Evaluate different ways the water can become contaminated

Evaluate different ways the water can become contaminated

Groundwater and Surface Water Interactions

Investigation Manual

ENVIRONMENTAL SCIENCE

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GROUNDWATER AND SURFACE WATER INTERACTIONS

Overview Clean drinking water is vital for all human life. In this lab, students will learn how freshwater sources interact through the natural processes of the hydrosphere (all the water on the planet) and what happens to drinking water supplies when our planet becomes altered by human activities. Students will design models of different scenarios that affect the earth’s surface water and groundwater. The models will demonstrate overconsumption and drought situations, along with water conditions influenced by point and non-point source pollution, to examine human-induced effects on the earth’s water cycle.

Outcomes • Describe the importance of freshwater availability to the health of

human populations. • Construct multiple groundwater and surface water models and

analyze different ways the water can become contaminated. • Distinguish between point and non-point pollution sources and

explain the impact of each. • Recognize the interconnectedness of groundwater and surface

water in the environment.

Time Requirements Preparation …………………………………………………………… 15 minutes Activity 1: High Withdrawal and Recharge ………………… 45 minutes Activity 2: Point Source Pollution …………………………….. 15 minutes Activity 3: Non-Point Source Pollution ……………………… 45 minutes

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Table of Contents

2 Overview 2 Outcomes 2 Time Requirements 3 Background 7 Materials 8 Safety 8 Preparation 9 Activity 1 10 Activity 2 11 Activity 3 13 Submission 13 Disposal and Cleanup 14 Lab Worksheet

Background The hydrosphere encompasses all the water on the planet. It includes freshwater and saltwater; liquid, solid, and vapor; and water that is both above ground and underground. All of these different sources of water interact and transform into one another through processes within the biogeochemical cycle known as the hydrological or water cycle (see Figure 1). Water falls to the earth as precipitation and runs off the land’s surface, infiltrates the ground, or evaporates from surface waters such as oceans, lakes, and rivers. The evaporated water vapor condenses in the clouds and falls to the earth over time as precipitation. Then the process begins again. The water that has infiltrated the ground, known as groundwater, is located in and below the water table, which is the top layer of the soil in which groundwater fills

most of the pores. In the water table, water is able to enter the ground through unsaturated surface soil voids, filling the soil below this level due to natural gravitational pull. With this natural movement of water, the hydrosphere continuously cycles all phases of water to all parts of the earth.

While water encompasses approximately 70% of Earth’s surface, freshwater, which accounts for only 3% of Earth’s water, is the only type of water that is readily accessible for human consumption. However, of that 3%, just under 1% is readily accessible, with the remaining water being held in Earth’s icy regions, which include glaciers and polar ice caps. This is known as the cryosphere, or the frozen portion of the hydrosphere (see Figure 2).

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Figure 1.

GROUNDWATER AND SURFACE WATER INTERACTIONS

Background continued

Groundwater Freshwater available for human use is made up of surface water and groundwater. When precipitation falls from the atmosphere to the earth, it becomes part of the environment by either washing across the land and into bodies of water or by percolating through the surface of the soil. Here, it can be taken up by plants or filtered deep into the ground. In the latter case, this surface water enters the ground through areas known as recharge zones. Water enters these unsaturated zones on the surface of the land by the natural pull of gravity. The porosity of a material is a measure of the void spaces in the rocks and soil, and the ability of water to pass through those void spaces is known as permeability. This water now enters the groundwater system and saturates the ground beneath. People rely on these zones to recharge aquifers. Through the use of wells, people can supply water to their homes.

Deeper into the ground, multiple layers of unsaturated and saturated soil of many different pore sizes and material types exist. Some of these layers are permeable, whereas others are impermeable, which means that water cannot easily pass through them. Many types of ground consist of permeable materials, like rocky sediment, fine sand, or soil. Others are made of less permeable materials that impede the percolation of water, such as claylike dirt, thicker sand, or man-made structures such as paved streets and sidewalks. The types of material that make up the consistency of the ground impacts the ability to access the groundwater.

Groundwater can sometimes be accessed by pumping wells placed in aquifers. Aquifers are underground basins from which water can be removed at a reasonable rate, with the most ideal aquifers containing many pore spaces for water storage. However, the size, depth, and amount of water within an aquifer can vary greatly, making the process of extracting groundwater from an aquifer variable as well. While most of Earth’s accessible freshwater is held in the ground, much of it is too deep for humans to access.

Surface Water The small amount of remaining freshwater accessible for human use is made up of all the surface water from lakes, rivers, and ponds as well as the water vapor in the atmosphere (see Figure 2). There are many regions that don’t have access to groundwater sources and must rely on reservoirs, such as natural and man-made lakes, as a source of drinking water. With surface water making up a small

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67% Saltwater 30% Land 2% Frozen Water 1% Groundwater/Surface Water/

Atmosphere

Figure 2.

percentage of freshwater worldwide, events such as droughts or excessive withdrawal from reservoirs within these areas can cause rapid depletion of vital water for highly populated, metropolitan areas that rely on these sources of drinking water. Also, many human-induced factors can lead to inaccessible freshwater. Impervious surfaces such as roads, parking lots, and buildings can limit the quality of accessible water by creating a surface for the runoff of pollutants into nearby bodies of water. Additionally, most water that is withdrawn from a waterway or aquifer is returned to the environment, but some is taken up by plants and animals or lost to evaporation, adding another source of inaccessible freshwater for humans.

To understand how surface water and groundwater affect each other, let’s investigate some of these same scenarios but from a different perspective. For instance, impervious surfaces not only negatively affect the quality of surface water, but they can also block access to and pollute groundwater sources. Also, when excessive water is withdrawn from a groundwater well that is pumping water stored in the water table, surface water levels can be reduced greatly and can ruin the quality of the water. Similarly, pumping water from a freshwater reservoir can lower groundwater levels and possibly cause contamination.

On the positive side, if there is sufficient rainfall in an environment, the water could overflow the land, feeding into marshes, rivers, or lakes. In contrast, if surface water receives excess rainfall, it could run onto and infiltrate the land to become groundwater. All in all, to truly understand the availability of water in a

region, recognizing the interconnectedness of groundwater and surface water is of vital importance.

Human-Induced Actions that Affect the Water Cycle There are many ways to limit or contaminate the freshwater available to humans. The overload of substances that are harmful to the environment, known as pollution, is a major issue affecting today’s freshwater supply. It is easier to determine the origin of certain pollutants than others; in turn, it is easier to prevent certain pollutants from occurring in the future than others. Point source pollution is pollution that can be tracked to one specific source. This source of pollution is identifiable and able to be limited if proper action is taken to control the pollutant source. A pipe from a wastewater treatment plant discharging waste into a water source (see Figure 3) and a person dumping gasoline into a water supply (such as a lake)

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Figure 3.

GROUNDWATER AND SURFACE WATER INTERACTIONS

Background cont