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Concentrations of radionuclides in Lake Ontario water from measurements on water treatment plant sludges
V~ater Research Vol. 15, pp. 83 to 86 C' Pergamon Press Lid 1981. Primed in Great Britain
0043-1354/81/0101-0083S02.00/0
C O N C E N T R A T I O N S OF R A D I O N U C L I D E S IN LAKE ONTARIO WATER FROM MEASUREMENTS ON WATER TREATMENT PLANT SLUDGES* R. W: DURHAM and S. R. JOSHI Environmental Contaminants Division. National Water Research Institute, Canada Centre for Inland Waters, Environment Canada, P.O. Box 5050. Burlington, .Ontario LTR 4A6, Canada (Received May 1980)
Abslract--The purpose of this investigation was to compare the results of indirect measurements of radionuclide concentrations in water with those measured directly. The levels of lS~Cs and 22°Ra in western Lake Ontario nearshore waters were derived from high-resolution -:-spectrometric measurements on aluminum hydroxide sludge samples obtained from four water treatment plants. The concentrations of lS~Cs evaluated by this indirect technique averaged 0.036 compared with 0.023 pCi 1-1 measured directly, while those of 226Ra averaged 0.047 compared with the direct measurement of 0.03 pCi I- 1 The concentrations of a number of other radionuclides at these locations were also calculated from the sludge y-ray measurements. INTRODUCTION
dishes about 25 cm in diameter were frozen for 2-4 h and then freeze-dried for 4-7 days. The dried samples were ground to pass a 60-mesh sieve and known amounts transferred to standard polystyrene counting vials.
The levels of various y-emitting radionuclides in Great Lakes waters are routinely measured by the Environmental Radiochemistry group of the National Water R e , a r c h Institute ~ R l ) using methods described by Durham (1974). Briefly, a large volume (typically 50 13 of the lake water is acidified before evaporating down to a standard counting volume of 40 e l . The individual radionuclides are identified and their concentrations determined using a standardized low-background Ge(Li) detector coupled to a minicomputer-based pulse height analyzer. The samples are usually counted for 2.5 x 10Ss or more before statistically significant results are obtained at the extremely low concentrations of radionuclides occurring in the lakes. Recently, Roy et al. (1979) have shown that a number of radionuclides are quantitatively removed from the raw water entering a treatment plant by the aluminum hydroxide sludge. The sludge forms as a result of the addition of aluminum sulphate (alum) to the raw water. They have further shown that y-spectral measurements on the dried sludge provide a method of determining the concentrations of ),-emitting radionuclides in raw water. In this communication, we report the results obtained using this approach at four water treatment plants drawing raw water from western Lake Ontario (Fig. t). The validity of these measurements is assessed by comparison with direct analyses of lake water.
Aluminum analyses These analyses were carried out by two methods. In the first, weighed quantities of dried sludge were extracted overnight with I M HC1 and then filtere,d. The extracts were made up to a standard volume with distilled water and the aluminum concentrations determined by atomic absorption spectrometry. In the second, pelletized samples of dried sludge were analyzed by X-ray fluorescence using an AMR-100 scanning electron microscope beam as an excitation source. Emitted X-rays were detected by a liquid nitrogen-cooled Si(Li) detector and analyzed by a Tracor Northern minicomputer-based pulse height analyzer. Nuclear spectrometry The ),-ray spectra of processed samples were obtained using a 70¢m 3. liquid nitrogen-cooled Ge(Li) detector coupled to a Nuclear Data minicomputer-based pulse height analyzer. The y-ray events were accumulated in 2000 channels at 1 keV per channel for counting times which were typically 7.5 x 104 s. The counting rates of the photopeaks were converted to disintegration rates using detector efficiency data obtained from measurements of dried sludge samples spiked with known amounts of standard radioisotope solutions.
