efflu-Research conducted and field experience obtained over the past severaldecades indicate that soil and site conditions necessary for treatment andultimate dispersal of septic tank efflu
Trang 1efflu-Research conducted and field experience obtained over the past severaldecades indicate that soil and site conditions necessary for treatment andultimate dispersal of septic tank effluent are not necessary for the treatmentand ultimate dispersal of secondary or better quality effluent Hence, weneed to look at soil and site conditions in a totally different manner whenadvanced onsite wastewater systems are considered and soil and plant sys-tems are used mainly for “polishing” secondary or better quality effluentrather than for reduction of organic waste load This is the concept mentioneddemand (BOD) or total suspended solids (TSS) and does not serve as amedium for mineralization of nitrogen from organic to inorganic forms.Instead, those functions are performed by an advanced treatment system forwhich the conditions and the material of construction can be controlled,leaving soil to be used for what soil is best for — recycling residual nutrientsand polishing the microbiological quality of effluent.
in Chapter 1 in which soil is not required to remove biological oxygen
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Alternatives to conventional septic systems are needed in areas wheresoil and site conditions are not suitable for treating septic tank effluent orwhen use of septic systems is not cost effective or not desired, or wheredesired lot density cannot be achieved by using traditional septic systems.Such systems can also be used for rejuvenating septic tank effluent drainfields that are failing due to age and accumulated biomat Introduction ofaerobic effluent into an old drain field breaks down the biomat and allowsthe assimilation of aerobic effluent into the subsurface environment, thus insome cases, offering an effective and efficient repair option for old septicsystems
Dispersal of advanced secondary effluent
Aerobic treatment of wastewater to secondary or better quality effluentshould be a key component of any permanent managed onsite wastewaterinfrastructure Subsurface dispersal of secondary effluent can be achieved in
an environmentally sound manner on any buildable site that is currentlyviewed as unsuitable for a septic system, as long as adequate land area isavailable for hydraulic assimilation of the secondary or better quality effluentand reduction in nutrient or bacteriological contaminant load
Because a secondary treatment system reduces organic waste load ically measured as BOD5; TSS; and fat, oils and grease [FOG]) prior tointroducing the effluent to the soil dispersal system, performance of aneffluent dispersal system for secondary or better quality effluent is notinfluenced by biomat formation In traditional septic systems, the formation
(typ-of a biomat in the drain field is considered an important part (typ-of the treatmentfor removal and reduction of bacteriological contaminants Therefore, aquestion typically arises among regulators about what happens to thosecontaminants when a biomat is not formed in the dispersal systems thatreceive secondary or better quality effluent Dispersal of aerobic effluentinto a subsurface soil environment allows the soil to retain aerobic condi-tions (unlike the dispersal of septic tank effluent) and thus enhancesremoval (neutralization) of bacteriological contaminants even without theformation of a biomat Whenever necessary, aerobically treated effluent can
be disinfected using a variety of advanced onsite disinfection technologies,such as ultraviolet or ozone disinfection systems When chlorination sys-tems are used, effluent should be dechlorinated prior to subsurface dispersalmainly to prevent any adverse impact of the residual chlorine on soil micro-organisms
Effluent dispersal technologies
Technologies available for dispersal of secondary or better quality effluentcan be grouped as follows:
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• trenches or beds filled with gravel or other media (gravity fed orpressure dosed)
• gravelless trenches or beds with chamber systems (gravity fed orpressure dosed)
• at-grade or above-grade (shallow trench, filter bed, mound, cappingfill, etc.)
