35 



Sources of Uncertainty: Note that 

 the identification of an unsuccessful 

 colonization may be attributed solely 

 to an observed physical factor when, in 

 fact, the cause is multifactorial. For 

 example, quasi-fluid sediments may 

 also contain high inventories of 

 sedimentary sulfides and/or particle- 

 bound metals, PAH's, or insecticides. 

 The identification of a physical factor 

 is sufficient to identify a cause for an 

 anomalous colonization, but it may 

 not identify all contributing factors. 



423 Tier Three: Chemical Effects and 

 Related Management Decisions 



This tier is addressed if an 

 anomalous rate of colonization is 

 identified, yet no physical factor has 

 been identified in Tier 2 as a potential 

 and likely cause. 



Box 2,7 "Sediment Bioassays and 



Other Measurements " 



Because disposal mounds tend to 

 be heterogeneous physical and 

 chemical mixtures of sediments, it is 

 likely that only part of a mound will 

 show anomalous rates of colonization 

 related to the discontinuous spatial 

 distribution of inhibitory substances or 

 conditions. Once locations of poor 

 recruitment have been identified in a 

 REMOTS® survey, sediment samples 

 are taken at these stations using a grab 

 or box core to collect sufficient volume 

 for the required laboratory tests. 

 These near-surface sediments are then 

 used to conduct sediment bioassays 

 using either the same protocols as 

 required in the original permit 

 (EPA/NED, 1989) or additional tests 

 may be added to evaluate the 



sensitivity of the initial permit tests. 

 Other analyses may be included at this 

 point such as ammonia and sulphide 

 leachate tests, or an evaluation of 

 dissolved oxygen at the site. 

 Numerous causes for the apparent 

 toxic response are possible, and 

 evaluation of the appropriate tests and 

 measurements must be considered on 

 a project-by-project basis. 



Box 2.8 



"Toxic Response?" 



Results from the laboratory 

 bioassay tests (animals placed in 

 sediment from the disposal mound) 

 are compared with animals in 

 sediment from the reference stations; 

 as before, the bioassay tests are for 

 acute response. Chronic tests 

 currently are under development by 

 the USACE and EPA and could be used 

 when they become available. The 

 unstated null hypothesis is: 



H : Mortalities of organisms in 

 sediment from the disposal 

 mound are not significantly 

 different from reference. 



Rejection of the null hypothesis will 

 place you in Box 2.10 and requires 

 following the tiered protocol outlined 

 in Section 5 of this report; acceptance 

 will place you in Box 2.9, indicating no 

 cause for alarm and will lead to 

 repeated periodic monitoring (Box 2.3). 

 If high mortalities are observed in 

 both the disposal site and reference 

 sediments resulting in acceptance of 

 the null hypothesis, one will need to 

 re-evaluate either the assessment 

 technique or explore the possibility 

 that the reference sediments have been 

 contaminated. 



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



