NC0025453_correspondence_19910927

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State of North Carolina
Department of Environment, Health, and Natural Resources
Division of Environmental Management
512 North Salisbury Street • Raleigh, North Carolina 27611
James G.Martin,Govemor George T.Everett,Ph.D.
William W.Cobey,Jr.,Secretary Director
September 27, 1991
Mr. Robert Hyatt
Town Manager
Town of Clayton
P.O. Box 879
Clayton,North Carolina 27520
Subject: Town of Clayton
Effluent Nutrient Limitations
NPDES Permit No. NCO025453
Johnston County
Dear Mr. Hyatt:
Your consulting engineer,Mr. Bryan Blake,recently contacted our office to
request whether the State had updated its recommendations for phosphorus removal
at the Clayton wastewater treatment plant(WVV P) based.upon its study of the
receiving waters. As explained In our letter dated February 20, 1990, it has been DEM's
experience that the discharge of nutrient-laden wastewater in the headwaters of a lake
or pond contributes to excessive algal growth in the receiving impoundment. This algal
growth is associated with eutrophic conditions which impair the best usage of the
waterbody as defined by 15NCAC 213.0101 (c). The Technical Support Branch of DEM
has recently analyzed water quality data collected during the summer of 1990 in the
pond downstream from the Town of Clayton WWTP discharge. In light of the sfudy
results,the following comments are provided In.reference to the nutrient limitations and
monitoring requirements of the subject NPDES permit.
DEM's study results Indicate nutrient enrichment In the receiving surface waters
with a high probability of more severe algal growth under those physical and chemical
factors which stimulate productivity. The physical factors (i.e. high water temperature,
sufficient solar radiation,shallow water body,and a detention time of more than seven
days) are present in the pond during the summer months. The chemical factors(i.e.
high nutrient concentration levels)already exist at the current WWTP's discharge flow
and total phosphorus(TP) removal efficiency. Furthermore,our calculations indicate
that wastewater flow increases(i.e. from the current average flow)with a total
Mullion Prewndon Pays
P.O.Box 27687,Raleigh,North Carolina 27611-7687 Telephone [phone]
An Equal Opportunity Affirmative Action Employer

Mr. Robert Hyatt
Page Two
phosphorus concentration of 2 mg/I (i.e. based on the basinwide "Nutrient Sensitive
Waters" TP limitation)will also violate an instream target concentration of 0.1 mg/1 TP in
the pond.
Although the 1990 study clearly indicated nutrient enrichment,the actual
eutrophic response indicators(i.e. chlorophyll-a,pH and dissolved oxygen)were not far
from meeting State standards in the pond. Therefore,the Division will not require the
Town of Clayton to meet an NPDES TP limit lower than 2 mg/I at this time. However,
given that this decision was based on a very limited amount of data,DEM will be
requiring the Town to increase its instream monitoring to further assess the impact of its
discharge on the quality of the receiving waters. Therefore,upon renewal of your
NPDES permit in 1992,you may expect the following instream monitoring requirements:
INSTREAM MONITORING REQUIREMENTS
INSTREAM MONITORING UPSTREAM DOWNSTREAM DOWNSTREAM
PARAMETERS SITE SITE I SITE 2
DO WEEKLY WEEKLY WEEKLY'
TEMPERATURE WEEKLY WEEKLY WEEKLY'
CONDUCTIVITY WEEKLY WEEKLY WEEKLY
PH WEEKLY WEEKLY WEEKLY
FECAL COLIFORM WEEKLY WEEKLY WEEKLY
TOTAL PHOSPHORUS 2/MONTH 2/MONTH 2/MONTH
PO4 2/MONTH 2/MONTH 2/MONTH
TKN,TN,NH3-N 2/MONTH 2/MONTH 2/MONTH
CHLOROPHYLL 2 MONTH 2 MONTH 2/MONTH
UPSTREAM LOCATION: AT NC 42
DOWNSTREAM LOCATIONS:
SITE 1: AT NCSR i 560
SITE 2: IN THE POND BELOW NCSR 1560(AT THE DAMS CREST)
INSTREAM MONITORING(EXCEPT TOTAL PHOSPHORUS,PO4,TKN,TN,NH3-N&CHLOROPHYLL A)IS TO BE
SAMPLED 3/WEEK DURING JUNE,JULY,AUGUST&SEPTEMBER
THESE PARAMETERS,AT THIS STATION SHOULD BE SAMPLED BEFORE 8:00 AM
TOTAL PHOSPHORUS,PO4,TKN,TN,NH3-N&CHLOROPHYLL A PARAMETERS ARE TO BE SAMPLED 2/MONTH
DURING JUNE,JULY.AUGUST&SEPTEMBER ONLY
While the State will not be placing a limit In your NPDES permit that is more
restrictive than 2 mg/I TP,you may wish to proceed with a phosphorus/removal
equipment design that achieves as low of a TP concentration as is economically
reasonable and environmentally sound in order to lessen the risk of downstream water
quality violations and subsequent reopening of the permit to enforce a lower limit. The
closer the Town is able to come to the instream target concentrations of 0.05 to 0.1 mg/I
TP and 0.5 to 1.0 mg/I TN,the less risk there will be for a forced requirement through a
modified permit limit. Alternatively,the Town may wish to explore relocating its
discharge downstream of the pond.

Mr. Robert Hyatt
Page Three
If you have any questions about this matter, please contact Mr. Juan C.
Mangles or myself at(919) 733-5083.
Sinc ely,
T e r Clements,Asst. Chief
o er Quality Section
JCM/JTC
CC. Tim Donnelly
Dale Overcash
1 44e �
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