Page 209 - Materials Chemistry, Second Edition

192 Practical Design Calculations for Groundwater and Soil Remediation

the degree of water saturation is 100%. The following formula can be used to
determine the volume of water (V water ) needed for bioremediation.

V water = (volume of soil) × (desired moisture content − initial moisture content)
= (V )(ϕ − ϕ )
w,f
w,i
soil
= (V )[(ϕ)(S − S )] (5.33)
soil
w,i
w,f
where
ϕ = initial volumetric moisture content
w,i
ϕ = desired volumetric moisture content
w,f
ϕ = porosity of soil
S w,i = initial degree of saturation
S = desired degree of saturation
w,f
Example 5.22: Determine the Moisture Requirement
for Soil Bioremediation
An underground storage tank (UST)-removal project resulted in 375 yd of soil
3
impacted by gasoline that has to be treated before disposal. Bioremediation
using static stockpiles has been selected as the treatment method. Determine
the amount of water needed for the first spray.
Use the following simplified assumptions in your calculation:

• Porosity of soil = 35%
• Initial degree of saturation = 20%

Solution:
(a) Based on Table 5.2, the optimal volumetric water content for
soil bioremediation is 25%–85% of the water-holding capacity.
Without conducting an optimization study, the middle value of
this range, 55%, is selected.
(b) Water needed = (375)[(0.35)(55% − 20%)]
= 45.9 yd = 1,240 ft = 9,280 gal
3
3
Discussion:
Addition of makeup water is often needed periodically.

5.4.3 Nutrient Requirements

Nutrients for microbial activity usually exist in the subsurface. However, with
the elevated level of organic COCs, additional nutrients are often needed to
support the bioremediation of the COCs. The nutrients to enhance microbial
growth are assessed primarily on the nitrogen and phosphorus requirements.