Groundwater & Surface Water:
Understanding the Interaction

A Guide for Watershed Partnerships

Introduction.
Water. It's vital for all of us. We depend on its good quality-and quantity-for drinking, recreation, use in industry and growing crops. It also is vital to sustaining the natural systems on and under the earth's surface.

Groundwater is a hidden resource. At one time, its purity and availability were taken for granted. Now contamination and availability are serious issues. Some interesting facts to consider...
Scientists estimate groundwater accounts for more than 95% of
       all fresh water available for use.
Approximately 50% of Americans obtain all or part of their
       drinking water from groundwater.
Nearly 95% of rural residents rely on groundwater for their
       drinking supply.
About half of irrigated cropland uses groundwater.
Approximately one third of industrial water needs are fulfilled by
       using groundwater.
About 40% of river flow nationwide (on average) depends on
       groundwater.

Thus, groundwater is a critical component of management plans developed by an increasing number of watershed partnerships.

Groundwater ABCs.
Groundwater is the water that saturates the tiny spaces between alluvial material (sand, gravel, silt, clay) or the crevices or fractures in rocks.

Aeration zone: The zone above the water table is known as the zone of aeration (unsaturated or vadose zone). Water in the soil (in the ground but above the water table) is referred to as soil moisture. Spaces between soil, gravel and rock are filled with water (suspended) and air.

Capillary water: Just above the water table, in the aeration zone, is capillary water that moves upward from the water table by capillary action. This water can move slowly in any direction, from a wet particle to a dry one. While most plants rely on moisture from precipitation that is present in the unsaturated zone, their roots may also tap into capillary water or into the underlying saturated zone.

Aquifer: Most groundwater is found in aquifers-underground layers of porous rock that are saturated from above or from structures sloping toward it. Aquifer capacity is determined by the porosity of the subsurface material and its area. Under most of the United States, there are two major types of aquifers: confined and unconfined.

Confined aquifers (also known as artesian or pressure aquifers) exist where the groundwater system is between layers of clay, dense rock or other materials with very low permeability.

Water in confined aquifers may be very old, arriving millions of years ago. It's also under more pressure than unconfined aquifers. Thus, when tapped by a well, water is forced up, sometimes above the soil surface. This is how a flowing artesian well is formed.

Unconfined aquifers are more common and do not have a low-permeability deposit above it. Water in unconfined aquifers may have arrived recently by percolating through the land surface. This is why water in unconfined aquifers is often considered very young, in geologic time.

In fact, the top layer of an unconfined aquifer is the water table. It's affected by atmospheric pressure and changing hydrologic conditions. Discharge and recharge rates depend on the hydrologic conditions above them.

Saturation zone: The portion that's saturated with water is called the zone of saturation. The upper surface of this zone, open to atmospheric pressure, is known as the water table (phreatic surface).

Water-bearing rocks: Several types of rocks can hold water, including:
Sedimentary deposits (i.e. sand and gravel)
Channels in carbonate rocks (i.e. limestone)
Lava tubes or cooling fractures in igneous rocks
Fractures in hard rocks

How Groundwater and Surface Water connect.

It's crystal clear. Groundwater and surface water are fundamentally interconnected. In fact, it is often difficult to separate the two because they "feed" each other. This is why one can contaminate the other.

A closer look.
To better understand the connection, take a closer look at the various zones and actions. A way to study this is by understanding how water recycles ... the hydrologic (water) cycle.

As rain or snow falls to the earth's surface:
Some water runs off the land to rivers, lakes, streams and
       oceans (surface water).
Water also can move into those bodies by percolation below
       ground.
Water entering the soil can...
infiltrate deeper to reach groundwater
which can discharge to surface water or return to the surface
           through wells, springs and marshes.
Here it becomes surface water again.
And, upon evaporation, it completes the cycle.

This movement of water between the earth and the atmosphere through evaporation, precipitation, infiltration and runoff is continuous.

How groundwater "feeds" surface water.
One of the most commonly used forms of groundwater comes from unconfined shallow water table aquifers.

These aquifers are major sources of drinking and irrigation water. They also interact closely with streams, sometimes flowing (discharging) water into a stream or lake and sometimes receiving water from the stream or lake.

