HEXAVALENT CHROMIUM in Soil and Water
Colorimetric
SW-846 Method 7196A *
HEXAVAIiENT CHROMIUM in Water
Atomic Absorption, Chelation-Extraction
EPA Method 218.4
Table 1.	Summary of Contract Required Detection Limits, Holding Times, and
Preservation for Hexavalent Chromium (Cr+S)
Analytical
Parameter
Contract
Required
Detection
Limit
(CRDL)
Technical and
Contract Holding
Times a
Preservation
Hexavalent
Chromium (Cr+6)in
Water Samples
20 iag/L b
10 iag/L c
Technical: 24 hours
from collection;
Contract: 12 hours
from receipt at
laboratory
Cool to 4 °C +2 °C e
Cr+6 in Soil
Samples d
2 mg/kg
Contract: 12 hours
from receipt at
laboratory
Cool to 4 °C +2°C
*	If the colorimetric method is not suitable, EPA Method 218.4 may be
used. If EPA Method 218.4 is designated for analysis, the
diphenylcarbazide colorimetric procedure discussed in Section 2.3 of EPA
Method 218.4 may NOT be used.
a	Laboratories bidding on this analysis must be located within a 3 hour
drive from the site of sample collection.
b	20 ng/L CRDL for analysis by SW-846 Method 7196A
c	10 ng/L CRDL for analysis by EPA Method 218.4
d	Soil Samples: Follow EPA SW-846 Method 3060A (January 1995) for sample
digestion.
e	Determine initial pH of water samples.
Data Calculations and Reporting Units:
Calculate the sample results from the standard curve. Calculate soil sample
results using the equation provided in Section 7.10.1 of Method 3060A.
Report water sample results in concentration units of micrograms per liter
(ng/L). Report soil sample results in concentration units of milligrams per
kilogram (mg/kg) . Cr+6 concentrations that are less than 10 ng/L or 10 mg/kg
to 1 significant figure, and Cr+6 concentrations that are greater than or
equal to 10 ng/L or 10 mg/kg to 2 significant figures.
For rounding results, adhere to the following rules:
a)	If the number following those to be retained is less than 5, round down;
b)	If the number following those to be retained is greater than 5, round up;
or
c)	If the number following the last digit to be retained is equal to 5, round
down if the digit is even, or round up if the digit is odd.
All records of analysis and calculations must be legible and sufficient to
recalculate all sample concentrations and QC results. Include an example
calculation in the data package.
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Table 2.	Summary of Calibration Procedures for Hexavalent Chromium
Calibration Element
Frequency
Acceptance
Criteria
Corrective Action
Initial Calibration
(minimum blank + 5
points for each
analyte) (ICAL) a' b
Initially; whenever
reguired, due to
failure of ICV or CCV
r > 0.995
1.	Terminate analysis
2.	Recalibrate and verify before sample
analysis
Initial Calibration
Verification (ICV) at
midpoint of ICAL
(Separate source from
ICAL standards)
Daily, prior to
sample analysis;
immediately following
ICAL
+10% from
expected
concentration
1.	Identify and document problem
2.	Reprep ICV and reanalyze all associated
samples
3.	Recalibrate and reanalyze reprepped ICV
and all associated samples
Continuing
Calibration
Verification (CCV)
Following ICV and
before sample
analysis; after every
10 samples and end of
run
+ 10% from
expected
concentration
1.	Recalibrate and verify
2.	Reanalyze samples back to last good CCV
Calibration Blank
Verification (ICB,
CCB)
After ICV and every
CCV
< CRDL
1.	Terminate analysis
2.	Identify and document the problem
3.	Recalibrate, verify and reanalyze all
associated samples with results less than
10 times the level of contamination in the
blank.
CRDL Verification
Standard
After initial CCV/CCB
+20% from
expected
concentration
1.	Reprep and reanalyze standard
2.	Recalibrate and verify
The ICAL standards for SW-846 Method 7196A must include standard concentrations at the CRDL (20 ng/L)
through 500 ng/L.
The ICAL standards for EPA Method 218.4 must include standard concentrations at the CRDL (10 ng/L)
through 250 ng/L.
A calibration curve must be prepared with each set of samples.
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Table 3.
Summary of Internal Quality Control Procedures for Hexavalent Chromium
QC Element
Frequency
Acceptance
Criteria
Corrective Action
Laboratory
Method Blank
(MB)
One per Batch or SDG a
(1 per 20 samples
minimum)
< CRDL
1.	If lowest sample concentration is more than
10X the blank conc., no action
2.	If samples are non-detected, no action
3.	If detected sample concentrations are less
than 10X blank conc., all associated samples
must be prepared again with another method blank
and reanalyzed
Duplicate
Sample (DUP)
One per batch or SDG
(1 per 20 samples
minimum)
RPD <20% for
samples >5X
CRDL; + CRDL
for samples
<5X CRDL
1. Flag associated data with an
Matrix Spike
(MS)
One per batch or SDG
(1 per 20 samples
minimum)
+ 25% from
expected
value
1. Flag associated data with an "N"
Laboratory
Control Sample
(LCS)
One per batch or SDG
(1 per 20 samples
minimum)
+20% from
expected
concentration
1.	Terminate analysis
2.	Identify and document the problem
3.	Reanalyze all associated samples
a SDG - Sample Delivery Group - each case of field samples received; or each 20 field samples within a case;
or each 14 calendar day period during which field samples in a case are received.
Dilute and reanalyze samples with concentrations exceeding the range of the calibration curve. Results for
such reanalyses should fall within the mid-range of the calibration curve. Report results and submit
documentation for both analyses.
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