Water Wells for Yield and Health
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Transcript of Water Wells for Yield and Health
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Water Wells for Yield and Health
ByMichael L. Vaught
EGIS PA441 Northside Dr
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Ground Water Atlas of the United States
Map Segment 6Geographical provincesTypes of aquifers
Map Segment 11capp.water.usgs.gov/gwa/gwa.htm
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http://mapping.usgs.gov/mac/isb/pubs/booklets/usgsmaps/atlas.html
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Ground Water Atlas of the United States Segment 11
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Rock Type
Sedimentary, Metamorphic, and Igneous rocks.
Hard to crystalline rock verses unconsolidated granular aquifers.
Reference the Ground Water Atlas of the United States and the Geological Surveys Maps.
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Water Wells for Yield
Depth
Diameter
Screens
Test yield
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Depth & Diameter
Geographic or Physiographic location Coastal Plain Piedmont Mountains
Type of Well shallow or deep large or small diameter cased or “open hole”
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Well Depth & DiameterHard to crystalline rock
Charles Daniel III, 1989, Geological Survey Water-Supply Paper 2341-A. Wells below 400’
Large stress release fractures
12” wells have 4 times yield of 6” wells
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Ralph Heath, 1983, Geological Survey Water-Supply Paper 2220. Depth depends on lowest zone tapped
Aquifer Thickness & Composition
Diameter has little effect on yieldLimits pump size
Well Depth & Diameter unconsolidated granular aquifers
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Ratio of Yields by diameter
4inch 6 8 10 12
1.oo 1.05 1.09 1.13 1.16
1.oo 1.04 1.07 1.10
1.oo 1.03 1.06
1.oo 1.03
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Pump Size by well diameter
Well Yield Pump Size Casing Size
>100 GPM 4 6
75 – 175 5 8
150 – 400 6 10
350 - 650 8 12
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Well ScreensSizesTypes of material
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Test Yield
Required yield EPA 570/9-91-004
Homeowner per resident 50-75 gpdCampgrounds per camper 15 gpdCottages seasonal per resident 50 gpdRestaurants per patron 7 - 10 gpd
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Test Yield
Codes and regulations.
Well Capacity Domestic (not public, industrial,
irrigation)Max continuous quantity for 1 hourNote static and pumping WL’s and GPM
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Test YieldSpecific Capacity
Static LevelPumping LevelDrawdownPumping RatePump DepthRecharge RatesStatic Head
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Test YieldSpecific Capacity
100GPM Withdrawal
15’ Static WL
45’ Pumping WL
100gpm / (45-15)ft = specific capacity of 3.3 gpm/ft of drawdown
Specific Capacity of a newer well
65 GPM Withdrawal
15’ Static WL
65’ Pumping WL
65gpm / (65-15)ft = specific capacity of 1.3 gpm/ft of
drawdown
Specific Capacity after 15 years
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Water Wells for Health
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Well Health and Safety
Casing Sealing the Annulus
Wellhead Protection Air quality, drainage, and recharge
Well Maintenance Flushing and circulation
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Sealing the Annulus Administrative codes and regulations
Minimum of 20’ Bentonite, Cement, Concrete, Mixtures
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Wellhead Protection
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Wellhead Protection
Wellhead Protection Guidebooks WHPA Delineation Methods
Arbitrary fixed or calculated fixed radius method
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Landscape so surface water drains away from the wellhead
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Well Maintenance
Homeowner
Campgrounds
Cottages
Non-community & Public Systems
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Well Maintenance
Pump DepthExercise (water usage)Chlorination
>200 ppm, 6 pHRecord keepingAnnual Testing for Bacteria
Chlorination not recommended for coliform
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Set pump intake As Shallow As Possible (ASAP).
Pumping influences motion within the borehole column Pumping oxygenates the well water from the top down.
Pumping draws shallow water downward.
Pumping utilizes water from two sources; Well Storage and Well Flow.
