Page 55 - Materials Chemistry, Second Edition

38 Practical Design Calculations for Groundwater and Soil Remediation

2.3.2 Amount of Packing Material and/or Bentonite Seal
Packing and seal materials need to be purchased and shipped to the site
before installation of monitoring wells. A good estimate of the amount of
packing material and bentonite seal is necessary for site assessment.
To estimate the packing and seal materials needed, the following proce-
dure can be used:

Step 1: Determine the diameter of the boring, d b.
Step 2: Determine the diameter of the well casing, d c.
Step 3: Determine the thickness interval of the well packing or benton-
ite seal, h
Step 4: Calculate the volume of the packing or bentonite seal using the
following formula:

π
Volume of packingorbentonite needed = ( b d 2 − d 2 c ) h (2.14)
4

Step 5: Determine the mass of the well packing or bentonite needed by
multiplying its volume with its total bulk density.
Information needed for this calculation

• Diameter of the borehole, d b
• Diameter of the casing, d c
• Thickness interval of the packing or the bentonite seal, h
• Total bulk density of the packing or bentonite seal, ρ t

Example 2.21: Amount of Packing Materials Needed
The four monitoring wells in Example 2.20 are to be installed 15 ft into the
groundwater aquifer. The wells are to be perforated (0.02-in. slot opening) 15
ft below and 10 ft above the water table. Monterey Sand #3 is selected as the
packing material. Estimate the number of 50-lb sand bags needed for this
application. Assume the total bulk density of sand is equal to 1.8 g/cm (112
3
lb/ft ).
3
Solution:
(a) Packing interval for each well
= perforation interval + 1 ft = (10 + 15) + 1 = 26 ft
Volume of sand needed for each well
= {(π/4)[(10/12) – (4/12) ]}(26) = 11.9 ft 3
2
2
Volume of sand needed for four wells = (4)(11.9) = 47.6 ft 3