NC0046728_Plan of Action_20080125

NPDES DOCUHENT SCANNING COVER SHEET
NC0046728
Mooresville / Rocky River WWTP
NPDES Permit:
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering
Alternatives (EAA)
Plan of Action
Instream Assessment (67b)
Speculative Limits
Environmental
Assessment (EA)
Permit
History
Document Date:
January 25, 2008
This document is printed on reuse paper - ignore any
content on the re rerse'side

Al
1

Agenda
• Introductions
• Background on Mooresville
• Current Flow Commitment
• Phased Planned Expansions
• Review of Re -Rating Application Package
• Discussion and Path Forward
Ro River
Expansion
January 25, 2008'
2

3

Population Growth
• Rapid growth leading to wastewater
capacity needs
- Master Plan finalized in 2006
- 20 year capacity need -19 mgd
- Interim phase -15 mgd
• Commercial, industrial growth strong
— Lowe's headquarters
— New exit from 1-77
Ro River
Favansron
4

110 CH2MHILL
Jr\CrC'r JL1! (D
80,000
70,000
60,000 -
c
0
50,000 -:
m
40,000
o_ 30,000 -
0
20,000
10,000
0
Mooresville Service Area
Projected Population Growth
74,031
2000 2005 2010 2015 2020 2025 2030
Year
5

410 CH2MHILL
r
`
.. n
Rocky River WWTP Projected Capacity Needs
(Maximum Month Flow)
Influent Row, mgd
N n
J (r O V1 O U
> C7 O O O C
18.7
Existing Capacity = 5.2 mgd 5.65
2030 Projected Needs
23
3.44
u.0 1
2000
t
1 , 1 1 1 1 1 1 1 1 1 1 1 1 1 , 1
2005 2010 2015 2020 2025
Year
, 1
2030
1
2035
".MMADF 1
6

Interbasin Transfer
• Current Grandfathered Amount = 9.54
mgd
• Water withdrawals from Catawba River
Basin
• Current discharge to Dye Branch (Rocky
River Basin)
• Current consumptive use in South Yadkin
River Basin
WWlf' Rivet
Expansion
7

Id CI-1211/11HILL
All.
...-
...,
Town of Mooresville
•:',.>
Ea CB ...
...
• 10°e'
sco-' ..••••• _Aro
.. .......... ••• owe v
:
.• s,c1ei
....
• *
.
Future
(IBT)
Inter -Basin Transfer
Trou.tu.ian
• 00
.4:1. 45.1._
I- 0 0
4. •
/
.P.ro• .
..............
iiilfr
Lake Norman
.
.. i
. `. . ..
. •
..
•..
Itl'ailk:' .•.. ‘
. .
• N.
.
Rocky Riv r
f WRF
-- -Mi. ,
„
1 n B 1 \
....y.c_ unc -i
.........
•..
.
• -
•.%
•... •
,„---
Mooresville
Catawba County
8

4 CH2MHILL
.J1,.�JI..
Town of Mooresville Rocky River WWTP Estimated Maximum Day Water Demand
and Transfer between Catawba and Yadkin -Rocky River Basins
(Assumes 50% Max Day Consumption)
en n
Water Demand and Inter -Basin Transfer, mgd
N N W W l
i 01 0 01 0 1r O (n C
D O b O O b O O C
Grandfathered
= 9.54 mgd
37.93 ■
33.93 a -
28.51
.12
15.48.•" •
- -
IBT •
1.05
7.69 ■" Estimated year when Grandfathered IBT reached -2008
-28
1 1
v. 1 1
2000
I i I 1 i i 1 11 { III 1 , 1 1 I
2005 2010 2015 2020 2025 2030
Year
i
2035
—e— IBT Cat to RR - - . - - Water Demand
9

cH2nam„ 111.1.1010
-11111.W=MIPIMIFF,
ift'kj,fektrROLJI ID
Town Catnip trn Pnits
VCompliance at WWTP
V Reduction of Infiltration & Inflow
V Reuse
V Stormwater Programs
1140, Rivet
w
Expansion
January 25, 2008;

-['
ow-n A ctivities
• Inflow & Infiltration Program
- FY 07-08 Budget includes $250, 000
• Plan to budget as an ongoing program
— 2008: Beginning Sewer System Evaluation
Survey
• Goal to evaluate system over next 5 years
• Crew established to repair in-house
- Aerial Sewer Crossing Elimination Program
• Reuse included in long term planning
Rocky River
WW7VExpansion
25, 2G0;2,
11

Ro River
W F�xpansion
Town Activities
• Stormwater Program
- Meeting Phase 11 requirements in stages or phases
before application deadline
- Land Development Design Standards Handbook
- Runoff leaving the site post -development shall not
exceed the pre -development volume for the local 2-
year, 24-hour storm event for all development
- Runoff rate leaving the site post -development shall not
exceed the Stormwater runoff rate leaving the site pre -
development for the local 1-year, 2-year, and 10 year,
24-hour duration storm events
Janua
5, 2JU
12

Rocky River
WW7P Expansion
.1 -'4 ro A ctivitif 3
• Stormwater Program
- Stormwater treatment shall achieve 85% TSS
removal from the first one -inch of rainfall
- General Requirements: Minimum of 35 foot
buffer on perennial and intermittent surface
waters
- WSW Requirements: increase to 50 feet, or
100 feet with high density development
- These engineering standards adopted in
October 2007
2;:), 2,Grja;
13

14

vi/V
n(ININI-FrriVID FT
Background on Wastewater Flows
• Wastewater Flows
- Actual flow: 3.1 mgd (60% of capacity)
- 5.2 mgd rated capacity
• Current and Planned Commitments
- New allocation policy being developed to
address current and future committed
capacity
Rocky River
WW7P Expansion
prinestay
January 25, 20081
15

16

110 CH2MHILL
p Mr -FA r7r) f---; 'r P AI 'IQ I P { 1\ I
Step
: Re -rating J - £d1ity
• Historical Data supports facility re -rating from 5.2 to
5.5 mgd
• Adding 300,000 gallons a day of capacity — would
•• .•
:•
...;..•
•� `
continue to discharge to Dye Branch with no
operational changes or modifications
•
.. ....at
• NPDES re -rating permit application submitted this
month to DWQ
• Re -rating needed to provide Town with breathing
,- `-.-.
room under allocation guidelines while implementing
S !
intermediate solution and conducting Tong -range
•
.
`River
Expansion
planning
i!LiL! /j, JVJJ
17

IVO CH2MHILL
P1-4 A Frr) P I sT
Step 2: Expansion via package plant
• Interim phase would increase discharge to Dye
Branch
• Dye Branch and Rocky River are 303(d) listed
streams
• Modeling of potential for sediment transport
concerns with increased discharge
• Increased discharge will not exceed
grandfathered IBT amount
Rocky River
WW7P Expansion
18

4001 Interim Plant Solutions
• "Pachage" Plant
- Increase total plant capacity by 2 to 4 mgd
- Need to meet permit limits of BODS of 5 mg/L
and NH3-N of 1 mg/L
Rocky River
ww-rpExpansion

CH2MHILL
rlEr
ant Solutions: The Future
• Integrate "package" plant into the
Phase 1 Facility Design/Expansion
1. °* - Residuals Filtrate Treatment
t• - Raw Wastewater Treatment
''•�•• of
• Other facilities/equipment could also
be integrated
W RockyRiver
WTP Expansion
January 25, 20081
20

Potential interini Site Pian with PackagePlant
'ff%
•
r
Rocky River
WWTP Eapansion
Package Plant
(incl Headworks)
• "1,
-1)
0 0 te
Av. .0. •,-;. 44. 41;•
UV Filters
....-0.1. --sr ..0.-.011116.1tiblillItiii1100
January' 2Sir 2008i
21

P T---__ A ,`-_-; Pi' D F; 1 P A I s-r a_ P { A I {,S3
Step 3; Long Term Expansion
to I 0 --
I5 mgd
•
Discharge to Dye Branch and LaF?e Norman
:••� •
.:
•
Addition of odor control, primary treatment,
anaerobic digestion, sludge blending, Lake
"
•.
`�•' r )
Norman Pump Station
.......
.'r".
•
Explore options for more affordable regional
solutions
'
r
Board allocated funds in FY08
e
, `.
- Board working with School of Government to
Rocky River
WWTP Expansion
promote regionalization
_
I •�ri�i�iry /J, �1JuJ
22

CH2MHILL
Phase I Proposed
Site Plan
Primary Sludge
Pump Station
Generators
Electrical
Substation
Headworks
Odor
• Control
Primary
Clarifiers
Influent Pump
Station
Filtrate EQ and
Treatment
Blower Building
-k 3 Cascade UV
Lake Norman Re -Aeration
Pump Station
NO
Basins
Odor
Control
Secondary
-Clarifiers
Sludge
Blending
Tanks,
f \Irc'
Thickening
Dewatering
C 0�
`RAS/WAS Pump Station
\ ',v/RAS Denite Zone
\ Filters
Chemical Facility -- x,1.41ts...+0
23

24

JRo River
W Favansion
300,000 gallon Re -Rating Request
• January 2008 request to DWQ for an
additional 30012 in capacity
- Re -rating of existing facility
- DWQ is concerned with future expansion plans
• Additional flow would discharge to Dye
Branch
• Summer Limits of 16/2
• Mooresville commitment to continue
addressing stormwater issues via Phase II
program
JanuatiNiErfa
25

26

Rocky River
W
W7-P FaPansion
rt0131-MktitrA
Future Expansions and Permitting
• Interim solution — packtage plant
• Environmental Assessment Required
• Regionalization Study - WSACC to east and
Catawba to west in search of most affordable
solution
• Long term capacity needs addressed, possibly
through regional solution
Irma r' %J,
27

Review of Future Tiirneline
• Permitting process will include NPDES, the
Environmental Assessment, and any
necessary 401/404 Permitting.
• The NPDES application for an expansion is
considered by DWQ after the completion of
the EA process (FONSI)
• Goal is a single EA submitted in summer
2008
• Phasing of this project may require 2 EAs
Ro Rivet
WW7P Expansion
January 25, 20081
28

Rocky &pans
W
WWT7TP"PP Exps
ion
Review of Future
• Permitting for the package plant phase will begin in
spring 2008
- permit review can take more than six months
- NPDES permit for increased Dye Branch discharge is
required
• Permitting for the larger expansion will begin upon
substantial completion of the regionalization study
- may take longer to complete considering an additional
discharge location and potential interbasin transfer
consideration
• Permit conditions may be required by DENR
Jafluyry 25, 2,(3(JJ
29

h
r
.411
taIV
t
OL1
41110 CH2MHILL
LIOfThi3
oMoo��.�
unu_ir, ZJ, YG O?
30

DRAFT TECHNICAL MEMORANDUM CH2IRRHILL
Town of Mooresville Rocky River WWTP Re -Rating
PREPARED FOR: NC DWQ, NPDES Division
PREPARED BY: CH2M HILL, Inc
DATE: January 3, 2008
This technical memorandum (TM) summarizes the background material required for the re -
rating of the Town of Mooresville Rocky River Wastewater Treatment Plant (RRWWTP)
from 5.2 to 5.5 mgd. The background material presented includes the following TMs
prepared as part of the Rocky River WWTP Expansion Preliminary Engineering Report:
• TM 201- Rocky River WWTP - Design Wastewater Flows, Loads and Characterization
• TM 202 - Rocky River WWTP Existing Facilities Assessment
• TM 203 - Rocky River WWTP Process Modeling
• TM 204 - Rocky River WWTP Hydraulic Analysis
Copies of the referenced TMs are provided in the Appendix.
Design Wastewater Flows, Loads and Characterization
Historical flows and loadings for the Rocky River WWTP are summarized in TM 201- Rocky
River WWTP Design Wastewater Flows, Loads and Characterization. The historical influent,
effluent and operating data was obtained from the Town of Mooresville and included data
from July 1, 2003 to April 30, 2005. The 22 months (670 days) of data consisted of daily
monitoring reports (DMRs) and daily operations reports. A summary of the historical
flows and loads data is presented in Table 1.
TABLE 1
Historical Flows and Loadings — July 2003 through April 2005
Parameter Avg Day Max Month Max Week Max Day Peak Hour
Flow (mgd) 2.62 3.00 3.75 9.10 12.1
cBOD (lb/day) 6,300 8,200 11,800 17,100 —
TSS (lb/day) 6,800 8,700 13,600 35,700 —
TKN (lb/day) 865 900 1,100 1,700 —
NH3-N (lb/day) 570 590 720 1,100 —
Total P (lb/day) 135 140 170 265 —
Alkalinity (lb/day) 4,370 5,010 6,260 15,190 --
Note: Alkalinity input data estimated at 200 mg/L.
CAPACITYRERATINGTM_DRAFT.DOC 1
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
As indicated in Table X, the historical flows and loadings analysis was based on data from
July 2003 through April 2005. Updated flows and loadings data was obtained from the
Town of Mooresville through October 2007. The updated data is presented in Table 2.
TABLE 2
Historical Flows and Loadings — July 2003 through October 2007
Parameter Avg Day Max Month Max Week Max Day Peak Hour
Flow (mgd) 2.78 3.57 5.04 9.10
cBOD (lb/day) 7,593 11,203 16,183 24,042
TSS (lb/day) 7,318 10,320 16,433 35,648
TKN (lb/day)' 842 1,084 1,153 2,006
NH3-N (lb/day) 612 787 838 1,457
Total P (Ib/day)' 125 161 172 298
Alkalinity (Ib/day)2 4,178 5,358 7,569 13,644
Note:
1Insufficient data to determine Max Month, Max Week, and Max Day Loads. Used NH3-N Peaking
Factors to determine the loadings.
2 Alkalinity input data estimated at 180 mg/L.
From comparison of Table 1 and Table 2, the average daily, maximum month, and
maximum weekly flows have all increased while the maximum flow has remained
unchanged. A longer term comparison of the flows between 2000 and 2007 indicates a
steady increase in flow over time (see Figures 1 and 2).
CAPACITYRERATINGTM_DRAFT.DOC 2
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
3.00
rn 2.00
E
0
LL
0▪ 1
0)
N
< • 1.00
0.00
2.97
2.75
rn,
2.64
2.56
2.49 2.52
2.44
.
2000
Li Influent Flow
2001
2002
2003 2004
Year
2005
2006
2007
10.000
9,000
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
o Influent BOD EI Influent TSS ❑ Influent NH3 ■ Influent TP
Figure 1- Mooresville RRWWP Average Daily Influent Flows and Loads
E
7.
4.00
3.80
3.60
3.40
320
2.80
2.60
2.40
220
2.00
1999
Average Loading, Lbs/day
■
1.57
,�
' -
■
325-
3.01
__
2.98
■
•
2.97
••
_ - -326
'
2.89
~
2.93
fig -
2.80
2.80
•
2.75
•
4, .
2.49
��
2.56
•
2.52
2.64
2.4
2000
2001
2002
2003
2004
2005
• ADF • MMQ - - - Eq'on. (MMQ) - - • Expon. (ADF )1
Figure 2 - Mooresville RRWWTP Average Daily and Maximum Monthly Flows
2006
2007
2008
CAPACITYRERATINGTM_DRAFT.DOC 3
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

s
TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
A comparison of the loadings is better presented in Table 3 which indicates that the average
daily concentrations of each constituent remained fairly close.
TABLE 3
Historical Flows and Loadings — Comparison of Average Daily Concentrations
Parameter July 2003 - April 2005
July 2003 - October 2007
cBOD (mg/L) 288.3 298.9
TSS (mg/L) 311.2 315.3
TKN (mg/L) 39.6 36.3
NH3-N (mg/L) 26.1 26.4
Total P (mg/L) 6.2 5.4
The plant performance was also reviewed. The plant effluent data determined that since
July 2003, the facility has been operating exceptionally well, although in March 2005 the
facility violated their NPDES permit for monthly average TSS as well in early August 2005
for peak week fecal coliforms. Table 4 summarizes the historical plant performance
between July 2003 and October 2007. Figures 4 through 5 depict the effluent BOD, TSS, and
NH3 by month using box and whisker plots. Figure 3 provides a brief description on how to
interpret the figures.
4—Maximum
75th Percentile
Mean
Median
25`h Percentile
4—Minimum
Figure 3 - Interpretation of Box and Whisker Plots
CAPACITYRERATINGTM_DRAFT.DOC 4
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TABLE 4
Rocky River WWTP Historical Plant Performance (July 2003 through October 2007)
NPDES Permit Limts
Days of Design
Parameter Data Avg Day Max Month Peak Week* Max Day Basis Avg Month Avg Week Max Day
Flow (mgd) 1094 2.87 3.57 5.04 9.09 5.2 5.2
cBOD (mg/L) 731 6.72 23.4 33.5 37.4 24 24 36
cBOD (lb/day) 731 171 596 1,032 1,709 1,040
TSS (mg/L) 748 7.74 32.7 50.6 60 30 30 45
TSS (lb/day) 748 201 809 1,640 2,939 1,300
NH3-N (mg/L) 425 0.27 2.37 4.60 4.90 13 2** 6**
NH3-N (lb/day) 425 7.29 74.1 122 154 565
Total P (mg/L) 52 2.67 4.81 N/A*** N/A*** N/A N/A N/A
Total P (lb/day) 52 65.6 195 NIA*"* N/A*** N/A N/A N/A
Fecal Coliform 747 120 109 530 14,500 N/A 200 400
(MPN/100 mL)
* Peak Week was based on a 7-day moving average except for Fecal Coliform which is the geometric mean based on work weeks.
** Most stringent limits (April 1 to October 31)
*** Only 1 sample taken per month for Total Phosphorus. Therefore,
CAPACITYRERATINGTM_DRAFT.DOC 5
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
Effluent BOD, mg/L
35
30
25
20
15
10
0
Effluent Performance Boxplot
Winter
(I
Summer
i4
_
_
L
—
Existing NPDES
Permit Limit and
Proposed (W)
Limit
Proposed NPDES
Permit Limit (S)
o") 5s) 0'') o'' 0.c4'
� eQ boa �aS< � .4,g �� �o5eQ boa,
05 05 05 ) o° ob off' ob 6\ 0 6\ o\ p\
÷4. 11 VY' �eQ boa" 1 � '��' ��� �eQ .04 \,0 4,3 0
Figure 4 - Effluent BOD
CAPAC ITY RERATINGTM_DRAFT.DOC
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL
6

