This has been a dry summer so far. The water year which runs from October 1- September 30 is running about around 30 inches in Prince William County. The average would be about 36 inches of rain by July 30th. After a wet decade, this is our second dry summer. The U.S. Drought Monitor map by the NOAA Climate Prediction Center indicates that 86% of Virginia is experiencing drought conditions, with 35% is experiencing severe drought conditions.
According to the ICPRB the rain deficit for the Potomac
Basin was about 2 inches in June. The U.S. Drought Monitor indicates that about
52% of the Potomac River Basin is experiencing moderate drought conditions,
while 38% is experiencing severe drought conditions. The Climate
Prediction Center’s U.S. Seasonal Drought Outlook, as of June 30, 2024,
indicates drought is likely to persist in the Potomac Basin over the coming
months.
The reason that ICPRB tracks the drought condition of the
Potomac River basin and the flow of the river is because the Potomac River, its
tributaries, reservoirs and the associated groundwater resources are the source
of drinking water for the over 6,000,000 people in the Washington Metropolitan
area. Although hidden in the subsurface, groundwater is the most important
freshwater compartment in the hydrological cycle by quantity. Groundwater
exists below all land with varying distance to the surface, but only in 20-30% of the land area is groundwater close
to the land surface. The conditions of the surface streams and the rainfall
provide some hints of what may be happening underneath the ground.
Groundwater is intricately linked to the other components of
the hydrological cycle (Sophocleous, 2002). Groundwater releases water to
streams sustaining the base flow of streams and rivers (Hare et al.,
2021). Groundwater is the primary source of springs and many wetlands (e.g.
marshes, peat bogs) (Bertrand et al., 2011; Havril et al., 2018;
Gleeson et al., 2020a). Finally, the groundwater saturated subsurface,
the hydroporic constitutes the largest
continental biome contributing to the health and purity of our water resource. The
small changes in the springs, seeps and streams is telling us that our
watershed is changing, and not in a good way.
Ground water flow and storage is often viewed as static
reservoirs that serves as the savings account for surface water flow. Through
the hyporheic zone groundwater feeds streams between rain storms, but
groundwater is dynamic and continually changing in response to human and
climatic stress [Alley
et al., 2002; Gleeson
et al., 2010]. Changes in precipitation patterns, the amount of
precipitation and the changes in land use impacts available groundwater and
surface water.
 |
| from the groundwater project |
Mankind’s hand in changing the land surface impacts water resources. Land use changes that increase impervious cover, add more suburban lawns, roadways, buildings, pavement and eliminates woodlands does two things. It reduces the open area for rain and snow to seep into the ground and percolate into the water table and on into groundwater and the impervious surfaces cause stormwater velocity to increase preventing water from having enough time to percolate into the earth, increasing storm flooding and preventing recharge of groundwater from occurring. Land use changes also potentially increases the use of groundwater by adding more homes and businesses (like Amazon who reports drawing millions of gallons of groundwater in the Manassas area).
Slowly, the changes in land use change the ecology of the
watershed and can reduce the water supply over time. As groundwater levels
fall, perennial steams that feed the rivers become intermittent during dry periods
like this past month and last July and August. I believe this is what is
happening in the area of the Bull Run Mountain Conservancy where for the second
summer in a row, what where perennial streams have stopped flowing in the
summer.
It appears that with the current level of development, the depth
to groundwater is increasing enough to disconnect some streams from the groundwater
during summer months. The ecology begins to die and streams become intermittent
and eventually become ephemeral- flowing only during rainstorms. It is believed
that this begins to happen at 5-10% impervious cover, but whatever level we are
at, we are seeing the beginning of the changes. The groundwater is becoming disconnected
from Little Bull Run and Catlett’s Creek in the area of the headwaters of those
streams. Once the hydrology and ecological biome is destroyed by development,
it cannot be easily restored, if at all. Though there have been a few attempts
we have not succeeded in restoring a watershed. We need to stop this now to
save our drinking water supply. A network of continuous monitoring well is
necessary to monitor the situation and take necessary actions to ensure that we
have sustainable drinking water for all our residents.
Protecting the Occoquan Reservoir requires protecting all the
water resources in a region because all water in the watershed is connected.
Precipitation moves into the water table (the hyporheic zone) down to
groundwater or into rivers and streams. Disrupting the balance of water flow
can have dire consequences. The available supply of fresh water is continually
renewed by the hydrologic cycle and in the case of the Occoquan Reservoir the
actions of mankind when we add the flow from the Upper Occoquan Service
Authority wastewater treatment plant. During low flows the fraction of treated
wastewater could exceed the amount of natural water.
The quantity and quality of ground water in Prince William
County varies across the county depending on the geologic and hydrogeologic
group and we must look at them all. Generally speaking, the groundwater in the
county is recharged in elevated areas and discharges to streams and estuaries.
However, the paths and duration of groundwater flow are different between
consolidated rocks and unconsolidated material, between the Culpeper Basin and
the Piedmont and the area within the Potomac Aquifer.
Changing land use and climate are impacting the Occoquan
Reservoir. High wastewater effluent additions to rivers under low flow conditions
can introduce pharmaceutical, personal care and cleaning chemicals into the
drinking water supply at higher concentrations. Due to declining water
potentials in groundwater aquifers and the infiltration of surface water into
the subsurface, contamination by these chemicals poses a serious risk for
groundwater quality (Bradley et al., 2014; Karakurt et al.,
2019; Kubicz et al., 2021). A multitude of micropollutants are
already being found in groundwater in the United States and worldwide at
increasing concentrations (Lapworth et al., 2012). Moreover, the rising
number of persistent micropollutants passing sewage treatment plants leads to a
complex mix of contaminants in surface waters.
We need more information before we destroy our precious
Occoquan Watershed. We are paving over the watershed with roads, data centers, parking
lots houses and infrastructure reducing the groundwater recharge, our stream
flow and increasing the water demand. The Virginia
Water Withdrawal Reporting Regulation only
requires the registration and annual reporting of surface water and groundwater
withdrawals of any entity withdrawing more than 300,000 gallons per month (that
is equivalent to the combined daily use of about 140 people). Though there is
no control or management of the water withdrawals except in the Groundwater
Management areas of Virginia, essentially the Tidewater and adjacent areas. Of
course, the way around the reporting requirements is to have several wells,
none of which exceed the limit. Much the way its done with back up generators
whose combined power equals a rather large on demand power plant that would
never be allowed to operate on diesel as a combined entity is just fine as
dozens upon of dozens of back up generators at the ever expanding fleet of data
centers. We need to begin now to ensure that our future has water for all.
This article includes ideas and comments from:
Anke Uhl, Hans Jürgen Hahn, Anne Jäger, Teresa Luftensteiner, Tobias Siemensmeyer, Petra Döll, Markus Noack, Klaus Schwenk, Sven Berkhoff, Markus Weiler, Clemens Karwautz, Christian Griebler,Making waves: Pulling the plug—Climate change effects will turn gaining into losing streams with detrimental effects on groundwater quality,
Water Research, Volume 220, 2022, 118649, ISSN 0043-1354,
https://doi.org/10.1016/j.watres.2022.118649
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