Water Resources Management Notes

Water Resources Management

Content

  • Surface water and groundwater hydrology, including major components associated with the collection and transmission of water to the water treatment plant.

Three Classifications

The current federal drinking water regulations define three distinct and separate sources of water:

  • Surface water

  • Groundwater

  • Groundwater under the direct influence of surface water (GUDISW)

    • This last classification is a result of the Surface Water Treatment Rule. The definition of what conditions constitute GUDISW, while specific, is not obvious.

Surface Water Hydrology

  • Surface water is water that is open to the atmosphere and results from overland flow.
  • It is also said to be the result of surface runoff.

Examples of Surface Water

Specific sources that are classified as surface water include the following:

  • Streams, Rivers, Lakes
  • Man-made impoundments (lakes made by damming a stream or river)
  • Springs: affected by precipitation that falls in the vicinity of the spring (affected means a change in flow or quality)
  • Shallow wells affected by precipitation (affected means a change in level or quality)
  • Wells drilled next to or in a stream or river
  • Rain catchments
  • Muskeg and tundra ponds

Advantages of Surface Water

The primary advantages to using surface water as a water source include the following:

  • It is easily located. It takes no sophisticated equipment to find a surface water source.
  • In many parts of the US, considerable data is available on quantity and quality of existing surface water supplies.
  • Surface water is generally softer than groundwater, which makes treatment much simpler.

Disadvantages of Surface Water

The most common disadvantages to using surface water as a water source include the following:

  • Surface waters are easily polluted (or contaminated) with microorganisms that cause waterborne diseases and chemicals that enter the stream from surface runoff and upstream discharges.
  • The turbidity (measured as NTU) of a surface water source often fluctuates with the amount of precipitation. Increases in turbidity increase treatment cost and operator time.
  • The temperature of surface water fluctuates with the ambient temperature. This makes it difficult to produce consistent water quality at a water treatment plant.
  • The intake structure may become clogged or damaged from winter ice, or the source may be so shallow that it completely freezes in the winter. This is a common problem with surface water sources in the arctic.
  • Removing surface water from a stream, lake, or spring requires a legal right, referred to as a water right. Water rights in Alaska are obtained from the Department of Natural Resources (DNR).
  • For many systems in Alaska, the source water is at its worst possible quality during the time of the year when the community needs to fill or top off its storage tank. This happens late in the summer when glacially fed streams have turbidities of 1000 NTU or greater.
  • Using surface water as a source means that the purveyor is obligated to meet the requirements of the Surface Water Treatment Rule (SWTR) of the State Drinking Water Regulations. This rule requires that, in most instances, any surface water source must have a filtration system.
  • Surface waters that are high in color, especially color that is the result of decaying vegetation, have the potential to produce high levels of Total Trihalomethanes (TTHM). These chemical compounds are formed when chlorine is added to the water. The problem with the TTHM is that some of them are carcinogenic (can cause cancer) and are referred to as disinfection by-products (DBP).

Surface Water Hydrology

  • A basic understanding of the movement of water and the things that affect water quality and quantity are important to those who manage and operate water systems.
  • The study of these items is called hydrology.
  • The components of hydrology include the physical configuration of the watershed, the geology, soils, vegetation, nutrients, energy, wildlife, and the water itself.

Drainage Basin

  • The area from which surface water flows is called a drainage basin.
  • With a surface water source, this drainage basin is most often called the watershed.
  • When dealing with a groundwater supply, this area is called the recharge area.
  • The drainage basin is difficult to identify when referring to a large river such as the Yukon.
  • However, on a smaller river, stream, or lake, the area is defined by marking on a map an outline of the basin defined by the ridge of the mountains that surround the basin.

Drainage Basin Area Measurements

The area of the basin is commonly measured in square miles, sections, or acres. If taking water from a surface water source, it is desirable to know the size of the watershed.

Location of the Basin

  • A parcel of ground such as a drainage basin can be identified by and described by standard terms used in land descriptions and surveying. This description is based on a series of horizontal and vertical lines that form a rectangle system. The ability to describe properly the location of a drainage basin, well, or surface water intake is important when communicating with the Department of Natural Resources (DNR) and ADEC.

Drainage Basin Baseline Data

  • Gathering precipitation and flow data plus water quality data is called baseline data.
  • This data is essential for long-term planning and determining the impact of activities in a drainage basin.

Raw Water Storage Purpose

Raw water storage areas are constructed to meet peak demands and/or to store water to meet demands when the flow of the source is below the demand.

