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HomeMy WebLinkAboutDRAFT Chlorine Evaluation Memo 020607DRAFT – Well 5A Chlorine Evaluation 1 City of Renton (Project Number 51403) Draft Memo To: Greg Pierson From: Andrew Hill Project: Renton Well 5A Pre-Design Date: 2-Feb-2007 Job No: 51403 Re: Chlorine Evaluation (DRAFT) 1.0 Overview and Purpose This technical memorandum has been prepared as part of Task 2-300 of the Renton Well 5A 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 the 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: The selected treatment train for the Well 5A facility will utilize the same approach as that at the 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 from the existing facility will be salvaged for this project. 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 with 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. DRAFT – Well 5A Chlorine Evaluation 2 City of Renton (Project Number 51403) 2.0 Chlorination Alternatives The following sections provide a brief overview of the two chlorination methods being considered. A more detailed analysis and comparison of the two methods is provided in the following sections. 2.1 Commercial Liquid Hypochlorite Process Description. The application of commercial liquid hypochlorite (12.5% strength) would involve a relatively simple storage and feed system. The hypochlorite solution would be stored in tanks/totes within a secondary containment area and injected into the water supply with diaphragm metering pumps. The solution would be delivered either in a tanker truck (i.e., bulk) or supplied in exchangeable totes (300 gallon capacity), with the preferred method of delivery 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 hypochlorite are as follows: Sodium hypochlorite solution (presumably above bleach-strength concentration) is listed as a hazardous material under the 2006 IFC (Chapter 27) for the following reasons: Physical Hazard – Oxidizer Class 2; Health Hazard – Corrosive. The 2006 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 IFC and IBC. The controlling MAQ for sodium hypochlorite solution is based on the Oxidizer Class 2 hazard rating, for which the storage capacity cannot exceed 81 gallons (assuming the storage tanks are located within an approved exhausted enclosure with automatic sprinklers). Because the stored volume of hypochlorite needed will exceed the MAQ, the chlorine system enclosure will need to meet H-3 occupancy requirements. 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 hypochlorite 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. Regarding operator safety, when working with or near concentrated liquid hypochlorite or “breaking” any pipe connection 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. DRAFT – Well 5A Chlorine Evaluation 3 City of Renton (Project Number 51403) Operations & Maintenance Requirements. The routine O&M activities associated with commercial liquid 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 2.0 hours per week during off-peak use for operations 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 (FTE). 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 in 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 pump, 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 Cl2 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 2006 IFC (Chapter 27), it is not clear if the Oxidizer and Corrosive designations 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. DRAFT – Well 5A Chlorine Evaluation 4 City of Renton (Project Number 51403) Additional measures may be required by the Fire Marshall, including a Hazardous Materials Management Plan. Regarding operator safety, when working with or near liquid hypochlorite or “breaking” any pipe connection 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 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: 5.8 hours per week during peak use for operations 1.4 hours per week during off-peak use for operations 0.9 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 full-time equivalents (FTE). 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 Preliminary 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 system basis of design technical memorandum. 3.1 Well Production The current nominal capacity of Well 5A 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 DRAFT – Well 5A Chlorine Evaluation 5 City of Renton (Project Number 51403) Certificate Record No. 12, Page 5834-A, 200 gpm). As Well 5A is one of several source of supply available to the City, it is anticipated that the new Well 5A treatment facility will be operated primarily during the summertime to meet peak demands. The following preliminary assumptions have been made regarding well operation and production: Continuous operation (100%) during the three peak months of July through September. 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. 