RESULTS AND DISCUSSION The municipal water treatment plants involved in the study were Hamilton, Burlington, Toronto (R.C. Harris), and Ajax. The water treatment process is similar for each plant where alum is added to the intake at an average concentration of 7.5mg of A12(SO,)3" 18 H 2 0 per litre of raw water. The concentration of alum is increased at times of high turbidity and. in some cases, polyelectrolytes are added to aid flocculation. The resultant floc of AI(OH)s scavenges suspended material from the raw water along with some dissolved ions, presumably by an
EXPERI MIENTAL METHOD
"~Sample preparation
Approximately 500g samples of the sludges spread on * Paper presented at the 15th Canadian Symposium on Water Pollution Research, Canada Centre for Inland Waters, Burlington, Ontario, February 21, 1980. 83
84
R.W. D u R I ~ and S. R. JOSHI
LAKEONTARIO Burlingt~
Y
f j
Harnilto~=~.~,~ Fig. 1. Locations of water treatment plants. ion-exchange process. The resultant sludge settles out in large underground settling chambers while the treated water, with an insignificant concentration of aluminum, is pumped to the filter beds. Once or twice a year, these settling chambers are drained and the sludge is flushed back to the lake. The sludge samples analyzed in this study were collected during the 1978 spring flushing of the chambers. The r adionuclide concentrations in the dried sludge samples were converted to those for raw water by determining the volume of lake water associated with the mass of dried sludge used in the measurement. This was obtained from-the relative concentrations of aluminum in the dried sludge and in the treated water. These relationships are outlined i n the following equations. Concentration of radionuclide in lake water (pCi I- t) = Concentration in dried sludge ( p C i k g - ' ) (1) Volume of water treated per kg dried sludge (I kg- t ) Volume of water (1) treated per kg dried sludge Ai per kg dried sludge = AI added per litre of raw water"
(2)
The concentrations of radionuclides in lake water determined by this procedure will, of course, have an unknown error associated with them due to the variability of the alum solution addition rate. Also, since the sludge is flushed out of the settling chambers only once or twice a year. the radionuclide concentrations will be averaged so that actual concentrations in lake water of radionuclides with half-lives of a year or less would have been higher than those determined by this method.
Another uncertainty arose in the determination of the volume of lake water corresponding to a given weight of dried sludge. The volume is directly proportional to the aluminum concentration in the sludge, and as Table 1 shows, the two analytical methods gave different results. We have chosen to use the acid extraction values for the water volume calculation because the X-ray fluorescence results include aluminum present in detrital material settling out with the aluminum hydroxide floe. X-ray fluorescence analysis of sludge from the Pickering water treatment plant which has no alum addition, only settling tanks, gave an aluminum concentration of 3%. This corresponds to the difference between the X-ray fluorescence and acid extraction methods of aluminum sludge analysis. An estimate of these errors can be made by comparing the calculated concentrations of two long-lived radionuclides, t3~Cs and '2SRa, shown by Roy et al. (1979) to be quantitatively removed using this method, with measured concentrations of these radionuclides in Lake Ontario. In 1977, we found an average concentration of 0.023 + 0.0t0 pCi l - t for t3:Cs in Lake Ontario (IJC, 1978) and an offshore average of 0.03 pCi 1- t for 22SRa near Port Granby (Durham & Joshi, 1980). Table 2 gives the concentrations of these two radionuclides found in the dried sludge from the four treatment plants and their lake water concentrations calculated using equations (1) and (2). The mean of the "6Ra values is 0.047 _+ 0.005 pCi I- z which is in agreement with the 0.03pCil - t measured in Lake Ontario at Port Granby. The standard deviation of the mean 2:6Ra concentration from the four plants is quite reasonable for such low values of radionuclide concentration.
