Aqueous Parts Cleaning iSEl. ^ .o Best Environmental Practices for Fleet Maintenance November 1999 Dissolving the myths about aqueous cleaning Myth O Aqueous cleaning units do not dean parts as well as solvent units. 0 Aqueous cleaning units cannot clean transmissions or carburetors. 6 Part rusting is a problem. © Aqueous cleaning is expensive. 0 Aqueous cleaning wastes are a hassle to manage. Fact Aqueous spray cabinets and ultrasonic units can clean even difficult-to-clean parts such as wheel bearings. Ultrasonic units can effectively clean transmissions and carbure- tors, including hidden areas. Rust inhibitors in aqueous cleaners decrease the chances of rusting. Rusting can be further minimized by drying parts immediately after cleaning. Most facilities can save money by l) implementing aqueous spray cabinets to reduce cleaning labor and 2) maximizing aqueous solu- tion life. W^ste aqueous solution with sludge typically requires disposal less than three times per year. Skimmed oil can be recycled along with used oil. Spent filters can be disposed of off site or sometimes recycled along with used oil filters. What's wrong with solvents? Mineral spirits is a solvent commonly used for part cleaning because of its ability to quickly dissolve oil, grease, dirt, grime, burnt-on carbon, and heavy lubricants. Although it is effective for cleaning, mineral spirits raises significant environ- mental and human health concerns: Mineral spirits contains volatile organic compounds (VOC) that contribute to smog formation and may be toxic when inhaled. Mineral spirits evaporates quickly, making worker exposure difficult to control. Solvent cleaning units are usually a facility's greatest source of hazardous waste. Some areas of the country have already restricted use of solvents in parts cleaning operations. Using solvents creates unnecessary environmental, worker health, and fire liabilities for your organization. Minimize your costs and regulatory liabilities by switching to aqueous solutions. What is an aqueous cleaner and how does it work? Aqueous cleaners are water-based solutions that, unlike petrole- um- based solvents, are typically nonflammable and contain little or no VOCs. Instead of dissolving grease and solids, aque- ous cleaners rely on heat, agitation, and soap action to break dirt into smaller particles. Although they clean differently, aqueous cleaners perform as well as solvents. For this fact sheet, aqueous cleaners are defined as water-based cleaners that contain less than 5% (50 grams per liter) of VOCs. Hundreds of aqueous cleaner formulations are commercially available. The California South Coast Air Quality Management District maintains a list of aqueous solutions that are certified to contain less than 5% of VOCs; this list is available on the Internet at www.aqmd.gov/tao/cas/prolist.html. Information presented in this fact sheet is derived from studies of more than 20 aqueous cleaning units in use at over 30 vehicle mainte- nance facilities in California. cz z a m 70 l/> -I > z o z CD -< o c 73 o to -p k) > Z 5 S o 70 71 -p s > z > 0 z CD S > V) -I m to ¦p in n > to m to o -< ¦p b\ ------- Aqueous Parts Cleaning Types of aqueous cleaning units The cleaning equipment used is critical to successful aqueous cleaning because it applies two important mechanisms to the cleaning process: mechanical force and heat. Four types of aqueous cleaning unitsmicrobial sink-top, spray, immersion, and ultrasonicsare described below. Each type of unit is designed for specific cleaning applications; therefore, most facilities will likely meet all their cleaning needs by implementing more than one type of unit. Microbial sink-top units: Best for quick, light-duty cleaning Aqueous sink-top units are used for manual cleaning of parts in the same way as conventional solvent sink-top units. Microbes present in the aqueous solution degrade oils and organic contaminants, sig- nificantly extending solution life. In addition, microbes are safe and pose no risk to technicians. Non-microbial aqueous sink-top units are also available; these units generally require more frequent solution changes, which may increase operating costs relative to microbial units. Applications Preventive maintenance and light-duty cleaning Parts with light to moderate soil buildup Small quantities of parts Parts for immediate replacement on a vehicle Key Features Solution heated to 110 to 120°F Filtering available to remove solids Microbes degrade oily contaminants Advantages Low capital cost relative to other aqueous cleaning units Little or no waste solution Does not dry or chap technician's hands Spray cabinets: For heavily soiled or large volumes of parts Aqueous spray cabinets clean parts by spraying high-temperature solution at high