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Water Quality Methods
for Deriving Site-Specific Water Quality Objectives Report
prepared by MacDonald Environmental Sciences Ltd. Role of Water Quality Objectives in Water Management Framework for the Development of Water Quality Objectives Review and Evaluation of Approaches and Procedures for Deriving
Site-Adapted and Recommended Methods for Deriving Site-Specific Water Quality Objectives
for Recommended Procedures for Determining Water Effects Ratios List of Tables
List of Figures
The author would like to acknowledge those individuals who contributed significantly to the production of this report. Timely access to unpublished data and other information was provided by many of the individuals listed in Appendix 1. Excellent comments and suggestions were provided by Les Swain, Narender Nagpal, Mike MacFarlane, Howard Singleton, Cecilia Wong, and Benoit Godin. This report was prepared with the assistance of M. L. Haines, T. Berger, and D. Tao.
Conservation of water quality in British Columbia and Yukon requires an integrated approach. Water quality guidelines produced by the CCME or water quality criteria produced by the province, establish safe limits for protection for the aquatic life upon unlimited exposure to toxicants. These guidelines provide generally adequate targets for the evaluation of waste discharges into the environment. However, the CCME guidelines recognize that variations in environmental conditions may affect water quality in different ways and consequently guidelines can be modified according to the local conditions. This document proposes appropriate procedures for the development of site specific water quality objectives. Four basic procedures for toxicants, which are non-persistent or which do not demonstrate cumulative effects, are described.
La conservation des eaux provinciales en Colombie Britannique et territoriales au Yukon demande une approche intégrée. Les lignes directrices de qualité des eaux énoncées par le CCME ou les critères de qualité des eaux produits par la province établissent des limites sécuritaires pour la protection de la vie aquatique exposée à des produits toxiques pendant une période illimitée. Ces lignes directrices fournissent généralement des objectifs adéquats pour l'évaluation des rejets industriels dans l'environnement. Par contre, les lignes directrices reconnaissent que des variations des conditions environnementales locales peuvent affecter la qualité de l'eau et par conséquent, engendrer des modifications des lignes directrices pour produire des objectifs spécifiques au site. Ce document propose des mesures appropriées pour le developpement d'objectifs liés à la qualité des eaux spécifiques au site. Quatre procédures de base sont décrites dans ce document pour des produits toxiques qui sont non-persistants ou qui ne démontrent pas d'effects cumulatifs.
British Columbia and Yukon are renowned for the myriad lakes, rivers, streams, and wetland areas that lie within their borders, many of which are relatively pristine. Conservation of the exceptional quality, and protection of the designated uses, of aquatic ecosystems in this region requires an integrated approach to water management. A cornerstone of such a water management strategy is the development of numerical water quality objectives (WQOs). Such WQOs provide benchmarks for environmental quality which can be used to guide decisions on land and water uses within drainage basins (i.e., for approving land use developments and establishing limits on the discharge of contaminants). Importantly, these management tools can also be used to assess the need for remediation at existing facilities and to establish target clean-up levels for priority substances (LaGoy and Hopkins 1991). Several general approaches have been used to address the question of what constitutes an adequate level of human health and environmental protection, including the adoption of zero-risk levels, implementation of best available technology, and establishment of use-protection strategies (Song and Marolf 1993). Using the zero-risk approach, WQOs are established by defining background levels of priority contaminants at the site. Implementation of this approach ensures that environmental receptors are not exposed to elevated levels of environmental contaminants and, hence, have no incremental risk of adverse effects. However, technological limitations and costs are likely to preclude the implementation of this option under most circumstances (USEPA 1988a). With the technology-based approach, discharge limits are frequently established based on the best available technology-economically-achievable (BAT-EA). As such, receiving water quality primarily depends on the effectiveness of the treatment technology and the dilution capacity available. The potential effects of wastewater discharges on designated water uses are generally not considered when limits are established using the BAT-EA approach. Therefore, the level of protection afforded the designated water uses is, at best, uncertain. In contrast to the other approaches, the use-protection strategy relies on the development of WQOs that are based on the protection of existing and potential uses of land and water at the site. This general approach allows environmental managers, in conjunction with stakeholders, to develop broad ecosystem management goals and to assess the benefits and costs of various management options in the context of these goals. Because the use-protection strategy accommodates the multiple use of aquatic ecosystems and minimizes conflicts between human and non-human competing interests, it has been incorporated as a central component of the approach to water management in British Columbia and Yukon. However, consistent application of this approach necessitates the development of defensible procedures for deriving WQOs for freshwater, estuarine, and marine waters in the region. Background Water quality objectives