COMt m»nag9<**» coniwinu

August 18,

vi CAMP DRESSER & McKEE INC,Tht«0 HonhftJtt E»tt8800 North Centra) Eiprotway. Sutc 400DftHM. T«ra« 752312U9KM909

r. John CoehranfedrsnmsfiEsX1201 Elm Street

Subject: u, of Mtet Data at Horth CavalcadeArsenic, copper, lead, chromiumDocument Control NO.: 141-RI1-EP-DDNU-1Dear John:

answers thethis letter.°fr Jposed. His analysis accompanies

sider this method again « inwiua again, or whenvery truly yours,CAMP DRESSER & McKEE INC.

-William F. Buchholz, Jr. ,Vice PresidentWFB:lgcec: ti. Hays

R. KierT. StClairH. EdgarR. PetrusJ. Sullivan

P.E

-tni.. or metO think about ^ w*consider any surrogate method.

002617

STATISTICAL ANALYSIS OF X-PfetAT THE NORTH CAVALCADE SITE

Analyses for four mstals (arsenic, chromium, lead, and copper) wereobtained on site using a Columbia Scientific X-Met 040 x-ray floureeeeneeanalyser. Thsse analyses were performed on sits to provide immsdtatainformation eenctrning anomalously high occurrences of these metals. Que*tiorm ecmeefi&ag the validity of the x~Mat dat

1. Are the X-Met data toe unreliable for use?2. Can the X-Met data be used to guide RI/FS decisions?

To address these questions several points need to be discussed: does theX-Met provide acceptable results at other sites; are the X-Met resultsreproducible; and how do X-Het and CLP results compare? Each of theseissues are considered individually and conclusions concerning the validityand usefulness of the X-Met data are reached.

The X-Met has been used at several sites in addition to the North CavalcadeStreet Site to measure the in-eitu metal concentration of the soil. Oneexample is the Hill Creek smelter site in Butte, Montana. Soils in thisarea contain high levels of arsenic and lead due to emissions from a nearbysmelter. To analyze the efficiency of the X-Met at this site, sauries weregplit and analyzed by the x~Met and the CLP (for more information see RSWII Document 228-TSl~I0~CYCA~l). The results from the lead and arsenicanalyses were plotted in scattergrams to provide a comparison of theresults. These scattecgrams are reproduced as figures 1 and 2.

Overall these geattergrams demonstrate that there is a strong correlationbetween the X~Met and CLF results. Thus, the X-Mst does, at this site,provide representative estimates of soil lead and arsenic concentrations.

002618

TT

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£

t.8Q

MILL CREEK SOIL SAMPLESUEAD

XRF

FIGURE 1

002619

MILL CREEK SO!L SAMPLESARSENIC

0.00 0.40 0.00 1.20(TbouaancJa)XRF

1.60 2-4®

2

002620

However, notice that theMat

Ctf rootilfo as win.

of tha Igad Euod arsenicand &-H&t occurs

Mow 500 mgAgf the x~mt dogs not

of tlie points in tftis portion ef the geattetgram ar© shifted tothe right of the solid line cunning diagonally through the figure, thisline coresponds to points for which CLF and x-Httt analyses are equal.Thus, for concanteations less than 500 mg/kg arsenic the X-Met systemicallyprovides a larger estimate of arsenic than the CLP. Similarly, the X-Metdoes not reproduce CLP lead results well (figure 1) when the concentrationis less than 300 mg/kg. The conclusion is that although the X-Met performsvery well at high concentrations, it is inaccurate at low concentrations.

These results from the Mill Creek site indicate that the X-Met is a valu-able and useful tool that provides reliable data if the concentration ofsoil contaminants is large. To examine the reliability of the X-Met dataat the North Cavalcade Street Site, the performance of the X-Met onvalidation samples is examined.

Performance_o£_the x-Het on Validation S

The X-Met analyzer was calibrated, before use, to eight validation samples«hich ware taken from eight different areas of the site. The locations ofthe validation samples were chosen to represent the range of contamination.Tte actual concentrations of the validation samples were obtained fromatomic absorption analyses performed by Southwestern laboratories inHouston.

X-Het U8age, four of the validation samples were analyzed each day.analyses of the validation samples provide a data base of replicateurenfcnts. prom C8plicateg an analygj[g Q

reliability of tha x-ffet can be obtainad,

002621

To analyse the reprodueibility of ths X-Met results, the results of thevalidation rwis are transformed into errors. That is, suppose validationsas ls si is analysed fcy x~#gt and 7 mf/feg of arsenic is efetained. Theaefcual arsenic coiiG0ntratlon @^ validation gamble 1 deteeMned tftoMc*«M.~-i * ,j ^§^2 gg/kf 1 ig swfe^a©|glr lEOffi re 3^5f§t g^sijf if

error (i,l§J« Errors for all additional analyses oj^gtfig alsfeas****^ *K *—• *-*—-•

If an analytical method is perfect, fcha concentration dgtennined by themethod will equal the actual concentration of the validation sample foreach replicate sample. That is, the analytical error is zero for eachreplicate sample. Obviously no analytical method is perfect, but thedefinition of a perfect method provides guidelines for assessing theperformance of imperfect methods. The first guideline is that the averageof all the errors should be nearly zero. A zero average error indicatesthat there are no systematic errors in the analyses. The second guidelineis that all individual errors should be small. Since large errors willcause a large variance, the variance of errors should be small. Finally,the statistical distribution of the errors should be bell shaped. That is,there should be a large number of small errors and few large errors. If ananalytical method has these three properties it is termed a reliablemethod.

