31 



contamination by disposal 

 operations or post-disposal 

 transport. This can be done by 

 locating the reference station at a 

 position that is offset from the 

 major downstream transport 

 direction(s) of the disposal site. 



The question arises what is considered 

 a significantly lower population 

 density on the disposal mound which 

 would trigger monitoring efforts to be 

 initiated in the next lower tier (Box 2.5 

 in Tier 2)? No absolute density can be 

 cited as a yardstick until historical 

 REMOTS® photographs from 

 immediate post-disposal surveys are 

 examined with this objective in mind. 

 One must also take into account 

 natural year-to-year variability in 

 recruitment of different pioneering 

 species. The important measure is a 

 test of significance between the 

 population mean for the disposal 

 mound compared with the reference 

 stations. Selection of the level of 

 significance to reject the null 

 hypothesis will be a judgement on the 

 part of the resource manager. It is not 

 necessary to set high levels of 

 significance for this test. It may be 

 sufficient for management purposes to 

 detect that the disposal site has mean 

 population densities that are 2 times 

 lower at the disposal mound at 80% of 

 the station replicates than on the 

 ambient seafloor before rejecting the 

 null hypothesis and proceeding to Box 

 2.5. These kinds of judgements about 

 decision thresholds initially must be 

 based on historical data and be revised 

 over time as information is 

 accumulated about the year-to-year 

 variability in this measure. 



Box 2.3 "Expected Response, No 



Immediate Action Required.. " 



If population densities of 

 pioneering polychaetes are equal to or 

 higher on the new disposal mound 

 than the ambient seafloor within 4-12 

 weeks after disposal has ceased, this is 

 the predicted response of normal 

 recovery following a disturbance; there 

 is no need for additional testing or 

 monitoring at this point. 



The frequency of periodic 

 monitoring will depend on the 

 political or ecological sensitivity of the 

 disposal site or operation. If high- 

 resolution monitoring is required, the 

 first year's monitoring may involve an 

 additional late summer and/or late fall 

 surveys. Otherwise, repeated surveys 

 on an annual basis are all that is 

 required to monitor the normal 

 development of subsequent 

 successional stages. 



Underlying Assumptions : The 

 population and successional response 

 is used as an indicator that 

 colonization is not being inhibited by 

 physical or chemical factors specific to 

 the disposal mound. However, this 

 does not mean that bioaccumulation is 

 not taking place. As stated in Section 

 4.1, methods for analyzing tissue 

 contaminant levels in pioneering 

 polychaetes do not exist at this time. 

 Once these are developed, it would be 

 possible to insert another level of 

 assurance to check the initial 

 evaluation protocol by analyzing tissue 

 contaminant levels in pioneering 

 polychaetes. This would verify that 

 there is no danger of biomagnification 

 as a result of disposal activities. Until 



An Integrated, Tiered Approach to Monitoring and Management of Dredged Material Disposal Sites 



