Push-pull Tests Research Articles

Estimation of very slow groundwater movement using a Single-Well Push-Pull test

An estimation method for evaluating groundwater velocity by means of the Single-Well Push-Pull (SWPP) test by Leap and Kaplan (1988) was applied to a confined aquifer at 100 m depth with a very slow groundwater movement. The SWPP test consists of a push phase, a drift phase, and a pull phase, and the groundwater velocity is evaluated based on the Breakthrough Curves obtained from the SWPP test. In this study, the accuracy of the SWPP test system was evaluated by performing a SWPP test without drift time four times in total. Also, four types of SWPP tests with different drift times from 10 to 1802 days were conducted to obtain an estimate of the regional groundwater velocity for a maximum of approximately five years. Furthermore, the stable isotope of water (δ18O and δD) and uranine, which are known as conservative tracers, were used as tracers in the SWPP tests so as to evaluate their availabilities.The SWPP test results showed a higher reproducibility of the SWPP test using δ18O and δD than that using uranine. The sorption of uranine in the aquifer was suggested based on the SWPP test results, indicating that the hydrological properties can be obtained by comparing the SWPP test results using δ18O, δD and uranine as tracers. The SWPP test yielded an actual groundwater velocity of 0.37 m/year, which is similar to approximately 0.1 m/year order of the estimated groundwater velocity based on the results of past studies. Moreover, setting the appropriate correction and drift time in the SWPP test played an important role in investigating the very slow groundwater flow in the aquifer. When a long-term drift time was set, the recovery rate of the tracer and the chaser of δ18O and δD was decreased by diffusion in the aquifer’s silt and clay layer.

A new solution to transient single-well push-pull test with low-permeability non-Darcian leakage effects

An accurate solute transport model is critical to the interpretation of single-well push-pull (SWPP) test. Previous studies of SWPP test generally consider solitary aquifer that is confined by impermeable layers. Also, existing solutions for solute transport in aquifer-aquitard systems only consider the injection phase and over-simplify the flow field by assuming uniformly distributed velocity in the aquitard. In this study, we developed a numerical model with Dirichlet boundary condition for SWPP test affected by leakage described by a low-permeability non-Darcian expression involving a threshold pressure gradient (I0). Our SWPP test model considered transient flow in multi-phases, which include injection, chase, rest and extraction phases. Finite-difference scheme was adopted to solve the models of flow and solute transport. The results indicate that an increasing hydraulic diffusivity leads to a greater peak value of breakthrough curve (BTC) while a medium with larger grain size results in less estimation error when using steady-state flow model to interpret the transient SWPP test. Additionally, A greater I0 makes the solute stored in aquitard more difficult to be extracted out due to dispersion dominance, which results in higher BTC values. For the purpose of application, a lumped dimensionless index called the non-Darcian index (NDI) was proposed to quantify the overestimation degree by neglecting leakage, and the underestimation degree by accounting for Darcian leakage, when interpreting the SWPP test with low-permeability non-Darcian leakage. The long-term slope of breakthrough curve coupled with the NDI can be employed to determine the cases in which the low-permeability non-Darcian leakage should be considered.

Contrasting subsurface denitrification characteristics under temperate pasture lands and its implications for nutrient management in agricultural catchments

Subsurface denitrification plays a key role in the reduction or ‘attenuation’ of nitrate contamination of groundwater and surface waters. We investigated subsurface denitrification characteristics in the vadose zone and shallow groundwater at four sites under pastoral farming in the Manawatū River catchment, located in the lower part of North Island, New Zealand. The denitrification potential of the vadose zone was determined by the laboratory incubation assays measuring the denitrifying enzyme activity (DEA) in soil samples collected from different soil horizons (up to 2.1 m below ground surface), whereas denitrification rates in shallow groundwaters were measured in situ by single-well, push-pull tests conducted in piezometers installed at multiple depths at the study sites. Soils and underlying geology, defining hydrogeologic settings, appear to influence the spatial variability of subsurface denitrification characteristics at the study sites. Where the vadose zone is thin and composed of coarse-textured soils, percolation of nitrate was evident in observed high nitrate-nitrogen concentrations (>5 mg L−1) in oxic and young shallow groundwaters, but low nitrate-nitrogen concentrations (<0.05 mg L−1) were observed in the reduced shallow groundwater found underneath the fine textured soils and/or a thick vadose zone. This was confirmed by the push-pull tests measuring denitrification rates from 0.08 to 1.07 mg N L−1 h−1 in the reduced shallow groundwaters (dissolved oxygen or DO < 0.5 mg L−1), while negligible in the oxic groundwaters (DO > 5 mg L−1) found at the study sites. These contrasting subsurface denitrification characteristics determine the ultimate delivery of nitrate losses from agricultural soils to receiving waters, where the fine textured thick vadose zone and reducing groundwater conditions offer nitrate reduction in the subsurface environment.

