CONSTRUCTION SPECIFICATION

NE-221 BENTONITE TREATED EARTH FILL

1\. SCOPE

This item shall consist of furnishing bentonite, mixing bentonite with
soil and placing bentonite-treated soil.

2\. MATERIALS

The bentonite shall be a free flowing, high swelling, granular sodium
bentonite. Bentonite in fine powder form shall not be used due to loss
from blowing dust. Bentonite shall be Envirogel 10 as manufactured by
Wyo-Ben Inc. or Granular Bentonite 12/40 mesh manufactured by Black
Hills Bentonite or equivalent. The bentonite shall have a free swell of
at least 18 cc/2gm as measured by ASTM Standard Test Method D 5890 and
shall meet the following gradation requirements:

  ---------------------------------- ------------------------------------
  Sieve Size                         Percent Passing

  10                                 98-100

  20                                 60-100

  200                                0-20
  ---------------------------------- ------------------------------------

3\. APPLICATION

Bentonite shall be applied only on relatively calm days to prevent
significant loss of material. Bentonite shall be applied to soil that is
free of all vegetation, trash, roots, frost, snow, ice, stones over 2
inches in diameter, and other objectionable material. Surfaces shall be
graded to remove irregularities and thoroughly tilled if necessary to
reduce the soil to its native particle size.

Bentonite shall be spread uniformly at the specified application rate
measured in pounds of bentonite per square foot of surface area per lift
thickness. The amount of bentonite per lift and the number of lifts
shall be as shown on the drawings or specifications.

The bentonite shall be uniformly spread on the surface using a truck
drawn spreader box, agriculture lime spreader, mechanized conveyor-fed
material spreader box or other type of drop spreader approved by the
engineer or technician. Broadcast spreaders are not acceptable.
Pre-measured tarpaulins or cloths placed in different locations shall be
weighed after spreading material to verify that the specified
application rate is met.

The bentonite may also be applied at the specified rate by distributing
100-pound bags of material in a marked grid pattern. Each bag shall be
opened and the material spread evenly within each grid square, using
hand rakes.

4\. MIXING

Bentonite shall be thoroughly mixed with a rototiller, soil stabilizer
or other similar mixing equipment approved by the engineer or
technician. Small or medium sized tractor drawn rototillers are
acceptable but self-propelled industrial rototillers are preferred. The
rototiller shall be capable of digging to a depth at least equal to one
compacted lift thickness. A minimum of two passes of the mixer shall be
used. For the first pass set the mixing depth to approximately ½ of the
full lift depth, then reset the mixer to full depth for the second pass.
The speed of the mixer shall be adjusted to insure complete and uniform
mixing of the materials. Bentonite may be incorporated with stockpiled
material and then placed in the desired area or incorporated with
material in place, such as the sides and bottom of the pit.

To yield sufficient water content, bentonite shall be applied and mixed
with a relatively dry soil, then watered, re-mixed and compacted. In
certain instances it may be necessary to wet the soil previous to
applying the bentonite to prevent the bentonite from "balling up".
Conversely, it may be necessary to dry the soil to achieve the
recommended moisture content. Practice runs are recommended with
unfamiliar material to find the most desirable application
mixing/(de)watering and re-mixing process.

A plant or pugmill type mixer may be used to produce the required
soil-bentonite mixture as specified. Heavy silts or clay type materials
shall pass through a soil pulverizer or hammermill to precondition the
soil prior to introduction into the mixing chamber. The mixed soil
bentonite material produced by a plant mixing system shall be directly
transported to the job site and placed immediately to minimize moisture
loss.

5\. COMPACTION

The thickness of the finished compacted bentonite treated earth fill
blanket or individual lifts shall be as shown in the drawings or
specifications.

Compaction with a sheepsfoot roller or a track type tractor shall not be
allowed.

When multiple lifts are specified or required, the interface between the
lifts shall be roughened or scarified a minimum of ½ inch prior to
placement of the next lift.

Compaction adjacent to structures protruding through the soil bentonite
mixture shall be compacted to a density equivalent to that of the
surrounding mixture by means of manually directed power tampers or plate
vibrators.

A protective cover layer of at least 12 inches of on-site material shall
be applied immediately after compaction, over the bentonite treated
earth fill blanket to protect it from forming drying cracks and from
weathering.

[Class A compaction.]{.underline} Each layer or lift shall be compacted
as necessary to make the density of the bentonite treated earth fill
material not less than the minimum density specified on the drawings.
The moisture content on the bentonite treated earth fill material shall
be maintained within the specified range shown on the drawings.

[Class C compaction.]{.underline} Each layer or lift shall be compacted
by the number of passes of the type and weight of roller or other
equipment specified.

Bentonite treated earth fill soil shall have a water content sufficient
to insure 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.

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 a
vibrating compactor may also be utilized on non-cohesive soils.
Partially penetrating pad foot compactors, such as those found on
landfill compactors, may be used on cohesive material or other suitable
equipment approved by the engineer or technician may also be used.

An alternative to heavy compaction equipment is traversing the entire
surface with a wheel type tractor (minimum 100 horsepower) with not less
than five passes. The lift thickness shall be reduced by one half of the
specified thickness if the total thickness of the blanket or lift is
more than five (5) inches. Tractors must exert a pressure of not less
than 10 pounds per square inch.

6\. SAFETY

Dust masks and goggles are recommended to be worn by all personnel on
the site during bentonite application and while mixing for protection
against bentonite dust.

7\. OPERATION AND MAINTENANCE

During hot, dry periods, bentonite treated earth fill liners shall be
inspected for drying cracks. Should drying cracks begin to develop, the
entire exposed liner area shall be watered. If the bentonite treated
earth fill blanket develops major cracks that watering will not heal,
the blanket shall be re-mixed and compacted as required in Section 5,
Compaction.