Transcript Document

Household Wastewater Systems
Mike Kizer
OSU Extension Biosystems & Agricultural Engineering
Typical Waste Water System
Well
Renovated Wastewater
Wastewater System Regulation
• Regulatory agency in Oklahoma is:
Department of Environmental Quality (DEQ)
707 N. Robinson, OKC (Tel: 405-702-6100)
• DEQ field offices in many counties
Check local listing under: Oklahoma – State of –
• Regulations are outlined in Title 252 of
Oklahoma Administrative Code, Ch. 641
• DEQ wastewater system website:
http://www.deq.state.ok.us/ECLSnew/septic.htm
Minimum Lot Size for
Wastewater Disposal Systems
Disposal System
Type
Water Supply Source
Private Well Public Supply
Aerobic w/ sprinklers
¾ acre
½ acre
ET/Absorption Trench
1 acre
1 acre
Subsurface (fast perc.)
¾ acre
½ acre
Subsurface (slow perc.)
1 acre
1 acre
2 ½ acres
2 ½ acres
Lagoon
Wastewater System Separation Distances
(distance in feet)
Tanks
(septic, pump,
aeration)
Perforated
Pipe or
Chamber
Solid Pipe
Lagoon
Sprinkler
Head
Spray
Head
Private Well
50 / 100
50 / 100
50 / 100
50 / 100
50 / 100
15
Public Well
300
300
50
300
300
15
5
5
NA
50
NA
NA
NA
10
NA
NA
NA
NA
Water Line
5
15
10
15
15
NA
Property Line
5
5
5
10
5
5
Stream/Lake
15
15
NA
15
15
15
Drains
15
15
NA
15
NA
15
Buildings
Other Structure
Wastewater System Components
• Water-tight sewer lines
• Septic tank
• Disposal system
– Subsurface drain field
• Absorption trenches
• Infiltration chambers
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ET/Absorption trenches
Aerobic system with sprinkler
Total retention lagoons
Pre-approved alternative disposal systems
Screen vent pipe opening to prevent
blockage by birds, squirrels, etc.
Household Plumbing
Sewer and Vent System
•Sewer lines in the house
collect waste water for
conveyance to the septic
tank
•Roof vents and the traps
under sinks, tubs, showers,
toilets and wall/floor drains
prevent sewer gas from
entering the house.
Main Sewer Pipe
Septic Tank
• All household wastewater systems will have a
septic tank
• Microbial action digests solid wastes
• Liquids flow through tank to disposal area
• Tank size
– 1000 gallon liquid capacity (4-BR house or less)
– Add 250 gallons per additional bedroom
Typical Septic Tank Installation
Two-Chamber Tank
Baffles
House
Foundation
Wastewater Piping Materials
• Water-tight Sewer Conveyance Lines
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Cast iron
PVC (Sch. 40 is preferred weight)
Transite (asbestos-cement)
Orangeburg (paper-tar product: old houses)
• Drain Field Lines
– Perforated PVC
– Polyethylene infiltration chambers
– Clay tile (old houses)
Effluent Disposal Area Options
• Absorption field
– Absorption trenches
– Infiltration chambers
– ET/Absorption trenches
• Lagoons
• Aerobic systems
• Authorized alternative systems
Subsurface Absorption Field Approval
• Percolation Test
– 3 test holes in drainage area perc at a rate of
60 min/inch of water or faster
• Soil Profile Description
– 3 test holes without any of the following:
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(1) impervious material (bedrock, clay pan)
(2) water saturated soil (discoloration)
(3) loamy coarse sand or coarser soil, or
(4) sandy clay or finer soil
The size and type of waste water disposal system
is very dependent on the soil at the building site.
Even before a percolation test or soil profile
evaluation you can get an idea of site suitability
from the county soil survey.
Cross-Section of Subsurface Absorption Trench
8-ft minimum distance to
center of next trench
Perforated Pipe
150’ MAX.
