(NPD) contained 83 pairs of replicate QC results

3

with concentrations above reporting limits, and

95 pairs with both QC and QA results above re-

2

porting limits. For these data, 6.0% of QC1/QC2

^

y = 0.134 + 0.795x

ratios and 13.7% of QC1/QA ratios were outside

"r" = 0.906

0.254.00 (Table B5). We concede that these limits

1

are arbitrary, but they form a reasonable starting

point and the rejection rate for QC/QA is only

moderately greater than 10%, which we consider

0

an acceptable goal. As noted in the VOC section,

we believe that it is imperative to seek improve-

ments in procedures that yield widely divergent

1

results.

In contrast to the results from contractors re-

porting to NPD, 28 of the 61 pairs (45.9%) of QC/

2

2

1

0

1

2

3

QA ratios from the Missouri River Division (MRD)

QC

Ethylbenzene Log

Concentration Ratio

databank were outside 0.254.00. No replicate QC

QA

values were included on these data reports. The

histograms of log QC/QA ratios shown in Figure

8 provide a very clear depiction of the difference

mal model appears to be a reasonable fit to the

sults. Hewitt et al. (1995) state, "Only those sam-

NPD QC/QA ratios between 0.254.00. This hy-

pling methods that maintain soil structural integ-

pothesis is reinforced by the probability plot of

rity, use a single soil transfer step, and preserve

against biological degradation should be

15

used when establishing VOC concentra-

Boundaries Corresponding to

tions." A tipless plastic syringe is sug-

MRD Results

Ratios 0.25 to 4.00

gested for obtaining soil samples, which

10

are immediately transferred to VOC vi-

als containing either methanol or water

5

acidified with NaHSO4. Details of this

approach, which satisfies SW-846, Method

0

8260A, are available from Hewitt. We be-

lieve that it is imperative for the Corps to

25

consider this or alternative methods to

NPD Results

improve the quality of analytical results

20

for VOCs in soil.

In contrast to the 42% of archived QC/

15

QA ratios outside 0.254.00, only 23% of

the most recent results (44 samples from

10

11 project locations) were outside of these

limits. It is interesting to note that 20% of

5

the QC1/QC2 ratios were also outside

0.254.00 (no QC1/QC2 values were avail-

able in the original archived data). Of the

0

20%, 17% of the ratios were above 4.00,

i.e., the first value was much larger than

the second value. Perhaps VOCs were be-

ing lost during storage, thus causing the

second values to be low.

QC

Logs of

Concentration Ratios

QA

The 102 data reports for TPH in soils

submitted by the North Pacific Division

12