37 



hypoxia or intense trawling activity 

 may be responsible for the anomalous 

 patterns observed. 



Sources of Uncertainty: If the logic 

 flow leads one into Box 2.9, this can be 

 a frustrating result from both a 

 scientific and management 

 perspective. A careful review of the 

 data and measurement program must 

 be made at this point. One must also 

 attempt to address the likelihood that 

 factors extraneous to the measurement 

 program may be influencing 

 colonization. For example, the 

 disposal site may have been affected 

 by hypoxia while the reference stations 

 (representing the ambient seafloor), 

 because of their location, were not 

 affected by hypoxia. If this appears to 

 a plausible hypothesis, near-bottom 

 oxygen measurements might be added 

 subsequently to the monitoring 

 program. 



It cannot be over-emphasized that 

 the monitoring protocol illustrated 

 (Figure 2) does allow for flexibility; as 

 additional management issues or 

 objectives are identified, the 

 monitoring protocol can be revised. If 

 the measurement program fails to 

 identify a specific cause for 

 recruitment, the option always exists 

 for a conservative management 

 approach; this would involve going 

 directly to box 2.11 (capping) instead 

 of Box 2.9 (reassessment). This option 

 might prove less costly if one is 

 adamant about determining the cause 

 for the anomalous recruitment, 

 especially if clean capping material 

 were readily available within the 

 dredging project area. However, if an 

 anomalous recruitment pattern is 



observed and one decides to cap 

 without determining the specific cause 

 for the departure from the expected, 

 any shortcoming in the initial 

 permitting evaluation which may have 

 been responsible will continue to exist 

 and potentially cause repeated 

 problems in the future. 



Box 2.10 "Re-Evaluate Assessment 



Procedure. Cap Disposal 

 Mound" 



If a toxic response of the tested 

 bloassay organisms is obtained, it is 

 necessary to re-evaluate the initial 

 permit testing procedure. Why did the 

 material originally tested pass the 

 permit evaluation screening while the 

 sediment from the disposal site fails 

 the test? These are the same issues 

 discussed above for Box 2.8. 



Underlying Assumptions : The 

 assumption is that the permit testing 

 was not adequate to identify toxic 

 sediment or that the toxics are more 

 available to the tested organisms due 

 to diagenetic or "weathering" factors of 

 the sediment at the disposal site. 



Sources of Uncertainty: It may not 

 be possible after-the-fact to identify the 

 causes for the disparity between the 

 permit test results (low levels from 

 bulk chemistry screening or bioassay 

 results showing no or equivocal 

 toxicity) and the post-disposal results 

 (toxicity shown in bioassay). To 

 further address this problem would 

 require a considerable research effort 

 on the bioavailability of a wide range 

 of contaminants under a wide range of 

 Eh-pH conditions. 



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



