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MSD Quality Charge Testing Program

MSD has a Quality Charge Testing (QCT) program in place for the purpose of billing industrial and commercial users proportionally for wastewater strengths or concentrations that exceed established allowances. The pollutants currently used by MSD to assess billing rates are Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS). The current allowances for BOD and TSS are 250 milligrams/liter and 270 milligrams/liter, respectively. Average BOD and TSS concentrations are computed using MSD laboratory analysis results from MSD sampling activity at each users’ facility. MSD sampling activity consists of obtaining the most representative sample possible of the wastewater discharged by the user. This includes obtaining accurate flow measurement via Louisville Water Company water meter readings and/or private meter readings (subtractor and/or add on meters owned by the user and certified by MSD).

The two most common questions asked about quality charges concern the computations used to derive the average BOD and TSS concentrations used to assess the billing rate and the calculation of the billing rates. Average BOD and TSS concentrations are determined using a flow weighted average. The current billing rate factors used by MSD are: BOD - 0.001660 and TSS - 0.0006838. Below is an example calculation based on a two day QCT survey. Quality Charge Program questions should be directed to Lisa A. Gaus at (502) 540-6467.

Average BOD And TSS Concentration Calculations

Day 1 BOD TSS Flow
  (mg/l)*       (mg/l)* (mgd)**
       
Outfall 1 300 325 0.250
Outfall 2 895 20 0.030
       
BOD =

((300 x 0.25) + (895 x 0.03))
(0.25 + 0.03)

364 mg/l
 
TSS =

((325 x 0.25) + (20 x 0.03))
(0.25 + 0.03)

292 mg/l
 

 

Day 2 BOD TSS Flow
  (mg/l)*       (mg/l)* (mgd)**
       
Outfall 1 130 367 0.350
Outfall 2 678 115 0.050
       
BOD =

((130 x 0.35) + (678 x 0.05))
(0.35 + 0.05)

198 mg/l
 
TSS =

((367 x 0.35) + (115 x 0.05))
(0.35 + 0.05)

335 mg/l
 

 

Day 3 BOD TSS Flow
  (mg/l)*       (mg/l)* (mgd)**
       
Outfall 1 420 252 0.240
Outfall 2 910 418 0.060
       
BOD =

((420 x 0.24) + (910 x 0.06))
(0.24 + 0.06)

518 mg/l
 
TSS =

((252 x 0.24) + (418 x 0.06))
(0.24 + 0.06)

285 mg/l
 

 

Sample Composite
       
  BOD TSS FLOW
  (mg/l) (mg/l) (mgd)
       
Day 1 364 292 0.28
Day 2 198 335 0.40
Day 3 518 285 0.30
       
BODAVG=

((364 x 0.28) + (198 x 0.40) + (518 x 0.30))
(0.28 + 0.40 + 0.30)

=343 mg/l
 
TSSAVG=

((292 x 0.28) + (335 x 0.40) + (285 x 0.30))
(0.28 + 0.40 + 0.30)

=307 mg/l
 

Therefore, the average BOD and TSS results for this user are:

BOD = 343 mg/l and TSS = 307 mg/l

Billing Rate Calculation

BOD: $0.001660 per mg/l per 1000 gallons (in excess of 250 mg/l)
TSS: $0.0006838 per mg/l per 1000 gallons (in excess of 270 mg/l)

 

BODRATE: = (343 - 250) x (0.001660) = $.1544/1000 gallons
TSSRATE: = (307 - 270) x (0.0006838) = $0.0253/1000 gallons
TOTALQCT RATE: = 0.1797/1000 gallons

*mg/l = milligrams per liter
**mgd = million gallons per day

Return to Pretreatment Overview
Last Updated: November 15, 2006

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