ASTM D5921-96(2003)e1
(Practice)Standard Practice for Subsurface Site Characterization of Test Pits for On-Site Septic Systems
Standard Practice for Subsurface Site Characterization of Test Pits for On-Site Septic Systems
SIGNIFICANCE AND USE
This practice should be used as part of the evaluation of a site for its potential to support an on-site septic system in conjunction with Practice D 5879 and Practice D 5925.
This practice should be used after applicable steps in Practice D 5879 have been performed to document and identify potentially suitable field areas.
This practice should be used by those who are involved with the evaluation of properties for the use of on-site septic systems. They may be required to be licensed, certified, meet minimum educational requirements by the area governing agencies, or all of these.
This practice requires exposing the soil to an appropriate depth (typically 1.5 to 1.8 m, or greater as site conditions or project objectives require) for examining the soil morphologic characteristics related to the performance of on-site septic systems.
SCOPE
1.1 This practice covers procedures for the characterization of subsurface soil conditions at a site as part of the process for evaluating suitability for an on-site septic system. This practice provides a method for determining the usable unsaturated soil depth for septic tank effluent to infiltrate for treatment and disposal.
1.2 This practice describes a procedure for classifying soil by field observable characteristics within the United States Department of Agriculture, Soil Conservation Service (SCS) classification system. The SCS classification system is defined in Refs (1-4), not in this practice. This practice is based on visual examination and manual tests that can be performed in the field. This practice is intended to provide information about soil characteristics in terms that are in common use by soil scientists, public health sanitarians, geologists, and engineers currently involved in the evaluation of soil conditions for septic systems.
1.3 This procedure can be augmented by Test Method D 422, when verification or comparison of field techniques is required. Other standard test methods that may be used to augment this practice include: Test Methods D 2325, D 3152, D 5093, D 3385, and D 2434.
1.4 This practice is not intended to replace Practice D 2488 which can be used in conjunction with this practice if construction engineering interpretations of soil properties are required.
1.5 This practice should be used in conjunction with D5879 to determine a recommended field area for an on-site septic system. Where applicable regulations define loading rates-based soil characteristics, this practice, in conjunction with D5925, can be used to determine septic tank effluent application rates to the soil.
1.6 This practice should be used to complement standard practices developed at state and local levels to characterize soil for on-site septic systems.
1.7 The values stated in SI units are to be regarded as the standard.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.9 This practice offers a set of instructions for performing one or more specific operations. This document cannot replace education or experience and should be used in conjunction with professional judgment. Nat all aspects of this practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.
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Designation: D5921 – 96 (Reappproved 2003)
Standard Practice for
Subsurface Site Characterization of Test Pits for On-Site
Septic Systems
This standard is issued under the fixed designation D5921; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—References 1 and 4 were updated editorially in November 2003.
INTRODUCTION
Many State and local jurisdictions have requirements for evaluating sites for approval of on-site
septic systems. This practice provides a method to describe and interpret subsurface characteristics to
evaluate sites for septic systems.All characteristics used in this practice influence the ability of a site
to provide treatment and disposal of septic tank effluent. However, this practice is not meant to be an
inflexible description of investigation requirements. State and local jurisdictions may require fewer or
greater numbers of subsurface features to evaluate a site.
This practice primarily follows the U.S. Department of Agriculture, Soil Conservation Service
(SCS) soil classification system, which encompasses a systematic framework for soil morphological
characterization. The SCS classification the most prevalent system in use for on-site septic systems.
This practice can be complemented by application of other soil description techniques as appropriate,
such as the Unified Soil Classification System (D2485).
1. Scope 1.3 ThisprocedurecanbeaugmentedbyTestMethodD422,
whenverificationorcomparisonoffieldtechniquesisrequired.
1.1 This practice covers procedures for the characterization
Other standard test methods that may be used to augment this
of subsurface soil conditions at a site as part of the process for
practice include:Test Methods D2325, D3152, D5093, D3385,
evaluatingsuitabilityforanon-sitesepticsystem.Thispractice
and D2434.
provides a method for determining the usable unsaturated soil
1.4 This practice is not intended to replace Practice D2488
depth for septic tank effluent to infiltrate for treatment and
whichcanbeusedinconjunctionwiththispracticeifconstruc-
disposal.
tion engineering interpretations of soil properties are required.
1.2 This practice describes a procedure for classifying soil
1.5 This practice should be used in conjunction with D5879
by field observable characteristics within the United States
to determine a recommended field area for an on-site septic
Department of Agriculture, Soil Conservation Service (SCS)
system. Where applicable regulations define loading rates-
classificationsystem. TheSCSclassificationsystemisdefined
based soil characteristics, this practice, in conjunction with
in Refs (1–4), not in this practice. This practice is based on
D5925, can be used to determine septic tank effluent applica-
visual examination and manual tests that can be performed in
tion rates to the soil.
thefield.Thispracticeisintendedtoprovideinformationabout
1.6 This practice should be used to complement standard
soil characteristics in terms that are in common use by soil
practices developed at state and local levels to characterize soil
scientists, public health sanitarians, geologists, and engineers
for on-site septic systems.
currentlyinvolvedintheevaluationofsoilconditionsforseptic
1.7 The values stated in SI units are to be regarded as the
systems.
standard.
