UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
JUN -9 2009
OFFICE OF
MEMORANDUM
SUBJECT: Definitions of Conventional Filtration Treatment and Direct Filtration
FROM: Ronald Bergman, Chief
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Regulation and Supporting Guidance
The preamble for the Long Term 2 Enhanced Surface Water Treatment Rule
(LT2) (71 FR 654, January 5, 2006) addressed the issue of what constitutes conventional
filtration treatment. Conventional Filtration Treatment (p. 675 Table IV B-2 footnote 1)
is said to "apply to a treatment train using separate, sequential, unit processes for
coagulation/flocculation, clarification, and granular media filtration. Clarification
includes any solid/liquid separation process following coagulation/flocculation where
accumulated solids are removed during this separate component of the treatment system."
The preamble for LT2 also clarifies what EPA means by designation of
conventional filtration treatment through the review of clarification process performance
studies. Specifically, these studies indicate that plants using clarification processes other
than sedimentation that are located after coagulation and prior to filtration can achieve
performance equivalent to conventional filtration treatment plants. Based on these
studies, any treatment train that includes coagulation/flocculation, clarification and
granular media filtration (e.g., sand-ballasted clarification or dissolved air floatation) may
be regarded as conventional filtration treatment and awarded treatment credit as
conventional filtration treatment.
EPA guidance for the filtration and disinfection requirements, The Guidance
Manual for Compliance with the Filtration and Disinfection Requirements for Public
Water Systems Using Surface Water Sources (March 1991 Edition, Section 4.3.3),
includes a reference to the Ten State Standards1 which states -
The minimum criteria in the Ten State Standards for conventional filtration
treatment are considered sufficient for the purposes of complying with the SWTR
with the following addition: The criteria for sedimentation should be expanded to
include other methods of solids removal including dissolved air floatation. Plate
separation and upflow-solids contact clarifiers included in the 1987 Ten State
Standards should also be considered.
In addition, EPA's guidance in Section 4.2.1(e), footnote 1, summarizes that package
plants, depending upon the type of treatment units in place, could be categorized as
conventional filtration treatment, direct filtration, slow sand filtration, diatomaceous earth
filtration or alternate technology at the discretion of the state.
Implementation Recommendations
For alternative filtration technologies, existing regulatory provisions require a
removal demonstration under 40 CFR 141.73(d) for Giardia, and 40 CFR 141.173(b) for
Cryptosporidium, The alternative technologies have to satisfy removal requirements at
the regulatory turbidity limit (or alternative performance criteria) over an expected range
of source water conditions. Examples of other alternative performance criteria include,
but are not limited to, removal/inactivation of viruses and Giardia lamblia. Systems
must demonstrate to the state how the alternative technologies are operated and that they
will routinely meet state specified criteria to be awarded treatment credit.
2
1 Ten State Standards are public water supply standards established by GLUMRB, a water board often Midwest states.
'This guidance is highly respected and widely used by state regulatory agencies. The standards can be accessed from
this website: http://IOstatcsstandards.com/waterstandards.html
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Conventional filtration treatment plants without the capacity to meet enhanced
coagulation TOC (Step I) removal requirements due to water quality parameters or
operational constraints may qualify for alternative compliance criteria or may apply for
TOC (Step 2) removal requirements. Conventional filtration treatment plants must apply
for alternative minimum TOC removal (Step 2) requirements within three months of
failure to achieve TOC removals required by 40 CFR 141.135(b)(2). The state may make
those requirements retroactive for the purposes of determining compliance. A Step 2
removal application at a minimum must include results of bench- or pilot-scale testing
conducted under 40 CFR 141.135(b)(4)(i). These results must be used in determining the
alternate enhanced coagulation TOC removal requirement.
Conclusion
States must be consistent in applying the provisions associated with conventional,
direct, and alternative filtration technologies. States must designate the technology to be
implemented by the water system, specify all associated treatment and performance
criteria (e.g., turbidity limits, flow rates, etc.), assign the appropriate filtration credit and
require compliance with precursor removal requirements in 40 CFR 141.135 as
appropriate.
If you have additional questions about conventional filtration treatment and direct
filtration, please contact Ed Moriarty, of my staff, at 202-564-3864.
cc: Jim Taft, ASDWA
MDBP Workgroup
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