NC0023884_Instream Assessment_19930126

DIVISION OF ENVIRONMENTAL MANAGEMENT
January 26, 1993
MEMORANDUM
TO: Rex Gleason, Water Quality Supervisor
Mooresville Regional Office
FROM: Betsy Johnson i3
Technical SuppoWBranch
THROUGH: Mike Scoville mpD
Ruth Swanek?GS
SUBJECT: Instream Assessment for the City of Salisbury - Grants Creek WWTP
NPDES Permit No. NCO023884
Rowan County
SOC Case No. 92-10
Summary and Recommendation
Technical Support has completed an instream assessment for the City of Salisbury's 67(b) request for
additional flow up to their permitted NPDES limit of 7.5 MGD. The City has requested an SOC because
its facility is out of compliance with its mercury limit. The facility is 97% domestic with no permitted
industrial sources of mercury. It is believed that the high mercury levels in the effluent are due to a
build-up of mercury in the sludge of the aeration basins. To remove this sludge, the aeration basins must
be taken off line. During this period, expected to be from four to eight months, the facility has requested
interim limits for BOD5 and NH3-N. For the remainder of the SOC period, the existing limits will be
met with the exception of mercury and toxicity testing. A mercury limit of 16.5 ug/1 and toxicity
monitoring have been requested. After the SOC period, the outfall will be relocated to the Yadkin River
and a new permit issued.
A Level-B analysis was performed to assess the impact of the additional flow and relaxed limits. The
modeling analysis for this assessment indicates that the additional wasteflow under the proposed interim
limits will cause a violation of EMC 67 (b) under summer low flow conditions. Under pre- SOC
conditions, i.e., existing average flow and relaxed limits, the DO is predicted to sag to zero fo- 1 mile.
Per 15 NCAC 2H. 1206 (d)(1)(E)(i), since the predicted DO is less than 3.0 mg/1, the EMC must approve
any additional flows. It is recommended that no additional wasteflow be permitted until the treatment
plant is fully operational.
A mercury limit of 16.5 ug/1 should not be permitted since it will lead to violations of the water quality
standards. Effluent mercury levels should be monitored daily. Instream monitoring of mercury should be
conducted monthly 100 feet above and below the discharge, Full range chronic toxicity monitoring is
recommended for the SOC period. ,L4
Background Information
The City of Salisbury's Grants Creek WWTP discharges into Grants Creek, a tributary to High Rock
Lake, a class WS-III B lake with severe eutrophication problems. Grants Creek drains approximately
65.8 square miles at the discharge site. The USGS estimates the following flows at the discharge site:
summer 7Q10 = 5.7 cfs, winter 7Q10 = 12.2 cfs, and average flow = 78 cfs. The creek is slow moving
with a stream bed gradient of 1.25 feet per mile.

