- Build­ing CR: Waste­water - Sep­tic Sys­tems

Part 1: Sep­tic Sys­tems

Howler Magazine - - Featured Contents - By Jar­ryd Jack­son

As men­tioned in my June 2017 Howler ar­ti­cle about plumb­ing, sep­tic sys­tems play an im­por­tant role in the treat­ment, re­cy­cling and reuse of waste­water from Costa Ri­can homes. Many res­i­dents here have ex­pe­ri­enced backed-up sep­tic sys­tems dur­ing the rainy sea­son. It's a very com­mon prob­lem with older sys­tems, most of which are poorly de­signed and built. More re­cent op­tions have be­come avail­able in Costa Rica for treat­ing and reusing waste­water, rather than just dis­pos­ing of it. What all of these sys­tems have in com­mon is a mech­a­nism for break­ing down the or­ganic mat­ter found in waste­water, mak­ing it very im­por­tant to pre­vent the in­tro­duc­tion of harm­ful and toxic chem­i­cals, soaps and de­ter­gents.

Waste­water can be cat­e­go­rized into two groups: black wa­ter and gray wa­ter. Black wa­ter comes from your toi­let. It con­tains co­l­iform bac­te­ria and there­fore must go into a sep­tic or wa­ter treat­ment sys­tem. Gray wa­ter comes from sinks, show­ers and wash­ing ma­chines. The lack of co­l­iform bac­te­ria means it can be sep­a­rated and reused or sent else­where.

Since there is no sewer sys­tem con­nected to a pub­lic wa­ter treat­ment plant in Gua­nacaste, ev­ery in­di­vid­ual prop­erty in the area needs its own waste­water treat­ment sys­tem. Typ­i­cally, these are stan­dard sep­tic sys­tems with an as­so­ci­ated drainage field. The sys­tem is de­signed to sep­a­rate sludge — ob­jects and solids that sink to the bot­tom — and float­ing de­bris such as oil and grease. These re­main in the first tank, while wa­ter from the mid­dle of the tank passes through the plumb­ing into the sec­ond tank. The sec­ond tank is ba­si­cally a hold­ing tank for the cleaner wa­ter, which then passes slowly into the drainage field. The drainage field should be rel­a­tively long and about 6 feet deep. It's filled with por­ous ma­te­ri­als such as rock, sand or de­bris that al­lows the wa­ter to per­co­late into the soil. Even­tu­ally this wa­ter makes it into the wa­ter ta­ble below, which is why a cor­rectly de­signed sys­tem is es­sen­tial to en­sure the break­down of co­l­iform and other bac­te­ria.

The im­por­tance of proper ca­pac­ity and con­struc­tion of sep­tic drain fields can­not be overem­pha­sized, with sep­tic sys­tem backup be­ing a fairly com­mon prob­lem here. Ev­ery year or two dur­ing rainy sea­son, sep­tic sys­tem back­ups pre­vent toi­lets, sinks and show­ers from drain­ing. There is of­ten a foul smell, and promptly a truck is called to drain the tank. In al­most all in­stances, the cause is a sat­u­rated drain field. Ei­ther the soil it­self has flooded and can no longer drain, or the drainage basin is not big enough and can­not han­dle the load of wa­ter be­ing dis­persed into it. If this is an on­go­ing prob­lem, the usual rec­om­men­da­tion is to in­stall a new drain field, likely much big­ger the the cur­rent one. Al­most in all in­stances, the sep­tic tank it­self is fine, but the drain field is un­der­sized or in­cor­rectly built.

The next Howler ar­ti­cle will dis­cuss al­ter­na­tives to a sep­tic sys­tem, in­clud­ing cheap and easy ways to re­cy­cle gray wa­ter at home. We'll also look at more ex­pen­sive sys­tems for clean­ing and treat­ing both gray and black wa­ter for use in gar­dens and ir­ri­ga­tion, po­ten­tially sav­ing thousands of gal­lons of wa­ter a month.

The im­por­tance of proper ca­pac­ity and con­struc­tion of sep­tic drain fields can­not be overem­pha­sized.

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