NC0037371_Authorization to Construct_19990819

NPDES DOCUMENT SCANNING COVER :SHEET
NPDES Permit:
NC0037371
North Iredell High School WWTP
Document Type:
Permit Issuance
Wasteload Allocation
1 }
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Document Date:
August 19, 1999
This document is printed on reuse paper - ignore any
content on the reYerse side

State of North Carolina
Department of Environment
and Natural Resources
Division of Water Quality
James B. Hunt, Jr., Governor
Wayne McDevitt, Secretary
Kerr T. Stevens, Director
August 19, 1999
Don Atkinson
Construction Manager
Iredell-Statesville Schools
P.O. Box 911
Statesville, NC 28677
Avi"'cirA
NCDENR
Subject: Authorization to Construct
Permit No. NC0037371
ATC No. 037371ACB
North High School WWTP
Iredell County
Dear Mr. Atkinson:
The Division received a letter of request for an Authorization to Construct (ATC) June 25, 1999 and final
plans and specifications for this project have been reviewed and found to be satisfactory. Authorization is hereby
granted for the construction/ alteration of the wastewater treatment facility discharging into Patterson Creek in
the Yadkin -Pee Dee River Basin. The wastewater treatment plant serves the North High School and is permitted
at a flow of 0.0125 MGD (monthly average); this authorization to construct permit does not alter the currently
permitted flow of 0.0125 MGD. The permit allows the following:
• alterations to the existing flow distribution box in the equalization basin;
• installation of new return activated sludge pumps (2, lh Hp submersible pumps at 9-10 gpm) along with
piping modifications,
• installation of a tertiary filtration system (2 cells at 16" x 16" each, with 2 feed pumps and 1 backup rated
at 7.3 gpm each),
and all associated piping and appurtenances.
After completion of construction, access to the treatment site and equipment must be restricted (via a fence
or other means, ref 15A NCAC 2H .0219).
Once construction under this ATC has been completed and an Engineer's Certificate has been submitted,
the permittee is authorized to operate with the above approved design components. At no time shall flow exceed
the permit limit of 0.0125 MGD (unless approved by the Division).
This Authorization to Construct is issued in accordance with Part III, Paragraph A of NPDES Permit No.
NC0037371 issued August 31, 1994, and shall be subject to revocation unless the wastewater treatment facilities
are constructed in accordance with the conditions and limitations specified in the permit.
1617 Mail Service Center, Raleigh, North Carolina 27699-1617 Telephone [phone]/FAX [phone]
An Equal Opportunity Affirmative Action Employer [e-mail]

Permit No. NC0037371
ATC No. 037371ACB
North Iredell High School WWTP
The sludge generated from the treatment facility must be disposed of in accordance with G.S. 143-215.1
and in a manner approved by the North Carolina Division of Water Quality.
In the event that the facility fails to perform satisfactorily, including the creation of nuisance conditions,
the Permittee shall take immediate corrective action, including those as may be required by this Division, such as
the construction of additional or replacement wastewater treatment or disposal facilities.
The Mooresville Regional Office, telephone number (704) 663 - 1699, shall be notified at least forty-
eight (48) hours in advance of operation of the installed facilities so that an in -place inspection can be made.
Such notification to the regional supervisor shall be made during the normal office hours from 8:00 a.m. until
5:00 p.m. on Monday through Friday, excluding State Holidays.
Upon classification of the facility by the Certification Commission, the Permittee shall employ a certified
water pollution control treatment system operator to be in responsible charge (ORC) of the water pollution
control treatment system. The operator must hold a certificate of the type and grade at least equivalent to or
greater than the classification assigned to the water pollution control treatment system by the Certification
Commission. The Permittee must also employ a certified back-up operator of the appropriate type and grade to
comply with the conditions of Title 15A, Chapter 8G, .0202. The ORC of the facility must visit each Class I
facility at least weekly and each Class II, III, and IV facility at least daily, excluding weekends and holidays, and
must properly manage and document daily operation and maintenance of the facility and must comply with all
other conditions outlined in Title 15A, Chapter 8G, .0204. Once the facility is classified, the Permittee must
submit a letter to the Certification Commission which designates the operator in responsible charge within: (A)
Sixty calendar days prior to wastewater being introduced into a new system or (B) within 120 calendar days of
the following, (i) after receiving notification of a change in the classification of the system requiring the
designation of a new ORC and back-up ORC or (ii) a vacancy in the position of ORC or back-up ORC.
A copy of the approved plans and specifications shall be maintained on file by the Permittee for the life
of the facility.
The Operational Agreement between the Permittee and the Environmental Management Commission is
incorporated herein by reference and is a condition of this Permit. Noncompliance with the terms of the
Operational Agreement shall subject the Permittee to all sanctions provided by G. S. 143-215.6 for violation of or
failure to act in accordance with the terms and conditions of this Permit.
Failure to abide by the requirements contained in this Authorization to Construct may subject the
Permittee to an enforcement action by the Division of Water Quality in accordance with North Carolina General
Statute 143-215.6A to 143-215.6C.
The issuance of this Authorization to Construct does not preclude the Permittee from complying with any
and all statutes, rules, regulations, or ordinances which may be imposed by other government agencies (local,
state, and federal) which have jurisdiction.
Upon completion of construction and prior to operation of this permitted facility, a certification must be
received from a professional engineer certifying that the permitted facility has been installed in accordance with
the NPDES Permit, this Authorization to Construct and the approved plans and specifications. Mail the
Certification to the NPDES Unit, 1617 Mail Service Center, Raleigh, NC 27699-1617.

Permit No. NC0037371
ATC No. 037371ACB
North Iredell High School WWTP
One (1) set of approved plans and specifications is being forwarded to you. If you have any questions or
need additional information, please contact Ms. Susan A. Wilson, telephone number [phone], extension
510.
Sincerely,
51,j4,;"....4,
f-,/
Kerr T. Stevens
cc: Central Files
NPDES Unit, Permit File
Technical Assistance and Certification Unit
Mooresville Regional Office, Water Quality/ Rex Gleason
Ivan Cooper, P.E. Cooper Environmental, Inc.
2300 Sardis Road North, Suite Q
Charlotte, NC 28227

MRO Staff Report — (ATC for N.High School WWTP)
SOC PRIORITY PROJECT: Yes
If yes, SOC No. EMC 98-011
To: Permits and Engineering Unit
Water Quality Section
Attention: Ms. Susan Wilson
Date: August 12, 1999
AUTHORIZATION TO CONSTRUCT
NPDES PERMIT
REPORT AND RECOMMENDATIONS
County: Iredell
MRO No.: 99-117
Permit No. NC0037371
PART I - GENERAL INFORMATION
Page 1 of 4
1. Facility and Address: North Iredell High School WWTP
c/o Iredell-Statesville Schools
Mailing Address Physical Address
P.O. Box 911 NCSR 1953
Statesville, NC 28677 Iredell County
2. Date of On -Site Investigation: July 30, 1999
3. Report Prepared By: Charley Schwartz, Environmental Engineer I
4. Persons Contacted and Telephone Number: Art Condren, Project Manager from Cooper
Environmental [phone]; Mike James, Iredell-Statesville Schools [phone]
5. Verified Discharge Point(s), List for All Discharge Points:
Latitude: 35 ° 55' 30" Longitude: 80° 52' 00"
Attach a USGS map extract and indicate treatment facility site and discharge point on
map.
USGS Quad No.: D 15 NE USGS Quad Name: Harmony, NC
6. Site size and expansion area consistent with application? Yes
7. Topography (relationship to flood plain included): Gently rolling with moderate slopes.
The facility does not appear to be located in a flood plain

MRO Staff Report — (ATC for N.High School WWTP)
Page 2 of 4
8. Location of Nearest Dwelling: No dwellings are located within 500 feet of the site.
PART II - DESCRIPTION OF DISCHARGE AND TREATMENT WORKS
1. Existing Treatment Facility
a. Volume of Wastewater (Actual Flow from DMRs): 0.0045 MGD
b. What is the current permitted capacity: 0.0125 MGD
c. Current design capacity: 0.0125 MGD
d. Date(s) and construction activities allowed by previous ATCs issued in the
previous two years: No ATCs or modifications to the WWTP in last two years.
e. Description of existing or substantially constructed WWT facilities: The existing
WWT facilities consist of a bar screen, 8,700-gallon flow equalization basin,
12,000-gallon aeration basin, 2,250-gallon clarifier, aerated sludge holding tank,
tablet chlorination/dechlorination, polymer addition (not in use), and effluent flow
meter with chart. 3 irEtr. Fm9Q1414r5 (1.3 CM
2 Tar- Frc ..5 (i6 x 6,.-� 4- .4 cPm/Pr - caau+) O
2. Type of Proposed Treatment Facility: The applicant proposes to change the piping and fors pups
flow distribution box in the equalization basin, replace the existing return activated 9 - (0 you
sludge pumps and piping, and design a tertiary filtration system.
A4,
3. Residuals Handling and Utilization/Disposal Scheme: a(rif
sti
a. Land applied, DWQ Permit No.: N/A
b. Residuals Stabilization: N/A
c. Landfill:
d. Other disposal/utilization scheme: Excess sludge is either removed by AAA
Enterprises, Inc. and disposed under Division of Solid Waste Management Permit
No. NCS00146 or is taken to a Charlotte-Mecklenberg Utility Department WWTP
for disposal.
4. Treatment Plant Classification: Class 2 (new rating sheet attached).
5. SIC Code(s): 8211 Wastewater Code(s): 03 Main Treatment Unit Code: 06017
6. Important SOC/JOC or Compliance Schedule Dates: N/A
Submission of Plans and Specifications — June 11, 1999 (Met)
Begin Construction — September 17, 1999
Complete construction — January 4, 2000
7. Alternative Analysis Evaluation
a. Spray Irrigation: Insufficient area available

MRO Staff Report — (ATC for N.High School WWTP)
b. Connect to regional sewer system: None available
c. Subsurface: Insufficient area available
d. Other disposal options: N/A
PART III - EVALUATION AND RECOMMENDATIONS
Page 3 of 4
The permittee has entered into an SOC agreement with the DWQ which requires
modification of the existing WWTP. Modification of the existing WWTP appears to be
necessitated due to the poor treatment history of the system. The facility violated the permitted
BOD5 limit four of the last eight months. The facility also exceeded permit limits for TSS, Fecal
Coliform, and pH within the previous 12 months.
Upon review of the facility's file and the ATC application, this Office identified a few
elements (both operational' and equipment elements) that required consideration during the
redesign process. These elements are described below, and the permittee's solution to the
element is presented in italics.
Influent Management — One of the main problems with school WWTPs is managing the
influent wastewater. School influent flow is defined by spikes of high flow and prolonged
periods of no flow. This flow must be contained and passed through the treatment plant in a
controlled manner. In addition, school staff may place substances into the wastewater which
increases the potency (BOD5) of the influent, introduces toxic compounds or otherwise
diminishes the treatment efficiency of the plant (i.e. ammonia cleaners, bleach, oil and grease,
etc.).
A flow equalization basin is a part of the existing treatment system. The basin is capable
of holding nearly two days of influent wastewater at the current flow rate. The equalization
basin does allow for the influent to be collected and released into the aeration basin at a
controlled rate. The permittee has proposed changes to the distribution box from the
equalization basin to the aeration basin to ensure a more controlled flow rate. The permittee is
also organizing an operations manual for employees to ensure that toxic and/or nuisance
substances are not placed into the collection system.
Extended No Influent Flow Periods - The school usually produces little if any
wastewater during weekends and holidays. Without a source of food for extended periods, the
bugs within the treatment system may become unhealthy and die.
The aeration basin and clarifier have detention times of 60 hours and 11 hours
respectively at the current flow rate (almost 3 days of detention total). The prolonged detention
time should minimize the effects of little or no flow during 2, 3 or 4 day weekends and holidays.
For more extended holidays, the permittee has proposed to feed the bugs periodically with a
mixture of glucose, slimfast and fertilizer (36 Nitrogen, 6 Phosphorous, 6 Potassium formula).
This should help maintain the bug population by supplying food and appropriate nutrients. The
permittee has outlined these procedures within the operations manual for the plant. In addition,
the permittee has outlined the process of sustaining and rebuilding a bug population prior to the
start of school (after an extended holiday with low flow).