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
Effluent NH3, mg/L
Effluent Performance Boxplot
6
5
4
3
2
0
o',) 0 o', ck 6), 0, �c?` ° �cP �0 0 0 `0 0 0cS� o� _o� ,� o'` o'` ` o� 5S\
1
_z=_
I
ill
r
D.O
z
_=
-r
Existing NPDES
Permit Limit (W)
/r
oar-6
_eI
Existing NPDES
Permit Limit (S)
-._
Figure 5 - Effluent NH3-N
CAPAC ITY RERAT INGTM_DRAFT.DOC
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL
7

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
Effluent DO, mg/L
Effluent Performance Boxplot
14
13
12-
11
10
4
6') p'') 6') c1)'` o` o°` � 53°` cP` 0 05 0' .0 0 6`) o�' off' ff' o'O �' d' � � o� ^ `
8
—
8
1
i
�
iY1
-1
T
T
-
Proposed NPDES Permit Limit
1
Existing NPDES Permit Limit
Figure 6 - Effluent DO
CAPAC ITYRE RATINGTM_DRAFT.DOC
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL
8

Process Modeling
Process capacities for various major unit processes were developed in TM 203 - Rocky River
WWTP Process Modeling. Data obtained from the town and summarized in TM 201- Rocky
River WWTP - Design Wastewater Flows, Loads and Characterization, were used to prepare and
calibrate the process model as well as develop the process capacities. The assessment of the
major unit process capacities are summarized in Table 5.
TABLE 5
Capacity Summary for Major Treatment Processes
Component
Process Capacity Remarks
Secondary Treatment
Overall 5.50 mgd Based on the aeration basins and Clarifiers coupled.
Aeration Basins
Secondary Clarifiers
Aeration System 7.51 mgd
RAS/WAS Pumping System 5.20 mgd Based on firm pumping capacity
Solids Handling
Rotary Drum Thickener 7 mgd
Aerobic Digesters 2.39 mgd Based on maintaining Class B compliance
As indicated in Table 5, the process modeling indicated that the treatment system can treat
approximately 5.5 mgd. It should be noted that while the aerobic digesters are limited to
2.39 mgd, this was based on the solids process meeting Class B stabilization requirements.
The existing facility currently dewaters and disposes of the biosolids at a local landfill which
does not require Class B stabilization. Based on continuing this practice, the aerobic
digestion process would not be limiting. However, the system may be limited by the
dewatering capability since that process needs to work sufficiently well to pass the paint
filter test for land -filling. This limitation may be avoided by renting additional portable belt
filter presses.
Hydraulic Analysis
Hydraulic capacities developed in TM 204 - Rocky River WWTP Hydraulic Analysis for
various major unit processes are summarized in Table 6. The limiting areas, in order of
magnitude, are the RAS piping (5.9 mgd), influent pumping (13 mgd - firm) and aeration
basin effluent piping (15.0 mgd). The maximum flow the facility could convey without an
overflow is approximately 25.9 mgd. At this flow the secondary clarifiers will overflow. As
noted in TMs 203 and 204, at the time of the evaluation the plant staff were actively pursing
UV disinfection to replace the existing gaseous chlorine disinfection system. In addition, it
CAPACITYRERATINGTM_DRAFT.DOC 9
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
was assumed that the existing cascade aerator would be replaced. Therefore, an evaluation
of the both the cascade aerator and disinfection system was not performed in either TM. For
the purposes of this TM, a supplemental evaluation of the existing disinfection and re -
aeration systems is provided below.
TABLE 6
Hydraulic Capacity Summary
Component
Hydraulic Capacity
Remarks
Headworks
Screening
Influent Pumping
Secondary Treatment
Aeration Basins
Secondary Clarifiers
RAS/WAS Pumping System
Process Piping
13.25 mgd (avg)
26.5 mgd (peak)
13.0 mgd
14.8 mgd
21.5 mgd
5.90 mgd (peak)
15.0 mgd
At 30.9 mgd, the screening channels will overflow.
Firm capacity. 19.5 mgd total capacity
Effluent Weirs will become submerged. At 26.8 mgd, the
basins will overflow.
Effluent Weirs will become submerged. At 25.9 mgd, the
clarifiers will overflow
Limited by RAS pipeline velocity (6.5 fps).
Limited by aeration basins effluent piping (-6.5 fps).
Disinfection Capacity
As presented in TM 202 - Rocky River WWTP Existing Facilities Assessment, secondary effluent
wastewater is disinfected using a gaseous chlorination system. The RRWWTP uses a one ton
chlorine gas cylinder with a 150 lbs chlorine gas cylinder as a backup. Both cylinders are
connected to a Regal automatic switchover gas chlorinator. The gas is injected using a Regal
Smart valve with a 250 lb/day injector and 100 lb/day rotometer. A 500 lb/day rotometer
and injector with manual controls are available as a backup.
The gaseous chlorine is injected to the secondary effluent prior to entering a chlorine contact
chamber. Currently, a dose of approximately 3 mg/L is provided. The chlorine contact
tank has a working volume of approximately 121,100 gallons which provides approximately
34 minutes of detention time at design maximum month flows. Typical design criteria for a
gaseous chlorine disinfection system from standard references are presented in Table 7. It
should be noted that a gaseous chlorine disinfection system is limited by the limiting feed
rate for gas withdrawal systems. These systems are dependent on the maximum, reliably
attainable evaporation rate from the storage vessels on line. The reliable evaporation rate for
a 150-lb cylinder is approximately 50 lb/day and for a ton container approximately 400
lb/day at 70°F.
CAPACITYRERATINGTM_DRAFT.DOC
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
TABLE 7
Gaseous Chlorine Disinfection System Design Criteria
Recommendations/Remarks Reference
Gaseous Chlorine Delivery:
Capable of providing chlorine with largest chlorinator out of
service
Chlorine Storage:
Capable of storing between 15 — 30 days of solution at max
month flow with largest tank out of service
Handbook of Chlorination, George Clifford White
(Second Edition, 1986)
Wastewater Engineering, Metcalf & Eddy, Inc.
(Fourth Edition, 2003)
Chlorine Contact Tank: Design of Municipal Wastewater Treatment
Provide a minimum of 30 minutes of contact time at design Plants, ASCE/WEF Manual of Practice No. 8
flow (200X)
Provide a minimum of 15 minutes of contact time at peak
hour flow
Chlorine demand and treatment capacities are summarized in Table 8. The treatment
capacity of the disinfection system is 5.2 mgd on a maximum month basis limited by the
firm capacity of the chlorinator system. However, the chlorine contact basin can only treat
up to 11.6 mgd on a peak hour basis while maintaining a 15 minute contact time. As
indicated previously, the peak hour flow historically for the RRWWTP has reached 12.1
mgd. This flow equates to a 4.03:1 Peak Hour Flow to Maximum Month flow peaking factor
based on historical data. Based on the historical peaking factor and the limiting peak hour
treatment flow, then the disinfection system capacity should be considered 2.88 mgd.
Storage capacity was not considered in the evaluation since additional chlorine cylinders
could be transported and stored on -site, if necessary.
TABLE 8
Disinfection System Capacity Summary
System
Component
Operation at Max
Month Design
Flow (5.2 mgd)
Firm Capacity Total Capacity Treatment
Available Available Capacity (mgd)
Delivery 130/434 Ibs/day1 250 Ibs/day 750 (400) Ibs/day2 10 mgd/5.2 mgd2'4
Storage 1,952/6,505 Ibs' 2,000 Ibs3 2,150 Ibs 5.33/2.78 mgd4.5
Contact 33.5 min N/A N/A 5.8 mgd (design)
11.6 mgd (peak)
Notes:
For Delivery and Storage Operation: X/Y = Average Dose Rate (3 mg/L)/Maximum Dose Rate (6 mg/L)
2 750 Ibs/day of equipment is installed. However, the system is limited by maximum withdrawal rate from a one
ton cylinder of 400 Ibs/day
3 For the Firm Storage capacity, it was assumed that another 1-ton cylinder could be stored on -site as
necessary
4 Delivery rate and Storage Capacity shown is based on the following dosage rates: (Average/Maximum)
5 Storage treatment capacity based maintaining a minimum 15 day supply with 1 tank out of service (firm
capacity)
6 Contact Tank capacity based on providing a minimum of 30 minute detention time at design flows and 15
CAPACITYRERATINGTM_DRAFT.DOC
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TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
TABLE 8
Disinfection System Capacity Summary
System
Component
Operation at Max
Month Design
Flow (5.2 mgd)
Firm Capacity Total Capacity Treatment
Available Available Capacity (mgd)
minutes of detention time at peak hour flows.
Following chlorination, the RRWWP practices dechlorination. Sodium bisulfite is added to
the chlorinated flow at the at the effluent flow measurement weir located at the head of the
cascade aerator. The reaction between the bisulfite and the chlorine is nearly instantaneous.
Design criteria states that approximately 15-30 seconds of detention time be provided to
insure adequate contact time. If 1-ft of water is provided on all the downstream steps (but
not including the effluent pipe), then approximately 1,200 gallons of volume is available for
reaction time. At a 15-second detention time, the 1,200 gallons provide capacity for
approximately 6.9 mgd.
Reaeration Capacity
A step -type cascade aerator provides re -aeration of treated effluent prior to final discharge.
Chlorinated effluent is measured using a Cippoletti weir as it exits the chlorine contact
basin. At this point, the flow is dechlorinated at the head of the cascade aerator. The
aerator consists of eight (8) 6-foot wide concrete steps dropping a total of 7-feet. Design of a
cascade aerator is independent of the flow rate and instead is based on the desired dissolved
oxygen (DO) to add. The Barrett Equation is used to calculate the height required for the
aerator:
h=r—
Where:
h = height which the water falls (ft)
r = deficit ratio at Temperature, T
a = water quality parameter equal to 0.8 for wastewater treatment plant
effluent
b = weir parameter (weir = 1.0; steps = 1.1; step weir = 1.3)
T = Temperature of Water (C)
The deficit ratio, r, is calculated as:
r=
Cs —Co
Cs—C
Where:
Cs = DO saturation concentration of wastewater at temperature T (mg/L)
Co = DO concentration of post -aeration influent (mg/L)
CAPACITYRERATINGTM_DRAFT.DOC
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TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
C = Required DO concentration after post -aeration (mg/L)
Therefore, assuming an initial DO of 0 mg/L exiting the chlorine contact basin and utilizing
the historical maximum temperature of 28°C, it was determined that the aerator would
require 8.10-feet to provide a DO of 5.0 mg/L. This height is greater than the 7-foot drop
installed. However historical data, as shown in Figure 3, indicates that the aerator has been
able to consistently maintain a DO greater than 6.0 mg/L even at a temperature of 28C. It is
speculated that extra DO addition is being achieved prior to the cascade aerator. These
sources are most likely the drop between the chlorine contact channels and the plant water
sump in addition to the drop across the Cipoletti flow measurement weir.
For the hydraulic loading rate, it is recommended to maintain less than 3-ft of head on each
step of the cascade aerator. The maximum hydraulic loading rate for the aerator can be
estimated by assuming each step is a weir without end contractions. To maintain proper
cascading flow, then the head on each step cannot exceed the step height of approximately
1-ft. Therefore, given the 6-ft width and the maximum head of 1-ft, then the estimating
hydraulic loading rate to the aerator is limited to 13 mgd.
30
28
P
26 - At • %V... -•-
24 - -•' ". -• to
` + •
• 4
22- - ` 7,. ♦ A. s
0
•
•
20
•
18
1J
LE 16
1-.
14
12 -
10 -
8-
6-
4
2
0
4
•
••
Z •
♦ 4 ❑ 3 -,
0 �u 8 ♦S{ A ♦_'+
goo. 611
♦• • • • •
� • ••.
38,
•
♦3 �♦ t•
-• •
••
3 0e
•
6 7 8 9
Effluent DO, mgJL
10
♦1)O GTemp
Figure 7 - Effluent D0 versus Temperature and Flow
12 13 14
10
8
6
E
4
Summary
The overall facility capacity assessment is provided in Table 9. The limiting processes at the
RRWWTP are the disinfection capacity (5.2 mgd) and the secondary treatment (5.5 mgd).
CAPACITYRERATINGTM DRAFT.DOC
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TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
The limitation due to the disinfection system is currently being addressed as part of future
facility upgrades.
TABLE 9
Capacity Summary for Major Treatment Processes
Component Process Capacity Hydraulic Capacity Comments
Headworks
Screening N/A 13.25 mgd (avg)
26.5 mgd (peak)
Influent Pumping N/A 13.0 mgd
Secondary Treatment
Overall 5.50 mgd N/A
Aeration Basins N/A 14.8 mgd
Secondary Clarifiers N/A 21.5 mgd
Aeration System 7.51 mgd
RAS/WAS Pumping System 5.20 mgd 5.90 mgd (peak)
Process Piping N/A 15.0 mgd
Disinfection System 5.2 mgd (avg)
11.6 mgd (peak)
Reaeration 13 mgd (avg)
Solids Handling*
Rotary Drum Thickener 7 mgd N/A
Aerobic Digesters 2.39 mgd N/A
Based on the aeration basins and Clarifiers
coupled.
Effluent Weirs will become submerged. At 26.8
mgd, the basins will overflow.
Effluent Weirs will become submerged. At 25.9
mgd, the clarifiers will overflow
Process limited on firm capacity.
Hydraulic limited by RAS pipeline velocity (6.5 fps).
Limited by aeration basins effluent piping (-6.5
fps).
Average limited by chlorinator capacity
Peak limited by minimum chlorine contact basin
detention time (15 min)
Limited by ability to maintain cascade.
Based on maintaining Class B compliance
* System may not be limited if facility hauls dewatered sludge to the landfill as long as dewatering equipment can continue to
pass the paint filter test required for landfilling. Otherwise, additional portable units may be required.
CAPACITYRERATINGTM_DRAFT.DOC
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TOWN OF MOORESVILLE ROCKY RIVER WWTP RE -RATING
Appendix
TM 201- Rocky River WWTP - Design Wastewater Flows, Loads and Characterization
TM 202 - Rocky River WWTP Existing Facilities Assessment
TM 203 - Rocky River WWTP Process Modeling
TM 204 - Rocky River WWTP Hydraulic Analysis
CAPACITYRERATINGTM DRAFT.DOC
COPYRIGHT 2008 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
FINAL DRAFT TECHNICAL MEMORANDUM 201 CH2MHILL
Rocky River WWTP - Design Wastewater Flows,
Loads and Characterization
PREPARED FOR: Town of Mooresville, NC
PREPARED BY: CH2M HILL
DATE: November 28, 2005
This technical memorandum (TM) summarizes Task 201- Data Collection and Review for
the Rocky River WWTP Expansion Project. The data summarized in this TM were derived
from plant historical data and conversations with Town of Mooresville Staff. The flows,
loads and characterization data presented in this TM will be used in Task 203 - Process
Modeling.
The memo is organized as follows:
• Plant Historical Data
• Influent Flow and Loadings
• Plant Performance
• Historical Operations Data
• Flow and Load Projections
• Summary
Plant Historical Data
Historical influent, effluent and operating data was obtained from the Town and included
data from July 1, 2003 to April 30, 2005. The 22 months (670 days) of data consisted of daily
monitoring reports (DMRs) and daily operations reports. Monthly flow totals from 2000
through 2005 in addition to seasonal diurnal flows were also obtained.
Influent Flow and Loadings
Review of the data revealed that the flow to the facility steadily increased from 2000 to 2005.
A wet season in 2003 and a dry season in 2004 may account for the jump and dip in flows, as
depicted in Figure 1. Figure 1 also shows the average daily influent BOD, TSS, and NH3
loading. Overall, the average daily flow has increased from 2.44 mgd in 2000 to 2.72 mgd in
2005 resulting in an 11.6 percent increase or 2.3 percent per year. Table 1 summarizes the
historical influent flow rate and peaking factors between July 2003 and April 2005. Figures 2
through 5 illustrate diurnal and seasonal variation in flow in addition to weekday versus
weekend flows. Overall, there appears to be inflow and infiltration within the Rocky River
WWTP collection system that should be addressed. It should be noted that in Figure 4, the
dry weather flow (August 28, 2004) is greater than the wet weather flow (July 17, 2004).
CLTIFINAL DRAFTS TM201.DOC 1

