302 



The Honorable Solomon P. Ortiz 

 May 10, 1993 

 Page 2 



In contrast, the average concentration of 2,3,7,8-TCDD at the Mud Dump site was 

 documented in a 1940 EPA-sponsored survey to be 24.1 pptr (in dry weight), with 

 concentrations ranging between 0.39 pptr to 229.2 pptr. 



According to EPA's Interim Report on the Assessment of 2,3,7,8-TCDD Risk to 

 Aquatic Life and Associated Wildlife (March 1993), sediment concentrations of 100 pptr in 

 sediments pose a "high risk" to sensitive species of fish. High risk is defined by EPA to 

 cause 50-100% mortality in embryos and young sensitive species. Sediment concentrations 

 of 21 pptr and 60 pptr are considered to pose a "low risk" to avian wildlife and fish 

 respectively. Low risk is defined as a no-effects threshold for reproductive effects 

 (mortality in embryos and young) in sensitive species. Low risk is not meant to be 

 defined as something that is acceptable, but defines a threshold above which effects will 

 occur. 



Therefore, the levels of 2,3,7,8-TCDD in sediments in the Port Authority's reaches 

 are 1) close to levels that pose a high risk to fish (in two out of three reaches); 2) above 

 levels considered a low risk to fish; and 3) three to four times as high as concentrations 

 that pose a low risk to birds. 



While the Mud Dump Site sediments are less contaminated, in terms of dioxin, than 

 those from the Port Authority's facility, they are by no means clean. The average level of 

 dioxin (from 38 stations) is above what EPA considers enough to pose a low risk to avian 

 wildlife. Three stations had levels above the concentration that is considered a low risk to 

 fish; two of those stations had levels higher than what is considered a high risk to fish. 



The sediments found at the Port Authority's facility or at the Mud Dump Site could 

 hardly be described as safe enough for a sandbox. First, the sediments proposed to be 

 dredged are mostly silt and clay, hardly appropriate as sandbox material. In the 1991 

 Public Notice, the grain size characteristics of the three reaches were described in the 

 following manner. 



Reach B: 2.7% sand, 61.3% silt and 36.0% clay. 

 Reach C: 6.9% sand, 56% silt and 37.1% clay. 

 Reach D: 9.2% sand, 57.8% silt and 32.0 clay. 



Much of the sediments inside the Mud Dump Site are also largely made up of silt 

 and clay, although some sandy spots do exist. It is important to note that pollutants are 

 most closely associated with silt content. 



