White Paper for Discussion Aesthetic Drinking Water Standards

Transcription

1 White Paper for Discussion Aesthetic Drinking Water Standards Version Date: July 8, 2009 Contributors: Audrey Wagenaar, Lavinia Zanini Issue Definition New drinking water (DW) guidance will focus on future aquifer use and result in more aquifers designated as a drinking water source. BC DW standards for contaminated sites were adopted from CCME DW guidelines (1996 with updates) based on Ministry of Health recommendation. A number of DW standards are based on aesthetic considerations and may be more stringent when compared to a toxicological based standard. In recent conversations with approved professionals, there has been particular concern with iron and manganese as these parameters are naturally elevated in many aquifers that make it difficult to delineate and remediate to the DW standards. While background determinations can be done for these parameters, it is sometimes onerous (i.e., expensive and difficult to find/drill appropriate background locations). As a result, many consultants prefer to use a risk based approach to deal with iron and manganese exceedances of the DW standard. The question arises: Is there a more efficient way to deal with exceedances of the aesthetic DW standards at contaminated sites? Issue Analysis A summary of how other jurisdictions assess iron and manganese in drinking water from a contaminated sites perspective is presented below: a. United States Environmental Protection Agency (US EPA Regions III, VI, IX; ORNL 2008): Toxicologically derived screening levels (formerly known as preliminary remediation goals) are used to determine whether levels of contamination found at a site warrants further investigation or site cleanup, or whether no further investigation or action may be required. Screening level tap water guidelines for iron and manganese are 26,000 ug/l and 880 ug/l, respectively. These values were derived with slightly different target risk levels than those typically used in BC (i.e., US EPA used an incremental lifetime cancer risk (ILCR) 1x 10-6 and a hazard quotient of 1). b. Ontario: Iron and manganese standards are not available in Part XV.1 of the Ontario Environmental Protection Act and Ontario Regulation 153/04 (Record of Site Condition). Risk assessors use professional judgement to determine whether iron and manganese should be included on a site-specific basis. In most cases, if iron and manganese are identified as contaminants of potential concern, the Record of Site Condition will specify the use of a treatment system to remove iron and manganese to aes thetic objectives. 07/08/2009 Science Advisory Board for Contaminated Sites in BC 1

2 c. Alberta: Alberta Environment has Tier 1 and Tier 2 guidelines. Tier 1 incorporates aesthetic guidelines (the guidelines are drawn from the Canadian Drinking Water Guidelines [CDWG] ) and separate guidelines are only developed where no CDWG (Maximum Acceptable Concentration [MAC] or Aesthetic Objective [AO]) is available and then only if toxicity benchmarks are available. Toxicologically based guidelines use Health Canada's calculation approach. Tier 1 DW groundwater guidelines for iron and manganese are 300 ug/l and 50 ug/l respectively. Tier 2 allows for a risk based approach for clean up goals. Background standards may also be calculated. d. Quebec: Groundwater criteria are applied within a contamination prevention framework. This typically implies monitoring groundwater quality upgradient from a DW well in order to prevent groundwater degradation, including aesthetic degradation. This framework takes background water quality into account while evaluating impact of contamination. When interpretation of an exceedance at the DW well is needed or if such an exceedance is apprehended (i.e. believed to exceed soon), one must touch base with a human health ministry representative. The groundwater criterion for manganese in drinking water is 50 ug/l. There is no DW groundwater criterion for iron. e. Washington: Ground Water Quality Standards (which incorporate aesthetic standards) are designed to be preventative in nature and protect ground water from contamination. They are not intended to be used as remediation standards. Remediation standards are regulated under the Model Toxics Control Act which uses a risk based approach to specifically regulate environmental remediation activities. Summary: Many jurisdictions use aesthetic standards for ascertaining drinking water quality. However, they rely on toxicologically derived screening levels or background values as remediation goals. The following options were evaluated as possible means to identify the most efficient way to deal with exceedances of the aesthetic DW standards at contaminated sites: 1. Evaluate the ability to determine regional background groundwater values. It was determined that the historical and current data the Ministry has on groundwater quality is insufficient to establish background values for all regions. However, background values may be derived for the most heavily used aquifers. 2. Evaluate the ability to determine toxicologically based standards. Table 1 presents a summary of the parameters in CSR Schedule 6 (BC MOE 2009) which have drinking water standards based on aesthetic objectives. A review of the World Health Organization Drinking Water Guidelines (WHO 2006) was conducted to see whether WHO guidelines are readily available for any of these substances. The WHO guidelines are generally based on a toxicological derivation. Additionally, USEPA IRIS (2009) and Health Canada (2009) were consulted to determine whether toxicity reference values are available for the parameters listed in Table 1. It is recommended that for aesthetic parameters from CSR Schedule 6 for which a toxicity reference value is available, toxicologically based criteria should be developed using the same approach as CCME (1996). This is consistent with the approach utilized to develop the toxicologically based drinking water standards which have been adopted for the other substances in CSR Schedule 6. The CCME (1996) approach generally utilizes an apportionment factor of 0.2 for toxicity reference values for non-carcinogens. It should be noted that there may also be toxicity reference values available from regulatory agencies other than US EPA or Health Canada; however, an exhaustive search of toxicity reference values was beyond the scope of this white paper. 3. Estimate the impact of changing the CSR Schedule 6 standards for iron and manganese from an aesthetic based objective to a toxicologically based criterion. 07/08/2009 Science Advisory Board for Contaminated Sites in BC 2

