Method for Constructing a Synthetic Infiltration Collection System

1. Technical Field

This invention relates to the field of desalination of seawater and more specifically, to a method for constructing a filtered seawater collection system which removes suspended solids, debris and biological material prior to subjecting the seawater to desalination.

2. Background

Seawater desalination is becoming an attractive source of drinking water in coastal states as the costs for desalination decline. A prime consideration for seawater desalination is a source of feed water that is reliable and consistent to sustain operations and produce potable water effectively and efficiently. The amount and quality of feed water entering a desalination plant is greatly dependent upon the placement of the feed water intake. Up to the present time, feed water intakes have been of two basic types, namely: 1) directly from the sea; and 2) indirectly from the sea. Each of these types of intakes has significant benefits and significant drawbacks which will be further explained below.

Open ocean intakes, or direct intakes, can be as simple as dredged channels through a nearshore region to draw in seawater. More sophisticated direct intakes involve the construction of pipelines from shore to beyond the nearshore, out to waters deeper than 35 meters. Deeper water is desirable in that the intake is less affected by wave and tidal action, but added pumping costs and pipeline costs limit the depth to which direct intakes can be practically placed. Direct intakes are fairly long lived in that they can have a service life of 30-50 years. They also provide an unlimited supply of seawater to a desalination plant as the seawater is pumped directly to the plant. However

a first drawback of direct intakes is that they are hampered by impingement and entrainment of planktonic organisms that require additional filtration and pretreatment once the seawater arrives at the plant, thereby driving up fresh water production costs. Other common problems associated with direct intakes include biological fouling of intake pipes, trash and other debris in intakes, hydrocarbon products in feed water and recirculation of discharge to intakes. Additionally, uncertain construction permitting outcomes related to direct intakes in light of modified regulatory practices derived from Section 316(b) of the Clean Water Act plague desalination plant developers.

Indirect seawater intakes include vertical beach wells, Ranney wells, and infiltration galleries. Common among these indirect seawater intakes is that they are all dependent upon the nearshore geology in which they are placed, to provide a filtered seawater product.

Vertical beach wells are placed near a shoreline, typically very close to the nearshore in order to capture seawater filtering through the local nearshore geology. The beach well is a subterranean reservoir that is sunk approximate to sea level coupled to a pipe that is rammed outward from the bottom of the reservoir into the nearshore geological formation, the pipe having a plurality of through-holes for allowing the flow of seawater into the pipe. The distance that the pipe can be driven into the surrounding geology limits the ultimate length of pipe. As water flows into the reservoir, it fills the reservoir until the level of water in the reservoir is the same as at sea level. The water is then pumped from the reservoir to the desalination plant to be de-salted. Beach wells are advantageous because they avoid issues related to volatile organic spills and lessen potentially harmful algal blooms. Hence, the water quality provided by beach wells is excellent. However a drawback exists in that the water supply produced by a beach well is totally dependent on hydrogeologic conditions at the site. Furthermore, in comparison to the unlimited seawater supply from direct intakes, beach wells typically provide water volumes in the range of only 400-4000 cubic meters per day.

A Ranney well employs a plurality of radially arranged collector wells located horizontally beneath a beach. The collector wells channel filtered seawater to a central sunken reservoir from which the seawater is pumped to a desalination plant for desalting. Ranney wells typically have higher infiltration rates than vertical beach wells, in

that they can produce filtered seawater volumes in a range of 8,000-20,000 cubic meters per day. However, like beach wells, they are limited by the nearshore geology. Also, Ranney wells can be hampered by silt buildup and may also influence onshore groundwater resources, so careful evaluation of site characteristics must be employed before a Ranney well can be installed.

Indirect seawater intakes also suffer from a shorter life span, usually 15-20 years, when compared with the 30-50 year life span of direct intakes. Further, the limitation in production capacity limits the use of indirect seawater intakes to only small desalination plants. Also, due to the fact that indirect seawater intakes must be placed near the nearshore, they are vulnerable to storm damage or damage from beach erosion.

