HomeMy WebLinkAbout5 - Final recommendation on the Wastewater Treatment Master Plan
C I T Y O F B O U L D E R
WATER RESOURCES ADVISORY BOARD
AGENDA ITEM
MEETING DATE: March 19, 2007
AGENDA TITLE:
Final recommendation on theWastewater Treatment Plant (WWTP)
Master Plan
PRESENTERS:
Ned Williams, Director of Public Works for Utilities
Robert Harberg, Utility Planning and Project Management Coordinator
Floyd Bebler, Coordinator of Wastewater Treatment
Randy Earley, Engineering Project Manager
BOARD ACTION REQUESTED:
Consideration of a motion to recommend to City
Council that the Wastewater Treatment Plant (WWTP) Master Plan be accepted.
EXECUTIVE SUMMARY:
The attached draft Wastewater Treatment Plant (WWTP) Master Plan is presented to the
Water Resources Advisory Board (WRAB) for review and consideration of a motion to
recommendto City Council that the WWTP Master Plan be accepted. This WWTP
Master Plan was presented to the WRAB in January as a strategic plan but planning staff
determined that the document should go forward as a master plan that will include a
Planning Board recommendation and City Council acceptance. This Master Plan
presents the approach used to meet the new regulatory requirements and community
goals described in the Boulder Valley Comprehensive Plan (BVCP).
Previous planning documents for the WWTP include The Facilities Plan, prepared in
1990, and the Utility Plan, revised in 2002. This Master Plan has been developed to
recognize the significant wastewater treatment improvements required by the 2003
discharge permit and to plan for future improvements that may be required by new permit
restrictions in 2008.
The Wastewater Utility will eventually have a single, utility wide, master plan. The
WWTP Master Plan will inform that Wastewater Utility Master Plan on wastewater
AGENDAITEM # V PAGE1
treatment issues. The utility staff expects to develop the system wide Wastewater Utility
Master Plan later this year and present it for approval in 2008.
This agenda item requests a recommendation of acceptance of the draft Master Plan by
the Board. The attached draft plan has been revised based upon comments and ideas
received at, and since, the January WRABmeeting. Additional comments can still be
included in the draft plan. The current draft plan has been posted on the city's Web site
for public review.
IMPACTS:
Fiscal Impacts:
Budgetary:
The plan itself has no budgetary impact. Funding for the first phase
of the construction cited in the plan is in place. Additional funding will be
required to carryout the second phase of the construction. The Capital
Improvements Project (CIP) budget includes $18,500,000 of WWTP
improvements in 2010. Future funding of additional construction will probably
require additional user rate increases.
Staff Time:
The impact of the potential improvements identified on staff time is
unknown at this time.
Other Impacts:
The future projects identified in theplan generally improve water quality in
Boulder Creek, protect downstream water users or reduce local impacts from the
treatment facility. The potential future improvements will keep the plant in
compliance with its discharge permit and local requirements.
Economic
: The future projects could potentially result in unbalanced social
impacts because lower income customerswould be dis-proportionallyimpacted
by any rate increase.
Community:
The impacts depend upon the improvements selected. For example,
residents in close proximity to the facility could have fewer odors and noise if
noise and odor treatment components are required in future work.
ANALYSIS:
In most communities WWTP improvements are driven by growth and regulatory
requirements. However, Boulder’s growth limitations have minimized the impact of
growth as a ‘driver’ of plant improvements. Boulder’s WWTP improvements are
typically driven by regulatory requirementsincluded in the Colorado Department of
Public Health and Environment (CDPHE) issued discharge permit. The discharge permit
focuses on reducing impacts of the wastewater discharge to the aquatic habitat and
protecting downstream water uses.
This Master Plan addresses the improvementsto the existing facility required to meet the
2003 discharge permit limits. The plan also attempts to conservatively estimate
improvements required to meet more stringent discharge permit limits that will likely be
associated with the 2008 permit renewal. The plan presents some future decisions that
will be vital to the WWTP facility’s continued success in meeting regulatory
AGENDAITEM # V PAGE2
requirements and the Boulder Valley Comprehensive Plan Goals. The Master Plan
explains the approach that has been used to keep the WWTP in compliance with
regulatory requirements and meet community objectives.
The projects defined in the Master Plan are considered to be “Essential Services” and
“Action Level” per the city’s Business Plan guidelines.
PUBLIC PROCESS TO DATE:
The Master Plan is in revised draft formand has not been presented outside of the
January WRAB meeting to the public or other Boards. It has been posted on the city's
Web site for interested parties to review.
NEXT STEPS:
WRAB can comment on the draft plan either at the March 19 WRAB meeting or by e-
mailing comments to earleyr@bouldercolorado.gov. This WWTP Master Plan will be
presented to the Planning Board for review and to city council for final acceptance.
All the potential second phase and future improvements presented here will require a
Community Enviornment Assessment Process (CEAP) and a Boulder County 1041
‘Matters of State Interest’ review and approval. As previously mentioned, this plan will
be incorporated into the Wastewater Utility Master Plan anticipated to be developed later
this year.
STAFF RECOMMENDATION:
Staff recommends that the WRAB recommend acceptance of the revised, draft Master
Plan and note additional comments or revisions they would like to see to improve the
final document prior to moving forward through the approval process.
Attachments
Attachment A: City of Boulder’s Draft Wastewater Treatment Plant (WWTP)
Master Plan
AGENDAITEM # V PAGE3
Draft
Wastewater Treatment Master Plan
CITY OF BOULDER WASTEWATER TREATMENT PLANT
MASTER PLAN
TABLE OF CONTENTS
TOPIC PAGE
EXECUTIVE SUMMARY 3
INTRODUCTION 5
Background 5
Purpose of the Master Plan 6
CURRENT SITUATION 6
Meeting the Needs of the Community 6
Strengths of Existing Wastewater Treatment System 10
Weaknesses of Existing Wastewater Treatment System 10
RELATIONSHIP OF THE WASTEWATER TREATMENT
IMPROVEMENTS TO CITY AND BOULDER VALLEY
COMPREHENSIVE PLAN (BVCP) GOALS 11
Improving and Protecting Water Quality 12
Reducing Waste and Improving Recycling and Reuse 14
Protecting the General Health and Safety of Plant Workers 16
Meeting Future Demands 16
Creating a Sustainable Community 16
HOW THE MASTER PLAN AFFECTS LIFE IN BOULDER 20
PRINCIPALS GUIDE APPROACH TO WASTEWATER TREATMENT
IMPROVEMENTS 22
LIQUID STREAM ALTERNATIVES ANALYSIS 23
Basis of Economic Evaluation 23
Basis of Non-Economic Evaluation 24
SOLIDS DEWATERING ALTERNATIVE ANALYSIS 28
INVESTMENT PROGRAM 31
Investment Strategies 32
Phase 1 Implementation Schedule 34
MEASURING PERFORMANCE 35
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CITY OF BOULDER WASTEWATER TREATMENT PLANT
MASTER PLAN
TABLE OF CONTENTS
TOPIC PAGE
PHASE II IMPROVEMENTS 36
Disinfection System 37
2009 Discharge Permit Limits 37
Biosolids Stabilization 37
Noise and Odor 37
FUTURE CONSIDERATIONS FOR WASTEWATER TREATMENT
NEEDS 37
Stringent Total Inorganic Nitrogen and Phosphorus Discharge Permit
Limits 37
Emerging Contaminants 38
Biosolids Recycling or Disposal Flexibility 38
MASTER PLAN TO MEET CITY GOALS 39
TRIPLE BOTTOM LINE INDICATORS 41
SUMMARY 42
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:
Executive Summary
The purpose of this master plan is to document past decisions, the facility today, to
present the approach that has been used to reach decisions on process selection and
introduce some future decisions that will be facing the utility. To continue to provide the
level of service required by federal regulations and match the expectations of the
community presented in the Boulder Valley Comprehensive Plan Goals, ongoing
improvements to the treatment facility are necessary.