Table I. Comparison of the two methods for aluminum analyses Plant location Hamilton Burlington Toronto Ajax
Percent aluminum in dried sludge Acid extraction method X-ray fluorescence method 3.25 1.60 2.50 3.25
6.9 6. t 6.7 7.0
Concentrations of radionuclides in Lake Ontario
+1 +t +1 +1
+l +1 +1 +t m
-+-I +1 -I-I +1
~_~_
+1 -H "H "H
e-
e-
w'~¢',4,~'
°~
e-
8 e.i X
e-
X
X
x
85
These correlations suggest that the calculated values of water volume treated per kg of dried sludge from each plant axe reasonably accurate. Similarly, the t37Cs mean of 0.036 + 0.021 pCi 1-1 is in agreement with the 0.023 pCi 1-1 found in the open waters of Lake Ontario, although the spread of results is much greater than that for 226Ra. This spread could be due to the tendency of 13~Cs to attach itself to sedimenting particulates which settle into a flocculent layer at the sediment/water interface. Resuspension of this material during storm activity in the nearshore zone and its conveyance through the plant intake could result in enrichment of the sludge in 137Cs. The ),-spectra obtained from an evaporated 42-1. lake water sample and from a typical sample of dried treatment plant sludge are compared in Fig. 2. Many more radionudides can be identified in the sludge ),-spectrum than in that of the evaporated water sample which consists mainly of photopeaks due to detector background. The concentrations in Lake Ontario water of the remaining ~,-emitting radionuclides which contribute to the ),-spectra of the sludge samples have been calculated for each plant and are given in Table 3. These radionuclides axe all due to fallout from atomic weapons testing with the exception of the naturally-occurring ~Be, :2SRa, and 22STh. No effect of the nearby nuclear generating station at Pickering on Lake Ontario water quality is apparent because the radionuclide 134Cs was not detected. This radionuclide is produced only in long-irradiated nuclear fuel. but not in nuclear explosions. The calculated concentrations of a particular radionuclide vary somewhat between treatment plants, although not unreasonably so when the extremely low concentrations and uncertainties in precipitation efficiencies of aluminum hydroxide for radionuclides are considered. The precipitation efficiency for 12SSb is obviously quite low since the mean concentration in Lake Ontario for 1 9 7 7 was 0.040 pCi 1- ~ (IJC, 1978). while it was only detected in the Ajax sludge corresponding to a lake water concentration of 0.003 pCi 1-1. On the other hand, it is surprising that radium is precipitated quantitatively since the high calcium concentration of 40 ppm in the lake water should serve to hold it in solution. Both 226Ra and 2 2 8 R a a r e found in the sludge, the latter being detected by the ),-ray at 911 keV from its 6.13-h daughter 228Ac.
m.'=
~8
~='~
CONCLUSIONS
The results of this investigation show that there is reasonably good agreement between the direct and the indirect methods of determining ~3~Cs and 226Ra in Lake Ontario water. Even better results should be obtainable if the rate of alum addition at the particulax water treatment plant is known precisely. The indirect method is capable of determining concentrations of many radionuclides which are not detected by direct measurements in 50-1. water samples. The
86
R.W. DURHAMand S. R. Josm
8 :
~"
'q" ~
~ea
~
TORONTO FLTRAT~N Pt.ANT ~.t.CX~ ~ T~ne 1.5x lO~s
~
! ,,,-
~
"~
~
~
~
~
...
=__.,==,..
-
.
,~._
t000
t.AKE ~qTm:lIO ¢#¢mR C o m ~ Tone 3 x ' ~ s Vogille of Wate¢ 42 I (b)
o-2£-
M s o
o
!
IOO0
Fig. 2. Ge(Li) "/-spectra of(a) Toronto treatment plant sludge and (b) representative Lake Ontario water sample processed by evaporation method. Energies are expressed in keV. Table 3. Radionuclide concentrations in Lake Ontario waters Radionuclide ~Be 9SZr 9SNb l°SRu t°6Ru ~2SSb l'iCe t"~Ce Z2SRa Z2STh
Energy (keV)
Half-life
Hamilton
477.6 756.6 765.8 497.0 622.3 427.0 145.4 133.4 911.0 238.6
53.6 day 64 day 35.1 day 40 day I year 2.7 year 32.5 day 284 day 6.7 year 1.9 year
0.030 + 0.001 0,005 -l- 0.001 0.019 4- 0.006 <0,001 0.009 4- 0.001 <0,001 <0,001 0.013 4- 0.001 0.024 5- 0.003 0.030 4- 0.001
quantification may not be reliable for shorter-lived radionuclides because of the long residence times of the sludges in the settling basins. This shortcoming will disappear when newer treatment processes utilizing continuous sludge removal replace older systems (AWWA, 1971).
Acknowtedoements--We are grateful to T. Bistricki for the X-ray microanalyses of the sludge samples and D. Sturterant for the atomic absorption analyses. We also wish to acknowledge the cooperation of the Water Works staff of the Regional Municipalities of Hamilton-Wentworth, Halton, and Durham and that of Metropolitan Toronto in obtaining the sludge samples.
Concentration (IK~i1- ~) Burlington Toronto 0.019 4- 0.003 0.004 ± 0.001 0.006 5- 0.001 <0,001 <0.001 0.002 4- 0.001 <0.001 0.025 4- 0.002 0.038 4- 0.002 0.031 5- 0.001
0.037 0.017 0.039 0.003 0,012 0.003 0.005 0.089 0.025 0.022
4- 0.004 + 0.001 4- 0.001 _+ 0.001 + 0.003 2:0.001 + 0.001 5- 0.002 + 0.002 4- 0.001
Ajax 0.020+ 0.005 0.004 _+ 0.1301 0.007 4- 0.001 <0.001 0.021 + 0.005 0.003 4- 0.001 <0.001 0.026 5- 0.001 0.015 4-_0.002 0.026 4- 0.001
REFERENCES American Water Works Association (1971) Water Quality and Treatment--A Handbook of Public Water Supplies. McGraw-Hill, New York. Durham R. W. (1974) Radionuclide levels in the Great Lakes Waters--1973. Inland Waters Directorate. Canada Centre for Inland Waters, Burlington. Scientific Series No. 48. Durham R. W. & Joshi S. R. {1980) Investigation of Lake Ontario water quality near Port Granby radioactive waste management site. Water Air Soil Pollut. 13, 17-26. International Joint Commission (1978) Great Lakes Water Quality 1977, Appendix D, Radioactivity Subcommittee Report. Roy J.-C,, Barbeau C., C~te, J.-E. & Turcotte J. 11979) A very sensitive sampling method for the measurement of radioactivity in waters from various sources. Nucl. lnsrrura. Merh. 160, 187-191.
0043-1354/81/0101-0083S02.00/0
C O N C E N T R A T I O N S OF R A D I O N U C L I D E S IN LAKE ONTARIO WATER FROM MEASUREMENTS ON WATER TREATMENT PLANT SLUDGES* R. W: DURHAM and S. R. JOSHI Environmental Contaminants Division. National Water Research Institute, Canada Centre for Inland Waters, Environment Canada, P.O. Box 5050. Burlington, .Ontario LTR 4A6, Canada (Received May 1980)
Abslract--The purpose of this investigation was to compare the results of indirect measurements of radionuclide concentrations in water with those measured directly. The levels of lS~Cs and 22°Ra in western Lake Ontario nearshore waters were derived from high-resolution -:-spectrometric measurements on aluminum hydroxide sludge samples obtained from four water treatment plants. The concentrations of lS~Cs evaluated by this indirect technique averaged 0.036 compared with 0.023 pCi 1-1 measured directly, while those of 226Ra averaged 0.047 compared with the direct measurement of 0.03 pCi I- 1 The concentrations of a number of other radionuclides at these locations were also calculated from the sludge y-ray measurements. INTRODUCTION
dishes about 25 cm in diameter were frozen for 2-4 h and then freeze-dried for 4-7 days. The dried samples were ground to pass a 60-mesh sieve and known amounts transferred to standard polystyrene counting vials.
The levels of various y-emitting radionuclides in Great Lakes waters are routinely measured by the Environmental Radiochemistry group of the National Water R e , a r c h Institute ~ R l ) using methods described by Durham (1974). Briefly, a large volume (typically 50 13 of the lake water is acidified before evaporating down to a standard counting volume of 40 e l . The individual radionuclides are identified and their concentrations determined using a standardized low-background Ge(Li) detector coupled to a minicomputer-based pulse height analyzer. The samples are usually counted for 2.5 x 10Ss or more before statistically significant results are obtained at the extremely low concentrations of radionuclides occurring in the lakes. Recently, Roy et al. (1979) have shown that a number of radionuclides are quantitatively removed from the raw water entering a treatment plant by the aluminum hydroxide sludge. The sludge forms as a result of the addition of aluminum sulphate (alum) to the raw water. They have further shown that y-spectral measurements on the dried sludge provide a method of determining the concentrations of ),-emitting radionuclides in raw water. In this communication, we report the results obtained using this approach at four water treatment plants drawing raw water from western Lake Ontario (Fig. t). The validity of these measurements is assessed by comparison with direct analyses of lake water.
Aluminum analyses These analyses were carried out by two methods. In the first, weighed quantities of dried sludge were extracted overnight with I M HC1 and then filtere,d. The extracts were made up to a standard volume with distilled water and the aluminum concentrations determined by atomic absorption spectrometry. In the second, pelletized samples of dried sludge were analyzed by X-ray fluorescence using an AMR-100 scanning electron microscope beam as an excitation source. Emitted X-rays were detected by a liquid nitrogen-cooled Si(Li) detector and analyzed by a Tracor Northern minicomputer-based pulse height analyzer. Nuclear spectrometry The ),-ray spectra of processed samples were obtained using a 70¢m 3. liquid nitrogen-cooled Ge(Li) detector coupled to a Nuclear Data minicomputer-based pulse height analyzer. The y-ray events were accumulated in 2000 channels at 1 keV per channel for counting times which were typically 7.5 x 104 s. The counting rates of the photopeaks were converted to disintegration rates using detector efficiency data obtained from measurements of dried sludge samples spiked with known amounts of standard radioisotope solutions.
RESULTS AND DISCUSSION The municipal water treatment plants involved in the study were Hamilton, Burlington, Toronto (R.C. Harris), and Ajax. The water treatment process is similar for each plant where alum is added to the intake at an average concentration of 7.5mg of A12(SO,)3" 18 H 2 0 per litre of raw water. The concentration of alum is increased at times of high turbidity and. in some cases, polyelectrolytes are added to aid flocculation. The resultant floc of AI(OH)s scavenges suspended material from the raw water along with some dissolved ions, presumably by an
EXPERI MIENTAL METHOD
"~Sample preparation
Approximately 500g samples of the sludges spread on * Paper presented at the 15th Canadian Symposium on Water Pollution Research, Canada Centre for Inland Waters, Burlington, Ontario, February 21, 1980. 83
84
R.W. D u R I ~ and S. R. JOSHI
LAKEONTARIO Burlingt~
Y
f j
Harnilto~=~.~,~ Fig. 1. Locations of water treatment plants. ion-exchange process. The resultant sludge settles out in large underground settling chambers while the treated water, with an insignificant concentration of aluminum, is pumped to the filter beds. Once or twice a year, these settling chambers are drained and the sludge is flushed back to the lake. The sludge samples analyzed in this study were collected during the 1978 spring flushing of the chambers. The r adionuclide concentrations in the dried sludge samples were converted to those for raw water by determining the volume of lake water associated with the mass of dried sludge used in the measurement. This was obtained from-the relative concentrations of aluminum in the dried sludge and in the treated water. These relationships are outlined i n the following equations. Concentration of radionuclide in lake water (pCi I- t) = Concentration in dried sludge ( p C i k g - ' ) (1) Volume of water treated per kg dried sludge (I kg- t ) Volume of water (1) treated per kg dried sludge Ai per kg dried sludge = AI added per litre of raw water"
(2)
The concentrations of radionuclides in lake water determined by this procedure will, of course, have an unknown error associated with them due to the variability of the alum solution addition rate. Also, since the sludge is flushed out of the settling chambers only once or twice a year. the radionuclide concentrations will be averaged so that actual concentrations in lake water of radionuclides with half-lives of a year or less would have been higher than those determined by this method.
