Abstract:
The systems and methods described herein allow for intercepting submarine groundwater discharge to be used as a supply source for desalination processes. In one practice a dye-dilution seepage meter is employed as a device for locating water sources. These meters can be placed in estuaries and other locations that may be candidate locations to test for flows of groundwater. In areas of suspected SGD, the meters can be deployed to quantify the potential yield and quality (e.g. salt content) of the resource. Regarding the water quality, it is important to note that even brackish water sources can greatly reduce the energy needed to achieve potable water by desalination.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/069,085, filed on Mar. 12, 2008. The teachings of the foregoing application are hereby incorporated by reference herein in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The quality and availability of freshwater resources are becoming increasingly stressed as coastal human populations rise throughout the globe. In existing and emerging coastal cities where surface water pollution increases and supply declines (often triggered by changing climate), governments may turn to groundwater as an alternative source; those that have done so already may not be utilizing this resource using best management practices. In arid climates, countries are already relying on desalination of coastal seawater for the majority of their freshwater needs. For example, the acute lack of natural water resources and the wealth of Kuwait have created a unique water sector where about 90% of the potable water production comes from seawater desalination. Though this unusual situation has been maintained for decades, and probably will continue into the foreseeable future, it has resulted in serious drawbacks. At a per capita demand of 493 L/day and a $3/cubic meter production cost, the ever-increasing economic burden of satisfying the water demand is bound to slowdown the pace of development. 
         [0003]    Thus, although desalination is an effective way to generate a fresh water supply for a coastal community, the process can be expensive and this expense can interfere with the ready availability of potable water to the local population. 
         [0004]    Thus there exists a need to develop desalination processes that are more cost effective. 
         [0005]    In many instances where desalination is used, the processes are not as efficient as possible and in particular fail to harvest coastal groundwater as the supply source. This can result in coastal groundwater being underutilized and lost to the ocean via submarine groundwater discharge (SGD), or trapped in offshore aquifers. Once it exits the aquifer, the freshwater component of SGD is lost to the sea. Recovery of this resource for desalination (or direct use) purposes has been under consideration for a number of years and has been tested through a number of feasibility studies. The Municipal Water District of Orange County (MWDOC) has installed a slant well into the beach-face near Dana Pt., Calif. (http://www.mwdoc.com/). There, brackish to saline groundwater will be extracted and desalinated at a soon to be constructed test facility. A French company has successfully mined offshore SGD (mainly as freshwater springs) in a number of countries around the world (http://www.nympheawater.com/). 
       SUMMARY OF THE INVENTION 
       [0006]    The systems and methods described herein allow for intercepting submarine groundwater discharge to be used as a supply source for desalination processes. In one practice a dye-dilution seepage meter is employed as a device for locating water sources. These meters can be placed in estuaries and other locations that may be candidate locations to test for flows of groundwater. In areas of suspected SGD, the meters can be deployed to quantify the potential yield and quality (e.g. salt content) of the resource. Regarding the water quality, it is important to note that even brackish water sources can greatly reduce the energy needed to achieve potable water by desalination. 
         [0007]    Once resources are tapped, the meters can be used as part of a monitoring network designed to ensure that extraction rate does not exceed the natural output of the source. In such an application, the seepage meter would be monitoring for a change in the salt content of the SGD or excessive seawater intrusion into the aquifer (also known as “reverse flow”). 
         [0008]    Once the devices have identified viable source of groundwater discharge, the desalination plant, will by way of an extended in-flow pipe to the location of the groundwater discharge to capture the groundwater for use by the desalination plant. The devices can then become part of a water source and inflow control system that monitors and controls how the desalination plant pulls in water for processing. It is understood that use of this identified water supply will reduce the energy needed to produce potable water. 