are science-based tools that provide an effective basis for managing the resources in aquatic ecosystems. These tools describe conditions that environmental managers and stakeholders have agreed should be met to protect the designated uses of freshwater, estuarine, and marine ecosystems. They are used in conjunction with other management tools, such as permitting processes, technology development, and enforcement, to achieve environmental conditions that support sustainable resource use. Water quality objectives are numerical concentrations or narrative statements that establish the conditions necessary to support and protect the most sensitive designated use of water at a specified site. Objectives are typically based on generic water quality guidelines (WQGs) and criteria (WQC), which may be modified to account for local environmental conditions or other factors. In general, WQOs are prepared only for those waterbodies and water quality variables that may be significantly affected by human activities, either now or in the future. (Please note that the terms criteria and guidelines are used interchangeably in this discussion and are considered to be functionally equivalent. This nomenclature reflects the fact that the term criteria is preferred by provincial agencies, while the term guidelines is commonly used in federal government programs). Water quality objectives have no legal standing at this time and, therefore, are not enforced directly. Instead, discharges of contaminants into surface water systems are regulated through permits issued under the BC Waste Management Act or licenses issued under the Yukon Waters Act. While a formal mechanism has not been established, the WQOs are often used in the permitting and licensing processes in the region. In addition, the WQOs can be employed to support a broad range of land use management decisions. Furthermore, decisions on the need for habitat restoration and other remedial actions may be based, in part, on the WQOs. Water quality objectives are usually a starting point for conducting water quality assessments and determine the acceptability of project proposals. WQOs are used in conjunction with applicable legislation such as Fisheries Act. Importantly, the WQOs also provide standards for assessing the performance of water managers in protecting water uses.
In British Columbia and Yukon, generic WQC (which are developed by the Water Management Branch, BCMOELP [now called, BCMOWLAP]) or WQGs (which are prepared by the Canadian Council of Ministers of the Environment) provide a consistent basis for assessing water quality conditions throughout much of the region. These generic WQC are derived for the protection of five major water uses (BCMOE 1986; CCREM 1987), including:
Such generic guidelines and criteria provide basic scientific information about the effects of water quality variables on water uses in order to assess water quality issues and concerns and to establish WQOs (BCMOE 1986, CCREM 1987). These guidelines and criteria are designed to be conservative and, hence, are likely to be applicable to the vast majority of sites in this region. The broad applicability of these management tools makes them useful for assessing water quality conditions in freshwater, estuarine, and marine ecosystems throughout British Columbia and Yukon. Additionally, these guidelines and criteria provide a scientific basis for the establishment of numerical WQOs for receiving water systems. The national WQGs and regional WQC are intended to protect the designated uses of aquatic ecosystems. However, it is possible that the guidelines and criteria are over-or under-protective at sites with unique conditions. For example, the most sensitive species represented in the toxicological data set used to derive the generic criteria and guidelines may not be present at the site of interest or may be more or less sensitive than laboratory test samples indicate. Similarly, a substance may be more or less toxic in site water (i.e., due to factors such as pH, water hardness, complexing agents, etc.) than it is under the range of conditions that are represented in the toxicological data set. Under these circumstances, it might be necessary to modify the generic criteria to account for conditions that occur at the site. In part, concerns related to the applicability of the guidelines and criteria can be addressed through the development of site-adapted WQOs. Commonly, a criteria-based approach has been used to develop such site-adapted objectives, in which the most sensitive water use is identified and the criterion for that water use is adapted to account for the site-specific factors. While this approach is effective at many sites, atypical conditions exist at certain locations which necessitate further modification of the generic WQG and WQC. A number of procedures have been developed to support the development of site-specific WQOs. Several new approaches have also been developed in recent years that could be adapted to site-specific WQC development (e.g., toxicity identification evaluation procedures, toxic units modelling, etc.; Ankley and Thomas 1992; Ankley et al. 1996). One, several, or a combination of these methods are likely to provide environmental managers with the tools that they need to establish methods for deriving site-specific WQOs for freshwater, estuarine, and marine ecosystems. The purpose of this report is to review the various procedures for deriving WQOs and provide specific guidance on the methods that should be used to derive site-specific WQOs in British Columbia and Yukon. The procedures recommended in this document apply directly to the development of WQOs for metals and metalloids in freshwater systems; however, they are also likely to be generally applicable to organic substances and to marine and estuarine systems, with minor modifications. These procedures, however, will not apply to substances that tend to bioaccumulate and/or biomagnify in the