Proposed Directive: Groundwater Resource Management
Questions and Answers related to Groundwater
May 1, 2014
1. What is groundwater, and how does it get into the ground?
Groundwater is the portion of precipitation (snow and rain) that infiltrates into the soil and bedrock.
When rain falls or snow melts, some of it evaporates into the atmosphere, some of it flows across the
ground surface directly into lakes, streams and wetlands, some of it is taken up by plants and transpired
into the atmosphere, and the rest seeps into the ground to become groundwater (see the diagram of the
water or hydrologic cycle below).
2. What is the hydrologic cycle?
The hydrologic cycle describes how water moves from the atmosphere to the land to the ocean and back
(see the diagram below). Precipitation that falls on the land surface evaporates, runs off into surface
waters or infiltrates. Some of the infiltrated moisture evaporates and transpires, while the rest becomes
part of the groundwater as recharge. The groundwater flows in the subsurface until it discharges into
streams, lakes, springs, seeps and wetlands, where it becomes surface water. Some surface water
evaporates and transpires, some recharges groundwater and the rest flows to the ocean. Eventually, all of
the water vapor accumulated in the atmosphere falls to the earth as precipitation, completing the cycle.
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3. What is the significance of groundwater?
Groundwater is divided into two major components: the unsaturated zone above the water table and the
saturated zone, below the water table (as shown in the hydrologic cycle diagram, above).
Household and other water supplies are drawn from the saturated zone. However, land plants develop root
systems and extract water and nutrients they need for growth from the unsaturated zone. The saturated
zone provides the water that keeps perennial streams flowing during periods without precipitation.
A well open in the saturated zone below the water table would have standing water in it because spaces
between the soil or rock particles (fractures and pores) are filled with water. However, a well open only in
the unsaturated zone above the water table would be dry because its fractures and pores are filled with a
mixture of water and air.
4. What is a hydraulically interconnected system?
Under the proposed groundwater directive, surface water and groundwater would be managed as a single
hydraulically interconnected resource unless site-specific data demonstrate otherwise. This assumption is
consistent with well-accepted scientific understandings of the hydrologic cycle. Under this assumption, all
water in a watershed, whether in a stream, lake, wetland or in the groundwater, is considered part of a
single container or reservoir of water. In most places, pumping groundwater from a well would cause a
reduction in water flow in nearby streams or in water levels in nearby lakes or wetlands. To protect
National Forest System natural resources and other water users, an evaluation needs to be conducted to
determine whether the reduction is significant in terms of water quality, quantity and timing.
5. How does groundwater affect homeowners?
Approximately 99 percent of rural U.S. residents and approximately 51 percent of urban and suburban
U.S. residents get their drinking water from groundwater. Thus, adequate supplies of high-quality
groundwater are critical to the nation’s quality of life. In addition, most rural and many suburban residents
dispose of household wastewater through discharge to groundwater from septic systems. Groundwater
quality can be adversely affected through direct discharge of contaminants (e.g., leaky landfills, oil spills,
agricultural chemicals and septic systems) and through substantial reductions in groundwater levels that
release contaminants from soil and rock.
6. Why is groundwater resource management on national forests and grasslands important?
The Forest Service manages the headwaters and recharge areas of locally and regionally important rivers
and aquifers. In most places, springs, streamflow and associated ecosystems are sustained during dry
periods by the discharge of groundwater. To manage watersheds on National Forest System land, the
Forest Service needs to address all the water resources on those lands as a single hydrologic system.
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