NC0031879_Correspondence_19830503

Z
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
�ti'4cPRO-tE`, REGION IV
MF 3 /J
li i 1983 3G5 COA. GEORGIAG STREET v� /1D �i /Q 7(`•(f
f'1 ATLANTA. 30365 �{/ /c U y
REF: 4WA-FP
Forrest R. Westall, Head
Operations Branch
Division of Environmental Management
North Carolina DeparLffient of Natural
Resources & Community Development
Post Office Box 27687
Raleigh, North Carolina 27611-7687
Dear Mr. Westall:
As requested in your letter of Marcy. 3, I have reviewed the report, "Marion
Corpening Creek WWTP Analysis of Impact on Lake Rhodhiss." My comments are
summarized in the following paragraphs.
I agree that relaxation of the phosphorus limitation for the Marion WWTP will
not substantially increase inlake phosphorus concentrations in the near
future. The initial increase in loading from the Marion W;'TIP should be offset
by the decrease in loading from the regional Valdese facility for the duration
of the existing Marion NPDES permit.
However, I do not feel that a permanent waiver of phosphorus limitations for
the Marion WWTP is justified at this time. Based on the estimation techniques
in the report and design flogs of the treatment facilities in the basin, the
average future loading of total phosphorus to the lake will be increased in
the range of 30 to 100 per cent over existing levels, depending on the level
of control of point source phosphorus.
Prior to a decision concerning final effluent limitations for phosphorus for
the Marion WAD (or for any other facilities in the basin), I suggest that a
more detailed study of water quality data and point source loadings be made.
Timing for tnis analysis should depend on availability of new water quality
data used to augment historical data used in the report. After conclusion of
this analysis, a basin wide control strategy should be developed which
addresses future discharge scenarios, equal levels of treatment for all
dischargers, and seasonal.variation of effluent limitations.
Several questions particular to the Marion WWTP may be easily answered via
inclusion of monitoring requirements. in a modified permit. The monitoring
requirement for total phosphorus could be expanded to address the questions of
effluent concentration (without phosphorus removal), background concentrations
in the receiving stream, and conservation of effluent phosphorus loadings
downstream towards Lake Rhodhiss.
R E
se'as
3

-2-
I hope that these comments will be helpful. Please call me if you have any
questions concerning the comments and suggestions.
Sincerely),
ohn T. Marlar, Chief
Facilities Performance Branch

MARION CORPENING CREEK
WWTP
ANALYSIS OF IMPACT
ON LAKE RHODHISS
N.C. Department of Natural Resources
and Community Development
Division of Environmental Management
Water Quality Section

Table of Contents
I. Summary
II. Introduction
III. Methods and Results
1
3
4
A. Loading Calculations 5
1. Method 2 8
2. Method 2 11
3. Marion-Corpening Creek WWTP 14
Contribution to the Total Phosphorus
of Lake Rhodhiss
B. Modified Vollenweider Model 17
IV. Conclusions and Recommendations 26
V. References 28
VI. Appendix A 29
VII. Appendix B 33
VIII. Appendix C 36

List of Tables
1. Major Tributaries to Lake Rhodhiss 6
below Lake James
2. Existing Point Sources to Lake Rhodhiss
Drainage Basin with Design Flow
0.5 MGD
7
3. Calculation of P Loading into Lake Rhodhiss 9
Method 1
4. Calculation of Loading Coming into
Lake Rhodhiss
12
5. Lake Rhodhiss Ambient Monitoring Stations 15
August 1979
6. General Characteristics of Lake Rhodhiss
19
7. Projected Total Phosphorus Concentrations 21
in Lake Rhodhiss Using Clements and Wolf's
Modified Vollenweider Equation
8. Projected Total Phosphorus Concentrations in 22
Lake Rhodhiss Using Clements and Wolf's
Modified Vollenweider Equation
9. Projected Total Phosphorus Concentrations 25
in Lake Rhodhiss Using Clements and Wolf's
Modified Vollenweider Equation

I. Summary
The Marion Corpening Creek WWTP was given monthly average
phosphorus limits of 2 mg/l. Of particular concern was the
impact that this facility would have on eutrophication in Lake
Rhodhiss. The Marion plant is 29 river miles from the head-
waters of Lake Rhodhiss. Other domestic dischargers with
design capacities greater than the Marion facility are
discharging directly into the headwaters of the lake. These
facilities are not employing phosphorus removal. This has
necessitated a re-evaluation of Marion's oontribution to the
nutrient loading of Lake Rhodhiss.
Employing phosphorus removal, Marion's contribution to the
total P entering Lake Rhodhiss is 5%. Assuming Marion had a
"medium strength" waste (8 mg/1 total phosphorus removal its
contribution of the total loading would increase to 11%. Using
a modified Vollenweider model, it was predicted that this would
increase the total P concentration in Lake Rhodhiss from 65 ug/1
to 70 ug/1, a change of only 5 ug/1.
Normally, when a prediction is made, it cannot be said
what certainty one should attach to the prediction. In order to
overcome this weakness, an uncertainty analysis was conducted
to accompany the above projection. Under present conditions
(i.e. Marion employing phosphorus removal), it can be said
that 90% of the time the average total phosphorus concentration
of Lake Rhodhiss will be between 53 and 76 ug/l. This range is
due to variability between lake stations, measurement error and
yearly fluctuation. If Marion ceased its phosphorus removal and
discharged a waste containing 8 mg/1 total phosphorus, 90% of
the time the total phosphorus concentration of the lake will
vary between 54 and 86 u6/1. That is, assuming Marion has a
medium strength waste, it can be stated with 90% confidence that
there will be no more than a 10 ug/1 increase in the average
total phosphorus concentration of the lake.
1

