Destry N DiViesti Jonathan Casey Root Scott A Hynek Thomas M Marston 20260324 spreadsheet Denver, CO U.S. Geological Survey https://doi.org/10.5066/P1HC6OCB This U.S. Geological Survey (USGS) data release contains data that allows for calculation of total dissolved-solid loads for high-flow and baseflow conditions in the Upper Colorado River Basin (UCRB) collected between 2021 and 2023. High-flow hydrologic events are critical periods for salinity transport but are often underrepresented in existing datasets due to limited sampling and modeling constraints. To address this gap, samples were collected at five USGS streamgage sites: San Rafael River near Green River, Utah (09328500); Uncompahgre River at Delta, Utah (09149500); Dirty Devil River above Poison Springs Wash near Hanksville, Utah (09333500); Loutsenhizer Arroyo below North River Road near Delta, Colorado (383946107595301); and Virgin River below confluence of Beaver Dam Wash, Nevada (365342113551701). The dataset includes measurements of total dissolved solids (TDS), specific conductance, and stream discharge, which were used to refine estimation techniques for peak-flow conditions. The purpose of this data release is to provide measurements and supporting information that allow for calculation of salinity loads during high-flow and baseflow conditions in the Upper Colorado River Basin (UCRB). By including data collected from 2021 through 2023 at five USGS streamgage sites, this release supports improved estimation techniques for salinity loads during peak-flow conditions. These data are intended to enhance the accuracy of total load calculations, strengthen watershed assessments, and inform salinity management strategies for water quality planning and resource management. 20210810 20231027 ground condition Complete None planned Area of interest -114.0820 -107.9572 38.8782 36.7213 ISO 19115 Topic Category environment None water quality total dissolved solids monsoon salinity specific conductance residue on evaporation automatic sampler ISCO streamgage USGS Thesaurus water quality salinity USGS Metadata Identifier USGS:68ade2e9d4be02406c8cecec None Colorado River watershed San Rafael River Dirt Devil River Virgin River Uncompahgre River Loutsenhizer Arroyo Utah Colorado None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Destry N. DiViesti U.S. Geological Survey, Rocky Mountain Region Hydrologist mailing and physical

