21_ 



— 1000 mg/kg spike). All metal recoveries were within acceptable limits for the 

 laboratory control sample, indicating acceptable accuracy for the metals data. 



TOC Accuracy. Sample GR-1 was selected for MS/MSD analysis. Recoveries of 

 TOC in both the MS and MSD samples, as well as eight analyses of the standard reference 

 material, indicated acceptable accuracy of the TOC data. 



2.8.5.4 Assessment of Analytical Precision 



Analytical precision is expressed as the relative percent difference (RPD) between 

 two results. Precision for this dataset was calculated from the RPD between the MS and 

 MSD recovery values. The closer the numerical values of the measurements are to each 

 other, the lower the RPD. Low RPD values indicate a high degree of analytical precision. 

 The relative percent difference (RPD) between two sample results was calculated using the 

 following equation: 



Samp Re s - Dup Re s 



RPD = — T- — — r — - X 100 



(Samp Re s + Dup Re s / 2) 



Sample GR-1 was selected for MS/MSD analyses, except for pesticides/PCBs (GR-9). 

 Precision limits for the RPD of the MS/MSD samples was 35% for PAHs. Of 16 PAH 

 compounds analyzed, 2 were outside of the 35% limit (phenanthrene and benzo(a)an- 

 thracene). Overall, the PAH data were considered to be acceptably precise. All pesticide 

 compound MS/MSD recoveries were within 20%, indicating acceptable precision of pesticide 

 data. Pesticide and PCB (all below detection for WLIS samples) detection limits were 

 reported on a sample-specific basis based on the on-column reporting limit, with a PCB on- 

 column calibration standard of 100 ng/ml; these data provide supporting information for the 

 precision of the reporting limit. 



All RPDs for MS/MSD metals samples were < 10% (most <5%) indicating good 

 precision, except for Al. As stated above, the low relative concentrations of the Al spikes 

 make the MS/MSD recovery data not acceptable for assessment of precision. The RPD 

 between actual sample results of Al was within 10%, indicating acceptable precision of Al 

 analyses. Finally, the RPD results of TOC recoveries in the MS/MSD samples were 2.8% 

 for one day of analysis, and 38.3% for the second. Precision of duplicate TOC analysis 

 for the sample GR-1 was within 10%. Cumulatively, the RPD data indicate an acceptable 

 level of precision for TOC. 



Monitoring Cruise at the WLIS Disposal Site, September 1997 and March 1998 



