Total Pageviews

Friday, August 27, 2010

Reticulated Sewage vs Septic Tanks

It is obvious that a modern reticulated sewage system with the sewage piped to a modern sewage treatment plant is far better, more hygienic, more reliable and just plain nicer that a system where every household has a septic tank feeding its water to either a soak pit or drain tile system. Well isn't it? Maybe yes, maybe no. Lets go through the systems and see where we come out.

This has all come about because here in Waipara where I live, the district council wants to put in a reticulated sewage system and right at the start, I admit to a vested interests. I have just installed a mini, aerated sewage treatment plant of my own which after three years is working perfectly with no problems. The council will want me to connect up despite the fact that I will have to pay more than I paid for my own sewage system. (go figure). However I will try to be objective.

Note:  Sept 2019.  An item on the radio opined that people will have to more and more take responsibility for their own sewage.  This came about due to a report on the abysmal state of piping that carries sewage to sewage plants in one of our largest cities.

While I am talking about vested interests, lets have a quick glimpse at vested interests on the other side of the argument. The council is proposing to limit subdivided lot sections to 1100square meters if we don't have a sewage system and 700 square meters if we do. A few of our residents want to make some money by subdividing their properties and can squeeze in more properties if we have a sewage system. I can't believe they would subdivide their properties and loose their present vegetable gardens, fruit trees etc and end up living cheek by jowl with a couple of new neighbors so the only conclusion I can reach is that they intend to subdivide and then scamper to a new location with the same or more space than they have now. So there are vested interests on both sides.

Another vested interest involves a number of commercial properties which cater for tourists.  They have a far greater output of sewage but will only be charged the single connection fee that will be charged to every individual household.  Just another example of the poor subsidizing the rich.  

First a bit about Waipara. Waipara has been here from before 1900. In 1900 it had a hotel, 50 full time residents and 163 railway workers. At its peak, it had three stores although it now only has one. At present there are 110 households in Waipara. In the early days, the sewage systems consisted of long drops while today it is mainly septic tanks. The earlier septic tanks used a soak pit consisting of a hole filled with rocks. Some newer septic tanks have have drain tiles systems. These are lines of loosely jointed ceramic pipes which leak at the joints and hence distribute the water from the septic tank over the area of the garden. Just recently a new system of mini. aerated sewage treatment plant like the one I have installed has become available and some houses have these. They produce treated water which is dripped on to shelter belts etc.

The surface geology of the township is of interest with respect to septic tanks. We are on a peniplane* and if you look across the river, you can see the continuation of the terrace we are on. If you dig down a few meters, you come to alternate layers of shingle (gravel) and layers of fine silt which approach clay in its consistency. Canterbury where Waipara is located has fast growing mountains to the West. Rivers flowing out of the mountains carry a lot of sediment that they begin to drop as they flow on to the plains. Over the 11,000 years since the major glaciers retreated, the rivers acted like grouting machines spreading layers of gravel in high flow times and layers of silt when the river flow was low. This may be the explanation for the alternate layers of silt and gravel we live on.

At present, when we have severe rain events, many fields are flooded and it takes considerable time for the water to seep down into the ground. Soak pits intersect alternate layers of gravel (called shingle in New Zealand) and fine compacted silt. Water flowing into these soak pits spreads horizontally in the gravel bed with its downward flow impeded by the silt layers. Basically it is a system of multiple perched water tables.

*When a plane is later cut by rivers, the remnants of the plane are called a peniplane.

Waipara obtains her water from a well approximately 100m down stream of the main highway bridge over the Waipara River close to the Waipara Garage which is on the intersection of the main N-S highway and the Weka pass road. It is down slope from Waipara Village. The District council has reported that in tests done on our water, there is no sign of any contamination and in fact, our water is so pure that it is not even chlorinated*. This is despite the fact that Waipara village has been here, upslope of our water supply and using long drops and septic tanks, for over 100 years. If our septic tanks were a health hazard, there has been plenty of time for any escaping pollution to seep down into the water table. In an appendix, below** I will explain what I suspect is the reason for the lack of pollution. This is for the benefit of anyone who is interested in sewage disposal. The important fact to keep in mind, though, is the bottom line. There is no contamination in our drinking water.