It is important to note that the above projections are
conservative. These projections assume that all the phosphorus
discharged from Marion reaches Lake Rhodhiss. In actuality,
it is likely that a large percentage of the phosphorus gets
trapped in the 29 mile stretch of stream between the Marion
discharge and the headwaters of the lake.
The results of algal growth potential tests conducted by
the Environmental Protection Agency indicate that the enrichment
on Lake Rhodhiss from the Marion-Corpening Creek plant appears
to be minimal. Greater impact on the lake is coming from the
dischargers at the headwaters of the lake such as the Morganton
WWTP. The Morganton facility does not employ phosphorus
removal.
According to the Mooresville Field Office, there have been
no complaints concerning the eutrophication of Lake Rhodhiss.
Considering the above findings, it seems both equitable and
technically justifiable to no longer require Marion to employ
phosphorus removal.
2

II. Introduction
The phosphorus limits for the Marion Corpening Creek WWTP
were developed primarily as a product of limited work by the
U. S. Environmental Protection Agency in the headwater lakes of
the Catawba River. (Please see appendix - August 3, 1981 letter).
This work was accomplished during 1973 and 1974. However, major
changes have .occurred in the Lake Rhodhiss drainage area which
necessitates a re-evaluation of the impact of the Marion discharge.
Significant among these changes was the introduction of several
new domestic discharges with design capacities greater than the
Marion WWTP. The Marion facility presently has a design capacity
of 3 MGD. It has total phosphorus limitations of 2 mg/1
(monthly average) and 3 mg/1 (weekly average). Phosphorus
removal is accomplished by the addition of lime and other
coagulants just prior to the secondary clairfier.
Of particular concern is the impact that the Corpening Creek
plant will have in contributing to the eutrophication of
Lake Rhodhiss. This lake is located on the southeastern
border of Caldwell County and in the central and eastern portion
of Burke County. As are most lakes located in North Carolina,
Lake Rhodhiss is an impoundment; it is generally riverine in
nature with an approximate length of 13 miles. The Marion
Corpening Creek plant is located 29 river miles from the
headwaters of Lake Rhodhiss.
3

III. Methods and Results
The removal of phosphorus limits and its projected impact
on Lake Rhodhiss was analyzed in several ways. First, the load-
ing of total phosphorus (total P) into Lake Rhodhiss was calculated.
The amount of total p that Marion contributes presently was
then compared to the amount that Marion would contribute without
phosphorus removal. A Vollenweider model adapted to southeastern
lakes was also used to compare projected total P concentrations
in Lake Rhodhiss with and without Marion employing phosphorus
removal. Finally, a series of algal growth potential tests
(AGPT's) were performed by EPA's Region IV Surveillance and
Analysis Division in order to determine the relative impact of
Marion on Lake Rhodhiss. The findings of these tests are
included in the Appendix.
4

Loading Calculations
A preliminary way of assessing Marion's impact on Lake
Rhodhiss is to ascertain the present loading of phosphorus to
Lake Rhodhiss and the percentage of this loading contributed by
Marion employing phosphorus removal. This may then be compared
to the projected loading to the lake assuming no phosphorus
removal by Marion. Assuming a linear relationship between in -lake
phosphorus concentration and phosphorus loading, the effect on
Lake Rhodhiss of suspending Marion's phosphorus removal may be
estimated.
The major tributaries to Lake Rhodhiss located below Lake
James are listed in Table 1. Also indicated are the drainage
areas and average flows of these tributaries at or near their
mouths. It is important to note that the average flows estimated
by USGS are those due to natural runoff and do not include point
sources.
There are 53 point sources located in the river basin
below Lake James. These include the 52 point sources from
subbasin Catawba 31 and the Marion Corpening Creek plant which
discharges into Corpening Creek, a tributary of South Muddy Creek.
South Muddy Creek enters into Muddy Creek which then enters the
Catawba River just below Lake James. Of these 53 dischargers
there are seven with design flows greater than or equal to 0.5
MGD (Table 2). Table 2 lists the actual flows obtained from
self -monitoring data for these major dischargers. Total P
concentrations for the Marion-Corpening Creek plant were obtained
from approximately two years of self -monitoring data. The total P
concentrations for the six other facilities were averages from
3 to 4 samples taken over a 24 hour period (Intensive Survey
Report).
.mod,
5

Tributary
Table 1
Major Tributaries to
Lake Rhodhiss below
Lake James
D.A. Q avg 7/10
Location USGS # .2
mi(cfs) (cfs)
Muddy Creek at Bridgewater 02.1388.1000 97.8 217 37
Canoe Cr. at SR 1284 nr. Morganton 02.1390.5850 15 22 4
Silver Cr. at SRR nr. Morganton 02.1391.9255 67 117 24
Hunting Cr. below SEO nr. Morganton 02.1398.0600 25 42 10
Warrior Fork at SR 1440 nr. Oak Hill 02.1393.9000 79.9 156 28
Johns River Rt. 18 nr. Morganton 02.1410.0000 209 450 45
°i Lower Cr. 0.4 mi below Miller Cr. 02.1412.0780 52 74 11
near Lenoir
Smoky Cr. near Baton 02.1412.6850 3.9 5.7 1.2
Howard Cr, 0.7 miles above mouth 02.1413.2310 5 7.5 1.5
near Drexel
McGaillard Cr. near Valdese 02 .1414 .2400 7.4 13 2
Hoyle Cr. ab. Sta #2 near Valdese 02.1414.5400 4.7 8.5 1.5
Stafford Cr. at SR 1240 at Baton 02.1413.4970 2.3 3.3 0.5
Island Cr. at Mouth nr. Rutherford Col. 02 .1414 .6325 6 8.4 2.1
Freemason Cr. 0.2 mi below SR1200 at 02.1414.6565 0.5 0.7 0.04
Saw Mill
Hayes Mill Cr. at Saw Mill 02.1414.7550 0.3 0.4 0.04
In addition to these tributaries, there is flow from the Catawba River. Data provided by Duke Power
over the last three years indicated the average flow from Bridgewater Dam, located at the mouth of
Lake James, to be 754 cfs.
An additional 103 cfs was calculated for average runoff from Bridgewater Dam to N.C. 181 which is
located near the headwaters of Lake Rhodhiss.

