Any non-domestic customer that discharges BOD or TSS in excess of 250 mg/l or oil and grease in excess of 100 mg/l will be assessed a surcharge of 25% of the total sewer charges or a surcharge of 50% if the BOD or TSS of the discharge is 500 mg/l or more or oil and grease is 200 mg/l or more. The threshold for surcharging shall be based on any single incident of a discharge in excess of the limits. Only one surcharge per month shall apply and it shall be based on the highest detected discharge in excess of the limits.