The Potomac River supplies D.C.s drinking water.s drinking water.

The U.S. Forest Service is working on a plan for the George Washington National Forest that has some experts concerned for the future safety of D.C.’s drinking water.

Last week, the Forest Service pushed back its release of the plan, which was originally set for late August or early September, to late October or early November. Still up in the air is the issue of hydraulic fracturing, or fracking, a process of natural gas extraction. The Forest Service’s Ken Landgraf tells the Associated Press that no decision has been made on fracking in the forest, which is located mainly in Virginia and partly in West Virginia.

In 2011, Tom Jacobus, managing director of the Washington Aqueduct, wrote a letter to Landgraf that has not previously been made public, expressing his concern about the potential effects of fracking on D.C.’s water supply.

“Washington Aqueduct strongly supports the selection of an Alternative that prohibits the use of horizontal fracturing (hydrofracking) for natural gas development within the Forest,” Jacobus wrote. “Although studies on the technique are still needed in order to fully understand the potential impact on drinking water, enough study on the technique has been done and information has been published to give us great cause for concern about the potential for degradation of the quality of our raw water supply as well as impact to the quantity of the supply.”

Jacobus could not be reached for comment.

The general manager of the Fairfax County Water Authority wrote a similar letter to Landgraf in 2011, explaining “Natural gas development activities have the potential to impact the quantity and quality of Fairfax Water’s source water through consumptive use of water, generation of wastewater with high levels of Total Dissolved Solids (TDS) and often unknown chemical ‘fracking-fluid’ additives, land-disturbing activities associated with the well pad and related features, and the disruption of natural groundwater flow pathways.”

The fracking process requires the use of large quantities of water, some of which comes back out of the drilling site. Disposal of this potentially harmful wastewater is a challenge for the gas-mining companies. In other states, gas drillers have sometimes dumped this water into nearby rivers. The Potomac, not far from the forest, is the source of D.C.’s water supply.

Jacobus’ letter is reprinted below:

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Photo via Flickr user JoshuaDavisPhotography