* I have been told that some tests came up positive for e coli but there is as yet no indication that the source is from Waipara. Our water is now chlorinated.

And one last comment regarding the cost of the system. At present, the Hurunui Council estimates that the $1.7million Waipara sewage system will cost each household $15,000. A new Oasis (home sewage treatment system) costs $11,500 installed. One financing option presented was to pay the $15,000 off in your rates like a mini mortgage. The interest rate has been variously estimated but seems to be projected at between 6 and 7%. Below is the amount per year that you would pay off just to take care of the interest at the start of your $15,000 loan. You would, of course have to pay more than this to start to reduce the principle,  and the interest you have to pay would decrease as you reduce the principle.

Yearly Amount of interest you will have to pay at the beginning of your $15,000 loan
Rate Amount
5%   $750
6%   $900
7%   $1050
8%   $1200

Note that rates are about $1000 per year in Waipara so just paying off the interest at the beginning of the scheme will just about double your rates. How fast this decreases depends on how much extra the individual household pays off to reduce the principle.

So what are the reasons for continuing with septic tanks rather than installing a central reticulated sewage system.

1. There is no need for the new system. Our water supply, after 100 years of Waipara being up-slope of our water supply is completely uncontaminated.

2. Reticulated sewage systems and their treatment plant are very vulnerable to electrical outages and earthquakes. This has been amply demonstrated in the recent Christchurch earthquake. After the recent earthquake, sewage was flowing in the streets.   Septic tanks are also vulnerable to earthquakes but any damage is localized, small and easily repaired. Recently on the radio, they have stated that in some earthquake effected areas in Christchurch they are thinking of digging holes in the ground and putting in cement tanks to take care of the sewage. (in other words septic tanks).

3. The price quoted for the sewage system is only for the construction. Further rate increases will be necessary for maintenance and operation. The cost of construction operation and maintenance is for a system with no demonstrable benefit.

4. While the adoption of "high-Tech" solutions is often beneficial, they also increases one's vulnerability to outages. A chain saw is vulnerable to far more outages than an axe. The difference is that the chain saw provides a considerable benefit in the rate one can cut up logs. We are often willing to put up with increased technical vulnerability because of the benefits technology brings us. In the case of the proposed reticulated sewage system, there is no benefit to make up for the increase in cost and vulnerability.*

*unless you consider it a benefit to be able to subdivide your property into very small lots in order to make money so that you can move to somewhere less crowded and leave crowded slum like housing for the remaining citizens of Waipara to contend with.

5.  At present, the water flowing from one's house via a septic tank is taken up by ones grass, shelter belt and other trees and plants.  If we send all this water to a sewage plant, we will have to increase the amount of water we use just to keep the garden in its present state.

6.  With payments per connection, businesses with high sewage loading are riding on the back of individual households.  Money once again from the poor to the rich.

7.  Sewage systems all over New Zealand have had cost overruns and bankrupted comminities.

8.  Sewage systems all over New Zealand have run into problems when there have been electrical outages or excess water into the system, both resulting in sewage being let out into the adjacent river.  Sewage, when spread out over a large area is a resource.  When concentrated in one area, it is a pollutant.

** How the present system of septic tanks probably works
After the water leaves a septic tank it is loaded with nutrients and some particulate matter.  When this flows through permeable soil, sand or gravel, it feeds a wide variety of microorganisms.  Bacteria are the primary producers and generally grow in films attached to the various surfaces in the substrate.  If sewage is let into a sand bed, once the sand bed  has matured, you find that the bacterial load decreases very rapidly from the source of water.  A meter or two away from the supply pipe, bacteria levels are down to the natural loading of the surrounding soil.  A second effect occurs due to the roots of trees, shrubs and grasses.  They seek out water and the nutrient rich water from a septic tank is just what they need. Grasses are typically rooted a meter or two below the surface, shrubs more deeply and trees more deeply still. It is doubtful if there is any nutrient seeping into our water table and this is born out by the analysis of our drinking water which is taken from a well down-slope from the town.


Below is the full submission which I sent to the Hurunui Council.

