NC0025381_instream assessment_19900105

DIVISION OF ENVIRONMENTAL MANAGEMENT
January 5, 1990
TO: Roy Davis A`
THRU: Trevor Clements (J`'
Thomas Stockton
Carla Sanderson
FROM: Jackie Nowell
SUBJECT: Instream Assessment for Town of Lake Lure
NPDES No. Permit NCO025381
SOC Case No. 89-57
Rutherford County
Summary and Recommendations,
. The Technical Support has completed the instream assessment in
response to an SOC request for the Town of Lake Lure. The Town is seek-
ing interim limits for the parameters of flow, BOD5, TSS, and fecal
coliform. The Town has serious inflow problems because of lake water
that infiltrates through leaks in the collection system, which is par-
tially submerged in Lake Lure. During the life of the SOC, the Town
intends to repair the underwater leaks, tighten the manholes to correct
the inflow and infiltration problems, and replace and repair the sand
filter system.
Because of the flow infiltration problems, the Asheville Regional
Office is recommending a total SOC flow of 1.40 MGD. This exceeds the
design capacity (0.600 MGD) of the Lake Lure facility and Technical Sup-
port generally does not recommend that new sources of wasteflow to a
facility be allowed in these cases. However, for the purpose of the
instream assessment, the impact of the Lake Lure WWTP's wasteflow on
dissolved oxygen (DO) levels in the Broad River was evaluated using the
Level B modelling framework. The results of this analysis indicate that
the requested wasteflow increase of 0.09 MGD with the SOC limit of 45
mg/1 of BOD5 will not cause a significant impact of more than 0.5 mg/1
of DO sag or extend the streamlength predicted to violate the DO stan-
dard by more than 0.5 miles.
Discussion
The Lake Lure WWTP has a design capacity of 0.600 MGD and discharges
into the Broad River just downstream of the Lake Lure Dam. The summer
7Q10 flow at the discharge point is an estimated 6.6 cfs, with a drain-
age area of 96 square miles and an average flow of 169 cfs.
The average monthly wasteflow from March, 1989 to October, 1989 was

0.7722 MGD. The estimated amount of inflow of 0.5378 MGD has been
added to the monthly wasteflow (0.7722 MGD) for a total Pre-SOC flow of
1.31 MGD. The amount of additional domestic wasteflow requested by the
Town is 0.09 MGD. Therefore, the post-SOC flow is 1.40 MGD with interim
limits of 45 mg/1 BODS, 75 mg/l TSS, and 15,000/100ml fecal coliform. A
review of the facility's self monitoring data shows that flows begin to
elevate in July, 1988. The Town had the leaks in the system repaired
and the flows were down to normal levels (at or below design capacity)
in November, 1988. In March 1989, Lake Lure again went out of com-
pliance for flow and has remained the same until present. Flow data for
September, 1989 shows that the facility discharged an average of 1.0
MGD.
In spite of the elevated flows, the Lake Lure facility has not
violated their BOD5 limit at anytime during these periods. Problems
have occurred with. TSS and fecal coliform, which could be attributed to
the high flows and a malfunctioning sand filter system. It is the opin-
ion of the Asheville Regional Office that Lake Lure's problems can be
solved by tightening manholes and repairing leaks in the collection sys-
tem.
A Level B model analysis was used to assess the impact of the Lake
Lure WWTP discharge on DO in the receiving stream. Two models were run,
one at 1.31 MGD (pre-SOC flow) and the other at 1.40 MGD (post-SOC
flow). The waste input for CBOD was 67.5 mg/l (45 mg/l X 1.5 multiplier
for 100% domestic waste). The NBOD waste input was 26 mg/l, which was
determined by using the maximum summer NH3 value of 5.75 mg/l X 4.5 mul-
tiplier.
The model results at 1.31 MGD and 1.40 MGD predict DO minimums of
5.70 mg/1 and 5.60 mg/l, respectively. This is a difference of 0.10
mg/1 in the instream DO levels and is considered an acceptable depres-
sion of the instream DO level per 67(b) criteria.

Table 1. Instream Assessment for The Town of Lake Lure WWTP
Wasteflow Assumption
mmend
Design Capacity 0.60 MGD
Pre-SOC Flow 1.31 MGD
Requested SOC Flow 0.09 MGD
Post-SOC Flow 1.40 MGD
Model Input mmar
Headwater Conditions:
Summer 7Q10
Qavg
Design Temperature
CBOD
NBOD
DO
Wastewater Inputs:
1st Wasteflow
2nd Wasteflow
CBOD (1.5*recommended BODS)
NBOD (4.5*summer NH3)
6.6
cfs
169.0
cfs
25.0
Celsius
2.0
mg/l
1.0
mg/l
7.4
mg/l
Model Output Summary
1.31 MGD
1.40 MGD
67.5 mg/l
26.0 mg/l
DO
Net
Qw
Minimum
Change
(MGD)
--------------------------------------
(mg/1)
(mg/1)
--------------------------------------
1.31
5.70
-
1.40
5.60
0.10
Recommended
SOC Effluent
Limits
Qw 1.40
MGD
BOD5 45
mg/l
TSS 75
mg/l
Fecal 15000
/100ml

SUMMER
MODEL FOR PRE-SOC FLOW OF 1.31
MGD FOR LAKE
LURE SOC
---------- MODEL
RESULTS ----------
Discharger
:
TOWN OF LAKE LURE
Receiving Stream :
BROAD RIVER
----------------------------------------------------------------------
The End D.O.
is 7.58
mg/l.
The End CBOD
is 15.65
mg/1.
The End NBOD
----------------------------------------------------------------------
is 6.14
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
5.69
0.00 1
----------
Reach 1
67.50
26.00
0.00 1.31000

