Water well design, installation and completion

Question 1

Requirements for designing a water well

Answer 1

Need to know both current and future uses of the water well

Question 2

Before water well field investigations

Answer 2

a) geophysical surveys
b) test drilling – wells drilled to better delineate the aquifer
c) log the cuttings to create a stratigraphic log

Question 3

After water well field investigations

Answer 3

a) down hole geophysics

b) pump tests

Question 4

Considerations in choosing a well location are:

Answer 4

1. Geology of the area/ aquifer
2. location of contaminant sources
3. minimal distances - buildings, septic tanks
4. accessibility for cleaning, testing, monitoring, maintenance and repair
5. ground slope in immediate vicinity of the well

Question 5

4 types of water wells:

Answer 5

1. Dug - by hand
2. Driven or jetted - pushed or hydraulic
3. Bored - auger wells
4. Drilled - rotary

Question 6

4 general components of a water well

Answer 6

1. casing
2. intake design
3. annulus fill
4. surface considerations - mounding caps

Question 7

Casing

Answer 7

1. solid pipe - steel or plastic
2. large enough diam to have pump
3. casing must extend > 20cm above ground
4. casing must be > 60 cm higher than record flood
5. if non-metallic, must be protected by steel casing

Question 8

Intake design:

Answer 8

1. allow water not sediment in

2. only placed across from the aquifer section of the well

Question 9

2 main types of screens

Answer 9

1. wire-wound stainless steel well screen for sand or gravel

2. slotted or perforated liner for caving bedrx

Question 10

Size of openings in the screens

Answer 10

Use a slot size that allows 60% of the aquifer material to pass through the screen during the development phase

D60

Question 11

Annulus fill

Answer 11

Annulus is the area b/t the borehole and the well casing

Question 12

2 main types of annular fill

Answer 12

1. annular seal

2. filter pack/gravel pack

Question 13

Annular seal and its purpose

Answer 13

Annulus must be filled with impermeable, chemically inert material from the surface to immediately abve the perforated zone or screen

Prevent surface contaminants from entering the well
prevents fluids from poor quality or contaminated zones from entering the aquifer

concrete, bentonite, grout mix

Question 14

Filter pack/gravel pack and its purpose

Answer 14

Often gravel, clean quartz sand or glass beads

Placed in the annulus of finer-grained aquifers to improve well yields

Question 15

Surface considerations

Answer 15

1. Mound around the well
2. water wells must be securely covered
3. pump house must contain only the water well and pump
4. pump house made so water will not pool on floor

Question 16

Well completion tasks

Answer 16

1. well development
2. well disinfection
3. yield test

Question 17

Well development purpose

Answer 17

1. remove any fine sediments and drilling mud from around the well screens
2. to remove water introduced to the aquifer (surface h2o, other aquifers)

Question 18

Methods used to develop a well

Answer 18

1. over pumping - pump water out of the well until its clear - 1 direction of flow
2. Jetting - blowing high P water or air through the screens
3. surging - Water surged in and out through the openings, pump used to remove sediment ladened H20 - 2 direction flow

Question 19

Naturally developed well

Answer 19

Development methods used remove the fine material leaving the coarse material behind, directly in contact with well screens – Non-cohesive sediments

Question 20

Gravel packed well

Answer 20

Sand or gravel is placed in the annulus after drilling. NOT material from the area – BED RX

Question 21

Well disinfecting

Answer 21

Done after all eqpt has been installed. Chlorine at a min [] of 200 mg/l in the well for 12 hours

Question 22

yield test

Answer 22

1. Minimum of 2 hoours or until the well is back to 90% of it original level
2. determines rate at which to pump the well and where to put the pump

Question 23

Pump must not lower wtr level below

Answer 23

1. top of aquifer
2. top of perforations
3. top of pump intakes

Question 24

Submissions to AEP

Answer 24

1. General stratigraphic log

2. Well construction and design details