Ground Water Atlas of the United States Segment 11
Rock Type zSedimentary, Metamorphic, and Igneous rocks. zHard to crystalline rock verses unconsolidated granular aquifers. zReference the Ground Water Atlas of the United States and the Geological Surveys Maps.
Water Wells for Yield zDepth zDiameter zScreens zTest yield
Depth & Diameter zGeographic or Physiographic location yCoastal Plain yPiedmont yMountains zType of Well yshallow or deep ylarge or small diameter ycased or “open hole”
Well Depth & Diameter Hard to crystalline rock zCharles Daniel III, 1989, Geological Survey Water-Supply Paper 2341-A. yWells below 400’ xLarge stress release fractures y12” wells have 4 times yield of 6” wells
zRalph Heath, 1983, Geological Survey Water-Supply Paper 2220. yDepth depends on lowest zone tapped xAquifer Thickness & Composition yDiameter has little effect on yield xLimits pump size Well Depth & Diameter unconsolidated granular aquifers
Ratio of Yields by diameter x4inch6 8 1012 1.oo1.051.091.131.16 1.oo1.041.071.10 1.oo1.031.06 1.oo1.03
Pump Size by well diameter Well YieldPump SizeCasing Size >100 GPM46 75 – 17558 150 – 400610 350 - 650812
Test Yield zRequired yield yEPA 570/9-91-004 xHomeowner per resident 50-75 gpd xCampgrounds per camper 15 gpd xCottages seasonal per resident 50 gpd xRestaurants per patron 7 - 10 gpd
Test Yield zCodes and regulations. zWell Capacity yDomestic (not public, industrial, irrigation) xMax continuous quantity for 1 hour xNote static and pumping WL’s and GPM
Test Yield Specific Capacity zStatic Level zPumping Level zDrawdown zPumping Rate zPump Depth zRecharge Rates zStatic Head
Test Yield Specific Capacity z 100GPM Withdrawal z 15’ z Static WL z 45’ z Pumping WL z 100gpm / (45-15)ft z = specific capacity of z 3.3 gpm/ft of drawdown z Specific Capacity of a newer well z65 GPM Withdrawal z15’ zStatic WL z65’ zPumping WL z65gpm / (65-15)ft z= specific capacity of z1.3 gpm/ft of drawdown zSpecific Capacity after 15 years
z Landscape so surface water drains away from the wellhead
Well Maintenance zHomeowner zCampgrounds zCottages zNon-community & Public Systems
Well Maintenance zPump Depth zExercise (water usage) zChlorination y>200 ppm, 6 pH zRecord keeping zAnnual Testing for Bacteria yChlorination not recommended for coliform
Set pump intake As Shallow As Possible (ASAP). zPumping influences motion within the borehole column zPumping oxygenates the well water from the top down. zPumping draws shallow water downward. zPumping utilizes water from two sources; Well Storage and Well Flow.
Well Storage zStored water lies above the intake and the above the highest water zone zWell Storage- Zone of the water column within or draining to the borehole that is both above the pump and above the most shallow production zone,( called the “ Storage Cell”). zIn Storage Type Wells the pumping water level continuously falls during the stress test.
Well Flow zFlowing water moves between the production zones and the pump intake. zWell Flow – Zone of the water column between the pump and any contributing production zone (called the “Flowing Cell”). zIn Flowing Type Wells the water level stabilizes during the stress test.
Flowing type wells generally remain cleaner. zFlowing type wells minimize the borehole Storage and maximize the Flowing Cells by the correct pumping depth. zFlowing Cells remain cleaner because of the borehole turbulence and lack of enrichment. zFlowing type wells = Long term reliability + controlled biofouling.
Storage type wells require periodic maintenance. zTypically Storage Cells become enriched and biofouled in the top of a water well. zStorage type wells must be exercised regularly to flush biofilm and enriched water from the cell. zStorage type wells = Short term maintenance + rapid biofouling.
Minimize Storage and Enlarge Flow Cells zExcess Storage generates uncontrolled growth of naturally occuring biofilms within the well. zEnrichment of the excess or recycled Storage accelerates biofouling from the top down. zSet the pumping depth in a well based on Actual Maximum Demand. zSet the pumping depth no more than twenty feet below the actual maximum demand level in the average Domestic size water well.
Set pump intake depth for actual maximum demand. zActual Maximum Demand Water Level – Depth to water within the well during one hour of continuous pumping while hooked to the system under simulated intense usage. zSet the pumping depth no more than twenty feet below the actual maximum demand level in the average Domestic size water well.
Rehabilitating biofouled wells means controlled biofilms. zRecondition homeowners dirty wells by cleaning the biofouling and repositioning the pump (ASAP). zRepairs eliminate shallow water. zBorehole flow diverters change the Flowing Cells to eliminate turbidity.
Well Abandonment zDisinfecting zSealing zDecommissioning
Responsibility for Well Abandonment zCodes and Regulations zWell owner zWell contractor zPump installer zForms ______
Abandonment of Bored Wells zLarge diameter, 18-36 inches yRemove plumbing or obstructions yDisinfect with calcium hypochlorite yRemove well casing (3’ BGL) yFill with cement, concrete, bentonite, dry clay, natural material. yC ap with 1’ cement plug extending 1’.
zGravel packed, screened, unconsolidated yRemove or grout the casing yDetermine well depth yDisinfect with calcium hypochlorite yFill with neat cement or Bentonite grout zCased open hole ySame as above except……... yFill to 10’ below TOR or 5’ below CSG with cement, bentonite, sand, gravel, or cuttings. yFill to surface Abandonment of Drilled Wells
Summary zWell characterization is essential for sustained quantity and quality. It is the first step in configuring a water supply system for long-term yields of consistent water.” “Use-it-or-loose-it”, if the well is set up to supply more water than is routinely needed, maintenance must include maximum demand pumping either quarterly or monthly. “Private Water Systems Handbook” says; “A home water system must be able to supply the peak use rate continuously for one hour.” zWhen the pump depth is set to maximize the well yield, the well may accumulate enriched water above the pump. Pump depth should be sufficient to allow only 10 to 20 feet of water above the pump during peak demand intervals. Adequate drawdown can stop oxygen enrichment and prevent biofouling.
References zWeb sites ( yahoo search - water well drawdown ) zBooks and Supplier Materials zProfessional Organizations yAmerican Groundwater Trust yGroundwater Associations yWater Systems Council zGovernment yEPA, USDA, USGS yState Agencies yExtension Service