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 $0.7411 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 $0.6047 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 {[0.7411 x (614 - 200)] + [0.6047 x (111 - 200)]}
- S = 0.0116 x 8.34 x {[0.7411 x 414] + [*0]}
- S = 0.0116 x 8.34 x 306.82
- S = $29.68/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 $0.3294 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 $0.6047 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 {[0.3294 x (1860 - 450)] + [0.6047 x (799 - 200]}
- S = 0.0934 x 8.34 x {[0.3294 x 1410] + [[0.6047 x 599]}
- S = 0.0934 x 8.34 x [464.45 + 362.22]
- S = 0.0934 x 8.34 x 826.67
- S = $643.94/month
Optional: You can verify the results using the Surcharge Calculator