Abstract:
Bioventing systems create a bacterial treatment zone at a contaminated site by supplying a hydrocarbon food source to the treatment zone, and recirculating the hydrocarbon to the treatment zone. The bioventing systems may inject, circulate, extract and reinject hydrocarbons such as butane or other alkanes to the subsurface at a contaminated site to create a bacterial treatment zone. Contaminated vapors extracted from the soil and/or groundwater may be reintroduced into the site. Hydrocarbons that are not consumed by the bacteria in the treatment zone may be extracted and recovered for recirculation into the treatment zone.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/403,934 filed Aug. 16, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to remediation of sites contaminated with pollutants such as petroleum pollutants, chlorinated solvents and the like. More particularly, the invention relates to bioventing systems for remediating such sites. 
     BACKGROUND INFORMATION 
     Gasoline and other volatile organic compounds such as chlorinated aliphatic hydrocarbons released into the subsurface may become distributed into different phases such as an adsorbed phase (on soil surface), a vapor/volatilization phase (in soil gas), a dissolved phase (in groundwater) and a free phase (e.g., a pure petroleum or chemical product floating on the groundwater table as a light non-aqueous phase liquid (LNAPL) or sinking below the water table as dense non-aqueous phase liquid (DNAPL). 
     Soil vapor extraction (SVE) is a physical means of removing or reducing concentrations of volatile organic compounds (VOCs) that partition into the vapor phase. SVE technology was developed to remove volatiles from the subsurface. This technology targets the adsorbed, vapor and NAPL phases of the VOCs present in the unsaturated (vadose) portion of the subsurface. Dissolved-phase VOCs found beneath the groundwater table is not directly addressed by using an SVE system. 
     Remediation by SVE involves applying a vacuum to soils in the unsaturated zone above the water table in order to induce airflow. Contaminated mass removal is achieved by drawing contaminant-free air into the soil void spaces. The contaminant-free air creates a concentration gradient and the compounds diffuse into the air stream. This VOC-laden air is continuously extracted and replaced with contaminant-free air. An additional benefit of SVE is the continuous flow of oxygen into the area where hydrocarbons are adsorbed on the soil. This continuous oxygen supply enhances the biodegradation of the hydrocarbons within the soil matrix. 
     A typical SVE system consists of one or more vapor extraction wells strategically located. The SVE wells can be placed vertically or horizontally, depending on depth to groundwater and other site-specific characteristics. The piping system is commonly placed underground, primarily to provide extra protection from accidental damage. The piping system usually ends at a common header pipe, which is connected to a blower or a pump depending on the flow and vacuum desired. An air/water separator and or filter is required prior to the vacuum pump in order to protect equipment from moisture and particulates drawn into the system. Discharge from the blower or vacuum pump is either vented to the atmosphere or connected to an off-gas treatment system, depending upon emissions requirements and the nature and extent of VOCs. 
     SVE alone is not effective for removing heavier material such as diesel fuel, jet fuel or fuel oils, because of the nonvolatile high-molecular weight fractions they contain. Venting techniques have been developed which utilize SVE hardware and vertical piping as a means of introducing or injecting and reinjecting air (oxygen) into the treatment zone. Such venting techniques may be appropriate when the water table is deep and the contaminant has not reached the groundwater. 
     In-situ air sparging, also known as in-situ air stripping or in-situ volatilization, is a technology utilized to remove VOCs from the subsurface saturated zone. In-situ air sparging, when utilized with an SVE system, may greatly extend the utility of SVE to the saturated zone. Air sparging is a process in which contaminant-free air is injected under pressure (sparged) below the water table of an impacted aquifer system. In air sparging applications, the air injection pressure is the sum of the hydrostatic pressure (also known as breakout pressure), which is a function of submersion depth of the air sparging point, and the air entry pressure of the geologic formation, a function of capillary resistance to pore water displacement. 
     Volatile compounds exposed to the injected air are transferred to the vapor phase, similar to air stripping. Once captured by an SVE system, the VOC-laden air is transferred to a subsequent emissions treatment system. Air sparging systems must operate in tandem with SVE systems intended to capture this VOC-laden air stream. Implementing an air sparging system without an SVE system can potentially create a net positive pressure in the subsurface, inducing groundwater migration into areas previously less affected by dissolved-phase VOCs. Air sparging systems may also add oxygen to the groundwater, thus accelerating the natural biological decay process. 
     The primary mechanisms responsible for VOCs removal during operation of air sparging systems are believed to be in-situ stripping of dissolved-phase VOCs, volatilization of dissolved-phase and adsorbed-phase VOCs beneath the water table and in the capillary fringe, and aerobic biodegradation of both dissolved-phase and adsorbed-phase VOCs as a consequence of additional oxygen supplied by the injected air. When an air sparging system is optimized for stimulating biodegradation, it is sometimes referred to as biosparging. Typically biosparging systems are initially operated for volatilization and stripping. The system is then fine-tuned for enhancement of biodegradation. 
     SUMMARY OF THE INVENTION 