Evaluating a new injection method of liquid/gas mixture spray injection via performing long-term in situ bioremediation tests

During in situ bioremediation, continuous injection of growth substrates such as carbon sources, electron donors, or electron acceptors inevitably results in microbial growth, resulting in biological clogging in an aquifer. Therefore, for successful bioremediation, development of a new injection method is needed to reduce or alleviate this clogging problem. In this study, we carried out field tracer tests using single-well push-pull tests (SWPPTs), single-well natural gradient drift tests (SWNGDTs), and long-term in situ well-to-well tests to develop and evaluate a new method of liquid/gas mixture spray injection. The effectiveness of the new method was evaluated by estimating the factors as follow: longitudinal dispersivity (αL), radius of influence (RI), shear stress on the surface of aquifer particles (σ), biofilm-shear-loss rate (Rs), and the ratio of volume occupied by cells grown to the original pore volume. At the tested site, the liquid/gas mixture spray injection method turned out to have several advantages compared to the traditional solution injection method: 1) transport of solute to a larger proportion of an aquifer by a factor of 1.3–1.7, 2) application of higher shear stress onto the surface of soil particles by a factor of 4.2–5.0, 3) faster biofilm sloughing rates by a factor of 2.3–2.6, 4) reduction in the ratio of the volume occupied by microorganisms to total pore volume (Volmicrobes/Volpore), and 5) efficient trichloroethylene (TCE) dechlorination for a period of 550 days without any injection problems. This new injection method showed positive effects on the hydrogeological and physical characteristics of the system, thus alleviating the biological clogging problem.

Efficacy of in situ well-based denitrification bio-barrier (WDB) remediating high nitrate flux in groundwater near a stock-raising complex

This study assessed the feasibility of an in situ well-based denitrification bio-barrier (WDB) for managing groundwater contaminated with high-strength nitrate. To evaluate the efficacy of WDB using fumarate as a carbon source and/or electron donor, three sequential single-well push-pull tests (SWPPTs) were conducted at six test sites. The values of the isotope enrichment factor (ɛ) ranging from −6.5‰ to −22.6‰ and the detection and degradation of nitrite and nitrous oxide confirmed complete in situ denitrification of nitrate to nitrogen gas. The ratio of the first-order rate coefficient of fumarate to nitrate (k1,fum/k1,NO3) was obtained to estimate the amount and frequency of fumarate injection for the effective design of WDB. At three sites, the ratios ranged from 0.67 to 0.80, while the other two sites showed higher ratios of 2.97 and 2.20 than the theoretical values and significant amounts of sulfate reduction, theoretically equivalent to 6.5% of total fumarate consumption. Considering the theoretical mole ratio of fumarate to nitrate of 0.98, the amount and frequency of fumarate injection is site specific. During the operating WDB, the average annual nitrate mass degraded (95% CI) was 2.2 ± 1.0 kg N/yr/well. The amount of N reduced by one well of WDB is equivalent to treating 110 m3 of groundwater at 30 mg N/L to the level of 10 mg N/L for one year. WDB would be an effective remediation option for managing high nitrate flux in groundwater.

Spatially-distinct redox conditions and degradation rates following field-scale bioaugmentation for RDX-contaminated groundwater remediation

In situ bioaugmentation for cleanup of an hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)-contaminated groundwater plume was recently demonstrated. Results of a forced-gradient, field-scale cell transport test with Gordonia sp. KTR9 and Pseudomonas fluorescens strain I-C cells (henceforth “KTR9” and “Strain I-C”) showed these strains were transported 13 m downgradient over 1 month. Abundances of xplA and xenB genes, respective indicators of KTR9 and Strain I-C, approached injection well cell densities at 6 m downgradient, whereas gene abundances (and conservative tracer) had begun to increase at 13 m downgradient at test conclusion. In situ push-pull tests were subsequently completed to measure RDX degradation rates in the bioaugmented wells under ambient gradient conditions. Time-series monitoring of RDX, RDX end-products, conservative tracer, xplA and xenB gene copy numbers and XplA and XenB protein abundance were used to assess the efficacy of bioaugmentation and to estimate the apparent first-order RDX degradation rates during each test. A collective evaluation of redox conditions, RDX end-products, varied RDX degradation kinetics, and biomarkers indicated that Strain I-C and KTR9 rapidly degraded RDX. Results showed bioaugmentation is a viable technology for accelerating RDX cleanup in the demonstration site aquifer and may be applicable to other sites. Full-scale implementation considerations are discussed.

