direct sampling methods and down-hole sensors module at a glance

Volume 2

Innovative Technologies Reference Manual

Direct Sampling Methods and Down-Hole Sensors – i

Direct Sampling Methods and Down-Hole SensorsMODULE AT A GLANCE

Types of Available Tools

SLIDE DP-1 – Direct Sampling Methods and Down-Hole SensorsSLIDE DP-2 – Direct-Push PlatformsSLIDE DP-3 – Samplers and Down-Hole SensorsSLIDE DP-4 – Overview of Soil and Soil Gas SamplersSLIDE DP-5 – Overview of Groundwater SamplersSLIDE DP-6 – Overview of Geotechnical SensorsSLIDE DP-7 – Overview of Analytical InstrumentationSLIDE DP-8 – Overview of Analytical Instrumentation (continued)

Operating Principles

SLIDE DP-9 – Operating Principles

Platforms

SLIDE DP-10 – Rotary HammerSLIDE DP-11 – Typical Rotary Hammer RigsSLIDE DP-12 – Other Rotary Hammer ConfigurationsSLIDE DP-13 – Cone PenetrometerSLIDE DP-14 – Typical Cone Penetrometer System

Samplers

SLIDE DP-15 – Soil SamplersSLIDE DP-16 – Piston- and Latch-Activated SamplersSLIDE DP-17 – Dual-Tube SamplersSLIDE DP-18 – Soil Gas SamplersSLIDE DP-19 – Simulprobe® Soil and Soil Gas SamplerSLIDE DP-20 – Groundwater SamplersSLIDE DP-21 – Continuous Groundwater SamplersSLIDE DP-22 – Exposed Screen Groundwater SamplerSLIDE DP-23 – Enhanced Continuous Groundwater SamplerSLIDE DP-24 – Single-Use SamplersSLIDE DP-25 – Sealed-Screen SamplerSLIDE DP-26 – Evacuated Chamber SamplerSLIDE DP-27 – Evacuated Chamber Sampler (continued)

Direct Sampling Methods and Down-Hole Sensors – ii

SLIDE DP-28 – Mini-WellsSLIDE DP-29 – Multiport Sampler

Geotechnical Sensors

SLIDE DP-30 – Geotechnical SensorsSLIDE DP-31 – Cone Penetrometer SensorsSLIDE DP-32 – Cone Penetrometer ConfigurationsSLIDE DP-33 – Interpreting Sleeve-Friction and Tip-ResistanceSLIDE DP-34 – Comparing Multiple InstrumentsSLIDE DP-35 – Electrical Conductivity and Resistivity LoggingSLIDE DP-36 – Electrical Conductivity Sensor

Analytical Systems

SLIDE DP-37 – Analytical InstrumentationSLIDE DP-38 – Organic AnalysisSLIDE DP-39 – Fluorescence InstrumentsSLIDE DP-40 – Laser-Induced Fluorescence (LIF)SLIDE DP-41 – LIF Theory of OperationSLIDE DP-42 – LIF - Two Major SystemsSLIDE DP-43 – LIF - Fluorescence PlotsSLIDE DP-44 – Interpretation of LIF DataSLIDE DP-45 – Membrane Interface Probe (MIP)SLIDE DP-46 – MIP Theory of OperationSLIDE DP-47 – Interpretation of MIP DataSLIDE DP-48 – Direct-Sampling Ion Trap Mass Spectrometer (DSITMS)SLIDE DP-49 – Hydrosparge™SLIDE DP-50 – Hydrosparge™ Theory of OperationSLIDE DP-51 – Hydrosparge™ Theory of Operation (continued)SLIDE DP-52 – Thermal Desorption Sampler (TDS)SLIDE DP-53 – TDS Theory of Operation


DP-1Module: Direct Sampling Methods and Down-Hole Sensors

DP-1EPA

Direct Sampling Methods and Down-Hole Sensors



DP-2EPA

Direct-Push Platforms

Rotary hammer

Cone penetrometer (CPT)

Notes:

• Unlike conventional drilling techniques in which soil is removed and a borehole is produced,direct-push units use hydraulic pressure to advance sampling devices and geotechnical andanalytical sensors into the subsurface. The weight of the truck, combined with a hydraulic ramor hammer, is used to “push” the tool string into the ground. No soil is removed, and only asmall borehole is created.

• Rotary hammer systems are usually mounted on pick-up trucks or tracks. Cone penetrometer(CPT) systems are usually mounted on a 10- to 30-ton truck.

• The general principals of operation, advantages, and limitations are the same for all units. Thedistinction between these units is that a CPT systems advances the tool string by applying ahydraulic ram against the weight or mass of the vehicle alone, while rotary hammer units add ahydraulic hammer to the hydraulic ram to compensate for their lower masses. As a result,rotary hammer rigs are lighter and more maneuverable, while CPT (hydraulic push) rigs canachieve greater push depths due to their larger size.

• A wide array of samplers and analytical tools have been developed for both platforms, and areincreasingly adaptable to either.



DP-3EPA

Samplers and Down-Hole Sensors

Soil and soil gas samplers

Groundwater samplers

Geotechnical sensors

Analytical instrumentation

Notes:

• Direct-push platforms can advance a full range of soil, soil gas, and groundwater samplers,geophysical sensors, and a growing list of down-hole chemical sensors and analyticalinstruments. Specially-designed samplers are used to collect high-quality groundwater, soil gas,and soil samples. Geophysical sensors provide a rapid, reliable, and economical means ofdetermining soil stratigraphy, relative density, and strength (hydrogeologic conditions such ashydraulic conductivity and static and dynamic pore pressure).

• Many of the soil, soil gas, and groundwater samplers resemble the physical samplers used withrotary hammer direct-push systems. These samplers are advanced by the rod. Either retrievingthe rod and sampler, or physically collecting a soil gas or groundwater sample through the rodretrieves the sample. Sampler types, sensors, and analytical instrumentation are increasinglycompatible with both the rotary hammer and CPT platforms.

• The diagram above shows the Hydrosparge™ sampler developed for CPT systems.



DP-4EPA

Overview of Soil and Soil Gas Samplers

Soil samplers

»Continuous samplers (open or dual-tube)

»Discrete samplers

Soil gas samplers

»Sample through the rods

»Sample through tubing (discrete)

Hybrid samplers (Simulprobe®)

Notes:

• Direct-push soil and soil gas sampling systems can be used for practically any environmentalpurpose, including site assessment, site characterization, and removal assessment.

• As their name implies, continuous soil samplers allow the investigator to collect soil samplesfrom multiple depths in the same boring, and to retrieve soil profiles as sample cores.

• Discrete soil sampling systems have been developed by several vendors to collect soil samplesfrom a pre-determined depth interval, without removing the soil from above the interval orcross-contaminating samples.

• In general, soil gas sampling may be placed into two categories: sampling through the proberods, or sampling through tubing. A vacuum pump is used to pump the sample into a containerfor analysis. Unlike sampling through the rods, tubing systems typically attach to a soil gasprobe or rod tip that allows the sample to be collected from a discrete interval.

• The Simulprobe® is an innovative multiple matrix sampler that allows the operator to samplesoil, soil gas, or even water during the same boring. The Simulprobe® will be discussed in moredetail in the next section.



