J2LCD/V E,S,™«ai protection             Office of Water (4303T)            EPA-821-R-13-006
%^Iiiiirlr1% Agency                        Washington, DC 20460                 March 2013
  Guidance for Limited Use Alternate Test Procedure Applications for
                  ASTM Method D7575 for Oil and Grease
As explained in the Federal Register notice dated March 6, 2013, EPA determined that ASTM
D7575 is a good stand-alone method for the measurement of oil and grease as defined by the
method. The method was single- and multi-lab tested following ASTM Standard Practice D2777
(Standard Practice for the Determination of Precision and Bias of Applicable Test methods of
Committee D19 on Water) and produced recoveries and precision as good as or better than EPA
Method 1664A for those matrices tested and in the range of ASTM D7575 applicability (5-200
mg/L). EPA's primary concern is that the two methods may produce different results.

Therefore, for limited use ATP applications that request consideration of ASTM D7575 as an
analytic method in place of those promulgated in 40 CFR Part 136 (e.g., EPA Method 1664A/B),
the applicant needs to submit an application form (see reference below), demonstrate that the lab
can successfully perform the method, and document comparability by performing side-by-side
(parallel) testing of the method's performance in a  clean matrix and an actual wastewater matrix.
The QC elements and the QC acceptance criteria must be specified.  EPA suggests using the
specific side by side comparison procedures recommended in the guidance document that was
originally developed when Method 1664A was promulgated as a comparison to EPA Method
413.1 (see Analytical Method Guidance for EPA Method 1664A Implementation and Use [40
CFR Part 136], EPA/821-R-00-003, February 2000). To perform and document a side-by-side
comparison of EPA Method  1664A and ASTM D7575, we suggest, at a minimum, analysis of
three replicates of each sample by each method on  any seven days over a minimum 30-day
period, for a total of 42 analyses (21 by ASTM D7575 and 21 by EPA Method 1664A). For this
side-by side comparison, the analyst should use the separately funnel liquid/liquid extraction
(LLE) procedure, not the optional SPE procedure, in Method 1664 A because of the possible
confounding of results that could occur when two variables (SPE and the solvent) are changed
simultaneously. If all six results for a given day associated with any sample are less than the
minimum level (< ML), these results should not be used in the comparison because it is
necessary to have actual measured values to test equivalency.  In the event that a test result less
than the ML is obtained, samples should be collected on an additional day (i.e., the number of
tests should be increased to provide a minimum of seven paired triplicate results for the
comparison).

We suggest testing for statistical significance using procedures for development of the root-
mean-square deviation (RMSD) as detailed below using results obtained with the EPA Method
1664A as the reference method. If the RMSD is within the acceptance limit, the results obtained
using the different methods are considered comparable. If the RMSD is not within the
acceptance limit, the difference is significant and the results are not considered comparable.

Example Calculations for Side-by-Side Comparisons

To allow you to make the calculations necessary for comparison easily, we have produced a
Microsoft Excel® spreadsheet that does all calculations  automatically after you have entered the

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necessary results.  This spreadsheet is available on EPA's website at
http://water.epa.gov/scitech/methods/cwa/update_index.cfm and is named "Oil and Grease ATP
Comparison Worksheet."  You must have Microsoft Excel 97® or a later version to run the
spreadsheet.
Example 1

Steps 1-3.  Eight sample replicates were collected on a total of seven days spaced over a
minimum of a one month period.  For the sample replicates collected on each day, three were
analyzed by EPA Method 1664A/B, three by ATP1 (for a total of 6 samples per day) and two
were used for QC. All QC tests were performed and the results of the QC tests (including the
matrix spike test) met the QC acceptance criteria in Method 1664A/B.  Results of the triplicate
analyses by each method on each day are listed in Table 1.  The yellow shading indicates the
cells where the applicant must enter data.

Step 4.  The (natural log) log-transformed results are listed in Table 2.