MRO Staff Report — (ATC for N.High School WWTP)
Page 4 of 4
Return Activated Sludge (RAS) Pumps - The minimum achievable pumping rate of
the existing RAS pumps is 60 gpm which is nearly 20 times the current flow rate through the
plant. As a result, it is difficult for a properly thickened sludge blanket to form at the bottom of
the clarifier, and the MLSS levels are high in the aeration basin and clarifier. These conditions
lead to unhealthy bugs in the aeration basin (Food to micro-organism ratio (F/M) is too low), and
limited filtration and/or digestion within the clarifier (Poor sludge blanket). As a result, BOD5
levels remain high and TSS levels may exceed permitted limits.
The permittee has proposed to replace the existing RAS pumps with two smaller pumps
capable of a pumping rate of 9-10 gpm. This should allow for a more suitable sludge blanket to
form in the clarifier and maintain the MLVSS level in the aeration basin at a more sustainable
and healthy level.
Day to Day Operations - Without knowledgeable staff operating the treatment system,
modifications to the system will be of little value. In addition, staff devoted to the operation of
the system must have sufficient time to operate the system.
The permittee has stated that the ORC for the system will have as his/her primary duty
the responsibility of maintaining the WWTPs run by the school system (ORC job duty confirmed
during an August 10, 1999 phone conversation with Mike James, Safety Training and
Compliance Officer with the Iredell-Statesville Schools). The permittee is also preparing a
reference manual for the operation of the WWTPs. Some of the manual elements have been
discussed already, but the following items are to be included:
1) procedure to increase/decrease sludge wastage and recycle rates (identify when);
2) procedure to increase/decrease aeration rates (identify when);
3) procedure to clean tertiary filters;
4) feeding bugs during holidays (calculating feed amount and proper mixing offeed);
5) outline equipment inspection procedure; and
6) outline system monitoring procedure (locations and frequency for DO, pH, MLVSS).
The modifications outlined above should significantly improve the effluent quality from
the plant, if not bring the effluent in compliance with the permitted limits. The permittee is also
constructing a tertiary filter after the clarifier to provide some additional treatment prior to
discharge. The permittee has also been informed that the effluent line running from the plant to
the creek should be checked as flow was exiting the plant but was not entering the receiving
stream on the day of the site inspection by MRO staff
Art Condren the project manager at Cooper Environmental, reviewed the evaluations and
recommendations above for accuracy. Based on the ATC application and commitments made by
the permittee discussed within this report, this Office recommends approval of the ATC.
Signature of Report Preparer
io /?,
Water Quality Regio
1 Supervisor
00›.
Date
h:Aatc\NHidATC.doc

State of North Carolina
Department of Environment
and Natural Resources
Division of Water Quality
James B. Hunt, Jr., Governor
Wayne McDevitt, Secretary
Kerr T. Stevens, Director
July 9, 1999
Don Atkinson
Construction Manager
Iredell-Statesville Schools
PO Box 911
Statesville, North Carolina 28677
4617471eirCIripAk
AW
NCDENR
Subject: ATC Request Acknowledgment
NPDES Permit NC0037371
ATC Number 037371ACB
North High School WWTP
Iredell County
Dear Mr. Atkinson:
The Division of Water Quality's NPDES Unit hereby acknowledges receipt of your request for
Authorization to Construct (ATC) in accordance with NPDES Permit Number NC0037371 on
June 25, 1999. This application has been assigned the number highlighted above.
Please be aware that the Division's regional office, copied below, must provide recommendations
from the Regional Supervisor prior to final action by the Division.
The ATC review process generally takes 90 days from the date your complete submittal is
received. This 90-day process may be extended if additional information is required. Should any
additional information be required, the review engineer will contact you. If you have any
questions, please contact Ms. Susan Wilson, at [phone], extension 510.
PLEASE REFER TO THE ABOVE APPLICATION NUMBER WHEN MAKING ANY
INQUIRIES ABOUT THIS APPLICATION.
Sincerely,
David A. Goodrich
Supervisor, NPDES Unit
cc: Mooresville Regional Office
NPDES Unit Permit File
Mr. Ivan Cooper, Cooper Environmental, 2300 Sardis Rd. N, Suite Q, Charlotte, NC 28227
P.O. Box 29535, Raleigh, North Carolina 27626-0535 Telephone [phone] FAX [phone]
An Equal Opportunity Affirmative Action Employer 50% recycled/ 10% post -consumer paper

Jun 22 99 04:11p Cooper
704-841-8901 p.l
To Kim Murphy
via fax [phone]
To be placed on ISS letterhead
June 22, 1999
Ms. Kim Murphy
DENR/DWQ
NPDES Unit
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
RE: Permit No. NC0037371 - North Iredell Wastewater Treatment Plant
Cooper Environmental, Inc. (CEI) Authorization
CEI File No. 97264
near Ms. Murphy:
This is to inform you that the Iredell-Statesville School System has
requested Cooper Environmental, Inc. (CEI) to represent the them in obtaining
an Authorization to Construct Permit for the Phase II Improvements to the
North High School Wastewater Treatment Plant.
Sincerely,
Iredell-Statesville School System
Don Atkinson
Art/c/Mt Documents/Murphy-1.doc

IREDELL STATESVILLE SCHOOLS 77048712834 06/24/99 16:04 J :01/01 NO:841
Iredell-Statesville Schools
•
11.11111P Post Office Box 911, 549 North Race Street, Statesville, NC 28f77, Phone [phone], Fax; 704-871-2834
June 23, 1999
Ms. Kim Murphy
DENR/DWQ
NPDES Unit
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
Re: Permit No. NC0037371 — North Iredell Wastewater Treatment Plant
Cooper Environmental, Inc. (CEI) Authorization
CEI File No. 97264
Dear Ms. Murphy:
This is to inform you that the Iredell-Statesville School System has requested Cooper
Environmental, Inc. (CEI) to represent them in obtaining an Authorization to Construct
Permit for the Phase II improvements to the North Iredell High School Wastewater
Treatment Plant.
Sincerely,
Ctb6,44,,„„,
Don Atkinson
Construction Manager
Pith

e
June 23, 1999
COOPER ENVIRONMENTAL
ENGINEERS • GEOLOGISTS • SCIENTISTS
Mr. David Goodrich
NCDENR - Division of Water Quality
P.O. Box 29535
Raleigh, North Carolina 27626-0535
RE: Request for Authorization to Construct - SOC EMC-WQ-98-011
Proposed Phase II Improvements
North High School Wastewater Treatment Plant
CEI File No. 97264
Dear Mr. Goodrich:
DENR - WATER QUALITY
POINT SOURCE BRANCH
Attached for your review are plans and specifications for the Phase II
Improvements to the Iredell North High School Wastewater Treatment Facility. These
plans and specifications are in response to Section 2C.2 of the Special Order of
Compliance EMC-WQ-98-011 issued by the NCDENR for this facility.
The improvements contained herein are being proposed by Cooper
Environmental, Inc. (CEI) and center around three (3) primary activities:
• Changing the piping and the flow distribution box in the equalization basin to be
more properly aligned with current and foreseeable future wastewater flow rates;
• Selecting new return activated sludge (RAS) pumps and piping to better convey
currently required and foreseeable future RAS flow rates; and
• Designing a tertiary filtration system to polish the treatment plant effluent before
its discharge to the receiving waterway.
2300 SARDIS ROAD NORTH • SUITE Q
CHARLOTTE, NORTH CAROLINA • 28227
[phone] • FAX [phone]
5101 COUNTRY CLUB ROAD
WINSTON-SALEM, NORTH CAROLINA • 27104
[phone] • FAX [phone]

Mr. David Goodrich
June 23, 1999
Page 2
As the School District has elected to construct the Phase II Improvements with
force account work, a construction contract will not be issued. Because of this,
appropriate construction specifications are included on the drawings.
The attached plans and specifications are for review purposes only; they are not
intended to be construction documents. Upon completion of review, your comments
will be addressed by the CEI staff, after which plans and specifications will be finalized
and sealed to allow for construction of the Phase II Improvements to the Iredell North
High School Wastewater Treatment Plant.
In compliance with established dates in the SOC, we would appreciate your
prompt review, comments, and approval so that construction may start within thirty
(30) days.
Sincerely,
COOPER ENVIRONMENTAL, INC.
Ivan A. Cooper, P.E.
President
IAC\ac\ \ \Art\c\My Documents\iredell-draft.doc
Attachments
cc: D. Atkinson, H. Beaver, ISS
D. Fountain, Esq., Smith Helms Mulliss & Moore
R. Gleason, NCDENR/Mooresville

Control Box Flow Distributions
__
Ileac], ft
22.5 (legrcc
gal/min
One 6"
gal/min
'I'olal Flow
gpm
0.00
0.0
0.0
0.0
1;O(t(lil ( It'V.ltim11 )I.'» ri degree weir
0.0 1
0.0
0.0
0.0
0.02
0.0
0.0
0.0
0.03
0.0
0.0
0.0
0.041
0.1
0.0
0.1
0.05
0.1
0.0
0.1
0.06
0.2
0.0
0.2
0.07
0.3
0.0
0.3
0.08
0.4
0.0
0.4
0.09
0.5
0.0
0.5
0.10
0.7
0.0
0.7
0.11
0.9
0.0
0.9
Bottom ( lcval.ton )1-6-inch rectangular weir
0.12
1.1
0.7
1.8
0.13
1. 1•
2.1
3.5
0.14
1.6
3.8
5.4
0.15
1.9
5.9
7.8
Flow to control box wiil1 oiu (1) put-1) ol)c:rating
0.16
2.3
8.2
10.5
Minimum
1.9 5 gpin---_..__ ...--
0.17
2.7
10.7
13.4
Maximum ..
28.51?l)m
0.18
3.1
13.5
_ . 16.6
0.19
3.5
16.4
19.9
Flow to control box with two (2) pumps operating
0.20
41.0 -
19.1
23.1
Minimum
:i 1.0 g1)111
0.21
4.5
22.7
27.2
Maximum
57.0 gpm
().22
5.1
26.1
31.2
0.23
5.7
29.6
35.3
0.2,1
6.3
33.2
39.5
0.25
7.0
37.0
44.0
0.26
7.7
40.8
48.5
0.27 --
.. . 8.4
44.8
53.2
0.28
9.3
48.8
58.1
0.29
10.1
53.0
63.1.
Art \r\ My 1)octimenls\wcirs3.xls
C1'.1 File No. 9726-1

