Specific_Oxygen_Uptake_Rate_Testing_Compliance_20090923

State of North Carolina
Department of Environment
and Natural Resources
Division of Water Quality

James B. Hunt, Jr., Governor
Wayne McDevitt, Secretary
A. Preston Howard, Jr., P.E., Director

Contact Name
Facility Name
Street Address
City, State Zip
Subject: Specific Oxygen Uptake Rate Testing Compliance
Land Application of Residuals
Permit Number: Permit Number
County County

Dear Sir:

The Division has noted in several Annual Reports that the Specific Oxygen Uptake Rate (SOUR) test has been improperly used for proof of compliance with the Vector Attraction Reduction
(VAR) requirements of 40 CFR 503. Currently, the SOUR test may only be used if all of the following conditions are met:

Percent Total Dry Solids. The residual must be less than 2 percent total dry solids. Diluting thickened sludges is not acceptable.

Temperature Range. The SOUR may only be applied to sludges which are at temperatures between 10ºC and 30ºC.

Temperature Correction. The SOUR test must be conducted at the same temperature that the digester is operating. The SOUR test must be temperature corrected to an equivalent 20ºC value.
The temperature correction equation is as follows:

SOUR20 = SOURT x ((20-T)

where: T = sludge temperature in degrees Celsius
( = 1.05 above 20ºC
( = 1.07 below 20ºC

Continuous Aeration. The SOUR test may only be used on sludges which have been stabilized in aerobic environments. Sludge holding tanks which are used primarily for sludge gravity
thickening and only periodically aerated to minimize odor generation may not use the SOUR test to indicate compliance with the VAR requirements.

Sample Holding Time. The maximum holding time is two hours. If the SOUR test cannot be started within 15 minutes of sampling, then the sample must be maintained under aeration until
the test can be completed.

Specific Oxygen Uptake Rate Testing Compliance Permit Number: Permit Number
Page 2.

6. Testing Frequency and Arithmetic Mean Compliance. Variability in digester detention times, operating temperatures, and sludge characteristics results in variability in SOUR test
results for a facility during the operating year. For VAR compliance purposes, the arithmetic mean of SOUR data from seven samples taken periodically during the monitoring period specified
in your permit will be considered sufficient.

For facilities using aerobic digestion for sludge stabilization, the Division suggests that Vector Attraction Reduction compliance be indicated by calculation of a volatile solids reduction
percentage of 38 percent or more in accordance with 40 CFR 503.33 (b)(1). If compliance cannot be shown by calculation of Volatile Solids Reduction, then the SOUR test may be used
only if the requirements listed above are met. If both the 38 percent volatile solids reduction cannot be met and the SOUR test is not valid, then the permittee must use an alternative
vector attraction reduction technique, such as the bench-scale extended aerobic digestion test - 40 CFR 503.33(b)(3).

The Division encourages you to immediately review your method of meeting the vector attraction reduction requirement, and to take action to ensure you provide valid proof that your sludge
has met the requirements of 40 CFR 503 for the 1997 year. These requirements are being enforced by both the Division of Water Quality and USEPA Region 4 until the Division of Water
Quality is delegated authority for the 40 CFR 503 program.

Attached please find a copy of the most current standard method and an example of a SOUR test form with calculations. If you have any questions, regarding these tests you are encouraged
to contact Kevin Barnett with the Division of Water Quality at [phone] ext. 529.

Sincerely,

Dennis R. Ramsey, P.E.
Assistant Chief for Non-Discharge

Cc: Non-Discharge Compliance / Enforcement Unit
Non-Discharge Permitting Unit
Region Regional Supervisor
Training and Certification Unit
Central Files
Madolyn S. Dominy, EPA Region 4