pressures within an enclosed cabinet. Spray cabinets are available in a full range of capacities from small to extremely large. Applications Parts with heavy or difficult-to-remove soils Moderate to very large quantities of parts Medium to large sized parts Heavy-duty repairs and rebuilding Key Features Solution heated to 130 to 190°F Spray pressures of 40 to 60 pounds per square inch Oil skimming options Solution concentration typically maintained between 10 and 15% Advantages Significant reduction in cleaning labor High level of cleaning performance Large cleaning capacities available Lower waste management costs compared to solvent units Disadvantages May require more scrubbing effort than solvent Difficult to clean heavy or stubborn soils Keeping microbes alive requires proper worker training Disadvantages Moderate to high cost Unit Selection Considerations Make sure the unit is at a comfortable height for your workers Greater sink-top size allows larger parts to be cleaned Higher pump pressure improves cleaning action Workers may react negatively to certain odors Unit Selection Considerations Pump power, spray pressure, flow rate, and number of nozzles (higher spray pressures and greater coverage result in better cleaning performance) A 220-volt outlet is often required Temperature adjuster helps to optimize cleaning performance Insulated units are more energy efficient ^Cost: $1,000 to $1,500 Cost: $1,700 to $11,500 ------- Best Environmental Practices for Fleet Maintenance Selecting the right type of unit for your facility Most fleet maintenance facilities require more than one type of aqueous unit to meet their cleaning needs. For example, a facility may main- tain walk-up sink-top cleaning stations for clean-and-replace operations, as well as a centrally-located spray cabinet for cleaning heavily soiled or large parts. If the facility services transmissions or carburetors and does not subcontract the cleaning of these parts, the facility may also require an ultrasonic unit. After converting to aqueous cleaning, most facilities have fewer cleaning units because spray cabinets and ultrasonic units typically can handle a large number of parts. Immersion units: When soak option is needed Immersion units consist of a rectangular tank filled with aqueous solution and a removable false bottom. Immersion units give tech- nicians the option of soaking parts in the aqueous solution below the false bottom to loosen soils on the parts or manually scrubbing parts on top of the false bottom, as performed in a sink-top unit. Ultrasonic units: Clean blind areas Ultrasonic units consist of a steel tank filled with an aqueous solu- tion and are equipped with transducers along the bottom or sides of the tank. The transducers generate high frequency sound waves that produce and intense microscopic scrubbing action on parts surfaces, including blind holes and interior surface areas. c z o m TO l/l -I > z o z cr> -< o c 50 O o Z V) Applications Parts with light to moderate soil buildup Small to moderate quantities of parts Light- to medium-duty repairs Applications Transmissions, carburetors and other hard-to-clean parts Parts with blind holes and hidden surface areas Heavy-duty repairs and rebuilding Key Features Allows soaking of parts Solution heated to no to i2o°F Filter and oil skimming options Solution concentration typically maintained between 25 to 30% Key Features Transducers generate ultrasonic waves Solution heated to 140 to i85°F Filter and oil skimming options Advantages Soaking can improve cleaning and reduce scrubbing time Advantages Very high performance cleaning Ability to clean hidden areas on parts Significant reductions in cleaning labor Disadvantages More expensive than sink-top units May be difficult to clean heavy or stubborn soils Unit Selection Considerations Make sure unit is at a comfortable height for your workers Greater size allows larger parts to be cleaned Workers may react negatively to certain odors Unit available in stainless steel or plastic construction Disadvantages High cost . Some units make a "hissing" noise Unit Selection Considerations Greater ultrasonics power provides better cleaning ability A 220-volt outlet is required for some units Greater unit size provides more cleaning capacity Cost: $1,700 to $3,500 Cost: $5,000 to $12,000 ------- Aqueous Parts Cleaning * as O S 13 Z < 2 Maximizing aqueous solution life Aqueous cleaning solutions last longer than solvents. Further extending the life of an aqueous solution will save you money by reducing your chemical purchase and waste disposal costs. To maximize aqueous solution life, you should: Use microbe technology for sink-top units. Solutions for these units have very long lives and with proper use rarely require disposal. Filter