water well design august 6, 2015 al/ms awwa ralph hayes, p.e., bcee engineering director msdh,...

Water Well Design August 6, 2015AL/MS AWWA

Ralph Hayes, P.E., BCEEEngineering Director

MSDH, Bureau of Public Water Supply

Water Well Design

-Why drill a water well?-How to get started.-Where to drill a water well-Steps in drilling a water well

Why Drill a Water Well--usually when someone decides they need more

water, or a more dependable water supply.

Longer Run Times- if consistent run times of 12 hrs +

Average Well Life- if average well service life is high, expect failures to occur more frequently

Back up Supply- if lose water service, need supply to bring plant or factory down

How to Get Started• MUST DETERMINE

-- How much water needed (maybe need 2 wells)-- Where is water needed (have it close to demand

point)- What quality? ( potable or process water)

How to Get Started

• First Round Considerations

– -Once preliminary considerations are resolved, the investigation begins. The question now is, can you get the amount of water needed, delivered to where it is needed, in the quality needed.

How to Get Started

• Resources to help determine the likely availability of water………..

• DEQ, with location can get other wells in area• Well Driller, can get specific data of existing

wells in area• MSDH, Bureau of Public Water Supply• USGS, or USGS Retired

How likely is water available

• Take collected data, interpolate between wells to determine “expected” well depth, static water level, well yield.

Sample Example

• For this discussion, we will estimate the following parameters-

• --500’ to bottom of aquifer• --aquifer thickness is 60 feet• --pump rate needs to be 500 gpm

Test Hole

• A Test Hole is a pilot hole drilled to expected Total Depth (TD) of the well, expecting to penetrate the aquifer completely. Sand samples are collected and an e-log is run on the Test Hole.

• Sand Sample when analyzed, help determine the slot size of the well screen.

• E-log determines where the top and bottom of the screen begin and end.

Electric Log (E-Log)

Electric Log

• E-log, marked up

Test Well

• A Test Well is a small diameter (4” -6”) well and screen, set in the “sands” seen from the e-log and a pump capable of pumping 100-200 gpm.

• The Test Well is set and developed and pumped until a representative sample is collected and tested.

Sample Test Well Results• 1

Test Well

• Pro- get good idea of water quality before making permanent well.

• Con- 20-40 feet of screen might not cover entire aquifer and water quality might be different in areas not screened

• Com- pump rate of 100-200 gpm usually significantly less that permanent pump rate,

• Chance of 500 gpm pump producing turbidity

Permanent Well

• Ream Test Hole and set & cement casing to top of water bearing sands.

• Under ream sand zone (below casing) and set screen/lap, gravel

Casing

• Have to determine if you want Foreign or Domestic Pipe, (foreign typically cheaper).

• Have to determine if you want Prime (w/mill certs) or Structural grade pipe, (Prime is more expensive).

• Determine is welded or threaded joints, welded is the standard.

• Specify pipe must have factory bevel, not torch cut

Setting Casing

• 1

Welding Casing

• 1

2-Piece Well

We Drawing• 1

Well Screen

• Typical well screen is referred to “Stainless Steel Wire Wrapped Rod Base Screen”

• Typical in 20’ or 10’ scetions• Slot size determined from info obtained in TH

Stainless Steel WW Rod Base

• 1

Drill Rigs

• 1

Drill Rig

24

Mud Pits, Mud Pump

• 1

Drill Rig

26

Finished Water Wells

• Various ages

28

Well w/ Generator

• 1

Tight Location

• 1

Questions ?

• Ralph Hayes• Ralph.Hayes@msdh.state.ms.us• 601-576-7518