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               Table 1.  Example results for side-by-side study*  (units: mg/L)
Reference
Matrix =
Method =
1664A/B
Refinery


Collection
Date
1/2/2013
1/8/2013
1/17/2013
1/25/2013
1/28/2013
2/4/2013
2/7/2013
Analysis
Date
1/4/2013
1/11/2013
1/24/2013
2/1/2013
2/4/2013
2/13/2013
2/15/2013
Time Held
(Days)
2
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Alternate Test Procedure =
ATP1

Results
EPA Method 1664A/B
Rep#1
13
10
22
12
20
37
11
Rep #2
18
12
26
17
17
35
14
Rep #3
12
14
22
15
12
31
13

Units: mg/L
Alternate Test Procedure
Rep#1
13
10
22
12
20
37
11
Rep #2
18
12
26
17
17
35
14
Rep #3
12
14
22
15
12
31
13
: Data in this data set are estimations of data that could be produced in a side-by-side study and are not "real-world" data.
                             Table 2. Log-transformed results

Collection
Date
1/2/2013
1/8/2013
1/17/2013
1/25/2013
1/28/2013
2/4/2013
2/7/2013
Analysis
Date
1/4/2013
1/11/2013
1/24/2013
2/1/2013
2/4/2013
2/13/2013
2/15/2013
Time Held
(Days)
2
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Results
EPA Method 1664A/B
Rep_#1
2.56
2.30
3.09
2.48
3.00
3.61
2.40
Rep #2
2.89
2.48
3.26
2.83
2.83
3.56
2.64
Rep #3
2.48
2.64
3.09
2.71
2.48
3.43
2.56
Units: mg/L
Alternate Test Procedure
Rep_#1
2.56
2.30
3.09
2.48
3.00
3.61
2.40
Rep #2
2.89
2.48
3.26
2.83
2.83
3.56
2.64
Rep #3
2.48
2.64
3.09
2.71
2.48
3.43
2.56

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Step 5. The 14 triplicate means of the log-transformed results are listed in Table 3.


                            Table 3. Triplicate means (My)
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B
(i=1)
2.65
2.48
3.15
2.68
2.77
3.53
2.53
ATP (i=2)
2.65
2.48
3.15
2.68
2.77
3.53
2.53
Step 6. The 14 triplicate standard deviations of the log-transformed results are listed in Table 4.


                     Table 4.  Triplicate standard deviations (sy)
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B
(i=1)
0.215
0.168
0.096
0.176
0.261
0.090
0.124
ATP (i=2)
0.215
0.168
0.096
0.176
0.261
0.090
0.124
Step 7. The mean-square error is:



    MSE  =— [(0.215)2 +(0.168)2 +(0.096)2 +...+ (0.090)2 +(0.124)2] = 0.029
            14
Step 8. The method-specific means are:



    MMI=- T!  Mi, =-[2.65 + 2.48 + 3.15 + 2.68 + 2.77 + 3.53+ 2.53] = 2.83
           7,ic,
7
    Similarly, MM2 = 2.83.

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   Msl =-[2.65+ 2.65] = 2.65


   Similarly, MS2 = 2.48, MS3= 3.15, MS4 = 2.68, MS5 = 2.77, MS6 = 3.53, and MS7= 2.53.


   Mo =-[2.83 + 3.32] = -  ^[2.96+ 2.71+ 3.38+ 2.96 + 3.00 + 3.69 + 2.81] = 2.83
         2              7
Step 9. TheRMSDis:


    RMSD = -^[(2.65 - 2.65)2 + (2.48 - 2.48)2 +... + (2.53 - 2.53)2] = 0.000
Step 10. TheRMSDMAxis:
                 J2 * 0 029
                 	:	* 2.36 =0.215
Step 11. The compared result is:

   Because the RMSD is < than the RMSD MAX, the difference between the two methods is
   not significant.

Based on the results shown above, Method ATP1 is comparable to Method 1664A/B over the
course of 9 days in a Refinery matrix.

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Example 2

Eight sample replicates were collected on a total of seven days spaced over a minimum of a one
month period.  For the sample replicates collected on each day, three were analyzed by EPA
Method 1664A/B, three by ATP2 and two were used for QC. Results  of the triplicate analyses
are listed in Table 5.

Step 4.  The log-transformed results are listed in Table 6.

