The MassDEP Office of Research and Standards (ORS) issues guidance for chemicals other than those with Massachusetts MCLs in drinking water. These ORS guidance values are known as ORS Guidelines or ORSG and are usually developed for use by Departmental programs in the absence of any other federal standards or guidance. ORSG may be based upon US EPA IRIS toxicity values or derived based on a review and evaluation of all available data for the chemical of interest. Some ORSG may be based on US EPA Health Advisories. Standards promulgated by the US EPA but not yet effective may also be included on the list of Massachusetts Drinking Water Guidelines. ORSG are updated when IRIS toxicity values change so as to reflect the current toxicological guidance for the chemical.
ORS uses methodology similar to that used by the US EPA's Office of Groundwater and Drinking Water (OGWDW) when setting guidelines for chemicals in drinking water. Concentrations of chemicals having evidence of carcinogenicity are minimized as much as feasible; therefore, guidelines are set at a target excess lifetime cancer risk of one in one million (1 x 10-6) or at the lowest practical quantitation limit (PQL) if the concentration at 1 x 10-6 is below the PQL. This practice applies to chemicals classified as A or B carcinogens under the old cancer classification scheme of US EPA (US EPA, 1986). Class C carcinogens are individually evaluated for a decision regarding whether to set the guidelines on cancer effects. For carcinogens classified under US EPA’s Carcinogen Risk Assessment Guidelines (US EPA, 2005), MassDEP will follow US EPA OGWDW’s procedures for development of guidance.
To derive guidance for potential non-carcinogenic effects for a chemical, ORS applies a percentage (usually 20%) to published or derived route-specific reference doses and then uses standard exposure assumptions to convert the dose to a drinking water concentration. This practice allows for the possibility of human exposures from sources other than drinking water.
All guidelines are current with the information listed in the U.S. EPA Integrated Risk Information system (IRIS) as of May 3, 2017 except where noted.
 The MCLs for aldicarb, aldicarb sulfone and aldicarb sulfoxide have been stayed.
 See footnote 11 above.
 See footnote 11 above.
 This guideline applies to non-chlorinated water supplies. For chlorinated drinking water supplies, please contact the Drinking Water Program.
 See Secondary Maximum Contaminant Level below and endnote to US EPA Health Advisories.
 The health-based guideline for MTBE was reviewed by ORS in 2000.
 The MCL for Nickel has been remanded and is no longer in effect; however, the current EPA IRIS chronic oral reference dose for soluble salts of nickel (https://cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=271) supports this value and it is also the currently listed EPA Life-time Health Advisory value.
 Monitoring for these compounds is not required but is done on a case-by-case basis. These limits may be used when evaluating health risks posed by clearly identified mixtures of petroleum hydrocarbon compounds. The analytical methods to use to generate data to compare to the Drinking Water Guidelines are the Volatile Petroleum Hydrocarbon (VPH) and the Extractable Petroleum Hydrocarbon (EPH) methods developed by the MassDEP (MassDEP 1998).
 The overlap in the C9-C12 range is the result of the VPH and EPH analytical methods used to quantitate these ranges of petroleum hydrocarbons in drinking water. The choice of the most appropriate range to use is based on the identity of the petroleum product of concern and is therefore determined on a case-specific basis.
 See footnote 9 above.
 All detections of sodium must be reported. Please refer to 310 CMR 22.06A for the specific requirements. The sodium guideline of 20 mg/L is based on an eight (8) ounce serving.
 The ORSG for tetrahydrofuran was updated in April 2014.
 The ORSG level is for the sum of six PFAS compounds: PFDA, PFOA, PFOS, PFNA, PFHxS and PFHpA. When some or all of these compounds occur together in drinking water, the detected concentrations for these PFAS should be summed and compared to the ORSG. This value is also applicable to the individual compounds.