This data release provides total and aqueous arsenic (As) determinations and associated field readings collected from groundwater sampled from 254 newly constructed private residential wells from 2014-2016. The study focuses on three regions of Minnesota that differ geologically: south-central (herein called central), northwest, and northeast. These study regions were chosen due to their prevalent elevated As concentrations in drinking water. Each of the 254 wells were sampled in three rounds by the Minnesota Department of Health (MDH). The timing of the three sampling rounds was (1) immediately or shortly after well construction (round 1); (2) 3-6 months after initial sample collection (round 2); and (3) 12 months after initial sample collection (round 3). During each round, samples were collected for both total and aqueous As. Physicochemical characteristics, including specific conductance, pH, dissolved oxygen, oxidation reduction potential, and temperature, were also measured to gage the well water stability prior to sample collection. Round 1 sampling was timed to co-occur and mimic well driller regulatory sampling. Drillers collected samples after well development from the drill rig groundwater pump or from the residential plumbing and the MDH sampler replicated the sample location and timing used by the driller. Sampling from the drill rig's groundwater pump occurred after the well was drilled and developed, when the water was visibly clear, with little visible sediment particles. Samples from plumbing were collected after the plumbing was flushed out and physicochemical characteristic readings stabilized. Round 2 and round 3 by MDH staff were collected only from plumbing. Samples collected from plumbing were taken from faucets, hydrants, or pressure tanks prior to filters or treatment systems.

This dataset provides aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate measurements in groundwater samples from 254 newly constructed private residential wells between 2014 and 2016. The study focuses on three geologically distinct regions of Minnesota: central, northwest, and northeast. These study regions were chosen due to their prevalent elevated As concentrations in drinking water. Each of the 254 wells were sampled in three rounds by the Minnesota Department of Health (MDH). The timing of the three sampling rounds was (1) immediately or shortly after well construction (round 1); (2) 3-6 months after initial sample collection (round 2); and (3) 12 months after initial sample collection (round 3). During each round, samples were collected for both total and aqueous As, aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate. Physiochemical characteristics, including specific conductance, pH, dissolved oxygen, oxidation reduction potential, and temperature, were also measured to gage the well water stability prior to sample collection. Round 1 sampling was timed to co-occur and mimic well driller regulatory sampling. Drillers collected samples after well development from the drill rig groundwater pump or from the residential plumbing, and the MDH sampler replicated the sample location and timing used by the driller. Sampling from the drill rig’s groundwater pump occurred after the well was drilled and developed, when the water was visibly clear, with little visible sediment particles. Samples from plumbing were collected after the plumbing was flushed out and physiochemical characteristic readings stabilized. Round 2 and round 3 by MDH staff were collected only from plumbing. Samples collected from plumbing were taken from faucets, hydrants, or pressure tanks prior to filters or treatment systems.

This dataset provides aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate measurements in groundwater samples from 254 newly constructed private residential wells between 2014 and 2016. The study focuses on three geologically distinct regions of Minnesota: central, northwest, and northeast. These study regions were chosen due to their prevalent elevated As concentrations in drinking water. Each of the 254 wells were sampled in three rounds by the Minnesota Department of Health (MDH). The timing of the three sampling rounds was (1) immediately or shortly after well construction (round 1); (2) 3-6 months after initial sample collection (round 2); and (3) 12 months after initial sample collection (round 3). During each round, samples were collected for both total and aqueous As, aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate. Physiochemical characteristics, including specific conductance, pH, dissolved oxygen, oxidation reduction potential, and temperature, were also measured to gage the well water stability prior to sample collection. Round 1 sampling was timed to co-occur and mimic well driller regulatory sampling. Drillers collected samples after well development from the drill rig groundwater pump or from the residential plumbing, and the MDH sampler replicated the sample location and timing used by the driller. Sampling from the drill rig’s groundwater pump occurred after the well was drilled and developed, when the water was visibly clear, with little visible sediment particles. Samples from plumbing were collected after the plumbing was flushed out and physiochemical characteristic readings stabilized. Round 2 and round 3 by MDH staff were collected only from plumbing. Samples collected from plumbing were taken from faucets, hydrants, or pressure tanks prior to filters or treatment systems.

This dataset provides aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate measurements in groundwater samples from 254 newly constructed private residential wells between 2014 and 2016. The study focuses on three geologically distinct regions of Minnesota: central, northwest, and northeast. These study regions were chosen due to their prevalent elevated As concentrations in drinking water. Each of the 254 wells were sampled in three rounds by the Minnesota Department of Health (MDH). The timing of the three sampling rounds was (1) immediately or shortly after well construction (round 1); (2) 3-6 months after initial sample collection (round 2); and (3) 12 months after initial sample collection (round 3). During each round, samples were collected for both total and aqueous As, aqueous nitrate+nitrite, aqueous manganese, aqueous iron, and total sulfate. Physiochemical characteristics, including specific conductance, pH, dissolved oxygen, oxidation reduction potential, and temperature, were also measured to gage the well water stability prior to sample collection. Round 1 sampling was timed to co-occur and mimic well driller regulatory sampling. Drillers collected samples after well development from the drill rig groundwater pump or from the residential plumbing, and the MDH sampler replicated the sample location and timing used by the driller. Sampling from the drill rig’s groundwater pump occurred after the well was drilled and developed, when the water was visibly clear, with little visible sediment particles. Samples from plumbing were collected after the plumbing was flushed out and physiochemical characteristic readings stabilized. Round 2 and round 3 by MDH staff were collected only from plumbing. Samples collected from plumbing were taken from faucets, hydrants, or pressure tanks prior to filters or treatment systems.

