NC0025526_Instream Assessment_19930122

NPDES DOCUMENT SCANNING; COVER SHEET
NPDES Permit:
NC0025526
Walnut Cove WWTP
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Staff Report
Speculative Limits
Instream Assessment (67b)
Environmental Assessment (EA)
Permit
History
Document Date:
January 22, 1993
This document is printed on reuse paper - ignore any
content on tine reverse side

DMSION OF ENVIRONMENTAL MANAGEMENT
January 22, 1993
MEMORANDUM
TO Steve Mauney
THROUGH: Ruth Swanek Qc-5
Carla Sanderson
FROM: Susan A. Wilson
SUBJECT: Instream Assessment for the Town of Walnut Cove WWTP
NPDES No. NC0025526
Stokes County
Summary and Recommendations:
The Technical Support Branch has completed the instream assessment for the Town
of Walnut Cove. The Town requests an increase in domestic flow of 0.02 MGD and
relaxed BOD5 limits. With the addition of 0.02 MGD flow to the average yearly flow of
0.1597 MGD, the plant will reach a flow of 0.1797 MGD, which is below their permitted
flow limit (0.192 MGD).
The Town of Walnut Cove WWTP has operational problems, due to the lack of
process control capabilities of their dual facultative lagoons. With this SOC, the Town
requests an increase in domestic flow and an interim BOD5 limit of 60 mg/1. The facility
has had no previous SOC requests.
A Level-B analysis was performed to assess the impact of the additional flow and
relaxed BOD5 limits. The modeling analyses for this assessment indicate that the additional
wasteflow under the proposed interim limits will not cause a violation of the EMC 67 (b)
criteria (not causing a DO sag of greater than 0.5 mg/land not extending the DO sag length
greater than 0.5 miles).
The Town of Walnut Cove WWTP may add up to their design flow in domestic
waste (approximately 0.0323 MGD) without violating the 67 (b) criteria.
Background Information:
The Town of Walnut Cove WWTP discharges into Town Fork Creek, a class "WS-
IV" stream, which flows to the Dan River in the Roanoke River Basin. Town Fork Creek
drains approximately 113 square miles at the discharge site. The estimated flows at the
discharge site are as follows: summer 7Q10 = 8.9 cfs, winter 7Q10 = 20 cfs, and average
flow = 130 cfs.
The Town currently has dual facultative lagoons and cannot meet its BOD5 limit.
The Town has proposed to expand its wastewater capabilities to 0.5 MGD and install ne»
treatment. The new treatment would consist of extended aeration, clarification,
chlorination/dechlorination, post aeration and sludge holding.

Analysis and Discussion:
An instream assessment was performed using the Level B framework. A
comparison was made using the monthly average flow for the past year (0.1597 MGD) and
the monthly average flow for the past year plus the requested increase in domestic flow
(0.1-797 MGD). Both model runs were performed with the requested BOD5 limit of 60
mg/1. Ammonia was modeled with the ammonia value estimated to protect aquatic life from
ammonia toxicity (24 mg/I). The BOD5 and NH3-N parameters were input to the model as
CBOD and NBOD using multipliers of 1.5 for BOD5 and 4.5 for NH3-N. No significant
change in instream DO was noted between the two model runs (Table 1).
A comparison using the Level B framework at the facility's design flow (0.192
MGD) and requested BOD5 limits was also performed. This condition did not violate the
67(b) criteria. Therefore, the facility may add domestic wasteflow approaching their design
flow if the Region approves and if the flow is deemed necessary before their expansion.
cc: Kent Wiggins
Central Files