Another uncertainty arose in the determination of the volume of lake water corresponding to a given weight of dried sludge. The volume is directly proportional to the aluminum concentration in the sludge, and as Table 1 shows, the two analytical methods gave different results. We have chosen to use the acid extraction values for the water volume calculation because the X-ray fluorescence results include aluminum present in detrital material settling out with the aluminum hydroxide floe. X-ray fluorescence analysis of sludge from the Pickering water treatment plant which has no alum addition, only settling tanks, gave an aluminum concentration of 3%. This corresponds to the difference between the X-ray fluorescence and acid extraction methods of aluminum sludge analysis. An estimate of these errors can be made by comparing the calculated concentrations of two long-lived radionuclides, t3~Cs and '2SRa, shown by Roy et al. (1979) to be quantitatively removed using this method, with measured concentrations of these radionuclides in Lake Ontario. In 1977, we found an average concentration of 0.023 + 0.0t0 pCi l - t for t3:Cs in Lake Ontario (IJC, 1978) and an offshore average of 0.03 pCi 1- t for 22SRa near Port Granby (Durham & Joshi, 1980). Table 2 gives the concentrations of these two radionuclides found in the dried sludge from the four treatment plants and their lake water concentrations calculated using equations (1) and (2). The mean of the "6Ra values is 0.047 _+ 0.005 pCi I- z which is in agreement with the 0.03pCil - t measured in Lake Ontario at Port Granby. The standard deviation of the mean 2:6Ra concentration from the four plants is quite reasonable for such low values of radionuclide concentration.
Table I. Comparison of the two methods for aluminum analyses Plant location Hamilton Burlington Toronto Ajax
Percent aluminum in dried sludge Acid extraction method X-ray fluorescence method 3.25 1.60 2.50 3.25
6.9 6. t 6.7 7.0
Concentrations of radionuclides in Lake Ontario
+1 +t +1 +1
+l +1 +1 +t m
-+-I +1 -I-I +1
~_~_
+1 -H "H "H
e-
e-
w'~¢',4,~'
°~
e-
8 e.i X
e-
X
X
x
85
These correlations suggest that the calculated values of water volume treated per kg of dried sludge from each plant axe reasonably accurate. Similarly, the t37Cs mean of 0.036 + 0.021 pCi 1-1 is in agreement with the 0.023 pCi 1-1 found in the open waters of Lake Ontario, although the spread of results is much greater than that for 226Ra. This spread could be due to the tendency of 13~Cs to attach itself to sedimenting particulates which settle into a flocculent layer at the sediment/water interface. Resuspension of this material during storm activity in the nearshore zone and its conveyance through the plant intake could result in enrichment of the sludge in 137Cs. The ),-spectra obtained from an evaporated 42-1. lake water sample and from a typical sample of dried treatment plant sludge are compared in Fig. 2. Many more radionudides can be identified in the sludge ),-spectrum than in that of the evaporated water sample which consists mainly of photopeaks due to detector background. The concentrations in Lake Ontario water of the remaining ~,-emitting radionuclides which contribute to the ),-spectra of the sludge samples have been calculated for each plant and are given in Table 3. These radionuclides axe all due to fallout from atomic weapons testing with the exception of the naturally-occurring ~Be, :2SRa, and 22STh. No effect of the nearby nuclear generating station at Pickering on Lake Ontario water quality is apparent because the radionuclide 134Cs was not detected. This radionuclide is produced only in long-irradiated nuclear fuel. but not in nuclear explosions. The calculated concentrations of a particular radionuclide vary somewhat between treatment plants, although not unreasonably so when the extremely low concentrations and uncertainties in precipitation efficiencies of aluminum hydroxide for radionuclides are considered. The precipitation efficiency for 12SSb is obviously quite low since the mean concentration in Lake Ontario for 1 9 7 7 was 0.040 pCi 1- ~ (IJC, 1978). while it was only detected in the Ajax sludge corresponding to a lake water concentration of 0.003 pCi 1-1. On the other hand, it is surprising that radium is precipitated quantitatively since the high calcium concentration of 40 ppm in the lake water should serve to hold it in solution. Both 226Ra and 2 2 8 R a a r e found in the sludge, the latter being detected by the ),-ray at 911 keV from its 6.13-h daughter 228Ac.