environment, since water quality criteria/guidelines for these substances generally are not based on their toxicity but their potential to bioaccumulate in aquatic organisms to levels that may be harmful to the consumers. If, by chance, water quality criteria or guidelines are based on the toxicity of these substances to aquatic organisms, then, and only then, the procedures outlined in this document could be used to derive site-specific water quality objectives for the bioaccumulative substances. Users should be careful of the fact that the site-specific objectives thus derived for the bioaccumulative substances, may not be protective of the consumers of the aquatic life. This report is not intended to provide guidance on the administrative processes (policy, public participation, other guidance and documentation, implementation, etc.) applicable in British Columbia and Yukon. A brief overview is provided in the next section, but for specific aspects, the reader should consult the respective agencies in charge of managing water resources in the area concerned.
Role of Water Quality Objectives in Water Management Water quality objectives (WQOs) represent a integral component of the overall water management process in British Columbia and Yukon. In British Columbia, WQOs are being jointly prepared for specific freshwater, estuarine, and marine ecosystems by Environment Canada and the Ministry of Environment, Lands, and Parks (now called Ministry of Water, Land and Air Protection). In Yukon, the federal government plays a lead role in managing aquatic resources, including the establishment of WQOs. While there are many similarities between the federal and provincial approaches to objectives development, there are also some important philosophical differences that can influence the overall process. The similarities and differences between the two philosophies are described in the following sections.
Water quality objectives form a cornerstone of the Federal Water Policy (Minister of Environment 1987). In addition, the need for WQOs is explicitly recognized in the Canadian Environmental Protection Act [Section 8(1)]. To guide federal government staff, Environment Canada and Fisheries and Oceans Canada jointly developed a policy statement on the use and application of WQOs in the Pacific and Yukon Region. In addition, the policy statement outlines the federal approach for reviewing WQOs that are derived by other agencies. In the federal policy, WQOs are defined as numerical concentrations or narrative statements that have been established to support and protect the designated uses of water at a specified site (CCREM 1987). Such objectives are based on the best scientific information available. When insufficient information exists, provisional WQOs (PoWQOs) are applied until the data required to develop scientifically-defensible objectives are available. Provisional WQOs are deliberately conservative and implemented with due caution. Water quality objectives are developed to conserve and protect the designated water uses in the waterbody under consideration. The designated water uses recognized in the federal policy include:
While the provincial philosophy recognizes waste assimilation as a valid water use, a non-degradation policy has been adopted by the federal government. This policy states that all reasonable and preventative measures should be taken to maintain existing conditions when they are better than the conditions specified by the WQOs. Hence, the existing conditions should be adopted as the objectives for waters of superior quality. For waters with impaired quality, the objectives may be used as a basis for improving water quality. The federal policy identifies a number of applications for the WQOs. For example, evaluation of attainment with the objectives provides a useful means of predicting and assessing whether effluent quality standards (which are based on best available or practicable technology) provide adequate protection for designated water uses. However, the objectives cannot be used to derive allowable effluent contaminant concentrations, if they would result in relaxation of effluent treatment requirements such that legislated effluent standards (e.g., Metal Mining Liquid Effluent Regulations) are no longer met. The objectives also provide a basis for identifying emerging water quality problems resulting from multiple point and diffuse sources and for determining the need to address such problems when they arise. The federal policy recognizes that the management and control of certain toxic substances cannot be achieved using WQOs. For many toxic and/or bioaccumulative substances, it is difficult to develop objectives due to the lack of aquatic toxicity data. Additionally, it may be necessary to establish objectives at levels below current analytical limits of quantification for substances that exhibit high acute toxicity or bioaccumulative potential. In these cases, more information will be needed to prescribe appropriate objectives. The federal policy recognizes the concept of the initial dilution zone (IDZ), wherein effluents mix with receiving waters. According to the policy, the extent of the IDZ should be defined on a site-specific basis and should be located to avoid impairments to designated water uses (e.g., not located near important fish or migratory bird habitat). While the water in the IDZ should not be acutely toxic to fish, contaminant concentrations may exceed the WQOs. The objectives should be met outside the IDZ. However, the federal policy may be considered more stringent than the provincial policy. The federal policy (consistent with Fisheries Act) specifies that effluent concentration of contaminants should not be acutely toxic before discharged into a waterbody. The Yukon Territory's waters are managed by the Department of Indian and Northern Affairs. There is no specific policy on water quality objectives at the moment. The general principles of the federal policy apply.
