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. Divide the total flow by 1,000.
Volume = 90,000 gal./year ÷ 1,000= 90 K gal./year
Step 3
Multiply the results of step 2 by the current rate for moderate strength wastewater of $5.25 per 1,000 gallons*.
Volume: 90 x $5.25 = $472.50
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 K gal./year
- COD = 1043 lbs/year ÷ 1,000 = 1.043 K lbs/year
- SS = 250.3 lbs/year ÷ 1,000 = 0.2503 K lbs/year
Step 4
Multiply the results of Step 3 by the current rates to arrive at the total yearly Sewer Service Charge.
- Volume = 100 x $2.48* = $248.00
- COD = 1.043 x $328.24* = $342.35
- SS = 0.2503 x $763.48* = $191.10
TOTAL = $704.14
*FY 2020 rates - July 1, 2019 through June 30, 2020
Questions on how your charges have been determined can be answered by calling Customer Service Representatives at (510) 477-7500.
