Refer to the provided Site Plan. The project must capture or otherwise retain all rainwater that falls on the roof. Control or conveyance facilities must be sized to handle 1.5 inches of rainfall over a 24-hour period. Based on this, 100 square feet of impervious surface* will generate 12.5 cubic feet or 94 gallons of water. One gallon of rainwater weighs 8.4 lbs. There are 7.5 gallons of rainwater in one cubic foot.

* Calculated as a footprint area. Ignore slopes when calculating the area of pervious surfaces.

RAINWATER CONTROL MEASURES

DRY WELLS

• Dry Wells shall be 48” deep
• 60% of the volume of each Dry Well is filled with stone, gravel and sand, per the typical Dry Well detail. The remaining 40% may be used when calculating the rainwater capture capacity of a Dry Well
• No more than 1,000 sq ft of impervious surface may drain to any one Dry Well
• Each Dry Well costs $250 plus $20.83 per cubic foot to intsall
• The thickness of the Dry Well walls can be omitted when calculating capacity and cost.
• Dry Wells can not be installed when grade slopes up more than 10% from the downspout invert height.
• Can be designed and approved with standard details provided by the AHJ

RAIN BARREL

• Each rain barrel can hold 90 gallons of rainwater
• The property owner is required to empty rain barrels after each rainfall
• Each rain barrel costs $338.28 installed

OUTFALL TO STREET

• Rainwater may be routed directly to the street
• Downspout invert must be 30 feet from the Public Right of Way or nearest public improvement
• Cost is $0

MICRO BIOREMEDIATION (PLANTER BOX)

• Above grade or semi-buried retention area
• Single Planter Box can capture all rainwater from the roof.
• Must be designed by licensed Landscape Architect or Civil Engineer
• May require engineered concrete retaining wall

QUESTIONS

1. Which option(s) is best if the Owner doesn’t want to do any maintenance? (or at least the bare minimum)
   
   
2. Is outfall to the street an option? Why or why not?
   
   
3. What is the total size, in cubic feet, of Dry Well that must be constructed in order to capture the required amount of rainfall? Round up to the nearest whole number.
   
   
4. What is the minimum number of Dry Wells that could be constructed? Place an X at one or more locations that might be ok for a Dry Well.
   
   
5. What would be the cost of constructing two Dry Wells to capture the required rainfall? Round up to the nearest whole dollar.
   
   
6. What would be the cost of using only rain barrels? Would it look good?