Document ID: EPA-HQ-OPP-2006-0606-0006
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2006-09-15T04:00Z

SEQ CHAPTER \h \r 1 	UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

	WASHINGTON, D.C. 20460

OFFICE OF                  

PREVENTION, PESTICIDES AND 

    TOXIC SUBSTANCES        

May 30, 2006

Memorandum

SUBJECT: 	Review of the, “Osmose ACC 50% Wood Preservative: 
Determination of Hexavalent Chromium Residues In and On Wood Following
Treatment with Acid Copper Chromate”.  MRID No. 466447-01.  DP Barcode
329688.

FROM: 	Tim Leighton, Environmental Scientist 

		Antimicrobials Division 

							

TO:		Mark Hartman, Branch Chief

Antimicrobials Division 

	Attached is a review of the post-application residue wipe study
conducted with ACC-treated wood.  The study was submitted by Osmose,
Inc. 

EXECUTIVE SUMMARY

	

The purpose of this study was to examine the potential dermal exposures
to treated wood associated with use of Acid Copper Chromate (ACC) as a
wood preservative through pressure treatment application methods.  In
particular, the goals of the study were to examine the changes in
dislodgeable hexavalent chromium residues and the extent of reduction of
hexavalent chromium over time.  The registered product examined in this
study, Osmose ACC 50% Wood Preservative, is not currently produced or
available.  An equivalent test material was prepared using cupric oxide
and Osmose chromic acid.  This study was conducted under normal
commercial practices at a reduced scale treatment plant. In commercial
settings, the lumber to be treated (typically 2 x 6 x 8 pieces) is dead
stacked (i.e., no space between layers) and metal banded into units,
which are 8 pieces wide and 16 pieces high.  Each unit is treated once
and maintained as a unit through the drying, storage and shipment
processes.  The lumber chosen for this study included southern pine and
Douglas-fir.   

Two different treatment schedules were used for the two types of lumber
to be treated.  For each, the treatment solution was drawn into the
cylinder by an initial vacuum.  Douglas fir is much more difficult to
treat; therefore, that type of lumber was subjected to full cell
treatment, which has a longer initial vacuum period and a longer
pressure period.  The southern pine was subjected to a modified full
cell treatment.

	After treatment, the wood units were stored outdoors.  Temperature on
the surface of the wood units and in the interior of the wood units was
monitored every 30 minutes over the 58 day monitoring period.  The 30
minute temperatures ranged from 8 to 85oF (-13 to 29.4oC) on the outside
of the unit and from 23 to 77oF (-5 to 25oC) in the interior of the
unit.  Average daily temperatures in the interior of the stacked wood
ranged from 31.6 to 54.7oF.  Over the course of the sampling intervals,
temperatures appeared to decrease at first, with a gradual warming trend
up until the end of the study.  Ambient conditions were recorded at a
nearby NOAA reporting station and indicated that the temperatures
recorded at the test site during the monitoring period were slightly
below normal.  Precipitation over the two months of the study period
totaled 5.88 inches and was reported to be normal.  

Three types of samples were taken post-treatment:  (1) wipe samples were
taken from the surface of boards in each unit immediately after
treatment and at certain intervals after treatment,  (2) liquid samples
were expressed from cross sections cut from interior pieces of lumber to
determine the reduction of chromium in the interior of the board, and
(3) borings were taken for confirmation of penetration and retention
immediately after treatment and for qualitative determination of the
presence of hexavalent chromium at certain sampling intervals
post-treatment.  Wipe, wood expressate and boring samples were taken on
0, 3, 9, 23, 36, and 58 days after treatment.  

Samples were analyzed for the active ingredients (test material,
treating solutions, treated wood) and hexavalent chromium (borings, wipe
samples, expressate samples).  The study report did not mention the
analysis of control, field fortification or concurrent laboratory
fortification samples.  All bore samples taken immediately after
treatments were reported to have passed the AWPA requirements for
penetration (AWPA Standard M2-01 Section 4) and target retention.  

μg/cm2) and to have no significant trend among wood type or target
retention.  The study report states that these results indicate that
there is no correlation between the treatment rate and the initial level
of dislodgeable hexavalent chromium.  Levels of hexavalent chromium are
greater than EPA’s level-of-concern (0.0088 rounded to 0.009 μg/cm2)
for both wood types at the target retention of 0.5 pcf throughout the
entire study (up to DAT 58).  At a retention rate of 0.25 pcf, the
hexavalent chromium levels dropped below EPA’s level of concern by the
last sampling interval (DAT 58) for both wood types in all samples. 

The initial levels of hexavalent chromium in the interior of the wood
(i.e., wood expressate results) were also reported to be very high.  The
levels on DAT 0 were of similar magnitude to the initial treating
solution levels (only 32% to 83% reduction of hexavalent chromium). 
Calculation of the percent reduction in hexavalent chromium on each
sampling day after treatment suggests a fairly rapid reduction of Cr+6
to Cr+3 over time. However, the study authors note that although the
percent reduction appears to be fairly rapid, the absolute value of Cr+6
remains high throughout the study (up to 58 days after treatment).  At
the end of the study, Cr+6 was still present in the Douglas fir wood at
0.85 ppm and 15.78 ppm at retention rates of 0.25 pcf and 0.50 pcf,
respectively.  In the southern pine wood, Cr+6 was still present at
72.83 ppm and 134.33 ppm at retention rates of 0.25 pcf and 0.50 pcf,
respectively.  

Examination of the borings using chromotropic acid, which detects the
presence or absence of hexavalent chromium at levels (15 ppm, further
support the study authors’ suggestion of the importance of considering
the absolute amount of Cr+6 found in the interior of the wood, and not
just the percent reduction.  For southern pine wood, all samples were
found to contain at least 15 ppm Cr+6 for the entire study.  For Douglas
fir wood, the number of samples containing at least 15 ppm of Cr+6
decreased over the course of the study, but still remained high in
certain samples.  

Several limitations have been noted in this study.  The limitations of
this study that would tend to under estimate the residues of Cr+6
include no recovery samples were reported and there were insufficient
number of passes with the cloth wipes to establish equilibrium or
maximum residues to mimic human exposure from contacting treated wood.  
On the other hand, the cloth wipe methodology without a hand transfer
reduction factor tends to overestimate the amount of residues available
for human exposure.  These data provided in this report are useful as a
range finder to determine dermal exposure to ACC treated wood.  A more
refined study would be necessary to accurately determine the amount of
Cr+6 available for human exposure.  EPA will develop a separate risk
assessment to determine potential dermal risks.

1.0  INTRODUCTION

	The purpose of this study was to examine the potential dermal exposures
to treated wood associated with use of Acid Copper Chromate (ACC) as a
wood preservative.  In particular, the goals of the study were to
examine the changes in dislodgeable hexavalent chromium residues and the
extent of reduction of hexavalent chromium over time.  The experiment
was conducted under typical, commercial conditions.

