Vertical Wellbore Flow Monitoring for Assessing Spatial and Temporal Flow Relationships with a Dynamic River Boundary (original) (raw)
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River-Induced Flow Dynamics in Long-Screen Wells and Impact on Aqueous Samples
Ground Water, 2011
Previously published field investigations and modeling studies have demonstrated the potential for sample bias associated with vertical wellbore flow in conventional monitoring wells constructed with long-screened intervals. This article builds on the existing body of literature by (1) demonstrating the utility of continuous (i.e., hourly measurements for ∼1 month) ambient wellbore flow monitoring and presenting results from a field experiment where relatively large wellbore flows (up to 4 L/min) were induced by aquifer hydrodynamics associated with a fluctuating river boundary located approximately 250 m from the test well. The observed vertical wellbore flows were strongly correlated with fluctuations in river stage, alternating between upward and downward flow throughout the monitoring period in response to changes in river stage. Continuous monitoring of ambient wellbore flows using an electromagnetic borehole flowmeter allowed these effects to be evaluated in concert with continuously monitored river-stage elevations (hourly) and aqueous uranium concentrations (daily) in a long-screen well and an adjacent multilevel well cluster. This study demonstrates that when contaminant concentrations within the aquifer vary significantly over the depth interval interrogated, river-induced vertical wellbore flow can result in variations in measured concentration that nearly encompass the full range of variation in aquifer contaminant concentration with depth.
Influence of vertical flows in wells on groundwater sampling
Journal of contaminant hydrology, 2014
Pumped groundwater sampling evaluations often assume that horizontal head gradients predominate and the sample comprises an average of water quality variation over the well screen interval weighted towards contributing zones of higher hydraulic conductivity (a permeability-weighted sample). However, the pumping rate used during sampling may not always be sufficient to overcome vertical flows in wells driven by ambient vertical head gradients. Such flows are reported in wells with screens between 3 and 10m in length where lower pumping rates are more likely to be used during sampling. Here, numerical flow and particle transport modeling is used to provide insight into the origin of samples under ambient vertical head gradients and under a range of pumping rates. When vertical gradients are present, sample provenance is sensitive to pump intake position, pumping rate and pumping duration. The sample may not be drawn from the whole screen interval even with extended pumping times. Samp...
Ambient vertical flow in long-screen wells: a case study in the Fontainebleau Sands Aquifer (France)
Hydrogeology Journal, 2008
A tritium (3 H) profile was constructed in a longscreened well (LSW) of the Fontainebleau Sands Aquifer (France), and the data were combined with temperature logs to gain insight into the potential effects of the ambient vertical flow (AVF) of water through the well on the natural aquifer stratification. AVF is commonly taken into account in wells located in fracture aquifers or intercepting two different aquifers with distinct hydraulic heads. However, due to the vertical hydraulic gradient of the flow lines intercepted by wells, AVF of groundwater is a common process within any type of aquifer. The detection of 3 H in the deeper parts of the studied well (approximate depth 50m), where 3 H-free groundwater is expected, indicates that shallow young water is being transported downwards through the well itself. The temperature logs show a nearly zero gradient with depth, far below the mean geothermal gradient in sedimentary basins. The results show that the age distribution of groundwater samples might be biased in relation to the age distribution in the surroundings of the well. The use of environmental tracers to investigate aquifer properties, particularly in LSWs, is then limited by the effects of the AVF of water that naturally occurs through the well.
Water Resources Research, 2019
Depth-resolved chemistry samples are critical to a wide range of groundwater investigations. If a well intersects zones of variable concentrations, a pumped sample is a composite of the inflows, which mix in the well. Where discrete concentrations are required, excessive mixing makes samples less useful and potentially misleading. However, installations for depth-discrete sampling are expensive, particularly for regional studies, so sometimes there is incentive to use existing infrastructure designed for other purposes (e.g. supply wells). This paper shows how the resolution of groundwater chemistry derived from long-screened and open borehole wells can be improved by measuring and sampling the in-well vertical flow regimes in ambient (un-pumped) and/or pumped conditions. The ambient flow regime, driven by a natural vertical head gradient, is shown to be particularly useful to sample groundwater native to defined inflow zones (head in the zone > head in the well), and avoid zones impacted by the invasion of intraborehole flow (head in the zone < head in the well). Depth-specific samples are interpreted either as native groundwater from a discrete source, subject only to analytical error, or a mixture from multiple sources that can be deconvolved, incorporating error in both flow and concentration measurement. Depth-resolved age tracers (CFCs, 14 C and He) in groundwater from three supply wells are verified with samples from a multi-depth nest of piezometers. Results show old groundwater at all depths and the simultaneous occurrence of young water at shallower depths in undisturbed dual-porosity fractured aquifers in the Pilbara region of Western Australia.
