Adding Yeast To A Septic System Won't Do Any Good

DEAR MS. H.E.: Do you have any information on care of septic tanks? My son, who lives in another state, has been told a package of yeast at least once a month is enough to renew the bacteria. A neighbor tells me he feels the expense of a box of dried bacteria is worth the peace of mind. He used such products previously in another state and the septic system was in perfect shape after 10 years.

DEAR READER: According to Selden Hall, public health adviser at the State Department of Health's Wastewater Management Section, there are no additives that would be beneficial to your son's septic tank. Each flush of a toilet that washes feces into the septic tank brings in hundreds of millions, if not billions, of bacteria with it.

Adding bacteria in the form of dried yeast or a commercial bacteria additive is like dropping a teaspoonful of salt in the ocean to make it saltier. A complete waste of time and money, in other words.

(Other additives, such as organic solvents promising to "open up" failing septic systems, are worse than useless. They are sources of dangerous groundwater pollution.)

Many septic system owners misunderstand the workings of the system. It is designed to separate solids from liquids, retain most of the solids and allow wastewater to filter through surrounding soil.

In the tank, solids slowly separate from liquids and sink to the bottom. Lightweight fats float to the top. In between is a layer of cloudy wastewater that contains suspended and dissolved particles.

This liquid seeps out into the soil. It trickles slowly down through the air spaces in the soil, and the rich biological community that exists around those air spaces basically digests the yucky stuff in the wastewater.

Meanwhile, back in the tank, solids accumulate. Experts recommend that you have the tank tested every two years. When enough solids build up, the system must be pumped. No amount of added bacteria in the world is going to forestall that. The system is designed to be pumped, not to digest solids.

If solids are not pumped in time, they begin to spill out into the surrounding soil. Now you are polluting groundwater and clogging those vital air spaces in your soil. If you don't intervene in time, the soil's effectiveness will be destroyed and you will have a big problem on your hands.

This is a long way of saying tell your son that what he is adding to his septic tank is simply wishful thinking. For more information, have him call his local health department. They may have pamphlets that can teach him to test the tank himself.

DEAR MS. H.E.: Enclosed is an excerpt about plastics from the book "The Nontoxic Home and Office," by Debra Lynn Dadd. In general, plastics do not seem too healthy.

I have a question specifically about PVC plastic (polyvinyl chloride). We are considering installing mini-blinds, which are very rigid. Are they as toxic as more pliable PVC products such as shower curtains? Or, in general, does the greater rigidity of a plastic equal less toxicity due to greater stability and less outgassing?

DEAR READER: The experts I talked to believe that flexible PVC does outgas more than rigid PVC does. In general, your nose will tell you that. Your new plastic shower curtain will stink for quite a while. Your rigid PVC mini-blinds may not smell at all.

Susan McGrath's column runs every two weeks in the Home/Real Estate section. Send questions and comments to: The Household Environmentalist, P.O. Box 70, Seattle, WA, 98111.