NC0020389_Staff Comments_19881221

DIVISION OF ENVIRONMENTAL MANAGEMENT
December 21, 1988
MEMORANDUM
TO: Dale Overcash
THROUGH: Steve Tedder 144
FROM: Thomas Stockton
Trevor Clements
SUBJECT: Town Of Benson WWTP NPDES permit monitoring requirements
NC0020389
Johnston County
The Town of Benson has requested the following revisions in the draft NPDES
permit: 1) reduction of the monitoring frequency for lead, copper, zinc, and
chromium from monthly to semi-annually, 2) deletion of monitoring for cyanide, 3)
retention of the current upstream monitoring site and, 4) deletion of one down-
stream monitoring site. Please find attached- copies of the effluent limits and
monitoring pages from the draft NPDES permit.
In February 1988 the Division advised the Town that the monitoring frequency
for metals would be re-evaluated after a period of monthly monitoring and
subsequent sampling data review. In November 1988 the Town submitted the follow-
ing data for the period March through September 1988.
Month Lead Copper Zinc Total Chromium
(mg/1) (mg/1) (mg/1) (mg/1)
March 0.008 0.09 0.81 0.003
April 0.014 0.12 0.09 0.005
May 0.011 0.17 0.22 0.010
June 0.010 0.12 0.18 0.003
July 0.012 0.18 0.15 0.014
August 0.009 0.15 0.49 0.010
September 0.009 0.12 1.18 0.010
Effluent concentrations for these metals warrant concern. The Town dis-
charges to Hannah Creek which has an estimated 7Q10 of 0.0 cfs at the point of
discharge. Since the receiving stream provides no dilution, water quality stan-
dards/action levels for the metals in question must be met in the effluent.
Effluent concentrations of zinc and copper all severely violate the action levels
for these metals. Of special concern is the September zinc concentration of 1.18
mg/1. Lead concentrations for this period were all above or within 2 ug/1 of the
proposed standard of 10 ug/l. Effluent total chromium concentrations were also
elevated. Total chromium in the July sample exceeded the proposed standard for
hexavalent chromium of 11 ug/1 though the form of the chromium in the effluent is
unknown.

With these concentrations effluent toxicity would be expected, however, dur-
ing this period the facility has "passed" three chronic pass/fail self -monitoring
toxicity tests and one acute toxicity test performed by the Division found no
acute toxicity. Significant reproduction suppression was found in an effluent
chronic toxicity test performed by the Division in November 1987, however, ele-
vated residual chlorine was a likely major contributor to the observed toxicity.
It is probable that the metals measured were biologically unavailable and, there-
fore, their effects were not reflected in the chronic toxicity tests. These met-
als may reappear, released from the sediments in a biologically available form as
the swamp alternates between an anaerobic and an aerobic environment during high
flow/low flow periods. Due to these uncertainties and in consideration of the
high metals concentrations, Technical Services recommends that the Town of Benson
continue their monthly monitoring.
As with zinc, lead, copper, and chromium, the monthly cyanide monitoring
should be conducted until a baseline database is developed that will allow an
assessment of the need for continued monitoring.
The Town requested that the current upstream monitoring site, NCSR 1158, be
retained in favor of the site recommended in the draft permit, NCSR 1211. Samp-
ling at NCSR 1211 was recommended based on accessibility considerations with con-
struction of I-40 observed during site visits. NCSR 1158 appears to be a prefer-
able site if the Town finds it acceptable.
The draft NPDES permit for this facility includes a design capacity expansion
to 1.5 mgd. A modeling analysis of the impact of this expansion proved intract-
able due to the low flow and swampy characteristics of Hannah Creek. On -site
inspections were conducted in lieu of a modeling analysis to identify potential
impacts and likely alternatives to expansion of the discharge to Hannah Creek.
Water quality problems in Hannah Creek have been identified through both self -
monitoring data and the on -site inspections (see memos dated 1/27/88, 5/23/88,
and 10/30/88 in Central Files). These problems will likely be exacerbated by any
increases in loading. This situation warrants a comprehensive self -monitoring
program which includes two downstream monitoring sites.
Regarding the confusion on the location of the downstream monitoring sites,
the locations should read NCSR 1171, not NCSR 1711, and the I-95 culvert,
cc: Bill Kreutzberger
Central Files
Ken Eagleson

State of North Carolina
Department of Natural Resources and Community Development
Division of Environmental Management
512 North Salisbury Street • Raleigh, North Carolina 27611
James G. Martin, Governor
S. Thomas Rhodes, Secretary
December 6, 1988
Mr. Larry Horton
The Wooten Company
120 North Boylan Avenue
Raleigh, North Carolina 27603
R. Paul Wilms
ctor
ij
DEC K„+?
88
TECHNICAL SERVICES SRANC
H
SUBJECT: Draft Permit Comments
NPDES No. NC0020389
Benson WWTP
Johnston County
Dear Mr.Horton:
This letter is to acknowledge receipt of your letter dated November 24, 1988,
containing comments on the subject Draft Permit. The Division of Environmental
Management will consider your comments in making its decision on the issuance of the
permit. If you feel that your comments are not addressed in the issued permit, you
may request an adjudicatory hearing in accordance with Chapter 150B of the General
Statutes of North Carolina within 30 days of issuance of the permit.
If you have any questions, please contact me at [phone].
Sincerely,
fl?‘
M. Dale Overcash
Supervisor, NPDES Permits Group
MDO/tla
cc.The Honorable Charles W. Matthews
Mr. Trevor Clements (with attachments)
Mr. Bill Kreutzberger (with attachments)
Pollution Prevention Pays
P.O. Box 27687, Raleigh, North Carolina 27611-7687 Telephone [phone]
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