Or. Admin. Code § 340-071-0290 - Conventional Sand Filter Systems
(1)
Criteria for approval. Construction of conventional sand filter systems may be
approved for single family dwellings or commercial facilities.
(2) Sites approved for sand filter systems.
Sand filters may be permitted on any site meeting requirements for standard
onsite systems in OAR
340-071-0220 or for pressurized
distribution systems in OAR
340-071-0275 if site conditions
in this section can be met.
(a) Separation
from the temporary groundwater table must satisfy the requirements in this
subsection.
(A) The high level attained by a
temporary groundwater table is:
(i) Twelve
inches or more below ground surface where:
(I) The ground slope does not exceed 12
percent;
(II) Equal distribution
methods are achieved by gravity or using either a hydrosplitter or pressurized
distribution method; and
(ii) Eighteen inches or more below ground
surface where equal distribution methods are achieved by gravity or through the
use of a hydrosplitter or pressurized distribution.
(iii) Twenty-four inches or more below ground
surface where serial distribution methods are used.
(B) Methods used in OAR
340-071-0315 for tile dewatering
systems may be used to achieve separation distances from temporary
groundwater.
(C) Absorption
trenches may not be installed deeper than the highest level of the temporary
water table. The minimum backfill depth within the absorption trenches is 6
inches for trenches using equal distribution methods and 12 inches for trenches
using serial distribution.
(b) Separation from the permanent groundwater
table must satisfy the requirements in this subsection.
(A) The highest level attained by a permanent
water table does not exceed the minimum separation distance from the bottom of
the absorption area as follows:
(i) For
gravel and Soil Group A: sand, loamy sand, sandy loam - 24 inches;
(ii) For Soil Group B: loam, silt loam, sandy
clay loam, clay loam - 18 inches;
(iii) For Soil Group C: silty clay loam,
silty clay, clay, sandy clay - 12 inches.
(B) Shallow absorption trenches placed not
less than 12 inches into the original soil profile may be used with a capping
fill to achieve separation distances from permanent groundwater. The fill must
be placed under OAR 340-071-0265(2)
and 340-071-0265(3)(a) through
(c).
(C) Methods used in OAR
340-071-0315 for tile dewatering
systems may be used to achieve separation distances from permanent
groundwater.
(c) Sand
filter systems installed in soils with rapid or very rapid permeability as
defined in OAR 340-071-0100 (148)(a) and (b) in
areas with permanent water tables may not discharge more than 450 gallons of
effluent per 1/2 acre per day except where:
(A) Groundwater is degraded and designated as
a nondevelopable resource by the Oregon Water Resources Department; or
(B) A detailed hydrogeological
study determines loading rates exceeding 450 gallons per 1/2 acre per day would
not increase nitrate-nitrogen concentration in the groundwater beneath the site
or any downgradient location to above 5 mg/L.
(d) Sand filter systems may be installed in
soils, fractured bedrock, or saprolite diggable with a backhoe if, in the
judgment of the agent, the soils, fractured bedrock, or saprolite is permeable
to the extent that effluent will absorb adequately and not hinder the
performance of the filter or absorption field. The agent may require that an
absorption test be conducted to determine the permeability of the bedrock or
saprolite. Test methods must be acceptable to DEQ.
(A) Where ground slope does not exceed 12
percent, a capping fill, 12-inch deep trench may be installed under OAR
340-071-0265, except that when
installed in fractured bedrock or saprolite, the cap material must be Soil
Group B.
(B) Where ground slope
exceeds 12 percent but is not greater than 30 percent, a standard 24-inch deep
trench may be installed.
(e) A sand filter absorption facility may be
installed on slopes of 30 percent or less if other conditions in this section
are satisfied.
(f) An absorption
facility following a sand filter may be installed on slopes above 30 percent
and up to 45 percent where:
(A) Projected
daily flow does not exceed 450 gallons and the installation is sized under sand
filter absorption area criteria;
(B) The soil is diggable with a backhoe to a
depth of at least 36 inches and 12 inches below the bottom of the trench;
and
(C) The temporary water table
is at least 30 inches below the ground surface and 6 inches below the bottom of
the trench.
(g) Setbacks
in Table 1 can be met, except the minimum separation distance between the
sewage absorption area and surface waters must be at least 50 feet. [NOTE: All
tables are found in OAR
340-071-0800.]
(3) Absorption trenches. Absorption trenches
for sand filter absorption facilities must satisfy the requirements in this
section.
(a) The minimum length of a standard
absorption trench per 150 gallons of projected daily sewage flow is:
(A) For gravel and Soil Group A: sand, loamy
sand, sandy loam -- 35 linear feet;
(B) For Soil Group B: loam, silt loam, sandy
clay loam, clay loam -- 45 linear feet;
(C) For Soil Group C: silty clay loam, silty
clay, sandy clay, clay -- 50 linear feet;
(D) For permeable saprolite or fractured
bedrock -- 50 linear feet;
(E) For
high shrink-swell clays (Vertisols) -- 75 linear feet.
(b) On lots created before January 1, 1974,
which do not have sufficient, suitable area for an absorption facility sized
under this section, the agent may allow seepage trenches if:
(A) The design criteria and limitations in
OAR 340-071-0280(2)
are met;
(B) The soil is not a high
shrink-swell clay;
(C) The
temporary water table is at least 30 inches below the ground surface;
and
(D) All other requirements of
this rule are met.
(c)
Trench designs in Vertisols.
(A) Absorption
trenches in Vertisols must contain 24 inches of drain media and 24 inches of
soil backfill in areas with an annual rainfall of 25 inches or less, minimum
slopes of 5 percent, and a temporary water table at least 48 inches below the
ground surface.