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                     Table 5.  Example results for side-by-side study*
 Matrix =
Method =
1664A/B
Meat Packer
                                           Alternate Test Procedure =
ATP2

Collection
Date
1/2/2013
1/8/2013
1/17/2013
1/25/2013
1/28/2013
2/4/2013
2/7/2013
Analysis
Date
1/4/2013
1/11/2013
1/24/2013
2/1/2013
2/4/2013
2/13/2013
2/15/2013
Time Held
(Days)
2
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Results
EPA Method 1664A/B
Rep#1
13
10
22
12
20
37
11
Rep #2
18
12
26
17
17
35
14
Rep #3
12
14
22
15
12
31
13
Units: mg/L
Alternate Test Procedure
Rep#1
23
21
41
26
26
52
21
Rep #2
28
19
36
27
23
48
20
Rep #3
29
17
35
24
27
40
25
* Data in this data set are estimations of data that could be produced in a side-by-side study and are not "real-world" data.
                             Table 6.  Log-transformed results

Collection
Date
1/2/2013
1/8/2013
1/17/2013
1/25/2013
1/28/2013
2/4/2013
2/7/2013
Analysis
Date
1/4/2013
1/11/2013
1/24/2013
2/1/2013
2/4/2013
2/13/2013
2/15/2013
Time Held
(Days)
2
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Results
EPA Method 1664A/B
Rep_#1
2.56
2.30
3.09
2.48
3.00
3.61
2.40
Rep #2
2.89
2.48
3.26
2.83
2.83
3.56
2.64
Rep #3
2.48
2.64
3.09
2.71
2.48
3.43
2.56
Units: mg/L
Alternate Test Procedure
Rep_#1
3.14
3.04
3.71
3.26
3.26
3.95
3.04
Rep #2
3.33
2.94
3.58
3.30
3.14
3.87
3.00
Rep #3
3.37
2.83
3.56
3.18
3.30
3.69
3.22

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Step 5. The 14 triplicate means of the log-transformed results are listed in Table 7.


                            Table 7. Triplicate means (My)
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B
(i=1)
2.65
2.48
3.15
2.68
2.77
3.53
2.53
ATP (i=2)
3.28
2.94
3.62
3.24
3.23
3.84
3.09
Step 6. The 14 triplicate standard deviations of the log-transformed results are listed in Table


          Table 8. Triplicate deviations (sy) of the log-transformed results
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B
(i=1)
0.215
0.168
0.096
0.176
0.261
0.090
0.124
ATP (i=2)
0.125
0.106
0.084
0.060
0.084
0.134
0.117
Step 7. The mean-square error is:



    MSE  = — [(0.215)2 + (0.168)2 + (0.096)2 +... + (0.090)2 + (0.124)2] = 0.020
           14
Step 8. The method-specific means are:
    M=-
      MI
, = -[2.65 + 2.48 + 3.15 + 2.68 + 2.77 + 3.53 + 2.53] = 2.83
    Similarly, MM2 = 3.32.

-------
   Msl =-[2.65+ 3.28] = 2.96


   Similarly, MS2 = 2.71, MS3= 3.38, MS4 = 2.96, MS5 = 3.00, MS6= 3.69, andMS7= 2.81.


   M0 =-[2.83 + 3.32] = -  ^[2.96 + 2.71 + 3.38+ 2.96 + 3.00 + 3.69+ 2.81] = 3.07
         2              7
Step 9. TheRMSDis:


    RMSD = -^[(2.65 - 3.28)2 + (2.48 - 2.94)2 +... + (2.53 - 3.09)2] = 0.503
Step 10. TheRMSDMAxis:
                =^=•2.36=0.178
Step 11.  The compared result is:

   Because the RMSD is > than the RMSD MAX, the difference between the two methods is
   significant.
Based on the results shown above, Method ATP2 is NOT comparable to Method 1664B over
the course of 7 days in a Meat Packer matrix.

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Appendices 1 and 2 of this guidance document provide examples of spreadsheets with results
that:
    1.  pass RMSD comparability test for Oil and Grease methods.
    2.  fail the RMSD comparability test for Oil and Grease methods. This example also
       indicates Pass or Fail for the IPR and MDL QC elements.

Listed below are additional tools and sample forms that may be used when processing limited
use applications for D7575.  These documents are available on the EPA website at
http://water.epa.gov/scitech/methods/cwa/update index.cfm .