*** MODEL SUMMARY DATA ***
Discharger : TOWN OF LAKE LURE Subbasin : 030801
Receiving Stream : BROAD RIVER Stream Class: C
Summer 7Q10 : 6.6 Winter 7Q10 : 33.4
Design Temperature: 25.0
ILENGTHI SLOPEI VELOCITY I DEPTHI Kd I Kd I Ka I Ka I KN I
I mile I ft/mil fps I ft Idesignl @2014 Idesignl @2016 Idesignl
--------------------------------------------------------------------------------
I I I I I I I I I I
Segment 1 1 1.401 18.401 0.417 1 1.18 1 0.40 1 0.32 115.41 1 13.831 0.44 1
Reach 1 1 1 1 1 1 1 1 1 1 1
--------------------------------------------------------------------------------
I
Flow
I CBOD
I NBOD I
D.O. I
I
cfs
1 mg/1
I mg/l I
mg/l 1
Segment 1 Reach 1
Waste 1
2.030 1
67.500
1 26.000 1
0.000
Headwatersl
6.600 1
2.000
1 1.000 1
7.440
Tributary 1
0.000 1
2.000
1 1.000 1
7.440
* Runoff 1
0.180 1
2.000
1 1.000 1
7.440
* Runoff flow is in cfs/mile

'
SUMMER
MODEL FOR PRE-SOC FLOW OF 1.31
MGD FOR
LAKE LURE SOC
I Seg #
I Reach #
I Seg Mi I
D.O. I
CBOD I
NBOD I
Flow
1
1
0.00
5.69
17.41
6.88
8.63
1
1
0.10
6.08
17.28
6.83
8.65
1
1
0.20
6.40
17.15
6.77
8.67
1
1
0.30
6.65
17.01
6.71
8.68
1
1
0.40
6.85
16.88
6.66
8.70
1
1
0.50
7.01
16.76
6.60
8.72
1
1
0.60
7.14
16.63
6.55
8.74
1
1
0.70
7.24
16.50
6.50
8.76
1
1
0.80
7.32
16.38
6.44
8.77
1
1
0.90
7.39
16.25
6.39
8.79
1
1
1.00
7.44
16.13
6.34
8.81
1
1
1.10
7.49
16.01
6.29
8.83
1
1
1.20
7.53
15.88
6.24
8.85
1
1
1.30
7.56
15.76
6.19
8.86
1
1
1.40
7.58
15.65
6.14
8.88
Seg # I
Reach # I
Seg Mi I
D.O. I
CBOD I
NBOD I
Flow

SUMMER
MODEL FOR
LAKE LURE
WWTP @POST
SOC FLOW,
BOD5=45, NH3=5.75
---------- MODEL
RESULTS ----------
Discharger
:
TOWN OF LAKE LURE
Receiving Stream :
BROAD RIVER
----------------------------------------------------------------------
The End D.O.
is 7.56
mg/l.
The End CBOD
is 16.38
mg/1.
The End NBOD
----------------------------------------------------------------------
is 6.42
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
5.60
0.00 1
Reach 1
67.50
26.00
0.00
1.40000

*** MODEL SUMMARY DATA ***
Discharger : TOWN OF LAKE LURE
Receiving Stream : BROAD RIVER
Summer 7Q10 : 6.6
Design Temperature: 25.0
Subbasin : 030801
Stream Class: C
Winter 7Q10 : 33.4
ILENGTHI SLOPEI VELOCITY I DEPTHI Kd I Kd I Ka I Ka I KN I
I mile I ft/mil fps I ft Idesignl @2034 Idesignl @2034 Idesignl
--------------------------------------------------------------------------------
I I I I I I I I I I
Segment 1 1 1.401 18.401 0.422 1 1.18 1 0.40 1 0.32 115.60 1 13.991 0.44 1
Reach 1 I 1 I I I I I I I I
--------------------------------------------------------------------------------
I
Flow
I
cfs
Segment 1 Reach 1
Waste 1
2.170
Headwatersl
6.600
Tributary 1
0.000
* Runoff 1
0.180
I CBOD
I NBOD I
D.O. I
I mg/l
I mg/l I
mg/l I
167.500
i 26.000 I
0.000
I 2.000
1 1.000 1
7.440
1 2.000
1 1.000 1
7.440
1 2.000
1 1.000 1
7.440
* Runoff flow is in cfs/mile

SUMMER
MODEL FOR
LAKE LURE WWTP @POST
SOC FLOW,
BOD5=45, NH3=5.75
I Seg #
( Reach #
I Seg Mi I
D.O. I
CBOD I
NBOD I Flow I
1
1
0.00
5.60
18.21
7.19
8.77
1
1
0.10
6.01
18.07
7.13
8.79
1
1
0.20
6.33
17.93
7.07
8.81
1
1
0.30
6.59
17.80
7.01
8.82
1
1
0.40
6.80
17.66
6.96
8.84
1
1
0.50
6.96
17.53
6.90
8.86
1
1
0.60
7.10
17.40
6.84
8.88
1
1
0.70
7.20
17.26
6.79
8.90
1
1
0.80
7.29
17.13
6.73
8.91
1
1
0.90
7.36
17.01
6.68
8.93
1
1
1.00
7.42
16.88
6.63
8.95
1
1
1.10
7.46
16.75
6.57
8.97
1
1
1.20
7.50
16.62
6.52
8.99
1
1
1.30
7.53
16.50
6.47
9.00
1
1
1.40
7.56
16.38
6.42
9.02
I Seg # I
Reach # I
Seg Mi I
D.O. I
CBOD I
NBOD I Flow I

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