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Water Quality Ambient Water Quality Criteria for Chlorine Overview Report Prepared
pursuant to Section 2(e) of the H.
J. Singleton B.Sc. RPBio. Original
signed by Richard L. Dalon This report is one in a series which establishes ambient water quality criteria for British Columbia. The criteria are safe conditions or levels of contaminants, applicable province-wide, which are set to protect various water uses. This report sets criteria for chlorine to protect aquatic life in fresh water and marine water. It also sets a criterion to protect plants grown in soil-less media against chlorine in irrigation water. The criteria are summarized in the tables. The criteria to protect aquatic life are set for either continuous exposure to chlorine or for intermittent exposure. For continuous exposure, we have a single criterion expressed as an average measured over a period of time. For intermittent exposure, the criteria are expressed as both average and maximum values, and are less stringent than for continuous exposure. These criteria are more flexible and detailed than the single criterion of the CCREM (now known as CCME) Canadian Water Quality Guidelines (1987). We set the criterion for irrigation water as a maximum value to protect plants grown hydroponically or in inert media. We did not set criteria for other uses, such as drinking water, wildlife, or recreation because these uses can tolerate chlorine at levels far above those likely to occur in ambient waters. A
major use of the criteria is to set ambient water quality objectives.
The objectives are the criteria modified or adopted to protect
the most sensitive
water use in a particular body of water. The objectives are used in the
preparation of waste management permits, which are the only entity to have
legal standing. The objectives, however, are not usually part of the permit. Table 1. Summary of Water Quality Criteria for Chlorine
THE MINISTRY OF ENVIRONMENT, LANDS and PARKS (now called MINISTRY OF WATER, LAND and AIR PROTECTION) develops province-wide ambient water quality guidelines for variables that are important in the surface waters of British Columbia. This work has the following goals:
Neither guidelines nor objectives which are derived from them, have any legal standing. The objectives, however, can be used to calculate allowable limits or levels for contaminants in waste discharges. These limits are set out in waste management permits and thus have legal standing. The objectives are not usually incorporated as conditions of the permit. The definition
adopted for a guideline is:
The guidelines are set after considering the scientific literature, guidelines from other jurisdictions, and general conditions in British Columbia. The scientific literature gives information on the effects of toxicants on various life forms. This information is not always conclusive because it is usually based on laboratory work which, at best, only approximates actual field conditions. To compensate for this uncertainty, guidelines have built-in safety factors which are conservative but reflect natural background conditions in the province. The site-specific water water quality objectives are, in most cases, the same as guidelines. However, in some cases, such as when natural background levels exceed the guidelines, the objectives could be less stringent than the guidelines. In relatively rare instances, for example if the resource is unusually valuable or of special provincial significance, the safety factor could be increased by using objectives which are more stringent than the guidelines. Another approach in such special cases is to develop site-specific guidelines by carrying out toxicity experiments in the field. This approach is costly and time-consuming and therefore seldom used. Guidelines
are subject to review and revision as new information becomes
available, or as other circumstances dictate.
These criteria are based on a detailed analysis given in a technical document. The criteria are consistent with the Canadian Water Quality Guidelines (CCREM Guidelines) issued by the Canadian Council of Resource and Environment Ministers (1987), except as noted (the CCREM is now known as the CCME, or Canadian Council of Ministers of the Environment).
Total residual chlorine (TRC) is the sum of the free available chlorine plus the combined available chlorine. This includes all the forms of chlorine which are able to act as an oxidant.
In marine or estuarine waters, the term chlorine-produced oxidants (CPO) is used because of the high concentrations of bromide naturally present in seawater. Bromide, in the presence of residual chlorine, forms free available bromine or combined available bromine which are able to act as oxidants.
Application of Guidelines for Aquatic Life To determine whether monitoring is necessary, a worst-case scenario should be formulated using site-specific information which includes the effluent concentration of TRC and the minimum dilution available at the edge of the initial dilution zone. If the average criterion value for continuous exposure is not exceeded by the calculated estimate under worst-case conditions, then monitoring is unnecessary regardless of whether the exposure is intermittent or continuous. If calculations show that the average criterion value for continuous exposure could be exceeded, for freshwater or seawater as appropriate, then monitoring should be initiated. When monitoring for TRC or CPO is necessary, the amperometric method of analysis is recommended. Furthermore, it is recommended that an individual, experienced in the operation of an amperometer, be designated to perform the analyses. While frequent monitoring may be necessary to determine if criteria are being met, usually only a short-term monitoring program is necessary. Such a monitoring program should be performed at times when minimum dilution is available, in keeping with the worst-case scenario. An initial assessment should be made to determine whether exposure at the edge of the initial dilution zone is continuous or intermittent. In some situations this determination may be obvious. For example, if a discharge is continuously chlorinated then, in all likelihood, the exposure will be continuous and the appropriate criteria will apply. However, if a discharge is intermittently chlorinated it does not necessarily follow that exposure is intermittent. For example, if the discharge is to a moving body of water such as a river then, in all likelihood, exposure will be intermittent. On the other hand, if TRC is discharged intermittently to a relatively motionless body of water such as a lake, exposure may be intermittent or continuous depending upon whether residuals persist between the chlorination periods. If residuals do persist through the periods of non-chlorination, then the situation should be treated as continuous exposure and the continuous exposure criteria should apply. If residuals do not persist at the edge of the initial dilution zone, then the intermittent exposure criteria should apply. While the monitoring schedule should be somewhat flexible to determine if criteria are being met, enough samples should be taken to provide a relatively accurate profile of the exposure characteristics. For continuous exposure situations, at least 5 samples, equally spaced in time, are recommended to determine an average concentration over the averaging periods. The minimum duration of the averaging periods is 4 days for freshwater, and only 2 hours for marine or estuarine waters, but may be as long as 30 days. For an intermittent exposure situation, some knowledge of the chlorination schedule, including the start times, duration of the chlorination period, and daily frequency, would be helpful prior to monitoring. This prior knowledge would provide an indication of when to start monitoring so that samples could be collected over the entire exposure period. Monitoring should be continued as frequently as possible over the chlorination period and until the concentration at the edge of the initial dilution zone drops below the continuous exposure criterion (i.e., 2 or 3 µg/L for fresh or marine water as appropriate). The concentrations measured over the uninterrupted duration of exposure should be averaged and the average value should not exceed the appropriate freshwater 1.2(a) or marine and estuarine 2.2(a) criterion. No individual sample should exceed 100 µg/L TRC in freshwater or 40 µg/L CPO in marine or estuarine water, as per Sections 1.2(c) or 2.2(c). Since the intermittent exposure criteria formulae (1.2(a) or 2.2(a)) are based on the acute toxicity threshold, application of these criteria at the edge of the initial dilution zone could lead to acutely toxic conditions for a short time within the initial dilution zone, depending upon the dilution available and upon the exposure time of organisms in the initial dilution zone. These items should be considered on a site-specific basis. It should
be noted that while intermittent exposures are not restricted
by a lower chronic criterion, they are restricted in terms
of a maximum exposure
period of 2 hours in any consecutive 24-hour period. If the duration of
exposure at the edge of the initial dilution zone exceeds 2 hours in any
consecutive 24-hour period, then the more stringent continuous criterion
should be applied.
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