Your Homes Wastewater System Explained

The wastewater your home produces is referred to as effluent and consists of blackwater (toilet waste) and greywater (kitchen, shower, sink, and laundry waste). Effluent flows directly from your house into a "watertight", underground, two compartment septic tank where solid waste settles into a sludge layer on the bottom and fats float to the top. Between these two scum layers is a zone of clarified liquid effluent which is internally piped to the second compartment of the septic tank for additional settling. As effluent fills the first compartment, clarified liquids are forced to leave the second compartment of the sewage tank and flow out to the leach field or leach pit. The typical leach field is a series of trenches where effluent is "purified" as it slowly percolates through the soil. A leach pit is a hole filled with rock for disposing of wastewater.

 

F Stamped, engineered, septic system plans are typically not necessary unless your property's percolation test was "extreme" (greater than 60 minutes per inch or less than 5 minutes per inch); or the site has seasonal groundwater; or there is bedrock or unsuitable soil less than four feet below the proposed leach field; or if the ground slope is in excess of 30% in the area of the proposed leach field. "Engineered systems" require a local engineer to approve ("stamp") your site's septic tank and leach field plans. Anyone can draw up their own septic system plan ("design"), but legal liability lies with the approving regulatory officials when you are "pulling a permit" unless they require ("code") an engineer's approval." Local engineers are familiar with local codes which vary from town to town, year to year, and sometimes, inspector to inspector. When the soil percolation rate of your site is "extreme", the local regulatory officials ("health department") defers to a licensed and insured local engineer to "stamp" the plans as being "safe" for the client, his/her neighbors, and the environment." This releases the local government from future legal liability for your "extreme" septic system's failure.

    I Most areas of Costa Rica do not get concerned with any of this. There is no "code", "stamp", "design", or "health department" to be concerned with. Chances are they have never heard of a "perc" test, and besides you would need that done in San Jose. Whom ever your General Contractor is not required to be concerned with this either. The contractor will do whatever they think is right, and that will be your homes system. If there are any problems later with that system or your families health, you can discuss it with them.

F When you apply for your building permit, the local health department official will most likely help you design the sewage disposal system and may even offer to have their office perform a soil test (LTAR) in lieu of a percolation test. This involves digging a "soil profile hole", which is generally an eight foot deep trench in the area of the leach field. Most building departments wisely require a visual confirmation that there are no problematic soil conditions, groundwater, or bedrock in the area where you intend to put the leach field. Check with your local officials, you may only need to provide a site plan survey (ILC) of your property (to establish setbacks from buildings, wells, streams, and property lines) and fill out some forms.

    I Most areas of Costa Rica do not get concerned with any of this. There is no "code", "stamp", "design", or "health department" to be concerned with. Chances are they have never heard of a "perc" test, and besides you would need that done in San Jose. Whom ever your General Contractor is not required to be concerned with this either. There are no "forms" here to complicate things. Setbacks are not a concern either, many local contractors just dump into your closest stream. The contractor will do whatever they think is right, and that will be your homes system. If there are any problems later with that system or your families health, you can discuss it with them.

F Your septic system site plan is typically drawn right on top of your property survey showing the septic tank within 5-10 feet from the house, the leach field at least 20 feet from the house and at least 100 feet away from wells, 75 feet away from streams, 25 feet away from dry gulches, and 10 feet away from the property lines. Or whatever the local regulatory officials require.

    I Most areas of Costa Rica do not get concerned with any of this. There is no "code", "stamp", "design", or "health department" to be concerned with.  You probably won't have a well to worry about anyway. Unless you put one in later, and know where all your underground is located. You will know after a year or more if the setbacks were not followed, you will smell it! Whom ever your General Contractor is not required to be concerned with this either. The contractor will do whatever they think is right, and that will be your homes system. If there are any problems later with that system or your families health, you can discuss it with them.

F The home's sewer line drain needs to slope at least 1/4 inch per foot downhill to the inlet side of the septic tank and the outlet pipe needs to flow downhill at least 1/8 inch per foot downhill to the leach field where the septic tank effluent enters a manifold or distribution ("D") box. Beyond the manifold or D box the leach field trenches (for an Infiltrator chamber system) are excavated perfectly level at a depth of seven inches below the grade of the manifold pipes or D box.

    I Ask your contractor to explain this to you and show you the drawings.

F If the leach field is uphill from the septic tank (or if the local health regulations simply require it) a "lift station" is installed in-line after the septic tank. An electric pump in the lift station forces effluent out to the leach field every time it fills to a certain level ("dosing"). Please note that most ISDS codes allow field size reductions with dosing or automatic siphons, so there may be a certain advantage to installing a lift station (small building lots and/or nearby streams or ponds).

    I Ask your contractor to explain this to you. He will explain what ISDS codes are, if he knows what ISDS stands for. (Individual Sewage Disposal System)

F Never grind up ("macerate") your sewage before sending to a septic tank. Pumping treated sewage up to the leach field is always and option ("pump or lift station"), but do not macerate. The septic tank operates by digesting solids. Digestion is best when sludge settles to the bottom and grease floats to the top of the septic tank. Macerating the sewage before entering the septic tank will create a septic tank without any solids, just a cloud of ground up sewage. When you send these particles out to the leach field, you are bound to eventually clog the soil and the leach field fails.

    I Do not worry much on this one. You probably won't have a leach field anyway. In Costa Rica the use of any form of pumps is very rare! The leakage from the concrete tank will be with-in 10 feet of your home.

