Sample Sewer Service Charge Calculations

General Assignment Method

Assume a retail outlet uses a total of 100,000 gallons of water per year, is given a landscape irrigation allowance of 10% and a general strength assignment of moderate. What is the annual Sewer Service Charge?

Step 1

Convert the total water consumption to the amount of wastewater discharge using the landscape irrigation factor. Given the 10% allowance, 90% of the total water consumed is wastewater.
100,000 gal./year x 0.90 = 90,000 gal./year

Step 2

The total flow must be converted into units of 1,000 gallons each. Divide the total flow by 1,000.
Volume = 90,000 gal./year ÷ 1,000 = 90 units

Step 3

Multiply the results of step 2 by the current rate for moderate strength wastewater of $6.06 per 1,000 gallons*.

Sewer Service Charge: 90 x $6.06 = $545.40

Direct Sampling or Specific Assignment Method

Assume an industrial business discharges 100,000 gallons of wastewater per year and is given a specific assignment of 1250 mg/L COD and 300 mg/L SS. What are the annual Sewer Service Charges?

Step 1

First, a calculation must be done to convert strength assignments in milligrams per liter (mg/L) to pounds per gallons (lbs/gal.).  The conversion factor is .000008344.

• COD = 1250 mg/l x 0.000008344 = 0.01043 lbs/gal.
• SS = 300 mg/l x 0.000008344 = 0.002503 lbs/gal.

Step 2

Use the loadings calculated in Step 1 in lb/gal. times the total flow to get total pounds per year.

• COD = 0.01043 lbs/gal. x 100,000 gal./year = 1043 lbs./year
• SS = 0.002503 lbs/gal. x 100,000 gal./year = 250.3lbs/year

Step 3

Convert volume, COD and SS to units compatible with the rates which are in increments of 1,000. Divide all three figures by 1,000.

• Volume = 100,000 gal./yr. ÷ 1,000 = 100 units
• COD = 1043 lbs/year ÷ 1,000 = 1.043 units
• SS = 250.3 lbs/year ÷ 1,000 = 0.2503 units

Step 4

Multiply the results of Step 3 by the current rates to arrive at the total yearly Sewer Service Charge.

• Volume = 100 x $2.99* = $299.00
• COD = 1.043 x $338.87* = $353.44
• SS = 0.2503 x $909.90* = $227.75

TOTAL = $880.19

*FY 2021 Rates effective - July 1, 2020 through June 30, 2021

Questions on how your charges have been determined can be answered by calling Customer Service Representatives at (510) 477-7500.