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A Computer Model for the Estimation of Effluent Standards for Priority Pollutants from a Wastewater Discharge Based Upon Aquatic Life Criterion of the Receiving Stream
A Computer Model for the Estimation of Effluent Standards for Priority Pollutants From a Wastewater Discharge Based Upon Aquatic Life Criterion of the Receiving Stream J.R. Nuckols Certified Professional Eydrologi~t,Lezington, Kentucky, USA S.F. Thomson University of Kentucky Computing Center, Lesington, Kentucky, USA A. G . Westerman Kentucky Department for Environmental Protection, Frankfort, Kentucky, USA ABSTRACT A computer model, the Parameter Estimation Model (PEM), has been developed to provide the user with a numerical calculation of risk associated with the discharge of priority pollutants, as defined by the United States Environmental Protection Agency ( U S . E.P.A.), on the aquatic ecosystem of the receiving stream. The model uses an application of the SASTM statistical computing system in conjunction with standard mass balance analytical techniques to determine the risk associated with the discharge of any pollutant f o r which ambient water quality criterion has been established. The model was developed primarily to assist in the determination of specific numerical values to be used as limits for priority pollutants in permits required by the Federal Clean Water Act. This paper discusses the development of the model, data requirements and procedure for its application, and provides examples of use of the model as a policy-support tool in prescribing specific effluent limits for two Publicly Owned Treatment Works (POTW) in Kentucky. INTRODUCTION
Historically, the estimation of waste assimilation capacity for a stream receiving discharge from a municipal and/or industrial wastewater treatment works has been based on dissolved oxygen depression from organic loading of the stream. Currently, it has been determined that there are design factors other than maintaining desired oxygen levels that have a significant influence on the waste load assimilation capacity of a stream. The U.S. Environmental Protection Agency5 has identified at least 129 pollutants which may adversely impact aquatic ecosystems and the health, safety, and welfare of humans who might use water resources that are downstream to wastewater discharge points. There are an estimated 50,000 additional substances which have yet to be tested for their potential impact on the aquatic environment (U.S.E.P.A.5; Birge, et a1.l). The need for establishing rational standards for these pollutants as they occur in wastewater effluents is an important topic to
357
358 environmentalists, public health advocates, and the industrial and municipal sectors of our society (Garber3; Chalmers2; Stephan4). The purpose of this paper is to introduce a computer model that was developed f o r the purpose of assisting the design engineer, community planner, regulatory authorities, and other citizens that might be concerned about the potential impact of a wastewater discharge on the aquatic life of a receiving stream. The Parameter Estimation Model (PEM) can be used to calculate the risk associated with effluent limits for any pollutant that has been evaluated by the U.S.E.P.A. in its Ambient Water Quality Limits series (U.S.E.P.A.6). The model was designed to be used in addition to, not as a replacement for, waste load assimilation models f o r organic loading such as Biological Oxygen Demand (BOD), etc.
TWE PARAHETER ESTIM&TION MODEL (PEM) The Parameter Estimation Model (PEM) is based upon essentially four criteria: (1) streamflow frequency of flow duration data for the proposed receiving stream; ( 2 ) ambient water quality data for the receiving stream at the proposed discharge point; ( 3 ) a profile of expected pollutants from the discharge; and (4) the recommended ambient water quality limit for each pollutant to be analyzed as prescribed by the U.S.E.P.A. Definition of Variables Q1
C1
=
=
EXPCONC
Q3-
C3
9 Q2* c2
Streamflow in receiving stream. Background concentration of pollutant (j) as F (Q1) .
=
CONSTANT
- Discharge from pollution source.
- CONC - inConcentration discharge.
of pollutant (j)
Qp- Combined discharge of receiving
stream and pollution source.
