BICARBONATE OF SODA BLASTING TECHNOLOGY
FOR AIRCRAFT WHEEL DEPAINTING
by
Abraham S. C. Chen, Lawrence A. Smith, and Robert F. Olfenbuttel
Battelle
Columbus, Ohio 43201
Contract No. 68-CO-0003
Work Assignment No. 2-36
Technical Project Monitor
Ivars Licis
Pollution Prevention Branch
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
) Printed on Recycled Paper
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NOTICE
Study of the material in this report has been funded wholly or in part by the U.S.
Environmental Protection Agency (U.S. EPA), under Contract No. 68-CO-0003 to Battelle. This
report has been subjected to the Agency's peer and administrative review and approved for
publication as a U.S. EPA document. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. EPA or Battelle; nor does mention of trade names or
commercial products constitute endorsement or recommendation for use. This document is
intended as advisory guidance only to the coating removal industry in developing approaches to
waste reduction. Compliance with environmental and occupational safety and health laws is the
responsibility of each individual business and is not the focus of this document.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the increased generation of materials that, if improperly dealt with,
can threaten both public health and the environment. The U.S. Environmental Protection Agency is
charged by Congress with protecting the Nation's land, air and water resources. Under a mandate of
national environmental laws, the Agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural systems to support and nurture
life. These laws direct EPA to perform research to define our environmental problems, measure the
impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning, implementing, and
managing research, development and demonstration programs to provide and authoritative, defensible
engineering basis in support of the policies, programs, and regulations of the EPA with respect to
drinking water, wastewater, pesticides, toxic substances, solid and hazardous wastes, and Superfund-
related activities. This publication is one of the products of that research and provides a vital
communication link between the researcher and the user community.
Passage of the Pollution Prevention Act of 1990 marked a strong change in the U.S.
policies concerning the generation of hazardous and nonhazardous wastes. This bill implements the
national objective of pollution prevention by establishing a source reduction program at the EPA and by
assisting States in providing information and technical assistance regarding source reduction. In support
of the emphasis on pollution prevention, the "Waste Reduction Innovative Technology Evaluation
(WRITE) Program" has been designed to identify, evaluate, and/or demonstrate new ideas and
technologies that lead to waste reduction. These methods reduce or eliminate transportation, handling,
treatment, and disposal of hazardous materials in the environment. The technology evaluation project
discussed in this report emphasizes the study and development of methods to reduce waste and prevent
pollution.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
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ABSTRACT
This evaluation addressed product quality, waste reduction/pollution prevention and
economics in replacing chemical solvent strippers with a bicarbonate of soda blasting technology for
removal of paint from aircraft wheels. The evaluation was conducted in the Paint Stripping Shop at
Ellington Field, National Aeronautics' and Space Administration/Lyndon B. Johnson Space Center
(NASA/JSC), in Houston, Texas. The evaluation used limited new test data, information from previous
tests by NASA/JSC as part of their program to adopt this process as a nondestructive inspection of
aircraft wheels, cost estimates for the chemical stripping and bicarbonate blasting based on facility
records. Because the paint being removed contained hazardous metal constituents, the liquid and solid
wastes as well as the cloud of spray generated were evaluated for metal concentrations present and
their teachability. Analyses for Cd, Cr, Cu, Pb, Mn, Ni, and Zn were made as well as total metals
concentrations, Ph, total suspended solids, and oil and grease. The blasting technology is effective for
removing paint from aircraft wheels without significant damage to the anodized surface under the paint.
Engineering improvements that avoid the need of respirators, reduce noise levels and minimize water
use could enhance the application. Applications that do not contain hazardous materials in the coating
being removed could be significantly more lucrative. In comparison to solvent depainting this
technology reduced the amount of hazardous waste generated as well as cost savings due to operating
and disposal costs, resulting in a 15% return on investment in about 4 years.
This report was submitted in partial fulfillment of Contract Number 68-CO-0003, Work
Assignment 2-36, under the sponsorship of the U.S. Environmental Protection Agency. This report
covers a period from June 1991 to May 1992, and the study was completed as of May 31, 1992.
iv
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i
TABLE OF CONTENTS
NOTICE H
FOREWORD . . . HI
ABSTRACT iv
LIST OF TABLES ., v!I
LIST OF FIGURES . . . . .. ... vm
ACKNOWLEDGEMENTS (X
SECTION 1 i
PROJEECT DESCRIPTION . 1 ,
1.1 PROJECT OBJECTIVES .. 1 ,
1.2 PAINT STRIPPING TECHNOLOGIES .2
1.2.1 Technologies to Be Replaced: Chemical Strippers 2
1.2.2 Alternative Paint Stripping Technologies 3
1.2.3 Description of ARMEX®/ACCUSTRIP™ Process 4 ;
1.3 TECHNOLOGY EVALUATION SITE 7 i
1.3.1 Past Stripping Process 9
1.3.2 Current ARMEX®/ACCUSTRIP™ Stripping Process 9
1.4 EVALUATION APPROACH 12
1.4.1 Product Quality Assessment 12 j
1.4.2 Waste Reduction/Pollution Prevention Potential
Assessment 14
1.4.3 Economic Assessment 15
SECTION 2
PRODUCT QUALITY EVALUATION 16
2.1 EXPERIMENTAL METHODS 17
2.1.1 Stripping of Aircraft Wheels 17
2.1.2 Anodized Surface Damage Inspection ... 17 i
2.2 RESULTS AND DISCUSSION 18 '
2.3 PRODUCT QUALITY ASSESSMENT '.'..'.'.'.'.'.'. 24
SECTIONS
WASTE REDUCTION/POLLUTION PREVENTION POTENTIAL EVALUATION 25
3.1 SOLID AND LIQUID WASTE REDUCTION POTENTIAL 25
3.1.1 Experimental Methods 26
3.1.2 Results and Discussion 28
3.2 AIR AND NOISE POLLUTION PREVENTION POTENTIAL '.'.'.'.'.'.'.'.'.'. 32 i
3.2.1 Experimental Methods , 32 •'
3.2.2 Results and Discussion .......... 34
3.3 WASTE REDUCTION/POLLUTION PREVENTION ASSESSMENT ... I ......... 38
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TABLE OF CONTENTS (Continued)
SECTION 4
ECONOMIC EVALUATION ..... . ................. ....... 41
4.1 CAPITAL INVESTMENT ........ 41
4.2 OPERATING COSTS ........ ____ " ' ................ ............ 42
4.3 RESULTS OF ECONOMIC ANALYSIS ..... ............................... ' 4fi
4.4 ECONOMIC ASSESSMENT . . . . ............ . ..... ...... '.'.'.'.'/.'.'.'.'.'.'.'.'.'.'.'.'. 46
SECTIONS
QUALITY ASSURANCE
5.1 QUALITY ASSURANCE OBJECTIVES . . ............................. 50
5.1.1 Precision ........ ............................... ............. 51
5.1 .2 Accuracy ........ ............. . .............. ............ 54
5.1.3 Completeness ...... ..... ....... 54
5.2 LIMITATIONS AND QUALIFICATIONS . . •. ...... '•'.'•'.'.'.'.','.'.'.'.'.'.''..'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 54
SECTION 6
REFERENCES
APPENDIX A
METHOD OF ASSESSING ANODIZED SURFACE DAMAGE .................... 61
APPENDIX B
EFFECTS OF ARMEX®/ACCUSTRIP SYSTEM™ ON FATIGUE CRACKS
IN ALCLAD TEST PANELS ..... „,.
........................ • ..................... bo
APPENDIX C
ICP CALIBRATION VERIFICATION AND ICP INTERFERENCE CHECK .................. ... 69
VI
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LIST OF TABLES
Table 1-1. Dimensions and Capacities of the ACCUSTRIP SYSTEM™ 7
Table 1-2. Aircraft Maintained at the NASA/JSC Ellington Field ..., 7
Table 1-3. List of Measurements Performed 13
Table 2-1. Summary of Anodized Surface Damage Inspection . 19
Table 3-1. Sampling Procedures ; 27
Table 3-2. Quantitative Quality Assurance Objectives 29
Table 3-3. Oil and Grease, TSS, pH, and Metal Contaminants in
Wastewater Collected from the Vat 31
Table 3-4. Total and Leachable Metals in Solid Waste Collected from the Vat 33
Table 3-5. pH, TSS, and Metal Contaminants in Wastewater Collected
from Rotoclone Separator 33
Table 3-6. Airborne Metals Collected During Bicarbonate Paint Removal 36
Table 3-7. Projected 8-Hour Noise Exposures and Required Noise Attenuation 38
Table 3-8. Summary of Pollution Prevention Potential for Bicarbonate Paint Removal 39
Table 4-1. Inputs and Outputs for Capital Costs 42
Table 4-2. Man-Hours Required and Solid and Liquid Waste Generated Annually 44
Table 4-3. Stripping Time 45
Table 4-4. Annual Operating Cost of Bicarbonate Blasting Compared
to Solvent Stripping 47
Table 4-5. Annual Operating Savings from Bicarbonate Blasting Compared
to Solvent Stripping 48
Table 4-6. Return on Investment for Change from Solvent Stripping
to Bicarbonate Blasting 49
Table 5-1. Precision of TSS and Metals Measurements 52
Table 5-2. Precision and Accuracy of Oil and Grease Measurements 53
Table 5-3. Precision of pH Measurements 53
Table 5-4. Accuracy of Metals Measurements 55
Table 5-5. Accuracy of Airborne Metals Measurements 53
Vii
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LIST OF TABLES (continued)
Table C-1. ICP Calibration Verification . 7Q
Table C-2. ICP Interference Check
LIST OF FIGURES
Figure 1-1. Typical ACCUSTRIP SYSTEM™ Flow Diagram ,..
71
5
Figure 1-2. ACCUSTRIP SYSTEM™ with Wet Blast Head
o
Figure 1-3. Flow Diagram of Aircraft Wheels Maintenance Program
at the NASA/JSC Ellington Field
: • 8
Figure 1-4. Layout of Paint-Stripping Shop (Building 137) 10
Figure 1-5. Paint-Stripping Shop Modified for ARMEX®/ACCUSTRIP™ Process . n
Figure 2-1. Photographs of Aircraft Wheel (SN 6264 Outboard) Taken
after the First (Top) and Second (Bottom) Blasting 21
Figure 2-2. Photographs of Aircraft Wheel (SN 6264 Inboard) Taken
after the First (Top) and Second (Bottom) Blasting 22
Figure 2-3. Photographs of Aircraft Wheel (SN 7755 Outboard) Taken
after the First (Top) and Second (Bottom) Blasting 23
Figure A-1. Anodized Surface Damage Data Sheet ....:..... 64
Figure B-1. Alclad panel (#7 of 8) Prior to Painting 67
Figure B-2. Painted Alclad Panel (#7 of 8) 67
Figure B-3. Alclad Panel (#7 of 8) after Blasting with ARMEX® Blast Media at 80 psi 68
viii
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ACKNOWLEDGMENTS
The U.S. Environmental Protection Agency and Battelle acknowledge the important
contribution made by representatives of the Washington Department of Ecology, Office of Waste !
Reduction, Recycling, and Litter Control (Robert Burmark), in assisting in identifying and locating a site j
for this technology evaluation. K. B. Gilpreath. Director, NASA/JSC Center Operations, is acknowledged :
for providing the site and support for the on-site evaluation. In particular, J. P. Herrmann and J. Kines, :
NASA/JSC Environmental Services Office, are acknowledged for coordinating the on-site activities and
sharing data and overall assessment of the technology. G. Caylor and S Hulka, NASA/JSC
Environmental Health Services, are acknowledged for providing analytical supports for airborne metals I
and noise exposure studies. M. Doty of Church & Dwight Co., Inc. provided useful information about the '
stripping media and system. ;
IX
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SECTION 1
PROJECT DESCRIPTION
The objective of the U.S. Environmental Protection Agency's (U.S. EPA) Waste Reduction
Innovative Technology Evaluation (WRITE) Program is to evaluate, in a typical workplace environment,
examples of prototype technologies with potential for reducing wastes at the source or for preventing
pollution. In general; when evaluating each technology, three issues are addressed.
