NC0021474_INSTREAM ASSESSMENT_19901221

XPDES DOCUMENT SCANNING COVER SMEET
NPDES Permit: NCO021474
Mebane WWTP
Document Type: Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Engineering Alternatives Analysis
201 Facilities Plan
Ciiii
7AVorrespon : draft permit
Permit History Date Range:
Document Date: ece� E bear 21 199
dais document is pri=mted oaa reuse paper-i@Pzore aiay
content on tlae re-%rerse side

DIVISION OF ENVIRONMENTAL MANAGEMENT "
December 21, 1990
MEMORANDUM
TO: Larry Coble, Regional Supervisor
Winston-Salem, Regional Office
,FROM: ,..; _ - Betsy�Johnson.?� F
' Technical Support,Branch
THROUGH'• •Mike Scoville )Rps '
Ruth Swanek 2(,S
Trevor Cleme nts (ZGS_,
r SUBJECT:'-,{' + 1' Ilnstream Assessment for the City of,Mebane .
< < r+ ! f"r6�A f 7 ,yi•"NPDES�:Permit�No NC0020339•' - x •• -.< ',
'-
)`
yt SOC CasetNo 90-66
1 r 1_ n J�/; L•'rfi ':t'"r'y'``17�' ;3`EY Tp' .l' -f-Fi• _ 1
. . t krra "r • ,.
t .F Sii++�3}rvVand•(Recommendations
^G r a� krw rF, i ;`w•,ti"k l27 a�r3 1 R "��t
Technica +Suppo hastcompleted an.ins s tream4dsessment ity,"of M for,�the .Cebane
l rt
rrgi� Y xf
X h b �,, �itn _
+s u i y r ,M1 The Tow%has.,�rd' sted-an�SOC`because its.,,facilityr isr outs,ofSrcompl fine with its 14 r
toxicity limitJ^and cannot'meet pits,new metals limits "r The City would",like to'
ielax the limits for cadmium from»2"ug/l to 11 .u'g%land.me=cury„fi6m 0,012rugL1
s
.ug/1 ': ' In addition;„the'City would,like:-6i add .0.,25`MGD-of`-domesEic:waste'
it to the.existinq 0 6613 average MGD. With the additional 0.25 MGD,% the plant
will„reach4a flow of10 9113rMGD.-which is well under the permitted flow of 1.25
The :requested'dadmium and Mercury limits will not;be permitted • 'There'.should be'
sufficient monitoring of these;metals, influent; effluent;. and.instream, to
determinehthe source and extent of pass-thrii diolations by'.industries"on water `
quality .Inst ream monitoring,should be conducted.monthly `100 Meet above and
belOWathe discharge"` Additionally, -oil and,greise:-should bet ncluded inrthe
r+ headworksianalysis_and monitored monthly ,at thetaeffluent for therduration,of 'the 'a
St. ".The;quarterly,toxicity'testing limit should 'remain during,the BOC. perio
OC d.
The':region-should'work'.with the,Pretreatment "andToxicity groups .to develop .
mileetonesfor`the •SOC to-ensure compliance'=with the limits for ,cadmium and '
mercur t.the end. of the_:Order.
Moadams Creek is .a zero flow stream, and since the Level-B model, is,not .ieliable
for non steady-state flows, a Level-B analysis was not performed. Per 61 (b)
criteria, the instream assessment is based on actual instream.00nditions and
expected impacts of additional wasteflow. Since the instream DO standard is
currently being met and an expansion to 2.5 MGD has been approved, the
additional domestic flow of 0.25 MGD (which is within the design flow of 1.2
MGD) ; should not be a problem with respect to DO.

