Wastewater Treatment Plant Capital Improvement Plan€¦ · Wastewater Treatment Plant . Capital Improvement Plan . ... C. Water Treatment Plant Lime ... 1978 and 2000 to provide

Hubbell, Roth & Clark, Inc. www.hrc-engr.com

Wastewater Treatment Plant Capital Improvement Plan Final

March 2010

HRC Job No. 20090075

WWTP Capital Improvement Plan y:\200900\20090075\design\report\text\01cip110609.doc i City of Howell

Table of Contents

Executive Summary ................................................................................................................ ES-1

Section 1 - Project Background ................................................................................................ 1-1 A. General ..................................................................................................................................... 1-1 B. Wastewater Treatment Plant Description ................................................................................. 1-1

Section 2 - Condition of Existing Wastewater Treatment Plant Infrastructure ..................... 2-1 A. General ..................................................................................................................................... 2-1 B. Main Sanitary Interceptor and Influent Force Main ................................................................. 2-1 C. Water Treatment Plant Lime Sludge Disposal System............................................................. 2-2 D. Wastewater Treatment Equipment ........................................................................................... 2-2 E. Solids Handling System ........................................................................................................... 2-9 F. Electrical System .................................................................................................................... 2-10 G. SCADA System ...................................................................................................................... 2-11 H. Structural ................................................................................................................................ 2-11 I. Buildings ................................................................................................................................ 2-11

Section 3 - Wastewater Treatment System Capacity and Hydraulic Evaluation .................... 3-1 A. General ..................................................................................................................................... 3-1 B. Hydraulic Profile Evaluation .................................................................................................... 3-2 C. Unit Process Capacity ............................................................................................................... 3-4

Section 4 - Recommended Improvements ................................................................................ 4-1 A. General ..................................................................................................................................... 4-1 B. Main Sanitary Interceptor ......................................................................................................... 4-1 C. Marion Township Influent Force Main .................................................................................... 4-1 D. Water Treatment Plant Lime Sludge Disposal System and Former Drying Bed

Underdrains .............................................................................................................................. 4-2 E. Raw Wastewater Pumping ....................................................................................................... 4-2 F. Raw Wastewater Screening ...................................................................................................... 4-7 G. Influent Flow Measurement ..................................................................................................... 4-7 H. Grit Removal System ............................................................................................................... 4-8 I. Wet Weather Storage Basins .................................................................................................... 4-8 J. Primary Settling Tanks ............................................................................................................. 4-9 K. Biological Treatment System ................................................................................................... 4-9 L. Final Settling Tanks ................................................................................................................ 4-12 M. Tertiary Treatment System ..................................................................................................... 4-13 N. Disinfection System ................................................................................................................ 4-14 O. Biosolids Handling System .................................................................................................... 4-14 P. Electrical System .................................................................................................................... 4-15 Q. SCADA System ...................................................................................................................... 4-16 R. Structures ................................................................................................................................ 4-16 S. Buildings ................................................................................................................................ 4-16

WWTP Capital Improvement Plan y:\200900\20090075\design\report\text\01cip110609.doc ii City of Howell

Section 5 - Capital Improvement Plan Implementation Schedule .......................................... 5-1 A. Project Prioritization and Costs ................................................................................................ 5-1 B. Financing .................................................................................................................................. 5-5

Appendices:

A - Meeting Notes

B - Cost Opinion Detail

C - Equipment Catalog Information and Vendor Quotes

List of Figures:

Figure 1-1 Site Plan

WWTP Capital Improvement Plan y:\200900\20090075\design\report\text\01cip110609.doc ES-1 City of Howell

Executive Summary A. General

Hubbell, Roth and Clark, Inc. (HRC) completed a Wastewater Treatment Plant (WWTP) Master

Plan/Capital Improvement Plan (CIP) for the City of Howell WWTP. This CIP provides guidelines and

a schedule for infrastructure repairs and replacement, treatment system upgrades, and expansion of the

WWTP to increase treatment capacity. This document has been developed in consideration of the age

and condition of existing facilities and projections for future wastewater flow.

B. Wastewater Treatment Plant Description

The City's WWTP is located at 1191 Pinckney Road and provides wastewater treatment for the City of

Howell and Marion Charter Township. The facility was originally constructed in 1936, and expanded in

1978 and 2000 to provide a design treatment capacity of 2.5 MGD and a maximum hydraulic capacity of

8.6 MGD (the current average flow is approximately 1.7 MGD). Treatment processes at the plant

include vortex grit removal, primary settling, aeration tanks with fine bubble air diffusers to supply

oxygen to the activated biological solids, secondary clarification and ultraviolet light disinfection.

Figure 1 shows a site plan of the existing plant.

C. Future Flows

Future flow projections were determined. These results indicate that the annual average, peak hour and

peak sustained treatment rates are expected to increase as shown in the table below.

WWTP Flow Statistic Current

Design Flow (MGD)

Future Design Flow

(MGD)

Annual average flow 2.5 3.6

Peak hour flow 8.6 11.3

Peak sustained treatment 5.0 8.5


D. Condition Assessment

Several meetings with WWTP staff were held and various field inspections were performed to gather

information regarding the condition of existing structures, buildings, equipment and facilities. An

inventory of existing structure and equipment conditions was prepared that listed the areas of concern,

which are described in detail in Section 2 of this report.

E. Wastewater Treatment and Hydraulic Capacity

A review of the existing capacity of the Howell WWTP was performed for both the hydraulic capacity

and the biological treatment capacity. The biological wastewater treatment capacity was compared for

the existing tanks based on currently accepted treatment parameters. It was verified that the existing

tanks are sufficient to provide adequate treatment to meet the existing NPDES permit limits. However,

there are some process and equipment changes that will be necessary to more effectively treat current

flows and to treat the estimated future flows. The hydraulic capacity was also evaluated and it was found

that it will be possible to handle the future anticipated flows with some minor modifications and

equipment replacement. The most significant impacts to improve operational efficiency and to reduce

solids buildup in the influent sewer will be the requirement for a replacement or supplemental raw

wastewater pump station. An additional pair of aeration basins and a final settling tank will be necessary

to handle the projected higher flow rates. Also as permit limits are tightened, it may be necessary to

provide for tertiary filtration at the plant.

F. Recommended Capital Improvements

The recommended CIP for the Howell WWTP totals approximately $9.6 million over the next 15 years.

The capital projects for the plant were sorted into four categories of projects, as described below:

Improvement Category 1 Projects – Projects that are required due to a potentially imminent

operational failure or capacity exceedance of the existing equipment within the foreseeable future.

Improvement Category 2 Projects – Projects that would provide for a somewhat longer term return on

the investment than Improvement Category 4 projects. These items could be driven by permit

compliance, operational or treatment process savings or other efficiencies, but may not be as cost-

effective as Improvement Category 1 projects.


Improvement Category 3 Projects – Projects primarily driven by growth and expansion within the

system. These projects could be implemented as needed, depending on the growth of the system. They

may also be coordinated with other equipment replacement projects.

Improvement Category 4 Projects – Projects primarily driven by operational cost savings. These

projects could be implemented as needed or coordinated with other equipment replacement projects.

Improvement Category 1 and 4 projects would likely be implemented within the first five years of the

CIP. Improvement Category 2 and 3 projects could be implemented within 5-10 years and 10-15 years,

respectively as part of a long-term CIP. These timeframes are not absolutes, but are provided as a

general reference.

The project cost opinions were developed based on input provided by equipment manufacturers and

previous project experience by HRC. They are based on current construction bid experience. In most

cases, general allowances were added for mechanical installation, electrical installation, administrative,

legal, engineering and contingencies so that each project component represents a complete project cost.

In general, some of the smaller projects may actually have a higher cost if they are completed separately,

due to economies of scale. It may also be possible to complete some of the smaller projects within the

normal operation and maintenance budget, and therefore these would not need to be part of a bond debt

or financing program.

A summary of the project costs by implementation priority are as follows:

Overall Project Implementation Summary

Improvement Category and Year Total Capital

Needs

Improvement Category 1 Projects (0-5 years) $2,053,000




TOTAL ANTICIPATED PROGRAM COST $9,674,000


It is important to note that filter system replacements at a project cost of approximately $5.0 million to

$5.5 million is not included above anticipated cost estimate. The need for filter improvements would be

determined in the future if the Michigan Department of Environmental Quality (MDEQ) modifies the

existing permit limits. Also, new raw wastewater pumping improvements of approximately $400,000 to

$1,100,000 are not included above anticipated costs.

There are several options available for financing of the improvements contained in this program.

Conventional municipal bond financing is an option as well as obtaining a low interest loan through the

MDEQ’s State Revolving Loan Fund (SRF) program. However, the use of the SRF program also

requires that a Project Plan be prepared along with the requisite public hearings and other requirements.

In addition, there are third-party financing options available that can pay for energy-related

improvements through the energy costs savings. However, the interest rates can be slightly higher than

what most communities can achieve through conventional financing opportunities.

It may be advantageous for Howell to prepare a Project Plan for a portion of the recommended projects.

The recent economic stimulus programs are likely to increase funding to the SRF program for 2011 and

2012. If a Project Plan is prepared, it is likely that Howell can have an SRF-eligible project on the

MDEQ Priority List for 2011.

G. Improvement Category 1 and 4 Recommendations

The Improvement Category 1 and 4 projects recommended for implementation are described in Section 5

of the report, and are also summarized in the table below:


Improvement Category 1 and 4 Projects Recommended for Implementation

Project Improvement

Category Project Cost

Influent Screw Pump Upgrades (ventilation/carbon canister) 1 $292,000

Bypass Channel with Manual Screen 1 $146,000

Grit Pump Enclosure 1 $384,000

Primary Concrete Structural Rehab 1 $74,000

Two New Final Settling Tank Mechanisms 1 $586,000

Replace Aeration Blower 4 $161,000

Flow Storage Basin Fill Concrete (manual flushing) 1 $290,000

Raise Aeration Influent MH Walls 1 $91,000

RAS Pump and Valve Replacements 1 $80,000

Sludge Storage Decant Valves 1 $75,000

Marion Twp Force Main Biocide Addition 1 $20,000

Primary Scum Pit Pumping 4 $40,000

Repair Slope East of Sludge Storage Tank 4 1 $15,000

Convert 15 Remote Sites to Cellular Telemetry 4 $360,000

Miscellaneous Site and Building Improvements 4 $500,000

TOTAL IMPROVEMENT CATEGORY 1 AND 4 PROJECT COST $3,114,000

WWTP Capital Improvement Plan y:\200900\20090075\design\report\text\01cip110609.doc 1-1 City of Howell

Section 1 - Project Background

A. General

The WWTP CIP provides guidelines and a schedule for infrastructure repairs/replacement, elimination of

hydraulic restrictions and treatment system upgrades.

B. Wastewater Treatment Plant Description

The City’s WWTP is located at 1191 Pinckney Road and provides wastewater treatment for the City of

Howell and several areas in Marion Township. The original facility was constructed in 1936 and various

upgrades and improvements were implemented in 1960, 1978, and 2001. The current average flow is

approximately 1.7 MGD and the design treatment capacity is 2.5 MGD average flow, 5.0 MGD peak

equalized flow and 8.6 MGD peak instantaneous flow. The WWTP improvements completed in 2001

were designed to accommodate future expansion of the WWTP to increase the design treatment capacity

to 3.6 MGD average flow.

