HomeMy WebLinkAboutFINAL Chlorine Evaluation Memo 022307.pdfKJl I Memorandum
J.D. Wilson, Ray Sled, Renton Water Utility
From: Andrew Hill, Greg Pierson, HDR Project Renton Well 5A Pre-Design
Date: 23-Feb-2007 J°bNo: 51403
Chlorine Evaluation
1.0 Overview and Purpose
This technical memorandum has been prepared as part of Task 2-300 of the Renton Well 5 A Water
Treatment Improvements Project. The purpose of this memorandum is to provide an overview and
comparative evaluation of two types of chlorination systems that are being considered for the new
Well 5A treatment facility. This evaluation is intended to provide enough information to assist the
City of Renton (City) in selecting the preferred chlorination method.
As outlined in die project scope, the following two chlorination methods are being considered:
Method 1: Commercial liquid hypochlorite (12.5% strength by weight)
Method 2: On-site hypochlorite generation (0.8% strength by weight)
The following general assumptions were made as part of this memorandum:
n The selected treatment train for the Well 5 A facility will utilize the same approach as that at tihe
Maplewood Water Treatment Facility. During operation, chlorine would be fed continuously
ahead of the greensand filters. Booster chlorination would be applied at the end of the contact
basin as needed to meet finished water quality goals.
□ Gas chlorination will not be used at the new Well 5A facility; therefore, it is not considered as
part of this evaluation.
□ The chlorine storage and feed system components will be housed in a new treatment building.
□ All mechanical equipment used for the chlorine system will be new; i.e., none of the chlorine-
related equipment firom the existing facility will be salvaged for this project.
O The applicable code requirements include the 2003 International Building Code (IBC) and the
2006 International Fire Code (IFC).
This technical memorandum is organized as follows: Section 2 provides a brief process description
of each of the two chlorination methods, along wifii general facility, equipment, and operations and
maintenance (O&M) requirements; Section 3 provides preliminary design criteria used to support
further evaluation; Section 4 provides planning-level capital, O&M, and life-cycle cost estimates;
Section 5 summarizes information from the previous sections and provides a comparison of the
two methods; and Section 6 provides a recommendation for the chlorination method.
Well 5A Chlorine Evaluation
City ofRenton
Project Number 51403
2.0 Chiorination Alternatives
This section provides an overview of the two chiorination methods under consideration, while a
more detailed analysis and comparison of the two methods is provided in later sections.
2.1 Commercial Liquid Hypochiorite
Process Description. The application of commercial liquid hypochiorite (12.5% strength) would
involve a relatively simple storage and feed system. The hypochiorite solution would be stored in
tanks/totes within a secondary containment area and injected into the water supply with metering
pumps. The solution could be delivered either in a tanker truck (i.e., bulk delivery) or supplied in
exchangeable totes (250 to 300 gallon capacity each), with the preferred method driven in large
part based on the storage requirements. In either case, a commercial vendor would be contracted to
supply the chlorine; however, the City would need to coordinate the delivery schedule.
Safety and Code Compliance. The applicable safety considerations and code requirements for
12.5% strength liquid hypochiorite are as follows:
□ Sodium hypochiorite solution is considered a hazardous material per the 2006 IFC for the
following reasons: Health Hazard - Corrosive. It should be noted that while some material
data safety sheets list sodium hypochiorite solution as an oxidizer, neither the 2006 IFC nor
the National Fire Protection Agency define sodium hypochiorite solution as an oxidizer.
The IFC stipulates Maximum Allowable Quantities (MAQs) for storage and open system
use that, if exceeded, trigger an H-3 occupancy rating as defined in the IBC. Assuming the
2006 IFC hazardous material designation is based solely on Health Hazard - Corrosive, the
controlling MAQ for sodium hypochiorite solution is 500 gallons. However, if the storage
area heis automatic sprinklers, the MAQ is increased to 1,000 gallons.