DP-5EPA

Overview of Groundwater Samplers

Continuous samplers

Single use samplers

Notes:

• Although many commercially available sampling devices have been developed for both the CPTand rotary hammer systems, only a few basic varieties of sampling tools possess a wide rangeof technical enhancements. Most groundwater sampling tools may be placed into one of twocategories – continuous or single-use.

• Continuous sampling tools collect a series of groundwater samples from a single borehole. Thetool proceeds to a target depth, a sample is collected, and the tool is driven to the next depthwithout decontaminating the equipment.

• For single-use sampling, the tool is driven to the target depth and then removed to collect thesample. After decontamination, the tools may be driven to the next depth in the same boreholeor moved to a different location.

• Multiple approaches and technologies have been developed to retrieve groundwater samples tothe surface for analysis. Some methods are specific to the class of samplers, while othermethods can be used with either continuous or single-use samplers.



DP-6EPA

Overview of Geotechnical Sensors

Provide rapid, detailed information about subsurface conditions

May be “stacked” with other samplers and analytical instruments

Determine characteristics such as:

» Depth to groundwater

» Stratigraphy

» Approximate hydraulic conductivity

» Presence of free product

Notes:

• Geotechnical or geophysical sensors used with direct-push platforms provide information aboutthe physical properties of the subsurface environment at a given site. At a minimum, theinvestigator must understand the subsurface conditions to adequately characterize the site, asthese conditions will affect sampling strategies and technologies applied. This informationultimately may be crucial in determining the location extent, fate and transport, or attenuation ofsubsurface contaminants.

• Direct-push methods allow the investigator to gather a lot of detailed information about shallow(less than 100 feet) subsurface conditions in an efficient and cost-effective manner. Many ofthese technical sensors provide continuous data throughout the depth of the boring, can logmultiple holes in one day, and may be "stacked" onto other samplers or sensors forsimultaneous operation. Data may be obtained more quickly and to a greater level of detailthan conventional methods such as hollow-stem auger drilling, and may be obtained fromlocations that a larger drill rig cannot access.

• The depth of investigation is limited to the shallow subsurface and unconsolidated deposits.

• In addition to use for collecting samples of soil, soil gas, and groundwater, specialized direct-push and hybrid sensors are also available for collecting in situ geotechnical information such asstratigraphy, depth to groundwater, approximate hydraulic conductivity, and may even provideclues to the presence of free product.



DP-7EPA

Overview of Analytical Instrumentation

Analytical systems analyze organic and inorganic contaminants with integrated instruments

Allow (near) real-time site characterization

May be “stacked” with other instruments and samplers for “all-in-one” approach

(continued)

Notes:

• Direct-push analytical systems are attachments designed to be used with direct-push platforms. These systems are a diverse and growing class of instrumentation. These systems all allow theuser to quickly characterize a site in the field using relatively agile and minimally intrusive direct-push platforms. Direct-push analytical instrumentation allows real-time or near real-time data tobe generated in the field while sampling, without the many requirements associated with samplemanagement, and while generating minimal investigation-derived waste. This "all-in-one"approach potentially allows the user to conduct a more rapid and detailed assessment at alower overall cost than achieved with more traditional methods such as drill rigs and off-sitelaboratories.

• Some of the systems incorporate a sensors such as laser-induced fluorescence (LIF) or x-rayfluorescence (XRF), directly into the probe that is advanced with the direct-push tooling intothe subsurface.

• Other systems are sophisticated closed systems that retrieve volatile organic compounds(VOC) from the subsurface and route them into an integrated instrument for analysis.

• Analytical instruments are often "stacked" with geotechnical sensors or samplers into a multi-functional sampling and analytical package, further increasing the amount of data that can beobtained during one investigation and decreasing investigation time and costs.



DP-8EPA

Overview of Analytical Instrumentation

Uses:

»Site assessment

»Site characterization

»Removal assessment

»Monitoring natural attenuation

Particularly applicable to voluntary cleanup and Brownfield sites

An integral component of the “Triad Approach”

Notes:

• Direct-push analytical systems can be used for practically any environmental purpose, includingsite assessment, site characterization, removal assessment, or even monitoring of naturalattenuation.

• Direct-push analysis is well-suited for application in a Triad Approach to conducting sitecharacterization and removal monitoring, particularly voluntary cleanup and Brownfield sites. Under this approach, on-site analytical tools are used in conjunction with systematic planningand dynamic work plans to streamline sampling, analysis, and data management conductedduring site assessment, characterization, and cleanup. Field analysis in general, and direct-pushsystems in particular, are often used to speed collection and reduce costs on projects where thesites are large, a high volume of data points are needed, the sites are partly or totallyinaccessible by a large drill rig, or to minimize sampling disturbances in sensitive habitats.



DP-9EPA


Direct-push platforms

Direct-push samplers

Direct-push geotechnical sensors

Direct-push analytical systems

Notes:

• This section will provide more information on the operating principles of platforms, samplers,sensors, and analytical instrumentation that are available for direct-push tools.

Operating Principles – Platforms


DP-10EPA

Rotary Hammer

Uses a combination of static reaction force and dynamic loading (hammering) to drive probes into the subsurface

Does not remove soils or generate cuttings

A wide variety of samplers and analytical tools have been developed or adapted for rotary hammer systems

Notes:

• These rigs generally weigh less than 4 tons. They are generally mounted on pick-up or lightduty trucks and vans also can be mounted on tracks. To compensate for the reduced reactionforce, many of the rigs also employ hydraulic hammers to help advance sensors or samplers. The technology can be used only in unconsolidated formations.

• No soil is removed to the surface, so no cuttings must be handled.

• A variety of samplers for retrieving soil, soil gas, and groundwater samples are commonly usedwith rotary hammer systems and will be discussed more later in this section.

• Geotechnical sensors developed for use with hydraulic CPT systems are now being adapted forrotary hammer systems, including tip-resistance sensors that map soil texture, and hydraulicconductivity sensors that map soil conductivity.

• Chemical sensors have been developed for use with rotary hammer platforms to detect,delineate, and monitor sites contaminated with petroleum and VOCs.



DP-11EPA

Typical Rotary Hammer Rigs

Depth capability is determined by static weight of the rig and hammer

Depth of push is limited by formation structure

Multiple platforms are available

Some platforms allow for directional drilling

Notes:

• The photograph above shows a typical rotary hammer rig of the type commonly used forenvironmental applications.

• The depth capability of a rotary hammer system depends on the composition of the formationand structure, the amount of force of the hammer, and the static weight of the vehicle in whichthe system is mounted. The “pushing” of tools into the subsurface depends on the hammerforce (torque) of the system, which ranges from 135 to 613 foot-pounds, and the pull-downforce, which ranges from 250 to 30,000 pounds. The extraction force, which is necessary toremove tools from the subsurface, ranges from 13,000 to 70,000 pounds.

• Rotary hammer systems are outfitted on a number of platforms capable of accessing areaswithin a building. Some platforms are small enough to pass through a standard doorway. Rotary hammer systems have also been outfitted on track-mounted vehicles and all-terrainvehicles that permit access to off-road areas.

• Some rotary hammer systems are capable of directional drilling into the subsurface at up to37.5 degrees. Most systems are equipped with a standard cylinder capable of advancing 54-and 66-inch-long tools into the subsurface; however, some systems are designed for advancingup to 12-foot lengths.



DP-12EPA

Other Rotary Hammer Configurations

Notes:

• The photograph on the left shows a track-mounted rig.