This master plan will be a component of a utility wide Wastewater Utility Master Plan.
The City of Boulder’s most recent wastewater planning documents were the 2002
Utilities Plan and the 1990 Facilities Plan and the more recent Collection System Master
Plan was completed in 2003.
The City has adopted a new framework for City departmental planning documents since
these documents were prepared. The new framework includes a single master plan for
each of the three Utilities; Water, Wastewater, and Stormwater and Flood Management.
Master plans will address the major categories of each utility. For example the
Wastewater Utility MasterPlan will include sections on the collection system, the
treatment system, and water quality that will be informed by master plans on those
components of the utility. The following graphic illustrates the hierarchy of the City’s
Wastewater Utility masterplans and master plans.
City Wastewater Utility Planning Documents
Wastewater
Utility Master
Wastewater
Water Quality
Wastewater
Treatment
Master Plan
Collection
Master Plan
System Master
Plan
The existing treatment facility includes a trickling filter – solids contact secondary
process. This secondary treatment process is being upgraded to an activated sludge
process in the Phase 1 improvements project currently under construction. Phase 1
improvements will also include a dissolved air floatation thickener to thicken the solids
produced in the activated sludge process and solid handling improvements. These
improvements, when put on line in early 2008 will allow the effluent to meet the limits in
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the 2003 discharge permit. The application of the new limits in the permit has been
delayed by a compliance schedule intended to allow completion of the new secondary
process construction needed to meet the new limits.
The Phase 2 construction, currently planned for 2010, will include any process changes
needed to meet permit limits in the 2008 permit. Additionally, it may include noise and
odor control units, a UV disinfection system,and solids stabilization (anaerobic digester)
improvements. The components of the Phase 2 project are still speculative at this time.
The 2008 permit will again drive the facility needs in the Phase 2 project to a large
extent. The 2008 permit could contain requirements for nitrogen and/or phosphorus
removal that would require additional treatment processes that would have to be included
in Phase 2 construction.
The Colorado Department of Public Health and Environment (CDPHE) issues renewed
discharge permits to the city every five years. Federal requirements developed by the
Environmental Protection Agency (EPA) are incorporated in the permits. Wastewater
contaminates that may be regulated in the future include endocrine disrupters and
disinfection byproducts (DBPs).Endocrine disrupters have been shown to pass through
the plant untreated and DBPs are formed in the disinfection process. Although it is
uncertain what the future permit requirements will be, discharge permits will continue to
be the primary driver for wastewater improvements in the future.
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TH
CITY OF BOULDER 75 STREET WASTEWATER TREATMENT PLANT
INTRODUCTION
Background
th
The City of Boulder 75 Street Wastewater Treatment Plant (WWTP) is located at 4049 N.
th
75 Street in the SW ¼ of Section 13, T1N, R70W, Boulder County, Colorado. Treated
effluent from the WWTP is discharged to Segment 9 of Boulder Creek. The WWTP is
defined as a major facility and operates under a Colorado Discharge Permit System (CDPS)
permit (Number CO-0024147) dated February 1, 2003, which expires on January 31, 2008.
The WWTP is being upgraded to meet future wastewater treatment capacity demands and
new ammonia-nitrogen limits that were incorporated in the CDPS permit. The upgrades
include improvements to both the liquid stream treatment and solids dewatering processes
(Phase 1). The WWTP improvements currently under construction (Phase 1) will increase
the treatment capacity to 25.0 million gallons per day (MGD) on a maximum month basis
and provide the capability to reduce ammonia-nitrogen concentrations in the wastewater to
levels below that required by the 2003 discharge permit. The Phase 1 improvements will
also keep the total nitrogen discharge at or below the current level.
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In addition to the liquid stream improvements, the solids dewatering process is being
improved to handle increased solids from the liquid stream treatment process and to reduce
the volume of de-watered solids that must be transported from the WWTP site.
It is anticipated that Phase 2 improvements will be implemented in 2010 in response to:
more stringent CPDS discharge permit limitations in 2008,
the desire to replace the existing chemical disinfection (chlorine and sulfur dioxide)
process with an ultraviolet (UV) disinfection process,
and the need to address biosolids stabilization (digester capacity) limitations.
Purpose of Master Plan
This master plan describes how the current WWTP improvements were selected, how they
will establish the City of Boulder as a proactive environmental steward with regards to water
quality preservation, and how these improvements will position Boulder to meet anticipated
future wastewater treatment requirements. The plan also presents:
The current WWTP improvements and how they conform to City and County
policies and goals;
A comparison with historic operations;
The economic impacts of the current WWTP improvements;
The implementation plan for current improvements (Phase 1);
Strategies for measuring system performance; and
Anticipated future requirements and implementation plan (Phase 2)
CURRENT SITUATION
Meeting the Needs of the Community
The existing WWTP is not capable of treating wastewater to the level required to comply
with the 2003 discharge permit requirements for ammonia removal. But the city has been
issued a compliance schedule to allow construction of the new unit processes before those
limits go into effect. In addition, the existing plant rating for organic material (Biochemical
Oxygen Demand) removal is not adequate to treat the increasing organic loads.
The existing WWTP capacity is adequate to meet the needs of the existing community;
however, it is not adequate to treat the wastewater generated by anticipated population and
employment growth in the Boulder wastewater service area. The 2004 and 2005 annual
average wastewater treatment plant influent flow has been 15.2 mgd and 14.7 mgd
respectively. As shown in Figure 1, annual average flows have been trending down, or at
least not increasing, since 1995 which averaged 18.4 mgd due to the high infiltration
experienced during that very wet year.
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Figure 1. 1995-2005 WWTP Flows
1995-2005 WWTP Flows
19
18
17
16
15
14
13
12
11
10
1994199619982000200220042006
Year
This graph of recent annual average influent flows at the WWTP is informative in depicting
the variability that necessitates conservative future flow projections. In 1995 Boulder
experienced a very wet year with near record rainfall in May. Then 2002 was the driest in the
last 300 years and the utility requested water conservation efforts that continued into 2003
before they were retracted. However, the customHUV·ZDWHUFRQserving behavior seems to
KDYHFRQWLQXHG$GGLWLRQDOO\WKHFLW\·s ongoing system rehabilitation has reduced
groundwater infiltration and surface water inflows (I & I) in the collection system. So, this
graph shows the impact wet weather, drought, I & I reduction and conservation efforts can
have on wastewater treatment plant flow.
Hydraulic capacity projections were based upon historic flow per resident and employee,
industrial hydraulic load, land use and zoning mapping, and population and employment
projections. The extremes, both high and low, were excluded from the averages used to
project future hydraulic capacity needs at the WWTP. More historic wastewater flow data
can be foundLQWKH¶-XO\&LW\RI%RXOGHU:DVWHZDWHU&ROOHFWLRQ6\VWHP Master Plan
8SGDWH·
7KH::73VHUYHVWKHQLQHVXEFRPPXQLWLHVRI%RXOGHU·VZDVWHZDWHUXWLOLW\VHUYLFHDUHD
(WUSA) depicted in Figure 2.
