Green Roof Benefits. Green Roof Media Selection for the Minimization of Pollutant Loadings in Roof Runoff

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1 Green Roof Media Selection for the Minimization of Pollutant Loadings in Roof Runoff Brett Long Shirley Clark Robert Berghage Katherine Baker Green Roofs: The New BMP (at least in the US) Green roofs = vegetated roof covers Plants Growth media Drainage layers Waterproof membranes Green roof medium (Extensive green roof) Depth: 2. to 6 inches Low organic content Plant selections: typically alpine-type (most are drought-,, wind-,, frost-,, and heat-tolerant) tolerant) Photo Courtesy Penn State Center for Green Roof Research Green Roof vs. Traditional Roof Design Conventional gravel-ballasted roof Green roof Swarthmore College Swarthmore, PA Gravel Protection layer Waterproofing Substrate Filter fabric Drainage layer Protection layer Waterproofing Montgomery Park Baltimore, MD. Illustrations courtesy of the Federal Energy Management Program Green Roof Benefits Provide green space in ultra urban areas Reduction of urban heat island effect Personalize property Increased value Increased roof life Decreased roofing costs Increased insulation and energy efficiency U.S. Green Building Council: The Leadership in Energy and Environmental Design (LEED) program Biodiversity and wildlife values Filtering airborne pollution. Photos Courtesy of the Penn State Center for Green Roof Research 1

2 Wildlife Habitat Photo Courtesy of the Penn State Center for Green Roof Research Photo Courtesy Penn State Center for Green Roof Research Green Roof Design Considerations Green Roof Design Considerations Cost comparison for new construction: Green roof - $1-$3 $3 per square foot Traditional roof - $-$1 $1 per square foot Roof load evaluation required for retrofits Tested membranes highly recommended Plastic root barrier above membrane? Flood testing and leak detection units Membrane testing underway at Penn State Univ. (UP campus) Roof slope Typical failure mechanism: media slippage occurring at membrane or fabric layers to 3 3 vertical per 12 horizontal slopes: no additional engineering measures 3/12 to 6/12 slopes: may need baffles Over 6/12 slopes: engineering measures such as honey combs or square cells to hold media in place Green Roof Benefits for Stormwater Management Water retention and detention properties Monitoring by Penn State Center for Green Roof Research: % of annual average rainfall in Pennsylvania remained on a green en roof (DeNardo( DeNardo,, 23). In areas with SSO/CSO, lighten load on the sewer system? Relating to traditional stormwater design methods: Rational coefficients of green roofs: Green roofs have a rational coefficient of about. Equivalent to a grass lawn NOTE: Variable with time of year and rainfall intervals Research: Green vs. Non-Green Roof Looked at both stormwater s runoff volume and flow rates Intensity (in/hr) Depth (in) Retained =.18 in Rain Green Roof Runoff Time (hr) 1/2/22 Delayed Peak Peak Intensity Reduction Rain Intensity Runoff Rate Time (hr) 1/2/22 Jarrett et al. 2

3 Quality Issues Due to Wet Deposition Can Green Roofs Help? Will Replacing Traditional Roofing Materials with Green Roofs Reduce Urban Runoff Loads? Roof runoff shown to be contaminated with metals and organics due to: Atmospheric deposition Materials themselves Ongoing study at PSH shows materials can be a substantial source of pollutants Objectives of This Project METHODOLOGY: Phase I 1. To develop an effective medium for green roofing that will improve roof runoff quality while maintaining the known stormwater retention benefits of green roofs 2. To demonstrate that green roofing can reduce the pollutant loadings from roof runoff compared to traditional roof materials. Goal. Determine most effective medium for filtering atmospheric pollutants while not leaching additional pollutants into its runoff. Task 1. Evaluate the mineral component. Media used: two gradations of expanded shale, two expanded clays (with and without nutrient additives), and an expanded slate. Focus: Isolate contribution of mineral-only layer. Laboratory Test Setup Mineral Testing Phase (from Upper Left to Lower Right): Empty Filter Column, Drainage Material (Control), Filter Fabric (Control), Expanded Clay, Expanded Slate, Medium Grade Expanded Shale, Fine Grade Expanded Shale, and Expanded Clay with Other Additives). 3