         [0009]    To these ends, the systems and methods described herein include, among other things, a groundwater discharge detection system that includes an automated seepage meter, as well as networks, and other arrangements, of automated seepage meters, that detect and quantify groundwater outflow and seawater infiltration. In one embodiment, the meters employ a dye-dilution technique, that provides high resolution time series data for submarine groundwater discharge to the coastal zone. The dye dilution method involves two repeatable steps: (1) the timed injection of a water-soluble dye into a dye mixing chamber mounted in series with a seepage chamber and (2) the subsequent timed measurements of the absorbance of the dyed solution. The rate at which the dyed solution is diluted by the inflow or outflow of water is directly proportional to the flow rate of groundwater moving through the surface area of the seepage housing. In certain example embodiments described herein a fiber optic absorbance meter is placed within a mixing chamber into which groundwater is flowed. Injected into the flowing groundwater is a water soluble dye that will color the flowing groundwater. The fiber optic absorbance meter measures the relative proportion of dye within the mixing chamber and, through a series of timed measurements, measures the rate at which the dye is diluted within the mixing chamber. This, therefore measures the rate at which groundwater passes through the mixing chamber and is representative of the rate of flow of the groundwater. 
         [0010]    Accordingly, in one aspect, the invention provides methods for detecting and monitoring submarine groundwater discharge suitable for desalination that comprise providing at least one submersible seepage meter capable of measuring water salinity, disposing the seepage meter at at least one interface between a coastal aquifer and a body of saline water, and measuring, with the seepage meter, a flow of water through the interface, the flow direction of the flow of water, and the salinity of the flow of water. Optionally, the at least one seepage meter is automated. In certain embodiments, the at least one seepage meter comprises a plurality of seepage meters disposed in a network for detecting and monitoring the flow of water through the at least one interface. The at least one interface may be at the bottom of the body of saline water, and the at least one seepage meter may be submerged in and disposed at the bottom of the body of saline water. 
         [0011]    In another aspect, the invention provides systems for detecting and monitoring submarine groundwater discharge suitable for desalination that comprise at least one submersible seepage meter capable of measuring water salinity, disposed at at least one interface between a coastal aquifer and a body of saline water, and configured to measure a flow of water through the at least one interface, measure a flow direction of the flow of water through the at least one interface, and measure the salinity of the flow of water through the at least one interface. 
         [0012]    In all of the above aspects and embodiments, the at least one seepage meter may be a dye-dilution seepage meter, and includes a mixing chamber with a dye injector for making timed injections of a water soluble dye into the mixing chamber, a pump for distributing the dye equally about the chamber, and an optical absorbance meter in the chamber with a light source and a light receiver for passing a beam of light through the fluid flowing through the chamber and measuring a characteristic representative of absorbance of a wavelength of light, respectively. The dye-dilution seepage meter may also include a processor for processing the measured characteristics to determine a rate of flow for fluid passing through the at least one interface. Optionally, the seepage meter may include a timer for making a series of timed measurements and dye injections for determining a rate of flow of water through the at least one interface and/or a background sensor for measuring a characteristic representative of absorbance of a wavelength of light of fluid in the chamber and absent the injected dye. In certain embodiments, the seepage meter may include a sensor for measuring a direction of fluid flow and/or a chemical sensor for detecting and determining the rate of flow of at least one chemical element flowing through the interface, and wherein measuring the flow direction of the flow of water through the interface comprises measuring the flow direction with the sensor and measuring the salinity of the flow of water through the interface comprises measuring the salinity with the chemical sensor. In all of the above aspects and embodiments, the at least one submersible seepage sensor may include a watertight housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further description thereof, with reference to the accompanying drawings wherein; 
           [0014]      FIG. 1  is a depiction of a network of seepage meters deployed in seawater according to an embodiment of the invention; 
           [0015]      FIG. 2  is a second depiction of a network of seepage meters deployed according to an embodiment of the invention; 
           [0016]      FIGS. 3A and 3B  depict a seepage meter according to an embodiment of the invention; 
           [0017]      FIG. 4  depicts in more detail a mixing chamber of the type suitable for use in the seepage meter shown in  FIG. 3B ; 
           [0018]      FIG. 5  depicts in more detail a reflective absorbance meter of the type suitable for use with the mixing chamber depicted in  FIG. 4 ; 
           [0019]      FIG. 6  depicts a seepage meter system and groundwater collection device according to an embodiment of the invention; and 
           [0020]      FIG. 7  depicts a light source and a light receiver passing a beam of light through fluid in the mixing chamber of  FIG. 4 , according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    To provide an overall understanding of the systems and methods described herein, certain illustrative embodiments will now be described, including a method and system for intercepting submarine groundwater discharge to be used as a supply source for desalination processes. In particular, a network of strategically-placed seepage meters is described, along with an example of a seepage meter that may be used in the network. However, it will be understood by one of ordinary skill in the art that the systems and methods described herein can be adapted and modified for other suitable applications and that such other additions and modifications will not depart from the scope hereof. 