ROCKY RIVER WWTP-DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Mooresville Average Influent Flow and Loads
3.00 8,000
a 1.00-
0.00
2.44
2.49
2000 2001
2.56
2002
Year
2.72
2003
2.69
2004
2.72
2005
Influent Flow 0 Influent BOO
El Influent TSS
0 Influent NH3
FIGURE 1. ROCKY RIVER WWTP INFLUENT FLOW AND LOADING
Table 1. Influent Flow Rate (July 2003 to April 2005)
7,000
6,000
5,000
.0
0
4,000 a
0
3,000 E
2,000
0
Design Condition Historic Flow (mgd) Historic Peaking Factor
Annual Average Day 2.62 N/A
Maximum Month 3.01 1.15
Maximum Week 3.74 1.43
Maximum Day 9.09 3.47
Peak Hour 12.1 4.60
CLT/FINAL DRAFT3 TM201.DOC
2

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
200,000
180,000
160,000
140,000
120,000
a.
ea
100,000
O
80,000
60,000
40,000
20,000
0
Winter Diurnal Flow - Weekend
L
try •
* jci •
\
I
1
0'
0
%f•
sr
A'
a •
..
'Or.
,a'
♦ _or'
-c!-
. +q `. 9
..8.
:dam• . 4.
v` •
0
5
10
Hour
15
20
25
3,000,000
2,500,000
2,000,000
1,500,000 t�
E
1,000,000 a
500,000
0
—+— Dry Weekend —ter— Wet Weekend • - o - • Cum Flow - Dry Weekend • - 0 • Cum Flow - Wet Weekend
FIGURE 2. ROCKY RIVER WWTP WINTER WEEKEND DIURNAL FLOW
350,000
300,000
250,000
• 200,000
a.
150.000
100,000
50,000
0
Winter Diurnal Flow - Weekday
c
ri
��,Ii--_p'
3
t
,
f
p
.o
.O• .O'
.6
4°•
—4"
0
5
10
Hour
15
20
-0- - Wet Weekday —s— Dry Weekday - - Cum Flow - Wet - - a - • Cum Flow - Dry
FIGURE 3. ROCKY RIVER WWTP WINTER WEEKDAY DIURNAL FLOW
25
4.000,000
3,500,000
3,000,000
0
2,500,000
2,000,000 T.
a
eat
1,500,000 E
U
1,000,000
500,000
0
CLTIFINAL DRAFT3 TM201.DOC 3

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
160,000
140,000
120,000
1 00,0 00
L
a
0 80,000
60,000
40,000
20,000
0
Summer Diurnal Flow - Weekend
.o.".G
\--
'-'43\g--D.
13 "
•
. '
,
s1'
Ci'.' o.
'
.0'
O'
7
B` •
0
5
10
Hour
15
20
25
3,000,000
2,500,000
2,000,000
0
1,500,000 u-
3a
1,000,000 o
500,000
0
—0— Summer Dry Wkend --- -•- Summer Wet Wkend • • a • • Cum Row - Dry Wkend • • - Cum Flow - Wet Wkend
FIGURE 4. ROCKY RIVER WWTP SUMMER WEEKEND DIURNAL FLOW
600,000
500,000
400,000
r
o.
ea
300,000
LL
200.000
100,000
0
Summer Diurnal Flow - Weekday
y
r\
r'
. A.�
f
r
\
'0•.
IP
i
r
•a
r..
l.-.__yet.
. A'
fq..A'
c1•
.4
•o•
Cl.
O
0
5
10
Hour
15
20
25
7,000,000
6,000,000
5,000,000
T.
O
4,000,000
IT;
3,000,000
E
V
2,000,00o
1,000,000
0
ti Summer Wet Wkday —0—Summer Dry Wkday • • eF • • Cum Flow - Wet Wkday - - o • • Cum Flow - Dry Wkday
FIGURE 5. ROCKY RIVER WWTP SUMMER WEEKDAY DIURNAL FLOW
CLTIFINAL DRAFTS TM201.DOC 4

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
As shown in Figure 1 the average daily influent BOD to the facility has steadily increased.
Overall, average daily influent BOD loading to the facility has increased by 11.7 percent
since 2003. Similarly, the average daily influent TSS loading increases from 2003 to 2004, but
decreases in 2005. Tables 2 and 3 summarize the historical influent BOD and TSS,
respectively.
Table 2. Influent BOD (July 2003 to April 2005)
Design Condition
Historic Values
Concentration*
(mg/L)
Load
(lbs/day)
Load Peaking
Factor
Annual Average Day
Maximum Month
Maximum Week
Maximum Day
286
373
536
782
6,253
8,153
11,710
17,095
N/A
1.30
1.87
2.73
* Concentrations calculated as a function of the average daily flow
Table 3. Influent TSS (July 2003 to April 2005)
Design Condition
Historic Values
Concentration*
(mg/L)
Load
(lbs/day)
Load Peaking
Factor
Annual Average Day
Maximum Month
Maximum Week
Maximum Day
308
394
620
1,631
6,726
8,607
13,562
35,648
N/A
1.28
2.02
5.30
* Concentrations calculated as a function of the average daily flow
Measurement of influent Ammonia (NH3-N), Total Kjeldahl Nitrogen (TKN), and Total
Phosphorus (TP) loading to the WWTP did not begin until February 2005. Sixty-three (63)
measurements of NI-13-N were obtained, while only three (3) measurements of TKN and TP
were taken. Historic values for these parameters are summarized in Tables 4 through 6.
Due to the insufficient data, Load peaking factors were not able to be calculated for TKN and
TP. Review of the BOD and NH3-N peaking factors determined that although the NH3-N
peaking factors were approximately 25 percent lower overall, each increased by a similar
magnitude for each condition. Based on the similarity, it was assumed that the peaking
CLTIFINAL DRAFT3 TM201.DOC
5

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
factors for TKN and TP would also be comparable and therefore, similar values were
provided.
Table 4. Influent NH3-N (February 2005 to April 2005)
Historic Values
Design Condition
Concentration*
(mg/L)
Load
(lbs/day)
Load Peaking
Factor
Annual Average Day
25.7
562
N/A
Maximum Month
26.8
585
1.04
Maximum Week
32.6
713
1.27
Maximum Day
50.4
1,101
1.96
* Concentrations calculated as a function of the average daily flow
Table 5. Influent TKN (February 2005 to April 2005)
Historic Values
Design Condition
Concentration***
(mg/1)
Load
(lbs/day)
Load Peaking
Factor*
Annual Average Day
39.5
863
N/A
Maximum Month
41.1
898**
1.04
Maximum Week
50.1
1,096**
1.27
Maximum Day
77.4
1,692**
1.96
* Due to insufficient data, peaking factors assumed to be similar to NH3-N peaking factors
** Load calculated based on assumed peaking factor
*** Concentrations calculated as a function of the average daily flow and load
CLTIFINAL DRAFT3 TM201.DOC
6

ROCKY RNER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Table 6. Influent TP (February 2005 to April 2005)
Design Condition
Historic Values
Concentration***
(mg/L)
Load
(lbs/day)
Load Peaking
Factor*
Annual Average Day 6.13 134 N/A
Maximum Month 6.36 139** 1.04
Maximum Week 7.78 170** 1.27
Maximum Day 12.0 263'k* 1.96
* Due to insufficient data, peaking factors assumed to be similar to NH3-N peaking factors
** Load calculated based on assumed peaking factor
*** Concentrations calculated as a function of the average daily flow and load
Plant Performance
Review of the plant effluent data determined that since July 2003, the facility has been
operating exceptionally well, although in March 2005 the facility violated their NPDES
permit for monthly average TSS. Table 7 summarizes the historical plant performance
between July 2003 and April 2005. Figures 7 through 9 depict the effluent BOD, TSS, and
NH3 by month using box and whisker plots. Figure 6 provides a brief description on how to
interpret the figures.
1—Maximum
75th Percentile
Mean
Median
25th Percentile
Minimum
FIGURE 6. INTERPRETATION OF BOX AND WHISKER PLOTS
CLTIFINAL DRAFT3 TM201.DOC 7

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Table 7. Rocky River WWTP Historical Plant Performance (July 2003 - April 2005)
Parameter
Units
Days
Data
Min
Day
Avg
Day
Max
Month
Peak
Week*
Max
Day
Design
Basis
NPDES Permit Limts
Avg
Avg
Max
of
Month
Week
Day
Flow
mgd
670
1.84
2.62
3.01
3.74
9.09
5.2
5.2
BOD
mg/L
457
2.0
6.1
23.41
33.5
37.4
24
24
36
BOD
lbs/ d
457
38
143
575
1,032
1,470
1,040
TSS
mg/L
457
2.4
7.7
32.65
41.7
45
30
30
45
TSS
lbs/ d
457
50
183
25.8
1,010
2,488
1,300
Ammonia-N
mg/L
458
0.1
0.17
0.40
1.14
4.06
13
2'k'r
6'`
Ammonia-N
lbs/ d
458
1.74
4.06
12.27
40.9
109.9
565
* Peak Week was based on a 7-day moving average
** Most stringent limits (April 1 to October 31)
CLUFINAL DRAFTS TM201.DOC
8

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
40
36 -
32 -
J_
a)28-
E
0 24
co
8-
4-
0
co
9
Boxplot of Effluent BOD Concentration by Month
NPDES Monthly Average Permit Limit
co
9 i
U
0
M
9
>
0
Z
O C ▪ O
a▪ ) co a▪ )
0 -, LL_
Nr
O
(0
Nr
O
i
C
M
Month
0) a)
<
9
U
0
O
>
0
z
L ()
cmC
a) co
o
d'
FIGURE 7. ROCKY RIVER WWTP EFFLUENT BOD PERFORMANCE
CLTIFINAL DRAFT3 TM201.DOC
9

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
50
Boxplot of Effluent TSS Concentration by Month
45 -
40
-J
a,35-
E
0 30
c25-
a)
c)
020-
0
15
1-
10-
5-
0
NPDES Monthly Average Permit Limit
it El]
T
[1E1 EB l;?
Els
M
O
1
yr
0
O
or)
O
I
0
a)
gcr
O
1
m
O
1
Month
O
1
C
O
1
0
z
0
a)
0
LO
O
1
co
O
1
a)
LL
FIGURE 8. ROCKY RIVER WWTP EFFLUENT TSS PERFORMANCE
CLT/FINAL DRAFT3 TM201.DOC
10

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
4.5
Boxplot of Effluent Ammonia Concentration by Month
4-
�3.5-
E
c 3-
0
.t;
..E.0
2.5-
a.)
(.)
0 2
V
ca
•E 1.5-
0
E
a 1
0.5 -
0
I.
ON. INS
NPDES Monthly Average Permit Limits
I Z. ig I
B
O
BM
WAS I=
M M cr)
9O
—, = a)
<
M
9
U
a)
0
OOL a C O O
ID C.
LPL. M Q m -, z.',� Q
Month
d'
Q
a)
O
U
1)
0
lf) LO Lf)
Oi 9
m 0.
Ili 2 Q
FIGURE 9. ROCKY RIVER WW1? EFFLUENT AMMONIA PERFORMANCE
CLT/FINAL DRAFT3 TM201.DOC
11

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Historical Operations Data
Historical operations data was obtained from April 2001 through April 2005. Tables 8 and 9
summarize influent and effluent pH and temperature while Tables 10 and 11 summarize the
biological treatment process and solids processing operations, respectively. Design values
are also provided from the Rocky River Wastewater Facilities Basis of Design (Willis
Engineering, 5/1986).
Table 8. Influent and Effluent Temperature (°C)
Range
Single Day
7-day Average
30-day Average
Minimum
10.4
12.6
13.3
Influent
Maximum
30.0
26.6
26.4
Minimum
9.4
10.0
11.1
Effluent
Maximum
26.8
26.4
25.8
Table 9. Influent and Effluent pH (s.u.)
Range
Single Day
7-day Average
30-day Average
Minimum
5.82
6.65
6.80
Influent
Maximum
8.78
7.58
7.29
Minimum
6.06
6.48
6.69
Effluent
Maximum
8.42
7.58
7.36
CLTIFINAL DRAFT3 TM201.DOC 12

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Table 10. Summary of Biological Treatment Process Operations
Parameter
Units
Average
Std Dev
Minimum
Maximum
Design
Basin 1
MLSS
mg/L
4,024
911
1,590
8,360
3,000
MLVSS
mg/L
2,936
656
1,090
5,330
N/A
VS Inventory
lbs
63,710
14,227
23,650
115,645
N/A
DO #1/#2
mg/L
2.95/4.5
1.4/1.3
0.11/0.21
8.54/9.86
3
Temperature #1/#2
0C
18.9/19.0
5.0/5.0
9.2/9.2
27.3/27.4
20
pH
s.u.
6.80
0.23
5.85
7.85
N/A
SVI
mg/mL
97
40.1
15
221
N/A
RAS MLSS
mg/L
8,944
2,284
1,280
25,120
N/A
RAS MLVSS
mg/L
6,475
1,665
562
16,980
N/A
Basin 2
MLSS
mg/L
3,879
958
1,020
11,750
3,000
MLVSS
mg/L
2,879
658
610
5,995
N/A
VS Inventory
lbs
61,317
15,143
13,235
190,717
N/A
DO #1/#2
mg/L
3.27/4.84
1.43/1.4
0.06/0.11
9.07/10.66
3
Temperature #1/#2
0C
19.0/19.0
5.1/5.1
9.0/9.0
27.4/27.6
20
pH
s.u.
6.84
0.21
5.58
7.66
N/A
SVI
mg/mL
96
41.1
24
224
N/A
RAS MLSS
mg/L
8,812
2,273
1,240
25,420
N/A
RAS MLVSS
mg/L
6,390
1,647
440
17,180
N/A
Combined
MLSS
mg/L
3,950
904
1,408
8,005
3,000
MLVSS
mg/L
2,879
658
845
5,995
N/A
VS Inventory
lbs
125,012
28,417
41,658
260,147
N/A
Recycle Flow
mgd
1.28
0.61
0.34
7.92
N/A
R/Q Ratio
0.656
0.166
0.26
1.708
N/A
CLT!FINAL DRAFT3 TM201.DOC
13

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Table 10. Summary of Biological Treatment Process Operations
Parameter
Units
Average
Std Dev
Minimum
Maximum
Design
SRT
days
16.02
0.38
15.09
23.45
8.4
Table 11. Summary of Solids Processing Operations
Parameter
Units
Average
Std Dev
Minimum
Maximum
Design
WAS
MLSS
mg/L
11,147
7,163
1,820
54,592
5,000
MLVSS
mg/L
8,024
5,646
3,280
42,206
N/A
Volume
mgd
0.148
0.03
0.035
0.522
N/A
Quantity
lbs
7,662
1,746
3,036
14,243
N/A
Digester 1
MLS
mg/L
25,635
6,243
5,690
58,570
30,000
MLVS
mg/L
17,326
3,973
4,040
32,280
N/A
DO
mg/L
1.41
2.43
0.03
12.27
N/A
pH
s.u.
6.75
0.61
4.69
7.63
N/A
Temperature
0C
22.1
6.37
4.4
33.8
N/A
Digester 2
MIS
mg/L
27,055
7,034
8,920
42,302
30,000
MLVS
mg/L
- 18,440
4,957
6,120
50,712
N/A
DO
mg/L
1.22
1.76
0.02
9.70
N/A
pH
s.u.
6.74
0.83
3.94
8.15
N/A
Temperature
0C
23.2
6.3
6.4
35.3
N/A
Combined
Decant TS
mg/L
666
410
225
3,055
N/A
Decant VS
mg/L
308
302
17
2,045
N/A
Sludge Age
days
22.2
1.6
18.2
32.9
20
CLTIFINAL DRAFT3 TM201.DOC 14

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Flow and Load Projections
WWTP load projections were developed utilizing historical influent concentration data and
projected wastewater flows through 2025 provided by the Town of Mooresville. On
October 31, 2005, Town of Mooresville Staff directed CH2M HILL to use 19 mgd (on a
maximum month basis) as the design basis for the new expansion. Average day, maximum
week, maximum day, and peak hour flow rates were predicted utilizing the historical peak
factors derived previously. Similarly, projected loadings were predicted from a
combination of the historical annual average day concentration and the load peaking
factors. These values are summarized in Tables 12 though 17.
Table 12. Projected Influent Flow Rate
Design Condition
Projected Flow (mgd)
Historic Peaking Factor
Annual Average Day
Maximum Month
Maximum Week
Maximum Day
Peak Hour
16.5*
19.0
23.6*
57.3*
76.0*
N/A
1.15
1.43
3.47
4.60
* Flow rates derived utilizing historical peak factors
Table 13. Projected Influent BOD Loadings
Design Condition
Concentration (mg/L)
Projected Load
(lbs/day)
Historic Load
Peaking Factor
Annual Average Day
286*
39,408
N/A
Maximum Month
372**
51,231
1.30
Maximum Week
535**
73,694
1.87
Maximum Day
781**
107,585
2.73
* Historical annual average day concentration
** Concentrations calculated as a function of the average daily flow
CLTIFINAL DRAFT3 TM201.DOC
15