Natural Storage

  • Natural storage can be found in lakes like the one used by Haines and large rivers like the Yukon used by St. Mary’s. Natural storage includes muskeg and tundra ponds used by logging camps in the Southeast, in oil field camps, and by resorts in the arctic region.

Man-made Storage

  • In many areas, there are no natural storage areas, and dams must be built. These dams can be either masonry or embankment dams.
  • There are three different concrete masonry dam designs:
    • Gravity dam
    • Buttress dam
    • Arched dam
  • In Alaska, the most common dam used for potable water is a concrete gravity dam less than 30 feet in height. Examples of concrete dams can be found at the City of Craig and Port Alexander Raw Water Storage.

Embankment Dams

  • Embankment dams are made from local materials. The key to an embankment dam is a tightly compacted impermeable clay core. This core is held in place either by rock or earth. When rock is used, the dam is called a rock fill embankment dam.
  • Riprap is placed on the face of the dam to prevent erosion by the water. The major advantage to this type of construction is its ability to give with small movements of the earth. An example of an embankment dam is the village of Saxman, which uses a small embankment dam for holding its drinking water.

Raw Water Storage Tanks

  • In many locations in the arctic region, it is common to use a large man-made storage tank to store raw water for use during the winter months. These structures normally hold one million gallons or more and are made of wood or steel.

Surface Water Intake Structures Location Criteria

Regulations and Standards

  • In order to protect high quality drinking water, the water works industry has developed standards and specifications for separation of the intake from potential sources of contamination. In addition, the Alaska Department of Environmental Conservation has established minimum separations distances from sources of contamination. The following listing includes industry standard practices as well as those items included in the ADEC regulations:
    • There can be no wastewater disposal systems, including septic tanks and drain fields, within 200 feet of the intake for CWS, NTNCW, or TNCWS systems and 150 feet for Class C systems.
    • There should be no community sewer line, holding tanks, or other potential sources of contamination within 200 feet of the intake of a CWS, NTNCW, or TNCWS system or within 100 feet in a Class C system.
    • Fuel not used for on-site emergency pumping equipment or heating cannot be stored within 100 feet of the well for a CWS, NTNCW, or TNCWS system or within 75 feet of the well for a Class C system.
    • Fuel for onsite emergency generators or building heating system can be stored onsite if the total volume is less than 500 gallons.

Recommendations

  • The following are recommendations and not regulations:
    • The water purveyor should own or have a restricted area within 200 feet radius of the intake. There should be no roads within 100 feet of the intake.

Structures

  • The intake structure is used to collect the raw water from the source and place it into the transmission line. The types of intake structures used in the water industry vary greatly to meet the specific needs and construction conditions of each site. The following discussion will explore a few of the most common types as they apply to small streams, lakes, rivers, and reservoirs.

Small Streams

  • Small Dam
    • One of the most common intake structures on a small stream is a small gravity dam placed across the stream. Water behind the dam can be removed by a gravity line or pumps. This type of system is susceptible to ice damage in the winter.
  • Diversion in Stream
    • A second common intake for a small stream is a diversion of some type built next to the stream. Water is collected in the diversion and either carried away by gravity or pumped from a caisson. This type of intake is sometimes called a submerged intake.

River Float

  • A common intake on small and large streams is to use an end-suction centrifugal pump or submersible pump placed on a float. The float is secured to the bank, and water is pumped to a storage area. In the winter, the float is replaced with a hole in the ice and a platform for holding the pump controls.

Intake Johnson Screen

  • One of the simple intake structures used on muskeg ponds and small streams is a section of Johnson screen placed on the end of a swing joint. The operator can select the best location of the pipe, raising and lowering it by a mechanical arm attached to the swing joint.

Infiltration Gallery Description

  • There are several uses and designs for the infiltration gallery. These include intake structures for a spring and intake structures placed in the bed of a stream.
  • The most common infiltration galleries are built by placing Johnson well screens or perforated pipe into the streambed or water-bearing strata.
  • The pipe is covered with clean graded gravel. As water percolates through the gravel, a portion of the turbidity and organic material is removed.

Infiltration - Caisson

  • The water collected by the perforated pipe flows to a caisson placed next to the stream.
  • The water is removed from the caisson by gravity or pumping.

Other Intakes

  • Springs
    • A common method of collecting water from a spring is to dig back into the mountain and place Johnson screens or perforated pipe into the water-bearing strata. This is then covered with clean washed rock and sealed with clay. The outlet is piped into a spring box.
  • Roof Catchments
    • In various parts of the world, including Southeast and Southwest Alaska, a primary source of water is rainwater. Rainwater is collected from the roof of buildings with a device called a roof catchment.