    1.  Oil and Grease ATP Comparison Worksheet.  An interactive Excel® spreadsheet that
       does all calculations automatically after the necessary raw data are entered in the
       highlighted fields made available for use by applicants. This spreadsheet does all
       calculations automatically after the necessary raw data are entered in the highlighted
       fields. The spreadsheet also indicates Pass or Fail when data are entered for the IPR and
       MDL QC elements. This single version of the  spreadsheet generated examples above and
       is password protected to prevent changes being made to the equations used to
       automatically calculate the results. (Mentioned above in this guidance on pp. 1-2.)

    2.  NPDES Chemistry Limited Use Alternate Test Procedure Application. An ATP
       application form that lists the required attachments to be submitted by the applicant, with
       an example. (Tillable form, MS Word 2007®)

    3.  NPDES Chemistry Limited Use Alternate Test Procedure Method Documentation
       Form. This form describes all the necessary sections of the method and/or Standard
       Operating Procedure. (Tillable form, MS Word 2007®)

    4.  Performance Comparison Form (Clean Matrix, Laboratory Pure Water). This form
       describes the basic QC elements such as IPR, MDL and Proficiency Testing with the  QC
       acceptance criteria. A Certification Statement  (last page of this form) must be signed and
       attached with the raw data. (Tillable form, MS Word 2007®)

    5.  Performance Comparison Form (Effluent Matrix).  This form describes side-by-side
       (parallel) testing of D7575 and 1664A/B method performance in the actual wastewater
       matrix with QC elements and QC acceptance criteria specified.  A Certification
       Statement (last page of this form) must be signed and attached with the raw data.
       (Fillable form, MS Word 2007®)
                                          10

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Appendix 1. Example of Oil and Grease ATP with Passing Results
                                   11

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 Guidance for Comparison of an Alternative Test Procedure and an Approved Reference Method
                              for Oil & Grease - February 2013
Enter your data in the pale yellow cells.                             	
    Reference Method =
              Matrix =
1664A/B
    Refinery
Alternate Test Procedure =  |   ATP1   |
Table 1: Results of the triplicate analyses by each method on the individually collected sample replicates/day.

Collection
Date
1/2/2013
1/8/2013
1/17/2013
1/25/2013
1/28/2013
2/4/2013
2/7/2013
Analysis
Date
1/4/2013
1/11/2013
1/24/2013
2/1/2013
2/4/2013
2/13/2013
2/15/2013
Time Held
(Days)
2
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Results
1664A/B
Rep#1
13
10
22
12
20
37
11
Rep #2
18
12
26
17
17
35
14
Rep #3
12
14
22
15
12
31
13
Units:
mg/L
ATP1
Rep#1
13
10
22
12
20
37
11
Rep #2
18
12
26
17
17
35
14
Rep #3
12
14
22
15
12
31
13
Scroll to the right to see the calculations for the side-by-side comparison.

Click here to see the side-by-side comparison of your results

Enter the data for your Initial Precision and Recovery (IPR) study in the pale yellow cells below
Alternate Test Procedure =
Preparation
Date
1/2/2013
Analysis
Date
1/2/2013
Time Held
(Days)
0
Spike
Level
40
IPR Rep
#1
38.0
ATP1
IPR Rep
#2
38.5
Units:
IPR Rep
#3
39.0
mg/L
IPR Rep
#4
39.5
Click here to see the evaluation of your IPR results
Enter the data for your method detection limit (MDL) .
Alternate Test Procedure =
Preparation
Date
1/2/2013
Analysis
Date
1/2/2013
Time Held
(Days)
0
Spike
Level
6
MDL Rep
#1
5.6
study in the pale yellow cells below
ATP1
MDL Rep
#2
5.5
Units:
MDL Rep
#3
5.3
mg/L
MDL Rep
#4
5.9

MDL Rep
#5
5.8
MDL Rep
#6
5.6
MDL Rep
#7
6.0
Click here to see the evaluation of your MDL results
                                                      12

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Table 2: Log-transformed results