         [0022]      FIG. 1  is a depiction from the side of a network of seepage meters  100  deployed to detect and monitor submarine groundwater discharge according to an embodiment of the invention. Submarine groundwater discharge (SGD) is the flow of water from coastal aquifers into the ocean. Most SGD derives from inland precipitation that recharges aquifers, and then flows into the sea. The cross section in  FIG. 1  shows the principle features of a coastal groundwater system. Freshwater flowing down gradient from the water table may either discharge from a seepage face at the shore, or flow directly from the saltwater interface into the sea. The hydraulic gradient, which drives freshwater toward the sea along the interface also, drives saltwater back to sea, creating a saltwater circulation cell. If multiple aquifers and confining layers exist, then each aquifer will have a saltwater interface, and deeper aquifers may discharge farther off shore. The network  100  of seepage meters  102   a - 102   f  may be placed to detect and monitor SGD at the saltwater interface. The location and placement of individual seepage meters may vary depending on the groundwater discharge characteristics. For example, if multiple aquifers are discharging groundwater, as shown in  FIG. 1 , the use of the network  100  of multiple seepage meters may be desirable in order to locate the multiple discharge sites as well as to provide adequate monitoring of the groundwater discharge process. If there is only one aquifer discharging groundwater, multiple seepage meters may still be desirable, because the aquifer may discharge groundwater at multiple depths, and may also being discharging groundwater at different locations due to, for example, erosion. 
         [0023]      FIG. 2  is a depiction from above of a network  200  of seepage meters deployed to detect and monitor SGD according to an embodiment of the invention. Seepage meters  210   a - d  may be positioned at a coastal region  200 , where  202  is land,  204  is a body of water, and  206  is the coastline delineating the boundary between land  202  and water body  204 . One or more coastal aquifers may discharge groundwater at locations  208 . The placement of the network  200  of seepage meters  210   a - d  may assist in the initial detection of SGD. For example, if water of lower salinity than the water in water body  204  is detected by meters  210   a  and  210   c  and meters  210   b  and  210   c  do not detect water of lower salinity than the water in water body  204 , then that may be an indication that SGD is occurring at the locations of meters  210   a  and  210   c.  Similarly, if meters  210   a  and  210   c  detect flows of water into water body  204 , that may be an indication of SGD at the locations of meters  210   a  and  210   c.    
         [0024]    Once SGD locations have been detected by seepage meter networks  100  and/or  200 , determinations of whether it is feasible to recover the SGD for desalination can be done. The economic feasibility of recovering SGD for desalination may depend on a number of factors, such as, for example, cost of water in that coastal region, distance to the nearest desalination facility, flow rate of the SGD, and the relatively salinity of the SGD compared to the salinity of water body  204 . If it is deemed desirable to recover the SGD for desalination, pipes or other methods for recovering the SGD may be put in place, and the seepage meter networks  100  and/or  200  may be left in place to continue monitoring the SGD. Changes detected in SGD salinity or SGD flow by seepage meter networks  100  and/or  200  may assist in controlling the desalination process at the desalination facility. For example, if SGD salinity increases, or SGD flow decreases or reverses, the aquifer may be being tapped faster than it is being replenished. In this case, it may be desirable to lower the throughput of the desalination facility to allow the aquifer to replenish. 
         [0025]    In certain embodiments, the seepage meters  102   a - f  and  210   a - d  may employ a dye-dilution technique that provides high resolution time series data for submarine groundwater discharge to the coastal zone. The dye dilution method includes two repeatable steps: (1) the timed injection of a water-soluble dye into a dye mixing chamber mounted in series with a seepage chamber and (2) the subsequent timed measurements of the absorbance of the dyed directly proportional to the flow rate of groundwater moving through the surface area of the seepage housing. 