Treatment processes include influent screening, grit removal, wet weather storage, primary settling,

activated sludge biological treatment, final setting, disinfection and solids handling. The facilities also

include a tertiary treatment system which is no longer operational. The wastewater collection system

includes a 12-inch sanitary sewer, 36-inch main sanitary interceptor, 8-inch Marion Township force main

and a pumping station/force main which conveys water treatment plant lime sludge lagoon filtrate to the

WWTP. In addition, a 12-inch/18-inch sanitary sewer located on the WWTP site conveys various

process recycle/drain flows to the raw wastewater pumping station.

A general site plan of the facility is indicated in Figure 1-1.

The WWTP includes the following major equipment and processes:

Three 54-inch diameter inclined screw pumps with a firm capacity of 8.6 MGD (2 pumps

running).

Automatically cleaned, 3.5-feet wide, influent screen with 0.375-inch clear openings between

bars and screenings washer/compactor.

Parshall flume for influent flow measurement.


Vortex type grit removal system with 12.0 MGD capacity grit tank, grit pump, grit classifier and

grit washer.

A four compartment wet weather storage basin with a total storage volume of approximately

0.5 MG including an aeration system, manually operated drain valve and 6-inch Parshall flume

for return flow measurement.

Two 45 foot diameter, 9 foot side water depth primary settling tanks.

Four 24 foot wide, 90 foot long, 15.7 to 17.8-feet side water depth aeration tanks with a ceramic

fine bubble diffuser aeration system and associated blowers and diffuser cleaning system. The

total aeration tank volume is approximately 1.15 MG at the peak operating depth.

Three 55 foot diameter by 10 foot water depth final settling tanks.

An abandoned tertiary filter system including three horizontal pressure filters and associated

filter feed and backwash pumps.

A dual channel, vertical lamp type ultraviolet disinfection system.

Solids handling system including three rectangular sludge storage tanks with a total capacity of

1.48 MG, one 115,000 gallon waste activated sludge day tank with diffused air mixing system,

one 63,000 gallon lime stabilization tank with mechanical mixer, a lime slurry storage and feed

system and one rotary drum type sludge thickener and associated sludge transfer pumping

system. The lime stabilization and sludge thickening systems are no longer in service.

The water treatment plant located adjacent to the City DPW facility pumps lime sludge to two

storage/filtration lagoons with an underdrain system and pump station/force main. The system

was designed to discharge lagoon filtrate to the receiving stream after pH adjustment. However,

the system has been modified to convey filtrate to the WWTP influent sewer. The dewatered

lime sludge is used on agricultural land as a soil supplement.


Section 2 - Condition of Existing Wastewater Treatment Plant Infrastructure

A. General

Meetings with DPW and WWTP staff were held and various field inspections were performed to gather

information regarding the condition of existing structures, buildings, equipment, and facilities. This

section includes a description of the assessments and general recommendations. The specific

recommendations for system improvements are summarized in Section 4 of this report.

B. Main Sanitary Interceptor and Influent Force Main

The main sanitary interceptor serving the City extends from Pulford Road south to the WWTP and

consists of approximately 20 feet of 42-inch sewer, 900 feet of 36-inch sewer and 454 feet of 29-

inch x 45-inch horizontal elliptical sewer. The grade of the sewer varies from 0.03% to 0.09%. This

sewer has been in service since 1978 and has never been cleaned or inspected. The City has indicated

that excessive inflow/infiltration may be occurring at manhole structures, pipe joints, structural failures,

etc.

The Marion Township force main, which conveys approximately 120,000 gpd of raw wastewater to the

WWTP, is an 8-inch diameter pipe approximately 1.5 miles long. It is suspected that the excessive

detention time in the force main is a major cause of hydrogen sulfide release and the associated corrosion

at the WWTP influent wet well.

The following issues related to the main sanitary interceptor and the Marion Township force main are

reviewed in Section 4 of this report:

Proposed main sanitary interceptor pipe/structure repairs to minimize inflow and infiltration.

Consideration of alternate measures to minimize the formation of hydrogen sulfide in the Marion

Township force main system.


C. Water Treatment Plant Lime Sludge Disposal System

Lime sludge resulting from the water treatment process is

discharged to either of two storage/filtration lagoons for

dewatering. Filtrate percolates through the soil and is

collected in an underdrain system. Initially, the pH of the

filtrate was adjusted as necessary and discharged to the

receiving stream. The operation of the pH adjustment system

proved to be unreliable and, therefore, filtrate is now

discharged to the WWTP. This system introduces

unnecessary WWTP inflow since the lagoons collect

precipitation in addition to the lime sludge loading.

Improvements to the lime sludge disposal system which should be considered are as follows:

Installation of a new pH adjustment system for treatment of lagoon filtrate.

Revisions to the existing filtrate pumping system to provide for normal discharge of treated

filtrate to the receiving stream.

D. Wastewater Treatment Equipment

The general condition of liquid treatment equipment is as follows:

1. Raw Wastewater Pumping

The design pumping capacity of the raw wastewater pumps is 8.6 MGD with two pumps

operating. However, all three pumps have operated

during a few peak flow events in the past, and the

excess flow has caused overflows in downstream

treatment units. Resolution of the main sanitary

interceptor inflow/infiltration issues will probably

eliminate the need to operate three pumps at the

same time. However, the hydraulic capacity of flow

channels/treatment units should be adequate for the

peak influent pumping capacity. Currently, the

Lime Sludge Lagoons

Raw Wastewater Pumps


upper influent channel overflows and spills to the lower grit dewatering area during peak flow

conditions.

The fiberglass covers over the screw pumps traps moisture/condensation and creates a corrosive

atmosphere which has resulted in the failure of bearing lubrication lines and pump channel

isolation gates. The existing wet well ventilation system has proven to be inadequate to control

corrosion.

A submersible, grinder type, raw wastewater sample pump previously served to supply an

automatic sampler located near the laboratory. The grinder pump failed frequently and,

therefore, the pump/sampler system is no longer used. The original equipment has been replaced

with a portable sampler located in the Headworks Building. The portable sampler includes an

integral peristaltic pump with the suction line located downstream of the influent screening

system to minimize plugging problems.

The screw pump lower bearing grease lubrication lines are installed in flow channel locations

where rags and debris collect on the piping.

The following raw wastewater pumping system upgrades should be addressed:

Refurbishment or relocation of the raw wastewater sampling system.

Replacement of pump channel isolation gates.

Rework/replacement of pump bearing grease lines.

Improved corrosion control.

Potential replacement of the wetwell or construction of a supplemental wetwell at an

elevation to allow for free flow from the sewer into the wet well. This will be discussed

further under Section 4, Alternatives.


2. Raw Wastewater Screening

The fine screen system has functioned adequately during normal

flow conditions. However, during peak flow conditions, the

increased volume of debris has blocked the screen and caused

screen channel overflow when all three raw wastewater pumps

are operating. Additional information regarding the hydraulic

capacity of the screen system is included in Section 3 of this

report.

The following suggested improvements to the influent screening

system are reviewed in Sections 3 and 4:

Construction of a second screening system to serve as an emergency standby system and

to supplement the existing system during peak flows.

Installation of new screen channel with isolation gates and motorized actuators or gates

installed at a lower elevation to allow for automatic overflow to the standby channel.

Control system upgrades to allow for the new screen channel to be automatically placed

in service during peak flow conditions.

3. Influent Flow Measurement

The Parshall flume used for influent flow measurement is located in the flow channel upstream

of the grit removal system. The system hydraulics appear to be adequate for accurate flow

measurement at normal influent flow rates. However, at higher flow rates the hydraulic gradient

downstream of the flume increases as flow begins passing over the wet weather flow basin

overflow weir and the flume may become surcharged leading to inaccurate flow readings. The

flow vs. upstream head curve for the flume changes as downstream water level increases and,

therefore, flow measurements using the Parshall flume at higher flows may be inaccurate.

Various options for improvements to the influent flow metering system are discussed in

Section 4 including:

Installation of new primary influent and wet weather storage basin influent flow meters.

Installation of individual influent flow meters for each primary settling tank.

Influent Screen System


4. Grit Removal System

The vortex type grit removal system has functioned

adequately except that the grit pumping system heat

tracing equipment has proven to be inadequate

during extreme winter conditions. A temporary tent

style enclosure has been utilized in the past to

minimize freezing problems. System improvements

which could be implemented to reduce cold weather

problems are as follows:

Installation of a pre-fabricated building enclosure to protect the grit pump.

Relocation of the grit pump inside the Headworks Building.

5. Wet Weather Storage Basins

The original aeration basins were converted to wet

weather storage basins as part of the 1998 WWTP

expansion project. However, since there is not a

means for automatic control of return flow, this

system cannot practically be used for flow

equalization. The system functions adequately to

store some excess raw wastewater during wet weather

influent flow conditions, but the total storage volume

of 0.5 MG is very limited. The following operational

issues should be addressed:

The overflow weir at the end of the grit tank effluent channel allows for excess raw

wastewater flow to be discharged to the wet weather storage basins. However, a system

for adjusting and metering the flow split between the wet weather flow basins and

primary settling tanks is not available. Additional information regarding this issue is

included in Section 3 of this report.

The storage basins are not equipped with an emergency overflow or an isolation gate to

shut off flow into the basins when they are full.

Solids/debris deposits must be manually removed from the basins or flushed with a hose

to the basin drain. A more effective means of flushing the tank floors after a storage

Grit Pump & Grit Collector Drive

Wet Weather Storage Basins


event could be accommodated by installing influent valves or gates, a sloped concrete

floor and possibly a flushing system.

The basin drain system consists of a manually operated valve and a gravity drain

connection to the WWTP process drain sewer. A means of automatically controlling the

discharge rate in response to a flow rate set point should be considered. A modulating

valve could be positioned in response to a flow signal in order to maintain the desired

drain rate.

6. Primary Settling Tanks

The primary settling tank’s scum removal/pumping system has proven to be labor intensive since

manual flushing/mixing of the scum pit is required prior to pumping. In addition, the scum

beaches within the settling tanks become submerged during peak flow conditions. The scum pit

has overflowed in the past since the top of the pit is lower than the settling tank water surface.

The ammonia concentration in the primary effluent

is generally higher than the primary influent.

Initially, the WWTP staff assumed that the ammonia

concentration increase was caused by co-settlement

of primary sludge and waste activated secondary

sludge (WAS). However, a brief full scale test

indicated the ammonia level still increased when the

WAS flow was discharged to sludge storage in lieu

of the primary settling tanks.

The primary settling tank improvement concepts which are reviewed in Section 4 include:

Raising of the scum beaches to minimize the potential for overflow during high plant

flows and refurbishment of the scum removal/pumping system to reduce labor

requirements and to minimize the potential for scum pit overflow.

Additional research to determine the cause of ammonia concentration increase in the

primary treatment system.

Structural rehabilitation of the concrete tank structure

Primary Settling Tank Scum Beach


7. Biological Treatment System

The fine bubble aeration system has operated adequately and the hydrogen chloride gas diffuser

cleaning system has proven to be sufficient to prevent diffuser clogging problems. The aeration

tank effluent gates are manually adjustable slide gates with a single 120 degree V-notch. These

gates are used in conjunction with a sonic level sensor to provide flow measurement and to

control tank level. The current sonic level sensors are not rigidly attached to the gate and thus do

not take the gate position into account. The current system does not automatically provide for

flow splitting between the aeration tanks. A manual check of the flow is required in order to

verify that an approximately equal flow split is occurring.

