10 



values were estimated because a particular compound was present in a concentration above 

 the method detection limit, but below the practical quantitative limit. The practical 

 quantification limit is the lowest level of measurement that can be reliably achieved within 

 specified limits of precision and accuracy during routine laboratory operating conditions for a 

 sample of a particular matrix. 



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 that the laboratory may have contributed during sample preparation. These 

 method blanks were free of contaminants. Analysis of matrix spike samples provides a 

 measure of the efficiency and effectiveness of sample preparation and analysis procedures. 

 They also indicate how tightly a compound is bound to its matrix and whether or not 

 interfering compounds are present. Matrix spikes are 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 were standard reference materials analyzed using identical 

 procedures as for the samples. Accuracy for the reference materials was within the control 

 limits for the metals as well as the PAHs except for one value of fluoranthene. No other QC 

 samples indicated laboratory problems with this compound, so no qualifiers were necessary. 



2.4 CTD and Dissolved Oxygen Sampling 



Speed of sound measurements were obtained prior to and following the bathymetric 

 survey using a Seabird SEACAT SBE 19-01 CTD probe. The CTD was lowered over the 

 side and allowed to equilibrate in ambient seawater for one to two minutes before initiating 

 the cast. In addition, the CTD cast characterized depth gradients and assessed near-bottom 

 DO concentrations relative to REMOTS® benthic analyses on and near the disposal site. The 

 Seabird CTD collected salinity, temperature, and DO profiles at the center of the three 

 reference areas (2500W, 4500E, and CLIS-REF) and at the center of the CLIS-90 disposal 

 mound. Water samples from a Niskin cast approximately 1 m below the surface and 1 m 

 above the bottom were sampled to measure near-surface and near-bottom DO values. A 

 300 ml subsample was drawn from the bottle, preserved, and titrated (duplicate aliquots of 

 50 mis) within twelve hours using a modification of the standard Winkler titration method 

 (Strickland and Parsons 1972, Parsons et al. 1984). The intent of obtaining the titrated 

 samples was to provide additional DO information should there be a problem with the CTD. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, June 1991 