Screens

  • Bar Screens
    • The intake pumps, valves, and piping need to be protected from debris that would normally be drawn into the intake. One of the primary protection devices are large steel or concrete bars set vertically in the flow. This is called a bar screen and is designed to protect against large material.
  • Screens
    • After the bar screens is usually a smaller screen, designed to remove leaves and other small material that can clog the pumps and valves. The screens can be either self-cleaning or manually cleaned. Manually cleaned screens often require daily cleaning during certain times of the year.

Pumps

Noise

  • When using gas or diesel powered equipment, you should be aware of the noise level.
  • If the noise in the area in which you are working is above 85 db, you should wear hearing protection. Damaged hearing cannot normally be repaired. For instance, a gas-powered pump installed in a caisson or on a boat requires hearing protection anytime you are in or directly above the caisson when the pump is running.

Confined Spaces

  • Most caisson and valve boxes associated with intake structures are confined spaces and; therefore, require the following:
    • A written permit before you enter
    • The use of an air ventilation system
    • Monitoring the air quality with an oxygen and combustible gas meter every 15 minutes

Carbon Monoxide

  • When running the gas-powered pump in a caisson, take special care to ensure that the exhaust is out of the caisson. However, the wind can easily blow carbon monoxide back into the caisson. Check for oxygen and combustible gases before entering the caisson.

Records and Data Collection

  • To properly operate and maintain a surface water system, you should keep the following records:
    • As-built drawings of all facilities
    • Copy of the water rights certificate
    • Copy of the watershed management use agreement
    • Map of drainage basin showing land ownership, potential or existing contamination sites, activity sites, and location of any water system structures
    • Baseline quality and quantity data
    • Water quality survey reports
    • Water monitoring reports

Recommended Activities

  • To properly operate and maintain a surface water system, you should routinely obtain the following data and/or perform the following tasks: (Note: The test frequency described below is for CWS or NTNCWS systems and depends on particular system and monitoring summary.)
    • Test turbidity
    • pH and temperature (Daily)
    • If there is color in the water (Daily)
    • Test for bacteriological quality (Monthly)
    • Collect a sample and have it tested for inorganic contaminants (Yearly)
    • Collect a sample and have it tested for organic contaminants (Yearly)
    • Inspect the intake structure (Frequency depends on type of structure but at least weekly)
    • Make an on-site investigation of the drainage basin and waterway looking for existing or potential contamination (Yearly). This contamination can be natural or man-made. This process is called a water quality survey.
    • Collect stream flow and precipitation data (Weekly)

Definition (Groundwater)

  • Groundwater is considered to be water that is below the earth’s crust, but not more than 2500 feet below the crust. Water between the earth’s crust and the 2500-foot level is considered usable fresh water.

Examples of Groundwater

  • Groundwater is obtained from the following:
    • Wells
    • Springs that are not influenced by surface water or a local hydrologic event

Under the Influence

  • When a well or spring is influenced by an adjacent surface water source or by a local hydrological event, the supply is said to be groundwater under the direct influence of surface water (GUDISW).

Advantages and Disadvantages of Groundwater

  • There are both advantages and disadvantages to groundwater.
    • Advantages – The advantages of groundwater sources in relationship to surface water include the following:
      • Groundwater is not as easily contaminated as surface water.
      • The quality of groundwater, while not always as good as would be preferred, is stable throughout the year.
      • Groundwater sources are generally lower in bacteriological count than surface water sources.
      • Groundwater is available in most locations throughout the continental US and Alaska.
    • Disadvantages – When comparing groundwater sources with surface water, the following are disadvantages to using groundwater:
      • Once a groundwater source is contaminated, it is difficult for it to recover. There is no easy way to remove the contaminants.
      • Groundwater usually contains more minerals than surface water, including increased levels of hardness. Because groundwater is in contact longer with minerals, there is more time to bring them into solution.
      • Removal of groundwater normally requires a pump, thus increasing operation cost.
      • Groundwater is more susceptible to long-term contamination from fuel spills.
      • Groundwater supplies often have high levels of iron and manganese, thus increasing treatment cost and/or causing stains on plumbing and the clothing of customers.
      • Wells in the coastal areas are subject to salt water intrusion into the aquifer and well. This contamination is difficult to predict and costly to treat.
      • Sources of contamination can be hidden from sight.