In British Columbia, the Guidelines and Standards Policy and Procedures of the Ministry of Environment, Lands and Parks provide a framework for setting guidelines and standards to protect the environment and promote sustainability by integrating environmental, economic, health and social considerations. The water quality objectives in the province are also set in accordance with the policy. In British Columbia, WQOs are established for water bodies on a site-specific basis (Water Management Branch 1984). These objectives are primarily based on the provincial water quality criteria (WQC; Nagpal et al. 1995) and Canadian water quality guidelines (WQGs; CCREM 1987). Such WQC and WQGs are developed for the physical, chemical, or biological characteristics of water, sediment, or biota and define the conditions necessary to support specific water uses. The uses of aquatic ecosystems that are considered in the development of the criteria and guidelines include:
There are other valid water uses (e.g., power generation, water storage, waste assimilation, navigation, etc.), but they are not as sensitive as those listed above and may impair the more sensitive water uses. Recognizing that there is a virtually limitless number of waterbodies and characteristics for which objectives could be established, objectives are developed on a priority basis for waterbodies and water quality characteristics that may be affected by human activities, either now or in the foreseeable future (Water Management Branch 1984). Water quality objectives are intended to consider the water use(s) to be protected and the existing water quality in the waterbody. Other factors that may be considered in the objectives development process include: the temporal and spatial variability in water, sediment, and biological characteristics; the aquatic organisms that exist or could occur in the waterbody; the flow pattern of the waterbody; and, the fate and existing loadings of contaminants from point and diffuse sources. In some cases, socio-economic factors are also considered in the establishment of site-specific objectives. Final WQOs are established when sufficient scientific information is available; however, provisional objectives may be set when insufficient data exists to develop definitive objectives. The provisional objectives are deliberately conservative and are accompanied by a recommended monitoring or study program that will lead to the establishment of final objectives. A monitoring program is also recommended with WQOs to determine the level of compliance and to identify situations where designated water uses may be endangered. While the WQOs are intended to protect the designated uses of the aquatic ecosystem, they may allow for changes from background conditions. However, such alterations in ambient water quality are permitted only when the Ministry of Environment, Lands and Parks (BCMOELP) considers that some waste assimilative capacity is available and can be used without compromising use-protection. Consistent with this philosophy, the objectives do not apply within the initial dilution zone (IDZ) for point source wastewater discharges. However, the maximum (instantaneous or an average value) objectives that are generally developed are intended to protect against acutely toxic effects within the IDZ. Where water quality has already been degraded, the objectives will establish the goal to be met by corrective measures. Therefore, the objectives provide an effective basis for water management (including setting effluent permit limits), when used in conjunction with other regulatory tools.