In situ field method for evaluating biodegradation potential of BTEX by indigenous heterotrophic denitrifying microorganisms in a BTEX-contaminated fractured-rock aquifer

ABSTRACT Generally different anaerobic degradation potentials for benzene, toluene, ethylbenzene and xylene isomers (BTEX) has been reported due to site specific conditions, such as the indigenous microbial population, electron acceptors (EA) available and concentrations of each BTEX compound. It was of interest to estimate relative biodegradation potential of each BTEX compound during enhanced anaerobic bioremediation of a BTEX-contaminated aquifer. In this study, an in situ method for assessing the degradation potentials of each BTEX compound present as a mixture under NO3 −injecting conditions by performing a series of single-well push-pull tests and well-to-well tests (WWTs) was developed. During the 1st and 2nd WWTs, biological heterotrophic dissimilative NO3 − denitrification was confirmed by simultaneous detection of both NO2 − and N2O and significant production of CO2 during the NO3 − degradation. The biodegradation fractions of NO3 − injected during the 1st and 2nd WWTs were 1.7% and 5.0%, respectively, with 7.18 and 8.85 mmol N/L/day of in situ zero-order denitrification rate coefficients. The concentrations of benzene, ethylbenzene, and xylenes measured were similar to values calculated when considering only dilution, but the measured concentrations of toluene were significantly lower than the values calculated were. These results indicate that in situ method presented in the study successfully evaluate anaerobic biodegradation potential of individual BTEX compounds by indigenous heterotrophic denitrifying microorganisms.

Skin effect on single-well push-pull tests with the presence of regional groundwater flow

Single-well push-pull (SWPP) test is one of the most important ways to estimate flow and transport parameters, e.g. porosity, dispersivity, regional groundwater flow velocity. Usually the wellbore is surrounded by a finite-thickness skin, such as a gravel pack. The positive skin has a smaller hydraulic conductivity than the aquifer formation zone, and the negative skin has a greater one. In this study, a numerical model of a SWPP test considering skin effects was established using the finite-element COMSOL Multiphysics program to estimate aquifer parameters. Several important results were obtained. Firstly, regional groundwater velocity affects the types of breakthrough curves (BTCs) through changing the flow pattern. Secondly, a positive (or negative) skin leads to a slower (or faster) tracer transport process, and a smaller ratio between the hydraulic conductivity of the skin and that of the aquifer formation zone results in greater solute plume retardation in the skin zone. Thirdly, a larger thickness of the positive skin leads to a higher tracer concentration around the well, and the opposite is true if the skin is negative. Besides, the model of Leap and Kaplan (1988) underestimates the regional groundwater velocity for the second type of BTCs, and a larger longitudinal dispersivity can lead to a greater error, where the second type of BTCs has a rising limb at early stage followed by a falling limb at late stage. The general conclusion is that the estimations of groundwater velocity from SWPP tests are also affected by skin effects.

Fatigue resistance of asphalt binders and the correlation with asphalt mixture behaviour

The prediction of asphalt pavements performance in relation to the main distresses has been proposed by different researchers, by means of laboratory characterisation and field evaluation. With respect to fatigue, there are different approaches to determine what failure criterion to be considered, what testing conditions to be used and which specimens’ geometry to be produced. Tests performed in asphalt binders and mixtures have been recommended to characterise the fatigue resistance, and correlations among the several scales are proposed in order to make it more practical and more precise to predict the performance of asphalt layers. In terms of laboratory fatigue characterisation of asphalt mixtures, some of the most common tests are the four-point bending beam, diametral compression, the push-pull tests, among others. The characterisation of asphalt binders is also relevant, since fatigue is dependent on their rheological characteristics. Linear viscoelastic parameters of the binders, time sweep and amplitude sweep tests were used to rank three asphalt binders (one neat 30/45 penetration grade binder; one SBS-modified binder; and one highly modified asphalt, HiMA) in terms of fatigue behaviour. HiMA showed the highest fatigue resistance. One dense hot mix asphalt (HMA) mixture (prepared with the AC 30/45 neat binder) was characterised in terms of different fatigue test methods and correlated with binder tests, comparing the two scales approaches. The fatigue life of the asphalt mixture followed in agreement with results from the asphalt binder.

