WQ0008778_Compliance_19981117

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` State of North Carolina
Department of Environmentand Natural Resources
Division of Water Quality
James B. Hunt, Jr., Governor
Wayne McDevitt, Secretary. _
A. Preston Howard, Jr., P.E., Director
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NoRTH CARo-INA DEPARTMENT of
ENVIRONMENT AND NnruRAL REsouRCEs
November 17, 1998
RICHARD N. HICKS
FARMViLLE, TOWN-BIOSOLIDS
PO BOX 86
FARMVILLE, NC 27828
Subject: Specific Oxygen Uptake Rate Testing Compliance
Land Application of Residuals
Permit Number: WQ0008778
PITT 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:
1. Percent Total Dry Solids. The residual must be less than 2 percent total dry solids. Diluting thickened
sludges is not acceptable.
2. Temperature Range. The SOUR may only be applied to sludges which are at temperatures between 10°C
and 30'C.,
3. Temt)erature 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 20°C value. The temperature
correction equation is as follows:
SOURIo= SOURS x eczan
where: T = sludge temperature in degrees Celsius
0 = 1.05 above 20°C
e =1.07 below 20°C
4. :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 VAS requirements.
5. '.Sample Holding Time. The maximum holding time is two hours. If the SOUR test cannot be completed
within 15 minutes of sampling, then the sample must be maintained under aeration until the test can be
completed..:
P.O. Box 29535, Raleigh, North Carolina 27626-0535 Telephone [phone] Fax [phone]
An Equal Opportunity Affirmative Action Employer 5017,7 recycled/10% post -consumer paper

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Specific Oxygen Uptake Rate Testing Compliance Permit Number. WQ0008778
Page 2.
6. _Testing Frequency andArithmeticMean Compliance. Variability in digester detention times, operating
temperatures, and sludge characteristics results in variability in SOUR test results for afacility 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 1 Enforcement Unit
Non -Discharge Permitting Unit
_ Washington Regional Supervisor
�y Training and Certification Unit
Central Files
MadoIyn S. Dominy, EPA Region 4
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CE�7RAL FILES