3.0 RESULTS 



3.1 Data Quality Analysis 



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

 and supported by appropriate documentation, with some data qualified as discussed below. 

 Sample data were evaluated using protocols developed by the EPA (EPA 1988a, 1988b), 

 including a review of laboratory detection limits, sample holding times, and laboratory 

 quality control (QC) samples. QC samples consisted of method blanks, matrix spikes, and 

 duplicate samples. No QC sample results were submitted with the TOC data; consequently, 

 all TOC data were qualified "J" as estimated. Data qualified as estimated are acceptable, but 

 a greater degree of uncertainty is associated with these values than with unqualified data. 



Method detection limits (MDLs) are the minimum concentrations of a substance that 

 can be measured and reported with 99% confidence that the analyte concentration is greater 

 than zero. The MDL incorporates all of the analytical operations. All MDLs were 

 acceptable as proscribed by each method (Table 2-2) for all sample results, except for two 

 basic, neutral, acidic semivolatile (BNA) results for samples 8-5 and 9-8. These samples 

 were diluted tenfold which resulted in detection limits an order of magnitude higher than the 

 other samples. Samples are diluted either because the presence of high concentrations of a 

 measured compound can interfere with accurate quantification of chromatographic peaks, or 

 because the sediment matrix itself causes interference. All compounds were below detection 

 in these samples except for one estimated value of di-n-octyl phthalate (1900 ppb). The 

 result of this dilution is that the potential presence of PAHs at concentrations above the 

 normal detection limit at these two stations cannot be determined. This uncertainty was 

 taken into account in discussing the MBDS chemical results (Section 4.1). 



The EPA recommends a limit to the amount of time samples can be stored before 

 analysis; this period is called the holding time. There are no formal holding times for 

 sediment matrix samples. Samples were extracted for organic analyses less than forty-five 

 days after sampling, and analyzed less than thirty-eight days after extraction. No organics or 

 metals samples were qualified based on excessive holding times (EPA 1988a, 1988b). 



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

 only reagents, and are used to test for contamination which may have been contributed by the 

 laboratory during sample preparation. An acceptable number of method blanks were 

 analyzed with all sample sets except that there were no method blanks for Hg or total organic 

 carbon (TOC) analyses. TOC results were already qualified, so no further qualification was 

 necessary. Mercury results were also qualified as estimated. Method blanks were below 

 detection for all pesticides, PCBs, and metals except Hg. BNA compounds were also 

 undetected in the associated method blanks with the exception of bis(2-ethylhexyl)phthalate 

 which was detected in three of the four BNA method blanks at estimated concentrations 



Chemical Analyses of Sediment Sampling at the Massachusetts Bay Disposal Site, June 1989 