To examine the properties of the X-Het for the four metals of interest theerrors for all validation runs were computed and histograms of the errorswere computed (figures 3, 4, 5, 6). A histogram is a data analysis toolwhich graphically portrays the number of data falling within a small-rangeof values. For instance, in figure 3 (the histogram of arsenic errors) oneerror is larger than S but less than 5,5 mg/fcg. This error represents1 .22% of fch© total number of errors.

The histogram of arsenic errors shows that the X-Mst is a reliable techni-que for measuring arsenic concentration at this site. The average error( . 04 mg/kg) is vary small so there is no systematic error in th© analyses.

002622

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002623

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002624

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002626

A large number (73%) of the errors are less than 1.5 rag/kg. This fact isreflected in the small (2.22 mg/fcg2) variance of the errors. Finally,distribution of the errors follows a bell shaped distribution indicatingthat aost of eh® errors are small with occasional occurrences of larger

histograms of errors for copper, lead, and chromium do not demonstrateany of the properties necaesary to term the analytical methods reliable*Thff means of these errors are far from zero, indicating that the X-Metintroduces a systematic error into each measurement. Although the system-atic error is troubling, the worst feature of the histograms for thesemetals is that large errors are far more common than zero errors- Thisfact is indicated by the large variance of these errors and the shape ofthe histograms. These histograms of errors do not show bell shaped distri-butions, hence the analytical method is more likely to yield a large errorthan a small error. For this reason, the x~ffet is not a reliable methodfor determining copper, lead, or chromium at the North Cavalcade StreetSite. The values obtained by the X~Met are too unreliable for use andcannot be used to guide RT/FS decisions.

The reasons why the x-Met copper, lead, and chromium results are unreliableare a function of the X-Met method and site specific causes. As shownearlier, the X-Met is, in general, inaccurate when concentrations are low.The concentrations of copper, chromium, and lead observed at NorthCavalcade are simply too low to be determined accurately with the X-Met.The observed errors are due, in part, to the random nature in which x-raysare emitted from the radio isotope source and excitation occurs in thesample. As concentrations increase, these random errors become lessimportant and the method becoiaes more accurate. A second possible cause ofthe errors are site specific interferences caused by other metals withinthe* soil matrix.

In contrast to the other three metals, the X-Met performs well on arsenic,The next step in the analysis of the X-Met data is determining th& X-Metdetection limit for arsenic and con>paring arsenic CLP and X-Mel results.The X-Met results for copper, chromium, and lead are not consideredfurther.

002627

X-Het Arsenic Detection Limit

When analytical results are reported it is extremely likaly that thereported values will not be equal to Che actual vstaea* This analyticalerror is expected, but, it is generallyjmfQfipiHlWi£ fe& Eap^t a f@$iiivsconcentration for a compound when, in fact, the compound is not preaent inth«r sample, fha use of a detection limit icw^ng fchs risk of fihie occur-rence to an acceptable level. For X-Mst arsenic analyses, ths detectionlimit is set so that if a value is reported above the detection limit,there will &e greater than a 99% chance that arsenic is actually present inthe sample.

The determination of detection limit is based on the distribution of analy-tical errors, The magnitude of analytical errors is often a function ofthe magnitude of the actual values, To investigate whether this is truefor the arsenic analyses, the errors for each validation sample are exam-ined separately.

The actual concentrations of the 4 validation samples and the number ofreplicate measurements of each sample are as follows:

Sample As^gncentratipn5.12 mg/kg2,37 mg/kg2.76 mg/kg33.7 wgAg

# of Measurements251920

The histograms of errors for each o£ the four validation samples are shownas figures 7, 8, 9, and 10. Notice that the histograms of errors indicatethat the X-Met arsenic analyses are accurate for all four validation sam-ples. Thus, within the range o£ 2.4 to 23.7 mg/kg arsenic, the X-Het is atellable method.

Jo determine if the analytical errors are a function o£ concentration,examine the mean and variance of the errors for each validation sample.

002628

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002630

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002631

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002632

Validation Sample Mean Error1 .782 -.803 .674 - 7j3

iajMfrUtiaMMWiJ.*!*™^^

Variance of Errorst 92.fc t Sft1,3,82.14

ftttt not a ftmetion! of the concentration of the, Hsnss, it i« assumed that ttre magnlu«de of analytieal

errors are indapandant of concantcation within the rang« of 0 to 23.7mg/kg- Furthermore, it is aeaumed that the distribution of errors followsa nofsial distribution with msan .04 ing/kg and variance 2.22 (mgAg)2*mean and variance are taken from the errors for all arsenic replicates(figure 3) .