Citation 	

Author:			Robert Inwards

Title:               			“Osmose ACC 50% Wood Preservative: 
Determination of

				Hexavalent Chromium Residues In and On Wood Following

				Treatment with Acid Copper Chromate”

Report Date:			September 13, 2005

Performing Laboratory:	Osmose Holdings, Inc.

				980 Ellicott Street

				Buffalo, NY 14209

Identifying Codes:		Report #:  ACC-2005-001

				MRID 466447-01

	

Sponsor:			Osmose, Inc.

				980 Ellicott Street

				Buffalo, NY 14209

	The study included the signed and dated Good Laboratory Practices (GLP)
and Data Confidentiality statements. A Quality Assurance statement was
not provided. The study sponsor waived claims of confidentiality within
the scope of FIFRA Section 10(d) (1) (A), (B), or (C).  The study
sponsor and author stated that the study was conducted under EPA Good
Laboratory Practice Standards (40 CFR part 160), with six exceptions. 
These exceptions were noted in the study report.  None of these GLP
deviations are believed to compromise the scientific integrity of the
study.

2.0  TEST MATERIALS

2.1  Treatment Solution

The application process used in this study for treating wood with ACC
was taken from the following label:  Osmose ACC 50% Wood Preservative
(EPA Reg. No. 3008-60).  This product was not used as the test material,
however, since it is not currently produced or available.  An equivalent
test material was prepared using the following products:  (1) cupric
oxide (EPA Reg. No. 65345-1; 98.6% ai) and (2) Osmose chromic acid (EPA
Reg. No. 3008-78; 99.7% ai).  The treatment solution was reported to be
identical to a diluted version of the Osmose ACC 50% registered product
and was formulated according to Standard P5-05 of the American
Wood-Preservers’ Association (AWPA).  

	Six separate batches of ACC treating solution were prepared.  The
initial batch contained 600 pounds (approximately 64 gallons) of test
material and the remaining five batches contained 55 pounds.  The study
report provided the following information on the production process for
the 600 pound batch and stated that the smaller batches were prepared in
a similar way with adjustments for the smaller size.

218 pounds chromic acid were added to 295 pounds (~35 gallons) of water
at room temperature in a 55 gallon high density polyethylene (HDPE) open
head drum during agitation provided by a Neptune air motor which drives
a Neptune marine propeller and shaft.

Agitation was continued for at least 30 minutes to ensure formulation of
the solution.

Cupric acid (87 pounds) was added slowly to the solution while
monitoring the temperature (desired reaction temperature of 150oF or
65.6oC) and maintaining agitation.

After the cupric acid was fully added, the agitation continued for a
minimum of 2 hours after which the product was allowed to sit for 12
hours undisturbed. 

The liquid portion was removed, using a drum pump, and stored in another
55-gallon HDPE drum.  Undissolved solids were left in the bottom of the
drum since they occur in the normal commercial process and are typically
filtered out in the manufacturing process.

The liquid product was analyzed by X-ray spectroscopy for chromium
(expressed as CrO3) and copper (expressed as CuO) to confirm compliance
with the AWPA Standard P5-05.  

The resulting product was used to prepare and replenish treatment
solutions.

The results of the analysis of the formulated test material are provided
in Table 1.  The overall average concentration for the active
ingredients was reported to be 46.8%, with CrO3 comprising 71.3% and CuO
comprising 28.7%.

Table 1.  Summary of Results of Test Material Analysis

Batch	Pounds	Analysis (% by weight)	% of total (a)

CrO3	CuO	Total

CrO3+ CuO 	CrO3	CuO

1	600	33.2%	13.3%	46.5%	71.3%	28.7%

2	55	33.6%	13.7%	47.3%	71.0%	29.0%

3	55	33.5%	13.6%	47.1%	71.1%	28.9%

4	55	33.7%	13.7%	47.4%	71.1%	28.9%

5	55	34.0%	13.8%	47.8%	71.1%	28.9%

6	55	33.9%	13.8%	47.7%	71.1%	28.9%

Weighted averages	33.4%	13.5%	46.8%	71.3%	28.7%

%of total for CrO3 = % by weight (e.g., 33.4%) / % by weight total
(e.g., 46.8%)

The study report noted that the total percent active ingredient (46.8%)
was lower than that indicated on the Osmose ACC 50% Wood Preservative
label (49.53%), but that the relative proportion of the two active
ingredients was the same as on the product label.  The report indicated
that the amount of concentrate added to water to form the test solution
was adjusted to account for the slight difference.  

	2.2  Lumber

In commercial settings, lumber to be treated (typically 2” x 6” x
8’ pieces) is dead stacked (i.e., no space between layers) and metal
banded into units, which are 8 pieces wide and 16 pieces high.  Each
unit is treated once and maintained as a unit through the drying,
storage and shipment processes.  

	The lumber chosen for this study included southern pine and
Douglas-fir. Table 2 provides the characteristics of the lumber chosen.

Table 2.  Summary of characteristics of the lumber

Lumber type	# Units Treated	Size of pieces	Stacking	Lumber grade

Flat sawna 

Southern pine	2	2” x 6” x 8	8 pieces wide and 16 rows tall	No. 2
KD19b

Flat sawna 

Incisedc Douglas fir	4 ½ units

8 pieces wide by 8 rows tall	SEL. STR. S-GRNd

Flat sawn = sawn parallel to the pith (or the small, soft core occurring
near the center of a tree trunk, branch, twig, or log) and approximately
tangent to the growth rings.

No. 2 = Lumber recommended for most general construction uses where
moderately high design values are required; allows well-spaced knots of
any quality.  KD19 = Lumber that is kiln-dried to 19% moisture content.

Incised = small slits are made on the surface of the wood.

SEL. STR. = Select Structural: Dimension lumber of this quality is
limited in characteristics that affect strength and stiffness values.
This grade is recommended for use in applications where both high
strength and stiffness values and good appearance may be required. 
S-GRN = moisture content of greater than 19%.

The lumber was received in November 2004 and stored outdoors and
uncovered for about 2 months prior to treatment.  The study report
states that this is typical procedure in commercial practice.

3.0  STUDY DESIGN

	According to the GLP Statement, the study does not have an approved
written protocol.  The design and analytical methods are described
below.  

3.1  Treatment Procedure

		3.1.1  Pretreatment Handling and Preparation

	The units were taken indoors and sloped end to end at a minimum of 3
degrees for at least 3 days prior to treating to allow for temperature
rise and drainage of moisture.  The units were restacked on different
pallets for handling and treating processes. 