The Grants Creek WWTP cannot comply with its current mercury limit of 0.018 ug/l. During the past
year, mercury values .of up to 16.5 ug/l were reported. Since there are no permitted industrial sources of
mercury to the plant, the mercury must be due to uncontrolled commercial and domestic sources.
The Level B model was run with the region's requested effluent limit of 45 mg/l BODS and no ammonia
limit and pre-SOC flow of 4.77 MGD. Ammonia was modeled to accommodate the expected ammonia
values for a secondary treatment plant (20 mg/1 NH3-N). The BODS and NH3-N parameters were input
to the model using multipliers of 3.0 for BODS and 4.5 for NH3-N (see Table 1.) Using these effluent
characteristics and the summer 7Q10, the model predicts a DO sag to 0.0 mg/l for 1 mile.
Per 15 NCAC 2H.1206 (d)(1)(E)(i), no additional wastewater will be allowed if measured or predicted
dissolved oxygen levels at any stream flow at or above 7Q10 are less than 3.0 mg/1 unless specific
approval is granted by the Environmental Management Commission. Therefore, no additional wasteflow
should be permitted during the phase of the SOC during which the treatment plant cannot meet the
existing permitted limits. Upon completion of the WWTP servicing, the existing limits for oxygen
consuming wastes will apply and additional domestic wasteflow up to the permitted flow may be
allowed.
Additional flows will only be allowed under an SOC when the nature of the additional flows is such that
the waste characteristics do not exceed those generally associated with domestic waste or are pretreated
to domestic strengths. Waste of greater than normal domestic strength may be accepted if the
parameter(s) are not those for which interim limitations have been developed and it can be demonstrated
to the satisfaction of the Director that the additional waste will not adversely affect the treatment
efficiency of the treatment system for any modified parameter or.result in the violation of any other
permit limitation.
Technical Support recommends approval of the interim SOC limits at the existing average wasteflow
with the recommendation that the work be begun immediately to take advantage of winter flow
conditions and temperatures. With higher flows and lower temperatures, impacts to water quality should
be minimal. Effort should be taken to minimize the time frame during which the aeration basins are out
of service.
The requested limit for mercury may cause instream levels of mercury which will exceed both the Sate
chronic criteria of 0.12 ug/l and the Federal cute criteria of 2.4 ug/l. Under summer 7Q10 conditions (53
cfs), the dilution is 1.5:1. Thus, an effluent level of 16.5 ug/l at 7.5 MGD would lead to an instream
mercury level of 11 ug/l. DEM will not assign permit limits which will not protect aquatic life.
Sufficient effluent and instream monitoring is recommended such that any instream water quality
violations can be documented.
cc: Kent Wiggins
Julia Storm
Central Files

Table 1. Instream Assessment Model Input Summary for the City of Salisbury.
Wasteflow Assumptions
Design Capacity 7.5 MGD
Pre-SOC 4.77 MGD
Additional SOC Flow Requested +2.73 MGD
Maximum Allowable SOC Flow 7.5 MGD
Headwater Conditions (summer):
7Q10 (cfs)
5.7
Qavg (cfs)
78
Design Temperature (oC)
25
CBOD (mg/1)
2
NBOD (mg/1)
1
DO (mg/1)
7.44
Wastewater Inputs:
Pre-SOC Flow
4.77 MGD
Post-SOC Flow
7.5 MGD
CBOD (3 * 45 mg/l BOD i)
135 mg/1
NBOD (4.5 * 20 mg/1 NHI-N)
90 mg/1
Table 1. Instream Assessment Model Output Summary for the City of Salisbury.
Summer Model Results
Limits:
GG-1
Wasteflow =
4.77 MGD
BODS =
45 mg/1
NHS-N =
no limit
DO =
5 mg/1
DO Min (mg/1) Net Change m /l
Pre-SOC 0.0 na
Post SOC 0.0 0.0
SOC
Wasteflow =
7.5 MGD
BODS =
45 mg/1
NHS-N =
no limit
DO =
5 mg/1

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SUMMER
PRE -SO(.','
---------- MODEL RESULTS ----------
Discharger : TOWN OF SPENCER SOC
Receiving Stream : GRANTS CREEK
______________________________________________________________________
The End D.O. is 7.35 mg/l.
The End CBOD is 2.96 mg/l.
The End NBOD is 1.64 mg/l.
______________________________________________________________________
WLA
WLA
WLA
DO Min
CBOD
NBOD
DO
Waste Flow
(mg/l)
______
Milepoint Reach #
_________ _______
(mg/l)
____
(mg/1)
____
(mg/l)
__
(mgd)
-----------
Segment
1
6.22
1.40 2
Reach
1
135.00
90.00
5.00
4.77000
Reach
2
25.50
31.50
6.00
0.75000
Reach
3
0.00
0.00
0.00
0'00000
SUMMER
POST-SOC
80%
ON 62.4
CFS
---------- MODEL RESULTS ----------
Discharger
:
TOWN OF SPENCER SOC
Receiving
______________________________________________________________________
Stream
:
GRANTS CREEK
The End
D.O.
is 7.30
mg/l.
The End
CBOD
is 3.50
mg/l.
The End
______________________________________________________________________
NBOD
is 2.00
mg/l.
WLA
WLA
WLA
DO Min
CBOD
NBOD
DO
Waste Flow
(mg/l)
Milepoint Reach #
(mg/l)
(mg/l)
(mg/l)
__
(mgd)
-------------
Segment
1
______
5.73
_________ _______
1'40 2
____
____
Reach
1
135.00
90.00
5.00
7.50000
Reach
2
25.50
31.50
6.00
0.75000
Reach
3
0.00
0.00
0.00
0.00000

