Results of Soil Testing & Wastewater Management

Sven Nielsen (Geotech Engineer) has provided his Soil Tests and Waste Management Report (the latter a requirement given that we don't have access to town sewerage and therefore need to have an onsite wastewater system.
While we are awaiting the (potential horror of the) preliminary costings for the driveway designs from the Civil Engineers, we thought we would update you with the outcome of the soil testing.
An extract of Sven's report notes that:

The site is underlain by Triassic Sandstone bedrock and is proximal to a contact with Jurassic Dolerite. The clay fraction is likely to show moderate to high ground surface movement and the soil may lose bearing potential when wet. The soil is likely to be variable in depth with colluvial cobbles and boulders to be expected throughout soil profiles over the site.
It is noteworthy that minor gully erosion (indicative of dispersive soils) was observed immediately to the north of the proposed house site. A soil sample from bore 2 was subjected to the Emmerson Test with a Class 4 (non dispersive) result. It is likely that the stratified clays associated with various weathering phases of the sandstone bedrock will show a range of dispersive classes over the proposed development area. This has implications for both recommended founding layers of any footings solution as well as the management of both stormwater and wastewater over the site. The development proposal involves significant site cutting into the underlying sandstone bedrock. The strength and hence excavatabilty of these rocks will vary over the site given their sedimentary nature, and unconfined compressive strengths (UCS) of up to 75 MPa are considered representative of harder rock phases over the site.

It looks like we should hopefully be able to excavate for the building site in its proposed location, with a sublayer of "rippable" sandstone (ie it won't need to be removed by dynamite!) and also have the foundations going directly into the bedrock.
The Soil Test Class was returned as M (standing for "Moderate Movement"), but for the purpose of building, if we are to put the foundations on the bedrock, we would instantly graduate with a Soil Class A.
Turning to the wastewater treatment, after spending a disproportionate length of time looking at composting toilets Viktoria and the Android elected to go with a septic system with raised absorption beds. To incorporate a composting toilet with a chute or external chamber would require significant redesign of the bathroom to accommodate it. And as for the ones with the internal compost chamber... they really are possibly the ugliest creatures ever invented.

Even superimposed on the ocean... they're still hideous

So, given the legal requirement that even rooms that could potentially be used as bedrooms (ie Viktoria and the Android's individual studios) be listed as bedrooms on the Council application, our downsized house is once again a 4 bedroom house and, as per Sven's recommendations:

It is proposed that this dwelling be serviced by a dual-purpose septic tank with effluent dosed into raised absorption beds. The absorption area could be catered for as two 10m x 3.5m raised absorption beds (core bed dimensions) shown on the site plan with adequate room for a 100% reserve if required. Care should be taken to ensure adequate setback distances from boundaries and sensitive down slope environmental receptors where applicable and installation should be compliant with the prescriptions contained within this report. Given the site investigation has been conducted prior to earthworks, further site inspection should occur after site works have been finalised. Bed locations may be relocated at this time. It is recommended that a standard domestic 4000L Dual Purpose Septic Tank and pump well be installed to accept and treat effluent flows.

Neal-the-Architect has intimated at a few design improvements to the house itself which will be on their way, but we don't anticipate receiving any of these until after Neal returns from his family vacation in the next couple of weeks.