First, is the new technology effective? Waste reduction and pollution prevention
technologies involve using either substitute materials or techniques, or recycling or reusing materials. It
is important to verify that the quality of the materials and the quality of the work product are satisfactory
for the intended purpose. Second, does using the technology measurably reduce waste and/or prevent
pollution? Last, the economics of the new technology must be quantified and compared with the
economics, of the existing technology and/or the technology to be replaced. It should be noted,
however, that improved economics is not the only criterion for using the prototype technology. There
may be harder to quantify justifications such as reduced liability, greater safety, better morale, and
improved company public relations that would encourage adoption of new operating approaches.
This evaluation involves a commercially available technology, offered by a specific
manufacturer, for coating removal. The technology evaluated is marketed by CDS Group, a joint
marketing venture of Church & Dwight Co., Inc. (Princeton, New Jersey) and Schmidt Manufacturing,
Inc. (Fresno, Texas). Other bicarbonate of soda blasting technologies for similar applications may be
commercially available from other manufacturers.
1.1 PROJECT OBJECTIVES
The goal of this study is to evaluate a bicarbonate of soda departing technology that uses
sodium bicarbonate-based blasting media, ARMEX®, to replace chemical solvents for stripping paints
from aircraft wheels. This study has three specific objectives:
1. To evaluate the effectiveness of the ARMEXe/ACCUSTRIP™ process in stripping paints from
aircraft wheels prior to a nondestructive inspection (NDI) for cracks and structural defects
(see Section 1.4.1 and Section 2),
2. To evaluate the waste reduction/pollution prevention potential of this technology (see
Section 1.4.2 and Section 3), and
3. To evaluate the cost of this technology versus that of the existing method using chemical
solvents (see Section 1.4.3 and Section 4).
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Because .of limited resources available for the project, only a small number of experiments were
performed during the on-site testing. The evaluation was designed based on the user's (NASA/JSC)
requirements in terms of product quality and waste reduction/pollution control. This study evaluated the
performance of the existing stripping equipment and pollution control devices and the wastestreams
generated from the use of the equipment and devices. The stripping process evaluated also may be
applicable to departing, degreasing, and/or cleaning other thick-skin aircraft parts. .However, the
wastes generated from these processes must be examined on a case-by-case basis.
1.2 PAINT STRIPPING TECHNOLOGIES
1-2.1 Technologies to Be Replaced: Chemical Strippers
The most common approach for paint removal is application of organic solvents, mainly
methylene chloride and phenol. The increasing concerns over the adverse effects of organic solvents on
the environment and human health have resulted in more stringent regulations governing the use of
these chemicals as paint strippers for aircraft departing. These include bans on certain chemicals at
some locations and restrictions on volatile organic compound (VOC) emissions and waste disposal.
Among the solvents, chlorinated and aromatic solvents have received the most attention
because they have been widely used as paint strippers in the aerospace and aviation industry and they
have been linked to numerous acute and chronic diseases, including cancers. Methylene chloride and
phenols are the most common major constituents of solvent paint removers. For example, methylene
chloride and several other solvents have been identified as some of the 17 priority chemicals in the 1988
Toxic Release Inventory (TRI) under Title 313 Superfund Amendments and Reauthorization Act (SARA).
By 1992, the U.S. EPA wishes to reduce the release of these chemicals by one-third, and by 1995,
reduce it by 50% (U.S. EPA, 1991).
Stringent environmental regulations have made the treatment and disposal of solvent-
containing wastes difficult and expensive. Costs will continue to rise in the future, making it desirable to
search for more environmentally and/or economically acceptable technologies for paint stripping.
1-2.2 Alternative Paint Stripping Technologies
Several new and "clean" paint stripping technologies are commercially available. These are
bicarbonate of soda blasting, plastic media blasting (PMB), liquid nitrogen cryogenic blasting, carbon
dioxide pellet cryogenic blasting, and nonhazardous chemical stripping. The first four technologies use
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physical methods, such as abrasion, impact, and extreme cold, to remove old coatings. The last
technology uses "environmentally acceptable" solvents as substitutes.
Nonhazardous chemical strippers contain no chlorinated solvents, phenols, creosois, or other highly
toxic organic compounds (Ignasiak, 1991). They remove most of the common aircraft and aerospace
coatings, including epoxies, polyurethanes, and epoxy primers. These strippers, however, cost more
than the traditional strippers and take more time to work. Some of these strippers corrode magnesium
and can cause hydrogen embrittlement of high-strength steels (Ignasiak, 1991). Therefore, workers must
mask assemblies containing these alloys before stripping them.
Plastic media blasting (PMB) involves propelling palletized plastic particles via compressed
air. The particles impact the painted surface, fracturing the coatings and separating them from the
substrate beneath. When used under a set of precisely controlled parameters, the plastic media impart
negligible damage to the substrates and achieve fast paint removal rates (Haas, 1991). However, the
media can impart significant damage to aluminum, composites, and fiberglass (Groshart, 1988). Other
drawbacks of the technology include initial capital costs, the cleanliness requirement of the media, the
amount of solid waste generated, and worker exposure to dust and noise.
The two cryogenic blasting technologies take advantage of extreme cold to embrittle and
shrink old coatings. Nonabrasive plastic pellets or carbon dioxide pellets are then blasted to make the
paint break away from the substrate. The technologies neither release toxic fumes to the atmosphere
nor produce large quantities of solid wastes. Industrial applications of these technologies, however,
have been limited because of their high capital costs.
Bicarbonate of soda blasting, the subject of this study, uses compressed air to deliver
sodium bicarbonate media from a pressure pot to a nozzle where the media mix with a stream of water.
The media/water mixture impacts the coated surface and removes old coatings from the substrate. The
water used dissipates the heat generated by the abrasive process, aids the paint removal by hydraulic
action, and reduces the amount of dust in the air (Lee and Kirschner, 1989). As another convenience,
the workers do not need to prewash or mask the surface. The dust, unlike that of plastic media, is not
an explosive hazard, nor is sodium bicarbonate toxic in this form. The airborne particulates generated
from the stripping operation, however, can contain toxic elements from the paint being removed (Atkins,
1989), One manufacturer claims that liquid waste may be disposed of to Publically Owned Treatment
Works (POTW) or other conventional wastewater treatment plants, and that the solid waste is suitable for
a sanitary landfill (Church & Dwight Co., Inc.) but these claims remain to be verified.
The effectiveness of bicarbonate of soda blasting depends on optimizing a number of
operating parameters including nozzle pressure, standoff distance, angle of impingement, media flow
rate, water pressure, and traverse speed.
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The present study evaluated the bicarbonate of soda blasting technology marketed by the
CDS Group (Arcola, Texas). The evaluation was conducted in the Paint Stripping Shop (Building 137) at
Ellington Field, National Aeronautics and Space Administration/Lyndon B. Johnson Space Center
(NASA/JSC) in Houston, Texas.
1.2.3 Description of ARMEX'/ACCUSTRIP™ Process
35
ARMEX is a sodium bicarbonate-based blast media formulation manufactured by Church &
Dwight Co., Inc. It is a white, crystalline material with a bulk density of 0.9771 g/mL (61 Ib/fl3), a
specific gravity of 2.22 g/mL (139 Ib/ft3), and a hardness of 2.5 to 3.0 on the Mohs' scale (Lee and
•Kirschner, 1989). It decomposes at elevated temperatures to give various mixed bicarbonate/carbonate
species, depending on time, temperature, and humidity. In aqueous solutions, it reacts with both acids
and bases and maintains the pH at 8.3 over a wide range of concentrations (Stumm and Morgan, 1989).
At the time of on-site testing, three different formulas were available for the specific needs
of industries. These include a composite formula (for delicate substrates such as plastics, graphites,
fiberglass, etc.) at a particle size of 75 yum, a maintenance formula (for maintenance and cleaning of
process equipment and parts) at 175 Mm, and an aviation formula (for aircraft skin and airframe) at 275
fj,m. The ACCUSTRIP SYSTEM™, engineered and manufactured by Schmidt Manufacturing, Inc., blasts
the sodium bicarbonate media. A typical flow diagram is illustrated in Figure 1-1. A typical ACCUSTRIP
SYSTEM™ and a wet blast head are presented in Figure 1-2. Four standard models are available; their
dimensions and capacities are listed in Table 1-1.
During operation, the system delivers a mixture of blast media and water at a pressure of
about 207 to 414 kPA (30 to 60 psi) through a blast nozzle. The hand-held, hand-actuated nozzle is
maintained at a standoff distance (distance from the nozzle to the surface to be stripped) of 0.31 to 0.61
M (12 to 24 in) and an impingement angle of 30 to 80 degrees. The media flow rate is 0.45 to 1.8
kg/min (1 to 4 Ib/min) and the water flow rate is 1.9 L/min (0.5 gal/min). The production rate is about
0.14 to 0.23 nf/min (1.5 to 2.5 ft2/min) (data based on urethane-type coatings up to 4 mils).
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POT
PRESSURE
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Source: Schmidt Manufacturing, Inc.
Figure 1-1. Typical ACCUSTRIP SYSTEM" flow diagram.
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• WATER LINE
BLAST HOSE BLAST NOZZLE
Figure 1-2. ACCUSTRIP SYSTEM™ with wet blast head.
6
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TABLE 1-1. DIMENSIONS AND CAPACITIES OF ACCUSTRIP SYSTEM™
Model
16W
16
13
220
Length
cm in
170 66
91 36
112 44
142 56
Width
cm in
137 54
81 32
86 34
97 38
Height
cm in
185 64
142 56
137 54
203 80
Approximate
Weight
kg Ib
549 1210
367 810
322 710
871 1920
Media Tank
m3 ft3
0.17 6
0.17 6
0.09 3
0.57 20
Water Tank
L gal
151 40
N/A N/A
N/A N/A
N/A N/A
No.
of
Operators
1
1
1
2
1.3 TECHNOLOGY EVALUATION SITE
The NASA/JSC Aircraft Operation Division is responsible for maintenance and repair of
a fleet of 37 aircraft (see Table 1-2) at Ellington Field. One of the many tasks is to perform
nondestructive inspection (NDI) of aircraft wheels. The process involves depainting and cleaning
the wheels, inspecting for cracks and structural defects, treating the surface, priming, and painting.
The NDI preparation of the wheels after depainting involves ultrasonic alkaline cleaning, penetrant
soaking, emulsifier soaking, water rinsing, and drying. The prepared parts are examined under
fluorescent light in a dark room. Figure 1-3 shows a flow diagram of these activities.
TABLE 1-2. AIRCRAFT MAINTAINED AT THE NASA/JSC ELLINGTON FIELD
Type of Aircraft
T-38
G-2
G-1
KC-135
WB-57
Quantity
28
5
1
1
2
Function
Flight training
Shuttle training aircraft (STA) - simulating shuttle
landing
Passenger plane
Zero-gravity experiments
High-altitude experiments, air sampling, experiments
on O3 layer, etc.
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1.3.1 Past Stripping Process
In the past, tire/wheel assemblies were removed from the aircraft in one of the three
large hangars and the one small hangar and taken to a tire shop. The wheels, including outboard
and inboard wheel pieces, were forwarded to the paint-stripping shop (Building 137, see layout in
Figure 1-4) for depainting. The wheels were soaked in a 1.22 m x 1.22 m x 1.22 m(4ftx4ftx4
ft) tank containing BB 9201 phenolic-based stripper heated to between 32.2 and 37.8°C (90 and
100°F). (Prior to January 1991, a Turco chemical stripper containing 55% methylene chloride,
20% phenol, and 1 % sodium chromate was used. However, because of lack of historical data, no
comparison was made to the bicarbonate system during this evaluation study.) After a certain
period of time, the wheels were removed for brushing, sanding, and rinsing on the handwork table.
