HomeMy WebLinkAbout6 - Staff presentation & WRAB discussion on Betasso Water Treatment Plant improvementsCITY OF BOULDER
WATER RESOURCES ADVISORY BOARD INFORMATION ITEM
MEETING DATE: October 17, 2005
AGENDA TITLE: Update on the Betasso Water Treatment Plant improvements
PREPARING DEPARTMENT: Robert E. Williams - Director of Public Work for Utilities
Anne Noble - Utilities Project Manager
Bob Harberg - Coordinator of Utilities Planning and
Project Management
Randy Crittenden - Water Treatment Coordinator
FISCAL IMPACT: The 2006-2011 Capital Improvement Program (CII') includes $1 million
in 2005 to evaluate and design improvements to the Betasso Water Treatment Plant, with $5
million budgeted in 2006 for constmction of near-term improvements. Also included in the
CIP is $500,000 in 2009 and $5 million in 2010 for design and constnaction of mid-term
improvements to the Betasso Water Treatment Plant.
PURPOSE: This memorandum provides informadon to the Water Resources Advisory Boazd on
the status of improvements to the Betasso Water Treatment Plant (WTP).
EXECUTIVE SUMMARY:
The 2005 budget includes $1 million to evaluate and design improvements to the Betasso Water
Treatment Plant in order to provide safe working conditions, improve the reliability of the water
treatment process for public health, comply with new safe drinking water act regulations and
extend the life of the water treatment plant. Carollo Engineers was selected to perform the
evaluation and develop the design far these improvements. A Faciliry Improvement Plan was
developed that evaluated the existing facilities and established the status and future vision for the
plant. The following ohjectives were evaluated:
• Establish the cunent treatment capabilities of the plant and deternune a neaz-term, mid-
term and long-term implementation plan for the plant.
• Identify and evaluate alternatives for improving residuals handling.
• Identify and evaluate alternatives for improving pretreaunent unit processes.
• Evaluate the condition and performance of the filters.
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• Identify and evaluate other plant improvements that aze necessary.
BACKGROUND:
The city of Boulder is served by two water treatment plants, the Betasso Water Treatment Plant
and the Boulder Reservoir Water Treatment Plant. Both were built in the 1960s and utilize
similar treatment processes. The Betasso WTP was built in 1962 and expanded in 1976 to its
cunent design capacity, which had originally been estimated to be 50 million gallons per day
(MGD). Raw water is conveyed to the Betasso WTP by pipeline from two watersheds (Silver
Lake and Bazker) to hydroelectric generators located at the plant site. Both of these sources aze
well-protected and provide higher quality water than the raw water sources for the Boulder
Reservoir WTP. Therefore, the focus of the city's work program effort for Betasso has been on
the treatment process rather than improving source water protection.
The treatment process at the Betasso WTP includes: rapid mix, flocculation, sedimentation,
filtration and disinfection. Solids from the sedimentation process aze dewatered in lagoons.
Vazious improvements have been made since the 1976 expansion. In 1993, a new chemical
building was added which updated all of the chemical storage and feed equipment. The filter
media was replaced in 1994. In 1995, administrative improvements were made to the facility to
update the laboratory and office space. For safety reasons, in 2000, the gaseous chlorine system
was modified to a liquid chlorine (sodium hypochlorite-"bleach") system, eliminating the use of
chlorine gas for disinfection.
The most recent improvements ro the facility were completed in May 2001 and addressed
pretreatment of the backwash water and residuals handling. The backwash pretreatment system
utilizes a dissolved air flotation thickener (DAF). The backwash pretreatment process helps
reduce the recycling of contaminants removed in the filVation process. In addition, the existing
north sludge drying beds were replaced witt~ two lagoons. During the construction phase of this
project, the lagoon azea was reduced in size by 1/3 in order to complete the project within the
city's budget. Other improvements that were recommended but were not completed due to
budgetary constraints include: the residual polymer feed system, a renovated PACL feed system,
scum baffles in the sedimentation basins and improvements to the South Lagoons.
ANALYSIS:
A preliminary Facility Improvement Plan for the Betasso WTP was completed by Carollo
Engineers in October 2005. The Plan evaluated the capacity and performance of each of the unit
processes and residual handling facilities based on water demand, regulatory requirements and
internal city water quality goals. This information was then used as the basis for process
alternative identification, evaluation and selection. The findings, recommendations and approach
resulting from this study will serve as the basis for future improvements to the plant.
