Commercial and industrial customers, including restaurants, nursing homes and manufacturing facilities, generate waste streams that are higher in strength than the average residential customer. The indicators of "strength" are BOD (biochemical demand) and TSS (total suspended solids). Higher strength wastes cost more to treat and are often more troublesome for maintenance of the sewer system. To recover costs and to make the difference between commercial/industrial and residential customers more equitable a strong waste surcharge program has been established. Many jurisdictions in the metropolitan area, in fact in the nation, have developed similar programs.
In Henrico County the BOD threshold is 250 mg/l (milligrams per liter) and the TSS threshold is 275 mg/l. Above these numbers a customer is subject to receiving a surcharge on the water/sewer bill. The volume of water used, or discharged to the sanitary sewerage system, is also an important factor in a strong waste bill. More water used greater is the surcharge. The formula for calculating a strong waste charge is:
(Volume of water discharged) X (Measured BOD - BOD threshold) X (rate)
and
(Volume of water discharged) X (Measured TSS - TSS threshold) X (rate)
The volume of water is measured in CCF, or hundred cubic feet.
Example:
BOD = (231 CCF) X (502 mg/l-250 mg/l) X (0.001598)* = $93.02/billing period
and
TSS = (231 CCF) X (645 mg/l-275 mg/l) X (0.001155)* = $98.72/billing period
The sum of the two amounts, $191.74, is the total strong waste surcharge applied to a water/sewer bill.
*Rates as of 1 July 2011
The quantity of oxygen utilized in the biochemical oxidation of organic matter under standard laboratory procedures for five days at 20 degrees Celsius, expressed in terms of weight and concentration (milligrams per liter)
All solids that either float on the surface or are in suspension in water, sewage, wastewater or other liquids and which are removable by laboratory filtering.