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Table 5.1.1 Daily Sewage Flow for Establishments
Type of Establishment
Daily Flow for Design
AIRPORTS ………………………………………………………………………………… 5 gal/passenger
Railroad Stations (does not include food service facilities)
Bus Terminals (does not include food service facilities)
BARBER SHOPS …………………………………………………………………………. 50 gal/chair
BARS, COCKTAIL LOUNGES
(does not include food service ……………………………………………………………20 gal/seat
BEAUTY SHOPS OR STYLE SHOPS……………………………………………………………
125 gal/seat
BOWLING LANES ………………………………………………………………………… 50 gal/seat
BUSINESSES
(other than those listed elsewhere in this table) ……………………………………………………………
25 gal/employee
CAMPS
Construction or Work Camps (with flush toilets) ……………………………………………………………
60 gal/person
(with chemical toilets) …………………………………………………………………… 40 gal/person
Summer Camps …………………………………………………………………………. 60 gal/person
Campgrounds with Comfort Station
(without water and sewer hookups) ……………………………………………………………
100 gal/campsite
Travel Trailer/Recreational Vehicle Park
(with water and sewer hookups) ……………………………………………………………
120 gal/space
CHURCHES (does not include a kitchen, food service
facility, day care center, or camp) ………………………………………………………5 gal/seat
COUNTRY CLUBS …………………………………………………………………………….
20 gal/member
FACTORIES (exclusive of industrial waste) …………………………………………………………………………….
25 gal/person/shift
Add for showers …………………………………………………………………………….10 gal/person/shift
FOOD SERVICE FACILITIES
Restaurants ……………………………………………………………………….….
40 gal/seat of 40 gal/15 ft2 of dining
area, whichever is greater
24-hour Restaurant …………………………………………………………………………….
75 gal/seat
Food Stands
(1) Per 100 Square feet of food stand floor space …………………………………………………………………………….
50 gal
(2) Add per food employee …………………………………………………………………………….
25 gal
Other Food Service Facilities …………………………………………………………………………….
5 gal/meal
HOSPITALS …………………………………………………………………………….
300 gal/bed
MARINAS …………………………………………………………………………….
10 gal/boat slip
With bathhouse …………………………………………………………………………….30 gal/boat slip
MEAT MARKETS
(1) Per 100 square feet of market floor space …………………………………………………………………………….
50 gal
(2) Add per-market employee …………………………………………………………………………….
25 gal
MOTELS/HOTELS …………………………………………………………………………….
120 gal/room
With cooking facilities …………………………………………………………………………….
175 gal/room
OFFICES (per shift) …………………………………………………………………………….
25 gal/person
RESIDENTIAL CARE FACILITIES, REST HOMES, NURSING HOMES …………………………………………………………………………….
60 gal/bed
With laundry …………………………………………………………………………….
120 gal/bed
DAY SCHOOLS
With cafeteria, gym, and showers …………………………………………………………………………….
15 gal/student
With cafeteria only …………………………………………………………………………….
12 gal/student
With neither cafeteria nor showers …………………………………………………………………………….
10 gal/student
BOARDING SCHOOLS …………………………………………………………………………….
60 gal/person
SERVICE STATIONS …………………………………………………………………………….
250 gal/water closet or urinal
24-hour Service Stations …………………………………………………………………………….
325 gal/water closet
STORES, SHOPPING CENTERS, AND MALLS
(Exclusive of food service and meat markets) …………………………………………………………………………….
128 gal/1000 ft2 of retail sales area
STADIUMS, AUDITORIUMS, THEATERS, DRIVE-INS …………………………………………………………………………….
5 gal/seat or space
SWIMMING POOLS, SPAS, AND BATHHOUSES …………………………………………………………………………….
10 gal/person
Table 5.1.2 Wastewater Characteristics
Characteristic
Total solids
Symbol
TS
Explanation
A measure of the total amount of substances in the wastewater, both
dissolved and suspended as particles.
Volatile solids
VS
The amount of matter in a wastewater that can be easily oxidized. This is
a rough measure of the organic substances in the water.
Total suspended solids
TSS
The amount of particles suspended, rather than being dissolved, in the
water. TSS includes mineral matter such as soil particles, nonliving
organic matter, and living microbes such as bacteria.
Volatile suspended solids
VSS
The easily oxidized suspended matter in water. VSS includes only
organic particles, bacteria, and living microbes.
Biochemical oxygen demand
BOD
A measure of the "strength" of the wastewater. This test determines the
amount of oxygen used by bacteria to degrade the substances in the
water.
Chemical oxygen demand
COD
Another measure of the strength of the wastewater. This test determines
the oxygen required to degrade all organic matter in the water, even
substances that bacteria cannot degrade.
Total organic carbon
TOC
A measure of the total amount of organic carbon substances in water.
This analysis can be useful for testing industrial wastewater because all
organic substances are included in this quantity, including substances that
cannot be degraded biologically.
Total nitrogen
N
The total amount of nitrogen compounds in the water. Nitrogen
compounds are important because they contribute to eutrophication in
water bodies.
Total Kjeldahl nitrogen
TKN
The total amount of organic nitrogen and ammonia. TKN nitrogen is
generally converted to nitrate and nitrite by sewage treatment.
Ammonia
NH3
One form of nitrogen usually found in raw sewage.
Nitrate
NO3
A form of nitrogen usually found in aerobically treated effluent. Nitrate is
very soluble in water and moves easily through the soil.
Nitrite
NO2
A form of nitrogen usually found in aerobically treated effluent. Nitrite is
easily converted to nitrate by certain bacteria in the presence of oxygen.
Total phosphorus
TP
The total amount of phosphorus compounds in water. Phosphorus
compounds are important because they contribute to eutrophication in
water bodies.
Phosphate
PO4
Total coliform
TC
The total amount of all types of coliform bacteria.
Fecal coliform
FC
The amount of those types of coliform bacteria that live in the intestines
of warmblooded animals and found in fecal matter.
E. Coli.
EC
The amount of Escherichia Coli , a type of fecal coliform bacteria, found
in the water. This bacterium is used as an indicator of pollution caused by
human waste.
Fecal Streptococci
FS
Fecal Streptococci are another type of bacteria found in the intestines of
warm-blooded animals. This type of bacteria is an indicator of the
disease-causing potential of a polluted water.
A form of phosphorus found in the dissolved form in treated effluent.
Table 5.1.3 Typical Characteristics of Household Water
Characteristic
Total solids
Volatile solids
Total suspended solids
Volatile suspended solids
Biochemical oxygen demand
Chemical oxygen demand
Total nitrogen
Ammonia
Nitrate and nitrite
Total phosphorus
Phosphate
Total coliform
Fecal coliform
Symbol
TS
VS
TSS
VSS
BOD
COD
N
NH3
NO3 and NO2
TP
PO4
TC
FC
Range of concentration in
milligrams per liter
680 - 1000
380 - 500
200 - 290
150 - 240
200 - 290
680 - 730
35 - 100
6 - 18
less than 1
18 - 29
6 - 24
10
12
10 - 10 cells per liter
108 - 1010 cells per liter
Mass loading in grams per
person per day
115 - 170
65 - 85
35 - 50
25 - 40
35 - 50
115 - 125
6 - 17
1-3
less than 1
3-5
1-4
Table 5.2.1 Important Factors in a Site and Soil Investigation*
Factor
Importance
On-site system located on correct There are many legal problems if treatment and disposal fields are constructed on
property
the wrong property.
Topography and landscape
positions
These factors affect how the land and soil will treat and absorb the effluent.
Topography is the slope, hills, valleys, ravines, and gullies on the property.
Landscape position is the shape of the ground surface and location.
Soil characteristics affect the treatment and absorption of the effluent. Soil
Soil characteristics
characteristics include texture, structure, clay mineralogy, and organic content.
Soil wetness
Soil wetness can reduce the absorption of effluent and can lead to ground water
pollution. Soil wetness can be caused by a high water table, perched water table,
tidal water, seasonal saturation, or by ground water movement.
Soil depth
Soil depth is extremely important in ensuring adequate capacity to absorb and treat
the daily flow of effluent.
Restrictive horizons in soils can severely limit the absorptive capacity of the soil. Soil
Restrictive horizons
borings must locate all restrictive horizons within 48 inches of the surface.
Available space
All sites must have enough space to install a treatment and disposal field of the
proper size. Additionally, sites must have space for a replacement system. For all
sites, it is best if there is enough space for a replacement field, even though an
exempti
Water wells on adjacent property
Required setback distances must be maintained for all wells near the proposed onsite system.
Large-capacity water wells
On-site systems may need to be installed farther away from a large-capacity well
than the usual separation distance for wells because of a larger drawdown cone
around the large-capacity well.
Massive failures of multipleresidence systems
One should consider the potential health hazard of a massive failure of an on-site
system that serves a large number of residences.
Water table mounding
On-site systems that handle more than 3000 gallons per day must predict the height
of the water table mound that will develop under the treatment and disposal field
from the flow of effluent into the soil.
*Reference
15A NCAC 18A.1939-1946(4)
Table 5.3.1 Tank Sizes for Small-Medium Houses
Minimum Liquid
Number of Bedrooms
3 or fewer
Equivalent Liquid
Capacity per Bedroom
Capacity (gallons)
(gallons)
900
300
4
1000
250
5
1250
250
Table 5.3.2 Long-Term Acceptance Rates of Soils by Soil Classification (From 15A NCAC 18A.1955(b)*
Soil Group
I
Soil Texture Classes
(USDA Classification)
Sands
Soils in Texture
Class
Sand
Loamy Sand
Long-term Acceptance Rate
(gallons/day/square foot)
1.2 - 0.8
II
Coarse Loams
Sandy Loam
Loam
0.8 - 0.6
III
Fine Loams
Sandy Clay Loam
Silt Loam
Clay Loam
Silty Clay Loam
Silt
0.6 - 0.3
IV
Clays
Sandy Clay
Silty Clay
Clay
0.4 - 0.1
*All soils must have SUITABLE or PROVISIONALLY SUITABLE structure and clay mineralogy.
Note: For on-site systems where there is a lot of grease in the wastewater, the long-term acceptance rate or LTAR cannot be higher than the average LTAR for
the Soil Group. For example, for Soil Group II, the LTAR for a greasy wastewater cannot be higher
Table 5.4.1 Decision Tree for Site Modifications
Soil wetness position
Site classification
Proper action
Is soil wetness between
0 to 12 inches deep?
UNSUITABLE
Cannot drain site, probably
classed as wetland. Site
cannot be used.
Is soil wetness between
12 and 36 inches deep?
UNSUITABLE
Can use shallow placement
system or site modifications.
Reclassify as PROVISIONALLY
SUITABLE.
Is soil wetness between 36 and
48 inches deep?
Is soil wetness more
than 48 inches deep?
PROVISIONALLY
SUITABLE
SUITABLE
Use shallow placement or site
modifications if needed.
Use conventional placement.
Table 5.4.1 Decision Tree for Site Modifications
Soil wetness position
Site classification
Proper action
Is soil wetness between
0 to 12 inches deep?
UNSUITABLE
Cannot drain site, probably
classed as wetland. Site
cannot be used.
Is soil wetness between
12 and 36 inches deep?
UNSUITABLE
Can use shallow placement
system or site modifications.
Reclassify as PROVISIONALLY
SUITABLE.
Is soil wetness between 36
and 48 inches deep?
PROVISIONALLY
SUITABLE
Use shallow placement or site
modifications if needed.
Is soil wetness more
than 48 inches deep?
SUITABLE
Use conventional placement.
Table 5.5.1 Requirements for an Approved Septic Tank
Tank Characteristic
Tank capacity
Requirement
750 gallons minimum
Tank length to width ratio
2 to 1, minimum
Number of compartments
2
Volume of inlet compartment
2/3 to 3/4 of total tank capacity
Volume of outlet compartment
1/4 to 1/3 of total tank capacity
Concrete compressive strength
3,500 psi at 28 days, minimum
Wall thickness, top, bottom, and sides
2 1/2 inches, minimum
Steel reinforcement for concrete (min.)
6-inch by 6-inch, 10-gauge welded wire mesh or equivalent,
minimum
Baffle wall thickness
2 1/2 inches, minimum
Interior height
45 inches, minimum
Liquid depth
36 inches, minimum
Freeboard (wall height above liquid)
9 inches, minimum
Baffle wall gas vent size
2 inches by 6 inches, minimum
Baffle wall liquid opening size
4 inches, minimum, entire width of tank
Baffle wall liquid opening
25 to 50% of the depth of the liquid measured from the liquid
surface
Sanitary tee — material
2-inch thick cast-in-place concrete or 160 psi PVC or PE pipe
Depth of sanitary tee in liquid
25% of the liquid depth measured from the liquid level
Difference in elevations of inlet and outlet
2 inches, inlet invert higher than outlet invert
Inlet pipe blockouts
3
Location of inlet pipe blockouts
on inlet end of tank and on sides of tank at the inlet end
Outlet pipe blockouts
1
Location of outlet pipe blockouts
on outlet end of tank
Blockout size
4 inches minimum, 3 inches maximum
Blockout concrete thickness
1 inch minimum
Access covers — size
18 inches by 18 inches, minimum
Access cover handle — material
Number 3 rebar, minimum
Manufacturer's imprint location
to right of the outlet pipe blockout
Joint detail
tongue-in-groove or equivalent
Joint sealing method
mastic or equivalent, 1-inch thickness (nominal)
Table 5.5.2 Crushed Stone Sizes and Limitations for On-Site Systems
Standard Size
Number
#3
#4
Size in inches
Average
1 1/2
1
Maximum
2 1/2
2
#5
#57
#6
1 1/2
1 1/2
1
Minimum
1/2
3/4
3/4
1/2
1/2
Limitations
Large pieces may dent or
break pipe when backfilling
trench.
Watch amount of fines
present in these sizes--fines
may plug openings in crushed
stone or plug soil.
1/2
1/4
3/8
Table 5.6.1 Trench Width and Trench Spacing
Trench width, in
inches
Trench spacing, in feet, center
to center
36 inches
9 feet
30 inches
7 1/2 feet
24 inches
6 feet
Table 5.8.1 Estimated Time for Pumping a Septic Tank (in Years)
Tank Size
(gallons)
900
1,000
1,250
1,500
Number of People Using the On-Site System
1
2
4
6
8
11
12
16
19
Number of Years
5
2
1
6
3
2
8
3
2
9
4
3
1
1
1
2
Adapted from Mancl, K. 1984. Estimated Septic Tank Pumping Frequency . Journal of Environmental Engineering,
110.