         [0026]      FIGS. 3A and 3B  depict a first embodiment of a seepage meter for sampling the candidate locations. In particular  FIG. 3A  depicts an absorbance meter of the type desired herein and  FIG. 3B  depicts a seepage meter using the absorbance meter depicted in  FIG. 3A . In particular,  FIG. 3B  depicts a seepage meter  10  that includes an absorbance meter  12  positioned above a mixing chamber  14 . The depicted absorbance meter  12  includes two sensor probes  16  that may pass into the mixing chamber  14  to measure characteristics that are representative of the rate of flow of fluid through the chamber  14 . In the depicted embodiment, the absorbance meter  12  is depicted as being on top of the mixing chamber  14  thereby having the sensor probes  16  enter into the mixing chamber from the top. However, other embodiments and configurations may be employed and optionally, the fiber optic probes may enter the mixing chamber  14  from the side, to thereby avoid putting the weight of the pressure housing on the two probes and the chamber  14 . The mixing chamber  14  is seated on and connected to a base  18  and the base  18  is capable of being deployed on to the ocean floor in such a way as to maintain the device  10  in a relatively stable state. As shown in  FIG. 3A  the absorbance meter  12  includes, in this embodiment, two stainless steel sensor elements  16  that extend outwardly from the housing of the absorbance meter. Additional optional elements, including battery power supplies, telemetry equipment, thermostats, water samplers, pumps for pumping dyes, groundwater and other fluids, and other sensors may also be contained in the housing of the meter  10 . For example, sensors to detect fluid flow direction, fluid salinity, or other fluid characteristics may be contained in the housing of the meter  10 . In certain embodiments, one or more seepage meters may be stand alone or networked together to provide information such as the daily rate of flow. 
         [0027]    In  FIG. 4 , the sensors  16  are shown as being disposed within the mixing chamber  14 . In particular,  FIG. 4  depicts the mixing chamber  14 , the stainless steel probes  16 , a dye injector  24 , an inlet/outlet port  20 , an inlet/outlet port  22 , and sensor ports  28  each of which are located at the distal end of the sensors  16 . Also depicted in  FIG. 2  is a mixing pump  29 . The mixing pump  29  is disposed within the mixing chamber  14  and mixes the fluid within the chamber  14 . Typically, the mixing pump  29  will mix the fluid in the chamber to keep the injected dye evenly mixed throughout the chamber  14 . The mixing pump  29  may be a conventional electrical circulation pump of the type commonly used for circulating fluid in a tank or chamber. 
         [0028]    As shown in  FIG. 4  the absorbance meter  12  can have two sensors  16 , although in other embodiments a single sensor may be used. The sensors  16  may be disposed at either end of the mixing chamber  14 . The port  20  can coupled with a source of groundwater discharge thereby allowing groundwater to flow into the interior of the mixing chamber  14 . The port  22  can allow for the groundwater within the mixing chamber  14  to pass out of the chamber  14 . The dye injector  24  can inject a water soluble dye into the interior of the mixing chamber of  14  thereby allowing the water soluble dye to mix with and color the groundwater flowing through the interior of the mixing chamber  14 . The pump  29  may optionally be coupled at a point that is external to the mixing chamber  14 , or located at some other position, and it will be understood that any suitable location for the pump  29  may be used as long as the pump is capable of evenly mixing the soluble dye with the fluid in the chamber  14 . The pump may mix the dye in the chamber  14  by drawing water from the chamber  14  in one port and pumping it back into the chamber  14  through a second port. The pump  29  will mix the dye so that the dye is substantially evenly distributed throughout the fluid in the sample. This is understood to establish a uniform absorbance characteristic for the volume of fluid in the chamber  14 . The pump  29  may optionally be operating continually to keep the dye evenly distributed throughout the chamber. This way changes in the absorbance characteristic may be modeled as representative of dilution of the dyed initial volume of fluid in the chamber by incoming volumes of non-dyed fluid entering the chamber through either of the ports  20  or  22  depending upon the flow of the groundwater. Additionally, the pump  29  may include a mechanism for flushing volumes of fluid from the mixing chamber  14 , to eliminate or substantially eliminate the presence of dye or other injected substance within the mixing chamber  14 . 