Repetitive soaking and handworking often were needed. The solvent-containing liquid along with
the paint chips flowed into two 1.22 m x 1.22 m x 0.61 m (4 ft x 4 ft x 2 ft) vats covered with
grates. After gravity settling, the liquid flowed into a sump and then was pumped to a 18,900-L
(5,000-gal) storage tank located just outside of the stripping shop. The solids in the vats were
manually drummed for disposal.
The spent chemical stripping fluid was hauled away for fuel blending in an incinerator.
The stripping sludge solids were drummed and disposed of at a rate of 8 to 10 drums per month at
a cO'St of about $200 to $300/drum. The wastewater was tanked every 3 months (about
15,000 L [4,000 gal]) for deepwell disposal at a cost of 5.3C/L (200/gal).
1.3.2 Current ARMEX®/ACCUSTRIP" Stripping Process
The paint-stripping shop was remodeled to accommodate the ARMEX /ACCUSTRIP™
process and began operation in December 1991. As shown in Figure 1-5, the BB 9201 stripper
tank remained in the stripping room and served as a backup. The ARMEX®/ACCUSTRIP SYSTEM"
(Model 16W), with necessary piping for water and air supplies, strips the wheels resting on either
one of the turntables mounted atop the grates. Vats collect the liquid and solids underneath. The
liquid, after gravity settling, is transferred to the 18,900-L (5000-gal) storage tank, whereas
workers continue the past practice of drumming the solids manually.
An exhaust ventilation system was installed to control/remove the particulate cloud
that forms as the blast media strike the surface. The exhaust system includes two ventilation
hoods (three-sided exhaust enclosures measured at 1.22 m x 1.22 m x 1.22 m [4 ft x 4 ft x 4 ft])
installed on top of the vats. The average face velocity of the hood was measured to be 87 m/min
(285 ft/min). Each hood is equipped with an exhaust duct at the top which draws air from the
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pper
Plastic Strip Separator
Overhead Door
Figure 1-5. Paint-stripping shop modified for ARMEX /ACCUSTRIP" process.
11
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enclosure and routes it through a rotoelone dust collection system external to the building.
NASA/JSC's Environmental Health Services also requires the operators of the ACCUSTRIP
SYSTEM" to wear a full-face air-purifying respirator (APR) with high-efficiency paniculate air
(HEPA) filters until the efficacy of the exhaust ventilation system can be evaluated (Atkins, 1989).
The operators also must wear hearing protection.
1.4 [EVALUATION APPROACH
Several measurements were performed during this evaluation study. Table 1-3 lists
the measurements performed. The anodized surface damage was the only parameter measured
when determining the paint removal process performance. The liquid and solid waste in the vat,
the waste water in the cyclone separator, the airborne particulates in the stripping room, and the
noise generated during the blasting were analyzed and monitored to determine the waste reduction
and pollution prevention potential. The time needed to strip each wheel was measured; the data
were used in conjunction with other historical data for the economic assessment. The rationale for
selecting these measurements is explained in the following sections.
1.4.1 Product Quality Assessment
NASA/JSC aircraft maintenance engineers determined the effectiveness of the sodium
bicarbonate blasting process based on complete paint removal without damage to the wheel
surface that either modified metal performance or masked any cracks during inspection. Complete
paint removal could be achieved by repeatedly blasting the wheel surface. After inspecting the
blasted wheels and other thick-skin parts, NASA/JSC ruled out the possibilities of metal damage
(Rountree, 1991). Other studies by Lee and Kirschner {1989), McDonald (1990), Stropki (1991),
and Van Sciver (1989, 1990, 1991) also suggested negligible metal damage to thin-skin
substrates. Based on a fatigue crack closure study (Williams, 1991) performed by the CDS Group
under the request of NASA/JSC, NASA/JSC also concluded that the blasting would not impede
conventional methods of fatigue crack detection.
One additional concern was the anodized layer below the paint. This thin (around
0.00001 of an inch) electrochemical oxide layer is used to improve the corrosion resistance of the
metal. Because of the relative vulnerability of this layer between the paint and the metal and
because, for practical purposes, the wheels could not be reanodized in the tire shop, the condition
of this layer after repeated blasting was used to determine the effect of the blasting process.
12
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TABLE 1-3. LIST OF MEASUREMENTS PERFORMED
Objective
Matrix Type
Parameter
Product quality
Aircraft wheel
Anodized surface damage
Waste reduction/
pollution prevention
potential
Liquid waste in vats
Total suspended solids (TSS)
Oil & grease
PH
Cd (total)
Cr (total)
Cu (total)
Pb (total)
Mn (total)
Ni (total)
Zn (total)
Volume produced per wheel
Solid waste in vats, Toxicity
Characteristic Leaching
Procedure (TCLP) test for
metals including:
Cd (total & leachable)
Cr (total & leachable)
Cu (total & leachable)
Pb (total & leachable)
Mn (total & leachable)
Ni (total & leachable)
Zn (total & leachable)
Volume produced per wheel
Wastewater collected in
cyclone separator
pH
TSS
Cd (total)
Cr (total)
Cu (total)
Pb (total)
Mn (total)
Ni (total)
Zn (total)
Airborne particulates in
stripping room
Noise level during ARMEX/
ACCUSTRIP" process
Cr
Cu
Pb
Zn
Noise
13
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Although NASA/JSC did not require an anodized surface damage inspection, this
evaluation study did include a test method to assess the condition of the anodized layer after
blasting. The test method, as suggested by NASA/JSC, involved inspection of the same wheel
pieces after they were first stripped and after they were stripped, repainted, and restripped under
the same operating conditions. The procedures of this method are detailed in Appendix A.
1.4.2 Waste Reduction/Pollution Prevention Potential Assessment
Bicarbonate of soda blasting eliminates the use of solvent strippers but still generates
liquid and solid wastes. Three types of wastes were generated: liquid and solid wastes collected in
the vats and wastewater collected in the rotoclone separator. The liquid waste in the vats was
sampled after the bulk of the solid waste gravity-settled. The wastewater in the rotoclone
separator was sampled at the completion of testing. The liquid waste had to meet local discharge
limits for wastewater disposal (City of Houston, 1989), so wastewater samples were quantified for
pH, total suspended solids (TSS), oil and grease, and heavy metal concentrations (including Cd, Cr,
Cu, Pb, Mn, Ni, and Zn).
From these analyses, it could be determined whether the wastewater could be
disposed of to the POTW or had to be tanked away for treatment and/or disposal. The total waste
volume produced by the bicarbonate blasting technology was required to allow comparison with
that produced by the previously used solvent stripping method.
The sodium bicarbonate blasting media alone will not result in the solid waste being a
RCRA hazardous waste. Pigments in the paint chips may contain metals included in the RCRA
TCLP, These metals may be sufficiently leachable to cause the solid waste to exhibit a RCRA
toxicity characteristic. In addition to the RCRA metals potentially in the paint chips, several other
metals were included in the analysis due to their presence in paint and their potential for risks to
human health and the environment. The total metal concentration also was measured to more fully
characterize the solid wastestream. The metals included in the analysis were Cd, Cr, Cu, Pb, Mn,
Ni, and Zn, The volume of solid waste generated also was measured. Knowing the waste volume
and the leachability characteristics could allow NASA/JSC to determine a proper means of disposal.
The hazards that the new technology might pose to workers were evaluated. These
included toxic airborne particulates and unsafe noise exposures. Air quality was measured in terms
of airborne metal concentrations. Noise levels were measured on a sound-level meter and a
dosimeter using an A-filter and a C-filter. The reading on an A-weighted scale enables one to
determine if unsafe noise levels are produced; if they are, then the reading on a C-weighted scale
expedites the selection of proper hearing protection.
14
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1.4.3 Economic Assessment
Evaluating the economic worth of the current technology was a comparative process.
All costs associated with the old stripping practices were identified, evaluated, and compared with
those associated with changing to and maintaining the ARMEX*/ACCUSTRIP" technology. In
general, cost estimation included capital, operating, and waste disposal costs.
Costs associated with the past practice included capital equipment and Turco chemical
stripper costs, as well as the total man-hours spent stripping the aircraft wheels. This total work
time included practicing safety procedures, soaking and scrubbing the wheels, and handling liquid
and solid wastes. Changing to the current technology demanded spending for capital equipment
and materials, miscellaneous startup costs, and operation and maintenance (O&M) costs. The
facilities were revamped to accommodate the pressurized nozzle operation. To address the
concerns over the workers' exposure to potentially toxic airborne particulates from paint removal
debris, an exhaust ventilation system composed of a cyclone separator, intake piping, and two
hoods was installed. Much of the economic assessment used historical data. However, certain
costs cannot be determined without data on the waste volume characteristics and other
performance characteristics of the bicarbonate blasting system determined by this study. To
estimate disposal costs, for example, one must estimate the volume of waste generated and
identify the particular disposal methods.
15
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SECTION 2
PRODUCT QUALITY EVALUATION
The product quality was measured in terms of anodized surface damage. Anodizing is
a commonly used electrochemical finishing procedure that forms an oxide coating on the metallic
surface to improve corrosion resistance of that metal. The anodized film on the aircraft wheels
often is less than one ten-thousandth of an inch thick. A special test method was developed to
qualitatively assess the anodized surface damage resulting from bicarbonate of soda blasting. The
method required visual inspection of the same wheel after it was stripped and after it was
repainted and restripped under the same stripping conditions.
This study did not evaluate the effects of bicarbonate stripping on metal substrate
damage and crack closure. Studies performed by the bicarbonate media manufacturer (Lee and
Kirschner, 1989; McDonald, 1990; Van Sciver, 1989, 1990, 1991; Williams, 1991), an
independent laboratory (Stropki, 1991), and the U.S. military (Haas, 1991; Singerman, 1991), have
demonstrated negligible metal substrate damage due to media impact or substrate corrosion, and
have shown no signs of impediment to conventional methods of fatigue crack detection.
The concern over the substrate corrosion caused by corrosive residues entrapped
within aircraft structures and crevices has been the focus of many studies (Lee and Kirschner,
1989; McDonald, 1990; Stropki, 1991; Van Sciver, 1989, 1990, 1991), but was not known to be
a problem. Sodium carbonate, a main contributing factor to metal substrate corrosion, was not
detected as a chemical decomposition by-product under simulated aircraft operating conditions
{Stropki, 1991).
The crack closure test was performed by the media manufacturer on 16 AI2024 T3
alclad (0.81-mm [0.32-in]) panels that were prepared according to ASTM Method E647 using a
Krouse 5-Kip, DOS fatigue machine. The cracks induced were about 6.35 to 9.5 mm (0.25 to
0.375 in) long. The test procedures and scanning electron micrographs of the alclad test panels
are presented in Appendix B. The electron micrographs were taken sequentially:
1. After fatigue cracks were induced (Figure B-1),
2. After the crack-induced panels were painted with military specification epoxy primer
and polyurethane topcoat (Figure B-2), and
3. After the ARMEX® media blasting at 551 kPa {80 psi) pressure using a 60-degree blast
angle, 30.5-cm (12-in) standoff, and 1.4-kg/min (3-lb/min) media flow (Figure B-3).
16
-------
The results of the study indicated that the bicarbonate of soda stripping did not impede
conventional methods of fatigue crack detection. Therefore, similar tests were not repeated during
this evaluation study.
2.1 EXPERIMENTAL METHODS
2.1.1 Stripping of Aircraft Wheels
The wheel piece (either outboard or inboard) to be stripped was placed on the
turntable mounted on top of the grates (Figure 1-5). The operator wearing the necessary safety
attire (see Section 3.2.1) blasted the wheel with aviation-grade ARMEX® media at a media flow
rate of 1.1 kg/min (2.5 Ib/min), a water flow rate of 1.5-L/min (0.4 gal/min), and a nozzle pressure
of 207 kPa (30 psi). The impingement angles ranged from 30 to 80 degrees and the standoff
distance was about 15 to 30 cm (6 to 12 in). At times, the operator had to halt the blasting, rinse
off the media from the stripped wheel, and examine the stripped area to determine if additional
stripping was required. The stripping was continued until the operator believed that all paint layers
had been removed from the surface of the wheel. After stripping, all eight outboard and inboard
wheel pieces were cloth-dried and transferred to the tire shop for the anodized surface damage
inspection.
