NC0040797_correspondence_19890327

MEMORANDUM
TO:
FROM:
THRU:
SUBJECT:
Randy Dodd
Trevor Clements
DIVISION OF ENVIRONMENTAL MANAGEMENT
March 27, 1989
Jim Holloway
Legal Affairs
V
Instream ramifications of BOD, violations
Per your request, I haveprepared a brief discussion of why there is a
concern for effluent limit violations of BOD, at the Hickory - Henry Fork
WWTP.
DEM issues BOD, limits for all dischargers that contain organic matter
which is biochemically oxidizable. The aerobic breakdown of organic matter
in surface waters requires oxygen, and therefore places a demand on the
oxygen resources of the natural system. BOD (biochemical oxygen demand) is
the acronym for the laboratory method for measuring the demand on the natu-
ral system. (The standard laboratory procedure is to measure BOD after five
days, and hence the term BOD,.)
Elevated BOD, levels in a discharge result in lower dissolved oxygen
(DO) levels in the receiving water. The amount of DO depression is a func-
tion of a number of factors. In a stream, the most important factors are
the temperature, the interaction with the atmosphere, the characteristics of
the river bottom, the type and amount of microorganisms, and the dilution.
These factors are loosely termed "assimilative capacity"; the purpose of a
given wasteload allocation and water quality model is to quantify the
assimilative capacity for a given stream (in this case, in terms of BOD,)..
The water quality standard for DO (5 mg/1 in most surface waters, including
the Henry Fork River) provides the criteria for determining the allowable
BOD,. The DO standard is based on assuring survival and propagation of the
indigenous fish species and other biota.
The theoretical and practical development of the linkage between BOD,
and DO is quite extensive, and has been a cornerstone of regulatory programs
since before the 1972 Clean Water Act. If you wish t further explore the
rationale, or have any questions, feel free to call T*evor or myself at
733-5083.
RD/gh
cc: Steve Tedder