Septic System: In Pursuit of a Variance

This is part 1 of a 3 part series of designing and installing our onsite sewage facility or septic system for the timber frame cabin. Part 1 covers my attempt to get a variance which was ultimately unsuccessful. In the end we installed a conventional gravity system but you might find my tale of lofty goals of dramatically reduced water consumption being crushed under the wheels of bureaucracy interesting. Otherwise, skip to part 2 covering the design.

In the fall of 2018 I went into our county development services office inquiring about permits required for the construction of the timber frame cabin. I was also interested in the possibility of using a biodigester in lieu of a septic tank.

A biodigester is similar to a conventional septic tank in that it accepts organic waste but a biodigester is typically an above ground tank located in an insulated enclosure with glazing on the top and possibly sunward facing side. This allows the sun to warm the water in the tank allow mesophilic(middle range warm loving) microbes to flourish. The mesophilic microbes produce methane gas which is captured for household use. I’d been to a building workshop where they were installing a biodigester and I loved the idea of function stacking waste management and energy production.

So, I came to the development services meeting with a preliminary site plan for the cabin, a biodigester diagram, and a folder full of articles and white papers about home scale biodigesters.

Early site plan with a larger version of the cabin located in the front of the property
The site plan for the cabin in its final location

Fortunately, permit requirements for the county were pretty light requiring a building permit and an onsite sewage facility (OSSF aka septic) permit.

Obtaining the building permit was fairly easy. It required a site plan showing the building location, the building square footage and lot setback lines. While I was at the meeting they checked and confirmed I wasn’t building in floodplain. Then it was just a matter of fifty dollars.

I asked about pursuing a variance for the OSSF permit to use a composting toilet and substitute a biodigester for the septic tank. From our conversation I drew the conclusion that if I could get a registered sanitarian or professional engineer to sign off on my design it was possible. Well, that sounded pretty promising.

Fast forward two years. I had applied for and been granted a building permit. The house had shrunk in size since the first site plan and moved to the back of our lot. My interest had also cooled in regard to the biodigester. I had also read Section 285 of Texas Administrative code many times at this point. There will be several references to section 285 for the rest of the article so here’s a little introduction.

Section 285 are the statewide rules and regulations for On-Site Sewage facilities (OSSFs) per the Texas Commission on Environmental Quality (TCEQ). It’s 120+ pages of exciting reading. Some counties will have their own rules and regulations (usually closely resembling the state guidelines) but many including ours just adopt the statewide rules. Section 285 has a bit to say about variances including this:

A variance may be granted if the owner, or a professional sanitarian or professional engineer representing the owner, demonstrates to the satisfaction of the permitting authority that conditions are such that equivalent or greater protection of the public health and the environment can be provided by alternate means.

– §285.3. General Requirements (h)(1)

Small septic tank design

My plans had changed significantly. We were still planning to use the composting toilet but instead of the biodigester I was using two 55 gallon high density polyethylene barrels plumbed to create two compartments where the solid waste would be confined to the first compartment. Note that as we would be using a composting toilet any solid waste would be food remnants from the kitchen sink. Although, kitchen sink waste water is considered black water per the definition of gray water:

For the purpose of this chapter, gray water is defined as wastewater from showers; bathtubs; hand washing lavatories; sinks that are used for disposal of household or domestic products; sinks that are not used for food preparation or disposal; and clothes-washing machines. Gray water does not include wastewater from the washing of material, including diapers, soiled with human excreta or wastewater that has come in contact with toilet waste.

– §285.80. General Requirements. (a)

Sizing a septic is based around having a minimum hydraulic retention rate (HRT) of 3 days. Waste water needs remain in the septic tank a minimum of 3 days before entering the drain field. So, a septic tank should have a capacity of at least 3 times the daily amount of waste water usage. I was planning to plumb the shower drain to a gray water system so that just left the kitchen sink and the bathroom lavatory. I estimated that those two sources would produce around 20 gallons of waste waster per a day. So, the 110 gallon septic tank would have a HRT of 5+ days.

Special Note: I’ve been tracking water usage since installing a water meter in December 2021 and we use 20-25 gallons of water per day in total. Once I have more data I’ll post more about it.

I modeled our composting toilet system on David Omick’s Bucket to Barrel Composting system. David Omick produced a white paper of sorts on the system you. I’ll put a link in the video notes. Here’s a summary though:

5 gallon buckets are used for defecation and urination. Urine is captured via a urine diverter mounted at the front of the bucket and plumbed into the OSSF. The buckets containing fecal matter and cover material are periodically emptied into a 55 gallon barrel and covered over with a thin layer of soil. Once filled a barrel is stored on site for a minimum of 1 year until the waste has composted. 

Advantages & Comments

  • The bucket to barrel system significantly reduces household water usage
  • Storing the fecal matter and cover material in 55 gallons barrels prevents leachate from contaminating soil and groundwater
  • Contamination during the bucket to barrel transfer is mitigated by lining the buckets with biodegradable bag liners and following handwashing procedures
  • A household of two adults requires approximately six(6) 55 gallon barrels to hold one year’s amount of waste and cover materials.

Joseph Jenkins is also a big proponent of simple composting toilets but David Omick’s article approached the subject with a little more gravitas then Jenkins more tongue and cheek “Everyone lets poop in a bucket” refrain.

So, I’d had a certain engineer in mind for a while. Back when I visited development services they gave me a list of approved designers and installers.

First, the tagline on this engineer’s(let’s call him Dave), Dave’s website, Planning and Engineering as if Water and Environmental Values matter. That’s a good start.

I noticed that his website also had his address which apparently was his home address. Pulling it up in street view I panned around seeing a several conventional grass lawns until I got to his front lawn. It was teeming with trees, shrubs and a strip of wildflowers along the frontage between the road and sidewalk. I could also see a rain cistern peeking out on the side of the house.

I had e-mailed a couple of other designers several years ago inquiring about pursuing an OSSF variance and gotten no replies. I e-mailed Dave and got a response back in about half an hour.

After talking for a bit he agreed to present my plans to the county development services. David emailed the chief environmental health specialist at development services. Let’s call him Tim for short. There were a series of exchanges over a few weeks. I’ve included below a summary and an only slightly redacted longer version.

Summary

Dave presented the 3 main points that would require variances

  1. The bucket compost toilet that definitely does not have NSF 46 certification. Note: NSF certified composting toilet start around $2000 and are typically big and bulky.
  2. Per section 285 750 gallons is the minimum septic tank size.
  3. A rubble/gravel pit dispersal area rather than conventional drain field consisting of trenches.

Tim responded that he “couldn’t imagine entertaining variances on any of the items.”

I talked to Dave and decided to drop the composting toilet argument and push for a conventional system with a smaller septic tank and drain field.

Dave followed up asking if there was any lee way for say a 300 gallon septic tank arguing that for a 3 day HRT it could accommodate 100 gallons of waste water per day. He cited some data he had collected demonstrating a household with flush toilets using less than 25 gallons of water per a person per a day.

Tim responded that he could not see a reason going below the 750 gallon state minimum. Here are a few Tim quotes and how I wish I could respond to them:

“The 300 gallon tank would probably work most of the time, there are times that they would have guests and their flows would go up for a short period.”

Hypothetically, yes, we could have a guest who came over hung out in the bathroom all day and continually flushed the toilet. But, we probably we wouldn’t invite that person over again.

Standard septic tanks are not very expensive and the price difference between a 300 gallon tank and a 750 tank is probably only about a few hundred dollars.”

Currently, a 750 gallon tank is $1559, a 500 gallon tank is $1000, a 300 gallon tank is $724. Slightly more than a few hundred dollars.

Having a 750 tank would be beneficial if they ever want to install regular flush toilets in the house at some point.”

The study Dave cited demonstrated 25 gallons per a day with flush toilets. Anecdotally, I checked with my parents and they use about 88 gallons of water per day. Further anecdotally, Dave said his household uses 37 gallons of water per a person per a day on average.

If they ever went to sell the house, having a 750 tank would probably help the sale.”

I didn’t realize I was seeking realty advice. Thanks!

Almost everyone I’ve personally seen with composting toilets eventually switches them out for flush toilets.  I can only remember one house that went for many years keeping their composting toilets.”

Thanks for the anecdotal evidence. Personally, I know lots of people with composting toilets and are quite happy with them. Check out YouTube and you can find people gushing over composting toilets.

We have lots of people inquiring about the use of composting toilets but when they find out that they still need to install an on-site sewage facility for the rest of the wastewater in their house, most abandon the idea.”

A self fulfilling prophecy. What about people who do the bare minimum to pass their OSSF inspection and then use a composting toilet anyway. Do you have a metric on that?

Long Version

Dave

Got the communications below from [Aaron], who wants to use a composting toilet and a gray water only system as the OSSF for a cabin he wants to build. A description of the sort of composting system he wants to use is described generally in his e-mail below, and more particularly in the link he provided. This is a system that is not on the TCEQ “approved list”, and I’d be real surprised if it had the NSF 46 “certification”. So I presume this would have to be approved under a variance. The “problem” with that, of course, is there is a course of action – use one of the way more “bulkier” approved composting units – that would allow him to serve the cabin without need the variance. So would you please tell me what the stance of [the] county would be on this variance?

The gray water only system is also likely to entail one or more variances. Aaron guessed their gray water use would be in the vicinity of 20 gpd. Obviously he expects to live rather “simply”. We’d need to know what sort of “standards” [the] county would look to in order to evaluate what design flow rate would be acceptable. Then there is the matter of what septic tank volume would be required. Even if the “acceptable” design flow rate would considerably larger, say 100 gpd for the sake of argument, with a “reasonable” HRT of 3 days, that would still only indicate a 300-gallon tank, but the minimum allowed under Chapter 285 is 750 gallons, basically no matter what. So here again we’d need a variance. So here again, can you please tell me what the stance of [the] county would be on this variance?

As you can see in the attached sketch of the proposed gray water system configuration provided by Aaron, he proposes a “rubble trench” dispersal system for the gray water system. This too would be a variance situation. So one more time, can you please tell me the stance of Hays County on such a variance?

Tim

I can’t imagine that we would entertain variances on any of the items. 

The toilet has to be NSF certified. This composting system doesn’t even resemble any NSF toilets. 

I’ve seen many NSF toilets fail because people don’t maintain them. I’ve also seen homemade composting toilets similar to this proposal fail and become a public health nuisance. 

20 gallons per day for non toilet use is not justifiable in my opinion.  

The 55 gallon barrels for the septic tanks will not work. 750 gallons is the minimum and the tanks need to meet chapter 285. 

The little rubble pit would need to meet chapter 285 requirements for a standard drain field, so there needs to be adequate soil in the location for a standard drain field. 

Dave

I’d like to think the regulatory system would be reasonable about the septic tank size. There’s a reason why they make plastic septic tanks as small as 300 gallons. You may disagree with the usage estimate offered, but even if it is much more, say 100 gallons, that’s still 3 days HRT. Is there indeed no “give” on that one?

Re the 20 gallons per day estimate for non-toilet usage, I presume he meant 20 gpd/person. That may not be all that unreasonable, particularly for someone who is really aware of conservation because they live on a rainwater supply, as [Aaron] says is planned for this cabin. See the attached spreadsheet, some of the data I gathered when I did the RWH study with the Meadows Center in 2012. As you see, a 4-person household used water at a average rate over 9 years of about 24 gpd/person, including toilets. For whatever it’s worth.

I advised him to ditch the composting toilet, or pay the piper for a code-compliant one if he is dedicated to a composting toilet. But a ULV toilet now uses very little water per flush, so would add rather minimal total demand.

So really it comes down to if he has the soil resources to do a conventional drain field, or if he’ll have to do something “better”. And then how it must be sized.

Tim

Although the 300 gallon tank would probably work most of the time, there are times that they would have guests and their flows would go up for a short period.

I don’t see any reason for going below the state minimum of 750 gallons.  Standard septic tanks are not very expensive and the price difference between a 300 gallon tank and a 750 tank is probably only about a few hundred dollars.  We would not approve the conversion of 55 gallon drums to be used as septic tanks.

Having a 750 tank would be beneficial if they ever want to install regular flush toilets in the house at some point.  If they ever went to sell the house, having a 750 tank would probably help the sale.

Almost everyone I’ve personally seen with composting toilets eventually switches them out for flush toilets.  I can only remember one house that went for many years keeping their composting toilets.

We have lots of people inquiring about the use of composting toilets but when they find out that they still need to install an on-site sewage facility for the rest of the wastewater in their house, most abandon the idea.

The Texas Water Development Board guidance document says that people using rainwater typically use 30-40 GPD per person.  https://www.twdb.texas.gov/innovativewater/rainwater/doc/RainwaterCommitteeFinalReport.pdf 

I think 40 gallons per person would be a good number to go with.  If it’s just a one bedroom cabin and it is only going to have 2 inhabitants, I think that 80 gallons would be reasonable.  If it is 2 bedroom you would need to increase it by another 40 GPD.

You will need to request  a variance for the reduced flow and you can use the document above or similar documents to show that you are providing equal protection.

Dave

[Aaron] is considering doing a straight conventional system. I’ve explained he would need to demonstrate sufficient soil resources to do that, so until that is investigated, we don’t know if he can. But in the course of planning what to do, we need to deal with the design flow rate. The minimum that is set in Table III is 180 gpd. That is based on presuming the occupancy is 3 persons. Until I see more detail on the cabin and what his occupancy plans are, I won’t know what would be “appropriate” for the presumption of occupancy, but the design flow rate criterion is the critical item here. That 180 gpd is rooted in the presumption that the daily water usage per person is 60 gpd. It is well understood that this is rather high for anyone who practices even a modicum of conservation. For example, my wife and I use at rate of about 37 gpd/person, even though we are on the Austin water system, so have no compelling reason to be highly conservative. Folks who design and install RWH systems routinely presume 35 gpd/person as the “standard”. A review of actually observed water usage rates in AWWA studies indicate that something like 45 gpd/person is what would be routinely “expected” in a house equipped with the latest state-of-the-art fixtures, even without any “conservation consciousness”. I showed you data from a rainwater harvester indicating that it is quite feasible to at least halve that 60 gpd rate. As best I understand [Aaron’s] situation right now, I would think that a rate of 30 gpd/person would be “liberal”. Can you characterize the sort of data/information you would need to allow a design flow rate criterion of less than 60 gpd/person? And if the nature of the cabin would indicate that, would you consider an occupancy presumption of 2 persons, rather than the “standard” of 3?

Tim

The Texas Water Development Board guidance document says that people using rainwater typically use 30-40 GPD per person. https://www.twdb.texas.gov/innovativewater/rainwater/doc/RainwaterCommitteeFinalReport.pdf 

I think 40 gallons per person would be a good number to go with.  If it’s just a one bedroom cabin and it is only going to have 2 inhabitants, I think that 80 gallons would be reasonable.  If it is 2 bedroom you would need to increase it by another 40 GPD.

You will need to request  a variance for the reduced flow and you can use the document above or similar documents to show that you are providing equal protection.

In the end the only leeway we got was a reduction in the size of the drain field. For a house with two bedrooms or less Section 285 requires that a drain field be able to accommodate 180 gallons of waste water per a day. The Texas water board says that people who solely use rainwater typically use 30-40 gallons per a person per a day. So, Tim did concede some ground and allowed an 80 gallon per a day drain field. Later, after submitting my permit I would find out that there was an internal development services 100 gallon per a day drain field rule that Tim didn’t know about but we’ll save that for part 2.

That’s the end of part 1. In the next article I’ll talk designing a conventional system