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 $0.5043 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 $0.1087 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 {[0.5043 x (614 - 200)] + [0.1087 x (111 - 200)]}
  • S = 0.0116 x 8.34 x {[0.5043 x 414] + [*0]}
  • S = 0.0116 x 8.34 x 208.78
  • S = $20.20/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 $0.2242 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 $0.1087 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 {[0.2242 x (1860 - 450)] + [0.1087 x (799 - 200]}
  • S = 0.0934 x 8.34 x {[0.2242 x 1410] + [[0.1087 x 599]}
  • S = 0.0934 x 8.34 x [316.12 + 65.11]
  • S = 0.0934 x 8.34 x 381.23
  • S = $296.96/month

Optional: You can verify the results using the Surcharge Calculator