Table 2
Existing Point Sources to Lake
Rhodhiss Drainage Basin + with
Design Flow ' 0.5 MGD
Total P
Discharger Design Flow (MGD) Actual Flow (MGD) Concentration (mg/1)
Morganton
Catawba River WWTP
(NC0026573)
8.0 3.8 7.8*
Lenoir -Lower Cr. WWTP 6.0
(NC0023981)
Valdese-McGdillard Cr. WWTP 3.2
(NC0020753)
- Marion-Corpening Cr. WWTP
(NC0031879)
Great Lakes Carbon -
Silver Creek WWTP
(NC0005258)
3.0
2.6
Valdese -Hoyle Cr. WWTP 1.0
(NC0021199)
Drexel -Howard Cr. WWTP 0.5
(NC002129)
2.0 3.3*
1.5 18.8*
1.8 3.4 mg/1**
2.4 4.05*
0.5
0.3
average of sampling from July 1982 survey
taken from self -monitoring data 9/79-6/82
Actual flow data were taken from self -monitoring reports 6/79-6/82
+ only dischargers entering below Lake James are listed
7.9*
5.7*

The phosphorus values for these six facilities are limited
due to the brief time over which they were monitored. However,
the values seem reasonable when compared to values that have
been reported for typical untreated domestic wastewater'.
Strong wastewaters typically have P concentrations of 15 mg/1,
a medium waste would average 8 mg/1 while a weak waste would yield
approximately 4 mg/l. When having to estimate loadings from
point sources other than the seven listed in Table 2, the design
flow was assumed to be the actual flow and the value of 8 mg/1,
corresponding to a medium strength waste, was used for the
effluent concentration. The design flows of water treatment
plants, oil/water separators and cooling water dischargers were
not included in the loading calculations.
Two different methods were used to get estimates of
present phosphorus loadings into Lake Rhodhiss. Both methods
utilized ambient water quality and point source data. No land
use data was included in the analysis. Thus, it was assumed
that the phosphorus entering Lake Rhodhiss could be accounted
for by considering the loadings coming from the major tributaries
and the point sources. The two methods were differentiated by
the degree to which existing ambient monitoring data was used
in the loading calculations.
1. Method 1
The calculation of the total phosphorus loading coming
into Lake Rhodhiss by Method 1 is presented in Table 3. In
this technique, ambient monitoring data was used whenever possible.
Where sufficient data was available, only ambient data from
June 1979 to the present was used. (June 1979 corresponds to the
approximate time that the Marion plant with phosphorus removal
went on line.)
-4401
1Metcalf and Eddy, Wastewater Engineering: Treatment, Disposal,
Reuse, second edition, revised by George Tchobanoglous, 1979,
p. 64 table 3-5.
8

Source
Catawba R.
tO Hunting Cr.
Warrior Fork
Johns R.
Lower Cr.
Avg. Flow(cfs)
2.79 (Marion
Corpening Cr.)
754 (Bridgewater)
217 (Muddy Cr.)
22 (Canoe Cr.)
120.7 (Silver Cr.
& Great Lakes
Carbon)
103 (runoff)
Table 3
Calculation of P Loading
into Lake Rhodhiss
Method 1
Average P lbs . /day
conc. (mg/1) P conc. (mg/1)
1219.5
42 (nat. flow)
0.11 (pt. sources)
156 (nat. flow)
.012 (pt. sources)
450 (nat. flow)
.0155 (pt. sources)
450.22
74 (nat. flow)
3.1 (Lenoir plant)
0.153 (other pt.
sources)
77.25
Smoky Cr. 5.7 (nat. flow)
0.039
.042
8
.042
8
.042
0.176
.042
256.2
9.5
4.7
35.3
0.52
101.7
73.2
Comments
ambient monitoring from
02139282, Catawba R. at
NC181
78/01/26-81/02/25
Nat. flow conc. from Johns
River
Nat. flow conc from Johns
River
ambient monitoring from
CTB031D1 Johns R. at
SR1438. 79/06/17 to
82/04/05.
ambient data from CTB0341A;
79/06-82/04/05
1.30 Nat. flow conc. from Johns