• The photograph on the right shows a portable unit with an air compressor for power.

• Other configurations include all terrain vehicle-, Bobcat®-, and barge-mounted systems.



DP-13EPA

Cone Penetrometer

Uses a static reaction force to advance the sensor

Depth of push is limited by formation structure

Soil, soil gas, and groundwater samplers are available

Sensors have been developed for physical and chemical site characterization

CPT Truck Setup

Notes:

• The static reaction force generally is equal to the weight of the truck. That weight issupplemented with steel weights. Cone penetrometer trucks that weigh more than 15 tons arecommon.

• The depth of penetration is limited by the structure of the formation; therefore, this technologycan be used only in unconsolidated material. Soft layers overlying hard layers, as well asboulders, sometimes limit penetration.

• Geophysical sensors include sleeve-friction and tip-resistance sensors that map soil texture;pore pressure transducers and electrical conductivity sensors log other soil properties.

• A variety of samplers for retrieving soil, soil gas, and groundwater samples are used with CPTsystems and will be discussed more later in this section.

• Chemical sensors, as well as downhole desorption or sampling techniques, have beendeveloped to detect, delineate, and monitor sites contaminated with petroleum, VOCs, metals,and explosives. In addition to the petroleum and VOC applications of the rotary hammer rig,the CPT also has the ability to sample or analyze down-hole for metals and explosives.

• The cone penetrometer method can provide continuous sensor data during a push. Sensorsgenerally are deployed and used during the advancement of the borehole.



DP-14EPA

Typical Cone Penetrometer System

Vehicle

» Push probe

» Sensors

» Samplers

» Grout capability

» Equipment decontamination

» Safe environment

Data acquisition and analysis

» Various sensors

» On-board analysis and visualization

» May be simultaneous with sampling

Data Processing Space

20-Ton Push TruckPipe Handling Space

Notes:

• Unlike most rotary hammer systems, the hydraulic ram apparatus and all support systems areenclosed within the CPT truck. CPT push rods are typically 1 meter long and are flush-threaded so that additional lengths may be added as greater depths are reached. Additionalrod sections are stored on-board for easy addition during probe advancement. Built-in groutsystems allow the remaining boreholes to be filled while the rods are retracted, and mostsystems also have an integrated decontamination system that cleans the rods with hot water orsteam as they are being withdrawn into the vehicles.

• A variety of samplers, geophysical sensors, and analytical instruments may be carried in theCPT truck. These instruments are attached to data acquisition systems inside the CPT truck bydata cables inside of the probe rods, allowing acquisition and analysis of data to be conductedwithin an enclosed, protected work space.

• In some cases, multiple samplers and sensors may be advanced simultaneously, allowinggeophysical data to be collected while advancing a soil or groundwater sampler, or whilecharacterizing contamination with an analytical instrument.

Operating Principles – Samplers


DP-15EPA

Soil Samplers

Piston samplers

Latch-activated samplers

Dual-tube samplers

Continuous profiling capability

Notes:

• Discrete soil sampling systems have been developed by several vendors to collect a soil samplefrom a pre-determined depth interval, without removing the soil from above the interval. Thetwo most common types of systems use a “piston-activation” mechanism and a “latch-activated” (or spring-activated) mechanism. Both systems use a sample tube or core barrelwhere the sample is contained. If the sample tube is not a “split barrel” it contains an acetatesleeve which is removed once the sample is collected. Either a “piston or latch-activated” pointis used to keep the sampling system closed while it is advanced by the direct-push platform.

• The other system is the dual tube sampling system. This system advances the sampling rodsinside a larger outer casing and the outer casing can be left in place while the sampling casing isretracted to collect the sample at a particular interval. All of these samplers can providecontinuous soil profiling.



DP-16EPA

Piston- and Latch-Activated Samplers

Notes:

• The piston-activated system, shown on the left image above, includes a cutting shoe or drive tipwhich is threaded to the bottom of the sample tube or core barrel. This component provides adual function of providing a “tight fit” for the point or piston tip during advancement of thesampler, and also a means to facilitate the cutting of a soil core during the collection process. Adrive head, or top cap is also threaded to the top of the sample tube. This component servesas a seat for the stop pin used in the piston-activated sampling system. The reverse-threadedstop pin is removed from the drive head using threaded extension rods which are sent down thetool string. The removal of the stop pin allows the piston tip to be displaced from the bottom ofthe sampler as it is advanced.

• The “latch-activated” system, shown on the right image above, does not include any additionalcomponents as it is activated through a pulling motion opposed to the removal of a component.



DP-17EPA

Dual-Tube Samplers

Notes:

• Sampling rates can be increased by using dual-tube samplers. One set of rods is driven into theground as an outer casing. These rods receive the driving force from the hammer and provide asealed hole from which soil samples may be recovered without the threat of crosscontamination. The second, smaller set of rods are placed inside the outer casing. The smallerrods hold a sample liner in place as the outer casing is driven one sampling interval. The smallrods are then retracted to retrieve the filled liner while the outer rods are left in place. After anyneeded decontamination, the sampling tool and inner rods can then be returned down the opencase, and sampling can continue at deeper depths.

• The dual-tube sampling system is recommended in sandy or loamy soils, where the boreholemight collapse. The outer tubing acts as a support for the walls of the borehole and allows thesoil sample to be collected without the risk of inadvertently collecting soil from shallower depthsthat fell into the open borehole. The dual-tube soil sampling system is also recommended foruse in highly contaminated soils. The outer tube prevents cross-contamination of a soil samplewith material from other soil horizons. In spite of these advantages, the larger diameter of thedual-tube system may be problematic in resistant soils and sediments, as larger diameter driverods are less able to penetrate hard layers.



DP-18EPA

Soil Gas Samplers

Collected through open rods

Discrete interval systems

Integrated systems combined with geotechnicalsensors

Notes:

• The most basic method of collecting soil gas is to collect samples from the open rod, whichprofiles soil gas throughout the boring.

• One common soil gas sampler consists of a steel tip that screws into the end of the direct pushtool string and holds a disposable steel point. The rod is pushed to the desired sampling intervaland then retracted. This leaves a void from which a vapor sample is collected using tubing thatis seated into the top of the steel tip. The sample is collected using a vacuum pump to draw thevapor sample through disposable tubing to the ground surface into an appropriate container foron-site or off-site analysis. The rods must then me removed, decontaminated, and advanced atanother location.

• Another soil gas sampler developed specifically for CPT rigs is located immediately behind aCPT geophysical sensor. The sampler is able to collect vapor samples at discrete depthintervals during advancement of a boring. This system has the advantage of collecting vaporsamples at multiple depth increments, while still measuring the soil stratigraphy with thegeophysical sensors.



DP-19EPA

Simulprobe® Soil and Soil Gas Sampler

Soil gas is drawn from a vapor sampling inlet at the top of the sampler

Soil gas samples can be collected or screened throughout the boring

When significant soil gas contamination is detected, the sampler releases the tip of the soil sampling chamber, filling it with a sample from the same interval

Notes:

• The Simulprobe® is an innovative multiple matrix sampler that allows the operator to samplesoil, soil gas, or even water during the same boring. The main body of the sampler is similar toa split barrel sampler commonly used with conventional drill rigs. The sampler is held in theclosed position using a unique latch-activated probe tip. Soil vapor is drawn into a meshcovered sample inlet at the top of the probe, allowing continuous soil vapor sampling duringadvancement or discrete samples to be collected for analysis. The soil sampler may then bedeployed at an interval selected based on the soil gas readings.



