Geoprobe Direct Push Services

The Probing Company is a Geoprobe Direct Push service company located in Atlanta, Georgia (GA). We conduct Geoprobe Direct Push work in Georgia, Alabama, Tennessee and other select states in the Eastern US.

SOIL SAMPLING

The Probing Company is qualified to complete any and all direct push soil sampling at your job site. Direct push sampling doesn’t generate soil cuttings like typical augering methods, and is well known throughout the environmental industry as the fastest and most economical way to collect soil samples from a site. The Probing Company utilizes both the Geoprobe MacroCore Sampling System and the Geoprobe® Large Bore Sampling System to collect soil samples.

Geoprobe MacroCore Sampling System

The Geoprobe MacroCore Sampling System utilizes a 4-foot long soil sampler that collects soil core samples from unconsolidated subsurface materials. These unconsolidated materials may include soils, sediments and waste materials, or a mixture of all three. This sampler works best in medium to fine grained soils such as silty clays. When a sand catcher is used, the MacroCore sampler works well in fine to medium grained sands and gravels as well as flowing sands. There are two options to consider when using the Geoprobe MacroCore sampling system: Open Tube or Closed Piston.

Open Tube Sampling

The most economical and common use of the Geoprobe MacroCore sampling system is the open tube method. Coring starts at the ground surface with an open ended sampler. The open ended sampler is assembled with a cutting shoe, drive head and the sampling sleeves. The open tube sampler is driven into the subsurface using the percussion of the Geoprobe rig until the sampler is at the target depth. Once at the target depth, the sampler is removed from the ground, the cutting shoe removed and the sample sleeve extracted with the soil inside. A new sleeve is placed in the sample tube and the sampler and the cutting shoe are replaced. Once together, the entire tool string is advanced beyond the last depth of penetration by adding a drive rod. This procedure is repeated until the sampler reaches the desired target depth.

Closed Piston Sampling

The closed piston system is best suited for unstable soils which tend to collapse or expand into the probe hole. The closed piston system locks a retractable drive point into the cutting shoe and prevents soil from entering the MacroCore sampler as it is advanced into the borehole. As a drive rod is added, an inner rod is placed into the center of the drive rod to lock the retractable drive point in place. Within the last four feet of the target depth, a final drive rod is added without the inner rod. This allows the drive point to retract into the MacroCore sampler as the sampler is advanced the final four feet. This method allows the soil to be collected into the sleeve from the exact target depth. Removal of the rods and the soil sample are the same as with the open barrel sampling system.

Geoprobe® Large Bore Sampling System

The Geoprobe Large Bore Sampling System utilizes a solid barrel sampling system like the MacroCore Sampling System, except that it is smaller in diameter, approximately 30-inches long and utilizes a 24-inch sample sleeve. The Large Bore sampler can be utilized as an open tube sampler or a closed piston sampler. We utilize the Large Bore sampler for select limited space interior sampling jobs.

GROUNDWATER SAMPLING

Groundwater sampling from a Geoprobe rig can be accomplished in many ways. Samples can be collected utilizing the Geoprobe Screen Point 15/16 sampler (SP-15/SP-16), installing small diameter temporary monitoring wells or installing permanent monitoring wells.

Geoprobe Screen Point 15/16 Sampling

The Geoprobe SP-15/16 is a protected screen, direct push groundwater sampling device utilized for sampling groundwater from unconsolidated materials. To collect a groundwater sample utilizing this device, a stainless steel screen is inserted inside a stainless steel sheath, and a drive head is attached to the sheath. A steel expendable point is then attached to the other end of the sheath, and a drive rod is threaded to the top. Once attached, the entire assembly is driven into the subsurface using the percussion of the Geoprobe rig. Drive rods are added to the string of tools as the sampler is advanced to the desired depth. Once the desired depth is reached, stainless steel extension rods are inserted down the center of the drive rods to hold the expendable point in place, and the drive rods are retracted approximately 4 feet. With the stainless steel screen exposed and the water table surface intersecting the screen, the extension rods are removed. The groundwater is extracted using disposable poly tubing and a peristaltic pump or a stainless steel check ball valve.

