Percolation test results

18" deep hole held approximately 10 gallons of water when full. Two trials, both required 8 hours to drain.

Drainage area

Neighboring roof is approximately 60' wide and 77' deep, netting a surface area of 4620 square feet. To check: if all of the roof runoff drains to the north side of the building or if a portion drains to other sides.

Rain garden area

20% of 4620 square feet = 924 square feet

A 115' long garden 8' wide would suffice. Or a 77' long garden running the length of the building would require an average width of 12'. (Based on the idea that all of the water drains to this area.)

Although this seems large, in times of large amounts of rainfall, this area floods, runs under the fence, and produces a 1' deep pool covering 3-4 parking spots in the apartment building's parking lot.