Radon-222 and Water Column Data Related to Submarine Groundwater Discharge Along the Western Margin of Indian River Lagoon, Florida—September 2016 to July 2017 (ver. 2.0, March 2018)

The positional accuracy of the track lines was determined by the boat-mounted Garmin echoMAP 50s GPS receiver. The positional accuracy for the Garmin GPS ranges from better than 3 m to 10 m as outlined by the manufacture when using WAAS (Wide Area Augmentation System) coverage. Mapping system USGS 1 generally consisted of RAD7 units 2265, 2528, and 2531, with units 2976 and 4217 substituted for unit 2531 during the March 2017 and May 2017 surveys respectively. Mapping system USGS 2 consisted of RAD7 units 1186, 1533, and 1534 for all surveys. All RAD7 detector units received the recommended annual calibration by Durridge. Durridge achieves a reproducibility of better than 2% with their standard RAD7 calibration and with the overall calibration accuracy in the range of 5%. A relative humidity of 10% or below was kept to maintain the high sensitivity of the instrument during radon mapping; this was sustained by placing a drying column of Drierite desiccant in the air path of the mapping system. Per the manufacturer’s description of factors influencing the response time of the RAD7 with RAD Aqua system to changes in radon-222 concentration in water, a radon-222 data set using a 21-minute offset is provided. The 21-minute offset for this system is based on influencing factors described in the manufacture’s manual, radioactive theory, and USGS laboratory experiments (data available upon request). The laboratory experiments involved manipulation of the system air volume and flow rate of water into the RAD Aqua to assess the impact to response time. Similar radon-222 mapping studies acknowledge a 10 to 20-minute delay in response time of the three RAD7s and one RAD Aqua system but have chosen to use a 10 minute time shift for their radon-222 data due to the high water flow rates in their system setups (Hosono and others, 2012; Stieglitz and others, 2010). While these studies’ response times were closer to 10-minutes, USGS laboratory experiments suggested that 21 minutes better characterized the response time for the mapping system used in this IRL study. Radon-222 data with a 3.5-minute offset (midpoint of the 7-minute count cycle) are provided as well. The 3.5-minute offset data have not been adjusted for a system lag but provide the most accurate data with respect to time of collection. The 7-minute measurement cycle was chosen to balance the need for higher spatial resolution along the survey transects with the 21-minute response time of the system. During the March 2017 and May 2017 surveys, RAD7 unit 2531 malfunctioned and for several days the mapping system USGS1 operated with only two RAD7 units, 2265 and 2528. During the March 2017 survey (3/27/17 to 4/2/2017), a replacement RAD7 unit, 2976, was used from 4/1/2017 to 4/2/2017. In the May 2017 survey (5/22/17 to 6/3/17), replacement RAD7 unit 4217 was used from 5/31/2017 to 6/2/2017. An outline of the RAD7 units and HOBO unit used in each mapping system for all survey dates is provided in the ‘IRL_Surveys_Equipment.pdf’ document. The YSI Pro Plus multiparameter water quality meter (YSI, Inc.) was calibrated for barometer, dissolved oxygen, specific conductivity, pH, and oxidation-reduction potential (ORP) on the first field day. The YSI was checked each subsequent day with pH 7 buffer solution and 50 mS/cm conductivity solution to determine if recalibration was necessary. Linear regression of the YSI recorded salinity for both mapping systems (USGS1 and USGS 2) was used to QA/QC the data. In each YSI file, a column includes a flag indicating which data passed the QA/QC process. If the YSI probe was out of the water, the salinity values used for Rn-222 activity calculations were estimated by averaging salinity readings from YSI data collected before and after the problem time period. During September 2016, no dissolved oxygen (DO) data is available due to a malfunctioning DO probe. DO values for September 2016 are reported as ND for no data reported. During the July 2017 survey, the ORP (oxygen reduction potential) values for 7/30/2017 to 8/1/2017 were erroneous due to an incorrect calibration of the ORP standard. The ORP values for this survey are reported as ND for no data reported. HOBO H8 temperature probes were inter-compared twice a year to check the device. Linear regression of the HOBO recorded temperature for both mapping systems (USGS1 and USGS 2) was used to QA/QC data. Significant outliers that broke with the pattern of the regression and had unrealistic values based on the rest of the survey were examined as potentially erroneous. If removing these significant outliers resulted in a large improvement of the r-squared value, the outliers were considered erroneous. In each HOBO file, a column includes a flag indicating which data passed the QA/QC process. If any inconsistencies or unexpected values in ‘c:*2’ temperature data were identified, they were addressed through some of the following methods. If one HOBO reported erroneous or negative ‘c:*2’ temperature values due to a compromised connection between the HOBO and the probe, the measurements from the HOBO that recorded consistent and reliable were data were used in place of the faulty HOBO. In a situation where errors or negative ‘c:*2’ temperature values occurred with both HOBOs data recording, the relationship between verified YSI and HOBO data were assessed to produce a linear regression which allowed estimation of the temperature values for the missing measurements. A table can be found in ‘IRL_Corrections.pdf’ identifying the erroneous and negative ‘c:*2; data and how the inaccuracies were resolved for each case. When no YSI data were available, a CT2X Submersible Smart Sensor (manufactured by INW) was used to obtain salinity data. The ‘IRL_Corrections.pdf’ table also outlines the salinity errors and how they were resolved. During the July survey HOBO 7728 was replaced with HOBO 4828 on 7/29/2017 in order to have a functioning HOBO for USGS 2. HOBO 7728 reported only negative values on 7/26/2017 and 7/27/2017 and therefore that data was not reported. Reported radon-222 data excludes the data at the beginning of each day where appropriate temperature data was unavailable because the HOBOs were not yet exposed to surface water at that time. Due to the depth limitations of the Garmin echosounder, the shallowest transects of the Eau Gallie North site are lacking recorded depths have been reported as ‘NR’ for not recorded. The transducer offsets are provided in the GPS csv files for each survey trip. When the transducer water depth was not measured in the field, the water depth measurements of a similarly positioned Solinist Levelogger (which includes level, temperature, conductivity (LTC) data) were used to adjust the Garmin GPS water depth values for the transducer offset. The water depths were averaged for each day and that offset subtracted from Garmin GPS water depths.