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Figure 2. Map of WUSA Area (WUSA area denoted by red line)
Boulder's population and employment continue to grow with the population expected to
reach 128,162 by 2025 based on a revised estimate of Denver Regional Council of
Governments (DRCOG) projections. The Boulder Valley Comprehensive Plan (BVCP)
population and employment growth expectations are similar. The wastewater treatment
planning documents must use DRCOG's population projection when submitting plans and
applying for state level approvals for facility improvements.
The BVCP has recently been revised to include population and employment projections
through build-out of the service area. The build-out population is expected to be reached in
2030, but no specific year has been assigned to the employment build-out projections.
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Throughout the planning period, population and employment estimates from DRCOG
closely follow estimates from the BVCP. To keep the values consistent with each other, the
employment estimate value from DRCOG in 2025 has been recalculated to reflect the
BVCP build-out projection.
The revised values represent a population projection increase of approximately 7,000 people
over previous projections for the year 2030 and an employment increase of approximately
23,000 employed persons. Boulder population projections from DRCOG and the BVCP are
shown in Table 1.
Table 1. Population Summary and Projection for Areas I & II (WUSA)
Projected Population
Source 2000 2001 2005 2010 2015 2020 Build Out
BVCP 106,200 109,180 112,160 115,140 118,120 121,100 129,878
111112
DRCOG Analysis -- 106,614109,412112,341116,121119,500128,162
Original estimate provided by DRCOG
1
Estimate based on revised BVCP projections
2
Employment values and projections from the BVCP and DRCOG are summarized in Table
2.
Table 2. Employment Summary and Projection for Areas I & II (WUSA)
Projected Employment
Source 2000 2001 2005 2010 2015 2020 Build-
out
BVCP 101,000 109,260 117,520 125,780 134,040 142,300 167,564
111112
DRCOG Analysis -- 106,407111,062119,656125,228130,721155,921
Original estimate provided by DRCOG
1
Estimate based on revised BVCP projections
2
Based on historical values of 102 gallons of wastewater generated per capita per day and 50
gallons of wastewater generated per employee per day, an additional flow of approximately
1.1 MGD are anticipated as a result of the changes in population and employment
projections. This also represents an additional loading of approximately 2,130 pounds of
five-day biological oxygen demand (BOD) per day. This represents an increase of 4.4% in
5
the design flow and an increase of 7% in BOD design loading. These increases are
5
generally within the range of accuracy of the initial flow and load projections and therefore
are considered to have no significant impact on the capability of the upgraded wastewater
treatment facilities to handle the projected flows and loads.
The existing facility is designed to treat 20.5 MGD; however, the projected capacity
requirement to meet the 2030 population and build-out employment is approximately 25
MGD. Industrial flow projections are estimated to be 6% of the total annual flow based on
the 2000 and 2001 significant industrial user flows of approximately 0.97 MGD.
Figure 3 shows existing WWTP capacity (20.5 MGD) versus projected flows.
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Figure 3. Projected Maximum Month WWTP Flows and Treatment Capacity
26
25
24
23
22
21
20
19
18
200020052010201520202025
DRCOG based Max. Month Flow, mgd ((Average based on population at 102 gpcd, employment at 50 gpcd, and SIU flow at 6%) x 1.2)
BVCP based Max. Month Flow (Based on Census), mgd ((Average based on population at 102 gpcd, employment at 50 gpcd, and SIU flow at 6%) x 1.2)
Existing Treatment Capacity, mgd
New Treatment Capacity with WWTP improvements, mgd
If population values increase beyond those predicted (as shown in Tables 1 and 2) the
WWTP will not provide adequate treatment capacity. In that case, treatment capacity needs
will have to be re-examined before the expected build-out date of 2030, and additional
expansion of the WWTP capacity may be required before that time. However, as shown in
Figure 1 if recent influent flow trends continue, the WWTP will have adequate capacity for
the interim period.
Strengths of Existing Wastewater Treatment System
The existing WWTP liquid stream system includes a "Trickling Filter/Solids Contact"
process that has been operational since 1989. The existing system is shown schematically in
Figure 3. Over the past 18 years the facility has generally met the demands of City residents,
maintained permit compliance, and has discharged satisfactory treated wastewater, or
effluent, to Boulder Creek. For clarification, the liquid stream processes treat the wastewater
removing contaminates and the solid stream processes treat the solids removed from the
wastewater and the solids generated by the liquid stream process.
Weaknesses of Existing Wastewater Treatment System
The two primary drivers motivating the current WWTP improvements (Phase 1) are new
ammonia nitrogen discharge limits and increased wastewater flow. The existing facility, as
shown in Figure 4, will be unable to reduce ammonia nitrogen in the wastewater to the level
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required by the 2003 discharge permit, the rated BOD capacity is routinely exceeded and it
has insufficient capacity to treat the projected wastewater flows.
The improvements will allow the WWTP to treat projected flows and loads through 2030,
treat the wastewater to the level required to meet the 2003 discharge permit requirements,
provide more operational flexibility, and increase equipment efficiency.
Figure 4. Schematic of Existing WWTP
RELATIONSHIP OF THE WASTEWATER TREATMENT IMPROVEMENTS
TO CITY AND BOULDER VALLEY COMPREHENSIVE PLAN (BVCP) GOALS
Both the City of Boulder and Boulder County desire to maintain their proactive status
regarding environmental stewardship. Consequently, they have established goals in the areas
of sustainability and environmental quality. By meeting the objectives of the planned
process improvements, the Boulder WWTP will also meet several City and County
environmental goals. Relevant City and County goals are listed below:
Improving and protecting water quality;
Reducing waste by improving recycling and reuse of biosolids;
Protecting the general health and safety of plant workers;
Meeting future wastewater treatment capacity demands; and
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Creating a sustainable community through;
Improved energy efficiency,
o
Minimization of greenhouse gas emissions,
o
Cost savings, and
o
Minimizing chemical usage.
o
Improving and Protecting Water Quality
The Colorado "303 (d) List" is a list of surface waters within Colorado that are considered
´LPSDLUHGµZLWKUHVSHFWWRWKHZDWHUTXDOLW\required for their intended uses. The 2000
Colorado 303 (d) List identifies Segments 9 and 10 of Boulder Creek as being impaired for
aquatic life due to elevated unionized ammonia. The list identified municipal WWTPs and
possible non-point sources of ammonia as the cause of impairment. This listing necessitated
implementation of an ammonia Total Maximum Daily Load (TMDL) study, which
subsequently dictated the ammonia nitrogen limit contained in the Boulder Colorado
Discharge Permit. The current permit, issued February 1, 2003, is in effect until February
2008. Improvements under construction at the WWTPs will remove significant amounts of
DPPRQLDIURPWKHSODQW·V effluent and improve Segment 9s aquatic habitat. Additionally,
pretreatment efforts will continue to minimize thH¶hDUGWRWUHDW· contaminates discharged to
WKHFLW\·VVDQitary sewers. Although the permit does not place limits on specific nutrients,
the City of Boulder recognizes the need to put mechanisms in place to ensure that
anticipated future nutrient limits can be met with minimal additional construction. The
ammonia limit and potential future nutrient limits will contribute to the protection of aquatic
life in Boulder Creek. Figure 5 presents an image of Section 9 of Boulder Creek and the
location of the Boulder WWTP.