     The present invention provides bioventing systems which create a bacterial treatment zone at a contaminated site by supplying a hydrocarbon food source to the treatment zone, and recirculating the hydrocarbon to the treatment zone. The bioventing systems may inject, circulate, extract and reinject hydrocarbons such as butane to the subsurface at a contaminated site to create a bacterial treatment zone. In one embodiment, contaminated vapors extracted from the soil and/or groundwater are reintroduced into the site. Hydrocarbons that are not consumed by the bacteria in the treatment zone may be extracted and recovered for recirculation into the treatment zone. Butane is a particularly preferred hydrocarbon food source which stimulates the growth of butane-utilizing bacteria. However, other hydrocarbons, such as other alkanes and the like, may be used as a bacterial food source in addition to butane or in place of butane. 
     The bioventing system may be used to recirculate butane and/or other hydrocarbons at various locations such as in the unsaturated zone (above the water table), below the water table and/or at the capillary fringe (water table interface). The bioventing system may be used to remediate and restore contaminated soil and/or groundwater. When used to remediate soil alone, the butane may be reinjected above the water table. For arid or dry soils, it may be desirable to inject water in sufficient amounts to provide moisture to promote bacterial growth. 
     An aspect of the present invention is to provide a bioventing system comprising a source of hydrocarbon, an injector in flow communication with the source of hydrocarbon and a treatment zone, and an extraction vent communicating with the treatment zone. 
     Another aspect of the present invention is to provide a method of remediating a contaminated site comprising introducing a hydrocarbon bacterial food source to a treatment zone of the site, and extracting at least a portion of the hydrocarbon food source from the treatment zone. 
     These and other aspects of the present invention will be more apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is partially schematic elevation view of a bioventing system in accordance with an embodiment of the present invention. 
         FIGS. 2 and 3  are graphs illustrating petroleum contaminant levels at a site treated with a bioventing system as shown in  FIG. 1 , before and after treatment with the bioventing system. 
         FIG. 4  is a partially schematic plan view of a bioventing system in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a bioventing system  10  in accordance with an embodiment of the present invention. The bioventing system  10  includes a supply of butane  12  or other hydrocarbon bacterial food source and an air intake  14  connected to a compressor  16 . Butane and air are fed to a mixing panel  18  which controls the flow of the butane and air to injection wells  20  in the treatment zone. Extraction wells  22  recover a portion of the butane as well as other liquids or gases from the treatment zone. A blower  24  is used to recirculate the recovered materials back to the treatment zone via recirculation injectors  26 . 
     In one embodiment, the butane injection system may operate concurrently with an extraction system, such as a SVE system which is used to maintain a vacuum within vadose zone soils. Effluent from the SVE system may be piped back into the biobutane treatment zone, thus allowing vapor control while reducing operation costs by eliminating the need for carbon replacement or regeneration and by recycling the butane gas. The SVE system may further oxygenate the soil, resulting in enhanced microbial degradation of pollutants such as petroleum compounds. Butane injection may also be applied to traditional bioventing systems that are simply recirculating air into a treatment zone. 
     The following examples illustrate various aspects of the invention, and are not intended to limit the scope of the invention. 
     EXAMPLE 1 
     A butane injection panel was installed at a petroleum contaminated service station in Massachusetts. Three years prior to the installation, the site soil and groundwater were impacted by a release from a leak in a product line associated with a UST. The release also produced gasoline vapors that were detected in a building adjacent to the property. Drilling activities revealed the presence of VOCs in soil and contaminants on the water table. Initially, attempts were made to remediate the site by removing material via an ORS product recovery well and product recovery tank, as well as removal of 500 yards of contaminated soil, followed by installation of a conventional soil vapor extraction (SVE) system. The SVE system operated for 18 months and was shut down without successful remediation of the site. Subsequently, a biofeasibility study was conducted using site-specific groundwater. The data obtained from the study confirmed that butane-utilizing bacteria capable of effectively degrading the target pollutants existed at the site. 
     A butane injection system was then combined with the existing SVE system, as illustrated in  FIG. 1 . The butane injection system may be similar to those described in U.S. Pat. Nos. 5,888,396, 6,051,130, 6,110,372, 6,156,203, 6,210,579, 6,244,346 and 6,245,235, which are incorporated herein by reference. The butane injection system is used to stimulate the growth of butane-utilizing bacteria which degrade pollutants in the treatment zone. Examples of butane-utilizing bacteria are described in the aforementioned patents. The butane injection system may operate concurrently with the SVE system, which is used to maintain a vacuum within vadose zone soils to control potential migration of VOCs from the treatment area into adjacent buildings. The SVE system was converted to operate as a bioventing system to further oxygenate soils resulting in enhanced microbial degradation of petroleum compounds in the capillary fringe and vadose zone. The off-gas from the system is piped back into the biobutane treatment zone, thus allowing vapor control while reducing the overall operation and maintenance costs by eliminating the need for carbon replacement or regeneration, and by recycling the butane or other hydrocarbon gas. 
     Table 1 and  FIGS. 2 and 3  show the results of the bioventing process. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Groundwater Test Data 
               
