NCG140456_Alternative Flow Estimate Method Request_20190830

::WithersRavenel
Our People. Your Success.
August 30, 2019
North Carolina Department of Environmental Quality
Stormwater Program: Division of Energy, Mineral, and Land Resources
512 N. Salisbury Street
Raleigh, NC 27604
ATTN: Stormwater Group
RE: NCG140456 Quantitative Monitoring Method Approval
Dear Ms. Georgoulias,
On behalf of Capital Ready Mix Concrete, LLC, find the attached request for approval of an
alternative method for quantitative monitoring of truck -rinse wastewater daily flow for the
Turkey Creek Ready Mix Plant. Discharges of wastewater and stormwater from the Turkey
Creek facility are covered under NPDES permit number NCG140456.
The facility's truck -rinse wastewater treatment system discharges into Turkey Creek.
NCG140000 requires continuous daily wastewater flow monitoring. However, the current
discharge treatment system is planned to be replaced with a non -discharge system within one to
two years. Additionally, it has been observed that the existing discharge treatment system
typically discharges only during rain events.
Capital Concrete is therefore requesting to use the attached interim method of monitoring daily
flow based on conservative flow calculations described within the attachment. The attached
document presents details about the wastewater treatment system and the alternative method
for measuring flow, including calculations. The following attachments are included to aid in your
review:
• Alternative monitoring method description
• USGS site location map
• Site plan, including a schematic of the treatment system
• Drainage area map with contour lines and outfalls
• USGS guidance used to estimate 30Q2 flow of Turkey Creek
• USGS StreamStats basin area results
If you find the alternative flow monitoring method acceptable, we will incorporate it into the
Turkey Creek SPPP; otherwise, we will await your comments.
Sincerely,
WithersRavenel
ri- 0- 5 �' 1)� -I -
Todd St. John, PE, LEED AP
Senior Project Manager
115 MacKenan Drive I Cary, NC 27511
t: 919.469.3340 1 f: 919.467.6008 1 www.withersravenel.com I License No. C-0832
Asheville I Cary I Greensboro I Pittsboro I Raleigh I Wilmington

::WithersRavenel
Our People. Your Success.
Capital Concrete Turkey Creek Ready Mix Plant
SPPP Quantitative Monitoring Method
Site Description
Capital Concrete washes out its concrete trucks near the eastern boundary of their facility at a
paved concrete wash station that eventually discharges to Turkey Creek. The facility is located
at 270 Moncure-Pittsboro Road, Moncure, NC 27559, as shown on the attached USGS location
map. The facility's discharges are covered under NPDES permit NCG140456.
The truck rinse -out water treatment system consists of three settlement chambers with weirs
that flow into a settling basin. The system is located in the east corner of the property, as
shown on the attached site plan drawing that includes a schematic of the treatment area. The
wastewater treatment system drainage area and outfall are included on the attached site
drainage area map. The treatment system is described as follows:
o The settlement chambers and sedimentation pond slow and diffuse wastewater
flow, allowing heavier suspended matter to settle out.
o Overflow from the sedimentation pond drains through a corrugated metal riser and
an 8-inch diameter ductile iron outlet pipe that discharges over rip -rap and into
Turkey Creek.
o A FORTRAN pH unit treatment system has been installed at the pond to keep the
pH within discharge limits.
o Rinse water collected in the sedimentation pond is reused for rinsing out the trucks.
o Stormwater only enters the settling chambers and sedimentation pond by rain falling
directly on the treatment structures and concrete truck -rinse pad during rain events.
o A 6-inch concrete curb surrounds the treatment structures to ensure that all other
stormwater runoff is diverted around the system.
Alternative Monitoring Method
As an alternative to traditional means of continuous daily flow measurement, such as a weir or
flowmeter, it is proposed that a conservative estimate of discharge be used that is based on the
amount of rain received on site and the amount of water typically used to rinse out a truck. In
considering this alternative the following should be noted:
o The rinse -water treatment weirs and settling basin typically do not discharge, except
during rain events, because reuse limits the amount of water added to the system
and evaporation removes water from the settling basin.
o The combination of evaporation and rinse -water reuse has thus far limited the basin from
filling to the point of discharging under dry weather conditions.
o For this calculation to be used in lieu of traditional monitoring, it is assumed that the
rain water from every rain event causes a discharge from the basin. This is considered
to be conservative since smaller rain events may not result in the filling of the basin to
the point of discharge.
115 MacKenan Drive I Cary, NC 27511
t: 919.469.3340 1 f: 919.467.6008 1 www.withersravenel.com I License No. C-0832
Asheville I Cary I Greensboro I Pittsboro I Raleigh I Wilmington

