Geotech Report - Acid Sulfate Soil Assessment

 

The pH screening tests can be used for preliminary identification of potential or actual ASS, using a combination
of three trigger factors' as follows:

(a)

The strength of the reaction with peroxide is a useful indicator but cannot be used alone. Organic

matter and other soil constituents such as manganese oxides can also cause a reaction.

(b)

A pHrox value at least one unit below pHr may indicate a potential acid sulfate soil (PASS). The greater

the difference between the two measurements, the more indicative the value is of a PASS. The lower

the final pHrox value the better the indication of a positive result.
If the pHrox <3, and the other two conditions apply, then it strongly indicates a PASS. The more the

(°)

pHrox drops below 3, the more positive the presence of sulphides.

The results of the screening tests undertaken on samples recovered from the bores are given in Table 2,
together with an indication of which (if any) trigger factors were noted.

Sample
Depth
ea)
0.0-0.25

Bore

0.5-0.75
0.75-1.0
1 | 1.0-4.25
4.25-1.5
1.51.75
1.75-2.0
2.0-2.25
0.0-0.25
0.25-0.5
0.5-0.75
| 0.75-1.0
2 | 4.0-4.25

4.25-1.5

4.5-1.75
1.75-2.0

2.0-2.25

 

 

0.25-0.5 |

Table 2: Summary of Screening Test Results

Material
Type

Fill
Fill
Fill
Fill and Silty Clay
Silty Clay and Silty Sand
Silty Sand
“Silly Sand
Silty Sand
Silty Sand
‘Fill
Fil
Fill
Fill and Silty Clay
Silty Clay and Silty Sand
‘Silly Sand
Silty Sand
Silty Sand
~ Silty Sand

 

Reaction

Medium
“Medium —
Strong
Strong
Strong
Weak
Very Weak
Very Weak
Very Weak
Very Strong
Very Strong

Very Strong

Strong
‘Strong
Medium
Medium
Medium

"Medium

 

pHr

47
48
46
55
54

5.6

| Bia

5.0

“49

6.5
5.3

5.3

5.4
5.7
5.4

| 5.1

54 |

 

pHrox

2.0

29 |

1A
1.2
17
23
“4.9
28
~ 28
27
24
15
17
13
1.9
24
18

| 1.8

 

Screening Test Indicators

Strong reaction
with peroxide

 

PHr-pHrox>1 | pHrox<3
v v
v v
v v
v v
v v
v v
v —v
vo v
v v
vo v
v v
v v
—+——-
v v
v v
v v
v v
7 7

 

1 Ahern C.R., Ahern M.R., Powell B. Guidelines for Sampling and Analysis of Lowland Acid Sulfate Soils (ASS) in

Queensland 1988

 

Residential Development
215-219 David Low Way, Peregian Beach

Project No. 07160

Page 6 of 10

18 June 2007