Geosynthetic barrier to prevent wildlife access to contaminated sediments

A geosynthetic barrier adapted to deny wildlife access to contaminated seents (CS), includes a geocomposite (10) formed of a top layer (14) juxtaposed on a bottom layer (12) which is adapted to be placed on the sediments. The top layer includes a geosynthetic drainage matrix having a plurality of openings, and the bottom layer includes a geotextile having a plurality of openings (12H) formed so as to allow gases to escape from the contaminated sediments on which said geocomposite is placed. The openings in the bottom layer of the geosynthetic barrier have a size in the range up to 200 cm and are spaced apart on centers having a range of between 6 cm to 600 cm, for example. The geosynthetic drainage matrix may be a geonet, a geogrid or a geomesh, fabricated from polyethylene, polypropylene, high density polyethylene, low density polyethylene, polystyrene, or high impact polystyrene. The top and bottom layers may be either separate layers, or may be joined together to produce a unified geocomposite web; may be held in place by a gravel layer (G) or other means; may be used in a subaqueous (W) or a non-subaqueous environment; and may provide a suitable environment through which vegetation (V) can be rooted.

The present invention pertains to a method and apparatus for protecting 
wildlife, and more particularly to the use of a geocomposite to deny 
wildlife access to contaminated sediments. 
BACKGROUND OF THE INVENTION 
A problem which exists in contaminated areas is the poisoning of wildlife 
due to ingestion of contaminants contained in sediments. This invention 
proposes to prevent access to wildlife to contaminated sediments in 
wetlands and other areas when the sediment forms a part of the natural 
setting for the wildlife, e.g. feeding and/or resting area such as ponds. 
Usually this problem is dealt with by removing and treating the 
contaminated sediment, which destroys or severely alters the natural 
habitat. 
Previous methods of keeping wildlife and contamination separated include 
the construction of landfill liners and caps; but this applies to locales 
where the contamination is confined to a few relatively limited, well 
defined areas (since it was transported to and concentrates at the site): 
in addition, the contaminated material and capping is at least partially 
above the water table. The above two methods of reducing wildlife exposure 
to contamination, namely--1) removal and treatment of the material and 2) 
the construction of landfill liners and caps, are quite expensive, more 
complicated than the proposed barrier of the present invention, and don't 
pertain in situations where the contaminated sediment may lie on the 
bottom of ponds or other feeding areas for wildlife. 
A third possible method of keeping wildlife from exposure to contaminants 
is the placement of a thick fill or soil layer over the contaminated area. 
However, this method would be susceptible to erosion caused by water 
movements, and if it is not thick enough, would be damaged by movement of 
large animals (e.g. moose), which punch through the soil layer. 
Geosynthetic materials, including geotextiles, (see ASTM D4439-91a) are 
commonly used to separate dissimilar soils; but, on information and 
belief, have not been used to separate soil and wildlife, when the soil is 
submerged at least part of the time. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to deny access to wildlife 
to contaminated sediments, while permitting gas formed in the sediment 
layer to escape. 
It is also an object of the present invention to prevent access to wildlife 
to contaminated sediments in wetlands and other areas when the sediment 
forms a part of the natural setting for the wildlife, i.e. feeding and/or 
resting areas such as ponds. 
It is an additional object of the invention to provide a means of 
preventing poisoning of wildlife due to ingestion of contaminants 
contained in sediments. 
It is an additional object of the present invention to provide such a 
method and apparatus without removing and treating the contaminated 
sediment, thus avoiding the destruction or severe alteration of the 
natural habitat. 
A further object of the invention is the provision of such an apparatus and 
method which does not require the construction of landfill liners and 
caps. 
