water samples collected, samples were filtered to 0.45

microns using 0.45m cellulose filter paper (Millipore Corp.).

Filtered storm water runoff samples collected from the collection container of

each model green roof and control roof were transported to the SIUC plantphysiology lab for analysis using SpectrAA 220FS Atomic Absorbance Spectrometer

(Varian, Palo Alto, CA). Concentration ranges used to evaluate metals during theAAS analysis were determined using the following IEPA effluent standards: 0.5

ppm, 2.0 ppm, 1.0 ppm, 1.0 ppm, 0.15 ppm, 1 ppm, 0.2 ppm, 1.0 ppm, for Cu, Fe,Mn, Zn, Cd, Ni, Pb, and Cr respectively (IEPA 2006).

All recorded data was analyzed using SAS 9.1 to determine whether or not

there are differences in storm water runoff quantity among the different green roofsystems (ANOVA for a completely randomized design, p < 0.05) and graphed using

SigmaPlot 8.0.

Conclusion

For green roofs, metal leachability from these plant systems are quite

complex and are affected by several factors. Substrate depth, vegetation,substrate characteristics, drainage, fertilization, age of the green roof, and

local pollution sources are some influences. Green roofs are able to act aspollutant absorbents and filters, but they may also potentially release

pollutants into runoff due to composition of different substrates, plantinteractions, and fertilizers (Berndtsson et al. 2006).

Green roof systems have been touted as having significant

environmental benefits. In this recent evaluation of the water quality of thestorm water runoff from green roofs we have observed little downstream

contamination from heavy metals that may be coming from the green roofdesign, the underlaying roof itself, the components utilized, and the

contaminants in the precipitation that fall on the green roof.

References

Illinois Environmental Protection Agency (IEPA). 200 6. Title 35: Environ mental Protection Subtitle C:Water Pollution Chapter 1: Pollution Control Board. Part 304: Effluent Standards. Subpart A: GeneralEffluent Standards.

Berndtsson JC, Emilsson T and Bengtsson L (2006) The influence of extensive vegetated roofs on runoffwater quality. Sci Total Environ 355:48-63

Forrester, K. 20 08. Evaluation of Storm Water Runoff from a Midwest Green Roof System. SIUE.

Figure 1. October 18, 2007 collection event. Effect of different media treatments on iron

concentration (bars denote mean [iron] and standard error, n=3-4) measured from

leachate collected from empty built-in-place control roofs and from each planted media

placed in10 cm Green Roof BlocksTM; bars with same letter not significantly different at

the p