DP-20EPA

Groundwater Samplers

Two basic classes of groundwater samplers:

»Continuous samplers

»Single-use samplers

Multiple variations on each basic type

Several collection devices may be applied to one or both class of sampler

Notes:

• There are two basic types of groundwater samplers: continuous and single-use.

• Within these basic categories there are several variations, and multiple sample collectiondevices that may be used with either or both types of samplers, as described in the followingslides.



DP-21EPA

Continuous Groundwater Samplers

Collect a series of groundwater samples for different target depths in the same borehole

Consists of a drive-point with a collection port directly behind the tip

Groundwater enters the port and is conveyed to the surface using one of a variety of collection devices

When sampling is complete, the tool is advanced to the new target depth

Sample ports can clog, and cross-contamination is a potential issue

Notes:

• Continuous sampling tools are used to collect a series of groundwater samples for differenttarget depths in the same borehole. The tool consists of a drive-point with a collection portdirectly behind the tip. Groundwater enters the port and is conveyed to the surface using one ofa variety of collection devices, including bailers, pumps, or wireline collectors.

• Continuous sampling provides the advantages of speed and convenience, but does introducethe risk of cross-contamination, either from sediment or groundwater. In addition, samplingports may become clogged with sediment when sampling in fine-grained aquifers.

• Some of the limitations associated with continuous samplers can be minimized by usingenhanced continuous groundwater samplers. These samplers use pressurization to prevent thesample chamber from filling until reaching the desired depth, filters to prevent clogging of thesampling inlet and flushing systems to clean filters and sample inlets prior to sample collection.



DP-22EPA

Exposed Screen Groundwater Sampler

Screen remains open throughout the push

Rod does not need to be retrieved before advancing to a deeper interval

Contaminant drag-down, cross-contamination, and inlet clogging may be issues

Notes:

• This diagram shows a traditional “vertical profile” sampler.



DP-23EPA

Enhanced Continuous Groundwater Samplers

Pressurization systems prevent filling until desired sample interval is reached

Filters prevent clogging of the inlet, reduce sample turbidity

Notes:

• To reduce the effects of the sample chamber filling too soon or becoming clogged, someinnovative samplers come equipped with systems to flush the ports with distilled water orcleaning solutions, and employ filters to prevent clogging and reduce sample turbidity. Thepump that is used to bring groundwater to the surface is reversed, driving the decontaminationfluids into the sampling chambers and through the sampling ports. This flushing also removesfine material from the sampling ports. The filters may be as simple as a fine-mesh screen overthe sampling ports. In some tools, the entire tool is surrounded by one or two sets of filterpacks. These filters can be cleaned by flushing with water or cleaning solution downhole orreplaced or cleaned between boreholes. To prevent dilution with distilled water orcontamination with cleaning solution, all tubing must be purged with groundwater beforesamples are collected.

• The diagram above shows a sampler system with an integrated pump, sample retrieval tubing,pressurization/back flush tubing, and filter element.



DP-24EPA

Single-Use Samplers

Used to collect one sample per borehole

Must be retracted and decontaminated prior to sampling the next interval or location

Several distinct variations include:

» Sealed screen samplers

» Evacuated chamber samplers

» Mini wells

Multiport samplers allow multiple intervals to be sampled from one sampler emplacement

Notes:

• Single-use sampling tools are typically used to collect a single groundwater sample from aborehole. The sampler must be advanced to the desired sampling interval, at which point thegroundwater sample is collected. The sampler cannot be advanced further, and must beretracted from the boring and decontaminated. After decontamination, the tool can be drivendown the same borehole to a deeper interval, or moved to a different location.

• Single-use sampling acts to reduce cross-contamination and is more cost-effective if multi-levelsamples are not required. However, because the tool must be removed after each sample, therate of sample collection is greatly reduced. In addition, because the drive tip and, sometimes,the screen remain downhole, this technology may not be appropriate for some sites.

• Several types of single-use samplers exist, including:

S Sealed screen, or drop-out screen samplersS Evacuated chamber samplersS Mini wells

• Multiport samplers, a relatively new innovation, allow multiple intervals to be sampled from asingle boring using mini-wells at different depths inside an inflatable borehole liner withoutmoving or retracting the tool string.



DP-25EPA

Sealed-Screen Sampler

Tool string is advanced to desired depth

Screen drops out as rods are retracted

Must be completely retracted and decontaminated prior to sampling the next interval or location

Notes:

• The sealed-screen sampler usually consists of a disposable drive-point that remains downholeand a screen that is pushed out from the bottom of the probe rods. Groundwater enters thescreen and is conveyed to the surface using one of a variety of collection devices, includingbailers, pumps, or wireline collectors. When sampling is completed, the tool is usually removedfrom the borehole.



DP-26EPA

Evacuated Chamber Sampler

The sample chamber is evacuated, creating a vacuum

The sampler is advanced to the desired interval

Exposing the screen allows the chamber to fill

The tool string is retracted and the sampler brought to the surface

Minimizes atmospheric interaction with the sample and loss of volatile compounds

(continued)

Notes:

• Before driving the tool the sampling chamber is evacuated, creating a vacuum.

• The point is advanced to the target depth, and a shield is retracted to expose the screen. Touse this sampling tool, the entire sampling chamber must be below the water table.

• As the chamber fills, a check valve prevents the groundwater from leaving the chamber.

• The probe rods are then retracted, and the entire tool acts as a bailer, bringing the groundwaterto the surface.

• The single-use sampling tool is designed to preserve gases and volatile compounds dissolved ingroundwater by reducing the interaction of groundwater with the atmosphere and agitation andaeration caused by pumping or bailing. Atmospheric contact is limited to decanting at thesurface. Even this contact may be eliminated if a wireline sampler is used with the tool.



DP-27EPA

Evacuated Chamber Sampler

Notes:

• This diagram shows a common evacuated chamber sampler.



DP-28EPA

Mini-Wells

Completed like monitoring wells

Allow repeated sample collection and water level elevations from same location

Cost-effective alternative to traditional wells

Pre-packed mini-wells available (see left)

Notes:

• In addition to one-time sampling, these tools can be left downhole to act as temporary orpermanent monitoring wells and piezometers. In the case of these mini-wells, the drop-out wellscreen is encased in one or two filter packs. After the probe rods are retracted, the mini-wellcan be surrounded by a gravel pack and grouted in the same way that a conventionally-installedwell would be completed.

• These mini-wells can also be used to collect other data related to movement and persistence ofcontaminants. The ease and lower cost of the installation of direct-push wells provides moredata points with which to determine groundwater gradients. Under certain conditions, themonitoring wells and piezometers installed using direct-push can be used for aquifercharacterization, including pump and slug tests. Because more data points can be used in thesetests, lateral variability in porosity and permeability can be better calculated.



DP-29EPA

Multiport Sampler

Sampler liner contains a flexible, perforated sleeve

Liner is inflated against the boring walls

Multiple mini-wells are inserted into the sleeve to different discrete depths

May be removed or left in place

Notes:

• Multiport samplers are another technological advance that acts to expand the functionality andincrease the sampling rate of single-use samplers.

• A multiport liner and a deflated membrane (sleeve) are emplaced using the probe rods. Therods are retracted while the sleeve is held in place, and the membrane is inflated (usually withwater); this pushes the membrane against the sides of borehole.

