Sunday, June 30, 2024

Groundwater Monitoring Well 49V 1


Last week Sam Caldwell a Hydrologist from the United States Geological Survey (USGS) who generally specializes in the areas of the Potomac Aquifer spoke at a panel discussion about groundwater and geology. In his presentation Mr. Caldwell walked us through  groundwater level depth data to help us understand the information that can be collected. 

from USGS S. Cadwall presentation

from USGS

In Prince William County the USGS has only two continuous monitoring wells.  Well 49V in the northwest corner of the county has been in operation for over 50 years.

from USGS S.Cadwell presntation

location of well 40V 1 in google maps

According to Mr. Caldwell groundwater level data can be very useful. With 10 years of data we can be very confident of the trend at one particular well. For most of the last 50 years  the water level in well 49V has been fairly stable. However, if you just look at the last 16 years it does not look quite as stable.

from USGS

 A slight downward trend is observed  in the data. This is a single well. To create a pantographic map of the groundwater in Prince William County you would need several wells in each aquifer and geographic region of the county collecting data for at least a decade. This way the USGS could create a potentiometric map of the surface of the aquifer.

from USGS S.Caldwell Presentation

When you add to this data, the precipitation data for the same period you see that July 2017 was very dry, and the complete recovery of the groundwater level only happened after a 2.5 inch rainfall on the 27th of July. What is intriguing is the amount of recovery that occurred during the dry period. The second and third recoveries align with the rainfall that month. 

Rain data from summer 2017 in inches of rain

from CoCoRHS precipitation monitoring station PW-15

from USGS S.Caldwell presentation

Looking at the groundwater level against the historical averages also in informative. Combining groundwater level data, with surface water data and precipitation data would allow use to quantify the recharge of the groundwater over time and model the groundwater level. Once more you can see that the groundwater level in the past year has with the exception of January, been average or below average. Gathering this data and tracking groundwater levels is the first step in ensuring that all Prince William County residents have sustainable water. 

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