[6 pts] A river sediment sample is analyzed and contains 950 ?g/kg of DDT. In a

Question

[6 pts] A river sediment sample is analyzed and contains 950 ?g/kg of DDT. In a reference book, you find that for this type of sediment a typical value of Kp is 2500 L/kg What is the predicted equilibrium concentration of DDT in the porewater of the sediment? a. b. Suppose the sediment were disrupted during a dredging operation and a cloud of sediment particles was formed in the overlying river. A sample of this cloudy water reveal a total solids concentration of 300 mg/L. If essentially all of these suspended solids are due to floating sediment particles, what is the total concentration of DDT in suspension in the cloudy river water. Give this in units of ug/L c. Chloride ions (CI are a by-product when TCE degrades, so the source of TCE also contains some CI. If a plume of a conservative tracer like chloride from the source takes 270 days to arrive at a nearby drinking water well, how long would it take for the TCE plume to arrive at the well?

Explanation / Answer

a) Kp is defined as

=concentration of a material in solid phase/equilibrium concentration of the material in the contacting liquid phase

So, the equilibrium concentration of DDT in the pore water of the sediment

=concentration of a material in solid phase/Kp

=950/2500 ?gm/L

=0.38 ?gm/L

b)Amount of DDT coming from the solids in the plume(per L)

= concentration of the DDT in the solid x .03

=0.3x(950 x 10-6/103) gm

=2.85x10-7 gm

=.285 ?gm

Amount of DDT coming from the solids in the plume(per L)

=equilibrium concentration of DDt in pore water

=0.38 ?gm

Total concentration

=(0.38+0.285) ?gm/L

=0.665 ?gm/L

c) It will take same time to reach the well. That is 270 days.

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