             
          
           
               
                   
                 C5-C8 
                 C9-C12 
                 C9-C10 
                 C9-C18 
                 C19-C36 
                 C11-C22 
               
               
                   
                 Ali- 
                 Ali- 
                 Aro- 
                 Ali- 
                 Ali- 
                 Aro- 
               
               
                   
                 phatic 
                 phatic 
                 matic 
                 phatic 
                 phatic 
                 matic 
               
               
                   
                   
               
             
          
           
               
                 Initial 
                 54 
                 830 
                 1200 
                 19000 
                 2400 
                 30000 
               
               
                 Levels 
               
               
                 Final 
                 0 
                 0 
                 583 
                 0 
                 0 
                 0 
               
               
                 Levels 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 2 
     A total of six butane/air sparge wells were installed in a treatment area as illustrated in  FIG. 4 . Each butane/air sparge well may consist of 1-inch or 1¼-inch inside diameter, black iron pipe or Schedule 80 PVC fitted with a 2-foot slotted screen, advanced from the ground surface to a clay deposit identified across the site at a depth of 9 feet below grade.  FIG. 4  illustrates the location of the injection wells labeled BAI-1 through BAI-6. 
     These wells were piped to a butane injector located in a treatment shed in the northern portion of the site, as shown in  FIG. 4 . An objective of the injection system is to oxygenate the groundwater without the customary effects and contaminant dispersal associated with aggressive air-sparging programs. The butane injector pulses butane gas at a selected volume into the flow stream of an air sparging well supplied with air by a compressor. The airflow was controlled to each well using valves. The airflow rate in each air sparge well is anticipated to vary between 3 and 5 cubic feet per minute. In addition, it is anticipated that in order to generate a dissolved butane concentration in groundwater of 10 to 20 ppm in the treatment zone, approximately 2.0 lbs (site total) of liquid butane was injected (as a gas) into the site aquifer daily (approximately 12.8 ft3). 
     The SVE system previously installed at the site was operated concurrently with the butane biostimulation treatment system and used to maintain a vacuum within vadose zone soils. The SVE system served as a control for potential migration of volatile organic compounds (VOCs) from the treatment area into adjacent buildings. In addition, the SVE system further oxygenated the soils thus resulting in enhanced microbial degradation of petroleum compounds in the capillary fringe and in the vadose zone. VOCs were monitored in each vapor extraction well using a photoionization detector (PID) during site monitoring visits. 
     The effluent from the SVE system was piped back into the butane biotreatment zone, as shown in  FIG. 4 , thus allowing for vapor control while reducing the overall O&amp;M costs by eliminating the need for carbon replacement or regeneration and by recycling the butane gas. 
     The recirculated effluent from the SVE system was monitored using a PID meter during site visits. The level of VOCs concentration measured by the meter is a very good indication of the effectiveness of the butane biotreatment system with particular emphasis on the soil contamination located in the vadose or unsaturated zone. The results of the effluent screening are summarized in Table 2 below. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 VOCs Content of SVE System Effluent 
               
