Water Wells for Yield and Health

ByMichael L. Vaught

EGIS PA441 Northside Dr

Ground Water Atlas of the United States

Map Segment 6Geographical provincesTypes of aquifers

Map Segment 11capp.water.usgs.gov/gwa/gwa.htm

http://mapping.usgs.gov/mac/isb/pubs/booklets/usgsmaps/atlas.html

Ground Water Atlas of the United States Segment 11

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.

Water Wells for Yield

Depth

Diameter

Screens

Test yield

Depth & Diameter

Geographic or Physiographic location Coastal Plain Piedmont Mountains

Type of Well shallow or deep large or small diameter cased or “open hole”

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

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

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

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

Well ScreensSizesTypes of material

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

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

Test YieldSpecific Capacity

Static LevelPumping LevelDrawdownPumping RatePump DepthRecharge RatesStatic Head

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

Water Wells for Health

Well Health and Safety

Casing Sealing the Annulus

Wellhead Protection Air quality, drainage, and recharge

Well Maintenance Flushing and circulation

Sealing the Annulus Administrative codes and regulations

Minimum of 20’ Bentonite, Cement, Concrete, Mixtures

Wellhead Protection

Wellhead Protection

Wellhead Protection Guidebooks WHPA Delineation Methods

Arbitrary fixed or calculated fixed radius method

Landscape so surface water drains away from the wellhead

Well Maintenance

Homeowner

Campgrounds

Cottages

Non-community & Public Systems

Well Maintenance

Pump DepthExercise (water usage)Chlorination

>200 ppm, 6 pHRecord keepingAnnual Testing for Bacteria

Chlorination not recommended for coliform

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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

Well Abandonment

Disinfecting

Sealing

Decommissioning

Responsibility for Well Abandonment

Codes and RegulationsWell owner Well contractorPump installer Forms ______

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’.

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

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.

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