2.1.2 Anodized Surface Damage Inspection
Two outboard and one inboard wheel pieces were selected for the anodized surface
damage inspection. The anodized surface damage was assessed according to the procedures
described in Appendix A. The stripped wheel pieces were first photographed from about 30 cm
(1 ft) away with a camera equipped with a close-range lens capable of documenting any nicks and
scratches or lack thereof. A team of three experienced NDI technicians then examined the three
wheel pieces and recorded their observations on the data sheet, specifying whether any noticeable
damage was observed and whether it was due to mechanical wear or incidental damage from the
blasting. The data sheet includes four questions that were designed to qualitatively measure the
incidental damage that wheels endured during the blasting.
After the inspection, all eight outboard and inboard wheel pieces were repainted with a
zinc chromate primer and a clear aluminum finish coat mixed with an aluminum paste in the paint
shop and allowed to dry for at least 12 hours. The wheel pieces were then restripped and
photographed as earlier. The same inspection team then reexamined the same wheel pieces,
17
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recorded new observations, especially signs of any new anodized surface damage, and documented
their opinions regarding the cause of the new damage. This procedure compared stripping of
recently dried paint with results of stripping significantly older paint and allowed effective
assessment of the anodized surface damage due to bicarbonate blasting.
2.2 RESULTS AND DISCUSSION
Table 2-1 summarizes the results of the inspection. The wheel pieces selected for
inspection were 6264 outboard, 6264 inboard, and 7755 outboard; their photographs after each of
the two blasting sessions are presented in Figures 2-1 through 2-3. The questions were asked for
each wheel piece during the inspection.
Question 1. Is there any surface damage?
The answers were unanimously yes for all wheel pieces inspected, indicating that
surface damage always existed in some form.
Question 2. If yes, is it anodized surface damage? Describe other damage.
Again, the answers were yes for all wheel pieces inspected. Anodized surface damage
was observed on all wheel pieces. In some cases, the damage was excessive. Other damage
observed included a worn surface in areas around slots, ridges, and bead rim. This damage was
believed to be caused by tool contact, wear, and tear. One inspector believed that the damage
was due primarily to the paint stripping process used in the past that involved repetitive
hand working such as brushing and sanding.
Question 3.1. Is the anodized surface damage due primarily to mechanical wear?
All three inspectors believed that the anodized surface damage was due primarily to
mechanical wear. The mechanical wear occurred mainly around slots, the head rim area, the tire
bead area, edges of the rim, holes for bolts, and areas where tools made contact. The wear was
caused by tool contact, metal-to-metal contact, paint stripping in the past, and everyday tire wear.
18
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Figure 2-1. Photographs of aircraft wheel (SN 6264 outboard) taken after the first (top)
and second (bottom) blasting.
21
-------
Figure 2-2. Photographs of aircraft wheel (SN 6264 inboard) taken after the first (top)
and second (bottom) blasting.
22
-------
Figure 2-3. Photographs of aircraft wheel (SN 7755 outboard) taken after the first (top)
and second (bottom) blasting.
23
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Question 3.2. Is the anodized surface damage due primarily to ARMEX* blasting? |
"' "' . "••''"' '' i
After careful examination, two inspectors did not believe that the anodized surface damage j
was caused by the bicarbonate of soda blasting. One inspector responded in three separate occasions i
suggesting adverse effects of the blasting on the anodized surface. However, his answers were >
inconclusive and inconsistent with his overall comment about the new stripping technology, 'The new '
stripping process is much better." • '
s- -f ' v , - i
Question 3.3. Is the anodized surface damage due primarily to other causes?
i
< I
The answers to question 3.3 were mixed. One inspector believed that the hot dip stripping 1
process.in the past had caused deterioration of the anodized surface. The others, however, did not \
seem to concur with him in his opinion. The question was left unanswered in several occasions. <
Question 4. If this is a second run, do you notice any difference between '
this and the previous inspection? ;
' " . 1
All three inspectors unanimously agreed that they had not found any noticeable differences ;
on the surface of the wheels after the two separate blasting sessions. \
2.3 PRODUCT QUALITY ASSESSMENT •
The major objective of NASA/JSC in depainting is to allow examination of the wheels for j
metal fatigue cracks. The blasting technology was effective in removing paint from the aircraft wheels. !
More importantly, bicarbonate blasting did not rework the surface to hide the fatigue cracks. !
NASA/JSC experience, and the results of this test indicate that the bicarbonate blasting !
system was at least as effective as solvent stripping in removing topcoat and primer without masking i
cracks or other defects. The question of the potential for damage to the anodized surface finish, I
however, had not been resolved by the NASA/JSC test program and, therefore, was studied in detail in 1
this project. The special test method developed qualitatively assessed the anodized surface damage |
and the results did not suggest such damage as a result of bicarbonate blasting. i
24
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SECTION 3
WASTE REDUCTION/POLLUTION
PREVENTION POTENTIAL EVALUATION
Pollution prevention is achieved by reduction of waste at the source. Pollution prevention
considers all waste types, for example, hazardous waste, solid waste, wastewater, air emissions, and
utility consumption. Reductions must be true reductions in the volume and/or toxicity of waste and not
simply a transfer of waste from one medium to another.
The waste reduction potential was measured in terms of volume reduction and toxicity
reduction. The reductions were quantified by comparing waste volumes and types from solvent stripping
with the wastes produced by bicarbonate stripping. Volume reduction addresses the gross wastestream,
such as solvent sludge and rinsewater from solvent stripping, as compared to liquid and solid wastes in
the vat and wastewater in the rotoclone separator from bicarbonate stripping. Toxicity reduction
considers concentrations and types of contaminants, such as solvents, oil and grease, TSS, and heavy
metals, in the gross wastestream.
The pollution prevention potential also considered hazards that the stripping technology
might pose to workers. These include toxic airborne particulates and unsafe noise exposures. Air
quality was measured in terms of airborne metal concentrations. Noise levels were measured on a
sound-level meter and a dosimeter. The results of these measurements will determine the proper safety
attire to be worn by the equipment operator.
3.1 SOLID AND LIQUID WASTE REDUCTION POTENTIAL
The bicarbonate stripping process generates wastewater, solid waste, a cloud of spray, and
paniculate in the vicinity of the nozzle and surface being depainted. This contaminated air is exhausted
via hoods over the blast enclosures and cleaned via the rotoclone separator. In cleaning the air, the
rotoclone separator generates wastewater with low concentrations of heavy metals. A full-face air-
purifying respirator (APR) was worn by the operator for this application. Noise measured during this test
was above Occupational Safety and Health Act (OSHA) and NASA permissible exposure limits (PELs),
requiring the operator to use hearing protectors.
The previous solvent-based depainting processes generated volatile organic solvent
releases to the atmosphere and, in the workplace, spent solvent, solid waste, and wastewater that
required off-site treatment and/or disposal as hazardous waste. The overall volume of hazardous waste
25
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for the previous system was larger, although the total volume of all waste (hazardous and sewerable)
generated by each system is comparable. However, the significant volume of nonhazardous waste (as
defined by local regulations) generated by the bicarbonate process could be reused or recycled as
process water, depending on the application.
The bicarbonate blasting system completely eliminates the use of hazardous organic
solvents, mainly methylene chloride and phenols. Both processes produce a sludge and wastewater.
However, the volumes and characteristics are different, as analyzed in the following sections. Use of this
technology for other applications can be expected to produce significant variations which need to be
investigated on an individual basis. The P2 potential in substituting the system when the paint or coating
itself is not hazardous appears lucrative. :
3.1.1 Experimental Methods
Sampling Procedures. At the conclusion of the stripping process (see Section 2.1.1), the
bulk of the solid waste in the vat had gravity-settled. The liquid waste was transferred, after sampling,
from the vat to the 5,000-gal storage tank sitting just outside the paint-stripping room. Samples of liquid
and solid wastes in the vat and/or the rotoclone separator were taken according to the sampling
procedures described in Table 3-1. (No solid waste samples were collected from the rotoclone
separator because solids were present only in a very small quantity in the bottom of the separator.) As
a precaution, all sample containers were prewashed with a mixture of surfactant and deionized water,
followed by deionized water alone. The number of samples collected is summarized in Table 1-3. The
sample bottles were carefully labeled and placed in a sample cooler for transport to the analytical
laboratory. Enough nonflammable packing material was spread around the sample bottles to ensure
that they did not break. The sample cooler accompanied by a chain-of-custody form was then labeled
and shipped to the analytical laboratory by Federal Express within 4 hours after sampling.
In addition to the samples collected, a field blank was taken of the blast media to assess
extraneous contamination during sampling handling and shipping. For the solid waste, a field blank was
taken consisting of the blast media shot directly from the nozzle into an open-mouth container. This
blank served to confirm that there was no significant contribution of any of the measured analytical
parameters to the samples collected from the blast system itself. The field blank also demonstrated that
samples had not become contaminated during shipping.
A sample of on-site tap water also was collected for analysis. The tap water supply is the
source of water for the bicarbonate blasting system, the part rinsing process, and the rotoclone
separator. The background sample allows an assessment of increases in contaminants due to the
process operations.
26
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TABLE 3-1. SAMPLING PROCEDURES
Analyte
Liquid waste
TSS
Oil & Grease
PH
Metals
Sample
Quantity
in vats
100 mL
1,000 mL
100mL
1 00 mL
Sampling
Method
Grabb
Grabb
Grabb
Grabb
Holding Time
(Days)
7
28
7
1 80
Sample
Preservation
4°C
4°C, HCI
to pH <2
4°C
Ambient, HN03
Container*
P
Gd
P
P
Solid waste in vat
Metals (total
and teachable)
1,000 mL
Grab0
180
to pH <2
4°C
Liquid waste in rotoclone
separator
Metals
100 mL
Grabb
180
4°C
* G - Glass, P - Polyethylene.
b EPA Method III - 1, Sampling Surface Waters Using a Dipper or Other Transfer Device.
c EPA Method II - 3, Collection of Sludge or Sediment Samples with a Scoop.
d Borosillcate glass.
Analytical Measurements. Table 3-2 lists all the anaiytes, their corresponding
analytical methods, and the expected quality assurance objectives. In accordance with the U.S.
EPA (1987) requirements, officially approved and validated methods were selected for these
analyses. Total suspended solids (TSS) are nonfilterable residues; TSS were measured
gravirnetrically using EPA Method 160.2. Oil and grease were measured by infrared
spectrophotometry (EPA Method 413.2), which has greater accuracy than gravimetric analysis.
Acidity was measured using EPA Method 150.1 to ensure that the pH level met proper disposal
standards. Concentrations of metals (i.e., Cd, Cr, Cu, Pb, Mn, Ni, and Zn) from paint residue were
monitored, as well, according to EPA Method 6010. Solid wastes collected from the vat were
measured for the same total and leachable metals using the TCLP test (EPA Method 1311) and EPA
Method 6010. These analyses were performed to determine the mobility of heavy metals. All
analytical measurements were performed by an independent laboratory. Instruments were carefully
calibrated according to the specified standard methods before sample analyses.
27
-------
3.1.2 Results and Discussion
Liquid Waste in the Vat. About 114 L (30 gal) of wastewater (exclusive of the rotoclone
separator) were generated during each of the two blasting sessions, or about 28.4 L (7.5 gal/wheel).
