SOURCE-WATER PROTECTION

9.2 SOURCE-WATER PROTECTION

In the United States, all states are required to develop source-water protection plans (SWPPs) to protect public water supplies from contaminant sources within the catchment area of drinking-water intakes. The catchment area of a drinking-water intake is typically the same as the watershed associated with the water body containing the intake, and this catchment area is called the source-water protection area (SWPA) of the intake. Key com- ponents of SWPPs are as follows:

1. Delineation of the source-water protection area. Water-supply intakes can be either surface-water or ground-water intakes, and the delineation of the corresponding protection area depends on the type of intake.

For ground-water systems, available information about ground-water flow and recharge is used to determine the source-water protection area. Ground-water intakes typically con-

sist of wells (vertical or horizontal) or infiltration galleries, and SWPAs are typically delin- eated using either distance, ground-water flow boundaries, time of travel, drawdown, or assimilative capacity. Water-supply wells very close to surface-water bodies can be classified as Ground Water Under the Direct Influence of Surface Water (GWUDI) and

WATERSHEDS

FIGURE 9.3 Wellhead protection: (a) sign; (b) wellheads. [(a) From South Dakota DNR, 2005; (b) from USGS, 2005k.]

treated as surface-water sources for delineation purposes. For ground-water intakes, source-water protection areas are commonly referred to as wellhead protection areas, and an example of a sign identifying a wellhead protection area and wellheads are shown in Figure 9.3. Wellhead protection areas are typically divided into three zones, with an inner zone given the most protection, an intermediate zone where detailed contaminant invento- ries are conducted and best management practices required, and an outer zone where the potential impact of contaminants on drinking water intakes is regarded as minimal. The inner zone is usually delineated using a distance criterion, the intermediate zone (also known as the inventory region) delineated by time of travel, and the outer zone delineated by a hydrogeologic boundary.

Surface-water systems draw water from a stream, river, lake, or reservoir; and the land area in the watershed upstream of the intake must generally be delineated. It is common to divide the watershed area into the following zones: (1) an inner zone closest to the intake where most types of contamination sources may be found to be significant; and (2) an outer zone that includes more distant areas. The inner zone is typically delineated by an upstream distance or travel time (based on the average annual high flow) plus a minimum buffer width, while the outer zone is typically delineated by the watershed boundary.

2. Inventory of the actual and potential sources of contamination. Sources of pollutants that could potentially contaminate the water supply must be identified. This inventory usu-

ally results in a list and a map of facilities and activities within the delineated area that could release contaminants into the watershed of the river or lake being used for water supply. Some examples of potential pollutant sources include urban runoff from streets and lawns, farms and other entities that apply pesticides and fertilizers, and sludge-disposal sites.

3. Determination of the susceptibility of the water source to contamination. Inventory results are combined with other relevant information to estimate the likelihood of contam- ination of the water supply by potential sources of contamination. Susceptibility is defined by USEPA as “the potential for a public water supply to draw water contaminated by inventories sources at concentrations that would pose concern” (USEPA, 1997c). Susceptibility determinations are typically based on the fate and transport of contaminants within the SWPA. The use of prescribed buffer zones and travel times are the most com- mon approaches to controlling the susceptibility of drinking-water intakes to contamina- tion (USEPA, 1997a, b). Buffer zones can be created through utility ownership or usage

WATERSHED-GENERATED POLLUTANT LOADS

restrictions, thereby providing for filtration of runoff through natural vegetation. No stan- dards for the creation of buffer zones around surface-water sources exist (AWWA, 1990), but the required buffer areas take into account exposure to contamination and the degree of treatment provided by the buffer. Wetlands are frequently used as buffers for water- supply intakes, and preservation of wetlands maintains the natural filtration and cleansing provided by these critical areas. In Florida, potential contaminant sources located within a source water protection area are evaluated and ranked as posing a low, medium, or high threat of contaminant release to the source water protection area. This analysis includes an evaluation of the likelihood of a release affecting the public water system.

4. Releasing the results of the assessments to the public. The information contained in the source-water protection plan must be is summarized for the public. Such summaries help communities better understand the potential threats to their water supplies and iden- tify priority needs for protecting the water from contamination. Local communities, work- ing in cooperation with local, regional, and state agencies, can use the information in the source-water protection plan to create a broader source-water protection program to address current and future threats to the quality of their drinking-water supplies.

Communities typically use a wide array of source-water protection methods to prevent contamination of drinking-water supplies. One management option involves regulations such as prohibiting or restricting land uses that may release contaminants in critical source-water protection areas. Along with regulations, many communities hold local events and distribute information to educate and encourage citizens and businesses to recy- cle used oil, limit their use of pesticides, participate in watershed cleanup activities, and a variety of other prevention activities. Another approach to source water protection is the purchase of land or the creation of conservation easements to serve as a protection zone for the drinking-water source.

Statutory drinking-water standards apply to public water systems, which provide water to at least 15 connections or 25 persons at least 60 days out of the year (most cities, towns, schools, businesses, campgrounds, and shopping malls are served by public water sys- tems). The 10% of Americans whose water comes from private wells (individual wells serving fewer than 25 persons) are not protected by these statutory drinking-water stan- dards. People with private wells are responsible for making sure that their own drinking water is safe. Bottled water is regulated by the U.S. Food and Drug Administration as a food product and is required to meet standards equivalent to those set by the U.S. Environmental Protection Agency (USEPA) for drinking water.