Water resources are being challenged to meet domestic, agricultural, and industrial needs. To complement finite surface water supplies that are being stressed by changes in precipitation and ...increased demand, groundwater is increasingly being used. Sustaining groundwater use requires considering both water quantity and quality. A unique challenge for groundwater use, as compared with surface water, is the presence of naturally occurring contaminants within aquifer sediments, which can enter the water supply. Here we find that recent groundwater pumping, observed through land subsidence, results in an increase in aquifer arsenic concentrations in the San Joaquin Valley of California. By comparison, historic groundwater pumping shows no link to current groundwater arsenic concentrations. Our results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping. We provide a quantitative model for using subsidence as an indicator of arsenic concentrations correlated with groundwater pumping.
•40km of Electrical Resistivity Tomography data, imaging to 280m.b.s.l.•ERT images the distribution of fresh and salt water in the subsurface at the coast.•Complex patterns of intrusion resulting ...from geology, pumping, and recharge.
Electrical Resistivity Tomography data were acquired along 40km of the Monterey Bay coast in central California. These data resulted in electrical resistivity images to depths of approximately 280m.b.s.l., which were used to understand the distribution of freshwater and saltwater in the subsurface, and factors controlling this distribution. The resulting resistivity sections were interpreted in conjunction with existing data sets, including well logs, seismic reflection data, geologic reports, hydrologic reports, and land use maps from the region. Interpretation of these data shows a complex pattern of saltwater intrusion resulting from geology, pumping, and recharge. The resistivity profiles were used to identify geological flow conduits and barriers such as palaeo-channels and faults, localized saltwater intrusion from individual pumping wells, infiltration zones of surface fresh and brackish water, and regions showing improvements in water quality due to management actions. The use of ERT data for characterizing the subsurface in this region has led to an understanding of the spatial distribution of freshwater and saltwater at a level of detail unattainable with the previously deployed traditional well based salinity mapping and monitoring techniques alone. Significant spatial variability in the extent and geometry of intrusion observed in the acquired data highlights the importance of adopting continuous subsurface characterization methods such as this one.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Summary Background Smoking cessation programmes delivered via mobile phone text messaging show increases in self-reported quitting in the short term. We assessed the effect of an automated smoking ...cessation programme delivered via mobile phone text messaging on continuous abstinence, which was biochemically verified at 6 months. Methods In this single-blind, randomised trial, undertaken in the UK, smokers willing to make a quit attempt were randomly allocated, using an independent telephone randomisation system, to a mobile phone text messaging smoking cessation programme (txt2stop), comprising motivational messages and behavioural-change support, or to a control group that received text messages unrelated to quitting. The system automatically generated intervention or control group texts according to the allocation. Outcome assessors were masked to treatment allocation. The primary outcome was self-reported continuous smoking abstinence, biochemically verified at 6 months. All analyses were by intention to treat. This study is registered, number ISRCTN 80978588. Findings We assessed 11 914 participants for eligibility. 5800 participants were randomised, of whom 2915 smokers were allocated to the txt2stop intervention and 2885 were allocated to the control group; eight were excluded because they were randomised more than once. Primary outcome data were available for 5524 (95%) participants. Biochemically verified continuous abstinence at 6 months was significantly increased in the txt2stop group (10·7% txt2stop vs 4·9% control, relative risk RR 2·20, 95% CI 1·80–2·68; p<0·0001). Similar results were obtained when participants that were lost to follow-up were treated as smokers (268 9% of 2911 txt2stop vs 124 4% of 2881 control RR 2·14, 95% CI 1·74–2·63; p<0·0001), and when they were excluded (268 10% of 2735 txt2stop vs 124 4% of 2789 control 2·20, 1·79–2·71; p<0·0001). No significant heterogeneity was shown in any of the prespecified subgroups. Interpretation The txt2stop smoking cessation programme significantly improved smoking cessation rates at 6 months and should be considered for inclusion in smoking cessation services. Funding UK Medical Research Council, Primary Care Research Networks.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The ability to identify, at potential managed aquifer recharge sites, the presence of connected pathways of hydraulically conductive sediments from the ground surface to the water table could help ...minimize costs and risks associated with recharge operations. A spatially dense dataset had previously been acquired in an almond Prunus dulcis (Mill.) D.A. Webb grove in Tulare, CA, using tTEM, a towed transient electromagnetic (tTEM) geophysical method. In order to interpret reliable information about sediment type from the tTEM data, a transform from the tTEM‐derived property, electrical resistivity, to sediment type is required. The uncertainty associated with derived models of sediment type can be significantly reduced if a site‐ and dataset‐specific transform is used. Cone penetrometer testing (CPT) was conducted at five locations, strategically selected based on a review of the tTEM data. Co‐located measurements of sediment type, derived from the CPT, and electrical resistivity, derived from the tTEM data, were used to create a resistivity‐to‐sediment‐type transform, with sediment type classified as either coarse‐grain‐dominated (sand and gravel) or fine‐grain‐dominated (silt and clay) material. The transform captured the uncertainty associated with variable water salinity and content, the resolution of the tTEM data, and other components of the tTEM measurement workflow. Using this transform, models of sediment type were generated for the unsaturated zone at the site. Within these models are features, which we interpret as potential recharge pathways, corresponding to high fractions of coarse‐grain‐dominated material amongst regions of fine‐grain‐dominated material. The workflow developed at this site can provide a framework for using tTEM and CPT for recharge site assessment.