Behavior of rare earth elements in an aquifer perturbed by CO2 injection: Environmental implications

Three cubic-meters of CO2-saturated water was injected into a subsurface fractured aquifer in a post-mined area, using a push-pull test protocol. Groundwater samples were collected before and after CO2-injection to quantify geochemical changes. CO2-injection initially reduced the pH of water from 7.3 to 5.7, led to the enrichment of major ions (Ca2+, Mg2+, and alkalinity), and dissolved trace metals (including Fe, Mn, As, and Zn) in the groundwater. Rare earth elements (REE) and yttrium concentrations were also measured in these samples before and after CO2 perturbation, to evaluate their behavior. An enrichment of total Y plus REE (REY) occurred. REY fractionation was observed with higher heavy REE (HREE) enrichment compared to light REE (LREE), and significant variations in La/Yb and Y/Ho ratios were observed following CO2 perturbation. Enrichment by a factor of three was observed for Y, Lu, and Tm, and by nearly one order of magnitude for Dy and Yb. A geochemical model was used to evaluate the amount of REE aqueous ions complexed throughout the experiment. Modeling of the results showed that speciation of dissolved REE with carbonate, along with desorption from iron oxyhydroxide surface were the main factors controlling REE behavior. This study increases an understanding of dissolved REE behavior in the environment, and the potential use for applying iron oxides for REE recovery from mine drainages. Furthermore, the description of REE fractionation patterns may assist in surveying CO2 geological storage sites, surveying underground waste disposal sites, and for understanding the formation of ore deposits and fluid inclusions in geological formations.

CORROSION AND FATIGUE OF HEAT TREATED MARTENSITIC STAINLESS STEEL 1.4542 USED FOR GEOTHERMAL APPLICATIONS

During capture and storage technology (CCS) as well as in geothermal energy production steels need to withstand the corrosive environment such as: heat, pressure, salinity of the aquifer and CO 2 -partial pressure. 1.4542 shows unusual corrosion phenomena, but is still sufficiently resistant in corrosive environments. To better understand its behaviour differently heat treated coupons of 1.4542 and for comparison X20Cr13 and X46Cr13 were kept in the artificial brine of the Northern German Basin at T=60 °C. Ambient pressure as well as p=100 bar for 700 h - 8000 h in water saturated supercritical CO 2 and CO 2 -saturated synthetic aquifer environment was applied. Fatigue tests were performed via push-pull tests with a series of 30 specimens from 150 MPa to 500 MPa (sinusoidal dynamic test loads, R=-1; resonant frequency ~ 30 Hz). FeCO 3 and FeOOH are corrosion products also after dynamic corrosion tests. Martensitic microstructure offers good corrosion resistance in geothermal environment. The S-N-curve showing no typical fatigue strength and very steep slopes of possible fatigue strength for finite life. Possible influencing artefacts, such as Al-inclusions could not be correlated to early rupture despite specimens containing inclusions at the fracture surface and cross section reached lower number of cycles. Applied potential proofed to enhance fatigue life tremendously. Article DOI: https://dx.doi.org/10.20319/mijst.2019.51.138158 This work is licensed under the Creative Commons Attribution-Non-commercial 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

Several Considerations on Well Treatment in a Numerical Model for Single-Well Push-Pull Tests in Carbon Dioxide Injection Simulation

Several Considerations on Well Treatment in a Numerical Model for Single-Well Push-Pull Tests in Carbon Dioxide Injection Simulation

Bayesian evidential learning: validation à partir de tests expérimentaux d’injection-pompage

Recent developments in uncertainty quantification show that a full inversion of model parameters is not always necessary to forecast the range of uncertainty of a specific prediction in Earth sciences. Instead, Bayesian evidential learning (BEL) uses a set of prior models to derive a direct relationship between data and prediction. This recent technique has been mostly demonstrated for synthetic cases. This paper demonstrates the ability of BEL to predict the posterior distribution of temperature in an alluvial aquifer during a cyclic heat tracer push-pull test. The data set corresponds to another push-pull experiment with different characteristics (amplitude, duration, number of cycles). This experiment constitutes the first demonstration of BEL on real data in a hydrogeological context. It should open the range of future applications of the framework for both scientists and practitioners.