the solution. Filters, typically cartridge filters, are used to remove solids as small as 50 microns in size. Perform oil skimming. Oil skimmers remove free-floating oil from the solution, reducing the amount of oil residuals left on parts and significantly extending solution life. Microbial units do not need oil skimming because microbes degrade the oil. Accept solution discoloration. Many aqueous solutions turn gray or brown during use, but this discoloration does not affect its clean- ing ability. Do not change your cleaning solution just because it looks dirty. Change the solution only when necessary. Change the solution only when its cleaning performance declines. Do not change the solution on a scheduled basis. Always dispose of cleaning solution appropriately. Maintain solution concentration. Perform chemical additions as needed to maintain the cleaning strength of your solution. Some vendors offer easy-to-use test kits to measure the concentration of your solution and determine when chemical additions are necessary. Recycle your solution using microfiltration. Some vendors offer an on-site microfiltration recycling service that removes contami- nants from the solution, eliminating waste solution generation and disposal. Your greatest cost for parts cleaning is labor. The time your workers spend cleaning parts is time they could otherwise use for servicing vehicles. Spray cabinets reduce cleaning labor by as much as 75 percent. .-Did You^ Know; convenience "I can put wheel bearings covered in heavy grease in the spray cabinet, turn on the machine, and go back to work. When I come back and pull out the bearings, they're all clean. " -Mark Foti MUNI technician, San Francisco, California Killing your microbes will result in an unpleasant odor, oil accumulation in your solution, or loss of cleaning performance. Be sure to keep your microbes alive and happy! Keeping your microbes alive and well Maintain solution temperature: Don't unplug your microbial sink- top unit, even overnight. Most microbes require a heated environ- ment to survive. Don't use aerosols above unit: Solvents from aerosols and other sources may harm microbe populations and contaminate the solution. Allow time for microbes to adjust to new soils: Microbes will adapt to the type of soils you are cleaning. If the microbe solution does not clean effectively at first, cleaning performance will improve after the microbes adapt and digest the new soils. Don't overload the unit: Do not pour oils or dump soils into the unit. Sudden loading of concentrated oils and grease may harm the microbes. Very heavily soiled parts should be precleaned by wiping with a rag. Monitor sludge and oil accumulation: Solids will gradually accu- mulate at the bottom of the solution, decreasing cleaning perfor- mance, and therefore may require removal every several years. Also, an oil layer may accumulate on top of some solutions. If the unit does not have aeration, significant oil accumulation may suffo- cate the microbes and should be skimmed off. ------- Best Environmental Practices for Fleet Maintenance Managing aqueous cleaning wastes The wastes generated from aqueous cleaning should be managed as described below. Waste Solution. Aqueous cleaning solutions may qualify as hazardous waste after extended use because concentrations of metals such as cadmium, copper, lead, and zinc may exceed state or federal limits. Therefore, fleet maintenance facilities should always use a licensed waste disposal company to manage waste solution. Many waste disposal companies will analyze the waste solution for you to determine whether it is hazardous. The cost of disposal will vary according to the characteristics of the waste and the volume generated, but will generally be $2 to $4 for a gallon if it is a haz- ardous waste and $1 to $2 for nonhazardous waste. Unless you obtain permission from your local sewage treatment agency, do not discharge waste solution to the sewer or septic system. Used Filters. Used filters may be recycled along with spent engine oil filters with the permission of the recycler. Contact your oil recy- cler to determine if they will take your filters. Some recyclers will only accept used filters if they are encased in metal shells like engine oil filters, and some states prohibit recycling aqueous filters with engine oil filters. If they are not recycled with engine oil filters, used filters should be managed as hazardous waste and disposed of by a licensed waste disposal company. Contact your state envi- ronmental agency to learn if any special rules apply to used filters. Skimmed Oil. Oil skimmed from an aqueous cleaning solution can be managed as used oil and recycled. Most recyclers will accept skimmed oil with used motor oil as long as it is