WSE 187 Spring 2000
Investigation of Ground and Surface Water
Introduction
Our project was the investigation of ground and surface water. Our task was to determine whether Roth Pond and the Kelly Stream were surface expressions of the water table. On February 3, 2000, we collected different samples of water from Roth Pond, Kelly stream and the well near the powerplant. We used two different approaches to test our hypothesis. One approach was using chemical measurements on the the different samples of water to observe any existing similarities that might allow us to conclude that they all originated from the same body of water. The second approach was to collect physical evidence and to use Darcy's Law. Darcy's Law allows us to measure rate of flow of water through different mediums and slopes. This allowed us to test our hypothesis in a different manner.
Darcy's Law:
Q = -KA(dh/dl)
Q: flow rate (volume/time)
K: hydraulic conductivity (how well water flows through the medium) (distance/time)
(for the sediments on the SUNYSB campus, we used a K of approximately 100 meters per day.)
A: cross sectional area of the flow path (meters squared)
dh: the change in hydraulic head for the flow path (the change in elevation above sea level) (distance)
dl: the length of the flow path (distance)
Background
Before we began our experiment, we needed to know about the geology of Long Island. Our main concern were the aquifers and sediment types common to our area. We found out that Long Island consists largly of sediments of varying size and texture. Two aquifers, the Upper Glacial and the Magothy, exist in this area. We learned that the Upper Glacial aquifer is quite polluted and that we get most of our water from the Magothy aquifer. Below the Magothy aquifer lies the Raritan Clay layer. This layer is largly impermeable and little water gets into the Lloyd Sand layer below.
The water table is the area in which all the spaces in between sediment is filled with water instead of air. If you dig into this area you will find that the soil will be saturated and water will enter the newly emptied space. Bogs are areas where the water table is even with the ground. Streams can be areas where the ground dips below the water table in a sloping area or they can be water running over an impermeant surface. Likewise many of the ponds on Long Island are kettle ponds which are areas dug out by glaciers that dip below the water table. There are also perched ponds, which are areas where water collects in a depression above an impermeable barrier, ie. clay.
Methods and Materials
We used a bailer (or containers right off the bat in some cases) to gather water, at one point we even had to use a geologic hammer to reach the water beneath the thick layer of ice. From that point, we tested each water sample for chemical analysis using the pH paper, DO kit and TDS meter. We measured the temperature of the water and air on site.
We then used contour maps to determine suface elevations and distances between each body of water for the application of Darcy's Law. For Darcy's Law, we needed to determine the elevations of each body of water so we could calculate the hydraulic gradient. The equation for Darcy's Law also requires the hydraulic conductivity constant for the sandy material that we were working with. In this case, the constant was supplied by our instructor from know data.
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| Surface Elevation (ft) | Depth to Water (ft) | Water Table Elevation (ft) | Time | Air Temp (°C) | Water Temp (°C) | DO (ppm) | pH | TDS (ppm) | |
| Roth Pond | 140 | 0 | 140 | 4:21 | 1 | 1 | 11 | 6.00 | 58 |
| Well #1 | 105 | 81 | 24 | 4:50 | 0 | 13 | 10 | 6.50 | 74 |
| Stream | 117 | 0 | 117 | 4:42 | 1 | 15 | 10 | 6.25 | 80 |
Analysis:
All the information taken from the sites: Roth Pond, the stream by Kelly Quad, and the well by the hydroelectric plant, were taken within half an hour. The air temperature was basically the same, about zero degrees Celsius (freezing point), at all three locations. The water temperature at Roth Pond was near freezing, and there was ice at it's surface. The water temperatures at the other sites were both well above freezing, and within two degrees of each other. The surface elevation above sea level differed, ranging from 105 feet at the well to 140 feet at Roth Pond. The depth to the water was 81 feet at the well, and zero feet at both Roth Pond and the stream. The water table elevations changed from site to site. The amounts of dissolved oxygen were virtually the same. The pH levels ranged from six at Roth Pond to 6.5 at the stream. The amounts of total dissolved solids varied.
Conclusions:
From the data and observations, it appears that Roth Pond is not part of the water table in Long Island. However, the well and the stream do seem to be connected through the water table. According to Darcy's Law, Roth Pond would empty in 11.5 days, if it were not refilled by rain or the fire hydrant. Due to observations year around, the elevation of Roth Pond has never significantly dropped in such a short period of time naturally. The well and stream had an underground origin (the water table) which were not as affected by the atmospheric temperature as Roth Pond, and that kept the water flowing. This is why the temperatures of the well and the stream were similar, whereas Roth Pond was near freezing. Therefore the orignal hypothesis has been disproven through Darcy's Law and through various chemical data.
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