Data Acquisition
Water Level Data Collection
DWR typically collects water levels from each well in the network on a quarterly basis. At each quarterly visit, a water level is collected from each well via a manual tapedown using an electronic water level indicator. Additionally, DWR personnel assess the condition of each well site and perform brush clearing and other light maintenance at these visits. More labor-intensive site and well maintenance is scheduled for later dates.
DWR also has 322 wells that have either Sutron 8400A, Global Water WL15, or Global Water WL16 automatic data recorders installed on them. The Global Water and Sutron devices collect water level data at hourly intervals. At each quarterly visit, DWR personnel download the previous quarter's data and install fresh batteries. Back at the office, daily water level data is extracted for each well and added to the DWR water level database. The original hourly data files are archived for future reference.
Chloride Sampling
One important component of monitoring Coastal Plain aquifers is assessing whether salty ground water is migrating. Regular sampling of a network of suspect wells for chloride concentration allows hydrogeologists to gauge whether salt water encroachment, either vertical (upconing) or horizontal (intrusion), is occurring.
Video Logging
One of the challenges of maintaining a monitoring well network is assessing problems in wells that can be located from a few feet to over a thousand feet below land surface. For these circumstances, DWR possesses a GeoVision Micro M2 downhole video camera capable of capturing real time video images of wells at depths exceeding one thousand feet. This tool has proven itself invaluable as we have initiated an aggressive program of well maintenance and rehabilitation over the last few years. Many of our monitoring wells are located in locations that make them prone to vandalism. Examples of items we have found in our wells include
- Logs, sticks, leaves and other organic debris
- Dead animals
- Rocks
- Pens and pencils
- Almost anything else you can imagine that is small enough to fit in a well
Additionally, time and the elements gradually weaken the well casing, screens, and earth materials that comprise our monitoring wells. The ability to visually assess casing collapses, clogged screens, and collapsed holes in bedrock save many thousands of dollars by allowing us to repair damaged wells, rather than having to replace the wells altogether.
Global Positioning Satellites (GPS) and Surveying
Water level data is useless unless we can accurately fix the position of the monitoring well from which it came. For this purpose, we utilize Global Positioning Satellite (GPS) units to derive accurate coordinates of our monitoring well locations. GPS works by triangulating locations on the earth using three to five GPS satellites. DWR typically attains accuracy within ten to fifteen feet using GPS systems.
Additionally, we must also know the elevation of our well sites to be able to correlate water level data from site to site on a local or regional scale. DWR uses surveyor grade leveling equipment to attain these elevation data to approximately one-foot accuracy.
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