		3.1.2  Treatment of Lumber

	The treatment of the lumber was performed at a reduced scale treatment
plant with similar configurations as a commercial facility.  The plant
was located in Buffalo, New York and treatment took place on February 28
and March 1, 2005.  A reduced scale treatment plant was used because ACC
is currently not commercially used. The plant consisted of a 5 foot
diameter 8 foot long carbon steel treating cylinder.  This cylinder was
manufactured by shortening a commercial cylinder.  Also included were a
commercial SIHI vacuum pump and a Grundfos pressure pump.  All valves,
sensors and relays were configured the same as a commercial plant.  In
addition, carbon steel piping and commercial process control software
were also used.  Since the operation was on a small scale, the chemicals
were measured and added manually.  

	The charge (or treatment batch) consisted of one full unit of dead
stacked 2” x 6” x 8” lumber.  The ACC concentrate was added to
water to achieve the required concentration for the treating solution
(about 1 or 2%) to reach a desired retention of 0.25 to 0.50 pounds per
cubic feet (pcf).  The treating solutions were analyzed for pH, the
active ingredients (CrO3 and CuO), and hexavalent chromium (Cr+6).  The
study report noted that the pH of the treating solution was found to be
higher than the recommended pH in the AWPA standard (for ACC: 2.0-3.9)
and, therefore, glacial acetic acid was added, as permitted by the
standard, to adjust the pH downward.  Table 3 provides the results of
the pH and active ingredient analysis.

Table 3.  Summary of the Analysis of the Treatment Solutions

Wood species	Target retention (pcf)	Percent active ingredient in ACC
concentratea	Percent active ingredients in treating solution (total %)b
Solution pH prior to wood treatmentc	Cr(VI) (μg/gm)

CrO3	CuO

	Southern pine	0.25	71.4	28.6	0.99	3.23	3231

	0.50	71.8	28.2	2.12	2.83	6882

Douglas fir	0.25	71.6	28.4	0.99	3.27d	3418

	0.50	71.8	28.2	2.14	2.80	7404

According to standard:  CuO = 28.0 – 31.8%; CrO3 = 63.3 – 68.2%.

According to study report:  1% or 2%.

According to standard:  2.0-3.9.

pH of solution after treatment

	Two different treatment schedules were used for the two types of lumber
to be treated.  For each, the treatment solution was drawn into the
cylinder by an initial vacuum.  The study report noted that Douglas fir
is much more difficult to treat; therefore, that type of lumber was
subjected to full cell treatment, which has a longer initial vacuum
period and a longer pressure period.

	Douglas fir:  Full Cell Treatment

Initial vacuum of ≥ 26 inches Hg (≥ 660.4 mmHg) for 40 minutes

Fill under vacuum

Press at ≥ 130 psig (pounds per square inch gauge) to a gauge
retention of 0.22 pcf (or 0.44 pcf for the higher retention)

Pressure release over 5 minutes 

Empty cylinder

Final vacuum at ≥ 22 inches Hg (558.8 mmHg) for 5 minutes 

Southern pine:  Modified Full Cell Treatment

Initial vacuum of ≥ 17 inches Hg (≥ 431.8 mmHg) for 5 minutes

Fill under vacuum

Press at ≥ 130 psig to a gross gauge retention of 0.30 pcf (or 0.60
pcf for the higher retention)

Pressure release over 10 minutes to 15 psig

Relieve pressure and empty cylinder

Final vacuum at ≥ 22 inches Hg (558.8 mmHg) for ≤ 40 minutes to
reach a target of 0.22 pcf net gauge retention (or 0.44 pcf for the
higher retention)

After treatment, the units were moved to a sealed concrete drip pad and
sloped at a minimum of 3 degrees until visual drippage ceased.  The
entire treatment cycle took about 3 hours.  

3.1.3  Post-Treatment Temperature Monitoring

	After treatment and once dripping ended, the units were transferred to
an unheated interior alleyway for storage temporarily until the weather
allowed for transport to an outside storage location for long-term
exposure.  The indoor storage time did not exceed 3 days and periodic
temperature checks indicated that the air temperature did not exceed
43oF (6.1oC).  

	During outdoor storage, the units had individual drip/runoff
containment.  The temperature was monitored using a DeltaTRAK FlashLink
Data Logger Model No. 20202, which was placed under protective cover on
the top of a treated unit of lumber.  In addition, a thermocouple
attached to the data logger was placed in the interior of the unit at
least 2 feet from the end to monitor the temperature inside the unit. 
Temperatures were monitored every 30 minutes and ranged from 8 to 85oF
(-13 to 29.4oC) on the outside of the unit and from 23 to 77oF (-5 to
25oC) in the interior of the unit.  Over the course of the sampling
intervals, temperatures appeared to decrease at first, with a gradual
warming trend up until the end of the study.  Appendix A presents the
daily minimum, maximum, and average temperatures for external (i.e.,
ambient) and internal (i.e., stacked wood) recordings.

	Ambient conditions recorded at the closest NOAA reporting station
indicated that the temperatures recorded at the test site during the
monitoring period were slightly below normal.  These temperatures ranged
from 9 to 77oF (-12.8 to 25oC).  Precipitation over the two months of
the study period totaled 5.88 inches.  The study report indicated this
was close to normal.  

The monitoring period (March 3 to April 28, 2005) included both cool and
warm temperatures based on ambient temperature and temperatures on the
surface of the units, however, the study report states that the
temperature on the inside of the stack fluctuated less than the outside
temperatures, due to the insulating nature of the stack.  

4.0  SAMPLING

4.1  Post-treatment Sampling 

	Three types of samples were taken post-treatment:  

wipe samples were taken from the surface of boards in each unit
immediately after treatment and at certain intervals after treatment, 

liquid samples were extracted from cross sections cut from interior
pieces of lumber to determine the reduction of chromium in the interior
of the board, and

borings were taken for confirmation of penetration and retention
immediately after treatment and for qualitative determination of the
presence of hexavalent chromium at certain sampling intervals
post-treatment.

According to the study report, wipe, boring and wood expressate samples
were taken on DAT (days after treatment) 0, 3, 9, 23, 36, and 58.  

Sampling was conducted using the following procedure:

At the sampling interval, the top layers of eight 2” x 6” pieces
were removed.

The next layer of eight 2” x 6” pieces exposed was used for
sampling.

Sampling occurred on the inner four pieces in this layer (four replicate
samples) and included: 

a 75.4 in2 section used for wipe sampling, and

a 1” x 1” block cut (1” x 1” x ~1.5”) for the expressate
sampling.

The areas for sampling on each piece were independent of one another and
were at least 4 inches from each end.

At certain sampling intervals, borings (to a depth of 1 inch) were
removed from the end of each piece.

At the end of sampling, the top layer of 2 x 6 pieces was replaced.  At
the next sampling interval, the top layers were removed to reveal a new
level of 2 x 6 pieces for sampling.