Framework for the Development of Water Quality Objectives In Canada, water quality objectives (WQOs) are defined as narrative statements or numerical concentrations of specific substances that are recommended to support and maintain the designated uses of a specific receiving water system (e.g., the Fraser River). The development of WQOs represents one component of an integrated process for ecosystem-based natural resource management in Canada (MacDonald 1994). Other elements of the process involve implementation of a regional basin assessment, consultation with stakeholder groups, and collection and interpretation of additional information on the ecosystem. Two distinct strategies are commonly used to establish WQOs in Canada. For waterbodies with aquatic resources of national or regional significance, the WQOs are established to avoid degradation of existing water quality. For all other waterbodies, the WQOs are established to protect the designated uses of the aquatic ecosystem. As long as the designated water uses are protected, some degradation of existing water quality is considered to be acceptable in these waterbodies. The use-protection strategy provides a consistent scientific basis for establishing WQOs that accommodate multiple water uses of aquatic ecosystems. Using this strategy, ambient WQOs can be derived using three separate approaches, including:
At most sites, the generic WQGs or WQC that have been established by BCMOELP (Nagpal et al. 1995) or the CCME (CCREM 1987) will provide an appropriate basis for establishing the WQOs. However, such generic guidelines may require modification before they are directly applicable to certain sites, especially those with atypical water quality conditions or resident species assemblages. Some of the factors that influence the applicability of the generic guidelines have been identified by the CCME (CCREM 1987; Appendix IV). It may be necessary to develop WQOs on a de novo basis in some cases, particularly when a high level of precision in the resultant objectives is required. Development of numerical WQOs from the generic WQC and WQGs involves a number of steps. The first step in this process involves identification of the designated uses of the aquatic ecosystem. Next, a list of water quality variables of concern is prepared using information on the existing and proposed developments in the basin. Screening the data on wastewater and receiving water quality using the generic WQGs and criteria also supports the identification of contaminants of concern. However, it may be necessary to utilize more sophisticated methods to identify the contaminants that represent significant hazards to aquatic organisms when complex mixtures of contaminants are present in wastewaters or receiving waters (e.g., toxicity identification evaluation procedures; Ankley and Thomas 1992). Once the contaminants of concern are identified, the available WQC or WQGs for each substance and each water use are compiled and modified to account for the ambient water quality characteristics of the waterbody (e.g., pH, water hardness, etc.). For each substance, the water quality guideline for the most sensitive water use is selected as the preliminary WQO. The preliminary WQOs are then compared to the natural background concentrations of each substance, and the higher of the two values is selected as the WQO for that substance. While adoption of generic water quality guidelines represents the primary procedure for establishing numerical WQOs, the presence of unique water quality characteristics or species assemblages at certain sites may necessitate the derivation of site-adapted WQOs. For example, the receiving water at a site could have high levels of dissolved organic carbon, which has the potential to complex dissolved metals and reduce their toxicity. Alternatively, the receiving water system could contain only a warm water fish assemblage, which may be less sensitive to certain contaminants than salmon and trout. In both of these situations, the development of site-adapted WQOs would be appropriate. Therefore, procedures are needed for deriving WQOs that consider the sensitivities of resident species and/or the effect of site water characteristics on contaminant toxicity. At a few sites, it might be necessary to develop WQOs that are directly applicable to the receiving water system under investigation. For example, it might be necessary to develop such site-specific WQOs when insufficient toxicological data are available to develop generic WQGs and WQC for a substance. Alternatively, the generic WQGs may have insufficient information on physical, chemical, and biological characteristics of receiving waters to modify the guidelines to consider site specific conditions. For instance, most toxicological data for the derivation of WQC or WQGs are from water at laboratory temperatures; it is difficult to see if hardness will act independently, in modifying toxicity, at temperatures around zero degrees for overwintering fish. The development of manufacturing processes that reduce the production of waste products and improve the performance of wastewater treatment systems are normal research and development activities that are actively pursued by all responsible corporations and government organizations. Nonetheless, it is possible that the costs associated with implementing the remedial measures necessary to comply with the WQOs could be substantial in certain situations. In such cases, more certainty in the WQOs may be required to assure that such expenditures are justified. Such site-specific WQOs should account for both the sensitivities of resident species and the effects of site water on contaminant toxicity simultaneously.