An unconfined aquifer that feeds streams is said to provide the stream's baseflow. (This is called a gaining stream.) In fact, groundwater can be responsible for maintaining the hydrologic balance of surface streams, springs, lakes, wetlands and marshes.

This is why successful watershed partnerships with a special interest in a particular stream, lake or other surface waterbody always have a special interest in the unconfined aquifer, adjacent to the water body.

How surface water "feeds" groundwater.
The source of groundwater (recharge) is through precipitation or surface water that percolates downward. Approximately 5-50% (depending on climate, land use, soil type, geology and many other factors) of annual precipitation results in groundwater recharge. In some areas, streams literally recharge the aquifer through stream bed infiltration, called losing streams.

Left untouched, groundwater naturally arrives at a balance, discharging and recharging depending on hydrologic conditions.

Defining Combined Boundaries.

The question of boundaries.
Partnerships using the watershed approach to protect natural resources identify and understand the individual resources-water, soil, air, plants, animals and people-early in the process.

This is why watershed partnerships select or define boundaries to address all natural resources - not just one. They realize that groundwater, surface water, air quality, and wildlife and human activities all affect each other.

Occasionally watershed partnerships run into difficulty combining boundaries of surface water (watersheds) and recharge areas (groundwater). If this occurs, consider combining surface and groundwater into a single, larger area. In other situations-for example if water is being transferred from one watershed or aquifer to distant users-there can be, and should be, two distinct areas.

Thus, watershed partnerships' boundaries may combine the wellhead area, aquifer, watershed, or many other areas depending on the issue(s).

Who determines watershed boundaries?
Larger sizes-ranging from the entire Missouri or Ohio River Basins-to three nested watersheds smaller are mapped by U.S. Geologic Survey (USGS).

Smaller areas like your creek's watershed or a small lake's watershed have been identified and catalogued in many states. The State Geological Survey, USDA Natural Resources Conservation Service, USDA Forest Service, USDI Fish & Wildlife Service, and USDI Bureau of Reclamation are the agencies that have identified these areas. Call your local office for details.

Common boundaries.
Aquifers are often difficult to delineate. It requires someone with an understanding of the aquifer, the geology, the surface above it, and the land that drains toward the surface.

An unconfined aquifer area often extends to the surface waterbody's (i.e. lake, river, estuary) watershed. When determining an aquifer protection area, pumping (working) wells are not considered.

The biggest risk to an unconfined aquifer is contaminated water moving through the permeable materials directly above it. This area is known as the primary recharge area. Depending on the depth and overlying geologic characteristics, travel time from the surface to the aquifer can be relatively short.

Less permeable deposits located at higher elevations than the aquifer form a secondary recharge area. These areas also recharge the aquifer through both overland runoff and groundwater flow. Because they are less permeable and tend to be a greater distance from the aquifer, they often filter out contaminants.

Additional recharge areas to consider include an adjacent stream that potentially contributes to the aquifer through infiltration. When pumping wells are located near a stream or lake, infiltration can be increased. Infiltrating streams typically provide an aquifer with large quantities of water and a pathway for bacteria, viruses and other contaminants.

A confined aquifer area may be limited to the outcrop of the aquifer unit and its immediate contributing area. This area may actually be isolated from the location of water supply wells within the aquifer.

Semi-confined aquifers may receive water from both outcrop areas and overlying aquifers. Delineating the aquifer protection area can be extensive and complex.

Sole-source aquifers are delineated based on aquifer type - confined, semi - confined or unconfined - and local geologic and hydrologic conditions. Defined as providing a minimum of 50% of the water for its users, sole-source aquifers usually exist only where there simply are no viable alternative water sources.

Wellhead protection areas (also known as zone of contribution and contributing areas) are the surface and subsurface areas surrounding a well or field of wells (wellfield) supplying a public water system.

The area is calculated by determining the distance contaminants are reasonably likely to move before reaching a well. Some common methods for determining the wellhead protection area include:
Arbitrary fixed radius
Calculated fixed radius
Simplified variable shapes
Analytical method
Numerical method
Hydrogeologic mapping

When selecting the best method, consider available funds and the level of concern. Other factors to consider include the cone of depression and drawdown.

Surface watersheds are defined by a simple process of identifying the highest elevations in land that drains to the surface waterbody (i.e. lake, pond, river, estuary, etc.). Watersheds are all shapes and sizes, ranging from just a few acres to several million acres ... many smaller watersheds "nested" inside a larger watershed.

