constant head borehole permeameter test procedure and test form

7/26/2019 Constant Head Borehole Permeameter Test Procedure and Test Form

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CONSTANT HEAD BOREHOLE PERMEAMETER TEST PROCEDURE

Use the following instructions to conduct a constant-head borehole permeameter test using a

Pask (constant head borehole) Permeameter. Other borehole permeameters may be used;

however these instructions relate only to the Pask permeameter. !his information is based on

"ppendi# $ of the %ova &cotia &ewage 'isposal uideline that can be found at the followingweb site

http**www.gov.ns.ca*nse*wastewater*sewagedisposalguide.asp

!he permeameter test measures the permeability (also called hydraulic conductivity) of the soil

at the bottom of a borehole above the water table. !he test measures the hydraulic

conductivity by temporarily saturating the soil at the bottom of the borehole. +t measures the

,eld-saturated hydraulic conductivity which is commonly abbreviated as /fs.

!he rst step is to make or buy a permeameter. &ee the %ova &cotia uideline for instructions

on building a permeameter. !his is a simple device to make but the clear plastic tube (pipe)

may be e#pensive or di0cult to source. !o avoid the clear plastic pipe common white P1$ pipe

may be used with a sight gauge constructed from clear plastic tubing (!ygon or similar). 2anypermeameters have a screw cap rather than a rubber stopper at the bottom. &ome

permeameters have a ball valve on the lower tube; this is useful but not necessary. !here are

companies that make and sell permeameters and suitable soil augers.

!he upper clear plastic tube or pipe is a small water reservoir. $onvenient dimensions are 3-45

cm inside diameter and 65 cm length but this reservoir can be di7erent diameters or lengths.

" smaller diameter reservoir is more accurate for low-permeability soils and uses less water.

8ou will need to know the inside diameter of the tube in order to calculate the volume of water

draining into the borehole.

http://www.gov.ns.ca/nse/wastewater/sewagedisposalguide.asp

http://www.gov.ns.ca/nse/wastewater/sewagedisposalguide.asp



Equipment and supplies:

2"%'"!O98

• Permeameter.

•

&upply of water. !he test uses about : liters per test if using a 45 cm diameterpermeameter. " -cm permeameter uses about one liter per test. <ater is usually supplied

by garden hose or erry cans.

• =and auger. " commonly used auger has a > cm auger bit but you can use augers of

di7erent diameters.

• <ristwatch with second hand or other timer with minutes and seconds.

• Pre-printed forms. &ee the following pages for a blank form and an e#ample completed

form.

OP!+O%"?

• <ire brush or length of pipe with protruding screws or similar device to roughen smeared

soils.

• !ripod sawhorse or other method to hold the permeameter vertical during the test. !his

can be useful for shallow auger holes or if conducting two of more tests at the same time.

• 'igging bar or steel probe. !his is useful for gravelly or stony soils.



Test proedure:

&elect the locations and depths for the auger holes. " common layout is to auger four holes

one at each corner of the proposed dispersal area. !esting in the receiving area may also be

needed and testing of deeper soil layers may also be useful or needed.

=oles should be augered to the same depth as the planned depth of the inltration surface. @orsand mounds and at-grade beds the auger hole depth should be A to B cm. <hen augering

the hole do not use e#cessive downward pressure on the auger and in general it is best to

remove the auger after ma#imum two turns to remove soil this is intended to reduce soil

compaction.

• "t each location auger a hole to the reCuired depth. +n stony soil it may help to probe

using a digging bar or steel rod to nd a suitable location to auger a hole.

• +f the sides of the auger hole are smeared gouge pick or roughen the side walls with a

wire brush ice pick or other sharp obDect. +mportant +f you roughen or gouge the side

walls of the auger hole you will also need to take eCual care to prepare the bottom and

side walls (the inltration surface) of the dispersal system.• 2easure and record the diameter of the auger hole.

• $omplete the top part of the permeameter form.

• <rite down the soil te#ture and structure.

• !urn the permeameter upside down remove the plug ll with water up to the ,air inlet

hole and then replace the plug.

• @ill the auger hole to a water depth of about A cm.