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Table 14. Projected Influent TSS Loadings
Design Condition
Concentration (mg/L)
Projected Load
(lbs/day)
Historic Load
Peaking Factor
Annual Average Day
308*
42,440
N/A
Maximum Month
394**
54,323
1.28
Maximum Week
622"
85,728
2.02
Maximum Day
1,632**
224,931
5.30
* Historical annual average day concentration
** Concentrations calculated as a function of the average daily flow
Table 15. Projected Influent NH3-N Loadings
Design Condition
Concentration (mg/L)
Projected Load
(lbs/day)
Historic Load
Peaking Factor
Annual Average Day
25.7*
3,531
N/A
Maximum Month
26.7**
3,683
1.04
Maximum Week
32.6**
4,497
1.27
Maximum Day
50.4**
6,941
1.96
*Historical annual average day concentration
** Concentrations calculated as a function of the average daily flow
Table 16. Projected Influent TKN Loadings
Design Condition
Concentration (mg/L)
Projected Load
(lbs/day)
Historic Load
Peaking Factor
Annual Average Day
39.g*
5,439
N/A
Maximum Month
41.1**
5,656
1.04
Maximum Week
50.1**
6,907
1.27
Maximum Day
77.4**
10,660
1.96
* Historical annual average day concentration
** Concentrations calculated as a function of the average daily flow
CLTIFINAL DRAFTS TM201.DOC
16

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Table 17. Projected Influent TP Loadings
Design Condition
Concentration (mg/L)
Projected Load
(lbs/day)
Historic Load
Peaking Factor
Annual Average Day
6.13*
845
N/A
Maximum Month
6.38**
878
1.04
Maximum Week
7.79**
1,073
1.27
Maximum Day
12.0'
1,656
1.96
* Historical annual average day concentration
** Concentrations calculated as a function of the average daily flow
Summary
Influent flows and loads were developed from plant data and master planning results. A
review of the data resulted in the development of two scenarios: a) existing plant data and
b) values based on a projected 19 mgd maximum month flow through 2025 provided by the
Town of Mooresville. Process models will be developed for each alternative to test the
sensitivity of the proposed design(s) over the range of flows and loads in the data sets.
Tables 1 through 17 are summarized as Model input data in Table 18 with plant design
criteria (Willis Engineering, 5/1986) presented in Table 19 for comparison. Results of the
modeling will be provided under Task 203 - Process Modeling. Alkalinity input data
shown is estimated to provide sufficient alkalinity for nitrification. Although alkalinity
data was requested, Town of Mooresville staff indicated that their current system is
adequate and they do not wish to replace or expand the system.
Table 18. Process Modeling Input Data
Parameter
Avg Day
Max Month
Max Week
Max Day
Peak Hour
July 2003 - April 2005 Data Set
Flow (mgd)
2.62
3.00
3.75
9.10
12.1
cBOD (lb/day)
6,300
8,200
11,800
17,100
—
TSS (lb/day)
6,800
8,700
13,600
35,700
--
TKN (lb/day)
865
900
1,100
1,700
—
NH3-N (lb/day)
570
590
720
1,100
—
Total P (lb/day)
135
140
170
265
—
Alkalinity (lb/day)
3,375
5,010
6,260
15,190
--
CLTIFINAL DRAFT3 TM201.DOC 17

730
725
720
Its
710
705
no
725
720
715
710
42'0
INFLUENT
ros
700
COARSE SCREENING
708.73 -707.17
708.24 707,17
T.O.C. = 714.25
INFLUENT SCREEN PUMPS
7
FINE SCREENING
730.14 729.86
729.20..''
729.10 - ,
'CH,4NNEL BOTTOM = 726.25
728.89-
FLOW MEASUREMENT
.729.62 -« 728A1
•
726.22
AERATOR BASINS
(SUBMERGED WEIR)
726.38 -' 724.92
TOP OF GRADING = 731.00
STATIC L.L. = 724.50
36"0
INV. EL. = 724.00
PARSHALL
FLUME
724.75
(SUBMERGED WEIR)
SECONDARY CLARIFIER DISTRIBUTION BOX
- 726.04
725.81
724.65 --., -
723.69... ,fF"
722.65
T.O.C. = 726.50 WEIR EL. = 724.50 -
STATIC LL = 724.50
INV. EL.=721.00
AERATION BASINS
BOTTOM EL. = 712.50
INV. EL. = 719.00
723.80
SECONDARY CLARIFIERS
721.48
HGL AT DESIGN FLOW
19 mgd WITH 19 mgd RECYCLE
MAX FLOW - 25.9 mgd WITH
19 mgd RAS (ALL UNITS IN SERVICE, CLEAN SCREEN)
CHLORINE CONTACT BASIN
& RE -AERATION
720.01 720.00 (SECONDARY CLARIFIER OVERFLOW)
719.82
719.19
720.99 719.33
719.63- f
719.13"� 718.73 i 25-YR
717.72 717.47 - 716.33 FLOOD
716.35 • � ELEVATION
, .716.86
716.63 716.61
36
INFLUENT SCREW PUMPS INV. EL. = 713.00
704.25
COARSE DISTRIBUTION BOX
BAR SCREEN
• T.O.W. = 722.0
STATIC L.L. = 719.50
STATIC LL = 719.50
7125
710.5
36"0
CLARIFIERS
T.O.C. = 721.50
-WEIR EL.= 719.50
715.46
TATIC LL = 715.5t.
713.85
713.59 713.0'
T.O.C. = 717.50
• TOP OF WALL
El. = 715.5
INV. EL.= 713.00 p5,5 706.0
705.0
INV. EL. = 706.00
CHLORINE
CONTACT
BASINS
WEIR EL. = 714.0
• T.O.W. = 716.0
4.
EFFLUENT
HEADWALL
FIGURE 3
MODEL DEVELOPED HYDRAULIC PROFILE
CH2MHILL
\Mooresvi lI eNCTownOf\330132\CADD\ Fig urea-HydProf. d wg

7351
730
70747-s_. 107.aa
7°6'98J_ -1 /08-78
L J
INFLUENT SCREW PUMPS
729.23
728.19
1727.80
::\s. 726.61
72721
BAR PARSHALL
SCREENS FWME
FLUME
724.91
STATIC LL.
724.50
36"A
724.70 723.91
724.58
STATIC L.L. 724.50
723.00-"
722.94
AERATION BASINS
723.51
722.33
720.73
720.24 ____-719.66
719-68-- 719.59
3 6'
TATIC LL.
19.50
HGL AT PEAK FLOW (THROUGH ONE UNIT)
13.0 MGD WITH 5.2 MGD RECYCLE
HGL AT AVERAGE DESIGN FLOW (THROUGH TWO UNITS)
5.2 MGD WITH 5.2 MGD RECYCLE
718.50
717.82
-719.26
718.46
7.63
715.90
STATIC LL. 719.50
DISTRIBUTION CLARIFIERS
Box
=.11MD
coil
'A1AB
5'
!0
5
10
NO.
DATE
REVISION
)NET.
-_= O'BRIEN 5I ERE I
VERT.
I
715.76
716.80
716.36
715.73
714.63 713.56
STATIC LL.71550
CHLORINE CONTACT BASINS
42 s
713.0 (d 25 YR.
FLOOD
EFFLUENT
HEADWALL
- 735
- 730
-725
- 720
- 715 EL 714.0
- - - I00YR. FLOOD
t 25YR. FLOOD
EL.7130
- 710
- 705
NORMAL CREEK
LEVEL
- 700 -4-EL.700.0
TOWN OF MOORESVILLE
WASTEWATER FACILITIES
HYDRAULIC PROFILE
FILE NO.
912.048. IOF
DATE
NOVEMBER 1979
G-9

730
725
720
7,5
710
705
730
725
720
715
710
42•01
INFLUENT
705
700
uJ
25
ce•
0.
co.
w
co
00 ,
< •
0
T.O.C. = 714.25
11
INFLUENT SCREW PUMPS
.704.25
COARSE
BAR SCREEN
INFLUENT SCREEN PUMPS
-
25
o
w
co
0
03 LLI
25
z
0
u_
728.78
72851
727.48
727.37
-
.•
728.37
725.67
AERATOR BASINS
724.89 724.72
727.30---
724.80
TOP OF GRADING = 731.00
STATIC L.L. = 724.50
26.25 BAR SCREENS
CHANNEL BOTTOM = 726.25
3 6.0
INV. EL. = 724.00
- PARSHALL
FLUME
724.75
724.59
724.23
' 721 54
''L__
723.48
720.18 "
T.O.C. = 726.50 WEIR EL. = 724.50
INV. EL. = 721.00
AERATION BASINS
BOTTOM EL. = 712.50
INV. EL...719.00
INV. EL. = 713.00
DISTRIBUTION BOX
SECONDARY CLARIFIER DISTRIBUTION BOX
SECONDARY CLARIFIERS
720.91
• 719.67 719.64
.719.48
02 717.28 --,..
719.56 ,
719.89
CHLORINE CONTACT BASIN
& RE -AERATION
718.40 /
715.96- 715.88
T.O.W. = 722.0 -T.O.C..= 721.50
STATIC L.L. = 719.50
712.5
710.5
36'0
CLARIFIERS
WEIR EL. = 719.50
715.85
715.14
13 mgd WITH 5.2 mgd RECYCLE
5.2 mgd WITH 5.2 mgd RECYCLE
25-YR
FLOOD
ELEVATION
714.62 713.04 713.0
T.O.C. = 717.50
TOP OF WALL
EL. = 715.5
WEIR EL. = 714.0
T.O.W. = 716.0
INV. EL. = 713.00
r; 705 °5'5 70
6.0
INV. EL. = 706.00
CKLOPJNE
CONTACT
BASINS
EFFLUENT
HEADWALL
FIGURE 2
MODEL DEVELOPED HYDRAULIC PROFILE
CH2MHILL

DRAFT
ROCKY RIVER WWTP HYDRAULIC ANALYSIS
A comparison of the 1979 hydraulic profile and the hydraulic modeling profile at 5.2-mgd
(100% recycle) reveals small differences. Water elevations in the major process units vary
slightly with the largest difference in elevation being in the chlorine contact tank where the
hydraulic modeling elevation is 0.12-ft higher than the original grade line. In addition, the
1979 profile does not include a head loss in the aeration basins while the new hydraulic
model includes a 2-inch (0.167-ft) loss. However, without the loss the elevation would be
the same. At the headworks the hydraulic elevation before the screens is about 0.3-ft lower
than the original elevation. This difference is due to the newer screens which result in a
smaller head loss that the originally installed screens.
At the projected average daily influent flow of 13-mgd, the differences are similar to those in
the 5.2-mgd profile. The largest difference between the 1979 profile and the hydraulic
modeling is 0.20-ft in the chlorine contact basin and while there was no head loss in the 1979
profile, a 2-inch head loss was included in the aeration basins for bulking due to aeration.
Also, the new screens result in a smaller head loss at the headworks resulting in a 0.55-ft
difference.
CLT/FINAL DRAFT2 TM4.DOC 7

DRAFT
ROCKY RIVER YWVTP HYDRAULIC ANALYSIS
Hydraulic Capacity Summary
Hydraulic capacities for various major unit processes are summarized in Table 3. The
limiting areas, in order of magnitude, are the RAS piping (5.9 mgd), influent pumping (13
mgd - firm) and aeration basin effluent piping (15.0 mgd). The maximum flow the facility
could convey without an overflow is approximately 25.9 mgd. At this flow the secondary
clarifiers will overflow.
Table 3. Hydraulic Capacity Summary
Component
Hydraulic Capacity
Remarks
Projected Influent Flows
Average Day Flow
Maximum Month Flow
Maximum Day Flow
Peak Hour Flow
Headworks
Screening
Influent Pumping
Secondary Treatment
Aeration Basins
Secondary Clarifiers
RAS/WAS Pumping
System
Process Piping
16.5 mgd
19.0 mgd
57.3 mgd
76.0 mgd
13.25 mgd (avg)
26.5 mgd (peak)
13.0 mgd
14.8 mgd
21.5 mgd
5.90 mgd (peak)
15.0 mgd
At 30.9 mgd, the screening channels will
overflow.
Firm capacity. 19.5 mgd total capacity
Effluent Weirs will become submerged. At
26.8 mgd, the basins will overflow.
Effluent Weirs will become submerged. At
25.9 mgd, the clarifiers will overflow
Limited by RAS pipeline velocity (6.5 fps).
WAS pipeline is capable of 1.47 mgd.
Limited by aeration basins effluent piping
(-6.5 fps).
Hydraulic Profile
Existing hydraulic profiles (O'Brien & Gere, 1979) are presented in Figure 1. Hydraulic
profiles created from the hydraulic modeling for the design, instantaneous peak, projected
maximum month, and maximum flow are provided in Figures 2-3. It should be noted that
this analysis will be updated in the future to address the hydraulic profiles of the upgraded
facilities.
CLT/FINAL DRAFT2 TM4DOC 6

DRAFT
ROCKY RIVER WWTP HYDRAULIC ANALYSIS
service. However, the clarifiers would not be able to handle the projected maximum day
and peak hour flow rates of 57.3 mgd and 76 mgd, respectively. Further review determined
that the existing clarifiers could treat up to 21.5 mgd before the effluent weirs would become
submerged and 25.9 mgd before the clarifiers overflow assuming both clarifiers are in
service. At a flow rate of 29.5 mgd, the clarifier distribution box will also flood.
RASNUAS Pumping
The existing RAS piping consists of an 18-inch gravity pipeline from each clarifier to the
RAS/WAS wet well and a 16-inch diameter force main from the RAS/WAS pumping
building to the head of the aeration basins. At the existing design RAS flow rate of 5.2 mgd,
the velocity within each 18-inch pipeline is approximately 2.3 fps while the 16-inch force
main is 5.8 fps. At a 19 mgd RAS rate, the velocity within the existing 18-inch pipeline
would approach 8.3 fps while the 16-inch force main would approach 21.1 fps. To maintain
a velocity less than 6.5 fps, the existing force main could convey a maximum RAS flow of
approximately 5.9 mgd. Therefore, either additional RAS piping or replacement of the
existing piping will be required to treat the projected maximum month flow of 19 mgd.
WAS is pumped to the digesters via an 8-inch force main from the RAS/WAS pumping
building. Assuming continuous pumping, the velocity within the force main at the
projected maximum month conditions (492 gpm) is approximately 3.1 fps. The force main
could convey 1,021 gpm (1.47 mgd) of WAS to the digesters while maintaining a velocity of
6.5 fps. Therefore, the existing WAS piping will be sufficient to convey WAS production at
the projected maximum month flow rate of 19 mgd. However, as previously mention in TM
203 - Rocky River WWTP Process Modeling, additional facilities may still be required due to
the location of additional clarifiers.
Process Piping
The process piping includes all piping between all the treatment process units. The piping
was evaluated to determine its ability to convey the projected flows. At the design
maximum month flow rate of 19 mgd, in general, existing process piping will be able to
maintain velocities below the design limit of 6.5 fps. The only exception is the aeration
basin effluent piping to the clarifier distribution box where the velocity in the pipeline is
well above design criteria at 8.3 fps. Influent flow would have to be reduced to just under
15 mgd to reduce the velocity to under 6.5 fps. These high velocities can cause floc shear
which can result in a poor settling sludge and possible lead to increased effluent TSS.
Disinfection System
As discussed previously in TM 202, Rocky River WWTP - Existing Facilities Assessment and
TM 203, a UV disinfection system is being actively pursued. Therefore, the hydraulic
capacity of the existing gaseous chlorine disinfection system was not evaluated. The UV
disinfection system to be designed must be capable of either providing sufficient contact
time or be capable of expanding to provide the sufficient contact necessary for adequate
disinfection at the projected peak hour flow rate of 76 mgd.
CLTIFINAL DRAFT2 TM4.DOC 5

