![]() To calculate the how long our trench needs to be we first need to know how many square feet of of absorption area (A) we need. We’ll take a look back at that soil class table focusing on that last column. Later that day he confirmed that it was class III. Either of these two cases would have ruled out using a standard absorptive drain field. He also confirmed that there was no sign of ground water seepage or a layer of bedrock or other restrictive horizon. He said the soil looked like Class III but he would take a baggie of the spoils and let me know. The engineer came out, confirmed the depth of the holes and jotted down some notes. It has been determined how many gallons of water a square foot of each soil class can absorb in one day. Soil Class TableĬhapter 285 identifies 4 soil classes with class I being divided into two sub types. So, I dug two four feet deep holes with my post hole digger and called the engineer back. ![]() My engineer advised me that it would significantly less expensive if I were to dig the holes. The required length of a drain field trench is largely determined by the soil class in the drain field area.Ĭhapter 285 requires that a site evaluator or professional engineer dig two holes two feet deeper than the proposed trench depth to observe the characteristics of the soil. ![]() Leaching chambers are bottomless chambers installed with the open bottom in direct contact with the bottom of the trench. There are several options for what goes in the trench but I opted for leaching chambers. The bottom of trench must be level to within one inch over every 25 feet. However, per Table II of the appendices of Chapter 285, 750 gallons is the minimum septic tank size.Ī standard drain field is a trench, 2 – 3 feet wide and a foot and a half to three and a half feet deep. See my story of rejection below.ġ00 gallons per a day X 3 days = 300 gallons. I wrote in the previous variance articles that we had negotiated down to 80 gallons per a day but that ultimately didn’t work out. Even though our cabin with one bedroom falls under the first category with a usage rate of 180 gallons per a day, our county has their own informal “tiny house” usage rate of 100 gallons per a day. Note, the code does allow some leeway for usage rates. Table III in the appendices of Chapter 285 lists waste water usage rates based on the number of bedrooms in a house. The length time wastewater is held before being released into the drain field is referred to as Hydraulic Retention time or HRT. It’s the statewide code for on-site sewage facilities otherwise referred to here as septic systems.Ī septic tank must be able hold a minimum of three days worth of wastewater. I’ll also refer and link to Texas Administrative Code Chapter 285 fairly often. I’ll cover sizing and locating both in this articles. A conventional septic system consists of a septic tank and an absorptive drain field.
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