1.8 This standard does not purport to address all of the
This practice is under the jurisdiction of ASTM Committee D18 on Soil and
safety concerns, if any, associated with its use. It is the
Rock and is the direct responsibility of Subcommittee D18.01 on Surface and
responsibility of the user of this standard to establish appro-
Subsurface Characterization.
priate safety and health practices and determine the applica-
Current edition approved Nov. 1, 2003. Published November 1996. DOI:
10.1520/D5921-96R03E01.
bility of regulatory limitations prior to use.
In 1995, the name of the SCS was changed to Natural Resource Conservation
1.9 This practice offers a set of instructions for performing
Service.ThisguideusesSCSratherthanNRCSbecausereferenceddocumentswere
one or more specific operations. This document cannot replace
published before the name change.
The boldface numbers given in parentheses refer to a list of references at the education or experience and should be used in conjunction
end of the text.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D5921 – 96 (Reappproved 2003)
withprofessionaljudgment.Natallaspectsofthispracticemay most suitable as a septic tank soil absorption field or filter bed
be applicable in all circumstances. This ASTM standard is not based on surface and subsurface observations.
intended to represent or replace the standard of care by which 3.1.6 unsaturated—soil water condition at which the void
the adequacy of a given professional service must be judged, spaces that are able to be filled are less than full.
nor should this document be applied without consideration of 3.1.7 vertical separation—the depth of unsaturated, native,
a project’s many unique aspects. The word “Standard” in the undisturbedsoilbetweenthebottomofthedisposalcomponent
title of this document means only that the document has been of the septic system and the limiting depth.
approved through the ASTM consensus process.
4. Summary of Practice
2. Referenced Documents 4.1 This practice describes a field technique using visual
examination and simple manual tests for characterizing and
2.1 ASTM Standards:
evaluating soils and identifying any limiting depth.
D422 Test Method for Particle-Size Analysis of Soils
D653 Terminology Relating to Soil, Rock, and Contained
5. Significance and Use
Fluids
5.1 This practice should be used as part of the evaluation of
D2325 Test Method for Capillary-Moisture Relationships
a site for its potential to support an on-site septic system in
for Coarse- and Medium-Textured Soils by Porous-Plate
5 conjunction with Practice D5879 and Practice D5925.
Apparatus
5.2 This practice should be used after applicable steps in
D2434 Test Method for Permeability of Granular Soils
Practice D5879 have been performed to document and identify
(Constant Head)
potentially suitable field areas.
D2488 Practice for Description and Identification of Soils
5.3 This practice should be used by those who are involved
(Visual-Manual Procedure)
with the evaluation of properties for the use of on-site septic
D3152 Test Method for Capillary-Moisture Relationships
5 systems. They may be required to be licensed, certified, meet
forFine-TexturedSoilsbyPressure-MembraneApparatus
minimum educational requirements by the area governing
D3385 Test Method for Infiltration Rate of Soils in Field
agencies, or all of these.
Using Double-Ring Infiltrometer
5.4 Thispracticerequiresexposingthesoiltoanappropriate
D5093 Test Method for Field Measurement of Infiltration
depth (typically 1.5 to 1.8 m, or greater as site conditions or
Rate Using Double-Ring Infiltrometer with Sealed-Inner
project objectives require) for examining the soil morphologic
Ring
characteristics related to the performance of on-site septic
D5879 Practice for Surface Site Characterization for On-
systems.
Site Septic Systems
D5925 Practice for Preliminary Sizing and Delineation of
6. Limitations
Soil Absorption Field Areas for On-Site Septic Systems
6.1 The water content of the soil will affect its properties.
Thesoilshouldbeevaluatedinthemoistconditionbecausethe
3. Terminology
normaloperatingstateofthesepticsystemisamoistcondition.
3.1 Definitions:
If the soil is dry, moisten it.
3.1.1 limiting depth—for the purpose of determining suit-
6.2 This practice is not applicable to frozen soil.
abilityforon-sitesepticsystems,thedepthatwhichtheflowof
6.3 Optimum lighting conditions for determining soil color
water, air, or the downward growth of plant roots is restricted.
are full sunlight from mid-morning to mid-afternoon. Less
3.1.2 mottle—spots or blotches of different colors or shades
favorable lighting conditions exist when sun is low or skies are
of color interspersed with the dominant color (5).InSCS (3)
cloudy or smoky. If artificial light is used, it should be as near
practice mottles associated with wetness in the soil are called
the light of mid-day as possible.
redox concentrations or redox depletions.
3.1.3 pocket penetrometer—a hand operated calibrated
7. Apparatus
spring instrument used to measure resistance of the soil to
7.1 Tools typically used are a soil knife or a flat blade screw
compressive force.
driver, tape measure, pencil and paper, Munsell soil color
3.1.4 potentially suitable field area—the portions of a site
charts (6), water bottle, wash rag, and a sack to carry samples
that remain after observing limiting surface features such as
if required. A pocket penetrometer may also be useful. When
excessive slope, unsuitable landscape position, proximity to
the presence of carbonate may be significant in soils, dilute
water supplies, and applicable setbacks have been excluded.
hydrochloric acid (10 % HCl) should be used.
