... 2 28 32 32 8 32 80Gravelly sand 8 30 35 1640–16,400Fine gravel 16 35 38 32 80 32 ,800Medium gravel 32 36 –40 32 ,800–164,000Coarse rock 128 38 –45 164,000–820,000 Note: ft/d × 0 .30 5 = ... Con-structed Wetlands for Wastewater Treatment: Municipal, Industrial and Agricul-tural, Hammer, D., Ed., Lewis Publishers, Chelsea, MI, 31 9 35 1.WEF. (2001). Natural Systems for Wastewater Treatment, ... DK804X_C007.fm Page 36 3 Friday, July 1, 2005 3: 46 PM© 2006 by Taylor & Francis Group, LLC 36 6 Natural Wastewater Treatment Systems At 6°C:Metric: As = 30 .1(Q) = m2 (Q in m 3 /d)U.S. units:...