Aluminium release by water-rock interaction during hydraulic tests in a siliciclastic aquifer in Berlin (Germany)

Two hydraulic tests of a Triassic sandstone aquifer were performed to determine hydraulic and geochemical parameters of the reservoir formation. Samples collected during all tests showed neutral and constant pH-value of about 7.5. During the initial step rate test, the aluminium concentration of the water remained below 0.005 mM, but it increased significantly during the production phase of the following single well push-pull test to 4.8 mM. Drill cuttings of the well, collected at reservoir depth (Exter Fm. and the overlaying Tertiary sand), were additionally characterized and used for leaching experiments. These experiments evidenced a strong release of aluminium from the Tertiary, pyrite containing sand, indicating processes of pyrite oxidation being responsible for aluminium mobilization.

Deoxygenation Prevents Arsenic Mobilization during Deepwell Injection into Sulfide-Bearing Aquifers.

Coal seam gas (CSG) extraction generates large volumes of coproduced water. Injection of the excess water into deep aquifers is often the most sustainable management option. However, such injection risks undesired sediment-water interactions that mobilize metal(loid)s in the receiving aquifer. This risk can be mitigated through pretreatment of the injectant. Here, we conducted a sequence of three push-pull tests (PPTs) where the injectant was pretreated using acid amendment and/or deoxygenation to identify the processes controlling the fate of metal(loid)s and to understand the treatment requirements for large-scale CSG water injection. The injection and recovery cycles were closely monitored, followed by analysis of the observations through reactive transport modeling. While arsenic was mobilized in all three PPTs, significantly lower arsenic concentrations were observed in the recovered water when the injectant was deoxygenated, regardless of pH adjustment. The breakthrough of arsenic was commensurate with molybdenum, but distinct from phosphate. This allowed for the observed and modeled arsenic and molybdenum mobilization to be attributed to a stoichiometric codissolution process during pyrite oxidation, whereas phosphate mobility was governed by sorption. Understanding the nature of these hydrochemical processes explained the greater efficiency of pretreatment by deoxygenation on minimizing metal(loid) mobilization compared to the acid amendment.

Correction: Push-pull tests for estimating effective porosity: expanded analytical solution and in situ application

Author(s): Paradis, CJ; McKay, LD; Perfect, E; Istok, JD; Hazen, TC | Abstract: In the recent article by Paradis et al. (2018), an error was made when developing a conceptual model and an analytical solution to describe the one-dimensional displacement of the center of mass of a non-reactive tracer during a single-well injection, drift, and extraction test (push-pull test).

Effect of Additive Elements Bi/Ni/Ge on Crack Initiation and Propagation for Low-Ag Solders

This study discusses an effect of additive elements on crack propagation behaviour for low-Ag contain Sn1.0Ag0.7Cu lead-free solders at high temperature. A cyclic push-pull loading tests for four kinds of Sn1.0Ag0.7Cu solders were conducted at 313 K with a single hole specimen. Stress amplitude of solders containing additive element Bi were bigger than that of Bi-free solders. Crack initiation cycle of solders containing Bi were earlier than that of Bi-free solders. Low-Ag solders containing Bi had shorter crack propagation cycles than that of Bi-free solders. These results indicate that the additive element Bi have the effects on the crack initiation and propagation cycles, that is, Bi accelerates the crack propagation rate. We also discuss the adaptation of J-integral range parameter to the crack propagation rate evaluation for solders. J-integral range parameter evaluates the crack propagation rate for low-Ag solders independent of the additive elements.