Most successful watershed partnerships work with a manageable size yet encompass all the different, but integrated, areas. This enables faster measurable progress and stronger ties between stakeholders and the waterbody they affect.

Threats to Groundwater.

Threats to quantity.
An increased quantity of groundwater is being withdrawn to meet the demands of a growing population. Some of the typical threats associated with this include overdraft, drawdown and subsidence.

Overdraft occurs when groundwater is removed faster than recharge can replace it. This can result in...
A permanent loss of a portion of its storage capacity.
A change that can cause water of unusable quality to
       contaminate good water.
In coastal basins, salt water intrusion can occur.

Generally, any withdrawal in excess of safe yield (the amount that can be withdrawn without producing an undesirable result) is an overdraft.

Drawdown differs significantly from overdraft. It results in a temporarily lowered water table generally caused by pumping. In this situation, the water table recovers when the supply is replenished.

Subsidence is one of the dramatic results from overpumping. As the water table declines, water pressure is reduced. This causes the fine particles that held water to become compacted. In addition to permanently reducing storage capacity, the land above the aquifer can sink ... from a few inches to several feet ... causing a sinkhole. This can damage property and fields.

Threats to quality.
Inorganic compounds, pathogens and organic compounds can harm water quality, affecting the health of humans, fish and wildlife. Scientists continually learn more about contaminants, their sources and prevention practices.

What's water quality?
Each state is responsible for designating uses for groundwater, surface waters, wetlands, etc. Designated uses include fishable, swimmable, drinkable, recreational, agricultural, aquatic life, and more. Each state is also responsible for developing water quality standards for each use.

For example, while most rivers are designated to be used for fishing, a few river sections are designated to be used for drinking water.

The same is true for groundwater. Uses are defined and standards identified. A few groundwater uses and standards are:

Note that, for most groundwater uses, quality and quantity are important, while for surface water uses, generally quality is the primary concern (with the realization the quantity affects quality).

Inorganic Compounds include all compounds that do not contain carbon. Nutrients (nitrogen and phosphorus) and heavy metals are two examples.
Nitrates can cause problems in drinking water or marine waters
Phosphorus can reduce uses of fresh surface waters
Heavy metals include selenium, arsenic, iron, manganese, 
       sulfur, cadmium and chromium and others. Some (iron,
       manganese and arsenic) occur naturally

Pathogens, including bacteria and viruses, have been credited with causing more than 50% of the waterborne disease outbreaks in the U.S. Cryptosporidium Parvum and Giardia both commonly cause illnesses when consumed.

Organic Compounds include Volatile Organic Compounds (VOCs) like benzene, toluene, xylene; semi-volatile compounds like napthaline and phenol; PCBs and pesticides.

Potential sources.
Point sources are easily identified because they usually come out of a "pipe." Examples include sewage treatment plants, large injection wells, industrial plants, livestock facilities, landfills, and others.

Regulated by the state water quality agency and the U.S. EPA, point sources are issued a National Pollutant Discharge Elimination System (NPDES) permit when they meet regulations.

Many point sources were established generations ago, before the threat they posed was understood. Some of these sources have been "grandfathered" into compliance with some regulations. Thus, you may find some point sources located in areas that would be considered inappropriate now.

Nonpoint sources refer to widespread, seemingly insignificant amounts of pollutants which, cumulatively, threaten water quality and natural systems.

Examples of nonpoint sources include septic systems, agriculture, construction, grazing, forestry, recreational activities, careless household management, lawn care, and parking lot and other urban runoff.

Nonpoint sources are not required to have a permit. Individually, each may not be a serious threat, but together they may be a significant threat.

Other sources that aren't classified under point or nonpoint sources include underground petroleum storage systems and many large and small businesses like dry cleaners, restaurants, and automotive repair shops. Although a large number of underground storage tanks have been removed or upgraded, a significant number remain. Businesses can threaten groundwater with a wide variety of potentially contaminating substances.

Management Approaches.