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Well Storage
Stored water lies above the intake and the above the highest water zone
Well 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”).
In Storage Type Wells the pumping water level continuously falls during the stress test.
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Well Flow
Flowing water moves between the production zones and the pump intake.
Well Flow – Zone of the water column between the pump and any contributing production zone (called the “Flowing Cell”).
In Flowing Type Wells the water level stabilizes during the stress test.
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Flowing type wells generally remain cleaner.
Flowing type wells minimize the borehole Storage and maximize the Flowing Cells by the correct pumping depth.
Flowing Cells remain cleaner because of the borehole turbulence and lack of enrichment.
Flowing type wells = Long term reliability + controlled biofouling.
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Storage type wells require periodic maintenance.
Typically Storage Cells become enriched and biofouled in the top of a water well.
Storage type wells must be exercised regularly to flush biofilm and enriched water from the cell.
Storage type wells = Short term maintenance + rapid biofouling.
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Minimize Storage and Enlarge Flow Cells
Excess Storage generates uncontrolled growth of naturally occuring biofilms within the well.
Enrichment of the excess or recycled Storage accelerates biofouling from the top down.
Set the pumping depth in a well based on Actual Maximum Demand.
Set the pumping depth no more than twenty feet below the actual maximum demand level in the average Domestic size water well.
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Set pump intake depth for actual maximum demand.
Actual 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.
Set the pumping depth no more than twenty feet below the actual maximum demand level in the average Domestic size water well.
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Rehabilitating biofouled wells means controlled
biofilms. Recondition homeowners dirty wells by cleaning the
biofouling and repositioning the pump (ASAP).
Repairs eliminate shallow water.
Borehole flow diverters change the Flowing Cells to eliminate turbidity.
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Shallow Pump with Flow Sleeve
Bottom of 6.25” Casing
500’. Bottom of the well from downhole video.
Ground Level Top of Casing
Flow sleeve or flow pipe
Six inch open rock borehole.
176’. Documented by video. Water producing zone.
160’. Water producing zone from video record.
P U M P
300’ submersible pump with flow sleeve
71.5’ Shallow water zone. 7 gpm
Grout
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Deeper Pump with Flow Sleeve
42’ Bottom of 6.25” Casing
500’. Bottom of the well from downhole video.
Ground Level Top of Casing
45.4’ Water Level. Static or full level
Six inch open rock borehole.
176’. Documented by video. Water producing zone.
160’. Water producing zone from video record.
P U M P
300’ submersible pump with flow sleeve
50’Shallow water zone.1gpm
Grout
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Liner with Flow Sleeve
42’ Bottom of leaky well casing
500’. Bottom of the well from downhole video.
Ground Level Liner pipe
Packer or seal to hold grout
Six inch borehole.
160’. Water producing zone from video record.
P U M P
Flow sleeve or flow pipe
50’Shallow water zone.1gpm
Grout
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Well Abandonment
Disinfecting
Sealing
Decommissioning
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Responsibility for Well Abandonment
Codes and RegulationsWell owner Well contractorPump installer Forms ______
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Abandonment of Bored Wells
Large diameter, 18-36 inches Remove plumbing or obstructions Disinfect with calcium hypochlorite Remove well casing (3’ BGL) Fill with cement, concrete, bentonite,
dry clay, natural material. Cap with 1’ cement plug extending 1’.
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Gravel packed, screened, unconsolidated Remove or grout the casing Determine well depth Disinfect with calcium hypochlorite Fill with neat cement or Bentonite grout
Cased open hole Same as above except……... Fill to 10’ below TOR or 5’ below CSG with
cement, bentonite, sand, gravel, or cuttings. Fill to surface
Abandonment of Drilled Wells
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Summary
Well 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.”
When 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.
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References
Web sites (yahoo search - water well drawdown)Books and Supplier MaterialsProfessional Organizations
American Groundwater Trust Groundwater Associations Water Systems Council
Government EPA, USDA, USGS State Agencies Extension Service