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Figure 5. Segment 9 of Boulder Creek and the Location of the Boulder WWTP
Current improvements to the WWTP (Phase 1) will allow Boulder to discharge water of
substantially higher quality than the 2003 discharge permit requires, while also achieving no
net increase in the total amount of nitrogen discharged to Boulder Creek. By complying with
SHUPLW·VOLPLWVWKHZDWHUGLVFKDUJHGIURPthe Boulder WWTP will improve the water quality
of Boulder Creek to a level that has been determined will protect downstream users and
support aquatic life. Figure 6 presents WWTP effluent constituent concentrations that must
be met to ensure compliance with the 2003 discharge permit.
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Figure 6. Current Effluent Limits for Selected Constituents*
160
150
140
120
100
80
60
40
30
25
20.5
13.8
20
0.004
0
Flow CBODTSS TotalE. ColiTotal Residual
(MGD)(mg/L)(mg/L)Ammonia NBacteriaChlorine
(mg/L)**(#/100 ml)(mg/L)
Note: All values are based on 30-day averages.
*Effective until January 31, 2008
**The ammonia nitrogen value shown is the annual average. Regulatory limits vary monthly and range from
10.9 to 16.9 mg/L. Effective January 25, 2008, the TMDL-based ammonia limits come into effect resulting in
a limit of 5.3 mg/l for March, the most stringent month.
Reducing Waste and Improving Recycling and Reuse
7KHFLW\·V:WTP represents the one of the biggest investments and efforts the city
continues to make to reduce and recycle waste generated by the city.
As shown previously in Figure 1, water conservation can effectively reduce wastewater
influent flows but do not reduce the pollutant load in the wastewater. So if hydraulic
capacity limitations are approached, water conservation efforts in conjunction with
collection system rehabilitation to reduce infiltration may be used to extend the useful life of
treatment unLW·VFDSDFLW\XQGHUFHUWDLQ conditions. But hydraulic loads, organic loads and
solids loads must all be within the overall treatment capacity of the facility to achieve
adequate treatment.
The upgraded liquid stream treatment processes and the anticipated increase in wastewater
flows at the WWTP are expected to increase solids production by 25 to 30 percent. The
solids dewatering improvements are designed to treat this new volume and to remove
substantially more water from the solids than has historically been the case. By reducing the
amount of excess water contained in the solids, the volume of material removed from the
WWTP will decrease by nearly 50%, resulting in reduced hauling costs and associated fuel
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usage, and disposal costs. Figure 7 presents a comparison of the existing and anticipated
volume of sludge produced as cubic yards per day.
Figure 7. Biosolids Production Volumes
100
80
60
40
20
0
Existing ProcessAnticipated AfterAnticipated After
Liquid StreamLiquid and Solid
ImprovementsStream
Improvements
The volumes of sludge presented in Table 7 were calculated from the historical and
projected sludge quantities presented in the Community Environmental Assessment Process
th
for 75 Street Wastewater Treatment Plant Dewatering Improvements. Biosolids densities
were assumed to be 64.3 and 66.1 lbs/cubic foot for solids concentrations of 10 and 20
percent respectively.
Solids generated in the wastewater treatment process will be anaerobically digested,
dewatered, and used as a soil amendment on agricultural lands on Colorado's eastern plains.
Alternatively, the solids could be used by a private firm on a contract basis for landscape
amendments or other uses.
Boulder also has a pretreatment program that reduces waste loads from industries and some
commercial enterprises. The program requires categorical and significant industrial
dischargers to limit the pollutants they discharge under a permit issued by the city. The
pretreatment program protects the liquid stream processes from harmful loads, protects the
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quality of the solids, and protects the Boulder Creek from the effects of pollutants that could
pass thought the facility untreated. This program will be important in protecting the plant
from future increases in metals and other non-treatable pollutants.
Protecting the General Health and Safety of Plant Workers
There was no work time lost from on the job injuries during 2005. The planned
improvements will provide improved working conditions and reduce exposure to hazardous
chemicals. The upgrades will replace old and outdated equipment with newer equipment
that will require less maintenance and reduce potential for possible injury associated with
operation. This will provide a safer environment for plant workers and for the surrounding
neighborhoods and natural areas and will help maintain baseline conditions of zero injuries.
Meeting Future Demands
The population of Boulder is expected to grow to approximately 128,160 people by 2030
and the number of people employed in Boulder to increase to approximately 155,920. The
existing facility is not equipped to treat the volume of wastewater generated by this projected
growth, subsequently; an increase in treatment capacity from 20.5 to 25 MGD is needed.
After the Phase 1 improvements in place, the facility will meet these future demands.
Creating a Sustainable Community
Sustainability in wastewater treatment is achieved through resource conservation, recycling
and waste reduction. Resource consumption will be minimized through proper process
selection, use of energy efficient equipment, and operational process optimization.
Primary issues of concern include:
Energy usage,
Greenhouse gas generation,
Costs, and
Chemical usage
Energy Usage
Although the energy efficiency of the new plant equipment will be greater than that of the
older plant equipment, overall energy consumption is expected to rise due to the higher level
of treatment provided and the anticipated higher wastewater flows. In evaluating higher
level treatment alternatives, additional energy usage was considered to be an acceptable
tradeoff when evaluated against increased chemical usage.
In addition to the criteria listed above, the City is incorporating Leadership in Energy and
Environmental Design (LEED) concepts into the design of the new dewatering facility.
Facility upgrades will improve energy efficiency in several ways:
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Less fuel consumed
The mileage associated with hauling of solids offsite will be decreased by
o
approximately 50%.
The anticipated replacement of chemical disinfection (chlorine and sulfur
o
dioxide) with UV disinfection (Phase 2) eliminates the fuel consumption
associated with the manufacture and transportation of these chemicals.
Electricity consumed
Improved energy efficiency of newer equipment will reduce energy waste in the
o
liquid stream and solids dewatering processes (however, due to energy demands
of the new activated sludge process, electrical energy usage is expected to
increase).
Energy produced
Increased production of solids will result in more methane production as
o
wastewater flows increase.
Figure 8 presents data on energy usage of existing system.
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Figure 8. Energy Usage
20000
15000
10000
5000
0
FuelEnergyElectricityNatural Gas
Consumed*Produced*Consumed**Consumed**
(gal)(KWh)(MWh)(MMBtu)
*Based on 2004 data; 2005 data represented an atypical year due to digester cleaning
**Based on 2005 data; 2004 data not available.
Greenhouse Gas Generation
The City of Boulder participates in the Cities for Climate Protection Campaign, an
agreement between U.S. cities that calls for a reduction in greenhouse gas emissions
equivalent to those identified in the Kyoto Protocol. Improvements in energy usage and
reduced fuel consumption lower the WW73·VJUHHQKRXVHJDVHPLVVLRQV KRZHYHULQFUHDsed
solids production creates more methane gas, one of the six primary greenhouse gases.
Costs
WWTP operating costs are based on:
Fuel consumption
Energy usage
Chemical usage
Equipment costs
Personnel costs
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The improved wastewater treatment processes will be more efficient in many ways, and
therefore, some operational costs are expected to be reduced. A considerable portion of the
2005 budget was spent on repair and rehabilitation work at the existing WWTP. In addition,
biosolids recycling costs increased by approximately 10% and chlorine costs increased by
25% in 2005. Overall upgrades to the treatment process are expected to minimize
maintenance and repair costs; however, because the new process will be treating the
wastewater to a higher level, some additional costs will be incurred. Figure 9 presents
various expenditures from the existing WWTP.
Figure 9. Summary of Existing WWTP Costs
Diesel fuel cost includes diesel fuel consumption resulting from biosolids recycling operation. Estimation
based on city and contractor hauled biosolids loads and an efficiency 4 mpg.