□ An H-3 occupancy rating would require the following for the storage and use areas:
o Spill control and secondary containment,
o Liquid-tight surfacing in the containment area.
o Automatic sprinkler system designed to no less than Hazard Group 2 requirements,
o Mechanical exhaust ventilation system with standby power,
o Temperature control.
o Emergency alarm, both local and possibly call-out.
o One-hour fire-resistance rating for walls/barriers,
o Hazardous Materials Management Plan,
o Additional measures may be required by the Fire Marshall.
□ Sodium hypochiorite solution is not listed as a hazardous material under either OSHA
regulated Title 29 CFR, 1910.119 — process safety management of highly hazardous
chemicals; or EPA regulated Title 40 CFR, 68 - chemical accident prevention provisions.
n Regarding operator safety, when working with or near concentrated liquid hypochiorite or
"breaking" any pipe connection that is subject to hypochiorite exposure, operators should
wear personal protective equipment including safety goggles and chemical-resistant gloves.
An emergency shower and eyewash station should be provided.
Well 5A Chlorine Evaluation
City of Renton
Project Number 51403
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Operations & Maintenance Requirements. The routine O&M activities associated with commercial
hquid hypochlorite storage and feed include:
□ Recharging the supply of hypochlorite, i.e., attending to deliveries of new solution.
□ Chlorination process monitoring and physical inspections.
□ Preparation of records and reports.
□ Periodic calibration and maintenance of the chemical metering pumps.
□ Periodic cleaning of the tanks and injection assemblies.
□ General housekeeping and preventative maintenance for chlorine system components.
Based on similar projects, the labor estimates associated with these tasks are as follows:
□ 5.0 hours per week during peak use for operations (13 weeks/year)
□ 2.0 hours per week during off-peak use for operations (39 weeks/year)
□ 0.6 hours per week (five-year average) for routine maintenance
Over the course of an average year, this chlorine method will require about 165 hours of routine
O&M labor effort, or about 0.08 full-time equivalents (PTE). It should be noted that this estimate
only applies to O&M labor for the chlorine system-related components.
Other Considerations. Commercial liquid hypochlorite is prone to strength decay over time. As a
result, it is common to limit onsite storage capacity to no more than a two- to three-week supply
(i.e., 14 to 21 days). During periods of infrequent well operation, a reduced supply quantity and
onsite storage capacity is desirable to minimize strength decay.
2.2 On-Site Hypochlorite Generation
Process Description. In this process, an electrical current is applied to brine solution m electrolytic
cells to produce a low-strength solution (0.8% by weight) of liquid sodium hypochlorite. The brine
solution is prepared from coarse sodium chloride salt dissolved in water. Salt must be delivered to
the site on a regular basis and loaded into a brine saturator tank as needed. For small applications
such as this, the generation system is typically supplied as a pre-engineered package system which
typically includes: a water softener, brine saturator tank, brine transfer pximp, electrolytic reactor
cell, power rectifier, hypochlorite solution tanks with venting system, chemical metering pumps,
and associated controls and piping. The process uses about three pounds of salt and 2.5 kWh of
energy per pound of CI2 generated.
Safety and Code Compliance. The applicable safety considerations and code requirements for 0.8%
strength sodium hypochlorite generated on-site are as follows:
□ Although sodium hypochlorite solution is listed as a hazardous material under the 2006IFC
(Chapter 27), it is not clear if the Health Hazard - Corrosive designation would apply to
such a low-strength solution. This issue and the associated occupancy requirements would
need to be resolved with the Fire Marshall.
□ For this stage of planning, it is assumed that H-3 occupancy requirements would not apply;
however, the secondary containment measures would be applied to preclude spills/release
to the environment.
Well 5A Chlorine Evaluation
City ofRenton
Project Number 51403
n Additional measures may be required by the Fire Marshall, including a Hazardous
Materials Management Plan.
