Edward Lu. Liwei Yang

Transcription

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2 Edward Lu Liwei Yang

3 Ground Water ABE 325 Soil & Water Conservation Engineering Water quality lab site: Lecture site: For Oct. 24 groundwater.pdf

4 Ground water is the water below the land surface that completely fills (saturates) the pore spaces in the subsurface materials.

5 Ground water is a vital part of rural life. Nearly 95 percent of rural families in the United States rely on ground water as their source of drinking water. Many agricultural uses for ground water such as irrigation and livestock watering. The quality of life in the rural community depends on an abundant and dependable supply of potable ground water (i.e. suitable for drinking).

6 About 70 percent of the Earth surface is covered by water. But more than 97 out of every 100 drops of water on earth are saline and, therefore, not potable The largest storage of fresh water on earth are the ice caps. But they are not easily accessible sources of drinking water. Ground water is the premier source of readily available fresh water for human consumption. Data from World Water Balance and Water Resources of the Compared to other fresh water sources, ground Earth, Copyright, UNESCO, 1978 water is 25 times more abundant than all the lakes, reservoirs and rivers of the world combined!

7 The ground water system is poorly understood by most people. People need to have: An appreciation of the benefits of ground water an understanding of the basics of ground water movement an understanding of the cause-effect link between our actions on the land surface and ground water quality

8 Water Quality "It isn't pollution that's harming the environment. It's the impurities in our air and water that are doing it." -- Vice President J. Danforth ("Dan") Quayle's, Biological water quality Microorganisms, pathogen contamination Macroorganisms, fish and plant Chemical water quality Farm chemicals, fertilizer and pesticide Heavy metal, mercury Discharge from sewage, septic tanks, and waste water treatment plant

9 CHEMICALS IN THE FARM WATER CYCLE The most effective approach to protect ground water quality: Appropriate management at the land surface Land surface or uppermost few tens of feet of the subsurface are the focus: The entry ways for most ground water contaminants. The area that land owners can control directly. Examples of Best Management Practices (BMP) on Farms: inspecting fuel storage tanks soil testing for fertilizer application rates sealing abandoned wells

10 Chemical Application, Contaminant & Pollutant Definitions Chemical application spreading of a chemical on the land surface or incorporating it into the plow layer of a field. Examples of chemical applications spraying a weed killer on your lawn, spraying a road surface to reduce dust incorporating anhydrous ammonia as a nitrogen fertilizer. A contaminant or pollutant is any chemical within the farm-water cycle that has moved away from the area of its intended use and is present in water in concentrations defined as unacceptable for the water s intended use. Pollution any reduction of the quality of water bevond levels established as safe for the intended use.

11 Sources Of Concentrated Chemical Pollutants In Ground Water Business and industrial activities: dry cleaners, paper processors, metal coating companies, and gas stations. Farm operations farm chemical spills during mixing and loading, excessive fertilizer and pesticide applications, inappropriate manure storage techniques, and improper disposal of farm chemical residuals and containers. Household activities: improper use or disposal of chemicals include: paint thinners, used motor oil, drain openers and discharge of water softeners.

12 Chemical Transport Focus: movement with water away from the unsaturated zone Process overview: Rain or irrigation Dissolve with the water and begin to travel Infiltration to the unsaturated zone Surface runoff will begin Travel toward surface waters (e.g. streams, ponds, or lakes). Downward movement of chemicals toward the saturated zone

13 Plant uptake Broken down by chemical or microbial action Volatilization Adsorbed (i.e. chemically bonded) by soil particles (clays and organic matter)

14 Flow with groundwater Mixing Spread Removal impossible Remediation only solution (point-of-entry/point-of-use)

15 Source Concentration Health risk Cause Prevention Remediation Point source pollution Single, indentifiable High Acute Accidental Safe practice Relatively easy but costly Non-point source pollution Over large area, unidentifiable Low Chronic Effectively intentional Difficult even with safe practice Impossible

16 The region of point source pollutant concentration within an aquifer zone is called a plume. The plume describes a three-dimensional zone of contamination, at some specified level of concentration(s), which moves with the ground water. Pollutants enter aquifer 1) a continuous release over a long period of time 2) as a concentrated slug of pollutant that is released, more or less all at once Point source contaminant plume is easiear to cleanup (than NPS), but the costs are great. Prevention is the most economical approach.

17 A pumped well which taps a contaminated region of an aquifer has the potential to pull either high-concentration pollutants (typical of point sources) or lower-concentration contaminants (typical of nonpoint sources) directly into the well Contaminated water in the aquifer zone travels by the same mechanisms for confined and unconfined aquifers.

18 Methods for groundwater quality protection Identify potential sources of contamination at the farm site and in the surrounding area and learn about water supply source location Point sources: fuel storage tanks, pesticide and fertilizer storage facilities and animal waste storage structures. Non-point sources: Septic systems and the chemicals applied to farm fields or lawns. Questionnaire such as the Water Quality Serf-Help Checklist published by the American Farm Bureau Federation can help.