• Multiple mini-wells may then be pushed down into the sleeve to various depths; perforations inthe liner allow groundwater to enter into the mini-well screens. Samples from a range of depthscan be collected from a single borehole.

• The whole assemblage can be removed by removing the mini-wells from the sleeves anddeflating the membrane, or it can be left downhole to function as a multiport monitoring well.

Operating Principles – Geotechnical Sensors


DP-30EPA

Geotechnical Sensors

Common sensors include:

» CPT

» Pore pressure transducers/piezocones

» Conductivity/resistivity

» Seismic sensors

» Downhole video imaging

Notes:

• Cone penetrometers, instruments by which CPT rigs are now generically known, use sensors inthe cone tip to measure soils’ and sediments’ resistance to penetration, which varies by soiltype. The resistance to penetration, calculated by determining the ratio of sleeve friction to tipresistance allows data analysts to classify soil types such as sands and clays.

• Pore pressure transducers, also called “piezocones,” measure the ambient pressure in the porespaces of soils and sediments. This measurement is similar to that generated by a piezometer,and may be used as a proxy for estimating hydraulic conductivity and determining groundwaterflow directions.

• Electrical conductivity and resistivity sensors measure the conductance of resistivity of soils andsediments to an electrical current. These measurements vary by soil type, and may be used inconjunction with data from the CPT sensors to further refine soil stratigraphy measurements.

• Seismic sensors measure compression and shear wave velocities in addition to the standardCPT parameters. The shear measurement is a key parameter for the analysis of soil behavior inresponse to dynamic loading from earthquakes, ice, vibrating machine foundations, waves, andwind.

• Downhole video imaging systems allow investigators to visually classify soils and sediments, andpotentially identify gross contaminants that are visible to the naked eye.



DP-31EPA

Cone Penetrometer Sensors

Sleeve-friction

Tip-resistance

Measured pore-pressure

Excess pore-pressure

Plumbness

Notes:

• Sleeve-friction, tip-resistance, and pore-pressure measurements commonly are used with directpush technologies for stratigraphic logging in soft soils, as well as for identifying specifichydrogeologic properties.

• The friction ratio is the ratio of sleeve-friction to tip-resistance, expressed as a percent. Sleeve-friction is the resistance to penetration developed on the side walls of a tool being pushedthrough the subsurface, which is equal to the sum of friction and adhesion. The resistancedeveloped at the tip of a tool being pushed through the subsurface is the tip-resistance, which isequal to the vertical force applied to the tool divided by its horizontally projected area.

• If a pressure transducer is added to the tool being pushed through the subsurface, the responseof soil pore water pressure to the penetration can be measured. The technique is similar to thatused for monitoring in situ pore water pressures with push-in piezometers, except for theadded factor of dynamic pressures related to penetration. If advancement of the tool ceases,the pressures related to penetration will dissipate and the in situ pore water pressure can bemeasured. The total measured pressure is equal to the in situ pressure, plus the excesspressure developed by penetration.

• The inclination, or plumbness of the tool as it advances into the subsurface, can also bemeasured in order to assess the true depth and placement of the instrumentation.



DP-32EPA

Cone Penetrometer Configurations

Penetrometer tip» Sensors» Sensor cables

Sounding or push rods

Truck-mounted hydraulic ram

Data acquisition system

Porous probe groundwater sampler

Water tank and steam cleaner

Hydraulic ram

Computerdata acquisition

system

Grout pump Rod wash chamber

100+ ft depth capability

PENETROMETER

Friction resistance

Electrical conductivity

Piezometer

Cone end bearing resistance

Notes:

• Penetrometer tips typically house tip-resistance, sleeve-friction, and piezometer sensors in aconical tip and cylindrical friction sleeve. Tips typically are about 5 inches long with a cross-sectional area from 1.5 to 2.5 square inches. The sensors are connected to the surface byelectronic cables.

• Sensor cables are inserted through the push rods and connected to a data acquisition system atthe surface.

• The hydraulic ram or rotary hammer is used to push the penetrometer tip and push rods into thesubsurface.

• A multichannel data acquisition system is used at the surface to record and provide preliminaryanalysis of the sensor data.



DP-33EPA

Interpreting Sleeve-Friction and Tip-Resistance

Stratigraphy from tip-resistance and friction ratio

NO

RM

AL

IZE

D C

ON

E E

ND

BE

AR

ING

(M

Pa

) 100

10

1

0.10 2 4 6 8 10 12

SAGRAVELTO GRSAND

SA GR TOSI GR SA

GR SI SANDTO CL GRSAND

SAND TOSILTY SAND

SILTY SANDTO SA SILT

GR CL SANDTO GR SACLAY

GR SA CLAYTOHARDPAN**

HARDPAN TO WEAK ROCK

SANDY CLAYTO SILTY CLAY**

GR CLSA TOGR SASILT GR SA CL

TO GR SICLAY**

SANDY CLAYTO CLAY**

SANDY CLAYTO CLAY*

CLAYSILTY CLAYTO CLAY

SANDY CLAYTO CLAY*

SA SITO

CL SA SA CLTO SICL*

SA SILTTO CL SI

CL SILTTO SI CLAY

CLAY TO ORGANIC CLAY

ORGANICS TO PEAT

FIBROUSORGANICS

SENSITIVEFINE-GRAINEDSOIL

CLAY TO ORGANIC CLAY*

* Overconsolidated** Heavily overconsolidated or cemented

FRICTION RATIO (%)

Notes:

• The graphic depicts a correlation chart used to determine soil type on the basis of data onfriction ratio and tip-resistance.

• The friction ratio and tip-resistance data are collected continuously as the penetrometer isadvanced into the subsurface. Site stratigraphy is inferred by comparing the relationshipobserved between friction ratio and tip-resistance as a function of depth. The scale for tip-resistance is logarithmic.

• In general, sandy soils have high tip-resistence and low friction ratios, while soils that have highclay content have lower tip-resistence and higher friction ratios.



DP-34EPA

Comparing Multiple InstrumentsCONE BEARING

Qc (tsf)SLEEVE-FRICTION

Fs (tsf)FRICTION RATIO

Rf (%)PORE-PRESSURE

U (psi)RESISTIVITY

(ohm-m)STATIGRAPHY

COMMENTS0 0 0 -10 0200 2.5 7.5 15 400

0 0 0 0 0

60 60 60 60 60 60

42

33

1816

9

40

20

High Bearing

Low Bearing

High Bearing

Low Bearing

Low Bearing

High Bearing

LowFriction

HigherFriction

Low Friction

HighFriction

LowerFriction

LowFriction

No P.PResponse

BeginP.P

Resp

NegativeP.P =

DilatentMaterial

Very HighResistivity

LowerResistivity

ResistPeak

Even LowerResistivity

SlightlyHigher

Resistivity

HigherResistivity

Dry Fill Sand

Silty Clay

Sand Seam

Clay

Silty Clay

Sand

G.W.Sample

G.W.Sample

Notes:

• The graphic illustrates common ways of presenting data from multiple, stacked instruments. The figure has a geologic cross-section format that shows the various instrument measurementsat the same relative depth. Friction ratio and tip-resistance data are displayed on the cross-section for direct comparison with the implied stratigraphy. The figure also provides moredetailed data (including pore-pressure and friction resistance logs) for a single measurementlocation.