-
Cp- LIMIT Maximum concentration of pollutant ( j ) allowable i n order to protect aquatic environment at level (k) . Figure 1 Schematic Diagram of PEM Model Basically, the model uses the following flow dilution formula to evaluate the risk potential for a range of values f o r each pollutant to be analyzed:
359 CONC =
(Q2
*
-
LIMIT) (Q1 CONSTANT
*
EXPCONC)
This mass balance relationship is shown schematically in Figure 1. along with a definition of the variables. The model has been designed so that it can simultaneously evaluate any number of pollutants for different levels of protection to the aquatic ecosystem of the receiving stream. These levels of protection currently include acute aquatic life impact, chronic aquatic life impact, and impact on use of the stream as a water supply and fishery by humans. Frequency of flow duration data is required as input data for the model in order to calculate the RISK factor in the output. The United States Geological Survey (U.S.G.S.) publishes flow duration tables for most active and discontinued stream gauging stations operated by that agency. Tables reflecting current data for most U.S.G.S. gauging stations can be assembled from the output of computer program A969 in the U.S.G.S.'s National Water Data Storage and Retrieval System, (acronym WATSTOR; U.S.G.S., 7). In the PEM model, the RISK factor of assigning specific numerical effluent standards to the wastewater stream at the discharge point being analyzed is the inverse of the probability that a flow value will be exceeded. These probabilities are available from the flow duration tables published by the U.S.G.S. The PEM model requires the input of ambient water quality data for each of the pollutants that are desired to be analyzed. The data are inputted as measured average concentration values of the pollutant and must be entered with the corresponding flow value for variable Q1 at the upstream station for each measurement taken. It should be attempted by the model user to provide a measured value for each pollutant over the range of design streamflow values desired to be analyzed. It is especially important to input such data points at the endpoints of the flow duration curve to be analyzed. For each pollutant parameter selected to be analyzed by the PEM model, a value for the desired final stream concentration of the pollutant must be entered into -the model by the user. These values can be obtained from published data such as the Water Quality Criterion documents published by the U.S.E.P.A.6, which are continually being updated. Data is availabl? for approximately 177 different pollutants in these documents. OPERATIONAL INFORMATION AND -EL
OUTPUT
The modeling process is shown in Figure 1.
Basically, PEM
computes an effluent concentration limit, variable CONC, which corresponds to each value of the design streamflow variable, Q1, specified by the user. The 42, or downstream discharge values, are calculated in the model by adding the average discharge value of the point source being analyzed, variable CONSTANT, to the upstream streamflow variable, Ql. The expected background instream concentrations o f the pollutant being analyzed, variable EXPCONC, are computed by linear interpolation of the user specified Ql flow values with the observed concentration and flow values. Finally the program associates the RISK values input when specifying the values of Q1, to the calculated CONC values. The actual analysis was performed using an integrated reporting and statistical computing language, SASTM on the IBM 3081 at the University of Kentucky. SAS has sorting, data manipulation, and statistical capabilities that made it particularly easy to implement the PEM model. Recommended E f f l u e n t L i m i t Level of P r o t e c t i o n : No a c u t e Impact on AQuatic L i f e Pollutant
Dis. Cadmium Concentration
Limit
I
T . Chromium
Concentration Limit
I
T. Comer
T.Cyanide
Concentratio
Concentratio
Limit
Limit
1.79
16.00
9.22
22.00
1.34
16.80
9.74
23.59
0.00
19.83
11.73
29.65
10
0.00
24.29
14.66
38.58
15
0.00
29.39
10.01
40.70
20
0.00
36.72
22.82
63-45
25
0.00
45.65
20.68
01.30
30
0.00
56.81
36.01
103.62
50
0.00
84.26
58.61
171.22
0.00
83.51
102.70
293.01
North Elkhorn Creek below GeorQetovn No.2
POTW
S c o t t County, Kentucky
Figure 2 . Tabular Output Format of the PEM Model. The PEM model provides final output in two formats, a tabular form and a graphical form. An example of the tabular format is presented in Figure 2. In this example, the model was used to evaluate the potential for adverse impact of a proposed publicly owned wastewater treatment discharge in terms of acute toxicity for a small stream in Central Kentucky. An example of the graphical output format from an application of the PEM model is presented in Figure 3 . In this application, the model was used to assist a client in determining which pollutants originating from a leather tanning operation should be subject to regulation in order to
361 protect a receiving stream in Southeastern Kentucky. In the graphical output format of the model, the risk associated with discharging each pollutant as a function of its maximum allowable concentration is presented for each level of protection addressed by the model.
-
R8comm.nd.d
POUUTANT
I
Effluent Umit
2.4.8 mcblorophenol
6UU1
500 4
c
/
9400 I
0
0
300
6
g 200
0
100 0
0
1
0
L
o
9 0 Rink
4
0
0
w
0
Yellow Creek Below Middlesboro POTW
Bell County, Kentucky u v t ~ i - n ~ . c u t . t m p . c t ~ ~ t ~ ~ n ~ ~ uvte ~ no ahronic t m p d 01) -tio IU. U V U S - W a t e r k q.or#mi.nu n f e for human UI
-
Figure 3 . Graphical Output Format of the PEM Model DISCUSSION The PEM model was developed with a number of "end-product" applications in mind; including implementation of policy set forth by the federal Clean Water Act, scientific research in regards to protection of aquatic ecosystems, and development of a scientific method for establishing reasonable and attainable effluent limitations for priority pollutants on a site specific basis In its present form, the model is useful as a policy support tool. For example, in the applications cited above, the primary motivation for implementation of the model was to provide a screening mechanism for pollutants which should be of concern to the regulatory agency. In both cases, the regulatory agency, involved had made the policy decision not to require effluent limits for any of the non-conventional priority pollutants in the Pollution Discharge Elimination System (NPDES) permits for the two Publicly Owned Treatment Works (POTW's) being constructed. This was in spite of the fact that each of the POTWs involved were known to be recipients of significant industrial waste loads; and that the receiving streams had, prior to receiving these discharges, been used extensively for contact recreation and sports fisheries, and in one case, as a secondary water supply. The PEM model was developed to
.