Chemical Usage
The anticipated implementation of UV disinfection, potentially in Phase 2 improvements,
will eliminate the need for chlorine and sulfur dioxide chemicals. Figure 10 presents actual
chemical usage data for the existing plant.
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Figure 10. Chemical Usage Data for the Existing WWTP
The use of additional chemicals was considered during the selection process. Several
alternatives evaluated required the addition of methanol to achieve nitrogen removal. The
chosen process can remove a substantial amount of nitrogen and phosphorus without the
need for chemical addition. This is important since it is anticipated that 2009 CPDS permit
discharge limitations will limit the discharge of one or more of these substances (Phase 2).
HOW THE MASTER PLAN AFFECTS LIFE IN BOULDER
WWTP improvements are necessary for the City of Boulder to continue to meet their
environmental stewardship goals. By addressing the two main drivers of wastewater
treatment improvements, lower ammonia nitrogen limits and increased wastewater treatment
capacity, City goals of furthering community sustainability goals and protecting water quality
will be met. The improvements represent a prRDFWLYHRU´DFWLRQµDSSURDFKWRLPSURYLQJ
water quality in Boulder County because they go beyond the minimum required to meet
regulatory requirements.
A comparison between operation goals met by the existing WWTP and the WWTP after
Phase 1 improvements are implemented is shown in Table 3.
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Table 3. Comparison of WWTP Capabilities
Existing WWTP WWTP After Phase 1
Improvements
Meet future capacity demands
Meet new ammonia limits
(CDPS 2003)
Provide treatment options for
additional nutrient removal
Provide shorter operating time
(biosolids dewatering)
Eliminate chemical use
²3KDVH
Reduce solids handling
Minimize long-term
1
operational costs
2
Minimize energy requirements
Minimize greenhouse gas
emissions
Minimize neighborhood traffic
3
Provide adequate odor control
Minimize visual impairment
Improve air quality
Long-term operational costs associated with the existing plant would increase due to reoccurring equipment
1
repair and rehabilitation.
Energy use will increase based on Phase 1 Improvements due to the increased level of treatment provided.
2
Energy savings from more efficient equipment and the improved dewatering process will help to offset the
greater energy demand from larger, more extensive treatment.
Odor controls will be placed on solids processes.
3
The CDPS permit dated February 1, 2003 includes a compliance schedule that allows the
City until January 31, 2008 to comply with the new ammonia limits. The Phase 1
improvements are on schedule to be completed and online before that date.
A schematic flow diagram of the WWTP after implementation of Phase 1 improvements is
shown in Figure 11.
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Figure 11. Schematic Flow Chart of the New WWTP
PRINCIPLES GUIDE APPROACH TO WASTEWATER TREATMENT
IMPROVEMENTS
As mentioned previously, the primary motivators behind the WWTP upgrades that
simultaneously serve City and County goals were:
Improving ammonia nitrogen reduction capability,
Increasing treatment capacity, and
Improving the dewatering process capabilities to meet increased capacity
requirements.
Secondary drivers include:
Replacing inefficient equipment with newer, improved equipment; and
Reducing chemical usage.
The City is required to provide adequate treatment capacity and meet regulatory
requirements and these upgrades will allow the City to do so. The secondary drivers could
be met simultaneously with only moderate additional cost. These improvements optimize
the system and establish the City as responsibly proactive by implementing treatment
options that improve effluent quality while potentially minimizing future costs.
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LIQUID STREAM ALTERNATIVES ANALYSIS
As part of the preliminary design evaluation, nine process alternatives were initially
considered for upgrading the Boulder 75th Street WWTP. For more information on the
original nine treatment options and the selection process refer to the City of Boulder
Wastewater Utility Plan Amendment 1 and Site Application Report (Brown and Caldwell,
2005).
Based on the initial process review the following five alternatives were selected for detailed
evaluation.
Alternative 3.7ULFNOLQJ)LOWHU²6ROLGV&RQWDFW7DQN²1LWULI\LQJ7ULFNOLQJ)LOWHUV²
Trickling FiltHU5HF\FOH²'HQLWULILFDWLRQ)LOWHUV²&KHPLFDO3KRVSKRUXV5HPRYDO
(TF-SC-NTF-TFR-DNF)
Alternative 6. Trickling Filter²$FWLYDWHG6OXGJH 7)$6
Alternative 7. Activated Sludge (AS)
Alternative 8.7ULFNOLQJ)LOWHU²0HPEUDQH%LRUHDFWRUV 7)0%5
Alternative 9. Membrane Bioreactor (MBR)
These alternatives were evaluated in detail and the results of the evaluations are presented in
Figure 13 and Table 4.
Basis of Economic Evaluation
The economic evaluation includes consideration of initial construction costs and ongoing
operation and maintenance (O&M) costs. It is important to consider both types of costs
since some alternatives may be capital cost intensive and yet require minimal annual O&M
costs, while other alternatives may be less capital cost intensive but require high annual
O&M expenditures. Present Worth Analysis is a technique used to put construction and
O&M costs on a comparable basis so alternatives can be appropriately evaluated. Present
worth costs were evaluated over a period of 20 years.
Figure 12 shows the results of the economic, or present worth, evaluation of these
alternatives.
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Wastewater Treatment Master Plan
1
Figure 12. Economic Evaluation for Process Alternatives
Total PW O&M Cost
70
Phase 2 PW Construction Cost
Phase 1 Construction Cost
60
50
40
30
20
10
0
Alternative 3Alternative 6Alternative 7Alternative 8Alternative 9
TF-SCT-TF-ASASTF-MBRMBR
NTF-TFR-
DNF
Values rounded to the nearest hundred thousand dollars.
1
As shown in Figure 12, the most economically feasible alternatives are Alternative 6
(trickling filter-activated sludge) and Alternative 7 (activated sludge).
Basis of Non-Economic Evaluation
Non-economic factors were also considered in the evaluation of the wastewater treatment
alternatives. These non-economic factors are particularly important when the economic
evaluation indicates similar costs for two or more alternatives (such as the case with
Alternatives 6 and 7 as indicated in Figure 14) or when non-cost issues represent a high
priority. The non-economic evaluations for the secondary treatment process alternatives are
displayed in Table 4. Each non-economic criterion was scored a value between 1 and 5, with
5 representing the highest or best alternative.
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Table 4. Non-Economic Evaluation for Process Alternatives
Criteria
Alt. 3 - TF/SC, NTF, TFR,
DF, CPR 3 4 3 3 5 4 3 5 4 4 38
Alt. 6 - Trickling Filter -
Activated Sludge 4 4 4 3 3 4 4 3 4 3 36
Alt. 7 - Activated Sludge
5 4 5 5 4 5 4 4 5 4 45
Alt. 8 - Trickling Filter -
Membrane Bioreactor 5 2 2 2 5 2 5 1 4 5 33
Alt. 9 - Membrane Bioreactor
5 2 3 4 5 2 5 1 5 5 37
Note: A higher score is more favorable.
Refer to the City of Boulder Wastewater Utility Plan Amendment, September 2004, for more
details on the non-economic evaluation. As seen from the rating information presented in
Table 4, Alternative 7 (activated sludge) was rated the highest overall from a non-economic
standpoint.
Disinfection Alternatives
th
The Boulder 75 Street WWTP currently uses chlorine gas to disinfect the treated
wastewater. Gaseous sulfur dioxide is used to remove residual chlorine following
disinfection and prior to discharge of the wastewater to Boulder Creek. The existing
chlorine disinfection system has adequate capacity to meet the needs of the proposed
th
expansion of the 75 Street facility from 20.5 MGD to 25 MGD, however it does not meet
current industry standards associated with the safe handling of chlorine and sulfur dioxide
gases (both chlorine and sulfur dioxide gases are considered hazardous chemicals). This,
along with a broader concern about the safety aspects of transporting and handling
hazardous chemicals and the environmental impacts associated with using chlorine as a
disinfectant, prompted the City to evaluate replacing the existing chlorine disinfection system
with a different system.
