NC0021890_Instream Assessment_19810623 (2)

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NorTh Carolina Geocrtment of Natural
Resource, &coy m' unity Development
j'v ' Pe Ser,pzary
DIVISIGN OF ENVIRONMENTAL MANAGEMENT
une 23, 1981
MEMORANDUM
TO: Dick Peace, Regional Supervisor
Mooresville Regional Office
Original signed By
FROM: Forrest Westall, mead FORREST .R. WESTALL
Technical Services Branch
SUBJECT: In -Stream Assessment
Granite Falls WWTP
Granite Falls, Caldwell Count;
Per your request, a Level B analysis was done for the Granite Falls discharge
into Gunpowder Creek. Self -monitoring reports from January 1980 through
March 1981 indicate the following average values for the effluent characteristics
listed below:
Flow = 0.24 MGD
BODS = 28 mg/1
NH3-N = 9.6 mg/l
D.O. = 3.0 mg/1
BODultimate = 66.4 mg/1*
An analysis was performed using the above parameters at 7Q10 conditions. The
model predicted a D.O. minimum of 6.3 mg/l 0.4 miles below the discharge.
The model was also run with an additional flow of 15,000 gpd. The same treatment
efficiency was assumed. The model predicted the D.O. sag to be the same as that
using the lower flow. Thus, the additional flow will have no observable impact
upon dissolved oxygen resources in Gunpowder Creek. The dissolved oxygen values
are expectee to remain well above standard under both flow regimes.
There have been no DO violations indicated in the monthly reports either upstream
or downstream of the plant. The lowest DO recorded downstream of the plant was
6.9 mg/l. However, the downstream monitoring station is located 500 ft. below
the discharge. The model predicts the DO sag to occur 0.4 miles below the outfall.
*BODultimate = BODS + 4 (NH3-N)
P () R;• R.0- gh, Norlh Cerwm.n: ,•,i'

Thus, the actual DO minimums may be somewhat lower than self -monitoring reports
indicate.
If. you have any questions, please call.
cc: Mark Lewis
Arthur Mouberry
0

s::teary cf Granite Falls WWTP Impact Analysis
The Granite Falls 1,ITP discharges into Gunpowder Creek which is a "C" class
stream. At the discharge point, 'the creek has a drainage area of 36 m12, with a
7Q10 of 7.2 cfs.
There is a dam located approximately 0.4 miles below .the discharge on Gunpowder
Creek. Titus, the plant actually discharges into the backwaters of the lake created
by the dam. The velocity in the lake was estimated to be 0.009 f.p.s. The DO
sag was calculated to be located at the dam. There is reaeration over tie dam;
once over the dam, Gunpowder Creek actually becomes the backwaters of Lak( Hickory
(Catawba River, Class A -II and B) which is 3.4 mi further downstream. DO remains
high in -this section of Gunpowder Creek.
Using the present flow of 0.24 MGD and present monthly effluent parameters
(BOD5 = 28 mg/l, NH3-N = 9.6 mg/l, D.O. = 3 mg/1), the DO sag at the dam during
7Q10 conditions is 6.3 mg/l. The same DO minimum is predicted assuming an additional
flow of 15,000 gpd and the same plant efficiency.