1.2: Source Water Quality
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Learning Objectives
After reading this chapter you should be able to identify and explain the following:
- The Earth’s Hydrologic Cycle
- Sources of groundwater
- Sources of Surface Water
- Water math: Area and Unit Conversions
A very finite amount of water on our planet (0.34%) is available to treat for human consumption. Knowing where the water comes from assists certified operators in treating raw source water to make it potable. Newer technology has been developed to treat salinized or salty water found in the ocean. These treatment methods are still extremely expensive and not widely accessible. Supplying water to the public is an extremely important function in society as water is the basic building block of life. Because water quality is of the utmost importance new regulations and water quality standards are continually changing and evolving to make sure the public has safe sources of drinking water. The first drinking water standards were written in the Safe Drinking Water Act (SDWA), which was signed into law by President Ford in 1974. Throughout the text, new concepts will be introduced and an acronym will be given and used subsequently. You are going to learn to love acronyms if you become a certified operator. We use them quite frequently!
The Hydrologic Cycle
The Hydrologic cycle is the continual movement of water on the surface of the planet. The water moves above, below, and across the Earth’s surface as a liquid, gas, or solid. The 12 elements of the hydrologic cycle are defined as follows:
- Evaporation—Water moves in the gas state from the Earth’s surface to the atmosphere
- Transpiration—Water moves in the gas state from plants to the atmosphere.
- Advection—Water in the gas state moves through air currents in the atmosphere
- Condensation—Water vapor converts from gas to liquid state in the form of water droplets.
- Precipitation—Water as a liquid and/or solid falls from the atmosphere. We commonly refer to this as rain, snow, sleet, and hail.
- Interception—Water in the liquid state that is captured by plants
- Infiltration—Water in the liquid state that soaks into the surface of the ground. This will be what is known as groundwater which will be detailed later in this chapter.
- Subsurface Flow—Water in the liquid state flows below the Earth’s surface. The movement is generated by gravity and obstructions below the surface of the Earth.
- Runoff—Water in the liquid form travels to bodies of water. This would include the ocean, lakes, rivers, and streams. This is also known as surface water which will be detailed more later in this chapter.
- Channel flow—Water in the liquid form that flows from small channels into rivers and streams
- Storage—Water is naturally stored in liquid form in lakes, ponds, wetlands, and groundwater aquifers. In solid form, water is naturally stored in ice, snow, and glaciers. This natural storage provides much of the water treated for human consumption.
- Snowmelt—Water in the solid form converts to water in the liquid form and is returned to the hydrologic cycle. Note: In California, snowpack is a critical water supply indicator as it is the melting snowpack that recharges rivers and the general supply of water
There are other important terms to note in regard to the hydrologic cycle. The surface to atmosphere movement of water is known as evapotranspiration. This is the combination of evaporation and transpiration from plant life to the atmosphere. The most widely known movement of water is precipitation which is when water in various physical states falls from the atmosphere to the surface of the Earth. The movement of water from the surface to subsurface is known as percolation. Percolation might also be referred to as infiltration or recharge. These terms are commonly associated with underground aquifers. Finally, surface to surface flow is called runoff.
Groundwater
Groundwater is one of the two main sources of storage used by municipalities to produce potable water. It is formed by the percolation (infiltration and/or recharge) of water from the surface of the earth to the subsurface. Water moves through holes and cracks in the subsurface and collects in an underground aquifer. An aquifer is a geologic formation that accumulates water due to its porousness. Important characteristics of groundwater include consistent water quality and the ability to remain safe from surface contamination. With greater technology and testing methods chemicals and constituents known to be harmful to humans have been found in numerous well sites throughout the United States. Wells close to industrial areas have been contaminated with harmful chemicals and substances. New regulations are continually being updated to ensure source groundwater is safe to drink. In normal circumstances, very little treatment is required to yield groundwater.
The Groundwater Treatment Rule (GWTR) was enacted in 2006 to prevent microbial contamination from underground water supplies. The purpose of the new rule was to classify water systems that were at a greater risk for fecal contamination. These systems must employ a multiple-barrier protection similar to the surface water treatment rule which will be covered in more detail in the next section.
There are two kinds of aquifers, confined and unconfined. In an unconfined or water table aquifer the water table is free to rise and fall. The water table in unconfined aquifers rise and fall depending on the amount of precipitation that recharges the aquifer. Confined aquifers, also known as artesian wells, contain water that is confined due to layers of low permeability. These layers, which restrict movement, are comprised of rock or hard clay and are referred to as confining beds, aquitards, or aquicludes. Artesian wells are generally under pressure when drilled. Once drilled the water level at which the column of water will rise is known as the piezometric surface. Sometimes, the water will rise to the surface or past the surface but in the instance, the water remains below it is known as a non-flowing artesian well.
Wells
The construction of wells is critical in the extraction of water from underground water supplies. The placement of wells is very important because proper location will produce the greatest yield. Important terms related to underground wells:
- Static Water Level—The level in the well when no water is being removed from the aquifer. This level can be measured in feet or elevation.
- Pumping water level—The level when water is being removed from the aquifer. This level can vary depending on the rate of flow from the well.