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Wastewater Treatment Master Plan
The following disinfection alternatives were considered:
Alternative 1²&KORULQH*DVZLWK6XOIXU'LR[LGH ([LVWLQJ*DVHRXV&KHPLFDO
System)
Alternative 2²+LJK6WUHQJWK6RGLXP+\pochlorite with Sodium Bisulfite (Liquid
Chemical System)
Alternative 3²2QVLWH6RGLXP+\SRFKORUite Generation with Sodium Bisulfite
(Liquid Chemicals System)
Alternative 4²'LVLQIHFWLRQZLWK8Otraviolet Light (UV Disinfection)
Figure 13 presents an economic evaluation for disinfection alternatives to be used with the
activated sludge process.
Figure 13. Economic Evaluation for Disinfection Alternatives
7
Construction CostO&M Cost
6.3
6
5.2 5.2
5
3.4
4
3
2
1
0
Gaseous ChlorineHigh Strength LiquidDisinfection withUV Disinfection
DisinfectionSodium HypochloriteLow Strength Liquid
DisinfectionSodium Hypochlorite
Generated on Site
As shown in Figure 13, the most economical alternative is continued gaseous chlorine
disinfection.
The results of an evaluation of non-economic factors for disinfection alternatives are
presented in Table 5.
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Wastewater Treatment Master Plan
Table 5. Non-Economic Evaluation of Disinfection Alternatives
Criteria
Alt. 1 - Gaseous Chlorine
5 4 4 2 4 4 4 5 1 3 3 39
Alt. 2 - High-Strength Sodium
Hypochlorite 5 4 5 4 4 4 4 4 3 4 4 45
Alt. 3 - On-Site Sodium
Hypochlorite Generation 5 4 3 3 4 4 4 3 4 4 4 42
Alt. 4 - UV 5 3 5 5 4 4 5 2 5 5 5 48
Note: A higher score is more favorable.
UV disinfection was rated the highest of the disinfection alternatives from a non-economic
standpoint. UV disinfection is the safest for the WWTP staff and the community and it
eliminates the need for hazardous chemicals to be shipped to and stored at the WWTP. UV
disinfection is also very easy to operate and maintain, and will allow the City of Boulder to
continue to meet their effluent disinfection requirements without the negative aspects of
chemical addition. Even though UV disinfection was not the most economical alternative, it
was selected as the preferred disinfection method based on the non-economic criteria.
Because of funding limitations, replacement of the existing chemical disinfection (chlorine
and sulfur dioxide) with UV disinfection is not being implemented as part of the Phase 1
improvement project. It is anticipated this improvement will be implemented as part of the
Phase 2 improvements in 2010.
Activated sludge and UV disinfection were selected as the preferred wastewater treatment
process to mHHW%RXOGHU·VFXUUHQWDQGDQWLFLSDWHG wastewater treatment needs. Figure 14
illustrate the components of the recommended WWTP upgrades.
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Figure 14. WWTP Upgrades to Existing Facility
SOLIDS DEWATERING ALTERNATIVES ANALYSIS
Three alternatives were evaluated for the solids dewatering process. These alternatives
included:
Alternative 1: Do nothing
Alternative 2: Maintain semi-solid (10-12% solids) dewatering (existing process)
Alternative 3: Transition to a cake (20-24% solids) product (new process)
The Do Nothing alternative requires no capital investment and neither the operations and
maintenance nor the total present worth costs have been estimated. The Do Nothing
approach is not a valid selection because the existing facility cannot treat the projected
generated solids resulting from the new liquid stream improvements
.
Alternatives 2 and 3 are based on centrifuge dewatering of digested biosolids produced from
the liquid treatment process. Figure 15 presents an economic evaluation of the biosolids
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dewatering improvement alternatives. Present worth costs were evaluated over a 20-year
period.
Figure 15. Economic Evaluation for Dewatering Improvements Alternatives
45
Total Present Worth
40
O&M Cost
Capital Cost
35
30
25
20
15
10
5
0
Do Nothing*Dewatered Semi-SolidDewatered Cake Solid
*Note: The Do Nothing approach is not a valid selection.
Table 6 presents a summary of the non-economic evaluations of the dewatering
improvements alternatives.
The economic evaluations of these alternatives is based upon hauling solids to disposal sites
in tractor trailer type trucks that average 5 miles per gallon (mpg) when on the open road but
realize an average of only 3 mpg when loading, unloading, and local road travel is
considered. The average mileage of 3 mpg was used in the evaluation. While the semi-solids
alternative generates 10-12% solids, the dewatered cake solids are in the 20-24% solids
range. This results in needing to only haul ½ the volume with the thicker product.
Tractor trailer trucks made 560 trips in 2006 with an average roundtrip distance of 130 miles
per trip. Assuming that the majority of the trip is conducted on the open road with an
average mileage of 5 mpg the average yearly fuel consumption is 14,560 gallons (24,266
gallons if based on a mileage of 3 mpg). Assuming 2006 was an average year, by reducing
the number of trips by half, approximately 7,280 gallons (or 12,133 if based on 3 mpg) of
fuel will be saved each year. Based on an approximate fuel price of $2.50 this results in an
average yearly savings of approximately $18,200 (or $30,332 if based on 3 mpg).
More information on this economic evaluation can be found in the Community
th
Environmental Assessment Process for 75 Street Wastewater Treatment Plant Dewatering
Improvements document in the appendix of this plan.
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Table 6. Non-Economic Evaluation Criteria for Dewatering Improvements
Alternatives
Alternatives Description Advantages Disadvantages
Alternative 1Maintain
Low costs. Existing system does not have
Do Nothing existing system.
capability to meet future WWTP solids
No construction impacts.
(10-12% solids)
loading rate at flows of 25 MGD.
Existing system is 20 years old and it is
difficult to find replacement parts,
reducing reliability and plant
redundancy.
Would lead to regulatory non-
compliance.
Inability to store non-dewatered
biosolids at plant.
Alternative 2New centrifuges
Regulatory compliance. New centrifuges would be smaller and
Semi-solid (10-would replace
would be required to operate longer.
Makes maximum use of
12% solids) with existing ones in
existing structures. Structural concerns if existing building
existing solids existing
are modified again, limited ability to
Similar operation to existing
dewatering dewatering
modify existing building.
process; staff is familiar with
building building.
process. Opinion of probable cost is highest for
this alternative due to retrofitting
difficulties, longer run times, more
frequent equipment failure, and greater
staffing needs.
Alternative 3Producing cake
Regulatory compliance. Cake storage is needed.
Cake solid (20-product and new
Makes maximum use of Requires construction of new facility.
24% solids) with high-solids
existing structures.
new solids centrifuge in
Lower biosolids volume.
dewatering new building.
Fewer truck costs equal lower
building
O&M costs.
Opinion of probable cost is
lowest due to properly sized
structure and equipment,
reducing staffing and hauling
requirements.
As indicated in Table 6, Alternative 3 represents more advantages and fewer disadvantages
than the other alternatives.
Based on the economic and non-economic analysis, the recommended improvements for
the solids dewatering facility are a new, dewatered cake solid processing facility.
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In summary, Alternative 3 was chosen because:
1.A cake product is becoming the norm in the industry and produces drier material,
which results in fewer truck trips from the WWTP site.