362 provide a basis for requesting specific limits for priority pollutants that could be discharged by these POTWs. The PEM model provides a basis for implementation of a reasonable first definition of pollution control. The procedure prescribed by the model provides the regulatory agency with a basis for establishing specific limits, the discharger with a basis for optimizing its own treatment system ( including establishing reasonable pretreatment standards), and the downstream water user with a level of protection that has a scientific basis. At the same t i . & , the economics for implementation of such a procedure are bound to be costeffective in the long run, especially if we begin to include social and environmental costs into our equations, as we should have been doing all along. REFERENCES 1.
Birge, W.J., J.A. Black and A.G. Westerman. (1985), Shortterm fish and amphibian embryo-larval Tests for Determining the Effects of Toxicant Stress on Early Life Stages and Estimating Chronic Values for Single Compounds and Complex Effluents, Journal of Environmental Toxicology and Chemistry, Vol. 4, pp. 807-821.
2.
Chalmers, R. K. (19841, Standards for Waters and Industrial Effluents, Water Science and Technology, Vol. 16, pp. 219-244.
3. Garber, W.F. (1977), Effluent Standards - Effect Upon Design, Journal of the Environmental Engineering Division, Vo1. 103, pp.1115-1127, American Society of Civil Engineers. New York. 4.
Stephan, C.E. (1985), Are the Guidelines for Deriving Numerical National Water Quality Criterion for the Protection of Aquatic Life and Its Uses Based on Sound Judgements, Aquatic Toxicology and Hazard Assessment, Proceedings of the 7th Symposium of the American Society for Testing and Materials. ASTM STP 854.
5.
U.S. Environmental Protection Agency. (1986). Quality Criteria for Water 1986. Office of Water Regulations and Standards. EPA 440/5-86-001. Washington, D.C.
6. U.S. Environmental Protection Agency. (1980, Revised 1986) Water Quality Criteria Documents. Federal Register, Vol. 45 No. 231, Friday, Nov. 28, 1980. pp. 79318-79379. Washington, D.C.
.
7. U.S. Geologic Survey. (1981). WATSTOR: A Water Data Storage and Retrieval System. Branch of Distribution. U.S.G.S. Alexandria, VA.
Historically, the estimation of waste assimilation capacity for a stream receiving discharge from a municipal and/or industrial wastewater treatment works has been based on dissolved oxygen depression from organic loading of the stream. Currently, it has been determined that there are design factors other than maintaining desired oxygen levels that have a significant influence on the waste load assimilation capacity of a stream. The U.S. Environmental Protection Agency5 has identified at least 129 pollutants which may adversely impact aquatic ecosystems and the health, safety, and welfare of humans who might use water resources that are downstream to wastewater discharge points. There are an estimated 50,000 additional substances which have yet to be tested for their potential impact on the aquatic environment (U.S.E.P.A.5; Birge, et a1.l). The need for establishing rational standards for these pollutants as they occur in wastewater effluents is an important topic to
357
358 environmentalists, public health advocates, and the industrial and municipal sectors of our society (Garber3; Chalmers2; Stephan4). The purpose of this paper is to introduce a computer model that was developed f o r the purpose of assisting the design engineer, community planner, regulatory authorities, and other citizens that might be concerned about the potential impact of a wastewater discharge on the aquatic life of a receiving stream. The Parameter Estimation Model (PEM) can be used to calculate the risk associated with effluent limits for any pollutant that has been evaluated by the U.S.E.P.A. in its Ambient Water Quality Limits series (U.S.E.P.A.6). The model was designed to be used in addition to, not as a replacement for, waste load assimilation models f o r organic loading such as Biological Oxygen Demand (BOD), etc.