Review and Evaluation of Approaches and Procedures for Deriving Site-Adapted and de novo Water Quality Objectives. A number of procedures have been developed to support the derivation of water quality objectives (WQOs). While many of these are risk-based or technology-based, several procedures are criteria-based and provide a basis for deriving WQOs that consider the hazards to aquatic organisms associated with exposure to water-borne contaminants, including:
Although most of the procedures are concerned about alteration of the chemical characteristics of the site-specific conditions, physical conditions may also affect significantly the protective values of the WQOs. For example, cold temperature for overwintering may be an issue as some fish are subject to winter stress syndrome. Information on these procedures for deriving WQOs has been reviewed and summarized to provide the reader with adequate information for assessing their applicability in British Columbia and Yukon. In each case, the review has been divided into two main sections, including a brief description of the methodology and an evaluation of its applicability for use in the Pacific and Yukon Region.
In the background concentration procedure, the natural background concentrations of a contaminant in water are determined and these levels are used to define acceptable water quality conditions at the site under consideration. Its use is based on the premise that surface water systems with superior water quality should not be degraded (CCREM 1987). This approach has been used most commonly to define WQOs for relatively pristine waterbodies in Canada, including several river systems (e.g., Dunn 1989; MacDonald and Smith 1990) and Burrard Inlet (Nijman and Swain 1989). Information on background levels of water quality variables is essential for evaluating the suitability of the WQO derived using effects-based procedures (e.g., water effect ratio, resident species, etc.). Site-specific WQOs, developed using the background concentration approach, may be established in at least two ways. First, the upper limit of background may be established as the WQO. In general, statistical procedures are used to estimate the upper limit of background. For example, Dunn (1989) defined the upper limit of background for 15 water quality variables as their mean value plus two standard deviations, while Breidt et al. (1991) used the 90th percentile value to establish these limits. Other statistical procedures have also been recommended for analyzing data on background water quality conditions (Warn 1982; Van Hassel and Gaulke 1986). Second, the WQO may be set at a level which is slightly above the background level. For example, Singleton (1985) suggested that fish and aquatic life in stream systems would be protected if suspended sediment concentrations were elevated by no more than 10% above background levels (this approach was used by the CCREM for their guideline). For flow- or temperature-dependent water quality variables, the WQO may be set at the upper 95% prediction limit of the regression equation for the dependent and independent variables (i.e., either temperature or flow; Schropp et al. 1990). This approach would result in the establishment of WQOs that vary over time and space, in contrast to the single values that are routinely derived. Three general approaches have been used to define background concentrations of water quality variables, which involve:
Determination of the most appropriate method for establishing background concentrations requires consideration of a number of factors related to the waterbody under study. For example, one of the major difficulties associated with the implementation of background concentration procedure relates to the variability of water quality over time and space. River systems and estuaries are subject to large variations in water quality on daily, seasonal, and annual bases. In these types of waterbodies, extensive sampling effort is required to accurately define background concentrations. In addition, it may be difficult to identify suitable reference sites in areas that have been affected by anthropogenic activities for extended periods (e.g., in areas affected by mining or urban development; Runnels et al. 1992). In such cases, it may be necessary to identify nearby reference areas with similar geological, topographical, physiographical, and climatological features to define background levels of naturally occurring substances. The background concentration approach is directly applicable to the development of site-specific WQOs for waters of national or regional significance in British Columbia and Yukon. In addition, the procedures that have been developed to support this approach may be used directly in the process for developing WQOs using the use-protection strategy. Specifically, information on background levels is required to assess the applicability of the preliminary water quality objectives (PeWQOs) that are selected from the available effects-based WQGs and WQC. This assessment is needed to ensure that the WQOs represent realistic targets for water management (i.e., the WQOs should not be lower than background concentrations).
