ASTM D5921-96e1
(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
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 D 5879 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 D 5925, 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.
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e1
Designation: D 5921 – 96
Standard Practice for
Subsurface Site Characterization of Test Pits for On-Site
Septic Systems
This standard is issued under the fixed designation D 5921; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Paragraph 1.9 was added editorially October 1998.
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 (D 2485).
1. Scope 1.3 This procedure can be augmented by Test Method
D 422, when verification or comparison of field techniques is
1.1 This practice covers procedures for the characterization
required. Other standard test methods that may be used to
of subsurface soil conditions at a site as part of the process for
augment this practice include: Test Methods D 2325, D 3152,
evaluating suitability for an on-site septic system. This practice
D 5093, D 3385, and D 2434.
provides a method for determining the usable unsaturated soil
1.4 This practice is not intended to replace Practice D 2488
depth for septic tank effluent to infiltrate for treatment and
which can be used in conjunction with this practice if construc-
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-
classification system. The SCS classification system is defined
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.
the field. This practice is intended to provide information about
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.
currently involved in the evaluation of soil conditions for septic
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 D-18 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 Feb. 10, 1996. Published November 1996.
In 1995, the name of the SCS was changed to Natural Resource Conservation bility of regulatory limitations prior to use.
Service. This guide uses SCS rather than NRCS because referenced documents were
1.9 This practice offers a set of instructions for performing
published before the name change.
one or more specific operations. This document cannot replace
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.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
e1
D5921–96
with professional judgment. Nat all aspects of this practice may 3.1.7 vertical separation—the depth of unsaturated, native,
be applicable in all circumstances. This ASTM standard is not undisturbed soil between the bottom of the disposal component
intended to represent or replace the standard of care by which of the septic system and the limiting depth.
the adequacy of a given professional service must be judged,
4. Summary of Practice
nor should this document be applied without consideration of
a project’s many unique aspects. The word “Standard” in the 4.1 This practice describes a field technique using visual
examination and simple manual tests for characterizing and
title of this document means only that the document has been
approved through the ASTM consensus process. evaluating soils and identifying any limiting depth.
2. Referenced Documents
5. Significance and Use
2.1 ASTM Standards:
5.1 This practice should be used as part of the evaluation of
D 422 Standard Test Method for Particle-Size Analysis of
a site for its potential to support an on-site septic system in
Soils
conjunction with Practice D 5879 and Practice D 5925.
D 653 Terminology Relating to Soil, Rock, and Contained
5.2 This practice should be used after applicable steps in
Fluids
Practice D 5879 have been performed to document and identify
D 2325 Test Method for Capillary-Moisture Relationships
potentially suitable field areas.
for Coarse- and Medium-Textured Soils by Porous-Plate
5.3 This practice should be used by those who are involved
Apparatus
with the evaluation of properties for the use of on-site septic
D 2434 Test Method for Permeability of Granular Soils
systems. They may be required to be licensed, certified, meet
(Constant Head)
minimum educational requirements by the area governing
D 2488 Practice for Description and Identification of Soils
agencies, or all of these.
(Visual-Manual Procedure)
5.4 This practice requires exposing the soil to an appropriate
D 3152 Test Method for Capillary-Moisture Relationships
depth (typically 1.5 to 1.8 m, or greater as site conditions or
for Fine-Textured Soils by Pressure-Membrane Apparatus
project objectives require) for examining the soil morphologic
D 3385 Test Method for Infiltration Rate of Soils in Field
characteristics related to the performance of on-site septic
Using Double-Ring Infiltrometer
systems.
D 5093 Test Method for Field Measurement of Infiltration
6. Limitations
Rate Using a Double-Ring Infiltrometer with a Sealed-
Inner Ring
6.1 The water content of the soil will affect its properties.
D 5879 Practice for Surface Site Characterization for On- The soil should be evaluated in the moist condition because the
Site Septic Systems
normal operating state of the septic system is a moist condition.
