課程名稱︰環境土壤物理學
課程性質︰探討土壤的結構與質地如何跟空氣與水作用
課程教師︰李達源
開課學院：農學院
開課系所︰農化系第一類群組必修
考試日期（年月日）︰Jun. 22, 2006
考試時限（分鐘）：兩節課，100鐘
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
1. Please define or explain the following terms in a few sentences. (15%)
(a) Heat capacity
(b) Richars'equation
(c) Damping depth for thermal oscillations
(d) Tortuosity factor for oxygen diffusion in soils
(e) Retardation factor for a pesticide transport in soils
2. Draw a curve showing a typical relationship between hydraulic conductivity
and soil water content and describe a laboratory experiment for measuring
the hydraulic conductivity-water content functional relationship in
unsaturated soil. Indicate what measurements must be taken and how the
data is analyzed to produce K(θ). (10%)
3. A vertical soil column is in steady state evaporation. Three tensiometers
read
h z
──── ────
-15cm 10cm
-40cm 20cm
-100cm 30cm
Calculate K (h) for two points in this system if the evaporation from the
colum is 1cm/day (10%)
4. Oxygen is being consumed in a root zone at a rate R(z) = R0[1+(z/L)] for
-L < z < 0. The units of R0 are mass of oxygen/volum soil/time. If the
flux at z = -L is zero, calculate the steady state flux of oxygen for
-L < z < 0. (10%)
5. What would the steady state volatilization flux be for a volatile organic
chemical (VOC) through a soil cover assuming an industrial waste containing
high concentrations of the VOC has been placed in a landfill and covered
with 200cm thick of soil? Assume the soil had a constant and uniform water
content (θ=0.1) and porosity (φ=0.4). The gaseous diffusion coefficient
of this VOC in air is 4000cm^2/day and the saturated vapor density of the
VOC is 0.3ng/cm^3. Assume the vapor density of the VOC in the soil surface
was always maintained to be zero. (10%)
6. A max-min thermometer registers an annual temperature difference
(Tmax - Tmin) if 10C at Z = -100cm in an area where the average max-min
annual soil surface temperature difference Tmax-Tmin is 20C. Calculate:(10%)
(a) soil damping depth
(b) soil thermal diffusivity
7. You are asked to determine how deep to bury a water pipe in soil to prevent
the pipe from freezing. Describe what measurements you would need to make,
what information you need to obtain, and what calculations you would need to
make. (10%)
8. Benzene which exists in gas form, dissolve in water, reacts in soil, and
also adsorbs to soil solids. (10%)
(a) In words write down the mass balance for this chemical for a unit
volume located in soil.
(b) If Henrys law is valid for this chemical, what simplifications may be
made in the general solute flow equation
rs + δ/δt[aCg +θCl +ρbCs] =
δ/δZ[Dg^soil δCg/δZ ÷ δ/δZ[Dl^soil δCl/δZ - δ/δZ(JwCl)
from the equation above?
(c) If he linear, equilibrium adsorption is valid for describing the
adsorption of this chemical by soil solids, what additional
simplification may be made? (10%)
9. A trace organic chemical has a linear, equilibrium adsorption isotherm of
Cs = 50μg/s soil for each CL = 1μg/mL solution (i.e. KD=50mL/g) for a
saturated soil with bulk density ρb = 1.2g/cm^3 and saturated water
content θs = 0.6. The soil has a saturated hydraulic conductivity
Ks = 100cm/day in a column of L = 100cm height. Water is ponded continously
to a height d = 20cm above the column. The bottom is open to the
atmosphere. (15%)
(a) Calculate the steady state water flux Jw and the average pore water
velocity V.
(b) If th ponded inlet solution is suddenly switched (at t = 0) to a
solution containing chloride and the trace organic, calculate the
chloride breakthrough time and the trace organic breakthrough time.
(c) Draw breakthrough curves of chloride and the trace organic chemical and
discuss how the diffusion-dispersion coefficient affects the shape of
the breakthrough curves.
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