You will need the following information:
Gallons of wastewater produced per animal per day:
The number of gallons produced may be determined from water bills or through actual measurements of water use.
Length of time wastewater must be stored:
Use Critical Storage Period from Table 1 - Approximate days of winter storage required.
Number of gallons of contaminated lot runoff expected during the storage period:
Determine lot runoff by estimating the amount of effective precipitation (in inches) received during the critical storage period and multiplying by the lot area (length x width). Note that facilities must be able to contain lot runoff up to and including a 25 year, 24 hour storm event.
For normal and 25 year, 24 hour storm precipitation data see the Internet web pages: http://www.wrcc.dri.edu/pcpnfreq/ and http://www.wrcc.dri.edu/climsum.html