TABLE 1. Instream Assessment Summary for the Town of Walnut Cove.
Wasteflow Assumptions
Design Capacity
Pre-SOC (9/'91- 7/92)
SOC Flow Requested
Pre-SOC + SOC Flow
Model Input Summary
Headwater conditions:
0.1920 MGD
0.1597 MGD
0.0200 MGD
0.1797 MGD
7Q10 8.9 cfs
Qavg 130.0 cfs
Design Temperature 25.0 °C
CBOD 2.0 mg/1
NBOD 1.0 mg/1
DO 7.44 mg/1
Wastewater Inputs:
1st Wasteflow
2nd Wasteflow
CBOD (1.5*BOD5)
NBOD (4.5*NH3-N)
Model Output Summary
0.1597 MGD
0.1797 MGD
90.0 mg/1
108.0 mg/1
Qw End DO Net Distance Net
(MGD) Min. Change <5.0 mg/1 Change
(mom) (mom) (mi) (mi)
0.1597 6.78 NA NA NA
0.1797 6.70 0.08 NA NA
Design Flow
0.1920 6.65 0.13 NA NA

tJci 0 4 ?
41-ANT (JG
4/1 F4 a"l '-2 0 k1
qFF = o. i9Lir �J
If
53 , f
,417.
301;5' 30,' �o
-.i
/9j
lot i 5 )or ' • —t' — A4,2 Er / .' C /Af %F /JO B`_ ! Foi,1
It JJ7 1/,
- •f/r S J/11
f
Fo.i :Z%'
r /.ter.. i -7-c /J.J
•
9•!a riD
&Ow r�i
%• l
/)- r:ON ! CiJ� �� 9• Jr Y �L'Di _ ..'iC OW( )
i
rl -if ,'^. Qom. < -;, ,r . 1-7zo' r?G y / o fir'; fh';
`f% 2 Q. :/=. cx_cLs. 4- rIJ F-JUC// 3 , 7 170. ._ 0.73. -(s.id r
(1
7r7t 4 d 0• 5,4 i tic, ;t! �, ' - 9 • -- <.� v, r,'L6 .
0.. A- _P.O.�1i
,A/1 t , -•:. c' P . .
tLD.-, J. • 5
/ yiI-1�_
FLGr I-'�

GKEX88/MP
COMPLIANCE EVALUATION ANALYSIS REPORT
0i/i9/93
PAGE i
PERMIT--NC0025526 PIPE--00i REPORT PERIOD, 012-92ii
FACILITY --WALNUT COVE WWTP, TOWN OF DESIGN FLOW-- .1920 CLASS-4
LJCATION--WALNUT COVE REGION/COUNTY--04 STOKES
50050 003iO 00530 00610 3i6i6 50860 000i0 0040O
MONTH Q/M�D BOD RE%/T%% NH3+NH4- FEC COLI CHLORINE TEMP PH
LIMIT F .1920 F 30.00 F 90.0 NOL F i008.0 NOL NOL 9.0 6.0
9i/i2 .i527 45.80F 23.0 9.30 .0 i.000 5.80 6.3-6.3
92/01 .i79i 44.35F i8.0 i3.30 .0 i.0i6 3.80 6.9-6.8
92/02 .i574 45.30F .0 12.45 17.1 i.000 6.75 6.8-6.8
92/03 .i4i6 39.75F 33.0 8.i8 .0 i.000 9.50 6.6-6.6
92/04 .i404 48.95F 34.0 7.62 .0 i.100 i4.33 6.5-6.4
92/05 .i357 27.40 28.5 3.70 .0 i.05i i4.75 6.6-6.5
92/06 .i6i2 48.25F 42.5 7.95 .O 1.063 i6.60 6.0-5.81::'
92/07 .0828 4i.00F 33.0 6.38 .0 i.000 21.00 6.2-6.2
92/08 .i787 21.i5 .00 .0 i.00O 20.00 6.3-6.3
92/09 .193OF 29.45 36.0 9.86 .0 .926 i8.60 6.8-6.7
9200 .i832 38.85F 29.5 8.i8 .O i.000 i4.77 6.8-6.8
0,'4^ r4 4 7r AA oor is8 ii.38 .0 l.000 i0.80 6.8-6^7

