Why a good onsite wastewater land capability assessment can save you money......

[Callum EHO]

It might save you the cost of a high maintenance, high power consumption, high service cost, high component replacement cost, high analysis cost system that still needs desludging every three years or so. The savings on this alone on many sites could save you the cost of the land capability assessment within a few years.

A good land capability assessment may save you a considerable amount of money on materials, materials handling with heavy earthmoving equipment and soil disturbance, retainment or assistance with the establishment of vegetation.

It will also place wastewater in logical locations for reuse by vegetation or be available for diversion in times of drought. All of these details save you money in the long term and add value to your property.

Some land capability assessments are better than others and it is worth shopping around and asking reasonable questions of prospective assessors. Some sites require more expensive up front works for long term benefit and awareness of land purchasers about the issues associated with onsite wastewater management is about to rise significantly.

What are the hard questions you should ask prospective land capability assessors?

[purplepear]

soils type? natural water ways? High rain events? Useful trees that use water?

[Callum EHO]

soils type? natural water ways? High rain events? Useful trees that use water?

All these things but also a lot more. A good Land Capability Assessment with start off with the general site uses and outlook desired by the owner then scientifically assess what the needs of the site are and how some of these need protection from wastewater. Then it is a matter of working through the ranges of technologies available that can bridge the gap between the user and the environment. A good assessor will consider things like greywater reuse and composting toilets where there is an interest by the land owner.
A fully occupied house will generate its own volume in wastewater every year in some situations so it is not an easy task to design a soil based absorption system that is going to last approximately 15 years or more under most use and climate conditions but that is where some of the industry is at at the moment.

There is a lot more permaculture that could be built into some LCA's though and permaculture should be a priority site need that can also benefit from the water and nutrients.

Cheers

Callum

[purplepear]

How would the assessment deal with fluctuating demands? Grey waste needs a reasonably constant flow but family visits and seasonal gatherings can put a great strain on a system and a system designed to take these flows can be short of water for the less busy periods

[Callum EHO]

How would the assessment deal with fluctuating demands? Grey waste needs a reasonably constant flow but family visits and seasonal gatherings can put a great strain on a system and a system designed to take these flows can be short of water for the less busy periods

This is what we call surge loadings. Some people use 4 times as much water as others so it is important to build in storage capacity and enough absorption capacity for peak use and high rainfall conditions.

Actually with greywater now we are looking into using tipping box "drainwave" technology to hold back greywater flows until they reach about 10 litres then send it down a greywater distribution pipe in a surge. This helps with distribution to not overload soils and microbes but also helps to flush through things that might cause blockages. We are using air gaps of 100mm to stop root growth into pipes.

Ultimately the aim is to get as much greywater as we can into vegetation and a robust permaculture system is the best way of achieving this.

[purplepear]

I am using Australian hardwoods (spotted gum and iron bark) to absorb the water on a system designed for ten. I think this will allow for coppicing and timber, The area is about a half acre.
I would love to know more about the drainwave tipping box - can I manufacture it myself? It would need to be below ground level ?? And come after a surge tank for solid removal.??
I some times wonder if it is over kill to have a grease trap, a surge tank, a reed bed and a subsurface irrigation of a tree lot on a 14 acre property but we are on reactive clay and sit above a water catchment.
I agree that Pc must get involved in this type of system. We teach all our students the importance of cleaning the water if it needs discharging from the property and rely on swales to clean water from the market garden and ponds.

[purplepear]

I looked up the drain wave - a great unit.
http://www.savewater.com.au/products/Drainwave

[Ark Angel]

What are the hard questions you should ask prospective land capability assessors?[/QUOTE]

As an assessor with several years’ experience, I recommend that householders considering installing an onsite sewage system ask the following questions of any perspective professional land capability assessor:
1. Are you tertiary qualified with a degree in a soil science discipline, e.g. agricultural science, soil science, civil engineering, etc.?

2. Have you had at least 1 year experience assessing and designing onsite sewage systems?

3. Do you carry professional indemnity insurance?

4. Is the proposed assessment independent of any treatment plant manufacturer requirements?

5. Wherever possible are you prepared to design low cost and low maintenance traditional septic tank systems?

6. Do you do a water balance analysis for the design of drip and trench irrigation systems?

7. Do you carry out a salinity and nutrient balance analysis for drip irrigation systems?

8. Do you assess the permeability of all soil horizons to a depth of 2m or more as standard procedure where possible?

If the perspective assessor answers “Yes” to all of the above questions and provides a compliant report with the assessment procedures described above; then there is a good chance that you will have good quality assessor and a good quality low cost outcome.

[Callum EHO]

Sometimes Local Councils have general information on Land Capability Assessments or Township Land Capability Assessments conducted in the area in nature strips that will provide an indication of the soil types, variety and issues to help with working out the types of assessment that might be needed and approximate sizes of wastewater systems for the various technologies available. This is only a benchmark and usually a site specific land capability assessment is also needed but sometimes only with a slight modification.

It is also an EPA guideline that assessors contact the Local Council Environmental Health Officer before they conduct an assessment so they can include all the issues already identified in the neighbourhood already and get a copy of any Town Land Capability Assessments as a guide and benchmark. Things like making sure that assessors provide a design for the depth, width, design and grade for cut-off drain designs that are appropriate are important and detailed. The licensed plumber needs to follow the assessment design and permit. Poor quality assessments lack detail and try to blame the plumber or the Council if the system fails or they just always refer to top shelf systems without putting in the effort needed to design a potentially more practical and low cost system in the long term.

I am increasingly expecting assessments to include integration of the wastewater system with landscaping and site stormwater management systems. This is about sustaining vegetation, utilising vegetation for wastewater uptake and making sure root systems and overshading are not going to be detrimental.

Systems are typically the same or larger than the floor area of the house so thought has to be given to maintenance. How often do you want to mow your lawn and will it compact the soils? Do you want to grow desired plants with the wastewater or a troublesome collection of very fast growing hardy weeds!

Give some thought to how the system might be protected from high rainfall in winter and help trap rare rainfall events in drought by blocking a stormwater bypass pipe.

Also think about future development potential for the site or future site uses such as house extensions and granny flats etc..

Finding the appropriate technology for the user and the site is also very important but a good unbiased assessor with give a range of options and technologies to choose from and also provide an example to the types of assessments they have done in the past.

Some assessors have expertise in certain soils and some have expertise that extends to landslip issues, groundwater springs or native vegetation protection and the these may be very important on some sites.

I am sure this thread is going to end up with quite a list of assessment considerations..........