TWE PARAHETER ESTIM&TION MODEL (PEM) The Parameter Estimation Model (PEM) is based upon essentially four criteria: (1) streamflow frequency of flow duration data for the proposed receiving stream; ( 2 ) ambient water quality data for the receiving stream at the proposed discharge point; ( 3 ) a profile of expected pollutants from the discharge; and (4) the recommended ambient water quality limit for each pollutant to be analyzed as prescribed by the U.S.E.P.A. Definition of Variables Q1
C1
=
=
EXPCONC
Q3-
C3
9 Q2* c2
Streamflow in receiving stream. Background concentration of pollutant (j) as F (Q1) .
=
CONSTANT
- Discharge from pollution source.
- CONC - inConcentration discharge.
of pollutant (j)
Qp- Combined discharge of receiving
stream and pollution source.
-
Cp- LIMIT Maximum concentration of pollutant ( j ) allowable i n order to protect aquatic environment at level (k) . Figure 1 Schematic Diagram of PEM Model Basically, the model uses the following flow dilution formula to evaluate the risk potential for a range of values f o r each pollutant to be analyzed:
359 CONC =
(Q2
*
-
LIMIT) (Q1 CONSTANT
*
EXPCONC)
This mass balance relationship is shown schematically in Figure 1. along with a definition of the variables. The model has been designed so that it can simultaneously evaluate any number of pollutants for different levels of protection to the aquatic ecosystem of the receiving stream. These levels of protection currently include acute aquatic life impact, chronic aquatic life impact, and impact on use of the stream as a water supply and fishery by humans. Frequency of flow duration data is required as input data for the model in order to calculate the RISK factor in the output. The United States Geological Survey (U.S.G.S.) publishes flow duration tables for most active and discontinued stream gauging stations operated by that agency. Tables reflecting current data for most U.S.G.S. gauging stations can be assembled from the output of computer program A969 in the U.S.G.S.'s National Water Data Storage and Retrieval System, (acronym WATSTOR; U.S.G.S., 7). In the PEM model, the RISK factor of assigning specific numerical effluent standards to the wastewater stream at the discharge point being analyzed is the inverse of the probability that a flow value will be exceeded. These probabilities are available from the flow duration tables published by the U.S.G.S. The PEM model requires the input of ambient water quality data for each of the pollutants that are desired to be analyzed. The data are inputted as measured average concentration values of the pollutant and must be entered with the corresponding flow value for variable Q1 at the upstream station for each measurement taken. It should be attempted by the model user to provide a measured value for each pollutant over the range of design streamflow values desired to be analyzed. It is especially important to input such data points at the endpoints of the flow duration curve to be analyzed. For each pollutant parameter selected to be analyzed by the PEM model, a value for the desired final stream concentration of the pollutant must be entered into -the model by the user. These values can be obtained from published data such as the Water Quality Criterion documents published by the U.S.E.P.A.6, which are continually being updated. Data is availabl? for approximately 177 different pollutants in these documents. OPERATIONAL INFORMATION AND -EL
OUTPUT
The modeling process is shown in Figure 1.
Basically, PEM
computes an effluent concentration limit, variable CONC, which corresponds to each value of the design streamflow variable, Q1, specified by the user. The 42, or downstream discharge values, are calculated in the model by adding the average discharge value of the point source being analyzed, variable CONSTANT, to the upstream streamflow variable, Ql. The expected background instream concentrations o f the pollutant being analyzed, variable EXPCONC, are computed by linear interpolation of the user specified Ql flow values with the observed concentration and flow values. Finally the program associates the RISK values input when specifying the values of Q1, to the calculated CONC values. The actual analysis was performed using an integrated reporting and statistical computing language, SASTM on the IBM 3081 at the University of Kentucky. SAS has sorting, data manipulation, and statistical capabilities that made it particularly easy to implement the PEM model. Recommended E f f l u e n t L i m i t Level of P r o t e c t i o n : No a c u t e Impact on AQuatic L i f e Pollutant
Dis. Cadmium Concentration
Limit
I
T . Chromium
Concentration Limit
I
T. Comer
T.Cyanide
Concentratio
Concentratio
Limit
Limit
1.79
16.00
9.22
22.00
1.34
16.80
9.74
23.59
0.00
19.83
11.73
29.65
10
0.00
24.29
14.66
38.58
15
0.00
29.39
10.01
40.70
20
0.00
36.72
22.82
63-45
25
0.00
45.65
20.68
01.30
30
0.00
56.81
36.01
103.62
50
0.00
84.26
58.61
171.22
0.00
83.51
102.70
293.01
North Elkhorn Creek below GeorQetovn No.2
POTW
S c o t t County, Kentucky
Figure 2 . Tabular Output Format of the PEM Model. The PEM model provides final output in two formats, a tabular form and a graphical form. An example of the tabular format is presented in Figure 2. In this example, the model was used to evaluate the potential for adverse impact of a proposed publicly owned wastewater treatment discharge in terms of acute toxicity for a small stream in Central Kentucky. An example of the graphical output format from an application of the PEM model is presented in Figure 3 . In this application, the model was used to assist a client in determining which pollutants originating from a leather tanning operation should be subject to regulation in order to
361 protect a receiving stream in Southeastern Kentucky. In the graphical output format of the model, the risk associated with discharging each pollutant as a function of its maximum allowable concentration is presented for each level of protection addressed by the model.