Lnprovements were categorized as neaz-term, mid-term and long-term. Improvements were
prioritized using the following criteria and dtivers:
o Capacity (CAP)
o City of Boulder Internal Water Quality Goals (BWQ)
AGENDA ITEM # b Page 2
o Potential Raw Water Degradation (RWQ)
o Equipment Condition (ECD)
o Impact on Downstream Treatment Processes (IDP)
o Anticipated or Current Regulatory Requirements (REG)
o Operational Flexibility (OF)
Hvdraulic Canacit
The hydraulic capacity and treatment capacity of each unit process was evaluated and compared
to water treatment demands. The Treated Water Master Plan prepazed in 2000 by Integra
Engineering indicates the future peak day summer water use plus reserve will require a total
treatment plant capacity of 62 million gallons per day (MGD). It suggests this capacity will be
achieved through use of both existing water treatment plants. The Boulder Reservoir Water
TreaUnent Plant (BRWTP) was recendy upgraded and now has a malcimum capacity of 16 MGD.
Therefore, it was concluded that a 46 MGD capacity will be necessary at the Betasso WTP to
meet fuWre peak day water demands. As a result, 46 MGD is the tazget design capacity for
improvements at the Betasso WTP; however, recent changes in water use as a result of the 2002-
2003 drought indicate that the timing of the targeted design capacity should be reviewed prior to
implementing major capacity improvements beyond 32 MGD as discussed below.
Re ug lator~ uirements
The Safe Drinking Water Act addresses a wide range of water quality issues including microbial
contamination, disinfection byproducts, metals, azsenic, radionuclides as well as biological and
chemical contaminants. The United States Environmental Protection Agency (EPA) has focused
special attention on reducing the potential for the occurrence of certain microbial pathogens,
most importantly Cryptosporidium, because they aze resistant to traditional disinfection methods.
In recent years the EPA has issued the Interim Enhanced Surface Treatment Rule (IESWTR) and
has proposed a new regulation called the I,ong Term 2 Enhanced Surface Water Treatment Rule
(LT2ESWTR). This regulation would requue certain public water systems to provide additional
treatment for Cryptosporidium by implementing one or more source water protection or
treatment options.
The proposed LT2ESWTR requirements for each system aze based on the wlnerability of the
source water to contamination, as measured by the occurrence of Cryptosporidium. This strategy
stems from recognition that only some systems may need to provide additional protection from
Cryptosporidium and that such decisions should be made on a system-specific basis. The
regulations specify categories (bins) based on the quality of the source water and corresponding
additional source water protection or treatment from a"toolbox" of options. Based on current
source water quality data, it appeazs that the Betasso WTP source water falls into a Bin 1
category, indicating that no further treatment is required from a regulatory perspective.
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Another important aspect of the proposed LT2ES'WTR is promoting a multi-barrier approach for
treating drinking water. A multi-barrier treatment process provides a number of protective
"layers" against contamination by using more than one method of prevention and treatment to
remove/inactivate pathogens and minimize disinfection byproducts (DBPs).
Facility Improvement Plan Recommendations
Based on the recommendations of the Facility Improvement Plan the following neaz-term
improvements are being proposed:
Betasso Near-term Improvements
Unit Process Estimated Cost Improvement
Alternative Description Criteria/Driver
Residuals Contract residuals $ 380,000 OF
dewatering support
facilities
Residuals Residuals drying pad $ 181,000 OF
Residuals South Lagoon $ 1,242,000 ECD
improvements
Residuals $60,000 Does not meet
North Lagoon sand
replacement current capacity
ECD
Rapid Mix pump diffusion flash $ ~91,000 IDP & REG &
mixing ECD
pH control CO2 Improvements $ 294,000 IDP & REG
Coagulation PACl Improvements $ 198,000 ECD
Total Estimated $3.15 Million
Project Costs
These improvements aze needed to address deficiencies in the treatment processes. The near-
term improvements aze being proposed to optimize the coagulation process by providing better
rapid mixing and pH control, and to enable the facility to handle the dewatering of the residuals
produced. Optimizing coagulation could also result in lowering the production of residuals and
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improve removal of organics thereby reducing disinfection by-product and aiding in compliance
with the disinfection by-product regulation.
Residuals
The purpose of residual handling facilities is to dewater residuals to a level suitable for off-site
disposal. Current residuals production often exceeds existing residuals handling capacity at the
Betasso WTP. This is a result of insufficient surface azea to dry the residuals. In recent yeazs,
contract dewatering has been utilized in order to provide some capacity relieF and offset the gap
between residuals production and residuals handing capabilities. Staff has also indicated that
staging of residuals that have been removed from the lagoons prior to hauling for off-site
disposal is difficult at times. The lack of a solid surface for residuals staging is especially
challenging during poor weather periods. In addition to these challenges, staff feels that there is
not adequate storage for equipment and maintenance needs.
Several residuals handling alternatives were evaluated. Upon examining capital, and operations
and maintenance costs it became appazent that the least costly altemative is to enter into a long-
term contract for residuals dewatering services. The proposed improvements listed as "Contract
Dewatering" facilitate this operation and include the following:
Continued use of North and South Lagoons
Installation of permanent utility hook-ups (power, water, etc.) and a 2,000 ft2 concrete pad
for dewatering contractor staging.
Use of contract dewatering on a quarterly basis.
In addition to these site improvements, a concrete drying pad is recommended for use as a
residual staging area. The pad can provide additional drying time before residuals aze hauled off-
site. It would also be helpful during periods of poor weather conditions when it is more difficult
to access the off-site disposal facility. Improvements to the South Lagoons include providing
lighting and constructing an asphalt bottom and a concrete divider wall, as well as a new
decanting structure. The goal of these improvements is to improve ease of operation and
maintenance.
The residual lagoons at the Betasso Water Treatment Plant were designed to dewater the
residuals primazily through settling of the solids and decanting of the liquid on top, with
evaporation aiding in the drying process. The North Lagoons aze equipped with an underdrain
system. When originally wnstructed, the lagoons also provided drainage, which enhanced their
performance. After several years of operation, the sand media became clogged and performance
of the lagoons declined. City staff recently visited the Denver Water Department, Foothills
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Water Treatment Facility that utilizes engineered sand drying beds for its water residual
dewatering. Based on the experience of that facility, staff has decided to start implementing
some modifications to a portion of the existing North Lagoons. The proposed modifications will
include the removal and replacement of the sand media with sand that meets the specifications of
the Denver Water Department. Staff will monitor the benefit of these modifications. If they
prove to be effective, then the remaining area of the North Lagoons could be modified into
engineered sand drying beds in the future, minimizing the need to rely on outside contractor for
dewatering the solids residuals.
Ravid Mix
The purpose of rapid mix is to quickly and unifornily disperse treatrnent chemicals throughout
the raw water to promote effective coagulation. Downstream treatment process performance is
highly dependent on coagulation effectiveness. As a result, proper design of rapid mix facilities is
of critical importance. Staff has reported poor mixing and poor reliability associated with the
existing rapid mix system. It is currently not being udlized and is turned off at the present time.
Full-scale coagulant dosages aze currently higher than detemtined to be optimal during bench
testing conducted by University of Colorado. Since improvements to the rapid mix process could
potentially improve settling and reduce the quantity of residuals produced, construction of these
improvements were included in the near-term.
CO~
Cazbonic acid or COZ is used to adjust the pH of the water upstream of the rapid mix process in
order to optimize coagulation. It is also used at the end of the treatment process to provide
corrosion control in the distribution system. This alternative includes relocation of the COZ
application point to the yazd piping upstream of the clearwells. This will enable COz to be fed
regazdless of which clearwell is in service. It is assumed that COZ will be fed as a liquid feed
solution which is more efficient than when applied as a gas. In addition, COz application
upstream of the rapid mix will be implemented at the same time to provide pH adjustment to the
raw water prior to chemical addition.
Coa lgu ation
Polyaluminum Chloride (PACI) was added as a coagulant to supplement aluminum sulfate
(alum) several yeazs ago. It has been found to improve coagulation when the alkalinity in the
source water is low. Staff utilized exisung storage equipment available at the time. The existing
storage and containment equipment needs to be modified to provide the proper amount of storage
and safe containment. PACI improvements include demolition of the existing tank pad structure,
removal of the existing large PACL storage tanks and installation of two new tanks and
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associated containment curb and liner. These improvements were scheduled to be included in the
most recent plant improvement project and were deleted due to budget constraints.
Aside from the deficiencies that aze being addressed with the near-term improvements, the
existing facilities at the Betasso WTP perform well up to about 32 MGD. Above this flow rate,
the sedimentation process fails to reliably and consistently meet design criteria and water quality
goals. All of the other unit processes can meet regulatory requirements, as well as internal city
goals up to the tazget plant capacity of 46 MGD. Current peak day water demands have not
caused the Betasso Water Treatment Plant to exceed the 32 MGD capacity of the settling
processes;. however, because increases in water demands in the future may cause capacity
limitations, mid-term improvements are conceptualized to increase the capacity and reliability of
the settling process. As discussed earlier, recent changes in water use as a result of the 2002-
2003 drought indicate that the timing of the tazgeted design capacity should be reviewed prior to
implementing major capacity improvements beyond 32 MGD.
Mid-term Imnrovements
Mid-term improvements aze proposed to increase the overall capacity of the Betasso WTP to 46
MGD. These improvements total approximately $15 million and include the following:
• Flocculation/Sedimentation Improvements ($4.65 million)
o Baffle of the inlet and within the basins
o Flocculator equipment modifications
o Flocculation aid polymer addition
o Sedimentation effluent weirs
• Addition of high rate process such as plate setders or DAF ($6.5 to $7.5 million)
• Engineered sand drying beds for residuals dewatering ($3.4 million)
• Baffle finished clearwell ($209,000)
Flocculation/Sedimentation
The purpose of flocculation is to promote gentle mixing and agglomeration of destabilized
particles that will settle and filter. Sedimentation is a process intended to sepazate the coagulated
solids from the liquid. There aze a number of challenges with the existing
flocculation/sedimentation basins including flow distabution, baffling confguration, mixing
energy, equipment condition, lack of flocculation aid polymer provisions, and operating strategy.
AGENDA ITEM # ~ Page 7
Historically, turbidity removal has been relatively effective as the basins aze lighdy loaded at low
plant flows most of the year; however, it is expected that process performance will not be ideal at
higher plant flows. This correlates with plant operational experience suggesting basin
performance is significantly reduced as evidenced by higher settled water turbidities (above the
city's internal goal of lA Wrbidity unit) at plant flows in excess of 32 MGD. Therefore, the
proposed improvements to the existing flocculation/sedimentation process includes a
combination of modifications to the existing facilities and the addition of high rate treatment
technologies. These technologies were selected for the Betasso WTP to both ma~cimize the use
of existing infrastructure and utilize the available space at the site.
The mid-term improvements presented in the plan for the flocculation/sedimentaUOn processes
aze recommended to increase the capacity from 32 MGD to 46 MGD and to provide more
consistent and reliable performance under varied flow and water quality conditions. One of the
main benefits of increased solid removal performance in the flocculation/sedimentation process
is to provide added protection to filters by lowering the solids loading rate on the filters,
especially at higher flow rates. One of the proposed options is to install stainless steel lamella
plates. These plates would be added to all four existing sedimentation basin. This alternaUve
includes demolition of a portion of the roof of each existing sedimentation basin and installation
of lamella plates in the upper deck of all four existing sedimentation basins. It should be noted
that all other recommended mid-term improvements to the existing flocculation/sedimentation
basins would also need to be implemented in addition to adding plate settlers to produce
improved performance of these unit processes when treating 46 MGD.
A second option to improve perFormance at 46 MGD for the flocculation/sedimentation process
would be to replace one of the existing basins and associated process components with DAF
thickeners. These two DAF units would operate in pazallel to three of the existing basins. Under
this option only three of the four remaining existing basins would also need to be upgraded with
the recommended mid-term improvements discussed above.
En~ineered Sand DryinQ Beds for Residuals DewaterinQ
As stated above, the recommended near-term improvements include contract dewatering of the
residuals to handle the lack of storage capacity. The mid-term improvements include the
modification of the North Lagoons into engineered sand drying beds. As discussed above,
included in the neaz-term improvements is the removal and replacement of the sand media in one
of the exisung North Lagoons. If these improvements prove to be effective, then the remaining
North Lagoon could be modified into an engineered sand drying bed~in the future, minimizing
the need to rely on outside contractor for dewatering the solids residuals. The cost shown in the
mid-term improvements for engineered sand drying beds also includes an increase in the surface
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azea to provide adequate solids residual handling facilities to treat solids generated by a 46-MGD
facility.
Clearwell BafflinQ
This mid-term improvement includes baffling in Clearwell No. 2 to provide an increased level of
disinfection. At the Betasso WTP there are two treated water reservoirs (clearwells). The newest
reservoir (Clearwell No. 1) is currenfly baffled, but the older reservoir (Clearwell No. 2) is not.
The level of disinfection is deternuned as "log inactivation" of a particular pathogen, Giazdia.
