(b) Water Engineering Basics

Transcription

1 NRRI Training for the Oklahoma Corporation Commission March 14-16, 2017 Topic 3 (b) Water Engineering Basics Kathryn J. Kline Research Associate National Regulatory Research Institute kkline@nrri.org

2 Industry Structure Phelan, Dan. (2016). Fragmentation in the Water Industry and Regulatory Impacts [Presentation, 2016 NARUC Winter Meeting]. National Regulatory Research Institute. The majority of systems serve less than 3,300 people (i.e. small systems) K. Kline, NRRI - Topic 3(b) 2

3 The Water Cycle 70% of precipitation ends up in streams, rivers, and the ocean the remaining 30% seeps into the water table Some of this resurfaces from springs, flowing wells, etc. Some ground water is absorbed by plants and trees Seepage into the ground water table depends on soil properties K. Kline, NRRI - Topic 3(b) 3

4 Water Sources Impounding Reservoir Utilize dams to collect water In may cases, can flow to treatment pant w/o pumping reservoir systems w/o mechanical interface are considered the most reliable and economical source Fresh-Water Lakes Lakes are supplied by streams and rivers Good supply of water as long as lines are below ice formation level Generally, water must be pumped Examples: Great Lakes and Finger Lakes Wells Pulls ground water Artisan or flow wells may have sufficient pressure to move water to treatment plants Other types of wells require pumps A primary source of water for populations under 5,000 Oceans/Bays Until recently, desalination was not a cost-effective option Water systems have been using ocean and bay water for fire protection for over a century in cities like New York, Philadelphia, and San Francisco K. Kline, NRRI - Topic 3(b) 4

5 Uses Thermoelectric power, Irrigation, and public supply cumulatively account for 90% of the national total. K. Kline, NRRI - Topic 3(b) 5

6 How Treated Water Reaches the Home K. Kline, NRRI - Topic 3(b) 6

7 How Drinking Water is Treated K. Kline, NRRI - Topic 3(b) 7

8 Water Treatment Process Step 1: Screening - Water passes through a series of screens designed to remove debris such as twigs, leaves, paper, stones, and other foreign matter. Screens are frequently removed for cleaning or are back- washed from high-pressure pumps to prevent clogging. Step 2: Presedimentation - While the water moves slowly through each reservoir, much of the sand and silt settles to the bottom. Step 3: Coagulation - A coagulant, aluminum sulfate, is added to the water as it flows to sedimentation basins. Coagulants aid in the removal of suspended particles in the water by causing them to consolidate and settle. Step 4: Flocculation - The water is gently stirred with large paddles to distribute the coagulant. This takes approximately 25 minutes. Step 5: Sedimentation - The water flows into sedimentation basins where particles settle to the bottom. After about 4 hours, roughly 85% of the suspended material settles out. Step 6: Filtration - Water at the top of the basins flow to large gravity filters, traveling through layers of small pieces of hard coal, sand, and gravel. The filters help remove smaller particles from the water. Step 7: Disinfection Frequently includes the addition on chlorine to water Step 8: Additives - Depending on water quality, the following additives may added: Fluoride is added to reduce tooth decay Calcium hydroxide is added to reduce corrosion in the pipes and equipment of the distribution system K. Kline, NRRI - Topic 3(b) 8

9 Challenges for Maintaining Uninterrupted Supply Maintaining an uninterrupted supply of water can be a major challenge because of the following conditions: Droughts Growing demand Lack of adequate storage capacity Other communities drawing water from the same supply sources such as a lake or river (e.g. Tri-state Water Wars (AL, GA, FL)) A major commercial fire or wild land/urban interface fire that exhausts water supply Undetected underground leakage K. Kline, NRRI - Topic 3(b) 9

10 Case Study: Tri-State Water Wars For decades, Georgia, Alabama, and Florida have been battling over the future allocation of water in two major river basins that cross their borders (the Alabama-Coosa-Tallapoosa and the Apalachicola-Chattahoochee-Flint basins). The dispute has involved several local, state and federal agencies, as well as numerous courts and mediators, and its outcome is one of the most important environmental issues facing the region today. Case study provided by the Southern Environmental Law Center. Georgia Needs water for metro area growth + agriculture Georgia is not a water-rich state Water supply is entangled with other states Alabama Concerned GA s growing water needs will disrupt supply Needs water for power generation, municipal supply, & fisheries Florida Needs water in Apalachicola Bay for multi-million $ shellfish industry Water shortages cause sever ecological stress on area K. Kline, NRRI - Topic 3(b) 10

11 Groundwater as a Storage Medium Advantages Reliable source Bacteriologically safe, provided pollution is controlled It may supply water at a time when surface water resources are limited It is not affected by evaporation loss if deep enough Disadvantages Limited resource Can be expense because of pumping costs Recovery may have serious impact on land subsidence or salinisation Often difficult to manage K. Kline, NRRI - Topic 3(b) 11