not contaminated with solvent. Simple sludge management Little or no sludge will accumulate in aqueous cleaning units with filtration, but units without filtration may accumulate sludge at the bottom. This sludge may be disposed of along with waste solution. Most waste disposal companies will accept a certain percentage of solids in the waste solution. If the sludge is separated from the solution, the sludge may not be disposed of as solid waste unless tested to determine if it is nonhazardous. To eliminate waste solu- tion disposal, some spray cabinets are available that evaporate the solution, leaving behind a sludge that requires proper disposal. Check with state and local regulators for potential permitting issues associated with evaporation. Full service lease agreements Convenience at a cost. Most fleet maintenance facilities enjoy the hassle-free arrangement of full servicing and waste management provided by a solvent management company. Although some aque- ous cleaning vendors offer similar servicing and waste management arrangements, most do not, usually because it's not necessary. Here's why: Aqueous solutions can last significantly longer than solvents and therefore do not need to be changed as frequently. Even with heavy use, a spray cabinet can clean effectively for as long as 3 months between solution changes. With proper use, microbial sink-top units may clean effectively for several years before requiring solution change. Servicing aqueous units requires minimal time and effort. Servicing requirements are shown below. SERVICING REQUIREMENTS TIME TO PERFORM AND FREQUENCY Add water and chemical Skim oil (not on microbial units) Replace filter Drain and replace solution For 10 minutes, daily to every 2 weeks For 5 minutes, every 2 weeks to every 2 months For 5 minutes, every 2 weeks to every 2 months 1 hour, every 2 months to every few years Self servicing aqueous cleaning units may be easier than you think! .-Did YouO Know; Numerous vendors offer aqueous cleaning equipment Before purchasing a unit, always: Obtain and check references from vendors to learn about unit performance at other facilities and the servicing support provided by the vendors. Cleaning performance and maintenance requirements can vary significantly among different vendors and units. Demonstrate aqueous cleaning units and solution before making a purchase. Most vendors allow facilities to demonstrate units for two to four weeks. 2 > z > 0 z o £ > (/> ~5 j ------- Aqueous Parts Cleaning >- o t/> LU «/l < u Case study: MUNI converts to aqueous cleaning The City and County of San Francisco Hazardous Waste Management Program is helping Municipal Railway (MUNI) repair and maintenance facilities identify cost-effective alternatives to sol- vent part cleaners. Between February and December 1998, 14 differ- ent aqueous cleaning units were demonstrated at three MUNI fleet maintenance facilities. Based on the demonstrations, the following conclusions were drawn: All MUNI facilities can convert entirely to aqueous cleaning without compromising their cleaning performance. Facility cleaning requirements are best met by implementing two or more types of aqueous cleaning units. Significant cost savings can be realized with aqueous spray cabinets and ultrasonic units because of reduced cleaning labor and larger cleaning capacities. These cost savings can offset unit capital costs and result in short payback periods. MUNI can reduce the total number of cleaning units used by implementing spray cabinets and ultrasonic units because these units have large cleaning capacities. MUNI is considering the following vendors for full implementation of aqueous cleaning: f Ultrasonic Units: Immersion Units: Electric bus facility conversion to aqueous -Alpha - GlobalSonics - KleenTec - Mirachem From To (Solvent Units) (Aqueous Units) Spray Cabinets: Microbial Sink-Tops: 2 2 microbial sink-top - EMC - EcoClean (cost: $1,300 per unit) - Landa - ForBest 2 1 spray cabinet - Safety-Kleen (cost: $11,4300 per unit) Electric bus facility Total: 4 solvents ~ 3 aqueous Operations: Light-duty repair, preventive maintenance Number of Solvent Sink-Top Units: 4 Average Daily Cleaning Labor: 3.7 hours Total capital cost: $14,030 Annual savings: $13,250 Payback period: 1.1 years The electric bus facility used a microbial sink-top unit and a spray cabinet for a 3-month demonstration period. The estimated cost savings is largely from the reduced labor from the spray cabinet and reduced servicing and waste management The sink-top unit met most of the facility's cleaning needs for costs of the microbial sink-top units. small parts. The spray cabinet was used to clean large parts. Facility workers responded positively to both units. ------- Best Environmental Practices