The following biological treatment system issues should be addressed:

The primary effluent manhole upstream of

the aeration tanks is equipped with a bolted

and gasketed manhole cover. This manhole

is surcharged approximately 6 feet and,

therefore, presents a flooding potential

should it fail.

The aeration blowers are generally

significantly oversized. The dissolved

oxygen concentration in the effluent end of

the aeration tanks is typically 8.0 to 9.0 ppm, during winter months, with only one

blower operating. Controlling the air flow to a lower rate is not possible with the current

blowers. An additional smaller capacity blower should be considered.

One blower is out of service due to failure of the electrical “soft start” equipment.

An improved system for splitting the primary effluent flow between the aeration tanks

should be considered when additional aeration tanks are constructed in the future.

Installation of a mechanical mixer and baffling in the first and/or second portion of each

aeration tank would allow for the initial 25 to 50% of each tank to be operated as an

anoxic, anaerobic or aerobic (swing) zone. This could be used to minimize aeration

volume and maximize the amount of biological nutrient (mainly phosphorus) removal.

In the event of high concentrations of ammonia nitrogen, these cells could be switched

to aerobic mode to enhance nitrification.

Aeration Tanks


8. Final Settling Tanks

Two of the final settling tanks sludge collector

mechanisms (from the 1970’s plant improvements)

have served their useful life and are in poor

condition. However, the sludge collector drives on

these units were replaced as part of the most recent

(2000) WWTP improvement project and are in

satisfactory condition. Scum removed in the final

settling tanks is conveyed by gravity to the primary

settling tank scum pit. The gravity drain is

approximately 300 feet long and a portion of the drain is always surcharged. This drain is

subject to plugging because of the length and surcharge conditions.

The geometry of the final settling tank influent splitter box does not appear to be optimum for

equal flow split. Some gate adjustment is necessary

The improvements to the final settling tanks which should be addressed are as follows:

Replacement of two of the final settling tank sludge collector mechanisms.

Scum removal system upgrades.

Modification of the final settling tank influent splitter box to provide additional baffling

for improved flow splitting.

9. Tertiary Treatment System

Tertiary filtration is not needed to meet current

discharge permit limits. The existing tertiary

treatment system has been abandoned in place as a

result of several problems related to the operation of

the pressure filtration system. Complete

replacement of the pressure filtration equipment with

one of several current technology gravity filtration

equipment alternatives should be considered when

permit conditions warrant. Some potential

alternatives include:

Final Settling Tank

Pressure Filter Face Piping


Travelling bridge type gravity sand filters.

Cloth media disk filters.

Wire mesh media disk filters.

10. Disinfection System

The existing vertical lamp ultraviolet disinfection system has been reliable and has functioned

properly for disinfection purposes. However, the following issues should be addressed:

The equipment is located outdoors and is difficult to maintain during inclement or winter

weather conditions. In addition, a temporary tent type awning has been installed to

minimize exposure to the elements. (Sunlight has previously damaged electrical cables

and snow accumulation has caused leakage in electrical enclosures.)

Equipment maintenance is labor intensive since

an automatic mechanical system for cleaning

the UV lamp quartz sleeves is not included.

Plant staff indicated that the transformer for the

UV system power supply has inadequate

capacity if the UV system is operated at full

power.

Lamp replacement costs are excessive.

UV sensors used to control the dosage rate are

no longer functional.

It may be possible to incorporate a revised UV disinfection system (reusing the existing

equipment or with new equipment) in conjunction with new tertiary filtration equipment within a

new filter building and, therefore, separate weather protection for the UV system would not be

required.

E. Solids Handling System

The current biosolids handling system consists of co-settlement of primary/secondary waste activated

sludge in the primary settling tanks, long term biosolids storage in several below grade tanks, biosolids

storage tank decanting and land application of liquid biosolids. Secondary WAS is discharged to the

primary influent piping manifold.) The biosolids lime stabilization system and biosolids thickening

UV System


systems have been abandoned in place. Long term biosolids storage has provided adequate pathogen

destruction to allow land application of liquid biosolids without further stabilization efforts. The

following issues associated with the solids handling system should be considered:

The pipe support system for the WAS day tank aeration diffuser system has failed due to

corrosion of ferrous metal components. However, it has not been found to be necessary to aerate

these tanks so complete removal of this diffuser system and blowers could be considered.

Some biosolids storage tank decant valves have corroded and are in need of replacement.

If biosolids volumes increase in the future, the detention time in the storage tanks may become

inadequate for the degree of pathogen destruction required for land application. Additional tanks

could be considered.

A positive means of biosolids stabilization and thickening/dewatering would improve the

reliability of the solids handling system and could potentially reduce the volume of biosolids to

be disposed of off-site.

The east side of Biosolids Storage Tank No. 4 is showing signs of slope failure due to steep

grades and washout from storm runoff. The inadequate backfill conditions present the potential

for structural failure of the tank.

Biosolids Storage Tanks No. 3 and No. 4 decant valves are located inside of the decant chamber

and are, therefore, subject to corrosion. Tank No. 5 has decant valves in a dry chamber which

has provided longer valve component life since the valves are not exposed to corrosive fumes

released during decanting.

Tank No. 4 needs a secondary access hatch.

Groundwater leakage into Biosolids Storage Tank No. 3 has been identified.

F. Electrical System

The existing 600kW main diesel generator dates from the original plant expansion in the 1970’s. There

is difficulty in obtaining replacement parts for this unit. In addition, the main switchgear condition and

reliability and the availability of replacement parts is problematic. Considering the age and make of

switchgear it may be desirable to consider replacement however, replacement breakers may be retrofit to

provide prolonged service. A more detailed analysis of the switchgear should be performed before

proceeding with any replacement.


G. SCADA System

The SCADA Operating System (RSView®) was recently upgraded. Originally the plant had a

Wonderware® system but there was difficulty in getting it operational and support was limited. The

plant now receives excellent support from RS Technical Services. The plant currently has a blend of two

communicating systems with remote sites and has about 6 sites on dial-up modems and 6 sites using a

radio communication system. The radio system is a SCADAPack® by Control Microsystems. The

City’s water plant currently utilizes a cellular based system. It may be desirable to switch the

communication mode for all of the wastewater sites, including the Marion Township facilities as well, to

cellular.

H. Structural

In general, the concrete structures still in use at the Howell WWTP are in fairly good condition, with the

exception of the primary settling tanks and the wet weather storage tanks. Needed structural

rehabilitation of the primary settling tanks includes crack filling and surface repair of spalled concrete

areas and handrail post socket repairs.

The concrete on the wet weather storage tanks is in marginal condition but the railings around the

structure should be reconditioned and the post sockets also repaired.

I. Buildings

1. Headworks Building

The door between the raw wastewater pump motor room and the influent screening area is a

code violation since it interconnects a hazardous area to a non-hazardous area. The makeup air

unit supplies both the hazardous and non-hazardous areas and, therefore, the discharge ductwork

also provides an interconnection between the areas when the unit is not in operation.

In addition, small openings in the pump motor mounting plates present the potential for

hazardous gases from the pump discharge area to migrate into the pump motor room. The grit

tank influent channel opening in the west wall of screenings room allows heated make up air to

escape to the building exterior during the heating season. This opening also allows uncontrolled

exchange of air between the building interior/exterior when the makeup air unit is not in service.


A low hanging vinyl or rubber baffle should be placed at the wall so that it is just slightly above

the flow line at the normal water surface. This will help to minimize the amount of building heat

loss.


Section 3 - Wastewater Treatment System Capacity and Hydraulic Evaluation

A. General

Hydraulic and flow capacity problems have occurred in the past during wet weather events:

Excessive influent flow has required the operation of all three raw wastewater pumps to prevent

sanitary interceptor manhole overflow.

Operation of all three raw wastewater pumps has flushed out the main sanitary interceptor and

caused the influent screen to clog and the screen channel to overflow.

Excessive influent flow has resulted in flooding of the primary tank scum beaches and overflow

of the scum box.

The screw pump wet well was not constructed low enough to allow the influent sewer to

completely drain. This contributes to solids buildup in the sewer over the long term since

adequate flushing velocities are not possible at low flows.

The wet weather storage basins have filled completely and overflowed to the storm drainage

system.

In addition, the existing headworks facilities do not provide for an accurate method to control or meter

the flow split between the primary settling tanks and the wet weather storage basins. Therefore, the

available primary treatment capacity may not always be fully utilized and the storage basins may

overflow as a result.


The following hydraulic capacity information is included in the 1998 WWTP Expansion Project

construction drawings and basis of design:

Flow Description Current Design

Capacity (MGD) Future Design

Capacity (MGD)

Average Flow 2.5 3.6

Firm Raw Wastewater Pumping Capacity 8.6 11.3

Peak Flow Thru Influent Screen/Grit Removal System 8.6 11.3

Peak Flow Thru Treatment Process 5.0 8.5

Peak Wet Weather Storage Basin Influent Flow 3.6 2.8

This section includes a general assessment of the WWTP hydraulics and the flow capacity of various

treatment systems. The specific recommendations for system improvements are summarized in

Section 4.

B. Hydraulic Profile Evaluation

Evaluation of the current WWTP hydraulic profile indicates the lack of current/future capacity and other

hydraulic issues in the following areas:

Raw wastewater wetwell

Influent screen

Primary settling tanks influent piping

Primary settling tanks skimming system

Secondary effluent piping between the final settling tanks and the UV contact channel

Raw Wastewater Wetwell

The influent sewer arrives at the plant at an invert elevation of 895.0. The screw pump wet well invert is

also 895.0. This means that the influent sewer never completely drains since there is not a free fall into

the screw pump wetwell. Good sanitary sewer design practice usually allows for the sewer to completely

drain into a wetwell so that flushing velocities can be maintained in the sewer, especially at lower flows.

Given the current situation, the minimum submergence on the screw pumps is the minimum elevation

that can be maintained, which is approximately 18-inches or about half the depth of the 36-inch sewer.

This contributes to solids buildup in the influent sewer during dry weather. Potential solutions include


installing longer screw pumps and modifying the wetwell or modifying the wet well to allow for

submersible pumps. These options will be discussed further in Section 4 of this report.

Influent Screen

The influent screen hydraulic issues are presented in this section under “Unit Process Capacity.”

Primary Settling Tank Influent

The hydraulic evaluation of the 16-inch/20-inch primary influent piping system indicates that inadequate

capacity is available to convey the design peak flow of 5.0 MGD to the primary tanks without

overflowing the current grit tank effluent channel overflow weir (El. 921.33). The head loss in the

primary influent line at approximately 4.0 MGD causes a backup into the grit tank effluent channel and

results in overflow to the equalization basins at influent rates 4.0 MGD and greater. Installation of a

motorized gate on the overflow weir to the wet weather storage tank will allow for better control of the

influent flow to the process as well as conserving the storage volume in the wet weather storage tank

until it is really needed. This may allow the plant to sustain longer storm events given that the limited

volume in the storage tank could be retained for times when it is really needed.

Alternately, the primary influent conveyance capacity could be increased to 5.0 MGD by raising the grit

tank effluent channel overflow weir to approximately El. 922.5. However, the resultant 1.2 foot increase

in the grit tank effluent channel water level will impact the upstream influent flow measuring flume.

Additional primary influent hydraulic capacity is required to provide for the current/future design peak

regulated flow through the treatment process (5.0/8.5 MGD).