Request Form for In -stream Assessment for 67B
NAME OF FACILITY
6;4-/-"7 SUBBASIN �Q� (�I
COUNTY 571•/, REGION 1�415220K7 DESIGN FLOW .a L 9 - ,// 0PP
RECEIVING STREAM
BACKGROUND DATA :
A. Why is SOC needed? (Facility is out of compliance with whicJ
ef, luent��limits?) �j��q•��yey, / S' l�/��rj7/-/�/ em3;/ l/,��1'
as / 6//¢�7/ive0;,/ C25,.
l,/r k / /-// 37? fo 4,(1,471
B. History of SOC requests: �o p7/11D4,6-
1. Monthly Average waste flow
prior to any SOC
/_<G1? mgd
Time period averaged /// `- 1/ thru
2. Previously approved SOC's:
Date:
Date:
OAP
flow:
flow:
total of previously approved SOC flow:__
3. Flows lost from plant
(facilities that have gone
off line)
4. Current SOC request
5. Total plant flow post-SOC
(sum of original flow and
SOC flow minus losses)
flow:
mgd
mgd
mgd
mgd
flow: mgd
flow: e / �t )fmgd
6. Is this an accurate flow balance for plant? Why/why not?

C. Please attach DMR summary for past year for all permitted parame-
ters. If possible, include reports from previous years if
facility has been under SOC for more than a y r.
CURRENT SOC RE2UEST :
A. Request is for domestic or industrial waste? If it is a combin-
ation, please specify percentages.
eY":771- .„;)4?29,e2,7 7/7„.(;2 A-0(0.5-7
�r7 ems' C t''/�4,) 429,77 �G/.s/ /',,sers
B. What type of industry? Please attar) any pertinent data.
/ T 04117 rls /7i2 /;?�,GIS-&/� / /, 7 /(''4TL,.
C. The region proposes the following SOC limits:
BOD5 p O mg/1
NH3 _7 4�, O mg/1
DO mg/1
TSS 9c',, r mg/1
fecal coliform#/100m1
pH �,•9.- Q, SU
other parameters
D. What is the basis for these limits?
/e---r//'P1,2 r Os..72" ,llfit7 /IX- iC G 17e / ;l�
rev/7 fY71" y
YiK �i �,���ass �o!?7jer- / lil`rr/71af' e- 476 ).
zi"/". / nr/ 7` e / 7� �/ ,
/t/i1( s/(/ / 77 /� //v /7 74 41.4��
‘?'7< ��O ��s�� (-6 �� ///` jf-

MODEL RESULTS
Discharger : WALNUT COVE PRE-SOC
Receiving Stream : TOWN FORK CREEK
SUMMER
PRE-SOC FLOW = 0.1597 MGD
BOD5=60 MG/L, NH3-N=24 MG/L
The End D.O. is 6.82 mg/1.
The End CBOD is 3.18 mg/1.
The End NBOD is 2.31 mg/l.
WLA WLA WLA
DO Min CBOD NBOD DO Waste Flow
(mg/1) Milepoint Reach # (mg/1) (mg/1) (mg/1) (mgd)
Segment 1 7.18 0.20 1
Reach 1 90.00 108.00 0.00 0.15970
Segment 2 6.79 0.10 1
Reach 1 45.00 49.50 0.00 0.05000
Segment 3 6.78 2.38 1
Reach 1 0.00 0.00 0.00 0.00000
i o . 5A = 6.75 �,8 /,t,
�.0 . sA 4 L&Q4" fl - 2.55 - 2.2 (- 0.3+ M ► LC 5
1,3 P Z5

