Example 1:

Example Assumptions

BOD Average = 614 mg/L
SS Average = 111 mg/L
COD Average = 1200 mg/L
WW Average = 0.0116 Million Gallons per Month (MGM)


Step 1: Calculate the ratio of COD to BOD to determine which Surcharge Formula applies.

  • 1200 divided by 614 equals 1.95.

This ratio is less than 2.25, so we know that the following formula should apply:

S = V x 8.34 [A (BOD-200) + B (SS-200)]

Where:

S = Surcharge in dollars that will appear on the customer's monthly bills.
V = Wastewater billed in millions of gallons during the billing period.
8.34 = Pounds per gallon of water
A = Unit charge in dollars per pound of BOD in excess of 200 mg/L, currently $0.6622 per lb. If measured BOD is less than 200, the rate does not apply.
BOD = Biochemical Oxygen Demand in milligrams per liter (mg/l).
200 = Normal BOD and normal SS in mg/l.
B = Unit charge in dollars per pound of SS in excess of 200 mg/L, currently $0.4394 per lb. If measure SS is less than 200, the rate does not apply.
SS = Total Suspended Solids in milligrams per liter (mg/l).


Step 2: Calculate the Surcharge.

  • S = V x 8.34 [A (BOD - 200) + B (SS - 200)]
  • S = 0.0116 x 8.34 x {[0.6622 x (614 - 200)] + [0.4394 x (111 - 200)]}
  • S = 0.0116 x 8.34 x {[0.6622 x 414] + [*0]}
  • S = 0.0116 x 8.34 x 274.15
  • S = $26.52/month

* There are no SS charges because the SS was below the 200 mg/L surcharge limit.

 

Example 2:

Example Assumptions

BOD Average = 614 mg/L
SS Average = 799 mg/L
COD Average = 1860 mg/L
WW Average = 0.0934 Million Gallons per Month (MGM)


Step 1: Calculate the ratio of COD to BOD to determine which Surcharge Formula applies.

  • 1860 divided by 614 equals 3.03.

This ratio is greater than 2.25, so we know that the following formula should apply:

S = V x 8.34 [C (COD - 450) + B (SS - 200)]

Where:

S = Surcharge in dollars that will appear on the customer's monthly bills.
V = Wastewater billed in millions of gallons during the billing period.
8.34 = Pounds per gallon of water

 

C

 = Unit charge in dollars per pound of COD in excess of 450 mg/L, currently $0.2943 per lb. If the COD is less than 450 mg/L, the rate does not apply.
COD = Chemical Oxygen Demand in milligrams per liter (mg/l)
450 = Normal COD in milligrams per liter (mg/l).
B = Unit charge in dollars per pound of SS in excess of 200 mg/L, currently $0.4394 per lb. If measure SS is less than 200, the rate does not apply.
SS = Total Suspended Solids in milligrams per liter (mg/l).
200 = Normal BOD and normal SS in mg/l.


Step 2: Calculate the Surcharge.

  • S = V x 8.34 [C (COD - 450) + B (SS - 200)]
  • S = 0.0934 x 8.34 x {[0.2943 x (1860 - 450)] + [0.4394 x (799 - 200]}
  • S = 0.0934 x 8.34 x {[0.2943 x 1410] + [[0.4394 x 599]}
  • S = 0.0934 x 8.34 x [414.96 + 263.20]
  • S = 0.0934 x 8.34 x 678.16
  • S = $528.26/month

Optional: You can verify the results using the Surcharge Calculator