Primary Settling Tanks Skimming System

The crest of the existing primary settling tank scum beaches is located in close proximity to the tank

water surface at average flow. During peak flow conditions, the tank water surface rises approximately

0.4 inches and causes the scum beaches to overflow. The scum beach crest elevation should be raised

and the beach lengthened in order to provide greater freeboard against immersion at high flows. In

general, the scum beach crest should be about 0.2 feet (about 2.5 inches) above the water surface at the

maximum flow rate. This would require that the existing scum beach be raised approximately 0.2 feet.

This can be done by adding a spacer flange in the mounting piping and by adjusting the supports. The

existing beach may be long enough to have enough submergence at low flows but the actual length

would need to be confirmed before attempting this modification.


Secondary Effluent Piping

The secondary effluent is conveyed from the final settling tanks to the pressure filter influent wet well

through an 18-inch diameter pipeline. The pipeline velocity is 4.3 fps at the current peak equalized flow

(5.0 MGD) and 7.4 fps at the future peak equalized flow (8.5 MGD). There are approximately 500

equivalent linear feet between the junction manhole and the UV contact channel. Additional secondary

effluent piping will likely be required in the future to supplement or replace the existing piping and

provide additional flow capacity. The future pipe sizing and necessity would depend on the type and

elevation of the potential future tertiary treatment system.

C. Unit Process Capacity

The capacity of the various treatment units has been evaluated based on the Ten States Standards and

normal design practices. The results of the evaluation are as follows:

1. Raw Wastewater Pumping

The three screw type raw wastewater pumps have adequate capacity to deliver 8.6 MGD peak

instantaneous flow with one pump out of service. Additional pumping capacity will be required

in the future to provide the design firm capacity of 11.3 MGD peak instantaneous flow.

2. Raw Wastewater Screening

The 3.5 feet wide influent screen provides a flow area of approximately 4.7 square feet at 2.4-

feet water depth with approximately 2.8 fps velocity through the screen at the design peak raw

wastewater pumping rate (8.6 MGD). The estimated velocity is less than the normal maximum

design velocity (3.0 fps) provided the screen is maintained in a clean condition. However, the

plant operating experience is that the mechanical cleaning system capacity is inadequate during

peak flow conditions and the screen becomes blinded to an unacceptable degree when solids

from the sanitary interceptor are flushed out during wet weather events.

An overflow/bypass channel should be considered to provide additional relief/redundancy for

current conditions and could be utilized to provide an additional mechanical screen in the future

to provide screening capacity for the proposed peak raw wastewater pumping rate of 11.3 MGD.

3. Influent Flow Measurement

The influent meter is a Parshall flume with an 18-inch wide throat and a flow range of 0.3 to

15.9 MGD with free flow conditions. The meter is probably adequate for the current design


peak flow (8.6 MGD) and the proposed future 11.3 MGD design peak flow provided the

downstream hydraulics does not surcharge the flume. Flume surcharge would cause inaccurate

flow metering unless the flow vs. head calculation is automatically adjusted as downstream head

varies. The current arrangement does not guarantee that the flume will not be surcharged.

Individual magnetic flow meters installed in the primary influent or effluent lines and the wet

weather storage basin influent line would provide more accurate flow measurement and would

also serve to account for the portion which is diverted to the wet weather storage basin.

Installing magnetic flow meters appears to be more feasible on the primary effluent lines.

Although metering at this location would not account for the small amount of flow through the

primary scum or sludge lines, the overall accuracy of metering should be substantially improved

since magnetic pipe meter measurement is more accurate than measuring the level on an

improperly functioning Parshall flume.

4. Grit Removal System

The grit removal system has a rated maximum capacity of 12.0 MGD and is therefore adequate

for the current 8.6 MGD peak raw wastewater pumping capacity and the proposed future 11.3

MGD pumping capacity.

5. Wet Weather Storage Basins

The wet weather storage basins provide a total storage volume of approximately 0.5 MG which

allows for approximately 3.3 hours of operation with an 8.6 MGD influent flow rate, 5.0 MGD

primary influent flow rate and 3.6 MGD equalization basin influent flow rate. Resolution of the

main sanitary interceptor inflow/infiltration issues should reduce the demand for excess wet

weather flow storage capacity.

Installation of an automatic control valve system for the basin drain would allow for automatic

initiation and control of basin return flows during periods of low WWTP influent flow.

Therefore, the basin could likely be drained earlier and more efficiently so it would normally be

in an empty condition to provide additional storage/equalization capacity during subsequent peak

flow periods.

6. Primary Settling Tanks

The two 45 foot diameter primary settling tanks provide a total surface area of 3,180 square feet

which results in a surface overflow rate of 770 gpd per square foot at the design average flow


(2.5 MGD) with both tanks in service and the surface overflow rate is 1,570 gpd per square foot

at the peak equalized flow (5.0 MGD).

The surface overflow rate at the future average flow (3.6 MGD) would be 1,140 gpd per square

foot with both tanks in service and the surface overflow rate at the future peak equalized flow

rate of 8.5 MGD would be 2,670 gpd per square foot. The current and future surface overflow

rate at the peak equalized flow exceeds the Ten States Standards recommended maximum

overflow rate of 1,200 gpd per square foot for co-settlement of primary/secondary waste

activated sludge. Additional primary settling tanks should be considered for a future expansion

in order to provide overflow rates within the Ten States Standards criteria and thus optimize the

loading to the secondary process and continue to allow for waste activated sludge co-settling for

thickening.

Two additional circular primary tanks, or equivalent sized rectangular tanks, would increase the

total surface area to 6,360 square feet and the overflow rate at the future peak equalized flow rate

of 8.5 MGD would be reduced to 1,340 gpd per square foot with all tanks in service. If slightly

larger rectangular tanks were utilized, the overflow rate could be kept at or below the Ten States

Standards criteria of 1,200 gpd per square foot. The overflow rate at the future average flow of

3.6 MGD would be 760 gpd per square foot with one tank out of service.

7. Biological Treatment System

The four aeration tanks provide a total biological reactor volume of approximately 1.15 MG

which results in a hydraulic residence time (HRT) of between 10 and 11.3 hours at the design

average flow of 2.5 MGD depending on the level in the tank. The biological reactor volume is in

compliance with Ten States Standards recommended loading of 40 lbs. BOD/day per 1,000

cubic foot volume at the plant design average BOD concentration at current flow rates. As flows

and loadings increase, the existing reactor volume will likely remain sufficient at average design

flow rates and a primary effluent BOD concentration of 165 mg/l (the average primary effluent

BOD concentration since 2006 has been approximately 115 mg/l). At maximum monthly flow

rates and if primary effluent BOD concentrations climb to 165 mg/l, the biological reactor

loading rates may approach unacceptable levels thus requiring that two additional tanks be

constructed. This will not likely happen until both the maximum month flow rate approaches 5.0

MGD and the primary effluent BOD concentration reaches 165 mg/l.


Additional aeration tank volume and associated oxygen transfer capacity may be required in the

future, along with considerations for implementing enhanced biological phosphorus removal

(EBPR) and an anoxic selector for filamentous control.

8. Final Settling Tanks

The three 55 foot diameter final settling tanks provide a total surface area of 7,125 square feet

which results in a surface overflow rate of 702 gpd per square foot at the peak equalized flow

(5.0 MGD) with all tanks in service and 1,050 gpd per square foot with one tank out of service.

Therefore, the existing tanks comply with the Ten States Standards recommended maximum

overflow rate of 1,000 gpd per square foot. However, the 10 ft. side water depth if less than the

minimum 12 ft. depth required by the Ten States Standards.

One additional tank would be required in the future to provide a surface overflow rate of 895 gpd

per square foot at the future equalized peak flow of 8.5 MGD with all tanks in service and 1,190

gpd per square foot with one tank out of service.

9. Tertiary Treatment System

The existing pressure filtration system has not been functional for several years and is not

currently necessary for permit compliance. As plant loadings increase, or if phosphorus limits

become more stringent, tertiary treatment could be provided with current technology tertiary

treatment equipment as indicated in Section 4 of this report. Approximately 11.2 feet of head is

available between the final settling tanks and UV disinfection system, for operation of a filtration

system, which should be more than ample to provide for gravity filtration for most filtration

technologies.

10. Disinfection System

Effluent from each UV channel flows into a narrow weir trough and dead ends against a concrete

wall. Effluent flow spills over the weirs on both sides of the troughs and is discharged to

effluent chamber below. This flow pattern is somewhat unconventional with flow from inside

the weir trough to the outside. The velocity in the trough causes surging in the level inside of the

UV channel. In addition, it appears that there is inadequate weir length in the channel which

also contributes to the surging. The horizontal velocity in the trough is approximately 3.9 fps at

the current peak equalized flow of 5.0 MGD and the velocity would increase to approximately


6.6 fps at the future peak equalized flow of 8.5 MGD. Excessive splashing may occur at the

dead end of the trough with the future velocity conditions.

A revised weir arrangement with traditional over the weir into the trough flow pattern and

additional weir length would be required if the existing vertical lamp UV system is replaced with

a horizontal lamp system. The additional weir length would be required to minimize the

variation of UV channel water depth. This could be accomplished within the existing structure

or in a new UV contact structure depending on the final arrangement of the system and if a new

filtration system is incorporated into the plant.

11. Solids Handling System

The current annual average combined sludge volume is approximately 11,400 gpd based on 1.9

MGD annual average raw wastewater flow. Approximately 320,000 gallons of additional

biosolids storage volume would be required in order to provide for 180 days of storage without

decanting or thickening when the annual average flow rate increases to 3.6 MGD assuming

current average biosolids concentrations. If the biosolids can reliably be thickened to 8% solids

concentration only 240,000 additional gallons of storage would be required.


Section 4 - Recommended Improvements

A. General

This section includes recommendations for improvements to the existing WWTP treatment systems and

associated buildings, concrete structures, electrical systems, instrumentation and controls, heating and

ventilation systems and ancillary systems. These improvements are the result of investigations and

analysis associated with Sections 2 and 3 of this report. Breakdowns of cost opinions are included in

Appendix B and information on various equipment options is included in Appendix C.

B. Main Sanitary Interceptor

The evaluation of the main sanitary interceptor condition has been deferred since the cost to mobilize to

inspect the sewer is almost approaching the cost of replacing the sewer. Until a new pumping

arrangement, discussed later, is addressed, even a replacement sewer would also plug with solids.

C. Marion Township Influent Force Main

Potential options for addressing corrosion control in this force main include the addition of sodium

nitrate or Biocide™ to the force main at the pump station. This is one of the most common types of

corrosion control abatement technologies in use throughout the industry. Using this technique would

involve the addition of a chemical at the pump station so space would be needed for a double wall tank to

store the chemical along with a chemical feed pump to deliver the chemical. The receptacle would need

to be wired so that the feed pump runs when the pump runs.