□ Regarding operator safety, when working wi1h or near liquid hypochlorite or "breaking"
any pipe coimection that is subject to hypochlorite exposure, operators should wear
personal protective equipment including safety goggles and chemical-resistant gloves. An
emergency shower and eyewash station should be provided. In general though, the
exposure risks for 0.8% hypochlorite solution are significantly less than those for a 12.5%
hypochlorite solution.
Operations & Maintenance Requirements. The routine O&M activities associated with on-site
generation, storage, and feed of 0.8% hypochlorite solution include:
□ Recharging the supply of brine, i.e., deliveries and handling of salt and loading salt into the
brine saturator (i.e., opening and dumping bags).
□ Periodic calibration, maintenance, and eventual replacement of metering pumps, transfer
pumps, and blowers.
□ Periodic cleaning of the tanks, injection assemblies, and electrolyzers.
□ Replacement of electrodes approximately once every five to seven years.
□ Monitoring and recording of chlorine use and chlorine concentrations.
□ General housekeeping and preventative maintenance for chlorine system components
Based on similar projects and estimates from the equipment supplier, the labor estimates associated
with these tasks are as follows:
□ 6 hours per week during peak use for operations (13 weeks/year)
□ 2 hours per week during off-peak use for operations (39 weeks/year)
□ 1 hours per week (five-year average) for routine maintenance
Over the course of an average year, this chlorine method will require about 167 hours of routine
O&M labor effort, or about 0.08 fiill-time equivalents (PTE). It should be noted that this estimate
only applies to O&M labor for the chlorine system-related components.
Other Considerations. Because of its low-strength, 0.8% hypochlorite solution is quite stable and
can be stored for long periods of time. Also, since the system is used to produce hypochlorite "on-
demand", it could be shut down as needed to preclude the storage of hypochlorite and the need for
extensive equipment O&M during extended periods of well downtime.
3.0 Prelimiriary Design Criteria
Preliminary design criteria for the chlorination systems have been developed in order to support the
evaluation. These criteria have been developed for the purpose of a planning-level comparison and
should not be considered the firm design criteria for the new facility. Firm design criteria will be
established as part of the treatment systeni basis of design technical memorandum.
3.1 Well Production
Well 5A Chlorine Evaluation
City ofRenton
Project Number 51403
The ciirrent nominal capacity of Well 5 A is 1,500 gallons per minute (gpm), based on the approved
instantaneous withdrawal water right (Certificate Record No. 8, Page 3591-A: 1,300 gpm, and
Certificate Record No. 12, Page 5834-A, 200 gpm). As Well 5A is one of several sources of supply
available to fiie City, it is anticipated that the new Well 5A treatment facility will be operated
primarily during the summer to meet peak demands. The following preliminary assumptions have
been made regarding well operation and production:
n Continuous operation (100%) during the three peak months of July through September (e.g., 13
weeks per year). This translates into 2.2 million gallons per day (mgd) of production,
neglecting plant process water losses and downtime for backwashing.
□ Intermittent operation (10%) during the nine off-peak months of October through June (e.g., 39
weeks per year). This translates into an average day off-peak production of 0.22 mgd,
neglecting plant process water losses and downtime for backwashing.
Therefore, on an annual basis. Well 5A would be operated about 33% of the time. This translates
into an annual average day supply of 0.70 mgd and an annual supply of 786 acre-feet/year (afy),
which is well below the approved annual withdrawal water right of 2,320 afy (Certificate Record
No. 8, Page 3591-A: 2,000 afy and Certificate Record No. 12, Page 5834-A, 320 afy).
3.2 Chlorine Feed
The chlorine system will be designed to allow the City to reliably achieve a free chlorine residual
of 1.0 mg/L as CI2, or any desired setpoint between 0.3 and 1.5 mg/L as CI2, in the finished water
prior to distribution. The applied chlorine dose must be adequate to satisfy the chlorine demand
due to naturally-occurring iron, manganese, srilfide, and ammonia. As documented in the Well 5A
Water Treatment Improvements Draft Pilot Test Report (HDR, July 2006), the average chlorine
demand of the Well 5A raw water is 2.4 mg/L as CI2; however, the demand may fluctuate from 1.8
to 3.2 mg/L as CI2 due to variability in raw water quality, primarily the ammonia concentration.
Therefore, in order to reliably achieve a finished water free chlorine residual of 1.0 mg/L as CI2,
the feed system should allow for dosages between 2.8 and 4.2 mg/L as CI2. The average expected
dose requirement is 3.4 mg/L as CI2.
Table 1 provides a summary of the chlorine dose and instantaneous feed rate requirements. The
feed rate requirements were based on the Well 5 A maximum production rate of 1,500 gpm and are
expressed as pounds per day of chlorine (lb/day of CI2), gallons per day of commercial 12.5%
hypochlorite solution (assuming 1.25 lb/gal of CI2), and gallons per day of on-site generated 0.8%
hypochlorite solution (assuming 0.067 lb/gal of CI2). The actual daily consumption (in gallons of
solution per day) would depend on the fraction of time the well is operated on a given day.
Table 1.
Chlorine Dose and Instantaneous Feed Rate Requirements
Scenario Chlorine Dose
(mg/L as CI2)
Feed Rate
(lb/day of CI2)
12.5% Liquid
Feed (gal/day)
0.8% Liquid
Feed (gal/day)
Minimum 2.8 50 40 756
Average 3.4 61 49 918
Well 5A Chlorine Evaluation
City ofRenton
Project Number 51403
Maximum 4.2 76 60 1,134
For 12.5% hypochlorite, the metering pumps should be sized to deliver about 1.5 to 2.5 gallons per
hour (gph), and potentially more if flexibility to provide a finished water free chlorine residual of
1.5 mg/L as CI2 is desired. For 0.8% hypochlorite, the metering pumps should be sized to deliver
about 30 to 50 gallons per hour, and potentially more if flexibility to provide a finished water free
chlorine residual of 1.5 mg/L as CI2 is desired. Regarding the feed systems, for the purpose of cost
estimation, it was assumed that two identical chemical metering pumps would be provided. Only
one pump would be on-line at any given time, with the oflier pump maintained as a backup.
Re-chlorination metering pumps will also be provided to boost free chlorine residual, if necessary,
following the extended contact period. It was assumed that these pumps would be sized to provide
a nominal chlorine dose of 0.5 mg/L as CI2. For 12.5% hypochlorite, the metering pumps should be
sized to deliver about 0.3 gallons per hour. For 0.8% hypochlorite, the metering pumps should be
sized to deliver about 5.6 gallons per hour. As before, it was assumed that two identical chemical
metering pumps would be provided. Only one pump would be on-line at any given time, with the
other pump maintained as a backup.
The chemical metering pumps would be housed in the new treatment facility along with additional
system components, including the piping manifold, calibration cylinder, and valving for isolation,
backpressure, and pressure/air-relief.
The on-site generation process requires salt at a rate of about three pounds per pound of chlorine
produced. At a peak month chlorine production rate of 61 lb/day as CI2, the salt consumption rate
would be about 185 pounds per day or 1,300 pounds per week. This would require use of about 26
salt bags (at 50 pounds each) per week. It may also be possible to use supersacks, which typically
contain about 1,500 pounds of salt.
3.3 Storage Capacity
3.3.1 Commercial Liquid Hypochlorite
For 12.5% hypochlorite solution, it is common to limit the onsite storage capacity to no more than
a two- or three-week supply in order to preclude strength decay. For this evaluation, it has been
assumed that adequate storage would be provided for a 15-day supply under the peak month
conditions (assuming average dose conditions), which would require about 740 gallons of solution.
Owing to this relatively low storage volume, it may be more economical to use three 250- to 300-
gallon totes as opposed to bulk delivery from a tanker truck. This is due to the fact that the costs for
a tanker truck delivery are based on freight of a full truck, but since only a small fraction of the
fruck capacity would be supplied (i.e., 740 of about 4,000 gallons), the unit cost of hypochlorite
(i.e., in dollars per gallon of solution) would be extremely high. Regardless of the approach used,
the storage containers would be located within a secondary containment area sized to hold the
contents of the largest container plus fire sprinkler flow. During periods of infrequent well use, the
solution storage time will inevitably be higher, which could pose problems with regard to strength
decay and/or off-gassing. During this period, it may be desirable to supply only one 300-gallon
tote.
Well 5A Chlorine Evaluation
City ofRenton
Project Number 51403
3.3.2 On-Site Hypochlorite Generation
For 0.8% hypochlorite solution, the storage requirements are reduced since the system would be
designed to generate hypochlorite at the maximum anticipated instantaneous chlorine use rate. For
this evaluation, it has been assumed that adequate storage would be provided for a three-day supply
under peak operating conditions (assuming average chlorine dose conditions), which would require
about 2,800 gallons. For redundancy, it was assumed that two 1,400-gallon dedicated tanks would
be provided. These tanks would be located within a secondary containment area sized to hold the
contents of a single tank.
The on-site generation process also requires periodic salt delivery and unloading into a brine tank.
During the peak well operation period, it is estimated that the process will require about 185 lb/day
of salt. Over the course of a week, this will require about 1,300 povmds of salt, which is about 26
bags at 50-lb each. Because the cost of delivered salt is primarily attributed to transportation costs
(i.e., cost per delivery as opposed to cost per amount of salt), it is desirable to reduce the frequency
of delivery by storing more salt onsite. Therefore, it was assumed that adequate storage capacity
and space would be provided for a one-month supply under the peak operating period. This
translates into about 100 bags at 50-lb each. The 50-lb salt bags are typically supplied with 48 per
pallet; therefore, a two-pallet supply would be required about once per month during peak well
operation. Altematively, the City could have four 1,500-lb supersacks delivered to the site.
It was assumed that the brine saturator salt capacity would be adequate for about one-week of
operation during peak well use, plus some additional capacity to provide a minimum salt level.
Therefore, about once per week, plant operators would need to replenish the saturator with about
26 bags (50-lb each) or one supersack (l ,500-lb each). For the supersack option, special equipment
such as a hoist may be required to move the supersack from the storage area above the brine tank
for salt unloading.
4.0 Cost Estimation
Preliminary capital and O&M cost estimates have been developed for the two chlorination
methods. It should be noted that the estimates presented in this section are only intended to address
the specific elements of the chlorine-related components. They are provided for comparative
purposes only and therefore should be considered incremental to the costs for other facility
construction requirements, such as civil/site work and structural, including building space. Finally,
the cost estimates do not include design, legal, administration, permitting, contractor overhead and
profit, or construction-related services.
4.1 Construction Costs
Consfruction-related capital cost estimates were developed using bid results from similar projects
and vendor-supplied budgetary proposals. The cost estimates have been updated to January 2007
using the Engineering News Record construction cost index. Labor costs for equipment installation
were assumed to be 10% of the equipment cost (EQ). Allowances for mechanical, electrical, and
instrumentation & control (I&C) have also been included. An estimating contingency of 30% has
been applied to the sub-total reflect the fact that these are conceptual-level estimates.
Welt 5A Chlorine Evaluation 7
CityofRenton
Project Number 51403
While project permitting costs have not been addressed in the estimates, an incremental permitting
and code-related cost of $10,000 was assumed for the commercial hypochlorite method. For the
on-site hypochlorite generation system, a budgetary estimate was obtained for the Wallace &
Tieman OSEC® B-Series, assuming a 90 lb/day of CI2 production capacity (note: the OSEC® B-
series production capacities are discretized; furthermore, a capacity above the expected maximum
day production is desirable to permit some eqioipment downtime during a portion of the maximum
day).
For either method, a concrete or asphalt-paved access area would be needed to allow a coimnercial
vendor to unload the consumables. Since this cost is common to both alternatives, it has not been
included in the estimates. Note that the delivery trucks are typically equipped with a lift gate and
electronic pallet jack or forklifl; therefore, a City-owned forklifl would not be required. However,
if the City elected to use salt supersacks, a hoist or other equipment may be required to move the
supersacks for loading into the brine saturator.
