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