Monday, 7 April 2014

Where Does the Groundwater Flow?

There has been renewed interest in groundwater resources in the Northern Rivers of late. In part this is due to peoples concern about "unconventional" gas exploration and production in the area. Surprisingly, less known is the release of Rous Water's Future Water Strategy which includes groundwater as first on the list for new water sources. Rous Water is a major bulk drinking water supplier in the region. I've previously covered an area within the coastal sands groundwater source called the Woodburn Sands but this was a cursory look and I'd not covered where the groundwater actually goes.


Groundwater do not exist as an underground lake
Image courtesy of International Association of Hydrologists - Netherlands Chapter
Groundwater is often seen as a bit of an unknown, a black box, or some kind of underground lake (see the cartoon). It is quite difficult to observe and therefore people can get the wrong idea of what goes on underground.

One area that is not understood is that groundwater usually discharges somewhere. Sometimes groundwater discharge is obvious through springs. But where it intersects with permanent surface water it is much less obvious. The Evans Head area is a good example of where discharge from the Woodburn Sands aquifer and broader Coastal Sands aquifers is concealed.
Spring-fed creek on Chinaman's Beach.


While walking along Chinaman's Beach south of Evans Head during a recent long dry spell, I couldn't help notice the dark coloured water flowing over parts of the beach. This is one of those discharge areas I'm talking about (most people might be more used to seeing freshwater flowing over a beach from contaminated urban stormwater drains). The coastal sands above Chinaman's Beach holds groundwater and slowly discharges it at the beach. The dark colour of the water is from dissolved humic matter from coastal vegetation soaking into the sand. Tasting the water it was apparent there was no salt in it and understanding the groundwater area I knew it was clean. The springs I observed on Chinaman's Beach were obvious areas of groundwater discharge. The vegetation in the springs was lush and clearly reliant on the groundwater. This is formally known as as groundwater dependent ecosystems.

The lesser known discharge is not all through visible springs like those on Chinaman's Beach. Much of the discharge from the coastal sands aquifers is actually concealed by the sea. It might be a surprise to many in some areas just off the coast there are zones with freshwater. The amount of water that can be discharged underground into the sea can exceed the discharge from terrestrial springs (e.g. Santos et al. 2009). These are the undersea equivalent of the Chinaman's beach springs. This is interesting from a aquatic ecology point of view because it may mean that there are ecosystems in the ocean that are dependent on freshwater! That is, groundwater dependent ecosystems in the sea.

Groundwater is an interesting feature of our region. It is a source of drinking water, irrigation water and even industrial water. It is often important as some ecosystems are dependent on it. It is also surprising since ecosystems can be dependent on fresh groundwater even when out to sea.


References/Bibliography:
*Santos, I.R, Burnett, W.C., Chanton, J., Dimova, N. & Patterson, R. (2009). Land or Ocean?: Assessing the driving forces of submarine  groundwater discharge at a coastal site in the Gulf of Mexico. Journal of Geophysical Research. vol114.

Tuesday, 1 April 2014

Filling a gap with weathering textures

I've been a bit slack lately in posting. I usually have a post ready to go on the first day of every month with a few more over the month. But not so this time. It seems that life just hasn't given me the time to write over the last few weeks. So instead no post at all, here are a few pretty pictures of weathering patterns from the area.


Phyllite of the Neranleigh-Fernvale beds. In this case the darker part of the rock has been preferentially eroded by wind and wave action creating the early stages of a tessellated pavement. The quartz veins that are present stand proud from the surface. Technically this is not actually weathering per se... but oh well it looks pretty.
Weathering of the cross-bedding in this sample of Kangaroo Creek Sandstone develops a very pretty pattern.
Differential weathering in phyllite of the Neranleigh-Fernvale beds. The fabric of the rocks leads to some minerals being more susceptible to weathering by reactive sea water.

