UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                                                                               WSG61
                                                              Date Signed: July 18, 1991
MEMORANDUM

SUBJECT:   Policy for Applicability of the SWT Regulation to
             Seawater

FROM:      Connie Bosnia, Chief
             Drinking Water Branch

TO:          Drinking Water/Ground Water Protection Branch Chiefs
             Regions I - X

       This memorandum is intended to clarify the intent of a letter from Mike Cook to Ms.
Charlene Denys of the Alaska Department of Environmental Conservation. Ms. Denys had asked
whether the Public Water Systems (PWSs) on oil rigs, which use reverse osmosis to purify
seawater, should be required to comply with the requirements of the Surface Water Treatment
(SWT) Rule.

       Mike Cook's response to Ms. Denys is attached. Our response recommended to States
that PWSs using water from open seas not be required to comply with the SWT Rule. We made
this recommendation for three reasons. First, seawater is not generally affected by surface runoff,
due to depth and volume — the rate of dilution in sea water is much more substantial than in
fresh waters. Second, pathogenic organisms are inactivated quickly due to the high salt
concentrations in seawater. Third, and most significantly, seawater is generally treated through
reverse osmosis or distillation. These processes achieve a removal and inactivation of viruses
that far exceeds the levels required under the SWT Rule.

       However, note that water from sources such as estuaries, river deltas and inland salt lakes
is not considered to be seawater.  Such sources are required to comply with the SWT Rule.

       I would like to clarify another point. The attached letter was intended to excuse seawater
systems from monitoring according to the provisions of the SWT Rule only. Seawater systems
are vulnerable to contaminants covered by other drinking water regulations. For example,
contamination from Volatile Organic Chemicals (VOCs) is a risk. Also, storage reservoirs and
distribution systems, regardless of the source, are always vulnerable to bacteriological growth, so
coliform monitoring must be performed.

       Please call Clive Davies with any questions. He can be reached at (202)260-1421.

Attachment

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                                                                                WSG61
                                     March 11, 1991
Ms. Charlene Denys
Manager, Drinking Water Program
Dept. of Environmental Conservation
P.O. Box "O"
Juneau, Alaska 99811
Dear Ms. Denys,

       I am writing to confirm our understanding of a series of telephone conversations between
yourself, Wendy Mabile of BP Exploration and Stig Regli, the person who chaired the
development of the Surface Water Treatment (SWT) Rule. The discussion involved the question
of whether systems that obtain water from open seas and treat water using distillation or reverse
osmosis are subject to the SWT Rule. During the phone calls, Mr. Regli stated that EPA did not
intend to regulate such systems under the provisions of the SWT Rule.

       "Surface waters" are regulated by the SWT Rule. The definition of surface water in the
SWT Rule is water open to the atmosphere and subject to surface runoff.  It is our view that
seawater sources are not, by virtue of their depths and volume, generally affected by surface
runoff. Accordingly, such sources would not come under the definition of "surface waters."
Moreover, seawater sources of drinking water are generally treated by distillation or through
reverse osmosis. These processes achieve a removal or inactivation of viruses and Giardia cysts
that far exceeds the levels required under the SWT Rule. Additionally, the health risk from
pathogens is generally much less significant in sea water than in fresh surface water sources.
Typically, pathogenic organisms are quickly inactivated in sea water due to the high salt
concentration. Also, the rate of dilution of pathogens released into sea waters is generally much
more substantial than in fresh waters.

       Once a state adopts regulations, interpretation of definitions and the scope of State
regulations is left to State discretion as long as any changes result in a regulation which is more
stringent than Federal requirements. We recommend to states that PWSs using seawater
sources not be required to comply with the SWT  rule. States should, however, ensure that
design and operating conditions of systems using seawater sources are optimized.

       We intend to propose and promulgate amendments to the SWT Rule in June 1993 and
June 1995 respectively. These amendments will include special provisions for systems using  sea
water as their source water and recognize the technologies of reverse osmosis and distillation as
a means for achieving compliance.
       Please call Clive Davies of my staff with any questions. Clive can be reached at
(202)260-1421.

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                                                                              WSG61
Sincerely yours,
Michael B. Cook, Director
Office of Drinking Water
cc:     Wendy Mabile
       EPA Drinking Water/Ground Water Protection Branch Chiefs, Regions I-X

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