Water resources consist of two categories: groundwater and surface water.
Groundwater refers to all the water found below the ground’s surface.
While most groundwater comes directly from rainwater, some comes from seepage from the sides and bottoms of lakes and streams. The water usually passes down through a layer of partially saturated material to a zone of saturation in which all the pore spaces between the soil or rock particles fill with water. The water table is the upper level at which this saturation occurs. An aquifer is the area where the groundwater resides. Aquifers vary widely in size, depth, and use. Some cover hundreds of miles and are the main supply of drinking and irrigation water, such as the Ogallala Aquifer in the Great Plains.
The supply of groundwater depends upon a balance between the amount of water entering the ground and the amount being withdrawn. Substantial increases in impervious surfaces associated with urban land development can reduce precipitation’s ability to recharge the aquifers. Excessive pumping, especially in areas prone to drought or highly seasonable precipitation, can cause wells to run dry, increase the concentration of dissolved minerals, cause saltwater intrusion if near the ocean, and cause land subsidence. Changes in precipitation quantity and frequency due to climate change can further exacerbate these problems.
The depth of the water table can vary tremendously annually and seasonally depending on the amount of rainfall. High water tables can result in basement flooding and surface puddles. Discharge from poorly designed, installed, or maintained septic systems to drinking water wells can cause health hazards.
Some areas have experienced ground subsidence due to the pumping of groundwater and the dewatering of the underground strata and aquifers. In Gulf Coast communities, such as New Orleans, excessive pumping has lowered the ground level and made the area more prone to coastal flooding.
In many types of superficial geological formations, groundwater quantity and quality are directly related to the quality and presence of surface waters. Excessive well pumping can induce infiltration from streams and ponds, causing surface water levels to drop. If these surface waters are polluted, groundwater quality degrades. Often, groundwater flows discharge to streams. Polluted groundwater can degrade the quality of otherwise unaffected surface waters.
Surface water ranges from very large rivers and lakes to small ponds and streams.
Surface water plays an important role in nearly every community as a source of drinking water, a means of transportation, a recreational resource, a source of water for irrigation, and a fishery.
Urban development can, however, have a serious negative impact on water quality. Surface waters, chiefly rivers and large lakes, frequently suffer from the effects of pollution that factories, urban sewerage systems, power plants, and agricultural runoff generate. Degraded surface water quality can have short-term and long-term human health implications, can affect aquatic habitats and species, and can have aesthetic and olfactory consequences.
While water quality problems may be due to point sources such as effluents from sewerage treatment plants and industrial waste outfalls, non-point sources such as new commercial and residential developments can also adversely affect surface water quality. The chief source of such pollution is from urban runoff, primarily when rain carries oil and gasoline from impervious surfaces such as streets, parking lots, and sidewalks into surface water.
Landscaped areas treated with insecticides and fertilizer can also introduce polluted runoff into surface water. Fertilizer runoff, a common problem in surface waters with proximity or navigable connection to agricultural communities, can cause nutrient loading which can lead to toxic algal blooms (blue-green algae). These blooms can decimate native fish communities, make the water unsafe for swimming or recreational purposes, and interfere with drinking water resources. The frequency and severity of such blooms may also increase as the world’s climate warms. While most common in inland waters, toxic algal blooms have also occurred in coastal areas, including the Chesapeake Bay. Also, failing septic systems and other sources of polluted groundwater (landfills and waste disposal areas) can seep untreated sewage and other wastes to surface waters, which can further contribute to toxic algal blooms and other water quality concerns.
- Is the site subject to rapid water withdrawal problems that change the depth or character of the water table or aquifer? Are there many wells that pump large quantities of water from the water table near the proposed project site? (Consider both current and future conditions that are likely due to increased water stress from climate change.)
- Will the project use a septic system? If so, is the system in proximity to sensitive natural receptors (e.g., wetlands) that could be adversely impacted by the design or location? Is there a large variance in the water table? (A high seasonal water table can prevent the proper functioning of septic tank drain fields.)
- Are there visual or other indications of water quality problems on or near the site (e.g., algal blooms or state listing as an impaired stream/waterway)? Will the proposed project(s) maintain, diminish, damage, or destroy the riparian buffer (e.g., a natural wooded buffer adjacent to a stream)?
- Will the project involve a substantial increase in impervious surface area? Does the design include runoff control measures or permeable surfaces?
- Will the project substantially reduce groundwater recharge due to an increase in impervious surface area? If so, could the project affect sensitive groundwater-dependent features (e.g., rare wetlands)? If yes, does the design include appropriate measures to promote groundwater recharge?
- Is the project located in a state or locally designated sensitive watershed area or the watershed of a particularly sensitive natural area (e.g., a unique wetland)? If so, what run-off control measures does the design include (e.g., the storm-year design is increased from 10 years to 25 years, buffers are placed along surface waters)?
- Will the project involve the discharge of non-sewage pollutants (i.e., agricultural fertilizer, insecticides, road salts, etc.) into surface water bodies? If so, will it meet state, federal, and other applicable standards?
- Does the project limit the access to or quality of water for downstream communities?
