ASCE M&R No. 62 (WPCF MoP FD-6) "Existing Sewer Evaluation and
Rehabilitation" has some information on inflow, from an undated report
by Neenah Foundry Co. Check Page 26 and Table 2.1. Tests were done
under three conditions: splashing, 3 mm head, and 25 mm head over
maintenance hole cover. Two cover types were tested: non-machined
bearing surface, and machined bearing surface. Average inflows (gallons
per minute) were:

Test 1 Test 2 Test 3
Non-machined 3.99 10.63 16.80
Machined 1.06 1.81 2.54

A table footnote provides inflow rates for each test:
Test 1. 0.25 gpm/sq in
Test 2. 1.00 gpm/sq in
Test 3. 4.94 gpm/sq in

gpm x 5.45 = m^3/day

Neil Jordan
NJordan@EXPONENT.COM