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ATTACHMENT 1 GENERAL FACILITY INFORMATION Fourche Creek Wastewater Treatment Plant 1.

Facility Name: Activated Sludge Wastewater Treatment Plant

2. Type of Facility: 3.

Population Served: Present:

_18 _ 7. .,.!-4 _ 5_

______ _

Design:

187 ,452

4. Flow: Average Maximum Peak

Present

Design

10.25MGD

12MGD

13.61 MGD

24MGD

32.83MGD

52MGD

5. Water Quality: Assumed

D

Actual

�

Source: Plant Data Jan 1998 - April 2009 Effluent:

Influent: BOD5

166

m

l

12.3

TSS

182

mgll

10.0

NH 3-N

14.5

mg/l

mg/l

m II

I 19.1

mg/f

Basis for Assumptions, if made:

6.

Is the system above the 1DO-year flood plain?

7.

List Treatment System: a.

�

No

D

Existing: 1

b.

Yes

.

Screening

2.

Grit Removal

3.

Primary Clarification

4.

Aeration

5. 6. .. 7.

Secondary Clarification Chlorine Disinfection Dechlorination

8.

Anaerobic Sludge Digestion

5.

Secondary Clarification

Proposed: 1.

Screening

2.

Grit Removal

6.

Chlorine Disinfection

3.

Primary Clarification

7.

Dechlorination

4.

Aeration

8.

Anaerobic Sludge Digestion

ATTACHMENT 7 CLARlFIERS 1. Type: Circular Secondary 2.

Number of Tanks: 1

3. Surface Dimensions (ft): Width

__

Length

__

4.

Sidewall Depth: 19.58 ft

5.

Detention Period (minutes): At design flow 346

6.

Diameter 1 70

At peak flow 80

2 Overflow Rate (gpd/ft ): At design flow 1200 At peak flow 52MOD (27MOD in New C larifier)

7.

2 Surface Area: 22,698 ft

Little Rock Wastewater: Fourche Creek Wastewater Treatment Plant Improvements, Schedule 2

-

Secondary Clarification - Design Calculations Prepared by: Aaron Benzing, P.E. - Camp Dresser & McKee, Inc. (COM) The following design calculations are provided to demonstrate conformity with the 2004 Edition of the Recommended Standards for Wastewater Facilities (Ten States Standards). These design calculations also highlight areas where the design may deviate from the Standards and provide the necessary justification.

Design Criteria • • • • • • • • •

Plant Minimum Flow - 4 MOD Plant Average Flow - 12 MOD Plant Maximum Month Flow - 24 MOD Plant Peak Day flow - 36 MOD Plant Peak Hour Flow - 36 MOD Plant Future Peak Hour Flow - 52 MOD Non-Potable Water System Peak Flow - 1 MOD Proposed Clarifier Average Day Flow - 6.5 MOD Proposed Clarifier Peak Hour Flow - 27 MGD

Secondary Clarification • • • • • • • •

Minimum Side Water Depth - 12 ft 2 Maximum Surface Overflow Rate at Design Peak Hour Flow - 1,200 gpdlft 2 Peak Solids Loading Rate - 50 Ib/day/ft Minimum Freeboard - 2 ft Average MLSS = 3,000 ppm Average Recycle Rate - 33% (4 MGD) Maximum Recycle Rate - 150% ( 18 MGD) Waste Sludge Pump Capacity - 25% (3 MOD)

CDM ------

Page 1

Fourche Creek WWTP Design Calculations

CHAPTER 70 Section 72

-

-

SETTLING

DESIGN CONSIDERATIONS

Section 72.1 - Dimensions The length of flow from the inlet to the outlet is approximately 80 feet. The vertical side water depth is designed to be a minimum of 17 feet.

Section 72.232 - Surface Overflow Rates: Final Settling Tanks - Activated Sludge The Fourche Creek WWTP utilizes the step feed and stabilization variations of the activated sludge process. The maximum surface overflow rate at the proposed clarifiers design 2 2 peak hourly flow of 27 MGD is 1,200 gpdlft . The peak solids loading rate is 37 Ib/day/ft .

Section 72.3 -Inlet Structures The proposed clarifier was designed with a energy dissipating inlet (EDI) with a maximum inlet velocity of 1.5 ftlsec. Openings are included at the top of the EDI to prevent scum and floatable materials from accumulating inside the ring.

