Water Quality
WATER MANAGEMENT BRANCH
ENVIRONMENT AND RESOURCE DIVISION
MINISTRY OF ENVIRONMENT, LANDS AND PARKS
McKean, Colin J. P. (Colin John Pearce), 1955- Cowichan-Koksilah Rivers water quality assessment and objectives [Vol. 2] constitutes technical appendix. Includes bibliographic references. ISBN 0-7726-1606-x 1. Water quality - British Columbia - Cowichan River. 2. Water quality - British Columbia - Koksilah River). I. BC Environment. Water Management Division. II. Title. TD227.B7M334 1992 363.73'942'097112 C92-092267-8
The Cowichan River, which originates at the south end of Cowichan Lake, is the most important river on Vancouver Island for recreational fisheries (steelhead, cutthroat, rainbow, brown trout and kokanee) and commercail fisheries (coho, chinook and chum). The river is also important for water contact recreation such as kayaking, canoing, etc. and as a source of water for domestic, irrigation and industrial uses (BC Forest Products Crofton Pulp Mill). The Village of Lake Cowichan obtains its water supply from Cowichan Lake while the City of Duncan obtains its water from wells adjacent to the Cowichan River downstream from the Island Highway.
The Koksilah River is also important for recreational and commercial fish species as well as recreational activities and domestic, irrigation and industrial water supplies. However, since the river does not have a large lake within its watershed to provide water storage, summer stream flows are approximately 95% lower than flows in the Cowichan River. Consequently, the value of the above uses in the Koksilah River are reduced relative to the Cowichan River.
There are three permitted discharges on the Cowichan River. The sewage discharge from the Village of Lake Cowichan and the discharge of ground water used in a Ministry of Environment fish hatchery have little of no impact on the water quality of the Cowichan River. The third permitted discharge is sewage from the Duncan/North Cowichan treatment plant. The effluent is not adequately diluted in the Cowichan River during the summer low flow period. High concentrations of nitrogen and phosphorus cause excessive periphyton growth for several kilometers downstream from the discharge.
Water quality objectives are set in the Cowichan River for a number of possible contaminants. These originate from a sawmill located at Youbou, a small abandoned base metal mine adjacent ot Cowichan Lake, future base metal mining in the upper Cowichan watershed, public wharves near the outlet of the lake and the sewage discharges to the river.
Water quality objectives are set in the Koksilah River to protect water uses from two sources of contantamination: potential bacterial contamination from dairy farms near Dougan Lake and contaminants from the Cowivchan Valley Regional Distruict incinerator/landfill and gravel washing operations near Duncan.
Water quality objectives are set to protect the most sensitive water uses in both rivers. The objectives and a monitoring program for the Cowichan and Koksilah rivers are summarized in Table 1, Table 2, Table 3 and Table 4.
Water quality objectives are prepared for specific bodies of fresh, estuarine and coastal marine surface waters of British Columbia as part of the Ministry of Environment, Lands and Parks' mandate to manage water quality. Objectives are prepared only for those waterbodies and water quality characteristics that may be affected by human activity now or in the near future.
How Objectives Are DeterminedWater quality objectives are based the BC approved and working criteria as well as national water quality guidelines. Water quality criteria and guidelines are safe limits of the physical, chemical, or biological characteristics of water, biota (plant and animal life) or sediment which protect water use. Objectives are established in British Columbia for waterbodies on a site-specific basis. They are derived from the criteria by considering local water quality, water uses, water movement, waste discharges, and socio-economic factors.
Water quality objectives are set to protect the most sensitive designated water use at a specific location. A designated water use is one that is protected in a given location and is one of the following:
Each objective for a location may be based on the protection of a different water use, depending on the uses that are most sensitive to the physical, chemical or biological characteristics affecting that waterbody.
How Objectives Are UsedWater quality objectives routinely provide policy direction for resource managers for the protection of water uses in specific waterbodies. Objectives guide the evaluation of water quality, the issuing of permits, licences and orders, and the management of fisheries and the province's land base. They also provide a reference against which the state of water quality in a particular waterbody can be checked, and help to determine whether basin-wide water quality studies should be initiated.
Water quality objectives are also a standard for assessing the Ministry's performance in protecting water uses. While water quality objectives have no legal standing and are not directly enforced, these objectives become legally enforceable when included as a requirement of a permit, licence, order, or regulation, such as the Forest Practices Code Act, Water Act regulations or Waste Management Act regulations.
Objectives and MonitoringWater quality objectives are established to protect all uses which may take place in a waterbody. Monitoring (sometimes called sampling) is undertaken to determine if all the designated water uses are being protected. The monitoring usually takes place at a critical time when a water quality specialist has determined that the water quality objectives may not be met. It is assumed that if all designated water uses are protected at the critical time, then they also will be protected at other times when the threat is less.