4.2  Core Boring to Confirm Penetration and Retention

A core boring was removed from the edge of each of 20 pieces from the
sides of each unit within 4 hours of treatment.  This core was used to
evaluate the preservative penetration and retention to ensure compliance
with the AWPA Use Category System Section 6 for Sawn Products.  The
study report states that Chrome Azurol, a copper sensitive indicator,
was used to detect the depth of penetration according to AWPA Standard
A3-04, Method 2 (“Method for determining penetration of
copper-containing preservatives”).  However, it appears that this
standard has been replaced by Standard A3-05, which is the standard
provided in the Appendix of the study report.  The wood borings were
also analyzed according to AWPA Standard A9 (“Standard Method for
Analysis of Treated Wood and Treating Solutions by X-ray
Spectroscopy”) for the active ingredients.  At certain sampling
intervals, borings (to a depth of 1 inch) were removed from the end of
each piece and evaluated using Method 11 of the AWPA Standard A3-05
(“Method for Determination of the Presence of Hexavalent Chromium in
Treated Wood”).

	4.3 Wipe Sampling

	The following procedure was followed to conduct the wipe sampling:

Personnel wore powder free latex gloves which were changed as necessary.

A polyester cloth wipe (4.5 in2) was weighed and moistened with
deionized water to double its weight.  It was squeezed and worked to
uniformly distribute the water throughout the wipe.  

The wipe was attached to a 1.1 kg steel block (covered in Parafilm®)
using heavy duty rubber bands and pulled across a 75.4 in2 area of the
wood five times, rotated 90o, and pulled across another five times.

The wipe was removed and placed in a labeled four ounce glass jar and
immediately given to Analytical Services for extraction and analysis for
hexavalent chromium.

Before the next wipe sample was taken, the Parafilm® and rubber bands
were replaced.

4.4  Expressate Samples to Determine Reduction of Chromium in the
Interior of the Board

	A 1 x 1 x 1.5 inch sample of wood was removed from the center of the
board.  This block of wood was subjected to pressure in a pelletizer and
the liquid expressed was collected and analyzed.  Four replicate samples
were taken at each sampling time.

5.0  METHODS

5.1  Analytical Methods

	Determination of the Active Ingredients in the Test Material, Treatment
Solution, and Treated Wood:  The test material (ACC concentrate),
treatment solution, and treated wood were analyzed for total chromium
(CrO3) and total copper (CuO) by X-ray spectroscopy, following the AWPA
Standard A9. 

	Determination of Hexavalent Chromium in the Treatment Solution and
Expressate samples:  The treatment solution and expressate samples were
analyzed for total hexavalent chromium using the
diphenylcarbazide-UV/Vis spectroscopy method (Osmose SOP QC7-K/0).  

	Determination of Hexavalent Chromium in the Wipe Samples:  The wipe
samples were analyzed using the diphenylcarbazide-UV/Vis spectroscopy
method (Osmose SOP QC7-N/0).

	Determination of Hexavalent Chromium in Bore Samples Using Chromotropic
Acid:  The presence of the hexavalent chromium in wood boring samples
was made using the chromotropic acid complexation method (AWPA Standard
A3-Method 11).  This industry standard method confirms if Cr+6 is
present in the boring at level of 15 ppm.

5.2  Quality Control Samples

It was stated in the study report that the core boring samples were
performed to provide quality control as to the penetration and retention
of the pressure treatment (see results in Section 6.1).  

5.2.1  Method Validation and Storage Stability

	The methods used in this study were mostly published AWPA Standard
Methods.  However, the performing laboratory did not provide method
validation information for these methods.  Osmose Standard Operating
Procedures (SOPs) were used to determine hexavalent chromium in the
treatment solution, the wipe samples and the wood expressate samples. 
No information was provided on the method efficiency or the limit of
quantification of these methods either.  All methods and SOPs were
provided in the Appendices to the study report.  

		5.2.2	Storage Stability

	Storage stability studies were not mentioned in the study report;
however, the wipe, expressate, and chromotropic acid boring sample
analyses were performed on the same day the samples were taken (except
for four expressate samples which were stored frozen 5 days prior to
analysis).  The analysis of the borings for quality control purposes
(penetration and retention) were conducted within a few days of
sampling.

5.2.3  Concurrent Laboratory Recoveries

	Concurrent laboratory recoveries were not mentioned in the study
report.  A review of the methods and SOPs provided in the Appendices
revealed mention of concurrent laboratory recovery samples in the method
for analysis of the wipe samples (Osmose SOP QC7-N/0).  The results of
these samples were not provided in the study report.

5.2.4  Field Recoveries

	Field fortification samples were not mentioned in the study report. 

5.2.5  Blank Controls

	Blank controls were not mentioned in the study report.  A review of the
methods and SOPs provided in the Appendices revealed mention of blank
control samples in the method for analysis of the wipe samples (Osmose
SOP QC7-N/0).  The results of these samples were not provided in the
study report.

6.0  RESULTS

6.1 Results of Core Boring Sample Analysis (Quality Control)

The study report states that all bore samples taken immediately after
treatment pass the AWPA requirements for penetration (AWPA Standard
M2-01 Section 4).  According to the AWPA, the penetration for southern
pine must be 2.5 inches or 85% of the sapwood length, with 80% of the
borings meeting that requirement.  The penetration for Douglas fir must
be 0.4 inches or 90% of the sapwood depth, with 90% of the borings
meeting that requirement.  Appendix 10 of the study report provides the
pass/fail evaluations.  

	The study report states that the results indicate that the retention
treatments meet the requirements of the AWPA Standard.  At target
retentions of 0.25 and 0.50 pcf, the required minimums for CrO3 are
0.136 and 0.273 pcf, respectively, and are 0.065 and 0.127 pcf for CuO,
respectively.  The measured retention data are not provided for each
sample; only averages are reported in the study report and are provided
below in Table 4.

The combined results of the penetration and retention tests are reported
to confirm that the treatment procedures met the commercial
requirements.  Therefore, the authors state that the units treated can
be used to examine the changes in dislodgeable Cr+6 residues over time
and the extent of reduction of hexavalent chromium over time.  

Table 4.  Summary of Average Retention

Wood species	Target Retention (pcf)	Average Assayed Retention (pcf)

CrO3	CuO	Total 

Southern Pine	0.25	0.180	0.095	0.275

	0.50	0.392	0.172	0.564

Douglas Fir	0.25	0.156	0.074	0.230

	0.50	0.318	0.132	0.450

 

6.2  Residues of Hexavalent Chromium on the Surface of the Boards

	Table 5 provides a summary of the wipe sample residues.  The day after
treatment (DAT) 0 values were reported to all be high (averages of 10 to
30 μg/cm2) and to have no significant trend among wood type or target
retention. The high values at DAT 0 were reported to be a result of the
treated surface having unabsorbed treatment solution immediately after
treatment. The study report states that the DAT 0 results indicate that
there is no correlation between the treatment rate and the initial level
of dislodgeable hexavalent chromium.  Appendix B provides individual
sampling results.

