Standard Test Method for
Silt Density Index (SDI) of Water1
This standard is issued under the fixed designation D 4189; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of the last revision. A number in parentheses indicates the year of the last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of the silt
density index (SDI) of water. This test method can be used to
indicate the quantity of particulate matter in water and is
applicable to relatively low (<1.0 NTU) turbidity waters such
as well as water, filtered water, or clarified effluent samples. Since
the size, shape, and nature of the particulate matter in water may
vary, this test method is not an absolute measurement of the
quantity of particulate matter.
1.2 This test method is not applicable for reagent grade
water Types I, II, and III of Specification D 1193, or effluents
from most reverse osmosis and ultrafiltration systems.
1.3 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.
2. Referenced Documents
2.1 ASTM Standards:
D 1129 Terminology Relating to Water2
D 1193 Specification for Reagent Water2
D 3370 Practices for Sampling Water from Closed Conduits2
E 1 Specification for ASTM Thermometers3
3. Terminology
3.1 Definitions—For definitions of terms used in this test
method, refer to Terminology D 1129.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 silt density index (SDI)—an index calculated from the
rate of plugging of a 0.45-µm membrane filter.
4. Summary of Test Method
4.1 Water is passed through a 0.45-µm membrane filter at a
constant applied gage pressure of 207 kPa (30 psi), and the rate
of plugging of the filter is measured.
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