Samples of the wastewater were collected at the conclusion of the first blasting session and analyzed for
oil and grease, TSS, pH, and total metals; the results are presented in Table 3-3. The only measurement
that exceeded the planned deviation for precision was oil and grease (mean value, 49.1 mg/L; standard
deviation, 13.8 mg/L for a relative percent deviation of 28%). The variation was expected because
samples collected sequentially from the vat might contain different amounts of insoluble oil and oil
sheen. The TSS was 253 mg/L. The pH measured in the wastewater was 8.37, indicating an NaHCQj-
saturated solution. The average total metal concentrations were 0.033, 8.090, 1.240, 1.430, 0.022, 0.006,
and 5.990 mg/L for Cd, Cr, Cu, Pb, Mn, Ni, and Zn, respectively. The Cr concentration did not meet the
locat discharge limits (City of Houston, 1989), so the wastewater could not be disposed of to the POTW.
Consequently, the liquid waste had to be temporarily stored in the 19,000-L (5,000-gai) storage tank
before off-site disposal.
Solid Waste in the Vat. The amount of the solid waste settled to the bottom of the vat
after the first blasting session was about 8 gal (or 2 gal per wheel), based on the following
data/assumptions:
<• Media flow rate-1.1 kg/min (2.5 Ib/min)
• Stripping and rinsing time- 12 min/wheel set
• Total nozzle blast time - 75%
• Moisture content of the solid waste- 50% (based on laboratory analysis)
• Media density- 2.22 g/cc
« Solubility of NaHCQ - 1 in 10 parts of water.
Samples of the solid waste were taken for total metal and TCLP analyses. As shown in
Table 3-4, 2.73, 146.07, 32.97, 70.87, 2.77, 0.72, and 281.33 mg/kg of Cd, Cr, Cu, Pb, Mn, Ni, and Zn,
respectively, were found in the solid waste. Among these amounts of metal, only a very small fraction
was leachable under the TCLP conditions. TCLP requires the waste to meet limits of 1.0 mg/L Cd, 5.0
mg/L Cr, and 5.0 mg/L Pb. No regulations have been set for Cu, Mn, Ni, and Zn. The results of the
study indicated that the metals analyzed were in lower concentrations than the established limits. No
analyses were made for As, Ba, Hg, or Se, because for the purposes of this application they were not
considered as important.
28
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Liquid Waste in Rotoclone Separator. The wastewater in the rotoclone separator was
sewerable. It contained less than detection limit of TSS and a very small amount of heavy metals,
ranging from 0.005 mg/L of Cd to 0.489 mg/L of Zn (see Table 3-5). The pH of the wastewater was
8.23. The amount of wastewater generated from each of the two blasting sessions was about 980 L (260
gal). At this location, the wastewater was sent to the sewer without treatment. Potentially this water
could be reused or recycled as process water, depending on the application.
3.2 AIR AND NOISE POLLUTION PREVENTION POTENTIAL
The air and noise levels around the operator of the bicarbonate blasting were monitored to
quantify the occupational hazards. Bicarbonate of soda does not pose health risks, but the blasting may
release toxic metals to the ambient air from the paint chips. Based on the concentrations of metals in
air samples and considering exposure time, estimates of the health risk were made for bicarbonate
blasting. Also, A-weighted dosimeter readings were converted to time-weighted averages to determine if
sound levels exceeded federal regulations. If they did, C-weighted readings were used to determine the
proper noise reduction rating (NRR) of the hearing protection.
3-2-1 Experimental Methods
Airborne Metals Exposure Study. During the blasting process, the operator wore a North
full-face APR with stacked high-efficiency particulate air (HEPA) and organic vapor cartridges. Earplugs,
earmuffs, gloves, and a waterproof slicker outfit were also worn. During blasting, the debris and media
formed a wet cloud that extended outside the confines of the exhaust hood and partially over the
operator during blasting. Most of the cloud was drawn back into the hood by the ventilation system.
No particulates were observed escaping the building.
NASA/JSC Environmental Health Services (EHS) collected air samples during the two
blasting sessions. One primary and two replicate samples were taken from the breathing zone of the
operator on each occasion (Atkins, 1992a). One background sample was collected one day before the
first test blasting occurred. Calibrated Gilian pumps, model HFS 513A, and 37 mm, 0.8 micron/and
mixed cellulose ester membrane filter cassettes were used for sample collection. Samples were
collected at 2.96 to 3.13 L/min. The sample collection and analyses were performed following the
National Institute for Occupational Safety and Health (NIOSH) Method 7300 for the analysis of metals by
inductively coupled plasma (ICP) atomic emission spectroscopy (AES). The samples were analyzed for
Cd, Cr, Cu, Pb, and Zn at NASA/JSC EHS Laboratory.
32
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Noise Exposure Study. Significant levels of noise were generated by the bicarbonate of
soda blasting. NASA/JSC EHS evaluated the operator's exposure to the potential noise hazards (Atkins,
1992b). The two main sources of noise to the operator were the blast nozzle and the ventilation system.
The operator opted to wear double hearing protection in the form of foam plugs and muffs for the
duration of the process. The combined noise reduction rating for the double hearing protection was 40
decibels (dB).
Noise exposure monitoring was performed during the two separate blasting sessions. The
first session lasted 59 min and the second 70 min. Sound-level measurements were made with a
calibrated Bruel and Kjaer (B & K) Model 2230 sound-level meter, which conforms to the requirements
for a Type 1 sound-level meter as specified in American National Standards Institute (ANSI) S1.4-1971.
Several periodic measurements were made in the immediate area of the process. These measurements
represent noise produced by the blast nozzle and the ventilation systems. In addition, two calibrated
Metrosonics Model db-308 sound-level dosimeter/analyzers were placed on the operator to log sound-
level exposures while stripping wheels. The dosimeters met the requirements of ANSI S 1.25-1978 and
were programmed to integrate sound levels from 80 to 130 dB. Two dosimeters were used so
measurements could be collected in both "A" and "C" scales. The dosimeter microphones were clipped
vertically within the operator's hearing zone with the data-loggers secured at the waist. These
measurements represent noise produced by the blast nozzle, the ventilation systems, and all other noise
created in the proximal environment during the blasting session.
3.2.2 Results and Discussion
Airborne Metals Exposure Study. The Occupational Safety and Health Administration
(OSHA) and the American Conference of Governmental Industrial Hygienists (ACGIH) have established
PELs and Threshold Limit Values (TLVs) for the airborne metal contaminants of concern in this study.
The PELs and TLVs are listed in Table 3-6. Excluding chromates, all specified PELs and TLVs are based
on an 8-hr time-weighted average (TWA) exposure. The OSHA PEL for chromates is based on a ceiling
concentration. Cadmium has both an 8-hr PEL and a ceiling concentration limit; Because of the
number of primary and replicate samples required for this study, only the 8-hr TWA was considered for
the zinc chromate and cadmium fractions. The ceiling limits for zinc chromate and cadmium were not
evaluated during this study. .
The results of the airborne metal exposure study are presented in Table 3-6. The results
indicate that 8-hr TWA exposures to the airborne metals were below specified OSHA and ACGIH limits.
Regardless of sample types (i.e., primary and replicate samples, background sample, and field blanks)
34
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no metals were detected by ICP/AES. The ICP/AES detection limits were 0.001 mg for Cd; 0.005 mg
for Cr, Cu, and Pb; and 0.009 mg for Zn.
A similar experiment (Atkins, 1989), conducted earlier by NASA/JSC EHS inside a hangar
with the hanger doors closed, resulted in a serious overexposure to Cr (i.e., 0.4 mg/m3). Exposures to
the other contaminants such as Cu, Pb, and Zn did not exceed the PELs, but the reported
concentrations of Cu and Zn were as high as 0.47 and 0.83 mg/m3, respectively. (The Pb
concentrations were below the detection limit for the analytical method and time period sampled.) The
results of this study prompted NASA/JSC EHS to recommend that the blasting process not be
performed in hangars or situations where the waste and/or paniculate cloud could not be contained and
that operators of this blasting equipment be required to wear a full-face APR with HEPA filters.
Meanwhile, NASA/JSC EHS endorsed plans to construct the exhaust ventilation system in place during
this test.
Noise Exposure Study. Sound levels measured periodically in the operator's hearing zone
during the two separate blasting sessions ranged from 76.8 dB on the "A'-weighted scale (dBA) to. 120.0
dBA. Levels ranging from 64.6 to 67.4 dBA were measured outside the flapped doors of the stripping
room. Dosimetry samples integrated cumulative noise exposures of 106.6 and 101.7 dBA for the first
and the second blasting session, respectively. These samples are based on 8-hr TWA calculated from
dosirnetry results recorded during the period sampled. If the actual work period were increased to a full
8 hr, the projected 8-hr TWAs would be 121.3 and 115.9 dBA, respectively. A peak level of 146 dB, the
maximum level the dosimeter is capable of measuring, was recorded during both periods sampled.
According to 29 CFR 1910.95 (OSHA, 1990) the OSHA PEL for noise exposure is 90 dBA
per 8-hr day as a TWA. OSHA also requires that any worker exposed to an action level of 85 dBA
(TWA), or greater, be included in a hearing conservation program. Hearing protectors must attenuate
employee exposure at least to an 8-hour TWA of 90 decibels. The NASA Health Standard on Hearing
Conservation, NHS/IH-1845.4 specifies 85 dBA (TWA) as a PEL per 8-hr day and requires any worker
exposed to an action level of 80 dBA (TWA), or greater, 30 days or longer per year, to be included in a
hearing conservation program. The NASA standard states that hearing protectors must attenuate
employee exposure to a level of 85 dBA or lower. Both standards require engineering controls to be
used as a primary means of exposure control and additional hearing protector attenuation for workers
experiencing a standard threshold shift based on audiometric testing.
35
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Noise exposure may be controlled by means of work duration limitations through
administrative control or by use of personal protective equipment, or both, while engineering controls are
being developed or are not feasible. Due to the variation of actual time spent by workers operating the
blasting equipment, Table 3-7 was developed listing the projected noise exposures based on increased
work periods and hearing protector attenuation requirements as a function of work duration. The
attenuation required was calculated based on 29 CFR 1910.95, Appendix B, "Methods for Estimating the
Adequacy of Hearing Protector Attenuation," Method (ii). The attenuation required ranges from 23.6 to
38.3 dBA under the OSHA criterion, and from 28.3 dBA to 43.3 dBA under the NASA criterion. The
double hearing protection worn by the operator during blasting reduced exposures to below regulatory
limits.
TABLE 3-7. PROJECTED 8-HOUR NOISE EXPOSURES AND REQUIRED NOISE ATTENUATION
Work Duration
(hi)
-0.995 (Actual)
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28.6
33.6
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33.3
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41.3
43.3
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3.3 WASTE REDUCTION/POLLUTION PREVENTION ASSESSMENT
Pollution prevention benefit is the net difference between the old system and the new. In
this case, a solvent paint removal system was replaced with bicarbonate blasting. Because the types of
wastestreams generated by each system vary in species, concentrations, amounts released, and the
associated health and ecological impacts, a direct comparison of reductions of similar wastes is not
possible. There is no common denominator to determine improvements on an absolute scale. We can
list the two sets of data and draw relative significance, as shown in Table 3-8.
38
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TABLE 3-8. SUMMARY OF POLLUTION PREVENTION POTENTIAL FOR BICARBONATE PAINT
REMOVAL
Environmental
Media/Concern
Bicarbonate Blasting
Solvent
Solvent Liquid
Solid Waste
Water
Air Emissions
Noise
• None
• Bicarbonate and paint debris
610 gallons/year
• Water from blasting and floor rinse
5,000 gallons/year
(exceeds POTW limits)
• Water from off-gas treatment
scrubber (rotoclone)
36,000 gallons/year (does not
exceed POTW limits)
• Particulates (metals in room air
below detection limits)
• Potential for > 90 dBA hearing
, protection or administrative limits
on work time required
Spent solvent
220 gallons/year
Solvent sludge and paint debris
6,600 gallons/year
Rinsewater
16,000 gallons/year
(exceeds POTW limits)
Organic vapors
Ambient levels maintained
The most obvious pollution prevention benefit gained by using bicarbonate blasting is the
complete elimination of solvent use, which eliminates generation of spent solvent wastes and releases.