	A regression analysis was performed (by EPA) using the data points for
each retention and each wood species using the results from 3, 9, 23,
36, and 58 DAT.  The residues for DAT 0 were excluded because of the
unabsorbed treatment solution and the fact that the wood would remain on
the drip pad at the facility while wet.  Table 6 provides the daily
predicted residues over time.  The coefficient of determination (R2) was
higher, and therefore a better predictor, for the lower ACC retention
(i.e., 0.25 pcf) then the R2 for the higher retention (i.e., 0.5 pcf). 
The R2 for the 0.25 pcf retention is 0.67 for Southern Pine and 0.80 for
Douglas Fir.  The R2 for the 0.5 pcf retention is 0.36 for Southern Pine
and 0.02 for Douglas Fir.

	The predicted DAT for residue levels to reach the Cr+6 level-of-concern
of 0.009 μg/cm2 for Southern Pine at a retention of 0.25 pcf is 45 days
and 100 days at a retention of 0.5 pcf.  For Douglas Fir, Cr+6 reduces
to 0.009 μg/cm2  at 36 DAT at a retention of 0.25 pcf and not until 197
DAT at a retention of 0.5 pcf.

Table 5.  Levels of Hexavalent Chromium on the Surface of the Wood 

(as determined by wipe samples)

Retention (pcf)	Hexavalent Chromium found in Wipe Samples (average
µg/cm2 ± standard error)

	DAT 0	DAT 3	DAT 9	DAT 23	DAT 36	DAT 58

Douglas fir

0.25	14.028 ± 0.800	0.0681 ± 0.0089	0.0809 ± 0.0353	0.0193 ± 0.0069
0.0105 ± 0.0017	0.0029 ± 0.0008

0.50	16.198 ± 3.532	0.0352 ± 0.0012	0.0108 ± 0.0018	0.1193 ± 0.0153
0.1050 ± 0.0253	0.0111 ± 0.0038

Southern pine

0.25	10.164 ± 2.684	0.1104 ± 0.0278	0.0477 ± 0.0108	0.0964 ± 0.0306
0.0123 ± 0.0042	0.0048 ± 0.0005

0.50	30.173 ± 7.527	0.1361 ± 0.0435	0.1699 ± 0.0105	0.1338 ± 0.0190
0.0809 ± 0.0332	0.0305 ± 0.0076

Table 6.  Predicted Daily Dislodgeable Residues of Cr+6 For ACC Cloth
Wipes. 

DAT	SP @ 0.25 pcf	SP @ 0.5 pcf	DF @ 0.25 pcf	DF @ 0.5 pcf

1	0.106	0.161	0.075	0.040

2	0.100	0.157	0.071	0.039

3	0.095	0.152	0.066	0.039

4	0.090	0.148	0.063	0.039

5	0.085	0.144	0.059	0.038

6	0.080	0.140	0.056	0.038

7	0.076	0.136	0.052	0.038

8	0.072	0.132	0.049	0.038

9	0.068	0.128	0.047	0.037

10	0.064	0.125	0.044	0.037

11	0.061	0.121	0.041	0.037

12	0.058	0.118	0.039	0.037

13	0.055	0.114	0.037	0.036

14	0.052	0.111	0.035	0.036

15	0.049	0.108	0.033	0.036

16	0.046	0.105	0.031	0.035

17	0.044	0.102	0.029	0.035

18	0.042	0.099	0.027	0.035

19	0.039	0.096	0.026	0.035

20	0.037	0.094	0.024	0.034

21	0.035	0.091	0.023	0.034

22	0.033	0.088	0.022	0.034

23	0.032	0.086	0.020	0.034

24	0.030	0.083	0.019	0.033

25	0.028	0.081	0.018	0.033

26	0.027	0.079	0.017	0.033

27	0.025	0.077	0.016	0.033

28	0.024	0.074	0.015	0.032

29	0.023	0.072	0.014	0.032

30	0.022	0.070	0.013	0.032

31	0.020	0.068	0.013	0.032

32	0.019	0.066	0.012	0.032

33	0.018	0.065	0.011	0.031

34	0.017	0.063	0.011	0.031

35	0.016	0.061	0.010	0.031

36	0.015	0.059	0.009	0.031

37	0.015	0.058	NA	0.030

38	0.014	0.056	NA	0.030

39	0.013	0.054	NA	0.030

40	0.012	0.053	NA	0.030

41	0.012	0.051	NA	0.030

42	0.011	0.050	NA	0.029

43	0.011	0.048	NA	0.029

44	0.010	0.047	NA	0.029

45	0.009	0.046	NA	0.029

46	NA	0.044	NA	0.028

47	NA	0.043	NA	0.028

48	NA	0.042	NA	0.028

49	NA	0.041	NA	0.028

50	NA	0.040	NA	0.028

51	NA	0.039	NA	0.027

52	NA	0.037	NA	0.027

53	NA	0.036	NA	0.027

54	NA	0.035	NA	0.027

55	NA	0.034	NA	0.027

56	NA	0.033	NA	0.026

57	NA	0.032	NA	0.026

58	NA	0.032	NA	0.026

100	NA	0.009	NA	0.019

197	NA	NA	NA	0.009

NA – not applicable, predicted values below the level of concern.

Predicted Residue = exp(intercept + slope * Day)

Where:  

Wood @ retention (pcf)	intercept	Slope	coefficient of determination (R2)

Southern Pine @ 0.25 pcf	-2.19	-0.05	0.67

Southern Pine @ 0.5 pcf	-1.80	-0.03	0.36

Douglas-Fir @ 0.25 pcf	-2.53	-0.06	0.80

Douglas-Fir @ 0.5 pcf	-3.22	-0.01	0.02

	6.3  Residues of Hexavalent Chromium in the Interior of the Wood

	The levels of hexavalent chromium in the interior of the wood were
assessed by analyzing the expressate of the wood.  The study report
states that the initial levels on DAT 0 are very high and are of similar
magnitude to the treating solution levels. As the number of days after
treatment increases, the levels in the expressate decrease.  The percent
reduction in hexavalent chromium on each sampling day after treatment
was determined using the initial levels of treating solution.  Table 7
provides a summary of the levels of hexavalent chromium and the average
percent reduction over time.  Figure 1 depicts the fairly rapid
reduction of Cr+6 to Cr+3 over time.   However, the study authors do
note that although the percent reduction appears to be fairly rapid, the
absolute value of Cr+6 remains high throughout the study (up to 58 days
after treatment).  At the end of the study, Cr+6 was still present in
the Douglas fir wood at 0.85 ppm and 16 ppm at retention rates of 0.25
pcf and 0.50 pcf, respectively.  In the Southern pine wood, Cr+6 was
still present at 73 ppm and 134 ppm at retention rates of 0.25 pcf and
0.50 pcf, respectively.  Appendix B provides individual sampling
results.