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 Cl2, or any desired setpoint between 0.3 and 1.5 mg/L as Cl2, 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, sulfide, 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 Cl2; however, the demand may fluctuate from 1.8 to 3.2 mg/L as Cl2 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 Cl2, the feed system should allow for dosages between 2.8 and 4.2 mg/L as Cl2. The average expected dose requirement is 3.4 mg/L as Cl2. Table 1 provides a summary of the chlorine dose and instantaneous feed rate requirements. The feed rate requirements were based on the Well 5A maximum production rate of 1,500 gpm and are expressed as pounds per day of chlorine (lb/day of Cl2), gallons per day of commercial 12.5% hypochlorite solution (assuming 1.25 lb/gal of Cl2), and gallons per day of on-site generated 0.8% hypochlorite solution (assuming 0.067 lb/gal of Cl2). 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 Cl2) Feed Rate (lb/day of Cl2) 12.5% Liquid Feed (gal/day) 0.8% Liquid Feed (gal/day) Minimum 2.8 50 40 756 Average 3.4 61 49 918 Maximum 4.2 76 60 1,134 DRAFT – Well 5A Chlorine Evaluation 6 City of Renton (Project Number 51403) 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 Cl2 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 Cl2 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 other 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 Cl2. 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, pulsation dampener, and isolation, backpressure, and pressure-relief valves. 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 Cl2, 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 would 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 truck capacity would be supplied (i.e., 740 of about 4,700 gallons), the unit cost of hypochlorite would be extremely high. Therefore, for the remainder of this evaluation, it is assumed that three 250- to 300-gallon totes would be used (for periods of frequent well operation). These totes would be located within a secondary containment area sized to hold the contents of one tote plus fire sprinkler flow. During periods of infrequent well use, the solution storage time (and delivery frequency) 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 or 55-gallon drums. DRAFT – Well 5A Chlorine Evaluation 7 City of Renton (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 pounds 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. Alternatively, 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 (1,500-lb each). For the supersack option, special equipment such as a hoist may be required to move the supersack above the brine tank. 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 Construction-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. 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 DRAFT – Well 5A Chlorine Evaluation 8 City of Renton (Project Number 51403) on-site hypochlorite generation system, a budgetary estimate was obtained for the Wallace & Tiernan OSEC® B-Series, assuming a 90 lb/day of Cl2 production capacity. For either method, a concrete or asphalt-paved access area would be required to allow the commercial 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 forklift; therefore, a City-owned forklift 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 summary 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 $9,000 $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 $19,800 $188,800 Other Nominal Allowances $10,000 $0 WA State Sales Tax @ 8.8% $2,600 $16,600 Estimating Contingency @ 30% $9,700 $61,600 Estimated Capital Cost $42,100 $267,000 4.2 Operations & Maintenance Costs In developing annual O&M cost estimates for each method, the following assumptions were made: 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 Cl2. 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. 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. 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. DRAFT – Well 5A Chlorine Evaluation 9 City of Renton (Project Number 51403) Regarding labor costs, an annual unit cost of $60,000 per FTE 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 summary 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 $100 $2,600 Estimated Annual O&M Cost $16,500 $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% discount 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. Table 4. Life-Cycle Cost Comparison Parameter Method 1: Commercial Hypochlorite Method 2: On-Site Generation Estimated Construction Cost $42,100 $267,000 Estimated Annual O&M Cost $16,500 $11,800 NPW of Annual O&M Costs(a) $189,300 $135,300 Overall Net Present Worth(a) $231,400 $402,300 (a) Based on 6% discount rate and 20-year time horizon DRAFT – Well 5A Chlorine Evaluation 10 City of Renton (Project Number 51403) 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-ft 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 forklift 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 footprint for this system is about 420 sft. As noted earlier, 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- to-no use during other periods. With extended storage or system downtime, commercial