Source
Howard Cr.
Avg. Flow(cfs)
7.5 (nat. flow)
0.47 (Drexel)
7.97
(continued)
Table 3
Calculation of P Loading
into Lake Rhodhiss
Method 1
Average P
conc. (mg/1)
McGaillard Cr. 13 (nat. flow)
2.33 (Valdese WWTP)
.0155 (other pt.
sources)
Hoyle Cr.
Stafford Cr.
Island Cr.
15.35
8.5 (nat. flow)
0.78 (WWTP)
9.28
3.3 (nat. flow)
0.23 (pt. sources)
8.4 (nat. flow)
Freemason Cr. 0.7 (nat. flow)
Hayes Mill Cr. 0.4 (nat. flow)
0.011 (pt. sources)
Morganton 5.89
Catawba R. WWTP
Totals 2002
0.658
2.73
0.222
.042
8
.042
.042
.042
8
7.8
lbs . /day
P conc. (mg/1)
28.3
225.7
11.10
0.75
1.0
1.90
0.159
.091
.474
247
998.9
Comments
Ambient data taken from
CTB036 below SEO 71/11/02-
72/01/31
ambient data based on
CTB038
71/11/23 - 72/01/31
79/01/23 - 79/08/28
ambient data from CTB 040
located below SEO
nat. flow conc. from Johns
conc. from Johns R.
conc. from Johns R.
nat. conc. from Johns

Most of the ambient data had a minimum detection limit of
0.05 mg/I. In averaging data from stations, values below the
detection limit were assumed to be equal to .025 mg/1. Using
this assumption the total loading to Lake Rhodhiss was calculated
to be 989.9 lbs/day.
The heavy reliance on ambient data which was used in this
technique does have a major drawback. A significant amount of
the ambient data used in this calculation was obtained in the
early 1970's (Table 3). It is quite possible that treatment
plant flows and precesses may have changed since then and would
thus not be adequately reflected in the data.
2. Method 2
Another method was used in order to get an estimate of
loading without such heavy reliance on ambient data. In this
technique the ambient data from the Catawba River at NC 181
(station 02139282) was used to get an estimate of loading
coming from the Catawba River. This station contained data as
recent as early 1981. However, for the rest of the tributaries
natural loading and point source loading were totaled separately.
The total P concentration of natural runoff flow was assumed
to be equal to the average total P concentration of the Johns
River which is relatively unimpacted. For dischargers above
0.5 MGD, the total P concentrations and average flows listed
in Table 2 were used. All other point sources were assumed
to be operating at design flow and have an average total P
concentration of 8 mg/l. The calculation of total loading using
this technique is listed in Table 4. Using this method, the
total average P loading to Lake Rhodhiss is 1029.8 lbs./day
which is in close agreement with the 998.9 lbs./day calculated
by Method 1.
11

Source
Catawba R.
Hunting Cr.
Warrior Fork
Johns R.
Lower Cr.
Smoky Cr.
Table 4
Calculation of Loading
Coming into Lake Rhodhiss
Method 2
average P Loading
Avg. flow (cfs) conc. (mg/1) lbs./day
2.79 (Marion Corpening
Cr . )
754 (Bridgewater Dam)
217 (Muddy Cr.)
22 (Canoe Cr.)
120.7 (Silver Cr. and
Great Lakes Carbon)
103 (runoff)
.059 (other pt. sources)
1219 .5
42 (nat. flow)
0.302 (pt. sources)
156 (nat. flow)
0.012 (other pt. sources)
450 (nat. flow)
74 (nat. flow)
3.1 (Lenoir Plant)
0.153 (other pt. sources)
5.7 (nat. flow)
Howard Cr. 7.5 (nat. flow)
0.47 (Drexel)
Mc Gaillard Cr.
Hoyle Cr.
Stafford Cr.
Island Cr.
Freemason Cr.
13 (nat. flow)
2.33 (Valdese WWTP)
0.0155 (other pt. sources)
8.5 (nat. flow)
0.78 (Valdese WWTP)
3.3 (nat. flow)
.023 (pt. sources)
8.4 (nat. flow)
0.7 (nat. flow)
Hayes Mill Cr. 0.4 (nat. flow)
0.011 (pt. sources)
.039 256.2
.042 9.5
8 4.7
.042 35.3
8 0.52
.042 101.7
0.042 16.7
3.3 55.1
8 6.59
0.042 1.30
0.042 1.70
5.7 14.4
.042 2.94
18.8 236
8 0.67
.042 1.92
7.9 33.2
.042 0.75
8 1.0
.042 1.90
.042 0.158
.042 0.091
8 0.474
12

Source
Table 4 (continued)
,average p Loading
Avg. flow(cfs) conc. (mg/1) lbs./day
Morganton Catawba R . 5.89
WWTP
7.8 247
Total P Loading 1029.8
Total Flow 2002 cfs
13

. Marion-Corpening Creek WWTP Contribution to the
Total Phosphorus of Lake Rhodhiss
The Marion Corpening Creek Plant has been discharging at a
rate of 1.8 MGD with an average total p concentration of 3.4
mg/1 (Table 2) . This would equal a total loading of 51 lbs./day.
The total loading of Lake Rhodhiss will be taken as 1014
lbs./day which is the average of two values derived from Methods
1 and 2 (Tables 3 and 4) . Thus, the loading of the Marion plant
is 5% of the total loading going into the Rhodhiss basin.
It is important to note that the above conclusion assumes
that all of the phosphorus coming from the Marion plant enters
Lake Rhodhiss. This is doubtful. There are 8.5 stream miles
in which the Marion effluent is in the Muddy Creek system before
it enters the Catawba River. The effluent then travels another
20.5 miles in the Catawba River before it enters Lake Rhodhiss.
It is likely that a significant portion of the total P gets
trapped in these river systems before entering Lake Rhodhiss.
Assume Marion stops its present phosphorus treatment and
discharges approximately 8 mg/1 total P which would correspond
to a medium strength domestic waste. This would mean that
Marion would contribute an additional loading of 69 lbs./day total P.
This would increase the total loading to Lake Rhodhiss to 1083
lbs./day which is an increase of 6.8%. Marion's contribution
of total P would increase from 5.0% to 11%.
The present average total P concentration of Lake Rhodhiss
is 0.065 mg/1 (Table 5). If, as most lake models assume, there
is a linear relationship between total P loading and the
total P concentration in the lake, the 6.8% increase in total P
loading would raise the total P concentration of Lake Rhodhiss
to 0.069 mg/1. This would be an increase of only 4 ug/l.
14