• drip dispersal (subsurface or surface)
• spray dispersal (above ground)
• minimum or zero discharge (evapotranspiration or greenhouse)
• point source discharge into surface water or on the ground
• existing onsite dispersal systems after removal of accumulated water from them
waste-dispersal systems Information on many other projects that use such persal systems is available on our web site Designing, sizing, and layout ofthese types of effluent dispersal systems can be done using common senseunderstanding of soil and site conditions and the owners’ requirements Adequately treated effluent can be safely released into the environmentusing any of the above effluent management systems, including existingonsite disposal systems (such as cesspools, trenches, seepage pits, infiltrationgalleries, or beds) that are failing due to excessive build up of a biomat.Highly treated effluent can also be used for flushing toilets or other nonpo-table applications prior to release into the environment, thereby reducingthe net amount of liquid discharge
dis-Since septic systems depend mainly on soil for the treatment of primaryeffluent, soil evaluation has been an integral part of the onsite wastewaterbusiness However, with the availability of a variety of treatment systems,
we no longer need to depend on soil for treating septic tank effluent Theinstallation of small, shallow or deep trenches, filter beds, drip, spray, orminimum or zero discharge systems for adequately treated effluent can beachieved on almost any site where adequate square footage of space isavailable Performance of such dispersal systems does not depend on type,depth, or color of soil present at the site In the 21st century, emphasis needs
to be put on the use of appropriate onsite treatment and dispersal systemsand on the permanent operation and maintenance of those systems ratherthan on the acceptance or rejection of a lot for an onsite system based onsoil evaluation and soil criteria
With the availability of pre-engineered and prepackaged treatment andeffluent management systems in the market today, engineers now have morethan 500 different ways of developing onsite solutions for wastewater sys-tems Soil and site characteristics as well as environmental sensitivity typi-cally determine which onsite system may be used for a given project How-ever, a designer may decide to standardize onsite wastewater solutions using
a small number of system categories that address most of the soil and siteconditions in a given region
Photos 5.1 through 5.10 show various projects that use advanced effluent
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Photo 5.1a Installation of a small (10-ft long and 1-ft wide) trench on a slope Note that the backhoe is digging in the trench just by scratching the ground surface
Photo 5.1b Close view of the small and shallow trench Notice the fiberglass cover placed on typical four inch perforated drain pipe placed in the trench There is no gravel used in this trench
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Photo 5.1c Side view of the small and shallow trench before covering the trench with soil material removed from the area
Photo 5.1d Side view of the same trench after covering the trench with the top soil that was removed from the area
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Soil and site evaluation: then and now
Soil and site evaluation has been an integral part of the onsite wastewaterbusiness and its regulation With the availability of various treatment sys-tems, the use of soil for treatment of primary effluent or raw wastewater(septic tank effluent) is not necessary When the use of advanced onsitewastewater systems is proposed, subsurface effluent dispersal systems can
be adequately sized, designed, installed, and operatedfor any soil and siteconditions; thus, there is no need to have regulatory requirements for soiland site conditions to determine whether a proposed site is “suitable” for
an onsite system
The soil and site evaluation that is typically done for septic systemsgenerates such information as a soil description and the depth to limitingconditions This information is not needed for sizing of a dispersal systemfor secondary or better quality effluent A simplified approach for developingregulatory requirements for using advanced onsite systems is proposed later
in this chapter along with a proposal for set-back requirements and sizingcriteria Some of the other factors associated with site evaluation wouldremain important, including determining slopes; location and distance toenvironmentally sensitive areas; location of water supplies; location of sur-face water bodies; location of utilities and easements; availability, location,
Photo 5.1e Looking at the house from the bottom of the slope The small and shallow trench is located between the house and the shrub.