Section 72.4 72.41

-

Weirs

General

The overflow weirs have been designed with 4 inches of adjustment to allow for correction if required due to differential settling of the tank. This is twice the typical allowance for circular clarifier weirs. The additional adjustment capability was included due to the large size of the proposed clarifier. 72.42

Location

The secondary effluent weirs are located on the clarifier's periphery. They are located approximately 3 feet from the clarifier wall. 72.43

Design Rates

The design weir loading rate at the design peak hourly flow of 27 MGD is approximately 52,400 gpdllinear ft. It is CDM's position that weir loading rates have no bearing on the performance of a properly designed clarifier. When a clarifier is designed properly, settleable solids have been removed prior to the weir so velocity over the weir does not present a risk of drawing solids out of the tank. In addition, a Stamford Baffle is included in the design of this clarifier to further minimize the possibility of solids carryover. The function of the weir in the proposed clarifier design is to minimize short circuiting by evenly distributing the flow across the entire clarifier. 72.44

Weir Troughs

The weir troughs have been designed to prevent submergence at the peak hourly design flow assuming a 100 year storm level on the plant's receiving stream (Arkansas River).

CONI

Page 2

Fourche Creek WWTP Design Calculations

Section 72.6

-

Unit Dewatering

The proposed clarifier is designed to be dewatered using the proposed RAS Pumps.

Section 72.6

-

Freeboard

The proposed clarifier is designed with a minimum freeboard of 2.5 feet.

Section 73 Section 73.1

-

-

SLUDGE AND SCUM REMOVAL Scum Removal

A full surface scum collection system is included in the design of this clarifier. The scum will be pumped to the plant's anaerobic digesters for treatment.

Section 73.2

-

Sludge Removal

Mechanical sludge collection and removal systems are included in the design of this clarifier. Sludge withdrawal rates are set for an average flow of 4 MGD and a peak flow of 18 MGD. The sludge withdrawal line is designed to have a maximum velocity of less than 3 fUsee to minimize shearing of the floc.

73.21

Sludge Hopper

The proposed clarifier is designed with a sludge withdrawal ring in lieu of a traditional sludge hopper. The purpose of the ring is to minimize short circuiting of mixed liquor through the clarifier allowing the solids to be removed with a higher percent solids concentration.

73.23

Sludge Removal Pipeline

Per standard design practice, the sludge withdrawal line is designed to have a maximum velocity of less than 3 fUsee to minimize shearing of the floc.

73.24

Sludge Removal Control

The sludge withdrawal rate will be controlled by the proposed variable speed RAS pumps. Magnetic flow meters are included in the design to provide a means of measuring the sludge removal rate.

Section 92 Section 92.4 92.41

-

-

BIOLOGICAL TREATMENT Return Sludge Equipment

Return Sludge Rate

The design minimum return sludge rate is 33% of the plant's design average flow. The design maximum return sludge rate is 150% of the plant's design average flow. The rate of sludge return will be varied by the operators by means of the proposed variable speed RAS pumps.

92.42

Return Sludge Pumps

Page 3

Fourche Creek WWTP Design Calculations

All three of the proposed RAS pumps have the same capacity. The maximum return sludge capacity ( 18 MGD) can be obtained with one pump out of service. A positive head (or submerged suction condition) is provided for the R AS pumps. The pumps have 24" suction and discharge connections. 92.43

Return Sludge Piping

The RAS discharge piping is 24 inches in diameter and is designed to maintain a velocity in the range of 2 - 5 ftlsec. Devices are included to allow for sampling of the R AS. 92.44

Waste Sludge Facilities

The waste sludge pumps are designed with a capacity of 25% of the plant's average daily flow and with adequate turn down capacity. The waste sludge flow will be controlled by variable speed submerged suction pumps and measured by magnetic flow meters. Sludge will be wasted to the plant's anaerobic digesters for additional treatment.

CDM

Page 4

ICDM

Job #: 8521-64020 Client:Little Rock Wastewater CHK By/Date: Sun 03/18/09 Project:Fourche Creek Hydraulic Upgrade RVW By/Date: Keenan/03/06/09 Detail:Existing Secondary Clarifiers

Calc By: Benzing Date: March 2. 2009 Calc #: _______

Secondary Clarifier Design Fourche Creek WWTP 1.0 Purpose/Objective Perform calculations necessary to design the new circular secondary clarifier for the Fourche Creek WWTP in Little Rock, AR

2.0 Procedure I. Calculate acceptable surface overflow rates 2. Calculate minimum required surface area and clarifier diameter 3. Size Energy Dissipating Inlet 4. Size Flocculating Feed Well 5. Calculate Weir Loading Rate 6. Calculate Solids Loading Rate

3.0 ReferencesjData Sources Recommended Standards for Wastewater Facilities (2004 Ed.) - Chapter 70 Flow Data -Fourche Creek WWTP International Water Association (lAW)

