A Discrete Point Sampler for Ground Water Monitoring Wells

A discrete point sampler has been developed that overcomes disadvantages inherent in several current small-volume samplers. It is designed to obtain ground water samples after a well has been purged with a pump. It consists of a sample chamber, two ports, and a stopcock for withdrawing sample aliquots. After lowering the sampler into a well, sampling is initiated by pulling on a line that sequentially removes the plugs in the lower and the upper level ports. The sample chamber fills from the bottom port and vents air from the top port. The device is suitable for sampling for volatile organic compounds in ground waters that are not subject to spontaneous bubble degassing. The upper port is sufficiently far above the lower port that none of the water that is sampled is exposed to the vented air. The sample chamber fills in such a way that the water that is taken from the chamber for analysis is not exposed to the headspace in the chamber.     

A Portable Membrane Contactor Sampler for Analysis of Noble Gases in Groundwater

To enable a wider use of dissolved noble gas concentrations and isotope ratios in groundwater studies, we have developed an efficient and portable sampling device using a commercially available membrane contactor. The device separates dissolved gases from a stream of water and collects them in a small copper tube (6 mm in diameter and 100 mm in length with two pinch‐off clamps) for noble gas analysis by mass spectrometry. We have examined the performance of the sampler using a tank of homogeneous water prepared in the laboratory and by field testing. We find that our sampling device can extract heavier noble gases (Ar, Kr, and Xe) more efficiently than the lighter ones (He and Ne). An extraction time of about 60 min at a flow rate of 3 L/min is sufficient for all noble gases extracted in the sampler to attain equilibrium with the dissolved phase. The extracted gas sample did not indicate fractionation of helium (³He/⁴He) isotopes or other noble gas isotopes. Field performance of the sampling device was tested using a groundwater well in Vienna and results were in excellent agreement with those obtained from the conventional copper tube sampling method.     

A Diffusive Sampler for Passive Monitoring of Underground Storage Tanks

Passive measurements of volatile organic compounds (VOCs) provide a method for early detection and long-term monitoring of potential leaks from underground storage tanks (USTs) and associated fuel service lines. A diffusive sampler was constructed of a sorbent tube that fits inside a specially designed sampling chamber. VOCs in the soil enter the chamber by molecular diffusion and are collected by the sorbent. The sorbent is easily retrieved for laboratory analyses by thermally desorbing into a gas chromatograph/mass spectrometer (GC/MS), or qualitative concentrations can be determined directly in the field with specific-indicator detectors.
The diffusive samplers were evaluated in an exposure chamber under controlled conditions. Laboratory measurements of the sorbed mass of organic vapor were found to be in close agreement with theoretical values and indicate the passive sampling approach is viable for detecting relatively low concentrations of organic vapors in the vadose zone over a one-day sampling period, as well as providing relatively long-term monitoring periods up to 58 days. A field test found the sampling approach successful in identifying an area where the vadose zone was contaminated by leaking petroleum USTs.     

Novel Well Completions in Small Diameter Coreholes Created Using Portable Rock Drills

Difficult access conditions have limited techniques for groundwater system characterization and monitoring in bedrock exposed landscapes. This condition is common in the mining industry and resulted in the development of lightweight portable drills. This paper describes how these drills were used at a contaminated site to understand the groundwater flow system by adapting piezometer designs, ensuring effective seals to obtain reliable hydraulic head, hydrochemistry, and contaminant concentrations. Two drilling machines were evaluated: the Shaw Portable Core Drill? fits in a backpack and can advance continuously cored rock holes, nominal 51 millimeters (mm) diameter, to depths up to approximately 15 meters (m); and the larger Winkie Drill? requires a two or more people to mobilize and can advance continuously cored holes, nominal 48 mm diameter, to depths of approximately 45 m. The resulting small diameter coreholes were accommodated in the design of each well using a seal created by injecting grout into a semipermeable fabric sleeve. This “fabric sleeve” serves as a means to contain the grout and ensures that the entire annulus above the screen is sealed without loss of grout into the formation, allowing the well to perform as a piezometer. To develop and demonstrate this methodology for groundwater monitoring in bedrock, the two drills were used in drainages located along the slopes of an elevated sandstone outcrop near Los Angeles, California. Unique insights into the groundwater flow system of this bedrock environment, which would otherwise be unattainable, were achieved. This methodology overcomes the accessibility limitations of conventional drilling methods that prevent installation of wells in remote and rugged mountainous terrains.     

A Sample-Freezing Drive Shoe for a Wire Line Piston Core Sampler

Loss of fluids and samples during retrieval of cores of saturated, noncohesive sediments results in incorrect measures of fluid distributions and an inaccurate measure of the stratigraphic position of the sample. To reduce these errors, we developed a hollow drive shoe that freezes in place the lowest 3 inches (75 mm) of a 1.88-inch-diameter (48 mm), 5-foot-long (1.5 m) sediment sample taken using a commercial wire line piston core smapler. The end of the core is frozen by piping liquid carbon dioxide at ambient temperature through a steel tube from a bottle at the land surface to the drive shoe where it evaporates and expands, cooling the interior surface of the shoe to about - 109°F (- 78°C). Freezing a core end takes about 10 minutes. The device was used to collect samples for a study of oil-water-air distributions, and for studies of water chemistry and microbial activity in unconsolidated sediments at the site of an oil spill near Bemidji, Minnesota. Before freezing was employed, samples of sandy sediments from near the water table sometimes flowed out of the core barrel as the sampler was withdrawn. Freezing the bottom of the core allowed for the retention of all material that entered the core barrel and lessened the redistribution of fluids within the core. The device is useful in the unsaturated and shallow saturated zones, but does not freeze cores well at depths greater than about 20 feet (6 m) below water, possibly because the feed tube plugs with dry ice with increased exhaust back-pressure, or because sediment enters the annulus between the core barrel and the core barrel liner and blocks the exhaust.     

