Last month, we discussed potential impacts on septic system design and operation if an elderly family member in need of additional care moves into the existing household. Another caregiving scenario becoming more common involves a granny pod, where a separate small residence is placed in the backyard. These are essentially temporary tiny houses.
Depending on the health needs of the intended resident, these pods take the form on the inside of either a luxurious hotel suite or a well-equipped extended care suite complete with hospital bed, medical equipment and any other necessary features. Typically, the pods have one bedroom, a kitchen, and a living room, with a size of 400 to 500 square feet.
When the backyard is in an urban area served by municipal sewer, the granny pod is connected directly to the sewer line. When the backyard is in an area served by septic systems, handling the waste becomes more of an issue. The question is somewhat the same as moving into created living space in the home; but in this case, there is a detached small residence that probably deserves or, in a lot of areas, requires it’s own waste treatment system on the lot.
ESTIMATED FLOW CHANGES
Obviously the first thing that needs to be checked is whether there is room for the granny pod and the necessary system on the lot as well as meeting all the setback requirements. Not every lot is going to be large enough.
Estimated daily sewage flow for such a residence under our state code would be 180 gallons per day. With this estimated flow, a 1,000-gallon septic tank would be required (since that is the minimum allowed by code). Some other codes we have seen allow 500-750 gallon capacity tanks to serve a one-bedroom residence.
The required soil treatment area depends on the soil conditions. For example, a loam soil would require about 400 square feet of trench bottom area to accommodate a flow of 180 gpd. This would be 133 lineal feet of 3-foot wide trench. This could be two 70-foot-long trenches installed 8 feet on center for a required area of about 600 square feet. As we indicated above, not every lot is going to have the area needed to accommodate a separate system. Where it makes sense or is necessary to use the existing system and add to it, effluent from the septic tank serving the pod can be connected by the supply line to the system.
Similarly, if grandma moves into a basement apartment where a bedroom is added, estimated sewage flow would increase by 150 gpd. Approximately 333 square feet of trench bottom area would be required or 111 lineal feet of 3-foot wide trench. In this case, the current system will need to be enlarged in both cases to accommodate the increased flow. Whether that can be accomplished depends on the soil conditions and the layout of the current system.
If the existing system has dropbox distribution, adding a trench assuming good soil conditions will be relatively easy. If the current system is a mound or at-grade system or trenches with pressure distribution, it becomes more difficult to add capacity. All parts of the distribution system will need to be revaluated, redesigned and changed as necessary. Increased flow may require a larger pump tank and a larger pump may be needed to serve the larger pressure distribution system in addition to physically increasing the size of the soil treatment area.
DEALING WITH MEDS
Some of the stories we’ve seen about granny pods make the point they have the same characteristics as a hospital room or extended care unit. When the resident is on numerous medications or chemotherapy, additional antibiotics, cleaning supplies and other chemicals may be introduced to the system. This will require continual monitoring and more frequent cleaning of septic tanks.
If an existing soil treatment unit is going to be used, timing of effluent flows from the two residences may suggest a time-dosed type of system makes sense. This is where the pump tank is sized large enough to hold flow from peak use times to be spread out during the entire 24-hour period. It is also a way to manage washing machine flows because there may be the need for increased usage due to elderly medical conditions such as incontinence. For pressure distribution systems (mounds, at-grades, pressure trenches), time dosing is a desired practice to meter out the flow during the day.
When using a pretreatment unit other than a septic tank, such as a media filter or ATU, checks will also be necessary to determine if they handle the increased flows. A larger system may be necessary or adding to the existing device, or even employing a different type of pretreatment.
The bottom line is that before the family decides to have grandma come and live with them, there are a number of factors concerning the septic system to be considered. Make sure there are no surprises lurking that cannot be fixed or managed.