4.0 Assumptions Includes: •

Design Peak Day Flow

•

Average Day Flow

•

15% Increase in Surface Overflow Rate Allowance Due to Clarifier Optimization Features

•

Acceptable Surface Overflow Rate

=

=

27 MGD

6.5 MGD

=

Average Flow -50 gpd/ft2 x side water depth x 1.15 Max Month Flow -70 gpd/ft2 x side water depth x 1.15 Peak Day Flow -100 gpd/ft2 x (side water depth -1) x 1.15 •

Average MLSS

•

Peak Solids Loading Rate

•

Peak Weir Loading Rate (Peak design hourly flow)

•

=

3,000 mg/i, 50% Recycle Rate at Peak Flow =

50 lb/day/ft2 (from 10-States Standards) =

30,000 gpd/lin ft (Ten States)

Circular Clarifier with EDI & Flocculating Feed Well. Center feed, periferal draw, inboard launders.

•

MLmax

•

Center Column Velocity

•

Velocity at exit ports < 1.5 ft/sec, HRT in ED! approx 10 seconds

•

=

Peak Day

+

100% Average Day (RAS). MLavg <

2.5 ft/sec @ Q max and

<

=

Qavg + 50% Qavg

1 ft/sec @ Q average

Flocculation Feed Well Vertical Velocity < 2.5 ft/sec @ Q max and Feed Well Horizontal Velocity

MathCAD V14 P:\8521 - LRWU\64020 - FCWWTP Hydraulic

=

<

1 ft/sec @ Q average,

90% of Vertical Velocity

Saved 8/27/200910:13 AM

Page 1

ICOM

Calc By: Benzing Date: March 2, 2009 Calc #:. _______

Job #: 8521-64020 Client Little Rock Wastewater CHK By/Date: Sun 03/18/09 Project:Fourche Creek Hydraulic Upgrade RVW By/Date: Keenan/03/06/09 Detail:Existing Secondary Clarifiers

5.0 Calculations Peak Day & Hour Flow Max Month Flow

==

Qpd:=

=

Qmm

Average Day Flow =

27 mgd

:==15 mgd

Qavg :==

gal gpd==­ day

1

ppm

==

6,5 mgd

1000000

Calculate Acceptable Surface Overflow Rates:

Side Water Depth =

SWD:==

17 gpd

Surface Overflow Rate at Average Day =

SORavg :=

50 2 ft

Surface Overflow Rate at Max Month =

SORmm :==

70

Surface Overflow Rate at Peak Day

SORpd :==

==

Surface Overflow Rate at Peak Hour per Ten States =

SWD •

1,15

•

SWD •

1,15 == 1368.

gpd

2 ft

Qavg

Aavg :=

SORavg

Max Month =

Amm:=

Peak Day

Apd:=

=

Peak Hour (10 States) =

Qmm SORmm Qpd

SORpd

�:==

=

2 6649,6164ft

=

10961ft

==14674ft Qpd

--'--

SORph

=

2

SORph :=

1200

2 22500ft Diameter

:

avg

=

4. mm Pd

4•

Pd

4•

=

2 ft gpd

1840. 2 ft

2

J : J : J : J

Diameter =

==

gpd

gpd

4•

Diameter =

Diameter =

2

978.2 ft

gpd

Calculate Minimum Surface Area: ==

==

100 - .(SWD -1) .1,15 2 ft

ft

Average Day

gpd

•

92ft

== 118ft

=

137 ft

==

169 ft

Set Clarifier Diameter at 170 ft based on Peak Hour SOR at 1200 gpd/ft2 Clarifier Diameter

=

D

:=

Clarifier Area

170ft

=

At :=

n.D

2

4

==

22698 ft

2

Calculate Diameter of Center Column: MLmax

:==

Qpd + Qavg

== 34 • mgd

MLavg

4.

:==

Qavg +

,5

•

Qavg ==

10 • mgd

MLmax

2.5 � Minimium Diameter at Peak:

MathCAD V14 P:18521 - LRWUI64020 - FCWWTP Hydraulic

Dp :==

sec

�

Saved 8/27/200910:13 AM

==61.7.in

Page 2

CDM

Job #: 8521-64020 Client Little Rock Wastewater CHK By/Date: Sun 03/18/09 ProjectFourche Creek Hydraulic Upgrade RVW BylDate: Keenan/03/06/09 Detail:Existing Secondary Clarifiers

4-

Calc By: Benzing Date: March 2, 2009 Calc #: _______

MLavg

ft

1-

Da

Minimium Diameter at Average:

Say minimum center column diameter Use 6 exit ports, max exit velocity

=

=

:=

sec

"IJ

=

52,6 - in

62 in

1.5 ftlsec:

Port Area

MLmax =

ft

2

= 5,8ft

1,5--6 sec

Size ports as 22-in wide by 38-in tall, set top of ports at 3" above max water level Calculate Pertinent Dimensions of EDI:

Set diameter of EDI at approximatly 10% of clarifier diameter or 17ft Calculate minimum depth of ED!:

Set depth of EDI at 41 in. Set top of EDI at 3" above max water level Assume 12 exit ports, velocity at exit ports < 1.5 ftlsec at peak flow

__M_L_m_a_x_

Calculate minimum ED! port area:

ft

= 2

1 5- -12 , sec

2

ft ,9

Size ports as 16-in wide by 28-in tall, set top of ports at 3" above max water level Calculate Size of Flocculation Feed Well:

Calculate minimium diameter of Feed Well: 4-

MLmax

4-

min

=

min

39,8ft

----

Set diameter of Flocculation Feed Well at:

Vvmax

MLmax

ft

:= ...----�

7T

_

(FFd)

2

ft

1,5-

2,5� ----

MLavg

= 1.6 ---

min

:=

4

MathCAD V14 P:18521 - LRWU\64020 - FCWWTP Hydraulic

27,7ft

:= 50ft

FFd

Vvavg

=

MLavg .,..----_

7T

_

2 (FFd)

= 0.46 -

ft --

min

4

Saved 8/27/200910:13 AM

Page 3

Job #: 8521-64020 Client Little Rock Wastewater CHK BylDate: Sun 03/18/09 Project Fourche Creek Hydraulic Upgrade RVW By/Date: Keenan/03/06/09 Detail:Existing Secondary Clarifiers

Calc By: Benzing Date: March 2, 2009 Calc #:

_ ______

o

------

l

tVv

------------

. .

d

_ . __.,'

Vh

Q/A Q/(u· At Qmax: Vh Q/lu

At Qavg: Vh

=

D

=

=

At Qavg, d

I_f-

•

D

• •

d) (d 2.5)]

ft .9.1,5-,

=

0.9

VV

-

MLavg

=

Horizontal Velocity (Vh)

-=---

----

=

, ft 43

min

At Qrnax, d

MLmax

=

ft ,9.2.5-,

+

2.5ft

=

11 ,3ft

min

Set Depth of Flocculation Feed Well at 5 ft - 8 in Set Clarifier Side Water Depth at 17ft Calculate Size of Effluent Launder:

MathCAD V14 P:\8521 - LRWU\64020 - FCWWTP Hydraulic

Saved 8/27/200910:13 AM

Page 4

lalM

Job #: 8521-64020

Client Little Rock Wastewater

Calc By: Benzing Date: March 2. 2009

CHK BylDate: Sun 03/18/09 Project Fourche Creek Hydraulic Upgrade RVW BylDate: Keenan/03/06/09 Detail:Existing Secondary Clar,ifiers

Calc #: ______

Effluent 'launder Serves as Density Current Baffle Baffle Width =18" + (Clarl. D' - 30') x 0.2"

Example:

Clarifier Diameter = 100Ft Density Current Baffle Width = 18" + (100 - 30) x 0.2" = 32"

Baffle Width =

18in + (170 - 30) • 0.2in = 46

•

in

Calculate Weir Loading Rate: Weir Length =

WL:= 1\. [170ft - (36in

Weir Loading Rate =

Qpd --

WL

=

52405.

•

2)]

gpd -

ft

=

515 ft .

> 30,000 gpd/lm ft Suggested by 10 States

Calculate Solids Loading Rate (Peak Day Flow): Assume MLSS = 3,000 mg/I, 100% Avg Day RAS:

Ib

8.34-. (MLmax). 3000ppm gal

At

< 50 Ib/sf x day Max Required by 10 States _

_

2 ft . day

6.0 ConclusionsjResults I.

Side Water Depth = 17-ft

2.

Clarifier Diameter = 170-ft

3.

Center Column Diameter = 62-in

4.

Use 6 Center Column Exits 22-in Wide x 38-in Tall, Set Top of Ports 3" above Max Water Level

5.

Use 17 ft Diameter EOI, 41-in deep. Set Top of EDI 3-in Above Max Water Level. Use 12 EDI

6.

Use a 50-ft Diameter Flocculation Feed Well, 5 ft - 8 in Deep.

7.

Use 46-in Wide Effluent Launder

Exit Ports, 16-in Wide by 12-in Tall.

MathCAD V14 P:18521 - LRWUI64020 - FCWWTP Hydraulic

Saved 8/27/200910:13 AM

Page 5