other gave a concentration above the reporting

tistical evaluation. Suffice it to say that such re-

limit, the ratios were often outside the factor of

3.00 criterion. By far the poorest metal in this re-

Another common extreme is represented by

spect was Cd, where 25 of 40 such ratios failed

several analytes in VS233 where the QA labora-

tory reported < 1.1 g/kg and the QC laboratory

this test. The failure rate for Ag was 6 in 16 pairs,

reported < 7000 g/kg. Such examples suggest

for Hg it was 4 in 27, and only 2 of 21 Se pairs

failed to be within a factor of 3.00. In general,

the need for standardization of reporting proce-

most values above reporting limits were from the

dures for samples requiring dilution to permit de-

QA laboratories, although several were flagged

termination of one or more high concentration

with "J," meaning they were estimates but below

analytes. If such guidelines are already in place

reporting limits. The QA laboratories may be pro-

but are misunderstood or ignored by laborato-

viding a slightly more reliable analysis than the

ries, a training program might improve the situa-

QC laboratories, but there still is insufficient real

tion. Alternatively, if low concentration analytes

evidence to defend this statement.

really are of no interest when one or more analytes

are present at very high concentration, data com-

pilations could be greatly simplified.

For the 69 sets of VOCs in soils, there was a

For the 134 QC/QA ratios with concentrations

total of 134 analyte pairs having both a QC and

above reporting limits, ratios ranged from 0.015

QA concentration above reporting limits. Ethyl-

to 2830! The distribution of these ratios by analyte

benzene with 25 pairs, toluene with 35 pairs, and

and for the total is shown in Table B4. We note

total xylenes with 36 pairs represented the bulk

that the distributions are very similar for indi-

of the data. The remaining 38 pairs were distrib-

vidual analytes and for the group collectively. This

uted among benzene (eight pairs), chloroform (one

suggests that statistical analysis applied to the

pair), total 1,2-dichloroethenes (five pairs), me-

entire group would adequately represent results

thyl ethyl ketone (two pairs), tetrachloroethene

for VOCs in soils. It is also apparent that extreme

(11 pairs), and trichloroethene (11 pairs). Carbon

values are excessive. Over 40% of the ratios are

tetrachloride, chlorobenzene, 1,2dichloroethane,

outside the limits 0.254.00 and 24% are outside

1,1-dichloroethene, and vinyl chloride yielded no

limits of 0.1010.0. While we know of no stan-

pairs. Although samples VS260 through VS266

dard for acceptability of analytical results on split

used GC methods rather than GC/MS, there was

or co-located samples sent to different laborato-

no apparent reason to treat those results sepa-

ries, it stretches the boundaries of credibility to

rately.

think that analysts would describe agreement

Most analytes also had examples where either

within a factor of 10 as acceptable quantitation.

the QC or the QA result was a real number but

Nonetheless, we will base statistical characteriza-

the other was below reporting limits. In many

tion on the 76% of ratios within 0.1010.0.

cases it was impossible to judge how well (or

A histogram of the logs of all 134 ratios is

badly) these pairs compared because reporting

shown in Figure 4. Logs of the 102 ratios between

limits were based on dilutions made to accom-

0.10 and 10.0 form a tolerable approximation to a

modate a high concentration analyte. For example,

normal distribution. Further support for the hy-

benzene in sample VS217 was reported as 59.7

pothesis of a lognormal distribution is provided

g/kg by the QA laboratory (reporting limit of

by the linear cumulative probability plot of these

6.1 g/kg) while the QC laboratory reported <

logs on normal probability paper (Fig. 5). When

2500 g/kg. These results may agree, but it is

separate lognormal plots were prepared for

impossible to tell. Possibly this issue is unimpor-

ethylbenzene, toluene, total xylenes, and the re-

tant given the very high concentration of xylene

maining analytes collectively (Figs. 6a6d), all pro-

in this sample. One thing is clear: reporting these

vided reasonable fits to this model.

concentrations to three significant figures is a gross

Based on the lognormal model, the geometric

misrepresentation! In other cases, such as methyl

mean of the 102 ratios between 0.10 and 10.0 was

ethyl ketone in sample VS218, the QA labora-

0.95 and the 95% confidence limits on this mean

tory reported 271 g/kg and the QC laboratory

were 0.77 to 1.16. The 99% tolerance intervals for

reported <12 g/kg. Although the disagreement

individual ratios were 0.062 to 14.4. The fact that

of these results could be represented by a ratio if

these intervals are considerably wider than the

we assigned the QC result a value of 12 g/kg,

boundaries used for editing suggests that some

we decided not to include such results in the sta-

values outside the range of 0.10 to 10.0 may also

8