Septic tank inspection process – listing options for failed sites
10 February 2015
Author: Féidhlim Harty, director, FH Wetland Systems Ltd environmental consultants
The septic tank inspection process is now well under way, and the first feedback report from the Environmental Protection Agency (EPA) has now been published (EPA, 2015). The document reviews the 2013-2014 inspection year and calls for proposals for the coming inspection phase (deadline 3 March next).
Almost half of all systems inspected failed. Not a great record, but hardly surprising given that the septic tank inspection process specifically targets systems in vulnerable areas, which often have suboptimal site conditions. In this light, perhaps it is surprising that so many passed at all. Of those that failed, the most common cause of failure was inadequate maintenance. This suggests that although site conditions may be challenging, they are actually not the most common cause for concern, and that with suitable remediation, a cost-effective solution is often possible.
The responsibility for finding a solution on a failed site rests with the homeowner, in liaison with the local authority and a wastewater professional. So how do we, as wastewater professionals working in this area, advise our clients as to the options available? In this respect, the EPA’s ‘Remediation and Replacement of DWWT (Domestic Waste Water Treatment) System’ web page specifies, inter alia, the following:
- The standards that need to be met are set out in the Water Services Act 2007 and 2012 (Domestic Waste Water Treatment Systems) Regulations, S.I. 223 of 2012;
- The remediation solution should follow best practice;
- Remediation may follow the Code of Practice, but is not necessarily bound by it. However, the EPA suggests that it “would be prudent to have regard to the provision for alternative technologies” in the Code, namely that they be certified, fit for purpose and meet the performance requirements of the Code;
- The waste-water professional must demonstrate that any proposal will lead to improved treatment and reduced risk to human health and the environment;
- The proposed upgrade should be cost effective.
When it comes to direct examples of acceptable solutions, the government guidance is less clear. Nonetheless, there are many practical solutions that can be employed to provide environmental protection on a site. Note that the options presented below are based on my experience in offering environmentally sustainable solutions to clients since the mid 1990s. The list is not EPA- or local authority-approved, but is rather an example of both conventional and innovative options that may be employed to good effect for environmental gain on even the most challenging sites.
With this in mind, what are the options available, whether for remediation of failed systems on suitable sites or on unsuitable ground conditions? The initial list of possibilities should begin by exploring the options for the tank and percolation system: desludge the existing tank; fix the old tank or percolation area; install a new tank or percolation area; or pump to a polishing filter or raised percolation area, where conditions allow.
Where a straightforward upgrade is not sufficient; secondary treatment of the effluent may be required prior to percolation. Treatment wetlands, mechanical treatment units and package filter-media units are three categories that are outlined in the EPA Code of Practice. Additional guidance is available in the Department of the Environment’s Integrated Constructed Wetlands Guidance Document, 2010.
Treatment wetlands can have the advantage of having low- to zero-energy inputs for ongoing running of the system where gradients allow. This not only saves on costs to the homeowner, but reduces the overall carbon footprint of the project on an ongoing basis. Treatment wetlands also provide wetland habitat for wildlife and can make a very attractive garden feature. Where the soil is particularly heavy, a straightforward soil-based or integrated constructed wetland can be a very cost-effective treatment method prior to discharge. Treatment wetlands may be categorised as follows:
- Soil-based constructed wetlands;
- Integrated constructed wetlands;
- Horizontal-flow gravel reed beds;
- Vertical-flow gravel reed beds;
- Vertical-flow sand reed beds;
- Packaged tertiary treatment reed beds.
Mechanical treatment units are a more common solution. These provide a relatively easy option in that they will achieve secondary treatment in a very compact footprint area, and essentially look like a septic tank within the overall garden layout. There are many different types, with varying costs, energy inputs and maintenance requirements:
- Activated sludge (including extended aeration) systems;
- Biological/submerged aerated filter (BAF/SAF) systems;
- Moving bed bioreactor (MBBR) systems;
- Rotating biological contactor (RBC) systems;
- Sequencing batch reactor (SBR) systems;
- Membrane bioreactor (MBR) systems.
Packaged filter-media units typically require a pumped feed, but generally have considerably lower electricity requirements than standard mechanical treatment systems. They also have a relatively compact footprint area. Systems include peat filter-media systems and plastic, textile and other media systems.
Usually on a failed site, the challenge is not so much treating the effluent, as finding a suitable disposal route. Typical disposal options include either percolation or surface discharge, but in practical terms, other possible routes may also provide a solution where conventional disposal routes are not available. Note that percolation to ground may still be a practical solution on sites with t>90, where some percolation exists and where the effluent has been treated so that it does not cause any soil pore-clogging.
Similarly, discharges to surface waters may not be a legal possibility without a discharge licence, but there are de facto surface discharges from failed percolation areas throughout the country. On such sites, it may be better to treat the effluent cost effectively prior to discharge rather than employ extraordinary measures to dispose of the effluent by other means. Cesspits are mentioned below, and although these are not used in Ireland, they are common in some other EU countries for storing effluent on sites without other disposal means. Options for disposal include the following:
- Percolation to ground; depth is dependant upon the level of effluent treatment;
- Discharge to surface water; whether via direct or indirect discharge;
- Evapotranspiration to air; via willows or other quick growing biomass crop;
- Recycling of treated effluent for flush water or irrigation;
- Export from the site via sewer or cesspit.
