Environmental Engineering Reference
In-Depth Information
6.4. A 150-ha wheat farm in central Iowa consists of
predominantly loamy sand soil with approxi-
mately 1% organic matter, and the ground surface
has approximately a 1% slope. During the off-
season, plowing is up and down the land slope. The
annual runoff volume is 10 cm and the maximum
runoff rate is 3 cm/h.
flow direction toward the river is 300 m. A soil
analysis classifies the soil texture as a loam, with a
water content of 0.1, a bulk density of 1700 kg/m 3 ,
and a 4% fraction of organic carbon. Of particular
concern is that the soil analysis also shows that
malathion is present in the soil at a concentration
of 2 mg/g and could potentially be washed into the
river sorbed onto the sediment that is dislodged
by erosion. A delivery ratio of 15% and an enrich-
ment ratio of 2 is expected for erosion and mala-
thion transport. A literature review indicates that
malathion has a solubility of 145 mg/L and a log
octanol-water partition coefficient of 2.89. (a)
Estimate the aqueous concentration of malathion
in the pore water of the soil, and determine
whether you would expect to find malathion in the
soil as a NAPL. (b) If the catchment is located in
an area with Type III rainfall characteristics, esti-
mate the mass of malathion carried into the river
(sorbed onto the eroded soil) due to a single 24-
hour storm with a rainfall amount of 200 mm, a
runoff amount of 85 mm, and a peak runoff rate
of 2 cm/h.
(a) If the typical overland flow distance from the
beginning of overland flow to a drainage
stream is 1.1 km, estimate the average annual
soil loss.
(b) If the delivery ratio is 5%, what is the sedi-
ment load on the receiving water body?
6.5. The soil in a watershed has an average mercury
concentration of 1.2 µ g/kg, annual sediment load
in the runoff of 7.2 × 10 5 kg, and a mean enrich-
ment ratio of 3.5. Estimate the annual mercury
loading from sediment-laden runoff into the
receiving water body.
6.6. A typical square 1000-ha corn farm in central
Nebraska has an average annual runoff of 200 mm
and an average maximum runoff rate of 10 m 3 /s.
The soil consists primarily of 70% sand, 15% silt,
and 15% clay, and has a ph of 6.8, bulk density of
1600 kg/m 3 , porosity of 0.3, and contains 2%
organic matter. The average land slope is 1%, and
the typical farmer tries to control erosion by
plowing across the slope. During the growing
season, farmers typically apply 50 kg P/ha and
250 kg N/ha, typical delivery ratios to adjacent
streams are on the order of 0.15, approximately
10% of the applied fertilizer is bound in erodible
soil (top 15 cm), with an enrichment ratio on the
order of 2.5. Estimate the annual loading of P on
the watercourse adjacent to the farm and the
annual buildup of P in the farm soil.
6.8. A 0.5-m 3 sample of soil is found to contain 32 g of
carbofuran (an insecticide) and to have a water
content of 0.2 and a bulk (dry) density of 1600 kg/
m 3 . If the soil has an estimated distribution coef-
ficient of 0.3 mL/g, estimate the concentration of
carbofuran in the pore water. The solubility of
carbofuran is 700 mg/L.
6.9. Repeat Problem 6.8, accounting for vaporization
of carbofuran by taking K h = 7.9 × 10 6 and a soil
porosity of 0.25.
6.10. The half-life of carbofuran is estimated to be 35
days. If the pore water concentration of carbofu-
ran in a soil is found to be 5 mg/L, estimate how
long it will take for the concentration of carbofu-
ran to decrease to the drinking-water standard of
0.040 mg/L.
6.7. The insecticide malathion is regularly applied to a
50-ha pasture that is 60% grass. The pasture slopes
toward a river at 2% and the average length in the
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