Fuel Finder™ Overview and Technical Background
© 2000, Chapman Engineering

I. Purpose

To give the informed technician, scientist, practitioner, or prospective client general background and outline of services related to Fuel Finder™.

II. Scope

Applies to request for bid, process description, or training for all interested parties; this document is not confidential.

III. References

See related typical drawings, flow charts, and UST release detection procedures.

IV. Reviews and Acceptances/Approvals

The Fuel Finder™ process has been independently reviewed by Carnegie-Mellon Research Institute in April 1993. Review results met and exceeded all U. S. EPA requirements. Copies are available upon request.

Fuel Finder™ is approved or accepted by state regulatory agencies in Texas, Louisiana, New Mexico, Arkansas, Kansas, Missouri, Nebraska, Tennessee, Alabama, Georgia, Maryland, Pennsylvania, Massachusetts, among others.

Fuel Finder™ is accepted by the San Antonio Water System for UST release detection. It is an allowed method of system integrity testing before and after cathodic protection system installation in Texas, per the Texas Natural Resource Conservation Commission (TNRCC).

V. Overview and Technical Background of Fuel Finder™ UST Release Detection System, U. S. Patent # 5,003,813

Fuel Finder™ performs as a soil vapor monitoring system per EPA monthly monitoring method descriptions. It also performs ground-water monitoring and interstitial monitoring when circumstances provide for such use. Fuel Finder™ is based on the use of a proprietary polymer called Reclaim® (please see Reclaim® Remediation Services Technical Summary for physical description, MSDS and physical/biological testing results). The polymer, contained in a stainless steel mesh housing ("sampling device", "sampling sensor", or "sensor"), is exposed in observation wells within the underground storage tank (UST) and product line excavations. Polymer in the sensor adsorbs and concentrates hydrocarbon vapors or liquids, which typically comprise hundreds of different compounds in gasoline, kerosene or diesel fuels.

After a known exposure period, all sensors are removed from the wells on site, sealed, and transported to a central laboratory for testing. Test results compare total hydrocarbon content, the fuel "fingerprint" (types and relative amounts available of many different fuel-related compounds) from each well, and the degree of weathering of the available fuel residues. These analytical results indicate whether new product is available and, if so, which product type it may be. The process is roughly equivalent to performing a TPH/BTEX sampling event and analysis, for fuel-related vapors or liquids, from each well on a monthly basis.

Reclaim® porous polymer affects its immediate surroundings through diffusion and adsorption. As the available hydrocarbons in backfill change in composition (due to spillage or a hole in equipment), so will the fuel residues held in each sensor adsorb or desorb to closely resemble the current hydrocarbon mix (because the physical adsorption is a completely reversible process). Through a series of physical, chemical, biological and environmental studies, Chapman Engineering has demonstrated that Reclaim® is completely inert at ambient conditions. It offers neutral or beneficial consequences when used in environmental sampling or remediation.

A. System Advantages

1. Fuel Finder™ is inexpensive to use. Costs for site assessment and well installation for a typical service station depend on state well installation requirements and the conditions of the site. Monthly test fees are determined, as are the installation costs, on a site specific basis. Site operation never shuts down for installation or for testing.

2. Fuel Finder™ is simple. There are no moving parts in the field, other than the well plug. All testing is performed in a central laboratory, so no field equipment or calibrations are needed. Quality control is assured through the use of trained company employees for all sensor installation and retrieval operations, and good laboratory practices.

3. Fuel Finder™ is sensitive to very small releases, due to its ability to concentrate available hydrocarbons through the adsorption process. Once an upward trend in fuel residues (vapor or liquid) is confirmed, gas chromatographic (GC) analyses of each stored product are used to identify the offending product and, by comparing concentration differences at various wells, estimate the approximate location of a break. In the case that chromatographic testing does not yield conclusive information, tracing chemicals may be introduced to tank systems. After an exposure period each sensor is then checked for the presence of tracers outside tank systems.

4. Fuel Finder™ is safe. Wells are installed after lines and tanks are located, and all holes are probed before casings are put in place. Unless the Client requests otherwise, we do place wells in between tanks, thereby getting better coverage of tankhold for new releases. The wells are the only equipment needed at the site.

5. Fuel Finder™ is a continuous monitoring system. Sensors are able to store the majority of hydrocarbons adsorbed during the test period so they reflect the near-maximum concentrations attained in that period.

6. Fuel Finder™ is a complete system, in that it can provide not only the positive indication that a release has occurred, but can also identify the product and estimate a release's location. In addition, through the use of tracing chemicals and chromatographic analyses, Fuel Finder™ shows whether hydrocarbon contamination is related to a product on site or may be from an unknown source.

7. Fuel Finder™ sensors may be used to store field samples indefinitely without a significant loss of volatile compounds. This storage may be done at room temperature, provided the vial is metal- or paraffin-sealed properly.