Discharger i TOWN OF SPENCER SOC
Receiving Stream a GRANTS CREEK
}5 n
Design Temperature: ur"e: 25.0
Winter 7Q10 . 1.12..2
!LENGTH! SLOPE! VELOCITY i DEPTH! Kd ; Kd i Ka # Ka i Kid # KN # KNR i KNO # SOD i SOD i
# mile # ft/mi# fps # it #design# iL`201 Idesign! v21071 #design# l201 #design# @204 Nesign! 3200- 1
! f F 1 1 1 1 1 1 1 1 1 ! 7 7
Segment, 1 1 £.5Di 1.251 0.244 # 2.18 i 0.27 i 0.21 i OA4 i D.401 OA4 # 130 i OA4 i 010 # 010 i 010#
Reach 1 , , 1 1-- - --- 1 1 i 1 1 , , , 1 1 ! I , , !
1 , , 1
7 i 1
i 1 I 1 1
i 1 i 3 7
1 3
Segment 1
# 0.901 1.25 i 0.257
i 2.20 # 017 # 011 # 0. 4 7 #
kL Q OA4 44 i E 30 # OA4 44 i O JO i
O AO # O AO i
Reach 2
--------------------------------------------------------------
# ---;- -
1 # # # #
-----------------------------------------------------
# # # # i
Segment 1
!
1 0.501 1.25! 1.217
1 118 1 017 1 012 1 1.49 1
1&1 9.Ik4 1 L30 1 3.44 1 3AD i
010 1 010 1
Reach 3
# ---# ;------#i
------------------------
# # #
=----------------------------------------------------------------
# # # i #
# # m 1.
o L'J i
t.. E.1 0 D
#0 D
#
T.) . 0 ,. #
# c.'r's
#
ing/1.
# ing/.#.
#
1rgif.1 #
Segment I
Reach
J.
Waste
# 11.625
#
45.000
# 27.000
#
5.000
Headwaters!
5.700
i
2.000
i 1.000
'
7.440
Tributary
' 0.000
'
0.000
1 0.000
1
7.440
* Rt..tr'yr..,•f'f
1 0.200
'
. `"y i:.fi.'; 0
' 1.000
#
7.4.40
Segfrlr-_nt i Reach 2
Waste
L1•'a � #: e
i
1 1.163
1 . 1. t.'a:::1
! 2Z G^i'_ 0
1 r_..�t ..�
1
31.500
1
f� ..
t%f � 0
�.
Tributary
' t..s.i��0
1 i.'�
i 0 �pi;0
, .. 1
1 0 #�0
1 .. �:
1
,
._,rr0
`r'
i• i•:..
* Runoff
' 0.300
1 2.000
1 0.000
1
7.440
aet"#fiient 1.
Reach 3
Waste e
# 0.000
# 0.000
i 0.000
i
0.000
Tributary
1 {.l2 t,.�f .ji0
3 � r_.1... . �
1 ...) !.'.f rf ry
1 ,.._ . i_ i..
1 �,1.. 0 :�f 0
1 is • s
1
7 .
4.4. ?j
•A RLir'iCIff
1 0.300
1 2.000
1 0.000
1
7.440

e+� - - by
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c�
Division of Environmental Management
December 15, 1992
MEMORANDUM TO: Ruth Clark-Swaneekk
FROM: D. Rex Gleason \
PREPARED BY: Richard Bridgeman�
SUBJECT: Request for In -stream Assessment
Additional Flow Under SOC
City of Salisbury - Grant Creek WWTP
NPDES Permit No. NCO023884
Rowan County
Please find attached a request for an in -stream assessment.
The request is made to provide a basis for allowing additional flow
in excess of the current 12-month average for the subject facility.
Please advise if additional input is required.
Enclosure
RMB
i( J
RECEIVED
DEC 16 19Q
TECHNICAL SUPPORT BRANCH
a

