UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                     GUIDANCE FROM HOTLINE COMPENDIUM
                                                                             WSGH39
                                                            Date Issued: December 1991
                                                                         Revised: 12/99
SUBJECT:   The Effectiveness of Slow Sand Filtration in Total
             Coliform Removal

SOURCE:    Stig Regli, OGWDW
             (202) 260-7379
The Guidance Manual for Compliance with the Filtration and Disinfection Requirements for
Public Water Systems Using Surface Water was prepared by EPA to assist public water systems
in the implementation of the Surface Water Treatment Rule.  Part 4.3.5, Section 4-19 of the
manual describes slow sand filtration design criteria.  This section states that, "The effective
sand size should be between 0.15 mm and 0.35 mm rather than the current 0.30 mm to 0.45
mm." However, citation #13 states that, "Significant decreases in total coliform removals were
shown at effective sand sizes less than 0.35 mm (Bellamy et al., 1985)."  The design criteria
seems to contradict the Bellamy study evidence.

Was it EPA's intent to reduce effective sand size range to 0.15 mm - 0.35 mm despite the cited
evidence that total coliform removal decreases at sand sizes lower than 0.35 mm, or was the
Bellamy study incorrectly cited in citation #13?
       Response:

       The Bellamy study concerning sand sizes was incorrectly quoted in citation #13.  The
       corrected text should read, "Significant increases in total coliform removals were shown
       at effective sand sizes less than 0.35 mm (Bellamy et al., 1985)."

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