DEQp00021067

North Carolina Division of Environmental Management
Water Quality Sectioi/Rapid Assessment Group
October 18, 1993
MEMORANDUM
TO: Greg Nizich
THROUGH: Carla Sanderson4
FROM: Dave GoodricO/A
SUBJECT: Permit Renewal Issues for DuPont (Fayetteville) NPDES Permit
NPDES No. NC0003573
Bladen County
030616
This is in response to questions regarding the NPDES permit referenced above.
Five concerns were voiced in the 9/21/93 meeting with Mike Gell, Bruce Youtsey
(DuPont), Coleen Sullins and you which were referred to me in a 9/22/93 memorandum
"Why is oil and grease monitoring required for the 001 outfall?" In reviewing an
annual pollutant analysis from the 001 outfall, it was discovered that some oil and grease
had been found in the effluent (19 mg/1). It is recommended that this parameter be kept in
this permit. After 12 months of monitoring and demonstrating this is not a concern,
DuPont may request to delete it from their permit.
"Can monitoring of OCPSF parameters be reduced to annually?" This is based on
monitoring done since April 1990 which has not documented any OCPSF chemicals in the
effluent. I was not aware that such monitoring had been done by DuPont at the time of the
wasteload allocation. Monsanto has similarly collected data prior to the issuance of their
NPDES permit and DEM allowed a reduction of sample collections for all OCPSF
chemicals from quarterly to annually. Monsanto still had to sample for parameters which
were found above detection limits on a quarterly basis. DuPont, on the other hand, has
consistently shown that no OCPSF chemicals have been detected in 12 samples collected
over three years on a (more or less) quarterly sampling frequency. It therefore seems
reasonable to reduce their monitoring for such parameters to annual collections with a
provision that those parameters which are found above laboratory detection levels be
monitored on a quarterly basis until the parameter in question is not found above laboratory
detection limits for four consecutive sampling periods.
"What flow was used in determining the limit for PAH?" An average flow should
have been used, but was not. The correct limit for PAH should be changed to 57 µg/l.

- page 2 -
Comments on DuPont (Fayetteville) NPDES Permit
October 18, 1993
"Can the limit for fluoride be revised to a summer/winter limit?" This has not been
something that DEM has done when limiting toxicants because the standard is meant to
protect for acute effects around the pipe as well as chronic effects. Two other points
should be noted about the chloride limit: first, it is a water -quality based limit (i.e., based
on a standard), and second, it seems unlikely that DuPont will have a problem meeting
such a limit. By way of example on the second point, the maximum single -day fluoride
value from 10/91 - 9/92 was 941 lbs/day. If a concentration is back -calculated using the
single -day minimum flow from the same time period, this will represent the highest
possible fluoride concentration for that time period. This calculation yields a predicted
fluoride concentration of 16.7 mg/l. Mass limits and seasonal limits do not seem
warranted.
"What is the appropriate toxicity test limit and why is an acute toxicity test required
when the IWC is less than I%?" Since the 001 and 002 outfalls combined before the WET
test was collected, the IWC was calculated based on the total flow from these sources (17
MGD). The resulting IWC was so similar to the old WET test limit that the Rapid
Assessment Group recommended the same limit be given for this permit to be consistent
with the old permit. From discussions with you, DuPont is willing to collect the sample
for WET testing either before or after the combination of wastestreams. I agree that there
should be consistency between permits with regard to where to sample for WET testing.
After speaking with Larry Ausley (Aquatic Toxicology), this should be decided on a case-
by-case basis. Again, to be consistent with the last permit, I recommend keeping the same
analysis and sampling point (i.e., after the combination of wastestreams). The appropriate
toxicity test should be a quarterly, chronic pass/fail test at 3.3% using ceriodaphnia as the
test organism.
As dilution increases, chronic toxicity becomes less likely as mixing dissipates the
effluent. Acute (or end -of -the pipe) toxicity remains a concern regardless of dilution. An
administrative decision was made to have complex dischargers perform chronic WET tests
when IWC is >1%. Below this concentration, acute tests are required.
cc: Grady Dobson, FRO