The recalculation procedure is a method for deriving site-specific WQC that accounts for any significant differences between the sensitivity range of the species of aquatic organisms represented in the complete toxicological data set and that of the species that occur (or have historically occurred) at the site under consideration (USEPA 1983). Using this procedure, data on species that are not resident at the site under consideration are eliminated from the data set that was assembled to formulate the generic WQC or WQG. Then, a site-adapted WQO is calculated using the same methodology employed to derive the generic WQG. The recalculation procedure may be used to derive site-specific WQOs only if the minimum data requirements established for formulating national WQGs (CCME 1991 - Appendix IX) are met. Otherwise, additional toxicity testing on resident species in laboratory water is needed to generate the information necessary to derive the site-adapted WQOs. The recalculation procedure is directly applicable to the derivation of site-adapted WQOs in British Columbia and Yukon. When used in conjunction with the protocol for the derivation of WQGs for the protection of aquatic life (CCME 1991), the recalculation procedure provides a very practical means of modifying the generic WQGs to reflect the sensitivities of the species that are present at the site in question. The principle advantage of the recalculation procedure is that it provides a simple, but defensible, basis for deriving site-adapted WQOs. For many substances (metals, toxic compounds of nitrogen, several pesticides, certain polycyclic aromatic hydrocarbons), the data required to derive the site-adapted WQOs are likely to be available in the toxicological data set that was used to develop the generic WQGs. Also, missing data may be generated by conducting acute and/or toxicity bioassays on resident species. Hence, it should be possible to derive the site-adapted WQOs for many substances. Several limitations of the recalculation procedure have been identified by USEPA (1983). First, this procedure requires an evaluation to determine if the site-adapted WQO is significantly different from the generic WQG. However, no guidance has been provided on which statistical tests should be used to conduct such an evaluation. Second, because the national WQC in the United States are derived by determining the 5th percentile value from the overall data set, reductions in the number of families represented in the toxicological data set may result in a reduction in the criterion value. This is particularly evident when the four most sensitive species remain unchanged. This limitation does not apply to the Canadian protocol (CCME 1991), however. Third, elimination of information on non-resident species from the data set may necessitate the generation of additional toxicological information on resident species to support the derivation of site-adapted WQOs. Depending on the number of species and chemicals for which data are required, this process could be costly and time-consuming. Also, the recalculation procedure does not account for bioavailability, multiple uptake routes, pulsed doses, or non-steady state conditions.
The water effect ratio procedure represents a powerful tool for modifying generic WQGs to account for the unique characteristics of the site under investigation. This procedure is based on the fact that the physical and/or chemical characteristics of water can vary among sites and may influence the bioavailability and hence, toxicity of environmental contaminants. In many cases, the factors that influence the toxicity of xenobiotic substances have been identified. For example, relationships between water hardness and acute toxicity to fish have been established for several metals (e.g., cadmium, copper, lead, nickel and zinc; CCREM 1987; Nagpal 1997). Likewise, the toxicity of ammonia to fish is known to be a function of pH and temperature (MacDonald et al. 1987). The presence of other contaminants and other factors (such as suspended particulate matter) at a site could also affect the bioavailability of the substance under consideration. Therefore, consideration of the factors that could influence the toxicity and/or bioavailability of a substance at a site is likely to improve the applicability of the WQO. Using the water effect ratio procedure, acute and/or short-term chronic toxicity tests are conducted with indicator species using both site water and laboratory water (i.e., standard reconstituted laboratory water). Indicator species are acceptable non-resident species that are used as surrogates for resident species. Typically, rainbow trout (Onchorynchus mykiss), fathead minnows (Pimephales promelas), the water flea (Ceriodaphnia dubia), and the alga (Selenastrum capricornutum) are used as indicator species because they are easy to culture, widely available, and consistently generate reliable data (Willingham 1988; MacDonald et al. 1989). Moreover, they are representative of species that are typically found in British Columbia and Yukon (i.e., they are good surrogates). The information generated in these toxicological investigations is used to determine the ratio of the toxicity of the substance in water from the site to its toxicity in laboratory water; this is known as the water effect ratio. The calculated water effect ratio is then used directly to convert the generic WQG to a site-adapted WQO. For example, if a substance is twice as toxic in site water as it is in laboratory water, then the generic WQG would be divided by a factor of two to obtain the site-adapted value. Toxicity data on at least one fish and one invertebrate species are required to calculate the geometric mean water effect ratio, which is then used to modify the generic WQG (USEPA 1994). The water effect ratio procedure is likely to be directly applicable to the derivation of site-adapted WQOs in British Columbia and Yukon. The methods for assessing the acute and short-term chronic toxicity of water-borne substances have been well established (see USEPA 1993a; 1993b; DOE 