Temporary and Permanent Monitoring Wells

Both temporary and/or permanent monitoring wells can be installed with the Geoprobe rig. We install temporary monitoring wells by one of two methods:

• By removing the soil column with a Geoprobe MacroCore sampler and installing the small diameter slotted PVC screen and well pipe into the open borehole to the desired depth; or

• By advancing 2.125 or 2.25-inch steel casing (rods) fitted with an expendable drive point to the target depth and inserting the screen and casing in the open rods. Once the screen and well pipe are threaded together and placed inside the rods, the steel casing is removed from the subsurface while holding the temporary well in place.

The groundwater is extracted from these wells using disposable poly tubing and a peristaltic pump or a stainless steel check ball valve.

Permanent monitoring wells are also installed with the 2.125 or 2.25-inch steel casing fitted with an expendable drive point in a similar fashion to the temporary monitoring well installation; however, the well screen is wrapped in stainless steel mesh filled with sand (pre-pack well screen). This aids in well development and sampling by ensuring that a sand filter media is uniformly placed around the well screen. Once the well is in place at the bottom of the rods, additional sand is added to the rods to raise the sand level by two feet on the top of the pre-pack well screen. A two foot thick bentonite seal is then placed on top of the sand and the rods are extracted from the subsurface. The annulus is then filled to the surface with a grout slurry. Permanent wells are typically completed with either a flush-mounted vault or a stand-up well cover.

SOIL GAS SAMPLING

Soil gas sampling is increasing in frequency across the country as vapor intrusion continues to gain regulatory attention. When evaluating the potential for vapor intrusion at a particular site, it is useful to collect soil gas samples to find out how vapors and contaminants of concern are migrating in the subsurface, and whether or not those vapors are migrating indoors. Soil gas sampling, used in conjunction with screening criteria and/or modeling, is often an intermediate step between screening based on groundwater concentration and collecting indoor air samples.

The goal of soil gas sampling is to collect a sample of the vapor that resides in the interstitial soil pores near a source of contamination and/or near a receptor. To sample soil gas, a temporary or permanent soil vapor probe is installed to facilitate the collection of a sample of the soil gas. Soil gas sampling can be completed with hand tools or with a Geoprobe rig.

Sub Slab Soil Gas Sampling - Hand Tools

Sampling with hand tools is the fastest and most economical way to sample sub slab soil gas. It doesn’t require a Geoprobe rig, and the borings can easily be abandoned after use.

The following describes a typical method for collecting sub slab soil gas samples:

• Drilling a hole through the concrete surface to the target depth;
• Inserting a tube into the open hole;
• Sealing the hole with bentonite;
• Purging the sub-slab sampling point as necessary with a peristaltic pump; and
• Collecting soil gas samples in Summa canister or Tedlar bag.

Once the sample is collected, the tubing is removed, and the hole is refinished to match the surface grade.

Although more costly to install, permanent vapor monitoring points can also be installed by this method.

Soil Gas Sampling - Geoprobe Rig

Soil gas samples can be collected at any depth using a steel expendable point system and tubing (PRT System). To facilitate the collection of the soil gas sample, the steel expendable point is placed in an expendable point holder that is attached directly to a drive rod. Once attached, the drive rod is driven to the target depth. The drive rod and expendable point holder are retracted and the steel expendable point is separated from the point holder thus creating a void beneath the drive rods in the soil. An adapter and tubing are advanced down the inside of the drive rods and threaded to the point holder. The tubing at the surface is attached to a peristaltic pump or equivalent pumping system to purge the line and draw a sample. Most applications utilize Teflon or nylon tubing; however, other materials can be utilized if desired. Once the line has been purged, samples are typically collected in a Tedlar bag or Summa canister.