This dataset provides well construction information provided by driller well logs. Well logs can be accessed on the Minnesota Well Index online (http://www.health.state.mn.us/ divs/eh/cwi/).

This data release provides total and aqueous arsenic (As) determinations and associated field readings collected from groundwater sampled from 254 newly constructed private residential wells from 2014-2016. The study focuses on three regions of Minnesota that differ geologically: south-central (herein called central), northwest, and northeast. These study regions were chosen due to their prevalent elevated As concentrations in drinking water. Each of the 254 wells were sampled in three rounds by the Minnesota Department of Health (MDH). The timing of the three sampling rounds was (1) immediately or shortly after well construction (round 1); (2) 3-6 months after initial sample collection (round 2); and (3) 12 months after initial sample collection (round 3). During each round, samples were collected for both total and aqueous As. Physicochemical characteristics, including specific conductance, pH, dissolved oxygen, oxidation reduction potential, and temperature, were also measured to gage the well water stability prior to sample collection. Round 1 sampling was timed to co-occur and mimic well driller regulatory sampling. Drillers collected samples after well development from the drill rig groundwater pump or from the residential plumbing and the MDH sampler replicated the sample location and timing used by the driller. Sampling from the drill rig's groundwater pump occurred after the well was drilled and developed, when the water was visibly clear, with little visible sediment particles. Samples from plumbing were collected after the plumbing was flushed out and physicochemical characteristic readings stabilized. Round 2 and round 3 by MDH staff were collected only from plumbing. Samples collected from plumbing were taken from faucets, hydrants, or pressure tanks prior to filters or treatment systems.

This dataset provides well construction information provided by driller well logs. Well logs can be accessed on the Minnesota Well Index online (http://www.health.state.mn.us/ divs/eh/cwi/).

This data release contains: (1) ASCII grids of predicted probability of elevated arsenic in groundwater for the Northwest and Central Minnesota regions, (2) input arsenic and predictive variable data used in model development and calculation of predictions, and (3) ASCII files used to predict the probability of elevated arsenic across the two study regions. The probability of elevated arsenic was predicted using Boosted Regression Tree (BRT) modeling methods using the gbm package in R Studio version 3.4.2. The response variable was the presence or absence of arsenic >10 µg/L, the U.S. Environmental Protection Agency’s maximum contaminant level for arsenic, in 3,283 wells located throughout both study regions (1,363 in the Northwest region and 1,920 in the Central). The original database used to develop the BRT model consisted of 127 predictor variables which included well characteristics, land use, soil properties, aquifer properties, depth to water table, and predicted nitrate. After optimization steps, a final database of 33 predictor variables was used to predict the occurrence of elevated arsenic across the two study regions.

This data release contains: (1) ASCII grids of predicted probability of elevated arsenic in groundwater for the Northwest and Central Minnesota regions, (2) input arsenic and predictive variable data used in model development and calculation of predictions, and (3) ASCII files used to predict the probability of elevated arsenic across the two study regions. The probability of elevated arsenic was predicted using Boosted Regression Tree (BRT) modeling methods using the gbm package in R Studio version 3.4.2. The response variable was the presence or absence of arsenic >10 µg/L, the U.S. Environmental Protection Agency’s maximum contaminant level for arsenic, in 3,283 wells located throughout both study regions (1,363 in the Northwest region and 1,920 in the Central). The original database used to develop the BRT model consisted of 127 predictor variables which included well characteristics, land use, soil properties, aquifer properties, depth to water table, and predicted nitrate. After optimization steps, a final database of 33 predictor variables was used to predict the occurrence of elevated arsenic across the two study regions.

Groundwater samples from public and private drinking water wells throughout the state of New Hampshire were analyzed for total Arsenic (As). Samples were collected after pH, specific conductivity, dissolved oxygen, and water temperature had met stabilization criteria as outlined in the USGS National Field Manual (United States Geological Survey 2005).The As analyses were carried out in the geochemistry laboratory in the Department of Earth Sciences at the University of New Hampshire (UNH). Not including replicate analysis, a total of 527 samples were analyzed via a hydride generator-inductively coupled plasma mass spectrometer (HG-ICP-MS) using a Cetac HGX-200 plumbed into a Nu Instruments Attom high-resolution inductively coupled plasma mass spectrometer following procedures adapted from Klaue and Blum (1999). Diluted aliquots of sample were run in triplicate, and the reported uncertainty is the standard deviation on the mean of these analyses. Generally, the data have a detection limit of ~ 0.2 μg/L as determined from repeated assessment of analytical blanks and using the conventional approach of defining the detection limit as the mean blank + ten times the standard deviation around the mean blank. These data are sensitive as they include sampling locations from privately owned wells, hence, latitude and longitude information is not included with the data set.