3 Based on a small sample size of ten (10) sites, if the manganese standard was changed from 50 ug/l (aesthetic) to 400 ug/l (WHO toxicologically bas ed guideline), the number of background groundwater applications would be reduced in half. Insufficient data are available to estimate the impact of changing the iron standard. Options to Address Issue The following are the primary options which have been identified by the task group to address the issues associated with groundwater standards for iron and manganese based on aesthetic considerations: 1. Develop regional background groundwater concentrations for many parameters that naturally exceed DW standards. 2. Develop toxicologically based standards for those aesthetic standards that are deemed problematic (e.g., iron and manganese). 3. Develop toxicologically based standards for all aesthetic DW standards (preferred approach) - Most practical, scientifically defensible and efficient solution to evaluate groundwater contamination clean up goals. Recommendations The task group recommends that the Ministry reassess existing policy and look at establishing remediation standards based on toxicological data. References British Columbia Ministry of Environment (BC MOE). 2009a. B.C. Reg 375/96, O.C. 1480/96. Environmental Management Act: Contaminated Sites Regulation including amendments up to B.C. Reg. 343/2008, January 1, Accessible on-line at CCME Guidelines for Canadian Drinking Water Quality. Prepared by the Federal-Provincial-Territorial Committee on Health and the Environment. Updated Health Canada Federal Contaminated Site Risk Assessment in Canada. Part II: Toxicity Reference Values. Version II, January Oak Ridge National Laboratories (ORNL) US EPA Risk-Based Screening Tables. Available on-line at: United States Environmental Protection Agency (US EPA) Integrated Risk Information System (IRIS) On-Line Database Search. US EPA, Cincinnati, OH. Available on-line at: World Health Organization (WHO) Guidelines for Drinking Water Quality. Incorporating the First Addendum to the Third Edition. Volume 1: Recommendations. Available on-line at 07/08/2009 Science Advisory Board for Contaminated Sites in BC 3

4 SAB White Paper for Discussion: Risk Forum Workshop - April 2009 Table 1 Summary of Parameters with Aesthetic Standards in the BC CSR Schedule 6 and Comparison to WHO Drinking Water Guidelines Parameter Aesthetic Standard (mg/l) WHO Drinking Water Quality Guideline Available? WHO Toxicologically Based Guideline? Toxicity Reference Value s Available from USEPA or Health Canada? Chloride 250 NA Chlorinated Benzenes 1,2- Dichlorobenzene Yes (1 mg/l) Yes Yes 1,2 1,4-Dichlorobenzene Yes (0.3 mg/l) Yes Yes 1,2 Monochlorobenzene NA Chlorinated Phenols Dichlorophenol NA Yes 1,2 Monochlorophenol NA Pentachlorophenol Yes (0.009 mg/l) Yes Yes 1,2 Tetrachlorophenol NA Yes 1,2 Trichlorophenol NA Yes 1,2 Copper 1 Yes (2 mg/l) Yes Yes 2 Ethylbenzene Yes (0.3 mg/l) Yes Yes 1,2 07/08/2009 Science Advisory Board for Contaminated Sites in BC 4

5 SAB White Paper for Discussion: Risk Forum Workshop - April 2009 Iron 0.30 Yes derivation present but not officially adopted as a guideline [2 mg/l] Yes Manganese 0.05 Yes (0.4 mg/l) Yes Yes 1,2 Magnesium 100 NA Sodium 200 Yes (200 mg/l) firm conclusions could be drawn between the possible association between sodium in drinking water and the occurrence of hypertension. WHO guideline is based on unacceptable taste. Sulphate 500 Yes (>500 mg/l) Existing data are not sufficient to identify a level in drinking water which causes adverse health effects. However, concentrations exceeding 250 mg/l may cause a noticeable taste and corrosion in pipes. Concentrations exceeding 500 mg/l have the potential to cause gastrointestinal effects in populations and health authorities should be notified if concentrations exceeding 500 mg/l are present. Sulphide as H 2 S 0.05 NA Toluene Yes (0.7 mg/l) Yes Yes 1,2 Xylenes 0.3 Yes (0.5 mg/l) Yes Yes 1,2 Zinc 5 NA Yes 1,2 tes: 1) US EPA IRIS (2009) 2) Health Canada (2009) 07/08/2009 Science Advisory Board for Contaminated Sites in BC 5