B. Other System Considerations

1. Based on EPA recommendation of 0.01 cm/sec for hydraulic conductivity of soil for vapor monitoring around tanks and lines, Fuel Finder™ is typically used in backfills that are relatively permeable. However, a number of studies show Fuel Finder™ works well in soils of low permeability, and works far better than other technologies in those challenging soils.

2. If background contamination is so high that a sensor "saturates" during each test period, the basic testing regimen for Fuel Finder™ sensors requires some change. The use of larger sensors, that is, more Reclaim® polymer, allows for work in higher backgrounds without saturating. The Fuel Finder™ process has been used successfully to find a new release when the existing tankhold has free product – from an older release – present on perched ground water.

3. When a small-volume, intermittent leak exists, being masked either by fluctuating water table or by small-capacity use of a tank with periodically higher fuel levels, Fuel Finder™ may not indicate a large enough hydrocarbon increase in 30 days to warrant further investigation. However, as the Reclaim® polymer adsorbs dissolved-phase hydrocarbons as well as product on water surface, the Fuel Finder™ process will still indicate suspicion of a release over two to three test periods. And if a tank takes on water, which Client must check for at least monthly, that serves as an independent method of release detection when high ground-water is present.

C. Site Survey, Site Assessment and Location of Underground Structures; Installation or Retro-Fit of Wells

1. Preliminary work includes identifying site in state registration records and obtaining all information pertaining to tanks and lines – their composition, volumes, dimensions, etc. At the site, this information is confirmed or corrected. All utilities in area are identified when possible.

2. Metal vent lines, product lines and any other system plumbing are traced using inductive locator, in order to identify line locations and (usually) one end of each tank. Any utility lines near the excavation are located to make sure they do not affect installation. In the case of fiberglass tank, tank's centerline is usually determined by positions of fill port and submersible pump access hatch. In some cases, an "in-tank snake" is used to delineate the tank's long axis and ends (we find that newer installations usually possess better, more accurate site plan information than do old sites). Fiberglass lines are located when necessary by hand-cutting trenches perpendicular to the probable line run and manually identifying lines.

3. Prospective well locations are identified, and one well is started in order to obtain soil sample. Once ground is broken and overburden removed until backfill is found, a column of backfill is cored. Over this core is placed a measured column of water, and, using a stopwatch, the soil column is monitored for water to appear at lower end. This serves as an estimate of soil's hydraulic conductivity.

4. Wells are always located following these guidelines:

a. A minimum of three wells in a tankhold, unless there is only a single tank in the hold;

b. One tankhold well is placed adjacent to the line trench's exit from the tankhold;

c. For line trenches shorter than 10 feet in length to island, no well is placed in the trench; for line trenches longer than 10 feet, or for multiple islands, a minimum of one line trench well is placed near each island (more than one well per line trench is often indicated). The only exception to this is when line runs and multiple dispensers dictate the use of annual line testing; in this case, Chapman Engineering places one well near each dispenser island, in order to detect dispenser- and pipe-fitting-related leaks;

d. Well locations in tankhold are determined by tank geometry, line trench and island location(s); some state agencies require wells to serve a "working radius" of no more than15 to 20 feet;

e. Provided that excavation backfill meets conductivity threshold, or work is warranted in tighter soils, each well is opened to the top of quality backfill. The well's "plumb-line" is probed to show that no underground structures are in the way of proposed well casing. Well casing, slotted with 0.020- or 0.010-inch slots per EPA specifications, is placed through backfill to the boundary with native soil. A PVC point seals the lower end of the casing prior to driving. In the case of backfill being fine-grain sand to silt or other tight native soil, each well is hand-augered to a depth of at least six inches below tank base, or to tighter native soil, whichever condition limits the well depth. Once the augered hole is clean, casing is inserted and coarse sand is used to pack the annular space left around casing. The top six inches of casing are concreted in place, with casing top ("finish-out") protruding about ½ to one inch above ground level. Concrete is "feathered" from the casing lip away to original grade to afford positive drainage. Well plug is water-tight and has a lock-out device.

5. Existing observation wells may be evaluated for use if Client insists. In most cases, however, these wells are not located in positions best suited for monitoring; often, the well construction or slotting is not sufficient for monitoring.

D. Initial Testing

Company technician places first set of sampling sensors upon completion of wells. Sensors are hung from stainless steel lanyard or heavy monofilament line tied to eye-bolt on base of lock-out cap or in casing wall, and are usually hung three to eight feet deep in well. In the case of high water table, the sensor may be on a line as short as one-half foot in length.

After a period of three days to one month, the first sampling sensors are retrieved by Chapman Engineering personnel, and are tested as described above. Should the hydrocarbon "spectrum" appear to be very new and unweathered, Chapman Engineering immediately begins a diagnostic procedure to find whether there is currently a leak in equipment at the facility.