F If allowed, always divert greywater to a separate leach field. Greywater contains soaps, which are designed to kill bacteria (clean and disinfect things). You want to encourage helpful "good" bacteria (digesting anaerobic cultures) to grow in your septic tank, not kill them with soap laden graywater.

        I Do not worry much on this one. You probably won't have a leach field anyway. In Costa Rica most contractors will dump the greywater into the nearest river or stream.

Septic System Maintanence

Septic system additives are truly a waste of money and harmful to leach field health in the long run. A leach field eventually fails due to formation of "bio-mat" in the soil underneath lateral lines and/or percolation chambers. Solids, grease, and smaller particulates allowed to leave the septic tank, build-up as a bio-mat of viscous slime over the years, clogging soil pores and rendering the leach field inoperable for percolation. Septic system additives break down fats and solids in the septic tank, allowing smaller particulates to pass through the septic filter (hopefully you have one) where they re-unite in the leach field. We would never suggest flushing septic system additives into your septic tank, but they might be helpful if presented directly to the leach field itself. Theoretically, these digestive additives could be poured down the leach field vents at end of the lateral lines and then filled with water to disperse them evenly throughout the leach field. If they manage to digest some of the bio-mat formation, it would help the leach field maintain effectiveness percolating sewage. You just have to ask yourself if you would like to see these additives find their way into your well water. Anything that can digest raw sewage would personally scare me to have in my drinking water and thus my digestive system. A properly designed septic tank (two compartments and large enough) is going to operate just fine without additives. If you want to help your leach field health, pour a 50 gallon barrel of hydrogen peroxide down the vents at end of each lateral line. The same thing it does on a cut, it will do in the leach field lines, loosening up the bio-mat and restoring healthy aerobic culture to the soil underneath. Avoid those "too good to be true" septic system additives on the market today.
Every septic system (except the cesspool) has two distinct components: septic tank (to catch grease & solids) and treatment area (to dispose of liquid effluent). Cesspools allow direct discharge of sewage (solids and liquid) into a pit, pond or perforated tank. Effluent evaporates up and leaches down into surrounding soil; an outhouse privy toilet is a classic cesspool.

Septic tanks use one of seven treatment area designs to dispose of effluent:

F Leach Fields are trenches (or rectangular beds) dug in yard and filled with a foot of 3/4" - 1-1/2" gravel and a four inch diameter perforated pipe. The pipe-in-gravel leach line is covered with geotextile fabric (landscaping weed barrier) and then backfilled with a foot or two of native soil. Gravity sends effluent to leach field (1/8 inch per foot drop minimum) and dispersed into soil evenly (leach field pipe is level).

F Pressurized Systems make use of an electric pump to force effluent into trenches, beds or chambers. Even distribution of effluent is key to smaller leach field sizing and better treatment of the waste water. Poor soil percolation sites often require pressure distribution sand mounds with two inch diameter pipe drilled with 1/4 inch holes every two feet, or so. Drip systems utilize small nozzles for even more uniform distribution of waste water.

F Evapotranspiration / Drip Beds are pressurized systems with smaller holes or nozzles (drip) for even more uniform distribution of waste water. In Costa Rica long shallow trenches can be run through yard, sending waste water into the root zone near surface. The plants transpire water through growth, some water evaporates being so close to surface, and a smaller portion percolates down into water table.

F Chamber Systems are a tried and true advancement in leach field design with arched plastic panels (chambers) in the trench. Effluent is sent to three foot wide cavities underneath the yard with the entire bottom (and sides) open for leaching. With no gravel inside the chamber, it has ample air to keep leach field soil aerobic and healthy.

F Drywells are plastic or concrete perforated tanks for discharging effluent into large, fabric covered, gravel-filled holes: Leach Pits. Drywells are a passive (no pump) solution for small/odd lots where a long leach field is not possible or desired. Pits take advantage of surface area around sides to dispose of large amounts of water in the right soil. Always allow at least six feet of space between pits to ensure maximum percolation and treatment.

F Lagoons are man-made ponds where the effluent percolates and evaporates, often assisted by a fountain or bubbler. Normally reserved for high clay soil areas where percolation is difficult, lagoons can be lined to prevent percolation in a fragile area - evaporation being the only means of disposal. Six foot fencing and a locked gate is standard practice with a lagoon - legal liability is an issue.

F Constructed Wetlands are shallow lagoons, mainly designed in hot climates. Active plant growth year-round is desired as the constructed wetland plants help dissipate the nitrogen and truly treat the liquid. Constructed wetlands show the most promise for a carefree low-maintenance treatment area, but you do need to be in a non-freezing climate. They are an excellent choice for greywater disposal, taking a major load off the septic tank and leach field system (blackwater only - toilets and dishwasher)

Costa Rican Septic Tanks & Leachfields

The normal septic tank here is constructed on site. It will consist of a self made concrete hold tank, normally 10' from your home. There maybe a few holes drilled in it for the liquids to get out. There are no perc tests or inspections during construction. The only inspections are made by the Engineer/Architect, if they come to the site. Your construction contractor will do whatever is cheapest to get your dream home finished quickly and cheaply. If there are any problems with this system later you will need to talk with them. You will also need to find a contractor (NOT US!) to fix this. Your yard and existing septic system will will need to be dug out and repaired. Most contractors don't do this kind of work (like us), so you might have to do this yourself!