NC0050342_correspondence_19900228

PUBLIC WORKS
DEPARTMENT
City of Winston-6alem
February 28, 1990
Mr. Trevor Clements
North Carolina Department of Environment,
Health and Natural Resources
Division of Environmental Management
Post Office Box 27687
Raleigh, North Carolina 27611-7687
RE: 12-18-89 "Notice of Violation" for Muddy Creek
Plant's 002 Discharge (NC0050342)
Dear Mr. Clements:
MAR 1990
PREIR
f
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The violations cited in the above referenced notice of vio-
lation resulted from actions taken by the City to prevent mechani-
cal damage and solids "washout" at the plant during a severe flood
on October 2, 1989. For your convenience, I have attached a copy
of the violation letter.
T
Since the permit limits were exceeded for reasons beyond he
city's control, it is requested that the violations be remove.'
from the record. Parts II B.3 and II B.4 of the permit provi es
that violations incurred because of situations such as flooding
are excusable in that they meet the definition of an "upset".
The Winston-Salem regional office was notified on October 2,
1989 that the plant was receiving a flow nearby three times the
permit limit and that all the plant's pump capacity was on line to
prevent the water level in the influent sump from rising high
enough to damage the lower bearing assembly on the pumps.
Partially treated wastewater was also discharged during this
period because the majority of the plant's activated sludge system
had to be bypassed to prevent solids loss. A copy of a confirma-
tion letter that was sent to the regional office regarding this
incident is attached. This letter describes in detail the events
which occurred and the actions taken by the city to ensure the
future treatment of wastewater.
MAR 0 6 1990
Box 2511, Winston-Salem, North Carolina 27102

Mr. Trevor Clements
February 28, 1990
Page 2
The Muddy Creek Plant must attempt to treat all the flow
which enters the headworks during precipitation events because
the plant's influent wet well is not equipped with a high
overflow to prevent the water level from rising to the point where
the equipment is damaged.
On October 2, 1989 and on three other occasions since 1987,
the lower bearing assemblies on the influent screw pumps were
flooded when the influent flow rate exceeded the plant's 44 MGD
pumping capacity.
The city is concerned that one of these occurrences could
damage the pumps sufficiently to render them unserviceable for an
extended period of time. Should this occur, a major portion of
the raw sewage flowing to the plant would have to be diverted to
the stream while repairs were made.
To prevent a situation such as this, the city is considering
initiating an engineering review to determine the feasibility of
constructing an overflow line to prevent flood damage to the in-
fluent pumps during events such as that of October 2, 1989. The
overflow would only be used to avert flood damage and it would be
designed so the plant's headworks could not be bypassed voluntar-
ily.
Since the feasibility study would be relatively expensive,
the city would appreciate a response from DEM as to whether or
not such a modification would be considered for approval.
In regard to the violations cited for the 002 discharge, we
wish to reiterate that the permit limits assigned to this dis-
charge point should not be based on the 7Q10 flow of Muddy Creek.
The city can only discharge through 002 during flood conditions
when the stream flow is well in excess of the 7Q10 rate. There
are no diversion valves allowing the discharge to be used other-
wise.
To illustrate this, please consider that the flow rate in
Muddy Creek during the flood of October 2, 1989 was 6350 CFS! The
16 mg/1 BOD limit the plant was cited for violating, however, was
calculated based on a 7Q10 flow of 74 CFS. The plant's discharge
contained 23 mg/1 BOD and did not pose a threat to the water qua-
lity in the stream.

Mr. Trevor Clements
February 28, 1990
Page 3
It is the City of Winston-Salem's policy to operate our waste
treatment facilities in a manner to ensure compliance with all ap-
plicable permit limitations and to protect the environmental qua—
lity of the surface waters. There are times, however, when acts
of God make it necessary for our ORC's to take steps to protect
the treatment works, even though those steps may result in the
violation of the permit.
The city feels that the actions taken on October 2, 1989 were
necessary to prevent a prolonged period of noncompliance and, in
this respect, the water quality of the receiving stream was en-
hanced, rather than harmed.
Please contact me if you have any questions regarding this
matter and your cooperation is appreciated.
Sincerely,
Stanley „Webbzzha
Plant Manager -Muddy Creek Plant
pc: Tom Griffin, Utilities Superintendent
Larry Coble, W-S Regional Office
NPDES NC0050342 File
Attachment(s)
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