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0 D 4646 - 03
<br />9. Procedure
<br />9.1 Geomedia samples are spread out on a flat surface, no
<br />more than 2 to 3 cm deep, and allowed to air dry for 7 days or
<br />until constant weight (a change that is less than 5 %/24-h
<br />period) is achieved (do not oven dry).
<br />9.2 After the sample has air dried, it is passed through a
<br />2-mm screen sieve. Large aggregates are to be crushed, without
<br />grinding, using a clean mortar and a rubber-tipped pestle.
<br />9.3 Mix the sieved material until the sample is homoge-
<br />neous. Use a riffle splitter, or other unbiased splitting proce-
<br />dure, to obtain subsamples of appropriate size.
<br />9.4 Remove subsamples and determine the moisture content
<br />of the air-dried sample (refer to Test Method D 2216).
<br />9.5 Determine the mass of geomedia sample, corrected for
<br />moisture content:
<br />Determination of air-dried soil mass equivalent to the desired
<br />mass of oven-dried soil:
<br />A = M11 + (M/100)] (1)
<br />where:
<br />A = air dry soil mass
<br />M, = mass of oven-dried soil desired, and
<br />M = moisture, %.
<br />9.6 Place between 5 and 70 g (oven-dried basis) of the
<br />weighed air-dried sample into the appropriate container. The
<br />samples should be weighed to a minimum of three significant
<br />figures.
<br />9.7 Add to the container an amount of solute solution
<br />necessary to yield a 1:20 soil-to-solution ratio. This is deter-
<br />mined on the oven-dried basis:
<br />Determination of solution volume needed per sample for a
<br />soil-to-solution ratio of 1:20:
<br />V = (Ma X 20)/p (2)
<br />where:
<br />p = density of solution, g/cm3,
<br />V = volume of solution per sample, cm3, and
<br />Me = mass of soil to be used, g, (oven-dried basis).
<br />9.8 Retain a separate, appropriately preserved aliquot of the
<br />initial solute solution for analysis.
<br />9.9 Close the container and place it on the rotary extractor
<br />(Test Method D 3987).
<br />9.10 Agitate continuously for 24 t 0.5 h at 29 ± 2 r/min at
<br />room temperature (22 t 5°C).
<br />9.11 Open the container. Note the temperature of the solu-
<br />tion and any changes in the sample or solution (that is, color,
<br />odor, etc.).
<br />9.12 Separate the solution phase from the majority of the
<br />solid phase by decantation.
<br />9.13 Filter the solution phase through a 0.45-µm pore size
<br />membrane filter (see 7:2), or centrifuge a subsample at the
<br />predetermined rate of rotation and time for the centrifugation
<br />equipment employed at constant temperature (the temperature
<br />recorded after 24 h):
<br />t = 9/2 \? rPr In (Rb/R,) (3)
<br />where:
<br />W2 =
<br />4,.' 2(r/mitt)Z
<br />60
<br />= angular velocity,
<br />rp = particle radius, cm,
<br />q = viscosity of water, 8.95 x IV g/s-cm at 25°C,
<br />pp = particle density,
<br />p = density of solution,
<br />r/min = revolutions per minute,
<br />R, = distance from center of centrifuge rotor to top of
<br />solution in centrifuge tube, cm,
<br />Rb = distance from center of centrifuge rotor to bottom
<br />of centrifuge tube, cm, and
<br />t = time, min.
<br />To remove particles >0.1-µm radius and 2.65-g/cm3 density
<br />from solution:
<br />3.71 x 10 $
<br />t ) In (Rb/R,)
<br />(r/min) i (4)
<br />Note that if filtration is used, the affinity of the filtration
<br />membrane for the solute must be evaluated. Failure to do so
<br />may lead to erroneous results.
<br />9.14 After a clear solution has been obtained, place an
<br />aliquot in an appropriate container (see 7.3), and analyze or
<br />store in a refrigerator at 4 t 2°C until analyzed.
<br />9.15 Each geomedia sample is to be subjected to the
<br />procedure in three or more replicates. The number of blanks
<br />(that is, solute solution without geomedia) carried through all
<br />steps of the procedure: should be a minimum of 5 % of the total
<br />number of geomedia samples, but not less than three.
<br />10. Calculation
<br />10.1 Calculate the distribution as follows:
<br />Kd _ (A - B)V (5)
<br />(M, B
<br />where:
<br />A = initial concentration of the solute defined as the mean
<br />concentration of the blanks, pg/mL,
<br />B = final concentration of the solute after 24 h in contact
<br />with the geomedia, pg/mL,
<br />V = volume of solution used, mL,
<br />MS = mass of soil expressed on an oven-dried basis, g, and
<br />Kd = distribution coefficient, mL/g.
<br />11. Report
<br />11.1 The Kd value must be clearly marked as nonequilib-
<br />rium 24-h distribution coefficient.
<br />11.2 Both the initial solute concentration (A in 10.1) and the
<br />final solute concentration (B in 10.1) must be reported.
<br />11.3 The initial and final solute concentration for each blank
<br />(solution without geomedia) must be reported.
<br />11.4 The mass of the sorbent (MS in 10.1), volume of
<br />solution (V in 10. 1), and the room temperature at which the
<br />rotary extractor was operated must be reported.
<br />11.5 Report the temperature of the solution and any changes
<br />noted in 9.11.
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