Leachate concentration

Danon-Schaffer [31] includes several leachate concentrations for PBDEs in her thesis. BDE congener BDE-209 (i.e. C-DecaBDE) has been chosen. The calculations given in Tables 12 and 13 are based on the assumption that the rainfall is constant over time. The table numbers refer to Danon-Schaffer [31], There is no information... 

Procedure Allelopathic aqueous leachate is prepared by soaking dried leaves (lg/100 mL or 1% w/v) in distilled water for 3 h. This leachate is filtered through Whatman paper (No. 4) and then through a sterile Millipore membrane (0.45 mm). Then, it is poured in Petri dishes and mixed with agar (2%) for a final aqueous leachate concentration of 0.5%. The volume will depend on the size of the Petri dish, 3 mL of leachate plus 3 mL of agar are enough for a 6 cm Petri dish. Osmotic potential of the leachate is measured with a freezing-point osmometer (Osmette A, Precision System Inc.). 

Measured concentrations of As(lll) and As(V) in leachate from a column experiment are compared with simulated concentrations using the model PHAST in Figure 1. Arsenic concentrations in leachate were below detection for the first 50 pore volumes of contaminated groundwater eluted through the column. Although initial As(lll) concentrations were 650 ptg/L, oxidation of As(lll) to As(V) by manganese oxides resulted in leachate concentrations of As(lll) near detection limits for 270 pore volumes. All of the As... 

Cumulative leaching plots (cumulative mass of element leached per mass dry weight of ash vs. cumulative mass of leachate collected vs. mass dry weight of ash) for Pb, Cu, and Zn are shown in Fig. 12. The plots are constructed using measured element leachate concentrations and volumes of leachate collected. In many cases, the detection limit of the element was used as the concentration, so that the traces are conservative. Over time, the pH of leachates has dropped from about 12 to about 9. Data for Cd are not shown because of the high number of detection limit values that were observed in both the unamended and amended lysimeters. 

Secondary phases predicted by thermochemical models may not form in weathered ash materials due to kinetic constraints or non-equilibrium conditions. It is therefore incorrect to assume that equilibrium concentrations of elements predicted by geochemical models always represent maximum leachate concentrations that will be generated from the wastes, as stated by Rai et al. (1987a, b 1988) and often repeated by other authors. In weathering systems, kinetic constraints commonly prevent the precipitation of the most stable solid phase for many elements, leading to increasing concentrations of these elements in natural solutions and precipitation of metastable amorphous phases. Over time, the metastable phases convert to thermodynamically stable phases by a process explained by the Guy-Lussac-Ostwald (GLO) step rule, also known as Ostwald ripening (Steefel Van Cappellen 1990). The importance of time (i.e., kinetics) is often overlooked due to a lack of kinetic data for mineral dissolution/... 

FIGURE 7 LEAD AND CADMIUM LEACHATE CONCENTRATIONS FROM CUPOLA EMISSION CONTROL SLUDGE TREATED WITH METALLIC IRON... 

FIGURE S LEAD LEACHATE CONCENTRATIONS FROM BRASS FOUNDRY SOLID WASTE TREATED WITH LIME OR MAGNESIUM HYDROXIDE. 

FIGURE 9. LEAD LEACHATE CONCENTRATORS FROM CUPOLA EMISSION CDNTROL SLUDGE FROM WASTEWATER TREATED WITH MAGNESIUM HYDRDXIDE... 

The purpose of leaching tests is to obtain aqueous phase concentration of constituents which are released from solids when placed in a land disposal unit. Leachate concentration constitute the source term for transport and fate in the environment and, therefore, the associated risk. Leaching potential for the same chemical can be quite different depending on a number of factors such as characteristics of the leaching fluid, form of the chemical in the solids, and the disposal conditions. 

The composition of pore waters from contaminated cores 1 and 2 were used to initialize the model (Table 2). Concentrations represent leachate collected from the initial half pore volume of each core. Eluent specified in the transport simulations had the composition of uncontaminated ground water in Table 2. Reactions proposed to describe concentration changes for selected constituents within the cores are based on comparisons between eluent and leachate chemistry and analysis of selected constituents in the core samples. Equilibrium constants and kinetic rates for the reactions were adjusted to give the best fit to leachate concentrations from core 1. The same reactions, equilibrium constants, and kinetic rates were then tested by modeling the concentrations of constituents in leachate from core 2. This geochemical model will be used in the future to simulate evolution of contaminated ground water associated with the Area 4 landfill at the aquifer scale. 

The physical reaction of the ash to aqueous leaching is an important factor when considering the potential contamination of groundwater by these leachates. Concentrations of elements in leachates will be determined by the amount of ash exposed to leaching solutions. Observations of this type are useful in determining the mode of disposal most suited for the ash being produced. For example, the WYO-FA sample would be better suited to a dry disposal system, with an occasional wetting, rather than the pond system which is most frequently used. 

Table 5.2. Change in Leachate Concentration of Total Soluble Al at the Adirondack Forest Site...

The authors found that the model-predicted As concentration is close to the leachate concentrations from the column packed with dust from the continuous reactor (1 120 H.gL-1 versus 1 330 xgL-1), when the solubility product of scorodite from Robins (1990) and the triple layer model is used. Only 11% As in the system was sorbed onto hydrous ferric oxide surfaces. Arsenic concentrations in the leachate are largely controlled by scorodite solubility. It should also be pointed out that simulations using solubility only and without including surface adsorption resulted in a closer match (1 270 n-gL-1 versus 1330 piglA1). For the simulation of the column experiments using wastes from the batch-reactor, the triple layer model predicted too low an As concentration (33 jigL-1 versus 120 pigL-1). 

A leaching model based on a sorption-desorption process is used for describing the contaminant release from the waste disposal. The leachate concentration, CL (Bq.m3), is determined by the a distribution or a partition coefficient, Kd (cnr .g1) which describes the relative transport speed of the contaminant to the water existing in the pores soil properties such as bulk density, p (g.cm3), and water content, 0, affect the extent of contamination, described by the contaminated zone thickness, xt (m), area, A (m2) and the amount of contaminant in the source, It (Bq), (EPA 1996 Hung 2000) ... 

Initial laboratory tests aimed at stabilizing the arsenic at pH 5 and 8 showed a lead solubility of 30 an 32 ppm. These tests were carried out without excess lime addition. During the TCLP test, acetic acid is added so that the pH of the leach solution is not controlled at any particular value. This explains the relatively high Pb solubility. Phosphate was then added during the arsenic precipitation stage, again without excess alkaline material. The results of the TCLP tests with phosphate additions showed a Pb leachate concentration of 40 to 60 mg/1. These data indicate that phosphate alone is not able to control the leaching of the lead. 

The amount of mass of each organic compound entering the aquifer via the double-liner system was calculated using these initial leachate concentrations. There was a continuous 12.2-meter head driving flie leachate through the liner. Leachate was predicted to... 

Mean leachate concentration after 50 years land operations 600 500 600 2 0.1... 

Table 10.6. Development of leachate concentrations of selected elements in a slag deposit (EKESA-ProJect 1992 Kersten et al. 1995)...

Monitor the performance of the system and match monitored performance against that expected. "Trigger" conditions may be developed (e.g. level of leachate mounding and concentration of contaminants in the leachate concentrations at volume of fluid collected from secondary collection systems) such that back-up measures can be implemented once a failure of part of the system has been detected, and before conditions have been established which will ultimately cause contamination of groundwater. 

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