The monitoring usually takes place during a five week period, which allows the specialists to measure the worst, as well as the average condition in the water.
For some waterbodies, the monitoring period and frequency may vary, depending upon the nature of the problem, severity of threats to designated water uses, and the way the objectives are expressed (i.e., mean value, maximum value).
This report discusses the water quality of the two rivers, interprets the impact of the non[point and point discharges and develops water quality objectives to protect the major uses of the rivers.
A detailed Technical Appendix was prepared by the author and forms the basis for the conclusions presented.
The Koksilah River has very low stream flows during the summer (0.3 m3/s) principally because the river does not have a large headwater lake with water storage to augment summer low flows.
The Village of Lake Cowichan anfd the City of Duncan do not obtain their domestic water from the Cowichan River. The Village of Lake Cowichan has water intakes at the east end of Cowichan Lake while the City of Duncan has wells located adjacent to the Cowichan River approximately 1 km downstream from the highway bridge.
The fisheries rersource of the Cowichan/Koksilah system has been estimated at 2 million dollars per year for sports fish (coho, chinook, steelhead, resident and anadromous trout), 2.5 million dollars per year in commercial fish (coho, chinook, chum) and 650 thousand dollars per year in angler-day value (cost of sport fishing). The Cowichan River contributes the bulk of the sport and commercial value ( approximately 80 to 90 percent).
Water based recreation is well represented along the Cowichan and Koksilah rivers. There are five provincial parks and other regional, municipal and community parks adjacent to the rivers. Kyaking and hiking trails are also important recreational uses of the watershed. Although no estimates of the recreational value are available, the Cowichan and Koksilah are considered to be recreationally important rivers.
The City of Duncan and the Municipality of North Saanich jointly operate a similar sewage treatment facility near the City of Duncan. The permit (PE 1497) allows the direct discharge of 13600 m3/d of effluent 1.5 km downstream from the highway bridge near the mouth of the river. The maximum discharge to date has been 7859 m3/day which is 57 percent of the maximum permitted discharge.
The third permitted discharge into the Cowichan River is ground water used for fish culture by a Ministry of Environment fish hatchery. The permit (PE 6603) allows for a maximum discharge of 5077 m3/day. The location of the discharge is 1 km upstream from the Duncan/North Cowichan sewage discharge.
The dilution of these discharges by the Cowichan River is important in determining their impact on water quality. Based on the Pollution Control Objectives for Municipal Waste Discharges, the preferred dilution of the sewage effluent is greater than 200:1. The theoretical minimum dilution ratios for the sewage discharges were calculated using the 1-in-2-year, 7-day average low flow for the Cowichan River and the average effluent discharges recorded in the low flow month (e.g., August or September). Using the above flow and discharge rates, the dilution ratios of the Village of Lake Cowichan and the Duncan/North Cowichan effluents are 330:1 and 68:1, respectively. Assuming the maximum permitted discharge of PE 1497 (13000 m3/day) the dilution ratio for the Duncan/North Cowichan effluent would be 33:1.
There are public wharves, a small abandoned mine and an operational sawmill upstream from the Cowichan River which may also impact the water quality of the river. Cowichan Copper (also known as Blue Grouse) was a base metal mine within the Cowichan Lake watershed. The mine site is not a source of metals to the system at this time. The public wharves are a potential source of copper from anti-fouling paints. Microbiological contamination is possible from boats without septic holding tanks. The sawmill operated by BC Forest Products at Youbou may discharge anti-sapstain compounds which are potentially toxic to fish. Water quality objectives are set at the outlet of Cowichan Lake to protect the water uses of the Cowichan River from contaminants produced from these sources.
The Koksilah River does not have any permitted discharges; however, nonpoint nutrient and bacteriological contamination from dairy farms adjacent to Dougan Lake and runoff from the Cowichan Valley Regional District incinerator/landfill and gravel washing operations near Duncan, are potential sources of contaminants to the Koksilah River.
Coliform bacteria are frequently detected at the outlet of Cowichan Lake and in the Koksilah River at the highway. The source of the fecal coliform contamination has not been determined.
Metals data have been collected on the Cowichan and Koksilah rivers for several years. Total copper, lead and, to a lesser extent, mercury and zinc are frequently detected in the Cowichan River near Riverbottom Road and the highway bridge, and in the Koksilah River at the highway. The concentrations of the above metals are generally low, with higher concentrations occurring during the winter months when stream flows are higher.
The impact of permitted discharges on the water quality of the Cowichan River is variable. The impact of the discharge from the Ministry of Environment fish hatchery is minimal throughout the year because of the low concentrations of nitrogen and phosphorus in the effluent. The impact of the effluent from the Village of Lake Cowichan is considered minor because of the high degree of dilution during the critical summer low flow period.
The discharge from the Duncan/North Cowichan sewage treatment facility has a detectable impact on the water quality of the Cowichan River. Fecal coliform concentrations remain low downstream from the discharge because of the adequate chlkorination and dilution. However, the low dilution ratio in the summer can cause minor increases in turbidity and suspended residues and significant increases in ammonia-nitrogen and dissolved phosphorus. The high nutrient loading causes excessive periphyton growth for several kilometers downstream from the discharge. The excessive periphyton growth can ionterfere with spawning salmonids, increase intra-gravel biological oxygen demand or decrease intragravel oxygen concentration thereby affecting incubating fish eggs or the benthic community. High ammonia nitrogen concentrations can cause an avoidance reaction or be toxic to fish.
The objectives are based on working criteria for water quality and on available data on ambient water quality, waste discharges, water uses and limnological characteristics. Some objectives will be provisional until the water quality monitoring programs provide adequate data and the Ministry has established approved water quality criteria for the characteristics of concern.
Water quality objectives have no legal standing and are not directly enforced. The objectives should be considered as policy guidelines for resource managers to protect water uses in specified water bodies. They will guide the evaluation of water quality, the issuing of permits, licences and orders and the management of the fisheries and the Province's land base. They will also provide a reference against which the state of water quality in a particular water body can be checked and serve in making decisions on whether to initiate basin-wide water quality studies.
Depending on the circumstances, water quality objectives may already be met in a water body, or may describe water quality conditions which can be met in the future. To limit the scope of the work. objectives are only being prepared for waterbodies and for water quality characteristics which may be affected by man's activity, now and in the future.
It is proposed that the following uses, not necessarily in order of importance, be adopted as the designated water uses to be protected in the rivers:
the fecal coliform and Escherichia coli densities shall not exceed 10 cells/100 mL, and the enterococci density shall not exceed 3 cells/100 mL in 90% of at least 5 weekly samples taken at any point within a 30-day period. The objective is based on the Ministry of Health guidelines for drinking water supplies (that require only chlorination or equivalent) and on the Ministry of Environment water quality criteria for microbiological indicators.Within the Cowichan Band Indian Reserve there are no domestic water users; however, the Cowichan Band uses the river to catch fish. This use is considered equivalent to secondary-contact recreation. The bacteriological objectives for this reach of the Cowichan River (from the Island Highway bridge to the mouth outside initial dilution zones are:
the fecal coliform and Escherichia coli densities shall not exceed geometric means of 100 and 385 cells/100 mL, respectively, calculated from at least 5 weekly samples taken during a 30-day period. The objectives for this reach are based the Ministry of Environment water quality criteria for microbiological indicators.Koksilah River
the fecal coliform and Escherichia coli densities shall not exceed 10 cells/100 mL, and the enterococci density shall not exceed 3 cells/100 mL in 90% of at least 5 samples taken at any point within a 30-day period.
The impact of the gravel washing operations adjacent to the Koksilah River near Duncan is not known, but they are potential sources of suspended residues to the Koksilah River.
The suspended residue objective for the Cowichan and Koksilah rivers outside initial dilution zones is:
not more than a 10 mg/L increase if background concentrations are less than 100 mg/L, or not more than a 10 percent increase if background concentrations are greater than 100 mg/L.
The turbidity objective for any point outside an initial dilution zone of a permitted discharge is:
if background turbidity levels are less than or equal to 50 NTU, the maximum increase should be less than or equal to 5 NTU; however, if background turbidity levels are greater than 50 NTU, the maximum increase should be less than or equal to 10% of background.
The Cowichan River downstream from the Duncan/North Cowichan sewage treatment discharge is used by the Cowichan Indian Band for salmon fishing. This activity is considered to require the same protection as secondary-contact recreation; consequently, a chlorophyll-a objective of 50 mg/m2 for aesthetics is used for the Cowichan River downstream from the Village of Lake Cowichan and the Duncan/North Cowichan sewage discharges beyond the initial dilution zones.
A 'total residual chlorine' objective of 2 micrograms/L is set on the Cowichan River outside the initial dilution zones for the protection of aquatic life.
| dissolved metals | 30-day average (mg/L) | maximum concentration (mg/L) |
| copper | 0.002 | 0.004 |
| lead | 0.003 | 0.008 |
| zinc | 0.030 | 0.180 |
| The 30-day average is calculated from a minimum of 5 weekly samples collected in 30-days. |
The objectives are expressed as the dissolved fraction to avoid confusion with metals associated with suspended residues which frequently increase down the length of the rivers.
| Characteristics | Cowichan River | Koksilah River | |
| Lake to Highway | Highway to Mouth | ||
| Designated uses | drinking, aquatic life, irrigation, industry, primary-contact recreation | aquatic life, irrigation, secondary-contact recreation | drinking, aquatic life, irrigation, industry, primary-contact recreation |
| fecal coliforms | less than 10/100 mL 90 th percentile |
not applicable | less than 10/100 mL 90 th percentile |
| Escherichia coli | less than 10/100 mL 90 th percentile |
less than 385/100 mL geometric mean |
less than 10/100 mL 90 th percentile |
| enterococci | less than 3/100 mL 90 th percentile |
less than 100/100 mL geometric mean |
less than 3/100 mL 90 th percentile |
| turbidity | -less than or equal to 5 NTU increase when background is less than or equal to 50 NTU -less than or equal to 10% NTU increase when background is greater than 50 NTU |
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| suspended residues | -less than or equal to 10 mg/L increase when background is less than or equal to 100 mg/L -less than or equal to 10% increase when background is greater than 100 mg/L |
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| ammonia nitrogen | AMMONIA TABLES | not applicable | |
| chlorophyll-a | 50 mg/m2 maximum | not applicable | |
| total chlorine residual | 0.002 mg/L maximum | not applicable | |
| dissolved oxygen | -11.2 mg/L minimum from October to May -8.0 mg/L minimum from June to September |
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| dissolved copper | -2 micrograms/L average -4 micrograms/L maximum -or 20% increase over background, whichever is greater |
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| dissolved lead | -3 micrograms/L average -8 micrograms/L maximum -or 20% increase over background, whichever is greater |
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| dissolved zinc | -30 micrograms/L average -180 micrograms/L maximum -or 20% increase over background, whichever is greater |
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| copper-8-quinolinolate | 0.5 micrograms/L maximum | not applicable | |
| Note: Objectives apply to discrete samples from all parts of the waterbody except from initial dilution zones of effluents. These excluded dilution zones are defined as extending 100 m downstream from the discharge point and no more than 50 percent across the width of the stream, from the surface to the bottom. 1. The fecal coliform, enterococci and Escherichia coli geometric means and 90th percentiles are calculated from at least 5 weekly samples taken in a period of 30-days. All bacteriological objectives apply on a year-round basis. 2. Since the chlorine residual objective is less than the minimum detectable concentration, it may be necessary to estimate the receiving water concentration using effluent loading and streamflow. 3. The ammonia nitrogen objective is an average of at least 5 weekly samples taken in a period of 30 days during low river flow. 4. The copper-8-quinolinolate is a provisional objective to be finalized when additional analysis by the Ministry of Environment has been completed. 5. The copper, lead, zinc, turbidity and suspended residues increase is over levels measured at a site upstream from a discharge or series of discharges and as close to them as possible, and applies to downstream levels. 6. The chlorophyll-a objective is based on the average from 5 to 10 individual samples collected on the same day outside the initial dilution zones. Natural substrates are to be used and, if the periphyon distribution is clumped, the percent cover of the community sampled must be noted. |
| Sites | Frequency and Timing | Characteristics to be Measured |
| Cowichan River E206108, 0120808, E206107, 0120801, 0120802, E206106 Koksilah River E207425, E206976, 0123981 |
5 weekly samples over 30 days during low flow (generally August) and high flow (generally January) | fecal coliforms, enterococci, Escherichia coli, (MF) |
| Cowichan River 0120808, E206107, 0120802, E206106 Koksilah River E206976, 0123981 |
turbididty, suspended residues | |
| Cowichan Lake (outlet) 0130180 Cowichan River E206108 Koksilah River 0123981 |
dissolved copper, lead and zinc | |
| Cowichan River E206108 |
copper-8-quinolinolate | |
| Cowichan River 0120808, E206107, 0120802, E206106 |
5 weekly samples over 30 days during low flow (generally August) | dissolved oxygen, temperature |
| Cowichan River E206107, E206106 |
ammonia nitrogen, field pH, temperature | |
| 5 to 10 individual samples collected on the same day during low flow (generally August) | chlorophyll-a, phaeophytin, biomass, taxonomy sample | |
| Duncan/North Cowichan sewage treatment facilities after dechlorination | 5 weekly samples over 30 days during low flow (generally August) plus monthly samples | total residual chlorine, discharge volume, stream flow |
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