Contributors (in alphabetical order)
|
|  Yüklə 2.47 Mb.
|
Elutriate FractionThe results of the laboratory analyses for the ambient pH elutriates, which are summarized in Table 20 and Table 21, are presented in Normandeau (1999b). Results include the number of samples analyzed, the number of samples above detection limits, the minimum value and maximum value detected, the arithmetic and geometric mean and the standard deviation for each parameter analyzed. The ambient pH elutriates were tested for the presence of organophosphorus pesticides, which as a group consist of 25 different organic compounds. The only organophosphorus pesticide detected was ethyl parathion, in one sample (LGO 8-4), at a concentration of 1.0 ppb (mg/l). Although identified in the one elutriate sample, ethyl parathion was not detected in any of the sediment samples. Parathion is a regulated substance in fresh waters in the states of Oregon and Washington with a maximum allowable concentration of 0.013 ppb (chronic). Table 21. Summary of average concentrations (ppb) of organochlorine pesticides and TPH in sediment collected during 1997 in the Lower Snake River (Corps 1999).
No organochlorine pesticides were detected in any of the ambient pH elutriate samples. The organochlorine pesticides DDT (and its metabolites) aldrin, dieldrin, endrin, heptachlor and lindane had been detected in several of the sediment samples tested. The results of the elutriate tests suggest that although these compounds are present in the sediments they do not readily partition into water. Glyphosate was detected in only 2 of the 94 ambient pH elutriate samples, while AMPA was not detected. Glyphosate was detected at a concentration of 0.69 µg/L in a sample collected from Lake Bryan and at a concentration of 0.58 µg/L in a sample collected from Lake Sacajawea. In comparison, the maximum contaminant level established for glyphosate by the USEPA in drinking water is 700 µg/L, well above the concentrations detected in the two elutriate analyses. Each of the 94 ambient pH elutriates were tested for the same suite of metals that were analyzed on their corresponding sediments. The results of the individual samples are summarized in a table included in Normandeau, 1999b. For the 18 metals analyzed only beryllium, silver and thallium were not detected in the elutriate samples. Of these metals only silver was not detected in the original sediment samples. The mean metal concentrations for the ambient pH elutriates are summarized by river reach in Table 22. The predominant metals detected include barium and manganese. The average concentration of barium, by river reach, in the ambient pH elutriates increases from 83.3 ppb for the samples collected from Lower Granite Lake to 243.6 ppb for the sediment samples collected from Lake Sacajawea. Although a corresponding trend in the concentration of barium in the sediment samples was not observed, it was one of the predominant metals detected. Its relatively high concentration in the ambient pH elutriates is most likely the result of its concentration in the sediments and its relatively high solubility in water (Hem 1989). Table 22. Summary of mean metal concentrations for ambient pH elutriate samples collected during Phase 2 (1997) of the Lower Snake River project (Corps 1999).
The predominant metal identified in the ambient pH elutriates was manganese. The average concentration of manganese, by river reach, in the ambient pH elutriates ranged from 504 ppb for the samples collected from Lower Granite Lake to 1,432 ppb for the samples collected from Lake West. In general, the trend in manganese concentrations in the ambient pH elutriate samples increases with distance downstream. As observed with barium, there does not appear to be a clear relationship between the concentration of manganese in the sediment samples and in the ambient pH elutriates. The maximum metal concentrations detected in the ambient pH elutriates (Normandeau 1999b) were also compared with the recommended surface water quality standards of the state of Oregon Department of Ecology (ODOE), the United Nations (agricultural water quality goals), EPA, and WDOE to identify any CoC. The maximum concentration of four metals: arsenic, copper, manganese, and mercury were found to exceed their applicable water quality standards. Because these metals also occur naturally in the environment, their concentrations were compared with representative background values to determine if they represent a CoC. The results of the ambient pH elutriate tests were compared with historical water quality data collected by the USGS from the Snake River near Anatone, Washington. The maximum detected concentration of arsenic, copper, and mercury were found to be less than their average background concentrations and as a result were not considered to represent CoC. The ambient pH elutriate samples were also analyzed for the following nutrients: ammonia, nitrate/nitrite, phosphate, sulfate and TKN (Normandeau 1999b). The mean concentration of each of these nutrients for the four reaches along the Lower Snake River are summarized in Table 23. Table 23. Summary of mean nutrient concentrations for ambient pH elutriate samples collected during Phase 2 (1997) in the Lower Snake River (Corps 1999).
The dominant form of nitrogen found in the elutriate samples was ammonia, which also was also the predominant form of nitrogen identified in the sediment samples. The dominance of ammonia may reflect the limited oxygen environment of the channel bed sediments as a result of the decomposition of organic material. The consumption of oxygen by the decay of organic material would lead to the reduction of nitrate/nitrite, thus limiting their concentrations in both the sediment and elutriate samples. | ||||||||||||||||||||||||||||||||||||||||||||||||