How Accurate is Wellntel?

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    Team Wellntel

    Wellntel Groundwater Information System Accuracy Standard

    Wellntel is a groundwater information system that combines next-generation acoustic groundwater-level measurement technology, remote telemetry, and a cloud platform, to collect accurate, consistent, and reliable groundwater-level measurements from a wide range of production and monitoring wells based on the best-available scientific methods.

    Wellnel is designed for efficient deployment in long-term monitoring networks for applications such as groundwater basin or community water systems management, and enables both stakeholder engagement and smarter programs and policy based on dense, reliable data. The system performs favorably compared to other instruments such as pressure transducers or electronic water level sounders and provides data that are accurate and reliable. The accuracy of the system complies with industry standards for groundwater-level monitoring applications.

    Continuous data collected by the WelIntel system enable accurate measuring and documentation of groundwater level trends in areas where water levels are typically measured manually at infrequent intervals. Real-time data allow rapid detection of groundwater-level changes, and provide greater confidence in long-term trends and compliance with measurable objectives and sustainability goals.

    The accuracy and precision of the Wellntel Groundwater Information System is within 0.1 foot from 10 to 1,000 feet depth to water (D2W) when installation and initial calibration procedures are complete.

    Wellntel Vs USGS Pressure

    Groundwater levels measured by a vented pressure transducer and a Wellntel Sensor collected from a monitoring well in Wisconsin during an USGS aquifer pumping test in September 2015.

    Wellntel System Design and Operational Accuracy

    Accuracy is defined as the closeness of a measurement to a known value. There are 5 critical factors of the Wellntel system’s operation that control accuracy.

    1) Basic Sensor Operation

    The Wellntel Sensor sends sound energy containing non-random programmable sequenced data into the well. The information is created digitally and converted to a distinctive analog signal delivered via a signal generator positioned either above the well cap on a port that provides a signal path, or in the well. Subsequent signal response is analyzed through a proprietary digital processing and statistical analysis method at the Sensor. This is, however, only an initial step toward a D2W measurement. The sensor alone does not have all of the information required to calculate depth, so raw data are bundled and transmitted to the cloud for vital processing steps.

    2) The Cloud: Data Processing and Verification

    With each Wellntel Sensor reading a series of raw measurements of signal time-of-travel are statistically ranked, based on signal response strength, and sent to the Wellntel Cloud. Using history, signal characteristics, and other auditable factors as guides, the Cloud sorts these data and identifies the water level value for presentation on online, near real-time, hydrographs available through the user’s and/or sponsor’s secure Wellntel dashboard.

    The system learns from errors and corrects for them. Data anomalies caused by pump noise or well equipment can result in inaccurate depth values reaching online hydrographs. If one of these erroneous values appears, it can be flagged by the user or sponsor and demoted, which then modifies the algorithm’s thresholds and promotes the correct water level value from the raw data.

    Calibration of the system can often be completed within hours of installation or, depending on environmental factors, may take a week or more. Once calibrated, the system will only require recalibration if there are dramatic changes in environmental factors, such as physical changes to the well equipment. There is no instrument “drift” as is experienced with many other methods because the acoustic signal is digitally created and programmable, and is, therefore, recreated exactly for every measurement.

    3.) Acoustic Sensor Precision

    Precision is defined as the closeness of two or more measurements to a known value. Precision is determined by the degree of small computer rounding errors, the Sensor sensitivity or sample rate, and how well air temperature and the speed of sound in the well are characterized.

    If the well temperature profile is well-characterized, the precision of the Wellntel system is better than 0.026 feet, within the operational depth measurement range: 10 – 1600 feet.

    Wellntel Sample-level Precision

    Wellntel Sensor sample level precision as percent of depth to water on a logarithmic depth scale with a known well-air-temperature. Precision: 0.025 feet at 10 feet depth and 0.026 feet at 1,000 feet depth).

    4.) Characterization of the Well Air Temperature Profile

    The Wellntel System utilizes two temperature measurements to ensure measurement accuracy. The sensor measures air temperature at the top of the well with a thermistor located at the end of the Sensor probe. This measurement is included as part of the Sensor message to the Cloud with each reading. The Sensor thermistor has a resolution of 0.1oC. The Wellntel Cloud combines these temperature readings with regional or on-site groundwater temperature observations in a well-air temperature profile model to calculate the average temperature in the well for each reading. The average temperature is used to calculate the speed of sound in the well and the D2W from the raw time values sent to the cloud from the Sensor.

    In cases where temperature-induced variation occurs, temperature profile improvements can be made based on local or remote observations. Historical D2W values, archived for every Sensor reading, can be recalculated from raw signal time of travel values retroactively by an administrator using the improved temperature characterization.

    Wellntel MP GuideWhile the sensor is designed to be installed by a handy do-it-yourselfer using common tools, installation methods directly impact accuracy. It is important to “zero” the groundwater level to a “Measuring Point” (MP), the location, or datum, that will be used as the continual point of reference for all readings, whether local, or in a network.

    5) Reference to Datum

    Accuracy of D2W measurements depends on consistent referencing to a specific vertical datum so that measurements between instruments and across a network are comparable. Measurements can be referenced to the ground surface and elevation using a standard datum, such as the North American Vertical Datum (NAVD).

    When a Wellntel user registers their Wellntel system, they are asked, by default, to measure and record the Sensor Elevation above the ground level (see diagram to the right). Sensor Elevation measurements to other reference points can be used instead of ground level as required.

    In the cloud, this Sensor Elevation value is subtracted from each original D2W measurement, in order to compute the D2W below the ground level or reference point.

    When compared to measurements derived from other methods, consistent differences in values can typically be traced to inconsistent vertical datums used for each measurement. Cloud storage of raw Wellntel Sensor data allows for historical information to be recalculated by an administrator if such a misunderstanding is found.

    The Wellntel groundwater information system meets the accuracy and precision standards of most groundwater monitoring applications. In fact, the system offers greater reliability than may be achieved by traditional manual water level measurements because there are no probes that may become tangled with well equipment, true static measurements can be observed and recorded, and there are no data transcription errors because data are automatically uploaded to a database. Furthermore, accuracy and precision can be checked and adjustments made remotely to make sure the system is properly calibrated and reporting high-quality groundwater-level data.

    Additional Resources

    Additional information about the Wellntel Groundwater Information System can be found on the Wellntel Forum: https://www.wellntel.com/blog/forums/forum/new-to-wellntel/

    Learn even more about Wellntel by listening in and asking questions during one of our online webinars hosted by Wellntel scientists and technicians: https://www.wellntel.com/webinars/

     

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