E. Monthly Monitoring

1. Company-trained technician runs a service route once a month to retrieve exposed sensors and place fresh sensors in wells. Technician typically visits 15 to 30 sites per day. For routes that are more remote, sensors may be shipped via UPS by the technician to the lab and vice versa.

2. Testing in laboratory is done as follows. Exposed sensors are sealed in vials in the field. Once received and logged in to the lab, contaminants held by sensors are “desorbed” with a pre-measured amount of liquid solvent. This solvent takes the majority of hydrocarbon sample from Reclaim® polymer in sensor, mixing those hydrocarbons in the solvent. An aliquot portion of the solvent/fuel residue mix is then removed by syringe and placed in a sealed "auto-sampler" vial, which is labeled and placed in the "auto-sampler" rack on a laboratory Gas Chromatograph. Up to 100 samples may be analyzed in a pre-programmed batch, with each sample analysis taking about 15 minutes. Data on each sample is logged to a computer, with a report printed for Chapman Engineering chemist's review and comments. The Client's report is prepared based on results from all sensors retrieved and analyzed from the site that month.

For technical emphasis:

Through passive "adsorption sampling" of fuel residues, usually from vapor phase, Fuel Finder™ picks up volatile and semi-volatile hydrocarbons. To give a sense of the availability in backfills of the heavier gasoline-related hydrocarbons (and lighter diesel compounds), we compare vapor pressures of n-nonane (C9H20) at 20 mm Hg, n-decane (C10H22) at 8 mm Hg, and the xylene isomers (C8H10) at approximately 30 mm Hg. Most of the gasoline components are well-represented in vapor phase, based on the fact that branched-chain hydrocarbons vaporize at lower temperatures than do the straight-chain isomers.

In the case of diesels, the light components have vapor pressures of 1 to 20 mm Hg (witness nonane to dodecane [C12H26] in straight chains, up to C15 in branched chains, the alkylbenzenes, and naphthalene – lightest of the polyaromatics). Sometimes the presence of weathered gasoline will mask diesel volatiles to a degree; Chapman Engineering’s Gas Chromatograph testing routinely tracks the presence of some in-fuel "marker" compounds – lighter compounds that are only related to kerosene and diesel – not gasoline.

3. Each monthly set of data includes an estimate of hydrocarbon mass obtained from each sensor, and the "chromatogram" or fuel fingerprint, showing how old or new the fuel residues are at each well. The current data is compared to previous test period's data, and to the trend of data over several periods. Hydrocarbon part-per-million concentrations (milligrams fuel per kilogram soil) are estimated according to pre-established correlations, and published as part of the monthly report to the client.

From experience gained in lab and field, fluctuations of 25 per cent, plus or minus, in hydrocarbon mass and relative weathering each month are fairly common. When increases of more than 50 per cent in a test period are seen, further field investigation and analysis are indicated.

F. Fuel Fingerprinting and Tracing Chemical Testing

Once monthly monitoring has shown significant increases in fuel residues and their "new-ness" around tanks and/or lines, samples of fuel stored at the site are obtained and run on the chromatograph. Comparison of chromatograms from fuel residues to new products is performed, in order to match a particular fuel's "fingerprint" with samples obtained by sensors. This comparison is often definitive, since the lighter (lower in molecular weight) components of a fuel are seldom present in the excavation in any quantity unless freshly introduced. Chromatographic testing may be performed for the full spectrum of hydrocarbon molecules, for continuous portions of the spectrum (C4 to C9 for gasoline, C10 to C20 for diesel, for instance), or even for type-specific compounds, such as alcohols, all oxygenated hydrocarbons, sulfurated hydrocarbons, etc. By testing for specific families of compounds, the fuel type may be confirmed in most cases.

As additional monthly monitoring information comes from the field, we can confirm (probable leak) or deny (probable spill or intermittent leak) continued rises in concentration. Also, by analyzing concentrations of particular compounds at each well, a break's location may be estimated.

If fingerprinting of fuels and sensor samples as described above does not lead to a conclusive finding – usually due to spillage of multiple products "masking" a particular product's presence due to a leak – then special tracing chemicals are added to tanks and lines. These compounds, not found in nature or in the fuels stored at the site, are compatible with internal combustion engines and steel or fiberglass tanks and piping. As little as 50 grams of a particular chemical may be added to up to 10,000 gallons of fuel. Tracers are very volatile, and migrate throughout the UST system in short order. If there is a break, and liquid fuel/tracer mix can escape, some of the tracer adsorbs in measurable quantity onto sensors in wells. Special detectors (usually an electron capture detector, or ECD) are then used to measure the type and amount of tracer, if any, in these sensors. This information shows which system has the break and, by concentration of tracers at each well, the break location is estimated.

© 2000-2008, Chapman Engineering