From: W.L. Hughes-Games
63 Glenmark Drive
Waipara 7447
Ph 314 6895
Fax 314 6897
To: Hurunui District Council
Subject: Proposed Sewage system for Waipara
My submission deals with a few technical aspects of sewage treatment systems and asks for certain information to be included in the disclosure by the council to the citizens of Waipara to allow us to make an informed decision on the proposal. It concludes that there are no compelling reasons to install a central sewage system and some very good reasons to maintain the status Quo
1. Substances which must be treated in domestic sewage include bacteria, fixed nitrogen, phosphorous, intestinal worm eggs and petroleum products.
2. Soil and shingle beds are very capable of treating all the above. The dosage rate is of critical importance.
3. Test to date have found none of the above contaminants in the ground water of Waipara despite the many decades Waipara has utilized septic tanks.
4. Concentrating the sewage of Waipara in one place leaves us vulnerable to electrical outages and earth quakes unlike the existing system, with unpleasant potential results.
5. If a central sewage system does go ahead, full and final disclosure must be given as to the cost per household to install and to operate the system, the obligations of people with operating septic tanks and Clearwater type systems and the financial commitment of new users such as the proposed Oaks project and The Wine Village.
6. If The Oaks and The Wine Village go ahead, there are good reasons for them to install their own sewage system and utilize the purified water themselves.
7. If the sewage system does go ahead, it should be conditional on an agreed price which is committed to by the council.
While not a qualified sewage engineer I have worked in a number of positions which give me a peripheral knowledge of the subject. I am most open to correction by anyone who is better qualified in the subject. I suggest you submit this paper to a qualified sewage engineer for his comments.
* Most of my working career was in fish/prawn/oyster farming research in which large quantities of feed (similar to chicken pellets) were fed to fish in ponds. A major part of our work was the treatment of the effluent from these ponds so that it wouldn't impinge on the environment - essentially a sewage disposal system.
* I worked for a number of years as the chemist for the Department of Hydrology of the University of Zululand, picking up some of the concepts of hydrology and of the movement of water in the environment.
* I taught high school in Hawarden Area School. One of my subjects was senior Chemistry.
Concepts upon which this submission is based
1. Domestic sewage water contains a number of problematic substances which should not be allowed to find their way into the water table. These are:
* bacteria including various pathogens. A common bacteria in all feces from warm blooded animals is E coli . While most E. coli varieties are benign, the presence of these bacteria in a water supply indicates contamination by the faces of warm blooded animals. They are easy to detect and that is why they are used as an indicator of fecal contamination.
* Eggs of human intestinal worms
* Nitrogenous ions (fixed nitrogen) such as Nitrate, Nitrite and Ammonium from the digestion of protein. Fixed nitrogen in a drinking water supply at very high concentrations can pose a health risk for young babies who's only nutrition is from milk. Once a baby is on solid food and has developed the normal gut fauna, this danger disappears. Nitrogen also can cause eutrophication when found in surface water.
* Phosphate, which to a small extent comes from excrement but is mainly from certain cleaning products.
* Petrochemical wastes such as spilled thinners, oil, diesel and petroleum.
2. When relatively small quantities of water (such as from a domestic residence on a reasonably large property with a septic tank and drain field or soak pit) containing the above materials enters the soil, the soil or shingle into which the water is seeping, very quickly develops a fauna which takes care of these materials. This is especially so in topsoil which already has a very rich fauna of organisms With the application of water rich in these substances, even sub-soil soon develops the necessary fauna. Specifically:
* bacteria whose natural environment is a 37 degree intestine are quickly predated by the soil fauna. Unless tunneling is occurring, you would be unlikely to be able to detect E. coli more than a couple of meters away from a drain field.
* Intestinal worm eggs, being relatively large, are filtered out by the soil and die, becoming part of the humus. They are ingested and ground up by earth worms and are predated and parasitized by everything from fungus to soil burrowing insects. This is in contrast to Sewage Treatment plants where large quantities of intestinal eggs are not removed and are found in the solid part of the final effluent. This is one reason why it is recommended to thermally compost human sewage effluent from sewage plants before utilizing it as a garden enhancer.
* Nitrogenous ions are to some extent denitrified (turned back into Atmospheric Nitrogen) if the soil contains aerobic and anaerobic zones. Nitrogenous ions are taken up by plant roots from grasses, in the upper parts of the soil, to tree roots in lower levels. The critical factor is the dosing level. If too much water which is rich in fixed nitrogen (ammonium, nitrate and nitrite) is put on the soil, some of it will find its way into the water table.
* Phosphate is not broken down but is utilized as an essential nutrient. If more is put on a soil than the plants can absorb, it may find its way into the water table. Many soils convert phosphate to an insoluble form which is only poorly available to plants and which does not reach the water table. Such fixed phosphate is mobilized by soil fungus in organically rich soil and made available to plant roots.
*Petrochemicals are utilized and oxidized into carbon dioxide and water once the bacteria have developed which can cope with these material. Again the dose rate is the important factor and in the case of petrochemicals, the aeration of the soil and the existence of other nutrients (from domestic sewage, for instance) is an especially important for their utilization and hence detoxification. Petrochemicals provide energy for certain bacteria but the bacteria need phosphate and nitrate to be able to use them; the very substances which are found in domestic sewage.