::WithersRavenel
Our People. Your Success.
Calculations & Parameters
o The approximate average annual rainfall for Moncure, NC is 47 inches (3.9 feet). The
truck rinse -out water treatment system, including wash pads, three settlement chambers,
and a settling basin, covers an area of approximately 0.1 acres (4356 square feet).
o Rinsing out each truck typically requires about 100 gallons, or 13.4 cubic feet, of water.
It is estimated that 7 trucks per day are rinsed out. For the purpose of this exercise, 10
truck per day were assumed, to be conservative. This could be verified by plant records.
As has already been stated, the water in the settling basin is typically reused, making this
estimate even more conservative.
o Based on the above, the average daily discharge of treated wastewater to Turkey Creek
can be calculated based on the annual rainfall amount over the 0.1-acre area as follows,
assuming all rainfall is captured (C-factor of 1.0):
Aug. Discharge = 3.9 (ft) x 4356 (ftz) _ 365 (days) = 46.7 ft3/day = 0.00054 f t3/s
o The calculation presented below assumes a wash water use rate of 100 gallons per truck
at 10 trucks per 12-hour workday:
Wastewater Generated = 13.4 (ft3/truck) x 10 (trucks) _ 12 (hours) = 11.2 ft3/hr
= 0.0031 f t3/s
o Combining the average daily rainfall with the daily wastewater discharged, the average
conservative daily discharge rate of wastewater to Turkey Creek would be:
Aug. Discharge = 0.00054 f t3/s + 0.0031 f t3/s = 0.00364 f t3/s
o The 30Q2 low -flow for Turkey Creek was estimated using a Regional Low -Flow
Frequency Regression Equation for the Raleigh region, published in the USGS guidance
document titled Low -Flow Characteristics of Streams in North Carolina (1993), with the
pertinent formula and land area highlighted. A scanned copy of the referenced
guidance document pages is attached to this document.
o The Turkey Creek drainage basin area at the discharge point was calculated using the
USGS StreamStats Calculator, and was estimated to be 4.08 square miles. A copy of the
StreamStats report is attached to this document. The 30Q2 flow is estimated as follows:
30Q2 Flow = 0.316 x [ 4.08 (sq. miles) ]0.83 = 1.015 ft3/s
o Meaning that the wastewater would make up:
Wastewater flow % = 0.00364 (ft3 / s) = 0.36%
(1.015 + 0.00364) (ft3 / s)
o This percentage of flow should be considered conservative for this calculation, since the
system does not typically discharge except during rain events, which would likely
increase the discharge of Turkey Creek above the estimated 30Q2 low -flow.
115 MacKenan Drive I Cary, NC 27511
t: 919.469.3340 1 f: 919.467.6008 1 www.withersravenel.com I License No. C-0832
Asheville I Cary I Greensboro I Pittsboro I Raleigh I Wilmington

::WithersRavenel
Our People. Your Success.
Furthermore, Capital Concrete is planning to upgrade its water treatment system to a recycle
system at the Turkey Creek facility in 1 to 2 years. The recycle system will cause discharge
from the current system to be eliminated. As such, Capital Concrete is requesting that
DEMLR allow the above calculations to serve as an alternate means of estimating daily
discharge in the interim. All other monitoring required by NCG 140000 would still be
performed per the permit requirements and as described in the facility's SPPP.
115 MacKenan Drive I Cary, NC 27511
t: 919.469.3340 1 f: 919.467.6008 1 www.withersravenel.com I License No. C-0832
Asheville I Cary I Greensboro I Pittsboro I Raleigh I Wilmington

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EXPLANATION
HA6 HA7
POTENTIAL TO SUSTAIN LOW FLOW — See appropriate
hydrologic area and low -flow statistics in table 2
- High
Intermediate
E] Low
Figure 2. Areas of similar potential to sustain low flows.
hydrologic area (HA9) are intermediate in potential
for sustaining base flow to streams.
REGIONAL LOW -FLOW FREQUENCY
REGRESSION EQUATIONS
Multiple regression analysis was used in
developing equations for estimating low -flow char-
acteristics of streams. The assumed form of the
regression equations was:
where
Y=Bo(XB')(XBZ)(XB3)... (XBn), (1)
Y is the low -flow characteristic of inter-
est (7Q10, W7Q10, 30Q2, or 7Q2),
B0 is the regression constant,
B1, B2, B3 are regression coefficients,
and
X1, X2, X3 are explanatory variables related to
low -flow characteristics.
Equation 1 is similar in form to that adopted in
other studies, such as those by Carpenter (1983) and
Barnes (1986). To assure linearity and constancy of
the error variance, equation 1 was log -transformed
to:
78° 77° 76°
A � I N A
COASTAL PLAN
A
IA6 HA1 and HA2
combined
1- 35'
P�
34°
36°
0 50 100 MILES
0 50 100 KILOMETERS
log Y=log B0+B1 log Xl+B2 log X2
+B3 log X3 ... (2)
Preliminary multiple regression analysis was
performed on a selected data set consisting of 74
continuous -record stations having a record of 30
years or more and 7 stations with records that were
extended to 30 years or more through regression
techniques. A number of basin characteristics were
also available for these stations, including drainage
area, stream length, channel slope, percentage of
basin forested, soil infiltration index, mean annual
precipitation, the 2-year 24-hour rainfall intensity,
mean January and July temperatures, Lane's vari-
ability index (Lane and Lei, 1950), and streamflow
recession indexes. In this and subsequent regression
analyses, stations for which low -flow characteristics
were zero were excluded because zero values cannot
be log -transformed. On a statewide basis, drainage
area was the most significant of the above variables;
in most regression analyses, mean annual precipita-
tion was the second most significant variable.
Subsequent regression analyses, based on 120
continuous -record and 403 partial -record stations
having drainage areas less than 400 mil, were used
to examine fewer variables: drainage area, mean
annual runoff, and average well yield by hydrologic
area. Mean annual runoff, which was not tested
with the preliminary 74-station data set, was used
Low -Flow Characteristics of Streams In North Carolina

