NC0081671_Renewal Application updates_20170413

RECEIVEDINCDEQIDWR
APR 2 5 2011
GREENSBORO
NORTH CAROUNA — Water Quality
Permitting Section
April 13,2017
Mr. Derek Denard
Division of Water Resources, DEQ
1617 Mail Service Center
Raleigh,NC 27699-1617
Dear Mr. Denard,
RE NPDES permit NC0081671
Thank you for your help and guidance concerning our Lake Townsend WTP NPDES renewal
application.
Listed below is the information requested in your letter of February 16,2017:
1. The flow reported on 01/03/2016 (749 MGD) is incorrect. The value recorded in our
operations database for that date is .79 MGD. Please see attached document showing the
plant operator-entered value for 01/03/2016.
2. The table below shows five (5) days of Total Hardness (CaCO3) for both,the Townsend
water treatment plant effluent and upstream from outfall 001 for Reedy Fork.
Townsend
Discharge Upstream
Total Hardness, Total Hardness, mg/L
mg/L
MAR 9, 2017 58 " 36
MAR 10,2017 63 29
MAR 13, 2017 67 50
- MAR 14, 2017 35 30
MAR 15,2017 62 35
Average 57 36
e40
PO BOX 3136 • GREENSBORO NC 27402-3136 • WWW.GREENSBORO-NC.GOV • 336-373-CITY (2489)

GREENSBORO
NORTH CAROLINA
3. Mr. J Curtis Weaver, Hydrologist, PE from the USGS South Atlantic Water Science
Center recommends that the minimum flow requirements for the operation of Lake
Townsend impoundment would be most meaningful in the assessment of low-flow
characteristics for this particular point of interest. Please see attached document detailing
Mr. Weaver's response to the City of Greensboro's query.
Minimum release design flow for Lake Townsend Dam across three tiers is 0.05 cfs to
0.12 cfs.
If you have any questions,please call or e-mail Marie Shandor.
Marie Shandor
Water Supply Lab Supervisor, Water Resources
Phone [phone]
Email: [e-mail]
cc: Mr. Michael Borchers,Assistant Director, Water Resources
Mr. Dell Harney, Water Supply Manager
Mr. Ali Khan, Operations Superintendent
PQ BOX 3136 • GREENSBORO NC 27402-3136 • WWW.GREENSBORO-NCGOV • 336-373-CITY (2489)

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Ms.Shandor,
In response to your inquiry about the low-flow characteristics(7Q10,30Q2)for Reedy Fork immediately downstream
from Lake Townsend in the vicinity of Browns Summit in northeastern Guildford County,the following information is
provided:
A check of the low-flow files here at the USGS South Atlantic Water Science Center(Raleigh office)indicates previous
low-flow determinations for locations on Reedy Fork in general vicinity of the lat/long coordinates(36 1126.25//79 43
51.99 NAD83)you identified in your email dated March 16,2017.
No USGS discharge records are known to exist for the point of interest.
In the absence of site-specific discharge records sufficient for a low-flow analysis,estimates of low-flow characteristics at
ungaged locations are determined by assessing a range in the low-flow yields(expressed as flow per square mile drainage
area,or cfsm)at nearby sites where estimates have previously been determined.
A basin delineation completed for the point of interest(36 1126.25//79 43 51.99 NAD83)using the USGS StreamStats
application for North Carolina(hrtn://water.usgs.gov/osw/streamstats/north carolina.html)results in a drainage area at 105
sqmi.
For streams in Guilford County,low-flow characteristics published by the USGS are provided in the following reports:
(1)The first is a basin-wide report for the Cape Fear River basin published in 2001. It is USGS Water-Resources
Investigations Report 01-4094,"Low-flow characteristics and discharge profiles for selected streams in the Cape Fear
River Basin,North Carolina,through 1998"(Weaver and Pope,2001). An online version of the report is available
through http://nc.water.usus.gov/reports/wri014094/. The report provides the low-flow characteristics(based on data
through 1998)for continuous-record gaging stations and partial-record sites within the Cape Fear River basin. The report
also provides low-flow discharge profiles(7Q10,30Q2,winter 7Q10,and 7Q2)for the Cape Fear River and selected
tributaries within the basin.
(2)The second is a statewide report published in March 2015. It is USGS Scientific Investigations Report 2015-5001,
"Low-flow characteristics and flow-duration statistics for selected USGS continuous-record streamgaging stations in
North Carolina through 2012"(Weaver,2015). The report is available online at httn://pubs.usgs.gov/sir/2015/5001/. The
report provides updated low-flow characteristics and flow-duration statistics for 266 active(as of 2012 water year)and
discontinued streamgages across the state where a minimum of 10 climatic years discharge records were available for flow
analyses.
Because the point of interest is located immediately downstream from an impoundment with no site-specific discharge
records available,low-flow characteristics at this location will be governed by the minimum flow releases applicable to
Lake Townsend. Per my request,you provided the required minimum flow releases for Lake Townsend via email dated
March 28,2017. The minimum releases range from 2.9 to 7 cfm(cubic feet per minute)among the 3 specified tiers,
equivalent to approximately 0.05 cfs to 0.12 cfs.
Estimation of low-flow characteristics based on nearby low-flow yields applied directly to the drainage area(105 sqmi)at
the point of interest is not meaningful for this particular location.
Inspection of the second report indicates the presence of 4 nearby continuous-record streamgages in the Reedy Fork basin
and adjacent upper Haw River basin in vicinity of the point of interest where low-flow characteristics were published.
For this point of interest,the low-flow characteristics were estimated for the intervening drainage area(26 sqmi)between
the point of interest and an active streamgage downstream on Reedy Fork near Gibsonville(station id 02094500,drainage
area 131 sqmi),using the ranges of 7Q10 and 30Q2 low-flow yields for the other three nearby streamgages(discontinued
02093500,active 02093800,and active 0209399200). The estimated discharges were then subtracted from the published
low-flow discharges for the downstream Gibsonville streamgage.
Using this approach results in an estimated 7Q10 discharge between zero flow and 0.12 cfs(but most likely zero flow)and
an estimated 30Q2 discharge between zero flow and 2.7 cfs(average approximately 0.7 cfs).

Bringing the above pieces of information together,(1)the high degree of uncertainty associated with the above estimated
low-flow characteristics for a site downstream of an impoundment with no available site-specific discharge records,(2)the
existence of minimum flow release requirements assigned to the impoundment,(3)the"partial overlap"of the ranges in
estimated 7Q10 low-flow discharges and minimum flow releases leads me to conclude that use of the minimum flow
releases would be more meaningful in the assessment of low-flow characteristics for this particular point of interest.
Please understand the information provided in this message is based on a preliminary assessment and considered
provisional,subject to revision pending further analyses.
Hope this information is helpful.
Thank you.
Curtis Weaver
3.Curtis Weaver,Hydrologist,PE Email:icweavertbusgs.aov
USGS South Atlantic Water Science Center Online:htto://nc.water.usas.gov/
North Carolina-South Carolina-Georgia
3916 Sunset Ridge Road
Raleigh,NC 27607
Phone:[phone]/ Fax:[phone]