• Data analysis is open to some interpretation based on the conclusions of the individualinstruments; presenting the data in this format allows the analyst to cross-check data fromseveral instruments.



DP-35EPA

Electrical Conductivity and Resistivity Logging

Notes:

• Electrical resistivity (ER) surveys involve the measurement of the apparent resistivity of soils asa function of depth and position. Electrical conductivity and resistivity are commonly usedbecause they are the inverse of one another. During ER surveys, electrical current is passedinto the earth through a pair of current electrodes. A second pair of electrodes (potentialelectrodes) monitor the difference in voltage as the current travels through the ground, and theresistivity is calculated. The apparent resistivity is the bulk average resistivity of all soilsinfluencing the flow of current.

• Although ER does not qualify as a qualitative or quantitative instrument for contaminantcharacterization, drastic differences in apparent resistivity may be noted when the probeencounters free product, providing an indication of contamination.



DP-36EPA

Electrical Conductivity Sensor

Notes:

• The diagram shows a soil moisture/resistivity sensor array. Soil moisture measurements takeadvantage of the relationship between the soil dielectric constant and the moisture content. Thisrelationship, known as Topp’s Equation, is not heavily influenced by soil type and resistivity ifthe dielectric measurements are performed above a critical frequency. The soil moisturecontent, or the volumetric percentage of water in soil, is determined by measuring the frequencyshift of a high frequency excitation signal as it passes through the soil.

Operating Principles – Analytical Systems


DP-37EPA

Analytical Instrumentation

Organic systems

» Fluorescence detectors

» Membrane interface probe (MIP)

» Hydrosparge» Thermal desorption sampler (TDS)

Inorganic systems

» X-ray fluorescence (XRF)

» Laser-induced breakdown spectroscopy (LIBS)

Explosives sensor

Radiation detection probes

Notes:

• The following currently-available analytical systems will be discussed by contaminant class.



DP-38EPA

Organic Analysis

In situ spectroscopy

»Fluorescence instruments

Integrated systems

»MIP

»Hydrosparge™

»TDS

Notes:

• Direct sensors and integrated systems are readily available for analysis of various VOCs andsemivolatile organic compounds (SVOCs).

• Fluorescence detectors are direct sensors that bombard subsurface soils and sediments withultraviolet light, causing petroleum compounds to fluoresce. The fluorescent response isdetected by the sensor and the signal returned to the surface for analysis.

• In contrast, several other closed systems have been designed to capture volatile contaminantsfrom the vadose and saturated zones and return them to an integrated instrument at the surfacefor analysis. These systems include:

S The MIP operates in both unsaturated and saturated conditions (although withsomewhat different precision and accuracy)

S The Hydrosparge™ for groundwaterS The TDS for soils



DP-39EPA

Fluorescence Instruments

Petroleum hydrocarbon detection only

Ultraviolet (UV) radiation excites polycyclic aromatic hydrocarbon (PAH) molecules

Molecules give off (fluoresce) excess energy

Two fluorescence systems:

»Laser-induced fluorescence (LIF)

»Fuel fluorescence detector (FFD)

Notes:

• Fluorescence instruments refer to a general class of technologies in which a subsurface sampleis bombarded with an ultraviolet (UV) light source that causes petroleum hydrocarbons in thesample to fluoresce. The resulting fluorescence is used to identify and measure the contaminant.

• The fluorescence is produced when molecules of a certain class of SVOCs, known aspolycyclic aromatic hydrocarbons (PAH), give off energy in an attempt to return to their naturalor “ground” state after becoming excited by the energy from the UV source.

• Fluorescence instruments were originally developed for use by CPT rigs but are now alsodeployed from rotary hammer rigs. Several energy sources, including lasers and mercurylamps, have been used in these instruments.

• Two types of fluorescence systems include laser-induced fluorescence (LIF) detectors and fuelfluorescence detectors (FFD). Each type will be discussed in more detail in the followingslides.



DP-40EPA

Laser-Induced Fluorescence (LIF)

Detects petroleum fuels and coal tar

Generates continuous, high-resolution data

Complex systems require highly skilled operators

Notes:

• LIF is a method for real-time, in situ, field screening of hydrocarbons in undisturbed subsurfacesoils and groundwater. This screening data can be used to guide an investigation or removalaction or to delineate the boundaries of a subsurface contamination plume prior to installingmonitoring wells or taking soil samples.

• Can be used as a collaborative tool, in conjunction with visual core inspections and totalpetroleum hydrocarbon (TPH) fingerprinting to provide qualitative results. The primary functionof the LIF is for determining the presence or absence of TPH; however, one commerciallyavailable LIF system known as the rapid optical screening tool (ROST) can be operated in thestatic mode to identify the general class of contamination present.

• LIF can detect gasoline, diesel fuel, jet fuels, fuel oil, motor oil, grease, and coal tar in thesubsurface, based upon the PAH content of each.

• LIF sensors are very complex, and must be operated by highly trained technicians familiar withthe technology and its application. For this reason these systems are not rented or leased, butare typically procured as a service.



DP-41EPA

LIF Theory of Operation

Notes:

• The method uses a fiber optic-based LIF sensor system deployed with a standard 20-ton CPTrig. Light at a specific wavelength generated from a laser is passed down a fiber optic cable toa sapphire window in the tip of the CPT rod string as it is advanced into the subsurface. Thelaser light excites two- or three-ring aromatic compounds, or PAHs, in the soil adjacent to thesapphire window, causing them to fluoresce. The relative response of the sensor depends onthe specific analyte being measured because of the varying ratios of PAHs in each hydrocarbonmixture. The induced fluorescence from the PAHs is returned over a second fiber optic cableto the surface where it is quantified using a detector system. The peak wavelength and intensitycan be used in conjunction with ex situ TPH fingerprinting samples to provide typicalwavelength and intensity signatures for known TPH products. The intensity of the fluorescenceis used as an indicator of the relative contaminant concentration, but results are not consideredquantitative.

• The diagram above shows a data plot that includes data from geotechnical sensors and an LIFsystem, all plotted by depth.

• LIF data quality is sufficient for qualitative screening, and relative intensities may be consideredquantitative screening level data only. Site-specific detection limits vary from levels of 50 to1,000 mg/kg, but will vary between sites and petroleum products.



DP-42EPA

LIF – Two Major Systems

Site Characterization and Analysis Penetrometer System (SCAPS) LIF

Rapid Optical Screening Tool (ROST™)

System comparisons

» Development

» Availability

» Deployment

» Components

» Calibration

Notes:

• The Site Characterization and Analysis Penetrometer System (SCAPS) LIF system wasdeveloped through a collaborative effort of the Army, Navy, and Air Force under the Tri-Services Program. The Rapid Optical Screening Tool (ROST™) system was developed byLoral Corporation and Dakota Technologies, Inc.

• SCAPS is available only through the U.S. Army Corps of Engineers (USACE) and the U.S.Navy. ROST™ is available commercially through Fugro, Inc.

• Both sensing devices can be used with CPT rigs designed for direct push technologies. Theyalso can be used in conjunction with stratigraphic sensing devices.

• The primary differences between the two systems are the laser and the detector systems.

S Laser systems — The SCAPS LIF system uses a pulsed nitrogen laser that produceslight at a wavelength of 337 nanometers (nm). The ROST™ system uses a tunable dyelaser that can produce light at variable wavelengths chosen by the operator. Thepreferred mode of operation is to lock the excitation wavelength at 290 nm.