3.1.5 recommended field area—the portion of the poten-
7.2 A backhoe will facilitate excavation of the test pits for
tially suitable field area at a site that has been determined to be
examination. However, if the site is inaccessible or funds are
limited, one may excavate by hand with a shovel. Depending
on site conditions, power driven or hand held soil augers may
also be suitable. Tube samplers allow description of soil
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
morphologic features providing the size of the feature does not
Standards volume information, refer to the standard’s Document Summary page on
exceed the diameter of the core.Augers generally destroy such
the ASTM website.
morphologic features as soil structure and porosity.The advan-
Withdrawn. The last approved version of this historical standard is referenced
on www.astm.org. tage of augers and tube samplers is that they are generally
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D5921 – 96 (Reappproved 2003)
faster and less expensive than excavated pits. Their disadvan- 9.6.5 Describe the texture of the<2mm fraction of the
tage is that they sample a smaller area of soil, preventing layer using the flow chart in Fig. 2 as a guide. See Table 3 for
characterization of lateral changes in horizon boundaries and abbreviations. For sandy soils, (that is, less than 20 % clay and
description of larger-scale morphologic features. Use of probes greaterthan50 %sandbyweight),afieldsieveanalysisallows
or augers as an alternative to excavated pits requires a higher more precise texture classification using Table 4.
degree of experience and knowledge about soils in an area. 9.6.6 Note the presence or absence of mottles. Describe
7.3 For preliminary examination of a site, one may probe
color (6); proportion (see Fig. 1); and abundance, size, and
vertically into the soil to get a feel for the presence and depth contrast of mottles (see Table 5).
to a compacted layer, or a water table.Tools that might be used
9.6.7 Describe soil structure by grade using Table 6 and
include a digging bar, tile probe, post hole digger, or hand soil shape and size using Fig. 3 and Fig. 4.
auger.
9.6.8 Describe soil-rupture resistance using criteria in Table
5.
8. Location of Sampling Points
9.6.9 If cementation is suspected, bring an intact soil clod
8.1 Test pits or other subsurface sampling points should be
from the site for further testing.Air dry the clod. Submerge the
locatedinthepotentiallysuitablefieldareaasdeterminedusing
clod in water for at least 1 h. Perform the same tests for rupture
Practice D5879, taking into consideration proximity of source
resistance as shown in Table 7. The sample is cemented if it
of waste water and down slope of source, if possible. Locating
meets the very hard classification test. Describe the degree of
down slope gives most flexibility in system design by allowing
cementation using classes given in Table 7.
either gravity flow or pressure distribution. A preliminary
9.6.10 Measure soil penetration resistance with a pocket
sizing of the field should be performed in accordance with
penetrometer and describe the condition of the soil following
Practice D5925 to determine placement of the sample points.
the criteria in Table 8.
Generally,samplepointsshouldbelocatedondiagonalcorners
9.6.11 Describe abundance, size, and distribution of roots
of the preliminary drainfield area so as to avoid disturbing the
using modifier criteria given in Table 9 and Fig. 5.
soil within the recommended field area. Depending on site
9.6.12 Describe abundance, size, distribution and type of
conditions, additional sample points may be required to iden-
soil pores using criteria in Table 10 and Fig. 5.
tify a recommended field area.
9.6.13 If presence or absence of carbonates is a diagnostic
soil property, use hydrochloric acid to determine depth to free
9. Procedure
carbonate. Describe effervescence as follows: (0) very slightly
9.1 Orient the excavation to expose the vertical face to the
effervescent (few bubbles), (1) slightly effervescent (bubbles
best light.
readily),(2)stronglyeffervescent(bubblesformlowfoam),(3)
9.2 Excavate the test pit to a depth sufficient to satisfy the
violently effervescent (thick foam forms quickly), and (4)
vertical separation required by the governing agency. If the
noneffervescent.
limiting depth is too shallow to meet the vertical separation
9.6.14 Describe layer boundaries according to its distinct-
requirement, it may be desirable to excavate deeper to deter-
ness and topography as shown in Table 11.
mine if the layer is underlain by permeable material.
9.6.15 Estimatemoistureconditionsofthesoilasdry,moist,
9.3 Enterthetestpitusingallapplicablesafetyrequirements
or wet using the guidelines in Table 12. Measure the depth to
andexaminethesoillayers,orhorizons.Selectarepresentative
zone of saturation, if encountered, immediately and remeasure
area to examine in detail.
periodically during evaluation of the site.
9.4 Using a soil knife or other tool, expose the natural soil
9.7 Evaluate changes in soil profile laterally within each pit
structure in an area approximately 0.5 m in width the full
and between the test pits, augmented by hand auger borings, as
height of the test pit.
necessary, to determine if more test pits are needed to fully
9.5 Describe master soil horizons following the criteria in
characterize the site.
Table 1.
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