NC0020354_Mercury Requiremnt_20030812

Hugh Montgomery
Town of Pittsboro
P.O. Box 759
Pittsboro, NC 27312
Dear NPDES Permittee:
Michael F. Easley, Governor
William G Ross Jr , Secretary
North Carolina Department of Environment and Natural Resources
Alan W. Klimek, P E, Director
Division of Water Quality
August 12, 2003
Subject: NPDES Permit NCO020354 Mercury Requirement
EPA Method 1631 / Additional Information
Pittsboro WWTP
Chatham County
In a previous letter dated August 30, 2002, your facility was notified of being subject to a new low-level mercury
analysis (EPA Method 1631) for NPDES monitoring requirements beginning September 1, 2003. The notification
letter was mailed to 155 subject facilities. Since that mailing, the Division has participated in several Mercury 1631
Workshops to provide the regulated community with information on the new analytical requirements and clean
sampling recommendations. Based on comments received at these workshops, the following items are intended to
clarify certain NPDES requirements for the 155 subject facilities.
1. Mercury Sampling and Comphance: It is recommended that facilities collect some effluent samples for Method
1631 analysis prior to the 9/1/2003 effective date, in order to gain experience with the recommended clean
sampling techniques as well as the analysis requirements. NPDES compliance will be judged using the new
method results beginning 9/1/2003.
2. What Samples are Subject to Method 1631: Beginning 9/1/2003, all effluent samples collected for mercury
from the subject facility are required to perform low level mercury analysis. This includes effluent samples
collected for any of the following requirements: a) monitoring specified in your "Effluent Limitations and
Monitoring Requirements" page of your NPDES permit; b) monitoring specified in your NPDES Pretreatment
Short Term Monitoring Plan (STMP) or Long Term Monitoring Plan (LIMP); and c) NPDES permit renewal
requirements. The effluent samples must be analyzed by a laboratory certified by the Division for Method 1631,
and effluent results must be submitted with the applicable monthly Discharge Monitoring Report (DMR).
3. Grab Samphng: The Environmental Protection Agency (EPA) currently recommends that mercury samples for
Method 1631 analysis be collected as grab samples, since automatic composite samplers may be more subject to
contamination. Therefore, the Division will allow permittees to collect single grab samples directly into lab -
provided sample bottles for permit requirements, even though the NPDES permit may specify "composite"
samples for mercury. The grab sample must be representative of the discharge.
4. Laboratory Reporting Level- Based on the Division's review of commercial laboratories currently performing
Method 1631, a majority of labs were reporting a minimum level of quantitation (NIL) of either 1.0 ng/l or less.
The Division will require an ML of 1 ng/l beginning 9/1/2003, which is considered reasonable and economically
achievable.
5. Field Blank Collection: Method 1631 requires that a minimum of one field blank accompany each set of samples
collected from the same site at the same time. The field blank is used to identify contamination during sample
collection and transport activities. If mercury is present in the field blank at levels that would compromise reliable
measurement of mercury in the wastewater sample, you should assume that the effluent sample was contaminated
during collection or transit, and you will need to eliminate any source of contamination that has been identified.
The permittee shall report all effluent sample results on the applicable monthly DMR. if a field blank fails to
meet quality control criteria, the permittee should note that fact in the DMR Comments Section, and append the
lab sheet for that field blank. For those facilities sampling for mercury under a limited monitoring frequency
(quarterly or less, such as Pretreatment LTMP/STMP monitoring), you must resample if the field blanks are
outside quahty control criteria. However, for those facilities with more frequent effluent monitoring requirements
N. C Division of Water Quality 1617 Mail Service Center Raleigh, NC 27699-1617 [phone]
Customer Service 1 800 623-7748
NCDEN

NPDES Mercury Requirement
Page 2 of 2
(i.e., monthly or more frequent), resampling is not required if field blank quality control criteria are not achieved
for a given sample event. Refer to Method 1631, Revision E (Section 9 4.5 2- Quahty Control- Field Blanks), for
specific quality control criteria regarding field blank acceptability and effluent sample rehabibty.
6. Field Blank Subtraction: Method 1631 provides for subtraction of field blanks (provided they meet quality
control criteria defined above) from the effluent sample result if deemed appropriate by a regulatory agency.
Upon review, the Division will not allow field blank subtraction from effluent samples for reporting purposes.
Based on a recent study using Method 1631 for wastewater samples collected at 38 wastewater treatment plants,
field blank concentrations were generally below the method quantitation level. Therefore, beginning 9/1/2003,
the permittee shall report the result of the effluent sample as provided by the certified lab, without field blank
subtraction, on the monthly DMR submission. In the event of a mercury limits violation, the permittee retains
the option to request remission of any penalty. If the permittee believes that the violation resulted from
background contamination as indicated by the field blank, the permittee will need to document that fact with field
blank quality control data.
7. Sample Preservation/Holding Times: Samples for total mercury analysis by Method 1631 must be collected in
tightly -capped fluoropolymer or glass bottles and preserved with BrCI or HCl within 48 hours of sample
collection. The time to sample preservation may be extended to 28 days if a sample is oxidized in the sample
bottle. Samples must be analyzed within 90 days of sample collection.
If you have any questions about the contents of this letter, please contact the applicable Division staff listed below:
Mercury Method:
Certified Labs for Method 1631
NPDES Permitting:
NPDES Compliance:
NPDES Pretreatment:
Roy Byrd
Fred Bone
Tom Belnick
Vanessa Manuel
Dana Folley
Sincerely,
919-733-3908, extension 213
919-733-3908, extension 273
919-733-5083, extension 543
919-733-5083, extension 532
919-733-5083, extension 523
Original Signed BY
®arid A. Goodrich
Alan W. Klimek, P.E.
cc (hardcopy): CLANC, c/o Lev Hicks, Environmental Chemist Inc., 6602 Windmill Way, Wilmington, NC 28405
DWQ Regional Offices, Water Quality
cc (email)- EPA Region 4, Madolyn Dominy, Marshall Hyatt
DWQ Water Quality Section, Regional Office Supervisors
DWQ Laboratory Section; Steve Tedder, Larry Ausley, Jim Meyer, Roy Byrd, Fred Bone
DWQ Modeling/TiVIDL, Michelle Woolfolk
DWQ NPDES Compliance, Vanessa Manual
DWQ Pretreatment Unit
DWQ NPDES Unit
NC League of Municipalities, Anita Watkins
NC Labs Certified for Method 163le