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and type of power (115 VAC, 230 VAC, single-phase or 3-phase); access tosite for construction purposes; and location of existing underground utilities Currently, for designing onsite systems, most of the site evaluation fac-tors required for choosing the appropriate advanced onsite wastewater tech-nology are simply ignored and a “site evaluation” is essentially a description
of the sidewalls of some pits dug on the property, which is typically donefor soil mapping purpose A true site evaluation includes many more factorsfor locating and choosing the appropriate wastewater treatment system andfocuses less on two pits excavated or four auger holes bored on the property
A site evaluation for use of onsite systems should not be an exercise in soilmapping The owners of onsite wastewater systems are not interested inknowing the color, texture, and structure of individual soil stratum, but theyare interested in making sure that their onsite systems work on their prop-erties and meet their needs for adequate wastewater management A siteevaluation process that truly results in meaningful information that adesigner needs and can use for selection, design, and layout of an onsitesystem can be justified and will be accepted by the onsite professional; but
a site evaluation process that simply meets the regulatory requirements forobtaining a permit cannot be justified and will not be accepted by onsitewastewater professionals
Photo 5.2 Small and shallow placed gravel-less trench that is used for dispersing up
to 1,000 gallons per day effluent from an advanced onsite treatment system Note that the trench is between Dr Craig Jowett and Dr Kevin Sherman
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A variety of dispersal systems for individual home or small (less than
1000 gal per day [gpd]) commercial systems can be pre-engineered with littleknowledge of soil characteristics and can be installed on a site in a mannerthat allows for adequate assimilation of effluent Based on the site charac-teristics of the proposed location, an appropriate type of pre-engineereddispersal system can be selected and installed It is possible to educate andtrain installers of onsite systems to install such pre-engineered dispersalsystems with the availability of onsite engineering and other design expertisewhen needed Effluent dispersal systems should be selected and sized based
on a site’s assimilative capacity for the design flow and the nutrient loading,rather than just based on soil characteristics Soil and site conditions that are
Photo 5.3a A 5-ft wide and about 100-ft long trench that was dug down to about 10-ft depth to the sand layer and filled up with gravel The “L” shaped trench is used
to disperse about 5,000 gallons per day effluent from an advanced onsite treatment system that serves a service station Photo courtesy of Mr Daniel Pavon of Aquarobic International, Winchester, VA.
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Photo 5.3b Chambers were used to cover the four inch perforated pipes placed in the trench Photo courtesy of Mr Daniel Pavon of Aquarobic International, Winchester, VA
Photo 5.3c Final view of the area where the trench is now dispersing the effluent from a SBR treatment system Note that one end of the “L” shaped trench is at the white observation pipe and the other end is next to the dumpster
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Photo 5.4a Drip dispersal system for an individual home Note that the drip tubing
is installed in five feet wide trenches Trenches are open and the system is being tested before covering the trenches
Figure 5.4b Drip dispersal system area a few months after installation Note that the grass is established and under the grass cover, effluent from an advanced onsite system is dispersed using drip lines
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Photo 5.5a Drip system for effluent dispersal installed in open area using a vibratory plow Source: Photo courtesy of Mr Robert Mayer of American Manufacturing, Inc., Manassas, VA.
Photo 5.5b Drip system for effluent dispersal installed in wooded area using a bratory plow.
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Photo 5.6a Spray irrigation system installed in the front yard used for dispersal of effluent from an advanced onsite wastewater treatment technology that serves a single family home.
Photo 5.6b Spray irrigation system installed in wooded area, back yard of a house, used for dispersal of effluent from an advanced onsite wastewater treatment tech- nology that serves a single family home.
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Photo 5.7a A filter bed system for dispersal of effluent from an advanced onsite wastewater treatment technology that serves a single family home Note this picture was taken a few days after the installation was completed.
Photo 5.7b Same filter bed system a few years after it was installed Note the happy homeowner standing between the two weeping-willow trees planted within the filter bed system.
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Photo 5.8a Effluent dispersal area with a sign to restrict any vehicular traffic within the area.
Photo 5.8b Picnic area over and around a large effluent dispersal area Note that the effluent is dispersed in subsurface environment with no adverse impact on the ground.
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Photo 5.9a Evapo-transpiration beds for dispersal of effluent from an advanced onsite wastewater treatment technology that serves three individual family homes Note the picture is taken few months after the installation.
Photo 5.9b Evapo-transpiration beds about four years after the installation Note the plant growth within the beds.
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Photo 5.10a A wetland treatment system installed within a greenhouse for dispersal
of effluent directly into atmosphere in form of humidity This system serves a munity center Note the picture is taken just before the system went online.
com-Photo 5.10b The wetland system within the greenhouse a few years after the system went online The final effluent from this treatment system is disinfected using Ul- tra-violet light disinfection system and the disinfected effluent is reused for flushing toilets inside the community center.