             
          
           
               
                   
                 Date of Soil Gas Screening 
                 PID Results (ppm) 
               
               
                   
                   
               
             
          
           
               
                   
                 Before Butane Bioventing 
                 690 
               
               
                   
                 4 Months After Initiation of 
                 95 
               
               
                   
                 Butane Bioventing 
               
               
                   
                 7 Months After Initiation of 
                 93 
               
               
                   
                 Butane Bioventing 
               
               
                   
                   
               
             
          
         
       
     
     The results clearly indicate that the VOCs concentrations in the soil gas were significantly decreased by continuous reinjection into the butane biotreatment zone established in the vadose zone soils. The soil gas represents the SVE system blower effluent prior to reinjection into the subsurface. This is the soil gas effluent normally piped into granular activated carbon canisters for treatment and eventual disposal. 
     Table 3 is a summary of the groundwater quality data from the site. Butane bioventing was initiated in Month No. 7. Significant improvements in groundwater quality were achieved. It is noted that the GP-3 monitoring well was believed to be located upgradient of the treatment zone of influence. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Summary of Groundwater Quality Data (System Startup Month No. 7) 
               
             
          
           
               
                 Sample 
                 Analytical 
                   
                   
                   
                   
                   
                   
                 C5-C8 
                 C9-C12 
                 C9-C10 
               
               
                 Location 
                 Method 
                 Benzene 
                 Ethylbenzene 
                 MTBE 
                 Naphthalene 
                 Toluene 
                 Xylenes 
                 Aliphatics 
                 Aliphatics 
                 Aromatics 
               
               
                   
               
             
          
           
               
                 Month No. 1 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 GBI-1 
                 MADEP VPH 
                 ND 
                 ND 
                 10.1 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-2 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-3 
                 MADEP VPH 
                 ND 
                 ND 
                 196 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-4 
                 MADEP VPH 
                 ND 
                 ND 
                 289 
                 ND 
                 ND 
                 122 
                 
                   1,460 
                 
                 
                   1,140 
                 
                 ND 
               
               
                 VW-1 
                 MADEP VPH 
                 ND 
                 ND 
                 15,700 
                 ND 
                 120 
                 2,404 
                 
                   22,600 
                 
                 
                   27,800 
                 
                 2.440 
               
               
                 VW-2 
                 MADEP VPH 
                 ND 
                 1,510 
                 
                   109,000 
                 
                 ND 
                 504 
                 4,090 
                 
                   37,600 
                 
                 
                   46,900 
                 
                 ND 
               
               
                 VW-3 
                 MADEP VPH 
                 
                   2,170 
                 
                 3,130 
                 12,700 
                 ND 
                 
                   34,600 
                 
                 
                   18,110 
                 
                 ND 
                 
                   12,200 
                 
                 ND 
               
               
                 VW-4 
                 MADEP VPH 
                 247 
                 1,540 
                 2,500 
                 517 
                 799 
                 
                   10,250 
                 
                 
                   6,610 
                 
                 ND 
                 
                   5,260 
                 
               
               