Table 2 provides a sxmnnary of the comparative construction-related capital cost breakdown for the
two chlorination methods. The on-site generation method has a substantially higher construction
cost due to the more extensive equipment requirements.
Table 2.
Capital Cost Comparison
Parameter
Method 1:
Commercial Hypochlorite
Method 2:
On-Site Generation
Equipment (EQ) Sub-Total $11,000 $173,800
Mechanical (M) Allowance $4,000 $6,000
Electrical (E) Allowance $4,000 $6,000
I&C Allowance $3,000 $3,000
EQ+M+E+I&C Sub-Total $22,000 $188,800
Other Nominal Allowances $10,000 $0
WA State Sales Tax @ 8.8%$2,800 $16,600
Estimating Contingency @ 30%$10,400 $61,600
Estimated Capital Cost $45,000 $267,000
4.2 Operations & Maintenance Costs
In developing annual O&M cost estimates for each method, the following assumptions were made:
n Regarding the costs of consumables and energy, the quantities were based on an annual well
production of 786 afy (average day 0.70 mgd) and an average chlorine dose of 3.4 mg/L as CI2.
It was assumed that well production would not increase significantly over the planning horizon.
□ The unit cost of commercial 12.5% hypochlorite solution delivered to the site in increments of
three 300-gallon totes is estimated at $2.00/gallon (Univar, 2007).
Well 5A Chlorine Evaluation
CityofRenton
Project Number 51403
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n The unit cost of coarse salt delivered in increments of two pallets at 48 bags (at 50-lb each) per
pallet is estimated at $0.15/lb (Univar, 2007).
□ Regarding energy costs (for on-site hypochlorite generation), a unit cost of $0.06 per kWh was
assumed. The energy costs associated with chemical metering and ancillary energy use for both
systems were neglected as they are assumed to be about equal and relatively small.
□ Regarding labor costs, an annual unit cost of $60,000 per PTE was assumed. The routine O&M
labor hours for each method were previously documented in Section 2.
□ An annual maintenance allowance of 1.5% was applied to the equipment (EQ) sub-total from
Table 2.
Table 3 provides a siraimary of the comparative annual O&M costs for the two chlorination
methods. The on-site generation method has a lower estimated annual O&M cost, due primarily to
the low cost of energy and salt relative to delivered commercial hypochlorite.
Table 3.
Annual Operations & Maintenance Cost Comparison
Parameter Method 1:
Commercial Hypochlorite
Method 2:
On-Site Generation
Chemicals $11,600 $3,300
Power $0 $1,100
Routine Labor $4,800 $4,800
EQ Maintenance Allowance $200 $2,600
Estimated Annual O&M Cost $16,600 $11,800
4.3 Life-Cycle Costs
Using the information in Tables 2 and 3, life-cycle costs were estimated to compare the methods
on a net present worth basis. The life-cycle cost estimates were developed based on a 20-year time
horizon and a 6% discoimt rate (consisting of 9% interest rate with 3% annual inflation). The
results, which are summarized in Table 4, indicate that the commercial hypochlorite method has a
significantly lower life-cycle cost. A brief sensitivity analysis was performed using a discoimt rate
as low as 3%. In this case, the commercial hypochlorite option was still about $150,000 less than
the on-site generation process on a life-cycle basis.
Table 4.
Life-Cycle Cost Comparison
Parameter Method 1:
Commercial Hypochlorite
Method 2:
On-Site Generation
Estimated Construction Cost $45,000 $267,000
Estimated Annual O&M Cost $16,600 $11,800
Well 5A Chlorine Evaluation
City ofRenton
Project Number 51403
NPW of Annual O&M Costs^"^$190,400 $135,300
Overall Net Present Worth^®^$235,400 $402,300
(a) Based on 6% discount rate and 20-year time horizon
5.0 Alternatives Comparison
The two chlorination methods were compared on the basis of the following evaluation criteria: life-
cycle costs; space requirements; operational considerations (e.g., complexity and flexibility); and
operator safety. A discussion of each method as it relates to these criteria is provided below.