4 Testing Methodology Analytes and Rain Concentration Replicates for all media columns Control columns Simulated rainwater at a ph of 4. and spiked with common stormwater pollutants poured through the columns using a spreading device Analyte ph Conductance Ammonia Nitrate Total Phosphate Diss. Cadmium Diss. Copper Diss. Lead Average Rain Concentration ms/cm 11.1 mg/l NH 3 as N 13.6 mg/l NO 3 as N 14.8 mg/l 21.8 µg/l 82.3 µg/l 16.8 µg/l Analytical Method Std Methods (S.M.) 2th ed., 21A-B S.M. 4-H+B HACH Water Handbook 3rd ed., Method 131 S.M. 4-NO3-D S.M. 4-P B, S.M B S.M. 3113B S.M. 3113B Additional Data Collected: Weight of Media and Volume of Rain Recovered Diss. Arsenic Diss. Mercury Diss. Zinc *Samples not yet analyzed *Samples not yet analyzed *Samples not yet analyzed S.M. 3113B EPA NERL Method 24.1 S.M. 3111B Methodology Additive Evaluation Task 2. Evaluate several filter sorbents, cation exchange materials, and anion exchange materials These materials were added to the mineral medium (selected in Task 1) using recommended dosages. Hypothesis: The addition of these materials will increase the ability of green roof media to capture pollutants Loads evaluated in similar manner to that of the original mineral evaluation Additive Testing Phase (from Upper Left to Lower Right): Drainage Material and Filter Fabric; / (v/v) Med./Fine Expanded Shale (mineral only); Expanded Shale Mix and ; Expanded Shale Mix and ; Expanded Shale Mix and ; Expanded Shale Mix and. Methodology - Organics Task 3. Evaluate several organic matter sources (in low volumes (1-2%)) to the mineral and additive combination selected in Task 2 using same testing methods of previous two phases. Leaf litter compost Peat NOTE: This phase will begin ~ Nov. 1, 26. RESULTS AND DISCUSSION Mineral Media Only Runoff ph is elevated compared to the acid rain, indicating neutralization/ buffering of the acid rain. ph ph Values for Green Roof Media Leachate After Four Simulated Storms 1 Expanded Clay Expanded Slate Med. Grade Ex. Shale Fine Grade Ex. Shale Expanded Clay w/ Add Age (days) ph = 7 4

5 Total Phosphate Load (mg) Total Phosphorus Cumulative Effluent Total Phosphate Loads from Column 3 NOTE: w/ additives effluent overrange for all sampling events to date Normalized Cumulative Total Phosphate Loadings Media (mg/kg) 14 NOTE: w/ additives effluent overrange for all sampling events to date Normalized Total Phosphate Load(mg/kg) Medium Type Retention occurs in fine grade expanded shale, and to a lesser extent, in other media types. Expanded clay with additives increases nutrient concentration in the runoff, likely due to added fertilizers. Dissolved Copper Load (ug) Dissolved Copper Cumulative Effluent Dissolved Copper Loads from Column w/add Normalized Dissolved Copper Load (ug/kg) Normalized Cumulative Dissolved Copper Loading (ug/kg) Media Type Similar results seen for dissolved lead and cadmium. w/add RESULTS AND DISCUSSION Mineral Media Mineral media have little effect on nitrate levels, while ammonia levels are only slightly lowered, especially by the fine graded expanded shale media. Metal loads (Cu, Pb, Cd) are substantially lowered in all of the media. They are the least in the fine graded expanded shale. Fine-graded expanded shale selected for Task 2. RESULTS AND DISCUSSION Column Tests Filter Additives Nutrient reductions based on effluent concentration: and provided slightly better reduction than other media For mass-loading loading-on-media, best Additives had little effect on metals removal At low concentrations seen in rain,, Expanded Shale effective alone Total Phosphate Normalized Cumulative Total Phosphate Loadings Media (mg/kg) Medium Type Cumulative Effluent Total Phosphate Loads from Column 3 Normalized Total Phosphate Load(mg/kg) Dissolved Copper Normalized Cumulative Dissolved Copper Loading (ug/kg) Media Type Cumulative Effluent Dissolved Copper Loads from Column 3 Normalized Dissolved Copper Load (ug/kg) Total Phosphate Load (mg) Mineral provided best removal on a per-weight basis. Also true for nitrate. Dissolved Copper Load (ug) Mineral Similar results seen for dissolved lead and cadmium.

6 Future Research: Field Testing Phase II. Following these tests, pilot scale roofs will be built outside on the Penn State Harrisburg campus Late Fall 26 Compare: control roofs (Plexiglass( Plexiglass), traditional roofs and green roofs side-by by-side All setups will have a drain at the bottom to capture all the runoff. Setup includes: Weather station Flow measurement (rate) Collecting cistern Methodology Field Testing At the end of each storm event, the quantity of water in these cisterns will be measured The quality of the runoff will be tested at PSH for at least two storms per month. Analytes same as listed for column tests: ph, conductivity, metals, and nutrients. Bacteria added to analytes for field testing. Conclusions to Date Engineering a green roof media for water quality improvement is possible. Evaluation methodology should consider mineral portion first since it makes up the majority of volume and mass. Green roof media can buffer acid rain ph. Fine-grade expanded shale had the highest buffering capacity Fine-grade expanded shale also removed many pollutants of interest. Conclusions to Date Based on these results, the expanded shale should be used in the engineered mix of green roof media, but needs to be mixed with coarser-grade medium to improve hydraulic properties. Of the additives, provided benefits. Its addition needs to be re-evaluated after testing of organic media. may not provide additional benefits compared to adding only peat or compost. ACKNOWLEDGMENTS Questions? The authors would like to thank the following funding sources and collaborators: Penn State Harrisburg Graduate Research Council Penn State Institutes of the Environment Center for Green Roof Research (for their donation of materials and expertise to the project development). Mountain Research Inc. of Altoona, PA for their donation of equipment The primary author would also like to acknowledge the assistance of his fellow students: Brad Mikula, Jim Elligson, Christina Sui, Ed Spayd and Julia Hafera. 6