In addition, the quantity of stripping media/solvent waste and paint debris is reduced by a factor of 10.
When using bicarbonate blasting, the operator can observe paint removal progress, make control
adjustments, and typically complete the removal in a single pass. With solvent stripping, the part is
soaked in solvent and then scrubbed with brushes and/or abrasive materials supplemented by
rinsewater. The soak and clean process usually is repeated several times. The multiple soak/clean
cycles and combination of solvent and flushing water produce a large volume of organic sludge and
wastewater.
The bicarbonate blasting process produces a greater total volume of wastewater. However,
the volume of water containing metal concentrations above POTW limits is smaller. The bulk of the
wastewater from bicarbonate blasting is produced by the rotoclone off-gas cleaning equipment. The
metal content of this water is near the background for local tap water.
39
-------
The main drawbacks to bicarbonate blasting are the production of paniculate emissions
and the increased noise levels. Particulates and noise have been controlled at the NASA/JSC
installation by a combination of engineered features and administrative controls.
The exhaust ventilation system reduced the hazardous airborne metals concentrations
outside of the three-sided exhaust enclosure to acceptable levels. However, a considerable amount of
blast media and debris was observed to be deflected onto the operator's APR and protective clothing
during blasting. The full-face APR used in the study provided adequate protection and should be
continued to be used. Meanwhile, modifications to the system to reduce the cloud of spray and
reducing wastewater generation should be investigated. These include installing baffles to reduce the
amount of visible paniculate cloud observed outside the enclosure and adding lighting fixtures to provide
good visibility inside the enclosure. Possible designs to handle debris and spray that require no
rotocloning should also be considered.
Noise measurements performed clearly indicate that, under the conditions encountered
during this study, hazardous noise exposures can result from this process. Therefore, engineering
control of noise exposures should be investigated. Hearing protection devices for all personnel who
operate or work in the vicinity of the operation should be provided. Evaluation of the hearing protectors
used during the actual times worked during this study indicate that the protectors reduced exposures to
below the OSHA and NASA permissible exposure limits. For compliance with the NASA NHS/IH-1845.4,
work durations using the blasting equipment and the hearing protectors assigned should not exceed 5
hr in an 8-hr work shift (Atkins, 1992b), NHS/IH-1845.4 requires use of both plugs and muffs when
exposures equal or exceed 110 dBA. NASA EHS also requires all personnel who routinely operate the
blasting equipment to be placed in a hearing testing and evaluation program at the NASA/JSC clinic.
Beyond this application, depainting via bicarbonate blasting could be considered as a
substitute for a spectrum of other operations requiring removal of paint, coatings or surface
contaminants. Paints or coatings and substrates, themselves containing no hazardous constituents,
could produce non-hazardous waste and totally eliminate the related concern and expense involved with
handling and disposition. The residue and waste water then could be candidates for reuse and
recycling. It sould be noted that this is one of a number of potential substitutes for toxic solvent use.
Each application should consider the best fit for its requirements.
40
-------
- SECTION 4
ECONOMIC EVALUATION
The comparison of costs between bicarbonate blasting and solvent stripping included the
use of data on stripping time per wheel using bicarbonate blasting, NASA/SJC's historical data on
chemical stripping and complimentary information from the vendor regarding the blasting system. The
capital investment, operating costs, and payback period were calculated according to the worksheets
provided in the Waste Minimization Opportunity Assessment Manual (U.S. EPA, 1988).
4.1 CAPITAL INVESTMENT
The following lists the capital investment and capital cost inputs used in the worksheet (see
Table 4-1):
• Equipment costs include $15,000 for an ACCUSTRIP SYSTEM™ Model 16W and $17,375 for an
INGERSOL-RAND trailer-mounted diesel-powered compressor, plus 10% for freight charges,
taxes, spare parts, etc.
• Materials and installation costs include piping, valves, fittings, and electrical and water supplies
for the blasting system, plus the costs for building and facility modification and installation of
pollution prevention equipment including a No. 12 Type W rotoclone, a separator, two hoods
with exhaust ducts, and a storage cabinet.
• Plant engineering costs are assumed to be 15% of the sum of the equipment, materials, and
installation costs.
• Contingency costs are assumed to be 10% of all of the above costs (or fixed-capital investment).
• Working capital is based on 1 month's supply of ARMEX® blast media (assuming that blasting is
performed monthly for 10 hours and 70% of the stripping time is nozzle blast time; the media
flow rate is 2.5 Ib/min; and the media price is $0.68/Ib).
.• Startup costs are based on 10% of the fixed capital investment.
• Equity of 100% is assumed because this is a government-funded project and there was no
money-lending involved. If a loan were taken, the percent debt and interest rate would have
been entered here.
• Because NASA/JSC does not incur taxes, no tax rate is included.
• The depreciation period is assumed to be 7 years, and the escalation rate and cost of capital are
assumed to be 5% and 15%, respectively.
41
-------
TABLE 4-1. INPUTS AND OUTPUTS FOR CAPITAL COSTS
Input
Capital Cost
Equipment
Materials and Installation
Plant Engineering
Contractor/Engineering
Permitting Costs
Contingency
Working Capital
Startup Costs
% Equity
% Debt
Interest Rate on Debt, %
Debt Repayment, years
Depreciation period
Income Tax Rate, %
Escalation Rates, %
Cost of Capital
$35,613
$127,900
$24,527
$0
$0
$18,804
$1,020
$18,804
100%
0%
0.00%
0
7
0.00%
5.0%
15.00%
Output
Capital Requirement
Construction Year
Capital Expenditures
Equipment
Materials and Installation
Plant Engineering
Contractor/Engineering
Permitting Costs
Contingency
Startup Costs
Depreciable Capital
Working Capital
Subtotal
Interest on Debt
Total Capital
Equity Investment
Debt Principal
Interest on Debt
Total Financing
1
$35,613
$127,900
$24,527
$0
$0
$18,804
$18,804
$225,648
$1,020
$226,668
$0
$226,668
$226,668
$0
$0
$226,668
4.2 OPERATING COSTS
The operating costs of stripping aircraft wheels using the ACCUSTRIP SYSTEM" are
calculated based on the following data and assumptions:
• Total working days per year are 250 days,
• Media cost is $0.68/lb.
• Media flow rate is 2.5 Ib/min.
• Media density is 2.22 g/cc.
42
-------
« Media solubility in water is 1 in 10 parts of water.
• Stripping time includes time for nozzle blasting (75%), rinsing-off blast media
from the stripped surface (15%), and inspecting (10%).
• Moisture content of the solid waste collected from the vat is 50%.
• Water usage for blasting and rinsing off is 1 gal/min. Water flow rate during blasting is 0.4
gal/min. Rinsing-off flow rate is assumed to be 0.6 gal/min of nozzle blasting.
• Water consumed for floor washdown is 10 gal/day.
• Rotoclone water flow rate is 5 gal/min.
• Total system operation time is twice the stripping time.
• Water cost is $6.12/1,000 gal (including $2.16/1,000 gal of potable water and
$3.96/1,000 gal of sewage discharge).
•• Electricity required to operate rotoclone is 4.15 kW/hr.
• Diesel fuel required to operate the INGERSOL-RAND compressor is 25 gal/month. The
diesel fuel cost is $0.684/gal.
• Cost of one reconditioned drum is $20.
• Cost to dispose of one drum of nonhazardous solid waste is $80.
• Cost to dispose of nonhazardous liquid waste is $0.20/gal.
• The labor cost is $18.14/hr.
Table 4-2 summarizes the man-hours required for stripping the wheels done annually
for the NDI, and the quantity of solid and liquid wastes generated as a result of the bicarbonate
blasting. About 60 hours are needed to strip all wheels. About 610 gal of settled bicarbonate
media and paint debris sludge and 2,500 gal of bicarbonate media propellent water will be
produced as solid and liquid wastes, respectively. Furthermore, 2,500 gal of floor washdown will
be combined into the liquid waste for off-site disposal. Therefore, the total quantity of the liquid
waste produced and required off-site disposal will be 5,000 gal annually. The disposal costs
(including costs for drums and waste disposal) for the solid and liquid wastes are $1,300 and
$ 1,000, respectively, per year.
43
-------
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44
-------
As shown in Table 4-3, the time required to strip a wheel piece and to rinse off blast
media and debris from the stripped wheel piece ranges from 3.65 to 8.62 min for an outboard and
from 4.5 to 9.23 min for an inboard. The average stripping time per wheel set (one outboard and
one inboard) is about 12 min. One earlier NASA/JSC (1989) study reported a 20-min stripping time
for one KC-97 wheel by bicarbonate blasting versus 8 hours by chemical strippers. The time saved
in that study was more than 95%.
TABLE 4-3. STRIPPING TIME
Stripping Time8 (min)
Serial Number
6264
2188
8312
7755
6748
Outboard/Inboard
ob
ic
o
i
o
i
0
' i
First Stripping
5.13
5.63
7.68
6.80
3.70
4.50
3.65
6.53
!1 ' "
Second Stripping
4.45
5.73
8.62
9.23
3.85
6.12
4.08
8.25
Average
4.79
5.68
8.15
8.02
3.78
5.31
3.87
7.39
8 Including time to flush blast media from stripped wheels
b Outboard.
cInboard.
Average,, = 5.15
Averagej = 6.60
The liquid waste produced from the rotoclone operation is 36,000 gal per year. The
wastewater can be discharged into the POTW; therefore, no extra costs will be incurred.
The operating costs for bicarbonate blasting are compared with those for the old
chemical stripping process. Four drums (55 gal) of spent chemical stripping fluid were used
annually. Disposal costs were $400/drum. The disposal of the spent stripper was $500/drum
(including $20 for a reconditioned drum). The wastewater volume produced was about 16,000
gal, which was disposed of at a rate of 4,000 gal every 3 months. Due to the presence of paint
debris and solvent, the wastewater was treated as hazardous and was tanked away for disposal at
$0.20/gal. Solvent sludge and paint debris were drummed for off-site disposal. About 10 drums
of stripping sludge were produced every month, and the disposal costs were about $300/drum.
45
-------
Other operating cost inputs used in the worksheet include (see Table 4-4):
• Raw material costs are based on an annual supply of ARMEX8 blast media and B&B 9201
chemical stripper.
• Operating labor hours for the blasting and chemical stripping processes are 120 and 886 hours,
respectively.
• The operating supplies and maintenance costs are assumed to be similar for both processes.
• Operating supplies are assumed to be 30% of the operating labor costs.
• Maintenance labor costs are assumed to be 2% of the capital cost, and the maintenance
material costs are 1% of the capital cost.
• Other labor costs include supervision (30% of O&M labor), plant overhead (25% of O&M labor
and supervision costs), and labor burden (28% of O&M labor and supervision costs).
4.3 RESULTS OF ECONOMIC ANALYSIS
Tables 4-5 and 4-6 present the results of the economic analysis. A return on investment
(ROI) greater than 15% (which is the cost of capital) is obtained in 4 years. This implies that the
payback period for NASA/JSC is 4 years. The relatively fast payback period occurs primarily because
waste disposal costs can be reduced by $38,900 per year.
4.4 ECONOMIC ASSESSMENT
Bicarbonate of soda blasting has good potential for reducing paint removal costs. Paint
stripping shops may find this technology highly beneficial, especially as more stringent federal and local
regulations are being implemented to govern the disposal of toxic solvent-contaminated wastes. Cost
reductions were realized from the decrease in hazardous waste and reduced labor. Savings in
elimination of solvent purchases are offset by blast media costs.
Applications that generate no hazardous waste when switching to the blasting process (i.e.
no toxics in the paints or coatings removed) may be more lucrative.
