NC0041696_wasteload allocation_19760622

ASSIMILATIVE CAPACITY EVALUATION
Areawide (208) Planning Area: Non - designated
Facilities (201) Planning Area: Burke County
Source of Pollution: Proposed Valdese Wastewater Treatment Facility
200
190
80
M 70
t 60
50
O 40
30
144
20
10
0
1130 .1
1123
1001
SMITH -
!W• 2000
CLASS "
10 20
Design Flow Imgd1
30
A proposed 25 mgd WWTP which
will serve the Town of Valdese is
located in the adjoining diagram.
This facility will discharge to
Island Creek, a class "C" stream
with a 7/10 low flow of 2.1 cfs.
The maximum allowable ultimate BOD
which may be discharged and the
degree of treatment required is
evaluated below.
The 1970 estimated population for
the entire Burke County Facility Planning
Area indicates a population of 35,000.
The 1980 projected population for this
area is 41,000.
Level "B" Analysis
This proposed treatment facility
must provide secondary type treatment
followed by nitrification and discharge
and effluent BODult of less than 20 mg/1.
CTB31 -VI I I-15

Assimilative Capacity Calculations
a) Slope on Island Creek
From USGS topographical maps the stream surface slope was estimated to be
40 ft/mile.
b) Velocity
Mean velocity and depth under 7/10 low flow conditions are estimated to be
1.6 feet per second and 1.0 feet respectively. These estimates are obtained from
USGS stream gauging data.
c) Reaeration Coefficient K2
The value of K2 was estimated by the method developed by E.C. Tsivoglov
and is given by the following equation:
K2(29°C) = 0.96 dh/dx v where dh/dx = water surface slope (ft/mile)
v = mean river velocity (fps)
K2 = (0.96)(40)(1.6)
K2 = 61 per day, base e @ 29°C
d) Deoxygenation Coefficient Ki
In the absence of adequate stream BOD data, Ki is assumed to be 0.35 per
day at 200C. This value is corrected for temperature and bed activity by the
following equation:
K1(29°C) = 1.51 (Ki + dv n) where K1 = assumed bottle deoxygenation rate,
(per day)
v = mean stream velocity (fps)
d = mean stream depth (feet)
n = coefficient of bed activity
Ki = 1.51 (0.35 + 1.6(0.52))
1.0
Ki = 1.18 per day, base e @ 29°C
e) Groundwater runoff was estimated to be 0.25 cfs/mile under 7/10 low flow conditions.
The following dissolved oxygen values were obtained using the above hydrologic
conditions and the following effluent parameters as initial conditions to a computer
model simulating on the affected reach.
Miles Below Outfall
0.5
1.0
1.5
Discharge (Qw) = 25 mgd
Effluent BODult = 20 mg/1
Effluent DO = 5 mg/1
DO(mg/1)
6.7
7.2
7.4
CTB31-VIII-16
BODu1t(mg/1)
18.6
18.1
17.7