7 Decisive Factors Influencing the Cost of your Sydney Water Sewer Concrete Encasement

This factor is quite obvious when you think of it: generally speaking, the longer the encasement, the dearer it costs. I wish it was that simple, however all estimators working for a Sydney Water accredited minor works constructor have been asked the million dollars question a few times:

What is your rate per lineal metre for sewer encasements?

And all the serious ones would have replied that it depends. Unfortunately there is no quick and easy “ballpark” figure that you can base your project costing on, as Sydney Water accredited constructors have high overhead costs related amongst others to fulfilling obligations to maintain their accreditation status with the water board (such as insurances, training, quality and safety audits, need for administrative personnel for work as constructed plans and transparent invoicing…). This leads the estimating departments to often have to factor in relatively high minimum daily charges to cover these overhead costs spread over each day of the financial year. The affordable price of the PVC pipes and fittings that are widely used for sewer encasement projects is dwarfed by these “upfront” or “overheads” or “site establishment” costs, and have therefore a relatively small impact when determining the cost of a sewer encasement. Unfortunately, bar the concrete supply, the pipe supply is pretty much the only cost that is 100% directly linked to the length of the encased section. As a reference, the adequate concrete mix itself costs constructors around $300+GST when delivered by normal trucks to most Sydney suburbs (rough estimate of quantity of concrete is multiplying the length of encasement by 0.36 – assuming encasement is a 0.6m square around the pipe, and neglecting the pipe volume) – that is about $1,000+GST worth of concrete for a 10m long encasement. However, multiple other factors will actually affect the involved costs.

Remember as a kid, when you were playing on the beach and were desperately trying to dig the sand all the way to the other side of the earth? You may have been frustrated by the sand walls of your hole not holding in place, and as you were digging deeper, you had to widen the hole to compensate for wall collapses. A similar phenomenon happens (at a bigger scale!) when professionals excavate within unstable geological strata (typically sand or fill strata, both present in Sydney region), resulting in greater wear and risk to damage equipment, need for extra labourers mobilized on site, and supply of additional materials and equipment (timber/shoring instead of benching as per common practice in self-supporting ground). The geological profile in the area is generally quite well known and free online maps are available from the Planning and Environment department website: https://www.resourcesandgeoscience.nsw.gov.au/miners-and-explorers/geoscience-information/products-and-data/maps/geological-maps/1-100-000 (chose the Sydney, Penrith, Port Hacking or Wollongong ones on the list depending on your suburb within the Sydney area). However local disparities with this macroscopic data are not too rare and a site specific geotechnical survey and/or a peg out report to Sydney Water’s standards would confirm the ground conditions of your site. The geological and geotechnical condition of your site is a given attached to the location of the developed land, and there is not much you can do to improve it as a small developer. However, the unknown is something estimators often price as “risk”, and risk has a cost: providing clear documentation on the site conditions to the Sydney Water accredited Minor Works constructors for pricing will prevent them having to assume the worst case scenario and accordingly adding a significant risk allowance to their quote. Generally speaking, clay and shale strata are favourable, rock is quite neutral (the trench would have been backfilled with imported material when the pipe was initially laid, so rock breaking costs are usually kept to a marginal amount for sewer encasements of existing assets), and excavation in sand or fill is expensive. Other examples of ground conditions that may affect a sewer encasement cost are water filled ground (dewatering measures can be costly and cause delays), tidal water, or site pollution (such as asbestos contamination).

