26 



5.0 CONCLUSIONS AND RECOMMENDATIONS 



Sediment chemistry results from the MBDS survey of June 1989 indicate that the 

 distribution of both organic and inorganic constituents reflects a difference in disposal 

 practices from the past to the present with lower contaminant concentrations observed in the 

 area of active disposal. Conversely, the highest concentrations of contaminants, especially 

 PAHs, are located along the western edge of MBDS where disposal in earlier decades was 

 concentrated. 



Relatively low trace metal concentrations and the spatial consistency of trace metal 

 data indicate no specific anthropogenic point sources of trace metals; maximum measured 

 concentrations of all metals are at stations north of the present disposal buoy. In general, the 

 data suggest no accumulation of elevated concentrations of trace metals at MBDS. Metal 

 concentrations are within MBDS reference area values. Overall, Pb concentrations are the 

 highest relative to both regional and national comparisons. 



Detected HMW PAHs clearly show the highest concentrations near Station 12-3, 

 located near the approximate center of the historical disposal site (1 nmi west of present 

 center). Approximately two-thirds of the stations at MBDS contained HMW PAHs at 

 concentrations within the range of values measured along coastal Massachusetts by the 

 National Status and Trends Program, and a trace of pyrene was detected (estimated) at 

 reference area FG-23. These factors indicate that the presence of PAHs at MBDS is 

 influenced by both background concentrations of PAHs in the Massachusetts Bay region and 

 historic disposal. 



The detection of 4, 4' -DDE in many samples is consistent with the fairly common 

 presence of pesticides in Massachusetts Bay sediments. PCBs, previously reported at the 

 same stations measured in the 1989 survey at concentrations of up to 1 ppm, were virtually 

 undetected; subsequent burial seems the most likely explanation. 



• The presence of relatively high concentrations of HMW PAHs along the western edge 

 of MBDS indicates that this area should be considered to receive new capping material 

 suitable for unconfined disposal. 



Future chemical sampling at MBDS should focus on the distribution of PAHs at 

 MBDS, including the eastern half of the site, in order to document background 

 concentrations of PAHs in the Massachusetts Bay region. Concentrations of PAHs at 

 MBDS are similar to coastal background, but are likely not as low as background 

 levels found in the Stellwagen Basin. 



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



