In the past, impoundment ponds for fluids have been constructed using layers of plastic for lining the surface of an excavation in the earth which are usually then covered with a layer of clay to maintain the plastic in a uniform condition, exclude air bubbles and to protect it from tears and the like. In my application Serial No. 252,676, I dis¬ close a vertical cut-off system that assures absolute water tightness wherein a pair of plastic films are used to line a slurry trench and a pervious layer fills the space between the two plastic layers to act as a filter. Draining of the filter material is used as a method of maintaining the effec¬ tiveness of the barrier and with a minimum amount of pumping at intervals guaranteeing that any pollutant which crosses the initial barrier is collected and eliminated. The object of the present invention is to extend that plastic, pervious layer and pump-plastic layer technique to large impoundment ponds without the use. of slurry walls. According to this invention, an impoundment pond is constructed in the usual fashion by excavating the impoundment pond space in the earth and lining same with a layer first layer of plastic. Thereafter, according to the present invention, a system of self-starting pumps are placed in collecting pipes at uni¬ form intervals along the slope of the impoundment walls or surf c-s. These pipes are of such a diameter as to receive conventional self-starting pumps e.g. pumps which sense the presence of a fluid and automatically begin pumping the fluid when it reaches a predetermined level. The pipes are covered with a pervious layer such as sand and then an inner layer of plastic, which in the preferred embodiment, is significantly thicker than the outer layer is applied over the pervious layer and then the conventional cap or layer of clay is applied thereover. The outer ends of the two plastic layers may be sealed or otherwise covered with a clay cap so as to prevent the draining of surface water thereinto.

BRIEF DESCRIPTION OF THE DRAWINGS:

The above and other objects, advantages and features of the invention will become more apparanet from the follow¬ ing specification taken in conjunction with the accompanying drawings wherein:

Figure 1 is an isometric sectional view of an impound¬ ment pond incorporating the invention;

Figure 2 is a sectional view of the walls of the impoundment pond incorporating the invention, and Figure 3 is an enlarged sectional view showning a drainage pipe and pumps therein incorporating the invention.

The basic method of this invention for constructing an impoundment pond comprises excavating the pond in the earth with the sidewalls being tapered or sloped so as to assure that all pollutants flow towards the center of the impoundment pond. It will be appreciated that the design of such impoundment ponds has been widely carried out in the past insofar as the depth, slopes and preparation of the side¬ walls and bottom is concerned and need not be described ^' herein. Moreover, the. plastic materials which are used according to this invention are conventional in that they are impervious plastic films such as polyethelyne with or without strengthening scrimms or meshes therein. As shown in Fig. 1, the impoundment pond 10 has sidewalls 11, 12, 13 and 14 and a bottom 15, the sidewalls 11-14 sloping, to the surface. Such ponds can vary in size from a few acres to many many acres and need not have square sides but can have irregularly shaped sides. The invention is in the construc¬ tion and operation of the surface of sidewalls 11-14 and the bottom wall 15.

According to this invention, after excavating to form the side and bottom walls of the impoundment ponds, a first or outer layer 20 of impervious material such as plastic, preferably polyethelyne or a similar product, with or without a strengthening mesh, is applied to the excavated surface 19

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which has been prepared to be as smooth and as freed of shar projections as possible. This first layer 20 of plastic fil is, in a preferred embodiment, 10 to 20 mils in thickness an is applied substantially uniformly to assure that ther e are no openings or gaps in this layer. Hence, when the plastic is layed down in parallel strips, the adjacent edges of the strips are all heat sealed or fused together either by sonic welding or by induction or electrical heating techniques, well known in the art. After the outer layer 20 has been layed and smoothed on the excavated surface and care taken to assure that all air bubbles have been removed, a network of drain pipes 21, which can be conventional casing pipes perforated and slotted so as to permit fluid to egress there¬ in is provided with a filter at the end. Such drain pipes 21 are of a diameter so as to permit the introduction therein and placement of self-starting pumps 25 which are used for monitoring the flow of fluid either from external of the pond or from the internal of the pond. In other words, as soon as any fluid flows into any of the drain pipes, the pump 25 automatically starts. These drain pipes 21 are typi¬ cally six to eight inches in diameter and are spaced between thirty to one hundred feet on centers depending on the degree of monitoring desired and the size of the pond. As shown, a standpipe in the center can be coupled to the self start- ing pump to remove seepage from the center of the pervious layer.

After the system of drain pipes has been installed, they are covered with a layer of fluid pervious material, preferably sand, of one to three feet in thickness, a two foot thickness being typical. This sand is smoothed to the contours of walls 11, 12, 13, 14 and bottom surface 15. A second or inner layer of plastic 30 is then applied over the sand, this layer of plastic being in a preferred embodiment substantially thicker than the outer or 'first layer ^" 20. This layer may for example be 60 mils in thickness but; one would not go beyond the invention if the two layers of plas¬ tic were of identical composition and thickness. Again, if the plastic is layed down in parallel strips, the adjoinin

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or juxtaposed edges are sealed to make them impervious as by sonic welding or by electronic heating.

Finally, a covnentional clay cap or layer 31 is applied over the inner plastic layer 30, such _, clay layer being typically of two to three feet in thickness and assures that the plastic films or layers remain in place and also serves as a protective barrier or layer against tearing and puncturing of such films.

Figure 3 is a section through a typical pump-plastic- pervious layer as illustrated. Here, the pump 25 is a typi¬ cal submerged subursible pump having means 41 for sensing the fluid at a drain level in the drain pipe and automatically turning the pump 25 on. Power lines 40 to 'the surface as well as the line 45 carrying the seepage material to the sur- face are contained in the drain pipe. At the surface, a monitoring unit 50 monitors and records on a strip chart, for example, the flow rate of seepage material below the impoundment level, the seepage material being returned to the impoundment pond. The monitor may also record the time of operation of the self-monitoring pumps to determine the degree of seepage.

While I have shown and described a preferred embodi¬ ment of the invention, it would be appreciated that various other modifications can be carried out without departing from the spirit of the invention as defined by the claims appended hereto.

WHAT IS CLAIMED IS:

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