City of Carrollton, TX
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The City of Carrollton has the ability to surcharge users water bills to compensate for increased treatment costs resulting from abnormal strength wastewater. Users that complete sampling in the city are also sampled for the following surcharge parameters:
- A five-day biochemical oxygen demand (BOD) greater than 250 mg/l; or
- Containing more than 250 mg/l of total suspended solids (TSS); or
- A chemical oxygen demand (COD) greater than 625 mg/l.
The surcharge shall be calculated according to the following formula:
Surcharge = [ Q ] [a (BOD - x) + b (TSS - y)] [8.34] [c]
Or, for those abnormal wastes having a COD concentration 2.5 or more times that of the BOD concentration, the surcharge may, at the discretion of the DCO, be based on the COD category in lieu of the BOD category. Thus the surcharge shall be calculated according to the following formula:
Surcharge = [ Q ] [a (COD - z) + b (TSS - y)] [8.34] [c]
Where:
| Q = | wastewater flow in million gallons per month |
| 8.34 = | weight in pounds of one gallon of water (factor for converting mg/l to pounds per million gallons of water) |
| x = | level of BOD in milligrams per liter (mg/l), above which a surcharge is assessed |
| y = | level of TSS in mg/l, above which a surcharge is assessed |
| z = | level of COD in mg/l, above which as surcharge is assessed |
| a = | unit cost in dollars, of treatment per pound of BOD or COD |
| b = | unit cost in dollars, of treatment per pound of TSS |
| c = | administrative overhead recovery factor in dollars |
| BOD = | measured amount of BOD, in mg/l |
| COD = | measured amount of COD, in mg/l |
| TSS = | measured amount of TSS, in mg/l |
and, where the value of BOD, COD and/or TSS concentrations in this calculation will be an average of values determined by testing procedures, as defined in this chapter, on samples collected and/or accepted by the DCO. If the average of these concentrations is less than the value for the respective x, y or z, that term of the equation shall be dropped from the surcharge calculation.