Economic and Environmental Implications of Phosphorus Control at North Bosque River Wastewater Treatment Plants Keith Keplinger, Alex Tanter, and James Houser
TR0312 July 2003 Economic and Environmental Implications of Phosphorus Controls Acknowledgments
The authors wish to thank a number of individuals for making this research possible. Data on wastewater treatment plant parameters and sewer use and rates for the City of Stephenville were made available by Danny Johnson and Mark Kaiser, City of Stephenville, and Johnie Davis, OMI, Inc. Information on sewer use and rates for other communities located along the North Bosque River was supplied by various municipal personnel from those communities. Larry Beran, TIAER, initiated the project while Ron Jones, TIAER, was instrumental in securing a working relationship with the City of Stephenville. Edward Osei, TIAER, assisted with calculus solutions, while Larry Hauck, TIAER, provided overall direction and review of this report.
The research upon which this report is based was financed by the U.S. Environmental Protection Agency, Office of Policy Development, cooperating agreement number CR 826807-01-1. For more information about this document or any other TIAER document, e-mail [email protected]. Authors
Keith Keplinger, research economist, TIAER, [email protected]
Alex Tanter, research associate, TIAER, [email protected]
James Houser, research scientist, TIAER, [email protected]
EI7.01.02
ii Economic and Environmental Implications of Phosphorus Controls Abstract
Phosphorus (P) control at wastewater treatment plants (WWTPs) in the United States has been practiced since at least the 1970s, when effluent limits were placed on WWTPs in the Great Lakes region and in Vermont in order to reverse eutrophication of the Great Lakes and Lake Champlain, respectively. The rise to prominence of total maximum daily loads (TMDLs) in the 1990s has led to the identification of numerous water bodies where P has been identified as the leading cause of impairment, thereby giving new impetus to P control at WWTPs throughout the United States. TMDLs were issued for 2 segments of the North Bosque River in 2001, specified goals of a 50 percent reduction in soluble reactive phosphorus (SRP) loads and a 47 percent reduction in SRP concentrations for the entire North Bosque River and expectations of 50 percent load reductions for both point and nonpoint sources. One control action considered was the implementation of phosphorus (P) controls at six North Bosque wastewater treatment plants (WWTPs) designed to meet ending effluent standards of 1 mg/L total P (TP). This report assesses the economic and environmental implications of meeting these standards utilizing aluminum sulfate (alum) to precipitate P.
Populations of North Bosque communities and corresponding sizes of their WWTPs vary considerably. Stephenville’s population is around 15,000, while the populations of the other 5 communities range from 360 to 3,500. Phosphorus removal was estimated to cost $5.13/person annually for the Stephenville plant, while it ranged from $13 to $124 per person annually at the other WWTPs, the great disparity, due mainly to high capital costs incurred, at the smaller WWTPs in relation to their small populations. The cost per pound of P removal is also considerably lower at the Stephenville WWTP versus the other plants: estimated to be $14 for the Stephenville plant but ranging from $36 to $269 for the smaller plants. The great disparity in unit costs suggests that P control obligations (or credits) could be traded among the six North Bosque WWTPs to their mutual advantage. The optimal trading scenario was determined to be one in which the control obligations of the three smallest WWTPs are transferred to the Stephenville plant while the three small WWTPs are allowed to operate without P control. This trading scenario results in estimated savings of $152,000 annually for the four trading WWTPs. Moreover, annual per person costs decline for all four trading plants, and dramatically for the three small WWTPs when we assume that pounds of TP are traded at Stephenville’s average cost of removal. For the small town of Irdell, estimated costs for P removal decline from $124/person annually without trading to $5.58 /person annually with trading.
iii Economic and Environmental Implications of Phosphorus Controls
iv Contents
Background ...... 1 Historical Perspective ...... 2 Current Status of Phosphorus Control...... 4 United States ...... 4 Europe ...... 5 Texas...... 7 Survey of Phosphorus Control Costs ...... 8 Discussion ...... 11 North Bosque Community and WWTP Parameters ...... 12 Cost of P Removal at North Bosque WWTPs ...... 16 Operation and Maintenance (O&M) Costs...... 17 Capital Costs ...... 19 Affordability ...... 20 Effectiveness Measures...... 24 Basis for Effectiveness Measures ...... 24 Analysis ...... 26 Cost-Effectiveness ...... 29 Trading Implications...... 30 Trades Between Stephenville and One Other North Bosque WWTP...... 31 Trades Between Stephenville and Multiple Smaller WWTPs ...... 32 Conclusions ...... 37 Addendum...... 37 References ...... 39 Appendix A Texas Regulation Impacting Phosphorus Control ...... 41 30 TAC Chapter 311 Watershed Rules ...... 41 TCEQ’s Antidegradation Policy ...... 41 The 75%-90% Rule ...... 42 Violation of Permit Effluent Limits...... 42 Appendix B Derivation of Adjusted Effluent Phosphorus Concentrations ...... 45 Appendix C Chemistry of Phosphorus Removal by Alum Addition...... 47 Chemistry of Alum and Phosphorus ...... 47 Determining Alum Dose for a Specific Wastestream...... 49 References...... 49 Appendix D Derivation of Concentration-Mile Effectiveness Measure ...... 51
v Economic and Environmental Implications of Phosphorus Controls
vi Tables
Table 1 Count by County of Number of WWTPs Having TP Limits in Their Permits ...... 9 Table 2 Average WWTP Phosphorus Control Cost Comparison ...... 12 Table 3 Wastewater Treatment Plant and Community Data for North Bosque River ...... 13 Table 4 North Bosque Community Monthly Sewer Rate Schedules...... 15 Table 5 Estimation of Alum Expense of North Bosque Communities, 1 mg/L TP Effluent Limit. . 18 Table 6 Annual Expense (Medium Estimate) for Phosphorus Removal at North Bosque River WWTPs ...... 20 Table 7 Cost and Affordability of Phosphorus Controls for North Bosque River Communities . . 21 Table 8 Phosphorus Control Effectiveness for North Bosque River Communities ...... 27 Table 9 Median Flows, TP Loads, and TP Concentrations for North Bosque River and WWTPs . . 27 Table 10 Cost-Effectiveness of Phosphorus Removal at North Bosque River WWTPs ...... 30 Table 11 Additional P Removal at Stephenville WWTP Equivalent to Meeting 1 mg/L ...... 31 Table 12 Effect on Stephenville WWTP of Trades with Iredell, Valley Mills, and Hico WWTPs. . . . 33 Table 13 Comparison of Optimal Trading Scenario with No Trading Scenario, North Bosque River WWTPs...... 36 Table 14 Analysis of TCEQ’s TMDL Load Allocations ...... 38
vii Economic and Environmental Implications of Phosphorus Controls
viii Figures
