13 



The presence of Stage III organisms is a rough indicator of the species progression of 

 that area. Only 20% of the replicates in the June 1991 survey at MQR contained signs of 

 Stage III organisms. This number doubled in the August 1992 MQR survey (39%). Again, 

 reference values were considerably higher; in the 1991 CLIS survey, 84% of the reference 

 area replicates contained Stage III organisms. 



3.2.2 Organism-Sediment Index 



The apparent RPD, the successional status, and indicators of methane or low oxygen 

 (Section 3.3) are summarized in a value called the Organism-Sediment Index (OSI). OSIs 

 can range from -10 (no apparent macrofaunal life and methane gas present in the sediment) 

 to 11 (aerobic bottom with a deep apparent RPD, evidence of a mature macrofaunal 

 assemblage, and no apparent methane). The index is useful in mapping disturbance and 

 ecosystem recovery. 



OSI values can vary widely even among three replicates at the same station. The 

 median OSI from three replicates is reported, therefore, to best represent the overall 

 conditions at that site. Since the index is a number, it also can be useful to track historical 

 changes at any site, if these numbers are compared with reference values. 



Median OSI values from all stations of the 1992 MQR survey ranged from 3 to 7. 

 This range is lower than the range measured at the CLIS reference area in June, 1991 (5-9). 

 Again, the value of this indicator has improved since the 1991 survey, when the OSIs ranged 

 from -8 to 3 within 200 meters of the center of the MQR mound (Figure 3-4). 



The distribution of OSIs displays no particular spatial pattern in either 1991 or 1992 

 (Figure 3-5). The southern part of the mound has higher OSI values, probably due to this 

 area being farthest from the MQR mound boundary. Since active disposal is no longer 

 taking place, a "footprint" of activity is no longer apparent. 



3.3 General Observations 



3.3.1 Methane 



Methane was present in both the REMOTS® surveys of 1991 and 1992. 

 Approximately 10% of the stations from the 1992 survey contained evidence of methane, 

 while double the number of stations (approximately 20%) within 200 meters of the center of 

 the 1991 survey contained methane. 



This persistence of methane, documented in several prior DAMOS reports (e.g., 

 SAIC 1990a, 1990b), is the most conclusive piece of evidence presented by REMOTS® data 

 that the capping material at MQR is conducive to the formation of methane. The presence of 



Recolonization of the Mill-Quinnipiac River Disposal Mound (MQR): Results of a REMOTS® Survey, August 1992 



