EXECUTIVE SUMMARY 



Biological and chemical monitoring results from the Mill-Quinnipiac River Disposal 

 Mound (MQR) have indicated slow, and perhaps retrograde, recolonization rates relative to 

 other mounds formed within the same time period. These results triggered a more intensive 

 investigation of the MQR mound. Monitoring data have been collected as a part of the 

 Disposal Area Monitoring System (DAMOS) Program since the formation of MQR during 

 the 1982-1983 disposal seasons. MQR was constructed as one of several disposal mounds at 

 the Central Long Island Sound Disposal Site (CLIS), including the two Cap Site mounds 

 (CS-1 and CS-2) and the uncapped Field Verification Program mound (FVP). 



REMOTS® sediment-profile photographs obtained in 1987 first identified the 

 anomalous species assemblages and low organism-sediment indices at MQR as compared to 

 both Cap Site mounds and FVP. Tissue body burden trace metal data were collected at 

 several CLIS capped mounds in 1986 and indicated elevated levels at both MQR and FVP. 

 Although benthic conditions had improved in the 1987 survey relative to the previous year, 

 the 1991 CLIS monitoring survey indicated retrograde benthic recolonization as documented 

 by REMOTS® photographs. 



In August of 1991, sediment was collected for a bioassay test, and, at the same time, 

 six gravity cores were collected from the mound center. The cores were described, and 

 sampled for inorganic and organic chemical analyses. Core samples were stored until 

 completion of the bioassay test; results showed that the MQR sediment caused significant 

 amphipod toxicity. Following the tiered approach to disposal mound monitoring, sediment 

 samples from the coring cruise were analyzed in order to identify the contaminant(s) 

 potentially responsible for the benthic conditions at MQR. 



Sediment core samples were analyzed for grain size, pesticides and poly chlorinated 

 biphenyls (PCBs), priority pollutant metals, polynuclear aromatic hydrocarbons (PAHs), and 

 volatile organics. Core descriptions indicated that two primary lithologies had been 

 recovered. The top 1-1.5 meters of each core consisted of black silty clay, overlying a 

 sandier interval with clasts and plant fragments. Chemical results and core descriptions 

 suggested that at least one core recovered ambient sediment below a depth of approximately 

 1.5 meters. This core was apparently recovered in the flanks of MQR, where the total 

 thickness of dredged material was thinner. 



Physical and chemical analyses were used to construct a stratigraphy of the MQR 

 mound in order to identify the origin of the surface sediments. Trace metal results were 

 compared with historical data compiled from the sources of the dredged material. Trace 

 metal ratios indicated that most of the cored sediments were derived from the New Haven 

 Harbor, the location of the capping material used to cover the MQR mound. The sandier 

 sediments in the lower part of the cores appeared to be either Mill or Quinnipiac River 

 sediments, or a combination of both. 