Figure 1 The locations of industrial and municipal WWTPs having phosphorus limits...... 4 Figure 2 Implementation of phosphorus effluent limits by year, 1970 to 1997 ...... 5 Figure 3 Map of classification of European waters ...... 6 Figure 4 Map of Texas highlighting those counties with TP in their WWTP’s permits...... 8 Figure 5 Per household cost of North Bosque River TMDL phosphorus control limits ($/month)...... 23 Figure 6 Per capita cost of North Bosque River TMDL phosphorus control limits ($/year) ...... 24
ix Economic and Environmental Implications of Phosphorus Controls
x Economic and Environmental Implications of Phosphorus Control at North Bosque River Wastewater Treatment Plants
Background The North Bosque River, located in North Central Texas, flows through 6 small communities ranging in population from 500 to 15,000, before draining into Lake Waco, a drinking water source for approximately 200,000 people located in and around the City of Waco. The headwater area of the North Bosque River basin is located in the state’s top dairy production region. Wastewater treatment plants in the communities along the North Bosque River also provide a significant portion of watershed phosphorus loads and contribute disproportionately to in-stream concentrations. Elevated levels of soluble phosphorus in lakes and streams can lead to accelerated eutrophication, a condition characterized by excessive algal growth and associated effects such as fish kills and unpleasant taste and odor. Sporadic algal blooms and associated taste and odor problems in drinking water from Lake Waco have been a longtime concern for the City of Waco and have focused attention on the North Bosque River as a possible source of impairment.1
Since 1992, when the Texas Commission on Environmental Quality (TCEQ) first compiled 303(d) lists, the North Bosque River has been included on the state’s impaired waters list. In the 1998 list as well as former lists, the TCEQ found the North Bosque River impaired under narrative water quality criteria related to excessive aquatic plant growth2 and TMDLs for two North Bosque River stream segments were initiated (TNRCC,3 2001). In-stream bioassays conducted in 1998 provided strong evidence that phosphorus was the limiting nutrient for algal growth under most conditions. Loading studies revealed that diary waste application fields (WAFs) and municipal wastewater treatment plants (WWTPs) were the major controllable sources of phosphorus (TNRCC, 2001). Additional research indicated that soluble phosphorus, measured as soluble reactive phosphorus, was statistically better correlated to algal levels than total phosphorus.
1 Lake Waco itself, however, has never been placed on the state’s impaired waters (303(d)) list.
2 The North Bosque River is also listed on Texas’ 303(d) lists for impairments other than excessive aquatic plant growth; the TMDL, however, is only for phosphorus.
3 Prior to September 1, 2002, TCEQ was known as the Texas Natural Resources Conservation Com- mission (TNRCC).
1 Economic and Environmental Implications of Phosphorus Controls
The Bosque River Advisory Committee (BRAC) was formed to comply with Texas’ TMDL public participation requirements, while a technical work group consisting of university and public agency scientists was assembled to provide technical support to the BRAC. The full BRAC or its subcommittees met a total of 20 times between February 1998 and August 2000 but did not reach consensus, and consequently provided no recommendations to TCEQ on key TMDL targets or allocations.
In February 2001, the TCEQ promulgated TMDLs for phosphorus in the North Bosque River, setting as its endpoint a significant reduction in average annual loading and annual average concentrations of soluble reactive phosphorus at various sites. A significant aspect of the TMDLs was that both point sources (i.e., WWTPs) and nonpoint sources were expected to reduce average annual loadings by approximately 50 percent. TCEQ issued an implementation plan for the North Bosque TMDLs in December 2002, which included phosphorus controls for North Bosque River WWTPs. Historical Perspective Phosphorus problems associated with wastewater first gained prominence in the United States towards the end of the nineteenth century. In the 1880s problems with algal growth were reported in the chain of Yahara lakes below Madison, Wisconsin. Direct discharge of sewage into one of these lakes (Lake Monona) from an expanding urban population, was regarded as the likely cause of these blooms. Further urban growth over the next 70 years in the Madison area led to the lower Yahara lakes all becoming heavily affected by the treated sewage discharged from municipal WWTPs (County of Dane, 2002). The lakes bloomed with different types of blue-green algae, whose presence in Europe had also been associated with treated discharges from urban areas. The problem was largely rectified by diversions of the wastewater first around Lake Monona in 1936, and subsequently, in 1958, around the entire chain of Yahara lakes.
In the mid 1950s, Lake Washington (near Seattle) was also observed to be suffering from a buildup of pollutants. The lake waters were observed to be getting cloudier and an algae increase was reported. Research by, University of Washington (UW) zoology professor, W. Thomas Edmondson established that blue-green algae were especially able to thrive on the phosphates contained in wastewater pollutants. Seattle discharged raw sewage from 1900 to 1941, when the wastewater was diverted to a treatment plant that discharged to the sea. Deterioration in water quality in the 1950s was not associated with the city itself, but with discharge from 10 new WWTPs serving its suburbs, with a combined daily effluent volume of 20 million gallons per day (mgd). By 1963, before full remediation activities had been completed, the water quality of the lake had decreased to such an extent that it had become known as “Lake Stinko.” The region responded by establishing a “metropolitan government” to centralize regional planning and to construct and divert all wastewater from around the lake to a large treatment plant that discharged deep under Puget Sound (University of Washington, 1996). Lake water quality soon improved with clarity levels rising and algae levels declining. By 1971 the lake was significantly clearer than it had been in 1950 (University of Washington, 1996).
2 Economic and Environmental Implications of Phosphorus Controls
Lake Tahoe, in California and Nevada, also experienced water quality problems related to wastewater in the late 1950s and early 1960s. Lake Tahoe is a large alpine water body known for its crystalline waters and exceptional clarity. During this time period there was significant growth in the urban population, and although direct discharge of sewage into its surface waters had been prohibited since 1915, the combination of a less than adequate sewage system, septic tanks, and a 2 million gallon effluent overflow from an overcapacity treatment plant lead to significant nutrient loadings in streams and health and water quality problems in and around the lake (Imperial, 2000). Diversion was again the strategy employed to mitigate the effects of wastewater on the lake. In this case, sewage treatment facilities and pipelines were constructed to export sewage from the lake basin. On the Californian side treated effluent was pumped 27 miles over mountains and discharged into Indian Creek Reservoir. By the late 1970s, all wastewater was exported from the basin (Imperial, 2000).