5.1 Life-Cycle Costs
A comparison of 20-year life-cycle costs was previously provided in Table 4. The commercial
hypochlorite method is expected to have substantially lower costs on both a capital and net present
worth basis.
5.2 Space Requirements
Commercial Hypochlorite: Hypochlorite storage space was based on the supply of three 300-gallon
totes. Assuming each tote is about 4-ft by 4-ft in size, and assuming 2-fl of clearance around each
tote, the secondary containment area would be about 160 square feet (sft). An additional area of
about 20 sft would be required for the metering pumps and feed system components. Therefore, the
total floor space for the commercial hypochlorite system is about 180 sft.
On-Site Generation: Salt storage space was based on the supply of two pallets, each carrying about
48 bags (at 50-lb each). Assuming each pallet is about 4-ft by 4-ft in size, and assuming 2-ft of
clearance around each pallet, the salt bag storage area would be about 110 sft. Depending on how
the salt bags were to be loaded into the brine tank, additional access space for use of a forkhft may
be needed. Hypochlorite storage space was based on the use of two 1,400-gallon tanks. Assuming
each tank has a diameter of 5.5-ft, and assuming 3-ft of clearance around each tank, the secondary
containment area would be about 160 sft. An additional area of about 150 sft would be required for
the on-site generation equipment, controls, brine saturator tank, metering pumps, and feed system
components. Therefore, the total estimated foo^rint for this system is about 420 sft.
As noted earher, the cost estimates do not include building footprint for the chemical storage and
feed systems. However, the on-site generation system will require substantial additional footprint
relative to the commercial hypochlorite method. This will increase the capital costs of the building.
5.3 Operational Considerations
Commercial Hypochlorite: This method is the most simple to operate and maintain. It is similar to
the hypochlorite feed system used at the Maplewood Water Treatment Facility, so City staff would
already be familiar with the O&M requirements. With concentrated hypochlorite solution, there is
the potential for off-gassing and vapor-lock issues, though these can generally be avoided with
proper design and operation. Another potential concern with this method involves its use in an
intermittent-type operation, such as near-continuous use during periods of high demand and little-
Well 5A Chlorine Evaluation 10
CityofRenton
Project Number 51403
to-no use during other periods. With extended storage and/or system downtime, commercial
hj^ochlorite solution may experience significant strength decay and there is a greater likelihood of
off-gassing and vapor-lock upon start-up. One possible approach to address this is to supply fewer
totes during periods of inJhequent well use.
On-Site Generation'. This method is expected to be more complicated to operate and maintain as it
relies on successful operation of several unit processes and pieces of equipment in order to produce
hypochlorite solution, i.e., there are more points of failure. The City does not currently have any
other on-site generation systems; therefore. City staff would require training to develop famiharity
with this technology. However, it should be noted that with proper preventative maintenance, these
systems have proven to be reliable at other installations. This method offers greater operational
flexibility for an intermittent-type operation because the generation system can be started quickly
(assuming enough salt is on-hand), hypochlorite can be produced in an "on-demand" mode, and
the 0.8% hypochlorite solution is relatively stable.
5.4 Safety Considerations
Commercial Hypochlorite'. Per 2006 IFC, hypochlorite solution is not considered a toxic material.
However, skin exposure to commercial hypochlorite can result in severe swelling and burmng
within a short period of time. Extended exposure can cause blistering and permanent skin damage.
Also, commercial hypochlorite solution poses a greater risk of chlorine off-gassing and inhalation
hazard in the event that the solution pH is reduced. It is imperative that operators wear personal
protective equipment when working with or near liquid hypochlorite or "breaking" any pipe
connection that is subject to hypochlorite exposure. An emergency shower and eyewash station
will be provided.
