UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                     GUIDANCE FROM HOTLINE COMPENDIUM
                                                                            WSGH30
                                                               Date Issued: August 1990
                                                                 Revised: February 1999
                                                                Revised by: Ed Thomas
SUBJECT:   VOC Monitoring Requirements and the Blending of Separate
             Water Supply Sources as a Form of Treatment

SOURCE:    Susan MacMullin
Section 141.24(g)(l) of the VOC rule (52 FR 25712) specifies that systems with ground water
supplies must sample at points of entry to the distribution system that are representative of each
well.  Furthermore, the preamble states that such ground water systems are required to sample at
those distributions system entry points that are located after any treatment (52 FR 25705).  Is the
blending of water from two separate ground water sources considered to be treatment?  If
blending is not considered treatment, the operator will need to sample at two locations prior to
where blending occurs.  If blending is regarded as treatment, the operator will be required to
sample at a single location subsequent to where blending occurs.

       Response:

       The blending of two separate supply of sources is considered treatment in the context of a
              system's ability to meet an MCL.  A State may require a system to sample at each
       well head prior to blending, however, the Federal regulations require  systems to sample at
       the point of entry to the distribution system.  The sample may be taken at any point
       between the treatment process (or blending) and the point of entry to the distribution
       system.  It is not, however, appropriate to blend sources of water in the distribution
       system.

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