Cunent regulatory requirements for disinfection aze based on a 0.5 log inacGvation. The Betasso
WTP cao meet the O.S log Giardia inacfivation requirement, up to about 43 MGD with both
clearwells in service, and about 10.5 MGD when Clearwell No. 1 is out of service for cleaning.
As discussed previously, plant demands aze not expected to approach the ultimate peak of 46
MGD in the neaz-term. It is also expected that the 10.5 MGD limit with Clearwell No. 1 out of
service is not presendy a significant constraint. As a result, the Cleazwell No. 2 baffling has been
deferred to the mid-term. When baffling is provided in Cleazwell No. 2, it will enable a treatment
rate of 46 MGD. Baffling of Clearwell No. 2 will also provide greater than O.S log inactivation as
is desired to comply with city internal goals.
Citv of Boulder Svstem Water Demand
Recorded peak day treated water demands have steadily declined over the past five yeazs from a
high of 42 MGD in 2000 to less than 35 MGD in 2004. Since the mid-term improvements aze
mainly driven by the need to meet a 46 MGD ultimate treatment capacity at the Betasso WTP,
data suggests the city may have more time before it is necessary to implement these mid-term
improvements. One important factor to recognize is that when the time comes to implement
some or all of the mid-term improvements, there will be a need to re-evaluate their
implementation in conjunction with proposed long-term improvements. One of the
recommended long-term improvements "Membranes" could eliminate the need to implement the
mid-term improvements to upgrade the settling process.
Lone-term Improvement Improvements
Long-term improvement possibilities include:
• iTV disinfection
• Membranes or
• Filter media replacement
The timing and implementation of the proposed long-term improvements at the Betasso WTP aze
AGENDA ITEM # ~ Page 9
not firmly established. These long-term improvements are estimated to cost between $5 million
for UV disinfection and up to $10 million for implementing membrane technology. The final
combination of long-term improvements will be deternuned by future regulatory requirements for
Cryptosporidium removaUinactivation and the city's intemal goals. Although no addiUOnal
source water protection or treatment may be required from a regulatory perspective, the city may
desire to improve treatment based on internal water quality goals. These goals relate primarily to
providing multiple barriers and securing additional removaUinactivation of pathogens. The body
of knowledge conceming pathogenic organisms is increasing, and there is the possibili[y that new
pathogens may be discovered or the estimated risk of pathogen exposure increased.
As diswssed above, when the times come to implement the upgrade to the
flocculation/sedimentation process, the plan recommends that technologies such as membranes
be considered. Membrane technology could eliminate the need to upgrade the flocculation,
sedimentation and filters at the Betasso WTP; however, cazeful evaluation will be required at that
time to determine the appropriate technology and balance the capital cost and operation and
maintenance cost of these various options. A present worth financial analysis could reveal that
even though membranes could be less costly to install, the maintenance cost over a 20-yeaz time
frame could offset a higher capital cost required to improve the existing processes at the plant.
Another factor that will need to be evaluated at that time will be the handling of the membrane
reject water, which can be problematic in some cases. At this time, based on current source water
quality data, it appeazs that the Betasso source water falls into a Bin 1 category for the proposed
LT2ESWTR, indicating that advance treatment technologies such as membranes or iJV are not
required from a regulatory perspective.
The plan recommends that ongoing monitoring activities be conducted to support future planning
efforts of mid- and long-term improvements. These activities include:
• Continue to monitor system-wide and Betasso water demand.
• Continue to monitor raw water quality (potenUal source water quality degradation over time).
• Continue to monitor plant performance.
Betasso WTP Capital Improvement Program (CIP)
The 2006-2011 Betasso WTP CIP includes $1 million in 2005 for the evaluation and the design
of the neaz-term improvements, with $5 million for construction in 2006 and $500,000 in 2009
for design of mid-term improvements, and $5 million for consWCtion in 2010. Funding has not
yet been included in the CIP for construction of the long-term improvements to the Betasso
Water Treatment Plant. The following table presents the proposed 2006-2011 Betasso WTP CIP.
2005 2006 2007 2008 2009 2010 2011
$1,000,000 $5,000,000 0 0 $500,000 $5,000,000 0
AGENDA ITEM # G Page 10
F~
PUBLIC COMMENT AND PROCESS:
This project was not identified as requiring a Community and Environmental Assessment
Process (CEAP). The Betasso Water Treatment Plant is located in Boulder County. All of the
required Boulder County Planning processes will be followed.
AGENDA ITEM # /„ Page 11
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