Patent Publication Number: US-2007108133-A1

Title: Method for constructing a synthetic infiltration collection system

Description:
1. CROSS-REFERENCE TO RELATED APPLICATIONS  
      This patent application claims the benefit of U.S. provisional patent application Ser. No. 60/737,252, filed on Nov. 15, 2005. 
    
    
     2. 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.  
     3. 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 entertainment 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 de-salting. 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&#39;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&#39;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&#39;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 biologics, 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 biologics 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% (¼ to ⅛, NSF/ANSI Standard A8073), flint 10.8% (½ to ¼ 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.