Table 7.  Levels of Hexavalent Chromium in the Interior of the Wood 

(as determined by expressate samples)

Retention (pcf)	Initial Treatment Solution (ug/g)	Average Hexavalent
Chromium found in Expressate Liquid (µg/g, ppm)

DAT 0	DAT 3	DAT 9	DAT 23	DAT 36	DAT 58

Douglas fir

0.25	3417.98	859.6	74.62	46.43	0.41	0.17	0.85

Average Percent Reduction	74.85%	97.82%	98.64%	99.99%	100.00%	99.98%

0.50	7403.96	1292.59	699.32	44.41	39.81	21.23	15.78

Average Percent Reduction	82.54%	90.55%	99.40%	99.46%	99.71%	99.79%

Southern pine

0.25	3230.73	1792.73	1005.83	682.64	258.76	178.71	72.83

Average Percent Reduction	44.51%	68.87%	78.87%	91.99%	94.47%	97.75%

0.50	6882.42	4708.51	1854.91	1320.28	630.38	359.88	134.33

Average Percent Reduction	31.59%	73.05%	80.82%	90.84%	94.77%	98.05%

 

	Examination of the borings using chromotropic acid further supported
the study authors’ suggestion of the importance of considering the
absolute amount of Cr+6 found in the interior of the wood, and not just
the percent reduction.  Figure 2 shows the percent of samples found to
contain ≥15 ppm Cr+6 over the course of the study.  For southern pine
wood, all samples were found to contain at least this amount for the
entire study.  For Douglas fir wood, the number of samples containing
this amount of Cr+6 decreased over the course of the study (0% by DAT 58
for 0.25 pcf and 50% by DAT 58 for 0.5 pcf), but still remained high in
certain samples.  

 

7.0  CONCULSION

The study report states that the data from this study do not suggest
that holding time can adequately predict the level of dislodgeable Cr+6
on the surface of wood that has been treated with ACC.  The internal
levels of Cr+6 are reported to be highly variable, even among individual
boards treated at the same time in one unit.  This high variability does
not allow for an estimation of the rate of reduction.  Additionally, the
study report states that there is no dependent relationship between the
concentrations in expressates and external residues; both internal and
external Cr+6 reduce to Cr+3 over time independently.

	The temperature range measured outside of the wood units and in the
interior of the wood units included both cool and warm weather
conditions over the course of the study.  Regardless of the temperature,
the predicted wood surface residues do not reach 0.009 μg/cm2 until 36
to 197 days after treatment depending on the wood species and retention
(Note:  The R2 is low for the higher retention).  The study report also
states that the treated wood will retain a significant amount of
unreduced hexavalent chromium in the interior of the wood over time.  

	EPA notes the following issues in its review of this study.

The protocol was not submitted to the EPA prior to the initiation of the
study.  

The study did not control the temperature of the wood while in storage. 
Instead, the study was conducted in late winter/early spring in Buffalo,
NY.  The reduction of Cr+6 to Cr+3 is temperature and time dependant. 
Reduction is slower at colder temperatures.  Once frozen, reduction is
thought to cease.  Average daily temperatures for some days were at or
below 32 F (for 24 of 57 days).  The effect would be to stop reduction
of Cr+6 on those days.

The study only monitored residues determined by cloth wipes.  The wipe
studies conducted previously to support CCA treated wood also included
hand wipes to determine the relationship between the amounts of residues
dislodged by a moistened hand versus a moistened cloth wipe.  Based on
the CCA data, the hand dislodges less than the cloth wipe.  A hand
transfer reduction factor (TRF) of ~18% was determined for CCA.  The TRF
for CCA is not believed to be the same for ACC treated wood because of
the differences in the amount of Cr+6 in the wood.  The effect of only
having cloth wipe samples overestimates the amount of Cr+6 available for
human exposure.

The cloth wipes included a total of 10 passes on the treated wood.  The
CPSC wood wipe protocol recommends a total of 20 passes.  The effect of
only 10 passes is that an equilibrium or maximum residue was not
achieved.  The weight used in the study (1.1 kg) is the standard used in
the CPSC protocol.  The effect of an insufficient number of passes/wipes
per sample would underestimate the amount of Cr+6 available for human
exposure.

The coefficients of determinations (R2) for the predicted daily
dislodgeable residues are 0.67 and 0.80 for the retention of 0.25 pcf. 
However, the R2 at the retention of 0.5 pcf is low (i.e., 0.36 and
0.02).  A study with more sampling intervals and controlled temperature
would be needed to determine if the reduction to Cr+3 is more
predictable.

Control samples were not mentioned in the study report for the wipe
samples; however, the SOP provided in the Appendix did mention the
inclusion of blank wipes.  If these samples were included, the results
were not provided in the study report or raw data provided in the
Appendix.  

The study report stated that the wipe samples were turned in immediately
to Analytical Services.  The study report did not mention the storage
time of the expressate samples or the borings.  However, in the raw data
table provided in the Appendix, the expressate samples collected on day
36 from the southern pine treated wood at a retention rate of 0.50 were
reported to have been sealed in a freezer bag in a freezer for 5 days
prior to analysis.  It is not clear how the other samples were kept
prior to analysis or for how long.  A storage stability study was not
provided.

Method validation information was not provided for AWPA methods followed
in the analysis of the samples.  The SOPs followed for determination of
the levels of hexavalent chromium in wood expressate and wipe samples
also did not provide information on method efficiency nor the limit of
quantification. 

Field and concurrent laboratory fortification samples and blank samples
were not reported in the study report or in the raw data table in the
Appendix.  The SOP for the wipe samples indicated a blank and fortified
wipe sample should be analyzed along with the study samples, but no
further information was provided.

No value was provided for the Douglas fir, 0.50 pcf, DAT 9 wood
expressate sample in the raw data table in the Appendix.  An explanation
for this omission was not provided.

In conclusion, the limitations of this study that would tend to under
estimate the residues of Cr+6 include no recovery samples were reported
and there were insufficient number of passes with the cloth wipes to
establish equilibrium or maximum residues to mimic human exposure from
contacting treated wood.   On the other hand, the cloth wipe methodology
without a hand transfer reduction factor tends to overestimate the
amount of residues available for human exposure.  These data provided in
this report are useful as a range finder to determine dermal exposure to
ACC treated wood.  A more refined study would be necessary to accurately
determine the amount of Cr+6 available for human exposure.  EPA will
develop a separate risk assessment to determine potential dermal risks.