7.t:-ziary :._ter Preliminary Design
Nor :h Iredell High School Wastewater Treatment Plan:
:e 10, 1999
References: Design of Municipal Wastewater Treatment Plants —
WEF/ASCF. 1992.
Recommended Standards for Wastewater Facilities, 1997.
Criteria:
• Hydraulic loading rate should be less than or equal to 5 gpm/sq ft at the
facility's peak hourly flow rate.
• Backwash rate should be capable of yielding a twenty (20) percent bed
expansion. It is noted that a backwash rate of about 12.5 gpm/sq ft at 200
C will provide for an approximate 10 percent expansion of a bed containing
anthracite with an effective size of 1.2 mm.
• Air scour rate shouid be in the range of 3-5 scfm/sq ft of filter area.
• A nine (9) inch thick layer of one-half (1/2) inch diameter pea gravel should
be placed in the bottom of the filter. This should be overlain with a three (3)
inch thick layer of one -quarter (1/4) inch pea gravel. Piping for the system
underdrainage, air scouring and backwashing should be imbedded in these
layers of pea gravel.
• An eighteen (18) inch laver of anthracite should be placed over the pea
gravel. The anthracite should have an effective size of 1.2 mm and a
uniformity coefficient of 1.6.
Design:
• Current weekday flow to the facility is approximately 4,800 gpd. Over a 24-
hour period, this equates to an average flow of about 3.33 gpm.
• Permit flow is 12,500 gpd. Because of flow equalization at the WWTP,
average flow through the facility can be regulated to about 8.68 gpm. Based
on a permitted flow of 12,500 gpd, required filter area is:
8.68 gp-n/5 gpm/sq ft = 1.74 sq ft
Use two (2) filters, each with an area of 1.77 sq ft. Each filter is to be 16
inches by 16 inches (16"X16") in cross -sectional area.
• Wastewater flow rate to each filter is to be 7.0-7.3 gpm through the use of a
Teel 1V356 gear pump (see page 2752 of Grainger catalog). This equates to a
hydraulic loading rate to each filter of 3.95-4.12 gpm/sq ft. Three (3) 7.0-
7.3 gpm feed pumps are to be provided, one (1) for each of the two (2) filters
and one (1 as a replacement unit.
.Art \c Doc1:-^ents\Fii:e:.doc I
CEI File No. 9 -54

Filter er Preliminary- Design
::::th Irece l High School Wastewater Treatment P1a_t
June 10, 1999
• Air requirement for air scouring each filter is 5.3-8.9 scfm.. Available plan:
air, at a=proximate:y (6 i psig, from the on -site Roots blowers is to be
used for air scouring each filter.
• Backwash water flow rate to each filter is to be 23.0-24.0 gpm through the
use of a -eel 1V366 gear pump (see page 2752 of Grainger catalog). This
equates to a backwash water flow rate of 12.99-13.56 gpm/sq ft. One 23.0-
24.0 gp:n backwash water pump is to be installed and is to be shared by the
nvo (2) f=: ters since the filters will not be backwashed at the same time. A
second backwash pump is to be provided as a replacement unit.
• A wetwe::.vith a volume of approximately 300 gal is to be provided for each.
filter. These wetweLis are to be installed between the secondary cla- fier
outlet any: the chlorination:dechlorination system inlet, and are to be
interconnected to allow for series flow from the first wetwell (A) to the second
wetwell i 3 ►.
• Secondary clarifier effluent flow to Filter A is to be from Wetwell A and
filtrate from Filter .A is to be returned to Wetwell A. Flow to Filter B is to be
from Wet:vell B and filtrate from Filter A is to be returned to Wetwell B. (It is
noted that the influent to Wetwell B is the effluent from Wetwell A which
contains partially filtered secondary clarifier effluent.)
• At a flow rate of 3.95-4.12 gpm/sq ft, clean water headloss through an 18"
layer of anthracite and a 12" layer of pea gravel should be approximately 1.0
ft.
• Solids storage capability- of 1.2 mm anthracite media, with a headloss of 4.0
ft induced by solids capture in the media, should be in the vicin it:: of 0.4 lb
TSS / sq f = of filter area. Based on this storage capacity, filtration system run
time in hours, before terminal headloss is reached, is presented in -the table
below for various secondary clarifier effluent TSS concentrations:
Influent TSS, mg 'I.
I
Filter Run, hours
10
I
61
20
I
56
30
i
33
40
i
24
50
1
18
60
i
15
70
E
13
• Because of the constant hydraulic loading rate to the filters, effluent TSS
concentration from the filtration system is expected to be relatively constant,
in the vicinity of five (5) to ten (10) mg/ L.
c\NIv- -__e..doc
CEI File No. .4

Tertiary Filter ?r eliminary Design
:: girth I: eclell High School '.Vastewa:er Treatment Play.:
June 10, 1999
• It should be noted that if terminal headloss to a filter is reached at a time
when the facility operator is not on -site, influent flow to that filter is
automacally re=urned to its respective wetwell via the filters' overflow
piping system. Return to this location is to avoid the wetwell being pumped
dry and subsequently causing damage to that filter's feed pump.
• Piping associated with the influent to the 7.0-7.3 gpm feed pumps should be
' -inch inside diameter pipe and should be made of Schedule 40 carbon
steel or approved equal. Piping associated with the discharge from the 7.0-
7.3 gpm feed pumps should be 1-inch inside diameter pipe and should be
made of Schedule 40 carbon steel or approved equal.
• Piping associated .with the influent to and discharge from :he 23.0-24.0 gpin
backwash pump should be 1-inch inside diameter pipe and should be made
of Sched•.!e 40 carbon steel or approved equal.
• Piping associated with the air scour system should be 1-inch inside
diameter pipe and should be made of Schedule 40 carbon steel or approved
equal.
• Piping associated with the backwash water conveyance system (from the
filters to the equalization basin) should be 2-inch inside diameter pipe and
should be made of Schedule 40 carbon steel or approved equal.
• The overflow line associated with each filter (from each filter to its respective
wetwell should be 2-inch inside diameter pipe and should be made of
Schedule 40 carbon steel or approved equal.
• The side-:: alls of the 16" by 16" tertiary filters should be constructed of 1/8-
inch thick stainless steel or approved equal. Stainless steel stiffeners
should be provided at elevations 1.0 ft, 4.0 ft and 7.25 ft from the top of the
bottom of :he filters. The bottom plate of the tertiary filters should be
construc:ed of 1, 4-inch thick stainless steel or approved equal, and should
have dimensions of 20" by 24". The bottom plate of each filter should be
bolted to he top of the concrete walls of the wetwell structure.
• The sigh: gauge associated with each filter should be 1-inch in diameter and
should be made of clear plastic or equivalent.
.-. c\lily Dec ments Falter.doc
CE: File No. _ -264

G4LL4R _1,IEDI4 FILTRATION
PROCESS DESCRIPTION. The objective of wastewater filtration is to
remove SS. G �.rular media filtration has been appiied for treating .municipal
wastewater in a variety of processing secuences. Usually, filtration is use-i
where the effluent limit is equal to or less than 10 mg'L SS. It may be applied
following secondary biological treatment to remove particulate carbonaceous
BOD5 and residual insolubilized phosphorus. L-i addition, combinations of
filtration with biooxidation or reduction systems have some applications in
tertiary treatment."' Systems combining filtration and biological cultures are
really fixed -growth biological systems and will not be disci' —i f„-,her in
this chapter (see Chapter 15). Tne degree of SS ._..,..•al when filtering
secondary effluens without the use of chemical coagulation depends on the
degree of bioflocculation achieved during secondary treatment, as shown in
Table 16.2. The presence of significant amounts of aigae impedes filtration
of lagoon effluens. Pretreatment with a primary coagulant is considered to
be a good practice for such cases.
With the nurrerous granular media filtration systems available, ±is chap-
ter cannot review all systems. many of which are proprietary. However,
granular media tides may be classified genericalh• according to direction of
flow, type and n_ -fiber of media comprising the bed. the driving force, and
the method of — d control.
Table 16.2 Normal average day effluent concentrations from granular media
filtration of secondary effluent.
Filter influent type
Without
chemical
coaaulation—
single or With chemical coagulation —
multimedia dual or multimedia filter
filter. effluent Effluent PO.. Turbidity,
SS. mgfL. SS. mg/1 mg,2 Jtu
High -rate trice ii:_ -.:er effluent 10-20 0 0.I 0.1-0.4
Two -stage tick::::, -.._r effluent 6-15 0 0.i 0.I-0.4
Contact stabiiiza::.::: effluent 6-15 0 0.1 0.1-0.4
Conventional ac::..2:e,: sludge
effluent 3-10 0 0.1 0.1-0.4
Extended aeraticn e:.._ent 1-5 0 0.1 0.1-0.4
Aerated/facultative _ n effluent 10-50 0-303 0.: ;Aa
a Poor removal efficiency:ar result troy.^. ?1:.. .' g: n e fit.em ?:aL'se. of :..e presence.
O? aisae.
others
these _
A:-
, ignt
the f.
pre
acnit
crn-
Figure 1(1.1
1016 Design of 1,uricipai Waste .,zter Treatment Plant-

shown .n Table - Filters .. _
- r municipal as:ew•ater-atment
coarser medium - rarely have a
rum :-.-.. 2.0 mm if effluent SS residuals of :0 mg/L or less are
necessa-:
Figure 16.3 ::::rags a tvpiea: _rain size ;: stribution as a function of
diameter on U.S. s:_„lard sieve sizes. Media s e ifications typically include
the effective size and the unifc--t'r• coefficient. The medium shown in the
Table 16.3 Media characteristics for dual -media and multimedia
filters.
Characteristicsa-b Range Ty pical
Dual media
Anthracite
Der.th, rnm
Effective size. --t
Uniformity ceef- :lent
Sand
Depth, mrn
Effective size. :r r
Uniformity :f ient
Filtration rate, L rr•min
Multimedia
Anthracite (top :aye: of quad -media filter)
Depth, mm
Effective size. "...
Uniformity ceefficient
Anthracite (s.,..,....-: • er of qu----tedia
ti;.
Depth. mm
Effective size.
Uniformity coefficient
Anthracite (top iayer of t-imedi, :Titer)
r)
Depth. „ ern
Effective size. -...
Uniformity .xffleient
Sand
Depth, mm
Effective size. -:...
Uniformity carT.ci_ nt
Garnet or iimeni::
Depth. mm
Effective size.
Uniformity coef= :lent
Filtration rate. L ,.•- in
Values
3i; -600 450
0.3-2.0 1.2
1.3-1.8 1.6
150-300 300
0.4-0.8 0.55
1.2-1.6 1.5
80-400 200
200-400 200
1.3-2.0 1.6
1.5-1.8 1.6
100-400 200
1.0-1.6 1.2
1.5-1.8 1.6
200-500 400
1.0-2.0 I.4
1.6
200.-400 250
0.4-0.8 0.5
1.3-1.8 1.6
50-150 100
0.2-0.6 0.3
1.5-1.8 1.6
80-400 200
Lim -nir, x 0.02= " zpr %sq ft.
1024
Design o,-Municipal Wastewater Treatment Plants
of '1 :
filter.
with
bed..
F.
uns:r
in
to Cr...
sUa:.
ran.
ion:
str-.
me:
The
rate
the:
in CS
me

is probabiy both inefficient and ineffective. Figures 16.6 and 16.7 show the
backwash rate requirements for 10% bed expansion as a function of medium
size, type, and water temperature.- Typically, the rates provide up to 10% ex-
pansion of the 60% finer -by -weight particle size. The bottom of the wash
trough is used as a guide, corresponding to the approximate rise anticipated
for the effective size.
Some researchers recommend selecting the rnaximum backwash rate from
the 90% finer medium size.2 Backwash purnp sizing should account for the
warmest wash -water temperature anticipated. Tne total backwash require-
ment will generally be about 3000 to 4000 L/m- (75 to 100 gal/sq ft) and will
be largeiy independent of the backwash rate.: Tnis observation is typical for
conventi= nal U.S. wash -trough spacing with trough edges approximately
0.9 m (3 ft) above the filter media. This requirement should not be applied to
proprietary systems without rigorous review of the proposed system. Selec-
tion of relative grain sizes for components of dual -media and multimedia fil-
ters generally should allow equal fluidization among the bed components.
Failure to provide equal fluidization may result in unplanned intermixing or,
in the worst extreme, a bed turnover.
Relying solely on an upward flow of water to clean granular filters is in-
adequate because the abrasive action among particles is the most effective
cleaning mechanism during backwash.9'10 Fluidized media are separated by
the flow of water, thus reducing the frequency of media grains rubbing
together)" biological solids in secondary effluent are strongly attached
52
2�
c . 3:2. ._
2.5
Figure 16.6 Minimum backwash rates for a bed expansion of 10°-o at 25=C (77' F)
(gpm/sq ft x 0.679 = L: m=•sl.
Figure 16.E
F.r'
as
a:
tie
5.:
u'
1 r_ Design of Municipal Wastewater Treatment Plants