0
DRAFT
ROCKY RIVER WWTP HYDRAULIC ANALYSIS
One screen will not be capable of treating the flow based on the manufacturer's design
capacity at 19 mgd. In addition, both screens will not be capable of treating the peak hour
hydraulic flow of 76 mgd. Therefore, approximately 50 mgd of additional screening
capacity will be required to treat the peak hour flow.
The existing influent screw pumps have a firm capacity of 13 mgd with the largest pump
out of service. The total pumping capacity is 19.5 mgd. Therefore, to meet the projected
peak hour rate of 76 mgd, approximately 63 mgd of additional firm pumping capacity will
be required.
Screened wastewater from the headworks is measured using a Parshall flume prior to
entering the secondary treatment system. Based on discussions with Utilities staff, the flow
measurement system is only capable of measuring flows up to 13-mgd. Therefore, to be
capable of measuring the peak hour flow rate of 76 mgd, a new/upgraded system will be
required.
Secondary Treatment
The secondary treatment process consists of the aeration basins, secondary clarifiers, and
RAS/WAS pumping systems. The following sections briefly describe each process and
potential hydraulic constraints.
Aeration Basins
Raw wastewater from the Parshall flume is split between two 5.2-MG aeration basins.
Mechanical aerators provide oxygen and mixing to the biological process. Mixed liquor
from each basin exits the process by flowing over an effluent weir. Flow from the Aeration
Basin No. 2 (east basin) is conveyed via a pipeline to Aeration Basin No. 1 (west basin)
where the effluent flow combines and is conveyed to the secondary clarifiers. For the
hydraulic analysis, the aeration basins were evaluated based on the basin effluent weirs and
overtopping of basin side walls. It should be noted that 2-inches of headloss was provided
to account for air bulking of the MLSS. The hydraulic review at the projected maximum
month flow of 19 mgd indicated that the aeration basins would be capable of conveying the
flow, however, the basin effluent weirs would be submerged. In addition, the aeration basin
would be overtopped at the projected peak hour flow rate of 76 mgd. Further review
determined that the existing aeration basins could convey up to 14.8 mgd before the basin
effluent weirs would become submerged and 26.8 mgd before the basins are overtopped
assuming both basins are in service.
Secondary Clarifiers
Effluent flow from the aeration basins is split between two secondary clarifiers. The flow
enters through a feed well where a quiescent environment allows for a separation of solids
from the liquid stream. Clarified effluent flows over a v-notch weir and is collected in a
collection launder. The launder, which encompasses the clarifier, conveys the flow to a
collection box where flow from both sides of the clarifier combines before exiting through a
pipeline. Similar to the aeration basins, the clarifiers were evaluated based on flooding of
the effluent weirs in addition to overfilling of the basin. The hydraulic review at the
projected maximum month flow of 19 mgd indicated that the secondary clarifiers would be
capable of handling the flow without hydraulic constraints, assuming both clarifiers in
CLTIFINAL DRAFT2 TM4.DOC 4

DRAFT
ROCKY RIVER WWTP HYDRAULIC ANALYSIS
The 1998 Water and Wastewater Planning Report (Willis Engineers, 1998) lists the firm
capacity of two Archimedean lift pumps as 13 MGD while the Rocky River Wastewater
Treatment Plant Headworks Renovations Contract Documents (Willis Engineers, 2001) list the
peak hydraulic capacity of each fine screen as 13.25 mgd. Table 2 summarizes capacity
analysis.
Table 2. Headworks Treatment Capacity
Component
Screening
Capacity Criteria
Treatment Capacity
Influent Lift Pumping
Two screens provide treatment at
peak hydraulic flow; One screen is
redundant at design flow
Pump the maximum flow with one
unit out of service
Headworks Treatment Capacity
13.25 mgd (avg)
26.5 mgd (peak)
13 mgd (firm)
19.5 mgd (total)
13 mgd
Based on the hydraulic modeling assuming clean screens and both screening units in
service, the maximum approach velocity of one screen with maximum flow (13 mgd) is
about 1.1 feet per second (fps) and the maximum velocity through the screen is 2.1 fps.
Similarly assuming a 30-percent blocked screen, the velocity through the screen increases to
approximately 3.1 fps while the velocity upstream would decrease to about 1 fps. While
there was no information on minimum flows, the approach velocity at the original design
average day (5.2 mgd) was 1.47 fps (one screen in service). Each of these velocities falls
within the typical design criteria.
At projected maximum month "design" flow (19 mgd) assuming clean screens and one
screening unit out of service, the maximum approach velocity of one screen is about 2.3 fps
while the maximum velocity through the screen is 4.5 fps. Using the same assumptions, but
with a 30-percent blocked screen, the velocity through the screen increases to approximately
6.0 fps while the upstream velocity reduces to 2.0 fps. From the design criteria, the
approach velocity of one clean screen at 19 mgd is just above the design criteria while the
velocity through the screen meets the criteria. However if the screen is 30-percent blocked,
the velocity through the screen increases to 6.0 fps which is well above the design criteria.
The high velocity through the screen could result in pass through of solids through the
screen.
The projected peak hour flow rate of 76 mgd was also evaluated. Based on the hydraulic
modeling it was determined that the existing headworks would be flooded. The maximum
flow the headworks could convey without flooding and both screens in service is
approximately 29.5 mgd. At this flow rate, the flow through two screens is 2.36 fps with an
approach velocity of 1.18 fps.
CLTIFINAL DRAFT2 TM4.DOC 3

•
f
DRAFT
ROCKY RIVER WWTP HYDRAULIC ANALYSIS
• The return activated sludge (RAS) flow rate was assumed to be 100 percent of the
RRWWTP design influent flow.
• Basin and piping dimensions and configurations were taken from drawings prepared by
O'Brien & Gere (1979) and Willis Engineers (2001).
• "Minor" hydraulic loss "K" values were taken from Hydraulics (Schoder, Dawson,
Giesecke, and Bladgett - Texas College)
• A Manning's N value of 0.013 was used for concrete friction losses.
• A Hazen - Williams C value of 100 was used for old pipe and 130 for new pipe
• A discharge coefficient of 0.6 was used for all submerged orifices.
Hydraulic Assessment
Design drawings by O'Brien & Gere (1979) give the facility design flow as 5.2 mgd and the
maximum hydraulic capacity as 13 mgd. Therefore, the treatment facility hydraulic
conditions were assessed at the following flow scenarios:
• Basis of design = 5.2 mgd with 5.2 mgd recycle
• Basis of design instantaneous peak =13 mgd with 5.2 mgd recycle
• Projected maximum month =19 mgd with 19 mgd recycle
• Project maximum hour flow = 76 mgd with 19 mgd recycle
Headworks
The plant headworks consist primarily of influent pumping and screening. Raw wastewater
enters the facility through a 48-inch sewer line and flows through a coarse bar screen. A 24-
inch sidestream collector pipe also enters at the same location. Archimedean screw pumps
convey the wastewater to a pair of fine screens. Design criteria for these devices are
summarized in Table 1. The criteria were developed from manufacturer's literature and
CH2M HILL historical data.
Table 1. Preliminary Treatment (Headworks) Design Criteria
Component
Design Criteria
Criteria Value (fps)
Reliability Requirement
Screening
Min. Approach
Velocity
1- 2 (use 1.5)
Two screens provide
treatment at peak hydraulic
flow;
Max. Approach
Velocity
3
One screen is redundant at
design flow
Max. Velocity
4.5
Through Screen
Influent Lift Pumping
Pump the maximum flow
with one unit out of service
CLT/FINAL DRAFT2 TM4.DOC
2

DRAFT TECHNICAL MEMORANDUM 204 CH2MHILL
Rocky River WVVTP Hydraulic Analysis
PREPARED FOR: Town of Mooresville, NC
PREPARED BY: CH2M HILL
DATE: November 28, 2005
This technical memorandum (TM) summarizes Task 204, Plant Hydraulic Analysis for the
Rocky River Wastewater Treatment Plant (WWTP) Expansion Project. The purpose of this
TM is to provide an assessment of the hydraulic capacity of the Rocky River WWTP.
Existing design and projected flows used are summarized in TM 201- Rocky River WWTP -
Design Wastewater Flows, Loads and Characterization.
The memo is organized as follows:
• Introduction
• Design Criteria
• Hydraulic Assessment
• Headworks
• Secondary Treatment
• Aeration Basin
• Secondary Clarifiers
• RAS/WAS Pumping
• Process Piping
• Disinfection System
• Hydraulic Capacity Summary
• Hydraulic Profile
Introduction
The plant hydraulic conditions at the Rocky River WWTP were evaluated using a hydraulic
modeling program. The objectives of the hydraulic analysis were to:
• Develop a hydraulic model for the existing facility and produce hydraulic profiles at the
various current and proposed design conditions
• Determine hydraulic constraints within the treatment system
• Determine the ultimate hydraulic capacity of the existing facility and expanded facility
Design Criteria
Design criteria used to define the hydraulic profile are as follows:
• The hydraulic grade lines starts just after the chlorine contact effluent Cippoletti weir at
a level of 713.00 as indicated on design drawings by O'Brien & Gere (1979)
CLTIFINAL DRAFT2 TM4.DOC 1

•
Vector Attraction and Pathogen Reduction Requirements for Class B Biosolids (40 CFR 503.32 and 503.33)
Criteria Remarks/Comments
Vector Attraction Reduction
Option 1 Meet 38% reduction in volatile solids content.
Option 2 Demonstrate VAR with additional anaerobic digestion in a bench -scale unit.
Option 3 Demonstrate VAR with additional aerobic digestion in a bench -scale unit (<15% VSS reduction over 30 days)
Option 4 Meet specific oxygen uptake rate (< 1.5 mg 02/hr/g-TSS) for aerobically digested biosolids.
Option 5 Use aerobic processes at greater than 40°C (degrees Celsius) for 14 days or longer.
Option 6 Alkali addition under specific conditions.
Option 7 Dry biosolids with no unstabilized solids to at least 75% solids.
Option 8 Dry biosolids with unstabilized solids to at least 90% solids.
Option 9 Inject biosolids beneath the soil surface.
Option 10 Incorporate biosolids into the soil within 6 hours of application to or placement on the land.
Cover biosolids placed on a surface disposal site with soil or other material at the end of each operating day. (Note: Only for surface
Option 11 disposal.)
Option 12 Alkaline treatment of domestic septage to pH 12 or above for 30 minutes without adding more alkaline material.
Pathogen Reduction
Monitoring Indicator Organisms
Alternative Testing for fecal coliforms is used as an indicator for all pathogens and is done prior to the biosolids use or disposal. Less than 2 million
1 Most Probable number (MPN) OR Colony Forming Units (CFU) per gram of dry biosolid is required to qualify as a Class B biosolid. EPA
suggests that seven test samples be taken over a 2 week period because the testing procedures lack precision and the biosolids lack
uniformity. Multiple samples should ensure a representable sampling of the biosolids.
Biosolids Treated with a PSRP
Biosolids must be treated by one of the five (5) Processes to Significantly Reduce Pathogens (PSRP):
Aerobic Digestion: Biosolids are kept under aerobic conditions for a specific time ranging between 40 days at 20 °C and 60 days at 15°C.
Air Drying. Biosolids are air dried on pads (sand or paved) for a minimum of 3 months, with at least 2 of the months having an ambient
Alternative average daily temperature above 0 0C.
2 Anaerobic Digestion. Biosolids are kept under anaerobic conditions for a specified time and under a specific temperature ranging
between 15 days at 35-55 oC and 60 days at 20 0C.
Composting. Using any of three methods of composting (in -vessel, static aerated pile, or windrowed), the temperature is raised to 40 °C
or higher and maintained for 5 days, 4 hours of which, the temperature of the pile must rise above 55 0C.
Lime Stabilization. Enough lime is added to the biosolids to raise the pH of the biosolids to 12 after 2 hours of contact.
Alternative Biosolids Treated in a Process Equivalent to a PSRP
3 The biosolids must be treated in a process equal to a PSRP as determined by the permitting authority (as determined by the EPA).
CLT/FINAL DRAFT3 TM203.DOC 23

DRAFT
ROCKY RNER WWI? PROCESS MODELING
Appendix B
40 CFR 503 Class B Biosolids Criteria
CLTIFINAL DRAFTS TM2O3.DOC 22

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Hydraulic Loading 403,800 GPD
Blowers
Type Centrifugal
Number Three
Capacity, Each 1,800 SCFM
Drive 100 HP
Mixers
Type Submerged Turbine
Number Two
Size 75 HP
Sludge Thickening
Type Rotary Drum
Number One
Capacity 200 GPM
Thickening Approx. 3.5%
CLT/FINAL DRAFT3 TM203.DOC
21

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
E. Settling Facilities
Type Circular Clarifiers
Number Two
Diameter 92-ft
Depth 13-ft
Overflow Rate @ 5.2 MGD 400 GPD/SF
Detention @ 5.2 MGD 6.0 Hours
Sludge Withdrawal Suction & Scraper Arm
F. Sludge Recycle Pumping Station
Recycle Pumps
Type Centrifugal
Number Two
Capacity, Each 3,640 GPM
Drive 50 HP, Variable Speed
Recycle Sludge Flow Measuring
Type Venturi Tube
Range 0 - 5,600 GPM
Waste Sludge Pumps
Type Centrifugal
Number Two
Capacity, Each 500 GPM
Drive 20 HP
Waste Sludge Flow Measuring
Type Venturi Tube
Range 0 - 750 GPM
H. Chlorination Facilities
Contact Basin
Number Two
Path Length 162-ft
Path Width 6-ft
Length:Width Ratio 27:1
Volume 134,200 Gallons
Contact Time @ 5.2 MGD 30 Minutes
Chlorinators
Number Two
Capacity, Each 500 Ibs / Day
Feed Rate 0 -10 mg/1
I. Effluent Reaeration
Type
DO Addition
Cascade Aeration
5.0 mg/I
J. Solids Handling Facilities
Aerobic Digesters
Number Two
Diameter 70-ft
Depth 19-ft
Volume, Each 592,600 Gallons
Solids Loading 16,850 Ibs / Day
CLTIFINAL DRAFT3 TM203.DOC 20

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Rocky River Wastewater Treatment Plant Existing Facilities Basis of Design
1. Design Parameters
A. Organic Loading
Average Daily (5 Day BOD) 250 mg/I
Suspended Solids 200 mg/I
TKN 24 mg/I
B. Hydraulic Loading
Design Average Daily
Instantaneous Peak Rate
5.2 MGD
13.0 MGD
C. Design Effluent Efficiency
BOD (5 Day) 24 mg/I
Suspended Solids 30 mg/I
TKN 13 mg/I
2. Plant and Process Equipment
A. Influent Pumping Station
Type Archimedian Screw
Number Three
Capacity, Two Pumps 9,100 GPM / 13.0 MGD
Drive, Each 50 HP
B. Screens
Type Mechanical
Number Two
Controls Differential Pressure
Opening Size Y4 - inch
C. Flow Measuring
Type Parshall Flume
Throat Width 18-Inches
Range 1 -13 MGD
Meter Indicate, Record, Totalize
D. Aeration Facilities
Basins
Number Two
Dimensions 400-ft x 100-ft x 12-ft SWD
Volume 5.2 MG
Detention 24 Hours
Lining Concrete
Aerators
Number Eight
Type Mechanical, Low Speed, Platform
Mounted
Drive Units, Each 100 / 45 HP, Two Speed
Oxygenation Capacity 3.2 Ibs / BHP -Hour (SOTR)
Oxygen Transfer, Total 55,300 Ibs / Day
CLTIFlNAL DRAFT3 TM203.DOC 19

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Appendix A
Major Facilities and Equipment
CLTIFINAL DRAFT3 TM203.DOC
18

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Table 17. Capacity Summary for Major Treatment Processes
Component
Projected Influent Flows
Average Day Flow
Maximum Month Flow
Maximum Day Flow
Secondary Treatment
Overall
Aeration Basins
Process Capacity
Remarks
Secondary Clarifiers
Aeration System
RAS/WAS Pumping System
Solids Handling
Rotary Drum Thickener
Aerobic Digesters
16.5 mgd
19.0 mgd
57.3 mgd
5.50 mgd
7.51 mgd
5.20 mgd
2.39 mgd
At 11.6 day SRT and 13.3°C
14.1 MG additional volume required.
Actual capacity limited by aeration system.
At 3,000 mg/L MLSS. 73,105-ft2 of
additional surface area is required.
Approx. 163,485 lbs/day of additional '
oxygen is required at 1.5 lbs/BHP-hr.
RAS system is limiting. Approx. 9,555 gpm
(13.8 mgd) of additional firm capacity is
required.
Approx. 438,900 gpd (304 gpm) of
additional thickener capacity is required.
Approx. 8.25 MG of additional digester
volume is required to meet 60 day SRT at
15°C.
CLTIFINAL DRAFTS TM203.0OC
17

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Table 16. Aerobic Digester Capacity Summary
2) SOUR = specific oxygen uptake rate at 20°C
Table 16 indicates that at the current flow conditions, the two existing aerobic digesters
provide an adequate SRT to meet the 40 CFR 503 regulations for pathogen reduction
(Alternative No. 2), although the model predicted VSS destruction does not meet the 38-
percent VAR requirement (Option No. 1). However, the model predicted specific oxygen
uptake rate (SOUR) demonstrates compliance with Option No. 4, with a value less than 1.5
mg-02/hr/g-TS. A review of the 2004 Biosolids Annual Report (Town of Mooresville, 2005)
determined that the facility typically demonstrated Class B compliance for pathogen
reduction utilizing Alternative No. 1 (Indicator Organism Monitoring). VAR compliance
was typically demonstrated utilizing either Option No. 3 (additional bench -scale digestion)
or Option No. 6 (alkali addition). See Appendix B for a summary of these alternatives and
options.
Evaluation of the projected loadings to the digesters assumed that the facility would utilize
Option No. 4 (SOUR) for VAR and Alternative No. 2 (SRT) for pathogen reduction Class B
compliance. At the projected loadings, the existing digesters will not have sufficient volume
to provide an adequate SRT although it should be capable of meeting the SOUR criteria. To
provide a minimum SRT of 60 days at 15°C, the aerobic digesters could only treat
approximately 19,750 gpd of thickened WAS at 3.25 percent solids or 89,150 gpd of WAS at
0.8 percent solids. This equates to a facility treatment capacity of 2.39 mgd at an 11.6 day-
SRT. It should be noted that utilizing an alternative pathogen reduction method, such as
monitoring indicator organisms (Alternative No. 1), could be used to demonstrate
compliance and increase the facility treatment capacity. Similar to the current conditions,
the model predicted VSS destruction does not meet the 40 CFR Part 503 vector attraction
reduction criteria (Option No. 1) of 38-percent. However, the model predicted SOUR would
meet alternative criteria (Option 4) of less than 1.5 mg-02/hr/g-TS. Therefore, to meet the
projected sludge production and provide a 60 day SRT to meet the 40 CFR 503 pathogen
reduction requirements, approximately 8.25 MG of additional digester volume would be
required. Finally, at least 3,592 scfm of aeration capacity would be required to meet the
projected oxygen demand.
Capacity Summary
Process capacities for various major unit processes are summarized in Table 17. The
limiting processes, in order of magnitude, are the aerobic digesters (2.39 mgd), RAS
pumping system (5.2 mgd), secondary treatment system (5.5 mgd) and aeration system (7.51
mgd). While the secondary treatment system as a whole is limited to 5.5 mgd, the
secondary clarifiers are capable of treating 11 mgd at a 3,000 mg/L MLSS. The facility is
also limited by the solids handling system. To meet the 40 CFR 502 pathogen reduction
criteria (Alternative No. 2) of 60 days at 15°C, the aerobic digesters are only capable of
accepting approximately 89,150 gpd of WAS at 0.8 percent solids. Based on an 11.6-day
SRT, the treatment system would be limited to 2.39 mgd.
CLTIFINAL DRAFT3 TM203.DOC 16