         [0029]    The mixing chamber  14  is typically a plastic, such as plexiglass, chamber, that is sealed against the environment and that is optionally sufficiently transparent to allow a user to observe that dye is passing into the chamber  14  and mixing with the groundwater therein. In may cases it will be noted that the seepage meter may be placed at a location that is proximate the upland shore and in water depths that are sufficiently shallow to allow an above sea observer to visually monitor whether a colored dye or other material is present within the mixing chamber  14 . The chamber  14  may be of any suitable size, volume and geometry and in one embodiment has an internal volume of about 50 mL to 1000 mL and more typically between 100 mL and 500 mL, however any suitable size may be used and the size selected will typically depend upon the application. One of the fiber optic sensors will extend outside of the chamber at location  22  so it may measure the background absorbance of the groundwater coming into the box. The second fiber optic sensor  16  may extend into the mixing chamber  14 . Optionally, two or more sensors  16  may be placed in the chamber  14  or external to the chamber. The background absorbance may be used as a baseline value to help monitor the change in absorbance of groundwater contained in the mixing chamber  14 . 
         [0030]      FIG. 5  illustrates that the seepage meter disposes an optical absorbance meter within the interior of the mixing chamber  14  so that measurements of the absorbance are made of fluid that is currently in the mixing chamber  14 . This reduces the need for pumps that will withdraw the fluid from the chamber  14  to be analyzed in a separate analytical device. By eliminating this pump, the device may be made smaller and will use less power. The reduction in power usage is important as the seepage meter is often placed at a remote location and therefore requires stand alone operation off of a self-contained power supply such as a battery. In certain embodiments, the seepage meter may include a self-contained power generation system. This power generation system may be capable of generating power from a stored energy or fuel source, or may collect energy from the ambient environment. For example, the power generation system may comprise solar panels, wind turbines, tidal power generators, or any such power collection devices. 
         [0031]      FIG. 5  shows in more detail one embodiment of the absorbance meter sensor probe  16 . In particular,  FIG. 5  shows that the fiber optic absorbance meter sensor probe  16  includes an open port  28 . The open port  28  is open to the flow of groundwater and allows the groundwater or other fluid in the chamber to pass through the port  28 . As shown in  FIG. 5  a source of light, typically a light emitting diode of known wavelength or being switchable among multiple known wavelengths, directs a beam of light downward toward the port  28 . 
         [0032]    In the embodiment shown in  FIG. 5  the port  28  includes two mirrored surfaces that are oriented at a 90 degree angle with respect to each other. The light passing through the sensor  16  in a downward direction reflects off the first mirror and is directed to the second mirror. Light from the second mirror is reflected upwardly back into the body of the sensor probe  16 , and typically into an optical fiber. In this way a light path is established through the port  28 . Accordingly, the amount of light that passes through the port  28  depends, at least in part, on the absorbance of any material that is passing through the port  28 . The dyed groundwater will have an initial absorbance characteristic that is in part representative of the concentration of dye within the mixing chamber  14 . The water soluble dye may be selected to be particularly interfered with and absorbed by the wave length of light being reflected between the two mirrors within the port  28 . It may also be selected to provide a characteristic absorbance to the dyed groundwater that is different from the characteristic absorbance of groundwater or other typical environmental moieties that naturally occur or may be known to likely occur within the area where the meter is placed. In one embodiment, the light source generates light at a wavelength of about 590 nm and the dye injected into the mixing chamber is selected to be absorbed at or about that wavelength. In one particular embodiment, the light source and absorbance meter were of the type manufactured and sold by Ocean Optics, Inc. of Dunedin, Fla. In any case, the relative concentration of dye within the mixing chamber  14  may be monitored by measuring the amount of light that is absorbed while ground water passes through port  28 . A series of time sequenced measurements will establish the rate at which the dye is being diluted by the passage of groundwater through the mixing chamber of  14 . Over time the groundwater will carry away the injected dye and sensor  16  will no longer measure a changing absorbance characteristic of the material within the port  28 . 
