13 



acceptance limits except for high recoveries of terphenyl-D u in all samples except the 

 method blank. The high surrogate recoveries were potentially caused by matrix interference. 

 The acceptable recoveries of 2 out of 3 surrogate compounds indicate no laboratory 

 extraction problem (USEPA 1988a). 



Specific QC samples for the PAH analyses included a method blank, a spiked sample, 

 and a spiked duplicate sample. These results are discussed in the QA/QC section below 

 (2.4.4). 



2.4.4 QA/QC 



Results submitted by the NED laboratory were found to be acceptable and supported 

 by appropriate documentation. Sample data were evaluated using protocols developed by the 

 EPA (USEPA 1988a, 1988b). Quality control checks from the NED laboratory consisted of 

 method blanks, matrix spikes, duplicate samples, and laboratory control samples. Method 

 blanks are laboratory QC samples processed with the samples but containing only reagents. 

 Method blanks test for contamination which may have been contributed by the laboratory 

 during sample preparation. Matrix spike sample analyses provide a measure of the efficiency 

 and effectiveness of sample preparation and analysis procedures, in addition to an indication 

 of how tightly a compound is bound to its matrix. Matrix spikes are also used to assess the 

 accuracy of analytical measurements. Duplicate samples indicate variability in laboratory 

 procedures and degrees of difference between individual samples. Duplicate blank spike and 

 duplicate matrix spike samples were used to measure precision in laboratory procedures. 

 Laboratory control samples used by the NED were EPA standard reference material (SRM) 

 samples analyzed using identical procedures as with the samples. 



All samples submitted for metals analysis were extracted and analyzed within EPA 

 recommended holding times, except for Hg samples which were extracted 32 days after 

 collection and analyzed the following day. EPA guidelines suggest a maximum holding time 

 of 28 days for Hg (USEPA 1988b). The Hg results were not qualified because of the short 

 time delay and the refrigeration of the samples. Samples analyzed for PAHs, PCBs, and 

 pesticides were extracted and analyzed within EPA recommended holding times (USEPA 

 1988a). 



Method blanks were below detection for all metals except for Zn (13 ppm). All 

 samples contained zinc in concentrations greater than 5 times the concentration detected in 

 the method blank, so no qualifications were necessary (USEPA 1988b). The method blank 

 samples for PAHs, PCBs, and pesticides were below the practical quantitation limit for all 

 compounds. 



Spike and spike duplicate samples were analyzed as an evaluation of laboratory 

 accuracy and precision. Duplicate spike samples were analyzed for all of the metals 



Monitoring Cruise at the Portland Disposal Site, July 1992 