hypochlorite 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 or use 55-gallon drums during periods of infrequent well use. DRAFT – Well 5A Chlorine Evaluation 11 City of Renton (Project Number 51403) 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 familiarity 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 (Chapter 37), hypochlorite solution is not considered a toxic material. However, skin exposure to commercial hypochlorite can result in severe swelling and burning 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 produced 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. DR A F T – W e l l 5 A C h l o r i n e E v a l u a t i o n 1 2 Ci t y o f R e n t o n ( P r o j e c t N u m b e r 5 1 4 0 3 ) Ta b l e 5 . Al t e r n a t i v e s S u m m a r y a n d C o m p a r i s o n M a t r i x Ev a l u a t i o n C r i t e r i a Me t h o d 1 : Co m m e r c i a l H y p o c h l o r i t e Me t h o d 2 : On - S i t e G e n e r a t i o n Ca p i t a l a n d O & M C o s t s • Th e e s t i m a t e d c o n s t r u c t i o n c o s t f o r t h e c h l o r i n e sy s t e m c o m p o n e n t s i s $ 4 2 , 1 0 0 . • Th e e s t i m a t e d a n n u a l O & M c o s t s f o r t h e c h l o r i n e sy s t e m i s $ 1 6 , 5 0 0 ( i n 2 0 0 7 d o l l a r s ) . • Th e e s t i m a t e d 2 0 - y e a r N P W i s $ 2 3 1 , 4 0 0 . • Th e e s t i m a t e d c o n s t r u c t i o n c o s t f o r t h e c h l o r i n e sy s t e m c o m p o n e n t s i s $ 2 6 7 , 0 0 0 . • Th e e s t i m a t e d a n n u a l O & M c o s t s f o r t h e c h l o r i n e sy s t e m i s $ 1 1 , 8 0 0 ( i n 2 0 0 7 d o l l a r s ) . • Th e e s t i m a t e d 2 0 - y e a r N P W i s $ 4 0 2 , 3 0 0 . Sp a c e R e q u i r e m e n t s • Se c o n d a r y c o n t a i n m e n t : 1 6 0 s f t • Ch e m i c a l f e e d c o m p o n e n t s : 2 0 s f t • Ad d i t i o n a l s p a c e r e q u i r e d f o r t o t e d e l i v e r i e s • Se c o n d a r y c o n t a i n m e n t : 1 6 0 s f t • Sa l t b a g a n d p a l l e t s t o r a g e a r e a : 1 1 0 s f t • Ge n e r a t i o n s y s t e m a n d b r i n e t a n k : 1 5 0 s f t • Ad d i t i o n a l s p a c e r e q u i r e d f o r s a l t d e l i v e r i e s Op e r a t i o n a l C o n s i d e r a t i o n s • Th i s w o u l d i n v o l v e a s i m p l e l i q u i d f e e d s y s t e m th a t i s c u r r e n t l y u s e d a t o t h e r C i t y f a c i l i t i e s . • Th i s m e t h o d i s l e s s d e s i r a b l e f o r i n t e r m i t t e n t u s e op e r a t i o n d u e t o s o l u t i o n s t r e n g t h d e c a y a n d v a p o r - lo c k c o n c e r n s . • Th i s i s a m o r e c o m p l i c a t e d s y s t e m t h a t r e l i e s o n mu l t i p l e u n i t p r o c e s s e s f o r s u c c e s s f u l o p e r a t i o n . • Th i s i s a h i g h l y r e l i a b l e t e c h n o l o g y f o r i n t e r m i t t e nt us e o p e r a t i o n d u e t o s o l u t i o n s t r e n g t h s t a b i l i t y a n d ab i l i t y t o o p e r a t e i n a n “ o n - d e m a n d ” m o d e . Sa f e t y C o n s i d e r a t i o n s • Co m m e r c i a l h y p o c h l o r i t e p o s e s a h e a l t h a n d s a f e t y ri s k u p o n e x p o s u r e t o s k i n o r i n h a l a t i o n . • Ex p o s u r e r i s k s c a n b e r e d u c e d t h r o u g h o p e r a t o r tr a i n i n g , u s e o f p e r s o n a l p r o t e c t i v e e q u i p m e n t , a n d de s i g n f e a t u r e s . • Th e r e i s a n e x p l o s i o n r i s k f r o m t r a p p e d o f f - g a s i n pi p i n g , w h i c h c a n m i t i g a t e d w i t h g o o d d e s i g n a n d op e r a t i n g p r a c t i c e s . • Be c a u s e o f i t s l o w s t r e n g t h , 0 . 8 % h y p o c h l o r i t e po s e s a l o w e r d e g r e e o f r i s k t o h e a l t h a n d s a f e t y up o n e x p o s u r e . • Ex p o s u r e r i s k s c a n b e r e d u c e d t h r o u g h o p e r a t o r tr a i n i n g , u s e o f p e r s o n a l p r o t e c t i v e e q u i p m e n t , a n d de s i g n f e a t u r e s d e s i g n f e a t u r e s . • Ov e r a l l , l o w - s t r e n g t h h y p o c h l o r i t e i s a s a f e r o p t i o n fo r h a n d i n g a n d o p e r a t i o n s . DRAFT – Well 5A Chlorine Evaluation 13 City of Renton (Project Number 51403) 6.0 Recommendation Based on the evaluation and comparison of liquid chlorination alternatives, the use of commercial 12.5% hypochlorite solution appears to be the preferred method for chlorine feed at the Well 5A facility. Because of relatively low chlorine consumption requirements, the use of exchangeable totes appears to be the most viable supply option. 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 three 300-gallon exchangeable totes will provide about 18 days of onsite storage during periods of peak well use, which is optimal. To improve system reliability and reduce solution strength loss during periods of infrequent well use, the supply quantities could be altered as needed. For example, the City could have fewer totes supplied, or use 55-gallon drums as needed. 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.