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
and options that can be used to demonstrate compliance with Class B biosolids
requirements is provided in Appendix B.
Table 15. Summary of Aerobic Digester Design Criteria
Recommendations/Remarks
Reference
Solids Retention Time (days)
40-60
Volatile Suspended Solids Loading (lbs/ft3/day)
0.10 - 0.30
Design Temperature (°C)
15-20
Design of Municipal Wastewater Treatment Plants
WEF Manual of Practice No. 8 (1991)
and
Wastewater Engineering
Metcalf & Eddy, Inc (4th Ed, 2003)
The aerobic digester capacity is presented in Table 16. In addition to the design values
provided in Table 15, the following specific criteria were used to evaluate the aerobic
digesters:
• WAS is thickened to 3.25 percent with 90 percent solids capture
• Process SRT of 11.6 days at 13.3°C
• A design digester temperature of 200C is specified
• A dissolved oxygen residual of 2.0 mg/L is specified
Flow
Condition
(mgd)
Current
"Average" =
2.62 mgd
"MM" =
3 mgd
Projected
"Average" =
16.52 mgd
"Design" =
19 mgd
SRT
(days)
67.9
49.2
8.55
7.61
Table 16. Aerobic Digester Capacity Summary
Predicted SOUR
(mg-O7/hr/g-Ts)
0.21
0.35
1.35
1.45
Predicted VSS
Destruction
(percent)
25.2%
28.5%
20.8%
20.1%
Oxygen
Demand
(lbs/day)
Est.
Aeration
Required
(scfm)
1,500 1,000
2,330 1,575
9,879 6,642
10,678 7,192
Ex. Aeration
Capacity
(scfm)
Firm Total
3,600 5,400
Notes:
1) Model predicted VSS destruction assumes adequate oxygen is provided to meet demand.
CLTIFINAL DRAFT3 TM203.DOC 15

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
previously in TM 202, Rocky River WWTP - Existing Facilities Assessment, Utilities staff are
actively pursing a UV disinfection system. Therefore, the treatment capacity of the existing
gaseous chlorine disinfection system was not evaluated.
Solids Handling
The solids handling system includes a rotary drum thickener (RDT) applied to WAS and
two aerobic digesters. WAS is pumped from the secondary clarifiers to a single RDT. The
RDT thickens the WAS from about 0.8 percent to between 3 and 3.5 percent. The thickened
WAS is then pumped to the aerobic digesters. Digested residuals meet Class B
requirements and are hauled away and land applied or are dewatered using a portable belt
filter press and landfilled.
Estimates of the current and projected sludge flow and production are summarized in Table
14.
Table 14. Sludge Production Summary
Flow Condition (mgd)
WAS Production
(lbs-TSS/day) (gpd)
Current
"Average" = 2.62 mgd
"MM" = 3 mgd
Projected
"Average" = 16.52 mgd
"Design" = 19.0 mgd
5,300 79,400
7,260 108,800
41,748 625,720
48,498 726,900
Notes:
1) Sludge flow values are based on a WAS at 0.8 percent solids
2) Current design flow assumes an 11.6 day SRT 13.3°C and 50% R/Q
Rotary Drum Thickener
The solids handling system uses a RDT rated at 200 gpm (288,000 gpd or 18,680 lbs/day at
0.8 percent solids). Plant staff typically operates the thickener at a flow rate of
approximately 170 gpm. Based on the projected sludge production, the existing RDT will
not be capable of treating the design daily sludge production. Approximately 438,900 gpd
(304 gpm) of additional thickening capacity will be required to meet the design sludge
production.
Aerobic Digesters
The aerobic digesters were evaluated on their ability to meet the 40 CFR 503 regulations for
Class B biosolids. Design criteria from standard reference sources are summarized in Table
15. A summary of vector attraction reduction (VAR) and pathogen reduction alternatives
CLT!FINAL DRAFT3 TM203.DOC 14

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
chosen for the simulations are similar for other facilities in the area and will be more fully
defined later in the project.
Table 13. Aeration System Capacity Summary
Oxygenation
Capacity Value
Oxygen Demand
(lbs AOR/day)
Mechanical Aeration
Power Requirement
(BHP)
Aeration Capacity Available
(lbs/day)
Current
Projected
Current
Projected
8 Ful1/0 Half
Speed
6 Full/2 Half
Speed
Manufacturer
"Design"
10,850
80,158
254
1,876
34,200
29,500
"Max"
21,200
192,285
496
4,501
Conservative
"Design"
10,850
80,158
301
2,227
28,800
24,850
"Max"
21,200
192,285
588
5,341
Notes:
1) "Design" values represent maximum month condition and "Max" condition presents maximum
day condition.
2) Current oxygen demand assumes meeting existing BOD (24 mg/L) and NH3-N (2 mg/L) permit
limits
3) Projected oxygen demand assumes meeting a future BOD and NH3-N limit of 5 mg/L and 1 mg/L,
respectively.
4) Oxygenation values are based on AOR maintaining a residual DO of 2 mg/L at 28°C and a MLSS of
3,500 mg/L
5) Manufacture oxygenation value =1.78 lbs/hp-hr and Alternative value = 1.5 lbs/hp-hr
6) "Conservative" aerator oxygenation capacity represents actual values CH2M HILL has measured
at full scale sites.
As previously indicated in Table 8, the aeration system can treat up to 7.51 mgd, based on
the alternative oxygenation capacity. From the information provided in Table 13, the facility
will need additional aeration capacity to meet the projected design and maximum day
oxygen demand. The projected oxygen demands are over three times the current capacity
due to the more stringent nitrification requirement assumed. Approximately 163,485
lbs/day of additional aeration capacity will be required to meet the future maximum day
demand using the alternative design oxygenation capacity assuming all eight aerators are
operating at full speed.
Disinfection System
Gaseous chlorine (in solution) is currently being used to disinfect plant effluent. The
chlorine solution is applied prior to entering a chlorine contact chamber. As discussed
CLTIFINAL DRAFT3 TM203.DOC 13

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Table 11. Estimated Future Secondary Clarifier Operating Data
Projected Flow
Existing
Required
Total
HOR with all
SLR with all
Condition
Surface Area
Additional
Surface
Clarifiers in
Clarifiers in
(mgd)
(ft2)
Surface Area
Area
Service
Service
(ft2)
(ft2)
(gpd/ft2)
(lbs/day-ft2)
"Design" =19
230
11
"Max" = 57.3
13,295
73,105
86,400
673
34.3
"Peak Hr" = 76
889
—
Notes:
1) SLR values are based on a RAS flow of 100 percent of the max month secondary influent
flow, a SVI of 150 and a MLSS concentration of 3,000 mg/L.
2) Max day SLR represents 79.9% of the SLR -Flux of 43 lbs/day-ft2
RASIWAS Pumping System
As indicated in Table 12, the existing RAS system does not have the capacity to meet the
projected firm maximum month pumping requirements. While the WAS pumping system
appears to have adequate capacity to meet the project requirements, it should be recognized
that in an expanded facility, a new RAS/WAS pump station will likely be required and
would include new RAW and WAS pumps.
Table 12. RAS and WAS Pumping Capacity Summary
Pumping
System
Current
Pumping
Operation
($lam)
Projected Required
Pumping Capacity
(gpm)
Firm Pumping
Capacity Available
(gpm)
Required Additional
Firm Pumping
Capacity (gpm)
RAS
WAS
890
103
13,195
492
3,640
500
9,555
None
Notes:
1) Capacities shown represent firm maximum month condition
2) Capacities based on MLSS of 3,000 mg/L, SRT of 11.6 days and R/Q of 100%
3) WAS pumping capacity based on 24 hour, 7 day operation, 71% R/Q at 8,000 mg/L
Aeration System
Oxygen demands, aeration requirements, and aeration capacities are presented in Table 13.
Similar to the aeration basin evaluation, the aeration capacity shows a comparison using all
eight aerators at full speed versus six aerators at full speed with the remaining two at half
speed. To predict the projected oxygen demand it was assumed that the facility would be
required to meet an effluent BOD of 5 mg/L and NH3-N of 1 mg/L. The effluent limits
CLTIFINAL DRAFTS TM203.DOC
12

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Secondary clarifier operating data and treatment capacity for current and project flows are
presented in Table 10. As indicated previously in the secondary treatment capacity
assessment, the secondary clarifiers do not have sufficient surface area to meet the projected
19 mgd maximum month flow. In addition, the existing clarifiers fail to meet design
standards at the current peak day flow with one clarifier out of service.
Table 10. Secondary Clarifier Operating Data
Flow Condition
(mgd)
HOR with all
Clarifiers in
Service
(gpd/ft2)
HOR with One
Clarifiers Out
of Service
(gpd/ft2)
SLR with all
Clarifiers in
Service
(lbs/day-ft2)
SLR with One
Clarifiers Out
of Service
(lbs/day-ft2)
Current
"MM" = 3.0
236
472
6.1
12.3
"Max" = 9.09
694
1,388
18.7
37.5
Projected
"Design" = 19.0
1,492
2,984
75.0
149
"Max" = 57.3
4,375
8,750
223
446
Notes:
1) Based on HOR and SLR criteria presented in Table 8, the secondary clarifier capacity is
approximately 11 mgd with all units in service.
2) SLR values are based on a RAS flow of 100 percent of the secondary influent flow, a SVI
of 150 and a MLSS concentration of 3,000 mg/L.
3) Underlined values ("XXX") indicate that value is greater than the design criteria
To treat the projected maximum day flow, it was estimated that an additional 73,105 square
feet of clarifier surface area would be required with all clarifiers in service. Extra surface
area will be required to insure proper clarification when one unit is out of service. Table 11
summarizes the estimated future clarifier performance.
CLT/FINAL DRAFT3 TM203.DOC 11

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
c Organic loading estimated using max month BOD loading (326 mg/L) utilizing the alternate
calculated aeration basin treatment capacity.
Table 8 indicates that the aeration basins will require an additional 14.1 MG to treat the
projected maximum month flow of 19 mgd. Aeration basin capacity was defined by the
limits of the existing mechanical aerators to transfer adequate oxygen to the treatment
system. An upgraded aeration system, mechanical or diffused aeration, could increase the
treatment capacity of the existing aeration basins and could reduce projected additional
basin volume requirements. Table 8 also shows the affect of only operating six aerators at
full speed and two at half speed. As mentioned previously in the condition assessment,
plant staff indicated that they could not operate the final aerator in each aeration basin at
full speed due to floc shear which resulted in turbidity issues in the secondary effluent.
The values presented in Table 8 assume that the aeration basins are not limited by specific
mechanical problems such as improper flow splits, poor aeration system distribution, dilute
RAS concentration, or improper RAS flow rate. The secondary treatment system must
function as a unified system with all components operating properly to maximize the
capacity of the existing components.
Secondary Clarifiers
The WWTP has two secondary clarifiers, each 92-feet in diameter, with a combined surface
area of 13,295 square feet. The final clarifiers were evaluated not only on their ability to
clarify (i.e. separate biological floc from the water), but also their ability to thicken the solids
that settle to the bottom. Thickening is necessary to insure a recycle sludge (RAS)
concentration that will allow the MLSS concentration to be maintained in the aeration basin.
The hydraulic overflow rate (HOR) represents the clarification capability while the solids
loading rate (SLR) represents the thickening component. The HOR and SLR have
historically been used to size secondary clarification systems and typical values are
presented in Table 9. A solids flux analysis method was used to estimate clarifier
performance based on an assumed settleability index (SVI). For the analysis, an assumed
SVI of 150 mL/g was used which, from a review of the plant data (TM 201- Rocky River
WWTP Design Wastewater Flows, Loads and Characterization), appears to be a conservative
value.
Average Day
Peak Day
Table 9. Summ
ary
of Second
ary
RRWWTP Design
HOR SLR
(gpd/ft2) (lbs/day-ft2)
500 20
<1,200 <80% SLR -Flux
Clarifier Design Criteria
Typical Values
HOR SLR
(gpd/ ft2) (lbs/day-ft2)
400-800a 20-30b
400-700b
1,000-1,200b <50b
1,000-1,600c
a Suspended Solids Removal, EPA Process Design Manual (1975) and Wastewater Engineering, Metcalf & Eddy, Inc. (4th
edition, 2003)
b Design of Municipal Wastewater Treatment Plants, WEF Manual of Practice No. 8 (1991)
CLTIFINAL DRAFT3 TM203.DOC
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DRAFT
ROCKY RIVER WWTP PROCESS MODELING
As summarized in Table 7, the model predicted treatment capacity of the secondary
treatment system is 5.5 mgd on a maximum month basis. At this flow rate, secondary
treatment system is limited by the secondary clarifier loading rate which begins to exceed
the design value of 20 lbs/day/ft2. This value is the maximum flow rate recommended for
sustained operation. The ultimate capacity, defined as the maximum short term (i.e. peak
day) flow rate, of the secondary treatment system is estimated to be 5.93 mgd. At this flow
rate, the clarifier solids loading rate has approached 80-percent of the limiting solids loading
rate flux (SLR -Flux). One measure of the SLR -Flux is defined by the Daigger-Roper
equation which estimates the operating condition at which the clarifier fails and the sludge
blanket begins migrating towards the weirs for a sludge of a defined settleability. This
value is termed the limiting solids flux rate. A solids loading rate of 80 percent of this
limiting value is suggested as a reasonable maximum solids loading rate that has not yet
crossed into failure mode.
Overall, the secondary treatment system appears to be capable of handling a projected
maximum month flow of 5.5 mgd; therefore, additional facilities will be required for the
expansion to 19 mgd. A review of the separate components is presented in the following
sections.
Aeration Basins
Treatment capacities for the aeration basins at current and projected flows are presented in
Table 8. While treatment capacities are shown as related to influent flow rate, it should be
noted that the actual treatment capacity is really based on pounds of BOD, TSS, and
ammonia -nitrogen load actually treated. Using flow as a rating value provides a more
easily comparable parameter since it is usually the identifier used when discussing
treatment capacity. The following specific criteria were applied in addition to those listed in
Table 5:
• MLSS was held to 3,500 mg/L for calculation of additional basin volume.
• SRT was set at 11.6 days for the minimum temperature of 13.3°C in order to provide an
adequate safety factor for nitrification.
• Sludge volume index (SVI) was set to 150 mL/g.
• Effluent ammonia was equal to or less than 1 mg/L.
• Residual DO was maintained at 2 mg/L.
Table 8. Aeration Basin Treatment Capacity
No. of
Aerators
Full/Half
Speed
Current
Max
Month
Row
(MGD)
Projected
Max
Month
Flow
(MGD)
Aeration Basin Treatment
Capacity (MGD)
Aeration
Basin
Organic
Loading
(1b/1000 ft3)c
Required
Additional
Basin
Volume
(MG)
Manufacturer Alt. Valueb
Values
8/0
6/ 2
3
19
8.95 7.51
7.72 6.48
28.45
14.1
24.54
a Manufacturer aerator oxygenation capacity = 1.85 lbs oxygen/BHP-hr (AOR at 13.3°C)
b Alternate aerator oxygenation capacity of 1.55 lbs oxygen/BHP-hr (AOR at 13.3°C) represents
actual values CH2M HILL has measured at full scale sites.
CLT/FINAL DRAFT3 TM203.DOC
9