Appendix A

Summary of Temperature Measurements



Temperatures throughout study period

Date	External Temperature	Internal Temperature

	Average	Maximum	Minimum	Average	Maximum	Minimum

3/3/2005	32.5	73.4	19.4	52.7	77.0	50.0

3/4/2005	25.6	34.0	18.3	46.6	50.0	43.2

3/5/2005	20.8	27.3	14.2	40.5	43.2	38.1

3/6/2005	30.4	35.4	21.9	36.7	38.1	35.4

3/7/2005	37.0	48.2	29.3	34.6	35.4	33.6

3/8/2005	17.9	29.3	12.0	32.9	33.6	32.5

3/9/2005	16.2	25.0	9.7	32.3	32.5	32.0

3/10/2005	20.4	27.3	14.5	31.8	32.0	31.8

3/11/2005	26.5	36.3	19.2	31.9	32.0	31.8

3/12/2005	26.9	35.2	17.4	31.9	32.0	31.8

3/13/2005	26.0	32.2	18.0	31.8	31.8	31.6

3/14/2005	19.0	30.2	10.8	31.7	31.8	31.6

3/15/2005	19.4	26.6	11.5	31.7	31.8	31.6

3/16/2005	23.0	31.1	16.0	31.9	32.0	31.8

3/17/2005	27.5	35.6	21.0	31.9	32.0	31.8

3/18/2005	28.3	37.8	20.8	31.8	32.0	31.8

3/19/2005	33.5	43.2	24.8	31.8	31.8	31.6

3/20/2005	35.0	40.6	32.0	31.9	32.2	31.8

3/21/2005	34.4	41.9	31.8	31.8	32.2	31.8

3/22/2005	30.6	34.5	27.0	31.7	31.8	31.6

3/23/2005	30.0	32.9	28.2	31.6	31.8	31.5

3/24/2005	33.9	44.4	29.0	31.8	32.0	31.8

3/25/2005	35.0	42.1	27.3	31.8	32.2	31.6

3/26/2005	31.9	43.5	22.6	31.7	31.8	31.6

3/27/2005	38.3	52.2	26.6	31.8	32.0	31.8

3/28/2005	43.7	50.2	40.3	32.1	32.2	32.0

3/29/2005	41.6	52.3	34.3	32.2	32.2	32.0

3/30/2005	44.4	59.2	30.7	32.0	32.2	32.0

3/31/2005	50.6	63.9	40.1	32.1	32.4	32.0

4/1/2005	42.3	50.4	37.2	32.0	32.0	32.0

4/2/2005	35.0	43.3	32.0	31.9	32.0	31.8

4/3/2005	32.4	33.3	32.0	31.8	32.0	31.8

4/4/2005	34.3	39.6	31.8	31.8	31.8	31.8

4/5/2005	41.8	57.2	30.7	32.0	32.2	31.8

4/6/2005	51.2	63.3	40.8	35.3	37.8	32.0

4/7/2005	48.1	57.4	40.1	40.6	42.6	37.9

4/8/2005	41.7	54.0	31.5	43.2	43.5	42.8

4/9/2005	43.9	62.8	30.6	43.1	43.3	42.8

4/10/2005	48.2	65.8	35.1	43.5	43.9	42.8

4/11/2005	42.9	51.6	35.4	44.5	45.0	43.7

4/12/2005	39.9	53.2	30.4	42.9	43.7	41.7

4/13/2005	41.3	55.8	26.8	41.4	42.1	40.8

4/14/2005	44.9	60.1	30.4	41.5	41.7	40.8

4/15/2005	47.4	65.5	33.6	42.5	42.8	41.7

4/16/2005	50.9	77.2	33.4	44.1	44.8	42.8

4/17/2005	51.8	73.6	36.3	46.6	47.5	44.8

4/18/2005	58.1	84.9	40.1	48.9	49.6	47.7

4/19/2005	59.5	82.9	43.2	51.9	53.2	49.8

4/20/2005	53.2	67.8	41.2	54.7	55.2	53.4

4/21/2005	47.4	65.7	33.6	53.1	54.9	50.9

4/22/2005	48.8	75.2	32.9	50.3	50.9	49.6

4/23/2005	45.8	49.3	39.9	49.5	49.8	49.1

4/24/2005	39.1	50.0	33.1	48.2	48.9	46.9

4/25/2005	38.5	41.9	35.4	45.5	46.8	44.2

4/26/2005	53.6	75.0	37.9	43.8	44.2	43.5

4/27/2005	52.9	71.1	41.5	46.8	48.7	44.1

4/28/2005	44.1	68.7	39.7	50.5	70.5	48.7

 

Appendix B

Hexavalent Chromium Individual Measurements 

from Douglas Fir Treated Wood and Southern Pine Treated Wood

Table B1.  Hexavalent Chromium Measurements for Douglas Fir Treated
Wood

Retention (pcf)	DAT	Sample number	Hexavalent Chromium on Surface of Wood
from Wipe Samples (µg/cm2)	Hexavalent Chromium in Interior of Wood from
Expressate Samples (µg/g; ppm)	Concentration of Hexavalent Chromium in
Treating Solution

(µg/g; ppm)	Reduction (%) of Hexavalent Chromium	Chromotropic Acid
Indication (Cr+6 detected at or above 15 ppm)