12 Factors Leading to Water Quality Deterioration Contamination via cross-connections or from leaky pipe joints Corrosion of iron pipes and dissolution of lead and copper from pipe walls and joints Loss of disinfectant residual in storage facilities with long resident time Bacterial regrowth and harboring of opportunistic pathogens Supply sources going online and offline Reactions of disinfectants with organic and inorganic compounds resulting in taste and odor problems Increased turbidity caused by particulate resuspension New formation of disinfection byproducts, some of which could be suspected carcinogens K. Kline, NRRI - Topic 3(b) 12

13 Water Quality and the Distribution System New pipes are added to distribution systems as development occurs. The additions result in a wide variation in: Pipe sizes Materials Methods of construction Age within individual distribution systems and across the nation As these systems age, deterioration can occur due to corrosion, materials erosion, and external pressures. Deteriorating water distribution systems can lead to: Breaches in pipes and storage facilities Intrusion due to water pressure fluctuation Main breaks K. Kline, NRRI - Topic 3(b) 13

14 Types of Water Systems Gravity feed Systems Pumping Pressure Systems High or low reservoirs that hold nonpotable water for gravity feed Pumping station systems that use ground water for impound water. In these systems, the raw water is pumped from the source point to the treatment plant and then either pumped directly into the distribution system or stored. Pumps at well sites that pump water to the treatment facility. Based on the difference in elevation, water may flow by gravity or need another pumping station between treatment and delivery. Composite systems can be a combination of gravity flow and one or more pumping stations K. Kline, NRRI - Topic 3(b) 14

15 High-Level Reservoir Systems Water source is at least 100 feet in elevation above treatment facility The water should be a natural impounded lake with a Flow pipe between the lake and treatment facility, or Created by a dam that will allow water to backup behind the dam This type of system is very reliable because: May not require any pumping No substantial power requirement to run system K. Kline, NRRI - Topic 3(b) 15

16 Low-level Reservoir System Are usually up to about 20 feet high Typically require a pumping station to transport water to treatment plants, and if the land is flat, a second pumping station is required to move treated water to the distribution system or to elevated storage K. Kline, NRRI - Topic 3(b) 16

17 Direct Pumping System Used for groundwater systems Pump station pulls water from the ground, directs water to the filtration plant, and then a second pumping system transports water to a storage holding area. Diverting water into storage minimizes the time when the pumps have to run K. Kline, NRRI - Topic 3(b) 17

18 Pumping at Well Sites and Gravity Storage Because the quality of groundwater in many areas of the country is good, the only treatment necessary is chlorination Treated water either flows by gravity to the distribution system or is pumped into elevated storage K. Kline, NRRI - Topic 3(b) 18

19 Composite Water Supply Systems Specific conditions may require a system that uses components from more than one system Some examples include: Adding pumping stations to a gravity reservoir system to increase pressure and volume during peak demand periods Booster pumping stations may be installed where there is a need for more than one service level based on pressure demand Direct pumping into the distribution system may be supplemented by gravity tanks that float on the system to maintain pressure and flow characteristics Gravity tanks are especially useful for improving reliability K. Kline, NRRI - Topic 3(b) 19

20 Three Classifications of Pipe Primary Feeders Usually ranging in diameter from inches Transport water from the water treatment plant to the corporation line of the community Secondary Feeders inches in diameter Connected to the primary feeders to transport water along major streets Distributor Mains 6-10 inches Transport water from the secondary feeders to individual streets K. Kline, NRRI - Topic 3(b) 20

21 Single-Point Feed System Water moves from the treatment plant to the community corporation line with a single primary feeder Note: demand point is fed from one direction Pipe size maximum daily consumption demand + needed fire flow (this results in larger pipes) This design creates dead-end mains which lead to stagnation of water (which rapidly reduces quality) K. Kline, NRRI - Topic 3(b) 21

22 Looped Water Distribution System Loops or cross-ties all the main, so that any demand point is supplied from two directions Less water stagnation Note: many older systems have updated by laying a primary feeder around the water system perimeter to tie in dead-end mains improving flow distribution & water pressure K. Kline, NRRI - Topic 3(b) 22

23 Freshwater Supply Concerns 40 of 50 state water managers expected shortages to in some portion of their states under average conditions in the next 10 years K. Kline, NRRI - Topic 3(b) 23

24 Freshwater Supply Concerns (continued) Key issues: Population growth straining water supply Lack of information on water availability and use The impacts of extreme weather events on water resources The effects of the energy sector on water quantity and quality Complicating issues: Uncertainty about patterns of economic growth Uncertainty about land use changes Over the past decade states have taken the following steps: Conducting freshwater resource studies and assessments Developing drought preparedness plans Developing water management tools Taking conservation actions K. Kline, NRRI - Topic 3(b) 24

25 Energy Efficiency for Water Utilities Energy costs often make up 25-30% of a utility s total operation and maintenance (O&M) costs Drinking water and wastewater systems account for 2% of energy use in the US Energy also represents the largest controllable cost of providing water and wastewater services By incorporating energy efficiency practices into water and wastewater plants, utilities can save 15-30% For more information: K. Kline, NRRI - Topic 3(b) 25

26 Lead Service Line Estimate by USEPA Regional Group K. Kline, NRRI - Topic 3(b) 26