FEATURE
Assessing cross=mediaimpacts A control strategy to achieve air quality may affect water quality adversely. Minimization of cross-pollution at least cost and greatest benefit is possible
Howard Reiquam
Norbert Dee
Paul Choi
El Paso Natural Gas Co. El Paso, Texas 79978
Battelle-Columbus Laboratories Columbus, Ohio 43201
Battelle-Columbus Laboratories Columbus, Ohio 4320 1
The Clean Air Amendments of 1970 and the Federal Water Pollution Control Act Amendments of 1972 mandate national ambient air quality standards on the one hand, and specific aqueous effluent standards for individual facilities on the other. These limitations on pollutant discharge often have important secondary impacts beyond the intended improvement in air or water quality. Certain control technologies aimed at achieving spe.cific limits generate new waste streams which, in turn, require controls. Without a systematic assessment of these impacts, there is a substantial risk that pollution control strategies for controlling pollution i n one medium will exacerbate problems in another medium. Using coal-fired central power stations as the example, the impacts upon other media nand, air, water) are analyzed when controls are imposed on one medium; the development of a methodology for assessing the cross-media impact of specific control technologies or strategies is illustrated. The assessment methodology consists essentially of evaluating an index for each control strategy and comparing it to a corresponding index for the uncontrolled case. The index is a function of the 0 rate of production of pollutants, 0 behavior of these pollutants in the environment, and 0 relative importance of each pollutant. Application of the methodology permits an evaluation of the net effect of a particular strategy upon the environment as a whole. Data assembled and used for illustration consist of the production rates of primary pollutants from 1000 MW coal-fired power stations to each of the three media, and of secondary pollutants caused by the application of each control strategy. Although not utilized directly in the assessment methodology, the costs associated with each strategy in terms of energy consumption, capital costs, and operating costs'are also presented. Assessment technique Waste streams from industrial processes and control strategies are defined by their physical and chemical parameters. The approach used for developing a comprehensive list of pollutants is described by a three-step structure. 0 Identification of industrial classification. EPA has grouped industries into major categories based, in part, on their effluent characteristics and volume. 0 .Identification of control strategies. Control strategies appropriate to the industrial category are identified. Pollutants associated with each control are then identified. 0 Organization of pollutants. Each pollutant identified is related to a specific medium. A two-level hierarchy is 118
Environmental Science & Technology
used to describe the pollutants: the medium at the first level and the pollutants at the second. The magnitude of environmental damage is a function of the production of the waste generated, and the behavior of the waste in the environment. The potential damage of waste production is measured by using damage functions. This potential is then adjusted by the pollutants' dispersal range, persistence, and interaction with other media. The damage function transforms the total production of a pollutant discharged into a corresponding index of potential environmental damage. The index is a number between 0 and l , where 0 denotes no potential environmental damage, and 1 extremely high potential environmental damage. The functional form relating the total production of a pollutant discharged to potential environmental damage can be described by an S-shaped curve. A damage function is constructed for each pollutant to be considered in evaluating a set of control strategies. For each industrial class, a set of damage functions can be constructed based on the production of the pollutants. The damage functions described are based on the maximum production of each pollutant within each industrial classification. Modifiers of each damage function are required to account for behavioral differences. These modifiers are based on the natural dispersion of the pollutants, their persistence in the environment, and their capability of being transferred by deposition, precipitation, or leaching from one medium to another. The magnitude of the damage is obtained in three steps. First, enter the appropriate damage function with the rate of production of pollutant produced by the strategy; second, read d, (damage); third, multiply d, by the appropriate damage function modifier, M. Assigning relative weights Besides measuring the magnitude of the damage caused by a pollutant discharge, it is also necessary to measure the significance of the damage to the environment. Each pollutant discharge causes a different type of environmental damage. The differentiation between pollutant discharges and their resulting damage is obtained by weighting all pollutants. This weighting explicitly indicates the relative significance of an environmental damage caused by each pollutant. The three media, air, water and land, used for disposal of wastes are constant for all industrial categories and pollution control strategies, but vary in importance throughout the U.S. depending on physical, economic, and social characteristics of the area. On the other hand,
the specific pollutants in each medium and their associated weights vary among industry categories and control strategies. For these reasons a hierarchical arrangement of weights was developed consisting of two levels: media weights and pollutant weights. The first level consists of weights for the three media -air, water, and land. These weights are a function of a specific location in the U.S., or they can be aggregated to represent the entire country. The second level consists of weights for the pollutants listed under a specific medium. The pollutants identified for each medium include those new pollutants resulting from the application of control strategies. There are many procedures available for assigning relative weights. Both the judgments of knowledgeable individuals, and the estimates of "social costs" were investigated in this study. Expert judgment, arrived at by using a Delphi procedure, a systematic technique for obtaining a concensus, was selected as the best means of obtaining the relative weights. The first level weights were obtained by using opinions of individuals from the Environmental Protection Agency located in regional offices throughout the U.S. The second level weights were obtained. by using opinions of experts at Battelle-Columbus Laboratories. The results of the first level weighting procedure are given below. The second level weights are a function of the industry type; those given in the case study presented are specific to power plants. The relative estimates of the three media, based on a total of 1000 points, are a national average of 48 subregions. For air, the relative estimate is 290 points, for water, 390 points, and for land, 320 points. These do not represent official EPA weights. The EPA employees simply acted as regional sensors of weights for this study.