In the late 1960s, excessive fertilization problems in the Great Lakes region gained national attention. Lake Erie was said to be dead, the Cuyahoga River which flows into Lake Erie had caught fire, the lake itself was smothered by algae, and its fish population was shrinking rapidly. The population of the Great Lakes basin increased by 36 percent in the 20 years leading to 1970, reaching a population of 30.8 million (Environment Canada, 2001). This population boom placed a strain on the ability of the lakes to assimilate the increased sewage, and inadequate sewage treatment led to similar water quality problems as those observed in the Yahara and Washington Lakes. In response, the USA and Canada signed the Great Lakes Water Quality Agreement (GLWQA) in 1972 which limited the phosphorus concentration in domestic wastewater from plants of 1 mgd or more to 1 mg/L. The 1 mgd flow cutoff was based on expected large cost differentials between small and large treatment plants in meeting the 1 mg/L limit. The estimated cost for plants larger than 1 mgd was $0.01/person/day whereas the cost for the smaller plants was estimated at $0.10/person/day (Lee and Jones, 1988). In 1978, the GLWQA was extended in Lakes Erie and Ontario to reduce the phosphorus limit to 0.5 mg/L for plants larger than 1 mgd, although since then this requirement has been deferred and more focus has been placed on the control of phosphorus from nonpoint sources. Phosphorus loadings to Lake Eerie, as a result of effluent limits and a phosphate detergent ban, declined from 14,000 metric ton in 1972, to 2,000 metric tons in 1990, an 85 percent reduction (Litke, 1999).
The state of Vermont’s efforts to control excessive fertilization of Lake Champlain in the 1970s initially focused on WWTPs discharging directly to the lake, which were subjected to effluent phosphorus limits of 1 mg/L. This was later modified under a State of Vermont statute that subjected all wastewater treatment facilities in the Lake Champlain basin to a 0.8 mg/L monthly average effluent limit (some smaller facilities, 0.2 mgd or less, were exempted from this limit). Lake Champlain is currently subject to a TMDL for phosphorus with point sources being part of the phosphorus load reduction. One strategy currently under consideration for achieving a reduction in point source loads is for selected larger facilities to meet a 0.6 mg/L phosphorus effluent limit.
3 Economic and Environmental Implications of Phosphorus Controls
In 1983, the Chesapeake Bay Program was formulated in response to an observed rise in pollution in the bay during the 1970s. In 1987, the Chesapeake Bay agreement instituted ambitious targets for reducing the levels of nutrients. Reductions of 40 percent for phosphorus and nitrogen loads entering the bay were targeted by the year 2000, with load reductions from both point and nonpoint sources (EPA, 1997). From 1985 to 2000, phosphorus loads from point sources were reduced by 58 percent (Chesapeake Bay Program, 2001). This reduction has been achieved through the implementation of a phosphate detergent ban, the implementation of phosphorus effluent limits, and a program of WWTP upgrades, focusing on biological nutrient removal (BNR) processes to achieve more efficient phosphorus and nitrogen removal. Current Status of Phosphorus Control
United States Currently there are approximately 16,000 WWTPs in the United States, serving almost 190 million people, roughly 75 percent of the population (EPA, 2000a). These plants treat around 30,175 mgd, and have an average plant flow of 2.01 mgd (EPA, 2000a). Currently, an estimated 7.6 percent of WWTPs in the United States (representing 17 percent of total WWTP discharge) have P limits in their permits, with most plants having effluent P limits ranging from 0.5 to 1.5 mg/L (Litke, 1999).
Figure 1 shows the regional distribution of WWTPs with phosphorus limits. Most plants are clustered around the Great Lakes, or on the Eastern seaboard, with a significant concentration around the Chesapeake Bay, a distribution which can be attributed to the P control programs instituted in those regions.
Figure 1 The locations of industrial and municipal WWTPs having phosphorus limits (Source: Litke, 1999)
4 Economic and Environmental Implications of Phosphorus Controls
Figure 2 presents a breakdown, by year, of the implementation of phosphorus effluent permits. The number of new municipal permits issued with phosphorus limits is observed to rise significantly towards the end of the 1970s, and reach a peak in the mid 1980s, which corresponds with GLWQA requirements for phosphorus limits. The still fairly high numbers of new permits issued in the late 1980s can be attributed to the initiation of the Chesapeake Bay program, after which the number of new permits issued settles to a level of around 40 permits a year.
Figure 2 Implementation of phosphorus effluent limits by year, 1970 to 1997 (Source: Litke, 1999)
The National Water Quality Inventory (EPA, 2000b) summarizes the extent and sources of impairments for the nation’s water bodies. The report indicates that 45 percent of surveyed lakes were assessed as impaired, 12 percent of which were impaired as a result of municipal point sources (EPA, 2000b). Additionally, 35 percent of surveyed river and stream miles were designated as impaired, 10 percent of which had municipal point sources listed as a leading source of impairment (EPA, 2000b). Nutrient emissions from WWTPs, thus, continue to be a major source of impairment for the nation’s waters.
Europe The European Union recently initiated implementation of an extensive program of water quality improvements through widespread mandatory wastewater treatment plant investments and upgrades. The main water quality problem identified in European waters is eutrophication. The major identified source of this eutrophication is urban wastewater. The European Commission introduced the Urban Waste Water Treatment Directive (UWWTD) in 1991, seeking, among other improvements, a 30 percent reduction in phosphorus levels by 2005.
5 Economic and Environmental Implications of Phosphorus Controls
The directive classifies different regions as either sensitive, normal areas, or less sensitive. Sensitive areas are directed to utilize rigorous treatment of wastewater. Less sensitive areas are more robust waters able to assimilate wastewater subject to only primary treatment (frequently seawaters). Normal areas are the remaining areas where comprehensive secondary treatment is assumed to adequately protect the environment. The directive requires that all urban areas with greater than 10,000 inhabitant equivalents discharging into sensitive waters must have secondary and tertiary treatment of wastewaters. Additionally, by 2005, all urban centers must have secondary treatment.
Figure 3 shows that large areas of Germany, as well as all of Denmark, the Netherlands, Finland, and Sweden are designated as sensitive and so subject to widespread tertiary WWTP phosphorus controls. Across the 14 European countries operating under the UWWTD, 37.2 percent of the total population reside in areas classified “Sensitive” (Europa, 2002). Data on phosphorus levels in European rivers indicate that since 1990 concentrations have decreased by around one third, indicating that the UWWTD may already be producing phosphorus control results (EEA, 2001).