                 VW-6 
                 MADEP VPH 
                 942 
                 1,260 
                 7.800 
                 332 
                 85.8 
                 3,740 
                 
                   18,500 
                 
                 
                   8,470 
                 
                 3.800 
               
               
                 VW-7 
                 MADEP VPH 
                 ND 
                 ND 
                 6.13 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 TRIP 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GP-3 
                 MADEP VPH 
                 1,380 
                 689 
                 
                   140,000 
                 
                 473 
                 
                   9,740 
                 
                 
                   17,520 
                 
                 ND 
                 ND 
                 
                   6,770 
                 
               
               
                 Month No. 5 
               
               
                 GBI-1 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-2 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-3 
                 MADEP VPH 
                 ND 
                 ND 
                 41 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-4 
                 MADEP VPH 
                 ND 
                 ND 
                 200 
                 ND 
                 ND 
                 ND 
                 220 
                 19 
                 160 
               
               
                 VW-1 
                 MADEP VPH 
                 ND 
                 ND 
                 16,000 
                 ND 
                 ND 
                 ND 
                 ND 
                 930 
                 ND 
               
               
                 VW-2 
                 MADEP VPH 
                 400 
                 ND 
                 24,000 
                 ND 
                 ND 
                 580 
                 620 
                 
                   2,400 
                 
                 960 
               
               
                 VW-3 
                 MADEP VPH 
                 130 
                 300 
                 72 
                 130 
                 3,200 
                 1,590 
                 
                   4,800 
                 
                 310 
                 1,900 
               
               
                 VW-4 
                 MADEP VPH 
                 360 
                 1,600 
                 7,100 
                 340 
                 440 
                 
                   9,600 
                 
                 
                   1,700 
                 
                 
                   3,600 
                 
                 
                   10,000 
                 
               
               
                 VW-6 
                 MADEP VPH 
                 690 
                 1,500 
                 4,500 
                 160 
                 110 
                 3,250 
                 
                   1,900 
                 
                 
                   1,900 
                 
                 
                   6,300 
                 
               
               
                 VW-7 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 TRIP 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GP-3 
                 MADEP VPH 
                 ND 
                 ND 
                 
                   74,000 
                 
                 ND 
                 ND 
                 1,500 
                 ND 
                 
                   3,500 
                 
                 3,400 
               
               
                 Month No. 8 
               
               
                 GBI-1 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-2 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-3 
                 MADEP VPH 
                 ND 
                 ND 
                 497 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-4 
                 MADEP VPH 
                 26.8 
                 ND 
                 923 
                 24.9 
                 5.7 
                 14.4 
                 ND 
                 81.6 
                 301 
               
               
                 VW-1 
                 MADEP VPH 
                 717 
                 ND 
                 10,600 
                 ND 
                 14.8 
                 321 
                 ND 
                 ND 
                 155 
               
               
                 VW-2 
                 MADEP VPH 
                 1.472 
                 292 
                 41,900 
                 337 
                 713 
                 4,012 
                 ND 
                 ND 
                 3,680 
               
               
                 VW-3 
                 MADEP VPH 
                 527 
                 820 
                 770 
                 271 
                 
                   11,400 
                 
                 
                   7,040 
                 
                 ND 
                 ND 
                 3,610 
               
               
                 VW-6 
                 MADEP VPH 
                 126 
                 1,810 
                 8,700 
                 283 
                 467 
                 3,719 
                 ND 
                 ND 
                 3,810 
               
               
                 VW-7 
                 MADEP VPH 
                 38.2 
                 ND 
                 11.5 
                 ND 
                 ND 
                 10 
                 ND 
                 ND 
                 ND 
               
               
                 TRIP 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GP-3 
                 MADEP VPH 
                 
                   4,320 
                 
                 1,000 
                 
                   83,300 
                 
                 947 
                 
                   16,900 
                 
                 
                   31,900 
                 
                 ND 
                 ND 
                 
                   9,440 
                 
               
               
