19_ 



The recommended maximum holding times between samphng and extraction are 

 Usted for the following: PAH, pesticide and PCB samples, 14 days; metals, 6 months; and 

 mercury (Hg), 28 days. PAH samples must be analyzed within 40 days of extraction (EPA 

 1997). All holding times for chemical analyses were met. The sediment samples were 

 collected on March 6, 1998. The samples were stored under refrigeration until they could 

 be delivered to the laboratory on March 9, 1998. PAH samples were extracted on March 

 11, 1998, and analyzed March 21, 1998, meeting the required holding times. Pesticide 

 and PCB extraction/analysis was conducted on most samples on March 19 and 27, 1998, 

 respectively, meeting holding times. Trace metal samples, including Hg, were digested on 

 March 12, 1998, and analyzed from March 13 to 17. 



2.8.5.2 Method Blanks 



Method blanks are laboratory QC samples that are processed with the samples but 

 contain only reagents. Method blanks test for contamination that the laboratory may have 

 contributed during sample preparation. No target compounds or metals were measured in 

 any of the method blanks. 



2.8.5.3 Assessment of Analytical Accuracy 



Analytical accuracy is determined by the percent recovery of a known concentration 

 of a compound that is spiked to the envirormiental sample before analysis. The closer the 

 numerical value of the measurement approaches the acmal concentration of the compound, 

 the more accurate the measurement. The percent recovery values are calculated using the 

 following equation: 



Ar-Ac 



xlOO 



Ac 



where: A^ = Total compound concentration detected in the spiked sample 



Aq = Concentration of the compound detected in the unspiked sample 

 Af = Concentration of the spike added to the sample 



Matrix spike samples (MS) and matrix spike duplicates (MSD) are prepared by 

 dividing a sample into multiple aliquots and spiking an aliquot with a known concentration 

 of analyte and finally proceeding with the analysis as though the spike were a sample. 

 Supporting accuracy data were provided by samples spiked with surrogate compounds, as 

 well as spiked blanks and laboratory control samples. Surrogate spikes are analyzed as a 

 check on the laboratory's ability to extract known concentrations of compounds not 



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