S Detector systems — The SCAPS LIF system uses a photodiode array (PDA) andoptical multichannel analyzer (OMA) as the fluorescence detector. The PDA and OMAquantify the fluorescence emissions spectrum from 350 to 720 nm. As the SCAPS LIF



sensor is pushed into the soil, real-time plots are generated of depth versus maximumfluorescence intensity and the wavelength at which the maximum intensity occurs. Thedetection system for the ROST™ consists of a monochromator, a photomultiplier tube(PMT), and digital storage oscilloscope (DSO). The monochromator acts as a variablewavelength narrow bandpass filter. By acquiring fluorescence data at a series ofwavelengths, the fluorescence technician can determine the wavelength of maximumintensity in the fluorescence spectrum. The light passing through the monochromator atthis wavelength is converted to an electrical signal by the PMT. The signal from thePMT is fed to the DSO, which displays the waveform (fluorescence intensity as afunction of time following the excitation laser pulse).

• The CPT rig is set up over the designated location for a push. The SCAPS LIF sensor’sresponse is checked using a standard rhodamine solution held against the sapphire windowbefore and after each push. The SCAPS LIF sensor is calibrated using spiked soil samplesrepresentative of the site. Diesel fuel marine standard or other petroleum hydrocarbons with afluorescence response appropriate for the site are used to spike the soil samples. The ROST™

system is calibrated with a proprietary blend of synthetic motor oil and other substances. Fluorescence emissions are measured at four wavelengths (340, 390, 440, and 490 nm). Thedata system is calibrated to read 100 percent fluorescence based on the fluorescence standardat the predetermined emission monitoring wavelength. All subsequent data is reported as apercent fluorescence relative to the standard.



DP-43EPA

LIF – Fluorescence Plots

SCAPS LIF

»Fluorescence intensity at maximum wavelength versus depth

»Fluorescence intensity versus wavelength

ROST™

»Dynamic mode: fluorescence versus depth (FVD)

»Static mode: wavelength-time-matrices (WTM)

Notes:

• For the SCAPS LIF system, a semiquantitative representation of the subsurface contaminationis gathered from the plots of real-time fluorescence intensity versus depth. A qualitativemeasure of different types of petroleum products can be gathered by examining plots offluorescence intensity versus wavelength for samples where the type of TPH contamination hasbeen evaluated by definitive analytical methods.

• In the dynamic mode, the ROST™ system operator chooses the excitation laser wavelength andfluorescence emission monitoring wavelength and they are held constant. The fluorescenceintensity is plotted as a function of depth below ground surface. Once areas of significantcontamination have been identified in the dynamic mode, the CPT is held at a fixed depth andthe ROST™ can be operated in the static mode to identify the general class of contaminationpresent. During the static mode, ROST™ can obtain wavelength-time-matrices (WTM) whichrepresent a 3-dimensional plot of relative fluorescence intensity versus fluorescence lifetimeversus wavelength. WTMs produce contaminant class-specific three-dimensional figures. Thisdata can be used to identify the type of fuel that is present. Normally, in the static mode, theexcitation wavelength is held constant and the emission monitoring wavelength is varied.



DP-44EPA

Interpretation of LIF Data

Notes:

• Two different approaches are used to analyze fluorescence intensity by wavelength.

• In the SCAPS LIF, the laser source emits light at a fixed wavelength. The returning signal isanalyzed using an optical multichannel analyzer spectrograph, where it is dispersed into aspectrum on a photodiode array detector. This arrangement allows for the rapid acquisition ofspectral data, so that as the sensor is pushed into the soil, real-time plots are generated of depthversus maximum fluorescence intensity and the wavelength at which the maximum intensityoccurs.

• In the ROST™ LIF, the laser source itself is variable and emits light at differing wavelengths thatmay be set by the analyst based on the compounds that are believed to be present. Theresponse is then compared with a plot of the fluorescence generated by the expectedcompounds to determine if there is a match. If there is no match, or if there is a partial matchand other compounds may also be present, the laser wavelength may be changed to scan forcompounds that respond to other wavelengths.

• The diagram above shows data from a variable wavelength LIF system, the ROST™ LIF, thathas been compared to library measurements and identified.



• Interpretation of LIF data requires the experience of highly trained technicians and the use ofcollaborative data such as visual core inspections and laboratory analytical data to supportconclusions.

• The area of soil exposed to the UV energy is limited to the surface area directly adjacent to thesensor window (approximately to size of pin-hole) and can vary significantly from ahomogenized sample taken from the same location.

• A number of factors can influence fluorescence wavelength and intensify results including:

S Variations in the soil matrix (soils with more surface area such as clays yield a higherfluorescence response than soils with less surface area such as sands).

S Naturally occurring minerals such as calcite and some organic matter products canfluoresce in the presence of UV, although they provide unique signatures different fromTPH signatures.

S Man-made non-hydrocarbon compounds such as deicing agents, anti-freeze additives,and detergent products are also known to fluoresce strongly in the presence of UV.



DP-45EPA

Membrane Interface Probe (MIP)

Notes:

• The permeable MIP was developed to allow for near real-time evaluation of subsurface VOCsusing rotary hammer units, and is now used widely with CPT (hydraulic ram) rigs as well. TheMIP is capable of multiple, discrete VOC measurements in a single penetration. VOCs aredrawn through the system’s semi-permeable membrane and carried to a detector at the surfacewhere they are analyzed and measured.

• The MIP system may be used to characterize any site with shallow subsurface VOCcontamination, including sites with fuel releases, chlorinated solvent releases, and dense non-aqueous phase liquid (DNAPL).

• The system is used to simultaneously characterize the subsurface soils and sediments withchemical contamination. Using the MIP in conjunction with electrical conductivity logs andadvancement speed logs provides information on contaminant distribution and migrationpathways in the same boring. The data collected can be used to accurately place a minimumnumber of conventional sampling points (soil bores and monitoring wells) for sitecharacterization and monitoring.

• The photograph above show a truck-mounted hydraulic hammer and MIP.



DP-46EPA

MIP Theory of Operation

Semi-permeable metal and Teflon membrane

Membrane is heated to between 80 °C and 125 °C

VOCs partition through the membrane

Carrier gas flushes the VOCs into the detector

Three detectors may be used (in series if desired)

» Photoionization detector (PID) for total VOCs

» Flame ionization detector (FID) for less volatile compounds

» Direct sensing ion trap mass spectrometer (DSITMS) for qualititative analysis

Notes:

• The MIP probe consists of a thin composite metal and a Teflon membrane impregnated into astainless steel screen on the face of a probe. A carrier gas line runs from the probe to thedetector through the inside of the tooling, and can be connected to several types of detectors,including flame ionization detectors (FID), photoionization detectors (PID), or direct samplingion trap mass spectrometers (DSITMS). DSITMS will be discussed in more detail in the nextsection.

• The MIP membrane is heated to between 80°C and 125°C as it is advanced through thesubsurface. VOCs present in the subsurface partition through the membrane by diffusion andmigrate into a helium carrier gas that flushes the back of the membrane and transports theVOCs to the aboveground detector.

• The system can operate in both the vadose zone and beneath the water table.



DP-47EPA

Interpretation of MIP Data

Notes:

• Total concentrations of aromatic VOCs may be measured continuously using a PID duringadvancement of the probe, while a FID is used to detect less volatile, straight chainhydrocarbons; and both detectors may be used in series.