Present seawater intakes for use with desalination plants require choices and compromises between high volume, long life direct intakes and the low volume, shorter life, but higher water quality provided by indirect intakes. Therefore a need exists for a seawater infiltration system that incorporates the high volume and long life of a direct intake while providing the high water quality of an indirect intake without being limited by surrounding nearshore geology. A need also exists for a method for constructing such a seawater filtration system.

The foregoing reflects the state of the art of which the inventor is aware, and is tendered with a view toward discharging the inventor's acknowledged duty of candor, which may be pertinent to the patentability of the present invention. It is respectfully stipulated, however, that the foregoing discussion does not teach or render obvious, singly or when considered in combination, the inventor's claimed invention.

SUMMARY OF THE INVENTION

The synthetic infiltration collection system, which is constructed by the inventive method, provides high quality water without being dependent upon local nearshore geological formations. The system also provides water volumes much higher than systems that depend upon indirect intakes that are dependent on nearshore geology. The system's ability to eliminate dependency upon local nearshore geology allows it to be placed in coastal areas of the world where the nearshore geology renders indirect intakes an impossibility. This dependency on local geology is eliminated primarily because the inventive method for constructing the system employs directional drilling techniques to

place the intake pipe of the system. Directional drilling allows for drilling through the nearshore geology in any coastal location, so that the intake pipe can be placed in the open ocean.

The inventive method is comprised of placing a subterranean reservoir in communication with the first end of an intake pipe. The reservoir is buried at a level approximate to sea level so that the inflow of water from the intake pipe occurs until the water in the reservoir reaches sea level. Directional drilling methods are used to create a bore for the placement of an intake pipe. Directional drilling can be used to place a single intake pipe. Alternatively, directional drilling can be used to place a very large pipe, such as a pipe having a 30" or greater bore diameter. The large pipe in this case acts as a bore lining so that a plurality of intake pipes can be placed inside of the large pipe and connected to the reservoir. This allows for the filtration of much higher volumes of seawater from the multiple intakes. Also, as desalination needs grow with population growth, this configuration would allow for more intake pipes to be added. The intake pipe extends from the reservoir out past the nearshore and into the open ocean where it is preferably anchored to the sea floor. The opposite end of the pipe terminates at an intake area where the pipe is perforated with a plurality of openings. In one embodiment, geological materials, preferably gravel, are filled into porous containers resembling bed mattresses and enclosed therein. The containers are then lowered precisely upon the intake so that the porous containers cover the intake openings. The containers then act as a portable geology causing only filtered seawater to enter the pipe. Undesirable suspended elements such as detritus, suspended solids, other suspended biologies, debris and hydrocarbons are either greatly reduced or eliminated altogether by the system. The placement of the intake in the open ocean also allows for the system to produce volumes of water above that of prior art indirect intake designs.

It is an object of this invention to provide an inventive method for constructing a system for filtering seawater that can bypass any nearshore geology.

Another object of the invention is to provide an inventive system and method for filtering seawater, which produces a higher volumetric flow of filtered seawater than existing indirect intake systems.

Still another object of the invention is to provide an inventive method for

constructing a system for filtering seawater, which allows desalination plants to be located in areas having undesirable nearshore geology.

Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention, without placing limitations thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

The ^" invention will be more fully understood by reference to the following drawings, which are for illustrative purposes only: FIG. 1 is a side view of the inventive filtered seawater collection system shown installed at a coastal location.

FIG. 2 is a plan view showing the intake portion of a filtered seawater collection system having a plurality of intakes which are encased within a large pipe, this system being accomplished through the use of large bore directional drilling methods. FIG. 3 is a side view of an alternative embodiment filtered seawater collection system which uses directional drilling beneath a sea floor to reduce the profile of system components on the sea floor.

FIG. 4 is a top plan view of the filtered seawater collection system shown without filter media packets installed on the intake portion of the system. FIG. 5 is a side cutaway view through a filter media packet of the inventive system.

FIG. 6 is a top plan view of a cutaway section of intake pipe showing the filter media packets arranged around a seawater intake in accordance with the present invention. FIG. 7 is an area view showing the filter media containers of the present invention being lowered upon the seawater intake by a crane and diver.