Core Ideas
tTEM data can be useful for sediment type mapping the subsurface at potential recharge sites.
The quality of a tTEM derived sediment type model depends on the resistivity transform used.
A site‐ and measurement‐specific transform can be created using collocated CPT and tTEM data.
Using a high‐quality transform, potential recharge pathways can be located in the subsurface.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Interferometric Synthetic Aperture Radar (InSAR) data from multiple satellite missions were combined to study the temporal and spatial variability of head and storage properties in a confined aquifer ...system on a decadal time scale. The area of study was a 4,500 km2 agricultural basin in the San Luis Valley (SLV), Colorado. We had available previous analyses of C‐band ERS‐1/2 data from June 1992 to November 2000, and L‐band ALOS PALSAR data from October 2009 to March 2011. We used C‐band Envisat data to fill in the time period from November 2006 to July 2010. In processing the Envisat data, we successfully employed a phase interpolation between persistent scatterer pixels to reduce the impact of vegetation decorrelation, which can significantly reduce the quality of C‐band InSAR data over agricultural basins. In comparing the results from the L‐band ALOS data and C‐band Envisat data in a 10 month overlapping time period, we found that the shorter wavelength of C‐band InSAR allowed us to preserve small deformation signals that were not detectable using L‐band ALOS data. A significant result was the finding that the elastic storage properties of the SLV confined aquifer system remained stable over the 20 year time period and vary slowly in space, allowing us to combine InSAR data acquired from multiple missions to fill the temporal and spatial gaps in well data. The InSAR estimated head levels were validated with well measurements, which indicate little permanent water‐storage loss over the study time period in the SLV.
Key Points
The elastic storage properties of the SLV confined aquifer system remained stable over the 20 year time period and vary slowly in space
The InSAR estimated head levels were used to fill the temporal and spatial gaps in well data
The recently developed PS interpolation algorithm were successfully used to correct vegetation decorrelation artifacts in C‐band InSAR data
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A commonly reported problem with the conduct of multicentre randomised controlled trials (RCTs) is that recruitment is often slower or more difficult than expected, with many trials failing to reach ...their planned sample size within the timescale and funding originally envisaged. The aim of this study was to explore factors that may have been associated with good and poor recruitment in a cohort of multicentre trials funded by two public bodies: the UK Medical Research Council (MRC) and the Health Technology Assessment (HTA) Programme.
The cohort of trials was identified from the administrative databases held by the two funding bodies. 114 trials that recruited participants between 1994 and 2002 met the inclusion criteria. The full scientific applications and subsequent trial reports submitted by the trial teams to the funders provided the principal data sources. Associations between trial characteristics and recruitment success were tested using the Chi-squared test, or Fisher's exact test where appropriate.
Less than a third (31%) of the trials achieved their original recruitment target and half (53%) were awarded an extension. The proportion achieving targets did not appear to improve over time. The overall start to recruitment was delayed in 47 (41%) trials and early recruitment problems were identified in 77 (63%) trials. The inter-relationship between trial features and recruitment success was complex. A variety of strategies were employed to try to increase recruitment, but their success could not be assessed.