While being easy to understand, this factor actually comes with a fair few consequences. Firstly, as always, safety considerations: the Safe Work Australia rules are that excavations deeper than 1.50m must be benched and/or properly shored. Engulfment of workers due to trench collapse is a real risk and sadly happens on a yearly basis recently in the Sydney Region. The deeper the excavation, the most time consuming (and therefore costly in labour) are proper benching and shoring measures. Adjacent structures might also become affected as you dig deeper and elaborated supporting solutions are engineered for the most challenging projects. Another direct side effect of excavation depth is the quantity of generated excess spoil and impact on adjacent areas: as a general rule, a deep trench will be wider at surface level than a standard one (as successive shoring/benching measures are implemented, they widen up from approx.. 0.6m wide at the bottom of the trench up to ground level), generating more additional excavation than just the normal volume that would be expected by digging at constant width, and creating bigger disturbed areas at surface level. The extra excavated volume generates great quantities of excess spoil that the constructors will usually stockpile in the vicinity of the trench as they dig down. Most soils, such as compacted clay actually take much less room in ground, when they have settled and have been compacted for years, than after having been disturbed and brought to the surface as part of the excavation process. As a result, not only the whole available area may be covered by excavated materials, damaging precious plants or other landscaping items, but this bulking effect also great affects the volume of excess spoil to dispose of once the trench has been backfilled. Some constructors offer removal of excess spoil services, but most often this task is left to the builder (which could be good for your finances, see later). Anyway this bears a cost, may it paid to your pipe laying constructor or to your builder. Another non-negligible impact of the asset’s depth is found in the equipment and haulage costs: most constructors use a range of excavators adapted to the different projects they are involved in the differnet kind of project they manage (usually for these kind of uses they pick one in the range from “baby” 0.8t models to 13.5t medium sized ones). The small models (up to 1.5t mostly) are very easily transported in manageable trailers, however they are only used for small projects and/or to reach sites prsenting tricky access conditions as their lack of power makes the excavating task slow, hence usually costlier than when using bigger machines. Due to their size, the use of these machines for deep excavation is highly impractical (they have limited reach capacity). That is why deep excavation within sites with poor access is one of the costliest combination of factors). The preferred and definitely most widely used excavators are within the 3 to 5t range, as they can usually be transported quite practically by well-equipped Sydney Water accredited constructors, using internal trucking capabilities. These also offer well balanced characteristics, with good efficiencies, extended reach capacities and are great for most sewer encasement projects. However if the sewer is very deep and out of reach, then the use of bigger machines will most likely require specialist haulage companies to get involved, and this will only add to the overall price of the sewer encasement.

This last point about the influence of the depth of the encased assets on haulage costs and equipment used introduces another crucial factor in determining the price of a sewer encasement project: the accessibility. The standard minimum access width for a 5t excavator is 2m, for a height of 2.6m (and it takes a skilled operator to drive through such a small access without damaging nearby structures). The optimal price for sewer minor works is often achieved only if these machines can access easily the digging site. Reduced accessibility will not only force the minor works constructor to use less efficient, slower machines, but may add ancillary costs to the total bill, such as concrete pumping, transportation and removal of excess spoil using small equipment (conveyor belts or labour intensive trolleys for example). Access to the frontage of the site itself is important too, as concrete trucks have limited turning radius and the use of mini trucks or safety measures such as traffic control (when entering site from main arteries for example) may be required to ensure safe delivery, all bearing additional costs. The key steps to try and keep the accessibility related costs as low as possible all lie in thorough upfront planning, preparation, and disclosure: if the Sydney Water constructors need to remove trees, or existing slabs or footings preventing them to start the actual excavation works early in the morning, they may need to delay the pouring of the concrete later in the day, which would delay the curing of concrete and may require to allow extra resources to secure the area overnight and come back to backfill the trench at a later date. Having your builder preparing the site with accessibility for the Sydney Water accredited constructor in mind, and carrying out the demolition works (if any pre-existing structures) prior to the encasement of the sewer will often result in savings. This is mostly due to builders generally committing longer term resources to their projects, hence being more flexible with organization and labour affectations for access preparation steps than Sydney Water specialized constructors (it makes sense if you think about why would one pay a pipe laying specialist to prune large trees or break large lumps of concrete!). Careful planning with your builder, and upfront discussion with the Sydney Water constructors that have project management resources (note that not all constructors have office based employees available to assist with the preparation stages) will probably help heaps here. What I called “disclosure” in the previous paragraph again relates to giving the estimators the most complete information you can (so you do not end up paying their “risk” allowance for assumed poor working conditions): if your site has currently poor accessibility for some reason, but you plan to demolish the existing structures, remove trees or branches as part of your landscaping plans, or if you do have the opportunity to arrange the use of the driveway next door to provide access to your backyard, I would recommend to make sure you let them know. Generally speaking, if you plan to make any efforts to get the sewer encasement project easier for the Sydney Water accredited constructors, be sure that they know about it so they can offer better pricing options. A frank communication approach works even though your site has specific complexities, as having an open discussion (ideally on site) with the constructors prior to mobilization of their crews will often avoid the annoying delays and uncomfortable variations in costs that can arise when the works have not been prepared with full knowledge of all the required details. For this reason, I recommend to let the estimators know about any known site difficulty upfront so they can plan for them and will not add last minute extra costs to your project.