FIG. 8 is a side view of a seawater intake attached to an alternative embodiment seawater filter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a preferred embodiment of the filtered seawater collection system 10 constructed by the inventive method is shown. The system 10 is comprised of

a subterranean reservoir 12 that is preferably sunk in the ground at an area that is protected from wind, beach erosion, littoral drift, storm surges and other damaging coastal forces. Here, the reservoir 12 is shown sunk behind a first set of dunes 14 adjacent to a beach 16. The reservoir 12 is connected to a first end 18 of an intake pipe 20, and the pipe 20 extends outward from the reservoir 12 through the nearshore 22 and out into the open ocean 24. The nearshore 22 as shown is a geologic area below the beach 16 and below sea level 26. In some coastal regions, the nearshore 22 has a porous geology, which allows seawater 28 to filter down free of biological material and debris. However, in other coastal regions the nearshore 22 has an all but impermeable geology. As noted previously herein, the geology of the nearshore is the limiting factor with regard to whether an indirect intake could be used in a seawater filtration system. The inventive construction method creates a seawater filtering system 10, which bypasses the nearshore 22 by extending the intake pipe 20 out through the surf line 30 and into the open ocean 24. The pipe 20 is inserted through a bore 32 (dotted line on either side of intake pipe

20) drilled through the nearshore geology 22 between the bottom of the reservoir 12 and through the surf line 30. The bore 32 is placed through the use of directional drilling techniques. Directional drilling can produce a bore 32 several hundred yards long or even up to a half-mile or more. This allows the reservoir 12 to be placed in a location that is safe from coastal forces such as beach erosion, wind, storm surges and the like. Here, as shown, the reservoir is placed behind a first set of dunes 14 which provides adequate shelter. This contrasts with indirect intake methods of the prior art where the reservoir is exposed to coastal forces due to its placement in or near the nearshore geology as a result of the limited ability to extend the intake pipes into the nearshore geology through pipe ramming methods.

The bore 32 created by directional drilling can be made to have a diameter of 30" or greater. As shown in FIG. 2 a 30" or larger bore 32 allows for the placement of a large pipe 34, which acts as a bore lining so that a plurality of intake pipes 20 can be placed inside of the large pipe 34 and connected to the reservoir 12. This allows for the filtration of much higher volumes of seawater from the multiple intakes. Also, as desalination needs grow with population growth, this configuration allows for more intake pipes 20 to

be added. The pipe 34 is preferably sealed with a cover 33 through which penetrate pipes 20. Cover 33 effectively prevents raw seawater from entering pipe 34 and potentially fouling the filtered seawater 29 contained in reservoir 12.

Referring still to FIG. 1, the reservoir 12 is sunk in the ground at a depth where the top portion 36 of the reservoir 12 is approximately at sea level 26 as shown. The top portion 36 of the reservoir 12 is sloped to approximate the slope of the beach 16 which helps prevent sand erosion from occurring around the reservoir 12. Filtered seawater 29 flows into the bottom of the reservoir 12 from the intake pipe 20 and achieves sea level 26. A submersible pump 38 placed into the reservoir 12 transfers the filtered water to the desalination plant (not shown) for de-salting.

The pipe 20 extends past the surf line 30 and out into the open sea 24 a sufficient distance from shore 40 and at a depth to avoid tidal effects. Generally, the pipe 20 is not restricted by water depth. The pipe 20 can be mounted 41 to the sea floor 42 as shown in FIG. 1 or else it could be placed in a bore 32 which extends beneath the sea floor 42 and only breaks the sea floor at the intake end 44 as shown in FIG. 3. The configuration shown in FIG. 3 is presented as a lower profile design which is meant to minimally disrupt the ecosystem and also presents a lower profile to avoid contact with sea dredges, bottom trawl nets and other man made activity. Once again the bore 32 extending beneath the sea floor as shown in FIG. 3 could be accomplished through the use of directional drilling.