Collection Date
01/02/13
01/08/13
01/17/13
01/25/13
01/28/13
02/04/13
02/07/13
Analysis Date
01/04/13
01/11/13
01/24/13
02/01/13
02/04/13
02/13/13
02/15/13
Time Held (Days)
2
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Results
EPA Method 1664A/B
Rep#1
2.56
2.30
3.09
2.48
3.00
3.61
2.40
Rep #2
2.89
2.48
3.26
2.83
2.83
3.56
2.64
Rep #3
2.48
2.64
3.09
2.71
2.48
3.43
2.56
Units:
mg/L
Alternate Test Procedure
Rep#1
2.56
2.30
3.09
2.48
3.00
3.61
2.40
Rep #2
2.89
2.48
3.26
2.83
2.83
3.56
2.64
Rep #3
2.48
2.64
3.09
2.71
2.48
3.43
2.56
Table 3: Triplicate means (Mij)
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B(i=1)
2.65
2.48
3.15
2.68
2.77
3.53
2.53
ATP (i=2)
2.65
2.48
3.15
2.68
2.77
3.53
2.53
Table 4: Triplicate standard deviations (sij)
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B(i=1)
0.215
0.168
0.096
0.176
0.261
0.090
0.124
ATP (i=2)
0.215
0.168
0.096
0.176
0.261
0.090
0.124
MSE=

MM1 =

MS1 =
MS2=
MS3=
MS4=
MS5=
MS6=
MS7=
0.029

2.83

2.65
2.48
3.15
2.68
2.77
3.53
2.53
MM2=

Mo=
Mo=

RMSD=
2.83

2.83
2.83

0.000
                                                                                                RMSDmax=|  0.215|
                                                    13

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Click here to go back to data entry page.

Results:     Because the RMSD is < than the RMSD MAX, the difference between the two methods is not significant.

Based on the
results shown
above:        Method ATP1     is comparable to       Method 1664A/B  over the course of   9 days in a Refinery    matrix.

Holding Time   The maximum time your comparison study samples were held MEETS the 28-day holding time
Check:        for the method.
                                                       14

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Click here to go back to the data entry page.

IPR Evaluation:

Spike Level:                 40

Mean IPR Result:           38.5

Recovery #1 (%):           95.0
Recovery #2 (%):           96.3
Recovery #3 (%):           97.5
Recovery #4 (%):           98.8

Mean Recovery (%):         96.9

Standard Deviation:          1.6

Recovery Test:      Your IPR MEETS the recovery requirements of the method

Precision Test:      Your IPR MEETS the precision requirements of the method

Holding Time Check: The maximum time your IPR samples were held MEETS the 28-day holding time for the method.
                                                      15

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Click here to go back to the data entry page.

MDL Evaluation:

Spike Level:                 6

Mean Result:               5.7

Standard Deviation:          0.2

Calculated MDL (7 reps):       0.8 mg/L

MDL Test:             Your MDL MEETS the method requirements

                    The maximum time your MDL samples were held MEETS the 28-day holding time for the
Holding Time Check:     method.
                                                     16

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Appendix 2.  Example of Oil and Grease ATP with Failing Results
                            17

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 Guidance for Comparison of an Alternative Test Procedure and an Approved Reference Method
                              for Oil & Grease - February 2013
Enter your data in the pale yellow cells.                            	
    Reference Method =
              Matrix =
1664A/B
  Meat Packer
Alternate Test Procedure =  |   ATP2  |
Table 1: Results of the triplicate analyses by each method on the individually collected sample replicates/day.

Collection
Date
1/2/2013
1/8/2013
1/17/2013
1/25/2013
1/28/2013
2/4/2013
2/7/2013
Analysis
Date
2/4/2013
1/11/2013
1/24/2013
2/1/2013
2/4/2013
2/13/2013
2/15/2013
Time Held
(Days)
33
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Results
1664A/B
Rep#1
13
10
22
12
20
37
11
Rep #2
18
12
26
17
17
35
14
Rep #3
12
14
22
15
12
31
13
Units:
mg/L
ATP2
Rep#1
23
21
41
26
26
52
21
Rep #2
28
19
36
27
23
48
20
Rep #3
29
17
35
24
27
40
25
Scroll to the right to see the calculations for the side-by-side comparison.