Figure 3 Map of classification of European waters (Source: Europa, 2000)
Sensitive Areas Normal Areas Less Sensitive Areas Undefined Areas Outside UWWTD Region
Atlantic Ocean North Sea
Mediterranean Sea
6 Economic and Environmental Implications of Phosphorus Controls
Texas Texas has no numeric water quality criteria for nutrients, including phosphorus, so ambient phosphorus concentrations at any level do not automatically trigger impairment status, which could lead to a total maximum daily load (TMDL) assessment. The state, however, has the ability to regulate nutrient emissions from point sources by specifying nutrient limits in the Texas Pollution Discharge Elimination System (TPDES) permits. All WWTPs in Texas must operate under the terms of TPDES permits obtained from the TCEQ. The permit describes the treatment processes used by WWTPs and the effluent limits plants must achieve. WWTPs must periodically be re-permitted, and also must be re-permitted if they significantly modify their treatment processes or start to have capacity problems (see Appendix A for a description of the 75 percent to 90 percent rule). Legal authority for applying nutrient limits in TPDES permits is provided by one of the following mechanisms:
1. Applying narrative criteria to address nutrient impairment at sites of concern4 2. Developing specific watershed rules mandating additional wastewater treatment near identified water bodies (See Appendix A for a description of 30 TAC Chapter 311 Watershed Rules) 3. Using the TCEQ’s antidegredation policies. (See Appendix A for a description of TCEQ’s antidegredation policies)
Under one or more of the foregoing criteria, TCEQ has placed total phosphorus (TP) concentration-based limits in the permits of 26 Texas WWTPs (out of a state total of around 1,300).5 Figure 4 and Table 1 indicate the geographic location of counties with TP limits in their TPDES permits and their number by county. Counties in Texas with TP limits in their permits are primarily centered around Austin, and the Guadalupe and Colorado rivers. Table 1 indicates Travis County (Austin’s location) having by far the most plants with TP permits (10), with neighboring counties Bastrop and Williamson tied for second most. These three counties are also those with the most permits with TP effluent limits of 1 mg/L or less. The TCEQ has cited three factors for this clustering of TP WWTP permits around Austin:
1. The exceptionally high quality waters of the regions two big rivers, the Colorado and the Guadalupe, both renowned for their clear and pristine waters, as well as the extensive and highly valued water based recreation they support.
4 Current narrative nutrient criteria in §307.4(e) of 30 TAC state that nutrient parameters “shall not cause excessive growth of aquatic vegetation which impairs an existing, attainable or designated use.” Under Texas water quality standards, designated uses include aquatic life, contact recre- ation, public water supply, and fish consumption.
5 In 1999, the City of Clifton’s TPDES permit was amended to include an annual average loading limit of 6.2 lb/day TP. Phosphorus load limits are currently the exception, and WWTPs with P load limits (thought to be three or less) were not included in the list of WWTPs, provided by TCEQ, having phosphorus (concentration-based) limits. It is noted, however, that the implementation plan for the North Bosque River TMDLs includes load-based phosphorus limits for North Bosque River WWTPs.
7 Economic and Environmental Implications of Phosphorus Controls
2. The watershed protection rules of TAC Chapter 311 (see Appendix A) that specify area water bodies for legislative, and hence TP based permit, protection (e.g., Lakes Travis and Austin, and segments of the Colorado river). 3. A concern for areas that have experienced, and are projected to continue to experience, high population growth (the Austin area was one of the fastest growing regions in Texas over the last 20 years).
Currently, WWTPs in Texas with TP (concentration) limits in their permits represent around 2 percent (26/1311) of the total number, although this figure is projected to grow.
Figure 4 Map of Texas highlighting those counties with TP in their WWTP’s permits
Austin
Trinity River
Colorado River
Guadalupe River
Survey of Phosphorus Control Costs6 An EPA report on phosphorus removal at WWTPs in the Lower Great Lakes (EPA, 1980) provides one of the earliest attempts to quantify the costs associated with phosphorus removal at WWTPs. The report was written to analyze the implications
6 All costs in this section have been adjusted for inflation to 2001 prices using the Consumer Price Index. Costs were converted to annual per capita figures and to dollars/lb of P removed for pur- poses of comparison.
8 Economic and Environmental Implications of Phosphorus Controls
Table 1 Count by County of Number of WWTPs Having TP Limits in Their Permitsa
County P Limited Permits < or = Permits 1mg/L Travis 10 7 Bastrop 33 Williamson 32 Collin 21 Hays 20 Burnet 11 Caldwell 11 Comal 11 Kerr 11 Llano 10 Wise 11 Total 26 18
a. The figures above do not include WWTPs that have annual average load limits for Phosphorus discharge per day, such as the Clifton WWTP in Bosque county. These WWTPs do not number more than a few statewide. of the 1978 GLWQA that lowered the phosphorus limit to 0.5 mg/L for Lakes Erie and Ontario WWTPs discharging more than 1 mgd. A survey of all potentially affected plants in the basin (229) revealed that 52 percent were achieving less than 1 mg/L phosphorus effluent concentration, and that 8.2 percent were meeting the 0.5 mg/L standard. The study reported that most of the plants were using secondary treatment processes enhanced by alum or iron salt addition. It was concluded from field studies, that plants utilizing this approach could reach a phosphorus effluent level of 0.75 mg/L without filtration. Four treatment plants, all of which were currently meeting the 1 mg/L level, were closely investigated. It was estimated that two of the four plants could reach the 0.5 mg/L limit without treatment process changes. The report’s estimated average phosphorus control costs were equivalent to $1.65/person/yr, with a range from $0.90/person/yr for the largest plant (100 mgd average daily flow) to $13.66/person/yr for the smallest plant (1 mgd average daily flow). The two plants most comparable to Stephenville in size were estimated to have phosphorus control costs of $12.25/person/yr (3 mgd average daily flow) and $13.66/person/yr (1 mgd average daily flow).7
An EPA Handbook on the retrofitting of Chesapeake Bay drainage basin (CBDB) WWTPs for phosphorus removal (EPA, 1987a) provides estimates of the costs associated with the attainment of various phosphorus effluent limits. The handbook reports that as of 1987, 99 of the 526 plants (19 percent) were removing phosphorus. The handbook estimates P removal costs for plants not currently removing phosphorus in the CBDB and provides a review of P removal costs from other literature.8 When updated to 2001 prices, retrofit costs were estimated at $11.77/
7 At two plants where the costs of meeting the 0.5 mg/L limit could be estimated, operating costs were estimated to increase by 8 percent and between 20 and 62 percent compared to meeting the 1 mg/L limit.
9 Economic and Environmental Implications of Phosphorus Controls
person/yr for plants with influent P concentrations of 6-10 mg/L, and $7.33/person/ yr for plants with influent P concentrations of 3-6 mg/L.9
Based on a survey of North American eutrophication control through phosphorus management, Lee and Jones (1998) report that P could be removed from domestic wastewater in the New York City/New Jersey area at a cost of $15.41/person/yr.10 The authors report anecdotally that European estimates of the per capita costs of phosphorus removal were similar to their USA-based estimates.
