Summary

Water levels, at the Fleming, Williams, and Wills well nests located on the University of Vermont's main campus, declined throughout the dry summer of 1999. Then, approximately 4 inches precipitation fell on September 16 and 17, 1999 increasing water levels as much as 4.94 feet in two weeks (well #8). For the September 16 and 17 event, well #2 had a recharge lag time of about 2 weeks. Water levels continued to increase until mid-November where they then decreased. Well screens for all wells are located in comparable material consisting of sand and varying amounts of silt and gravel.

Water temperatures generally decreased as the air/water interface depth increased. Well #2 was the most thermally dynamic well with a total temperature variation of 4.5 degrees. Well #2 also had the lowest temperatures, which I believe are a result of its location on a lawn, in contrast to wells at Williams and Wills, which are surrounded by asphalt and concrete.

The highest initial conductivity values were measured at well #7 (2.85 milliseimens/cm), #8 (2.74 milliseimens/cm), and #5 (2.54 milliseimens/cm) located in the Wills and Williams well nests. The highest water conductivity is found in wells near walkways and roadways where the University of Vermont applies salt to melt winter snow. The lowest conductivity was measured in Fleming well nest, well #2 (0.602 milliseimens/cm) where no salt is applied. The September 16 and 17 precipitation event increased conductivity in all wells; wells #8 (2.43 milliseimens/cm) and #5 (1.29 milliseimens/cm) increased most significantly, 87% and 41%, respectively.

Chloride, sodium, sulfate, calcium, potassium, magnesium, and sulfur are found in significant quantities dissolved in the ground water. After the September 16 and 17 precipitation event, concentrations of these constituents increased significantly in wells #8 and #5, the same wells in which conductivity rose significantly. Well #8 had the highest level of chloride (1620 mg/L) which exceeds the secondary maximum contaminate level set by the EPA by 6.5 times. Chloride and sodium were the best correlated of all elements, r2=0.93.

Groundwater Levels

Water levels showed an uneven, but overall decline throughout the summer. Levels were significantly affected by precipitation events greater than 0.5 inches. Almost 4 inches precipitation fell on September 16 and 17 increasing water levels as much as 4.94 feet in two weeks (well #8). Water levels recorded on September 21st show that all wells responded within a few days, except well #2, which shows a recharge lag time of approximately two weeks. After the September 16th event, precipitation occurred more frequently which caused individual well levels to increase throughout the rest of September, October, and the beginning of November. In mid-November, water levels began to decrease as precipitation decreased.

Groundwater Temperature

All ground water temperatures were generally in sync. Water temperatures generally decreased as the air/water interface depth increased. Ground water well #2 was most dynamic with a total temperature variation of 4.5 degrees Celsius.. On two occasions, July 30th and September 6th, 1999, well #2 changed approximately one degree Celsius more than other wells. Well #2 was also the coolest well over the study period despite the air/water interface of well #2 being located at an intermediate depth. The cooler temperatures probably reflect the abundance of vegetation on the Fleming lawn, which creates cooler ground temperatures than the concrete and asphalt at the Wills and Williams locations. Temperature variance is also minimized as asphalt and concrete act as a buffer releasing heat into the ground when the air temperature decreases and retaining heat as the air temperature increases.

Groundwater Conductivity

Water sampled from the Fleming well nest had considerably lower conductivity than water in the Wills and Williams nests. The highest conductivities were measured in water from wells #7 (Wills, 2.85 milliseimens/cm), #8 (Wills, 2.74 milliseimens/cm), and #5 (Williams, 2.54 milliseimens/cm). Ground water well #2 (0.602 milliseimens/cm) at Fleming had the lowest conductivity value.

This difference in conductivity likely reflects the University of Vermont's road/walkway salting policy. The Wills and Williams locations are salted during the winter months whereas the Fleming lawn is not. The university plows the excess snow and salt on top of the Williams and Wills nest located directly down gradient from impervious, salted areas (parking lots and driveways). There is also a general trend of higher conductivity in shallow wells than deeper wells at each site.

Data suggest a relatively large amount of precipitation in mid to late September caused conductivity to increase in all ground water wells. Salt applied to roadways and walkways over the 1999 winter is believed to have been flushed into the groundwater aquifer by this late summer precipitation. Wells #8 and #5 were most severely affected; conductivity increased 2.43 (87%) and 1.29 (41%) milliseimens/cm in a two week period, respectively. Wells #8 and #5 were also the most dynamic. All other well conductivity measurements increased over the study period; however, wells 2, 3, 4, 6, and 7 changed no more than 15% from the values initially recorded in July, 1999.

Groundwater Chemistry

Chloride, sodium, sulfate, calcium, potassium, magnesium, and sulfur were the only elements found in significant quantities by chemical analysis performed using ion chromatography (Dionex) and ICP. The most significant increases of these inorganic elements after the September storm were in wells #8 and #5. Well #8 experienced significant increases in all seven constituents: sulfate (192%), sulfur (115%), sodium (95%), chloride (88%), calcium (81%), magnesium (73%), and potassium (63%). Ground water well #5 experienced significant increases in magnesium (199%), calcium (184%), chloride (73%), and sodium (24%). Click here to see graphical representation of salt composition.

Data suggest the most significant correlation was between chloride and sodium, r2=0.93. Ground water wells #8 and #5 contained the highest level of chloride (#8=1620 mg/L, #5=950 mg/L) and sodium (#8=790 mg/L, #5=620 mg/L) as would be expected. Wells #8 and #5 have the most shallow water levels at their respective nests, the highest conductivities, and are located near heavily salted areas. The lowest levels for chloride (17 mg/L) and sodium (15 mg/L) were found in ground water well #3 which is drilled 303 feet in bedrock. However, the percent increase, over the four month study period was most significant for ground water well #2, located at an intermediate depth on the Fleming lawn. Chloride increased 273% and sodium increased 116% from July to November, 1999. Levels were low to begin with (chloride=18 mg/L, sodium=22 mg/L) and ground water well #2 is drilled in surficial material down gradient from where high concentrations of sodium and chloride were detected at the Wills and Williams nest. Therefore, I predict well #2 will significantly increase its total dissolved solids in the future as the plume of salty water moves down gradient.

 

Graphs:

Precipitation vs Comparative Water Levels

Precipitation vs Well Conductivity Comparison

Precipitation vs Change in Total Disolved Solids

Mean Air Temperature vs Well Temperature

Mean Air Temperature vs Change in Well Temperature

 

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