0
0
10 20
Tern°C
3V
F:2ure 16.7 Effect of water temperature on backwash rates necessary for a 10°"o bed
expansion (gpm/sq ft x 0.679 = L m2es).
to the media because of their "sticky" nature. Consequently, it is not surpris-
ing that fluidization alone cannot effectively clean the bed.t t-" Many inves-
tigators have reported and cited benefits associated with air scout before and
during backwash both with subcritical and fluidizing backwash rates.15 Sur-
face and subsurface washing or agitating equipment also are rear: ted to
assist successful cleaning.
Air scour on the order of 0.015 to 0.025 m3 Jm"'s (3 to 5 scirr;sq ft) is
advisable as a minimum for conventional systems; deeper beds may require
more and shallow beds may require less. Although most of the beneficial
action of the air scour will occur during the first 2 minutes, sufficient opera-
tional flexibility should be provided `cr 10 or more minutes of scour with
some control of the applied rate. Designers should also consider concur ent
washing and air scouring. This requires a capability of draining the filter to
just above its surface, followed by a brief simultaneous period of air and
water backwash until the water reaches within 150 to 200 mm (6 to 8 in.) of
the wash trough. Then, either the air or water wash is stopped. The design of
the backwash reservoir should provide for some flexibility by affording be-
tween 3- and 15-minute capacity at the maximum backwash rate.
A subsurface wash capability appears most necessary when two or more
filter media are used. The subsurface washer is located at the expected depth,
of the expanded interface. Rotary surface wash facilities typically are
designed with 276 to 414 kPa (40 to :0 psig) of water pressure a. -id 0.7 to
.odd -ors Processes for .Advanced % cs:ewater Trea:mer t
1033

water as a function of the filtration rate can be obtained either from pilot -
plant study or directly from the manufacturer. Figure 16.8 provides an ex-
ample of such a curve.19
i 1
=L=
KV-
1
I
I
0
4
o-
8
10
= I LTRATION RATE, gpmisq `•t
12
Figure 16.8 Head loss development for clear water flowing through a dual -media
filter with an effective size of 0.9 to 1 mm, a uniformity coefficient of 1.-
for the anthracite layer, and an effective size of 0.40 to 0.45 mm for the
sand (ft x 0.304 8 = m: gpm/sq ft x 0.679 = L/m=•s).
Clean water head loss curves for a given hydraulic load are influenced by
media type, size, uniformity, and depth. As the filtration rate increases for the
example particular filter, less head loss capacity is available for solids
storage. If the filter characterized in the figure were operated with a terminal
head loss of 1.8 m (6 ft), it would fail instantly at a hydraulic load of slightly
over 6 L/m".s (9 g;:n/sq ft). At filtration rates of 2.7 and 5.4 Llm2•s (4 and
8 gpm/sq ft), the corresponding head losses for solids retention would ap-
proximate 1.4 and 0.5 m (4.7 and 1.5 ft).
Tne solids capn:r e efficiency and solids storage capacity of the filter deter-
mine its effective r ,:n-time for a given head loss. A substantial solids break-
through generally does not occur when filtering secondary effluents if the
medium grain size is smaller than 2 ram. All filters containing a medium of
•
1r
I-Ieacl Loss, it
th
a-
a:
nr
sc
vt
sc
e:
c
t:
v.
a:
Figure 16.9
1038 Design of.%funiciaal Wastewater Treatment Plants .:

-media
:dent of 1.7
:n for the
Kt
6
2
this size cr smaller are likely to be capable of producing a product water with
approximately 5 mg/L SS, especially if the system includes u s ream co-
agulant addition. The solids storage capacity of a filter will vary with the
nature of the solids applied. Data for the head loss parameter as a function of
solids stored per area of filter medium are not readily available. This de-
ve!oped head loss should only be that associated with the accumulated
solids —not that associated with simple hydraulic loading corsideations. Fig-
ure 16.9 shows such data, obtained by compiling operating resuis.4'8 The
filtering media used in both investigations had uniformity coefficients ap-
proaching unity. The sand media data with the head Ioss development ter-
minating at 1.8 m (6 ft) were derived from processing activate sludge
effluent at a filtration rate of 4 LJrn2•s (5.8 gpm/sq ft).8 The other data were
developed from processing trickling filter effluent at a tilt adc ate of
2.7 L/m?'s (4 gpm/sq ft).4 The Figure 16.9 data show that ant: acite has a
clear advantage in terms of solids storage capacity. They also reveal a strik-
ingly diminishing return (exaggerated as the medium size increases) as
higher filter head loss, resulting from solids accumulation, is achieved.
The information displayed in Figures 16.8 and 16.9, if used with a fixed
total allowable head loss requirement and an appropriate safety factor, pro-
vide a basis for developing a trial -and -error solution for the ,r aximum allow-
abie hydraulic loading rate of a filter.
Sa
Size
o.Q9 0.66 0.98 l.o9; --
0 1
a. -
side I.2 w,.r,
0.2
c..
Hcic:rc tilt; of "cc.. Loss
Figure 16.9 Solids storage capabilities of filter media (ft x 0.304 8 = m: Ibisq ft/ft
x 16.02 = kgim=•m1.
Ad -on Processes for.4thanced Wastewater Treatment 1039

Preliminary Ter ._ary Filter System Back -washing Sec ::ence
North lr edell Wastewater Treatment Plant
June 10, 1999
At the end of a filter run ie.g., every morning):
1. :-•.:rn off pump FAP-1.
2. Close valves FAV-1.
3. Open valve FAV-2. Close valve FAV-2 when the water level has reached
he bottom of the sight gauge.
4. Open valve BV-1.
3. Alter one (1) minute of air scouring, open valve FAV-5 and turn on pump
FAP-1.
6. After another one (1) minute, close valve BV-1, turn off pump F Ate- i , and
close valve FAV-5.
7. Open valve FAV-6 and turn on pump FAP-2.
8. Pun pump F.AP-2 for up to nine (9) minutes.
9. Turn off pump FAP-2 and close valve FAV-6.
10. Open valve FAV-2. Close valve FAV-2 when the water level has reached the
bottom of the sight gauge.
11. Open valves FAV-1 and FAV-3.
12. Turn on pump FAP-1.
Filter A is now back in operation.
13. Turn off pump FBP-1
14. Close valves FBV-1.
15. Open valve FBV-2. Close valve FBV-2 when the water level has reached
the bottom of the sight gauge.
16. Open valve BV-1.
17. After one (1) minute of air scouring, open valve FBV-5 and ruin on pump
FBP-1
18. After another one (1) minute, close valve BV-1, turn off pump FBP-1, and
close valve FBV-5.
19. Open valve FBV-6 and turn on pump FBP-2.
20. Pun pump FBP-2 for up to nine (9) minutes.
21. Turn off pump FBP-2 and close valve FBV-6.
22. Open valve FBV-2. Close valve FBV-2 when the `eater level has reached
the bottom of the sight gauge.
23. Open valves FBV-1 and FBV-3.
24. Turn on pump FBP-1.
Filter 3 is now back in operation.
Note - if a higher backwash rate is needed, the feed pump and the backwash
pump can be operated concurrently.
A--\c. Documents\FilterOperation.doc 1
C-_ G _ `�o. "�726'
..a' i •�T

Preliminary- Operational Considerations
Nor:h Iredell High School Wastewater Treatment Plan:
June 10, 1999
Existing Facilities
Equalization Basin Volume - 8,700 gal
Aeration Tank Volume - 12,000 gal
Secondary Clarifier Volume - 2,250 gal
Secondary Clarifier Area - 55 sq ft
Chlorination/Dechlorination System Volume - 1,000 gal
Flow Monitoring System - V-notch weir
Permit Flow - 12,500 gpd
Current Influent Loadings
Flow - 4,800 gpd
BOD5 - 219 mg/L
TSS - 209 mg/L
Current Operational Conditions
Wastewater flow rate - 3.3 gpm
Detention Times, hr
Equalization Basin - 43
Aeration Tank - 60
Secondary Clarifier - 11
MLSS - 2,814 mg/L
MLVSS - 2,690 mg/L
F/M - 0.033 lb BOD5/day/lb MLVSS under aeration
Return sludge rate - 60 gpm
Secondary clarifier surface loading rate - 87 gpd/sq
Secondary clarifier solids loading rate - 38.9 lb MLS.S.. sq ft/day
It is noted that the current return activated sludge (RAS) system is
comprised of two air lift pumps, one in each of the two (2) secondary
clarifier sludge hoppers, and a 3-inch diameter RAS pipe from each air
lift pump. The minimum achievable pumping rate for the air lift pumps
is 30 gpm each (60 gpm total since both pumps must he in operation).
To effect sludge thickening in the secondary clarifier, solids loading rate
on the secondary clarifier should be less than approximately 15 lb
MLSS/sq ft/day. At present, this cannot be rea11ed because of the high
RAS rate and the higher than necessary MLSS concentration being
maintained in the aeration tank.
A c My Docu ents\ edellfacilities.doc 1
CE: No. 964

Prelimina.7- Operational Considerations
North iredell High School Wastewater Treatment Plant
June 10. 1999
Future Over ational Conditions + c:
=4.800 andl
Wastewater flow rate - 3.3 gpm
Detention Times, hr
Equalization Basin - 43
Aeration Tank - 60
Secondary Clarifier - 11
MLSS -1,200 mg/L
MLVSS - 1,000 mg/L
F/M - 0.088 lb BOD-/day-/lb MLVSS under aeration
Return sludge rate - 9.7 gpm
Secondary clarifier surface loading rate - 87 gpd/sq ft
Secondary clarifier solids loading rate - 3.4 lb MLSS/sq ft/day
Tertiary filter loading rate - 4.0 gpm/sq ft
It is noted that a R.4S rate of approximately 9-10 gpm can be effected by
using two (2) Little Giant submersible centrifugal pumps, one in each of the two
(2) secondary sludge hoppers, and one (1) 3/4-inch diameter return RAS pipe. To
increase system headloss, and thus the pumping rate of the RAS pumps, the
length of the RAS piping system has been lengthened.
It is also noted that the reduced RAS pumping rate and IVILSS
concentration in the aeration tank will lower the solids loading rate on the
secondary clarifier to a level where sludge thickening will occur.
Art\c\Doc=ents..iredelifacilities.doc 2
CEI File No. 9.7264

Preiir-inary Operational Considerations
Nor:h Ir edell High School Wastewater Treatment Plant
June 10, 1999
Future Operational Conditions 0 = 8.650 �pol
Wastewater flow rate - 6.0 gpm
Detention Times, hr
Equalization Basin - 24
Aeration Tank - 33
Secondary Clarifier - 6
MLSS -1.920 mg/L
MLVSS - 1,600 mg/L
F/MI - 0.099 lb BOD5/ day;'lb MLVSS under aeration
Return sludge rate - 9.7 gpm
Secondary clarifier surface loading rate - 157 gpd/sq ft
Secondary clarifier solids loading rate - 6.6 lb MLSS/sq ft/day
Tertiary filter loading rate - 4.0 gpm/sq ft
Future Operational Conditions 1'a Permit Flow of 12.500 gpol
Wastewater flow rate - 8.7 gpm
Detention Times, hr
Equalization Basin - 16
Aeration Tank - 23
Secondary Clarifier - 4
MLSS -2.700 mg/L
MLVSS -2,300 mg/L
F/M - 0.099 lb BOD5/day: /lb MLVSS under aeration
Return sludge rate - 9.7 gpm
Secondary clarifier surface loading rate - 227 gpd/sq ft
Secondary clarifier solids loading rate - 10.8 lb MLSS/sq ft/day
Tertiary filter loading rate - 4.0 gpm/sq ft
Art\c Documents\:redeUlacilities.doc
CEI File No. 972 4

COOPER ENVIRONMENTAL
ENGINEERS • GEOLOGISTS • SCIENTISTS
June 23, 1999
Ms. Kim Murphy
NCDENR/DWQ
NPDES Unit
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
RE: Two (2) Copies of Requested Notes
Permit No. NC0037371
North Iredell Wastewater Treatment Plant
CEI File No. 97264
Dear Ms. Murphy:
a 'o a
;1, \I
;c
IENR - WATER QUALITY
POINT SOURC�4NCN__---
Attached please find two (2) copies of design notes that you requested by
telephone this morning. These notes are associated with Phase II
improvements to the North High School Wastewater Treatment Plant.
Sincerely,
COOPER ENVIRONMENTAL, INC.
Iv: A. Co per, P.E.
P esident
Art/c/My Documents/Murphy-2.doc
2300 SARDIS ROAD NORTH • SUITE Q
CHARLOTTE, NORTH CAROLINA • 28227
[phone] • FAX [phone]
5101 COUNTRY CLUB ROAD
WINSTON-SALEM, NORTH CAROLIt.4 • 27104
[phone] • FAX [phone]

rL�� Iredell-Statesville Schools
MEW Post Office Box 911, 549 North Race Street, Statesville, NC 28677, Phone [phone], Fax: [phone]
June 23, 1999
Ms. Kim Murphy
DENR/DWQ
NPDES Unit
1617 Mail Service Center
Raleigh, North Carolina 27699-1617
J U L - 7 1999
DENR - WATER QUALITY
POINT SOURCE BRANCH
Re: Permit No. NC0037371 — North Iredell Wastewater Treatment Plant
Cooper Environmental, Inc. (CEI) Authorization
CEI File No. 97264
Dear Ms. Murphy:
This is to inform you that the Iredell-Statesville School System has requested Cooper
Environmental, Inc. (CEI) to represent them in obtaining an Authorization to Construct
Permit for the Phase II improvements to the North Iredell High School Wastewater
Treatment Plant.
Sincerely,
Don Atkinson
Construction Manager
Pkh

COOPER ENVIRONMENTAL
ENGINEERS • GEOLOGISTS • SCIENTISTS
June 11, 1999
Mr. David Goodrich
NCDENR - Division of Water Quality
P.O. Box 29535
Raleigh, North Carolina 27626-0535
RE: Request for Authorization to Construct - SOC EMC-WQ-98-011
Proposed Phase II Improvements
North High School Wastewater Treatment Plant
CEI File No. 97264
Dear Mr. Goodrich:
Attached for your review are plans and specifications for the Phase II
Improvements to the Iredell North High School Wastewater Treatment Facility. These
plans and specifications are in response to Section 2C.2 of the Special Order of
Compliance EMC-WQ-98-011 issued by the NCDENR for this facility.
The improvements contained herein are being proposed by Cooper
Environmental, Inc. (CEI) and center around three (3) primary activities:
• Changing the piping and the flow distribution box in the equalization basin to be
more properly aligned with current and foreseeable future wastewater flow rates;
• Selecting new return activated sludge (RAS) pumps and piping to better convey
currently required and foreseeable future RAS flow rates; and
• Designing a tertiary filtration system to polish the treatment plant effluent before
its discharge to the receiving waterway.
2300 SARD/S ROAD NORTH, SUITE Q, CHARLOTTE, NORTH CAROLINA 28227
[phone] • FAX [phone] • www.coopereng.com

Mr. David Goodrich
June 11, 1999
Page 2
As the School District has elected to construct the Phase II Improvements with
force account work, a construction contract will not be issued. Because of this,
appropriate construction specifications are included on the drawings.
The attached plans and specifications are for review purposes only; they are not
intended to be construction documents. Upon completion of review, your comments
will be addressed by the CEI staff, after which plans and specifications will be finalized
and sealed to allow for construction of the Phase II Improvements to the Iredell North
High School Wastewater Treatment Plant.
In compliance with established dates in the SOC, we would appreciate your
prompt review, comments, and approval so that construction may start within thirty
(30) days.
Sincerely,
COOPER ENVIRONMENTAL, INC.
I an A. Coop , P.E.
President
IAC\ac\\\Art\c\My Documents\iredell-draft.doc
Attachments
cc: D. Atkinson, H. Beaver, ISS
D. Fountain, Esq., Smith Helms Mulliss & Moore
R. Gleason, NCDENR/Mooresville

- JAMES B. HUNTJR'r r
.
:.=ri;--GOVERNOR :,
AYN
SECRETARY >'-
•
.. �=ECERRT STEVENS
DIRECTOR •
-,_..
i
NORTH CARt - NA DEPARTMENT OF
ENVIRONMENT AND NATURAL RESOURCES
DIVISION OF WATER QUALITY
June 9, 1999
) �n Atkinson, Executive Director of Facilities
Iredell-Satesville School System
P.O. Box 911
Statesville, NC 28677
Subject: Special Order by Consent
EMC WQ 98-011
Iredell County
Dear Mr. Atkinson
Attached for your records is a copy of the signed Special Order by
Consent approved by the Environmental Management Commission.
The terms and conditions of the Order are in full effect, and you are
reminded that all fmal permit limits contained in the permit must be met
except those modified by the conditions of the Order. Additionally, as
specified in paragraph two (2)(e) of the Order, submittal of written
notice of compliance or non compliance with any schedule date is
required to be submitted to this office.
Pursuant to amended North Carolina General Statute 143-215.3D,
effective January 1,1999, water quality fees have been revised to
include an annual fee for any permit covered under a Special Order by
Consent in addition to the annual fee for the permit Each school will be
subject to a fee of $250.00 on a yearly basis while under this order, in
addition to an annual permit fee of $715.00. The School System will be
billed for this at a later date.
If you have questions concerning this matter, please contact Marcia
Lieber at [phone] ext 530.
Attachment
cc: Regional Office Morresville
Mike Hom, EPA
SOC Files
Central Files
Jeanne Phillips
Sincerely, •
. Kerr T. Stevens
P.O. BOX 29535, RALEIGH, NORTH CAROLINA 27626-0535
PHONE [phone] FAX [phone]
AN EQUAL OPPORTUNITY / AFFIRMATIVE ACTION EMPLOYER - 50% RECYCLED/10% POST -CONSUMER PAPER

NORTH CAROLINA
ENVIRONMENTAL MANAGEMENT COMMISSION
COUNTY OF IREDEL1.,
IN THE MATTER OF
NORTH CAROLINA
NPDES PERMITS
HELD BY IREDELL
CO. SCHOOLS AS
IDENTIFIED IN
SECTION 1(a) BELOW
SPECIAL ORDER BY CONSENT
EMC WQ NO. 98-011
Pursuant to provisions of North Carolina General Statute (G.S.) 143-215.2, this Special Order by
Consent is entered into by the Iredell County Board of Education, hereinafter referred to as the ISSS
(Iredell-Statesville School System), and the North Carolina Environmental Management
Commission, an agency of the State of North Carolina created by G.S. 143B-282, and hereinafter
referred to as the Commission:
1. The ISSS and the Commission hereby stipulate the following:
(a) ISSS holds the following North Carolina NPDES Permits for operation of existing
wastewater treatment works and for making outlets therefrom for treated wastewater
to Waters of this State in the Yadkin -Pee Dee River Basin, but is unable to
consistently comply with final effluent limitations for Biochemical Oxygen Demand
(BOD5), Ammonia Nitrogen (NH, as N), and Total Suspended Residue (TSR) as set
forth in the NPDES Permits. Compliance may require preparation of plans and
specifications for construction or modification and operation of wastewater treatment
works.
(b)
NPDES PERMIT NO. CLASS/WATERS SCHOOL
NC0029238 GUT to Back Creek - W. Iredell Middle School
NC0037371 Cl Patterson Creek North Iredell High School
NC0037389 C UT to Brady Branch West Iredell High School
Noncompliance with the final effluent limitations constitutes causing and
contributing to pollution of waters of this State named above, and ISSS is within the
jurisdiction of the Commission as set forth in G.S. Chapter 143, Article 21.
(c) Since this Special Order is by Consent, neither party will file a petition for a
contested case or for judicial review concerning its terms.
(df " If any of the facilities are found to be in compliance pending completion of the pilot
studies noted in 2(c)1 below, such facilities will be removed from this Special Order
by Consent.

EMC SOC WQ No. 98-01
Page Two
2. ISSS, desiring to comply with the Permits identified in paragraph 1(a) above, hereby agrees
to do the following:
(a) Comply with all terms and conditions of the Permits except those effluent limitations
identified in paragraph 1(a) above. See Attachments A-C for all current monitoring
requirements and effluent limitations. The permittee may also be required to monitor
for other parameters as deemed necessary by the Director in future permits or
administrative letters.
(b) As settlement of all alleged violations of the NPDES Permits prior to entering into
this Special Order by Consent, ISSS agrees to pay the sum of $40,911.12
($18,277.69 for West Iredell Middle School, $8,827.69 for West Iredell High School,
and $13,805.74 for North Iredell High School). A certified check must be made
payable to the Department of Environment and Natural Resources and forwarded to
the Director of the Division of Water Quality, P.O. Box 29535, Raleigh, North
Carolina 27626-0535, by no later than fifteen (15) days following the date on which
this Order is approved and executed by the Commission and received by ISSS..
(c) Undertake the following activities in accordance with the indicated time schedule:
1) Complete Operation and Maintenance Pilot Studies by March 26,1999. /pCj
2) Submit request for authorization to construct and plans and specifications for
facility upgrades by June 11,1999.
3) Begin construction of facility upgrades by September 17,1999.
4) Complete construction of facility upgrades by January 4, 2000.
5) Attain compliance with final effluent limitations by March 1., 2000.
(d) During the time in which this Special Order by Consent is effective, comply with the
interim effluent limitations contained in Attachments A-C. The following reflects
only the limitations that have been modified from NPDES requirements by this
Order:

EMC SOC WQ No. 98-011
Page Three
Parameters Units
Permit Limits Modified Limits (SOC)
Monthly Daily Monthly Daily
Average Maximum Average Maximum
West Iredell Middle High School NC0029238
BOD5 mg/1 30 45 55
TSR mg/1 30 45 40
NH3 'as N mg/1 15.1/5.5 winter/summer Monitoring only
North Iredell High School NC0037371
85
55
BOD5 mg/1 30 45 45 90
TSR mg/1 30 45 30 60
West Iredell High School NC0037389
BOD5 mg/1 30 45 55
TSR mg/1 30 45 45
NH3 as N mg/1 12.0/3.3 winter/summer Monitoring only
85
90
(e) No later than 14 calendar days after any date identified for accomplishment of anvv
activity listed in 2(c) above. submit to the Director of the Division of Water Quality
(DWQ) written notice of compliance or noncompliance therewith. In the case of
noncompliance. the notice shall include a statement of the reason(s) for
noncompliance, remedial action(s) taken. and a statement identifying the extent to
which subsequent dates or times for accomplishment of listed activities may, be
affected.
3. ISSS agrees that for each individual school , unless excused under paragraph (4), the ISSS
will pay the Director of the Division of Water Quality, by check payable to the North
Carolina Department of Environment and Natural Resources, stipulated penalties according
to the following. schedule for failure to meet the deadlines set out in paragraphs 2(c) and 2(e),
or failure to attain compliance with the effluent limitations/monitoring requirements
contained in Attachment A-C.

EMC SOC WQ No. 98-011
Page Four
Failure to meet a schedule date
Failure to maintain compliance with
any modified limit contained in the
SOC _
Failure to achieve compliance with
limitations at final compliance _.
deadline
$100/c .. • . ; ' :.0 90/day
theieafcer
$ 1000/violation
$3000.00
' Monitoring frequency violations $100 per omitted value
per parameter
Failure to submit progress reports $50/day for the first 7
days; $250/day thereafter
4. ISSS and the Commission agree stipulated penalties are not due if the ISSS satisfies the
Division of Water Quality that noncompliance was caused solely by:
a. An act of God;
b. An act of war;
c. An intentional act or omission of a third party; but this defense shall not be available
if the act or omission is that of an employee or agent of the defendant or if the act or
omission occurs in connection with a contractual relationship with the Permittee;
d. An extraordinary event beyond the Permittee's control. Contractor delays or failure
to obtain funding will not be considered as events beyond the Permittee's control; or
e. Any combination of the above causes.
Failure within thirty (30) days of receipt of written demand to pay the penalties, or challenge
them by a contested case petition pursuant to G.S. 150B-23, will be grounds for a collection
action, which the Attorney General is hereby authorized to initiate. The only issue in such
an action will be whether the thirty (30) days has elapsed.
5. Noncompliance with the terms of this Special Order by Consent is subject to enforcement
action in addition to the above stipulations, including injunctive relief pursuant to G.S. 143-
215.6C.

EMC SOC WQ No. 98-011
Page Five
6. This Special Order by Consent and any terms, conditions and interim effluent limitations
contained herein, hereby supersede any and all previous Special Orders, Enforcement
Compliance Schedule Letters, and terms, conditions, and limitations contained therein issued
in connection with aforementioned NPDES Permits. In the event of an NPDES Permit
modification or renewal, any effluent limitations or monitoring requirements contained
therein shall supersede those contained in Attachment A-C of this Special Order by Consent,
except as modified and contained in paragraph 2(d). •
7. The Permittee, upon signature of the Special Order by Consent, will comply with all schedule
dates, terms, and conditions of this document.
8. This Special Order by Consent shall expire on May 31, 2000.
For the Iredell-Statesville School System:
JosE741 . S,Ale •L / IR' SePerinr Dr
Print Name and Title of Signing Official Dim
Date-//C/49
For the North Carolina Environmental Management Commission:
Date C-
Chairman of the Commission

EMC SOC WQ NO. 98-011
ATTACHMENT A
WEST IREDELL MIDDLE SCHOOL
NPDES PERMIT NO. NC0029238
IREDELL COUNTY
EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS -interim
During the period beginning on the effective date of this Special Order and lasting until March 1, 2000, the Permittee is authorized
to discharge from outfall serial number 001. Such discharge shall he limited and monitored by the Permittee as specified below:
Effluent Characteristics
Flow
BOD, 5-day, 20°C
Total Suspended Residue '
NIB as N
Fecal Coliform (geometric mean)
Total Residual Chlorine
Temperature
*Sample Location: E-Effluent, I -Influent
Discharge Limitations Monitoring Requirements
Units as specified
Monthly Avg. Daily Max.
0.010 MGD
55.0 mg/i 85.0 mg/1
40.0 mg/1 55.0 mg/l
Monitor only
200/100 ml 400/100 ml
Measurement Sample * Sample
Frequency Type Location
Weekly Instantaneous
Weekly Grab
Weekly Grab
Weekly Grab
Weekly Grab
2/Weelc . Grab
2/Week Grab
IorE
F
F
E
E
E
E
The pH shall not be less than 6.0 standard units nor greater than 9.0 standard units and shall be monitored weekly at the effluent by gr'-'
There shall be no discharge of floating solids or visible foam in other than trace amounts.
The permittee may also be required to monitor for other parameters as deemed necessary by the Director in future permits or letters.
Note: Parameters underlined and noted in bold lettering above are the only parameters modified as part of this SOC.

EMC SOC WQ NO. 98-011
ATTACHMENT B
NORTH IREDELL HIGH SCHOOL
NPDES PERMIT NO. NC0037371
IREDELL COUNTY
EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS -Interim .
During the period beginning on the effective date of this Special Order and lasting until March 1, 2000, the Permittee is auth:.”-:.,-.,t
to discharge from outran serial number 001. Such discharge shall be limited and monitored by the'Permittee as specified be!'T w:
Effluent Characteristics
Flow
BOD, 5-day, 20°C
Total Suspended Residue
NH3 as N
Fecal Coliform (geometric mean)
Total Residual Chlorine
Temperature
*Sample Location: E-Effluent, I -Influent
Discharge Limitations Monitoring Requirements
Units as specified
Monthly Avg.
0.0125 MGD
45.0 mg/1
30.0 mei
200/100 ml
Daily Max.
90.0 mg/l
60.0 mg/
400/100 ml
Measurement Sample * Sample
Frequency Type Location
Weekly Instantaneous I or E
Weekly Grab
Weekly Grab
Weekly Grab E
Weekly Grab E
2/Week Grab E
Weekly Grab E
The pH shall not be less than 6.0 standard units nor greater than 9.0 standard units and shall be monitored weekly at the effluent by grab sample.
There shall be no discharge of floating solids or visible foam in other than trace amounts.
The permittee may also be required to monitor for other parameters as deemed necessary by the Director in future permits or Administr^' : ;tters.
Note: Parameters underlined and noted in bold lettering above are the only parameters modified as part of this SOC.

EMC SOC WQ NO. 98-011
ATTACHMENT C
WEST IREDELL I-IIGI 1 SCHOOL
NPDES PERMIT NO. NC0037389
IREDELL COUNTY
EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS -Interim
During the period beginning on the effective date of this Special Order and lasting until March 1, 2000, the Permittee is au'' ::
to dig charge from outfall serial number 001. Such discharge shall be limited and monitored by the Permittee as specifier_' :..:' -
Effluent Characteristics Discharge Limitations
Flow
BOD, 5-day, 20°C
Total Suspended Residue
NH3 as N
Fecal Colifonn (geometric mean)
Total Residual Chlorine
Temperature
Units as specified
Monthly Avg. Daily Max.
0.015 MGD
55.0 mgf 85.0 mg/1
45.0 mg/1 90.0 mg/1
Monitoring only
200/100 ml 400/100 ml
Monitoring Requirements
Measurement Sample ;*Sample
Frequency Type Location
Weekly
Weekly
Weekly
Weekly
Weekly
2/Week
Weekly
Instantaneous
Grab
Grab
Grab
Grab
Grab
Grab
l or E
E
E
E
E
E
E
*Sample Location: E-Effluent, I -Influent
The pH shall not be less than 6.0 standard units nor greater than 9.0 standard units and shall be monitored weekly at the effluent by grab sample.
There shall be no discharge of floating solids or visible foam in other than trace amounts.
The permittee may also be required to monitor for other parameters as deemed necessary by the Director in future permits or Administrative letters.
Note: Parameters underlined and noted in hold lettering above are the only parameters modified as part of this SOC.

Control Box Flow Distributions
22.5 degree
One 6"
Total Flow,
Head, ft
gal/min
gal/min
gpm
0.00
0.0
0.0
0.0
Bottom elevation of 22.5 degree weir
0.01
0.0
0.0
0.0
0.02
0.0
0.0
0.0
0.03
0.0
0.0
0.0
0.04
0.1
0.0
0.1
0.05
0.1
0.0
0.1
0.06
0.2
0.0
0.2
0.07
0.3
0.0
0.3
0.08
0.4
0.0
0.4
0.09
0.5
0.0
0.5
0.10
0.7
0.0
0.7
0.11
0.9
0.0
0.9
Bottom elevation of 6-inch rectangular weir
0.12
1.1
0.7
1.8
0.13
1.4
2.1
3.5
0.14
1.6
3.8
5.4
0.15
1.9
5.9
7.8
Flow to control box with one
(1) pump operating
19.5 gpm
0.16
2.3
8.2
10.5
Minimum
0.17
2.7
10.7
13.4
Maximum
28.5 gpm
0.18
3.1
13.5
16.6
0.19
3.5
16.4
19.9
Flow to control box with two
(2) pumps operating
54.0 gpm
0.20
4.0
19.4
23.4
Minimum
0.21
4.5
22.7
27.2
Maximum
57.0 gpm
0.22
5.1
26.1
31.2
0.23
5.7
29.6
35.3
0.24
6.3
33.2
39.5
0.25
7.0
37.0
44.0
0.26
7.7
40.8
48.5
0.27
8.4
44.8
53.2
0.28
9.3
48.8
58.1
0.29
10.1
53.0
63.1
Art\c \My Documents \weirs3.xls
CEI File No. 97264

Tertiary Filter Preliminary Design
North Iredell High School Wastewater Treatment Plant
June 10, 1999
References: Design of Municipal Wastewater Treatment Plants -
WEF/ASCE, 1992.
Recommended Standards for Wastewater Facilities, 1997.
Criteria:
• Hydraulic loading rate should be less than or equal to 5 gpm/sq ft at the
facility's peak hourly flow rate.
• Backwash rate should be capable of yielding a twenty (20) percent bed
expansion. It is noted that a backwash rate of about 12.5 gpm/sq ft at 200
C will provide for an approximate 10 percent expansion of a bed containing
anthracite with an effective size of 1.2 mm.
• Air scour rate should be in the range of 3-5 scfm/sq ft of filter area.
• A nine (9) inch thick layer of one-half (1/2) inch diameter pea gravel should
be placed in the bottom of the filter. This should be overlain with a three (3)
inch thick layer of one -quarter (1/4) inch pea gravel. Piping for the system
underdrainage, air scouring and backwashing should be imbedded in these
layers of pea gravel.
• An eighteen (18) inch layer of anthracite should be placed over the pea
gravel. The anthracite should have an effective size of 1.2 mm and a
uniformity coefficient of 1.6.
Design:
• Current weekday flow to the facility is approximately 4,800 gpd. Over a 24-
hour period, this equates to an average flow of about 3.33 gpm.
• Permit flow is 12,500 gpd. Because of flow equalization at the WWTP,
average flow through the facility can be regulated to about 8.68 gpm. Based
on a permitted flow of 12,500 gpd, required filter area is:
8.68 gpm/5 gpm/sq ft = 1.74 sq ft
Use two (2) filters, each with an area of 1.77 sq ft. Each filter is to be 16
inches by 16 inches (16"X16") in cross -sectional area.
• Wastewater flow rate to each filter is to be 7.0-7.3 gpm through the use of a
Teel 1V356 gear pump (see page 2752 of Grainger catalog). This equates to a
hydraulic loading rate to each filter of 3.95-4.12 gpm/sq ft. Three (3) 7.0-
7.3 gpm feed pumps are to be provided, one (1) for each of the two (2) filters
and one (1) as a replacement unit.
Art\c\My Documents\Filter.doc 1
CEI File No. 97264