Estimated phosphorus removal costs are presented in a 1997 report investigating the potential for pollutant trading between point and nonpoint sources in Minnesota (Minnesota Pollution Control Agency, 1997).11 The unit cost of phosphorus removal was observed to decrease as the scale of the plant increased, with significant economies of scale resulting until a level of 2-3 mgd was reached. Economies of scale declined markedly for plant size above this level. The report estimated that the average cost of P removal was $15.37/person/yr.
Illustrating the crucial effect of investment timing, the report also examines five large Minneapolis/St. Paul (Twin Cities) WWTPs that implemented P control processes at the same time as plant expansion. For all plants examined, the costs of phosphorus treatment were drastically lower than estimated costs when controls were constructed separately. For example, at the largest plant examined, when phosphorus controls were installed in tandem with plant capacity expansion, the cost per pound of P removed was 70 percent lower ($5.66/lb of P removed, as opposed to $19.34/lb of P removed) than if the controls were installed separately. The relatively low cost of P removal at the large Twin Cities WWTPs of $3.55/person/yr reflects economies of scale associated with a large (78 mgd) design flow as well as the benefits of coordinating implementation of P controls with plant expansion.12
A Wisconsin study on the potential for point/nonpoint source pollution trading provides data on the cost and cost-effectiveness of phosphorus removal at WWTPs in
8 EPA (1987a) also conducted a survey of P-removing WWTPs achieving effluent P level of 1 mg/L or lower. The 74 responding WWTPs reported an average estimated phosphorus removal cost of $6.24/person/yr. It should be noted, however, that almost no capital costs were included in the survey data, hence, these figures reflect mainly chemical and other O&M costs, and should not be compared with total P removal cost reported in other studies.
9 Total capital costs of retrofitting all of the 429 CBDB plants not currently removing phosphorus to reach a an effluent limit of 0.5-1.0 mg/L was estimated to be between $42.8 and $45.3 million at 2001 prices.
10 This cost estimate assumes the WWTP serves at least 10,000 people (roughly equivalent to a flow of 1 mgd). It includes all aspects of P removal costs, including a 20-year amortization of the capital investment. Lee and Jones (1999) reported costs as being $0.04 per person per day, which is here converted to annual per capita value at 2001 prices.
11 The cost of P removal by ferric chloride treatment, to an effluent limit of 1 mg/L, was estimated in 7 small to mid-sized Minnesota treatment plants.
12 Based on the figures generated by this report, point/nonpoint source pollutant trading was not recommended because nonpoint source costs were estimated to be almost as high as point source costs.
10 Economic and Environmental Implications of Phosphorus Controls
the Fox-Wolf Basin, near Green Bay (Resource Strategies, 1999). Area WWTPs were surveyed to ascertain average costs of meeting their current P effluent levels (less than 1 mg/L for all but one small plant), and the additional costs of achieving a lower phosphorus effluent standard of 0.3 mg/L. The surveyed plants all used chemical phosphorus removal processes. The average cost of phosphorus removed was estimated to be only $0.70/lb, to reach an average P effluent level of 0.77 mg/L, which translates into a cost of $1.61/person/yr for phosphorus removal. However, estimated costs of reaching the 0.3 mg/L P effluent limit were much higher—$78.12/ lb of P removed (or $195.69/person/yr).13
The draft of the Vermont portion of the Lake Champlain phosphorus TMDL (Vermont Department of Environmental Conservation (VDEC), 2001) provides several estimates of the costs of P control at basin WWTPs. Currently, permitted limits are 0.8 mg/L at all the larger plants in the basin. The cost of reaching this limit was estimated at $17.20/lb of phosphorus removed (or $8.84/person/yr). The TMDL seeks alternative strategies to achieve further point source load reductions, among them one requiring all large facilities to attain an 0.2 mg/L effluent standard, and another requiring selected facilities (all those with current permit levels of 1 mg/L or lower) to achieve a 0.6 mg/L standard. Costs for achieving the large facility 0.2 mg/L standard were much higher, estimated at $86/lb.14 For the 0.6 mg/L strategy, net savings, relative to the costs of current policy, of approximately $14.30/lb of P removed ($0.95/person/yr) were estimated, over the 20 year lifetime of the strategy. These savings are attributed to the switching of the plants to a biological P removal process utilizing anaerobic selector zones, which is expected to result in significant operations and maintenance savings that would more than offset initial capital expenses over a 20 year life span.
Discussion The literature indicates that although total costs to WWTPs of implementing phosphorus controls rise with average daily flows, unit costs generally decline, indicating the presence of economies of scale for phosphorus removal. Additionally, the literature indicates an (sometime pronounced) inverse relationship between the costs of implementing phosphorus controls and the effluent level of phosphorus to be reached. While the literature generally indicates that reaching a P limit in the 0.5-1.0 mg/L can be achieved through standard chemical and biological approaches, attempts to reach lower levels of TP could result in much greater costs (Resource Strategies, 1999; VDEC, 2001). Some studies also indicate that certain biological treatment processes have the potential to generate significant cost savings when compared with chemical P removal processes (e.g., EPA, 1987a; Chesapeake Bay Program, 2001; VDEC, 2001).
13 The report suggested that the potential for point/nonpoint source pollutant trading did exist in some regions of the basin due to wide variations in point source control costs, the very high aver- age point source costs to reach the stricter 0.3 mg/L P effluent limit, and the availability of low cost nonpoint source reductions.
14 This cost is very similar to the Wisconsin estimated cost of $79.31/lb to reach a 0.3 mg/L P effluent limit (Resource Strategies, 2000).
11 Economic and Environmental Implications of Phosphorus Controls
Table 2 presents a summary of the costs (adjusted to 2001 levels) collated from the literature. Given the almost 30-year difference between the publishing of the earliest and latest reports, the summary figures present a fairly small range of cost estimates. On the low end of the cost range are the 1980 Great Lakes figures and the 1999 Wisconsin estimates (both around $1.65/person/year). The upper cost boundary for costs of phosphorus control at WWTPs is presented by the 1987 New York/New Jersey figures, and the estimated cost for small to medium sized WWTPs in Minnesota (both around $15.40/person/year). The most reliable of these costs may be the Vermont 2001 estimates ($8.84/person/yr), as these are based on actual costs incurred to reach the current 0.8 mg/L TP effluent limits.