Tuesday, 25 March 2014

Fracking qualifies for aged pension


Over on the About Geology Blog, Andrew Alden shows us that yesterday was the 65th anniversary of Hydraulic Fracturing (Fracking/Fraccing). I was quite surprised to learn that this “unconventional” technique was developed in my grandparent’s generation. In his blog post Andrew points out some of the controversies in the United States about “Fracking” and provides his opinion on the practice. I don’t want provide to provide any opinion here about the Australian situation, just to outline a very quick summary of how it is used.

Having said the above, I think it is important to mention that there is some differences in experience between Australia and the United States. The main difference being that any chemicals used in “Fracking” must be fully disclosed (unlike the USA where they are much more secretive). Another difference is that in the USA “Fracking” is most commonly used in “Shale Gas” formations where it has been reportedly been linked to many problems with regard to aquifer cross-connection and contamination. Coal Seam Gas in the USA are also a situation where Fracking is frequently used, though this has very few of the same issues of Shale Gas fracking (Blackam 2014).

In Australia “Fracking” is frequently used in “Tight Gas” situations where directional drilling alone is impractical. This practice is especially common in the Moomba Gas Fields of Queensland and South Australia now this field has become depleted in the easily accessible “Conventional” gas. Hydraulic fracturing is also sometimes used in Coal Seam Gas situations. In the Northern Rivers I understand there has only been one case of hydraulic fracturing which was used in a “tight” situation.

This is by no-means a clear bill of health for unrestricted use of the practice of Fracking. Many questions still remain about what damage the practice can cause (e.g. Batley & Kookana 2012).

I’ve done some posts on the different natural gas sources and summarised them on this page. Until I actually do a blog post on what hydraulic fracturing actually is, I recommend this summary from the CSIRO. Alternatively, this CSIRO/Industry publication, though developed in partnership with the gas industry is actually even more detailed and very good.

References/Bibliography:

*Batley, G.E. & Kookana, R.S. 2012. Environmental issues associated with coal seam gas recovery: managing the fracking boom. Environmental Chemistry. vol9 p425-428
*Blackam, M. 2014. Source, Fate and Water-Energy Intensity in the Coal Seam Gas and Shale Gas Sector: An Exploration of the relationship between energy and water in the unconventional gas sector. Water, Journal of the Australian Water Association. vol41 No.1 p51-56

Friday, 14 March 2014

Armidale submerged

Armidale is well known for its height above sea level, with some areas above 1000m it is at a relatively high altitude by Australian standards. The city is located in the New England, ‘Northern Tablelands’ which provides an indication of the landscape in which it is situated. The area resembles a very large plateau with comparatively light rolling hills compared with the nearby escarpment and edges of the tablelands. In fact, Armidale is just a tiny bit to the east of the crest of the Great Dividing Range. Surprisingly, this area was in part inundated by a lake, or lakes.

Examples of some rocks that make up the Armidale beds
The big sample at the front has been partially turned into silcrete.
One of the headwaters of the Macleay River, Dumaresq Creek flows through Armidale. In places this creek, as well as other creeks in the area, have cut through the basalt rock that covered the area. A description of this process was covered in an earlier post. In this post I’d like to describe the sediments that lie under the basalt. These are Eocene (or earlier) sediments named by Voisey (1942) the Armidale Series, now known as the Armidale beds.

The Armidale beds are comprised of fluvial (river) and lacustrine (lake) deposited sediments. These are principally conglomerates, siltstones, sandstones and shale. Interestingly, the shales are laminated possibly as a result of seasonal deposition in a lake. They also contain abundant plant fossils. The material that makes up the sediments is particularly obvious in the conglomerate. The conglomerate clasts are derived from the older underlying geology, for example clasts of jasper, quartzite and granites.

The Armidale beds occur in small remnant areas (the balance of the beds having been eroded away). These remnants occur throughout the Armidale area but almost as far away as Wollomombi to the west, near Dangars Falls to the south-east and Kellys Plains to the south-west. Voisey 1942 named this area Armidale Lake which is a palaeo-lake that only exists now in the sediments that it left. The formation of Armidale Lake occurred either before or during the volcanism that ended up covering a majority of the Armidale region in blankets of basalt lava (lavas of the Central Volcanic Province). In fact, the Armidale beds were preserved by this blanket of basalt both directly and through metamorphism beds in the area of contact. This metamorphism of the Armidale beds created a layer of hard silcrete (once known as greybilly) which itself was resistant to erosion and helped preserve the underlying un-silcretized sediment from being washed away.