Table 3. Low -flow frequency regression equations for selected hydrologic areas'
[nQm flow, the minimum n-consecutive-day discharge, in cubic feet per second, with a probability of 1/m of occurring in any one climatic year;
W7Q10 flow takes into account only the months of November through March; Rz, coefficient of determination; DA, drainage area in square miles;
MAF, mean annual flow in cubic feet per second]
Hydrologic area
name and number
Number
of sites
Regression equation
for nQm flow
R z
Standard error
of estimate
(percent)
Equation
number
Sand Hills (HA3)
24
7Q10=0.431DA 0-s9
0.86
55
3
W7Q10=0.789DA 0.90
.94
34
4
7Q2=0.655DA 0'9'
.93
37
5
30Q2=0.830DA 0-9'
.95
31
6
Raleigh and Charlotte
60
7Q10=0.196DA 0.53
.35
92
7
and Milton Belts
W7Q10=0.270DA 0'79
.67
65
8
and HA9,
702=0.253DA 0-78
.69
61
9
combined)
.78
49
10
Western Piedmont
299
7Q10=0.155MAF 1-01
87
50
11
and mountains
W7Q10=0.252MAF 0.99
.90
40
12
(HA10)
7Q2=0.281MAF 1.00
92
37
13
30Q2=0.344MAF 1.00
93
33
14
'See table 2 for drainage area limits below which indicated low -flow statistics are generally zero. Equations should not be used
for drainage areas less than these limits or for drainage areas greater than 400 square miles. Number of sites may differ slightly from
those shown in table 2 because sites with zero values for flow characteristics were not used to develop regression equations.
instead of precipitation because mean annual runoff
more accurately reflects areal differences in annual
evapotranspiration and infiltration than does precipi-
tation. On an annual basis, for example, more of the
precipitation that falls in the western Piedmont and
mountains (HA10) eventually becomes streamflow
because of the shorter growing season there as com-
pared with other areas of the State.
In statewide regressions, drainage area, mean
annual runoff, and well yield by hydrologic area
were all significant at the 1-percent level. A
1-percent level of significance indicates that there is
a 99-percent chance that there is a relation between
the dependent and the explanatory variable. How-
ever, when regressions were performed on separate
hydrologic areas or groups of similar hydrologic
areas, use of the well -yield factor did not substan-
tially improve the equations. Also, mean annual
runoff resulted in distinct improvements only in the
western Piedmont and mountains hydrologic area
(HA10).
Residuals from statewide regressions based on
drainage area alone and on drainage area and mean
annual runoff together as explanatory variables were
examined for areal bias. These examinations, along
with student's t-tests and analysis of variance by
ranks of low -flow characteristics, indicated that the
closely ranked Raleigh Belt hydrologic area (HA5)
and the Charlotte Belt and Milton Belt hydrologic
area (HA9) could be combined for purposes of
regression analysis. Conversely, the residuals analy-
sis and other tests of low -flow characteristics (pri-
marily t-tests) indicated that separate regressions
were more accurate for the Sand Hills hydrologic
area (HA3) and the western Piedmont and moun-
tains hydrologic area (HA10) than a single regres-
sion for the two hydrologic areas. Separate regres-
sions were particularly appropriate in the case of
W7Q10 values, which were significantly lower in
the western Piedmont and mountains hydrologic area
(HA10) than in the Sand Hills hydrologic area
(HA3). Tests indicated that a few combinations of
the remaining hydrologic areas were justifiable for
regression purposes, but the large percentage stand-
ard error of estimates of regression for these combi-
nations were unacceptable. Therefore, these combi-
nations were not used in this report. Despite some
statistical homogeneity, such hydrologic areas main-
tain separate identities in table 2 for one or more of
the following reasons: (1) physical separation, (2)
lack of statistical homogeneity in one or more low -
flow characteristics, and (3) clearly different topo-
graphic, geologic, or climatic characteristics.
Final regression equations 3-10 for the Sand
Hills hydrologic area (HA3) and the combined
Raleigh Belt (HA5) and the Charlotte Belt and Mil-
ton Belt hydrologic areas (HA9) are listed in table
3; these equations incorporate drainage area (DA) as
Regional Low -Flow Frequency Regression Equations

8/6/2019 StreamStats
StreamStats Report
Region ID: NC
Workspace ID: NC20190806131202846000
Clicked Point (Latitude, Longitude): 35.70331,-79.17445
Time: 2019-08-06 09:12:18 -0400
ry
G Uf
C�
Basin Characteristics
Parameter Code
DRNAREA
Parameter Description
Area that drains to a point on a stream
I
Value Unit
4.08 square miles
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StreamStats
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