Table 2 Average WWTP Phosphorus Control Cost Comparisona Plant Cost Region Year Limit Typeb $/Person/yr $/lb P Removed Great Lakesc 1972 1 mg/L > 1 mgdd 10.26 na Great Lakes 1980 1 mg/L 31 mgd 1.65 0.95 NY/New Jersey 1987 1 mg/L > 1 mgdc 15.41 na Influent P of 3-6 mg/L 7.32 2.85 Chesapeake Basin 1987 1 mg/L Influent P of 6-10 mg/L 11.77 2.93 78 mgd 3.54 3.12 Minnesota 1997 1 mg/L 3.4 mgd 15.37 13.42 Wisconsin 1999 1 mg/L 6.9 mgd 1.61 0.70 Vermont 2001 0.8 mg/L 1.7 mgd 8.84 17.20
a. All costs were adjusted for inflation to 2001 prices using the Consumer Price Index. Costs were converted to annual per capita figures and to dollars/lb of P removed for purposes of comparison. b. The plant type indicates permitted maximum average daily discharge of the plants examined, except where noted. c. The Great Lakes 1972 figure was calculated from the GLWQA $0.01/person/day estimate and is included for purposes of comparison. d. Average daily discharge. North Bosque Community and WWTP Parameters Remaining sections of the paper present research results on the costs and environmental effectiveness of phosphorus controls at North Bosque WWTPs. First, costs are estimated, which are, in large part, based on a site-specific engineering consulting report by Camp, Dress and McKee. An affordability analysis is subsequently pursued, where P removal costs are presented in terms of impacts on monthly residential sewer bills. Next, environmental effectiveness measures of P control, in terms of effects on P loads and concentrations, are estimated. Cost- effectiveness ratios for P removal at the six North Bosque WWTPs are next presented. The final section analyzes the economic implications and potential of P load trading among North Bosque WWTPs.
Community and WWTPs information for North Bosque communities, used as a basis for subsequent analyses, is presented in Table 3. Populations, based on the 2000 U.S. Census, for the six communities range from 360 persons for Iredell to 14,921 for the City of Stephenville. The communities of Hico, Meridian, and Valley Mills are of similar size, having populations ranging between 1,100 and 1,500 persons, while the
12 Economic and Environmental Implications of Phosphorus Controls
City of Clifton had a population of 3,542. The populations of the 6 communities totaled 22,778 in 2000, approximately two-thirds of which constituted the population of Stephenville. Average number of persons per residential hookup (single family and multi-unit combined) ranged between 2.0 and 3.4 among the North Bosque communities.
Table 3 Wastewater Treatment Plant and Community Data for North Bosque River Communities Valley Total/ Stephenville Hico Iredell Meridian Clifton Mills Avg. Population U.S. Census (2000) 14,921 1,341 360 1,491 3,542 1,123 22,778 Percent of total 66% 6% 2% 7% 16% 5% 100% Persons / hookup (res. + multi.) 3.38 2.85 2.01 2.56 2.95 2.48 3.12 Number of Hookups (2002) Single family residential 4,307 460 179 583 1,155 453 7,137 Multi unit residential 107 10 0 0 44 0 161 Commercial 576 89 10 57 197 46 975 Total 4,990 559 189 640 1,396 499 8,273 Sewer Usage (gal/mo in 2002) Single family residential 20,743,851 2,760,000 925,740 2,627,467 6,161,800 2,715,400 35,934,257 Multi unit residential 5,428,250 107,000 0 0 429,700 0 5,964,950 Commercial 11,793,503 952,300 17,760 1,715,267 2,151,200 538,433 17,168,463 Total 37,965,603 3,819,300 943,500 4,342,733 8,742,700 3,253,833 59,067,670 Sewer Usage (% of Total) Single family residential 54.6% 72.3% 98.1% 60.5% 70.5% 83.5% 60.8% Multi unit residential 14.3% 2.8% 0.0% 0.0% 4.9% 0.0% 10.1% Commercial 31.1% 24.9% 1.9% 39.5% 24.6% 16.5% 29.1% Avg. Gallons / Hookup (2002) Single family residential 4,816 6,000 5,172 4,507 5,335 5,994 5,035 Multi unit residential 50,731 10,700 - - 9,766 - 37,049 Commercial 20,475 10,700 1,776 30,092 10,920 11,705 17,609 WWTP Flow (mgd) Self reported (2001 mean) 1.373 0.087 0.025 0.360 0.328 0.081 2.254 Self reported (2001 median) 1.243 0.083 0.025 0.355 0.320 0.077 2.102 Billed water (2001-2002)a 1.248 0.127 0.031 0.145 0.282 0.108 1.942 WWTP Effluent TP (mg/L) Grab samples (mean 1993-2002)b 2.69 3.52 2.96 3.36 2.40 3.14 3.01 Grab samples (median 1993-2002)b 2.60 3.66 2.90 3.43 2.23 3.16 3.00
a. Based on from one to three months of winter (November 2001 - February 2002) water use data provided by North Bosque River communities. b. Grab samples at the Stephenville WWTP outflow were collected between December 1993 and May 2002. Grab samples at the Clifton, Meridian, and Valley Mills WWTPs were collected between December 1995 and May 2000. Grab samples at the Hico and Irdell WWTPs were collected between April 1996 and May 2000.
Communities typically categorize sewer accounts into three major account types: single family residential, multi-unit, and commercial. A survey of North Bosque community governments was conducted to ascertain the number of hookups by account type, sewer usage by account type, sewer rate structures, and average
13 Economic and Environmental Implications of Phosphorus Controls
monthly residential bills. This information was attained in order to conduct an affordability analysis, presented later in the report, and is also presented in Table 3.
Sewer usage is typically estimated based on metered water use, but is not always equal to metered water for a number of reasons. In some instances, residences and business on private wells drain wastewater into the public sewer system. In addition, landscape watering by businesses and residents often constitutes metered water not disposed of through the public sewer system. For this reason, the majority of North Bosque communities charge residential customers for sewer based on metered water use for three winter months, when it is expected that outside water use will not be significant. Similar adjustments are sometimes made for businesses for landscape watering and filling swimming pools.
Sewer usage and hookup figures for the six North Bosque communities are consistent with their populations and business activity. Sewer usage, here defined as estimated water draining into the public sewer system through account hookups, ranges from less than 1 million gallons per month for Iredell to almost 38 million gallons per month for the City of Stephenville. Single family residential usage ranged from 55 percent of total usage for Stephenville to 98 percent of total usage for Iredell. Multi- unit (i.e., apartments, duplexes, etc.) usage ranged from 0 percent (Iredell, Meridian, and Valley Mills) to 14 percent of total usage for Stephenville. While commercial usage ranged from 2 percent of total for Iredell) to 40 percent of total usage for Meridian. Average single family residential usage ranged between 4,500 and 6,000 gallons per month for the six communities. Multi-unit usage averaged between 9,800 and 51,000 gallons per month, while average commercial usage ranged between 1,800 and 30,000 gallons per month.
