Thursday, November 17, 2016

Lorton Quarry to Become Reservoir

At the end of October William Duke, President of Vulcan Materials Mideast Division, and Philip Allin, Chairman of Fairfax Water signed an agreement at a ceremony at the Griffith Water Treatment Plant in Lorton that sets the conditions for the transformation of a rock quarry into a water storage reservoir in southeastern Fairfax County.
from Google Maps

The Quarry will be converted to a reservoir in phases and continue to operate during phase 1 which will convert a portion of the quarry to a reservoir with storage of of about 1.8 billion gallons by 2035. Quarry operations will end with Phase II which will convert the remaining area to Fairfax Water reservoir with storage capacity of up to 15 billion gallons by 2085. To do this the existing quarry will be reconfigured to mine portions of Fairfax Water’s property. This will allow Vulcan to leave a “rock wall” that will segregate the quarry into the two parts. The two-reservoir Quarry reconfiguration addresses the water supply need projected to occur in the 2035-2040 timeframe.
from Fairfax Water

The Vulcan Quarry was identified as the favored alternative for meeting future water needs in the Northern Virginia Regional Water Supply Plan in 2011 and adopted by Fairfax County in early 2012. This new reservoir will be used to supplement water supply to accommodate population growth in Northern Virginia and ensure that Fairfax Water can continue to provide reliable, high-quality drinking water well into the future. 

Fairfax Water projects water need based on the most recent population and employee projections available from the Metropolitan Washington Council of Governments. Today, Fairfax Water serves nearly 2 million residents and more than 800,000 employees in Northern Virginia. Between 2010 and 2040, the population served by Fairfax Water, including wholesale customers, other communities that buy their water from Fairfax Water, is projected to increase by over 650,000 residents and nearly 550,000 employees. Fairfax Water needs to plan to reliably provide water to all.

All the regional water supply companies share the water resources of the Potomac. Fairfax Water, the Washington Aqueduct (WA) of the U.S. Army Corps of Engineers, and the Washington Suburban Sanitary Commission (WSSC), and the Interstate Commission on the Potomac River Basin (ICPRB) signed the Water Supply Coordination Agreement that established a framework for water supply planning, drought management, and resource optimization on the Potomac River back in 1982 and have worked together to manage the regional water resources since.

Every five years, the ICPRB conducts a study of projected demand and available water supply resources based on the best available information at the time- utilizes water use and demographic data along with assumptions regarding changes in water use patterns in the region. These are not certain. The ICPRB 2015 report assumes daily per capita water use will decrease by an additional 25%, incorporates various climate and weather scenarios and uses the projection of population growth provided by the Washington Council of Governments who forecast that the residential population is expected to grow by 23% and the workforce is expected to grow by 36% by 2040. They also looked carefully at the impact the climate change might have on water supply.

Historically, a key assumption was that the future flow of the Potomac River will mirror the hydraulic conditions for the past 79 years. If hydraulic conditions are changing or a 79 year period is inadequate to predict the possible extent of droughts, this could impact the availability of water. So, a couple of years ago the ICPRB engaged a study that created a model for various climate scenarios of water supply availability from Potomac Watershed to determine if the water supply would be adequate to serve the population. They used this model to examine the water supply adequacy of the current study.

The ICPRB found that the existing water supplies can meet demands of the forecasted population levels through the Year 2035, by implementing mandatory water restrictions during severe droughts. However, as the population and water demand continue to grow the current supply system including the Potomac River and all current and planned reservoirs and water storage would not be adequate to supply all needs during a severe drought even after using all the reservoirs to supplement flow and implementing water use restrictions.

This is why Fairfax Water has worked with Vulcan to develop the “two reservoir Quarry reconfiguration”, to provide interim water supply storage in 2035, as well as a significantly larger storage facility beyond 2085. With the delivery of the Northern Reservoir in 2035, Fairfax Water will be able to expand the Griffith Plant to 160 million gallons a day.  The Northern Reservoir will also provide an emergency source of supply to the Griffith water treatment plant when emergencies like chemical spills restrict the larger and newer Corbalis plant’s access to the Potomac River. This happened last year when Fairfax Water had to shut their intake to let a plume of contamination pass. 

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