Referring also to FIG. 4, the seawater intake end 44 of the pipe can have one opening 46 or a plurality of openings 46 in the pipe terminus. The openings 46 draw in the filtered seawater 29, which travels up the pipe 20 to the subterranean reservoir 12. The intake end 44 also preferably has an end cap 48 or other access point to periodically clean out and service the pipe intake. Likewise, the reservoir 12 includes a manhole access 50 for regular servicing, as needed. Additionally, the end cap 48 can be used for access to sterilize the intake once installed with oxidizing agents such as ozone. FIGS. 5 and 6 demonstrate the filter media portion of the system. In the embodiment of these figures, filter media packets 52 surround the intake end 44 of the pipe 20. The packets 52 are porous containers 53 containing a filter media 54. The filter media 54 must have the characteristics of removing undesired filtration elements

including garbage, debris, volatile organics and biologies such as toxic and harmful algal blooms found in seawater. Also, the media 54 must be inexpensive and be able to operate on the intake end 44 in a filtering capacity for a long while before becoming overloaded with undesired filtration elements. Further, it is preferable that upon becoming overloaded the media 54 be able to be cleaned and re-used or else replaced inexpensively. The inventors have found that geologic filtration medias meet these previous requirements; specific geologic filtration medias 54 include various gravel combinations. As shown in FIG. 5, the porous container 53 is filled with gravel media 54 and the container 53 has a flat, mattress-like quality. The containers 53 are made of porous and durable materials including nylon, geotextile fabrics, geomembranes and other engineering materials. The interiors of the containers 53 are partitioned 56 so that the gravel 54 is placed in separate compartments 58. This makes the packets 52 easier to handle and less unwieldy. The internal structure provides integrity to the containers. The pliable nature of the media containers allows for encasing the intake end of the pipe. Handling is further eased by the addition of attachment points 60 which can be coupled to a crane cable 62 for lowering into the sea 24 and guiding into place over the intake end 44 by a dive crew 64 as shown in FIG. 7.

An example of a filtration media 54 which enables this invention is a sequence of 27% filter sand (typically NSF/ANSI Standard A8071), flint 10.8% (#20 NSF/ANSI Standard A8072), flint 10.8% (1/4 to 1/8, NSF /ANSI Standard A8073), flint 10.8% (1/2 to ¹ A NSF/ANSI Standard A8074), anthracite 14.8% (#1, 0.6 to 0.8 mm, NSF/ANSI Standard A8029), and garnet 24.3% (#30 to #40, NSF/ANSI Standard A8037). Site specific factors can augment this recipe depending on the characteristics of nearshore oceanography and water quality. FIG. 6 illustrates how the packets 52 are arranged around the intake end 44 of the pipe 20 so as to cover all of the pipe openings 46 in a filtering manner. The pliable packets 52 settle around and form to the pipe 20, thereby helping to seal off the pipe intake openings 46 from raw seawater 28. Further, to make sure that the pipe intake openings 46 receive only filtered seawater, the packets 52 can be layered and overlapped to form a sealed geological unit around the pipe intake end 44. The packets 52 filled with gravel filter media 54 provide a filtering geology that can be transported to and adapted

to any coastal situation in the world. Therefore, the inventive method employing the described filter media packets 52 allow nearshore regions 22 having less than optimal filtration characteristics to be bypassed and further allows a more effective filter substrate geology to be installed near any coastline in the world. FIG. 8 is an alternative embodiment of the invention, which encloses the media

54 in canister filters 66 which can be coupled to the end of a solid pipe 20. The filter 66 shown here would have porous qualities, and a geologic gravel filter media would be the preferred. The intake end 44 of the pipe 20 would no longer be endowed with a plurality of openings 46. Instead, the pipe 20 would be solid up to the point of its terminus and would have a coupler 68 on the end of the pipe 20. The coupler 68 would have a sealing quality to prevent the influx of raw seawater. The coupler 68 could therefore be a threaded arrangement, a gasket arrangement or other known mechanical means, which could achieve the sealing coupling of the filter 66 shown.

Finally, although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. This invention may be altered and rearranged in numerous ways by one skilled in the art without departing from the coverage of any patent claims which are supported by this specification.