SITE INFORMATION AND CORRESPONDENCE_CASE 1

Home Browse Search

.f I R !r Lawrence Uvermcre Natiorml Labcrdtar'y To: James G. Giannocculos State Waxer Resourcys Control Board From: Anne Happel,Ph.D. Lawrence Livermore National Laboratory, L-530 Environmental Resraration Division 7000 East Ave.,P.Q. Box 808 Livermom CA 94550 Date: August 6, 1996 SUR.TFC Comparison of EPA 8020 and EPA 8240 Aaalydcal Results far Measuzernent of Methyl Tertiary Buryi Ether(MTBE) in Ground Water Samples from LLFT Sites. MEJHOUS We have reviewed MTBE ground water dam submitred;to us by scve:al oil companies, including Shell., Texaco, ARCO, and Unocal. We have evaluared.dam fecal ground water samples concun=dy analyzed for FTSE using EPA methods 8020 and 8240. In arc e:m compare the detection and quantification of MTBE by these two methods,vire restdczed our study to a total of 98 ground water samples that reported IME values greater or equal to 20 ug/L by EPIA method 8020 and/or VACL This data was cvaluzzed for the occurrence of etc positives and for the level of a&rxmcnt be ween values mported by each of these analytical met&ods. The MTBE values detuted by EPA methods 8020 and 8240 were compared without rhe assumption of knowledge of the lase value by calculating the Relative P=r-=t Difffimence (RPD). In dais reper.., RPD values gr==than 40% indicate an unacceptable level of disparity between the values obtained by these rwo anaiydcal methods. RESULTS 211d DISC11MON Occurrence of False Positives There has leen much discussion as to whether EPA method WM is adequate for determining M73E concentrations in LUFT ground water samples. Anecdotal information from analytical laboratories and remedianou engu== revaI false positive detectious of MME by EPA 8020. -%Ise uositive cases oc.-ter when EpX Sb20 analyst.:, a gas chrornatography/photo ionization detector(Gt?M) method,detect WME, wvhile confirmation by EPA 8240, a gas chromanography/mass,saectromcc y (GC/NO) method,, dctcrtnines MTBE to be non-detect (ND). These this-idendf=zioas of 1rinE by EPA 8020 analysis are amibuted to rhe presence of other hydrocarbons clute with NNE under standar*] (gasoline components) coat may ca- G ./PM coalitions used for BTEX analysis. In this data set, the overall occurrence of false positives by EPA 9020 was low. Among the toW 98 MTBE positive samples only 2 false positives wee repormd (71% of samples with MTBE cowentrations >20 ug/L). As exoected., false posinvcs only oc.^tiered in samples that ccntained elevated cnncrratradons of gasoline components (Table 1). False positives occurred in 4%, of the samples (2 out of 50 samples) that contained B= and/or B compounds at concentrations greater or eq=l to 150 ug/L. No false aega ive samples occ-,tr:.�in this dada ser. M Egos+G�prx�ng+ •Urarersiq of C,�fC.ri.•P.Q 8ar8G1B Lnerrraa►e,Car�rrrs SLSo r-Taiwhwre{sr.S7�2r r7o0-�wr 97G,�9r&�GCL:l LYXR I