Background Information
The City of Mebane WWTP discharges into Moadams Creek, a class "C" stream, which
flows 1.3 miles to Back Creek, a tributary of the Haw River. Moadams Creek
drains approximately 0.9 square miles at the discharge site. The USGS estimates
the following flows at the discharge site: summer 7Q10 = 0 cfs, winter 7Q10 = 01
30Q2 = 0.07 cfs, and average flow = 0.8 cfs.
' The Mebane WWTP has an inadequate pretreatment program. Pass-through violations
by industries have caused Mebane to violate its permit limits for cadmium and
mercury. Since the instream waste concentration is 100%, any exceedances of
Mebane's permit limits are exceedances of water quality standards and may
promote toxic effects to the stream. In addition, the City of Mebane has had
difficulty meeting its chronic toxicity testing requirements. Specifically,
Mebane failed its toxicity tests in November 1989, December 1989, and January
1990; cadmium levels exceeded the permit limit during January. The City has
passed its three tests since that time with cadmium and mercury levels within
permitted limits.
Analysis and Discussion .
Instream data indicate that there is additional assimilative capacity available
in Moadams Creek. Though the effluent dominates the streamflow at all times,
during low flow conditions, the effluent increases the downstream DO levels.
- - .. .Summer DO levels (July. - October) have improved over the last three years from
an average of 7.4 mg/1 to 8.2 mg/l. An additional 0.25 MGD of domestic waste is
not expected to impact Moadams Creek. The City has been placed under a
moratorium for additional industrial users.
As Mebane is under an industrial moratorium, requests for additions of
industrial flow will not be permitted without intense scrutiny by the regional
office and the pretreatment group. Any additions to industrial flow, such as .
that requested by GE, must include a corresponding reduction in pollutant
concentrations in order to maintain loading at the current levels.
The requested limits for cadmium and mercury exceed the State chronic criteria
of 2 and 0.012 ug/l respectively. The mercury limit exceeds the Federal acute
criteria of 2.4 ug/l. These limits will not protect aquatic life over time nor
during the SOC. DEM will not assign permit limits which will not protect
aquatic life. Since the metals violations are due to pass-through violations by
Mebang's industries, monitoring of the influent, effluent, and stream will be
required in order to track any violations of water quality and/or pretreatment -
limits. Mebane can then pass any assessments for violations on to the
appropriate industries.
cc: Steve Tedder
Kent Wiggins
Central Files

Request Form for In-stream Assessment for 67B
NAME OF FACILITY—� Q _!�G[1'/1_G__----- SU)B-B7ASIN =
//y� -- T / SIGN FLOW
COUNTY_s��!�=`_/1L"_LG REGION �11I/NSI�/� = F
RECEIVING STREAM 6.1 7
NOV 0 y 199U
BACKGROUND DATA JLITIES ASSESSMENT UNIT
h . why is SOC needed? (Facility is out of compliance with which
effluent limits?)
NOV 1 3 1990
— B . ,:i story of SOC requests : N
1 . Monthly Average waste flow "" ""•' %n.iia,H
prior to any SOC � ' mgd
U i
©Time period averaged 6- thru s ��
2 . Previously approved SOC ' s : /"tIDN6
Date : flow : mad
Date : flow : _mgd
total of previously approved SOC flow : ----mgd
3 . Flows lost from plant A10 flow : _mgd
( facilities that have gone
off line )
i
4 . Current SOC request f1o•.+ : (� , ZS� _mgd
5 . Total plant flow post-SOC
( sum of original flow and
soc flow minus losses) flow -- © � ' mgd
6 . Is this an accurate flow balance for p/�Hhy/why not?
L
NO ,
S �f

C . Please attach DMR summary for past year for all permitted parame-
ters . If possible , include reports from: previous years if
I
acility has been under SOC for more than a year .
CURRENT SOC_REOUEST .
A . Request is for domestic or industrial waste? If it is a combin-
ation , please specify percentages _ _�)OYrv,, 'c
5a /a'2 � � A/Aw a-yt 2;T ��
B . What type of industry? Please attach any pertinent data .
ON
C . The region proposes the following SOC limits :
BODS
NH3 / mg/l
DO_ mg/1
TSS_J (/30 _mg/1
fecal coliform_ 20 ( Zyo) #/100ml
pH (7 9 1116-�LsU
-�/ -
other parameters
D . What is the basis for these limits?
UGC/�`�"
be-
2em &f-'v o va/ o/ o�
VJ LA
-7/ZS4.
IyD