(A) User charges for normal domestic users shall be determined as follows.
(1) Calculation of unit cost for treatment of normal domestic strength wastewater.
Un = Uf + [.001 x 8.34 x Nbod x Ubod] + [.001 x 8.34 x Ntss x Utss]
Where:
Un = Unit cost for operation, maintenance and replacement to treat normal domestic strength in $/kgal
Uf = Unit cost for treatment of flow in $/kgal
Uf = [Total annual OM&R costs attributable to flow]
[Total annual billable flow in kgal]
Nbod = Normal domestic strength BOD concentration
Ubod = Unit cost for treatment of BOD in $/lb
Ubod = [Total annual OM&R costs attributable to BOD]
[Total annual billable BOD in lbs]
NTss = Normal domestic strength of TSS concentration
UTss = Unit cost for treatment of TSS in $/lb
UTss = [Total annual OM&R costs attributable to TSS]
[Total annual billable TSS in lbs]
(2) Calculation of user charge.
Uc = Un x bwv
Where:
Uc = User charge
Un = Unit cost for operation, maintenance and replacement to treat normal domestic strength in $/1,000 gal
bwv = Billable wastewater volume of a particular user in 1,000 gal
(B) User charges for users discharging wastes with concentrations greater than normal domestic strength.
(1) Calculating billable flows and loadings.
(a) Calculation of billable flows. The billable amount of flow will be calculated from the volume of metered water usage, or at the discretion of the city, from the measurement of effluent flow at user’s point of discharge. Measurements shall be according to a regular program prescribed by the city.
(b) Calculation of billable loadings.
1. The billable amounts of BOD and TSS will be calculated by the measurement of these wastes according to a program prescribed by the city in keeping with the latest edition of Standard Methods for the Examination of Water and Wastewater and in accordance with this chapter.
2. To ensure compliance with § 53.122(B), the following procedures shall be followed in determining average loadings per billing period for industrial users.
A. When a particular reading indicates concentrations greater than or equal to normal domestic strength, the actual reading shall be entered into the average for billing purposes.
B. When a particular reading indicates concentrations less than normal domestic strength, normal domestic strength shall be entered into the average for billing purposes.
(2) Determination of user charge for greater than normal domestic strength users.
(a) Calculation of unit costs for treatment of flow, BOD and TSS. For purposes of determining proportionate surcharges, unit costs for treatment of flow, BOD and TSS shall be determined and fixed annually in the sewer service charge system according to the following procedure:
1. Determine the annual OM&R budget;
2. Allocate total annual OM&R costs to flow, BOD and TSS proportionately; according to the costs of collection and treatment of flow, BOD and TSS; and
3. Divide the OM&R attributable to flow, BOD and TSS respectively, by the total annual billable volume and loadings of flow, BOD and TSS to arrive at unit costs.
(b) Calculation of user charges for treatment of wastewaters with concentrations exceeding that of normal domestic strength wastewater.
Uc = [Un x bwv] + [Ubod x K x bwv (Cbod-Nbod)] + [Utss x K x bwv (Ctss-Ntss)]
Un = Unit cost for the treatment of normal domestic strength wastewater
bwv = Billable wastewater volume of a particular user in kgal
Ubod = Unit cost for treatment of BOD in $/lb K = .00834
Cbod = Users concentration of BOD in mg/l
Nbod = 222 mg/l [concentration of BOD in normal domestic strength wastes]
Utss = Unit cost for treatment of TSS in $/lb
Ctss = Users concentration of TSS in mg/l
Ntss = 260 mg/l [concentration of TSS in normal domestic strength wastes]
(Ord. 407, passed 12-26-1989)