Tertiary Filter Preliminary Design
North Iredell High School Wastewater Treatment Plant
June 10, 1999
• Air requirement for air scouring each filter is 5.3-8.9 scfm. Available plant
air, at approximately six (6) psig, from the on -site Roots blowers is to be
used for air scouring each filter.
• Backwash water flow rate to each filter is to be 23.0-24.0 gpm through the
use of a Teel 1V366 gear pump (see page 2752 of Grainger catalog). This
equates to a backwash water flow rate of 12.99-13.56 gpm/sq ft. One 23.0-
24.0 gpm backwash water pump is to be installed and is to be shared by the
two (2) filters since the filters will not be backwashed at the same time. A
second backwash pump is to be provided as a replacement unit.
• A wetwell with a volume of approximately 300 gal is to be provided for each
filter. These wetwells are to be installed between the secondary clarifier
outlet and the chlorination/dechlorination system inlet, and are to be
interconnected to allow for series flow from the first wetwell (A) to the second
wetwell (B).
• Secondary clarifier effluent flow to Filter A is to be from Wetwell A and
filtrate from Filter A is to be returned to Wetwell A. Flow to Filter B is to be
from Wetwell B and filtrate from Filter A is to be returned to Wetwell B. (It is
noted that the influent to Wetwell B is the effluent from Wetwell A which
contains partially filtered secondary clarifier effluent.)
• At a flow rate of 3.95-4.12 gpm/sq ft, clean water headloss through an 18"
layer of anthracite and a 12" layer of pea gravel should be approximately 1.0
ft.
• Solids storage capability of 1.2 mm anthracite media, with a headloss of 4.0
ft induced by solids capture in the media, should be in the vicinity of 0.4 lb
TSS/sq ft of filter area. Based on this storage capacity, filtration system run
time in hours, before terminal headloss is reached, is presented in the table
below for various secondary clarifier effluent TSS concentrations:
Influent TSS, mg/L
Filter Run, hours
10
61
20
56
30
33
40
24
50
18
60
15
70
13
• Because of the constant hydraulic loading rate to the filters, effluent TSS
concentration from the filtration system is expected to be relatively constant,
in the vicinity of five (5) to ten (10) mg/L.
Art\c\My Documents\Filter.doc 2
CEI File No. 97264

Tertiary Filter Preliminary Design
North Iredell High School Wastewater Treatment Plant
June 10, 1999
• It should be noted that if terminal headloss to a filter is reached at a time
when the facility operator is not on -site, influent flow to that filter is
automatically returned to its respective wetwell via the filters' overflow
piping system. Return to this location is to avoid the wetwell being pumped
dry and subsequently causing damage to that filter's feed pump.
• Piping associated with the influent to the 7.0-7.3 gpm feed pumps should be
1/2-inch inside diameter pipe and should be made of Schedule 40 carbon
steel or approved equal. Piping associated with the discharge from the 7.0-
7.3 gpm feed pumps should be 1-inch inside diameter pipe and should be
made of Schedule 40 carbon steel or approved equal.
• Piping associated with the influent to and discharge from the 23.0-24.0 gpm
backwash pump should be 1-inch inside diameter pipe and should be made
of Schedule 40 carbon steel or approved equal.
• Piping associated with the air scour system should be 1-inch inside
diameter pipe and should be made of Schedule 40 carbon steel or approved
equal.
• Piping associated with the backwash water conveyance system (from the
filters to the equalization basin) should be 2-inch inside diameter pipe and
should be made of Schedule 40 carbon steel or approved equal.
• The overflow line associated with each filter (from each filter to its respective
wetwell should be 2-inch inside diameter pipe and should be made of
Schedule 40 carbon steel or approved equal.
• The sidewalls of the 16" by 16" tertiary filters should be constructed of 1/8-
inch thick stainless steel or approved equal. Stainless steel stiffeners
should be provided at elevations 1.0 ft, 4.0 ft and 7.25 ft from the top of the
bottom plate of the filters. The bottom plate of the tertiary filters should be
constructed of 1/4-inch thick stainless steel or approved equal, and should
have dimensions of 20" by 24". The bottom plate of each filter should be
bolted to the top of the concrete walls of the wetwell structure.
• The sight gauge associated with each filter should be 1-inch in diameter and
should be made of clear plastic or equivalent.
Art\c\My Documents\Filter.doc 3
CEI File No. 97264

GRANULAR MEDIA FILTRATION
PROCESS DESCRIPTION. The objective of wastewater filtration is to
remove SS. Granular media filtration has been applied for treating municipal
wastewater in a variety of processing sequences. Usually, filtration is used
where the effluent limit is equal to or less than 10 mg/L SS. It may be applied
following secondary biological treatment to remove particulate carbonaceous
BOD5 and residual insolubilized phosphorus. In addition, combinations of
filtration with biooxidation or reduction systems have some applications in
tertiary treatment.1'2 Systems combining filtration and biological cultures are
really fixed -growth biological systems and will not be discussed further in
this chapter (see Chapter 15). The degree of SS removal when filtering
secondary effluents without the use of chemical coagulation depends on the
degree of bioflocculation achieved during secondary treatment, as shown in
Table 16.2. The presence of significant amounts of algae impedes filtration
of lagoon effluents. Pretreatment with a primary coagulant is considered to
be a good practice for such cases.
With the numerous granular media filtration systems available, this chap-
ter cannot review all systems, many of which are proprietary. However,
granular media filters may be classified generically according to direction of
flow, type and number of media comprising the bed, the driving force, and
the method of flow control.
Table 16.2 Normal average day effluent concentrations from granular media
filtration of secondary effluent.
Filter influent type
Without
chemical
coagulation —
single or With chemical coagulation —
multimedia dual or multimedia filter
filter, effluent Effluent PO4, Turbidity,
SS, mg/L SS, mg,/L mg/L Jtu
High -rate trickling filter effluent 10-20 0 0.1 0.1-0.4
Two -stage trickling filter effluent 6-15 0 0.1 0.1-0.4
Contact stabilization effluent 6-15 0 0.1 0.1-0.4
Conventional activated sludge
effluent 3-10 0 0.1 0.1-0.4
Extended aeration effluent 1-5 0 0.1 0.1-0.4
Aerated/facultative lagoon effluent 10-50 0-30a 0.1 N/.4a
a Poor removal efficiency can result frorn filtering lagoon effluent because of the presence
of algae.
1016 Design of Municipal Ziastew•ater Treatment Plants
30-40 in.
Underdrain
Chamber
Most •
some prc
others, c,
these thr
Alten
higher si
medium
the fine -
prevents
achieve
or multi
In1luer
Fine'
=Sane
• '•Coe
(a'
Coarse '•'ec!a,
Interrno, Zone —
Finere—
F�nes. r.ledra'
Underdral
Caber
Figure 16.1 Fill
upt
i•
:;c

f
shown in Table 16.3. Filters for municipal wastewater treatment rarely have a
coarser medium than 2.0 mm if effluent SS residuals of 10 mg/L or less are
necessary.
Figure 16.3 illustrates a typical grain size distribution as a function of
diameter on U.S. standard sieve sizes. Media specifications typically include
the effective size and the uniformity coefficient. The medium shown in the
Table 163 Media characteristics for dual -media and multimedia
filters.
Characteristicsa'b
Dual media
Anthracite
Depth, mm
Effective size, nun
Uniformity coefficient
Sand
Depth, mm
Effective size, mm
Uniformity coefficient
Filtration rate, L/m2•min
Values
Range Typical
300-600 450
0.8-2.0 1.2
1.3-1.8 1.6
150-300 300
0.4-0.8 0.55
1.2-1.6 1.5
80-400 200
Multimedia
Anthracite (top layer of quad -media filter)
Depth, mm 200-400 200
Effective size, mm
Uniformity coefficient 1.1.6
Anthracite (second layer of quad -media filter) 1.5--1..8 1.6
Depth, mm 100-400 200
Effective size, mm 1.0-1.6 1.7
Uniformity coefficient
Anthracite (top layer of trimedia filter) 1.5-1.8 1.6
Depth, mm 200-500 400
Effective size, mm
Uniformity coefficient 1.1.6
Sand 1.4--1..8 1.6
Depth, mm 200-400 250
Effective size, mm 0.4-0.8 0.5
Uniformity coefficient 1.3-1.8 1.6
Garnet or ilmenite
Depth, mm 50-150 100
Effective size, mm 0.2-0.6 0.3
Uniformity coefficient 1.5-1.8 1.6
Filtration rate, L/m`•min 80-400 200
bmmx0.03937=in.
L/m2•min x 0.024 5 = gpm/sq ft.
1024
Design of Municipal Wastewater Treatment Plants
figure h
of 1.5.
filters,
with a
bed, sir
Filte
unstrati
inthep
to their
stratific
random
longer
stratific
mediur
The co.
filter bi
the nor
A11
most rr
media
,;
c
Percent Finer By Weight
Figur
Add -a

is probably both inefficient and ineffective. Figures 16.6 and 16.7 show the
backwash rate requirements for 10% bed expansion as a function of medium
size, type, and water temperature.2 Typically, the rates provide up to 10% ex-
pansion of the 60% finer -by -weight particle size. The bottom of the wash
trough is used as a guide, corresponding to the approximate rise anticipated
for the effective size.
Some researchers recommend selecting the maximum backwash rate from
the 90% finer medium size.2 Backwash pump sizing should account for the
warmest wash -water temperature anticipated. The total backwash require-
ment will generally be about 3000 to 4000 L/m2 (75 to 100 gal f sq ft) and will
be largely independent of the backwash rate.2 This observation is typical for
conventional U.S. wash -trough spacing with trough edges approximately
0.9 m (3 ft) above the filter media. This requirement should not be applied to
proprietary systems without rigorous review of the proposed system. Selec-
tion of relative grain sizes for components of dual -media and multimedia fil-
ters generally should allow equal fluidization among the bed components.
Failure to provide equal fluidization may result in unplanned intermixing or,
in the worst extreme, a bed turnover.
Relying solely on an upward flow of water to clean granular filters is in-
adequate
because the abrasive action among particles is the most effective
cleaning mechanism during backwash.9'10 Fluidized media are separated by
the flow of water, thus reducing the frequency of media grains rubbing
together.11 Also, biological solids in secondary effluent are strongly attached
Backwash Rates, gpm/sq ft
50
40
30
20
10
1 1
1 1
1
1 1
'1
k # /
9
''':
—e
�a�ra
Cd 2�0`5p/
/ `r aG�`e—
C,1 9~Ga/
/
/
/-------
i
1 1
1 1
1
1
1
0.25 0.5 0.75
1
1.5
Media Size. mm
2
2.5
Figure 16.6 Minimum backwash rates for a bed expansion of 10% at 25°C (77° F)
(gpm/sq ft x 0.679 = L/m-•s).
Backwash Rates, gpmisq ft
15
10
5
0
0
Figure 16.7 Effec
expar
to thg
ingf
tigat
durii
face
assi!
adv
moi
acti
tior
son
wa
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1032 Design of Municipal Wastewater Treatment Plants
A