Groundwater Hydrology

  • Groundwater, like surface water, is part of the hydrologic cycle. Groundwater is found in saturated layers under the earth’s surface called aquifers. There are different names given to aquifers, depending upon their type.

Three Types of Aquifers

  • There are three types of aquifers: unconfined, confined, and springs. The following is a brief description of the differences between these types of aquifers.

Unconfined Aquifers

  • Definition
    • The zone of saturation is an unconfined aquifer. It is not contained, except on the bottom. An unconfined aquifer depends on local precipitation for recharge. This type of aquifer is often called a water table aquifer.
  • Zones and Belts
    • Unconfined aquifers are composed of unconsolidated strata that are divided into two zones:
      • The zone of aeration contains two belts: the soil-water belt, where plants obtain their water, and the intermediate belt, where there is a mixture of air and water.
      • The zone of saturation is an unconfined or water table aquifer. The top of this zone of saturation is called the water table.

Unconfined Aquifer Wells

  • Wells drilled in an unconfined aquifer are normally called shallow wells and are subject to local contamination from hazardous and toxic material, such as fuel and oil, agricultural runoff containing nitrates and microorganisms, and septic tank discharge of increased levels of nitrates and microorganisms.

Groundwater Under the Influence

  • Water taken from wells drilled in an unconfined aquifer is not considered desirable as a public drinking water source. This type of well may be classified as groundwater under the direct influence of surface water (GUDISW) and therefore require treatment for control of microorganisms.

Definition (Confined Aquifers)

  • At various locations in the earth's crust are layers of saturated material that are contained between two layers of impermeable material such as rock, clay, or permafrost. This type of aquifer is called a confined aquifer.

Artesian Aquifers

  • Confined aquifers are also called artesian aquifers. Naturally a well drilled in an artesian aquifer is called an artesian well. An artesian well is described as any well where the water in the well casing rises above the saturated strata. There are two types of artesian wells: flowing and non-flowing.

  • Confined aquifers commonly yield large quantities of high-quality water. One exception is water confined by permafrost layers. This water is very poor quality. The aquifer may be relatively short or may extend several hundred miles into the mountains.

Recharge of Confined Aquifers

  • A confined aquifer is recharged by snow or rain in the mountains where it is close to the surface of the earth. Because the recharge area is away from the area of contamination, the possibility of contamination of a confined aquifer is very low. However, once contaminated, it may take hundreds of years before it recovers.

Wells in Confined Aquifers

  • A well in a confined aquifer is normally referred to as a deep well. If the well is properly installed, the water quality is not impacted by local hydrological events.

Springs

  • Types
    • Water that naturally exits on the crust of the earth is called a spring. The water in a spring can originate from a water table aquifer or from a confined aquifer. When a spring comes from a confined aquifer, it is commonly the result of a geological fault (a break in the confining layer). Only water from a confined aquifer spring is considered desirable for a public water system.

Composition of an Aquifer

  • An aquifer is made up of a combination of solid material, such as rock and gravel, and open spaces called pores. Regardless of the type of aquifer, the water in the aquifer is in motion. This motion is caused by gravity or by pumping. The flow of water through the aquifer is influenced by the size of the material, the number of pores, and the connection between the pores.

Volume of Water

  • The volume of water in an aquifer is dependent upon the amount of space available between the various grains of material that make up the aquifer. The amount of space available is called porosity.

Cone of Depression

  • Whenever a well is placed in a water-bearing stratum and pumped, water will flow toward the center of the well. In a water table aquifer, this movement causes the water table to sag toward the well. This sag is called the cone of depression.

Shape of the Cone

  • The shape and size of the cone depends on the relationship between the pumping rate and the rate at which water can move toward the well. If the permeability is high, the cone will be shallow, and its growth will stabilize. If the permeability is low, the cone will be sharp and continue to grow in size.

Zone of Influence

  • The area that is included in the cone of depression is called the zone of influence. Any contamination in this zone will be drawn into the well.

Static Water Level

  • As a pump operates in a well, the depth of water will move up and down. If the pump were shut off for several hours and that water level allowed to recover and stabilize, the level would be called the static water level.

Drawdown

  • When a well pump operates, the level of water in the well drops. The difference between the static level and the level that a pump operates to is called the drawdown.

Specific Yield

  • The drawdown level depends on the pumping rate and the transmissibility of the aquifer. One standard test that is used to compare the performance of a well from year to year is to determine the specific yield of the well. This is done by pumping the well at a set rate for a specific period of time and measuring the drawdown. The flow is then divided by the drawdown to give a value in gpm/ft of drawdown.