Station
CTB040A
CTB040B
CTB034A
Table 5
Lake Rhodhiss Ambient
Monitoring Stations
August 1979
Location
SR1001 nr. Baton
at end of SR 1544,
just upstream of
Hoyle Cr.
at Sr 1501 nr.
Drexel
Dates
avg. total p # of
mg/1 observations
79/08/22 .0690
- 82/10/21
79/08/22 .0325
- 82/03/30
79/08/16
- 82/03/30
mean =
st. dev.=
var. =
0.0648
0.0309
0.0009
Standard error = 1 29 x .0309 = 0.0057
15
0.0842
,
17
6
6

If Marion's effluent was assumed to be a strong waste having
a total P concentration of 15 mg/1, Marion's contribution of
the total loading would be increased from 5.0 to 19%. The
total P concentration of Lake Rhodhiss would be expected to
increase from 0.065 to 0.076 mg/l.
da
16

B.
Modified Vollenweider Model
The impact that the Marion-Corpening Creek WWTP has on
eutrophication in Lake Rhodhiss may also be analyzed by the use
of lake models. Several of these models have been developed by
Vollenweider (1975, 1976). However, these models were
•
developed for conditions specific to Canadian and Swiss lakes.
Marlar and Jutzman (1980) have proposed a refinement of the
Vollenweider (1975) model in order to account for conditions in
southeastern lakes and reservoirs.
A preliminary study based on a data set of 44 southeastern
lakes and reservoirs has been completed (Clements and Wolf, 1982
please see Appendix). Their work has been based on EPA National
Eutrophication Survey information from lakes in South Carolina,
Virginia, Georgia and North Carolina (including Lake Rhodhiss).
In addition, Reckhow and Simpson (1980) and Reckhow (1982,
attached) have developed a procedure by which error analysis may
be incorporated into the modeling procedure. The error analysis
allows the modeler to associate a probability with a range of
values generated by the model. This probability range is dictated
by the standard error of the model.
Clements and Wolf (1982) have used a modification of the
Vollenweider model. The basic Vollenweider model is:
p = L T
LT ( 1
P = Z € 1 + Tk
where P = phosphorus concentration in mg/1
L = phosphorus loading in g/m2-yr.
Z = mean lake depth in meters
T = hydraulic detention time (years)
17

In their preliminary study, Clements and Wolf have estimated K
to equal 0.368 for southeastern lakes. This modified model is
the mostcomprehensive for southeastern lakes to date and will
be used in this :analysis . A standard error of 0.411 (log
transformed units) was determined for this model.
Table 6 lists the general characteristics of Lake Rhodhiss
as determined by the recent NRCD study. This is also compared
with the data presented by EPA in the National Eutrophication
Survey. The basic difference is in the surface area reported
by the two studies. EPA's data was taken by Duke Power which
included surface area as all land up to the full pond
elevation level of 995.1'. This will tend to overestimate
surface area under average conditions. The NRCD study took as
surface area the area enclosed by Lake Rhodhiss just below the
Johns River. The NRCD data will be used for this analysis.
Given a change in existing loading,Reckhow (1982) has
presented two ways in which to project the change in total
phosphorus that is expected. One method (Method A) simply
calculates the new projected loading and replaces this in
the model to get a new predicted in -lake total phosphorus
concentration. The other method (Method B) utilizes the
existing data on in -lake total phosphorus concentration under
present conditions. The change in loading is used via the model
to project the net change in phosphorus concentration. This
value is then added to the present concentration to predict the
new in -lake value. Method B will tend to reduce the prediction
error. This is especially true if the model error is large and
the change in loading is relatively small. The model standard
error of 0.411 is a relatively large error. Thus, the use of
Method B will tend to reduce prediction error.
The change in phosphorus concentrations were analyzed
assuming Marion had both a medium waste (8 mg/1) and a strong
waste (15 mg/1). Projected phosphorus concentrations and their
18

Table 6
General Characteristics of Lake Rhodhiss
Surface Area (Ao)
As estimated by NRCD Study
11.1 km 2
4.3 miles
Mean Depth (Z) 6.3 m
20.7 ft
Determined by bathymetric measurement
(see Intensive Survey Report)
Volume (V=AoZ)
2
2.5 x 109 ft3
Flow (F) 2002 cfs
(from Table 4)
Hydraulic Detention Time (T) 14.5 days
T = V/F .040 year
As estimated EPA in NES #
Surface Area (Ao ) 14.4 km2 2
5.6 miles
Mean Depth (Z) 6.3 m
20.7 ft
Volume (V = AoZ) 3.1 x 109 ft3
Flow 1650 cfs
Hydraulic Detention Time 21 days
19