Review the project plans to determine factors such as water supply source location and type (municipal or on-site system; groundwater or surface water source), septic or municipal sewerage for wastewater, the depth of foundations, and the amount of proposed paved area. The regional office of the EPA can provide information on appropriate compliance procedures.
The following resources can provide data on groundwater conditions in the area:
- U.S. Army Corps of Engineers (USACE) Groundwater Modeling System
- USGS or State Geological Survey Hydrologic Maps/Reports
- USGS Groundwater Watch
- USGS Topographic Quadrangle Maps
- USDA Natural Resources Conservation Service (NRCS) Surveys
Field observation can sometimes indicate potential groundwater problems. Look for evidence of groundwater, especially the presence of groundwater-fed springs, seeps, and perennial streams. In addition, strips of distinctive vegetation, particularly deep-rooted plants, may indicate the presence of subsurface water in semi-arid areas. The United States Army Corps of Engineers (USACE) has developed a National Wetland Plant List, which helps identify present plant species that suggest a high probability of such water resources.
The impact evaluation consists of estimating the extent to which existing groundwater conditions are a hazard to the project, its users, and others, as well as the extent to which the proposed project will alter groundwater resources at the site and in surrounding areas.
Review the project plans to determine if paved areas are likely to generate polluted runoff into surface water. A review of proposed landscaping, drainage, and grading plans, along with a review of any wastewater treatment and water source facilities that are not a part of a municipal system can indicate potential problems.
- USGS Topographic Quadrangle Maps provide data on the location of surface water bodies.
- USGS Water Resources of the United States Maps and GIS Data
- Areawide Water Quality Management Plans (“208 Plans”) prepared by local agencies under this EPA program have information on local water quality conditions and plans for remedy.
Field observation can help indicate existing water quality problems on or near the site, such as the presence of odor, foam, or debris on surface water. Also, water discoloration and the existence of heavy industry or agriculture nearby can indicate problems. In severe circumstances, widespread death of marine organisms (“fish kills,” which can include non-fish marine animals) is a clear indication of surface water pollution and is primarily associated with toxic algal blooms, such as the toxic red tide algal blooms in Florida in 2018.
The Federal Water Pollution Control Act (33 U.S.C. §1251 et. seq.), as amended in 1972 as the Clean Water Act and again amended in 1977, defines water quality criteria, permit requirements, and compliance dates, and establishes a program of water quality planning and monitoring. State and local standards exist in most communities particularly with respect to on-site sewerage disposal (e.g., septic systems). See the Waste Water impact category factor for further discussion of water pollution abatement requirements and techniques.
The Safe Drinking Water Act of 1974 (42 U.S.C. 300 et seq.), protects sole-source aquifers (SSA). Under this Act, projects which might contaminate an aquifer that the EPA has designated as the sole source of drinking water for that area cannot receive federal assistance. In addition to mandatory compliance with the SSA provision at 24 CFR 58.5(d) or 24 CFR 50.4(d), environmental review preparers are encouraged to consider whether the project site may come to rely on an SSA in the future. As climate change affects local precipitation patterns, additional localities may increasingly rely on an aquifer for their drinking water, potentially increasing the number of aquifers receiving SSA protection. A current Map of SSA Locations can be accessed through the Environmental Protection Agency's (EPA’s) website.
Contact local public health agencies and sewerage treatment facility operators for data on existing conditions and plans. The Wild and Scenic Rivers Act of 1968 (16 U.S.C. 1271 et seq.) also applies in some localities. Additionally, as part of the Clean Water Act, the National Pollutant Discharge Elimination System (NPDES) (33 U.S.C. § 1342) regulates point sources, such as wastewater treatment plant outfalls, and non-point sources, such as development projects that could discharge pollutants into water features. The EPA regulates construction projects disturbing less than one acre of land under the Small Residential Lot NPDES Program. These projects, as well as larger-scale projects, require a Stormwater Pollution and Prevention Plan (SWPPP) to appropriately manage stormwater during project development.
The objective of impact mitigation is two-fold:
- To reduce the polluted water hazards on the project
- To reduce the project's contamination of local surface waters
Mitigation measures vary with the specific problem and site features. In areas where pumping poses a problem, limit the amount of pumping to safe annual yields. In aquifer recharge areas, limit the number of paved surfaces or use porous surfaces on roads and parking lots; however, porous road surfaces are practical only where traffic is light. In areas requiring impervious surfaces, angle and orient the surfaces so that rain does not carry potential pollutants (i.e., oil, road salts, etc.) into aquifer recharge areas.
Implementation of the required SWPPP during development minimizes the potential for contaminants (sediments, oil, fertilizer, etc.) to run off-site into surface water resources, or percolate into groundwater resources when it rains.
In locations with high water problems, design underground spaces such as basements to withstand the pressure of groundwater and to pump out seepage. Also, wastewater disposal systems may require special design to function properly in high water table conditions.
In many cases, the only way to remedy the overloading of public wastewater treatment facilities is to expand those facilities. Old or poorly built sewers which permit seepage may need reconstruction. Proper construction of on-site facilities helps mitigate potential adverse effects. Consider including in the site design runoff control measures such as on-site storage or routing to settling basins so that the water is below pollutant thresholds prior to discharge into surface waters.