46
-------
TABLE 4-4. ANNUAL OPERATING COSTS AND SAVINGS OF BICARBONATE BLASTING
COMPARED TO SOLVENT STRIPPING
Operating Cost/Revenue
Marketable By-Products
Rate
Price
Total $/yr
Utilities (per year)
Gas
Electric
Fuel Oil
Process Water
Total $/yr
Raw Materials
Total, $/yr
Waste Disposal Savings
Off-site Fees, $
Storage Drums, $
Total Disposal Savings
$0
$0
$0
$0
$0
$205
$110
$315
$2,651
$38,900
$0
$38,900
Operating Labor, Savings
Operator hr/yr
Wage rate, $/hr
Operating Supplies
(% of Operating Labor)
Maintenance Costs
(% of Capital Costs)
Labor
Materials
Supervision
(%of O&M Labor)
Overhead Costs
(% of O&M Labor + Super.)
Plant Overhead
Home Office
Labor Burden
766
$18.14
30%
2.00%
1.00%
30.0%
25.0%
0.0%
28.0%
47
-------
TABLE 4-5. ANNUAL OPERATING SAVINGS FROM BICARBONATE BLASTING COMPARED
TO SOLVENT STRIPPING
Revenue and Cost Factors
Operating Year
Number
Escalation Factor 1.
1
000 1.050
2
1.103
3
1.158
4
1.216
5
1.276
6
1.340
Increased Revenues
Increased
Production
Marketable By-
Products
Annual Revenue
Operating Savings (Numbers
Raw Materials
Disposal Costs
Maintenance Labor
Maintenance Supplies
Operating Labor
Operating Supplies
Utilities
Supervision
Labor Burden
Plant Overhead
Home Office
Overhead
Total Operating
Savings
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
in parentheses indicate net expense)
($2,784)
$40,845
$3,434
$1,717
$14,590
$4,377
($331)
$5,407
$6,561
$5,858
$0
$79,674
($2,923)
$42,887
$3,605
$1,803
$15,320
$4,596
($347)
$5,677
$6,889
$6,151
$0
$83,658
($3,069)
$45,032
$3,786
$1,893
$16,085
$4,826
($365)
$5,961
$7.233
$6,458
$0
$87,840
($3,222)
$47,283
$3.975
$1,988
$16^890
$5,067
($383)
$6,259
$7,595
$6,781
$0
$92,232
($3,383)
$49,647
$4,174
$2,087
$17,734
$5,320
($402)
$6,572
$7,975
$7,120
$0
$96,844
($3,553)
$52,130
$4,382
$2,191
$18,621
$5,586
($422)
$6,901
$8,373
$7,476
$0
$101,686
48
-------
TABLE 4-6. RETURN ON INVESTMENT FOR CHANGE FROM SOLVENT STRIPPING
TO BICARBONATE BLASTING
RETURN ON INVESTMENT
Construction Year
Operating Year
Book Value
Depreciation
(by straight-line)
Depreciation
(by double DB)
Depreciation
1
1
$225,648 $161,177
$32,235
$64,471
$64,471
2
$115,127
$32,235
$46,051
$46,051
3
$82,233
$32,235
$32,893
$32,893
4
$49,998
$32,235
$23,495
$32,235
5
$17,762
$32,235
$14,285
$32,235
6
$0
$32,235
$5,075
$17,762
Cash Flows
Construction Year
Operating Year
Revenues
+ Operating
Savings
Net Revenues
- Depreciation
Taxable Income
- Income Tax
Profit after Tax
•)- Depreciation
After-Tax
Cash Flow
Cash Flow for ROI
Net Present Value
Return on
Investment
1
1
$0
$79,674
$79,674
$64,471
$15,203
$0
$15,203
$64,471
$79,674
($226,668) $79,674
($226,668) ($157,386)
-64.85%
2
$0
$83,658
$83,658
$46,051
$37,607
$0
$37,607
$46,051
$83,658
$83,658
($94,129)
-19.18%
3
$0
$87,840
$87,840
$32,893
$54,947
$0
$54,947
$32,893
$87,840
$87.840
($36,373)
5.22%
4
$0
$92,232
$92,232
$32,235
$59,997
$0
$59,997
$32,235
$92,232
$92,232
$16,362
18.43%
5
$0
$96,844
$96,844
$32,235
$64,609
$0
$64,609
$32,235
$96,844
$96,844
$64,510
26.05%
6
$0
$101,686
$101,686
$17,762
$83,924
$0
$83,924
$17,762
$101,686
$101,686
$108,472
30.70%
49
-------
SECTION 5
QUALITY ASSURANCE
A Quality Assurance Project Plan (QAPjP) had been prepared and approved by the U.S.
EPA before on-site testing began (Chen, 1991). The QAPjP contains a detailed description of the
experimental design and specific quality assurance objectives. The QAPjP also includes analytical
procedures and calibration, as well as methods for internal quality control checks, performance and
system audits, and corrective action. Discussion pertinent to quality assurance is provided in Sections
5.1 and 5.2.
5.1 QUALITY ASSURANCE OBJECTIVES
The four quantitative data quality indicators, i.e., precision, accuracy, method detection limit
(MDL) and completeness, for the various measurements required for this study have been set at levels
shown in Table 3-2. Precision for most of the measurements is estimated by calculating relative percent
difference (RPD) of laboratory duplicates. Precision for pH is estimated by calculating the pH limit for
duplicates. Accuracy for most of the measurements is estimated using percent recovery of laboratory
matrix spikes. For pH measurements, bias is determined by analysis of standard reference materials.
Completeness is presented as the percentage of valid data over the total number of measurements.
The MDLs for ICP are 0.005, 0.007, 0.003, 0.017, 0.001, 0.005, and 0.003 mg/L for Cd, Cr,
Cu, Pb, Mn, Ni, and Zn, respectively. The MDLs for TSS and oil and grease are 10 and 0.5 mg/L,
respectively. The sensitivity for pH measurement is < 0.1 pH unit. The MDLs for airborne metal
particulates are 0.001 mg/filter for Cd, 0.005 mg/filter for Cr, Cu and pb, and 0.009 mg/filter for Zn. All
of these are within the limits set in Table 3-2.
In addition to the four data quality indicators, ICP calibration verification and ICP
interference check were also performed for the total and leachable metal analyses in the laboratory.
These data are included in Appendix C.
The data quality indicators calculation does not apply to the anodized surface damage test
arid the noise exposure test. Anodized surface damage was generally qualitative; therefore,
quantitatively assessing precision and accuracy did not apply. The precision and accuracy of the
sound-level meter and dosimeter are manufacturer-specified.
50
-------
No independent on-site audits were performed during on-site testing and laboratory
analyses. However, the Battelle Study Leader and QA Officer reviewed the analytical data for
compliance with the QA objectives after completion of laboratory testing.
5.1.1 Precision
Precision quantifies the repeatability of a given measurement. The RPDs for TSS and
metals measurements are calculated by equation (1) and presented in Table 5-1:
RPD(%)= I (Regular) - (Duplicate)) y 1QQ% n)
(Regular + Duplicate)/2 >
As shown in Table 5-1, the RPDs range from -12.9% to 14.3% for TSS and all metal
measurements (including total and leachable metals in liquid and/or solid wastes). The RPDs are
well within the limits (i.e., ±25%) specified in the QAPjP. The RPD for oil and grease
measurements (1 .2%, see Table 5-2) is calculated according to equations (2) and (3):
RPD{%) = 1 2 x 100% (2)
(C, + C2)/2
where Cx = (Spiked Sample)x - (Regular Sample)x x = 1 , 2 (3)
Precision limit for pH is estimated using the following equation (4):
Precision Limit = pH (Regular Sample) - pH (Duplicate Sample) (4)
The precision limit is -0.005 and 0 pH unit for the two wastewaters analyzed (see Table 5-3),
which, again, are within the limit specified (i.e., ±0.1 pH unit). The RPDs for airborne metals
measurements were not calculated because all analyzed data were beneath the method detection
limits.
5.1
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5.1.2 Accuracy
Accuracy refers to the percentage of a known amount of analyte recovered from a
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and grease measurements are estimated by equation (5) and presented in Tables 5-2, 5-4,
and 5-5:
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, (Spike Added)
All data in these tables are within the limits specified. The bias of pH measurements has
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5.1.3 Completeness
Completeness refers to the percentage of valid data received from actual testing
done in the laboratory. Completeness is calculated as follows:
Completeness • ' Number of Measurements Judged Valid x 100% (6)
Total Number of Measurements
Completeness for all measurements is 100%.
5.2 LIMITATIONS AND QUALIFICATIONS
Based on the above quality assurance data, the results from the laboratory
analyses provide a good basis for drawing conclusions about waste reduction and pollution
prevention.
54
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TABLE 5-5. ACCURACY OF AIRBORNE METALS MEASUREMENTS
Sample
Number
Metal 5147-
Background
Metal 5148-
Primary
Metal 5149-
Replicate
Metal 5150-
Replicate
Metal 5151-
Field Blk 1
Metal 5152-
Field Blk 2
Metal
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Actual
100.00
98.06
96.70
99.21
99.52
100.00
100.00
99.53
98.42
98.55
102.04
103.79
103.81
103.65
103.47
101.03
102.90
104.29
101.18
105.31
102.04
87.68
96.19
103.04
105.45
101.00
100.97
100.47
98.22
100.00
Recovery (%)a
QA Objective
75-125
75-125
75 - 125
75-125
75-125
75 - 1 25
75-125
75-125
75 - 1 25
75-125
75-125
75- 125
75- 125
75 - 125
75-125
75- 125
75 - 1 25
75 - 125
75-125
75-125
75-125
75-125
75- 125
75-125
75 - 1 25
75-125
75- 125
75-125
75-125
75-125
Method Recovery (%)b
95.54
94.55
93.73
99.90
85.53
95.54
94.55
93.73
99.90
85.53
96.46
93.70
93,93
95.02
92.60
95.50
93.89
94.09
95.68
88.97
96.46
93.70
93.93
95.02
92.60
95.54
94.55
93.73
99.90
85.53
56
-------
TABLE 5-5. ACCURACY OF AIRBORNE METALS MEASUREMENTS (Continued)
Sample
Number
Metal 5153-
Primary
Metal 5154-
Replicate
Metal 5155-
Replicate
Metal 5156-
Field Blk 1
Metal 5157-
Field Blk 2
Recovery (%
Recovery {%)"
Metal
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
Cd
Cr
Cu
Pb
Zn
j _ (Spiked Samole)
Actual
99.00
98.54
98.11
100.20
99.03
96.94
99.05
97.62
98.99
97.52
101.03
100.00
98.10
101.38
100.97
107.14
102.37
102.86
108.92
110.89
98.00
98.06
96.70
97.83
98.07
— (Reaular
QA Objective
75 - 1 25
75-125
75- 125
75-125
75-125
75-125
75- 125
75-125
75-125
75- 125
75-125
75 - 125
75-125
75-125
75-125
75- 125
75-125
75 - 125
75-125
75-125
75-125
75-125
75-125
75-125
75-125
Sample) „ mn%
Method Recovery (%)b
95.54
94.55
93.73
99.90
85.53
96.46
93.70
93.93
95.02
92.60
95.50
93.89
94.09
95.68
88.97
96.46
93.70
93.93
95.02
92.60
95.54
94.55
93.73
99.90
85.53
(Spike Added)
Matrix spikes were accomplished by spiking a known aliquot of metals of interest into the
digested solution. .
Method Recovery (%) = (Method Standard) - (Method Blank) x
(Pipet Standard)
57
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Most of the data for the economic analysis were obtained from NASA/JSC and the
vendor's management. Several assumptions made for the economic analysis have been discussed
in Section 4. Informed assumptions were made only when hard data were absent. These
assumptions are site-specific, and readers are encouraged to adjust them to their own cases.
58
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SECTION 6
REFERENCES
Atkins, D. C., Jr. 1989. "Abrasive Blasting Exposure Study for Building 137, NASA/Ellington
Field," NASA/JSC Environmental Health Services Memorandum (by Kelsey-Seybold Clinic, P. A.
