International Codes for Private Sewage Disposal

How does a person interpret the Code on size of leach field required for a septic tank? For a weekend flea market, it has an existing men's and a women's restroom. They want to add another of each. From Chapter 6, "Soil Absorption Systems" (which I assume is Leach Field Systems), using the formula A=U*CF*AA on p23, where A is the reqd area in sf, U is number of units (from p24), CF is the Conversion Factor (also fm p24), and AA is the Absorption Area frm p23.

I used U = 100 units, derived frm an Assembly Hall, no kitchen, estimated 100 persons * 1 unit/pers.

I used CF = 0.02, fm the same line,

and AA = 140 sf/unit, fm the assumptions (to be confirmed later) that the soil is of Percolation Class 1, and the existing leach field is of the Seepage Bed type of construction.

This gives a required area of 280sf. Since the existing leach field is 190 ft long, with 2 distribution pipes, and must be at least 5 ft wide (p25); thus providing 950sf of area, the conclusion is the existing field is adequate.

Did I do it right?