2.A new dewatering building is appropriate for the new equipment due to size
constraints and age of existing building.
3.Retrofitting the existing facilities would result in higher lifetime costs for the WWTP.
Cost advantages for constructing a new building include:
a.Installation of properly sized equipment with lower operating costs,
b.Lower staffing needs,
c.Redundant capacity,
d.Greater flexibility, and
e.Lower maintenance costs.
INVESTMENT PROGRAM
The 2005 Wastewater Utility Capital Improvement Program (CIP) developed by the Boulder
Department of Public Works includes improvements to both the liquid stream and solids
stream wastewater treatment process. In December 2005 the City issued a revenue bond to
finance the capital costs associated with the Phase 1 improvements.
The 2005-2010 Wastewater Financial Plan incorporates a series of multi-year rate increases
to cover the cost of these projects. Utility rate adjustments are approved by City Council on
an annual basis. For 2005 and 2006, the City implemented 20 percent increases to the
wastewater user charges. An additional rate increase of 6 percent was implemented on
January 1, 2007. Table 7 presents a comparison of Boulder wastewater rates compared to
those of surrounding communities based on 2005 rates.
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1
Table 7. Front Range Community Sewer Rates
Annual Sewer
Number Community Service Charge ($)
1 Erie 321.00
2 Colorado Springs 219.29
3 Fort Collins 210.30
4 Longmont 207.00
5Greeley195.00
6Westminster186.00
7 Broomfield 184.20
8 Northglenn 171.00
9 Boulder 170.76
10 Thornton 163.08
11 Louisville 153.60
12 Arvada 148.86
13 Lafayette 138.84
14 Aurora 130.20
15 Denver 128.16
Based on information collected of Front Range Communities conducted in 2005.
1
Investment Strategies
Figure 16 depicts the range of investment strategies considered in determining the extent of
th
wastewater treatment system upgrades at the Boulder 75 Street WWTP.
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Figure 16. Comparison of Investment Strategies
Visionary
Visionary
No budget constraints.
Meet all current and future needs initially.
Action
Action
Selected design
Additional funding with constraints.
strategy
Meet all current needs and prepare for future
growth.
Financially constrained.
Meet current needs
only.
The City of Boulder chose to pursue an action level approach to wastewater treatment
improvements. At this level each area that requires immediate attention has been addressed
and mechanisms have been put in place to prepare for anticipated future requirements.
Unlike actions taken at the visionary level, the upgrade alternatives were selected to provide
the City with the most long term value with respect to cost, system performance, and
environmental impact.
The system upgrade approach was initially based on two phases of implementation. This
phasing approach allows the City to balance capital expenditures by constructing only
necessary components in the near-term, while setting the stage for additional process
improvements that may be required to meet more stringent future effluent limits. Phase 1
improvements include those that were required to meet current design flows and permit
limits and processes that prepare the plant for the Phase 2 upgrades with only moderate
additional costs. Phase 2 upgrades include those that are anticipated to prepare the plant to
meet anticipated future limits, reduce chemical usage, and treat any odor concerns that may
arise.
Construction of Phase 1 improvements began in 2006 and Phase 2 improvements are
expected to begin in 2010. Phase 1 and 2 improvements are as follows:
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Phase 1 (2006): These improvements are required to address the 2003 discharge
permit limitations (ammonia nitrogen) and to increase the capacity of the
WWTP. In addition, these improvements position the plant to meet anticipated
future discharge permit requirements with only moderate additional construction
costs.
Phase 2 (2010): These improvements are anticipated in response to probable
more stringent CPDS discharge permit limitations (nitrogen and phosphorus) in
2008, the desire to replace the existing chemical disinfection (chlorine and sulfur
dioxide) process with an ultraviolet (UV) disinfection process, the need to
address biosolids stabilization (digester capacity) issues.
Phase 1 Implementation Schedule
Figure 17 depicts the implementation schedule for Phase 1 improvements. The schedule
includes the time required for total project implementation, beginning with project approval
and concluding with fully operational facilities.
Figure 17. Proposed Implementation Schedule
The following table presents the current capital improvement program (CIP) funding for
the wastewater treatment projects discussed in this master plan. It does not include
funding for on-going maintenance projects associated with the WWTP.
Table 8. Current CIP Funding for WWTP Projects
2006200720082009201020112012
Phase 1 – Liquid
Stream
$47,250,000$0$0$0$0$0$0
Phase 2 – Liquid
Stream$0$100,000$200,000$1,000,000$10,000,000$0$0
Phase 2 -
$
Biosolids Digester
0$0$0$850,000$8,500,000$0$0
Anticipated Rate
Increases for
Capital and Other
Needs6%4%4%10%4%3%
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MEASURING PERFORMANCE
City objectives were used as guiding principles for the design of wastewater treatment system
improvements and will be used as performance indicators to measure results from the
improvement projects. To accomplish this, a baseline of each indicator must be established
and compared to indicators measured at specific intervals following the completion of
improvement projects. Table 8 presents a summary of suggested performance indicators.
Table 8. Summary of Performance Indicators
Figure 18 provides an example of how the values of various performance indicators for the
City goals Performance Indicator
1. Number of occasions WWTP is not in
compliance with permit
Improving and protecting water quality
2. Nutrient concentration in effluent
Reduce waste and improve recycling and
Volume of exported solids
reuse
Improve health and safety of WWTP
Number of WWTP accidents
operators
Meeting wastewater treatment capacity
Wastewater flows
demands
1. Amount of Energy use
Creating a sustainable community through 2. Amount of Greenhouse gas emissions
resource conservation 3. Cost of operating plant
4. Amount of Chemical usage
existing process might be compared with values for the same indicators associated with the
WWTP performance following the improvements. The expected values from the WWTP
improvements are not shown; these parameters must be monitored in the future for
comparison.
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Figure 18. Relative Comparison of Performance Indicators
New Process
Existing Process
*Values vary from 16.9 mg/L to 10.9 mg/L depending on the month
PHASE II IMPROVEMENTS
The existing WWTP has met historical needs by providing adequate treatment capacity and
appropriate treatment capability. The WWTP is currently being upgraded to treat additional
wastewater flows and meet stricter effluent ammonia nitrogen limits in Phase1.
7KHVH3KDVHLPSURYHPHQWVUHSUHVHQWDQ´DFWLRQOHYHOµSRVLWLRQIRUWKH&LW\ This position
requires that immediate action be taken on items of the most urgent need; capacity
requirements and permit limits, with the incorporation of additional proactive elements
based on anticipated regulatory concerns, environmental quality, and available funding.
Many anticipated treatment challenges can be more cost effectively dealt with during current
construction activities than at a later date.
Additional phases of design and construction are expected to follow. Concerns to be
addressed for Phase 2 work include:
Disinfection system,
2008 discharge permit limits,
Biosolids stabilization (digester capacity)
Odor and noise
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Disinfection System
Because of funding limitations, replacement of the existing chemical disinfection (chlorine
and sulfur dioxide) with UV disinfection is not being implemented as part of the Phase 1
improvement project. It is anticipated this improvement will be implemented as part of the
Phase 2 improvements in 2010. For reasons outlined in previous sections the
implementation of an UV disinfection system is preferred over the existing chemical
disinfection process.
2009 Discharge Permit Limits
Discharge permit limits are revisited every five years, and it is anticipated that some level of
total inorganic nitrogen (TIN) and phosphorus removal may be required by future discharge
permits. Current construction includes provisions to allow these anticipated future limits to
be met with minimal additional capital expenditure.