for Fleet Maintenance Diesel bus facility Operations: Heavy-duty rebuilding and repair Number of Solvent Sink-Top Units: 13 Average Daily Cleaning Labor: 18 hours The diesel bus facility demonstrated three spray cabinets, two ultrasonic units, one immersion unit, and four sink-top units. Facility workers favored the spray cabinets and ultrasonic units because these types of units were able to clean almost all parts, including heavily soiled parts, while significantly reducing cleaning labor. One spray cabinet received an extremely positive response because of its 1) exceptional cleaning performance, 2) automatic water fill feature to make up for evaporative losses, and 3) timer that automatically reduces solution temperature overnight and returns it to the optimal level in the morning. The ultrasonic units impressed workers with their ability to clean interior surfaces and hidden areas on complex parts, including transmissions. However, some workers objected to a constant hissing noise made by some units. The sink-top and immersion units were used for quick, light-duty cleaning of small parts. Three of the sink-top units were disliked by facility workers inadequate height and sink-top capacity, and poor cleaning performance. r Diesel bus facility conversion to aqueous From (Solvent Units) To (Aaueous Units) 8 3 spray cabinets (cost: $3,500 per unit) 2 1 ultrasonic (cost: $12,000 per unit) 2 3 microbial sink-top (cost: $1,300 per unit) 1 2 immersion (cost: $3,500 per unit) Total: 13 solvent 9 aqueous Total capital cost: $33,400 Annual savings: $134,810 Payback period: 3 months The estimated cost savings is largely from significant reductions in cleaning labor from the spray cabinets and ultrasonic unit. less harmful "I like our microbial sink-top unit because I don't have to breath the heavy solvent vapors and its less aggressive on my skin. " -Daron Gee MUNI technician, San Francisco, California r> > m in o -< ------- Aqueous Parts Cleaning Best Environmental Practices for Fleet Maintenance THE DO'S AND DON'TS OF AQUEOUS CLEANING Dry parts immediately after cleaning to prevent rusting Demonstrate units before purchasing Use oil skimming to extend solution life Use filtration to extend solution life Don't Don't discharge waste solution into sewers Don't contaminate aqueous solution with aerosol solvents Don't use solutions with greater than 5% VOCs Your state or local government environmental agency has more information about compliance and pollution prevention for auto repair shops and fleet maintenance operations in your state or area. Additional fact sheets and information can be found at www.epa.gov/region09/p2/autofleet. This fact sheet is part of a package of fact sheets entitled either "The Pollution Prevention Tool Kit, Best Environmental Practices for Auto Repair" (publication number EPA-909-E-99-001) or "The Pollution Prevention Tool Kit, Best Environmental Practices for Fleet Maintenance" (publication number EPA-909-E-99-002). To obtain copies of either package, call (800) 490-9198. Accompanying videos, "Profit Through Prevention", are available at the same phone number for either auto repair (number EPA-909-V-99-001) or fleet maintenance (number EPA-909-V-99-002). ^ Y\ This fact sheet was produced by the Environmental Protection Agency (EPA) Region 9 pollution prevention program. Mention of trade names, products, or services does not convey, and should not be interpreted as conveying, official EPA approval, endorsement, or recommendation. ------- Aqueous Parts Cleaning Best Environmental Practices for Fleet Maintenance Aqueous cleaning cost worksheet for fleet maintenance facilities Complete this worksheet to calculate the costs of replacing solvent cleaning units with one or more types of aqueous cleaning units. Although many facilities may choose to lease aqueous cleaning units, this worksheet uses purchase prices to calculate a payback period. The sample calculations provided are for a facility with four solvent units that converts to one microbial sink-top, one spray cabinet and one immersion unit. The microbial sink-top handles 30% of the original workload, the spray cabinet handles 50% and the immersion unit 20%. The values provided in the sample column serve only as an example, as actual cost and savings will vary according to specific conditions. Start here by determining your current costs for solvent cleaning. c SOLVENT CLEANING (leased units with servicing) your facility \ sample A Number of solvent units leased 4 B Current cost per service visit per unit $90 C Number of times unit serviced per year 26 D Total annual solvent service cost (A x B x C) $9,360 E Loaded hourly labor rate of shop worker $50 F Total number of cleaning labor hours per week 20 6 Total labor cost (E x F x 