**NATURAL RESOURCES CONSERVATION SERVICE\
CONSTRUCTION SPECIFICATION**

**BENTONITE SEALANT**

1\. SCOPE

The work shall consist of applying and mixing bentonite, and compacting
bentonite-treated soil required by the drawings and specifications.

2\. TIMING

Construction work covered by this specification shall not be performed
if weather or soil moisture conditions are not suitable.

3\. MATERIAL

Bentonite shall be a free flowing, high swelling, granular sodium
bentonite. Bentonite shall be American Colloid Company, Volclay SG-40;
Wyo-Ben, Envirogel-10; or equivalent and meet the following gradation:

Sieve Size Percent Passing

10 100

20 60-100

200 0-20

4\. APPLICATION

a\. Bentonite shall be applied to soil that is free of all vegetation,
trash, roots, frozen soil, snow or ice, stones over 2 inches in diameter
or other objectionable material.

b\. Slopes to be treated shall be 3:1 or flatter.

c\. Holes shall be filled with on-site material compacted.

d\. Bentonite shall be spread uniformly at the rate specified in Section
9. The thickness of the finished compacted blanket shall be 8 inches.
Bentonite-treated soil shall be placed in two 4-inch finished lifts at a
rate of   pounds (1/2 of the total) of bentonite per square foot per 4
inch lift.

e\. The preferred method for applying bentonite is distributing
100-pound bags of material in marked grid patterns. Each square of the
grid should be of the proper square footage to be covered by a 100-pound
bag of bentonite.

Bentonite may also be applied using an agricultural seed or lime
spreader or other equipment as approved by the engineer. Premeasured
tarpaulin or drop cloths spread in different locations shall be weighed
after spreading material over them to ensure that the proper rate is
being applied. Spreaders must be a drop type. Broadcast spreaders are
not acceptable.

5\. MIXING

Bentonite shall be thoroughly mixed with a disk, roto-tiller or other
suitable mixing equipment approved by the NRCS engineer or the
designated representative. A recommended procedure to achieve adequate
mixing is as follows:

This procedure requires that the pond bottom be over excavated by 12
inches.

a\. Apply the one half of the bentonite application to the subgrade.
Chisel plow the area of bentonite application cross-directional.

b\. Disk plow the cross-directional to a depth of 6 inches across the
entire application area.

c\. Compact soil to meet the requirements under Section 6, Compaction.

d\. Place soil for the second lift, approximately 6 inches.

e\. Apply bentonite at the rate for the second lift and chisel plow
cross-directional to a depth of 6-8 inches across the entire application
area.

f\. Disk plow cross-directional to a depth of 6 inches across the entire
application area.

g\. Compact soil to meet the requirements under Section 6, Compaction.

6\. COMPACTION

The methods of compaction listed below are intended to achieve 90
percent of the maximum density as determined by the Standard Proctor
Test, ASTM-D 698.

a\. Bentonite-treated soil shall have a water content sufficient to
secure compaction. When kneaded in the hand, it will form a ball which
does not readily separate when struck sharply with a pencil and will not
extrude out of the hand when squeezed tightly.

Water should be added to the soil (or dried if too wet) before applying
bentonite to yield a sufficient water content.

b\. The thickness of the finished compacted blanket shall be 8 inches.
The thickness of each finished compacted lift shall be 4 inches. Each
lift shall be compacted by traversing the entire surface with not less
than two passes of a pneumatic-tired roller exerting a pressure of not
less than 50 pounds per square inch, a flat steel wheel roller exerting
not less than 100 pounds per inch of width of roller or by vibrating
compactor.

An alternative to heavy compaction equipment is to allow a wheel type
tractor (minimum 100 horsepower) traversing the entire surface with not
less than five passes. Tractors must exert a pressure of not less than
10 pounds per square inch.

Compaction with a sheepsfoot roller or a track type tractor shall not be
used on sand or other granular soils.

c\. A protective cover layer of 6 inches of on-site material shall be
applied over the bentonite-treated blanket to protect it from drying
cracks.

7\. SAFETY

Dust mask and goggles shall be worn by all personnel on the site during
bentonite application and mixing for protection against bentonite dust.

8\. OPERATION AND MAINTENANCE

During hot, dry periods, ponds shall be inspected for drying cracks.
Should drying cracks begin to develop, the entire exposed pond area
shall be watered sufficiently to reseal the cracks.

If the bentonite-treated blanket develops major cracks that watering
will not heal, the blanket shall be re-disked and compacted as required
in Section 6, Compaction.

9\. [additional items which apply to this job]{.underline}