         [0033]      FIG. 4  also illustrates the dye injector  24 . As shown, the dye injector may be a simple injector that is mechanically coupled to the exterior of the mixing chamber  14  and that has an injection needle that extends into the interior of the mixing chamber  14 . The dye injector may include an internal reservoir of concentrated dye and may, in one practice, inject about 1 mL of concentrated dye into the 500 mL chamber  14 . The dye injector may be a solenoid operated pump of the type that is commercially available and may optionally include a coupling to a remote reservoir of dye material that can be drawn into the injector  24  and delivered into the chamber  14 . The dye injector  24  may also include a timer that optionally runs under the control of a microprocessor or a microcontroller. The timer may generate a periodic timing signal that acts as a trigger for the solenoid pump to inject dye into the mixing chamber  14 . For example, the dye injector  24  may connect to a microcontroller, such as a PIC microcontroller, that generates a timing signal having a period of for example 30 minutes. At thirty minute intervals the dye injector  24  can deliver a 5 mL dose of water-soluble dye into the mixing chamber  14 . The pump  29  may be in continuous operation and will mix the dye with the fluid in the chamber  14 . Over the next thirty minutes, before the next injection of dye, the absorbance meter may take a plurality of measurements of the absorbance characteristic of the fluid in the chamber  14 . It is understood that groundwater seeping into or out of the section of ground being monitored will result in the dilution of the dyed fluid in the mixing chamber  14 . This will decrease the absorbance characteristic of the fluid in the chamber  14  and the rate of dilution will be representative of the rate of flow of fluid into the mixing chamber  14 . 
         [0034]    In certain optional embodiments, the processor or controller may be programmed to change the timing of the dye injections based on the rate at which the dye is being diluted from the mixing chamber. Thus, if measurements of the rate at which dye is being flushed from the mixing chamber indicates that the mixing chamber  14  is devoid of dye after ten minutes, the controller can reduce the length of the period for injecting dye to, for example, a period of once every fifteen minutes. Alternatively, if the rate of dye being flushed from the system is very slow, the period may be extended. The controller will record the delivery time of the dye injections and record the measured absorbance levels and determine the rate of seepage. A real-time clock may be added so that the seepage rate data is correlated to the time of day, and thus to specific times and tidal conditions. In certain embodiments, the processor or controller may be programmed or configured to allow the seepage meter to operate in an automated fashion, i.e. without outside intervention or control, for some time. 
         [0035]    It will be noted that the device  10  may also be used to detect the direction of groundwater flow. For example, in one process the sensor probe  16  may be located between the mixing chamber  14  and the funnel, or at some other suitable location. The sensor  16  may be used to measure the absorbance characteristic of water pumped from the funnel, formed by a collar and collection chamber as shown in  FIG. 6 , and into the mixing chamber  14 . If water pumped from the funnel appears to have dye contained therein then the indication is that surface water has been flowing into the sediment. If dye is absent from the water taken from the funnel, then the indication is that groundwater has been flowing out of the sediment. In other embodiments, other types of sensors, including mechanical flow sensors may be employed to determine the direction of groundwater flow. The collected flow rate information may be used to locate and operate intake pipes placed at the location of the best areas of SGD and the meters may be used to select which SGD sources, if any, the plant should use as a source of water for desalination. 
         [0036]      FIG. 6  illustrates one embodiment of the seepage meter of  FIG. 3B  and a seepage housing  30  may sit over a portion of the sea floor and that captures the flow of groundwater and channels it through a port that connects to the mixing chamber  14 . As shown in  FIG. 4 , the seepage meter  10  and the housing  30  may sit on the ocean floor and measure the flow of groundwater passing through the sediment that sits under the seepage housing  30 . In this embodiment, the housing  30  includes a lower collar that sits against the ocean floor and seals a collection chamber inside the housing  30  against the ocean floor. In one embodiment, the housing  30  is a metal can that is open at the bottom. The side wall of the housing forms a collar that penetrates into the ocean floor a sufficient distance to form a seal around a section of the ocean floor. This seal keeps ocean water from leaking into the interior of the housing  30  from the sides. The side wall also forms a collection chamber that holds fluid that may be passing into the mixing chamber  14 . In the depicted embodiment the housing penetrates about two or three inches (about 4 or 5 centimeters) into the ocean floor and the weight of the metal housing  30  is sufficiently large to keep the side wall of the housing  30  sealed against the ocean floor. Optionally, the housing may be sealed against the floor through other means, such as by using stakes that fix the housing  30  in place and sealed against the ocean floor. However, those of skill in the art will know other techniques for sealing the collar of the housing  30  against the ocean floor and any suitable technique may be employed. 
