Ferdinand K. Oberle Nancy G. Prouty Curt Storlazzi 20250508 comma-delimited text data release DOI:10.5066/P13RJCAJ Pacific Coastal and Marine Science Center, Santa Cruz, California U.S. Geological Survey Suggested Citation: Oberle, F.K., Prouty, N.G., and Storlazzi, C.D. 2025, Nearshore seawater-column measurements of coastal groundwater discharge, Ofu, American Samoa, February 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P13RJCAJ. https://doi.org/10.5066/P13RJCAJ https://www.sciencebase.gov/catalog/item/67e2f32cd34ee7f142216d0c In-situ nearshore seawater measurements of dissolved radon and water level were used to determine the advection rate of groundwater onto the fringing reef off Ofu, American Samoa. Radon (Rn-222) data were collected to characterize the advection rate of groundwater onto the nearshore reef. When analyzed in conjunction with measurements of changing water levels from tides the data can be used to assess the potential for terrestrial groundwater intrusion and the sources and fate of these water masses. Additional information about the field activity from which these data were derived is available online at: https://cmgds.marine.usgs.gov/fan_info.php?fan=2020-620-FA Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 20200201 20200207 ground condition at time data were collected Complete None planned -169.666217 -169.658219 -14.181312 -14.185000 ISO 19115 Topic Category biota geoscientificInformation Data Categories for Marine Planning Water Column Features USGS Thesaurus time series datasets marine water quality Marine Realms Information Bank (MRIB) keywords physical oceanography None U.S. Geological Survey USGS Coastal and Marine Hazards and Resources Program CMHRP Pacific Coastal and Marine Science Center PCMSC USGS Metadata Identifier USGS:67e2f32cd34ee7f142216d0c Geographic Names Information System (GNIS) Ofu Territory of American Samoa Papaloloa Point Fatuana Point South Pacific Ocean No restrictions or legal prerequisites for accessing the dataset. USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data. U.S. Geological Survey, Pacific Coastal and Marine Science Center PCMSC Science Data Coordinator mailing and physical

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Santa Cruz CA 95060 831-460-4747 pcmsc_data@usgs.gov Raw data from the DURRIDGE RAD7 radon detector were processed using the manufacturers software, DURRIDGE CAPTURE, on a Dell Personal Computer running Windows 7 Operating System. No formal attribute accuracy tests were conducted. DURRIDGE RAD7 radon detectors were calibrated using Durridge services to achieve a reproducibility of better than ±2% and an overall calibration accuracy of better than ±5%. Calibrations are carried out with a National Institute of Standards and Technology radon standard supplied through the U.S. EPA. Data fall within expected ranges. Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the metadata for each part of this data release carefully for additional details. A formal accuracy assessment of the horizontal positional information in the data set has not been conducted. The stated accuracy of the GPS unit used to determine the location of the instruments is +/- 5 m. A formal accuracy assessment of the vertical information in the data set has not been conducted. The stated accuracy of the Hastelloy pressure sensor used to determine the depth of the instrument is +/- 1 cm. Radon (Rn-222) concentration data were collected with a DURRIDGE RAD7 radon detector. The alpha decay of Rn-222 was detected at 3-minute intervals with the RAD7 in SNIFF mode. In SNIFF mode, the instrument detects radon entry points and gushers, and it recovers from high radon exposures in minutes. At the end of each run, the detector printed out a complete report. The RAD7 data were QA/QC’d, and raw counts of radon were exported using the manufacturer’s CAPTURE software. Conductivity and water level (CTD) data were collected with a YSI Castaway CTD Profiler. 20160803 Data were collected continuously at a single point at Papaloloa Point and Fatuana Point, Ofu, American Samoa. Point Point 776 0.000001 0.000001 Decimal degrees D_WGS_1984 WGS_1984 6378137.0 298.257223563 Ofu20_Rn_data_200off_1.csv, Ofu20_Rn_data_200on_2.csv, Ofu20_Rn_data_300off_6.csv, Ofu20_Rn_data_300on_5.csv, Ofu20_Rn_data_200east_off_4.csv, and Ofu20_Rn_data_200east_on_3.csv Comma Separated Value (CSV) file containing data. Producer Defined Date Date and time referenced to Universal Coordinate Time Global Positioning System 2/1/2020 16:08 2/7/2020 9:49 MM/DD/YY hour:minutes 1 Excess_Radon_(dpm/m3) Excess Radon Producer Defined -8.7000 147987.9773 Disintegrations per minute (dpm) per cubic meter (m3) 0.0001 Water_Level_(m) Water Level Producer Defined 0.031073130 1.084792501 meters 0.000000001 Latitude_(Decimal_Degrees) Latitude in decimal degrees Global Positioning System -14.185000 -14.181312 decimal degrees 0.000001 Longitude_(Decimal_Degrees) Longitude in decimal degrees Global Positioning System -169.666217 -169.658219 decimal degrees 0.000001 The first line of the csv file is a header line. U.S. Geological Survey U.S. Geological Survey - ScienceBase mailing and physical

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Denver CO 80225 1-888-275-8747 sciencebase@usgs.gov These data are available in comma-delimited (csv) format contained in a single zipped folder (Ofu20_Rn_Data.zip) accompanied by CMGDS FGDC-compliant metadata. 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 on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. comma-delimited text 20180818 CSV text file contains the data. WinZip or archive utility 0.013 https://www.sciencebase.gov/catalog/file/get/67e2f32cd34ee7f142216d0c https://doi.org/10.5066/P13RJCAJ Data can be downloaded using the Network_Resource_Name links. The first link is a direct link to download the zipped file of data and metadata. The second link points to a landing page with metadata and data for the entire data release. None. These data can be viewed with any text editor software. 20250508 U.S. Geological Survey, Pacific Coastal and Marine Science Center PCMSC Science Data Coordinator mailing and physical

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Santa Cruz CA 95060 831-460-4747 pcmsc_data@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998