For a more complete understanding of the invention and the objects and 
advantages thereof, reference should be had to the accompanying drawings 
and the following detailed description wherein preferred embodiments of 
the invention are illustrated and described.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIGS. 1, 2, and 3, a geocomposite made in accordance with 
the invention, designated generally by the reference numeral 10, includes 
a means to deny access of wildlife to contaminated sediments, while 
permitting gas formed in the sediment layer to escape. As explained 
hereinbefore, the problem to be solved is the poisoning of wildlife due to 
ingestion of contaminants contained in sediments. This invention provides 
means to prevent access to wildlife to contaminated sediments in wetlands 
and other areas when the sediment forms a part of the natural setting for 
the wildlife, i.e. feeding and/or resting area such as ponds. The 
geosynthetic barrier is a geocomposite 10 comprising a geotextile bottom 
layer 14 juxtaposed beneath a top layer 12 which might be a geonet, 
geogrid, entangled mesh or drainage matrix portion of a geosynthetic 
drain. The geotextile bottom layer 14 may have large holes 12H cut in it 
(up to 200 cm in diameter, spaced regularly approximately between 6 and 
600 cm on center, respectively) to allow for gas formed in the sediments 
to escape before it pushes the geocomposite to the surface. Many possible 
variations of hole patterns are possible, as illustrated very 
schematically in FIG. 2. Suitable materials are those found in 
Geotechnical Fabrics Report (ISSN 0882-4983), such as that manufactured by 
Akzo Industrial Systems Co., of Asheville, N.C. 
The essential features of the bottom layer 12 of the geocomposite 10 are 1) 
its large diameter holes compared to the geotextile bottom layer material 
per se to permit gas to escape, 2) the holes are small enough to provide a 
barrier across the large holes 12H in the geotextile to the wildlife being 
protected and/or to serve as a substrate to hold a fill material and 3) 
has the necessary tensile strength and other mechanical properties to 
survive construction and environmental stresses once it is placed. 
The geotextile 14 may be fabricated of polypropylene, polyester or other 
polymer fibers woven, knitted, needle-punched or otherwise matted together 
to form a textile. Its function is to keep the top layer 12 of the 
geocomposite (geonet, entangled mesh or other drainage matrix portion of 
the geosynthetic drain) from becoming incorporated into the sediment. As 
such, it functions as a separator, and it should be designed based on the 
grain size distribution of the sediment on which it is placed. 
The top layer 12 of the geocomposite is a hollow column drainage matrix 
portion of a geosynthetic drain, geonet, geogrid, or entangled mesh made 
of polyethylene, polypropylene, high density polyethylene, low density 
polyethylene, polystyrene, high impact polystyrene or other polymeric 
material. Its function is to serve as a barrier to the wildlife trying to 
gain access to the sediment which is contaminated (e.g. dabbling ducks) or 
to serve as a layer on which to place fill, which can also act as a 
barrier. In the latter case, this top geocomposite layer will have to be 
designed for the grain size distribution of the fill. In either case, it 
needs to cover any large holes in the geotextile holes cut to permit the 
gastoescope. 
The bottom layer 14 and top layer 14 may either be separate material webs 
laid one on top of the other, and fixed in place as described below, or 
may be a unitary web of material, with the top and bottom layers fixed 
together in an appropriate fashion to form the geocomposite 10. 
The geocomposite may be anchored and held in place by some combination of 
fill material placed on the top of it, vertical or diagonal pins, or long 
weighted tubes (e.g. pipes filled with granular material) fastened to it 
that lie on the ground surface or slightly below it. 
Other advantages and features of the geocomposite of the invention are: 1) 
It can be laid over the contaminated sediment, eliminating the need to 
remove and/or treat the sediment, while denying access to the wildlife to 
the poisonous substance. This maintains the natural setting to a large 
extant. 
2) It is lightweight and relatively easy to place compared to typical 
landfill caps or relatively thick layers of soil fill. 
3) It allows for the escape of gas that may be formed in sediments below 
this layer. This avoids the problem of the barrier layer "bubbling up" 
over the pond bottom. 
4) It is durable and may be designed to withstand relatively high 
construction and environmental stresses after it is put into place. 
5) It is not as susceptible to erosion as layers of fill. 
Furthermore, it is noted that the geocomposite on the invention may also 
used in non-sub-aqueous environments, in addition to the sub-aqueous 
environment described hereinabove. 
The units shown in FIGS. 1 2, and 3 are only a few of many possible 
configurations and designs for the top and bottom layers, materials, and 
placement and arrangement of the holes 12H, consistent with the design 
parameters as set forth hereinabove. 
Thus, while preferred embodiments of the invention have been illustrated 
and described in detail herein, it will be apparent that changes and 
additions may be had therein and thereto without departing from the spirit 
of the invention. Reference should, accordingly, be had to the appended 
claims in determining the true scope of the invention.