- Drawdown—The difference between the pumping water level and the static water level
- Cone of depression—The shape or “cone” created by the movement of water in all directions during pumping.
- Zone of influence—The area of water affected by the drawdown of water during pumping. It is important to note that wells cannot be placed too closely together because their zones of influence may affect each other.
- Well yield—The amount of water drawn from an aquifer over a specific period of time
- Specific capacity—The amount of water produced per drawdown expressed in gpm/ft
- Safe Yield/Perennial yield—The amount of water that can be pulled from an aquifer per year without a drop in the water table
- Overdraft—Too much water removed. Greater than the safe yield of a well
- Subsidence—The permanent drop in the water table due to overdraft
Specific Capacity Calculation
\[\text{Specific capacity} = \text{Flow (GPM)} ÷ \text{Drawdown (ft)} \label{Specific Capacity}\]
Example \(\PageIndex{1}\)
A well has a yield of 600gpm and the drawdown is 50 ft. What is the specific capacity of the well?
Solution
This is a direct application of Equation \ref{Specific Capacity}
\[\text{Specific Capacity = 600\, \text{GPM} ÷ 50\, \text{ft} = 12\]
Surface Water
Throughout the United States, surface water is the most widely used source of water for large cities and other municipalities. Groundwater is not as widely available so is not a sufficient water supply for major cities. Surface water includes lakes, ponds, rivers, and streams. California is unique as the southern half of the state has 2/3 of the population but only 1/3 of the available water and the northern half of the state has 1/3 of the population but 2/3 of the water. Snowpack in northern California is critical to the state’s water supply. Most of Southern California is very arid and densely populated so water travels from Northern California through the State Water Project to Southern California.
Surface runoff supplies water for all surface water sources. Influences of surface runoff include intensity of rainfall, duration of rainfall, composition of soil, amount of moisture in soil, slope of the ground, vegetation coverage, and human influences. One would think that a lot of rain would be ideal. However, if the rainfall density is too great, more water can be lost because the ground will no longer absorb the water. The same applies to the duration of rainfall. A prolonged rain even makes the soil too moist and unable to capture water. Vegetation coverage and the slope of the ground are very important to stopping runoff. If the slope of the ground is steep, the speed of runoff is increased. Vegetation slows the speed of runoff and allows more water to absorb or infiltrate into the ground. Human influences have a great impact on water runoff. Impervious surfaces like concrete entirely prevent infiltration.
Natural Watercourses
Key Terms
Natural water courses include rivers, creeks, streams, washes, and arroyos. They flow in one of three ways:
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Perennial streams—Watercourses which flow continuously throughout the year
- EX: Colorado River
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Ephemeral streams—Watercourses that flow sporadically, generally after rainfall
- EX: Santa Clara River which runs through Santa Clarita and Ventura County
- Intermittent—Watercourses which flow somewhere between ephemeral and perennial streams. Rainfall and high groundwater levels will affect how often these streams flow.
Rivers and Streams are a good water supply source but are not necessarily the best source for public water supplies.
Lakes
Lakes are the most widely used public water supply source. However, very few “natural” lakes exist. Most lakes used for public water supply are man-made and use a dam to create the lake and contain the water. This is known as an impoundment. Water from these lakes is piped to treatment facilities. Due to variances in temperature lakes develop “layers” also known as stratification. Denser, colder water will drop to the bottom (Benthic zone) of a lake during the summer. There are three layers:
- Epilimnion—The strata closest to the surface
- Hypolimnion—The strata near the bottom
- Thermocline—Middle strata with the greatest variance in temperature
Lake turnover will occur during seasonal temperature changes. When the temperature of a lake is uniform it is known as isothermal. Algae growth is a serious problem that causes taste and odor issues in treated water. Copper sulfate can be added to a lake to help remedy algae blooms. In severe cases, the water undergoes eutrophication which is the loss of oxygen. Complete or extreme oxygen depletion can kill all living creatures in the water including animals and fish.
Introduction to Water Math
Mathematics is a key component of water treatment. Operators use conversion tables and basic algebra to complete many daily tasks. Charts are available on the State Water Resources Control Board website that assist operators with most calculations you would find on the state exams or while on the job. Below is a list of basic units and their respective conversion factors:
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Measurement |
Equivalent |
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1 cubic foot of water |
62.3832lbs |
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1 gallon of water |
8.34lbs |
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1 liter of water |
1,000 grams |
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1 mg/L |
1 part per million (ppm) |
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1 ug/L |
1 part per billion (ppb) |
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1 mile |
5,280 feet |
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1 yard |
3 feet |
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1 yard3 |
27ft3 |
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1 acre |
43,560 square feet or ft2 |
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1 cubic foot or ft3 |
7.48 gallons |
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1 gallon |
3.785 Liters or L |
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1 L |
1,000 milliliters (ml) |
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1 pound |
454 grams |
Working with Fractions
NumeratorDenominator
44=11 or =1 42=21 or =1
Rounding
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Rounding the number 324.179 |
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3 = Hundreds |
The above number (324.179) rounded to the nearest tenth would be 324.2. Since the number in the hundredth place is at or above 5, the number in the tenth place is rounded up. If you were rounding this number to the nearest whole number it would be 323 since the number in the tenth place is below 5. |
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4 = Tens |
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9 = Units |
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1 = Tenth |
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7 = Hundredth |
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9 = Thousandth |
Unit Dimensional Analysis
This is the most important function in most water math problems. Make sure to always place your factors in the proper place or the equation will be impossible to solve correctly. The example below will use unit measurements. Water operators will commonly convert between different units of measurement.
