Pollution Mitigation: Green Roof Assessment Challenge
Scenario: You are an environmental scientist and given the task of assessing the effectiveness of “Aqualok” green roofs at taking up suspended solids (TSS), ammonium (NH4) and nitrate (NO3) on a DC fire station during rain events.
You have chemical concentration data for 3 rain events. You also have precipitation amounts and square footage of roofs.
Your task is to…
1. Determine the amounts of pollutants that fell on the roof (TSS, NH4, NO3 separately).
Hint: 1) take precipitation amounts and convert from cm to m. 2) convert total roof square footage to m2. 3) multiply the two and you get volume in m3. (right? m x m2 = m3). 4) Then multiply your m3 by 1000 to get liters of water.
Concentrations of the various pollutants (TSS, NO3 and NH4) are in mg or g/l. So you can get the amounts by multiplying liters of water by the concentrations.
2. Determine the amount of pollutants that would have “run off” if the roof wasn’t “green”.
Using the volume of rain for each storm, calculate the amounts of pollutants that would have “runoff” from the 7000 sg. ft. roof
3. Determine the amount of pollutants that drained (or would have drained) the two types of green roof.
Using the 1100 sq. ft unplanted and planted green roofs (as if the roofs weren’t there). Look at the pollutant retention (or release) in the planted and unplanted roof throughflow. for the July storm, the roofs “release” nutrients right? But they don’t for the January storm.
4. Determine the % effectiveness of the “bioswale” at removing pollutants from runoff.
For this one, you don’t need to find amounts. Just take the individual pollutant concentration in the bioswale throughflow and divide it by the pollution concentration in the runoff. Then subtract 1. This gives you the % of pollutants the bioswale retained (or released for the July storm).
5. Calculate these for each storm. Examine the trends over time. Do the roofs or bioswale get more effective over time? Less effective? Remember, you need to convert sq. ft. to metric AND then find volume of rain (or runoff).
1 sq. ft = 0.0929 sq. m
6. Washington DC has 3 million square feet of green roof! Using the data from the January 31, 2013 storm event, how many kg of TSS, NH4 and NO3 could have been prevented from running off into wastewater?
For this one, just find the volume of rain that fell on the 3 million sq. ft. Then multiply that many liters by the runoff concentrations for 1/31. That gives you the “dirty runoff” number. Then do the same calculation but using the planted and unplanted roof concentrations. What is the difference between the amounts of pollutants from the runoff and from the green roofs?
July 19, 2012. Precip amount 0.48 cm.
Precip. TSS= 0.108 g/L; NH4= .03 mg/L; NO3= .19mg/L
runoff TSS= 0.204 g/L; NH4= .06 mg/L; NO3= .17mg/L
bioswale TSS= 0.119 g/L; NH4= .05 mg/L; NO3= 1.24mg/L
unplanted TSS= 0.225 g/L; NH4= .01 mg/L; NO3= 1.17mg/L
planted TSS= 0.400 g/L; NH4= 1.06 mg/L; NO3= 3.79mg/L
November 13, 2012 precip. amount 2.67 cm
precip. TSS= 0.120 g/L; NH4= .0 mg/L; NO3= .29mg/L
runoff TSS= 0.040 g/L; NH4= .03 mg/L; NO3= .77mg/L
bioswale TSS= 0.034 g/L; NH4= .01 mg/L; NO3= .26mg/L
unplanted TSS= 0.002 g/L; NH4= .25 mg/L; NO3= .55mg/L
planted TSS= 0.0097 g/L; NH4= .23 mg/L; NO3= .53mg/L
January 31, 2013 precip. amount 2.514 cm
precip. TSS= 0.007 g/L; NH4= .08 mg/L; NO3= .36mg/L
runoff TSS= 0.137 g/L; NH4= .07 mg/L; NO3= .46mg/L
bioswale TSS= 0.030 g/L; NH4= .04 mg/L; NO3= .08mg/L
unplanted TSS= 0.0 g/L; NH4= .34 mg/L; NO3= .36mg/L
planted TSS= 0.0092 g/L; NH4= .18 mg/L; NO3= .16mg/L
the pdf file are hints for you,thanks
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