Here we go again, and I wish them luck. The Tasmanian Mercury newspaper’s front page story of 30 October 2013 featured an international team from the United Kingdom which is planning a series of searches in Tasmania’s wilderness for the elusive (some would say, extinct) Tasmanian Tiger, or thylacine. The team’s searches will, it is reported, focus on the northwest and southwest. Not the best places to look, and no need to search anyway – readers of my novel Thylacine Conspiracy will know that the animal is alive and well, and is being raised in captivity in a government compound in northeastern Tasmania, in preparation for its release on Maria Island.
Archives for October 2013
An assessor from Syracuse in the US noticed my discussion paper on bottomless sand filters (BSFs) and was asking about filter sand specifications and maximum slope angles for such installations. Richard Mason from Sorell Council has done more work on BSFs than anyone in Tasmania and I asked him to join the on-line discussion.
The filter sand specification was not an issue, but the slope angle side of things got me thinking – I’ve not seen any guidance on slope of a site and BSF suitability. Richard made the point that “the NYS regulations seem to be saying that maximum permissible slope for raised beds and mounds are 15% (8.5⁰) and 12% (just under 7⁰) respectively. (See “Alternative Systems – clauses (b)(2)(111) and (c)(2)(iv)”. I’m happy, for example, to place my nonconventional beds on almost any slope angle. The basic module for all system needs to be built level, and for the BSF this can easily be achieved by starting with a level base of filter sand on any slope. Treated effluent from a BSF moving through soil downslope and away from a basic module does three things:
- it evapotranspires vertically upwards,
- it infiltrates vertically downwards, and
- it moves parallel to the slope in the apron soil.
The first two ought to dominate over the third if the system has been sized and designed properly. But the steeper the slope below the module, the faster the treated effluent moves parallel to the slope through the apron soil, and the less chance it has to evapotranspire and infiltrate. So, there is more chance of leakage from the lower, outer limit of the apron.
So, we should perhaps lengthen the flow path. But then, we are dealing with highly treated effluent so downslope leakage should not be too much of a problem. Perhaps one answer is to install a cut-off drain along the lower edge of the apron.
Read what the US EPA has to say about BSFs and intermittent sand filters.
Trench®, born in 1999 and created using Microsoft’s Excel, was designed loosely around Australian Standard 1547:1994 Disposal Systems for effluent from domestic premises. If you are assessing sites for domestic wastewater in Tasmania, you will know the software has become an industry standard here. It’s used in some mainland states, too – notably Queensland, where it is also a teaching tool – and in New Zealand.
AS1547, in conjunction with our New Zealand counterparts, has changed twice in the intervening years (in 2000 and 2012), and some regulators and wastewater practitioners ask me when Trench® is going to catch up.
There’s no need. It’s true the software could be massaged to better suit the newer versions of Excel, but its fundamentals remain as valid as they did 14 years ago. That’s because it was deliberately designed to be independent of any particular Standard or protocol, and in fact has global application. Its site capability and environmental sensitivity factors, coupled with the very flexible ranking system, means Trench® is as equally valuable sizing a wastewater system in Dubai as it is in Glasgow. The assessor in Dubai, and the assessor in Glasgow, separately tweak the ranks of each factor to suit his or her local Standard and protocols.
I may tinker with Trench® a bit, though……
Mark Dwyer (National and State President, Environmental Health Australia) has invited me to present and talk about this website at an EHA professional development seminar at the Grange, Campbell Town, on December 4.
I’ll be continually adding new content to the site before the seminar, and will be covering issues such as the recently adopted Australian Standard 1547 (2012) On-site domestic wastewater management, my flowchart for on-site assessment, the two downloadable pdfs on wastewater systems, the status of Trench®3.0, the Cromer permeameter, my new permeability app for iPad and iPhone for iPad and iPhone, and other hydrology apps in the pipeline.
Just returned from a month touring in the UK, and made a point of stopping at Knockan Crag in the desolate, beautiful Scottish Highlands to climb up to, and poke my finger in, the Moine Thrust. Exciting. This is one of the most famous and studied geological outcrops on earth — its interpretation as a major overthrust (older rocks pushed over younger ones) was a critical step forward in early geological science.
Also could not resist a three day stay at the seaside resort of Lyme Regis on the famous Jurassic Coast in Dorset – the town that inspired The French Lieutenant’s Woman, the town that is England’s most popular fossil-hunting mecca, and the home of Mary Anning, 19th century fossil-hunter extraordinaire (“the greatest fossil hunter ever known”). Mary found the first ichthyosaur and plesiosaur skeletons, became world-famous in palaeontology, cemented Lyme Regis on the tourist map, and much more recently, was the real-life heroine of Tracey Chevalier’s best-selling historical novel Remarkable Creatures. A few days later, I was staring at one of Mary’s dinosaurs — still in its timber box — at the Sedgwick Museum of Earth Sciences in Cambridge, and soon after, on British TV, I watched an interview with Tracey Chevalier. Coincidences.
Almost 10 years ago, at an Australian Geomechanics Society meeting, I lamented how bad some Tasmanian “expert practitioners” were at doing soil testing and classification for houses. Mostly, like bad doctors, their work goes unchallenged – until something goes wrong.
Recently, when providing a second opinion about a house site to a client, I was reminded that people are still receiving bad geotechnical advice. The property in question was not in a declared landslide zone, but nearby, serious slope instability issues were reported on 15 years ago by Mineral Resources Tasmania, and house-threatening landslides are still occurring in the area. This situation ought to have been recognised by the classifier, but not only did his advice fail to refer to potential instability, it recommended on-site wastewater discharge on steep, hummocky, probably unstable ground immediately adjacent to mapped “old landslides”. Not a good idea.
How do you know when you have received bad or inadequate geotechnical advice? My thoughts on soil tests for house sites (PDF download) might help.