In situ decay of polyfluorinated benzoic acids under anaerobic conditions

Polyfluorinated benzoic acids (PBAs) can be used as non-reactive tracers to characterize reactive mass transport mechanisms in groundwater. The use of PBAs as non-reactive tracers assumes that their reactivities are negligible. If this assumption is not valid, PBAs may not be appropriate to use as non-reactive tracers. In this study, the reactivity of two PBAs, 2,6-difluorobenzoic acid (2,6-DFBA) and pentafluorobenzoic acid (PFBA), was tested in situ. A series of two single-well push-pull tests were conducted in two hydrogeologically similar, yet spatially distinct, groundwater monitoring wells. Bromide, 2,6-DFBA, and PFBA were added to the injection fluid and periodically measured in the extraction fluid along with chloride, nitrate, sulfate, and fluoride. Linear regression of the dilution-adjusted breakthrough curves of both PBAs indicated zero-order decay accompanied by nitrate and subsequent sulfate removal. The dilution-adjusted breakthrough curves of chloride, a non-reactive halide similar to bromide, showed no evidence of reactivity. These results strongly suggested that biodegradation of both PBAs occurred under anaerobic conditions. The results of this study implied that PBAs may not be appropriate to use as non-reactive tracers in certain hydrogeologic settings, presumably those where they can serve as carbon and/or electron donors to stimulate microbial activity. Future studies would benefit from using ring-14C-labeled PBAs to determine the fate of carbon combined with microbial analyses to characterize the PBA-degrading members of the microbial community.

Oxidation of Reduced Peat Particulate Organic Matter by Dissolved Oxygen: Quantification of Apparent Rate Constants in the Field.

Peat particulate organic matter (POM) is an important terminal electron acceptor for anaerobic respiration in northern peatlands provided that the electron-accepting capacity of POM is periodically restored by oxidation with O2 during peat oxygenation events. We employed push-pull tests with dissolved O2 as reactant to determine pseudo-first-order rate constants of O2 consumption ( kobs) in anoxic peat soil of an unperturbed Swedish ombrotrophic bog. Dissolved O2 was rapidly consumed in anoxic peat with a mean kobs of 2.91 ± 0.60 h-1, corresponding to an O2 half-life of ∼14 min. POM dominated O2 consumption, as evidenced from approximately 50-fold smaller kobs in POM-free control tests. Inhibiting microbial activity with formaldehyde did not appreciably slow O2 consumption, supporting abiotic O2 reduction by POM moieties, not aerobic respiration, as the primary route of O2 consumption. Peat preoxygenation with dissolved O2 lowered kobs in subsequent oxygen consumption tests, consistent with depletion of reduced moieties in POM. Finally, repeated oxygen consumption tests demonstrated that anoxic peat POM has a high reduction capacity, in excess to 20 μmol electrons donated per gram POM. This work demonstrates rapid abiotic oxidation of reduced POM by O2, supporting that short-term oxygenation events can restore the capacity of POM to accept electrons from anaerobic respiration in temporarily anoxic parts of peatlands.

Microbial Community and in situ Bioremediation of Groundwater by Nitrate Removal in the Zone of a Radioactive Waste Surface Repository.

The goal of the present work was to investigate the physicochemical and radiochemical conditions and the composition of the microbial community in the groundwater of a suspended surface repository for radioactive waste (Russia) and to determine the possibility of in situ groundwater bioremediation by removal of nitrate ions. Groundwater in the repository area (10-m depth) had elevated concentrations of strontium, tritium, nitrate, sulfate, and bicarbonate ions. High-throughput sequencing of the V3–V4/V4 region of the 16S rRNA gene revealed the presence of members of the phyla Proteobacteria (genera Acidovorax, Simplicispira, Thermomonas, Thiobacillus, Pseudomonas, Brevundimonas, and uncultured Oxalobacteraceae), Firmicutes (genera Bacillus and Paenibacillus), and Actinobacteria (Candidatus Planktophila, Gaiella). Canonical correspondence analysis suggested that major contaminant – nitrate, uranium, and sulfate shaped the composition of groundwater microbial community. Groundwater samples contained culturable aerobic organotrophic, as well as anaerobic fermenting, iron-reducing, and denitrifying bacteria. Pure cultures of 33 bacterial strains belonging to 15 genera were isolated. Members of the genera Pseudomonas, Rhizobium, Cupriavidus, Shewanella, Ensifer, and Thermomonas reduced nitrate to nitrite and/or dinitrogen. Application of specific primers revealed the nirS and nirK genes encoding nitrite reductases in bacteria of the genera Pseudomonas, Rhizobium, and Ensifer. Nitrate reduction by pure bacterial cultures resulted in decreased ambient Eh. Among the organic substrates tested, sodium acetate and milk whey were the best for stimulation of denitrification by the microcosms with groundwater microorganisms. Injection of these substrates into the subterranean horizon (single-well push-pull test) resulted in temporary removal of nitrate ions in the area of the suspended radioactive waste repository and confirmed the possibility for in situ application of this method for bioremediation.