1994
Well logging of electrical fluid specific conductance (C,) shows that penneable zones yielding ground water to intrawell flows and the water columns in some wells at INEL have highly different chemistry. with as much as a twofold variation in Ca. This suggests that dedicatedpump sampling of ground water in the aquifer may not be representative of the chemistry of the waste plumes migrating southwest of the nuclear facilities. Natural background C, in basalt-aquifer ground water of this part of the Snake River Plain aquifer is less than 325pS/cm (microSiemans/cm), and total dissolved solids in mg/L units, (TDS) = 0.6C,. This relationship underestimates IDS for waters with chemical waste. when C a is above 800 pS/cm. At well 59 near the ICPP waler of 1115 pS/cm (=670+ mg/L IDS) enters the well from a penneable zone between 521 and 537 ft depth ; the zone being 60 ft below the water level and water of 550 pS/cm. At the time of logging (9/14/93) the 1115pS/cm water was flowing down the well, mixing with less concentrated waters and exiting at 600 or 624-ft depth. Waste water disposed of down the injection weU at ICPP until 1984 was estimated to have a C, of 1140 pS/cm, identical to the water detected in logging. At well OW2, the highest C, water (760pS/cm) is in the upper 30 feet of the water column: water from two flow zones below have different chemistry with lower values of Ca. The Site 14 well and USGS 83 show unifonn values throughout the water column. The water column in Site 14 is dominated by a downward flow of 50 gaVmin probably entering between 475 and 500 ft depth and exiting near the bottom of the well at 700 ft depth. Impeller flowmeter and precision temperature logging are used to define and quantify temperature variations and inlrawell flows. At well 59 (depth=657 ft) and OW2 (depth=996 ft), are downward decreasing temperatures in the bottom wnes of no flow, suggesting that major flow zones lie beneath the deepest pans of these wens.
Groundwater - Surface Water Interaction Caused by Pumping from a Riverbank Inducement Well Field
Geological Society of America Abstracts with Programs, 2016
Background/Need: In parts of southeastern Wisconsin treated municipal wastewater effluent is entering the shallow aquifer via inducement of effluent-containing river water into the shallow aquifer. Because the surface sediments in southeastern Wisconsin are often glacial in origin with highly variable hydraulic properties the efficacy of using riverbank inducement (RBI) as a water source is not obvious. Objectives: The overall goal of this research was to develop a set of tools that can be used to evaluate the effect of riverbank inducement wells on local groundwaters. Methods: An existing RBI well field consisting of 2 riparian wells and a pristine groundwater well located in an urbanized stretch of the lower Fox River (Waukesha County) was used as the study site. All three wells are part of a municipal water supply system. A large proportion of Fox River flow at this site consists of treated municipal wastewater. This is an ideal site because it has been the subject of several previous studies and much is already known about the local hydrology and geochemistry. Results/Discussion: Fox River water is clearly entering the two RBI wells. The pristine well is hydrologically separate from the river and does not pump river water. Estimates obtained from major ion composition and B/Cl ratios indicate that the RBI wells produce up to 59% river water. This maximum was reached in late 2013 and has declined since. B/Cl ratios indicate that the source of sodium chloride in the Fox River, and therefore in the RBI wells, is dominantly wastewater treatment plant (WWTP) effluent originating from the three upstream WWTPs. The effect of road salt on the river itself and on the RBI wells is minimal. 97%-95% of the annual sodium chloride load carried by the Fox river originates from WWTP effluent with the balance coming from road salt contributed during the annual spring melt. Five pharmaceuticals and personal care products (PPCPs) were found in WWTP effluent and the Fox River adjacent to the wellfield. Of these, only sucralose was detected in the RBI wells. Sucralose is the most mobile of the PPCP contaminants found in the Fox River. More highly retarded PPCPs will likely begin appearing in the RBI wells in the future. qPCR data was collected and analyzed for the presence of fecal bacteria in the wellfield. Although both generic and human-specific fecal bacteria were found in the Fox River, no fecal bacteria was found in any well. Conclusions: The use of various geochemical tracers, in combination with numeric flow modelling (from another study) were used to demonstrate that RBI is occurring in these wells-a fact that is not obvious in an area with complex glacially deposited sediments. WWTP effluent, not road salt, is clearly the source of the elevated sodium chloride in the Fox River, and therefore in the RBI wells. This raises the possibility that more dangerous constituents may eventually enter the wellfield. So far, only sucralose has been detected in the wellfield although less mobile constituents will likely appear in the future. To date, no indication has been seen of fecal bacteria transport from the Fox River to the wellfield. Continued monitoring of this wellfield is the only way to see if these trends continue in the future.
Scientific Investigations Report, 2019
Graphs showing natural gamma, 16/64 normal resistivity, generalized lithology, hydrogeologic units, well construction, and pumped wellbore flow properties collected from test well NELT6 under pumped conditions, March 2012, Fort Irwin National Training Center, California ...
2003
The requirement to accurately measure subsurface groundwater flow at contaminated sites, as part of a time and cost effective remediation program, has spawned a variety of flow evaluation technologies. Validation of the accuracy and knowledge regarding the limitations of these technologies are critical for data quality and application confidence. Leading the way in the effo rt to validate and better understand these methodologies, the US Army Environmental Center has funded a multi-year program to compare and evaluate all viable horizontal flow measurement technologies. This multi-year program has included a field comparison phase, an application of selected methods as part of an integrated site characterization program phase, and most recently, a laboratory and numerical simulator phase.