(B) Seepage
trenches in Vertisols containing less than 24 inches of drain media may be used
if designed under the criteria and limitations in OAR
340-071-0280 in areas with an
annual rainfall of 25 inches or less, minimum slopes of 5 percent, and a
temporary water table at least 48 inches below the ground
surface.
(4)
Bottomless sand filter. Sites may use a bottomless sand filter if the site
meets the criteria in this section and section (3) of this rule.
(a) Saprolite; fractured bedrock; gravel; or
soil textures of sand, loamy sand, or sandy loam occur in a continuous section
at least 2 feet thick in contact with and below the bottom of the sand
filter.
(b) The agent determines
the saprolite, fractured bedrock, gravel, or soil is permeable over the basal
area to the extent that effluent will absorb adequately and not hinder the
performance of the filter. The agent may require that an absorption test be
conducted to determine the permeability of the basal area. Test methods must be
acceptable to DEQ.
(c) The
application rate is based on the design sewage flow in OAR
340-071-0220(2)(a)
and the basal area of the sand.
(d) The water table is at least 24 inches
below the ground surface throughout the year, and a minimum 24-inch separation
is maintained between a water table and the bottom of the sand
filter.
(5) Materials and
construction.
(a) All materials used in sand
filter system construction must be structurally sound, durable, and capable of
withstanding normal installation and operation stresses. Component parts
subject to malfunction or excessive wear must be readily accessible for repair
and replacement.
(b) All filter
containers must be placed over a stable, level base.
(c) In a gravity-operated distribution
system, the invert elevation of the outlet end of the underdrain pipe must be
at or above the final settled ground elevation of the highest absorption
trench.
(d) Piping and fittings for
the sand filter distribution system must comply with the requirements for
pressure distribution systems in OAR
340-071-0275.
(e) Septic tanks, dosing tanks, and other
components must comply with the requirements in OAR
340-071-0220 unless this rule
specifies different requirements.
(f) The design and construction requirements
in OAR 340-071-0295 must be met. A
bottomless sand filter unit does not require a watertight floor, but does
require watertight walls unless otherwise authorized by the agent.
(g) A bottomless sand filter unit does not
require a minimum 10-foot separation between the original and replacement
unit.
(6) Gravelless
absorption method.
(a) Absorption trenches
following a sand filter may be constructed without using drain media if they
meet the criteria in this section.
(A)
Absorption trenches must be 12 inches wide by 10 inches deep and incorporate
pressurized distribution and a chamber constructed of half sections of 12-inch
diameter plastic irrigation pipes (PIP). DEQ may consider deviations to the
depth requirement in this rule for alternative drainfield products.
(B) Trenches must be level end to end and
across their width.
(C) The agent
may allow trenches on minimum 3-foot centers maintaining at least 2 feet of
undisturbed earth between parallel trench sidewalls.
(D) Pressurized distribution piping must meet
the requirements of OAR
340-071-0275(4)(b),
except that orifice shields are not required.
(E) Distribution piping must be perforated
with 1/8 inch diameter orifices on maximum 2-foot centers at the 12 o'clock
position. The hydraulic design must provide at least a 2-foot residual head at
the distal orifice.
(F) The
chambers must have an adequate footing to support the soil cover and all normal
activity and at a minimum must be constructed of 12-inch PIP rated at 43 pounds
per square inch and meeting the appendix standards of ASTM D-2241. Each line
must be equipped with a minimum 6-inch diameter inspection
port.
(b) Except as noted
in subsection (a) of this section, all construction and siting criteria for
conventional sand filter systems in this division must be met. This includes
but is not limited to the absorption field sizing for sand filter systems in
OAR 340-071-0290(3)
and area sizing for an initial and replacement absorption facility meeting
standard trench separations in OAR
340-071-0220(7)(a)(E).
Plans must verify that a system can be installed on the parcel that will meet
the requirements in OAR
340-071-0290(3)
and 340-071-0220(7)(a)(E)
and all other applicable rules before a gravelless absorption method is
approved.
(c) A gravelless
absorption method may be used wherever this division allows a standard or
alternative-type absorption trench for sand filter systems, except in
Vertisols.
(d) A method to prevent
burrowing animals from entering the chamber must be provided in areas where
this is likely to occur.
(7) Operation and maintenance. Owners of
conventional and other sand filter systems must ensure the sand filter and all
other components of the system are continuously operated and timely maintained
as the Certificate of Satisfactory Completion and this rule require.
(a) Owners of conventional and other sand
filter systems must comply with the operation and maintenance requirements in
this section. The owner of a sand filter system must inspect the septic tank
and other components of the system at least annually for sludge accumulation,
pump calibration, and cleaning the laterals. Tanks must be pumped when there is
an accumulation of floating scum less than 3 inches above the bottom of the
outlet tee fitting, holes or ports, or an accumulation of sludge less than 6
inches below the bottom of the outlet tee fitting, holes or ports. Pump
calibration, cleaning of the laterals, and other maintenance must be completed
as necessary.
(b) Service
Contracts. The owner of a residential sand filter system and all sand filter
systems serving commercial facilities must maintain a contract, under OAR
340-071-0130(23),
with a maintenance provider to serve and maintain the onsite system. A service
contract must be entered before the system is installed and must be maintained
until the system is decommissioned.
[NOTE: All tables are found in OAR 340-071-0800.]
Notes
Tables referenced are available from the agency.
Statutory/Other Authority: ORS 454.625 & 468.020
Statutes/Other Implemented: ORS 454.615, 454.775 & 454.780
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