Recruitment problems are complex and challenging. Many of the trials in the cohort experienced recruitment difficulties. Trials often required extended recruitment periods (sometimes supported by additional funds). While this is of continuing concern, success in addressing the trial question may be more important than recruitment alone.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We present MATLAB codes for finite-difference time-domain (FDTD) modeling of ground-penetrating radar (GPR) in two dimensions. Surface-based reflection GPR is modeled using a transverse magnetic ...(TM-) mode formulation. Crosshole and vertical radar profiling (VRP) geometries are modeled using a transverse electric (TE-) mode formulation. Matrix notation is used in the codes wherever possible to optimize them for speed in the MATLAB environment. To absorb waves at the edges of the modeling grid, we implement perfectly matched layer (PML) absorbing boundaries. Although our codes are two-dimensional and do not incorporate features such as dispersion in electrical properties, they capture many of the important elements of GPR surveying and run at a fraction of the computational cost of more elaborate algorithms. In addition, the codes are well commented, relatively easy to understand, and can be easily modified for the user's specific purpose.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Sustainable groundwater management requires high-quality and low-latency estimates of changes in groundwater storage (∆Sgw). However, estimates of ∆Sgw produced using traditional methods, including ...groundwater models and well-based measurements, typically lag years behind the present because collecting the required on-the-ground data is a time consuming, expensive, and labor-intensive task. Satellite remote sensing measurements provide potential pathways to overcome these limitations by quantifying ∆Sgw through closing the water balance. However, the range of spatial scales over which ∆Sgw can be accurately estimated using remote sensing products remains unclear. To bridge this knowledge gap, this study quantified ∆Sgw for the period of 2002 through to 2021 using the water balance method and multiple remote sensing products in two subbasins (~2700 km2–3500 km2) within California’s Central Valley: (1) the Kaweah–Tule Subbasin, a region where the pumping of groundwater to support agriculture has resulted in decades of decline in head levels, resulting in land subsidence, damage to infrastructure, and contamination of drinking water and (2) the Butte Subbasin, which receives considerably more rainfall and surface water and has not experienced precipitous drops in groundwater. The remote sensing datasets which we utilized included multiple sources for key hydrologic components in the study area: precipitation, evapotranspiration, and soil moisture. To assess the fidelity of the remote sensing-based model, we compared estimates of ∆Sgw to alternative estimates of ∆Sgw derived from independent sources of data: groundwater wells as well as a widely used groundwater flow model. The results showed strong agreement in the Kaweah–Tule Subbasin in long-term ∆Sgw trends and shorter-term trends during droughts, and modest agreement in the Butte Subbasin with remote sensing datasets suggesting more seasonal variability than validation datasets. Importantly, our analysis shows that the timely availability of remote sensing data can potentially enable ∆Sgw estimates at sub-annual latencies, which is timelier than estimates derived through alternate methods, and thus can support adaptive management and decision making. The models developed herein can aid in assessing aquifer dynamics, and can guide the development of sustainable groundwater management practices at spatial scales relevant for management and decision making.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Core Ideas
We introduce a new geophysical imaging method to assess managed aquifer recharge sites.
This method provides high‐resolution 3D imaging of the subsurface down to a minimum depth of 50 m.
...We introduce Resistivity Distribution Plot as a new approach to assign a saturated–unsaturated boundary.
In many places around the world, much attention is focused on managed aquifer recharge (MAR) because of reduced groundwater levels due to droughts. To assess the suitability of a site for MAR, detailed three‐dimensional (3D) information about the subsurface materials and their hydraulic properties is needed. In areas where the groundwater level is at an intermediate depth (e.g., 20–40 m), such information is needed from the ground surface down to a minimum depth of ∼50 m. To achieve this goal, we used a new geophysical imaging system: a towed time‐domain electromagnetic system that is efficient for acquiring data at a significantly improved resolution and a scale needed for MAR. During a 2‐d period, we acquired ∼92 line‐kilometers of data in one almond Prunus dulcis (Mill.) D.A. Webb grove, one pistachio (Pistacia vera L.) grove, one open field, and two active recharge basins in the Tulare Irrigation District in the Central Valley of California. At each site, a detailed 3D resistivity model with a resolution down to the 10‐ by 10‐m scale is presented in terms of resistivity distribution plots, which are then used to assign a saturated–unsaturated boundary. In addition, we used a resistivity–lithology transform to interpret the resistivity models and create lithology maps at each site. We used this information to assess the suitability of each site for MAR.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Interferometric Synthetic Aperture Radar (InSAR), a remote sensing technique for measuring centimeter‐level surface deformation, is used to estimate hydraulic head in the confined aquifer of the San ...Luis Valley (SLV), Colorado. Reconstructing head measurements from InSAR in agricultural regions can be difficult, as InSAR phase data are often decorrelated due to vegetation growth. Analysis of 17 L‐band ALOS PALSAR scenes, acquired between January 2007 and March 2011, demonstrates that comprehensive InSAR deformation measurements can be recovered over the vegetated groundwater basin with an improved processing strategy. Local skeletal storage coefficients and time delays between the head change and deformation are estimated through a joint InSAR‐well data analysis. InSAR subsidence estimates are transformed to head changes with finer temporal and spatial resolution than is possible using existing well records alone. Both InSAR and well data suggest that little long‐term water‐storage loss occurred in the SLV over the study period and that inelastic compaction was negligible. The seasonal head variations derived from InSAR are consistent with the existing well data at most locations where confined aquifer pumping activity dominates. Our results demonstrate the advantages of InSAR measurements for basin‐wide characterization of aquifer storage properties and groundwater levels over agricultural regions.
Key Points:
InSAR can be used to measure head levels and storage properties in confined aquifers
The achieved temporal and spatial resolution is much finer than that of existing well data
Persistent scatterer techniques can be employed to correct vegetation decorrelation artifacts
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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