*** MODEL SUMMARY DATA ***
Discharger : WALNUT COVE PRE-SOC Subbasin : 030201
Receiving Stream : TOWN FORK CREEK Stream Class: C
Summer 7Q10 : 8.9 Winter 7Q10 : 20.
Design Temperature: 25.
'LENGTH' SLOPE' VELOCITY 1 DEPTH' Kd 1 Kd 1 Ka I Ka I KN 1
I mile 1 ft/mil fps I ft Idesign l @204 Idesign l @20'h Idesign'
1 1 1 1 1 1 1 1 I
Segment 1 1 0.201 4.901 0.188 11.80 10.27 1 0.22 11.85 1 1.661 0.44
Reach 1 1 1 1 1 1 1 1 1 I
I 1 1 1 1 1 1 1 I
Segment 2 1 0.101 5.201 0.100 1 0.85 1 0.27 1 0.22 1 1.04 I 0.941 0.44
Reach 1
1 1 1 1 1 1 1 I I
Segment 3 1 3.401 4.901 0.200 11.88 1 0.27 1 0.22 1 1.42 1 1.271 0.44
Reach 1 1 I 1 I I 1 1 I I
1 Flow 1 CBOD 1 NBOD 1 D.O. I
1 cfs 1 mg/1 1 mg/1 I mg/1 I
Segment 1 Reach 1
Waste I 0.248 1 90.000 1108.000 1 0.000
Headwaters) 8.900 I 2.000 1 1.000 1 7.440
Tributary 1 0.000 1 2.000 I 1.000 1 7.440
* Runoff 1 0.000 I 2.000 I 1.000 1 7.440
Segment 2 Reach 1
Waste 1 0.078 145.000 1 49.500 1 0.000
Headwaters) 1.000 1 2.000 I 1.000 1 7.440
Tributary 1 0.000 1 2.000 I 1.000 I 7.440
* Runoff 1 0.000 1 2.000 1 1.000 1 7.440
Segment 3 Reach 1
Waste I 0.000 1 0.000 1 0.000 1 0.000
Headwaters) 0.000 I 2.000 1 1.000 1 7.440
Tributary 1 0.000 I 2.000 I 1.000 1 7.440
* Runoff 1 0.250 1 2.000 I 1.000 I 7.440
* Runoff flow is in cfs/mile

SUMMER
I Seg # I Reach # I Seg Mi I D.O. I CBOD I NBOD I Flow I
1 1 0.00 7.24 4.38 3.90 9.15
1 1 0.02 7.23 4.37 3.88 9.15
1 1 0.04 7.23 4.37 3.87 9.15
1 1 0.06 7.22 4.36 3.86 9.15
1 1 0.08 7.21 4.35 3.85 9.15
1 1 0.10 7.21 4.34 3.84 9.15
1 1 0.12 7.20 4.34 3.83 9.15
1 1 0.14 7.20 4.33 3.82 9.15
1 1 0.16 7.19 4.32 3.81 9.15
1 1 0.18 7.18 4.31 3.80 9.15
1 1 0.20 7.18 4.30 3.79 9.15
2 1 0.00 6.90 5.09 4.49 1.08
2 1 0.01 6.89 5.08 4.48 1.08
2 1 0.02 6.88 5.08 4.46 1.08
2 1 0.03 6.87 5.07 4.45 1.08
2 1 0.04 6.86 5.06 4.44 1.08
2 1 0.05 6.85 5.05 4.43 1.08
2 1 0.06 6.84 5.04 4.42 1.08
2 1 0.07 6.82 5.03 4.40 1.08
2 1 0.08 6.81 5.02 4.39 1.08
2 1 0.09 6.80 5.02 4.38 1.08
2 1 0.10 6.79 5.01 4.37 1.08
3 1 0.00 7.14 4.38 3.85 10.23
3 1 0.17 7.08 4.31 3.75 10.27
3 1 0.34 7.02 4.24 3.65 10.31
3 1 0.51 6.98 4.17 3.56 10.35
3 1 0.68 6.93 4.10 3.47 10.40
3 1 0.85 6.90 4.04 3.38 10.44
3 1 1.02 6.87 3.97 3.29 10.48
3 1 1.19 6.85 3.91 3.21 10.52
3 1 1.36 6.83 3.85 3.13 10.57
3 1 1.53 6.81 3.79 3.05 10.61
3 1 1.70 6.80 3.73 2.97 10.65
3 1 1.87 6.79 3.67 2.90 10.69
3 1 2.04 6.79 3.61 2.83 10.74
3 1 2.21 6.78 3.55 2.75 10.78
3 1 2.38 6.78 3.50 2.69 10.82
3 1 2.55 6.78 3.44 2.62 10.86
3 1 2.72 6.79 3.39 2.55 10.91
3 1 2.89 6.79 3.33 2.49 10.95
3 1 3.06 6.80 3.28 2.43 10.99
3 1 3.23 6.81 3.23 2.37 11.03
3 1 3.40 6.82 3.18 2.31 11.08
Seg # I Reach # I Seg Mi I D.O. I CBOD I NBOD I Flow I
'� N-Ce.EA5e') INCI NtN15 ro0 55

