UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                     GUIDANCE FROM HOTLINE COMPENDIUM
                                                                            WSGH46
SUBJECT:   Monitoring for Unregulated Contaminants

SOURCE:    Jeff Sexton, OGWDW
             (202) 260-7276

In the Phase H Rule that was promulgated on January 30, 1991, (56 FR 3526) Section 141.40
requires all Community Water Systems (CWS) and Non-Transient Non-Community Water
Systems (NTNCWS) to monitor for 24 unregulated contaminants. The codified language does
not dictate the exact reporting requirements for analytical results that are below the Method
Detection Limits (MDLs). In a separate rule making, the Lead and Copper Rule promulgated on
June 7, 1991 (56 FR 26460), EPA mandated in Section 141.89 that contaminant levels below the
MDL be reported as zero.

By analogy to the Lead and Copper Rule, should zero be reported to the state when a value less
than the MDL is obtained for a Phase II unregulated contaminant?

       Response:

       No. The requirement for reporting of contaminant levels below the MDL as zero applies
       to the calculation of a running annual average of quarterly analytical results for the
       determination of compliance with an MCL. An example would be the determination of
       compliance with the VOC MCLs (a guidance document on reporting violations of the
       VOC [Phase I] requirements to FRDS was prepared by the Drinking Water Branch in
       1990.) The only violation that can be incurred relative to the unregulated contaminants,
       however, is a monitoring violation.

       In the Phase I VOC Rule (52 FR 25715), Section 141.35 states that the State "shall
       furnish to the Administrator for each sample analyzed under Section 141.40:  (1) Results
       of all analytical methods, including negatives; ..." The analytical results  for the
       unregulated contaminants that are below the Method Detection Limit (MDL) should be
       reported as less than the specified MDL.

       For example, if an unregulated contaminant could not be quantified at, or above, the
       MDL of say 0.5 ug/1, it should be reported as "< 0.5 ug/1" and not as zero or "ND" (not
       detected).

       In this way, the users of the data have a better "handle" on the actual value. Less-than
             values also give one an indication of the quality of the laboratory data; i.e., how
       low their MDLs are.  If statistical calculations then need to be made, the  less than value
       can be assigned a value such as zero or one-half of the MDL. OGWDW is developing
       reporting guidance for Phase U unregulated contaminants and expects it to be available
       late spring  1992.

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