• Place the permeameter in the auger hole with the ,water drain slots at the bottom of the

hole.

• <atch the clear plastic tube for large bubbles rising from the bottom.

• "s soon as the large bubbles appear start taking readings of the height of water in the

clear plastic tube (in millimeters) taking one reading every minute. +f the rate of fall is very

fast you can take one reading every B5 seconds. +f the rate of fall is very slow you can

take one reading every two minutes or more.

• 'uring the test record the rate of fall of the water level in mm per minute.

• <hen the rate of fall stabiliEes the test is complete. !he rate of fall is stable if the fall is

nearly eCual for three consecutive readings. <ith most soils this takes : to A5 minutes.

• "fter the test if a Fow restrictive horiEon is suspected close to the base of the hole then

auger or probe to this horiEon and measure the depth.

• 9epeat for the remaining auger holes.

• $alculate the /fs for each of the test holes using the calculation method below.



Calulation Met!od:

• <rite down the nal stable rate of fall in the water level in millimetres per minute.

• $alculate the @low 9ate (G) by multiplying the rate of fall by the volume $onversion @actor.

shows the factor for permeameters of various diameters.

Permeameter alulation "ators

+%&+'H '+"2H!H9 O@ !=H

9H&H91O+9 ($2)@"$!O9

45.AB I.AA

45.46 I.45

.A A.4>

• @or other siEes of permeameters the conversion factor may be calculated as follows

• 9 J 9adius in cm J +nside 'iameter K A.

• $onversion @actor J 5.B4:A # 9 # 9.

• <rite the Fow rate on the form in m? * minute.

• Use the chart (at the bottom of the page) to select the &oil @actor (@) based on the type of

soil and the diameter of the auger hole.

• $alculate the /fs. !his is the @low 9ate (G) multiplied by the &oil @actor (@) /fs J G # @.

• <rite this in the space at the bottom left part of the form.

• +f the highest measured /fs is more than 45 times higher than the lowest then the

minimum allowable number of tests is si#. This is because of the high variability of the soil.

• &elect the /fs to be used for siEing of the dispersal area. !his will be the median or middle

value from all the tests conducted.

2athematical-minded "Ps may want to set up a spreadsheet to calculate /fs from the

measured rate of fall using the formulas in the referenced web site and other technical papers.



Speial Situations:



Site #it! a $er% s!allo# &o#'restriti$e !ori(on:

+f the Fow-restrictive horiEon is within about B5 cm of the bottom of the auger hole then the

calculated /fs may be lower than the true /fs. +f it is important to calculate a more accurate

/fs then one option is to use the modied lover formula as outlined in the Permeameter

"ppendi# (below).



Testin) in !ot #eat!er:

+f the temperature of the water used for the permeameter test is above A degrees $elsius

then the test results should be adDusted according to the procedure on pages $-A and $-B of

the following reference

http**www.gov.ns.ca*nse*water*docs*O&!L44-&ection44-!echuide"ppendi#.pdf

http://www.gov.ns.ca/nse/water/docs/OSTG_11-Section11-TechGuideAppendix.pdf

http://www.gov.ns.ca/nse/water/docs/OSTG_11-Section11-TechGuideAppendix.pdf



Trou*les!ootin):



+ater le$el "alls too "ast:

+f the reservoir water level falls too fast to measure then it is only practical to estimate the

lower limit of the soil permeability. !he /fs should be reported as ,greater than B5555

mm*day. +n this situation conduct at least eight permeameter tests.

" rapidly falling water level could also be caused by a large pore such as an old root channel.+n this case the problem can be noted and further tests done to conrm the soil permeability.



+ater le$el is stati, does not !an)e:

+n soils of very low permeability if the auger hole lls with water to above the air hole the

water will drain slowly delaying the start of the test. ently remove some water from the

auger hole to e#pose the air hole and start the test. +f the reservoir still does not drain this

indicates soil of very low permeability and the /fs should be reported as ,less than 45

mm*day.

!he soil can be re-tested using a smaller diameter permeameter and a larger diameter auger

hole.