1990a; 1990b; 1990d; 1992a; 1992b; 1992c). These methods provide a reliable basis for determining water effect ratios for priority substances and hence, for modifying the generic WQGs for the protection of aquatic life. This type of information could also be used to derive site-specific objectives on a de novo basis, provided that the minimum data requirements identified in the protocol document have been met (CCME 1991). The water effect ratio procedure is an extremely useful tool for modifying generic WQGs to account for unique characteristics of the site under investigation. By explicitly considering the toxicity of a substance in the site water, this procedure supports the development of WQOs that are reliable and relevant to the site. In addition to this significant advantage, this procedure is supported by toxicity tests that are easy to run, reasonably inexpensive, and available at most biological testing facilities. The quality of these tests is easily evaluated using the results of the positive (reference toxicant) and negative (solvent only) controls that must be run simultaneously. Furthermore, the bioassays may be performed on site (both flow-through or static tests) or site dilution water can be shipped to a laboratory for off-site testing (static tests only); this adds a considerable level of flexibility to the process. The major limitation of the water effect ratio procedure is that it does not consider the temporal variability of water quality at the site (USEPA 1983). In general, the acute toxicity tests are conducted over a discrete time interval (usually about a week). As such, the water effect ratio that is calculated for the site reflects the sampling program that was used to obtain the site water. It is important to explicitly recognize this limitation because this procedure provides very precise results which tends to generate a great deal of confidence in the WQOs derived. Nonetheless, the WQOs might not be applicable under other circumstances outside the sampling program, such as freshet where the water samples for WER were collected during another period. Therefore, information on the variability of water quality conditions at the site is needed to design a representative toxicity testing program. Diurnal variability in water quality may be accommodated by conducting flow-through bioassays, while seasonal changes in the characteristics of the site water may be assessed by performing tests at key periods throughout the year (e.g., under high flow and base flow conditions). Another limitation of the procedure is associated with the complexity of the implementation guidance that is currently available (i.e., USEPA 1983; 1994). Many of the practitioners that were contacted found the guidance documents to be highly complicated and confusing. Therefore, the procedure needs to be simplified before it can be effectively implemented in British Columbia and Yukon.
The resident species procedure is designed to account for two major factors affecting the derivation of site-specific WQOs: the sensitivity of the species that occur at the site; and, the influence of site water characteristics on toxicity (USEPA 1983). This procedure involves the generation of a complete data set on the acute toxicity of the substance under consideration using site water and resident species (i.e., the data set must satisfy the minimum data requirements for deriving WQGs). Following the USEPA procedure, at least eight families of aquatic organisms that are resident at the site must be represented in this data set, unless fewer than eight families occur at the site. Following their generation, these site-specific acute toxicity data are used directly to establish the final WQOs for the substance at the site (i.e., using the procedures outlined in Stephan et al. 1985). The most serious drawback of this procedure is the cost of conducting the extensive suite of bioassays required to support the derivation of site-specific WQOs. These costs may be even higher than anticipated if significant daily or seasonal variability in water quality is evident at the site. Likewise, costs could escalate if difficulties are encountered in culturing and testing resident species. Many of the limitations discussed for the recalculation and water effect ratio procedures also apply to this procedure (USEPA 1983). The resident species procedure provides a very effective tool for deriving site-specific WQOs when the applicability of generic WQGs to the site is questionable or when such WQGs are not available. WQOs derived using this highly specific data set are likely to be very accurate and, hence, a great deal of confidence may be placed on them. Due to the costs associated with the implementation of this procedure, the resident species procedure is likely to have only limited applications in British Columbia and Yukon. Nonetheless, the procedure provides a consistent and reliable basis for deriving de novo WQOs when generic WQGs are not available and insufficient toxicological information is available to support their derivation. Implementation of this procedure may also be warranted at sites where a high degree of confidence in the WQO is required (e.g., at contaminated sites that are slated to be remediated). Likewise, it may be desirable to use this procedure when the costs associated with remediation are expected to be high.
Four distinct
procedures were reviewed to identify methods that could be
used to derive numerical WQOs in British Columbia and Yukon.
Evaluation of these procedures indicated that no single method
can adequately address all of the potential requirements of
objective development in the Pacific and Yukon Region (Table
1). For this reason, the most useful elements of each procedure
were identified and integrated into the recommended methods
for deriving numerical WQOs (Figure
1). A series of guiding
principles and rules were also developed to assist practitioners
in applying these methods in a consistent manner at sites throughout
the region (see the next section).
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