Sewer bills for all North Bosque communities, except for two instances, are based on water use as an estimate of sewer usage.15 Community sewer rate schedules are presented in Table 4. Rate schedules vary considerably by community. Iredell and Valley Mills utilize flat rates for residential accounts. A fixed fee plus a variable fee based on water usage is employed at Stephenville and Meridian. Hico uses a block rate structure based on water usage, while Clifton employs an initial block rate plus a usage fee for water use over 5,000 gallons.
Monthly self-reported WWTP effluent flows were obtained from the Texas Commission on Environmental Quality. These flows are average daily flows reported on a monthly basis in millions of gallon per day (mgd) units. Means and medians of reported flows for the 12 months of 2001 are reported in Table 3. Mean self-reported effluent flows range from 0.025 mgd for the Iredell plant to about 1.4 mgd for the Stephenville plant. These flows should bear some relationship to the actual total billed sewer usage, also reported in Table 3, but for a number of reasons, may not match. Sewer systems, for instance, may lose water to the ground during dry periods, and take on substantial amounts of water during wet periods. Also, billed water reported in Table 3 is based on one to three months of water use data during the winter of 2001/2002, supplied by communities, whereas mean and median WWTP flows are based on self reported WWTP effluent flows for all 12 months of 2001. Self-
15 Water use is metered, but sewer use is not.
14 Economic and Environmental Implications of Phosphorus Controls
Table 4 North Bosque Community Monthly Sewer Rate Schedules Community Residential Commercial First 2,000 gals: $12.00 Valley Mills $8 flat fee Thereafter: $1.50 per 1,000 gals. First 5,000 gals: $19.00 Clifton Thereafter: $2.25 per 1,000 gals. (Same as residential, but not (Based of average water use for Nov., averaged) Dec. and Jan.) (Same as residential, but not $3.60 + $2.00 per 1,000 gals. averaged and subject to add’l fees Meridian (Based of average water use for Dec., to handle heavy BOD and TSS Jan. and Feb.) flows) Iredell $7.78 flat rate $7.78 plus a fee based on usage Up to 2,000 gals: $7.50 Up to 5,000 gals: $20.00 2,001 – 4,000 gals: $8.00 5001 – 10,000 gals: $30.00 4,001 – 6,000 gals: $12.00 10,001 – 15,000 gals: $40.00 6,001 – 8,000 gals: $14.00 Hico 15,001 – 25,000 gals: $50.00 8,001 – 15,000 gals: $20.00 25,001 – 50,000 gals: $60.00 Over 15,001 gals: $25.00 50,001 – 100,000 gals: $75.00 (Based of average water use for Dec., Over 100,000 gals: $100.00 Jan. and Feb.) $8.77 + $2.43 per 1,000 gals. (Same as residential, but not Stephenville (Based of average water use for Dec., averaged) Jan. and Feb.) reported effluent for the City of Meridian departs markedly from billed water, being more than double the amount of billed sewer use. This is attributed to a leaky sewer distribution system, which allows infiltration.
Total phosphorus (TP) concentrations at outfalls of North Bosque community WWTPs, also reported in Table 3, are based on grab samples collected by TIAER between 1993 and 2002.16 Individual grab samples displayed a great range of concentrations. In a few cases, very high or very low values were considered outliers and removed from the analysis.17 Mean and median TP concentrations, as reported in Table 3, are very similar, indicating a lack of a pronounced or consistent skewness to the distributions of TP concentrations.
16 Grab samples at the Stephenville WWTP outflow were collected between December 1993 and May 2002. Grab samples at the Clifton, Meridian, and Valley Mills WWTPs were collected between De- cember 1995 and May 2000. Grab samples at the Hico and Irdell WWTPs were collected between April 1996 and May 2000.
17 Total phosphorus concentrations greater than 20 mg/L and less than 0.1 mg/L were considered outliers and dropped from the analysis.
15 Economic and Environmental Implications of Phosphorus Controls
Cost of P Removal at North Bosque WWTPs In 1999, during North Bosque River TMDL deliberations, TIAER contracted with James Miertschin & Associates, Inc. to estimate costs associated with phosphorus removal in the Bosque River basin. A generic approach was utilized, based on estimated phosphorus load to be removed and plant flow. Starting TP concentrations of 5 mg/L and 80 percent removal (resulting in ending concentrations of 1 mg/L) were assumed (Miertschin, 1999). Phosphorus removal utilizing aluminum sulfate (alum) addition was analyzed for all plants considered. The amount of alum required was estimated based on an alum:P weight ratio of 16:1.18
Upon further TMDL deliberation, members of the Bosque River Advisory Committee (BRAC) expressed a need for site-specific P removal costs at North Bosque River WWTPs in order to have more precise cost estimates on which to base TMDL allocation recommendations. Funding was obtained and the consulting firm, Camp Dresser & McKee (CDM), was commissioned to conduct a site-specific study, sponsored by the Brazos River Authority. Many assumptions, cost estimates, and elements of methodology in this analysis are consistent with the CDM (2001) analysis. This analysis, however, departs from the CDM study in some important aspects, which are described later in this report.
The four major types of phosphorus removal from WWTP effluent are chemical removal, biological removal with chemical polishing, wetlands treatment, and land treatment (CDM, 2001). Wetlands treatment does not appear to be cost effective for North Bosque WWTPs because of the large pond areas required (CDM, 2001). Land treatment may be feasible for the smaller North Bosque River plants (CDM, 2001) but is not investigated in either the Miertschin (1999) or CDM (2001) analyses as it would require detailed site-specific investigations. Both Miertschin (1999) and CDM (2001) investigated phosphorus precipitation by alum, while the CDM report also estimated costs of biological phosphorus removal (with chemical polishing) and identifies biological removal as the most cost-effective method of removal for the Stephenville and Clifton plants.19 This analysis develops cost estimates only for the alum treatment alternative, which is the chemical removal method most often used in Central Texas (Miertschin, 1999; CDM, 2001). While alum addition may be the most cost-effective P removal alternative for some or all of the North Bosque WWTPs, this analysis does not attempt to evaluate all P removal alternatives, nor does this analysis imply that alum addition is necessarily the most cost-effective P removal alternative for any given North Bosque WWTP.
18 This ratio corresponds to an 85 percent removal rate in a chart published in EPA (1976) although Miertschin (1999) assumes 80 percent removal (to 1 mg/L), based on conserva- tive principles.
19 It should be pointed out, however, that when the price of alum is reduced to the actual market price for bulk volumes, and current WWTP flows and measured TP concentra- tions are used in calculations, in accordance with this study, that alum treatment is the most cost-effective alternative for all North Bosque WWTPs.