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Table 6. Aeration Basin/Final Clarifier System Modeled Parameters
Parameter Value
Residual DO
Rotary Drum Thickener Efficiency
Influent cBOD
Influent TSS
Influent TKN
Influent NH3-N
Influent Total P
2.0 mg/L
90 %
326 mg/L
344 mg/L
35.89 mg/L
23.38 mg/L
6.36 mg/L
Table 7. Model Calculated Results
Parameter
Value
Current Maximum Month Flow
Design Treatment Capacity (Max Month Basis)
Modeled Aeration Basin/Clarifier Treatment Capacity
MLSS
Clarifier Overflow Rate
Clarifier Underflow Rate (RAS)
Clarifier Solids Loading Rate
RAS Concentration
% of RAS Capacity with one unit out of service
WAS Flow Rate
% of WAS Capacity with one unit out of service
Oxygen Requirements - AOR/SOR
Effluent cBOD
Effluent TSS
Effluent NH3-N
Effluent TP
3.0 mgd
5.2 mgd
5.5 mgd
3,791mg/L
422 gpd/ft2
211 gpd/ft2 (50% R/Q)
20.0 lbs/day-ft2
10,767 mg/L
53.5%
0.152 mgd
21%
21,801/ 37,805 lbs/ day
2.51 mg/L
10 mg/L (estimated)
0.47 mg/L
2.65 mg/L
CLT/FINAL DRAFT3 TM203.DOC 8

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Table 5. Secondary Treatment Design Criteria
Component
Design Criteria
Criteria Value
Aeration System ,
Sludge Pumping
Oxygen Requirements:
BOD
NH3-N
Return Activated Sludge (RAS)
Rate
1.11b oxygen/lb BOD removed
4.6 lb oxygen/lb NH3 converted
Provide firm capacity of 100% of
influent design flow
Notes:
OC degrees Celsius
of degrees Fahrenheit
WAS waste activated sludge
TSS total suspended solids
SRT solids retention time
MLSS mixed liquor suspended solids
Due to the performance co-dependency of the aeration basins and clarifiers from a process
perspective, they were evaluated as a system. As the flows and loads were increased to
determine the ultimate treatment capacity of the secondary system, the RAS flow rate was
adjusted to maintain an acceptable clarifier solids loading rate while remaining under 100
percent of the maximum month flow rate. The ultimate treatment capacity of the system
was determined when one of the existing secondary treatment components exceeded its
design value. A summary of the process modeling input parameters and results are
provided in Table 6 and 7, respectively. While it is recognized that the maximum month
flow and loading did not occur concurrently, for modeling purposes it was assumed that
that these events occurred simultaneously. The modeled influent loading parameters are
provided in Table 6 as well.
Table 6. Aeration Basin/Final Clarifier System Modeled Parameters
Parameter Value
Aeration Basin Volume, Each 2 Q 2.6-MG
Aeration Basin Volume, Total 5.2-MG
Clarifier Surface Area, Each 2 @ 6,647-ft2
Clarifier Surface Area, Total 13,295-ft2
Minimum 30-day Temperature 13.3°C (55.9°F)
Minimum SRT for Nitrification 5.8-days (@13.3°C, pH of 7.1)
Modeled SRT 11.6-days
SVI 150 mL/g
CLT/FINAL DRAFT3 TM203.DOC 7

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Table 4. Headworks Treatment Capacity
Component Capacity Criteria Treatment Capacity
Screening Two screens provide treatment at
peak hydraulic flow; One screen is
redundant at design flow
Influent Lift Pumping Pump the maximum flow with one
unit out of service
Headworks Treatment Capacity
13.25 mgd (avg)
26.5 mgd (peak)
13 mgd (firm)
19.5 mgd (total)
13 mgd
Secondary Treatment
Secondary treatment consists of the aeration basins, secondary clarifiers, aeration system,
and RAS/WAS pumping. The secondary portion of the Rocky River WWTP consists of two
aeration basins with mechanical aerators, two final clarifiers, and the RAS/WAS pumping
station. Secondary treatment design criteria against which the existing facility was
evaluated are available from various texts and are summarized in Table 5.
Table 5. Secondary Treatment Design Criteria
Component
General
Design Criteria
Criteria Value
Aeration Basins
Secondary Clarification
Minimum Water Temperature
Maximum Water Temperature
pH Range
Available Alkalinity
Effluent Ammonia Concentration
SRT
Average Dissolved Oxygen (DO)
Concentration
MLSS Concentration Range
Effluent TSS Concentration
Hydraulic Overflow Rate
Solids Loading Rate
RAS/WAS Concentration
13.3°C (55.9°F)
28.00C (82.O.F)
7.0 - 7.6
200 mg/L as CaCO3
<1.0 mg/L at design condition
5 -10 days at design condition
2.0 mg/L at design condition
(1.0 mg/L at peak condition)
2,000 - 4,000 mg/L
10 mg/L at design condition
<500 gpd/ft2 at design flow
<1,200 gpd/ft2 at peak flow
<20 lbs/ day-ft2 at design load
<50 lbs/day-ft2 at peak load
Greater than twice the MLSS at
a SVI 5150 mL/ g
CLTIFINAL DRAFT3 TM203.DOC 6

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
town and summarized in TM 201, Rocky River WWTP - Design Wastewater Flows, Loads and
Characterization, were used to prepare and calibrate the process model. Table 3 summarizes
the model inputs.
Table 3. Process Modeling Input Data
Parameter
Avg Day
Max Month
Max Week
Max Day
Peak Hour
July 2003 - April 2005 Data Set
Flow (mgd)
2.62
3.00
3.75
9.10
12.05
cBOD (lb/day)
6,300
8,200
11,800
17,100
-
TSS (lb/day)
6,800
8,700
13,600
35,700
-
TKN (lb/day)
865
900
1,100
1,700
-
NH3-N (lb/day)
570
590
720
1,100
-
Total P (lb/day)
135
140
170
265
--
Alkalinity (lb/day)
3,375
5,010
6,260
15,190
-
Flow and Load Projections
Flow (mgd)
16.52
19.00
23.63
57.33
76.00
cBOD (lb/day)
39,408
51,231
73,694
107,585
-
TSS (lb/day)
42,440
54,323
85,728
224,931
-
TKN (lb/day)
5,439
5,656
6,907
10,660
-
NH3-N (lb/day)
3,541
3,683
4,497
6,941
-
Total P (lb/day)
845
878
1,073
1,656
--
Alkalinity (lb/day)
27,558
31,692
39,408
95,627
--
Note: Alkalinity input data estimated at 200 mg/L.
The Basis of Design information from Rocky River Wastewater Facilities Basis of Design (Willis
Engineer, 5/1986) gives the facility design flow as 5.2 mgd (max month) with a peak hour
flow capacity of 13 mgd. Town of Mooresville staff directed CH2M HILL (October 31, 2005)
to a maximum month flow of 19 mgd as the basis of design for the expansion.
Headworks
The plant headworks consist primarily of influent pumping and screening. The treatment
capacities of each headworks component are controlled by the limiting hydraulic capacity,
which will be discussed in TM 204 - Rocky River WWTP Hydraulic Analysis. A summary of
the headworks treatment capacities is provided in Table 4.
CLT/FINAL DRAFT3 TM203.DOC 5

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
Table 2. Summary of Model Calibratio
versus Basis of Design
Parameter
Design Model
Model Input Data
Flow, mgd
BOD, lbs/day
TSS, lbs/day
TKN, lbs/day
NH3-N, mg/L
Total Phosphorus, mg/L
Temperature, 0C
SRT, days
Model Output Operations Data
MLSS, mg/L
RAS, mgd
RAS/WAS, mg/L
Total MLSS Inventory, lbs
WAS Rate, mgd
WAS, lbs VSS
Effluent Values
Effluent BOD, mg/L
Effluent NH3-N, mg/L
Effluent TP, mg/L
5.2 5.2
10,849 10,849
8,679 8,679
1,041 1,041
No Data 15.6
No Data 5
20 20
No Data 16.5
3,000 3,002
— 5.174
5,000 5,822
130,182 130,293
0.404 0.137
5,970 4,906
24 5.88
13 0.26
No Data 3.12
Similar to the calibration against the historical data, the model appears to match fairly well
with the basis of design values. WAS production fell within an acceptable range while BOD
and NH3-N values were well below design values.
Process/Capacity Assessment
The treatment capacity of the plant was assessed to determine which processes would need
expansion. The biological treatment process was assessed using a wastewater treatment
process model while the headworks will be assessed separately. Data obtained from the
CLTIFINAL DRAFT3 TM203.DOC 4

DRAFT
ROCKY RIVER WIMP PROCESS MODELING
Table 1. Summary of Model Calibration
Parameter
2002-2005 Average
Reported Model
2005 Average
Reported Model
February 2005 Average
Reported Model
Model Output Operations Data
MLSS, mg/L
3,950
3,779
3,483
3,486
3,589
3,645
RAS, mgd
1.282
1.285
1.182
1.182
1.244
1.357
RAS/WAS, mg/L
8,878
10,829
7,913
10,711
8,399
10,414
Total MLSS Inventory, lbs
171,342
164,013
151,642
151,642
155,719
155,719
Total MLVSS Inventory, lbs
125,012
123,620
115,956
108,158
124,259
112,129
WAS Rate, mgd
0.148
0.110
0.138
0.117
0.138
0.108
WAS, lbs
10,223
9,913
8,707
10,464
9,672
9,389
Effluent Values
Effluent BOD, mg/L
6.1
1.1
12.1
2.3
8.3
1.3
Effluent NH3-N, mg/L
0.17
0.17
0.19
0.16
0.10
0.15
Effluent TSS, mg/L
7.7
7.7
15.2
15.2
8.7
8.7
Effluent TP, mg/L
2.41
4.09
2.76
3.73
3.08
3.94
Notes:
* Typical range indicated from Utilities staff
As indicated in Table 1, the model was able to replicate the reported operations data.
Effluent BOD values were typically much lower than the reported values, which is normal
when comparing theoretical and actual operations. In addition, actual BOD testing cannot
report values less than 2 mg/L which artificially raises the average. Ammonia values were
generally very close to the reported values while phosphorus values were higher. The
model may be reporting higher effluent Ortho-Phosphorus values because it is not unusual
for mechanically aerated systems to have anoxic/anaerobic pockets in the basin and within
the floc itself which could result in some actual biological phosphorus removal despite
predominately aerobic conditions. The WAS production simulated in the model were
generally close to the reported values. The 2002-2005 and February 2005 simulations were
both within 6 percent of the reported value while the 2005 average was higher, but still
within an acceptable range (±20 percent). The model was also checked against the original
basis of design. A summary of the design values and the model results are provided in
Table 2.
CLT/FINAL DRAFTS TM203.DOC 3

DRAFT
ROCKY RIVER WWTP PROCESS MODELING
• Activated sludge biological treatment with mechanical aerators
• Secondary clarification
• .Return activated sludge (RAS) and waste activated sludge (WAS) pumping
• Gaseous chlorine disinfection
Waste activated sludge is thickened with a rotary drum thickener prior to aerobic digestion.
The digested solids are land applied (liquid) as Class B biosolids or dewatered using a
leased belt filter press and landfilled. A full list of major equipment is provided in
Appendix A.
Model Calibration
Calibration of the process model was determined by confirming the current operations.
Data summarized in TM 201- Rocky River WWTP - Design Wastewater Flows, Loads and
Characterization was utilized to confirm that the model was calibrated. Calibration
simulations were run against the 2002-2005 Average, 2005 Average, and February 2005
Average. A summary of the calibration is summarized in Table 1.
Table 1. Summary of Model Calibration
Parameter
2002-2005 Average
Reported Model
2005 Average
Reported Model
February 2005 Average
Reported Model
Model Input Data
Influent Flow (mgd)
2.62
2.62
2.72
2.72
2.74
2.74
Influent BOD, lbs/day
6,253
6,253
6,792
6,792
5,971
5,971
Influent TSS, lbs/ day
6,726
6,726
6,121
6,121
5,543
5,543
Influent NH3-N, lbs/day
562
562
562
562
564
564
Influent TKN, lbs/ day
863
863
863
863
844
844
Influent TP, lbs/day
134
134
134
134
133
133
Temperature, °C
19
19
15.8
15.8
15
15
SRT, days
16.27
16.27
16
16
16.5
16.5
SVI, mL/g
96
96
50
50
61.75
61.75
RAS, % Influent Flow
49.1%
49.1%
44.4%
44.4%
46.1%
46.1%
Effluent TSS, mg/L
7.7
7.7
15.2
15
8.7
8.7
Drum Thickener % Capture
N/A
42.7%
N/A
42.7%
N/A
42.7%
Drum Thickener % Solids
3-3.5 %*
3.25%
3-3.5 %*
3.25%
3-3.5 %*
3.25%
CLTIFINAL DRAFT3 TM203.DOC
2

DRAFT TECHNICAL MEMORANDUM 203 CH2MHILL
Rocky River WWTP Process Modeling
PREPARED FOR: Town of Mooresville, NC
PREPARED BY: CH2M HILL
DATE: November 28, 2005
This technical memorandum (TM) summarizes Task 203, Process Modeling for the Rocky
River Wastewater Treatment Plant (RRWWTP) Expansion Project. The purpose of this TM
is to provide an assessment of the treatment capacities of the various unit processes at the
Rocky River WWTP. Data summarized in TM 201- Rocky River WWTP - Design Wastewater
Flows, Loads and Characterization is used as the basis of the capacity assessment.
Recommended design criteria and sources are provided as part of the assessment of each
unit process.
The memo is organized as follows:
• Existing Facilities
• Model Calibration
• Process/Capacity Assessment
• Headworks
• Secondary Treatment
• Aeration Basin
• Secondary Clarifiers
• RAS/WAS Pumping
• Aeration System
• Disinfection System
• Solids Handling
• Rotary Drum Thickener
• Aerobic Digesters
• Capacity Summary
Existing Facilities
The following is a brief discussion of the existing facilities at the treatment facility. A
condition assessment of the facility is provided in TM 202 - Rocky River WWTP Existing
Facilities Assessment.
The RRWWTP is a complete mixed activated sludge -based treatment facility. The plant
facility was originally designed in 1976 and the headworks were upgraded in 2001. The
facility is rated at 5.2 mgd on a max month (MM) basis. The RRWWTP utilizes a single
headworks facility with screening, influent pumping, and caustic addition for pH control.
The biological treatment system employs the following additional unit processes:
CLTIFINAL DRAFT3 TM203.DOC 1

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
J. Solids Handling Facilities
Aerobic Digesters
Number Two
Diameter 70-ft
Depth 19-ft
Volume, Each 592,600 Gallons
Solids Loading 16,850 Ibs / Day
Hydraulic Loading 403,800 GPD
Blowers
Type Centrifugal
Number Three
Capacity, Each 1,800 SCFM
Drive 100 HP
Mixers
Type Submerged Turbine
Number Two
Size 75 HP
Sludge Thickening
Type Rotary Drum
Number One
Capacity 200 GPM
Thickening Approx. 3.5%
CLT/FINAL DRAFT TM202.DOC
11

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
E. Settling Facilities
Type
Number
Diameter
Depth
Overflow Rate @ 5.2 MGD
Detention © 5.2 MGD
Sludge Withdrawal
F. Sludge Recycle Pumping Station
Recycle Pumps
Type
Number
Capacity, Each
Drive
Recycle Sludge Flow Measuring
Type
Range
Waste Sludge Pumps
Type
Number
Capacity, Each
Drive
Waste Sludge Flow Measuring
Type
Range
H. Chlorination Facilities
Contact Basin
Number
Path Length
Path Width
Length:Width Ratio
Volume
Contact Time @ 5.2 MGD
Chlorinators
Number
Capacity, Each
Feed Rate
I. Effluent Reaeration
Type
DO Addition
Circular Clarifiers
Two
92-ft
13-ft
400 GPD/SF
6.0 Hours
Suction & Scraper Arm
Centrifugal
Two
3,640 GPM
50 HP, Variable Speed
Venturi Tube
0 - 5,600 GPM
Centrifugal
Two
500 GPM
20 HP
Venturi Tube
0 - 750 GPM
Two
162-ft
6-ft
27:1
134,200 Gallons
30 Minutes
Two
500 Ibs / Day
0-10mg/I
Cascade Aeration
5.0 mg/I
CLTIFINAL DRAFT TM202.DOC 10

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
Rocky River Wastewater Treatment Plant Existing Facilities Basis of Design
1. Design Parameters
A. Organic Loading
Average Daily (5 Day BOD) 250 mg/I
Suspended Solids 200 mg/I
TKN 24 mg/I
B. Hydraulic Loading
Design Average Daily
Instantaneous Peak Rate
5.2 MGD
13.0 MGD
C. Design Effluent Efficiency
BOD (5 Day) 24 mg/I
Suspended Solids 30 mg/I
TKN 13 mg/I
2. Plant and Process Equipment
A. Influent Pumping Station
Type Archimedian Screw
Number Three
Capacity, Two Pumps 9,100 GPM / 13.0 MGD
Drive, Each 50 HP
B. Screens
Type Mechanical
Number Two
Controls Differential Pressure
Opening Size '/4 - inch
C. Flow Measuring
Type Parshall Flume
Throat Width 18-Inches
Range 1 -13 MGD
Meter Indicate, Record, Totalize
D. Aeration Facilities
Basins
Number Two
Dimensions 400-ft x 100-ft x 12-ft SWD
Volume 5.2 MG
Detention 24 Hours
Lining Concrete
Aerators
Number Eight
Type Mechanical, Low Speed, Platform
Mounted
Drive Units, Each 100 / 45 HP, Two Speed
Oxygenation Capacity 3.2 Ibs / BHP -Hour (SOTR)
Oxygen Transfer, Total 55,300 Ibs / Day
CLTIFINAL DRAFT TM202.DOC 9

