NC0024112_Environmental Assessment_20040408

April 8, 2004
MEMORANDUM
TO: Hannah Stallings
Construction Grants & Loans Section
FROM: Mike Templeton
NPDES Unit
SUBJECT: City of Thomasville
Revised Draft Environmental Assessment, 2/4/2004
NPDES Permit No. NC0024112
Davidson County
Michael F. Easley, Govemor
State of North Carolina
William G. Ross, Jr., Secretary
Department of Environment and Natural Resources
Alan W. Klimek, P.E., Director
Division of Water Quality
Project No. CS370619-02
I have reviewed Thomasville's revised draft environmental assessment (EA) on behalf of the NPDES
Unit and offer the following comments. Feel free to call me at 733-5083, ext. 541, if you have any
questions or comments on these.
Effluent Limitations. Table 1 of the EA lists existing discharge limits and speculative limits for the
facility. Several of the speculative limits are incorrect.
• The speculative limits for BOD5 and ammonia are based on DWQ's letter of March 30,1995.
The Division has since established new permitting strategies in its Yadkin -Pee Dee River
Basinwide Water Quality Plan (1998, 2003), and these speculative limits should no longer be
used for planning purposes.
The permitting strategy in the Yadkin -Pee Dee plan calls for no increase in loading from
existing discharges to the Abbotts Creek Arm of High Rock Lake. In its 2001 comments, the
NPDES Unit referred to the Plan and noted that "the City should expect that discharge
limitations for BOD5 and ammonia for any expansions above 4.0 MGD will be no greater that
the currently permitted levels on a mass basis. Where the concentration -based speculative
limits developed in 1995 differ from these mass limits, the more restrictive of the two shall
apply." The revised EA still does not appear to reflect this strategy.
The City's current limits for BOD5 and ammonia are 5 mg/L and 2 mg/L, respectively
(summer). Assuming the ultimate CBOD is 2.0 times the BOD5 limit and ultimate NBOD is 4.5
times the ammonia limit, the load allowed under the current permit is:
((5 x 2.0) + (2 x 4.5)) mg/L x 4.0 MGD x 8.34 = 6341b/day (summer)
Using the speculative limits given in 1995, the load would increase substantially with the
expansion:
((5 x 2.0) + (1 x 4.5)) mg/L x 6.0 MGD x 8.34 = 726 lb/day (summer)
In order to maintain the currently permitted load at the higher flow limit, the Division must
reduce either the BOD5 limit or the ammonia limit or some combination of the two. The
following table summarizes the above results and shows possible combinations of BOD5 and
ammonia limits (summer) that would maintain the current loading at 6.0 MGD:
North Carolina Division of Water Quality
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
[phone]
FAX [phone]
On the Internet at http://h2o.enr.state.nc.us/

City of Thomasville - Draft Environmental Assessment
April 8, 2004
Flow
(MGD)
BOD5
(mg/L)
NH3-N
(mg/L)
Load
(Ib/day)
4.0
5.0
2.0
634
6.0
5.0
1.0
726
6.0
5.0
0.6
634
6.0
4.5
0.8
634
6.0
4.0
1.0
634
6.0
3.5
1.3
634
6.0
3.0
1.5
634
These results are presented for illustration only and are not intended to represent new
speculative limits.
• Upon permit renewal or modification, the Division will add weekly average limits for
ammonia to implement a recent policy change. The new ammonia limits will be three times
the corresponding monthly average limit. This change is being implemented in municipal
permits state-wide and is necessary to ensure consistency with federal NPDES regulations. (In
similar fashion, non -municipal permits will receive daily maximum limits set at six times their
monthly average limits.)
• The speculative limits for metals and cyanide are based on faulty assumptions. These limits
are calculated to prevent the instream concentrations from exceeding NC water quality
standards. As permitted flow increases, the limits will be reduced. Upon receipt of the permit
application for expansion, the Division will evaluate effluent data and determine which
parameters require limits and what those limits will be.
• The revised EA references a 2nd set of speculative limits that were provided by letter on July
16, 1999. There is no record of the letter in DWQ's Central Files. Please provide a copy for our
files.
Adequacy of Existing Discharge Line. The 2001 copy of the 201 Facilities Plan proposed to
discharge peak flows in excess of the discharge line's 10 MGD capacity into Hamby Creek adjacent
to the treatment plant. The NPDES Unit noted certain concerns with the proposal at that time. The
revised EA does not mention the proposed discharge, nor does it indicate whether the overflows are
still expected to occur. Please clarify how this matter has been resolved.
cc: Winston-Salem Regional Office
NPDES Files
2