corresponding 55% and 90% confidence intervals are presented in
Tables 7 and 8.* Table 7 is based on Method A while Table 8
is based on Method B.
It should be noted that the Clements and Wolf model gave a
fairly good prediction of present in -lake phosphorus concentration
based on existing loadings. The model predicted that the phosphorus
concentration in Lake Rhodhiss is 72.4 ug/1 (Table 7) while the
actual measured concentration is 64.8 ug/1 (Table 5).
The advantages in using Method B over Method A may be
seen by comparing the confidence limits in rable 8 versus Table 7.
Both methods predict a 5 to 6 ug/1 increase in total P if the
Marion WWTP increases its average total P concentration from
3.4 mg/1 to 8 mg/l. However, notice the difference in confidence
limits generated by the two different methods. In Table 7,
Method A indicates that one can say with a 55% probability that
the new P concentration will be between 0 and 164 ug/l.
Meanwhile, the use of Method B (Table 8) reduces the range of
the 55% confidence interval down to 15 ug/1 (from 62 to 77 ug/1).
This is a reasonable range for planning purposes. Using Method B,
we can even say with 90% confidence that with Marion discharging
at 8 mg/1 the new P concentration in Lake Rhodhiss will be
between 54 and 86 ug/l. This range is less than 1/5 of the
55% confidence limit generated by Method A.
During the intensive survey, a 24 hour composite sample
was collected at the Marion Corpening Creek WWTP at a point
just prior to phosphorus stripping. The total P concentration
of this sample was 5.20 mg/1. This would be more indicative of
a medium strength waste rather than a strong one.
* The 55% con idence interval is ± the standard error, while the
90% confidence interval is roughly ± 2 times the standard
error. Calculations for Tables 7, 8 and 9 are included in the
Appendix.
20

Table 7
PROJECTED TOTAL PHOSPHORUS
CONCENTRATIONS IN LAKE RHODHISS
USING CLEMENTS AND WOLF'S MODIFIED
VOLLENWEIDER EQUATION
Method A - Using Total Loading
Total P Conc. Total Loading to Projected P 55% 90%
@Marion (mg/1) Lake2Rhodhiss concentration Confidence Confidence
(g/m -yr) P (mg/1) Limits(mg/1) Limits(mg/1)
Present
3.4
Medium waste
without treatment
8 mg/1
Strong waste
without treatment
15 mg/1
15 .13
16 .16
17.73
0.0724 0.0071P`i0.152-.08660.23.
0.0786-.09285=P0.25
0.0862 -0 .008'LP50 .180
21

Table 8
PROJECTED TOTAL PHOSPHORUS
CONCENTRATIONS IN LAKE RHODHISS
USING CLEMENTS AND WOLF'S MODIFIED
VOLLENWEIDER EQUATION
Method B - Using Change in Loading
Total P ALoading to Projected P 55% 90%
conc. @ Marion Lake2Rhodhiss conc. Confidence Confidence
(mg/1) (g/m -yr) (mg/1) Limits Limits
Present
3.4 mg/1
0
medium waste 1.031
without treatment
8 mg/1
strong waste 2.60
without treatment
15 mg/1
0.0648 .0591_P`=.0705 .0534=P=.0762
(measured)
0.0698 0 .0619=P-.0777 .0540SP ....0856
0.0774 .0623P=-.0924 .0473'�P-=.107
.22

The new Valdese Lake Rhodhiss Pollution Control Facility
is expected to be on line sometime this year. It has total
phosphorus limits of 1 mg/1 monthly average and 3 mg/1 weekly
agerage in its permit. This new facility will be taking the
wastes of the two existing Valdese plants (Hoyle and McGaillard
Creek) as well as the Drexel WWTP.
It thus becomes important to consider predicted total P
concentrations under other scenarios. These predictions along
with their 55 and 90% confidence intervals are presented in
Table 9.
In Table 9, the existence of the new Lake Rhodhiss Pollution
Control Facility is indicated by the Valdese Hoyle and McGaillard
Creek plants and the Drexel WWTP employing P removal. It is assumed
that P removal corresponds to an effluent total P value of 3.4
mg/1 which is the present average value of the Marion WWTP.
Please note that only Method B was used to calculate projected
values since, as indicated before, this method gives projected
values with a substantial reduction in uncertainty when compared
to Method A.
Looking at Table 9 it is indicated that a total P concentra-
tion of 49 ug/1 is expected in Lake Rhodhiss when the new
Valdese Lake Rhodhiss Pollution control Facility and Marion
are both employing P removal. This would be a reduction of
approximately 10 ug/1 from present conditions, while if Marion
had a strong waste (15 ug/1), there would be little reduction,
if any. Finally, the last scenario represents all the major
dischargers (Table 2) employing P removal. The projected
total P concentration in Lake Rhodhiss in this situation is
38.9 ug/1 which is areduction in total P of approximately 26
ug/1.
tp
It should be noted that the uncertainty in projections
(i.e. range in confidence limits) tends to be larger in Table 9
than in Table 8. This is due to the fact that in Table 9
23

combinations of positive and negative loading changes are
being evaluated. The uncertainty in these changes are additive.
Thus, in these types of scenarios, it is still possible to
have a large uncertainty though the net change in loading is
small. (Please see Appendix for actual calculation of total
standard error.)
24