Lateral lines following the slope contour
150’ max. length
Infiltration Chambers
• Polyethylene infiltration
chamber has 100% open
volume vs. 50% for gravelfilled absorption trench
• Corrugated design gives
strength to support ground
traffic over its 2-ft width
• Chamber cost per unit
length is approximately
equal to unit cost of
perforated PVC pipe, plus
gravel and installation
ET/Absorption Trench System
• Used when soil percolation rate is too slow
for ordinary subsurface absorption trenches
• Uses evapotranspiration (ET) of grasses plus
soil absorption to dispose wastewater
• Plant a mix of cool and warm season grasses
for year-round ET
Cross-Section of ET/Absorption Trench
Cool-Warm Season Grass Mixture
Perforated Pipe
Lagoons
• Used when soil percolation rate is too
slow for soil absorption systems
• Require 2 ½ acre minimum lot size
• Fencing required around the lagoon
• Size based on house size, and rainfall and
evaporation of geographic zone
• Must retain all wastewater (no overflow)
Typical Lagoon Installation
- 2.5 acre minimum lot size required
- 4-ft high fence required
- lagoon size based on house size and local rainfall
4 ft
3
1
7 ft
5 ft max.
Concrete Pad
1 ft min.
Location & Lagoon Size
The required size of
total retention waste
water lagoons (because
of their annual
hydraulic balance)
makes them less
desirable the farther
east you build in
Oklahoma.
Aerobic Systems
• Used to treat septic tank effluent where
subsurface disposal is not possible
• Bubbling air through effluent supports
aerobic bacteria for further digestion
• Exposure to oxygen kills most pathogens
• Chlorination allows surface land application
of wastewater through sprinklers
Onsite Aerobic Treatment System
Onsite aerobic treatment systems treat septic tank
effluent further by aerobic digestion, chlorination to
kill pathogens, and surface application through a
spray head sprinkler system.
(Septic Tank)
EFFLUENT FROM
SEPTIC TANK
WASTEWATER
TO CHLORINATOR
& SPRINKLERS
DIFFUSER
Typical Aeration Chamber of Aerobic Treatment System
Stack-Feed Contact
Tablet Chlorinator
Chlorine Tablet
Feed Tubes
Effluent Outlet
Effluent Inlet
Ca(OCl)2
Tablets
Pump Chamber and
Surface Application System
Access Hatch
Pump
Pump Control &
Alarm Floats
Spray Heads
Finding Waste Water System Components
• Waste water components are normally downhill
from the house (gravity flow)
• Septic tank can be no less than 5 feet, and is
normally no more than 50 feet from house
• Two-way sanitary sewer clean-outs located:
– Within 5 feet of the house
– Within 5 feet of every bend greater than 45º
– Every 100 feet of straight sewer line
• Grass over septic tank may be brown in summer
• Grass over drain field will be greener in summer
Locating Waste Water System Components
Clean-outs on main sewer line
Locating Waste Water System Components
2 1/2-inch roof vent on branch line
4-inch roof vent on main sewer line
Sewer system roof vents
Locating Waste Water System Components
Largest roof vent on main sewer line
Clean-outs on main sewer line exiting house
Regular green stripes in a dry
lawn are the lateral lines
Household Water Use
• Typical Usage: 50-100 gallons/person-day
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Clothes washer:
30-50 gallons/load
Dishwasher:
7-15 gallons/load
Garbage Disposal: 4 - 6 gallons/day
Shower/Bathtub: 25-60 gallons/use
Ordinary toilet:
1.6 - 5 gallons/flush
Water softener:
50-100 gallons/regeneration
Septic System Additives
Biological
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Bacteria
Yeast
Enzymes
Combination
Chemical
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Acids
Bases
Organic Solvents
Flocculants
Biological Additives
• Will not eliminate need for tank pumping
• 20% of sludge is inorganic (indigestible)
• Billions of bacteria live in septic tanks-a few million more have little effect
• If natural bacteria have been killed,
added bacteria will die also
• Normal population is restored in 30-60
hours even if 99.99% has been killed
Maximum Safe Levels of Cleaners
(Single dose in 1000-gallon septic tank)
• Bleach (5.25% Cl):
• Cleansers/Disinfectants:
• Drain Cleaners:
1.3 gallons
2.5 gallons
0.65 ounces
Chemical Additives
Strong Acids and Bases
• Disrupt normal tank biological activity
• Harm soil structure in drain field
Organic Solvents
• Clean thin layers of sewer line build-up
• Contaminate ground water
Annual Cost of Additives
Amherst, MA Retailers Study - 1989
(using manufacturer’s recommended rates)
• Biological (11):
• Solvents (3):
• Acid/Base (8):
$19.75/yr
$78.00/yr
$13.48/yr
Annualized Pumping Cost
(USPHS Pumping Frequency Estimate)
$150 Pumping Cost for 1000-gal tank
Family Size
Pumping Freq.
