NC0065358_instream assessment_19960513

Memorandum
North Carolina Division of Environmental Management
Water Quality Section, Instream Assessment Unit
To: Dianne Williams Wilburn
From: Andrew McDaniel 4 ` 1(
Thru: Carla Sanderson
Ruth Swanek
Date: May 13, 1996
Subject: Hidden Forest MHP SOC assessment
NC0065358
The Rapid Assessment Group has reviewed the request for an instream assessment
of the Hidden Forest MHP discharge while under a SOC. The facility discharges to a
stream, UT to Deep River, which has an estimated S7Q10, W7Q10, and 30Q2 flow equal
to zero cfs. The Rapid Assessment Group typically does not model discharges to zero flow
streams because doing so would violate one of the steady state assumptions required by the
Level B model. Modeling discharges to zero flow streams often yields inaccurate
predictions of the magnitude and location of the dissolved oxygen sag in the receiving
stream. The flow estimates mentioned above suggests that the receiving stream has little, if
any, assimilative capacity under critical low flow conditions. Therefore, effluent
discharged at the proposed SOC limits of BODS monthly average equal to 20 mg/L (S)/35
mg/L (W) and NH3-N monthly average equal to 20 mg/L is likely to have a negative impact
on instream dissolved oxygen concentrations under low flow conditions. Accurately
quantifying the impact though is not possible with the modeling tools currently available to
the Rapid Assessment Group.
If you would like to discuss this SOC assessment further please do not hesitate to
call me at 733-5083 ext. 513.

DIVISION OF ENVIRONMENTAL MANAGEMENT
May 7, 1996
MEMORANDUM:
To: Ruth Swanek
From: Dianne Williams Wilburn
Subject: Hidden Forest MHP
Cape Fear Basin
Draft SOC 96-06
NPDES Permit Number NC0065358
Randolph County
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Please find attached a request for an assessment for the above subject facility. If you have any
questions, please let me know.
cc: Corey Basinger
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Request Form for In -stream Assessment for 67(b) Analysis
NAME OF FACILITY Hidden Forest MHP PERMIT # NC0065358
COUNTY Randolph REGION WSO PERMITTED DESIGN FLOW 0.027 MGD
RECEIVING STREAM UT to Deep River SUBBASIN CPF
REGIONAL CONTACT Corey Basinger
BACKGROUND DATA:
A. Why is SOC needed? The facility cannot consistently meet their NPDES
limits with their existing treatment system.
If out of compliance with Flow limit, is it due to inflow/infiltration? N/A
If I/I is a problem, then how much of the additional flow requested is the I/I? N/A
B. SOC Request:
1. Monthly Average Wasteflow in the last year 0.0203 MGD
(Pre-SOC Flow)
Time period Averaged 2/95 through 1/96
2. Current SOC Flow request Flow: MGD
(Flow added on during the Order) N/A for this facility
3. Total plant flow (Post-SOC Flow) Flow: MGD
(total of 1. and 2. above) N/A for this facility
4. Is this an accurate flow balance for plant? Why/why not? N/A
Are there any facilities that have recently gone off line?N/A
NOTE: The SOC may not include an addition of wasteflow; therefore B. above may not apply
and the region should fill out all other parts of this form. In cases where the SOC involves
violations of oxygen consuming or toxic limits, an evaluation may be necessary to predict the
water quality standard violations instream.
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.

Attachment L
D. Briefly explain measures taken during the Order which will enable the facility
to be in compliance with permit limits at the end of the Order.
CURRENT SOC REQUEST:
A. Is request for domestic or industrial waste? If a combination, please specify
percentages. This is domestic flow only.
B. If industrial flow, then what type of industry? Please attach pertinent data.
C. The region proposes the following SOC limits (all limits NOT listed here will
remain as in the current permit):
Conventional Parameters Toxics/Toxicity
BOD S/W Monthly Avg 20/35 mg/L NONE
NH3-N Monthly Avg 20 mg/L
D. What is the basis for these limits? During construction, the facility will have parts of
their treatment works offline. Therefore, we expect exceedances of these parameters.

Hidden Forest MHP and Surroundi
ng Dischargers
Vicinity Map
HIGH POINT; CITY -EAST SIDE WWT
NC0024210
16.00000
.4A
RTMMER MOBILE IIOIVIE COURT
IfC0069451r
002040 I
UT to Deep R.
HIDDEN FOREST ESTATES Mar
NC0065358
0.02700
411, RAYCO UTILITIES -MELBILLE HGHTS
NC0050792
0.03150
Randleman
• RANDLEMAN WWIT; CITY
NC0025445
1.74500
Legend
• NPDES Discharger
A/ River/Stream
,V County Bndry
City/Town
Fi River Basin Bndry
0 1 2 3 4 Miles
N
+VA
May 1996 DRAFT MAP