pH_Monitoring_for_Compliance_with_40_CFR_503_20090923

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

James B. Hunt, Jr., Governor
Wayne McDevitt, Secretary
Kerr T. Stevens, Director

August 17, 1999
Contact
Facility
Street Address
City, State Zip
Subject: pH Monitoring for Compliance with 40 CFR 503
Land Application / Distribution & Marketing of Residuals
Facility
Permit Number: Permit #
County County
Dear Contact:

The Environmental Protection Agency has amended 40 CFR 503 to redefine its definition of pH. The final rule will be promulgated as of August 18, 1999. The following guidance is to
be implemented to help you maintain compliance with both 40 CFR 503 and your state issued permit.

A high alkalinity (low sodium, glass electrode) probe must be used for all pH levels exceeding pH 10.0. Use of pH paper as a measurement method is not satisfactory. The pH meter must
be calibrated to a known high pH standard solution, or a fresh saturated solution on calcium hydroxide in distilled water to pH 12.454.
pH readings must be taken at 25°C, or corrected to 25°C. At other than 25°C, A conversion calculation may be used to correct the pH reading to the standard temperature of 25°C. Correction
Factor (CF) = 0.03 pH units * (T measured – 25°C ). Actual pH = measured pH +/- the Correction Factor.
Automatic temperature compensating devices on the pH meter do not correct for solution concentration due to solubility vs. temperature of samples. These devices only correct for variations
in the probe conductance due to temperature changes.
There must be significant moisture in the residual / lime mixture to ionize the lime, and allow migration of the OH- ions throughout the residual mass to achieve stabilization. There
must be sufficient moisture to convert all of the quicklime into hydroxic form.
Dry lime mixed with dry sludge may have difficulty meeting the standards set forth in 40 CFR 503. ( pH of 12.0 or greater within 2 hours of addition and maintain a pH of 11.5 for the
following 22 hours with no further addition.) There must be sufficient moisture in the lime / residual mixture to ionize the lime, (providing hydroxide ( -OH) ions throughout the mixture
pore water layer), in order to raise the pH levels to the regulatory requirement.

PH readings must be taken only after the ammonia gasses off. Ammonia gasses off at pH +10.5, temporarily raising the pH reading to +12.0; only to return to 10.5 after off gassing is
complete. There must be sufficient moisture and mixing of the residual / lime mixture to insure complete conversion of the ammonia and release of the gas prior to reading pH; assuring
proper lime application rates. This prevents “pH decay” which is due to insufficient lime dosage.
A slight excess of lime provides a buffering capacity and insures you continue to meet regulatory requirements for vector control.

Data to verify stabilization must include the:
Number of gallons of residual
pH at start
corrected pH at start
amount of lime added in pounds / gallons
pH measured at 2 hours
corrected pH (see attached chart)
pH measured at 24 hours (total elapsed time)
corrected pH (see attached chart)

Attached, please find a conversion chart for pH corrections. Use the measured temperature and add / subtract the Correction Factor.

If you have any question, please do not hesitate to contact me at 919-733-5083 ext. 529 or e-mail me at [e-mail]

Sincerely,

Kevin H Barnett
Environmental Specialist

cc: Madolyn Dominy, EPA Region 4
Non-Discharge Permitting Unit
Non-Discharge Compliance / Enforcement
Region
Central Files