+t may help to try permeameter tests at di7erent depths or at di7erent locations. !esting at

di7erent depths and locations will help in selecting the best location for the dispersal system

and the best depth for the inltration surface.



+ater le$el drops $er% slo#l%:

+n soils of low permeability the permeameter water level may drop very slowly about one

millimeter per minute. Potential strategies for low permeability soils include (4) re-test at

di7erent locations on the property; (A) re-test at di7erent depths; (B) roughen or scarify the

side walls of the auger hole; (:) re-test using a smaller diameter permeameter and larger

diameter auger hole; () use an alternate permeability test method such as a ring

inltrometer.



Permeameter test "orm



Location (address): File #:

Auger hole #: AH location:

AH depth: AH diameter (at bottom of hole): cm Date:

Height of air hole: 20 cm Permeameter inside diameter: cm Tested by:

onstant Head !orehole Permeameter Test "esults

Time of

day

Total

elapsed

time min

nterim

time min

$ater

le%el

reading

Mm

Drop in

le%el mm

"ate of fall

mm/min"emar&s or 'bser%ations

0 Start of test

Soil texture:

Structure:

table rate of fall in mm minute *

For small (+,-+ cm) permeameter: Flow rate (Q) = (Rate of fall) x 2.17 = ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, mL / min

For large (./,-0 cm) permeameter: Flow rate (Q) = (Rate of fall) x .22 = ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, mL / min



alculations "eference: 1ooers2 3,D,2 and D,H, $aller2 .440,

oil factor (F) as a function of auger hole diameter and soil type:

AH diameter 5 cm 6 cm 4 cm ./ cm .. cm .- cm .6 cm -/ cm -- cm

7ra%elly sand and coarse sand 6,4 6,. 5,+ 5,/ 8,8 8,- 9,+ 9,- 0,4

Finemedium sand2 loamy sand2

sandy loam2 structured soils5,- 8,8 8,. +,5 +,0 +,/ 0,5 0,9 0,-

1assi%e clays and silts 9,9 9,. 0,6 0,8 0,9 0,- -,+ -,0 -,.

!fs = Q x F = x = mm/"



E-ample o" a ompleted permeameter test "orm:

Location (address): Lot 11# $n% Roa"# &o 'own# File #: *LS+,

Auger hole #: 2 AH location: - m east of test it '*+,

AH depth: 0 cm AH diameter (at bottom of hole): 1 cm Date: 22 ul% 200

Height of air hole: 20 cm Permeameter inside diam: 10.2, cm () Tested by: *L

onstant Head !orehole Permeameter Test "esults

Time of

day

Total

elapsed

time min

nterim

time min

$ater

le%el

reading

mm

Drop in

le%el mm

"ate of fall

mm/min"emar&s or 'bser%ations

03:1 0 1.0 1-- Start of test

1 10 1-

2 12- 1-

, 110 1-

3 12

- 2 1

70 12

7 -- 1- Soil texture: San"% loam.

Structure: $! 2

$n4ular 5loc6% mo"erate

table rate of fall in mm minute * 1-

For small (+,-+ cm) permeameter: Flow rate (Q) = (Rate of fall) x 2.17 = ;A mL / min

For large (./,-0 cm) permeameter: Flow rate (Q) = (Rate of fall) x .22 = 12, mL / min



alculations "eference: 1ooers2 3,D,2 and D,H, $aller2 .440,

oil factor (F) as a function of auger hole diameter and soil type:

AH diameter 5 cm 6 cm 4 cm ./ cm .. cm .- cm .6 cm -/ cm -- cm

7ra%elly sand and coarse sand 6,4 6,. 5,+ 5,/ 8,8 8,- 9,+ 9,- 0,4

Finemedium sand2 loamy sand2

sandy loam2 structured soils5,- 8,8 8,. +,5 +,0 +,/ 3.7 0,9 0,-

1assi%e clays and silts 9,9 9,. 0,6 0,8 0,9 0,- -,+ -,0 -,.

!fs = Q x F = 12, x ,.7 = -- mm/"

Comment: The Kfs can be rounded o to 460 mm/d.

constant head borehole permeameter test procedure and test form

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