Based on the above assumptions the detection limit is determined as:

Pr (z < D) >_ 99%

where z is an errorD is the detection limit

Since the errors are normally distributed a normal probability table can beused to determine the detection limit D. The standard normal variablecorresponding to .99 is 2 . 3 3 . So the detection limit is:

D - m « 2 .33

where s is the standard deviation of the errorsm is the mean error

D - _^041 .49

2.33

0 » 3 .43

-6-

002633

So, if the X-Met reports greater than 3 .43 mg/kg arsenic there is at leasta 99% chance that arsenic is present. Prom the above computation, it isclear that X-Met detection limits cannot b$ computed for chromium, lead, orcopper.

Comparison of CLP and fr-Etefe Agganic Raaulfcs

A total of 41 soilCLP. The samples

samples were analyzed for arsenic by the X-Met and theand the results obtained are shown in Table 1*

Table 1Sample ftDB02-17DB02-28DB02-32DB02-30DB03-33DB03-36DB05-36DBOS-42DB05-50DB06-27DB06-030DB06-032DB07-023DB07-033DB07-041DB11-021DB14-019DBIS-020DB16-021DB17-019DB18-019DB19-015DB20-019DB21-018DB22-014DB23-014DB24-016DB25-023DB26-06GDB27-022DS2Q-018DB29-038DB31-019DB31-057

CLP

NO21.11.NDNDND8 .87. 1NDNDNDNDNDNDNDNDND14.12 .IS.NDNDNDNDNDNDND10.ND13.8NDND22.7

MetNDND29.521.48 .0514 .818.217 .735.8NDND20 .0ND2 4 . 4ND4.86NDND29 .751.553.642 .927 .6ND17 .86 .2275.917.131 .249 .229.212 .4ND40 .6

002634

ES40-0100^41-011BB42-015

CW02-Q24•020

Table 1 (Continued)CUP8.26 .8W9,34.33.33.0

ND indicates not detectedCt.P detection limit ranges f^om 1.2,toX-Met detection lirait = 3 . 4 3

8,628.69

18.714.9

mg/kg

A visual examination of. Table 1 indicates that there is little correlationbetween the CLP and X-Het data. A numerical comparison of the data con-firms this observation. Both the CLP and the X-Met detect arsenic in 16samples. The linear correlation coefficient between the CLP and X-Metanalyses of these data is only .42 . This low correlation value indicatesthat there is little, if any, linear correlation between the X-Het and CLPanalyses.

Hie lack of correlation between X-Met and CLP analyses is surprising. Theresults of the replicate analyses on the validation samples indicate thatthe X-Met is extremely accurate. The observed errors indicate that thereis a 95% chance that the actual value will lie within +3 mg/kg of thereported X-Met value. The comparison between CLP and the X-Met showserrors as large as 70 mg/k9* Obviously there are strong matrix effects orsome tsiknown factor which influence the CLP and X-Het results differently,thus causing the observed discrepancies.

There are 82 replicates which indicate that the X-Het analyses of arsenicaccurately reproduce atomic absorption analyses for a variety of soilsfound at the site. Thus, it is difficult to state that the X*-Het resultsare inaccurate in spite of the fact that they do not agree with the CLPanalyses. It is equally difficult to state that the Ci.P analyses areinaccurate since CLP analyses are subject to strict QVQC procedures.

002635

It can be stated that the X-Met arsenic values am numerically representa-tive of A& analyses of the typt performed by gouthwestem tabs. If theSouthwestern i^b analyses ars of acceptable quality, then the X-Met valuesare numerically reliable and can be used to gutdt EI/F3 decisions.

X-Met was used at the North Cavalcade gits to provide guiek turnaroundanalyses of m@tal& within soil sarnies. If high concentrations of metalswere found in the soil, the X~Met results would b0 used to guide th& fieldprogram. During the field program, the X-Met did not detect any extremelyhigh values* Thus, the X-Met did not directly drive the field program, butit did indicate that metals were not a major concern at Hiis site* Sincethe X-Met did not indicate high metals concentrations, the field programwas guided solely by the occurance of organics contamination as measuredby head space analyses and creosote odors noticed by field workers. TheX-Met therefore, eliminated an unimportant variable from consideration andallowed field personnel to concentrate their efforts on the importantorganic site contaminants.

The analysis presented here discussed the validity of the X-Met values. Itwas shown that the X-Met analyses are unreliable for copper, chromium, andlead. It was demonstrated with results from another site that when thesecompounds are present in sufficient quantities the X-Met is a reliablemethod. At this site, however, these metals are below the limit of quanti-fication of the X-Met. The x-Met does determine arsenic values quiteaccurately as shown by the performance of the X-Met on the four validationsamples. Thus, the X-Met is reliable for arsenic and the actual numberscan be used to guide any additional sampling. However, since the concen-trations of arsenic ar© relatively low, for the most part, the concen-tration of arsenic is no longer of major concern.

002636