2329 W Orton Circle

West Valley City UT 84119 801-908-5000 ddiviesti@usgs.gov Fishman, M.J. Friedman, L.C. 1989 05-A1 publication Denver, CO U. S. Geological Survey https://doi.org/10.3133/twri05A1 US Geological Survey 2015 publication Denver, CO US Geological Survey Continually updated (Chapters A1-A9) https://doi.org/10.3133/twri09 Replicate Samples - To ensure the quality and accuracy of laboratory data, a total of 91 replicate sample sets were analyzed, yielding an average relative percent difference (RPD) of 3.18% for residue on evaporation at 180 degrees Celsius (℃) (ROE180). This low RPD indicates a high level of consistency between duplicate measurements, demonstrating that the analytical methods used were both precise and reliable. By incorporating replicate samples into the quality assurance process, potential variability in lab procedures was monitored and minimized, thereby strengthening confidence in the integrity of the dataset. Reference samples - Reference samples were included with sample batches throughout the laboratory analysis period to monitor reproducibility and potential sample degradation over time. In-house standard SRI-58hgb1 is a 3 liter grab sample from USGS site ID 9328500 at San Rafael River near Green River, UT and was collected on 9/10/2021 at 13:00 MDT. SRI-58hgb1 was measured 19 times throughout the analysis period and resulted in an average ROE180 of 2214.71 milligrams per liter (mg/L) with a relative standard deviation of 1.53%. The consistent results across repeated analyses of this standard further support the reliability of the laboratory procedures and indicate minimal degradation, reinforcing the overall integrity of the dataset. Instrument Calibration - Calibration checks of the analytical balance were performed using certified reference weights prior to sample measurements. The balance readings were verified against the nominal values of the calibration weights to ensure accuracy and compliance with standard laboratory protocols. No significant deviations were observed, confirming that the instrument was operating within acceptable tolerance limits. The laboratory oven temperature was monitored using an external temperature display and verified with a calibrated thermometer placed inside the oven. This procedure ensured that the oven maintained the target temperature within acceptable limits throughout the experimental period, confirming accuracy and consistency of thermal conditions. A benchtop Jenway 3510 digital specific conductance(SpC) meter was used for SpC measurements. The meter was calibrated using a 1413 microsiemens per centimeter (µS/cm) standard solution prior to each sample batch. Instrument performance was further verified by confirming the meter was within 3% of multiple SpC standards, including 100, 1000, 2500, and 5000 µS/cm, to cover the range of values expected in the samples analyzed. These checks confirmed the accuracy and reliability of the measurements throughout the study. No formal logical consistency tests were conducted. Not applicable. No formal positional accuracy tests were conducted Site selection: Sites for the study were selected based on ease of access and the availability of historical streamgage records to ensure data continuity and reliability. Locations with established streamflow monitoring infrastructure were prioritized to facilitate integration with long-term hydrologic datasets. The selected sites included San Rafael River near Green River, Utah (09328500); Uncompahgre River at Delta, Utah (09149500); Dirty Devil River above Poison Springs Wash near Hanksville, Utah (09333500); Loutsenhizer Arroyo below North River Road near Delta, Colorado (383946107595301); and Virgin River below confluence of Beaver Dam Wash, Nevada (365342113551701). Each site was equipped with either a Teledyne ISCO 3700 or 6700 series automatic sampler to enable consistent and representative sample collection during high-flow events, ensuring accurate characterization of water quality under baseflow and monsoon conditions. 2021 Sample Collection: ISCO automatic samplers were programmed to collect water samples during monsoon events using two triggering methods. For routine sampling, samplers operated on pre-programmed intervals that varied from hourly to once every few days, depending on seasonality and site conditions. During high-flow events, samplers were configured to initiate collection based on rising stage height, ensuring that samples represented peak flow and associated water quality changes. This dual approach provided comprehensive coverage of both baseline and storm-driven hydrologic conditions. Once the ISCO samplers completed a full set of 24 samples, the collection bottles were capped, labeled, and replaced at the earliest opportunity. After bottle replacement, the samplers were reprogrammed for the next sampling cycle to ensure continuous data collection throughout the study period. 2021 Sample Processing: The protocol follows a modified version of Fishman and Friedman (1989). Jenway 3510 bench top SpC meter calibrated at 1413 (µS/cm). SpC for each sample was measured twice before the sample was filtered with a .45 micron disc filter into a dry precleaned 125 milliliter (mL) bottle. A clean, dry Pyrex beaker was weighed, approximately 30 mL of filtered sample was added to the beaker and the beaker with the sample was weighed again. The beaker was then placed into an oven at 105 degrees Celsius overnight or for approximately 15 hours. The beaker was removed from the oven and placed immediately into a glass desiccator to cool off for 2 hours. Once cool, the beaker was placed onto a scale and weighed again for the initial dry at 105 degrees Celsius measurement. The beaker was then placed back into the oven at 180 degrees Celsius for 2 hours. The beaker was placed back into the glass desiccator for 2 hours to cool down. Once cool, the beaker was placed onto the scale for the final weight measurement. 2023 Creation of Dataset - After lab analyses were completed, analytical results and field sample locations were compiled into a single dataset. A total dissolved-solids (TDS) calculation for ROE105 and ROE180 are calculated as follows using methods outlined in the USGS National Field Manual for the Collection of Water-Quality Data (2015). For both drying temperatures (105 °C and 180 °C), TDS is calculated using the following relationship: TDS (mg/L) = [(final beaker weight − initial beaker weight) × 1000] /[(beaker with sample weight − final dry beaker weight) × 1000] Where: • Final beaker weight = mass of beaker after drying the residue • Initial beaker weight = mass of clean, empty beaker • Beaker with sample weight = mass of the beaker and water sample before drying Note: The factors of 1000 convert grams to milligrams and liters, depending on the measured sample mass or volume assumed equivalent to 1 grams per/mL. 202601 Salinity Loads Table.csv Comma Separated Value (CSV) file containing data. Producer Defined Sample_ID Unique identifier for each sample; may include suffixes like _rep for replicate samples. Producer Defined The first three digits of the sample ID indicate what river the sample was taken from. SRI stands for the San Rafael River. VRI stands for the Virgin River; DDRI stands for the Dirty Devil River; URI stands for the Uncompahgre River; and LRI stands for the Loutsenhizer Arroyo. Flags such as ig (ISCO grab) or hg (hand grab) indicate alternative sampling methods. An ISCO grab sample is collected directly from the ISCO sampler, while a hand grab sample is obtained by dipping a bottle into the stream near the ISCO sampler inlet. These alternative sampling methods are used for quality control purposes. Replicate samples are indicated by the suffix _rep. These replicate samples are laboratory replicates and indicate more than analysis of the same sample. Field replicates are indicated by the same date and time of the sample. USGS_Station_ID The USGS station identifier for the location of the sample. Producer Defined Represents the USGS station ID where the sample was collected. In some instances the sample was collected at a different station from the station where the discharge was measured. Sample_Date_and_Time Date of sample collection, format MM/DD/YYYY HH:MM Producer Defined The recorded date and time when the sample was collected in the field. In some cases, samples were collected at times that did not align with a streamgage discharge measurement. For these samples, the collection time was rounded to the nearest quarter hour to match the corresponding streamgage discharge measurement. Average_SC_uScm Average laboratory measured specific conductance value for unfiltered water sample. Producer Defined 598 6000 microsiemens per centimeter ROE105_mgL Gravimetrically calculated total dissolved solids for residue on evaporation at 105 degrees Celsius Producer Defined 420 5830 milligrams per liter ROE180_mgL Gravimetrically calculated total dissolved solids for residue on evaporation at 180 degrees Celsius Producer Defined 395 5710 milligrams per liter USGS_Streamgage_Station_ID Identifier for the streamgage associated with discharge and gage specific conductance data. Producer Defined Identifies the USGS streamgage station where measurements of stream discharge and specific conductance were obtained. In some instances the sample was collected at a different station from the station where the discharge was measured. Discharge _cfs Instantaneous streamflow at the time of sampling. Producer Defined NA No Data Producer defined 0.44 5450 cubic feet per second SC_Streamgage_uScm Specific conductance recorded by the streamgage at sampling time. Producer Defined NA No Data Producer defined 700 5450 microsiemens per centimeter GS ScienceBase U.S. Geological Survey mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Although the data have been subjected to rigorous review and are substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, the data are released on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from authorized or unauthorized use. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital Data https://doi.org/10.5066/P1HC6OCB None 20260324 Destry N. DiViesti U.S. Geological Survey, Rocky Mountain Region Hydrologist mailing and physical

2329 W Orton Circle

West Valley City UT 84119 US 801-908-5000 801-908-5001 ddiviesti@usgs.gov FGDC Biological Data Profile of the Content Standard for Digital Geospatial Metadata FGDC-STD-001.1-1999