Sources of sodium and chloride in the Scituate Reservoir drainage basin, Rhode Island

Abstract

• Deicing of State and local roads was the largest source of sodium and chloride in the Scituate Reservoir drainage basin during Water Year (WY) 2000. Of approximately 1,000 tons of sodium and 2,300 tons of chloride introduced into the basin, 67 percent of the sodium and more than 90 percent of the chloride came from deicing of State highways, local roads, and other surfaces. Precipitation, individual sewage-disposal systems, and geologic weathering accounted for the remaining 33 percent of the sodium and 10 percent of the chloride inputs. The Scituate Reservoir system is the principal drinking-water supply for more than 60 percent of the population of Rhode Island. Sodium concentrations in the reservoir have been increasing slowly in recent years despite the long-term (12 years) use of a reduced-sodium deicing agent on State-maintained highways in the reservoir drainage basin. This report identifies the major sources of sodium and chloride in the drainage basin, and assesses the relative contribution of each source to the total amounts of these constituents that entered the basin from

Streamflow, water quality, and constituent loads and yields, Scituate Reservoir drainage area, Rhode Island, water year 2019

“…The highest annual mean 3 concentrations of chloride and sodium were estimated to be 59 and 35 mg/L, respectively, at the Moswansicut Reservoir (table 6). The relatively high annual mean concentrations of chloride and sodium at Bear Tree Brook (01115275; PWSB station 9; 48 and 28 mg/L, respectively) are the result of residual chloride and sodium leaching to groundwater from a formerly uncovered salt storage pile (Nimiroski and Waldron, 2002) and comparatively small surface-water flows. Annual mean concentrations of chloride and sodium, ranging from 32 to 52 mg/L and 20 to 30 mg/L, respectively, estimated at the unnamed tributary to the Regulating Reservoir (unnamed brook A; 01115120; PWSB station 18) and Peeptoad Brook also were relatively high (table 6).…”

“…The USGS also has been continuously measuring specific conductance at 14 monitoring stations since 2009 (table 1). Equations that relate specific conductance to concentrations of chloride and sodium in stream water were developed as part of previous cooperative studies of the USGS and the PWSB (Nimiroski and Waldron, 2002;Smith, 2015bSmith, , 2018aSmith, , 2021a. These equations, used together with measured (or estimated) streamflows, allow for nearly continuous estimation of chloride and sodium loads to the reservoir.…”

Streamflow, water quality, and constituent loads and yields, Scituate Reservoir Drainage Area, Rhode Island, Water Year 2017

“…1). Nimiroski and Waldron (2002) indicated that tributaries in basins with State-maintained roads had substantially higher concentrations of chloride and sodium than tributaries in basins with low road density, presumably because of deicing activities. In addition, sodium is a constituent of potential concern for human health; some persons on restricted diets might need to limit intake of sodium.…”

“…The highest annual mean 4 concentrations of chloride and sodium were estimated to be 60 and 35 mg/L, respectively, at the Moswansicut Reservoir (table 6). The relatively high annual mean concentrations of chloride and sodium at Bear Tree Brook (53 and 31 mg/L, respectively) are the result of residual chloride and sodium leaching to groundwater from a formerly uncovered salt storage pile (Nimiroski and Waldron, 2002) and comparatively small surface-water flows. Annual mean concentrations of chloride and sodium, ranging from 43 to 52 mg/L and 25 to 30 mg/L, respectively, estimated at the unnamed tributary to the Regulating Reservoir (PWSB station 18), Rush Brook, and Peeptoad Brook (PWSB station 16) also were relatively high (table 6).…”

“…The USGS also has been continuously measuring specific conductance at 14 monitoring stations since 2009 (table 1). Equations that relate specific conductance to concentrations of chloride and sodium in stream water were developed as part of previous cooperative studies of the USGS and the PWSB (Nimiroski and Waldron, 2002;Smith, 2015bSmith, , 2018a. These equations used together with measured (or estimated) streamflows allow for nearly continuous estimation of chloride and sodium loads to the reservoir.…”