Click here to see the side-by-side comparison of your results

Enter the data for your Initial Precision and Recovery (IPR) study in the pale yellow cells below
Alternate Test Procedure =
Preparation
Date
1/2/2013
Analysis
Date
2/2/2013
Time Held
(Days)
31
Spike
Level
40
IPR Rep
#1
37.0
ATP2
IPR Rep
#2
27.0
Units:
IPR Rep
#3
29.0
mg/L
IPR Rep
#4
35.0
Click here to see the evaluation of your IPR results
Enter the data for your method detection limit (MDL) .
Alternate Test Procedure =
Preparation
Date
1/2/2013
Analysis
Date
2/2/2013
Time Held
(Days)
31
Spike
Level
6
MDL Rep
#1
4.0
study in the pale yellow cells below
ATP2
MDL Rep
#2
3.5
Units:
MDL Rep
#3
4.5
mg/L
MDL Rep
#4
5.5

MDL Rep
#5
4.0
MDL Rep
#6
4.2
MDL Rep
#7
5.0
Click here to see the evaluation of your MDL results
                                                      18

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Table 2: Log-transformed results

Collection Date
01/02/13
01/08/13
01/17/13
01/25/13
01/28/13
02/04/13
02/07/13
Analysis Date
02/04/13
01/11/13
01/24/13
02/01/13
02/04/13
02/13/13
02/15/13
Time Held (Days)
33
3
7
7
7
9
8
Sample
1
2
3
4
5
6
7
Results
EPA Method 1664A/B
Rep#1
2.56
2.30
3.09
2.48
3.00
3.61
2.40
Rep #2
2.89
2.48
3.26
2.83
2.83
3.56
2.64
Rep #3
2.48
2.64
3.09
2.71
2.48
3.43
2.56
Units:
mg/L
Alternate Test Procedure
Rep#1
3.14
3.04
3.71
3.26
3.26
3.95
3.04
Rep #2
3.33
2.94
3.58
3.30
3.14
3.87
3.00
Rep #3
3.37
2.83
3.56
3.18
3.30
3.69
3.22
Table 3: Triplicate means (Mij)
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B(i=1)
2.65
2.48
3.15
2.68
2.77
3.53
2.53
ATP (i=2)
3.28
2.94
3.62
3.24
3.23
3.84
3.09
Table 4: Triplicate standard deviations (sij)
Sample (j)
1
2
3
4
5
6
7
EPA1664A/B(i=1)
0.215
0.168
0.096
0.176
0.261
0.090
0.124
ATP (i=2)
0.125
0.106
0.084
0.060
0.084
0.134
0.117
MSE=

MM1 =

MS1 =
MS2=
MS3=
MS4=
MS5=
MS6=
MS7=
0.020

2.83

2.96
2.71
3.38
2.96
3.00
3.69
2.81
MM2=

Mo=
Mo=

RMSD=
3.32

3.07
3.07

0.503
                                                                                                RMSDmax=|  0.178|
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Results:      Because the RMSD is > than the RMSD MAX, the difference between the two methods is significant.

Based on the
results shown
above:        Method ATP2    is NOT comparable to   Method 1664A/B  over the course of  33 days in a Meat Packer matrix.

Holding Time   The maximum time your comparison study samples were held EXCEEDS the 28-day holding
Check:        time for the method.
                                                      20

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IPR Evaluation:

Spike Level:                40

Mean IPR Result:           31.0

Recovery #1 (%):           92.5
Recovery #2 (%):           67.5
Recovery #3 (%):           72.5
Recovery #4 (%):           87.5

Mean Recovery (%):         80.0

Standard Deviation:         11.9

Recovery Test:      Your IPR FAILS the recovery requirements of the method

Precision Test:      Your IPR FAILS the precision requirements of the method

Holding Time Check: The maximum time your IPR samples were held EXCEEDS the 28-day holding time for the method.
                                                      21

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MDL Evaluation:

Spike Level:                 6

Mean Result:               4.4

Standard Deviation:          0.7

Calculated MDL (7 reps):       2.1 mg/L

MDL Test:             Your MDL FAILS the method requirements

                    The maximum time your MDL samples were held EXCEEDS the 28-day holding time for
Holding Time Check:     the method.
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