m.'=
~8
~='~
CONCLUSIONS
The results of this investigation show that there is reasonably good agreement between the direct and the indirect methods of determining ~3~Cs and 226Ra in Lake Ontario water. Even better results should be obtainable if the rate of alum addition at the particulax water treatment plant is known precisely. The indirect method is capable of determining concentrations of many radionuclides which are not detected by direct measurements in 50-1. water samples. The
86
R.W. DURHAMand S. R. Josm
8 :
~"
'q" ~
~ea
~
TORONTO FLTRAT~N Pt.ANT ~.t.CX~ ~ T~ne 1.5x lO~s
~
! ,,,-
~
"~
~
~
~
~
...
=__.,==,..
-
.
,~._
t000
t.AKE ~qTm:lIO ¢#¢mR C o m ~ Tone 3 x ' ~ s Vogille of Wate¢ 42 I (b)
o-2£-
M s o
o
!
IOO0
Fig. 2. Ge(Li) "/-spectra of(a) Toronto treatment plant sludge and (b) representative Lake Ontario water sample processed by evaporation method. Energies are expressed in keV. Table 3. Radionuclide concentrations in Lake Ontario waters Radionuclide ~Be 9SZr 9SNb l°SRu t°6Ru ~2SSb l'iCe t"~Ce Z2SRa Z2STh
Energy (keV)
Half-life
Hamilton
477.6 756.6 765.8 497.0 622.3 427.0 145.4 133.4 911.0 238.6
53.6 day 64 day 35.1 day 40 day I year 2.7 year 32.5 day 284 day 6.7 year 1.9 year
0.030 + 0.001 0,005 -l- 0.001 0.019 4- 0.006 <0,001 0.009 4- 0.001 <0,001 <0,001 0.013 4- 0.001 0.024 5- 0.003 0.030 4- 0.001
quantification may not be reliable for shorter-lived radionuclides because of the long residence times of the sludges in the settling basins. This shortcoming will disappear when newer treatment processes utilizing continuous sludge removal replace older systems (AWWA, 1971).
Acknowtedoements--We are grateful to T. Bistricki for the X-ray microanalyses of the sludge samples and D. Sturterant for the atomic absorption analyses. We also wish to acknowledge the cooperation of the Water Works staff of the Regional Municipalities of Hamilton-Wentworth, Halton, and Durham and that of Metropolitan Toronto in obtaining the sludge samples.
Concentration (IK~i1- ~) Burlington Toronto 0.019 4- 0.003 0.004 ± 0.001 0.006 5- 0.001 <0,001 <0.001 0.002 4- 0.001 <0.001 0.025 4- 0.002 0.038 4- 0.002 0.031 5- 0.001
0.037 0.017 0.039 0.003 0,012 0.003 0.005 0.089 0.025 0.022
4- 0.004 + 0.001 4- 0.001 _+ 0.001 + 0.003 2:0.001 + 0.001 5- 0.002 + 0.002 4- 0.001
Ajax 0.020+ 0.005 0.004 _+ 0.1301 0.007 4- 0.001 <0.001 0.021 + 0.005 0.003 4- 0.001 <0.001 0.026 5- 0.001 0.015 4-_0.002 0.026 4- 0.001
REFERENCES American Water Works Association (1971) Water Quality and Treatment--A Handbook of Public Water Supplies. McGraw-Hill, New York. Durham R. W. (1974) Radionuclide levels in the Great Lakes Waters--1973. Inland Waters Directorate. Canada Centre for Inland Waters, Burlington. Scientific Series No. 48. Durham R. W. & Joshi S. R. {1980) Investigation of Lake Ontario water quality near Port Granby radioactive waste management site. Water Air Soil Pollut. 13, 17-26. International Joint Commission (1978) Great Lakes Water Quality 1977, Appendix D, Radioactivity Subcommittee Report. Roy J.-C,, Barbeau C., C~te, J.-E. & Turcotte J. 11979) A very sensitive sampling method for the measurement of radioactivity in waters from various sources. Nucl. lnsrrura. Merh. 160, 187-191.