Description of Plants
Marion, Valdese (Hoyle and
McGaillard plants) and Drexel
WWTP employing P removal
(corresponds to the new Valdese
Lake Rhodhiss Pol;ution Control
Facility and Marion employing
P removal)
Table 9
PROJECTED TOTAL PHOSPHORUS
CONCENTRATIONS IN LAKE RHODHISS
USING CLEMENTS AND WOLF'S MODIFIED
VOLLENWEIDER EQUATION
Method B - Using change in loading
Present Lake Rhodhiss total P = 0.0648 mg/1
A Loading to L2 Rhodhiss Projected
(g/m -yr) AP(mg/1) P (mg/1)
Valdese (Hoyle & McGaillard) and
Drexel employing P removal., Marion
discharging at 8 mg/1 (Medium
strength waste)
Valdese (Hoyle & McGaillard) and Drexel
employing P removal, Marion discharg-
ing at 15 mg/1 (medium strength waste)
- 3.24
+1.03 Marion
- 3.24(Valdese
and
Drexel) -.0107
-0.01575 0.0491
+.0050
-.01575
+2.60 Marion
- 3.24 (Valdese
and
Drexel)
+.01264
-.01575
- .00311
0.0541
0.0617
Valdese (Hoyle & McGaillard), Drexel -5.33 -.0259 0.0389
Morganton and Marion employing P
removal. [Lenoir and Great Lakes Carbon
are already discharging at levels at or
below Marion's average of 3.4 mg/1
total P. Thus, this scenario would
cgrrespond to all major discharges
(-'0.5 MGD) employing P removal.]
55%
Confidence
Limits
.0209 P -.0673
.0354 P�.0728
. 0302- P-.0932
. 0100 -P �. 0678
90%
Confidence
Limits
.0126-P�.0855
. 0167 ?P?. 0915
-.001 P->0.125
.0189-P�.0966

IV. Conclusions and Recommendations
Assuming present conditions with Marion stopping its P
removal and discharging a medium strength waste, the projected
increase in total P concentration for Lake Rhodhiss is quite
small (Table 8). It should also be reemphasized that all the
analyses in the previous sections assumed that all the phosphorus
Marion would be discharging would find its way into Lake Rhodhiss.
With the 29 miles travel distance to Lake Rhodhiss, this is
very doubtful.
The Algal Growth Potential Test which were conducted by
EPA Region IV corroborate this conclusion. The results of the
tests are located in the Appendix. The results indicate that:
"The enrichment impact of the Marion Corpening Creek WWTP and
the Great Lakes Carbon - Silver -Creek WWTP appears to be minimal
in the Catawba River as bioavailable phosphorus concentration
decreases from 7.9 ug/1 to 1.3 ug/1, a range of concentration
within acceptable limits for potential algal production.
Higher MSC's (Mean Standing Crops) ranging from 7.50 mg
dry weight per liter to 13.57 mg dry weight per liter at the
headwaters of Lake Rhodhiss seem to reflect nearby greater
WWTP loadings to the lake."
The specific loading referred to in this last paragraph
is coming from the Morganton WWTP. Furthermore, there is the
question of equity. Presently, the Morganton WWTP is not
required to employ P removal. This facility which discharges
directly into the headwaters of Lake Rhodhiss is also discharging
more than twice the flow of the Marion plant. The new Valdese
Lake Rhodhiss Pollution Control Facility, which is located just
downstream of the Morganton plant, is, however, required to
employ P removal. It appears indefensible to continue_ requiring
Marion to employ P removal while not requiring it of Morganton
and possibly the Lenoir Lower Creek plant as well.
26

There appears to be two equitable possibilities. One
option is to require P removal from all the major domestic
dischargers (i.e. those dischargers listed in Table 2). The
other option is not to require any of the dishcargers to employ
P removal.
According to Rex Gleason (Mooresville Regional Office),
there have not been any complaints concerning eutrophication in
Lake Rhodhiss. This is further corrobrated by chlorophyll a data.
Ambient lake data taken from June 1979 to present indicate the
average chlorophyll a value of the lake to be 16 ug/1 which is
well below the water quality standard of 40 ug/1.
Assumming Marion has a medium strength waste, even under
the most conservative estimates, the cessation of P removal
should increase the total P concentration of Lake Rhodhiss by
only 5 ug/l. It is therefore recommended that Marion no longer
be required to continue phosphorus removal at its corpening Creek
plant.
27

References
Marlar, J. and Jutzman, J., (1980). A Holistic Lake System
Assessment. A paper presented at the National Water
Quality Management Conference, Atlanta, Ga., June 4-6,
1980.
Vollenweider, R. A., 1975. "Input -Output Models with .Special
Reference to the Phosphorus Loading Concept in Limnology.",
Schweiz. Z. Hydrol. 37, No. 1:53.
Vollenweider, R. A. .1976. "Advances in Defining Critical
Loading Levels for Phosphorus in Lake Eutrophication."
Mem . Inst. Ital. Idrobiol . 33:53
Reckhow, K. H. and Simpson, J. T. (1980). "A Procedure Using
Modeling and Error Analysis for the Prediction of Lake
Phosphorus Concentration from Land Use Information.",
Canadian Journal of Fisheries and Aquatic Sciences, Vol. 37,
No. 9, 1439-1448.
Reckhow (1982) attached
Clements, J. T. and Wolf, J. (1982) attached
tp
28

Appendix A
Calculation of Prediction Interval
Bounds for Table 7
Calculation of Prediction Interval
Bounds for Table 8
Calculation of Prediction Interval
Bounds for Table 9
29

Calculation of .prediction interval bounds for Table. 7
Conc. of total P
dal Marion
Proj. P•
(mg/1)
Prediction interval bounds
3.4 0.0724 10
8
log (0.0724) ± .411
.0281, 0.187
±.0795
.0786 10 log (.0786) ± .411
0.0305, .202
±.0857
15 .0862 10 log (.0862) ± .411
.0335, 0.222
±.0942
1p
30