The picture above is an example of the Armidale Beds that occur near the Armidale garbage disposal centre. A very accessible example is located on Madgwick Drive on the way to the University. It is actually one of the best remaining exposures of the unit and has been used for years by local schools and the university. Indeed, Banaghan & Packham 2000 have the road cutting as a stop on their Armidale-Yarowych geological tour.

References/bibliography:

*Branagan,, D.F. & Packham, G.H. 2000. Field Geology of New South Wales. Department of Mineral Resources.
*Fitzpatrick, K.R. 1979 The Armidale area. Geological Survey of New South Wales. Geological Excursion Handbook 1
*Voisey, A.H. 1938. The Geology of the Armidale District. Proceedings of the Linnean Society of New South Wales.
*Voisey, A.H. 1942. The Geology of the County of Sandon, NSW. Proceedings of the Linnean Society of New South Wales. V67.

Saturday, 1 March 2014

An Australian and Indonesian Geological Relationship

Australia got its most recent reminder about the power of volcanoes only a couple of weeks ago. Mount Kelud (or Kelut) erupted on the populous island of Java in the Indonesian Archipelago. The resulting ash cloud has caused immense problems for people travelling to Asia or even Europe. The Darwin Volcanic Ash Advisory Centre (Darwin VAAC) advised that aircraft travelling on many of the popular Indonesian (particularly Bali), South and East Asian routes, would be in great danger of having engines failing. Therefore many flights were grounded.

The Darwin VAAC is responsible for Volcanic Ash advice covering the Indian sub-continent and South East Asia (The most concentrated number of active volcanoes in the world). Very few people realise the essential role that Australia plays in understanding the way volcanic ash behaves in such an active region. This is despite Australia has only a few isolated or insignificant volcanoes itself. Like the role of the VAAC, Australians don’t realise just how significant volcanism is to our second nearest neighbour (or indeed our nearest one, Papua New Guinea).

Readers of my blog will be aware that I focus almost entirely on the geology of the Northern Rivers, Eastern New England Tablelands and Mid North Coast areas of the state. Regular readers will also be aware that on occasion I indulge myself with a discussion or some opinions on geological matters elsewhere. Indonesia is just too important from a geological perspective to ignore. Having Indonesia come to our attention only when immigrants on boats are reported, volcanoes affect plane flights to Bali or the name Chapelle Corby is mentioned misses how much we are involved in and how much more we should be involved in managing volcanic hazards in our region. Including supporting Indonesia in its efforts to keep people safe.

Here are some selected facts about dangerous volcanoes:
  • Volcanic eruptions can be compared by a logarithmic scale called the Volcanic Explosive Index (VEI). 
  • VEI 0 are small explosive eruptions, VEI 8 are huge catastrophic eruptions. 
  • All recorded eruptions of VEI 6 or greater has killed someone. 
  • Approximately 50% of recorded eruptions of VEI 4-5 have killed someone. 
  • The majority of deadly volcanoes (VEI 6 or less) claim about 80% of their victims between 7 and 10 kilometers from the eruption. 
  • Lava causes only 0.34%-0.79% of deaths from eruptions. 
  • Pyroclastic flows cause between 33-46% of deaths from eruptions. 
Here are some selected facts about Indonesian volcanoes:
  • Monitoring the effect of volcanic ash in Indonesia is the responsibility of the Australian Bureau of Meteorology (via the Darwin VAAC). 
  • On average for every volcano that erupts in Indonesia, 27 people will die.
  • Five volcanoes have has significant (and recurring) eruptions already this year (Jan-Feb 2014). Those are Sinabung, Saiu Island, Kukano, Raung and Kelut. 
  • The largest explosive eruption known occurred at Toba about 30 000 years ago. 
  • In 1815 Mount Tambora erupted killing approximately 60 000 people and led to the “year without a summer” in Europe. 
  • In 1883 Krakatoa erupted with the resulting in approximately 36 000 deaths, the sound of the eruption was reportedly heard in many parts of Australia. 
  • Approximately 76 different volcanoes have erupted in Indonesia in the last ~500 years. Most of these erupting frequently. 
Here is an example of what people are trying to do about the dangers of volcanoes in Indonesia: http://citiesonvolcanoes8.com/. This is a geology related conference that people in Australia probably never hear about.

