PASS Contracts, page-58

For anyone wondering what PASS is, this Fact Sheet from the WA Govt is a good intro. (The Link is at the bottom)

Extract from it:

Acid sulfate soils (ASS) are naturally occurring

soils and sediments containing iron sulfides,

most commonly pyrite. When ASS are

exposed to air the iron sulfides in the soil react

with oxygen and water to produce a variety of

iron compounds and sulfuric acid.

Initially a chemical reaction, the process is

accelerated by soil bacteria. The resulting acid

can release other substances, including heavy

metals, from the soil into groundwater and the

surrounding environment.

Although some ASS were formed millions of

years ago and occur in ancient marine rocks,

those of most concern were formed after the

last major sea level rise—within the past

10,000 years (Holocene period).

When the sea level rose and flooded the land,

sulfate in the seawater mixed with land

sediments containing iron oxides and organic

matter. 

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.der.wa.gov.au/images/documents/your-environment/acid-sulfate-soils/fact_sheets/ass_fact_sheets1.pdf&ved=2ahUKEwjpi9LnqZvgAhVXWH0KHbGyBKIQFjABegQIAhAB&usg=AOvVaw0OkDXALEzWbWzF_jUuQjbo