3. When contamination of ground water by surface sources is suspected, two pieces of information are necessary to confirm or deny the suspicion. First the direction of ground water flow must be known. Often this is in the same direction as surface water flow but not always. Fluorescent die studies are the preferred way of determining flow speed and direction. Secondly, sample wells must be drilled into the suspected plume of contamination, downstream of the suspected source, and water samples from these wells analyzed for contamination. If a number of wells already exist in the area, it may be possible to obtain some information regarding contamination by analyzing water from these wells. More specifically, since we are talking about contamination of drinking water supplies, samples from the Waipara drinking water well are of the most significance. Samples of water from wells upstream and downstream of a suspected source of contamination (Waipara) are necessary to give an indication of the existence and extent of ground water contamination by that source. In a recent meeting with the council, it was stated that no such contamination has been found in the Waipara drinking water well.
Present Sewage System
At present the majority of the dwellings in Waipara have a septic tank. Supernate from the tank flows either into a drain field which typically is a number of horizontal pipes, often ceramic which leak at each joint. Drain fields are usually at less than a meter depth.
Alternately, the supernate flows into a rock filled soak pit which typically is two to three metres deep. In the septic tank anaerobic breakdown of solid material takes place and typically every three to five years, one has the septic tank pumped out to remove refractory material. The removed material is taken to the Christchurch sewage plant for disposal.
In the drain field system the nutrient rich supernate is leaked out into top soil or near surface sub soil. The incredibly rich fauna in these surface layers of soil soon adapt to utilizing all the materials mentioned above which are found in domestic sewage. Shallow rooted vegetation utilizes the water and nutrients in this water.
When a soak pit is dug, it goes far enough down to intercept at least one shingle layer. The sub soil in Waipara is typically alternate layers of clay and shingle, deposited there by periods of flood (shingle) and normal water flow (clay). Water which is run into a soak pit, therefore flows horizontally through layers of shingle. Very few bacteria and other microscopic fauna live in free water. They live, typically in films attached to surfaces. When nutrient rich water flows into a shingle bed, the surface of the individual stones of the shingle are soon coated with bacterial films which utilize the materials in the water. Roots of plants seek out sources of water and utilize the water in these layers. Even grass roots of some grasses can penetrate four meters into the soil and roots of trees and shrubs go much deeper. The combination of natural treatment of the substances in the sewage water and the uptake of the water by plants is most likely the explanation of why no contamination has been observed in our fresh water well.
Some of the newer houses in Waipara have Clearwater sewage systems. This type of system has an aerated chamber with a plastic grid to provide the attachment surfaces for the bacterial films which treat the sewage. Aerobic processes are much more energetic than anaerobic processes and with the aeration along with a recycling feature, which takes any settling material from the last chamber back into the first chamber, Clearwater type systems treat sewage to the same level as sewage treatment plants. The final stage is a plate filter which removes particulate material down to well below the size of intestinal eggs. The filter also removes any material that could plug the downstream drip irrigation system. The treated water is run through a drip irrigation system, typically located in a shelter belt.
Disclosures which should be contained in the initial discussion document for consideration by the citizens of Waipara.
1. Is there any hard evidence of contamination of ground water by the existing septic tanks in Waipara. More specifically is there any increase in nitrates, E. coli or any other contaminant between wells upstream of Waipara and the drinking water well. If so, to what extent and how does the contamination compare with New Zealand water standards for potable water. A recent meeting with the council indicated that there is no such contamination
2. Is there any reasonable expectation that in the next decade or two, Waipara will achieve a population density similar to a suburb of Christchurch. Such densities would only be attained with approximately two extra houses on each Waipara property. Similar concentrations of housing would also have to occur in areas into which Waipara expands. Remember, the amount of water discharged per area of soil is critical and must be enough not to exceed the soils capacity to utilize the substances contained in the water. Nutrients only constitute contamination when they are applied in greater quantities than the soil can handle. Rumor has it that the Oaks development will be high density housing. Some thought should be given to whether there is actually a market in Waipara for such housing. Most people leave central cities in order to have a larger allotment. If such housing does go ahead, serious consideration should be given to them having their own Oasis type system with the water discharged on their own land to water their trees etc.
3. If a sewage collection reticulation pipe is installed then a sewage treatment plant must treat the collected sewage. Even if the treatment plant is very well run, the discharge still contains considerable undesirable materials. Two solutions to discharge are to spread this water over a sufficiently large area of land or to feed the water into oxidation ponds where further treatment occurs naturally and then discharge it into the environment. What do you plan to do with the sewage effluent which would now be concentrated into one point rather than being discharged safely over all of Waipara?
4. Sewage plants also produce a solid waste which is usually rich in the eggs of intestinal parasites. These are small enough to be wind born if stirred up. What do you intend to do with this waste?
5. Of most importance, what will be the cost to each household in Waipara for both installation and operation? I'm not talking about some sort of estimate but a firm commitment as to the cost of installation, operation, and maintenance which will be committed to and not changed in the coming years. Sewage piping and treatment plants are standard world wide. They are not innovations. A firm price should be possible for the Council to commit to. You don't sell a car to someone at an agreed price and then expect more money later at the discretion of the seller. Since there is an element of coercion in the promotion of a sewage system (objectors don't have the option of opting out) it is even more important that the price be up front and fixed.