-
R8comm.nd.d
POUUTANT
I
Effluent Umit
2.4.8 mcblorophenol
6UU1
500 4
c
/
9400 I
0
0
300
6
g 200
0
100 0
0
1
0
L
o
9 0 Rink
4
0
0
w
0
Yellow Creek Below Middlesboro POTW
Bell County, Kentucky u v t ~ i - n ~ . c u t . t m p . c t ~ ~ t ~ ~ n ~ ~ uvte ~ no ahronic t m p d 01) -tio IU. U V U S - W a t e r k q.or#mi.nu n f e for human UI
-
Figure 3 . Graphical Output Format of the PEM Model DISCUSSION The PEM model was developed with a number of "end-product" applications in mind; including implementation of policy set forth by the federal Clean Water Act, scientific research in regards to protection of aquatic ecosystems, and development of a scientific method for establishing reasonable and attainable effluent limitations for priority pollutants on a site specific basis In its present form, the model is useful as a policy support tool. For example, in the applications cited above, the primary motivation for implementation of the model was to provide a screening mechanism for pollutants which should be of concern to the regulatory agency. In both cases, the regulatory agency, involved had made the policy decision not to require effluent limits for any of the non-conventional priority pollutants in the Pollution Discharge Elimination System (NPDES) permits for the two Publicly Owned Treatment Works (POTW's) being constructed. This was in spite of the fact that each of the POTWs involved were known to be recipients of significant industrial waste loads; and that the receiving streams had, prior to receiving these discharges, been used extensively for contact recreation and sports fisheries, and in one case, as a secondary water supply. The PEM model was developed to
.
362 provide a basis for requesting specific limits for priority pollutants that could be discharged by these POTWs. The PEM model provides a basis for implementation of a reasonable first definition of pollution control. The procedure prescribed by the model provides the regulatory agency with a basis for establishing specific limits, the discharger with a basis for optimizing its own treatment system ( including establishing reasonable pretreatment standards), and the downstream water user with a level of protection that has a scientific basis. At the same t i . & , the economics for implementation of such a procedure are bound to be costeffective in the long run, especially if we begin to include social and environmental costs into our equations, as we should have been doing all along. REFERENCES 1.
Birge, W.J., J.A. Black and A.G. Westerman. (1985), Shortterm fish and amphibian embryo-larval Tests for Determining the Effects of Toxicant Stress on Early Life Stages and Estimating Chronic Values for Single Compounds and Complex Effluents, Journal of Environmental Toxicology and Chemistry, Vol. 4, pp. 807-821.
2.
Chalmers, R. K. (19841, Standards for Waters and Industrial Effluents, Water Science and Technology, Vol. 16, pp. 219-244.
3. Garber, W.F. (1977), Effluent Standards - Effect Upon Design, Journal of the Environmental Engineering Division, Vo1. 103, pp.1115-1127, American Society of Civil Engineers. New York. 4.
Stephan, C.E. (1985), Are the Guidelines for Deriving Numerical National Water Quality Criterion for the Protection of Aquatic Life and Its Uses Based on Sound Judgements, Aquatic Toxicology and Hazard Assessment, Proceedings of the 7th Symposium of the American Society for Testing and Materials. ASTM STP 854.
5.
U.S. Environmental Protection Agency. (1986). Quality Criteria for Water 1986. Office of Water Regulations and Standards. EPA 440/5-86-001. Washington, D.C.
6. U.S. Environmental Protection Agency. (1980, Revised 1986) Water Quality Criteria Documents. Federal Register, Vol. 45 No. 231, Friday, Nov. 28, 1980. pp. 79318-79379. Washington, D.C.
.
7. U.S. Geologic Survey. (1981). WATSTOR: A Water Data Storage and Retrieval System. Branch of Distribution. U.S.G.S. Alexandria, VA.