Computing the SEI A Strategy Effectiveness Index (SEI) is used to compare alternative control strategies. To compute a SEI for a specific control strategy, it is first necessary to calculate an Environmental Degradation Index (EDI) for the controlled and uncontrolled state. The ED1 is a function
How to calculate damage function modifiers Calculation of the modifier consists of two steps: (1) determination of the behavioral combination, C, and (2) transformation of C into a damage function modifier, M.
(1) C = x + t + e where x = dispersal range, and x = 1 = "short" where range is local; x = 2 = "moderate" where range is regional; x = 3 = "long" where range is continental or global; t
= persistence, and t = 1 = "short" where persistence is up to days: t = 2 = "moderate" where persistence is on the order
of weeks; t = 3 = "long" where a pollutant persists for months
or years: e = transferability, and e = 1 = no transfer; e = 2 = transferable. Transformation of C into damage function modifiers, M ... M = 0.1 when the pollutant in question is stable and subject to absolute and permanent containment. M = 0.3 when C = 3
M = 0.8 when C = 8
How to calculate SEI for 1000 MW coal-fired power plant in seven easy steps Step 1
Step 3
Step 6
All relevant waste streams that will be affected by the strategy must be identified. The production rates of all pollutants must be determined for the uncontrolled case and for each of the control strategies to be considered. Baseline data for the coal-fired power plant in terms of the uncontrolled production of pollutants released to each medium include: for airoxides of nitrogen, sulfur dioxide, carbon monoxide, flyash, total organic material, heat: for water-suspended solids, dissolved solids, total organic material, inorganics, heat; and for land-ash. The specific technologies examined for control of these pollutants and the resulting data are plotted on page 120.
The damages found in Step 2 are based on production rates. They must be adjusted to account for the behavior of pollutants upon discharge to the environment. Modifiers for each pollutant, to be multiplied by the damages found in Step 2, are a function of the persistence, mobility, and ability of the pollutant to be transferred among environmental media.
Environmental Degradation Indices (EDi) for the uncontrolled state and for each control strategy are then calculated from the relation,
Step 2
By inspection, the maximum production rate of each pollutant is identified: with that as an arbitrary maximum damage, damage functions are constructed.
Steps 4 and 5
The relative importance of individual pollutants associated with a given source or industry is assigned as a proportion of the relative importance of the three environmental media. In this methodology, the weights were obtained by drawing on the judgment of EPA personnel throughout the country to assign media weights which were then distributed among specific pollutants (Delphi procedure).
EDI, =
C(M,
X
d,,,
X
Wp)
P
where s = strategy index p = pollutant index dp,s= damage for pollutant p when strategy s is applied (0 Id, I1) wp = national weight of pollutant p M= , pollutant damage function modifier. Step 7 A Strategy Effectiveness Index (SEI) is then found for each strategy being evaluated:
SEIS = EDIcuncontrolled) -
EDI(contro11ed) In general, large values are desirable, and small or negative values indicate less desirable strategies which are relatively ineffective at controlling their target pollutants, or result in serious new waste streams. Volume 9, Number 2, February 1975
119
by strategy
%"-~tmmw
ion, by strategy
i 40
I
Nil
I $43.0
I
$2.26
I $17.5
of the environmental damage created by the discharged pollutant, and the significance of the damage. Then, it is necessary to subtract the ED1 controlled state from the ED1 uncontrolled state The resultant difference is a measure of the effectiveness of the strategy and is defined as the SEI. Among the strategies being compared, the best would be that strategy identified by the largest SEI. Small or negative values of SEI are undesirable. Negative values can occur owing to the cross-media impacts of certain strategies. The approach developed here is sufficiently general to allow for a more systematic assessment of the crossmedia impacts of proposed pollution control Handards. i t should prove useful as one of the tools for making decisions as to which control techniques are most appropriate for meeting standards. Ultimately, a regulatory agency seeks an optimum pollution control strategy with regard to both costs and environmental impact. However, the next step, constructing an optimization model, requires policy decisions regarding the relative importance of energy costs, capital costs, operating costs, and environmental impact. From a strictly environmental point of view, one would prefer to maximize the Strategy Effectiveness Index; realistically that maximization must be subject to constraints on energy demand and economic costs. 120
Environmental Science & Technology
$0.36
Additional reading "Development of Cro ss-Media Evaluation Methodology," Final Report. Contract No. EQC-315 January 15. 1974. Battelle-Columbus Laboratories (I'B232414/3WP). Howard Reiquam i: mental scientist wit Gas Co. Dr. Re&p18 for the identificatior environmental imf with companyprojei Norbert Dee is ser;liar environmental planner with Battell,?-Columbus Laboratorles. Dr. Dee has developed a computerized m o de l for evaluating environmental and economic tradeoffs. Paul S. Choi is r'esearch scientist L..^ I ",.--".--?-with Battelle-Columuua L ~ U W ~ V I I C Dr. Choi is involved in research programs concerned with energy and its environmental impact on several civilian sectors. Coordinated by LRE
. ~ ~ .
I ;
i
