Groundwater Quality

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  • Groundwater and Soil qualityQuality of GW as important as its quantityUsability of GW depends on the quality: chemical, physical, and bacteriologicalNeed studies: source and environment of GW, pollution sources, dan other aspects related to the quality of GWQuality of GW is affected by the quality of soil that holds the GW

  • Effect of Soils and PlantsMinerals mobilize in the soil mantle as clay and other soil particles weather, and planta and animal materials decompose rains make them leach to GWHumid areas salt concentration 400 500 mg/l leachate from an agricultural field Evaporation of water from surface and take up water by roots of plants increase the salt concentrationThe dominant ions Ca, Mg, Na, HCO3, SO4, and Cl.

  • Leachate from an irigation field in an arid climate several thousand milligrams per literSoil and plant effects ion exchange and other reaction of the water and its constituents with the soil, and uptake the nutrients by root plants.Ion exchangecations which are adsorbed and exchanged for other cations by the negatively charged clay and organic matterThe sequence: Li, Na, K, NH4, Rb, Cs, H, Mg, Ca, Sr, and Ba.i.e.: Li is replaced by Na, Na by K, etc.Dense clay layers (aquitards and aquicludes) act as semi permeable membranes that hold back certain ions while passing others

  • Chemical reactionsimmobilization of phosphate adsorbed and precipitated in most soils other than pure sandsHeavy metals can be fixed in the soil, particularly when the soil contains clay, has a pH above 7 and is aerobicAlkaline soils: calcium CaCO3, acid rain water, however, can dissolve CaCO3 in the soilPlan rootscan absorb nutrients like N, P, K, S, and certain heavy metals and other trace elementsits concentration will be reduced by the time the rainwater has reached the GW.

  • Chemical fertizersenrich the content of N, P, an KCanbon dioxide and organic acids produced by plants and other living materials in the soillower the pH of water accelerate the rate of weathering and enhances the mobility of metals

    Aquifer effectsWater continuously moves downwardreacts with soil and rock materials in the vadoze zone and aquifer these reaction primarily consist of solution of solid phase in accordance with the solution chemistry of the particular minerals range from almost insoluble to very soluble (evaporites) that are affected bytemperature and pressure

  • Other sources of dissolved saltsunderground waters of marine origin and salty connate waters intrude freshwater aquifers.Clay materials behave like membranes to screen water which can produce osmotic-pressure differences, salt seiving or ultrafiltration, and electric-poential differenceMeteoric GW tends to be of good quality except where it has been stagnant or otherwise isolated from the hydrologic cycle in mineral rich or clay rich aquifersE.g.:igneous and crystaline rocks generally yield excellent GW quality (salt content
  • Bacteriological qualityBacteria and micro-organism:

    HarmlessDiseas-causing pathogenic bacteriaNatural water, except very shallow aquifers, free from pahogenic bacteria or viruses many consumers treated GWNatural water polluted by polluted water and may lack of chlorination or other disinfectionSurface soils contain a myriad of microorganisms decrease rapidly below the root zoneMicrobiological activity can and will exist in many subsurface regions (e.g: extend to a depth of about 2000 m, assuming a normal temparature increases about 3oC per 100 m).

  • An example: coliforms present in the interstines of human beeing and other warm-blooded animals. They are harmless however their presence in GW indicates the precense of pathogenoc bacteriaBOD (biological oxygen demand) an indirect index of the presence of organic matter and waste

    Chemical qualityWater is an excellent solvent knowledge of the geochemistry of the dissolved constituents knowledge of methods of reporting of analytical data

  • Main constituents on groundwater:TDSHardnessAlcalinity, Acidity, pHOther constituents: Calcium, Magnesium, Iron, Potassium, Strontium, Manganese, Aluminum, Phosphorous, Nitrogen, Chloride, etcMinor and trace mineral: small quantity but sometimes dangerous (toxic), e.g. Arsenic

  • Reporting chemical analysisConcentration of dissolved salt or ions in water expressed by (i) weight and weight-volume relative weights of the solute and the solution in parts per million (ppm),i.e. One part by weight of the solute in one million part by weight of the solution miligrams in one liter (mg/l) for low concentration of dissolved solid; however, for high con it needs to be corrected(ii) chemical equivalent combination and dissociation of cations and anions are governed by their equivalent weights (combining weights) rather than their gravimetric weight.

  • The equivalent weight of an ion equals to its atomic or molecular weight devided by its valancy. By deviding ionic concentration (ppm) by the equivalen weight of that ion resulting the concentration in equivalents per million (epm), or more precisely in milligram equivalents per kilogramIf the original data are reported in milligrams per litre resulting: milligram equivalents per litre (meq/l)Since one equivalent weight of cation will combine with one equivalent weight of anion the sum of the cations should equal to the sum of anions when they are expressed in epm. Otherwise, errors or incompletness of chemical analysis are indicated

  • Analytical results are sometimes expressed in terms of hypothetical combinations by combining milliequivalents of the cations with the anions in the following sequence:CationAnionCalciumCarbonateMagnesiumBicarbonateSodiumSulphatePotassiumChlorideNitrate

  • Konsentrasi dalam satuan mg/l x faktor konversi pada tabel = meq/lSumber: Todd, 1980






  • Dissolved constituents in GWSilica from quartz (the cristalineof silica), feldspars, mica, silicate minerals, etc a few 60 ppmIron from pyroxenes, amphiboles, etc in the form of ferric hydroxide, < 0.5 ppmManganese from metamorphic and sedimentary rocks conc < 0.2 ppmCalciumMagnesiumEtc...


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