Discharger
Receiving Stream
MODEL RESULTS
WALNUT COVE SOC
TOWN FORK CREEK
SUMMER
SOC FLOW=0.1797 MGD
BOD5=60 MG/L, NH3-N=24 MG/L
The End D.O. is
The End CBOD is
The End NBOD is
6.74
3.36
2.49
mg/l.
mg/1.
mg/1.
DO Min
WLA
CBOD
(mg/1) Milepoint Reach # (mg/1)
0.20 1
90.00 108.00
Segment 1 7.14
Reach 1
Segment 2 6.79
Reach 1
Segment 3 6.70
Reach 1
0.10 1
2.38 1
sa4 - (0.7o ► /L
WLA
NBOD
(mg/1)
45.00 49.50
0.00 0.00
D. 0. 4Tt = Z.71 - Z . o4 - 0.68
WLA
DO Waste Flow
(mg/1) (mgd)
0.00 0.17970
0.00 0.05000
0.00 0.00000

v-'
*** MODEL SUMMARY DATA ***
Discharger : WALNUT COVE SOC Subbasin : 030201
Receiving Stream : TOWN FORK CREEK Stream Class: C
Summer 7Q10 : 8.9 Winter 7Q10 : 20.
Design Temperature: 25.
'LENGTH' SLOPE' VELOCITY 1 DEPTH' Kd 1 Kd 1 Ka I Ka 1 KN I
I mile I ft/mil fps I ft Idesignl @204 Idesign l @204 Idesign'
Segment 1
Reach 1
I 1 1 1 I 1 1 1
0.201 4.901 0.189 11.80 10.27 1 0.22 1 1.86 1 1.661 0.44
I I I 1 1 1 I I I
Segment 2 1 0.101 5.201 0.100 1 0.85 1 0.27 1 0.22 1 1.04 I 0.941 0.44
Reach 1 I I 1 1 1 1 1 1 I
1 1 I I 1 I 1 I I
Segment 3 I 3.40I 4.901 0.201 11.88 1 0.27 1 0.22 1 1.42 1 1.281 0.44
Reach 1 I 1 1 I 1 I I 1 I
I Flow 1 CBOD 1 NBOD 1 D.O. I
cfs I mg/1 1 mg/1 1 mg/1 I
Segment 1 Reach 1
Waste 1 0.279 190.000 1108.000 1 0.000
Headwaters) 8.900 1 2.000 I 1.000 1 7.440
Tributary 1 0.000 1 2.000 I 1.000 I 7.440
* Runoff I 0.000 I 2.000 1 1.000 1 7.440
Segment 2 Reach 1
Waste 1 0.078 1 45.000 1 49.500 I 0.000
Headwaters) 1.000 I 2.000 1 1.000 1 7.440
Tributary I 0.000 I 2.000 I 1.000 1 7.440
* Runoff I 0.000 1 2.000 I 1.000 1 7.440
Segment 3 Reach 1
Waste I 0.000 I 0.000 1 0.000 1 0.000
Headwaters) 0.000 1 2.000 I 1.000 1 7.440
Tributary I 0.000 I 2.000 1 1.000 I 7.440
* Runoff 1 0.250 I 2.000 1 1.000 1 7.440
* Runoff flow is in cfs/mile