Biosolids Stabilization (Digester Capacity)
Based on current projections, the capacity of the existing digesters will not be sufficient to
adequately stabilize the biosolids for continued land application after the year 2012. The
need for additional digester capacity will depend on the actual solids production once the
improvements are brought on-line in 2008, whether or not land application continues to be a
viable recycling alternative, and the success of privatized composting of the biosolids. These
issues will be evaluated over the next several years prior to any additional capital expenditure.
Odor and Noise
The Boulder County 1041 permit stipulates no net increase in either odor or noise from the
WWTP. Although additional control measures are not anticipated at this time, the City will
continue to monitor odor and noise in compliance with the permit conditions. After the
Phase 1 improvements are operational, the need for additional odor and noise control will be
re-evaluated and appropriate steps taken as necessary.
FUTURE CONSIDERATIONS FOR WASTEWATER TREATMENT NEEDS
Future considerations that are beyond the scope of this master plan and the current Capital
Improvement Program include 1) stringent total inorganic nitrogen (TIN) and phosphorus
discharge permit limits, 2) emerging contaminants and 3) biosolids recycling or disposal
flexibility.
Stringent Total Inorganic Nitrogen (TIN) and Phosphorus Discharge Permit Limits
Chemical addition and/or additional aeration basin volume may be required to remove
additional total nitrogen (TIN) and phosphorus. If extremely low TIN limits are
implemented in the future, a tertiary denitrification treatment process may also be required.
If extremely low phosphorus limits are imposed, tertiary filtration may be required.
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Emerging Contaminants
Emerging contaminants includes pollutants such as endocrine disrupting compounds and
disinfection byproducts. At present little is known about the significance of these
contaminants or appropriate treatment technologies for their removal from wastewater;
however, regulatory requirements associated with these contaminants may be adapted in the
future. If emerging contaminants removal becomes necessary, public education and
additional treatment processes will likely be required. This issue will be evaluated in the
future as appropriate.
Biosolids Recycling or Disposal Flexibility
The current WWTP upgrade projects will give the City a variety of future biosolids end-use
options. These options include maintaining the existing land application program,
transitioning to privatized land application and privatized composting. The method of final
disposal of the solids generated by the wastewater treatment process is going to be an issued
until a long term solution can be reached. Concerns have been raised about whether land
application should be used when biosolids contain varying quantities of emerging
contaminants. If regulations regarding the end-use of biosolids change, treatment and end-
use options will be evaluated. The current approach is to maintain flexibility in disposal
options so that the utility is in the best position to respond to regulatory changes and
community pressures. Ultimately, the final disposal decision could be dictated to the
wastewater permit holders like Boulder through regulatory restrictions.
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MASTER PLAN TO MEET CITY GOALS
Figure 19 illustrates how the current WWTP improvements and decisions for future
consideration are directed toward meeting City needs and goals. The top portion of the
figure addresses design elements already incorporated into the WWTP improvements. The
bottom portion of the figure identifies additional challenges that must be addressed to
continue to meet City goals.
Figure 19. Meeting City Needs and Goals
PhaseIImprovements
Phase I Improvements
DewateringImprovements
Liquid Stream Improvements
Meet Discharge Reduce biosolids
Increase Increase Solids
Permit Limits handling requirements
Dewatering Capacity
Plant
Capacity
CP
CP
ONTINUE TO SATISFY NEEDS OF ROACTIVELY DELIVER ON CITY
ONTINUE TO SATISFY NEEDS OF ROACTIVELY DELIVER ON CITY
GROWING COMMUNITY GOALS
GROWING COMMUNITY GOALS
PotentialPhase II Improvements
2008 Discharge Replace Chemical Biosolids Possible Odor
Permit Limits² Disinfection with Stabilization and Noise
TIN and UV disinfection (Digester Mitigation
Phosphorus Capacity)
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Future Considerations
Stringent TIN and
Emerging ContaminantsBiosolids Recycling
Phosphorus Discharge
and Disposal Flexibility
Permit Limits
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TRIPLE BOTTOM LINE INDICATORS
The incorporation of additional treatment processes or biosolids handling methods to meet
future regulatory requirements will affect environmental, economic, and social aspects of the
community. Figures 20 - 22 illustrate how future decisions may affect the Boulder service
community economically, environmentally, and socially.
Figure 20. Summary of future decision making on environmental impacts
Additional treatment for Improve water quality
TIN, phosphorous and for aquatic life
emerging contaminants
Maximize beneficial use
Implement enhanced
biosolids stabilization Reduce waste
1
from digester capacity Reduce GHG emissions
Replace chemical Improve water quality
disinfection system with Increase energy use
UV disinfection Decrease chemical use
1
GHGs (greenhouse gases)
Figure 21. Summary of future decision making on economic impacts
Additional treatment for Increased capital and
TIN, phosphorous and operating costs for
emerging contaminants additional treatment
Implement enhanced Increased capital and
biosolids stabilization decreased operating
from digester capacity costs
Replace chemical Increased capital costs,
disinfection system with decreased operating
UV disinfection costs
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Figure 22. Summary of future decision making on social impacts
Additional treatment for Improve water quality
TIN, phosphorous and for downstream users
emerging contaminants
Implement enhanced Greater flexibility for
biosolids stabilization biosolids end uses
from digester capacity
Replace chemical Improve safety of plant
disinfection system with workers and reduce
UV disinfection chemical use and
transport
SUMMARY
th
The Boulder 75 Street WWTP has historically served the City of Boulder well by meeting
regulatory requirements and discharging high quality effluent to Boulder Creek.
Improvements at the wastewater treatment facility are typically driven by state and federal
effluent discharge limitations. Phase 1 improvements to the WWTP were necessitated by
the imposition of more restrictive ammonia limits on the discharge and by anticipated
growth in the Boulder wastewater service area population. The system upgrades currently
under construction include improvement to the liquid stream treatment process and to the
solids dewatering process. The liquid stream treatment improvements include converting
the existing trickling filter solids-contact process to an activated sludge process. The solids
dewatering upgrades include the addition of new dewatering equipment to reduce the
volume of solids that must be hauled from the WWTP site. Additional improvements will
be required in the future as wastewater discharge and solids handling requirements change.
Plans have been made to accommodate these anticipated future upgrades with limited
additional capital expenditure.
The current improvements meet City goals and establish Boulder as a proactive
environmental steward.
The costs incurred in implementing the current WWTP upgrades have been paid through
bond sales and increased user fees.
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Draft
Wastewater Treatment Master Plan
The current WWTP improvements have been designed with the intent of meeting current
treatment requirements and strategically positioning the City of Boulder to economically
address anticipated future treatment requirements. The Phase 1 improvements are expected
to be completed in 2008. Anticipated future wastewater treatment and biosolids handling
improvements will be implemented as necessary.
REFERENCES
Boulder County. 2006 Boulder Valley Comprehensive Plan.
Brown and Caldwell. March 25, 2005. Amendment 1 and Site Application Report (March
25, 2005) to the City of Boulder Wastewater Utility Plan (November 15, 2002).
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Brown and Caldwell. March 8, 2004. City of Boulder 75 Street Wastewater Treatment
Plant Upgrades Community and Environmental Assessment Process (CEAP) Addendum
No. 1 March 8, 2004.
Brown and Caldwell, July 2003. City of Boulder Wastewater Collection System Master
Plan Update.
Rothberg, Tamburini & Windsor, Inc. May 2006. Community Environmental Assessment
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Process for 75 Street Wastewater Treatment Plant Dewatering Improvements.
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