19 The key is to choose the correct TIMING and AMOUNT of application * soil testing and establishing realistic yield goals to set fertilizer requtrements * taking credits for nutrients from legume crops and animal manure * timing/split applications to meet crop needs

20 Nutrient and pesticide management (cont d) Soil conditions: -- Texture: sandy or clay-rich, ease of drainage -- Amount of organic matter -- Chemical adsorption capability (persistence of chemical applied) Site conditions: -- Depth to water table -- Abandoned wells nearby You can always consult the local office of Soil Conservation Service and your -- Fractured county Extension or soluble Service bedrock to in help the area you plan a nutrient and pesticide management system. * Management -- Tillage method -- Application techniques -- Disposal of containers and remainder -- Integrated Pest Management (IPM) alternatives

21 Limiting the use of the land immediately around the well and ensuring proper maintenance and security of the well is called well head protection Risky activities: mixing and loading of chemicals or rinsing of equipment in the area immediately surrounding a well, improper construction or direct injection into the well. A spill in the well head zone could quickly contaminate well water and result in the loss of the well and permanent damage to the aquifer. The need for extreme care around wells can not be overemphasized.

22 Management for the well-head area includes many simple precautions: * ensure the well head is properly sealed to avoid direct injection * inspect the well-head casing for cracks that might allow contaminants to enter * mix and load chemicals at least 100 feet from the well * install a check valve on filling lines to prevent back-siphoning while filling a spray tank * ensure that all abandoned wells are properly sealed Consult your local health department for information on well-water testing and proper well construction and abandonment standards and methods.

23 Units: ppb: part per billion, i.e. µg/l ppm: part per million, I.e. mg/l

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25 Important: get a clean sample, minimize secondary contamination E. Coli is non pathogenic More abundant than other pathogenic microorganisms Use the concentration of coliform and E. coli as indication of potential presence of other pathogenic microorganisms Definition: Coliform: relating to, resembling, or being E. coli CFU: coliform forming unit

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27 Chemical water quality parameters ph Electrical conductivity nitrate and phosphorus levels (concentrations)

28 ph - expression of [H + ] of water Autoionization: H O + H O <--> H O + (aq) + OH - (aq) life (mostly) depends on waters that are neutral in acidity (ph 7-8) - convert [H + ] from 10-1 M ~ M to 1~14 via: - log 10 [H + ]

29 ph will have negative value if [H + ] > 1.0 M, such as for strong acid, sulfuric acid Acidic Basic Neutral

30 Water Electrical Conductivity Total Dissolved Solids Measurement Total dissolved solids (TDS) refers to total concentration of inorganic solids. (mg/l) TDS refers to ions like calcium, magnesium, sodium bicarbonate, nitrogen, phosphorous, iron and sulfur The presence of these chemical constituents gives water the ability to conduct electricity, hence, electrical conductivity (EC) of water is an indirect measure of its dissolved constituents EC is expressed in terms of the specific electrical conductivity, which is defined as the reciprocal of electrical resistance in ohm (Ω), in relation to a water cube of edge length 1 cm at 20 0 C The specific EC unit is given in siemens per cm (S.cm -1 ), where S = Ω -1 It has been found that 0.67 mg/l TDS contribute to 1 µs.cm -1 EC gives a determination of TDS, which is an acceptable indicator for water quality.

31 Some numbers to remember: A distilled water should typically have an EC of less than 0.3 µs.cm -1. For ground water, an EC of 500 µs.cm -1 suggests a pollution problem, while values as high as 2000 µs.cm -1 may be acceptable for irrigation water. Drinking water has a secondary MCL of 500 mg/l TDS.

32 Apply electrical charge record conductivity relate to TDS concentration Conductivity / TDS meter. Water samples Deionized water

33 ANION DETERMINATION OF WATER BY ION CHROMATOGRAPHY Speed 2 = d 2 /time Speed 1 = d 1 /time

34 ION CHROMATOGRAPHY Application IC Chromatogram of LMM acids in HanfordTank Waste (Tank ID AN-107) using AS-11 Column lmw2.htm

35 Take a whirlpak water sample bag Bring sample to school next Tuesday, put in frig On sample bag, record: sampling location date and time Your name and group

36 Point Source Pollution: A single, identifiable source that discharges (empties) pollutants into the environment. Point source pollution is characterized by high concentrations over a small area or at a point. It causes acute problems because their high concentrations. Point source pollution is generally accidental. Through increased awareness and safer practices, the number of point source pollution problems could be reduced. Non-point Source Pollution: A more difficult source of pollution to pinpoint because this pollution type enters the environment from a widespread land area. It is characterized by low concentrations over a large area. This is considered a chronic (as opposed to acute) problem because of the characteristic low concentration of the chemical that persists over a long time period. It is effectively intentional and can occur even with safe application practice is in place.