SUMMER
I Seg # I Reach # I Seg Mi I D.O. I CBOD I NBOD I Flow 1
1 1 0.00 7.21 4.67 4.25 9.18
1 1 0.02 7.21 4.66 4.23 9.18
1 1 0.04 7.20 4.65 4.22 9.18
1 1 0.06 7.19 4.65 4.21 9.18
1 1 0.08 7.18 4.64 4.20 9.18
1 1 0.10 7.18 4.63 4.19 9.18
1 1 0.12 7.17 4.62 4.17 9.18
1 1 0.14 7.16 4.61 4.16 9.18
1 1 0.16 7.16 4.61 4.15 9.18
1 1 0.18 7.15 4.60 4.14 9.18
1 1 0.20 7.14 4.59 4.13 9.18
2 1 0.00 6.90 5.09 4.49 1.08
2 1 0.01 6.89 5.08 4.48 1.08
2 1 0.02 6.88 5.08 4.46 1.08
2 1 0.03 6.87 5.07 4.45 1.08
2 1 0.04 6.86 5.06 4.44 1.08
2 1 0.05 6.85 5.05 4.43 1.08
2 1 0.06 6.84 5.04 4.42 1.08
2 1 0.07 6.82 5.03 4.40 1.08
2 1 0.08 6.81 5.02 4.39 1.08
2 1 0.09 6.80 5.02 4.38 1.08
2 1 0.10 6.79 5.01 4.37 1.08
3 1 0.00 7.11 4.63 4.15 10.26
3 1 0.17 7.04 4.56 4.05 10.30
3 1 0.34 6.98 4.48 3.94 10.34
3 1 0.51 6.92 4.41 3.84 10.38
3 1 0.68 6.88 4.34 3.74 10.43
3 1 0.85 6.84 4.27 3.65 10.47
3 1 1.02 6.81 4.20 3.56 10.51
3 1 1.19 6.78 4.13 3.47 10.55
3 1 1.36 6.76 4.07 3.38 10.60
3 1 1.53 6.74 4.00 3.29 10.64
3 1 1.70 6.72 3.94 3.21 10.68
3 1 1.87 6.71 3.88 3.13 10.72
3 1 �.04 6.70 3.81 3.05 10.77
3 1 2.21 6.70 3.75 2.97 10.81
3 1 2.38 6.70 3.69 2.90 10.85
3 1 2.55 6.70 3.64 2.82 10.89
3 1 2.72 6.70 3.58 2.75 10.94
3 1 2.23 b./1 3.52 2.69 10.98
3 1 3.06 6.72 3.47 2.62 11.02
3 1 3.23 6.73 3.41 2.55 11.06
3 1 3.40 6.74 3.36 2.49 11.11
I Seg # I Reach # I Seg Mi I D.O. I CBOD I NBOD I Flow I
4 1) GiLePh 9 (Ncitft:.rlT5 c9P- 53

•
MODEL RESULTS
Discharger : WALNUT COVE SOC
Receiving Stream : TOWN FORK CREEK
SUMMER
FLOW=0.192 MGD
BOD5=60 MG/L, NH3-N=24 MG/L
The End D.O. is 6.68 mg/l.
The End CBOD is 3.47 mg/l.
The End NBOD is 2.60 mg/l.
WLA WLA WLA
DO Min CBOD NBOD DO Waste Flow
(mg/1) Milepoint Reach # (mg/1) (mg/1) (mg/1) (mgd)
Segment 1 7.12 0.20 1
Reach 1 90.00 108.00 0.00 0.19200
Segment 2 6.79 0.10 1
Reach 1 45.00 49.50 0.00 0.05000
Segment 3 6.65 2.38 1
Reach 1 0.00 0.00 0.00 0.00000
ADO 5A4 = c.�8 6 (5
0.(3 + /4