An alternate approach would be to add a corrosion abatement device at the end of the force main and/or

to modify the discharge location so that it produces a more laminar flow regime so that turbulence which

causes acidic generation is minimized. Sometimes this requires that the discharge structure be modified

if the force main is discharging at a high location in the manhole or if the end of the force main is

draining out, which means that every time the pump turns on, corrosive gases inside of the force main are

evacuated. Once the flow has had a chance to co-mingle with additional flow, usually the corrosion

potential is reduced or mitigated. If there is a corrosive compound release inside of the manhole, the

structure may require lining to prevent further structural damage and an additional means of preventing

the corrosive compound release to the outside may be desirable. In some cases a carbon canister can

suffice but in other cases, a biofilter can be provided along with a forced air fan to provide continuous or

semi-continuous ventilation of the manhole at the discharge location. Since the biofilter requires


periodic wetting to maintain a healthy growth on the filter, a water line with back flow preventer could

be used. Another type of corrosion control unit that could be utilized is an iron sponge type scrubber

which utilizes iron oxide coated pellets. This system also requires periodic wetting in order to retain its

effectiveness. More details are needed before a firm decision can be made regarding the most

appropriate means of controlling this corrosive compound generation. For budget purposes, an

allocation of $10,000 should be included for a Biocide™ storage tank and feed pump until a more

definitive alternative can be determined.

D. Water Treatment Plant Lime Sludge Disposal System and Former Drying Bed Underdrains

The lime sludge lagoon filtrate pumping station should be modified to normally discharge to the

receiving stream, in lieu of the WWTP influent sewer, and thereby reduce the load at the WWTP. The

filtrate pumping system could be replaced with a new system complete with new pumps, two pH

adjustment tanks with mixers, chemical feed system, and automatic pH control. The new system would

operate on a batch basis whereby a pH adjustment tank would be filled after a few filtrate pumping

cycles. The automatic pH control system would then initiate tank mixing, monitor pH, feed pH

adjustment chemical and drain the tank by gravity to the WWTP outfall sewer after the pH control

setpoint is satisfied. This tank, chemical feed pumps could also be located closer to the WWTP so that it

could be more easily monitored and maintained. It may also be possible to utilize the former lime sludge

mixing tank for this purpose if the filtrate pumps are capable of discharging to this elevation and if

compensating biosolids storage can be provided in future biosolids storage tanks. Untreated filtrate

could alternately be discharged to the WWTP influent sewer during periods when the proposed pH

adjustment system is out of service for maintenance or repairs.

In addition to the lime sludge bed filtrate, the underdrains from the former drying beds also contribute

flow to the filtrate pump station. This flow could potentially be diverted to the river since the drying

beds are no longer used. However, they are still periodically used for sewer cleaning tailings and, as

such; they would need to be discharged to the WWTP until an alternate location for these tailings can be

provided.

E. Raw Wastewater Pumping

The following improvements to the raw wastewater pumping station are recommended:

1. Installation of a new raw wastewater sample pump with a discharge connection to the existing

sampler located in the sample building. The sample pump should be located in the primary sludge


building with a suction connection to the primary settling tank influent piping manifold. The new

sample discharge piping would also be required to connect the new pump discharge piping to the

existing below grade raw wastewater sample supply line to the sample building.

The proposed sample pump location downstream of the influent screening and grit removal system

will reduce the potential for problems with debris clogging the system versus the current

arrangement, which is immediately downstream of the screening equipment. However, the proposed

sampling location, which is equivalent to the existing sample point, provides a sample of raw

wastewater combined with all WWTP recycle flows. Considering the location of plant recycle

flows, this would be difficult to avoid at almost any sampling location.

The WWTP recycle flows include the following intermittent waste streams:

Grit washer overflow.

Wet weather storage basin return flow.

Treatment tank drains.

Biosolids tanks decant

The only return flows which would significantly regularly impact the sample are the biosolids decant

and tank drain waste streams. Therefore, whenever possible, the decanting and tank drain operations

should be scheduled to occur during periods when raw wastewater samples are not being taken. It is

acknowledged that wet weather storage basin return flows may affect the sample quality but a flow

meter exists on this line and periodic grab sample monitoring of return flows should provide a

guideline for the expected impact on primary influent quality during times when wet weather flows

are being returned.

As an alternative, raw wastewater sampling upstream of the recycle flow connection would require

installation of grinder type sample pumps at two locations:

36-inch sanitary interceptor manhole located upstream of the influent junction manhole.

12-inch sanitary manhole located in the southeast corner of the WWTP site.

In addition, extensive underground sample discharge piping would be required to convey the

samples to the sample building and sample blending proportional to influent flow would be required


for a representative sample. The existing sample line from the screw pumps to the sample building

could be used as a line to connect the revised sample pump location to the sample building.

2. Since the raw wastewater screw pumps are not capable of completely draining the main interceptor

sewer, it is recommended that the screw pump wet well be modified to allow for complete draining

of the sewer. This will help to promote flushing velocities in the interceptor on a routine basis.

Modification of the wet well will require construction of a deeper wet well and either replacement of

the existing screw assemblies and construction of longer screw pump bays to address the deeper wet

well or replacement of the screw pumps with submersible pumps. If submersible pumps are used for

replacements, several of the other improvements under consideration and discussed below including

the screw pump cover modifications, screw flight replacement and re-painting, grease line

lubrication modifications and corrosion control would not be required. Modification of the existing

station and replacement of the existing screw pumps with longer units capable of completely

allowing the existing sewer to drain into the wet well at moderate influent flows was considered but,

upon communication with some of the equipment vendors, it was realized that this alternative would

be significantly more expensive and therefore not feasible when compared with other options. It

would also be a significant structural challenge to modify the station concrete structure to allow for

the longer pumps. A summary of the potential modification alternatives are as follows:

Modify the existing station and replace the existing screw pumps with submersible pumps

capable of completely allowing the existing sewer to drain into the wet well at moderate

influent flows. The pumps would be rated to allow for the firm capacity of 12 MGD to be

achieved with three pumping units

Add a supplementary duplex submersible station with an approximate capacity of 2.0 to 2.5

MGD. This would allow for most of the normal wastewater flow to be handled with the

submersible pumps and the wet well could be positioned such that it would allow for the

interceptor sewer to drain completely to the wet well thereby maintaining higher velocities in

the influent sewer. During higher flow events, the existing screw pumps could be used to

supplement the capacity of the submersible station. The firm capacity of the submersibles

and two of the screw pumps would be in excess of the required 12 MGD desired capacity.

Add a supplementary duplex self-priming pump station with an approximate capacity of 2.0

to 2.5 MGD similar to the above option. Upon checking with the manufacturer, it was


discovered that installing larger capacity self-priming pumps to handle the future design

flows is not possible without installing the pumps at a lower level due to the suction lift

needed. It may be possible to install the pump skids inside of the lower level of the filter

building and position the wet well further to the south, however, this option was not

explored.

The modified stations could also be positioned so that they could pump from a deeper sewer if the

sewer from Pulford Street to the WWTP is eventually replaced. A 24-inch sewer placed at 0.5%

grade versus the existing 36-inch sewer which is placed at 0.06% grade would have a capacity of 10

MGD (a 24-inch sewer placed at 0.7% grade would have an approximate capacity of 11.6 MGD).

These deeper sewers would require that the invert of the sewer at the WWTP be approximately 3.75

feet deeper. If the supplemental wet well were placed so that the new sewer could be drained into

the wet well during normal operation it would need to be approximately 32 feet deep. It may not be

possible to utilize directional drilling (which requires a 1% grade) since the lift required would be

beyond what self priming pumps could handle. However, it may be possible to utilize submersible

pumps for this application.

An estimate of the life cycle cost of modification and operation for the next 20 years for each of the

above alternatives is summarized in the table below:

Raw Wastewater Pump Station Modification Alternatives

Alternative Capital Cost Annual

Power Cost 20 Yr PW of Power Cost

Total Present Worth Cost

New Submersible Pumps $658,000 $11,543 $143,849 $801,849

New Self Priming Pumps $1,098,000 $13,659 $170,221 $1,268,221

Supplemental Submersibles $376,000 $14,051 $175,107 $551,107

Supplemental Self Priming Pumps

$430,000 $12,656 $157,727 $587,727

The above analysis indicates that the various alternatives are fairly close in operating cost.

Therefore, further investigating will require before selecting a particular course of action.


Regardless of the selected alternative, it will be important to situate a wetwell low enough so that the

influent sewer can freely drain.

3. The raw wastewater pump channel isolation gates should be removed and replaced with new

stainless steel gates complete with ultra-high molecular weight polyethylene (UHMWPE) seals.

Stainless steel construction will minimize corrosion problems and the UHMWPE seal system will

prevent gate binding and minimize operating torque requirements. As an alternative, the gates could

be replaced with Coplastics™ type gates, which are mostly non-metallic and utilize UHMW, PVC

and polyethylene components in a metal reinforced frame. Limiting the amount of exposed metal

components reduces the chances for deterioration from corrosion. This gate replacement may only

be necessary if the screw pumps continue to be utilized as the primary pumping mechanism.

4. The existing #2 screw pump apparently had excessive wear during its early years of operation. This

caused the clearance between the flights and the grout to become excessive. As a remedy, the screw

was lowered on its bottom bearings, which, in effect changed the angle of the screw since the lower

flights wore more severely than the upper flights. In order to rectify this, the manufacturer has

recommended that the screws be removed and returned to the factory where the flights would be

refurbished to new condition by welding additional material on the entire flight screw. Doing so

would allow the screw to be returned to its original angle and efficiencies would be returned to “like

new” condition. This remedial fix may only be necessary if the screw pumps continue to be utilized

as the primary pumping mechanism.

5. The raw wastewater pump lower bearing grease lubrication lines should be removed and new lines

should be installed and protected in a manner which will prevent damage from large objects and

minimize the potential for rags/debris to collect on the piping. This would likely involve installing

them inside of a larger carrier pipe and rigidly attaching the carrier pipe to the screw channel walls

and/or location the carrier line above the water line.

6. If the screw pumps continue to be utilized as the primary pumping mechanism, the screw pump

suction wet well ventilation system should be removed and replaced. Improvements should include

a supply fan at the lower level and a scrubber to control the buildup of corrosive fumes. Another

alternative would be a carbon contactor ducted from the upper level of the screw chambers. The

ventilation system would operate continuously to provide a constant low volume supply of fresh air

turnover to minimize corrosion. As an alternative, the ventilation system exhaust could potentially


be ducted to the aeration tank blower building and eventually to the low pressure process air blower

intakes. Then the exhaust scrubber could be eliminated. The exhaust air flow would be used as a

partial intake supply, in lieu of fresh air, for the aeration blowers. This option would likely require

an auxiliary fan to push the air over to the blowers. Due to the duct length, this option may be

outweighed by a simple carbon canister located closer to the screws. It is preferable that the exhaust

be pulled from the top of the screw chamber so that full turnover of the air volume in the screw

chamber can be accomplished. In addition, pulling from the top of the chamber may enhance the

“chimney” ventilation effect thus augmenting the natural flow of air through this chamber. It may

not be needed to continually ventilate these chambers if the screw pumps are not utilized as the

primary mode of pumping at the WWTP.

F. Raw Wastewater Screening

An additional screen channel and screening system should be constructed to supplement the existing

screening system during peak flow conditions. New screen channel isolation gates, with slots placed at a

lower elevation than the top of the wall, would allow the proposed channels to provide for the redundant

channel to be automatically allow flow through it during peak flow conditions.

The initial bypass screen installation could potentially be a manually raked screen since the screen would

be used infrequently. The screen could be replaced with a mechanically cleaned unit in the future when

influent flows increase or if the manually cleaned screen proves to be inadequate for the additional debris

loading during peak flow conditions.

G. Influent Flow Measurement

The existing influent metering flume could be abandoned in place and new in-line magnetic type flow

meters should be installed in the primary influent or effluent lines and also in the wet weather storage

basin influent piping. It is desirable not to install the new meters below grade. It is likely possible to

install the meters in accessible occupied locations of the building and thus avoid confined space entry

provisions necessary for below grade installations.