Medical Support Services), NASA/JSC, Houston, TX, December 11.
Atkins, D. C., Jr. 1992a. "Airborne Metals Exposure Study, Bicarbonate Depainting, Building
137A, Room 100 Cleaning Room, NASA/Ellington Field," Memorandum from Deputy Project
Manager/SD23 to Technical Manager/SD26, NASA/JSC Environmental Health Services, March 18.
Atkins, D. C., Jr. 1992b. "Noise Study, Building 137, Room 100, Bicarbonate Soda Depainting
Operation, Strip Shop, NASA/Ellington Field," Memorandum from Deputy Project Manager/SD23 to
Technical Manager/SD26, NASA/JSC Environmental Health Services, March 6.
Chen, A. S. C. 1991. "A Bicarbonate of Soda Depainting Study at Ellington Field, Lyndon B.
Johnson Space Center, National Aeronautics and Space Administration, Houston, Texas," Quality
Assurance Project Plan submitted to and approved by U.S. EPA.
Church & Dwight Co., Inc. 1990. "ARMEX Blast Media Safety Profiles: Waste Disposal,"
Commercial Brochure, Princeton, NJ.
City of Houston. 1989. Industrial Waste Permit No. 1030. Issued to NASA-Ellington Field, March
Groshart, E. 1988. "The New World of Finishing," Metal Finishing. 33.
Haas, M. N. 1991. "Abrasive Paint Stripping with Bicarbonate of Soda: An Alternative to Solvent
Usage," presented at Waste Reduction Assessment and Technology Transfer Tele-Conf., Solvents:
The Good, the Bad, and the Banned.
Ignasiak, M. F. 1991. "Turco Environmentally Acceptable Stripper," Atochem North America, Inc.,
Marion, OH.
Lee, R. C. and L. Kirschner. 1989. "Accustrip: The Next Generation in Nontoxic Low Impact
Stripping," SAE Technical Paper Series, No. 890920, 25th Annual Aerospace/Airline Plating &
Metal Finishing Forum & Exposition. New Orleans, LA.
McDonald, E. P. 1990. "ARMEX®/ACCUSTRIP° Process." Proc. of the 1990 DoD/lndustrv Adv.
Coating Removal Conf.. Atlanta. GA. May 1-3.
NASA/JSC. 1989. Memorandum from P. R. Schleicher/CC2 to CC2 staff, January 14.
OSHA. "Occupational Noise Exposure," 29 CFR, Chapter XVII, Section 1910.95.
Singerman, H. H. 1991. "Evaluation of Sodium Bicarbonate Blasting Technology," Letter Report
from Commander, David Taylor Research Center to Commander, Naval Facilities Engineering
Command (FAC 183), February 13.
59
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Stropki, J. 1991. "Comparative Evaluation of Corrosion Resulting from B.O.S.S. and Chemical
Paint Removal Processes," Proc. of the 1991 DoD/lndustrv Adv. Coating Removal Conf.. San
Diego, CA, April 30-May 2.
Stumrn, W. and J. J. Morgan. 1989. Aquatic Chemistry: An Introduction Emphasizing Chemical
Equilibrium in Natural Waters. John Wiley & Sons, Inc., New York, NY.
U.S. EPA. 1987. Preparation Aid for RREL's Category III Quality Assurance Project Plans. U.S.
EPA, Office of Research and Development, Cincinnati, OH, June 22.
U.S. EPA. 1988. Waste Minimization Opportunity Assessment Manual. EPA/625/7-88/003, U.S.
Environmental Protection Agency, Cincinnati, OH.
U.S. EPA. 1991. The 33/50 Program: Forging an Alliance for Pollution Prevention. U.S. EPA,
Special Projects Office (TS-792A), Office of Toxic Substances, Washington D.C.
Van Sciver, J. H. 1989. "Aluminum Corrosion Study Electrochemical Tests," Proc. of the 1989
DoD/lndustrv Adv. Coatings Removal Conf.. Ft. Walton Beach, FLf April 11-1 a.
Van Sciver, J. H. 1990. "ARMEX® Sodium Bicarbonate Blast Media Integrity on Aluminum
Surfaces," Proc. of the 1990 DoD/lndustrv Adv. Coating Removal Conf.. Atlanta, GA, May 1-3.
Van Sciver, J. H. 1991. "ARMEX® Blast Media Metal Surface Stability," Proc. of the 1991
DoD/lndustrv Adv. Coating Removal Conf.. San Diego, CA, April 30-May 2.
Williams, T. 1991. "The Effects of the ARMEX®/ACCUSTRIP SYSTEM" on Fatigue Cracks in
Alclad Aircraft Aluminum," Church & Dwight Co., Inc., Princeton, NJ.
60
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APPENDIX A
METHOD OF ASSESSING
ANODIZED SURFACE DAMAGE
61
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SPECIAL METHOD OF ASSESSING ANODIZED SURFACE DAMAGE
1. Scope
1.1 This is a special method for testing under the Waste Reduction Innovative Technology
Evaluation (WRITE) Program to estimate anodized surface damage on aircraft wheels.
2. Summary of Method
2.1 This method measures the incidental damage that wheels endure when their paint is
stripped via bicarbonate of soda blasting.
3. Significance and Use
3.1 To a limited extent, this method assesses the effectiveness of stripping paint with
bicarbonate of soda.
3.2 This is a preliminary scoping test for use in the WRITE project evaluation of replacing
conventional chemical stripper with bicarbonate of soda stripping.
4. Terminology
4.1 NDI — Nondestructive inspection. This is a method used to inspect unpainted aircraft
parts for fatigue cracks and other signs of damage.
4.2 Standoff distance — Distance form the nozzle to the surface to be stripped.
5. Apparatus
5.1 Two rear wheels from a T-38 aircraft.
5.2 One ARMEX"/ACCUSTRIP™ sodium bicarbonate blast system, Model 16W.
5.3 One camera with a close-range lens.
5.4 Almigrip-brand polyurethane primer and topcoat.
5.5 Miscellaneous equipment for painting.
6. Procedures
6.1 Clean two rear wheels from a T-38 aircraft, using NASA standard procedures.
6.2 Prepare the blast system for operation (see manufacturer instructions). Media flow
rate should be 1-4 Ib/min at 40-60 psi pressure with a water flow rate of 0.5 gal/min.
6.3 Hold the blast nozzle at a standoff distance of 12 to 24 inches and an impingement
angle of 30 degrees. Completely strip the paint from one wheel.
6.4 Photograph the stripped wheel with a camera equipped with a close-range lens.
Distance from camera to wheel should be between 6 and 12 inches.
62
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6.5 A team of three experienced NDI technicians should examine the wheel and provide
the data required in the data sheet (see Figure A-1).
6.6 Repaint the wheel, applying polyurethane primer and topcoat. Allow at least 12 hours
drying time.
6.7 Repeat steps 6.2 through 6.4.
6.8 The same NDI technicians from step 6.5 should again examine the same wheel and
record the data in the data sheet.
6.9 Repeat steps 6.2 through 6.8 for the second wheel.
63
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Date:
Wheel number:
Media flow rate:
Stripping time:
FIGURE A-1. ANODIZED SURFACE DAMAGE DATA SHEET
Time: Operator:
Run number (circle): One Two
Nozzle pressure: Water flow rate:
1. Is there any surface damage?
2. If yes, is it anodized surface damage?
Describe other damages: .
Yes D No D
Yes D No D
3. Is the anodized surface damage due primarily
to mechanical wear?
Describe location, appearance, etc.:
Yes D No D
ARM EX" blasting?
Describe location, appearance, etc.:
Yes D No D
Other causes?
Describe causes, location, appearance, etc.:
Yes D No D
4. If this is a second run, do you notice any
differences between this and the
previous inspection?
If yes, describe it:
Yes D No D
ADDITIONAL COMMENTS:
64
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APPENDIX B
THE EFFECTS OF ARMEX®/ACCUSTRIP
SYSTEM" ON FATIGUE CRACKS IN
ALCLAD TEST PANELS
65
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THE EFFECTS OF THE ARMEX /ACCUSTRIP" SYSTEM
ON FATIGUE CRACKS IN ALCLAD AIRCRAFT ALUMINUM
During the introduction of the Armex/Accustrip process as an alternate method of paint removal
for the Aviation Industry/ questions arose concerning effects of the process on fatigue cracks in
alclad aluminum. The Aviation Industry has recently begun routinely stripping airframes and
inspecting for fatigue cracks in the skin of the aircraft. The concern was that the Armex/Accustrip
system may deform the alclad coating and fill in or mask the cracks.
In order to investigate these concerns, sixteen panels of A12024 T3 Alclad (.032") were
prepared according to ASTM E647 using a Krouse 5-KIP.DDS fatigue machine. The cracks induced
were roughly 174-3/8" long and all but invisible to the naked eye. The cracks were photographed
using a Scanning Electron Microscope at 100X. Eight of the panels were then prepared and
painted with mil. spec, epoxy primer and polyurethane topcoat. The panels were photographed
after conversion coating was applied and it was noted that the conversion coating application
partially filled in the cracks. The panels were then blasted with Armex Blast Media at 50, 60, 70,
and 80 psi nozzle pressure using a 60 deg. blast angle, 12" stand off, and 3 #/min media flow.
Two panels were blasted at each pressure setting. The next phase of the test was a dye penetrant
examination of the panels as per mil. spec. 410. In-all cases the cracks were readily identified
under ultraviolet light and photographed. One panel, blasted at 80 psi, did show some distortion at
the end of the crack. More importantly, eddy current inspection identified each crack readily.
In conclusion, the findings of this test are that the Armex/Accustrip system does not impede
conventional methods of fatigue crack detection. It should be noted that even though the
application of the chromate conversion coating with scotchbrite did partially mask the crack from
visual detection the crack was still located using eddy current inspection.
I would like to thank the Quality Assurance people at NASA's Ellington Field and Northrup
Worldwide Aviation Services Inc. for their assistance in the preparation of the panels and Bell
Evaluation Labs for their assistance in the inspection of the panels.
Tim Williams
Project Technician
CDS Group
Houston, Texas
66
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Figure B-1. Alclad panel (#7 of 8) prior to painting.
Figure B-2. Painted Alclad panel (#7 of 8).
67
-------
Figure B-3. Alclad panel (#7 of 8) after blasting with ARMEX* blast media at 80 psi.
68
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APPENDIX C
ICP CALIBRATION VERIFICATION AND
ICP INTERFERENCE CHECK
69
-------
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TABLE C-2, ICP INTERFERENCE CHECK"
Metal
Al
Ba
Be
Cd
Ca
Cr
Co
Cu
Fe
Pb
Mg
Mn
Ni
Ag
V
Zn
a Interferen
b _
Recovery
True (mg/L)
500.0000
0.5000
0.5000
1 .0000
500.0000
0.500
0.500
0.500
200.000
1 .0000
500.0000
0.5000
1 .0000
1 .0000
0.5000
1.0000
ce check was ca
jo£) _ Actual
True
Initial
Actual (mg/L)
488.7000
0.4858
0.4794
0.9083
498.5000
0.4712
0.4432
0.4676
179.5000
0.9893
486.7000
0.4339
0.8704
0.9721
0.4883
0.9372
rried out before ar
x 100%
Check
Recovery1* (%
97.7
97.2
95.9
90.8
99.7
94.2
88.6
93.5
89.8
98.9
97.3
86.8
87.0
97.2
97.7
93.7
id after sample
Final
>) Actual (mg/L)
471.3000
0.4607
0.4601
0.8901
494.2000
0.4765
0.4375
0.4456
179.7000
1.0450
478.2000
0.4259
0.8685
0.9825
0.4884
0.9270
analyses.
Check
Recovery (%)
94.3
92.1
92.0
89.0
98.8
95.3
87.5
89.1
89.8
104.5
95.6
85.2
86.8
98.2
97.7
92.7
71
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