A Dry Summer Here

From US Drought Monitor 8/27/19

In their weekly report last week the U.S. Drought Monitor published by the National Oceanic and Atmospheric Administration (NOAA) and Department of Agriculture reported that 17.4% of Virginia was categorized as D0, abnormally Dry. This means that short-term dryness will be slowing the growth of crops (impacting my CSA Farm Share), some lingering water deficits and our lawn and pasture are downright crispy and brown.

Though we saw lots of lightening and dark skies, it felt like all the rainstorms just passed us by over the spring and summer. When I reviewed my rain log I found that my perception was not exactly true-we have had more than 4.5 inches of rain over the past 30 days. When I checked the USGS monitoring well just up the road and the water level was down, but not bad at all for this time of year.

Groundwater is water beneath the surface of the earth. It is one of our nation's most important natural resources and is often taken for granted. According to the U.S. Geological Survey (USGS) 24.7% of the domestic water supply in Virginia comes from groundwater- 195 million gallons a day. Groundwater is the sole source of drinking water for the population large segments of Virginia even those connected to city or community water systems.

The water level in the aquifer that supplies a well does not always stay the same. Droughts, seasonal variations in rainfall, and pumping affect the level of the water table. If a well is pumped at a faster rate than the aquifer around it is recharged by precipitation or other underground flow, then water levels in the well begins to fall. This is what happens during the summer, in times of drought and in depleted aquifers.

Rainfall and pumping are not the only forces that impact wells. Land use changes that significantly increase impervious cover and stormwater velocity can prevent water from soaking into the earth and reduce recharge of the groundwater making existing wells more susceptible to drought and overtime reducing the amount of groundwater. Significant increases in groundwater use for irrigation of crops or playing fields, or commercial purposes can overtax and aquifer and dry out neighboring wells. Unless there is an earthquake or other geological event groundwater changes are not abrupt and problems with water supply tend to happen slowly as demand increases with construction and recharge is impacted by adding paved roads, driveways, houses and other impervious surfaces.

The water level in a groundwater wells naturally fluctuates during the year and between wet and dry years. This variation tends to mask a slowly decreasing aquifer or falling groundwater level. Since 2000 the longest drought on record in Virginia was 103 weeks from May 2007 to April 2009 (about the time I started this blog). The most intense drought was in August 2002 when almost a third of Virginia was in severe drought (D4).

from US Drought Portal

Groundwater levels tend to be highest in the early spring after winter snowmelt and spring rainfall when the groundwater is recharged. Groundwater levels begin to fall in May and typically continue to decline during summer as plants and trees use the available shallow groundwater to grow and streamflow draws water. Natural groundwater levels usually reach their lowest point in late September or October when fall rains begin to recharge the groundwater again so it is hard to see a slow and gradual loss of an aquifer unless the groundwater level falls below the pump level it is typically unnoticed. 

It is essential for the long term sustainability of our communities that the long term impact to the aquifer be assessed before the surrounding land use is changed or developments are approved. The above are the same well over two different time periods. Even with the incredibly wet year last year the long term impact on the well seems to have a negative trend. Judge for yourself.