Auckland Aquifers! What's the big deal?

It's hard to find good graphics or geological cross sections of Auckland. So here's one from somewhere else. The idea's the same though. It's all about groundwater, and underground water systems. When it rains, a lot of water goes into the ground. It percolates through rock and soil till it reaches the water table - the natural level of water you find when you dig down. This area is sometimes called an "unconfined aquifer" because that water flows sideways and downward. These are underground water flows. They are slow. Auckland's volcanic rock is fractured and cracked and contains lots of caves and spaces which are full of water. Many of these water volumes are "confined". Full of quite pure water. It's pure because it has flowed through rock to get there. Sort of like a natural filtration system. The volcanic rock beneath that is called bedrock.

This picture is from Hastings District Council website. Almost all of Hastings City's water comes from underground water sources. From aquifers. The graphic shows the water cycle. Evaporation, rain in the hills, some overland flow in the Heretaunga Plains, and then the water seeps underground, and percolates through and around various rock layers, till it gets into quite deep aquifers. Hastings Council pumps the city's water up from these aquifers, and then reticulates it to users.

Imagine this graphic is of Auckland. City in the background, soil on the surface (imagine those cacti are Pohutakawa Trees...). The water table is marked. There's a graphic showing rock and soil near the surface. Then beneath that is a saturated area full of groundwater. Below that is what is called the "upper aquifer", and so on...

Now let's imagine we dig a quarry into this. I show it here as "Quarry 1". It's reasonably shallow to start with. Stays above the water table mostly, so it is easy to dig the rock out (aggregate) without being troubled by water. That's why it's got a flat bottom....

But then the quarry operator wants more aggregate, and gets permission to pump out any groundwater that flows into the quarry. This means the quarry operator can dig down much deeper into the saturated groundwater system. He pumps out water, and digs out more rock. In doing so, of course the floor of the quarry gets nearer and nearer to the top of the upper aquifer. It means that there is much less rock between the bottom of the Quarry (Quarry 2) and the top of the aquifer.

So now the Quarry operator finds there's no more rock available to dig out. He's gone as far as he can go. The quarry can't expand outwards because by now there are houses all around it. So now he seeks permission to fill the quarry with cleanfill. People pay to dump their cleanfill in his empty quarry hole. You can see a purple pile of fill in this graphic at the bottom of the old quarry. There's no need now for the operator to pump groundwater from the quarry hole, and so groundwater seeps in from the walls of the quarry and rain comes down from above.

This water percolates through the cleanfill, leaching out anything that is mobile or soluble. This water has only a short distance to travel now, from the bottom of the quarry, before it gets into the top of the aquifer. Once it's in the aquifer it's free to flow wherever the aquifer water movements take it. The problem comes when there are contaminants dumped with the "cleanfill". Best practice suggests that cleanfill should be just that - the quarry operator should really be replacing like with like. Take out inert rock - put back inert rock. Then there will be confidence there is no risk to the aquifers. No health risks to those who draw water from the aquifer for drinking, or for emergency supplies. That's the big deal.

Proposed Three Kings "Clean" Landfill

This is a recent photo of Three Kings Quarry, operated by Winstone Aggregates. It is located in the middle of Three Kings Volcano - which was formed about 15,000 years ago. Several cones were formed. Three of these were prominent. Two have since been quarried away. Aggregate has been used for roading and other construction projects. Winstone Aggregates have operated the quarry since the 1920's, though quarrying has occurred there for over 150 years.

The red ring on this map shows the approximate location of the quarry. Most Aucklanders are not aware of its existence. From time to time local community groups have expressed concerns about activities there including dust from quarrying and truck movements and so on. A few years ago I was drawn into an issue that emerged. The quarry had been dug deep enough that groundwater was seeping into the floor of the quarry from adjacent aquifers and other underground water sources, and Winstones applied to "dewater" the quarry. This required water to be pumped out and disposed of. That was one issue. Another related issue was when Winstone Aggregates applied to have this water inserted into Auckland's water supply. They wanted to become a bulk water supplier alongside/in competition with Watercare. While the water was very clean - potable - concerns were raised that it would not be treated reliably to the same standard as existing drinking water supplies.

This is a recent aerial photo of the quarry. In 2009 Auckland Council and Auckland Regional Council processed resource consent applications from Winstone Aggregates (owned now by Fletcher Construction Ltd), to change the activity at the quarry from being a quarry to being a landfill. The application was for "cleanfill" to be dumped there - around 3 million cubic metres of it over a ten year period or so. There were many submissions against this proposal raising many issues including from dust and truck movements, but also concerns about what the resulting land would be used for/suitable for, and - critically - what effect a landfill would have on Auckland's underground water resources. In particular the large freshwater aquifers that underly much of Auckland and which are used by a few select organisations - including the Zoo - for their water supply.

This photo from Auckland Council's website shows the area in 1940. You can see a number of small quarry faces in the area.

This picture was taken in 1959. From time to time other activities have occurred on the site including storage of aggregate and storage of diesel fuel and lube oils and explosives.

This picture is dated 1966.

This one is dated 2001....

And this one is dated 2009.... I am at a loss to understand how Three Kings Quarry owner, Winstone Aggregates, was granted consent by the Auckland Regional Council a year and a half ago to fill the Mt Eden Road quarry - unlined and without a leachate collection system - with waste material that is permitted to contain elevated levels of contaminants including arsenic, copper, zinc and hydrocarbons. This and other related resource consent decisions have been appealed to the Environment Court. I understand this appeal is set down for a two week hearing beginning Monday, March the 7th The Mt Eden Road Quarry – also known as Three Kings Quarry - is above, and drains into, a large fresh water aquifer which is already a water source for some users, and which is a back-up drinking water source for Auckland in the event of a natural disaster affecting existing bulk water pipelines. The proposed Mt Eden Road quarry landfill project may result in Auckland’s aquifers becoming too contaminated over time to be used as a much-needed water source. Why should Auckland take that risk when industry best practice options exist to avoid it? If a natural disaster hit in Auckland – volcano or earthquake – good civil defence planning would be reliant upon Auckland’s underground water resources to meet the need for drinking water. Surely Auckland Council would not support any activities which might degrade the quality of Auckland’s underground water resources. And surely Watercare, whose duties include taking a leadership role in regard to Auckland's water resources - including underground resources - would be requiring this project to be cleaner than clean, and to adopt best practice. More later....