The Ensemble Kalman Filter for Groundwater Plume Characterization: A Case Study

The Kalman filter is an efficient data assimilation tool to refine an estimate of a state variable using measured data and the variable's correlations in space and/or time. The ensemble Kalman filter (EnKF) (Evensen 2004, 2009) is a Kalman filter variant that employs Monte Carlo analysis to define the correlations that help to refine the updated state. While use of EnKF in hydrology is somewhat limited, it has been successfully applied in other fields of engineering (e.g., oil reservoir modeling, weather forecasting). Here, EnKF is used to refine a simulated groundwater tetrachloroethylene (TCE) plume that underlies the Tooele Army Depot‐North (TEAD‐N) in Utah, based on observations of TCE in the aquifer. The resulting EnKF‐based assimilated plume is simulated forward in time to predict future plume migration. The correlations that underpin EnKF updating implicitly contain information about how the plume developed over time under the influence of complex site hydrology and variable source history, as they are predicated on multiple realizations of a well‐calibrated numerical groundwater flow and transport model. The EnKF methodology is compared to an ordinary kriging‐based assimilation method with respect to the accurate representation of plume concentrations in order to determine the relative efficacy of EnKF for water quality data assimilation.     

Successful Use of an Innovative Horizontal/Vertical Well Couplet in Fractured Bedrock to Intercept a Mobile Gasoline Plume

The horizontal directional drilling (HDD) technology was successfully used in a fracture-controlled sandstone matrix to intercept a gasoline plume and create a 150-foot-long hydrodynamic barrier preventing seepage of gasoline and contaminated ground water into a salmon-bearing stream within a public park. A 36-foot-deep vertical recovery well (VW) intercepts the central low point of the 420-foot-long HDD borehole to pump recovered fluids. Contaminant seepage into the creek ceased within hours of starting up the HDD/VW interceptor system in August 1999. Approximately 325 gallons of gasoline and 2 million gallons of contaminated ground water have been recovered to date.     

Cone Penetrometer Tests and HydroPunch® Sampling: A Screening Technique for Plume Definition

Cone penetrometer tests and HydroPunch® sampling were used to define the extent of volatile organic compounds in ground water. The investigation indicated that the combination of these techniques is effective for obtaining ground water samples for preliminary plume definition. HydroPunch samples can be collected in unconsolidated sediments and the analytical results obtained from these samples are comparable to those obtained from adjacent monitoring wells. This sampling method is a rapid and cost-effective screening technique for characterizing the extent of contaminant plumes in soft sediment environments. Use of this screening technique allowed monitoring wells to be located at the plume boundary, thereby reducing the number of wells installed and the overall cost of the plume definition program.     

A Particle Tracking Algorithm for Arbitrary Unstructured Grids

A new semi-analytical algorithm for generating the local groundwater velocity field within irregular three-dimensional grid cells (such as a Voronoi cell) is presented. The method supports particle tracking in the MODFLOW-USG software package for a variety of supported unstructured grid formats. It is shown to replicate the results from the fully analytical Pollock's method when used on a rectilinear grid, and is demonstrated for difficult test cases where there is high spatial variability in the flow field within individual cells. The method is now available as an option in the mod-PATH3DU software package and may be used with most MODFLOW-USG packages without additional intervention.     

Personal Sampler for Viable Airborne Microorganisms: Main Development Stages

A new personal bioaerosol sampler has been developed and verified as an efficient tool for monitoring of viable/non‐viable airborne microorganisms, including bacteria, fungi, and viruses. The operational principle of the device is based on continuous passage of an air sample through porous media submerged into a liquid layer. During motion along narrow and tortuous ways inside the porous media, the air stream is split into a large number of ultra small bubbles with the particulates are being scavenged by these bubbles and, thus, effectively trapped. The device was initially verified for monitoring of viable airborne bacteria and fungi, firstly, under controlled laboratory conditions and later in a field. It was demonstrated that bacterial recovery rates for these two groups of microorganisms were very high and the device was found to be fully feasible for such monitoring. The next step of the device investigation was performed in the laboratory on monitoring viable airborne viruses with a range of sensitivities to physical and biological stresses. As the result, the new personal sampler demonstrated a very high recovery rate even for viruses which are rather sensitive to environmental stress (Avian Influenza, SARS, Mumps, etc.). Some following field studies, undertook in a hospital and animal houses, also demonstrated an excellent performance of the new device for selective and reliable monitoring of viable airborne viruses even in environments highly contaminated by other microorganisms. This paper reviews the main development staged of the new personal bioaerosol sampler.     

Core Sampler for Soft Bottom Sediments with Lower Closing Mechanism

A novel sediment core sampler is represented. It is suitable for liquid sediments and for undisturbed sediment cores with a large core diameter from shallow and deep waters.