It is quite obvious that the size (nominal diameter, DN) of the pipe to be encased is a required information for site preparation and ordering materials and fittings. However its impact on the price of a sewer encasement project is mostly due to the indirect implications of a bigger sized pipe rather than major difference in pipe supplies pricing. There is an extra cost of about $30 per 3m length for the supply of DN300mm PVC pipes versus DN150mm ones: this is not a very impacting. What affects the price much drastically is the fact that larger pipes need to be installed in wider trenches, using wider buckets, bigger excavators (or additional labour to compensate for low efficiency of smaller excavators), hence generating more excess spoil and thus adding to the overall cost. Works on larger pipes sometimes also require specific flow management procedures (instead of the generic inflatable plugs and/or by-pass plugs with lay flat hoses used to work during non-peak hours) that could end up being costly and time consuming. Note that it is sometimes permitted to concrete encase large assets (such as pipes larger than DN300mm, brick oviforms, or sewer trunks) under a major works process. This process is usually not economically viable for the smaller developers and I would generally recommend trying and avoid having to concrete encase them if possible at all. While included within to the minor works scope, relined sewer mains can also add extra costs to the encasement project. Most of ancient Sydney Water’s sewer mains in residential areas are made of vitrified clay (with some variants such as salt glazed earthenware for example), a material widely used a few decades ago and for which the design service duration will be achieved soon in vast catchments within the region. Trenchless technologies, used for the in situ rehabilitation of damaged sewer mains, have been around for at least 40 years now, and due to their cost effectiveness, they are often the preferred mean of extending the lifetime for old pipe works. Typically in areas where the pipes are old, or have been subject to urban salinity, tidal water, polluted grounds, or heavy trafficable loads, it is not uncommon that the assets have been relined. Unfortunately it is not recommended to cut relined sewer pipes (because the liner can “spring” back either direction and create obstacles to the flow or, for some technologies, it would be like the endless process of pulling a piece of fibre off your woollen pullover until it is all gone: you cannot easily cut properly spiral wounded liners). It may not seem logical to people outside of the industry, but replacing an old pipe with uPVC is actually much simpler and quicker than excavating carefully all around an existing pipe without damaging it. The normal work methodology to concrete encase clay pipes is to cut them properly at each end, lay in lieu the required length of uPVC pipe and supporting them with star pickets and bricks so the concrete can flow under them, and reconnecting either side to the old clay pipe using rubber connectors (“Naylor Bands”). Once the existing pipe has been properly cut, removing it with an excavator is quite a quick task. Now with relined pipes, the excavator must not dig below a few hundred mm over the top of the existing pipe (as to not damage the clay collars, that will be pointed out by dedicated spotters assisting the operators of the excavators), then either change to smaller buckets (or even claws) to excavate carefully either side of the pipe when possible, or simply stop and manually detail excavate all around the pipe, and evacuate refuse up the top of the trench. This is a labour intensive and time consuming task that results in significant additional costs that clearly outweigh the savings in PVC pipes supplies. There is nothing you can do about the nature of the pre-existing pipes within your property, but one more time it is crucial for the constructors to know as much as possible so they can plan their project efficiently, knowing the risk of surprises is minimal. That is why hiring a reputable service protection reporter who can identify the size and nature of the affected assets early enough in the process will greatly assist in anticipating the costs of a building over the sewer kind of project.