                 Month No. 11 
               
               
                 GBI-1 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-2 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-3 
                 MADEP VPH 
                 ND 
                 ND 
                 1,530 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-4 
                 MADEP VPH 
                 ND 
                 ND 
                 922 
                 ND 
                 ND 
                 62.6 
                 908 
                 ND 
                 ND 
               
               
                 VW-1 
                 MADEP VPH 
                 ND 
                 ND 
                 5,254 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 VW-2 
                 MADEP VPH 
                 216 
                 ND 
                 35,200 
                 ND 
                 675 
                 1,500 
                 ND 
                 ND 
                 3,690 
               
               
                 VW-3 
                 MADEP VPH 
                 ND 
                 771 
                 587 
                 ND 
                 182 
                 753 
                 ND 
                 ND 
                 3,220 
               
               
                 VW-6 
                 MADEP VPH 
                 1,250 
                 1,930 
                 10,600 
                 ND 
                 ND 
                 4,068 
                 ND 
                 ND 
                 
                   9,030 
                 
               
               
                 VW-7 
                 MADEP VPH 
                 ND 
                 ND 
                 56.4 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 TRIP 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GP-3 
                 MADEP VPH 
                 
                   3,950 
                 
                 1,610 
                 
                   210,000 
                 
                 ND 
                 
                   16,600 
                 
                 
                   24,750 
                 
                 ND 
                 ND 
                 
                   19,600 
                 
               
               
                 Month No. 14 
               
               
                 GBI-1 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-2 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GBI-3 
                 MADEP VPH 
                 ND 
                 ND 
                 6,790 
                 ND 
                 ND 
                 ND 
                 ND 
                 15.4 
                 ND 
               
               
                 GBI-4 
                 MADEP VPH 
                 32 
                 28.7 
                 2,510 
                 ND 
                 58 
                 48.7 
                 ND 
                 33.6 
                 352 
               
               
                 VW-1 
                 MADEP VPH 
                 5.2 
                 5.4 
                 103 
                 29.3 
                 ND 
                 40.9 
                 ND 
                 ND 
                 303 
               
               
                 VW-2 
                 MADEP VPH 
                 551 
                 271 
                 13,100 
                 435 
                 44.3 
                 1,331 
                 ND 
                 
                   1,500 
                 
                 
                   4,710 
                 
               
               
                 VW-6 
                 MADEP VPH 
                 513 
                 799 
                 5,170 
                 418 
                 116 
                 1,073 
                 ND 
                 888 
                 3,740 
               
               
                 VW-7 
                 MADEP VPH 
                 ND 
                 ND 
                 385.0 
                 ND 
                 ND 
                 ND 
                 ND 
                 39.4 
                 ND 
               
               
                 TRIP 
                 MADEP VPH 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
                 ND 
               
               
                 GP-3 
                 MADEP VPH 
                 740 
                 958 
                 41,400 
                 ND 
                 243 
                 
                   16,920 
                 
                 ND 
                 ND 
                 
                   14,500 
                 
               
             
          
           
               
                 GW-2 STANDARD 
                 
                   2,000 
                 
                 
                   30,000 
                 
                 
                   50,000 
                 
                 
                   6,000 
                 
                 
                   6,000 
                 
                 
                   6,000 
                 
                 
                   1,000 
                 
                 
                   1,000 
                 
                 
                   5,000 
                 
               
               
                 GW-3 STANDARD 
                 
                   7,000 
                 
                 
                   4,000 
                 
                 
                   50,000 
                 
                 
                   6,000 
                 
                 
                   50,000 
                 
                 
                   50,000 
                 
                 
                   4,000 
                 
                 
                   20,000 
                 
                 
                   4,000 
                 
               
               
                   
               
               
                 All concentrations expressed in μg/l (ppb) 
               
               
                 Bold values exceed GW-2 and/or GW-3 Standards 
               
               
                 VW-4 was dry on Jan. 24, 2002, Apr. 24, 2002 and Jul. 31, 2002 
               
               
                 VW-3 was dry on Jul. 31, 2002 
               
             
          
         
       
     
     Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention.