WASHINGTON COUNTY DEVELOPMENT CODE
CHAPTER FOUR
INDIVIDUAL SEWAGE TREATMENT SYSTEM REGULATIONS
Table of Contents
SECTION 1. INTENTAND PURPOSE......................1
SECTION 2. DEFINITIONS.........................1
SECTION 3. ADMINISTRATION......................8
SECTION 4. PROHIBITIONS........................9
SECTION 5. PERMITS...........................10
SECTION 6. INSPECTIONS.........................11
SECTION 7. GENERAL REQUIREMENTS...................12
SECTION 8. SITEEVALUATION........................13
SECTION 9. SOIL TESTING........................14
SECTION 10. SEWAGE FLOW DETERMINATION...............17
SECTION 11. SEWAGE TANKS........................17
SECTION 12. DISTRIBUTION OF EFFLUENT.................22
SECTION 13. DOSING OF EFFLUENT....................25
SECTION 14. FINAL TREATMENT AND DISPOSAL..............26
SECTION 15. ALTERNATIVE SYSTEMS...................36
SECTION 16. EXPERIMENTAL SYSTEMS..................41
SECTION 17. MAINTENANCE........................42
SECTION 18. SYSTEM ABANDOIVMENT..................43
SECTION 19. ENFORCEMENT.......................43
SECTION 20. SEPARABILITY.......................43
SECTION 21. EFFECTIVE DATE.......................43
Effective 10/20/97 Chapter Four - Individual Sewage Treatment System Regulations
WASHINGTON COUNTY DEVELOPMENT CODE
CHAPTER FOUR: INDIVIDUAL SEWAGE TREATMENT SYSTEM REGULATIONS
This chapter shall regulate the location, design, installation, use
and maintenance of individual sewage treatment systems in all areas of
Washington County other than cities and towns that have adopted ordinances
that comply with Minnesota Statute 115.55 and are as strict as
this Chapter. This chapter is authorized under Minnesota Statute Section
115.55 and 111.56 and Minnesota Statutes Chapter 145A.
SECTION 1. INTENT AND PURPOSE
1.1 This chapter is adopted for the following purposes:
(1) To protect the public health and safety of the residents of the community.
(2) To regulate the location, design, installation, use and maintenance
of individual sewage treatment systems so
as to prevent contamination of the surface and groundwaters within the
community.
(3) To protect individual water supply wells of the community from contamination
by inadequate, improperly
designed, located, installed or maintained individual sewage treatment
systems.
(4) To provide for the orderly development of areas of the community which
are not served by central public
waste treatment systems and to reduce the need to install central public
systems in areas where they are not now
currently planned.
SECTION 2. DEFINITIONS
2.1 For the purpose of the Chapter, certain words and phrases are defined as follows:
(1) Absorption Area: The areas below a mound that is designed to absorb sewage tank effluent.
(2) Additive, Individual Sewage Treatment System: A product which is added
to the wastewater or to the system
to improve the performance of an individual sewage treatment system.
(3) Aerobic Tank: Any sewage tank which uses the principle of oxidation
to decompose sewage by introducing
air into the sewage.
(4) Alternative Site: That portion of real property that is designated
by a licensed ISTS Professional and
approved by the Department to be protected from all vehicular traffic,
construction and other disturbances. The
site must be maintained in its original, natural soil condition so a future
individual sewage treatment system or
device may be constructed which meets all requirements when the original
ISTS malfunctions, becomes
non-repairable or when it fails to comply with the regulations.
Washington County Development Code 1
5) Alternative System: An individual sewage treatment system employing
the methods and devices presented in
Section 15.
6) As-Builts: Drawings and documentation specifying the final in-place
location, size, and type of all system
components. These records identify the results of materials testing and
describe the conditions during
construction. As-builts also contain a certified statement.
7) At-Grade System: A pressurized soil treatment system where sewage tank
effluent is dosed to a drainfield rock
bed which is constructed on original soil at the ground surface and covered
by loamy soil materials.
8) Baffle: A device installed in a septic tank for proper operation of
the tank and to provide maximum retention of
solids, and includes vented sanitary tees and submerged pipes in addition
to those devices that are normally
called baffles.
9) Bedrock: That layer of parent material which is consolidated and unweathered.
Bedrock also includes layers of
which greater than 50 percent by volume consists of unweathered in-place
consolidated bedrock fragments.
(10) Bedroom: Any room or unfinished area within a dwelling that might reasonably be used as a sleeping room.
(11) Building: Any structure, either temporary or permanent, having a roof
and used or built for the shelter or
enclosure of any person, animal or property of any kind. For purposes of
this chapter, building includes any
structure whose foundation could be damaged and structural integrity jeopardized
by the seepage of sewage or
sewage tank effluent.
(12) Building Drain: That part of the lowest piping of the draninge system
which receives the sewage discharge
inside the walls of the building and conveys it to the building sewer beginning
at least one foot outside the
building footings.
(13) Building Sewer: That part of the drainage system which extends from
the end of the building drain and
conveys its discharge to an individual sewage treatment system.
(14) Certified Statement: A statement signed by a licensed installer or
qualified employee certifying that work was
completed in accordance with applicable requirements.
(15) Cesspool: An underground pit or seepage tank into which raw household
sewage or other untreated liquid
waste is discharged and from which the liquid seeps into the surrounding
soil, bedrock or other soil materials.
(16) Chambered System: A soil treatment system where sewage tank effluent
is discharged to a buried structure
creating an enclosed open space with the original soil surface to act as
a surface for the infiltration of sewage
tank effluent.
(17) Clean Sand: A soil texture composed by weight of at least 25 percent
very coarse, coarse, and medium sand
varying in size from 2.00 millimeters (sieve size 10) to 0.25 millimeters
(sieve size 60), less than 40 percent fine or
very fine sand ranging in size between 0.25 millimeters and 0.05 millimeters
(sieve size 270) and no more than 10
percent smaller than 0.05 millimeters and no larger than 2.00 millimeters.
Clean sand also means a soil texture
which meets American Society for Testing and Materials (ASTM) specification
C-33 (fine aggregate for concrete)
or Minnesota Department of
2 Washington County Development Code
Transportation (MNDOT) specification 3126 (fine aggregate for Portland
cement concrete). The ASTM
specification is found in the 1994 Annual Book of ASTM Standards, volume
4.02, which is incorporated by
reference. This document is provided by the American Society for Testing
and Materials located at 100 Barr
Harbor Drive, West Conshohocken, PA 19428-2959. The MNDOT
specification is found in the MNDOT Standard Specifications for Construction,
1988 Edition, and the May 2,
1994, Supplemental Specifications which are incorporated by reference.
These documents are provided by the
Minnesota Department of Transportation located at 395 John Ireland Boulevard,
St. Paul, MN 55155. All
references can be found at the Minnesota State Law Library, Judicial Center,
25 Constitution Avenue, St. Paul,
MN 55155. These documents are not subject to frequent change.
(18) Compliance Inspection: Any evaluation, investigation, inspection or
other such process to make
conclusions, recommendations, or statements regarding an individual sewage
treatment system to reasonably
assure an individual sewage treatment system is in compliance with regulations.
(19) Department: The Washington County Department of Health, Environment and Land Management.
(20) DNR: The Minnesota Department of Natural Resources.
(21) Disclosure: Any conclusions or statements regarding an ISTS made by
the owner of a property with or
served by an ISTS to fulfill the requirements of Minnesota Statutes, section
115.55, subdivision 6.
(22) Distribution Box: A device designed to concurrently and equally distribute
sewage tank effluent by gravity
to a soil treatment system.
(23) Distribution Device: A device used to receive and transfer effluent
from a supply pipe to distribution pipes
or downslope supply pipes, or both. These devices may also be known as
drop boxes, valve boxes distribution
boxes or manifolds.
(24) Distribution Medium: The material used to distribute the sewage tank
effluent within a soil treatment system.
This medium includes drainfield rock, gravel-less drainfield pipe in a
geotextile wrap or a chambered system.
(25) Distribution EM: Perforated pipes that are used to distribute sewage tank effluent into a distribution medium.
(26) Dosing Chamber, or Pump Pit or Wet Well: A tank or separate compartment
following the sewage tank which
serves as a reservoir for the dosing device.
(27) Dosing Device: A pump, siphon, or other device that discharges sewage
tank effluent from the dosing
chamber to the soil treatment system.
(28) Drainfield Rock: Igneous rock, or similar insoluble, durable, and
decay-resistant material between
three-fourths inch and 2-1/2 inches in size with no more than five percent
by weight passing a three-fourths inch
sieve and no more than one percent by weight passing a number 200 sieve.
Materials greater than 2-1/2 inches in
size shall not exceed five percent by weight.
(29) Drop Box: A distribution device used for the serial gravity application
of sewage tank effluent to a soil
treatment system.
(30) Dwelling: Any building or place used or intended to be used by human
occupants as a single family or two
family residence.
Washington County Development Code 3
(31) Experimental System: Any system which is considered new technology with limited data on reliability.
(32) Failing System: Any system that discharges sewage to a seepage pit,
cesspool, drywell, or leaching pit and
any system with less than three feet of soil or sand between the bottom
of the distribution medium and the
saturated soil level or bedrock. In addition, any system posing an imminent
threat to public health or safety shall
be considered failing.
(33) Gas Deflecting Baffle: An obstructing device on the septic tank outlet
that limits the escape of solids that are
carried by septic tank gases.
(34) Gravel-less Drainfield Pipe: A distribution medium consisting of a
corrugated distribution pipe encased in a
geotextile wrap installed in a trench.
(35) Greywater: Sewage that does not contain toilet wastes. Liquid waste
from a dwelling or other establishment
produced by bathing, laundry, culinary operation, and from floor drains
associated with these sources are
considered greywater.
(36) Hazardous Waste: Any substance which, when discarded, meets the definition
of hazardous waste in MN
Rules Chapter 7045.
(37) Holding Tank: A watertight tank for storage of sewage until it can
be transported to a point of approved
treatment and disposal.
(38) Imminent Threat to Public Health or Safety: Situations with the potential
to immediately and adversely impact
or threaten public health or safety. At a minimum, cesspools, ground surface
or surface water discharges and any
system causing sewage backup into a dwelling or other establishment shall
constitute an imminent threat.
(39) Individual Sewage Treatment System: A sewage treatment system, or
part thereof, serving a dwelling, or
other establishment, or group thereof, and using sewage tanks or advanced
treatment followed by soil treatment
and disposal.
(40) Invert: The lowest point of a channel inside a pipe.
(41) Liquid Capacity: The liquid volume of a sewage tank below the invert of the outlet pipe.
(42) Mottling: A zone of chemical and reduction activity, appearing as
splotchy patches of red, brown or gray in
the soil. In subsoils with a color value of four or more, the term mottling
also includes soil having matrix colors
with a chroma of two or less as described in "Keys to Soil Taxonomy" 5th
Edition, 1992 Soil Management
Support Services, technical monograph No. 19, which is incorporated by
reference. This document is provided by
the Agency for International Development, United States Department of Agriculture
Soil Conservation Service,
Soil Management Support Services. The document was printed by Pocahontas
Press, Inc., P.O. Drawer F.,
Blacksbury, Virginia 24063-1020. It can be found at the Minnesota State
Law Library, Judicial Center, 25
Constitution Avenue, St. Paul, MN 55155. This document is not subject to
frequent change.
(43) Mound System: A system where the soil treatment area is built above
the natural elevation of the soil to
overcome limits imposed by proximity to saturated soil or bedrock, or by
rapidly or slowly permeable soils.
4 Washington County Development Code
(44) New Construction: Installing or constructing a new individual sewage
treatment system in its entirety; or
altering, extending or adding capacity to an existing individual sewage
treatment system.
(45) Notice of Noncompliance: A document written and signed by a qualified
employee or licensee after a
compliance inspection which gives notice that an individual sewage treatment
system in not in compliance with
these regulations.
(46) Ordinary High Water Level: The boundary of water basins, watercourses,
public waters and wetlands, and
(1) the ordinary high water level is an elevation delineating the highest
water level that has been maintained for a
sufficient period of time to leave evidence upon the landscape, commonly
the point where the natural vegetation
changes from predominantly aquatic to predominantly terrestrial; (2) for
watercourses, the ordinary high water
level is the elevation of the top of the bank of the channel; and (3) for
reservoirs and flowages, the ordinary high
water level is the operating elevation of the normal summer pool.
(47) Original Soil: Naturally occurring, inorganic soil that has not been
moved, smeared, compacted, nor
manipulated with construction equipment.
(48) Other Establishment: Any public or private structure other than a dwelling which generates sewage.
(49) Owner: Any person having possession of, control over, or title to
property with an individual sewage
treatment system.
(50) Percolation Rate: The timed rate of drop of a water surface in a test hole as specified in Section 9.9.
(51) Permit: A building, construction, sanitary, planning, zoning or other
such permit issued for new construction,
replacement, repair, alteration or extension of an individual sewage treatment
system. Permit also means a permit
issued for the addition of a bedroom or bathroom on property served by
an individual sewage treatment system.
(52) Permittee: Any person who is named on a permit issued pursuant to these regulations.
(53) Permitting Authority: Any unit of government, state agency, or any
authorized representative who
administers or enforces these regulations through permitting.
(54) Plastic Limit: A soil moisture content below which the soil may be
manipulated for purposes of installing a
soil treatment system, and above which manipulation will cause compaction
and puddling. The soil moisture
content at the plastic limit can be measured by American Society for Testing
and Materials (ASTM) test number
D4318-84.
(55) Privy : An aboveground structure with an underground cavity meeting
the requirements of Section 15.5,
which is used for the storage or treatment and disposal of toilet wastes,
specifically excluding water for flushing
and greywater.
(56) Previously Developed Site: Land already containing a dwelling or other establishment.
(57) Public Health Nuisance: Any activity or failure to act that adversely
affects the public health.
Washington County Development Code 5
(58) Public Waters: Any public waters or wetlands as defined in Minnesota
Statutes, Section 103G.005,
subdivisions 15 and 19, or identified as public waters or wetlands by the
inventory prepared pursuant to
Minnesota Statutes, Section 103G.20 1.
(59) Qualified Employee: An employee of the Department who meets the minimum
criteria for employment as an
ISTS professional and who conducts site evaluations or inspects individual
sewage treatment systems as part of
employment duties.
(60) Replacement: The replacement of an existing sewage tank, holding tank,
dosing chamber, artificial drainage,
privy, collector system or soil treatment system.
(61) Required Absorption Width: That width, measured in the direction of
the original land slope and
perpendicular to the original contours, which is required for the sewage
tank effluent to infiltrate into the original
soil according to the allowable loading rates in Section 14.6, Table V.
(62) Restaurants: Any place where food is prepared and intended for individual
portion service regardless of
whether consumption is on or off the premises or whether there is a charge
for the food. This definition does not
include private homes.
(63) Saturated Soil: The highest elevation in the soil where periodically
depleted oxygen levels occur because of
soil voids being filled with water. Saturated soil is evidenced by presence
of soil mottling or other information.
(64) Seepage Bed: An excavated area larger than 36 inches in width which
contains drainfield rock and has more
than one distribution pipe.
(65) Seepage Pit, or Leaching Pit, or Dry Well: An underground pit into
which a sewage tank discharges effluent
and from which the liquid seeps into the surrounding soil.
(66) Sewage: Solids and liquids removed during periodic maintenance of
an individual sewage treatment system,
or solids and liquids which are removed from toilet waste treatment devices
or a holding tank.
(67) Setback: A separation distance measured horizontally.
(68) Septic Tank: Any watertight, covered receptacle designed and constructed
to receive the discharge of
sewage from a building sewer, separate solids from liquid, digest organic
matter, and store liquids through a
period of detention, and allow the clarified liquids to discharge to a
soil treatment system.
(69) Sewage: Any water-carried domestic waste, exclusive of footing and
roof drainage and chemically treated hot
tub or pool water, from any industrial, agricultural, or commercial establishment,
or any dwelling or other
structure. Domestic waste includes liquid waste produced by toilets, bathing,
laundry, culinary operations, and
the floor drains associated with these sources. Animal waste and commercial
or industrial waste are not
considered domestic waste.
(70) Sewage Flow: Flow as determined by measurement of actual water use
of, if actual measurements are not
available, by the best available data provided.
(71) Sewage Tank: A watertight tank used in the treatment of sewage and
includes, but is not limited to, septic
tanks and aerobic tanks.
(72) Sewage Tank Effluent: That liquid which flows from a septic or aerobic tank under normal operation.
6 Washington County Development Code
(72) Shoreland: Land located within the following distances from public
waters: 1000 feet from the ordinary high
water mark of a lake, pond or flowage; and 300 feet from a river or stream
or the landward extent of a flood plain
designated by ordinance on such river or stream, whichever is greater.
1.Site: The area bounded
by the dimensions required for the proper location of the soil treatment
system.
2.Slope: The ratio of the
vertical rise or fall to horizontal distance.
3.Soil Characteristics,
Limiting: Those soil characteristics which preclude the installation of
a standard system, including evidence
of water table
or bedrock and percolation rates faster than one-tenth or slower than 60
minutes per inch.
4.Soil Textural Classification:
Soil particle sizes or textural classification as specified in the Soil
Survey Manual, Handbook No. 18,
United States
Department of Agriculture, 1993, incorporated by reference.
5.Soil Treatment Area: The
area of trench, at-grade rock bed, or seepage bed bottom which is in direct
contact with the
distribution
medium of the soil treatment system. For mounds, that area to the edges
of the required absorption width and
extending five
feet beyond the ends of the rock layer.
6.Soil Treatment System:
A system where sewage tank effluent is treated and disposed of into the
soil by percolation and
filtration,
and includes trenches, seepage beds, drainfields, at-grade systems, and
mound systems.
7.St. Croix River Land Use
District: Those lands designated by the Commissioner of the Department
of Natural Resources as the
protected land
corridor along the Saint Croix River.
8.Standard System: An individual
sewage treatment system employing a building sewer, sewage tank, and the
soil treatment
system consisting
of trenches, seepage beds, or mounds.
9.Supply Pile: Any non-perforated
pipe whose purpose is the transport of sewage tank effluent. Supply pipes
must meet or exceed
the requirements
established in these regulations.
10.Surface Water Flooding-:
The 100-year flood plain along rivers and streams as defined by the DNR,
or in the absence of such
data, as defined
by the largest flood of record; on lakes, high water levels as determined
or recorded by the DNR or, in the case
of no DNR record,
by local records or experience. Other surface water flooding or high water
areas will be determined based on
local information.
11.Ten-year flood: That
flood which can be expected to occur, on an average, of once in ten years;
or the elevation to which flood
waters have
a ten percent chance of rising in any given year.
12.Toilet Waste: Waste commonly
disposed of in toilets including fecal matter, urine, toilet paper, and
any water used for flushing
and specifically
excluding sanitary napkins, tampons and disposable diapers.
13.Toilet Waste Treatment
Devices: Privies and other devices including incinerating, composting,
biological, chemical,
recirculating,
or holding toilets.
14.Trench: An area excavated
from 18 to 36 inches in width which contains drainfield rock or other distribution
medium.
Washington County Development Code 7
15.
16.Valve box: A watertight
structure designed for alternate distribution of effluent to a soil treatment
system.
(89) Water Table: The highest elevation in the soil where all voids are
filled with water, as evidenced by presence
of water or soil mottling or other information.
(90) Watertight: A device constructed so that no water can get into or
out of the device except through designed
inlets and outlets.
SECTION 3. ADMINISTRA TION
3..l This chapter
shall apply and be in effect in all areas in Washington County other than
cities and towns that have adopted
ordinances that
comply with Minnesota Statute Section II 5.5 5 and are as strict as this
Chapter. Pursuant to Chapter One, the
Washington County
Department of Health, Environment and Land Management shall be the Administrator
of these regulations.
1.The department or its agent
shall be qualified and certified by the Minnesota Pollution Control Agency
as competent in the
design, evaluation,
and inspection of individual on-site sewage treatment systems.
2.If the department finds
that, by reason of exceptional circumstances, the strict enforcement of
any provisions of this Chapter
would cause
undue hardship or that strict conformity with the standards would be unreasonable,
impractical, or not feasible
under the circumstances,
the Department may permit modifications in individual cases based on conditions
it may prescribe for
prevention,
control or abatement of pollution.
3.Consistent with the procedures
in Chapter One, Section 6.1 (1), the Washington County Board of Adjustment
and Appeals shall
hear and decide
appeals of any order, decision or determination made by the department
regarding the enforcement of this
Chapter. Appeals
of any administrative decision or determination may be filed by any person,
county department, or township.
4.Consistent with the procedures
in Chapter One, Section 6.1 (2), the Washington County Board of Adjustment
and Appeals shall
hear and decide
all requests for variance to the requirements of this Chapter. Pursuant
to Minnesota Rule 7080.0305, variances
to decrease
the three (3) foot of vertical separation required beneath the distribution
medium and the saturated soil or bedrock
must be approved
by the Commissioner of the Minnesota Pollution Control Agency in accordance
with Minnesota Rule
7080.0030, subp.
3.
3.2 The standards
in this chapter are not intended to cover waste systems treating industrial
or animal waste or other waste that
may contain
hazardous materials.
3.3 All individual
sewage treatment systems installed subsequent to the adoption of this Chapter
and all alterations, extensions,
modifications
or repairs to existing systems irrespective of the date of original installation
shall be regulated in accordance with
all requirements
of this Chapter.
3.4 Any existing
system which is a cesspool or leaching pit or which shows evidence of sewage
discharge to surface water,
sewage discharge
to ground surface, sewage backup, or any other situation with the potential
to immediately and adversely
affect or threaten
public health or safety is hereby declared to be a public health nuisance
and shall be considered an imminent
threat to public
health and safety and shall be repaired, upgraded, replaced or its use
discontinued within thirty (30) days of
notice and order
to comply by the department. Any
8 Washington County Development Code
further discharge
of effluent must be stopped immediately (by such methods as reducing or
stopping all water use or pumping
the tank as
necessary) until such time as the system is corrected.
3.5 Any individual
sewage treatment system or component thereof, irrespective of the date
of original installation, which is not
located, constructed,
installed or maintained in accordance with the provisions of this Chapter
shall be replaced or otherwise
brought into
compliance within ninety (90) days of notice and order to comply by the
department. An existing system that is not
otherwise considered
an imminent threat to public health and which was constructed under a permit
need not be upgraded,
repaired, replaced,
or its use discontinued notwithstanding the fact that at the time of a
compliance inspection, there appears to
be less than
the required three foot separation between the system bottom and mottled
soil.
3.6 Individual
sewage treatment systems serving establishments or facilities licensed
or otherwise regulated by Washington
County shall
conform to the requirements of this Chapter.
3.7 Industrial
wastewater systems and individual sewage treatment systems serving more
than twenty (20) persons (1200
gallons per
day) are regulated by the United States Environmental Protection Agency
as Class V. injection wells under Code of
Federal Regulations
Title 40 Part 144.
3.8 When a single
individual sewage treatment system, or group of individual sewage treatment
systems, is located on adjacent
properties and
under single ownership, the owner or owners shall make application for
and obtain a state disposal system permit
from the Minnesota
Pollution Control Agency if the individual sewage treatment system or group
of systems is designed to
treat an average
design flow of greater than 10,000 gallons per day.
3.9 Any new or
existing system which discharges to surface waters or the ground surface
must obtain either an NPDES or an
SDS permit from
the Minnesota Pollution Control Agency and shall comply with all NPDES
or SDS requirements.
3.10 Any individual
sewage treatment system requiring approval by the State of Minnesota shall
also comply with this Chapter
and all local
codes and ordinances.
3.11 Where work
requiring a permit under this Chapter has commenced without first having
obtained a permit, work shall be
ordered to stop
until all permit requirements have been met and a permit for installation
of a system has been approved.
3.12 To enforce
this Chapter, the department or its authorized agent my enter a building,
property or a place where there is
reason to suspect
a system is failing to properly treat or dispose of sewage.
3.13 Fees for
pen-nits, inspections, or other services rendered under this Chapter shall
be established by the Washington
County Board
of Commissioners.
SECTION 4. PROHIBITIONS
4.1 Sewage, sewage
tank effluent, or seepage from a soil treatment system shall not be discharged
into any well or boring as
defined in MN
Rules Chapter 4725 or any other excavation in the ground.
4.2 Footing or roof drainage and chemically treated hot tub and pool water shall not enter any part of the system.
4.3 Products
containing hazardous waste and hazardous substances must not be discharged
to a system other than in normal
amounts of household
products and cleaners designed for household use. Substances not intended
Washington County Development Code 9
for use in household
cleaning, including solvents, pesticides, flammables, photo finishing chemicals,
and dry cleaning chemicals
must not be
discharged to the system.
4.4 Unless specifically
permitted by the Minnesota Pollution Control Agency, sewage, sewage tank
effluent or seepage from a
soil treatment
system shall not be discharged to the ground surface or to surface water.
4.5 Uncontaminated
clear water waste from geothermal heat pump installations shall not be
introduced into individual sewage
treatment systems.
Such waste may be discharged to the ground surface or to a body of water;
however, in no case shall surface
discharge be
permitted where such discharge encroaches on adjoining property or public
way. Where subsurface disposal is
provided, such
installation shall be separated from the required sewage treatment site
and shall be designed and sized as
prescribed for
a standard soil treatment system.
4.6 Cesspools, seepage pits, dry wells and leaching pits shall not be installed and shall not remain in operation.
4.7 Installation of systems in low swampy areas, drainage swales, or areas subject to recurrent flooding is prohibited.
4.8 Systems shall
not be located within utility or drainage easements nor within dedicated
public or private rights-of-way
without proper
approvals.
SECTION 5. PERMITS
5.1 No construction shall be allowed until the permit required for the individual septic system has been issued.
5.2 No additions,
enlargements, improvements, or remodeling involving fifty (50) percent
or more of the structure, or alterations
that would affect
the water use, such as bedrooms, bathrooms or additions to living space
(excluding such areas as screen
porches, entry
ways, decks, attics, patios, nonhabitable storage space) shall be allowed
until the sewage treatment system has
been determined
to be both adequate and conforming or a permit for a new treatment system
has first been issued.
5.3 Permits shall be required for individual sewage treatment systems as follows:
(1) All new installations of sewage tanks, treatment systems and components thereof.
(2) All repair, extension, replacement or modification of existing systems and components.
(3) Any change in use of a facility served by an existing sewage treatment system.
5.4 Permits shall
not be required for normal routine inspection and maintenance of approved
individual septic treatment
systems.
5.5 Permit applications
shall be made in writing on forms provided by the department and shall
contain data including, but not
limited to,
the following:
(1) Correct legal description of the property on which the proposed work is to take place.
(2) Site plan, drawn to scale, showing the location of all proposed and
existing structures, property lines, water
supply wells within 100 feet, terrain features such as blufflines, water
bodies or water ways, buried utilities,
easements and other unique features of the site.
10 Washington County Development Code
(3) Soil test date, including soil boring logs, percolation test data with
field notes (where required) and location
and identification of test area.
(4) Plans and details of the proposed installation of work, including engineering data and final design.
(5) Building plans showing existing and proposed room arrangement and uses.
(6) For other than dwellings, calculated or measured water use rates, occupancy and occupant load.
(7) In certain cases, a property survey may be required identifying property
characteristics and including such
items as elevations, contour lines, normal high water marks, and ten (IO)
year and one hundred (I 00) year flood
elevations.
(8) Evidence of compliance with state or other jurisdiction regulations where applicable.
5.6 No permit
will be issued until a detailed system design is submitted for the current
proposed construction, including site
plan and at
least one current soil boring if there is reason to believe soil conditions
have been altered since the original soil
testing.
5.7 Permits shall
be valid upon issuance and shall continue for a period of one (1) year.
After one (1) year, the permit may be
renewed if no
changes are proposed. Such renewal shall require reapplication and payment
of the established fee.
5.8 Permits issued
under this Chapter may be revoked upon written notice by the department
when such permit has been issued
based on erroneous
or inaccurate data supplied by the applicant or erroneous interpretation
of the law by a building official.
SECTION 6. INSPECTIONS
6.1 Inspections
as required to determine compliance with this Chapter shall be performed
by the department or its authorized
agent under
the following circumstances:
(1) Site inspections to verify and evaluate soil and site conditions and
to determine the suitability of soils and
system design.
(2) Necessary investigation to determine compliance of existing systems
at the time of remodeling, alteration or
additions.
(3) For all new ISTS construction or replacement.
(4) Mound systems require a minimum of three construction inspections:
(A) When the original soil under the mound has been roughened, but prior
to placement of the
sand fill. Enough of the proposed sand fill must be present to be viewed.
(B) After placement of rock and piping, but prior to cover.
(C) When job is completed.
Washington County Development Code 11
6.2 Installation inspections shall be made prior to any work having been covered by backfill.
6.3 The licensed
installer shall be responsible to notify the department a minimum of twenty-four
(24) hours prior to the time
work is ready
for inspection or re-inspection.
6.4 Work which
is backfilled prior to required inspection may be ordered to be uncovered
whenever necessary to determine
compliance.
6.5 If upon inspection
any part of the system is determined not to be in compliance with this
Chapter, written notice shall be
provided by
the department indicating the deficiency and the required corrections.
Noted deficiencies shall be properly
corrected and
reinspected before any other work on the project is continued.
6.6 No system
shall be placed or replaced in service until final inspection has been
completed and the system installation has
been approved.
6.7 The owner
or occupant of a property shall be responsible to provide access at reasonable
time to the department or its agent
for the purpose
of performing inspections required under this Chapter.
6.8 The Contractor,
upon completion of installation, shall file with the department as built
drawings indicating the location of
system components
dimensioned from a permanent reference point.
6.9 If an inspection
is conducted as a part of preparation of the disclosure required by Minnesota
Statutes I 1 5.5 5, subd. 6 and
such inspection
is conducted by a party who is not the property owner, such party must
be licensed in accordance with MPCA
rules and regulations
and the notice of compliance or noncompliance provided to the property
owner must also be provided to
Washington County
within thirty (30) days of the inspection.
SECTION 7. GENERAL REQUIREMENTS
7.1 An individual
septic treatment system, or systems, shall be designed to receive all sewage
from the dwelling, building or
other establishment
served.
7.2 Sewage treatment
systems and each component thereof shall be located and installed to insure
that, with proper
maintenance,
it will function in a sanitary manner and will not create a nuisance nor
contaminate any domestic water supply well.
Location shall
consider lot size and configuration, proposed structures and other improvements,
topography, surface drainage,
soil conditions,
depth to ground water, geology, existing and proposed water supply wells,
accessibility for maintenance, and
potential expansion
or replacement of the system.
7.3 The design,
construction, and location of, and the materials for use in building sewers
shall be in accordance with the
Minnesota State
Building Code, chapter 1300, which incorporates by reference portions of
the Minnesota Plumbing Code,
chapter 4715,
and specific provisions of the Minnesota rules relating to wells and borings,
chapter 4725.
7.4 An individual
sewage treatment system defined as a collector, an alternative system,
or a system intended to serve other
establishments
shall not be installed unless a water meter is provided to measure the
flow to the treatment system. For metered
systems that
have sewage tank effluent pumped to a soil treatment area, an electrical
event counter must also be installed.
12 Washington County Development Code
SECTION8. SITE EVALUATION
8.1 Prior to
the issuance of a building permit for new construction, remodeling or alterations
that would affect water use, such as
bedrooms, bathrooms
or additions to living space; or the issuance of a permit to install, upgrade,
repair or alter an individual
sewage treatment
system; or approval for subdivision of land, a site evaluation shall be
made of all proposed sites for sewage
treatment systems
shall be completed by the applicant and reviewed and approved by the department.
Such site evaluation shall
consist of a
preliminary and field evaluation.
8.2 A preliminary evaluation shall consist of-.
(1) Flow determination for the dwelling or other establishment;
(2) The investigation of the proposed or existing location of water supply
wells within 100 feet of the proposed
ISTS, existing and proposed buildings on the lot, and existing and proposed
buried water pipes within 50 feet of
the proposed system;
(3) Easements on the lot;
(4) Ordinary high water level of public waters;
(5) Ten-year floodplain designation and flooding elevation from published
data as available or from data which is
acceptable to and approved by the permitting authority or the DNR;
(6) Property lines;
(7) All required setbacks from the system;
(8) The soils map unit, applicable soil characteristics, and soil suitability
as determined by soil borings and
percolation tests for each proposed site or installation;
(9) Legal description and lot dimensions; and
(10) Names of property owners.
8.3 A field evaluation shall consist of:
(1) Identifying lot lines, lot improvements, and easements;
(2) A description of the percent and direction of the slope at the proposed
system location, vegetation type, any
evidence of disturbed or compacted soil or flooding or run-on potential
and landscape position;
(3) Depth to the highest known or calculated ground water table or bedrock;
(4) The existence of lowlands, local surface depressions, and rock outcrops;
(5) All legal setback requirements from existing and proposed buildings;
property lines; sewage tanks; soil
treatment systems; water supply wells; buried water pipes and utility lines;
the ordinary high water level of public
waters; and the location of all soil treatment systems and water supply
wells on adjoining lots within 100 feet of
the proposed soil treatment system, sewage tank and water supply well.
Washington County Development Code 13
8.4 A written report on the site evaluation shall be prepared covering, at a minimum, the following:
(1) All of parts 8.2 and 8.3;
(2) Dates of preliminary and field evaluations;
(3) A map drawn to scale or dimension, with a north arrow, and including the following:
(A) A horizontal and vertical reference point of soil observation and percolation
tests and
distance to all required setbacks, lot improvements, easements, ordinary
high water mark of public
waters, property lines, direction and percent slope;
(B) The location of any unsuitable, disturbed/compacted areas; and
(C) The access route for tank maintenance.
(4) Estimated depth of seasonally saturated layer, bedrock, or flood elevation, if appropriate;
(5) Proposed elevation of the bottom of the soil treatment system;
(6) Final soil sizing factor;
(7) Anticipated construction-related issues; and
(8) Name, address, telephone number and signature of the individual
conducting the site evaluation.
SECTION 9. SOIL TESTING
9.1 Applicants
for sewage treatment system permits, site or subdivision approvals will
be required to submit soil test data
derived from
soil borings and percolation tests for each proposed site or installation.
The minimum testing shall be that
necessary to
verify suitable conditions for two complete soil treatment systems. Large
systems designed for 1,200 gallons per
day or more
shall require a hydrogeologic investigation in accordance with Section
15.7 (3).
9.2 All testing
shall be conducted in accordance with the requirements of this Chapter
and shall be done by qualified personnel,
certified under
the NWCA training and certification program and licensed by the MPCA.
9.3 All proposed
sites for sewage treatment systems shall be protected by fence or other
methods as necessary to avoid
excavations,
construction equipment or other traffic that could affect the soil conditions.
9.4 For subdivision
testing, enough soil borings must be done to assure that suitable soils
exist for each lot for long-term
sewage treatment.
Percolation tests are not required unless the permeability cannot be estimated
or there is reason to believe the
soil is not
original or has been compacted.
9.5 Complete
testing on each individual lot will be required prior to permit issuance
independent of any prior approved
subdivision
testing. A minimum of four (4) satisfactory soil borings outlining an area
of 5,000 square feet are required. Larger
areas may be
required where conditions of use, soils, topography or vegetation require.
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Effective 10/20/97 Chapter Four - Individual Sewage Treatment System Regulations
9.6 Where soil
tests require a mound, testing and design must clearly show suitable area
for installation of two (2) complete
mounds. Where
site conditions are such that the only backup mound will likely be disturbed,
the Department, at its discretion,
may require
both mounds to be constructed at once.
9.7 Soil borings shall be made as follows:
(1) Borings shall
be by auger or excavation and shall be staked and protected until notification
that the field evaluation has been
completed. Flite
augers which are continuous or disturb extracted soil samples are not allowed.
Borings shall be made to a depth
of at least
three (3) feet deeper than the bottom of the proposed system or until bedrock
or a water table is encountered,
whichever is
less.
(2) Any evidence of disturbed or compacted soil must be disclosed and may
result in the prohibition of utilizing
that test area.
(3) Particular effort shall be made to determine the highest known water
table by recording the first occurrence of
mottling observed in the hole, or if mottling is not encountered, the open
holes in clay or loam soils shall be
observed after standing undisturbed a minimum of sixteen (16) hours, and
depth to standing water, if present,
shall be measured.
9.8 A soil description
shall be written for each soil observation at the proposed site. Soils
should be evaluated under adequate
light conditions
with the soil in a moist state and including the following:
(1) The depth of each soil horizon measured from the ground surface. Soil
horizons are differentiated by changes
in soil structure, soil texture, soil color, mottling, bedrock, or any
other characteristic which may affect water
percolation or treatment of effluent.
(2) The soil matrix and mottled color described per horizon by the Munsell
Soil Color Charts, 1992 Revised
Edition, which is incorporated by reference. This document is available
from Macbeth Division, Kollmorgen
Instruments Corporation, Munsell Color, PO Box 230, Newburgh, New York
12551-0230. It can be found at the
Minnesota State Law Library, Judicial Center, 25 Constitution Avenue, St.
Paul, MN 55155. This document is not
subject to frequent change.
(3) The soil texture described using the United States Department of Agriculture
(USDA) soil classification
system as modified here:
Clay = Clay, sand clay, silty clay
Clay loam = Clay loam, sandy clay loam, silty clay loam
Loam = Loam
Sandy loam = sandy loam
Silt loam = Silt loam, silt
Loamy sand = loamy sand
Course sand = course sand
(Medium) sand = (Medium) sand
Find sand = Fine and very find sand
9.9 After soil
borings have outlined the minimum area of suitable soils, percolation tests
shall be made. The only exception to
this requirement
is for sandy soils clearly in the 5 mpi range. The design for sizing of
systems is such soils shall be 1.27 square
feet per gallon.
The requirements for percolation tests are:
Washington County Development Code 15
Chapter Four Individual Sewage Treatment System Regulations Effective 10/20/97
(1) Each test hole shall be six to eight inches in diameter, have vertical
sides, and be bored or dug to a depth of
the bottom of the proposed individual sewage treatment system. Soil texture
descriptions shall be recorded
noting depths where texture changes occur.
(2) The bottom and sides of the hole shall be carefully scratched to remove
any smearing and to provide a natural
soil surface into which water may penetrate.
(3) All loose material shall be removed from the bottom of the test hole
and two inches of one-fourth to
three-fourths inch gravel shall be added to protect the bottom from scouring.
(4) The hole shall be carefully filled with clear water to a minimum depth
of twelve (12) inches over the soil at the
bottom of the test hole and maintained for no less than four hours. Failure
to adequately saturate the test hole
may result in rejection of the test.
(5) The soil
shall then be allowed to swell for at least sixteen (16) but no more than
thirty (30) hours. In sandy soils, the
saturation and
swelling procedure shall not be required and the test may proceed if one
filling of the hole has seeped away in
less than ten
minutes.
(6) Measure the percolation rate as follows:
A.In sandy soils, adjust the water depth to eight inches over the soil at the bottom of the test hole.
From a fixed
reference point, a drop in water level shall be measured in inches to the
nearest one-sixteenth (1/16) inch at
approximately
ten minute intervals. Measurement can also be made by determining the time
it takes for the water level to drop
one inch from
an eight inch reference point. If eight inches of water seeps away in less
than ten minutes, a shorter interval
between measurements
shall be used, but in no case shall the water depth exceed eight inches.
The test shall continue until
three consecutive
percolation rate measurements vary by a range of no more than ten percent.
B.In other soils, adjust
the water depth to eight inches over the soil at the bottom of the test
hole. From a fixed reference point, the
drop in water
level shall be measured in inches to the nearest one-sixteenth (1/16) inch
at approximately 30 minutes intervals,
refilling between
measurements to maintain an eight inch starting head. The test shall continue
until three consecutive
percolation
rate measurements vary by a range of no more than ten percent. The percolation
rate can also be made by observing
the time it
takes the water level to drop one inch from an eight-inch reference point
if a constant water depth has been
maintained for
at least four hours prior to the measurement.
(7) Calculate
the Percolation Rate by dividing the time interval by the drop in water
level to obtain the percolation rate in minutes
per inch. The
percolation rates which are within the ten percent provision determined
for each test hole shall be averaged to
determine the
final percolation rate for that hole.
(8) The slowest final percolation rate for all holes within the soil treatment area shall be used for design.
(9) A percolation test shall not be run where frost exists below the
depth of the proposed soil treatment system.
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Effective 10/20/97 Chapter Four - Individual Sewage Treatment System Regulations
SECTION 10. SEWAGE FLOW DETERMINATION
10.1 Where the
construction of additional bedrooms, the installation of mechanical equipment,
or other factors likely to affect
the operation
of the system can be reasonable anticipated, the installation of a system
for the anticipated need shall be required.
10.2 For dwellings,
the average daily sewage flow and the measured percolation rate of the
soil shall be used to size the soil
treatment system.
Acceptable methods for estimating sewage flow are given in Table I. The
minimum daily sewage flow
estimated for
any dwelling shall provide for at least two bedrooms. For multiple residential
units, the estimated daily sewage flow
shall consist
of the sum of the flows of each individual unit. If a greywater system
is employed, estimated sewage flow shall
equal sixty
(60) percent of the amount provided in Table 1.
Table I
Number of Bedrooms Gallons per Day
2 300
3 450
4 600
5 750
6 900
10.3 For other
establishments, average design flow shall be used to size soil treatment
systems. Maximum design flow shall be
used to size
sewage tanks. Design flows shall be calculated using estimated or measured
values for other establishments
according to
the following:
(1) Estimated average and maximum design flows: the best available data
as provided by the department shall. be
used if estimating the average and maximum design flows.
(2) Measured average and maximum design flows:
A.The average design flow shall be determined by averaging the measured
daily flows for a consecutive seven-day
period in which the establishment is at maximum capacity or use; and
B.The maximum design flow shall be the anticipated peak daily flow.
SECTION II. SEWAGE TANKS
11.1 All tanks, regardless of material or method of construction must:
(1) Be watertight;
(2) Be designed and constructed to withstand all lateral earth pressures
under saturated soil conditions with the
tank empty;
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Chapter Four -.- Individual Sewage Treatment System Regulations Effective 10/20/97
(3) Be designed and constructed with adequate tensile and compressive strength
to withstand a minimum of
seven feet of saturated earth cover above the tank top and manhole cover;
(4) Not be subject to corrosion or decay;
(5) Have the manufacturer's name, model number, and tank capacity in gallons
permanently displayed on the tank
above the outlet pipe;
(6) Not be constructed on site when saturated soil conditions during construction
are closer than three inches to
the bottom of the excavation;
(7) Be protected against flotation under high water table conditions; and
(8) Have a written and graphic label affixed to maintenance hole covers
of sewage tanks warning of the hazardous
conditions inside the tanks.
11.2 All tanks, regardless of material or method construction, shall conform to the following criteria:
(1) The liquid depth of any septic tank or compartment thereof shall not be less than 24 inches.
(2) No tank or compartment thereof shall have an inside horizontal dimension less than 24 inches.
(3) Baffles shall be installed at each inlet and outlet of the tank and each compartment.
(4) The space in the tank between the liquid surface and the top of the
inlet and outlet baffles shall be not less
than 20 percent of the total required liquid capacity, except that in horizontal
cylindrical tanks, this space shall be
not less than 15 percent of the total required liquid capacity.
(5) Inlet and outlet baffles shall be constructed of acid resistant concrete,
acid resistant fiberglass, or plastic not
subject to corrosion or decay. Inlet baffles not conducive to the movement
of solids shall not be used.
(6) Baffles must be integrally cast with the tank, affixed with a permanent
waterproof adhesive, or affixed with
stainless steel connectors, top and bottom. Sanitary tees, which are used
as baffles, shall be affixed to the inlet or
outlet pipes with a permanent waterproof adhesive.
(7) The inlet baffle shall extend at least six inches but not more than
20 percent of the total liquid depth below the
liquid surface and at least one inch above the crown of the inlet sewer.
(8) The outlet baffle and the baffles between compartments shall extend
below the liquid surface a distance equal
to 40 percent of the liquid depth except that the penetration of the indicated
baffles or sanitary tees for horizontal
cylindrical tanks shall be 35 percent of the total liquid depth. They also
shall extend above the liquid surface as
required in 1 1.2(4). In no case shall they extend less than six inches
above the liquid surface. Gas deflecting
baffles shall be installed on the outlet of the final septic tank which
services an other establishment.
(9) The top of the inlet baffle may extend through the top of the tank
or maintenance hole cover. The cap must be
easily accessible.
(10) In a single compartmented tank, the inlet invert shall be at least two inches above the outlet invert.
1 8 Washington County Development Code
Effective 10/20/97 Chapter Four - Individual Sewage Treatment System Regulations
(11) The inlet and outlet shall be located opposite each other along the
axis of maximum dimension. The
horizontal distance between the nearest points of the inlet and outlet
baffles shall be at least four feet.
(12) Inlet baffles, other than sanitary tees, shall be no less than six
inches or no more than 12 inches from the end
of the inlet pipe to the nearest point on the baffle. Outlet baffles, other
than sanitary tees, shall be six inches
measured from beginning of the outlet pipe to the nearest point on the
baffle. Sanitary tees used as inlet or outlet
baffles shall be at least four inches in diameter.
11.3 Access to a septic tank shall be as follows:
(1) There shall be one or more manholes, at a minimum of 20 inches least
dimension, and located within six feet of
all walls of the tank. The manhole shall extend through the tank cover
to a point within six (6) inches of finished
grade. If the manhole is covered with less than six inches of soil, the
cover must be secured to prevent
unauthorized access.
(2) There shall be an inspection pipe of at least- four inches in diameter
over both the inlet and outlet baffles. The
inspection pipe shall extend through the tank cover or the maintenance
hole cover, be secured, and be capped
flush with or above the finished grade. A downward projection of the center
line of the inspection pipe shall be
directed in line with the center line of the inlet or outlet device.
(3) An inspection pipe at least four inches in diameter must be located
between the inlet and outlet baffles for the
purpose of evaluating scum and sludge accumulations. The inspection pipe
must extend through either the tank
cover or manhole cover and must be capped flush with or above finished
grade.
11.4 A septic tank larger than 3,000 gallons shall be divided into two or more compartments.
(1) When a septic tank is divided into two compartments, the volume of
the first compartment shall be between
one-half (1/2) and two-thirds (2/3) of the total tank volume.
(2) When a septic tank is divided into three or more compartments, one
(1/2) of the total volume shall be in the
first compartment and the other half equally divided in the other compartments.
(3) Connections between compartment shall be baffled to obtain effective
retention of scum and sludge. The
submergence of the inlet and outlet baffles of each compartment must be
as specified in 1 1.2 (7) and (8).
(4) Adequate venting shall be provided between compartments by baffles
or by an opening of at least fifty (50)
square inches near the top of the compartment wall.
(5) Adequate access to each compartment shall be provided by one or more
maintenance holes, at least 20 inches
in dimension, and located within six feet of all walls of the tank. The
maintenance hole shall extend through the
top of the tank compartment cover to a point between zero and a six (6)
inch depth below finished grade. If the
maintenance hole is between zero and six inches below finished grade, the
maintenance hole cover must be
secured to prevent unauthorized access.
11.5 Where more
than one tank is used to obtain the required liquid volume, the tanks shall
be connected in series. No more
than four (4)
tanks in series can be used to obtain the required liquid volume. The first
tank shall be equal to or larger than any
subsequent tank
in the series.
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Chapter Four -.- Individual Sewage Treatment System Regulations Effective 10/20/97
11.6 The outlet
pipe extending from the septic tank must not be of cast iron, but must
be of sound and durable construction, not
subject to corrosion
or decay. The outlet pipe must meet the strength requirements of American
Society for Testing and
Materials (ASTM),
schedule 40 plastic pipe and must be supported in a manner that there is
no deflection during the backfilling
and subsequent
settling of the soil between the edge of the septic tank and the edge of
the excavation. The soil around the pipe
must be compacted
to al least original density for a length of three feet beyond the edge
of the tank excavation.
11.7 Any liquid
depth which is greater than 78 inches shall not be used when calculating
the septic tank capacity. Liquid
capacity of
septic tanks is described as follows:
(1) For dwellings there shall be two septic tanks in series with the liquid
capacity based on the number of
bedrooms contemplated in the dwelling; such tanks shall be at least as
large as the capacities in Table 11. The
only exception to this requirement is for the upgrade of an existing conforming
system if the primary tank
capacity is met and there is no garbage disposal or sewage pump. System
replacement shall require two tanks in
series.
Table H
Number of Bedrooms Tank Liquid Capacities (Gallons)
Two or less 1,000 and 500
Three or Four 1,000 and 1,000
Five or Six 1,500 and 1,000
Seven, Eight or Nine 2,000 and 1,000
Ten or More Septic tank shall be sized as an other establishment
with the second tank in series being at least 50 percent
of the capacity of the first tank.
Multiple family dwelling Size shall be
the sum of the individual dwelling
unit
containing two or more units
requirements
(2) The liquid capacity of septic tanks serving other establishments shall
be sufficient to provide a sewage
detention period of not less than 36 hours in the tank for maximum design
flows of less than 1,500 gallons per
day, but in no instance shall the liquid capacity be less than 750 gallons.
For maximum design flows greater than
1,500 gallons per day, the minimum liquid capacity shall equal 1,125 gallons
per day plus 75 percent of the
maximum design flow. For restaurants and laundromats, twice the liquid
capacity detailed above must be
provided. For laundromats, the outlet baffle of the septic tank must be
submerged to a depth of 50 percent.
11.8 A sewage
pump must not deliver sewage to a one tank system if the pump cycle delivers
more than one percent of the
liquid capacity
of the tank. For systems with multiple tanks, at least two tanks in series
must be used, each having at least the
liquid capacity
specified in this Section. The volume of sewage delivered in each pump
cycle must not exceed five percent of the
liquid capacity
of the first tank.
11.9 The sewage
tank shall be placed so that it is easily accessible for the removal of
liquids and accumulated solids. The soil
cover over a
tank shall not exceed five (5) feet. The sewage tank shall be placed on
firm and settled
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Effective 10/20/97 Chapter Four - Individual-Sewage Treatment System Regulations
soil capable
of bearing the weight of the tank and its contents. Sewage tanks shall
be setback as specified in Table 111. Sewage
tanks shall
not be placed in areas subject to flooding or in floodplains delineated
by local regulations adopted in compliance
with MN Rules,
Chapter 6120 or in areas for which regional flood information is available
from the DNR, except that in areas
where ten year
flood information is available from and/or approved by the DNR, sewage
tanks may be installed as an alternative
system in accordance
with all provisions of Section 15.3.
Table III Minimum Setback Distances (Feet)
Feature Sewage Tank Soil Treatment Area
Water Supply Well less than 50 feet deep and not
encountering at least ten feet of impervious material. 50 100
Any other water supply well or buried water suction pipe 50 50
Buried pipe distributing water under pressure 10 10
Occupied buildings and buildings with basements or crawl 10 20
spaces
Non-occupied structures 5 10
Property lines 10* l0*
Above ground swimming pools 10 10
In ground swimming pools 10 10
The Ordinary High Water Mark of.
Natural Environment Lakes and Streams 150* 150*
Recreation Development Lakes and Streams 75* 75*
General Development Lakes and Streams 75* 75*
All unclassified waters 75* 75*
St. Croix River Rural Districts 150* 150*
St. Croix River Urban Districts 100* 100*
Blufflines:
St. Croix River Blufflines 40* 40*
Shoreland Blufflines 20* 20*
* These standards may be modified through the variance process.
11.10 Aerobic
tank treatment systems shall comply with the general requirements for sewage
tanks set forth in this Chapter, and
with the following:
(1) The treatment system including each individual unit or compartment
shall be easily accessible for inspection
and maintenance and shall be provided with secured covers.
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Chapter Four -.- Individual Sewage Treatment System Regulations Effective 10/20/97
(2) Aerobic tanks shall comply with National Sanitation Foundation Standard
(NSF) No. 40 (November 1990)
which is incorporated by reference. Effluent quality shall meet or exceed
NSF Class 11 standards.
(3) No additional reduction in soil treatment or absorption area shall be allowed with the use of an aerobic tank.
(4) An effective maintenance contract, approved by the permitting authority, shall be maintained at all times.
SECTION 12. DISTRIBUTION OF EFFLUENT
12.1 Supply pipes
must be protected from freezing where the pipe passes under driveways,
sidewalks, roadways, or other areas
where deep frost
penetration is expected.
12.2 Gravity Distribution.
(1) Serial distribution must be used to distribute effluent to individual
trenches in a soil treatment system unless
the necessary elevation differences between trenches for drop boxes cannot
be achieved by natural topography
or by varying the excavation depths, in which case parallel distribution
shall be used. If drop boxes are used,
they must meet the following standards:
A.The drop box shall be watertight and constructed of durable materials not subject to corrosion or decay.
B.The invert of the inlet pipe shall be at least one inch higher than the invert of the outlet pipe to the next drop box.
C.The invert of the outlet pipe to the next trench shall be no greater
than two inches higher than the crown of the
outlet pipe of the trench in which the box is located.
D.When sewage tank effluent is delivered to the drop box by a pump, the
pump discharge shall be directed against
a wall or side of the box on which there is no outlet.
E.The drop box shall be covered by a minimum of six (6) inches of soil and it shall be placed on firm and settled soil.
F.An inspection pipe at least 4 inches in diameter must be provided and capped flush with or above finished grade.
(2) Systems using valve boxes shall comply with the following requirements:
(A) The valve boxes shall be watertight and constructed of durable materials
not subject to
corrosion or decay.
(B) The invert of the inlet pipe shall be at least one inch higher than
the inverts of the outlet pipes
to the trenches.
(C) When sewage tank effluent is pumped to a valve box, either a baffle
wall must be installed in
the valve box or the pump discharge must be directed against a wall or
side of the box on
22 Washington County Development Code
which there is no outlet. the baffle must be secured to the box and extend
at least one inch above
the crown of the inlet pipe.
(D) The valve box shall be covered by a minimum of six (6) inches of soil
and it shall be placed on
firm and settled soil.
(E) An inspection pipe at least 4 inches in diameter must be provided and
capped flush with or
above the finished grade.
(3) Distribution boxes must meet the following standards:
(A) The box must be watertight and must be constructed of durable materials
not subject to
corrosion or decay.
(B) The distribution box shall be covered by a minimum of six (6) inches
of soils and it shall be
placed on firm and settled soil. An inspection pipe must be provided and
capped flush with or
above the finished grade.
(C) The inverts of all outlets must be set and maintained at the same elevation.
(D) The inlet invert must be either at least one inch above the outlet
inverts or be sloped such that
an equivalent elevation above the outlet invert is obtained within the
last eight feet of the inlet
pipe.
(E) Each drainfield trench line must be connected separately to the distribution
box and must not
be subdivided. Distribution boxes must not be connected to one another
if each box has
distribution pipes.
(F) When sewage tank effluent is delivered by pump, either a baffle wall
must be installed in the
distribution box or the pump discharge must be directed against a wall
or side of the box on which
there is no outlet. The baffle must be secured to the box and must extend
at least one inch above
the crown of the inlet pipe.
(4) Distribution Pipes.
(A) Distribution pipes used in trenches or beds for gravity distribution
must be at least four
inches in diameter and must be constructed of sound and durable material
not subject to
corrosion or decay or to loss of strength under continuously wet conditions.
Distribution pipes
must have a load bearing capacity of not less than 1,000 pounds per lineal
foot.
(B) Distribution pipes used for gravity distribution must have one or more
rows of holes of no less
than one-half (1/2) inch in diameter spaced no more than 40 inches apart.
Holes must be spaced to
prevent failure due to loads.
(C) The distribution pipes for gravity distribution must be laid level
or on a uniform slope away
from the distribution device of no more than four inches per 100 feet.
(D) Gravity distribution pipes in seepage beds must be uniformly spaced
no more than five feet
apart and not more than 30 inches from the side walls of the seepage bed.
12.3 Pressure Distribution.
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(1) Pressure distribution must be used for the following soil treatment systems:
(A) All mound systems;
(B) All at-grade systems; and
(C) Systems where the soil percolation rate is 0. I to five minutes per
inch if the effluent is pumped
to a seepage bed or to trenches that are all at the same elevation.
(2) Distribution pipes used for pressure distribution must be constructed
of sound and durable material not
subject to corrosion or decay or to loss of strength under continuously
wet conditions.
(3) Allpipesandassociatedfittingsusedforpressuredistributionmustbeproperlyjoinedtogether.
The pipe and
connections must be able to withstand a pressure of at least 40 pounds
per square inch.
(4) Perforations must be no smaller than 3/16 inch diameter and no larger
than one-quarter (1/4) inch diameter.
The number of perforations, perforation spacing and pipe size for pressure
distribution laterals must be as shown
in Table IV. The friction loss in any individual perforated lateral must
not exceed 20 percent of the average head
pressure on the perforations.
Table IV Maximum Allowable Number of One-Fourth Inch
Diameter, or Smaller Perforations Per Lateral
Pipe Diameter - Normal and Inside
Perforation 1 inch 1 1/4inch 1 1/2 inch 2 inches
Spacing in Feet 1.049 1.380 1.610 2.067
2.5 8 14 18 28
3 8 13 17 26
3.3 7 12 16 25
4 7 1.1 15 23
5 6 10 14 22
(5) Perforation holes must be drilled straight into the pipe and not at
an angle. The perforated pipe laterals must
be installed level with the perforations downward. Perforation holes must
be free of burrs.
(6) Laterals must be spaced no further than 60 inches apart in seepage
beds and mound rock beds and must be
spaced no further than a horizontal distance of thirty (30) inches from
the outside edge of a drainfield rock layer.
(7) Laterals must be connected to a header or manifold pipe that is of
a diameter such that the friction loss in the
header or manifold will be no greater than five percent of the average
head at the perforations. The header or
manifold pipe must be connected to the supply pipe from the pump.
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Effective 10/20/97 Chapter Four - Individual Sewage Treatment System Regulations
(8) Perforated laterals must be designed and installed in such a way that
no perforations are located closer than
12 inches from the edge of the drainfield rock.
SECTION 13. DOSING OF EFFLUENT
13.1 A dosing device is not necessary in all situations but, where used, shall comply with the following
requirements:
(1) The dosing chamber shall be watertight and constructed of sound and
durable materials not subject to
excessive corrosion or decay, vented, and must be designed and constructed
to withstand lateral pressures when
the tank is empty.
(2) There shall be one or more maintenance holes, at least 20 inches least
dimension and located directly above
the dosing device. The maintenance hole shall extend through the dosing
chamber cover to final grade and shall
be so constructed as to prevent unauthorized entry.
(3) The dosing chamber shall either include an alternating two-pump system
or have a minimum capacity of 500
gallons or 100 percent of the average design flow, whichever is greater.
(4) A dosing device must employ an alarm device to warn of failure.
(5) Pumps shall be elevated from the bottom of the dosing chamber to protect
the pump from settled solids. The
pump, pump controls, and pump discharge line shall be installed so as to
be accessible for servicing without
entering the dosing chamber.
(6) Electrical installations shall comply with applicable laws and ordinances
including the latest codes, rules and
regulations of public authorities having jurisdiction and with part 13
15.0200, incorporating the National Electrical
Code.
13.2 Dosing device for gravity distribution.
(1) Where a dosing device is employed, a pump or siphon shall deliver the
dose to the soil treatment system for
gravity distribution over the soil treatment area.
(2) For dwellings, the dosing device shall discharge at least 600 gallons
per hour, but no more than 2,700 gallons
per hour.
(3) For other establishments, the dosing device should discharge at a rate
at least ten percent greater than the
water supply flow rate but no faster than the rate at which effluent will
flow out of the distribution device.
(4) If the dosing device is a siphon, a maintenance inspection shall be
made every six months by the owner or the
owner's agent. The siphon shall be maintained in proper operating condition.
(5) If the dosing device is a pump, it shall be cast iron or bronze fitted
and with stainless steel screws or
constructed of other sound, durable, and corrosion-resistant materials.
(6) Where the soil treatment area is at a higher elevation than the pump,
sufficient dynamic head shall be
provided for both the elevation difference and friction loss.
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(7) Where the dosing device is a pump, an alarm device shall be installed to warn of pump failure.
13.3 Dosing devices for pressure distribution.
(1) The dosing device shall be a pump which is cast iron or bronze fitted
and with stainless steel screws or
constructed of sound, durable and corrosion-resistant materials.
(2) The pump discharge capacity shall be based upon the perforation discharges for an average head of
1.0 foot for dwellings and 2.0 feet for other establishments. Perforation
discharge will be determined by the
following formula:
q = 19.65 cd2 square root of h
where: q = discharge in gallons per minute;
c = 0.60 = co-efficient of discharge;
d = perforation diameter in inches; and
h = head in feet.
(3) The pump discharge head shall be at least five feet greater than the
head required to overcome pipe friction
losses and the elevation difference between the pump and the distribution
device.
(4) The quantity of effluent delivered for each pump cycle shall be no
greater than 25 percent of the average
design flow.
(5) A siphon will not be allowed as a dosing device to deliver effluent to a pressure distribution system.
(6) An alarm device shall be installed to warn of pump failure.
SECTION 14. `FINAL TREA TMENT AND DISPOSAL
14.1 Final treatment
and disposal of all sewage tank effluent shall be by discharge into the
soil treatment system. The required
soil treatment
area shall be determined by the daily sewage flow and the measured percolation
rate of the soil.
14.2 Acceptable
methods for estimating sewage flow for dwellings are given in Section 10.2,
Table 1. Methods for measuring
percolation
rate of the soil are given in Section 9.9. The required soil treatment
area size is determined in accordance with Section
14.6, Table
V.
14.3 Distribution shall be made in accordance with Section 12.
14.4 Location of trenches and seepage beds:
(1) On slopes greater than 12 percent, the soil profile shall be carefully
evaluated in the location of the proposed
soil treatment system and downslope to identify the presence of layers
with different permeabilities that may
cause sidehill seepage. In no case shall a trench be located within 15
feet of where such a layer surfaces on the
downslope.
(2) Seepage bed construction shall be limited to areas having natural slopes
of less than 6 percent. Beds shall not
be placed in soils with percolation rates slower than 60 minutes per inch
or in floodplain areas.
26 Washington County Development Code
(3) Soil treatment systems shall be located in accordance with setbacks established in Section 11.9, Table Ill.
(4) Soil treatment areas shall not be placed in areas subject to flooding
or in floodplains delineated by local
ordinances adopted in compliance with the "Statewide Standards and Criteria
for Management of Floodplain
Areas of Minnesota", Chapter 6120, or in areas for which regional flood
information is available from the DNR,
except that in areas where ten year flood information is available from
and/or approved by the DNR, soil
treatment systems may be installed in accordance with the provisions of
Section 15.3.
14.5 Distribution Medium for Trenches and Seepage Beds
(1) Distribution medium shall consist of drainfield rock, gravel-less drainfield pipe or a chambered system.
(A) Drainfield rock shall meet the requirements of Section 2.1(28). There
shall be a layer of at least
twelve (12) but no more than twenty-four (24) inches of drainfield rock
below the distribution pipe.
The drainfield rock shall completely encase the top and sides of the distribution
pipes to a depth
of at least two inches. The total thickness of rock-filled trenches shall
not exceed 30 inches.
(B) Gravel-less drainfield pipe including appurtenances shall be:
1. Of commercially fabricated corrugated pipe completely encased by the
manufacturer in a geotextile wrap specific to this purpose;
2. An eight-inch or ten-inch nominal ID pipe that conforms to the requirements
of
this section and meets the requirements of American Society of Testing
Materials
(ASTM) F667, which is incorporated by reference. Requirements under this
section
also include the following:
a.The pipes must be marked with an alignment stripe visible through the
geotextile
wrap and installed with this stripe at top center, and
(b) The pipes shall contain a row or rows of cleanly cut
three-eighths inch to one half inch diameter holes located in such a
manner to provide storage of solids. Each row shall contain a hole
in every other corrugation valley, staggered such that every
corrugation valley contain one hole.
3. Geotextile wraps specifically designed and tested for use with gravel-less
pipe
and for installation and use in individual sewage treatment systems and
designed
to transmit sewage at a long-term acceptance rate which corresponds to
the sizing
factor as prescribed in Section 14.6 (2);
4. Protected from heat and ultraviolet rays prior to installation.
(C) Chamber media including all piping and appurtenances shall be constructed:
1. Of commercially fabricated materials specific to this purpose;
2. Of materials resistant to sewage tank effluent;
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3. With an open bottom;
4. To support the load of overburden and sidewall soil;
5. With slotted or perforated sides to allow sewage to move laterally into
the soil
and prevent soil penetration into the chamber;
6. No greater than three feet in width; and
7. With vertical outside dimensions less than 30 inches.
14.6 Sizing of Trenches and Seepage Beds
(1) Drainfield Rock Media. Table V gives the required trench bottom assuming
12 inches below the distribution
pipe. The required bottom area may be reduced, for trenches only, by the
following
percentages: 20 percent for 18 inches of drainfield rock below the distribution
pipe; 34 percent for 24 inches.
Unless pressure distribution is used, all seepage bed bottom areas must
be 1.7 times the soil treatment areas
required in Table V. With pressure distribution, the bottom area must be
1.2 times the soil treatment area required
in Table V.
(2) Gravel-less drainfield pipe media. Sizing shall be based on a factor
of 1.2 times the soil treatment area required
in Table V, except that no reduction shall be given as specified in 14.5
(A). An eight-inch ID pipe shall be
equivalent to a two foot wide rock filled trench with six inches of drainfield
rock below the distribution pipe and a
ten-inch ID pipe shall be equivalent to a three foot wide rock filled trench
with six inches of drainfield rock below
the distribution pipe.
(3) Chambered Media. Sizing shall be based on Table V, with the depth of
slatted sidewalls being equivalent to
the corresponding depth of rock below the distribution pipe.
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Effective 10/20/97 Chapter Four Individual Sewage Treatment System Regulation
TABLE V
Percolation Rate (minutes per inch) 0.1-5 6-15 16-30 31-45 46-60
Number Tank Size Gallons Square Feet
of Bedrooms Per Day
2 1000 + 500 300 250 380 500 600 660
3 1000 + 1000 450 380 570 750 900 990
4 1000 + 1000 600 500 760 1000 1200 1320
5 1500 + 1000 750 630 950 1250 1500 1650
6 1500 + 1000 900 750 1140 1500 1800 1980
7 2000 +1000 1050 870 1330 1750 2100 2310
8 2000+ 1000 1200 990 1520 2000 2400 2640
Square Feet Per Gallon .83 1.27 1.67 2 2.20
Percolation Rate in Square Feet Per Gallons Per Day
Minutes Per Inch Soil Texture Gallon Per Day Per Square Foot
(MTI)
Faster than 0.1* Coarse Sand ---- ----
0.1 to 5** Sand 0.83 1.20
0.1 to 5 Fine Sand*** 1.67 0.60
6 to 15 Sandy Loam 1.27 0.79
16 to 30 Loam 1.67 0.60
31 to 45 Silt Loam 2.00 0.50
46 to 60 Clay Loam 2.20 0.45
Slower than 60* Clay --- ---
* Soil too coarse for sewage treatment
** Distribution
of sewage effluent shall be by pressure flow over the treatment area or
by dividing treatment area into a
minimum of four
(4) equal parts connected serially, by means of drop boxes.
*** For soils
having more than 50 percent of very fine sand by weight, plus fine sand
having a particle size range of 0.05
millimeters
(sieve size 270) to 0.25 millimeters (sieve size 60), the required soil
treatment area is 1.67 square feet per gallon of
sewage flow
per day.
**** Soil with too high a percentage of clay for installation of an
in ground standard system.
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14.7 Design and Construction of trenches and seepage beds.
1) The bottom and sides of trenches and beds shall be in original soils
at least three (3) feet above the saturated
soil or bedrock. In no case shall the bottom of the distribution medium
be deeper than 42 inches from the final
grade.
(2) The trenches shall not be less than 18 inches nor more than 36 inches
wide. Any excavation wider than 36
inches shall be considered a bed. No bed may be wider than 25 feet and
parallel beds must be at least 10 feet
apart. The width of the excavation for gravel-less drainfield pipe and
chambered systems shall be installed per
manufacturer's recommendation.
(3) Drainfield rock must be used as the distribution medium in seepage beds.
(4) There shall be a layer of at least 12 but no more than 24 inches of
drainfield rock in the bottom of trenches.
The drainfield rock shall completely encase the top and sides of the distribution
pipes to a depth of at least two
inches. The top of the drainfield rock in trenches, beds and mounds must
be level in all directions.
(5) The bottom and side of the soil treatment system to the top of the
distribution medium shall be excavated in
such a manner as to expose the original soil structure in an unsmeared
and uncompacted condition. Excavation
into the soil treatment area shall be made only when the soil moisture
content is at or less than the plastic limit.
(6) Excavation equipment or other vehicles shall not be driven on the soil
treatment area. Once the trench or
seepage bed is excavated, it shall not be exposed to rainfall prior to
placement of the final backfill.
(7) A vertical inspection pipe at least 1-1/2 inches in diameter shall
be installed and secured in the distribution
medium of every trench or seepage bed. The inspection pipe must be located
at an end opposite from where the
sewage tank effluent enters the medium. The inspection pipe must have three
eighths inch or larger perforations
spaced vertically no more than six inches apart. At least two perforations
must be located in the distribution
medium. No perforations shall be located above the geotextile cover or
wrap. The inspection pipe must extend to
the bottom of the distribution medium and must be capped flush with or
above finished grade.
(8) The top and bottom of the distribution medium shall be level in all directions.
(9) Drainfield rock must be covered by a durable non-woven geotextile cover
specific to this purpose- The cover
must be of sufficient strength to undergo installation without rupture.
In addition, the cover must permit passage
of water without allowing the passage of overlying soil material into drainfield
rock.
(I 0) The minimum depth of cover over the distribution medium shall be
at least six inches. The maximum depth of
cover over the distribution pipes shall be no more than 24 inches.
(11) The trenches or beds shall be backfilled and crowned above finished
grade to allow for settling. The top six
inches of soil shall have the same texture as the adjacent soil.
(12) A vegetative cover shall be established over the soil treatment system.
The soil treatment system shall be
protected until a vegetative cover is established. The vegetative cover
shall not interfere with the hydraulic
performance of the system and shall provide adequate frost and erosion
protection.
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(13) All joints for gravel-less drainfield pipes or chambered systems must
be secured as recommended by the
manufacturer.
(14) Backfilling for gravel-less drainfield pipe and chambered systems shall not crush or damage the medium.
14.8 Dual Field Systems.
(1) Dual field system shall be used only where the percolation rate is
slower than five minutes per inch unless a
liner or pressure distribution system is employed as specified in Section
13.3.
(2) Dual field systems shall be sized, designed and constructed as set
forth above for standard systems except as
follows:
(A) The soil treatment area shall be divided into two or more parts.
(B) Alternating soil treatment areas shall each be connected to a valve box outlet.
(3) A part of the soil treatment area shall be used no more than one year
unless the effluent level indicates that a
longer duration can be used.
14.9 Rapidly permeable Soils.
(1) Soil treatment systems placed in soils with a soil sizing factor of
0.83 gallons per day per square foot must
provide at least one of the following treatment techniques.
A.Distribute the sewage tank effluent by pressure flow over the treatment area as specified in Section 13.3.
B.Divide the total soil treatment area into at least four parts with no
part larger than 25 percent of the area required
by Section 14.6. and the parts constructed for serial application.
14.10 Mounds.
(1) Location of Mounds
(A) Mounds must be constructed on original soils so that there is at least
36 inches of separation
between the drainfield rock layer and limiting soil characteristics as
defined in Section 2.1(76).
(B) There must be at least 18 inches of original soil with a percolation
rate faster than 60 minutes
per inch above the limiting soil characteristics as defined in Section
2.1 (76).
(C) Exceptions are provided to Section 14. 1 0, (A) and (B) for previously
developed sites: a depth
of 12 inches of original soil may be used and a 61 to 120 minutes per inch
percolation rate may be
used.
(D) If original soil conditions do not exist on a site proposed for a mound,
as defined in Section
2.1(47), the site is deemed unsuitable for a mound.
Washington County Development Code 3 1
(E) Setbacks for mounds shall be as established in Table III and shall
be measured from t
absorption area.
(F) Absorption areas shall not be placed in areas subject to flooding as
described in Section
15.3(4).
(G) On slopes of one percent or greater, and where the percolation rate
in the top foot of
original soil is in the 61 to 120 minutes per inch range, mounds shall
not be located where the
ground surface contour lines directly below the long axis of the rock bed
represent a swale or
draw, unless the contour lines have a radius of curvature greater than
I 00 feet. Mounds must
never be located in swales or draws where the radius of curvature of the
contour lines is less
than 50 feet. In no case shall mounds be placed on slopes greater than
12 percent.
(2) Design of Mounds. Drainfield rock must be used as the distribution medium in mounds.
(A) The bottom area of the rock bed shall be calculated by multiplying
the average design flow
by 1.0 square feet per gallon per day.
(B) The width of a single rock bed must not exceed ten feet.
(C) A minimum of 12 inches of clean sand must be placed where the rock bed is located.
(D) The required absorption width is calculated by multiplying the rock
bed width by the
absorption ratio. The absorption ratio shall be determined according to
Table VI, using
percolation rate of the upper 12 inches of soil in the proposed absorption
area.
Table VI
Percolation Rate of
Original Soil Under Sand Absorption Ratio
Layer, Minutes per Inch
Faster than 5 1.00
6 to 15 1.50
16 to 30 2.00
31 to 45 2.40
46 to 60 2.67
61 to 120 5.00
(E) The required absorption width for mounds constructed on slopes from
zero to one percent
shall be centered under the rock bed width. The required absorption width
for mounds
constructed on slopes greater than one percent shall be measured downslope
from the
downslope edge of the rock bed width and measured in the direction of the
original land slope
and perpendicular to the original contours.
(F) The side slopes on the mound must not be steeper than three horizontal
units to one vertical
unit and shall extend beyond the required absorption area, if necessary.
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(G) On slopes of one percent or greater, the upslope edge of the level
drainfield rock must be
placed on the contour.
(H) Whenever mounds are located on slopes greater than one percent, a diversion
must be
constructed immediately upslope from the mound to intercept and direct
runoff.
(I) A maximum of two ten foot wide beds may be installed side by side in
a single mound if the
original soil percolation rate is between five and 60 minutes per inch
to a depth of at least 24
inches below the sand layer. The beds must be separated by at least four
feet of clean sand.
(J) Distribution of effluent over the rock bed must be by level perforated
pipe under pressure. A
pump must be used as specified in Section 13.3.
(K) The rock bed shall completely encase the top and sides of the distribution
pipes to a depth of
at least two inches above the pipe. The rock shall extend nine inches below
the pipe.
(L) A vertical inspection pipe at least 1-1/2 inches in diameter shall
be installed and secured at
each rock bed/sand interface of every mound. The inspection pipe must have
3/8 inch or larger
perforations spaced vertically no more than six inches apart. At least
two perforations must be
located in the rock bed. No perforations shall be located above the permeable
synthetic fabric.
The inspection pipe must extend to the bottom of the rock bed and must
be capped flush with or
above finished grade.
(M) The rock bed must be covered with a durable non-woven geotextile cover
specific to this
purpose. The cover must be of sufficient strength to undergo installation
without rupture. In
addition, the cover must permit passage of water without passage of overlying
soil material into
the drainfield rock.
(N) Sandy to loamy soil material must be placed on the rock bed to a depth
of one foot in the
center of the mound and to a depth of six inches at the sides. When two
rock beds are installed
side by side, the soil material must be 18 inches deep at the center of
the mound and six inches
deep at the sides.
(O) Six inches of top soil must be placed over the entire mound. Topsoil
does not include peat soil
textures.
(3) Surface preparation for Mounds.
A.The supply pipe from the pump to the mound area must be installed before
mound soil surface preparation. The
trench excavated for the supply pipe must be carefully backfilled and compacted
to prevent seepage of effluent.
B.All vegetation in excess of two inches in length and dead organic debris
must be removed from the absorption
area. Trees must be cut nearly flush with the ground and stumps should
not be removed.
C.All surface preparation must take place when the upper 12 inches of soil
has a moisture content of less than
plastic limit and soil conditions allow field testing of soil properties
and these properties are maintained
throughout installation.
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D.The absorption area must be roughened by backhoe teeth or moldboard,
or chisel plowed to a depth of eight
inches. Discing is allowed if the upper eight inches of soil has a texture
of sandy loam or courser. If plowed,
furrows must be thrown uphill and there must not be a dead furrow in the
absorption area. A rubber tired tractor
may be used for plowing or discing. Rototilling or pulverizing the soil
is not allowed. The original soil must not be
excavated or moved more than one foot from its original location during
soil surface preparation.
E.Prior to placement of six inches of clean sand, no vehicle shall be driven
on the absorption area after the surface
preparation is completed. If rainfall occurs on the prepared surface, the
site must be allowed to dry below the
plastic limit and roughened as specified in 14.9(C)4).
(4) Mound Construction.
(A) The clean sand must be placed by using a construction technique that
minimizes compaction.
If the clean sand is driven on for construction, a crawler or track-type
tractor must be used for
mound construction. At least six inches of sand must be kept beneath equipment
to minimize
compaction of the prepared surface.
(B) The sand layer upon which the rock bed is placed must be level in all directions.
(C) The top of the rock bed must be level in all directions.
(D) Construction vehicles must not be allowed on the rock bed until backfill is placed.
(E) A vegetative cover must be established over the entire area of the
mound. The soil treatment
system mound shall be protected until a vegetative cover is established.
The established
vegetative cover shall not interfere with the hydraulic performance of
the system and shall
provide adequate frost and erosion protection.
(F) Shrubs must not be planted on the top of the mound. Shrubs may be placed
at the foot and
side slopes of the mound.
14.11 At-grade systems.
(1) Location of at-grade systems
(A) At-grade systems must be constructed on original soils so that there
is at least 36 inches of
separation between the bottom of the rock bed and saturated soil or bedrock.
(B) Percolation tests shall be conducted in the upper 12 inches of original
soil. At-grade systems
are only allowed if constructed on soils with percolation rates faster
than 61 minutes per inch.
(C) At-grade systems shall not be installed in areas with slopes greater than 12 percent.
(D) Setbacks must be in accordance with Table 111. Setbacks shall be measured
from the edge of
the rock bed.
(2) Design of at-grade system.
34 Washington County Development Code
A.Rock bed absorption width shall be calculated by multiplying the linear
loading rate by the soil sizing factor as
identified in Section 14.6, Table V, using the percolation rate of the
upper 12 inches of soil in the proposed
absorption area. The linear loading rate shall be between two and eight
gpd/ft as determined by the relationship
between vertical and horizontal water movement in the soil. Total rock
bed width for sloping ground shall consist
of the rock bed absorption width plus enough rock on the upslope side to
provide stability.
B.Rock bed length shall be calculated by multiplying the soil sizing factor
by the average design flow and dividing
by the rock bed width.
C.At-grade systems shall be pressurized in accordance with Section 12.3
and Section 13.3. Distribution pipe shall
be installed in the center of the rock bed on slopes less than one percent
and on the upslope edge of the rock
bed absorption width on slopes one percent or greater.
1.Construction of At-Grade systems.
A.Surface preparation for
at-grade systems shall be the same as for mound construction, Section 14.1
0 (C), (D) and (E).
B.Drainfield rock must be
used as the distribution medium in at-grade systems.
C.The upslope edge of an
at-grade system shall be installed along the natural contour.
D.The rock bed shall completely
encase the top and sides of the distribution pipe to a depth of at least
two inches above the pipe.
There shall
be at least nine inches of rock below the distribution pipe.
E.The entire rock bed shall
be covered with a durable non-woven geotextile cover specific to this purpose.
The cover must be of
sufficient strength
to undergo installation without rupture. In addition, the cover must permit
passage of water without allowing
the passage
of overlying soil material into the drainfield rock.
F.One foot of loamy or sandy
cover material shall be installed over the rock bed. Cover shall extend
at least five feet from the ends
of the rock
bed and be sloped to divert surface water. Side slopes shall not be steeper
than four horizontal units to one vertical
unit. The upper
six inches of the loamy soil cover must be topsoil. Topsoil must be of
a quality that provides a good vegetative
cover on the
at-grade system and must exclude peaty material.
G.Three vertical inspection
pipes of at least 1.5 inches in diameter shall be installed and secured
along the downslope portion of
the rock bed.
These pipes shall be located within three feet of the downslope edge of
the rock bed at the middle and one-sixth of
the total rock
bed length and placed as measured from the ends of the rock bed. The inspection
pipes shall have three eighths
inch or larger
perforations spaced vertically no more than six inches apart. No perforations
shall exist above the permeable
synthetic fabric.
The inspection pipes must extend to the rock bed/soil interface and must
be stabilized and capped flush with or
above finish
grade.
H.A vegetative cover must
be established over the entire area of the at-grade system. The soil treatment
at-grade system shall be
protected until
a vegetative cover is established. The established vegetative cover shall
not interfere with the hydraulic
performance
of the system and shall provide adequate frost and erosion protection.
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Chapter Four 4- Individual Sewage Treatment System Regulations Effective 10/20/97
SECTION 15. ALTERNATIVE SYSTEMS
15.1 The intent of this part is to provide standards for the location,
design, installation, use and maintenance of alternative sewage treatment
systems. Alternative systems must meet the requirements below and can
only be used when a standard system cannot be installed or is not the
most suitable treatment. They may be employed
provided:
(1) Reasonable assurance of performance of the system is presented to the permitting authority;
(2) The engineering design of the system is first approved by the permitting authority;
(3) There is no discharge to the ground surface or to surface waters; systems
designed with a ground surface or
surface water discharge are not covered under this Chapter and must obtain
a National Pollutant Discharge
Elimination Permit (NPDES) or state disposal system (SDS) permit from the
Minnesota Pollution Control Agency;
(4) A three-foot minimum separation is provided between the bottom of the
distribution medium and the
saturated soil or bedrock;
(5) Treatment and disposal of wastes is completed in a manner that protects
the public health and general
welfare;
(6) The system complies with all local codes and ordinances and is subject
to periodic inspections by the
permitting authority to assure adherence to specifications;
(7) A mitigative plan is provided to the permitting authority indicating
what will be done if the system fails to
provide treatment and disposal; and
(8) A water meter is provided (located downflow of any outside sillcocks) to verify water use.
15.2 Artificial Drainage.
(1) Where natural drainage does not provide three feet of separation, artificial
drainage may be used to intercept
the high water table provided the water table has a slope of at least two
feet per hundred feet and that drainage
exists upslope of the soil treatment system. There shall be at least 10
feet of undisturbed soil between the
sidewall of the soil treatment unit and the artificial drainage. Monitoring
may be required.
(2) Where required, water table measuring piezometers shall be strategically
placed, capped and extend at least
three feet lower than the bottom of the soil distribution medium. Monitoring
shall occur by measuring water table
depths prior to installation and over time, including during wet periods.
Monitoring records must be maintained.
If the artificial drain includes a dedicated surface discharge, periodic
sampling as approved by the permitting
authority must occur.
(3) In all cases, the greatest practicable vertical separation distance
from the system bottom to saturated soil shall
be provided (with a minimum of three feet).
15.3 Floodplain Areas.
(1) There shall be no pipe or other installed opening between the distribution medium and the soil surface.
36 Washington County Development Code
(2) Trench systems shall be located on the highest feasible area of the
lot and shall have location preference over
all other improvements except the water supply well. The bottom of the
distribution medium shall be at least as
high as the elevation of the ten-year flood. The sewage tank may be located
so as to provide gravity flow to the
trenches.
(3) If a dosing chamber is used to move effluent from the sewage tank to
the trenches, provisions shall be made
to prevent the pump from operating when inundated with flood waters.
(4) When it is necessary to raise the elevation of the soil treatment area,
a mound system as specified in Section
14. 1 0 may be used with the following additional requirement: In no case
shall the sand fill for the mound exceed
48 inches below the rock bed. The elevation of the mound shall be such
that the elevation of the bottom of the
rock bed shall be at least one-half foot above the ten-year flood elevation.
Inspection pipes shall not be installed
unless the top of the mound is above the elevation of the regional flood.
(5) When the top of a sewage tank is inundated, the dwelling must cease
discharging sewage into it. This may be
accomplished by either temporarily evacuating the structure until the system
again becomes functional, or by
diverting the sewage into a holding tank sized and installed according
to Section 15.8.
(6) The building sewer shall be designed to prevent backflow of liquid
into the building when the system is
inundated. If a holding tank is used, the building sewer shall be designed
to permit rapid diversion of sewage into
the holding tank when the system is inundated.
(7) Whenever the water level has reached a stage above the top of a sewage
tank, the tank shall be pumped to
remove all solids and liquids after the flood has receded before use of
the system is resumed.
15.4 Greywater
Systems. A toilet waste treatment device shall be used in conjunction with
a greywater system. In all cases, only
toilet wastes
shall be discharged to toilet waste treatment devices. Greywater or garbage
shall not be discharged to the device
except as specifically
recommended by a manufacturer.
(1) Plumbing. The drainage system in new dwellings or other establishments
shall be based on a pipe diameter of
two inches to prevent installation of a water flush toilet. There shall
be no openings or connections to the
drainage system, including floor drains, larger than two inches in diameter.
For repair or replacement of an
existing system, the existing drainage system may be used. Toilets or urinals
of any kind shall not be connected
to the drainage system. Toilet waste or garbage shall not be discharged
to the drainage system. Garbage grinders
shall not be connected to the drainage system.
(2) Building Sewer. The building sewer shall meet all requirements of Section
7.3 except that the building sewer
for a greywater system shall be no greater than two inches in diameter.
(3) Sewage Tank. Greywater septic tanks shall meet all requirements of
Section I 1. 1. The sewage tank for a
greywater system shall be a single tank in accordance with the first tank
shown in Section 1 1.7, Table 11.
(4) The soil treatment area shall be 60 percent of the amount calculated in Section 14.6, Table V.
(5) Distribution and Dosing. Distribution and dosing of greywater shall
meet all requirements of Sections 12 and
13.
(6) Final Treatment and Disposal. A standard greywater system shall meet all requirements of Section 14.
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15.5 Privies.
(1) Privies shall only be considered when there is no water supplied to the dwelling.
(2) Pit privies shall not be installed where the bottom of the pit is less
than three feet above the saturated soil or
bedrock. A vault privy shall be used in areas not meeting the three foot
separation. The vault of a vault privy
shall be constructed in the same manner as a sewage tank.
(3) Privies shall be set back from surface waters, buildings, property
lines, and water supply wells as prescribed in
Table III.
(4) Pits or vaults shall be of sufficient capacity for the dwelling they
serve, but shall have at least 50 cubic feet of
capacity. The sides of the pit shall be curbed to prevent cave-in. The
privy shall be constructed so as to be easily
maintained and it shall be insect proof. The door and seat shall be self-closing.
All exterior openings, including
vent openings, shall be screened.
(5) Privies shall be adequately vented.
(6) When the privy is filled to within one foot of the top of the pit, the solids shall be removed.
(7) Abandoned pits shall have the solids removed and be filled with clean
earth and slightly mounded to allow for
settling. Removed solids shall be disposed of in accordance with Section
17.8.
15.6 Other Toilet Waste Treatment Devices.
(1) Other waste toilet treatment devices may be used where reasonable assurance of performance is provided.
(2) All devices shall be vented.
(3) All electrical, gas, and water connections shall conform to all local ordinances and codes.
(4) Operation and maintenance shall follow the manufacturer's recommendations.
15.7 Collector Systems.
(1) Where site and soil conditions do not allow for final treatment and
disposal on an individual lot, a soil
treatment system located on another lot or lots may be employed.
(2) Except for systems designed for 1,200 gallons per day or less, Collector
systems shall be designed by a
registered professional engineer, licensed in the State of Minnesota, and
certified by the MPCA as competent in
the field of on-site system design.
(3) Hydrogeologic Study: due to the effect large flows have on groundwater
quality and groundwater mounding,
a hydrologist shall determine site suitability based on the following.
A hydrogeologic study may not be required
for a collector system designed for 1,200 gallons per day or less.
A.Identification of the depth to the static groundwater level and any perched
water or areas likely to be seasonally
saturated;
B.Identification of the depth to bedrock;
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(C) Identification of the proposed depth of the distribution medium;
(D) Determination of the direction of groundwater flow, both horizontally and vertically;
(E) Determination of the background water quality at the location;
(F) Estimation of the height of groundwater mounding from the proposed
system to confirm
adequate vertical separation;
(G) Determination whether drinking water standards can be met at the property boundary;
(H) Estimation of the impact of water quality on existing or future downstream
wells. Depending
on this estimate, piezometer and/or monitoring wells may be required.
(4) Application to the department shall be accompanied by the hydrogeologic
study and engineering drawings
and specifications and shall demonstrate compliance with all applicable
local ordinances, the plumbing code and
issues related to joint ownership of land, joint system maintenance responsibilities,
homeowners associations,
easements, covenants, and such other items as may apply to the specific
proposal.
(5) Design.
(A) Sewer systems shall be designed based on the sum of the areas required
for each dwelling of
other establishment being served. Flows shall be increased to allow for
200 gallons of infiltration
per inch of pipe diameter per mile per day.
(B) The system shall be designed with each dwelling or other establishment
having a sewage tank
or with a common sewage tank. In the case of a common tank, the capacity
of the tank shall be the
sum of the tanks sized according to Section II. 7.
(C) The sum of a common soil treatment system shall be based on the sum
of the areas required
for each dwelling unit or establishment being served.
(D) The sewer for systems with common sewage tanks shall be constructed
to give mean
velocities, when flowing full, or not less than two feet per second. The
sewer for systems with
individual sewage tanks shall be so constructed and designed to hydraulically
conduct the flow
for which they were designed. In no case shall a gravity sewer be less
than four inches in
diameter. The diameter and grade line should be based on a flow equal to
50 percent of the
average design flow occurring in a one-hour period.
(E) Infiltration or exfiltration shall not exceed 200 gallons per inch of pipe diameter per mile per day.
(F) Cleanouts, brought flush with or above finished grade, shall be provided
wherever a common
sewer joins an individual building sewer or piping from an individual sewer
tank, or every 100 feet,
whichever is less, unless maintenance hole access if provided.
(G) There shall be no physical connection between sewers and water supply
systems. Sewers
shall be set back from water supply systems and piping as required for
building sewers. Where it
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Chapter Four Individual Sewage Treatment System Regulations Effective 10/20/97
is not possible to obtain proper separation distances, the sewer connections
shall be watertight
and pressure tested.
(H) Pipes and pipe joints shall be watertight.
(1) Dosing chambers shall meet all requirements in Section 13. 1.
(J) Pumps and dosing chambers shall be sized to handle 50 percent of the
average design flow in a
one-hour period. Common pump tanks shall have a pumpout capacity of ten
percent of average
design flow and two alternating pumps.
(K) A separate alarm system for each pump shall be provided for all pumping
stations to warn of
pump failure, overflow, or other malfunction.
(L) For systems with individual septic tanks, a stilling tank of at least
1,500 gallons liquid capacity
or ten percent of the average design flow, whichever is greater, should
be provided before the soil
treatment system.
(M) Pump stations shall have maintenance holes flush with or above finished
grade for cleaning
and maintenance. Maintenance covers shall be secured so as to prevent unauthorized
entry.
(N) All persons using a common individual sewage system shall assure, by
contract with
maintenance personnel or other equivalent means, that the system will be
maintained throughout
its useful life. The system so maintained includes common soil treatment
systems, common
sewage tanks, common pumps, common pump stations, common sewers, and all
individual tanks
connected to the common system.
15.8 Holding Tanks.
(1) Sewage holding tanks may be considered for installation on previously
developed sites, as a temporary
method for periods of up to one (1) year, during which time measures are
taken to provide municipal sewer
service or the installation of an approved system as provided in this Chapter.
Holding tanks may be considered
on a permanent basis for nonresidential, low water use establishments generating
less than 150 gallons per day
of waste, subject to the approval of the department. Holding tanks may
also be considered for floor drains for
vehicle parking areas and existing facilities potentially generating a
hazardous waste.
(2) A holding tank shall be constructed of the same materials and by the
same procedures as specified in this
Chapter for sewage tanks, Section I 1.
3) A cleanout pipe of at least six inches diameter shall extend to the
ground surface and be provided with seals to
prevent odor and to exclude insects and vermin. A maintenance hole of at
least 20 inches least dimension shall
extend through the cover to a point no less than six inches below the finished
grade. If the maintenance hole is
covered with less than 6 inches of soil, the cover must be secured to prevent
unauthorized access.
4) When installed in areas of high ground water within six feet of the
ground surface, holding tanks shall be
installed entirely above the groundwater level or shall be installed according
to an engineers design to prevent
flotation.
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Effective 10/20/97 Chapter Four- Individual Sewage Treatment Regulations
(5) For a dwelling, the minimum size shall be 1,200 gallons or four hundred
times the number of bedrooms,
whichever is greater. For other establishments, the minimum capacity shall
be based on measured or estimated
flow rates. Minimum capacity shall be equal to at least eight (8) times
the average design flow.
(6) Holding tanks shall be located as specified for sewage tanks in Table
III; in an area readily accessible to the
pump truck under all weather conditions; and where accidental spillage
during pumping will not create a
nuisance.
(7) A contract for disposal and treatment of the septage shall be maintained
by the owner with a pumper,
municipality, or firm established for that purpose.
(8) Holding tanks shall be monitored to minimize the chance of accidental
sewage overflows by installation of an
alarm or warning device which will activate a signal when the tank reaches
seventy five (75) percent of its
capacity.
(9) The permitting authority shall be provided right of access to perform
periodic maintenance and operational
inspections of the system.
SECTION 16. EXPERIMENTAL SYSTEMS
16.1 Systems utilizing innovative techniques or methods may be considered for new or existing development under the following conditions:
(1) The permit for experimental systems shall be recorded in the Washington
County Recorder/Registrar of Titles
Office setting forth the fact that this is an experimental system, including
the details of the performance
monitoring, mitigation plan, and mitigation cost agreement.
(2) Reasonable assurance of performance of the system is presented to the permitting authority.
(3) The system being proposed is supported by engineering data and approved by the permitting authority.
(4) The system is in compliance with Minnesota Pollution Control Agency Rules.
(5) Experimental systems will not be allowed in areas where a new system
or modifications to a new system are
not feasible if failure occurs; adequate area for long-term sewage treatment
by suitable soils, as required for
standard systems, is defined and reserved on the site. For the purposes
of this section, long-term sewage
treatment is considered space for two standard on-site soil treatment systems.
(6) Performance monitoring of the system, including but not limited to,
water use metering, effluent quality and
system inspection and maintenance as defined by the permitting authority
are provided.
(7) A mitigative plan must be provided to deal with possible system failure.
Such plan must include the planned
corrections and/or replacement, an agreement among the parties clarifying
who will pay the cost of mitigation,
and a statement of indemnification holding the County harmless from any
damages arising out of a system
failure.
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Regulations
17.10 LicensedpumpingcontractorsshalimaintainaccuraterecordsofpumpingactivityinWashingtonCountyand
shall report such data annually to
the department on forms provided.
SECTION 8. SYSTEM ABANDONMENT
18.1 Tank abandonment procedures for sewage tanks, cesspools, leaching
pits, dry wells, seepage pits, privies, and distribution devices are as
follows: all solids and liquids shall be removed and disposed of in
accordance with 17.8, and abandoned chambers shall be removed or filled
with soil material.
18.2 Access for future discharge to the system shall be permanently denied.
18.3 If soil treatment systems are removed, contaminated materials shall
be properly handled to prevent human contact and shall be disposed
of in a manner assuring that public health and the environment are
protected.
SECTION 19. ENFORCEMENT
19.1 It is hereby declared unlawful for any person, firm or corporation
to violate any term or provision of this Chapter. Violation thereof shall
be
a misdemeanor. Each day that a violation is allowed to continue shall
constitute a separate offense.
19.2 In the event of a violation or threatened violation of this Chapter,
the department, in addition to other remedies, may request appropriate
actions or proceedings to prevent, restrain, correct or abate such
violations or threatened violations. In addition, written notice in the
form of a
license complaint may be made to the Commissioner of the Minnesota
Pollution Control Agency.
19.3 In cases where a public health nuisance has been determined to
exist, the Department may institute enforcement action under the Local
Public Health Act, Minnesota Statutes Chapter 145A.
SECTION 20. SEPARABILITY
20.1 It is hereby declared to be the intent that the several provisions of this regulation are separable in accordance with the following:
(1) If any court of competent jurisdiction shall adjudge any provision
of this regulation to be invalid, such
judgement shall not affect any other provisions of this regulation not
specifically included in said judgement.
(2) If any court of competent jurisdiction shall adjudge invalid the application
of any provision of this regulation
to a particular property, building or structure, such judgement shall not
affect the application of said provision to
any other property, building or structure not specifically included in
said judgement.
SECTION 21. EFFECTIVE DATE
21.1 The regulations contained in this chapter shall become effective from and after October 20, 1997, after their publication according to law.
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