On-Site Generation: Low-strength hypochlorite generated on-site can produce similar effects as the
commercial hypochlorite; however, it would require longer exposure duration to do so. This would
allow operators to use an emergency safety shower and/or eyewash to reduce the degree of health
impacts following exposure. It is still advised for operators to wear personal protective equipment
when working with or near liquid hypochlorite or "breaking" any pipe connection that is subject to
hypochlorite exposure. An emergency shower and eyewash station may be required. There are no
chemical safety concerns for salt handling. The electrolyzers will require periodic cleaning with an
acid-solution, which also would involve operator training and use of personal protective
equipment.
5.5 Summary
Table 5 provides a qualitative summary and comparison of the two chlorination methods.
Well 5A Chlorine Evaluation H
CityofRenton
Project Number 51403
Tables.
Alternatives Summary and Comparison Matrix
Evaluation Criteria
Method 1:
Commercial Hypochlorite
Method 2:
On-Site Generation
Capital and O&M Costs
Space Requirements
Operational Considerations
Safety Considerations
• The estimated construction cost for the chlorine
system components is $45,000.
• The estimated aimual O&M costs for the chlorine
system is $16,600 (in 2007 dollars).
• The estimated 20-year NPW is $235,400.
• Secondary containment: 160 sft
• Chemical feed components: 20 sft
• Additional space required for tote deliveries
• This would involve a simple liquid feed system that
is currently used at other City facilities.
• This method is less desirable for intermittent use
operation due to solution strength decay and vapor-
lock concems.
• The tanks/totes should be vented to the exterior to
avoid vacuum conditions and off-gassing into the
building
• Commercial hypochlorite poses a health and safety
risk upon exposure to skin or inhalation.
• Exposure risks can be reduced through operator
training, use of personal protective equipment, and
design features.
• There is an explosion risk from trapped off-gas in
piping, which can mitigated with good design and
operating practices.
• There is an increased hazard related to reconnecting
totes to pump suction piping.
The estimated construction cost for the chlorine
system components is $267,000.
The estimated annual O&M costs for the chlorine
system is $11,800 (in 2007 dollars).
The estimated 20-year NPW is $402,300.
Secondary containment: 160 sft
Salt bag and pallet storage area: 110 sft
Generation system and brine tank: 150 sft
Additional space required for salt deliveries
This is a more complicated system that relies on
multiple unit processes for successful operation.
This is a highly reliable technology for intermittent
use operation due to solution strength stability and
ability to operate in an "on-demand" mode.
The storage tanks should be vented to the exterior so
hydrogen gas byproduct can be removed from the
building.
Because of its low strength, 0.8% hypochlorite poses
a significantly lower degree of risk to health and
safety upon exposure.
Exposure risks can be reduced through operator
training, use of personal protective equipment, and
design features design features.
Overall, low-strength hypochlorite is a safer option
for handing and operations.
DRAFT — Well 5A Chlorine Evaluation
City ofRenton (Project Number 51403)
12
6.0 Recommendation
Based on the evaluation and comparison of liquid chlorination altematives, the use of commercial
12.5% hypochlorite solution appears to be the preferred method for chlorine feed at the Well
5A facility. It would be possible to use either dedicated storage tanks or small exchangeable totes,
depending on the operational needs and preferences of the City. I ^ f n SVyl)
The following highlights summarize the basis for these conclusions:
□ A commercial hypochlorite system would involve lower construction and life-cycle costs
than a system involving on-site generation.
□ The commercial hypochlorite storage and feed system is relatively simple to operate and
maintain The City uses this technology at the Maplewood Water Treatment Facility and is
familiar with its operation.
□ The use of commercial hypochlorite would require substantially less building footprint (and
associated construction costs) than an on-site generation system.
□ Commercial hypochlorite can be safely stored and handled with proper equipment,
operations procedures, and operator training.
DRAFT - Well 5A Chlorine Evaluation 13
City ofRenton (Project Number 51403)