z
(77° F)
Backwash Rates, gpm/sq ft
15
10
5
0
Pt‘`rta•�e
0
10
20
Temperature, °C
30
Figure 16.7 Effect of water temperature on backwash rates necessary for a 10010 bed
expansion (gpm/sq ft x 0.679 = L/m2•s).
to the media because of their "sticky" nature. Consequently, it is not surpris-
ing that fluidization alone cannot effectively clean the bed.11-14 Many inves-
tigators have reported and cited benefits associated with air scour before and
during backwash both with subcritical and fluidizing backwash rates.15 Sur-
face and subsurface washing or agitating equipment also are reported to
assist successful cleaning.
Air scour on the order of 0.015 to 0.025 m3/m2•s (3 to 5 scfm/sq ft) is
advisable as a minimum for conventional systems; deeper beds may require
more and shallow beds may require less. Although most of the beneficial
action of the air scour will occur during the first 2 minutes, sufficient opera-
tional flexibility should be provided for 10 or more minutes of scour with
some control of the applied rate. Designers should also consider concurrent
washing and air scouring. This requires a capability of draining the filter to
just above its surface, followed by a brief simultaneous period of air and
water backwash until the water reaches within 150 to 200 mm (6 to 8 in.) of
' the wash trough. Then, either the air or water wash is stopped. The design of
the backwash reservoir should provide for some flexibility by affording be-
tween 3- and 15-minute capacity at the maximum backwash rate.
A subsurface wash capability appears most necessary when two or more
filter media are used. The subsurface washer is located at the expected depth
of the expanded interface. Rotary surface wash facilities typically are
designed with 276 to 414 kPa (40 to 50 psig) of water pressure and 0.7 to
Add -on Processes for Advanced Wastewater Treatment
1033

water as a function of the filtration rate can be obtained either from pilot -
plant study or directly from the manufacturer. Figure 16.8 provides an ex-
ample of such a curve.19
FILTER HEAD LOSS, ft
8
7
6
5
4
3
2
HL
K V'
0 2 4 6 8 10 12
FILTRATION RATE, gpm/sq ft
Figure 16.8 Head loss development for clear water flowing through a dual -media
filter with an effective size of 0.9 to 1 mm, a uniformity coefficient of 1.7
for the anthracite layer, and an effective size of 0.40 to 0.45 mm for the
sand (ft x 0.304 8 = m; gpm/sq ft x 0.679 = L/m2•s).
Clean water head loss curves for a given hydraulic load are influenced by
media type, size, uniformity, and depth. As the filtration rate increases for the
example particular filter,less head loss capacity is available for solids
storage. If the filter characterized in the figure were operated with a terminal
head loss of 1.8 m (6 ft), it would fail instantly at a hydraulic load of slightly
over 6 L/m2•s (9 gpm/sq ft). At filtration rates of 2.7 and 5.4 L/m2•s (4 and
8 gpm/sq ft), the corresponding head locces for solids retention would ap-
proximate 1.4 and 0.5 m (4.7 and 1.5 ft).
The solids capture efficiency and solids storage capacity of the filter deter-
mine its effective run-time for a given head loss. A substantial solids break-
through generally does not occur when filtering secondary effluents if the
medium grain size is smaller than 2 mm. All filters containing a medium of
Head Loss, It
10
8
6
4
2
0
this
appr
agul
natu
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velo
soli(
ure
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abl(
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049 0 t
Figure 16.9
1038 Design of Municipal Wastewater Treatment Plants
AL

1
11-media
ficient of 1.7
nm for the
d
co
0
J
f3
CD
S
10
0
8
this size or smaller are likely to be capable of producing a product water with
approximately 5 mg/L SS, especially if the system includes upstream co-
agulant addition. The solids storage capacity of a filter will vary with the
nature of the solids applied. Data for the head loss parameter as a function of
solids stored per area of filter medium are not readily available. This de-
veloped head loss should only be that associated with the accumulated
solids —not that associated with simple hydraulic loading considerations. Fig-
ure 16.9 shows such data, obtained by compiling operating results.4'8 The
filtering media used in both investigations had uniformity coefficients ap-
proaching unity. The sand media data with the head loss development ter-
minating at 1.8 m (6 ft) were derived from processing activated sludge
effluent at a filtration rate of 4 L/m2's (5.8 gpm/sq ft).8 The other data were
developed from processing trickling filter effluent at a filtration rate of
2.7 L/m2's (4 gpm/sq ft).4 The Figure 16.9 data show that anthracite has a
clear advantage in terms of solids storage capacity. They also reveal a strik-
ingly diminishing return (exaggerated as the medium size increases) as
higher filter head loss, resulting from solids accumulation, is achieved.
The information displayed in Figures 16.8 and 16.9, if used with a fixed
total allowable head loss requirement and an appropriate safety factor, pro-
vide a basis for developing a trial -and -error solution for the maximum allow-
able hydraulic loading rate of a filter.
media size • 1.2. ,
Sand
i 1
Anthracite
Effec-
tive
Media
1 1 ` `Size
0.49 0.68 0.98 1.09
1
0.1
1 A9 1.84
1 1
0.2 0.3
Solids Holding Capacity, lb/sq ft/ft of Head Loss
Figure 16.9 Solids storage capabilities of filter media (ft x 0.304 8 = m; lb/sq ft/ft
x 16.02 = kg/m2•m).
Add -on Processes for Advanced Wastewater Treatment 1039

Preliminary Tertiary Filter System Backwashing Sequence
North Iredell Wastewater Treatment Plant
June 10, 1999
At the end of a filter run (e.g., every morning):
1. Turn off pump FAP-1.
2. Close valves FAV-1.
3. Open valve FAV-2. Close valve FAV-2 when the water level has reached
the bottom of the sight gauge.
4. Open valve BV-1.
5. After one (1) minute of air scouring, open valve FAV-5 and turn on pump
FAP-1.
6. After another one (1) minute, close valve BV-1, turn off pump FAP-1, and
close valve FAV-5.
7. Open valve FAV-6 and turn on pump FAP-2.
8. Run pump FAP-2 for up to nine (9) minutes.
9. Turn off pump FAP-2 and close valve FAV-6.
10. Open valve FAV-2. Close valve FAV-2 when the water level has reached the
bottom of the sight gauge.
11. Open valves FAV-1 and FAV-3.
12. Turn on pump FAP-1.
Filter A is now back in operation.
13. Turn off pump FBP-1
14. Close valves FBV-1.
15. Open valve FBV-2. Close valve FBV-2 when the water level has reached
the bottom of the sight gauge.
16. Open valve BV-1.
17. After one (1) minute of air scouring, open valve FBV-5 and turn on pump
FBP-1
18. After another one (1) minute, close valve BV-1, turn off pump FBP-1, and
close valve FBV-5.
19. Open valve FBV-6 and turn on pump FBP-2.
20. Run pump FBP-2 for up to nine (9) minutes.
21. Turn off pump FBP-2 and close valve FBV-6.
22. Open valve FBV-2. Close valve FBV-2 when the water level has reached
the bottom of the sight gauge.
23. Open valves FBV-1 and FBV-3.
24. Turn on pump FBP-1.
Filter B is now back in operation.
Note - If a higher backwash rate is needed, the feed pump and the backwash
pump can be operated concurrently.
Art\c\My Documents\FilterOperation.doc 1
CEI File No. 97264

a
Preliminary Operational Considerations
North Iredell High School Wastewater Treatment Plant
June 10, 1999
Existing Facilities
Equalization Basin Volume - 8,700 gal
Aeration Tank Volume - 12,000 gal
Secondary Clarifier Volume - 2,250 gal
Secondary Clarifier Area - 55 sq ft
Chlorination/Dechlorination System Volume - 1,000 gal
Flow Monitoring System - V-notch weir
Permit Flow - 12,500 gpd
Current Influent Loadings
Flow - 4,800 gpd
BOD5 - 219 mg/L
TSS - 209 mg/L
Current Operational Conditions
Wastewater flow rate - 3.3 gpm
Detention Times, hr
Equalization Basin - 43
Aeration Tank - 60
Secondary Clarifier - 11
MLSS - 2,814 mg/L
MLVSS - 2,690 mg/L
F/M - 0.0331b BODs/day/lb MLVSS under aeration
Return sludge rate - 60 gpm
Secondary clarifier surface loading rate - 87 gpd/sq ft
Secondary clarifier solids loading rate - 38.9 lb MLSS/sq ft/day
It is noted that the current return activated sludge (RAS) system is
comprised of two air lift pumps, one in each of the two (2) secondary
clarifier sludge hoppers, and a 3-inch diameter RAS pipe from each air
lift pump. The minimum achievable pumping rate for the air lift pumps
is 30 gpm each (60 gpm total since both pumps must be in operation).
To effect sludge thickening in the secondary clarifier, solids loading rate
on the secondary clarifier should be less than approximately 15 lb
MLSS/sq ft/day. At present, this cannot be realized because of the high
RAS rate and the higher than necessary MLSS concentration being
maintained in the aeration tank.
Art\c\My Documents\iredellfacilities.doc 1
CEI File No. 97264

i
Preliminary Operational Considerations
North Iredell High School Wastewater Treatment Plant
June 10, 1999
Future Operational Conditions f(a?, Q = 4,800 gpd)
Wastewater flow rate - 3.3 gpm
Detention Times, hr
Equalization Basin - 43
Aeration Tank - 60
Secondary Clarifier - 11
MLSS -1,200 mg/L
MLVSS - 1,000 mg/L
F/M - 0.088 lb BOD5/day/lb MLVSS under aeration
Return sludge rate - 9.7 gpm
Secondary clarifier surface loading rate - 87 gpd/sq ft
Secondary clarifier solids loading rate - 3.41b MLSS/sq ft/day
Tertiary filter loading rate - 4.0 gpm/ sq ft
It is noted that a RAS rate of approximately 9-10 gpm can be effected by
using two (2) Little Giant submersible centrifugal pumps, one in each of the two
(2) secondary sludge hoppers, and one (1) 3/4-inch diameter return RAS pipe. To
increase system headloss, and thus the pumping rate of the RAS pumps, the
length of the RAS piping system has been lengthened.
It is also noted that the reduced RAS pumping rate and MLSS
concentration in the aeration tank will lower the solids loading rate on the
secondary clarifier to a level where sludge thickening will occur.
Art\c\My Documents\iredellfacilities.doc 2
CEI File No. 97264

Preliminary Operational Considerations
North Iredell High School Wastewater Treatment Plant
June 10, 1999
Future Operational Conditions 0,0 = 8,650 gpd)
Wastewater flow rate - 6.0 gpm
Detention Times, hr
Equalization Basin - 24
Aeration Tank - 33
Secondary Clarifier - 6
MLSS -1,920 mg/L
MLVSS - 1,600 mg/L
F/M - 0.099 lb BOD5/day/lb MLVSS under aeration
Return sludge rate - 9.7 gpm
Secondary clarifier surface loading rate - 157 gpd/sq ft
Secondary clarifier solids loading rate - 6.6 lb MLSS/sq ft/day
Tertiary filter loading rate - 4.0 gpm / sq ft
Future Operational Conditions a Permit Flow of 12,500 gpd)
Wastewater flow rate - 8.7 gpm
Detention Times, hr
Equalization Basin - 16
Aeration Tank - 23
Secondary Clarifier - 4
MLSS -2,700 mg/L
MLVSS -2,300 mg/L
F/M - 0.099 lb BODs/day/lb MLVSS under aeration
Return sludge rate - 9.7 gpm
Secondary clarifier surface loading rate - 227 gpd/sq ft
Secondary clarifier solids loading rate - 10.8 lb MLSS / sq ft/day
Tertiary filter loading rate - 4.0 gpm/sq ft
Art\c\My Documents\iredellfacilities.doc 3
CEI File No. 97264