6. What is your proposal with respect to households which already have either a septic tank or one of the Clearwater type sewage treatment units? The Aerated sewage treatment units are government approved because they treat water to an acceptable standard. They also spread the output of the unit over a larger area than does the drain field of a septic tank and hence have a lower(better) dosing rate into the soil. They are regularly monitored and serviced by a professional technician as part of the contract and so will maintain their effectiveness. You can't expect a household which has invested in such a system to contribute to this sewage treatment system.
7. And lastly, while anyone in or out of New Zealand can make a submission on this proposal I would suggest that Technical information is only relevant if it deals with our specific situation (such as, for instance, nitrate levels in the wells in and around Waipara) or if it deals with experience in similar communities to Waipara. It is of no relevance to us what the situation is in a city suburb with three times the housing density.
I would also suggest that a vote on whether or not to install this system be confined to Waipara residences which the sewage system will serve. Someone living outside of the area that the sewage line will not reach should have no part in voting for or against the proposal. If the sewage line is later extended to them, they can then have a vote. Unless there is a clearly researched, demonstrably detrimental effect of our present system which is affecting our environment, the vote of the affected citizens of Waipara should be final.
Some detrimental effects of a piped centrally treated sewage system.
1. With centrally treated sewage, the sewage of a whole town is concentrated into one small area. The treatment, if correctly carried out reduces the level of fixed nitrogen and may fix some phosphorous into the solid portion of the treated effluent. The liquid and the solid portion must then be disposed somewhere. By necessity, it will be disposed in a smaller area than at present. At present, the sewage of Waipara is disposed over the whole area of Waipara With sewage, dosage rate is critical.
2. The solid portion of effluent from a sewage treatment plant typically contains the eggs of intestinal parasites. This material must not be stirred up as the worm eggs are small enough to be carried by the wind. It must also be composted at high temperature to destroy these eggs if it is to be utilized. This adds further expense to the system. What is your plan for the solid effluent?
3. In the case of an electrical failure, if we have a central sewage treatment plant, aeration stops and we will likely be letting raw sewage out into the environment. This raw sewage is most likely to find its way into our river. Electrical outages have no effect on septic tank systems and even Clearwater type systems can be left without electricity for a day or so and go back to normal when the electricity comes back on. Even if electricity does go off, with clearwater systems, there is not a huge concentration of contaminated water in a small area. Each clearwater system must be installed so that any overflow goes off into a vegetated area and, of course, it is only the sewage from as single household.
Another problem connected with an electrical outage is that the lower (southern) end of Waipara is lower than the proposed sewage treatment facility. If the electricity goes off pumps will stop and effluent will exit at this low point or back up into individual properties (if the required valves are turned off).
4. In the case of an earthquake, the pipe of a sewage system can break anywhere unpredictably. If this happens, raw sewage from all of Waipara will flow out of the break. This is not the case with our present system of septic tanks. Hi tech is often better but often not.
5. At present, the water from each dwelling in Waipara flows into the ground of the property. This waters various trees, grasses and shrubs on the property. Remove this source of water and either the plants which depend on this water will die or the property owner will have to buy more fresh water to irrigate them. Besides the added expense to the property owner, this will put more strain on our water system and may necessitate a costly upgrade.
Costly upgrades are also carried by the property owners.
Proposed Developments in the Waipara Area
Two projects of relevance to the proposed sewage system are in the planning stage for Waipara. These are The Oaks, a proposed settlement to the North of Waipara on what is now farmland and The Wine Village which will be located on the corner on the highway opposite the Waipara garage.
If rumor is true, the Oaks is to be low cost housing of about 3 times the density of present housing. Lets leave aside for the moment the advisability of putting in crowded housing in an area that people come to to get away from crowded housing and the advisability of developing a project like this when the Waipara population has been pretty well stable for decades and there are properties on the market that are not selling. If this project goes ahead and if the houses sell, they will definitely need sewage treatment. There simply won't be sufficient area for the septic tanks and drain fields. I would suggest that they put in a communal clearwater-type system and use the water to irrigate their shelter belt trees. If there is an excess, I'm sure a nearby farmer would be most pleased to get this purified but nutrient rich water to irrigate a field of alfalfa. Utilizing the purified water for such purposes would put less strain on our water table and the Waipara drinking water reticulation, possibly saving us the cost of a total upgrade of the system. Note that the final stage of a Clearwater type system is a plate filter that removes any particulates including parasite eggs.
Similarly with the Wine Village. Part of this development includes a golf course. How much better if they install their own Clearwater type sewage treatment and use the purified water to irrigate their greens. (A modest proposal would be for the Wine Village development to install their own Clearwater type sewage treatment allowing the use of their treated water for their greens.) This should greatly reduce the amount of water that they must extract from our common ground water. If it was necessary to connect them to the Waipara fresh water reticulation, this should also lessen the expense of any needed upgrade to cater for their needs.
There seems to be no compelling reason to establish a central sewage system for Waipara and some very compelling reasons not to do so. The very absence of measurable contamination of our drinking water which is extracted down-stream from Waipara is the most compelling proof of all that the existing system is working. If it ain't broke, don't fix it.