This scope bears little risk when compared to others listed above, however it is worth noting that Sydney Water does not allow the domestic points of connection to their assets (usually called PCP: Property Connection Point) to be concrete encased (or under very specific conditions only), and even when the sewer encasement is not required, Sydney Water does not allow the construction of lightweight or any other structures over the Property Connection Points. This means that if your existing PCP is within the section of the sewer that will be concrete encased, it will have to be relocated at the end of the encased section (generally downstream for better drainage, but upstream configurations can work too if levels work fine). If the additional cost to construct a new junction per se is not very high (a few hundred dollars usually to cover additional work and fittings), the reconnection of the domestic line to the new junction can be a costly issue. Good communication with the domestic plumber who will reconnect the house plumbing to the new junction is really important here. It will guarantee that the Sydney Water accredited contractor who carries out the encasement works relocates the junction to the preferred end of the encased section, and uses the adequate fittings’ diameter (most old houses, in the Inner West area for example, are plumbed in DN150mm, while newer houses are usually plumbed in DN100mm). It is then up to the domestic plumber to reconnect the house drains to the new junction (including a new boundary trap for areas where it is required), at highly variable costs depending on the internal works involved. Ideally this reconnection of the domestic line to the new PCP can be done on the same day as the sewer encasement works so the excavation and backfilling costs are “split”, and continuity of service is assured. Good Sydney Water minor works constructors offer temporary reconnection solutions to avoid ground pollution and allow continuity of service in case your domestic plumber cannot attend to the permanent reconnection on the same day, however they tend to charge extra money for this, as this is usually done late in the working day and the pipe layers are paid one and a half, then double time after 8 hours of work in a day. Note that relocation of junctions in relined sewer mains is generally costlier, as specific clamp junctions (“WANG” type) must be used as to not cut the existing pipes, and these fittings are quite dear and sometimes have long delivery timeframes. As a developer and project planner, you have the means to keep this cost as low as possible (I mean $0.00): cancel it altogether by designing a structure that is away from the existing junction. Alternatively, if advantages outcome the financial drawback or if unavoidable, be sure to contact your domestic plumber upfront to get information on costs, required levels, required diameters, and to be sure they can be available to carry out the permanent reconnection of the sewer line in coordination with the Sydney Water constructor. It should prevent you from paying the plumber to re-excavate something that has been backfilled by the constructor, and also potentially save additional fees on the temporary service connection by the constructor.

Not all additional costs derive from unilateral requirements: Sydney Water accredited constructors with project management resources can often offer extra services and project management or coordination to make the whole operation stress free and successful. This will often result in extra costs that can be clearly identified in the negotiated price and included services, however cheap can be expensive in the long run, and the assistance of professionals can be worth the extra money when it comes to quality assurance, peace of mind and overall success of your project. Generally speaking accredited constructors will not explicitly charge a developer for project management services as it is part of their everyday duties, however, depending on the project specific circumstances, they can provide additional services such as:

• Removal of excess spoil. My advice is to get a quote from the builder as they are usually able to bulk it with their own site debris/spoil and provide competitive rates, and can sometimes reuse the spoil as backfill for the project, depending on the cut/fill profile and the nature of the excavated materials. If no builder has been appointed or if the builder cannot assist with this, the Sydney Water constructor should be able to help for an additional cost to be negotiated upfront. Contaminated materials will bear extra costs, while VENM/ENM will have least significant disposal rates when transported to the facilities,
• Traffic Control Plan and Traffic Control. Usually not required, unless the project implies to excavate within the road reserve. You can organize these yourself with one of the many traffic control specialised companies working in the Sydney Region, or ask the constructor to arrange them for you. They will usually apply a surcharge of about 15% to the actual invoice they receive from the Traffic Controllers, or can sometimes offer a fixed price lump sum to cover this. Note that if the fixed price seems to be a better option to anticipate the finances, it will probably contain a risk factor allowed for by the estimator, and you may end up paying for an extra day of traffic control that was factored in just in case the job progresses slowly. In some cases (properties fronting main roads) traffic control will be required to assist the concrete truck and pump to enter and exit the property,
• Week end works. For very urgent projects, you may be able to book a constructor for week end works, however please note that labour costs are high outside of normal working days. Restricted working hours (due to road occupancy licences or specific council conditions) may also bear extra costs as they impact the efficiency of the constructors.