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