The watershed management approach.
A quick review of key components of the local, voluntary watershed approach to protecting natural resources will help you evaluate groundwater management approaches and how they may be used in your particular situation. The most critical component to the watershed management approach is the involvement and consensus of all key stakeholders (or organizations representing them) at each step in the process. Other key components include:
Assess natural resources-soil, water (including groundwater), 
       air, plants, animals, and people.
Identify and prioritize problems.
Develop measurable objectives-based on local environmental,
       economic and social goals.
Identify and agree upon strategies for reaching objectives.
Implement strategies and assess results.

Some of the activities, as they pertain to groundwater, are described in this guide. For example:
Determing boundaries of the groundwater and watershed areas
       is typically part of assessment.
Discussing existing and future uses of water is part of setting
       goals.
Defining pollutants and sources is part of assessment, goal
       setting and solution identification.
Understanding various tools is part of identifying and
        implementing solutions.

Existing groundwater programs.
Over the past 20 years many federal and state programs have been developed to improve management of groundwater. Four of the most useful can also easily be incorporated into your watershed plan. These include:
Comprehensive State Groundwater Protection Program
Sole Source Aquifer Program
Source Water Protection Program
Wellhead Protection Program

These approaches can be used in a complementary fashion to manage all resources, including groundwater, for multiple uses-ranging from human consumption to industrial processes to maintaining ecological integrity within a wetland.

Comprehensive State Groundwater Protection Program is a statewide program that looks at groundwater's uses, including drinking water, and its role in sustaining the health of surface waterbodies (rivers, streams, wetlands, marshes).

The Sole Source Aquifer Program, Source Water Protection Program, and Wellhead Protection Program all are intended to protect a drinking water supply. The programs generally are compatible with the Comprehensive State Groundwater Protection Program, but are applied to very defined geographic areas...
The Sole Source Aquifer Program applies to the aquifer
       boundaries.
The Source Water Protection Program applies to water that
       drains into a reservoir (used as a drinking water source) or 
       intake.
The Wellhead Protection Program applies to defined wellhead
       areas.

Special issues.
Although groundwater programs are often used within the watershed framework, there are some issues that may arise as you attempt to integrate them. These issues have been listed to simply make you aware of them. Each is best addressed through cooperation and consensus.
Water quality use designations often do not reflect the
       presence of groundwater intakes for drinking water.
Water quality criteria and drinking water maximum contaminant
       levels (MCLs) often are not consistent in terms of chemical
       specific values and parameters.
Minor dischargers and permitted management measures under
       the NPDES program may not sufficiently reduce the risk to
       drinking water intakes.
Where agriculture activities are reducing drinking water quality,
       changes in management practices may or may not take a long
       time to result in water quality improvements depending on
       weather, geography etc.
Source water areas for groundwater drinking supplies (wellhead
       areas) generally do not coincide with surface water drainage
       areas.
Long-term drinking water treatment may be necessary for 
       certain public water supply systems because of the nature of 
       the contaminant sources and the size of the contributing area.

Additional information

State Sources
Public Health Agency
Water Quality Agency
Environmental Agency

Local Sources
Natural Resource Conservation Service
Conservation District
Extension Office
Water Utility

Management Tools.
There are many, many tools that can be used to manage groundwater resources. Before discussing this list of possible tools, your partnership will benefit from designating current and future uses of groundwater. Does it feed a lake used for swimming? Will urban growth require it to be used for drinking water?

With this in mind, your partnership might want to use this list of tools as a starting place for discussion. You may use several or may decide on another viable option.

Zoning: Regulations are used to segregate different, and possibly conflicting, activities into different areas of a community. This approach can be limited in its ability to protect groundwater due to "grandfather" provisions.

Overlay Water Resource Protection Districts: Similar to zoning regulations in their goals of defining the resource, these ordinances and bylaws map zones of contributing boundaries and enact specific legislation for land uses and development within these boundaries.

Prohibition of Some Land Uses: These are not typically considered very creative tools. However, prohibition of land uses such as gas stations, sewage treatment plants, landfills, or the use/storage/transport of toxic materials is a first step towards the development of a comprehensive groundwater protection strategy.

Special Permitting: The special permitting process can be used to regulate uses and structures that may potentially degrade water and land quality.

Large Lot Zoning: Large lot zoning seeks to limit groundwater resource degradation by reducing the number of buildings and septic systems within a groundwater protection area.

Eliminating/Modifying Septic Systems: Septic system problems can be reduced or eliminated by extending or developing community sewage treatment systems. Other options include specifying minimum design requirements like mound systems.