         [0037]    In the embodiment depicted in  FIG. 6 , the collection chamber of the housing  30  is fluidly coupled to the mixing chamber  14  so that fluid passing through the section of ground surrounded by the collar and under the housing  30  passes through the depicted port and into the mixing chamber  14 . In alternative embodiments, the mixing chamber may be at least partially open at the bottom and the mixing chamber  14  itself may seal against the ocean floor. 
         [0038]      FIG. 7  depicts an alternative embodiment of a sensor probe. In the depicted embodiment an LED  702  is mounted to a circuit board and a photodiode receiver  704  is mounted to the same board and is spaced away from the LED  702  to form a sensor  706 . A fluid carrying channel  708  is placed in the light path between the LED  702  and the photodiode  704 . The sensor  706  is sealed in a water tight package and may be placed into the mixing chamber  14 . As described above with reference to  FIG. 5 , light from the LED passes through fluid in the channel  708  and may reflect off mirror  710 . The photodiode  704  measures the intensity of light from the LED  702 , which passes through the fluid and reflects off minor  708 , and this provides a measure of the absorbance characteristic of the fluid in the channel  708 . Multiple ones of such sensors may be placed in the mixing chamber at different respective locations. 
         [0039]    The systems and methods described herein provide many advantages and benefits over the state of the art. These include, but are not limited to, providing systems that are less expensive that current configurations and may be made for about perhaps $6,000 to $8,000, as compared to the $25,000 cost of certain state of the art systems. These systems can have decreased power usage, allowing for longer deployment of the device than currently possible. The systems are less complex, having fewer moving parts, resulting in improved reliability. These systems may also achieve better time resolution, and data points are possible on time scales of seconds versus minutes. This can provide and the systems can achieve enhanced accuracy and the ability to detect and quantify contaminants contained within the flow of groundwater. 
         [0040]    In other embodiments, other types of seepage meters may be employed and the type of meters used in the systems and methods described herein may vary according to the needs of the operation and conditions, such as the depth of the SGD being harvested. In some cases, even simple bag type seepage meters may be employed as least for some areas of the site being monitored. 
         [0041]    Those skilled in the art will know or be able to ascertain using no more than routine experimentation, many equivalents to the embodiments and practices described herein. For example, the systems and embodiments described above have been shown as stand alone devices placed on the ocean floor. However, in other embodiments and configurations, the systems describe herein may be integrated into other devices and equipment on the ocean floor, including ocean floor observatories, sea floor mooring anchors and other devices. In certain embodiments and configurations, the seepage meters described herein may be provided with communication capabilities, either through a wired connection or a wireless connection, to each other or to one or more external sources. Further, it will be understood that the systems and methods described herein can be expanded to measure the flow of groundwater, as well as the flow of chemicals or other elements being carried in the groundwater, and further to measure other characteristics of a groundwater flow, such as the temperature or salinity of water seeping into the ocean. Additionally, the systems and methods described herein are largely discussed with reference to measuring seepage rates of groundwater into an ocean environment. However, the systems and methods described herein are not so limited in their applications and may be used to measure any type of fluid flow and the size and configuration of the devices may vary according to the application. Additionally, the systems and methods herein may be used to measure fluid flow into lakes, streams, and reservoirs as well as to measure fluid flow at underground/subsurface locations. 
         [0042]    Accordingly, it will be understood that the invention is not to be limited to the embodiments disclosed herein, but is to be understood from the following claims, which are to be interpreted as broadly as allowed under the law.