Alternative Onsite Wastewater Treatment Systems

1. Alternative Onsite WastewaterTreatment Systems Solutions for Sensitive Sites

2. Scott Robinson Terra Firma Advanced Designer Advanced Inspector Installer Service Provider

3. The Process • When faced with the necessity of replacing a non-compliant septic system, or trying to fit your onsite wastewater treatment system into your landscape without having a big mound placed in the yard, there are some alternatives that can be considered.

4. Sometimes There is plenty of room to fit the system, if it just wasn’t for those trees you don’t want to cut down

6. Design Considerations • A septic system is 3-dimensional In it’s design and construction

7. It requires vertical separation to ensure quality treatment of sewage. Laboratory tests have concluded that 36” of unsaturated soil can accomplish this treatment.

8. It also requires a horizontal plane to accept the volume of effluent that is produced, which is determined by the dwelling, or source of the wastewater and the type of soil on the site.

9. Vertical Separation • One of the aspects of the North Shore of Lake Superior that we all enjoy is the beautiful cliffs and rock outcroppings that add to the majesty of the area.

11. That beauty can, however, lead to difficulty in treating wastewater, because as mentioned, we need soil to “filter” the wastewater before it enters the water resources that we use and enjoy.

12. A minimum of 12” of unsaturated, in-situ soil is required to qualify a site for a “standard” designation. • This is an absolute requirement for platting, or creating, new lots of record, since 1996. • The process of determining that minimum requirement involves a site evaluation, including soil pit(s).

14. Situations Requiring Alternatives • Often times lots and residences have been around for much longer than the present rules and adjustments need to be made to accommodate these sites • If a site qualifies as standard, but due to landscape or aesthetic concerns, an adjustment is desired, alternatives can also be considered.

15. Considering Alternatives • In our area, vertical separation is usually the parameter that prompts a move to alternative wastewater treatment methods. • Less common, but within the realm, the “footprint” or length of the soil component can be adjusted, with pretreatment, if there is greater than the minimum 36” of unsaturated soil available.

16. Alternative Choices • The readily available pretreatment technologies that can be considered include aerobic treatment systems and filtering systems that include: sand, peat and textile filters. • These technologies include “Public Domain” technologies, as well as proprietary treatment devices.

17. “Stand-alone” toilets, such as vault privies, composting or incinerating toilets along with grey-water septic systems can also be included in this list. • These products, or methods, are included in a list of registered products, approved by the MPCA.

19. Which choice, then?

20. Aerobic Treatment Systems

21. Aerobic treatment systems can be used on residential sites, although they are, perhaps, better suited to commercial establishments that may be producing higher strength waste. • These systems introduce high levels of air (oxygen) into the waste, producing effluent that is lower strength, and acceptable for standard, soil based treatment, or in the residential application, extremely low strength, allowing a minimized vertical separation to a limiting layer.

22. Aerobic systems are among the more technical systems, so in making this choice, that needs to be considered. • They include some means of introducing the oxygen to the waste, so the power requirement is part of the decision.

23. There are 3 basic types of aerobic systems: suspended growth, fixed film reactors and sequencing batch reactors. • They are an “active” system, so all of the components (blower, filter, media, etc.) need to be functioning for effective treatment. An understanding of the activity is also critical

24. Aerobic treatment systems take up very little space, so as a choice for a small lot they have some merit, but there still needs to be a soil based dispersal component, so it may not be the first choice. • Aerobic systems are a good fit for restaurants, schools (where lunch is served) and establishments that produce high strength waste that could lead to premature “plugging” of the soil, in the dispersal phase of the treatment process.

25. Filter Technologies

26. The choices in this category include: sand filters (single pass and recirculating), peat filters and textile filters. • Single pass sand filters and peat filters can be installed directly on native soil, with an open bottom, minimizing the required vertical separation from grade to the limiting layer (saturated soil and/or bedrock).

29. Single-pass sand filters and peat filters can also be installed with a collection tank that receives the treated effluent for forwarding to a soil based dispersal zone, although that does add an additional mechanical component to the system.

31. That may be desirable for a totally, subsurface application, or perhaps, a shorter mound, though. The filter can be installed below grade, followed by shallow trenches for dispersal, provided the vertical separation is achieved between the treatment allowance and the limiting layer in the soil.

33. Recirculating sand (gravel) filters and textile filters accomplish treatment by multiple passes through the filter media. This requires a collection tank that receives the treated effluent that is forwarded to the final, soil-based treatment zone.

34. Because the media used for the filtration process is courser (gravel filter) or easily maintained (textile filter), higher strength waste can be introduced to these filters with diminished potential of premature failure of the media.

36. Treatment Levels • The various technologies that we have looked at are designed to achieve predetermined levels of treatment. • The rules in MN Chapter 7080 that define those treatment levels are broken into various categories: A, A2, B, B2 and C. • These categories dictate vertical separation allowances.

37. Other appliances can be added to enhance treatment levels, such as UV lighting (minimizes fecal counts) and/or combining technologies to minimize nutrient counts, etc., which can, in turn affect the separation requirements.

39. There’s your Overview • We can see that there are a multitude of choices that can be made regarding the treatment and dispersal of our wastewater.

40. Ultimately, treatment of that wastewater is the goal, but working within the constraints of the rules of Minnesota, there are acceptable alternatives that can enhance the final product. be it sizing for small lots, blending in with the landscape or providing acceptable treatment levels for dispersal to the world, working with your SSTS Professional can lead to a satisfying means to that end.