Example 1
Convert 48 inches into feet. (There are 12 inches in a foot.)
48 inches11 foot12 inches=4 ft1
Drop the one from the denominator and the answer is 4 ft.
The same process will be to convert between gallons and cubic feet.
Example 2
Convert 22.44 gallons into cubic ft. or ft3 (There are 7.48 gallons in one cubic foot.)
22.44 gallons11 ft³7.48 gallons=3 ft³1
Drop the 1 from the denominator and your answer is 3 ft³
Example 3
How many gallons are there in a tank which holds 300ft³ of water?
300ft317.48 gal1ft3=2,244 gallons
Area
Area will be important for many applications in water math. It may be necessary to calculate the area of a tank that requires painting or an area of ground cover near equipment.
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Rectangles
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Area = L × W |
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Circle
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Area = 0.785 × D 2 |
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Trapezoid
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Area = × H |
Example 1
A wall that is 10ft wide and 40ft in length needs to be painted. What is the total square feet of the wall?
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Area = Length x Width Area = 10ft x 40ft Area = 400ft 2 |
Example 2
What is the area of the top of a circular storage tank that is 100 feet in diameter? (Note: Use the formula .785 x d2. In most cases in water math, we will always be dealing with the diameter and not the radius. These short cuts will help as the problems become more difficult. In this problem I will demonstrate why we will use this formula and not the standard mathematical equation for solving area problems.)
Equation #1 Area= π (3.14) x r 2 (100ft ÷ 2 = 50 to find radius)
Area = 3.14 x 50 x 50
Area = 7,850 ft 2
Equation #2 Area= .785 x d 2
Area = .785 x 100 x 100
Area = 7,850 ft 2
In this example, the first equation was easy to solve because we were working with a pretty friendly number. As the equations become more difficult we do not want to take the extra step to divide the diameter by two to solve for the radius. If the diameter of the tank was 357ft, this problem would have been slightly more difficult using the first equation.
Example 3
The top of a circular storage tank needs to be painted. It is 100 ft. in diameter. Each gallon of paint covers approximately 200 square feet. How many gallons of paint will you need to buy?
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Area= .785 x d 2 Area= .785 x 100ft x 100ft Area= 7,850 ft 2 7850 ft²1x1 gal200 ft²=39.25 gal |
Chapter Review
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What is the middle layer of a stratified lake called?
- Thermocline
- Benthic Zone
- Epilimnion
- Hypolimnion
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What is the conversion of liquid water to gaseous water known as?
- Advection
- Condensation
- Precipitation
- Evaporation
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Water weighs ___________.
- 7.48 lbs/gal
- 8.34 lbs/gal
- 62.4 lbs/ft 3
- Both 2 and 3
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What is the static level of an unconfined aquifer also known as?
- Drawdown
- Water Table
- Pumping Water Level
- Aquitard
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What is the cause of taste and odor problems in raw surface water?
- Copper sulfate
- Blue-green algae
- Oxygen
- Lake turnover
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What chemical reduces blue-green algae growth?
- Chlorine
- Caustic Soda
- Copper Sulfate
- Alum
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A water-bearing geologic formation that accumulates water due to its porousness.
- Aquifer
- Lake
- Aquiclude
- Well
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What kind of stream flows continuously throughout the year?
- Ephemeral
- Perennial
- Intermittent
- Stratified
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The surface to atmosphere movement of water is known as ___________.
- Precipitation
- Percolation
- Stratification
- Evapotranspiration
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An aquifer that is underneath a layer of low permeability is known as ___________.
- Confined aquifer
- Water Table aquifer
- Unconfined aquifer
- Unreachable groundwater
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What is the middle layer of a stratified lake known as?
- Hypolimnion
- Benthic Zone
- Thermocline
- Epilimnion
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The amount of water that can be pulled from an aquifer without depleting.
- Drawdown
- Safe yield
- Overdraft
- Subsidence
Math Questions
Please show all work. On the State exams, you will not get credit if work is not shown.
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What is the area of the top of a storage tank that is 75 feet in diameter?
- 4,000 ft 2
- 4416 ft 2
- 1104 ft²
- 17,663 ft²
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What is the area of a wall 175 ft. in length and 20 ft. wide?
- 3,000 ft²
- 2,500 ft²
- 3,500 ft²
- 4,000 ft²
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You are tasked with filling an area with rock near some of your equipment. One (1) bag of rock covers 250 square feet. The area that needs rock cover is 400 feet in length and 30 feet wide. How many bags do you need to purchase?
- 40 Bags
- 42 Bags
- 45 Bags
- 48 Bags