One alternative metering system for the plant influent would be to install a new inline, magnetic type,

influent flow meter, for each primary settling tank. In addition, a flow meter could be installed in the wet

weather storage basin influent piping as previously described. The disadvantage to this alternative is that

the total influent flow rate is the summation of multiple flow signals. However, one advantage to this


system is that the influent flow split between the primary tanks could be easily monitored and the

manually operated tank influent valves could potentially be adjusted as required for proper flow splitting.

H. Grit Removal System

A pre-fabricated fiberglass building enclosure could be installed to protect the grit pump from the

elements. Open channel grating within the new enclosure would be replaced with solid covers in order

to control humidity and corrosion inside the building. The building would be complete with access

doors, lighting, heating and ventilation. The existing grit pump discharge line could be re-routed through

the liquid channels so as to minimize the potential for freezing of the line. Once inside of the building,

the line could be re-directed to it s existing location.

An alternative to a new grit pump weather protection system would be to retain the existing grit pump as

a standby pump and install a new pump within the existing headworks building. New pump

suction/discharge piping and valves with connections to the grit tank and grit washer would also be

required. This alternative is not desirable due to the extensive amount of equipment re-arrangement

that would be required in the building.

The advantage to this alternative is that freeze protection requirements would be eliminated. The

disadvantages to this alternative is that the suction piping length would be increased and special

construction techniques will be required to connect the suction piping to grit tank without undermining

the structure.

Of the two alternatives, the installation of a new enclosure over the existing grit pump is preferable.

I. Wet Weather Storage Basins

A new wet weather storage basin overflow line should be constructed to prevent basin overflow to the

storm sewer system. The new overflow would extend from the existing weir trough at the south end of

the tanks to the existing 12-inch return line. The basin overflow could be returned to the influent wet

well via the 12-inch return line. The influent line to the basin could be metered using a partial depth

magnetic flow meter on the influent line. This meter could be installed adjacent to the north edge of the

tank.

The existing 20-inch wet weather storage basin influent line and 12-inch waste backwash waterline

should be revised to include individual valved connections to the east and west basins.


The existing basin drain line should be modified to include a flow control valve or gate linked to the

existing return line flow meter. The control valve could be a modulating flow control valve linked to the

return flow meter. The valve would be automatically controlled in response to a manually input setpoint

flow rate to provide a relatively constant drain rate as basin level changes. The control valve could be

located inside of the existing east basin and have an extension stem and above grade motorized valve

actuator.

J. Primary Settling Tanks

There are two primary settling tanks at 45 feet diameter total area of 1590 SF per tank or 3,180 SF total.

If operated at 1000 gpd/SF (the standard for tanks providing co-settling), the total existing design peak

flow capacity is 3.18 MGD. The projected peak flow capacity is 8.5 MGD, so there would need to be

approx 5300 SF of additional settling area, which would equate to either two additional 60 feet diameter

tanks or four 90 feet long by 20 feet wide rectangular tanks. These additional volumes are based on the

required volume including co-settling of WAS. If the tanks are not utilized for co-settling, then the

required volume would be reduced to 2833 total and therefore no new tanks would be required since the

primary tanks could be operated at up to 3000 gpd/SF. Given that the plant has not had success with the

existing WAS thickening equipment, it is recommended that the plant pilot test the various types of

thickening equipment and focus on obtaining a thicker WAS prior to biosolids storage in lieu of building

additional primary tanks for future growth. However, operating the primary tanks at high loadings may

compromise removals and increase loading to the secondary process thus requiring that future biological

reactor capacity be constructed sooner. Thickening the WAS however may result in smaller biosolids

storage ultimately.

K. Biological Treatment System

The biological treatment system represents the greatest potential for cost savings. Typically aeration

costs represent about 45% of the annual power cost at a treatment plant. In addition, potential chemical

cost savings from biological phosphorus removal or less polymer usage for settling can be provided by

implementation of an anoxic or anaerobic/anoxic zones within the biological reactor. Operation of one

anoxic zone within each of the aeration basins would effectively reduce the aerated hydraulic retention

time but not have any effect on the overall biological reaction time since this is a measure of the entire

time that the mixed liquor is in contact with the flow so therefore would also include the holding time in

anaerobic, anoxic and aerobic zones. In general, Ten States Standards requires that conventional

biological reactors be operated at a loading rate of 50 pounds per day per 1000 cubic feet. The biological


loading to this plant was greatly influenced by the Pepsi Bottling Plant, which in 2008 began operation of

a pretreatment plant, which dramatically reduced the BOD loading to the Howell plant. In the years

2005-2007, the primary effluent BOD averaged 250 mg/l whereas from 2008 onward, the primary

effluent BOD has averaged 129 mg/l. For design purposes, a primary effluent concentration of 160 mg/l

is recommended which is approximately 65% of 250 mg/l or 35% removal in the primary tanks.

Given this concentration, the biological loadings as shown in the table below are anticipated for both the

minimum and maximum tank volumes (minimum to maximum depth).

Biological Loading Parameters

MGD PE BOD PPD PPD/KCF

Min PPD/KCF

Max

Current Avg. Design Flow 2.5 3320 24.4 21.5

Future Avg. Design Flow 3.6 4933 36.2 31.9

Assumed Max Mon. 6.5 8633 63.4 55.8

Since Ten States Standards requires a maximum of 50 pounds per day per 1000 cubic feet, a new

aeration basin will likely be required as the flows or loadings grow. It would be preferable to construct

two new aeration basins as the flows grow rather than additional primary tanks. This will likely be

required at some point as the annual average flows begin to exceed 3.5 MGD.

Incorporating an anoxic reactor zone within the front 25% of each tank is recommended to improve

settling and possibly obtain the benefit of some enhanced biological phosphorus removal EBPR. EBPR

is dependent upon the concentrations of volatile fatty acids (VFA’s), the BOD to P ratio and other

factors. Incorporating a swing zone which can either be operated in aerobic or anoxic mode in the

second 25% of each aeration basin is also recommended so as to enhance EBPR potential. Both of these

zones would be convertible to aerobic mode should ammonia loadings warrant. The aerobic hydraulic

retention time (HRT) should be sufficient to maintain nitrifying conditions. In general an aerobic HRT

of approximately 3.5 to 6 hours is usually sufficient to maintain an adequate population of nitrifiers

although this is not a hard and fast rule. The aerobic HRT’s under various conditions is shown in the

table below. Conversion of the tank to include an anoxic zone could be considered for future

implementation.


Aerobic Hydraulic Retention Times

Aerobic HRT (Hours)

Number of Aerobic Zones/Tank Two Three

Flow Condition MGD at Min.

Vol. at Max

Vol. at Min

Vol. at Max

Vol.

Current Avg. Design Flow 2.5 5.0 5.7 7.5 8.5

Future Avg. Design Flow 3.6 3.4 3.8 5.0 5.7

Assumed Max Mon. 6.3 1.9 2.2 2.9 3.3

It is recommended that all the tanks be retrofit with one anoxic zone per tank which will utilize

approximately one fourth of the entire tank volume. This also corresponds to the half of the aeration

tank piping divide, which is at the center of each tank. It is also recommended that the first aeration

diffuser zone be subdivided to allow for the first half to be operated in an un-aerated zone by blanking

off the diffusers and removing the ceramic heads. In the future, it may be recommended to operate the

second quarter of each tank in an unaerated manner as well. In order to do so, it would be necessary to

replace the ceramic diffusers with membrane diffusers that prevent reverse flow of water back into the

header piping. Although the membrane diffusers have a slightly different head loss, this approach has

been utilized in other plants in order to incorporate a swing zone in the biological reactor.

Currently the aeration blowers are operated at their minimum output, which is approximately 1,450

CFM. Since 2008, the oxygen demand is down due to the implementation of the pretreatment facility at

the Pepsi Bottling Plant. The existing positive displacement blowers located in the Lime Building have

been used very little since their original installation and they are rated at approximately 800 CFM at 12

psig. Ideally, a blower with a range of from 500 to 1400 CFM would provide the most optimum low end

range of air flows considering that if the tanks existing two tanks are converted to one half aerated, the

mixing limited air flow would be 520 CFM. During 2007 and 2008, the required air flow rate based on

the average oxygen demand during those periods would be 1112 and 1027 CFM respectively. It is also

likely that the minimum air flows are typically around 800 CFM or less during the evening periods.

Given these lower air demands, it may make sense to move one of the larger multi-stage centrifugal

blowers and replace it with one or two of the positive displacement blowers from the lime building. The

projected power cost savings using these two blowers along with a VFD to drive them would be

approximately $5,500 to $7,000 per year based on an average per KWH cost of $0.08. The anticipated

savings based on the projected air flow requirements based on actual loadings is shown below.


Anticipated Power Cost Savings Using Existing Rotary Positive Blowers Compared to Existing

Period AOR PPD

SOR (PPD) SCFM

PD HP

EX HP

PD Ann KWH

EX Ann KWH

PD Ann $$

EX Ann $$

Annual Savings

2007 3230 8346 1112 54 68 361213 450208 $28,897 $36,017 $7,120

2008 2982 7706 1027 52 62 341582 408328 $27,327 $32,666 $5,340

2009 (1st 4 Mos.) 3558 9193 1225 60 72 392296 473111 $31,384 $37,849 $6,465

A very conservative estimated project cost to relocate the existing rotary positive blowers from the lime

building along with a new DO control system is $161,000 whereas it would likely cost about $152,000 to

obtain a single new blower package with a custom built acoustical enclosure that would have the

appropriate size to handle the air range from 500-1400 CFM, which is the desired range of coverage that

is not currently possible with the existing blowers. As such, this is not an overly attractive project but

may be more beneficial a power costs rise.

L. Final Settling Tanks

The original two final settling tank sludge collector mechanisms installed during the 1970’s plant

improvements should be replaced with new equipment including rake arms, drive cage, center baffle, and

skimmer. The center column condition and all components should be reviewed when the bid

specifications are developed in order to determine the final extent of component replacement or whether

selective sandblasting and re-painting might be sufficient. If possible, a hydraulic collector mechanism

similar to the newer unit should be utilized for the replacement unit. As part of this upgrade, an energy

dissipating inlet baffle should be installed along with the center baffle in order to improve the inlet

hydraulics. The existing drive mechanisms on these tanks could be re-installed since these were just

replaced as part of the last plant upgrade in 2000.

The 6-inch scum line from each final settling tank should be rerouted to drain to a new scum pump

manhole located near the RAS Pump Station. The new scum pumping system would include a

submersible chopper type pump, discharge piping and valves to pump either to the sludge storage tanks

or to the WAS storage tank if it is desired to install new thickening equipment.

In addition, new Stamford Baffles should be considered for two of the existing final settling tanks (one

tank already has this). The cause of previous scum buildup under other baffles in the final settling tanks

should be investigated so that the new baffles can alleviate this buildup.


An energy dissipating inlet should also be considered for the existing third final settling tank

Additional baffling should be installed in the final settling tank influent flow splitter box to prevent

influent from flowing directly toward tanks No. 1 and No. 2 inlet gates. This could consist of a flared

baffle installed on the inlet in order to provide a symmetrical split on the flow. In addition, the

phosphorus coagulant chemical feed location should be revised so that it is fed approximately in the

center of the inlet feed pipe as the pipe enters the flow split chamber.