Annual Cost
2
20 yrs
$ 7.50/yr
3
12 yrs
$12.50/yr
4
8 yrs
$18.75/yr
5
6 yrs
$25.00/yr
6
4 yrs
$37.50/yr
Septic System Additives
Conclusions
• Biological additives are harmless but of little use
• Chemical additives can damage septic system
and contaminate ground water
• Don’t use if active ingredients are unspecified
• Annualized cost of additives is about the same as
for tank pumping on recommended schedule
• “These products make a lot of money for the
people that sell them.”
Waste Water System Failures
Common Causes
• Hydraulic overloading (too much water)
• Solids migration to drain field
– Failure to pump tank on schedule
– Baffle failure
• Root intrusion into sewer lines
• Traffic damage to drain field
• Garbage disposal overuse
Reducing Hydraulic Loading
• Equipment Adjustments
– Low flow toilets (1.6 gpf and 0.6 gpf)
– Water-saving showerheads
– Front-loading washing machines
• Lifestyle Adjustments
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Shower vs. bath
Distribute laundry loads throughout week
Distribute bathing morning & evening
Full loads only for washer & dishwasher
Root Damage
• Plant no trees or shrubs near sewer lines
• Copper sulfate to kill tree/shrub roots
– Treatment is not toxic to plants
– Once intruding roots are killed, absorption ends
– Add ½ cup of crystals to distribution box or to
cleanout downstream from septic tank
– If added through toilet, 2 pounds of crystals are
needed (not harmful to tank bacteria)
• See OSU CR-6428 for more information
Traffic Damage
• No vehicle parking over drain field
• No vehicle traffic except lawn mowers
• No traffic at all if ground is saturated
Solids & Drain Fields
• Solids must be retained in septic tank
• Baffles should be inspected when tank is
inspected or pumped
• Use of additives that “liquefy” sludge and
scum can lead drain field failure
• Septic tanks: like fuses in electrical wiring
(failure in controlled location; cheap to fix)
Garbage Disposals
• Add to hydraulic load (running water)
• Add to solids (more frequent pumping)
• Poorer digestion environment
– (Carbon:Nitrogen ratio is more unfavorable)
Water Softeners & Septic Systems
• Salt does not affect septic tank functioning
• Added hydraulic load (regeneration water)
– Use water meter or sensor controlled
regeneration rather than time clock alone
• Added sodium can affect marginal drain
fields (dispersal of clays slows perc rate)
– Use potassium chloride (KCl) salt if a problem
MWPS-24
Onsite Domestic Sewage
Disposal Handbook
Home*A*Syst
OK DEQ Ch. 641
Worksheet #3
www.deq.state.ok.us
On-Site Wastewater System Resources
If you don’t maintain your on-site wastewater system, it
will demand your attention when it is most inconvenient.