0.25	0	1	15.2451	1500.35	3417.98	56.1	N/A

2	12.8112	551.28

83.87	N/A

3	12.4925	528.34

84.54	N/A

4	15.5638	858.44

74.88	N/A

Average:	14.028	859.6

	Std Error:	0.800

	% of samples above level of concern	100%

	0.5	0	1	26.0438	1324.2	7403.96	82.11	N/A

2	9.5282	2297.28

68.97	N/A

3	15.8803	1066.54

85.6	N/A

4	13.3395	482.33

93.49	N/A

Average:	16.198	1292.59

	Std Error:	3.532

	% of samples above level of concern	100%

	0.25	3	1	0.057	144.09	3417.98	95.78	+

2	0.0493	0.1

100	+

3	0.0862	67.49

98.03	+

4	0.0798	86.79

97.46	+

Average:	0.0681	74.62

% detected:	100%

Std Error:	0.0089

	% of samples above level of concern	100%

	0.5	3	1	0.0359	312.83	7403.96	95.77	+

2	0.0382	72.71

99.02	+

3	0.0329	236.55

96.81	+

4	0.0336	2175.17

70.62	+

Average:	0.0352	699.32

% detected:	100%

Std Error:	0.0012

	% of samples above level of concern	100%

	0.25	9	1	0.1067	178.27	3417.98	94.78	+

2	0.0113	0.2

99.99	-

3	0.1679	6.74

99.8	+

4	0.0377	0.5

99.99	+

Average:	0.0809	46.43

% detected:	75%

Std Error:	0.0353

	% of samples above level of concern	100%

	0.5	9	1	0.0071	a	7403.96	a	+

2	0.0148	114.63

98.45	+

3	0.0127	4.4

99.94	+

4	0.0086	14.2

99.81	+

Average:	0.0108	44.41

% detected:	100%

Std Error:	0.0018

	% of samples above level of concern	75%

	0.25	23	1	0.0139	0.58	3417.98	99.98	-

2	0.0115	0.39

99.99	-

3	0.04	0.26

99.99	-

4	0.0119	0.39

99.99	-

Average:	0.0193	0.41

% detected:	0%

Std Error:	0.0069

	% of samples above level of concern	100%

	0.5	23	1	0.112	72.28	7403.96	99.02	+

2	0.0796	11.1

99.85	+

3	0.1495	43.74

99.41	+

4	0.1361	32.12

99.57	+

Average:	0.1193	39.81

% detected:	100%

Std Error:	0.0153

	% of samples above level of concern	100%

	0.25

0.5	36	1	0.0139	0.24	3417.98	99.99	+

2	0.0086	0.13

100	-

3	0.0127	0.2

99.99	-

4	0.0069	0.11

100	+

Average:	0.0105	0.17

% detected:	50%

Std Error:	0.0017

	% of samples above level of concern	75%

36	1	0.0652	0.19	7403.96	100	+

2	0.0716	67.56

99.09	-

3	0.1076	6.12

99.92	+

4	0.1755	11.04

99.85	+

Average:	0.1050	21.23

% detected:	75%

Std Error:	0.0253

	% of samples above level of concern	100%

	0.25	58	1	0.0017	1.07	3417.98	99.97	-

2	0.002	1.035

99.94	-

3	0.0028	0.51

99.99	-

4	0.0051	0.8

99.98	-

Average:	0.0029	0.85

% detected:	0%

Std Error:	0.0008

	% of samples above level of concern	0%

	0.5	58	1	0.0222	31.07	7403.96	99.58	+

2	0.0064	27.04

99.63	-

3	0.0097	2.44

99.97	-

4	0.0061	2.55

99.97	-

Average:	0.0111	15.78

% detected:	25%

Std Error:	0.0038

	% of samples above level of concern	50%

	a	No value provided in table in Appendix and no explanation provided
for why 

Table B2.  Hexavalent Chromium Measurements for Southern Pine Treated
Wood

Retention (pcf)	DAT	Sample number	Hexavalent Chromium on Surface of Wood
from Wipe Samples (µg/cm2)	Hexavalent Chromium in Interior of Wood from
Expressate Samples

(µg/g; ppm) 	Concentration of Hexavalent Chromium in Treating Solution

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36.45	N/A

3	7.6226	4719.3

34.34	N/A

4	37.9011	4767.74

30.73	N/A

Average:	30.173	4708.51

	Std Error:	7.527

	% of samples above level of concern	100%

	0.25	3	1	0.0709	1069.83	3230.73	66.89	+

2	0.1537	1236.24

61.73	+

3	0.0544	809.72

74.94	+

4	0.1626	907.52

71.91	+

Average:	0.1104	1005.83

% detected:	100%

Std Error:	0.0278

	% of samples above level of concern	100%

	0.5	3	1	0.0141	2251.79	6882.42	67.28	+

2	0.1387	1268.48

81.57	+

3	0.1768	1999.64

70.95	+

4	0.2149	1899.71

72.4	+

Average:	0.1361	1854.91

% detected:	100%

Std Error:	0.0435

	% of samples above level of concern	100%

	0.25	9	1	0.0571	746.9	3230.73	76.88	+

2	0.0453	725.5

77.54	+

3	0.0189	640.33

80.18	+

4	0.0693	617.83

80.88	+

Average:	0.0477	682.64

% detected:	100%

Std Error:	0.0108

	% of samples above level of concern	100%

	0.5	9	1	0.1842	1113.84	6882.42	83.82	+

2	0.1715	1727.92

74.89	+

3	0.1842	909.45

86.79	+

4	0.1397	1529.92

77.77	+

Average:	0.1699	1320.28

% detected:	100%

Std Error:	0.0105

	% of samples above level of concern	100%

	0.25	23	1	0.0828	367.05	3230.73	88.64	+

2	0.0204	241.52

92.52	+

3	0.1664	313.76

90.29	+

4	0.116	112.7

96.51	+

Average:	0.0964	258.76

% detected:	100%

Std Error:	0.0306

	% of samples above level of concern	100%

	0.5	23	1	0.1404	596.58	6882.42	91.33	+

2	0.1218	613.7

91.08	+

3	0.091	576.14

91.63	+

4	0.1819	735.09

89.32	+

Average:	0.1338	630.38

% detected:	100%

Std Error:	0.0190

	% of samples above level of concern	100%

	0.25	36	1	0.0027	153.44	3230.73	95.25	+

2	0.012	196.86

93.91	+

3	0.023	190.62

94.1	+

4	0.0115	173.91

94.62	+

Average:	0.0123	178.71

% detected:	100%

Std Error:	0.0042

	% of samples above level of concern	75%

	0.5	36	1	0.152	401.51	6882.42	94.17	+

2	0.0205	312.2

95.46	+

3	0.0284	338.73

95.08	+

4	0.1226	387.06

94.38	+

Average:	0.0809	359.88

% detected:	100%

Std Error:	0.0332

	% of samples above level of concern	100%

	0.25	58	1	0.0049	83.64	3230.73	97.41	+

2	0.0058	63.14

98.05	+

3	0.0048	56.17

98.26	+

4	0.0036	88.36

97.27	+

Average:	0.0048	72.83

% detected:	100%

Std Error:	0.0005

	% of samples above level of concern	0%

	0.5	58	1	0.0109	174.57	6882.42	97.46	+

2	0.0293	129.57

98.12	+

3	0.0342	81.88

98.81	+

4	0.0477	151.29

97.8	+

Average:	0.0305	134.33

% detected:	100%

Std Error:	0.0076

	% of samples above level of concern	100%

	

Page   PAGE  1 

Figure 1.  Percent reduction from Cr

+6

 to Cr

+3

 in the Expressate 

(as percent of initial treating solution level)

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

0

3

9

23

36

58

Days after Treatment (DAT)

% Cr

+6

 Reduction

Southern pine 0.25

Southern pine 0.5

Douglas fir 0.25

Douglas fir 0.5

Figure 2.  Percent of samples containing >=15ppm Cr

+6 

as detected in Borings using Chromotropic ACid

0%

20%

40%

60%

80%

100%

3

9

23

36

58

Days after Treatment

Percent of samples

Douglas fir 0.25

Douglas fir 0.50

Southern pine 0.25

Southern pine 0.50