D 5925 Practice for Preliminary Sizing and Delineation of If the soil is dry, moisten it.
Soil Absorption Field Areas for On-Site Septic Systems
6.2 This practice is not applicable to frozen soil.
6.3 Optimum lighting conditions for determining soil color
3. Terminology
are full sunlight from mid-morning to mid-afternoon. Less
3.1 Definitions:
favorable lighting conditions exist when sun is low or skies are
3.1.1 limiting depth—for the purpose of determining suit-
cloudy or smoky. If artificial light is used, it should be as near
ability for on-site septic systems, the depth at which the flow of
the light of mid-day as possible.
water, air, or the downward growth of plant roots is restricted.
7. Apparatus
3.1.2 mottle—spots or blotches of different colors or shades
of color interspersed with the dominant color (5).InSCS (3)
7.1 Tools typically used are a soil knife or a flat blade screw
practice mottles associated with wetness in the soil are called
driver, tape measure, pencil and paper, Munsell soil color
redox concentrations or redox depletions.
charts (6), water bottle, wash rag, and a sack to carry samples
3.1.3 pocket penetrometer—a hand operated calibrated
if required. A pocket penetrometer may also be useful. When
spring instrument used to measure resistance of the soil to
the presence of carbonate may be significant in soils, dilute
compressive force.
hydrochloric acid (10 % HCl) should be used.
3.1.4 potentially suitable field area—the portions of a site
7.2 A backhoe will facilitate excavation of the test pits for
that remain after observing limiting surface features such as
examination. However, if the site is inaccessible or funds are
excessive slope, unsuitable landscape position, proximity to
limited, one may excavate by hand with a shovel. Depending
water supplies, and applicable setbacks have been excluded.
on site conditions, power driven or hand held soil augers may
3.1.5 recommended field area—the portion of the poten-
also be suitable. Tube samplers allow description of soil
tially suitable field area at a site that has been determined to be
morphologic features providing the size of the feature does not
most suitable as a septic tank soil absorption field or filter bed
exceed the diameter of the core. Augers generally destroy such
based on surface and subsurface observations.
morphologic features as soil structure and porosity. The advan-
3.1.6 unsaturated—soil water condition at which the void
tage of augers and tube samplers is that they are generally
spaces that are able to be filled are less than full.
faster and less expensive than excavated pits. Their disadvan-
tage is that they sample a smaller area of soil, preventing
4 characterization of lateral changes in horizon boundaries and
Annual Book of ASTM Standards, Vol 04.08.
Annual Book of ASTM Standards, Vol 04.09. description of larger-scale morphologic features. Use of probes
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
e1
D5921–96
or augers as an alternative to excavated pits requires a higher greater than 50 % sand by weight), a field sieve analysis allows
degree of experience and knowledge about soils in an area. more precise texture classification using Table 4.
7.3 For preliminary examination of a site, one may probe 9.6.6 Note the presence or absence of mottles. Describe
vertically into the soil to get a feel for the presence and depth color (6); proportion (see Fig. 1); and abundance, size, and
to a compacted layer, or a water table. Tools that might be used contrast of mottles (see Table 5).
include a digging bar, tile probe, post hole digger, or hand soil 9.6.7 Describe soil structure by grade using Table 6 and
auger. shape and size using Fig. 3 and Fig. 4.
9.6.8 Describe soil-rupture resistance using criteria in Table
8. Location of Sampling Points
5.
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
located in the potentially suitable field area as determined using
clod in water for at least 1 h. Perform the same tests for rupture
Practice D 5879, 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 D 5925 to determine placement of the sample points.
the criteria in Table 8.
Generally, sample points should be located on diagonal corners
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
9. Procedure
soil property, use hydrochloric acid to determine depth to free
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) strongly effervescent (bubbles form low foam), (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 Estimate moisture conditions of the soil as dry, moist,
9.3 Enter the test pit using all applicable safety requirements
or wet using the guidelines in Table 12. Measure the depth to
and examine the soil layers, or horizons. Select a representative
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
...
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