Radon-222 Time-Series Data Related to Submarine Groundwater Discharge Along the Western Margin of Indian River Lagoon, Florida

All the GPS coordinates for the instrument moorings were recorded using the handheld Garmin GPSMAP 78sc except the EGN and RWP nearshore moorings from May 2017. The handheld accuracy ranges from 3 to 10 meters (m) as outlined by the manufacture when using WAAS (Wide Area Augmentation System) coverage. The location coordinates for EGN and RWP nearshore moorings in May 2017 were estimated from the distance to known markers. For the estimated site locations, the along shore uncertainty is 10 m and the uncertainty perpendicular to shore is 7 m. All RAD7 detector units received the recommended annual calibration by Durridge, Inc. 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 sustained to maintain the high sensitivity of the instrument during radon time-series collection; this was accomplished by placing a drying column of Drierite desiccant in the air path of the system. During the May survey on the morning of 5/23/17, RAD7 unit 1222 was discovered to have a flooded Drierite column and flooded tubing. The RAD7 unit was opened to inspect the interior but no water had entered the detector chamber. After the tubing was dried out and a Drierite column replaced, unit 1222 was reinstalled at the nearshore mooring. This accounts for the gap in the radon-222 time-series data on 5/23/17 from 6:45 AM to 10:11 AM. The level, temperature, and conductivity (LTC) sensors utilized for each survey were the Solinst M10 models with a full scale of 10 m ± 0.5 centimeters (cm). The accuracy of the LTCs was checked twice a year by laboratory inter-comparison prior to deployment. All water levels derived from the LTC pressure readings were corrected for atmospheric pressure using data obtained from a nearby Melbourne Airport weather station (KMLB) and listed on the Weather Underground website (https://www.wunderground.com). On 5/26/17, LTC 1070658 recorded erroneous values for level and temperature from 13:55 to 14:45 and the conductivity values were zero. This section of the LTC 1070658 data reports ‘N/A’ for not available. The Easy Log USB temperature probes were also evaluated by two separate inter-comparisons prior to deployment with the moorings. For the May survey at EGN, water levels were first adjusted according to the manufacturer’s suggested procedure using the atmospheric pressure readings recorded by the KMLB station. The manufacture recommended obtaining adjusted water level measurements by adding 950 cm to the water level values recorded in the field and then subtracting the atmospheric pressure from the measured water level. For the nearshore mooring LTC (1070658), the field observations of water level at the time of setup did not agree with the calculated values. Photographs of the half cinderblock containing the bilge pump show the water level was ~15 cm at the start of mooring deployment while the water level measurement by the logger at the start of deployment (5/22/17 16:10) was 115.8 cm. The best agreement between field observations and the logger’s recorded values was attained by subtracting 100 cm from the measured water levels. The 100 cm offset from the measured water levels is equivalent to subtracting 30.28 cm from the water level calculated using the manufacture suggested method. The EGN offshore LTC (1071718) produced negative water level values; this LTC was deemed unreliable due to the unrealistic data. The 1071718 LTC data files are not reported for either EGN or RWP in May data download files. The offshore water level was assessed by assuming an estimated water depth at the time of deployment of 44 cm based on C.G. Smith’s field observations. The raw water level measurements from the nearshore LTC (1070658) were adjusted by subtracting the recorded water level at the start of deployment for all values and then adding 44 cm. These adjusted water levels are reported in the data release. For the May survey at RWP, the LTC locations were swapped resulting in the more reliable LTC (1070658) sensor being deployed offshore while the unreliable LTC (1071718) was deployed nearshore. The same 100 cm adjusted offset used for the EGN nearshore LTC (1070658) water levels was applied to the RWP offshore LTC (1070658) water levels. The RWP nearshore water levels were adjusted using the same method as the offshore water level for EGN. The depth at the start of deployment was chosen as the time when the nearshore and offshore datasets overlapped (5/29/17 12:15) as the nearshore mooring had been setup a day prior to the offshore mooring. Photographs from the field show the cinderblock containing the LTC near resistivity cable electrodes where the measured water depth was approximately 40 cm. The resistivity cable was used in the concurrent electrical resistivity tomography surveying outlined in another 2018 data release (https://coastal.er.usgs.gov/data-release/doi-F7V40TFH/). The raw water level from the nearshore LTC (1070658) was adjusted by subtracting the recorded water level at start of deployment for all values and adding 40 cm. As the nearshore mooring was deployed almost 24 hours before the offshore mooring, no derived depths will be provided for the nearshore mooring prior to 5/29/17 and ‘N/A’ was reported for not available. Water levels during the September 2017 offshore mooring water level data were not recorded in a fixed position, due to attachment of the LTC to the bilge rather than the inflatable boat’s anchor. The offshore mooring water level data was adjusted by subtracting the nearshore water level at the start of deployment from the nearshore water record and then adding the offshore water level at the start of deployment. The water level data reported in this data release for September 2017 are the adjusted water level values.