REQUEST FORM FOR INSTREAM ASSESSMENT FOR 67b SOC
NAME OF FACILITY: City of Salisbury - Grant Creek WWTP
COUNTY: Rowan REGION: Mooresville DESIGN FLOW: 7.5 MGD
RECEIVING STREAM: Grant Creek SUBBASIN: YAD04
BACKGROUND DATA:
A. Why is SOC needed? Facility is unable to comply with
mercury limit.
B. History of SOC requests:
1. Monthly average waste flow prior to'any SOC:
4.7732 MGD
Time period averaged: 11/91 through 10/92
2. Previously approved SOC's: SOC EMC WQ 84-14
JOC 88-35
3. Flows lost from plant (facilities that have gone
off line): N/A
4. Current SOC Flow request: 2.7268 MGD or up to
permitted flow limit, whichever is the greater
5. Total plant flow post-SOC (sum of original flow
and SOC flow minus losses): 7.5 MGD
6. Is this an accurate flow balance for plant? N/A
C. Please attach DMR summary for past year for all
permitted parameters. If possible, include reports
from previous years if facility has been under SOC for
more than a year. Summary attached
CURRENT SOC REQUEST:
A. Request is for domestic or industrial waste? If it is
a combination, please specify percentages. Unspecified
domestic -strength waste
B. What type of industry? N/A

In -stream Assessment Request
City of Salisbury - Grant Creek WWTP
Page Two
C. The region proposes the following SOC limits:
A short term goal ( activity in progress) under the SOC is
to remove the aeration basin from service to clean all
old sludge from the unit. Although the basin has
concrete walls, there is an earthen bottom. After
removing the sludge, the City will do one of two things:
either install a bentonite clay liner or concrete the
bottom of the aeration basin. During the period the
facility is operating with only primary clarification,
trickling filters, and secondary clarification, short
term interim limits are needed. Depending on which
activity is undertaken, the needed short term interim
limits period is from four to eight months, which
includes a two months recovery period once the aeration
basin is returned to service.
For the short term period of from four to eight months,
'the region proposes the following SOC limits:
Monthly Weekly
Average Average
Sum/Win Sum/Win Units
BOD5 45.0 * 67.5 * mg/l
TSS 45.0 * 67.5 * mg/1
NH3 Monitoring Only
During the short term period and for the remaining life
of the SOC all other pollutants are proposed to be
limited as indicated below. Following the short term
period, BOD5, TSS, and NH3 limits will revert to final
effluent limits concentrations, as indicated below.
* Indicates that limits are applicable both summer and
winter.

In -stream Assessment Request
City of Salisbury - Grant Creek WWTP
Page Three
Monthly Weekly Minimum/ Daily
Average Average Maximum Maximum
Sum/Win Sum/Win Sum/Win Sum/Win
Flow 7.5
*BOD5 15.0/30.0 22.5/45.0
TSS 30.0 ** 45.0 **
*NH3 6.0/12.0 9.0/18.0
DO 5.0 Min **
*pH 6.0-9.0 **
Fecal
Coliform 200.0 ** 400.0 **
Chronic
*Toxicity - Monitoring Only (Full Range).
Chromium 75.0 **
*Lead 37.0 **
*Fluoride 2.7 **
Mercury 16.5 **
Units
MGD
mg/l
mg/1
mg/l
mg/1
s.u.
#/100 ml
ug/1
ug/1
mg/l
ug/l
* Denotes that there has been no change from Permit.
** Indicates that limits are applicable both summer and winter.
D. What is the basis for these limits? To take advantage
of dilution, and how it affects permit limits development,
under the SOC the City will relocate the outfall line to the
Yadkin River. The City is also removing old sludge from the
system, believing that sludge -entrained mercury is
contributing to the facility's noncompliance. The modified
interim limit for mercury is set at the maximum effluent
concentration of the review period from 11/91 through 10/92.
A7/- 7 5-11160/ B5.G , , eC-Zk-4-") (yAv�(\J4 )
! . & "5/1
4 nJ.vc cry 4