• For qualitative identification of specific compounds, a DSITMS is used. Detection limits aretypically in the range of 1 ppm or less with little or no sample preparation required, and asample analysis time of 2 to 3 minutes.

• Subsurface lithology is determined by comparing readings from the integrated electricalconductivity sensor with the rate of advance through the subsurface, as described previously.

• Running MIP logs on a grid or targeted pattern across an investigation area will provide athree-dimensional view of VOC distribution and lithology. Software is available that allowsconstruction of cross sections from the MIP and conductivity logs. The graphic above showsthe composite cross-sectional results from nine direct-push logs. The contamination isconcentrated primarily in sand and silt.



DP-48EPA

Direct-Sampling Ion Trap Mass Spectrometer (DSITMS)

Commonly used in integrated direct-push analytical systems

» MIP

» TDS

» Hydrosparge™

Quantitative real-time analysis

No compound separation

Provisionally approved EPA method

Notes:

• The DSITMS is a system for the measurement, continuous real-time monitoring, andquantitative and qualitative preliminary screening of VOCs in water, soil, and air. It isapplicable to the determination of VOCs in batch samples taken to the laboratory and on-sitemeasurement and monitoring, and for this reason is used with the MIP and several other in situanalytical systems (discussed below). Real-time detection limits for VOCs in aqueous systemsare in the range of 1 ppb and in gaseous streams detection limits are in the range of about 10ppb by volume.

• The DSITMS demonstrates the capability of meeting the precision and accuracy quality control(QC) performance criteria established for water analysis by EPA Method 624. EPA publisheda DSITMS field methodology (Method 8265) in March 2002.

• The DSITMS does not use a gas chromatograph (GC) for compound separation. A series ofscans identify ions unique to the target analytes indicating the presence of specific VOCcompounds. These ions are monitored for a selected period of time to establish an integratedor average response and the response is compared to a comparably generated calibrationfactor for quantitation.



DP-49EPA

Hydrosparge™

Groundwater sampling and analysis of VOCs

Single discrete-interval sample per boring

Closed system with DSITMS for analysis

Does not incorporate lithologic sensors

Notes:

• The Hydrosparge™ system is designed to collect VOCs from groundwater for real-timeanalysis by analytical instrumentation in the direct-push vehicle on the surface. TheHydrosparge™ system is similar to the MIP system in that it extracts VOCs from groundwaterand brings them to the surface for analysis via a closed system.

• Unlike the MIP, the Hydrosparge™ is active and physically purges VOCs from the sampleinterval rather than allowing them to passively diffuse into the sampler. The Hydrosparge™ isonly able to sample one discrete interval per boring, as the probe must be retracted to exposethe sampler and cannot be re-advanced (multiple depths may be characterized within thesampler screen). The Hydrosparge™ also does not incorporate a lithologic sensor of any sort.

• The system uses a DSITMS detector for sample analysis. As described previously, DSITMSis a method for the quantitative measurement, continuous real-time monitoring, and quantitativeand qualitative preliminary screening of VOCs in water, soil, and air.

• The Hydrosparge™ may be useful for characterizing any site with shallow groundwater VOCcontamination (for example, fuel releases, or chlorinated solvent releases and DNAPL plumes).



DP-50EPA

Hydrosparge™ Theory of Operation

Used with a sealed-screen groundwater sampler

Sparge unit is lowered beneath the water table

Carrier gas purges (“sparges”) contaminants from groundwater matrix

Analysis with a DSITMS

Detection limits in the ppb range

Quantitative results in the low ppm range

(continued)

Notes:

• The Hydrosparge™ system (shown on the next page) integrates a customized CPT probe witha small sampling port, a sparging device, a Teflon transfer line for carrier gas, and anaboveground DSITMS detector in the truck. The system is closed to ensure that VOCs arenot lost in transport to the surface and that a known quantity of sample volume is introducedinto the detector if quantitative analysis is to be performed. A commercially availableHydropunchTM or PowerpunchTM direct-push groundwater-sampling tool is used to access thegroundwater.

• The groundwater sampler is pushed to the desired depth and the push rods are retracted,exposing the screen to the groundwater. The in situ sparge module is then lowered about 1.5feet below the groundwater surface. The sparge module purges the VOC analytes from thegroundwater using a helium carrier gas to the DSITMS system in the truck, where VOCs areanalyzed in real time. The system is able to detect contaminant concentrations in the low ppbrange, and can quantitate concentrations in the low ppm range.



DP-51EPA

Hydrosparge™ Theory of Operation

Notes:

• The graphic below illustrates the Hydrosparge™ system.



DP-52EPA

Thermal Desorption Sampler (TDS)

Sampling and analysis of VOCs in soil

Single discrete-interval sample per boring

Closed system with DSITMS for analysis

Multiple samples per boring

Does not incorporate lithologic sensors

Notes:

• The TDS is similar in principle and practice to the MIP and Hydrosparge™ systems, and isspecifically geared toward in situ characterization of VOCs in vadose zone soils. The TDSsystem is a closed system that draws VOCs directly from the subsurface for analysis by asurface detector. The direct-push rod is advanced with a special probe that collects a soil pluginto a chamber where it is heated. An integrated pneumatic system transports purged VOCs tothe surface for analysis by DSITMS. The system may be used to collect VOCs onto analyticaltraps for later analysis. The TDS does not incorporate a lithologic sensor.

• As the probe is deployed the sample chamber is filled, resulting in a sample of known quantityfor quantitative analysis. The sample chamber itself is then heated to increase the mobility of theVOCs and an inert carrier gas transports them to the surface, where they adsorb onto ananalytical trap. This trap is then heated to drive (desorb) the VOCs into the DSITMS detectorfor analysis. The carrier gas system is closed to ensure that VOCs are not lost in transport fromthe surface.

• As with the MIP and Hydrosparge™ systems, the TDS may be useful for characterizing anysite with shallow subsurface VOC contamination from fuel releases, or chlorinated solventreleases.

• The TDS may be used to analyze multiple samples per boring.



DP-53EPA

TDS Theory of Operation

Notes:

• The TDS consists of a custom soil probe, carrier gas lines and supply, an analytical trap, and aDSITMS detector deployed from a direct-push platform. The sample probe incorporates aninternal piston and a heated thermal sample chamber that is connected to the carrier gas lines.

• The operation of the TDS is based on the capture of a known volume of soil. The TDS ispushed to the desired ground depth and an interior rod retracts the penetrometer tip, whichlocks into the top of the sample chamber. The probe is then pushed further into the soil,collecting a plug of about 5 grams in the sample chamber. The soil plug is heated, releasing theVOC gases from the soil. The vapors are drawn to the surface by the inert carrier gas, wherethey are trapped on an adsorbent media. The trap is then thermally desorbed into the onboardDSITMS, where VOCs are analyzed in near-real time.

• After analysis, the soil plug is expelled from the sample chamber by reseating the piston into thedrive position, and the sample chamber is heated and purged to remove any residualcontamination before the process is repeated, allowing for screening of multiple depths during asingle push.

• The TDS has been certified as achieving detection thresholds for trichloroethene (TCE) andtotal dichloroethene (DCE) comparable to those of EPA Method 8260A (which is nowsuperceded by EPA Method 8260B).

direct sampling methods and down-hole sensors module at a glance

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