52) $52,000 k H Total annual cost for solvent cleaning (D + G) $61,360 y If you want to implement one or more microbial sink-top units, continue below. If not, skip to the next section. c CONVERSION TO AQUEOUS MICROBIAL SINK-TOP CLEANING (units purchased) your facility sample 1 Number of microbial sink-top units to be purchased 1 J Purchase price plus installation costs per unit $1,400 K Total capital cost of sink-top units (IxJ) $1,400 L Cost per gallon of aqueous cleaner $6 M Estimated aqueous cleaner use per unit per year in gallons 60 N Aqueous cleaner purchase cost per unit per year (LxM) $360 0 Cost per replacement filter $10 P Number of replacement filters per unit per year 12 Q Total cost for replacement filters per unit (0 x P) $120 R Total number of cleaning labor hours per week 6 S Total annual labor cost (E x R x 52) $15,600 T Total sink-top unit operation and maintenance (O&M) cost ([N + Q ] x l]+S) $16,080 If you want to implement one or more aqueous spray cabinets, continue below. If not, skip ahead to the next table. ( ^ CONVERSION TO SPRAY CABINET CLEANING (units purchased) your facility example U Number of spray cabinets to be purchased 1 V Purchase price plus installation cost per spray cabinet $3,500 w Total capital cost of spray cabinets = U x V $3,500 X Cost per gallon of aqueous cleaner $6 Y Estimated aqueous cleaner use per unit per year in gallons 240 Z Aqueous cleaner purchase cost per unit per year = X x Y $1,440 AA Disposal cost per gallon of spent solution (including sludge) $5 BB Gallons of solution per spray cabinet 65 CC Number of solution changes per unit per year 6 DD Total cost for spent solution disposal per unit = AAx BB x CC $1,950 EE Number of cleaning labor hours per week (typically reduced up to 80%) 2 FF Total annual labor cost = E x EE x 52 $5,200 GG V Total spray cabinet O&M cost = [(Z + DD) x U] + FF $8,590 J Proceed to side two to calculate costs for converting to immersion, or ultrasonic units, as well as to calculate your potential cost savings. ------- Aqueous Parts Cleaning Best Environmental Practices for Fleet Maintenance Aqueous cleaning cost worksheet for fleet maintenance facilities, continued If you want to implement one or more immersion or ultrasonic units, continue below. If not, skip to the last table. CONVERSION TO IMMERSION/ULTRASONICS (units purchased) your facility sample HH Number of immersion/ultrasonic units to be purchased 1 II Purchase price plus installation cost per immersion/ultrasonic unit $2,200 J] Total capital cost of immersion/ultrasonic units (HH x II) $2,200 KK Cost per gallon of aqueous cleaner $6 LL Estimated aqueous cleaner use per unit per year in gallons 80 MM Aqueous cleaner purchase cost per unit per year (KK x LL) $480 NN Disposal cost per gallon of spent solution (including sludge) $5 00 Gallons of solution per immersion/ultrasonic unit 30 PP Number of solution changes per unit per year 4 QQ Total cost forspent solution disposal (NN x 00 x PP) $600 RR Number of cleaning labor hours per week (typically reduced) 4 SS Total annual labor cost (E x RR x 52) $10,400 TT V Total unit O&M cost = ([MM + QQ] x HH] +SS) $11,480 Summarize your calculations below to determine your potential cost savings and payback period. RESULTS your facility sample UU i Total capital cost of all units purchased (K + W + )J) $7,100 W; Total annual cost savings (including labor costs) (HTGGTT) $25,210 WW Payback period (year) (UU/W) ! °-3 Sample parts cleaning cost comparisons The tables below compare the cost of using an aqueous microbial sink-top unit and a spray cabinet to solvent units. These costs are based on actual demonstration results at two fleet maintenance facilities. SOLVENT UNIT VS. MICROBIAL SINK-TOP UNIT One Solvent Unit Annual costs Leasing, waste management $1,908 Electricity (est.) $120 Cleaning labor (239 hrs) $11,950 Total costs $13,978 One Microbial Sink-Top Unit Annual costs Purchase price (annualized)1 $266 Chemicals $365 Filters $60 Electricity (estimated) .$360 Solution disposal2 $125 Cleaning labor (239 hrs) $11,950 Total costs $13,126 Annual Savings: $852 Annualized over a 7 year period at 10 percent interest Assumes off-site disposal of 25 gallons of waste solution once per year TWO SOLVENT UNITS VS. ONE SPRAY CABINET Two Solvent Units Annual costs Leasing, waste management $3,816 Electricity (estimated). $369 Cleaning labor (738 hrs) $36,900 Total costs $41,085 One Spray Cabinet Annual costs Purchase price (annualized)1 $776 Chemicals $510 Solution and sludge disposal2 $3,672 Electricity (estimated)$3,ioo Cleaning labor (221 hrs) $11,050 Total costs $19,108 Annual Savings: $21,977 Annualized over a 7 year period at 10 percent interest Assumes off-site disposal of 64 gallons of waste solution 6 times per year ------- |