M. Tertiary Treatment System

As mentioned earlier, the plant does not currently need filtration in order to meet its discharge permit

limits and has not been filtering the effluent for several years. If discharge permit limits for phosphorus

become more stringent, there may be a necessity to install tertiary filtration again in order that the plant

not violate the phosphorus limits due to excess phosphorus associated with the suspended solids in the

secondary effluent.

Several types of tertiary filtration systems have been considered as part of this study, namely cloth media

disk filters, mesh media disk filters and travelling bridge sand filters. All of these types of filtration

device are continuous wash type devices and thus the backwash flow rate is more or less continuous

throughout their operation and thus a backwash surge tank or storage of backwash water can be avoided

since the backwash water can be returned along with the influent flow through the treatment process.

Cloth media disk filters have the advantage of a fairly small foot print however they are somewhat

mechanically intensive requiring drive motors and frames for the cloth media to rotate through a pool of

water. Similar in principle, mesh media disk filters also are somewhat mechanical intensive. Previous

testing of the mesh media filter at Howell WWTP did not produce an acceptable improvement in

secondary effluent quality. There is also a concern regarding the integrity and expected life of the mesh

media.

Travelling bridge sand filters are essentially a low profile sand filter that has a bridge that travels up and

down the length of the filter, washing a small portion of the filter bed as it travels up and down the length

of the bed. The backwash quantity is fairly small with respect to the plant flow and can be returned

without any equalization.


The capital cost of each type of filter equipment was compared and would be somewhat similar. The

operating cost for the disk type filters would likely be somewhat higher since media replacement could

be expected to occur more frequently since the media is fairly thin. Based on this comparison, it is

recommended that a travelling bridge filter system be considered for replacement filters at the Howell

WWTP if they are required in the future in order to meet more stringent permit limits.

N. Disinfection System

As mentioned earlier, the Howell WWTP currently utilizes a vertical lamp type ultraviolet light

disinfection system. This system is installed in an older section of the plant that is desirable to be

removed. The existing equipment could be re-utilized in a new contact channel that could be constructed

as part of a tertiary filtration system. It is also desirable to construct a more permanent superstructure

over the equipment in order to provide protection from the elements. It is recommended that a new UV

contact channel with a better designed level control system be constructed that could accommodate either

horizontal or vertical lamp designs if it is intended to re-use the vertical lamps. The new channel could

be constructed so that it could then accommodate the newer generation of horizontal lamp designs should

it be desired to change in the future. The level control system could either be a long overflow weir or a

weighted bascule gate designed to maintain a constant level. The UV channel should be designed so that

it can be incorporated into a future filtration system design should that become necessary. The UV

channel could be constructed over a portion of the existing old Service Building (possibly using the

existing structure as a portion of its foundation once it has been demolished and the below grade portion

filled with flowable fill) or alternately, adjacent to either the north or south sides of the existing pressure

filter building along with a new superstructure constructed to house the channel. Constructing along the

south side of the filter building would also require that the existing backwash storage tank be filled in

and abandoned. This tank could also serve as a portion of the foundation for the UV channel.

O. Biosolids Handling System

The existing biosolids handling system includes biosolids thickening, biosolids stabilization and long-

term biosolids storage prior to land application. Given that land application to agricultural land is likely

the most economical long term disposal means for the Howell WWTP, it is likely that additional storage

will be needed as plant flows increase. Currently the plant is generating approximately 6000 gallons of

waste primary sludge per day per million gallons of wastewater processed at about 3% composite solids.

The primary sludge includes the co-settled thickened waste activated sludge solids. Currently the plant

has a total of 1.65 million gallons of available storage between tanks 1-5 which provides for a total


storage of 145 days of storage at a plant flow of 1.9 MGD. If they are thickened to 4.5%, the resulting

storage is 218 days at current production rates. Currently the only thickening is accomplished by

decanting. In order to process a total of 3.6 MGD, it is recommended that improved solids thickening be

provided. This can probably be accommodated within the existing biosolids thickening building.

However a new or modified thickener may be required to accomplish this.

In order to handle the proposed annual average plant flows of 3.6 MGD, an additional volume of

biosolids storage of approximately 320,000 gallons is needed if the target thickened solids concentration

is 6% and 240,000 gallons is needed if the target thickened solids concentration is 8%. Stabilization is

currently accomplished with documented pathogen reduction and long term storage. This mode of

operation may be possible into the future if pathogen reduction can continue to be accomplished. This

may be possible due to the volatile reduction occurring in the secondary treatment process. This could

possibly be modified if aeration HRT’s are changed with the implementation of anoxic or anaerobic

holding times, however the extent of this change is not possible to quantify without actual field

measurements of pathogen reductions or with extensive computer modeling of the entire process.

It is recommended that improved thickening processes be implemented in the future as storage becomes

limited. Additional storage will also be needed as the annual average flow increases. A volume of

between 400,000 to 800,000 gallons would likely be needed dependent on the target solids concentration

that can be achieved. Stabilization through long term holding would likely continue to be the most cost

effective approach for this plant.

P. Electrical System

Replacement of the 600kW main diesel generator is estimated to cost $150,000 and is recommended due

to the age of this unit and the difficulty in obtaining replacement parts. A study of the plant loads

(present and future) is recommended prior to purchasing the generator in order to determine the required

generator size to handle all of the plant’s loads. This will depend on several factors and since the

existing aeration blowers are handled with a separate unit, a smaller generator may suffice at this

location. For long term planning and budgeting purposes, the cost of a 600 kW unit can be assumed.

Replacement of the main switchgear is estimated to cost $170,000; however, the condition and reliability

of the existing switchgear and the availability of replacement parts should be evaluated in more detail

prior to assigning a priority to this work. Other plants with this age and make of switchgear have


obtained several more years of beneficial use by retro-fitting replacement breakers and transfer controls,

rather than total replacement of the gear.

Q. SCADA System

As mentioned earlier, the SCADA Operating System (RSView®) was recently upgraded. The plant

currently has a blend of two communicating systems with remote sites. It has approximately 6 sites on

dial-up modems and 6 sites using a radio communication system. The radio system is a SCADAPack®

by Control Microsystems. The City’s water plant currently utilizes a reliable cellular based system and it

may be desirable to switch the communication mode for all of the wastewater sites to cellular as well.

R. Structures

In general, the concrete structures still in use at the Howell WWTP are in fairly good condition, with the

exception of the primary settling tanks and the wet weather storage tanks. An allowance for structural

rehabilitation of the primary settling tanks including crack filling and surface repair of spalled concrete

areas and handrail post socket repairs is included in the primary settling tank improvements costs.

The concrete on the wet weather storage tanks is in marginal condition but the railings around the

structure should be reconditioned and the post sockets eliminated or repaired. An allowance for

structural repair of these tanks is included in the wet weather storage tank modification costs.

S. Buildings

Headworks Building

1. A separate heating/ventilation system should be provided in the headworks building for both the raw

wastewater pump motor room and the screening area. The door between these rooms should be

provided with a positive closer to keep the door sealed at all times and to provide isolation between

the hazardous/non-hazardous areas.

2. Openings in the raw wastewater screw pump motor base plates should be sealed to prevent

hazardous gases from entering the motor room.

3. The headworks building heating/ventilation system should be revised to provide isolation between

the hazardous and non-hazardous areas. The ventilation system in the pump motor room should be

positive at all times so that there is no inward leakage of hazardous fumes from the other portion of

the building.


Installation of a motorized damper for the screening room supply air register would provide the

required isolation if the damper is automatically controlled to close when the makeup air unit is not

running.

Filter Building

1. The existing filter building is currently in need of a new roof,

2. Decay of interior steel components due to exposure to ferric chloride should be addressed with a

general re-painting. Most of the piping in this building could likely be removed since it is no longer

in use.

Miscellaneous Building Improvements

1. A preliminary placeholder for miscellaneous building improvements is prudent to account for door

and window replacements, roof replacements and other miscellaneous improvements that may be

necessary. A value of $500,000 is recommended to account for these items.

2. The Administration Building at the WWTP may be in need of upgrades for operational and energy

efficiencies. This evaluation work is outside of the scope of this report and will be addressed with a

separate evaluation study.


Section 5 - Capital Improvement Plan Implementation Schedule

A. Project Prioritization and Costs

The Howell WWTP is fortunate that most of the equipment is adequate to provide ongoing service. This

can be attributed to the City’s existing preventative maintenance program providing adequate support.

However, there are a few items that need immediate attention. The capital projects for the plant were

sorted into four categories of projects, as described below:

Improvement Category 1 Projects – Projects that are required due to a potentially imminent

operational failure or capacity exceedance of the existing equipment within the foreseeable future.

Improvement Category 2 Projects – Projects that would provide for a somewhat longer term return on

the investment than Improvement Category 4 projects. These items could be driven by permit

compliance, operational or treatment process savings or other efficiencies, but may not be as cost-

effective as Improvement Category 1 projects.

Improvement Category 3 Projects – Projects primarily driven by growth and expansion within the

system. These projects could be implemented as needed, depending on the growth of the system. They

may also be coordinated with other equipment replacement projects.

Improvement Category 4 Projects – Projects primarily driven by operational cost savings. These

projects could be implemented as needed or coordinated with other equipment replacement projects.

The projects are generally grouped by process area. With regards to the preliminary treatment, the most

significant project would be the upgrade of the raw wastewater pumping system at the plant. This is

recommended primarily because the existing screw pumps do not allow for the influent sewer to dewater

into the pump wet well since the invert of the wet well is the same as the influent sewer. Constructing a

new influent wetwell will allow the influent sewer to completely drain into the wetwell and will thus

allow higher velocities during normal conditions. It would also be advisable to construct the influent

wetwell low enough to allow for a steeper influent sewer to be constructed at some time in the future.

Constructing the influent sewer at a steeper grade may also allow for a smaller pipe to be utilized

depending on the desired sewer capacity. Based on preliminary numbers, constructing supplemental


pumping capacity of either submersible or self priming type pumps would allow for continued use of the

screw pumps however only for wet weather conditions, which would substantially prolong their life

since their run time would be substantially reduced. The decision as to whether submersible or self

priming pumps are utilized is somewhat based on the preference of City staff. Using the screw pumps

only for wet weather will also lessen the urgency to implement enhanced corrosion control facilities for

the screw pumps.

Within the preliminary treatment system, it is recommended that a supplemental bypass channel with

manual bar screen as well as a grit pump be installed within the existing building. This will allow for

emergency bypass of excess flows through a manual bar screen during high flow events and will also

allow for less problematic operation during winter months since the existing grit pump could be more or

less left as a standby unit.

As growth occurs, the expansion of the process treatment tank capacity will become necessary. The

decision to expand primary or secondary treatment capacity will depend somewhat on the means of

treating biosolids from the process. Given the current process of applying all biosolids to agricultural

land, additional primary treatment capacity may not be all that beneficial, since the plant is achieving

pathogen reduction through treatment by excess aeration and long term holding. Additional biosolids

holding capacity will also be necessary as flows increase.

Currently, there would be benefit in converting at least the front 25% of each process tank into an anoxic

zone to enhance the growth of more settleable microorganisms. In addition, there would also be

economic benefit to replacing at least one of the existing multistage blowers with a positive displacement

blower with a VFD or a single stage blower with inlet and outlet guide vanes capable of more variability

in output. A range of at least 500-1400 CFM is desirable in order to achieve the most economic benefit.

The existing positive displacement blowers in the former lime handling building are capable of only

about 400-800 CFM each and the cost to relocate these is likely in excess of the cost to purchase a

replacement blower of a more appropriate size.