More information on the Darwin VAAC can be found here.

References/bibliography:
*Auker, M. R., Sparks, R.S.J., Siebert, L., Crosweller, H.S. & Ewart, J. 2013. A statistical analysis of the global historical fatalities record. Journal of Applied Volcanology 2:2
*Smithsonian Institution. Smithsonian Institution / USGS Weekly Volcanic Activity Reports (All editions January-February 2014)

Monday, 17 February 2014

What is CSG?

What is CSG? Very simply Coal Seam Gas (CSG) is natural gas obtained directly from coal seams. Another common name for CSG is Coal Bed Methane (CBM). Like most natural gases, the chemical components of CSG are dominated by methane. Though some higher end hydrocarbons such as ethane or propane may also be present.  Carbon dioxide and nitrogen are usually significant components of CSG too and the higher the proportion of these non-hydrocarbon gases the lower the quality of the gas. This simple summary does not tell us very much, so more detail is required.

CSG is an interesting gas when compared to ‘conventional’ gases. ‘Conventional’ gas has migrated away from coal and organic rich sedimentary rocks into other porous rocks. The gas is then held in place by impermeable layers. What makes CSG different is that the gas has only migrated very small distances (if at all) to natural pore spaces such as fractures (cleats) in the coal layers. These pore spaces usually contain natural water that was left in the coal when it was laid down or water that subsequently migrated into the coal seam. The water associated with the coal seam is very important because it is actually the pressure of the water in the coal seam that keeps the gas in place. It is the hydrostatic pressure that keeps the gas in place.

In open cut or underground coal mining, CSG is a curse. It is considered a waste product and an explosion hazard. It is therefore vented as much as possible to make the coal mines safe to work in. The recent Pike River Mine explosion in New Zealand is an example where the failure to vent enough CSG caused a tragedy. As water is removed from coal mines the chances for gas mobilisation increases due to the above mentioned effect of hydrostatic pressure. This further increases the risk of explosion in coal mines.

Idealised relationship between CSG and water production
Natural gas became more popular for domestic and industrial use over the last few decades and the means to transport it economically became available (e.g. LNG). This meant gas that was often a by-product of the oil and coal industries became important in its own right. This lead to people searching for gas sources in their own right, CSG included. Petroleum engineers realised if you reduce the pressure of water in a coal seam and collected the gas you could actually use the gas as a resource leaving the coal in place. This means that drill holes can be placed into coal seams and the water drawn out. The water drawn out (called formation water) is actually a ‘by-product’ of the gas extraction process. The formation water is the nuisance that needs to be removed to allow the gas to escape. This means that a new gas well will produce very little gas at first and lots of ‘waste’ water. As the water is drawn down the gas production increases and the water production decreases. Interestingly this is the opposite of that which occurs for ‘conventional’ gas, where waste water is a problem in the later stages of production but not early on.

Many people are concerned about CSG in Australia, particularly in our northern rivers region. This concern is driven by the possible effect of CSG extraction on beneficial groundwater. The use of techniques such as hydraulic fracturing that may be used to increase or prolong gas production is also raised as a concern. To keep this post short I will cover both of these issues in future. However, I will suffice to say that there is evidence that groundwater can be affected during CSG extraction despite producers trying not to have any impact. These are particularly noted in certain geological formations. There are also situations where there is no impact on important aquifers too. This matter is clearly quite complex and a one size fits all understanding does not apply very well. Hopefully, my future posts will tease the details out a little bit more.