Transfer of Development Rights: A government entity prepares a plan designating land parcels from which development rights can be transferred to other areas. This allows land uses to be protected (i.e. for a gas station) while assuring that these uses are outside sensitive areas.

Growth Control/Timing: Growth controls are used to slow or guide a community's growth, ideally in concert with its ability to support growth. One important consideration is the availability of groundwater.

Performance Standards: This assumes that any given resource has a threshold, beyond which it deteriorates to an unacceptable level. Performance standards assume that most uses are allowable in a designated area, provided that the use or uses do not and will not overload the resource. With performance standards, it is important to establish critical threshold limits as the bottom line for acceptability.

Underground Storage Tanks: Three additional protection measures are often adopted to enhance local water resource protection. They include:
Prohibit new residential underground storage tanks
Remove existing residential underground storage tanks
Prohibit all new underground storage tank installation in
       groundwater and surface water management areas

Septic System Maintenance: Septic system maintenance is frequently overlooked. Many times the system will not function properly, causing "breakout" of solids at the surface, which can lead to bacterial contamination. In addition, when systems fail, any additives used can become contaminants.

Land Donations: Land owners are often in the position of being able to donate some land to the community or to a local land trust.

Conservation Easements: Conservation easements allow for a limited right to use the land. Easements can effectively protect critical lands from development.

Purchase Lands: Many communities purchase selected parcels of land that are deemed significant for resource protection.

Well Construction/Closure Standards: Wells are a direct conduit to groundwater. Standards for new well construction, as well as identification and closure of abandoned wells, can prevent groundwater from being contaminated.

Groundwater IQ Questions and Answers.

Test your groundwater IQ.

1. Which ways can groundwater move?
a. Up
b. Down
c. Sideways
d. All of the above

2. How is the speed of groundwater movement measured?
a. Feet per day
b. Feet per week
c. Feet per month
d. Feet per year

3. How is stream flow usually measured?
a. Feet per second
b. Feet per minute
c. Feet per hour
d. Yards per hour

4. What determines how fast groundwater moves?
a. Temperature
b. Air pressure
c. Depth of water table
d. Size of materials

5. Can the water table elevation change often?
a. Yes
b. No

6. Does aquifer storage capacity vary?
a. Yes
b. No

Answers:

1. d. All of the above
Although most movement is lateral (sideways), it can move straight up or down. Groundwater simply follows the path of least resistance by moving from higher pressure zones to lower pressure zones.

2. d. Feet per year
Groundwater movement is usually measured in feet per year. This is why a pollutant that enters groundwater requires many years before it purifies itself or is carried to a monitored well.

3. a. Feet per second
Water flow in streams/rivers is measured in feet per second.

4. d. Size of materials
Coarse materials like sand and gravel allow water to move rapidly. (They also form excellent aquifers because of their holding capacity.) In contrast, fine-grained materials, like clay or shale, are very difficult for water to move through. Thus, water moves very, very slowly in these materials.

5. a. Yes
Water table elevations often fluctuate because of recharge and discharge variations. They generally peak in the winter and spring due to recharge from rains and snow melt. Throughout the summer the water table commonly declines due to evaporation, uptake by plants (transpiration), increased public use, industrial use, and crop, golf course and lawn irrigation. Elevations commonly reach their lowest point in early fall.

6. a. Yes
Just like the water level in rivers and streams, the amount of water in the groundwater supply can vary due to seasonal, weather, use and other factors.

Sources of information.
To start down the road toward an effective local watershed partnership, you may want to read some of these other guides from the Conservation Technology Information Center by calling 765-494-9555. See our catalog to order this online.

Building Local Partnerships
Getting to Know Your Watershed
Leading and Communicating
Managing Conflict
Putting Together a Watershed Plan
Reflecting on Lakes
Wetlands: A Key Link in Watershed Management
Guide to Information and Resources
Nonpoint Source Water Quality Contacts

You may also find the following publications helpful. Some of these information sources were used to develop this guide.

Layperson's Guide to Ground Water, 1993, Water Education Foundation, 717 K Street, Ste. 517, Sacramento CA 95814.

A Primer on Ground Water, US Geological Survey Open-File Reports Section, Federal Center, Box 25425, Denver CO 80225.