Several of the projects are necessary to maintain existing system integrity and or prolong existing

equipment life. Also, if permit limits are tightened, other projects may be required to address this such

as a tertiary filter system replacement. Of the types considered, a more conventional sand filter may be

desirable over systems which provide for more capital or equipment intensive systems.


It is assumed that Improvement Category 1 and 4 projects would likely be implemented within the first

five years of the CIP. Improvement Category 2 and 3 projects would likely be implemented within 5 to

10 years and 10 to 15 years, respectively as part of a long-term CIP. However, these timeframes are not

absolutes since they are somewhat dependent on growth of the system, but are provided as a general

reference.

The table below contains the overall recommended improvement projects, along with their initial

recommended priority status. This table also includes several project alternatives that were considered

but are not included in the overall total since only one alternative need be completed. In some cases, the

initially assigned priority of a project may need to be adjusted if it is dependent on the completion of

another project that may have a different priority. In all, a total of approximately $9.6 million in projects

have been identified. The Improvement Category 1 and 4 projects comprise about $3.1 million of the

total while the Improvement Category 2 and 3 include about $2.0 and $4.5 million, respectively.

Breakdowns of the capital cost opinions for each of the projects is contained in Appendix B. In general,

the capital cost opinions were developed based on input provided by equipment manufacturers and

previous project experience by HRC. In most cases, an allowance of 40-60% of major process

equipment was added for mechanical installation and approximately 5-20% was provided for electrical

or special mechanical installation depending on the complexity of the equipment or process. The

individual estimates represent a project cost and include the additional costs to account for

administrative, legal, engineering and contingencies so that each project represents a complete project

cost assuming conventional municipal bond financing. In some cases, only a preliminary order of

magnitude “placeholder” number is included since a detailed estimate was not prepared. These

placeholders are there mainly to account for potential needs.

Project Cost Summary and Improvement Category Status

Project Improvement

Category Project

Cost Recommended

Project

Influent Screw Pump Upgrades (ventilation/carbon canister) 1 $292,000 $292,000 Rehabilitate Screw Pump Flights 3 $256,000 $256,000 Bypass Channel with Manual Screen 1 $146,000 $146,000 Grit Pump Inside Building 3 $221,000 Grit Pump Enclosure 1 $384,000 $384,000 Primary Metering and Tank Modifications 2 $111,000 $111,000 Primary Concrete Structural Rehab 1 $74,000 $74,000 Two New Circular Primaries 3 $2,270,000 Four Rectangular Primaries (4 @ 90 x 20 x 12 SWD) 3 $1,985,000


Project Improvement

Category Project

Cost Recommended

Project

Anoxic Mixers (floating type) 3 $326,000 $326,000 Two New Final Settling Tank Mechanisms 1 $586,000 $586,000 New Final Settling Tank 3 $923,000 $923,000 Replace Aeration Blower 4 $161,000 $161,000 Two New Additional Aeration Tanks (2 @ 90 x 24 x 20 SWD) 3 $1,804,000 $1,804,000 Travelling Bridge Filter Concrete Tank 2 $5,053,000 Disk Filter Cloth Media 2 $5,345,000 Disk Filter Mesh Media 2 $4,949,000 Open Channel UV Replacement 2 $1,803,000 $1,803,000 New Stamford Baffles in Older Final Settling Tanks 3 $95,000 $95,000 1930s Service Bldg Demo 3 $153,000 $153,000 Biosolids Storage (assumes 6% storage concentration) 3 $976,000 $976,000 Flow Storage Basin Fill Concrete (manual flushing) 1 $290,000 $290,000 Raise Aeration Influent MH Walls 1 $91,000 $91,000 Existing Filter Bldg Selective Demolition 2 $41,000 $41,000 RAS Pump and Valve Replacements 1 $80,000 $80,000 Sludge Storage Decant Valves and Hatch 1 $75,000 $75,000 Marion Twp Force Main Biocide Addition* 1 $20,000 $20,000 Supplemental Submersible Pumps (2 @ 2.5 MGD) 1 $376,000 Supplemental Self Priming Pumps (2 @ 2.5 MGD) 1 $430,000 Submersible Pumps to Replace Screw Pumps (3 @ 6 MGD) 1 $658,000 Self Priming Pumps to Replace Screw Pumps (4 @ 4 MGD) 1 $1,098,000 Ferric Chloride Tank Replacements* 3 $20,000 $20,000 Automatic Wet Weather Influent Gate Control* 2 $30,000 $30,000 Primary Scum Pit Pumping* 4 $40,000 $40,000 Primary Tank Performance Study* 2 $10,000 $10,000 Secondary Tank Flow Split Improvements* 3 $2,000 $2,000 Repair Slope East of Sludge Storage Tank 4* 1 $15,000 $15,000 Convert 15 Remote Sites to Cellular Telemetry* 4 $360,000 $360,000 Lime Sludge Lagoon pH System Repairs* 2 $10,000 $10,000 Miscellaneous Site and Building Improvements* 4 $500,000 $500,000 *Detailed Cost Estimate not included in Appendix B

TOTAL IMPROVEMENT CATEGORY 1 PROJECT COST $2,053,000




GRAND TOTAL PROJECT COST $9,674,000


The following table contains a summary of the capital needs by year based on the priorities established

for each project as shown in the tables above. This table assumes that the projects dictated by growth

will not likely occur for approximately 10 years and that those that might possibly be dictated by permit

compliance might occur between 6 to 10 years.

Overall Project Implementation Summary

Improvement Category and Year Total Capital

Needs

Improvement Category 1 and 4 Projects (0-5 years) $3,114,000



TOTAL ANTICIPATED PROGRAM COST $9,674,000

It is important to note that filter system replacements at a project cost of approximately $5.0 million to

$5.5 million is not included above anticipated cost estimate. The need for filter improvements would be

determined in the future if the MDEQ modifies the existing permit limits. Also, new raw wastewater

pumping improvements of approximately $400,000 to $1,100,000 are not included above anticipated

costs.

B. Financing

There are several options available for financing of the improvements contained in this program.

Conventional municipal bond financing is an option as well as the MDEQ’s SRF low interest loan

program. However, the use of the SRF program also requires that a Project Plan be prepared along with

the requisite public hearings and other requirements. In addition, there are third-party financing options

available that can pay for energy-related improvements through the energy costs savings. However, the

interest rates can be slightly higher than what most communities can achieve through conventional

financing opportunities.

If SRF funding is desirable, it would be advantageous for Howell to prepare a Project Plan for a portion

of the recommended projects. The economic stimulus programs are likely to increase funding to the SRF

program for 2010 and 2011. If a Project Plan is prepared, it is likely that Howell can have an SRF

eligible project on the MDEQ Priority List for 2011.

WWTP Capital Improvement Plan y:\200900\20090075\design\report\text\01cip110609.doc City of Howell

APPENDIX A

Meeting Notes

Y : \ 2 0 0 9 0 0 \ 2 0 0 9 0 0 7 5 \ P r o p o s a l \ P r o p \ N D A \ F i n a n c i a l s \ H o w e l l _ F e e _ e s t i m a t e . x l s

2 / 1 5 / 2 0 1 0

City of HowellEvaluation Study and Capital Improvement Plan for the WWTPBUDGETED HOURS AND FEES

HRC Project No. 20090075

Rate Classification & Estimated Hours

Work Description

Associate/ Project

Manager

Senior Project

Engineer

j Engineer & WW Spec.

Senior Technician Clerical Total Hours

Estimated Fees

1 Project Kick-OffKick-off Meeting (Review Scope of the Project) 5 5 5 15 1,880$ Provide Project Management Plan 1 1 1 3 300$

Subtotal 1 2,180$

2 Condition AssessmentAssess Existing Conditions 2 16 16 34 3,920$ Workshop No. 1 with City Staff 4 4 380$

Subtotal 2 4,300$

3 Evaluation of Existing Treatment Processes CapacityHydraulic Evaluation 4 4 520$ Treatment Process Evaluation Task 8 4 12 1,420$ Workshop No. 1 with City Staff 5 5 1 11 1,210$ Workshop No. 1 Summary 2 1 3 270$

Subtotal 3 3,420$

4 Alternatives EvaluationEvaluation of Improvement Alternatives 2 24 16 12 54 6,010$ Cost-Effectiveness Analyses of Alternatives 4 16 16 36 4,220$ Workshop No. 2 with City Staff 5 5 10 1,130$

Subtotal 4 11,360$

5 Implementation Schedule DevelopmentRanking of Alternatives 4 4 8 900$ Develop Implementation Schedule 2 8 8 18 2,110$ Workshop No. 2 with Plant Staff 5 5 5 1 16 1,960$ Workshop No. 2 Summary 2 1 3 270$

Subtotal 5 5,240$

6 Evaluation Study and Capital Improvement Plan (CIP)Prepare Draft Final Evaluation Study and CIP 2 20 20 12 54 5,880$ Submit Draft to City for Review 8 8 600$ Workshop No. 3 with City Staff 10 10 2 22 2,950$ Submit Final Evaluation Study & CIP 4 2 4 5 15 1,620$

Subtotal 6 11,050$

Subtotal 1 thru 6 36 133 117 24 20 330 37,550$

7 Influent Sewer EvaluationTask Kick Off Meeting 4 8 2 14 1,540$ Install By-Pass Pumping Equipment & TV Sewer * 50,330$ Analyze Findings and Develop Repair Recommendations 4 20 4 4 32 3,170$ Provide Repair Report to City 4 10 4 18 1,860$

Subtotal 7 12 - 38 6 8 64 56,900$

PROJECT TOTALS 48 133 155 30 28 394 94,450$

* Based on AUI February 19, 2009 proposal w/ the following assumptions; 10 hrs of heavy cleaning, 50 tons of debris disposal, 1 month bypass piping rental.

February 24, 2009

Y:\200900\20090075\Design\Corrs\Contact_List.doc

105 West Grand River Avenue Howell, Michigan 48843 Telephone 517 552 9199 Fax 517 552 6099 www.hrc-engr.com

WWTP Evaluation Contact List

City of Howell

Terry Wilson ................................................................................ Phone 517.546.3861 Fax 517.546.6030 Mobile 517.404.2518 [email protected] Erv Suida ...................................................................................... Phone 517.546.7510 Fax 517.546.6019 Mobile 517.404.2520 [email protected] Pat Gibbons .................................................................................. Phone 517.546.6230 Fax 517.552.7249 Mobile 517.404.8152 [email protected]

HRC

Curt Christeson ............................................................................. Direct 248.454.6893 Fax 407.838.0005 Mobile 321.246.2832 [email protected] Dennis Monsere ............................................................................ Direct 248.454.6584 Fax 248.338.2592 Mobile 248.535.3486 [email protected] Dennis Benoit ............................................................................... Direct 248.454.6831 Fax 616.454.4278 Mobile 616.826.5400 [email protected] Jon Booth...................................................................................... Direct 248.454.6340 Fax 517.552.6099 Mobile 248.535.3316 [email protected]

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APPENDIX B

Cost Opinion Detail


APPENDIX C

Equipment Catalog Information and Vendor Quotes


Figure 1-1

Existing WWTP Site Plan

Documents

Wastewater Treatment Plant Capital Improvement Plan€¦ · Wastewater Treatment Plant . Capital Improvement Plan . ... C. Water Treatment Plant Lime ... 1978 and 2000 to provide