Calculation of prediction interval bounds for Table 8
Conc. of total P
Lla Marion
3.4 mg/1
AP
(mg/1)
Prediction Interval Bounds
0.0648 ±.0057 (standard error)
measured
8 mg/1 0.0050
15 mg/1 0.0126
31
S.E. model = 10 log(.005)±.411
0 .00194 , 0 .0129
±.0055 1
Tot. S.E.=[(.0057)2+(.0055)27
2
=±.0079
S.E. model = 10 log(.0126)±.411
.00491, .0326
±.0139 j
Tot. S.E.=[(.0057)2+(.0139)2]�
=±.0150
tp

Calculation of preduction interval bounds for Table 9
Loading Proj. P
(g/m -yr) P mg/1 mg/1
-3.24
-0.01575 0.0491
Prediction Interval
bounds
S.E. mode1=101og(.01575)±.411
.006 , .0406
±.9173 2
Tot. S.E.=[ (.0057/0+61g1273 ) ] 2
+1.03 +.0050 .0541 S.E.=101og(.01625)±.411
-3.24-.01575 .0063,.0419
.01625* ±.Q178 2
(*errors are ) Tot. S . E . = C .0057) + (. 0178 ) J
11
additive =±.0187
2.60
-3.24
-5.33
±. 01264 0.0617
- . 015 75
.02839*
*(errors are additive)Tot.
-.0259 .0389
32
S.E. moded=101og(.02839)±.411
.0110, .0731
.0310
S.E.=[(.0057)2+(.0310)2]h
=± .0315
S.E. mode1=101og(.0259)±.411
.0101,.0667
±.9283 -�
Tot. S.E.=[(.0057) +(.0283)2 ]1±.0289

Appendix B
Memorandum Regarding Modified Vollenweider Model -
J. Trevor Clements
Memorandum Regarding Error Analysis for Lake Rhodhiss Study -
J. Trevor Clements
33

J. Trevor Clements
School of Forestry
Duke University
November 26, 1982.
Memorandum regarding modified Vollenweider model:
Vollenweider has developed criteria for relating Phos-
phorus loading and lake geomorphology to the trophic states
of lakes.1-3 Essentially, Vollenweider utilizes in -lake
Phosphorus concentration as a predictor of lake trophic status.
In -lake Phosphorus concentration(P in mg 1) is estimated as
a function of Phosphorus loading(L in g m2•yr), mean lake depth
(Z in m) and hydraulic detention time(''in yr's). The basic
model equation is represented by:
P = Lt/Z (1 - 1/ (1 * 1/•L ))
where k is a function of V emn4rically derived.
Vollenweider found k to be very close to .5 for a cross -
sectional set of Swiss and North American north temperate lakes.
In their preliminary study, Clements and Nolf4 have estimated
k to equal .368 for a set of forty-four southeastern lakes and
reservoirs. Their data set is based upon EPA NES information
and includes lakes from South Carolina, Virginia, Georgia and
North Carolina(including Lake Rhodhiss). :t should be recog-
nized that their estimate of k has not been finalized because
of an unacceptably large model standard error. Final revisions
may be subsequent to this report.
1. 7ollenwe i der , R . :. , 196E.
Paris, J S /CS /Fig 7
, 1.
Technical -eoor7. to . l .
2. Vollenweider, R.A., 1975. "Input -Output "odels with
Special Reference to the Phosphorus Loading 'once of
in Limnology." Schweiz. Z. Hydrol. 37, No. 1: 53 .
3. Vollenweider, R.A., 1976. "Advances in Defining Critical
Loading Levels for Phosphorus in Lake Eutrophication."
'hem. Inst. Ital. Idrobiol. 33:53.
4. Clements, J.T. and J..'iIolf. 1982. Study of Phosphorus
Modeling Technique Applications to Southeastern Lakes
(in progress).
34

J. Trevor Clements
School of Forestry
Duke University
November 26, 1982
Memorandum regarding error analysis for Lake Rhodhiss Study:
It is vital that a study of this sort include acknowle-
ment of the uncertainty with which model predictions and
policy recommendations are made. Without perfect information
of system variables and their relationships we cannot. be
certain of our predictions. Therefore, it is important that
an attempt be made at quantifying this uncertainty so that
these predictions can be place) within their proper perspec-
tive(i.e. How confident are we of our predictions?). Such
a quantification provides a measure of reliability or, .in
other words, an estimate of the value of our information.
Errors may arise from: natural system variability; inade-
quate sampling design; measurement error and bias; model :mis-
specification; model equation error; or because of error in
the model parameters and/or variables(Reckhow, 1982). In our
study, we have addressed two of these: model equation error,
and phosphorus concentration measurement error. These are
major sources of prediction error and are easily managed.
Reckhow, K. H., 1982. "A Method for the Reduction of Lake
Model Prediction Error," Water Research (in Print).
35

ti
Appendix C
August 3, 1981 letter from Mr. R. Helms (Director, D.E.M.)
to Mr. Howard Zeller (Acting Director, Enforcement Division,
EPA Region IV) . Letter seeks advice as to whether . EPA.,would
allow relaxation of Marion's limits if results of intensive
survey indicated this would be justified.
Intensive Survey - Lake Rhodhiss
City of Marion - Corpening Creek WWTP Study July 28 and 29,
1982
October 22, 1982 letter from Ron Raschke (Ecological Support
Branch, EPA, Region IV) to Steve Tedder (Head, Technical
Services Branch, D.E.M.). Letter explains results of Algal
Growth Potential Tests (AGPT) conducted by EPA.
A Method for the Reduction of Lake Model Prediction Error by
Kenneth H. Reckhow
36