Note: Since the sending of this submission, we have had the Christchurch Earthquake. The sewage system in Christchurch and the nearby town of Kaipoi was seriously damaged. Parts of Christchurch and Kaipoi smell like outdoor dunnies and portaloo's festoon the streets. Raw sewage is now being let into the rivers in the area. It has been reported that it will be up to a year before residents in the worse effected areas will again be able to use their indoor toilets.


Unknown said...

Sewage treatment plant and equipment- Delhi, India based manufacturer and supplier of sewage water treatment plant and sewage waste water treatment. said...

I have really enjoyed this blog. Keep up the good work. The Septic Tank Man said...

I have really enjoyed your site. Keep up the good work

septic tank cumming said...

Thanks for ones marvelous posting! I seriously enjoyed reading it, you're a great author.I will be sure to bookmark your blog and definitely will come back in the foreseeable future. I want to encourage you continue your great job, have a nice day!

Will said...

As a person directly involved in waste treatment systems and environment protection, I can’t express how much I enjoy reading the content written here. My writing and contribution on this subject can be found at wastewater system with main focus on topics related to groundwater bioremediation, future of microalgae biofuel production and dissolved air flotation system.

Unknown said...

Great points about reticulated sewage versus septic tanks. The idea of the reticulated sewage is nice but seems like it would be harder to maintain. A lot of people have septic tanks so that makes it a more consumer friendly system. Especially if you were to ever sell the home.