Wastewater users producing waste flows of higher than ordinary strength will add to the annual operation and maintenance costs of the sewage system. Therefore, a surcharge system is developed based on the strength of those wastes above the baseline values. The surcharge system is developed in Example VII.
Example VII |
Example VII | |
Any wastewater having a BOD and/or a SS of over 275 mg/l is considered excessive and is subject to a surcharge to cover the extra cost of treating the wastewater. | |
Annual BOD (0.005 * 8.34 * (500-275) * 365) = | 3,425 lb/year |
Annual cost to operate WWTP and collection system | $308,000 |
Annual industrial metered water | 1,000,000 gallons |
Annual residential/commercial metered water | 107,000,000 gallons |
Annual total metered water | 108,000,000 gallons |
Annual total wastewater BOD | 247,699 lbs |
Annual total wastewater flow | 146,000,000 gallons |
Estimated industrial BOD | |
(1,000,000/1,000,000) * 8.34 * 275 mg/l = | 2,294 lbs |
Estimated residential BOD | |
(107,000,000/1,000,000) * 8.34 * 275 mg/l = | 245,405 lbs |
For 5,000 gpd @ 500 mg/l BOD | |
(5,000 gpd * 365 days) = | 1,825,000 gallons/year |
Industrial portion - (1 % of $308,000) = | $3,080 |
Normal strength (1,825,000 * ($2.82/1,000) = | $5,147(1) |
Rate surcharge ($3,080/2,294) = | $1.34/lb BOD or SS |
Rate residential ($304,920/(108,000,000/1,000)) = | $2.82/1,000 gallons |
Residential percent | 99% |
Residential portion - (99% of $308,000) = | $304,920 |
Surcharge (3,425 * $1.34) = | $4,590 (2) |
Total annual bill | $9,737 (1+2) |
Example VIII
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At this time, there are no industrial discharges to the city’s wastewater treatment plant. A surcharge system will be developed at a time that higher than ordinary strength wastes are discharged to the treatment plant. |
(Prior Code, § 54.25) (Ord. passed - -)