Citizen's Guide to Ground Water Protection, April 1990, EPA 440/6-90-004, US EPA Office of Water, 401 M St. SW, Washington, DC 20460. Order from NCEPI, 11029 Kenwood Rd. Bldg. 5, Cincinnati, OH 45242. Fax: 513-489-8695.

Managing Ground Water Contamination Sources in Wellhead Protection Areas: A Priority Setting Approach, October 1991, EPA 570/9-91-023, US EPA, 401 M St. SW, Washington, DC 20460. Order from NCEPI, 11029 Kenwood Rd. Bldg. 5, Cincinnati, OH 45242. Fax: 513-489-8695.

National Assessment of Contaminated Ground Water Discharge to Surface Water, September 30 1993, US EPA Office of Ground Water and Drinking Water, Groundwater Protection Division, 401 M St. SW, Washington DC 20460. Order from NCEPI, 11029 Kenwood Rd. Bldg. 5, Cincinnati, OH 45242. Fax: 513-489-8695.

A Review of Methods for Assessing Nonpoint Source Contaminated Ground Water Discharge to Surface Water, April 1991, US Environmental Protection Agency, Office of Water, 401 M St. SW, Washington, DC 20460. Order from NCEPI, 11029 Kenwood Rd. Bldg. 5, Cincinnati, OH 45242. Fax: 513-489-8695.

Pesticide and Ground Water Strategy, EPA 21T-1002, US EPA, 401 M St. SW, Washington, DC 20460. Order from NCEPI, 11029 Kenwood Rd. Bldg. 5, Cincinnati, OH 45242. Fax: 513-489-8695.

National Water Quality Inventory, 1994 Report to Congress, December 1995. EPA 841-R-95-005. U.S. Environmental Protection Agency, Office of Water, 401 M St. SW, Washington, DC 20460. Order from NCEPI, 11029 Kenwood Rd. Bldg. 5, Cincinnati, OH 45242. Fax: 513-489-8695.

Assistance is available... Contact your local or state:
Natural Resource Conservation Service
Conservation District
Extension Office
Water Utility
Water Quality Agency

About this guide...
One of a series, this guide is intended for the layperson who wants to organize a local, voluntary partnership to protect their watershed. This series will not solve all your problems. It's our intention to provide guidance for going through the process of building a voluntary partnership, assessing your watershed, developing a watershed management plan and implementing that plan.

Because the characteristics of each watershed are unique, you may wish to select and use the portions of this and other guides that are applicable to your particular situation.

Although the series is written for watershed-based planning areas, the ideas and process can be used for developing plans (such as wildlife areas) to match the multiple concerns of the partnership.

Regardless of the area or issues, remember a long-term, integrated perspective-based on a systematic, scientific assessment-can be used to address more than one concern at a time.

Special thanks...
Special thanks to Nancy Phillips, Environmental Scientist, Hollis, New Hampshire, who dedicated long hours to writing this guide. Without her help this guide would not be possible.

Stephen Adduci, Studio d'adduci, Los Galos, California, provided the colorful illustrations used throughout the guide.

Special thanks also go to the professionals (below) who carefully reviewed this guide. Their experience and thoughtful guidance enriched it. Their time and insight is deeply appreciated.

Jerry Bernard
USDA Natural Resources Conservation Service
Bridget Chard
Cass County (MN)
Tom Davenport
US EPA, Region 5, Water Division
Nancy Garlitz
USDA Natural Resources Conservation Service
Susan Kaynor
Environmental Consultant
Frank Sagona
Tennessee Valley Authority
Susan Seacrest
The Groundwater Foundation
John Simons
US EPA, Office of Groundwater & Drinking Water
Perri Standish-Lee
Brown and Caldwell
Ceceilia Stetson
Minnesota Pollution Control Agency
Joan Warren
US EPA, Office of Wetlands, Oceans and Watersheds
Darlene Vogel
County of Erie (NY)

The Know Your Watershed campaign is coordinated by the Conservation Technology Information Center (CTIC), a nonprofit public/private partnership dedicated to the advancement of environmentally beneficial and economically viable natural resource systems. It provides information and data about agricultural and natural resource management systems, practices and technologies. The center was established in 1982 under the charter of the National Association of Conservation Districts.

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