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
Appendix A
Major Facilities and Equipment
CLTIFINAL DRAFT TM202.DOC 8

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
SCADA
The facility operates a SCADA system to monitor portions of the facility. Only the waste
pumps can be controlled via the SCADA system. The system monitors the on/off status of
the aerators, influent screw pumps, bar screens, digester mixers and blowers, thickener
operation (pumps, drums, mixers, and level), recycle pumps, plant water pumps, and the
generators. The system utilizes a Direct Logic 205 Koyo PLC and an ELPRO 905U-G-ET1
radio for communication. The following alarms are relayed:
• Influent Wetwell High/Low
• Influent Flow High/Low
• Effluent Flow High/Low
• RAS Flow High/Low
• WAS Flow High/Low
• Influent pH High/Low
• Aeration Basin DO High/Low
• Thickener Discharge High/Low
• Chlorine Leak
• Influent Screw Pumps Stopped
• RAS Pumps Stopped
• Clarifiers Stopped
• Thickener Stopped
Utilities staff indicates that the system works well. Ability to control certain operations is
desired but monitoring of operational status is the primary objective of the SCADA system.
It was indicated that secure Web access (view only) of the SCADA system should be
considered for the plant expansion project.
Administration Building
The administration building is located at the entrance to the facility. The building houses
the garage/maintenance shop/spare parts storage, chlorine feed room, general storage,
laboratory, conference room, and offices. Utilities staff indicated that the building is full and
they require more space. The facility has a trailer next to the administration building for
offices for some of the staff. Expansion and upgrade of Administration Building to
accommodate laboratory, administration/operations and maintenance/inventory space and
equipment needs is desired in the expansion project. The facility has installed a new security
system as a result of a recent vulnerability assessment. The system includes an entrance
gate camera, a keypad and automatic gate. Staff requested that the video system be
upgraded to have the ability to record activity.
CLT/FINAL DRAFT TM202.DOC 7

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
and 3.5% solids. Utilities staff prefer to thicken the WAS sludge with the thickener prior to
aerobic digestion, although at the time of the visit, WAS was going directly to Digester No.
1. Solids from Digester No. 1 were being thickened using
the drum thickener and discharged into Digester No. 2.
Utilities staff indicated that once a digester becomes full,
they allow it to settle and decant prior to land application.
A leased, portable 2-meter belt filter press (BFP) is located
adjacent to the digesters. The BFP is used only if both
digesters are full and land application is not readily
available. Utilities staff indicated that if a new sludge
processing facility is built, they would like to have another
BFP and a sludge drying system. Vaccum drying beds
and its control building are also located onsite, but are
abandoned. The control building is used for storage space.
Figure 9 - Thickener Polymer System
Plant Water Systems
The existing facility currently utilizes a combination of
potable water and chlorinated effluent. Potable water is
obtained from a well system onsite, although the facility is
planning to connect to the Town distribution system soon. The non -potable water system
consists of two (2) 2-hp vertical suction pumps conveying chlorinated effluent drawn from
the chlorine contact tanks. The existing system is wrapped in insulation due to issues with
freezing during the winter. Plant water system upgrades will need to be considered in the
system expansion.
Emergency Power/Electrical Systems
The facility maintains two generators for
emergency power. Both generators are diesel
providing 650 kW each. Generator 'A'
(Cummins) was replaced recently in 2005
while Generator 'B' (Caterpillar) is original
equipment. Power is transferred manually
with a Square D Type 3-R transfer switch.
All equipment except the aeration basin
aerators restart automatically. Utilities staff
indicated that they would like an automatic
transfer switch with time delays. As part of
the electrical contract, peak shaving/load
control is practiced by the facility using the standby power systems. Standby power system
upgrades will need to be considered in the system expansion.
Staff indicated the desire to replace the current outdoor electrical switchgear housings with
enclosed electrical buildings. Stainless steel or FRP type enclosures for outdoor electrical
panels/boxes are preferred.
Figure 10 - Generator Switchgear
CLT/FINAL DRAFT TM202.DOC 6

DRAFT
ROCKY RIVER W,VTP EXISTING FACILITIES ASSESSMENT
backup. Both cylinders are connected to a Regal automatic switchover gas chlorinator. The
gas is injected using a Regal Smart valve with a 250 lb/day injector and 100 lb/day
rotometer. A 500 lb/day rotometer and injector with manual controls are available as a
backup. A 55-gallon drum of sodium hypochlorite with metering pump is also available on
a temporary basis. Utilities staff indicated that the gaseous chlorine system works well,
although they would like to utilize Ultraviolet (UV) disinfection in the future. Utilities staff
mentioned that they have been discussing UV options with Wedeco.
Chlorinated effluent is held in two (2) concrete chlorine contact basins. The basins are
designed to provide 30 minutes of contact time at a design flow of 5.2 mgd. The facility
does not practice dechlorination, although their permit will require it starting January 1,
2007. Effluent leaving the basins is re -aerated using cascade aeration prior to discharge.
Effluent sampling is conducted at the end of the cascade aeration steps utilizing an ISCO
3710FR automatic sampler. The sampler is flow proportional utilizing the effluent flow
meter (Millitronics Hydroranger). Improved effluent flow monitoring is desired by the
utilities staff.
Sludge Processing
WAS pumped from the recycle pump station is
conveyed to two (2) aerobic digesters. Each
digester is 70-ft in diameter, 19-ft deep, and has a
volume of 592,600 gallons. The digesters have a
design solids loading rate of 16, 8501bs/day , a
hydraulic loading rate of 403,800 gallons per day,
and a design solids residence time of 20 days.
Three (3) Hoffman multi -stage centrifugal
blowers, each with a 1,800 scfm capacity and a
100-hp motor, deliver air to the digesters. Each
blower is approximately 5-10 years old. The most
recent maintenance on the blowers includes:
Figure 7 - Aerobic Digesters
• Digester Blower #3 motor and blower were rebuilt in 2004.
• Digester Blower #1 motor was rebuilt in 2003.
• Digester blower piping seals/ gaskets were replaced in 2003.
• Digester Blower #2 motor was rebuilt in 2000.
The digesters also utilize the originally installed
Philadephia submerged turbine mechanical
mixers (Model PSA-11QB). The mixers operate at
30 rpm and utilize 75-hp, 1780 rpm,
460V/60Hz/3-phase motors. The mixers,
digesters, and blowers all appeared to be in good
condition.
Sludge is thickened using a Roediger Rotary
Drum Thickener. The thickener has a capacity of
200 gpm and typically thickens to between 3%
Figure 8 - Rotary Drum Thickener
CLTIFINAL DRAFT TM202.DOC
5

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
need to be replaced as part of the expansion project. Discussions with the staff determined
that they would like a mechanical cleaning system for the clarifier weirs and sludge blanket
indicators.
RAS/WAS Pumping Systems
Mixed liquor within the secondary clarifiers is
recycled back to the front of the aeration basins
via two (2) variable speed centrifugal pumps
capable of conveying up to 3,640 gpm. The
pumps are located in the recycle pump station
adjacent to the secondary clarifiers. Both
pumps are original equipment however
Recycle Pump No. 1 was rebuilt in 2002 while
Recycle Pump No. 2 was rebuilt in 2000.
Recycle Pump No. 1 is equipped with a 100hp
motor with a Square D Econoflex drive that is
approximately 8 years old. Pump No. 2 is
utilizing its original 50-hp motor, however staff are prepared to replace the original motor
with a 60-hp 900 rpm motor and a new VFD drive. RAS flow is measured using a
ThermoPolysonics Doppler flow meter (model DDF5088). Staff has also abandoned the
original seal water system and have the pumps directly connected to a 2-inch potable water
supply line.
Sludge is wasted from the system utilizing two (2) 500 gpm centrifugal pumps driven by 20-
hp motors. Both pumps are original equipment however, they are driven by new VFD
drives installed approximately 1.5 years ago. The drives are AC Tech Model MH
4200BG1356 and are controlled using a Direct Logic 06 Koyo PLC located adjacent to the
drives. The pumps can also be controlled via the SCADA system or from a control panel
located in the Digester Building.
Other miscellaneous maintenance on the system
includes:
• Recycle Pump No. 1 telescoping valve has been
rebuilt and all bolts in the wet well replaced
with stainless steel bolts in 2002.
• New EIectric Controls for Recycle Pump No. 1
telescoping valve in 2004.
• Replacement of the valve connecting the WAS
and RAS wet wells in 1999.
• Replacement of WAS wet well valve operators Figure 6 - WAS Control Panels
and shafts in 2000.
Disinfection
Secondary effluent wastewater is disinfected using a gaseous chlorination system. The
WWTP utilizes a one (1) ton chlorine gas cylinder with a 150 lbs chlorine gas cylinder as a
CLTIFINAL DRAFT TM202.000
4

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
indicated that no floor drains were installed and water would pool in front of the control
panels.
Biological Treatment
Suspended growth biological treatment is performed in two (2) 2.6 MG aeration basins
utilizing 2-speed mechanical platform mounted aerators. Return activated sludge screens
are located at the north end of the east aeration basin. The screens were originally installed
to remove textile fibers from the wastewater prior to entering the aeration basins. The
screens are no longer in use, two have been removed and two are scheduled to be removed
this year.
The two aeration basins are concrete lined and r'
provide a 24 hour detention time at a design
flow of 5.2 mgd. Mixing and aeration are
performed within each basin utilizing four (4) Figure 3 Aeration Basins
US Motor, low speed, platform mounted
submerged mechanical aerators. The units are
driven via two speed 100/45-hp motors. The units are rated to deliver 3.2 lbs of oxygen per
hp -hour (SOTR basis). All of the aerators in operation are approximately 20 years old. In
1999, utilities staff replaced Aerator #3 with their spare unit and currently no spare is
available onsite. Utilities staff indicated that they could not operate the last aerator in each
basin at full speed due to floc shear which increases effluent turbidity and solids. Staff also
indicated that they wished to continue using the mechanical aerators and had developed a
program to replace one of the mechanical aerators (motor, gearbox and mixer) per year over
the next eight (8) years at a cost of approximately $65-70,000 per year. In addition, staff
wished to install VFDs and DO control on the aerators for more flexible operation. Finally,
the utilities staff indicated that they did not have a way to measure the volume of influent
flow or RAS flow split between the east and west aeration basins. The existing RAS system
consists of a valve on the discharge line to each aeration basin to allow the RAS flow to be
manually balanced. Utilities staff indicated that RAS flow measurement to the individual
aeration basins is desired. In addition, utilities staff indicated that they could not take a
basin offline without a major effort due to broken drain valves and old influent valves.
SedimentationlClarification
Mixed liquor from the aeration basins is clarified in
two 92-ft diameter, 13-ft SWD Envirex circular
clarifiers. The clarifiers are designed for an
overflow rate of 400 gpd/sf and a 6 hour detention
time at a design flow rate of 5.2 mgd. The clarifier
mechanisms are driven with 0.5hp, 1700 rpm,
230V/60Hz/3-phase SEW Eurodrive Inc. drive
systems. Utilities staff indicated that the drives for
the clarifiers were replaced in 2001 and 2002 and the
weirs were laser leveled in 2002, but need to be
replaced. Staff also indicated that the floors need to
be regrouted and the scraper system would likely
CLTIFINAL DRAFT TM202.DOC
Figure 4 - Secondary Clarifiers
3

DRAFT
ROCKY RIVER WWTP EXISTING FACILITIES ASSESSMENT
Flow enters the facility via a 42-inch sewer and flows through a manually cleaned coarse bar
screen. A 24" sidestream collector pipe also enters at the same location. A stop gate allows
for bypass around the screen if necessary. Materials removed from the manual screen are
placed in a barrel located nearby. A hoist, installed in 2004, lifts the barrel out of the
influent chamber for disposal in a dumpster located adjacent to the structure. The hoist and
screens both appear to be in good condition. Flooding of this low area from the receiving
stream has not created problems but should be considered when placing equipment in this
location.
Influent pumping utilizes three (3) enclosed Archimedian screw pumps manufactured by
Dodge Maxum. Each pump has a rated capacity of 6.5 MGD, for a firm pumping capacity
of 13 mgd and a total influent pumping capacity of 19.5 mgd. Each pump is driven by a 50-
hp motor. The pumps appear to be in good condition during the visit and utilities staff did
not indicate any problems with the pumps.
Pumped influent flow proceeds to two (2)
Parkson Bioguard mechanical bar screens. Each
screen is rated at 13.25 mgd. The screens operate
utilizing a differential pressure transmitter to
start and stop the mechanical screen. A 3-hp
and 0.5-hp motor operate each screen.
Screenings are transported to a nearby dumpster
via a conveyor driven by a 2-hp motor. The
screens were in good condition and utilities staff
were happy with their operation.
Screened influent flow is measured utilising, an ultrasonic level transmitter, a Parshall
flume and a Millitronics OCM III flow meter. The meter and flume are able to measure flow
between 1 and 13 mgd. While the system is in good condition, utilities staff indicated that
on a couple occasions, flow exceeded the measurement range. Utilities staff would like a
meter capable of measuring higher flows.
Prior to flow measurement, the pH of the screened flow is measured and caustic is fed to
increase the pH. The 50% Sodium Hydroxide (caustic) solution is stored in a 5,400 gallon
tank located adjacent to the Headworks Control Building. Two (2) Encore 700 Series 44
diaphragm metering pumps transfer the caustic solution from the storage tank to the
injection point just upstream of the Parshall flume to raise the pH to approximately 7. The
caustic storage tank and the chemical tubing utilize insulation and heat tracing to prevent
the solution from crystallizing. Drums of caustic are stored onsite for temporary addition in
the event that the feed system fails. Utilities staff indicated that they were happy with the
feed system and did not wish to investigate operating with lime or magnesium hydroxide.
The caustic tank, metering pumps and piping all appeared to be in good condition. The
utilities staff also indicated that they manually add two bags per day for 7 days of
powdered activated carbon to the influent flow starting on the first Thursday of every
month and do not wish to automate the carbon addition.
Figure 2 - Headworks
Control panels for all the headworks equipment and the caustic feed pumps are located in
the Headworks Control Building. The structure was built as part of the 2002 Headworks
Renovation. The structure appeared to be in good condition; however utilities staff
CLT/FINAL DRAFT TM202.DOC 2

DRAFT TECHNICAL MEMORANDUM 202 CH2MHILL
Rocky River WWTP Existing Facilities Assessment
PREPARED FOR: Town of Mooresville, NC
PREPARED BY: CH2M HILL
DATE: August 30, 2005
This technical memorandum (TM) summarizes Task 202, Existing Facilities Assessment for
the Rocky River Wastewater Treatment Plant (WWTP) Expansion Project. Assessment of
the existing facility was developed in conjunction with data obtained from the Town and a
plant tour on June 22, 2005.
The memo is organized as follows:
• Condition Assessment
• Headworks
• Biological Treatment
• Sedimentation/Clarification
• RAS/WAS Pumping Systems
• Disinfection
• Sludge Processing
• Plant Water Systems
• Emergency Power/Electrical
Systems
• SCADA
• Administration Building
Condition Assessment
Figure 1- Mooresville Rocky River WWTP
A plant tour was conducted on June 22, 2005 at the Rocky River WWTP with utilities staff.
The following sections summarize the treatment process and assessment. Major facilities
and equipment are summarized in Appendix A.
Headworks
Headworks equipment at the WWTP consists of influent pumping, solids screening, flow
measurement, and caustic addition. The influent pumping system and the screening were
both recently upgraded in a 2002 Headworks Renovation. Utilities staff indicated that if the
Headworks were to be upgraded as part of the plant expansion, they would like to have grit
chambers.
Influent samples are taken prior to influent pumping. The sampler is located in a sample
building adjacent to the headworks facility. Flow proportioned samples are taken using an
ISCO 3710FR. The building and sampler both appear to be good condition.
CLT/FINAL DRAFT TM202.DOC 1

ROCKY RIVER WWTP - DESIGN WASTEWATER FLOWS, LOADS AND CHARACTERIZATION
Flow and Load Projections
Flow (mgd)
16.5
19.0
23.6
57.3
76.0
cBOD (lb/day)
39,408
51,231
73,694
107,585
—
TSS (1b/day)
42,440
54,323
85,728
224,931
—
TKN (1b/day)
5,439
5,656
6,907
10,660
—
NH3-N (lb/day)
3,541
3,683
4,497
6,941
—
Total P (lb/day)
845
878
1,073
1,656
—
Alkalinity (lb/day)
27,558
31,692
39,408
95,627
—
Note: Alkalinity input data estimated at 200 mg/L.
Table 19. Design Basis of Existing Plant (1986
Parameter
Avg Day
Max Month
Max Week
Max Day
Peak Hour
Flow (mgd)
5.2
—
—
—
13.0
BOD (lb/day)
10,850
—
—
—
1,085
TSS (lb/day)
8,680
—
—
—
725
TKN (lb/day)
1,040
—
—
—
—
NH3-N (lb/ day)
—
—
—
—
—
Total P (lb/day)
—
—
—
—
—
Note: "--" indicates no basis of design was provided.
CLT/FINAL DRAFT3 TM201.DOC 18