Trinity trial: low-permeability soil
There is an EPA STRIVE report due for publication on the recommended treatment and disposal options for soils of low permeability. One of the trials that was carried out for this report was the investigation into the Danish zero-discharge willow facility model. This has worked satisfactorily in Denmark since the mid 1990s and was being trialled for Irish conditions. Designs for systems constructed under this trial were by Trinity College and by FH Wetland Systems in collaboration with the Centre for Recycling in Denmark.
Unfortunately, the systems tested in the Irish trials overflowed at some point during the trial period. This was due, at least in part, to the characteristics of the clay backfill used. Despite using Danish best practice in all cases, the Irish soil conditions made for a stickier clay than the drier, broken equivalent in Denmark – thus effecting the overall void space available in the systems. This is not to say that these systems cannot be built successfully here, but that updated design and construction methodology are needed.
Nonetheless, as a willow filter, these systems worked very well at providing good N and P uptake and protecting the receiving environment. The zero-discharge model is only one of a range of willow systems available for use on challenging sites:
- Zero-discharge willow facilities, mostly used for domestic applications;
- Willow filter systems; as used by Monaghan County Council and other applications in Ireland already;
- Partial evapotranspiration areas, for enhanced N and P uptake from any site;
- Willow buffer zones for subsoil remediation.
Something that the National Inspection Plan has done, for the first time, is to begin the process of drawing source separation technologies into the mainstream government guidance documents. Source separation of urine or faecal solids has long been carried out in countries such as those in Scandinavia, with good environmental records. These systems can provide the advantages of conventional flush-toilet appearance, with the environmental benefits of nutrient capture and biomass reuse.
In Ireland, the 2013 EPA STRIVE report on water-saving technologies examines urine diversion and dry toilets as being practical options for homeowners. Following is a list of the source separation systems available. These can have direct application for environmental protection as well as water conservation: urine diversion toilets, urinals, faecal separator systems and dry toilet systems.
There is a wide range of dry toilet systems available, and the technology is slowly becoming more familiar to many engineers, planners and site assessors. They can offer the advantages of pollution prevention, water conservation and nutrient and biomass recycling. Not all systems are suitable for all sites or all homeowners, so knowledge of the options and careful selection is needed to find the right system to meet your client’s particular values and priorities. These include: self-contained composting systems; either indoor or outdoor depending on the desing; remote composting systems; with separate outside composting set-up; micro-flush systems; electric drying systems; and chemical toilets.
Hand in hand with dry toilets is a requirement to treat grey water. With significantly lower pathogen loads, grey water does not need the same biological filtration as black water or mixed sewage. However, the presence of toxins from cleaning products and detergents means that treatment is still required. Following is a list of some of the options available:
- Grey water filters and grease traps, proprietary systems;
- Planted grey water filter systems, all of the treatment wetland or willow options listed above;
- Grey water irrigation systems, which may be used in some cases without formal planning;
- Grey water recycling systems: proprietary systems, route treated grey water to toilet cistern.
Not only do the above options have application in existing failed sites, but they can also be used to upgrade uninspected problem sites or for new green-field situations. Planning permission is generally required for voluntary upgrades, and it can be more difficult to get permission for systems not in compliance with the EPA Code of Practice.
Similarly green-field sites generally, although not always, need to be Code compliant. That said, the 2013 STRIVE report makes it easier to propose source separation technologies as part of the overall treatment process. Similarly, new willow filter applications should become easier with the publication of the new EPA STRIVE report due out soon from Trinity College.
DEHLG (2010) Integrated Constructed Wetlands – Guidance Document for Farmyard Soiled Water and Domestic Wastewater Applications. Department of the Environment, Heritage and Local Government, Dublin.
Dubber D and L Gill (2013) Strive Report Series No.108: Water saving technologies to reduce water consumption and wastewater production in Irish households. (2010-W-LS-3). EPA, Wexford.
EPA (2009) Code of Practice: Wastewater Treatment and Disposal Systems Serving Single Houses. Environmental Protection Agency, Wexford.
EPA (2015) National Inspection Plan – Domestic Waste Water Treatment Systems – A Review of the Period 1st July 2013-30th June 2014 & Consultation on Proposals for 2015-2017. EPA, Wexford.
EPA web page: Remediation and Replacement of DWWT System http://www.epa.ie/water/wastewater/guidance/remed/#.VNTk5ij3XQl
S.I. No. 223/2012 – Water Services Acts 2007 and 2012 (Domestic Waste Water Treatment Systems) Regulations 2012.
Féidhlim Harty is director of FH Wetland Systems Ltd environmental consultants and the author of Septic Tank Options and Alternatives – Your Guide to Conventional, Natural and Eco-friendly Methods and Technologies, published recently by Permanent Publications. See www.wetlandsystems.ie/watertips.html for additional online resources related to the above article.https://www.engineersjournal.ie/2015/02/10/septic-tank-inspection-failed-sites/https://www.engineersjournal.ie/wp-content/uploads/2015/02/Eco-1024x705.jpghttps://www.engineersjournal.ie/wp-content/uploads/2015/02/Eco-300x300.jpgCivilDenmark,environment,Environmental Protection Agency,Trinity College Dublin,waste,wastewater,water