GEOL 102 1st Edition Lecture 11 Outline of Last Lecture MidtermOutline of Current Lecture I. GroundwaterII. Rocks and GroundwaterIII. The Water TableIV. Extraction and ContaminationCurrent LectureI. GroundwaterPracticalities Component of hydrologic cycle (~1%) Human settlement: we settle near water supply Human need: to survive we must have 4 liters a dayProblems: over-extraction, land subsidence, contaminationBecoming Groundwater Precipitation enters soilThis infiltration will vary with soil type and if vegetation is creating large pores Deeper infiltration leads to groundwaterVoids are saturatedBeneath the water table, it is completely saturatedBottom of the groundwater systemThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.With increasing depth, pressure increases, voids decrease, minerals precipitate to fill voids 50% of groundwater is found in the upper 1 km Below 10 km, metamorphic processes affect waterDischarge, Recharge, and flow path Recharge: water entering the groundwater system Discharge: groundwater emerging at the surface, controlled by topography and bedrockII. Rocks and GroundwaterRock properties determine how water can flow Porosity: voids in rockRock appears solidPore: open spacePorosity is determined by the percentage of pore volume to total volumePrimary porosity: grain scale voids Varies with sorting and angularity As sorting goes down, porosity goes downAs angularities go up, porosity goes downSecondary porosity: factures and cracks in rock Permeability: ability to move fluidDepends on connectivity: the number of conduits, the size of conduits, and the tortuosity of conduitsGravel and sandstone have a high permeabilityGranite and clay have a low permeabilityGeologic Units Aquifer: permeability and porosity of rock Aquaclude: impermeable layers that seal aquifers Artesian aquifer: confined aquifer with high fluid pressuresIII. The Water TableWater table variation Topographic controls: water table is a subdued version of topography Climatic controls: water table elevation varies over short- and long-termThe water table is both renewable and non-renewable, it takes a long time to renew and can vary greatly with precipitation levelsWhere is the water table? Beaches, lakes, streamsGroundwater flow varies with: Hydraulic gradientPressure differences drive fluid flowPressure varies with the height of the water table Hydraulic conductivitySimilar to permeabilityHow fast can the fluid move?Flow rate: inches per day, slow because of torturous path and frictionIV. Extraction and ContaminationDrawdown: water table is lowered when extraction exceeds rechargeCone of depression: lowered water table below a point of extractionSaltwater intrusion (coastal areas): salt water is denser and with over-extraction, saltwater can flow into wellsSubsidence: pore collapse due to extraction, irreversible lowering of land surfaceContamination Dispersal: spreading contaminants through pores Plumes: zone of elevated