16 Economic and Environmental Implications of Phosphorus Controls
Costs are broken out into two major categories: operation and maintenance (O&M) costs and capital costs. O&M costs represent expenses that must be paid on an ongoing basis, whereas capital costs represent one time costs for the design and construction of physical facilities required for retrofitting existing plants for phosphorus removal. The methodology for developing cost estimates in this analysis is consistent with that employed in CDM (2001), although several parameters were changed to better reflect current conditions and prices.
Operation and Maintenance (O&M) Costs O&M costs consist of expenses such as materials, supplies, utilities, maintenance, and labor. Cost estimates for O&M costs, developed by CDM (2001), were used in this analysis, except for alum cost and sludge removal cost, where key parameters were modified to reflect current conditions, as described below.
Alum Expense
This analysis uses the same methodology as CDM (2001) to estimate alum expense, but changes key parameters. CDM, for instance, based alum use on an assumed effluent concentration of 4.5 mg/L TP and also assumed that WWTPs were operating at permitted flow rates. This study utilizes measured concentrations at WWTP outfalls and self-reported WWTP flow data to estimate alum use. Cost estimates developed in this report, therefore, are believed to be more reflective of what actual costs might be under current or near-term (versus “built out”) conditions.
Table 5 presents estimates of alum expense for North Bosque communities assuming a 1 mg/L TP effluent standard. Alum use is based on the amount of phosphorus removed which, in turn, is based on the reduction of TP concentration desired and plant flow. In practice, WWTPs that are required to meet TP effluent concentrations typically target effluent concentrations below the requirement.20 This provides a margin of safety if rapidly changing effluent conditions cause the effluent TP to be above the target on any given day. A study of P removal by WWTPs in the Great Lakes region (EPA, 1987b) revealed that plants having a 1 mg/L TP effluent limit actually achieved ending effluent TP concentrations ranging from 0.70 to 0.86 mg/L, and averaging 0.77 mg/L. Thus, actual amounts of P removal for North Bosque WWTPs are estimated assuming that they would actually achieve average TP effluent concentration of 0.77 mg/L. In addition, small upward adjustments were made to the mean TP effluent concentrations before removal for some of WWTPs due to the variability of effluent TP concentration and its possible influence on the amount of alum required.21 The methodology used to calculate the small upward adjustments is presented in Appendix B.
The amount of P removal per liter of water is found by subtracting the target concentration (0.77 mg/L) from the adjusted TP concentration for each WWTP. This value is then multiplied by plant flow and a conversion factor in order to estimate the
20 For example, a WWTP with a TP concentration limit of 1 mg/L, may in practice attempt to achieve an ending effluent concentration of 0.75 mg/L on a daily basis, and actually achieve an average monthly TP concentration very near the 0.75 mg/L target.
17 Economic and Environmental Implications of Phosphorus Controls
Table 5 Estimation of Alum Expense of North Bosque Communities, 1 mg/L TP Effluent Limit Stephenville Hico Iredell Meridian Clifton Valley Mills Total/Avg. River Data Adj. TP concentration (mg/L) 2.73 3.53 2.96 3.36 2.51 3.16 3.04 WWTP flow (mean) (mgd) 1.37 0.09 0.03 0.36 0.33 0.08 2.25 Avg. conc. after P removal (mg/L) 0.77 0.77 0.77 0.77 0.77 0.77 0.77 TP Removed mg/L 1.96 2.76 2.19 2.59 1.74 2.39 2.27 lb/day 22.38 2.00 0.46 7.76 4.75 1.61 38.96 Percent removal 73% 78% 74% 77% 73% 76% 75% Percent of total 57% 5% 1% 20% 12% 4% 100% Alum Dose Required Molar ratio assumed (Al:P) 2.2 2.2 2.2 2.2 2.2 2.2 2.2 Weight ratio (alum:P) 21.0 21.0 21.0 21.0 21.0 21.0 21.0 Daily dose required (lb) 471.0 42.2 9.7 163.3 100.1 33.8 820.0 Annual dose required (lb) 172,040 15,402 3,544 59,643 36,549 12,344 299,521 Annual dose required (gal) 32,290 2,891 665 11,194 6,860 2,317 56,216 Alum price ($/gal) 0.462 0.462 0.462 0.462 0.462 0.462 0.462 Alum cost ($/yr) 14,911 1,335 307 5,169 3,168 1,070 25,960
average daily load requiring removal to meet the 0.77 mg/L target. While the amount (lb/d) of TP removed varies considerably among plants, based largely on their size, percent of TP removed is similar among the 6 plants, ranging from 73 to 78 percent. The Stephenville plant, being the largest of the 6 plants, accounts for the majority (57 percent) of total estimated TP removed at all 6 plants, while removal at the other five plants ranges from 1 percent to 20 percent of total removal from all 6 plants.
Based on estimated amounts of phosphorus removal, alum requirements are calculated and also reported in Table 5. Alum removes phosphorus in effluent by chemically binding with phosphate thereby forming new compounds, which can be precipitated out by settling. The theoretical molar dosage required for phosphate remove is 1:1 aluminum:phosphate (Al:P),22 which translates into an alum:P dosage ratio of about 9.6:1, or 9.6 pounds of alum required to remove 1 pound of phosphate. The chemistry of phosphorus removal by alum addition is presented in Appendix C. Due to competing reactions, actual dosage rates at plants removing TP by alum addition are much higher than those which would be predicated on the theoretical 1:1
21 The reason for the adjustment is that we assume that a reduction in TP concentrations to 0.77 mg/ L will be attempted on a daily basis, versus targeting a monthly average concentration of 0.77 mg/ L. Daily TP concentrations vary considerably. Even if TP concentrations averaged 0.77 mg/L, TP concentrations would be above 0.77 mg/L approximately half of the time, thereby requiring P re- moval. Due to this variability of TP concentration, subtracting the target concentration from the mean concentration may, in some cases, underestimate the amount of P removal actually required (see Appendix B). All Bosque WWTPs were determined to have sufficient personnel to adjust alum concentrations on a daily or close to a daily basis. For this analysis, upward adjustments for the assumed starting concentration were very small or nonexistent.
22 The P in the theoretical Al:P 1:1 molar ratio refers (strictly speaking) to phosphate-P, rather than phosphorus. Al:P molar ratios, however, are often applied to the total amount of phosphorus needing removal, and are so employed in this analysis, unless otherwise specified.
18 Economic and Environmental Implications of Phosphorus Controls
Al:P molar ratio. Organic P, however, is also removed by flocculation at higher rates of alum addition. A review of empirical plant studies (EPA, 1987b) revealed that alum dosage rates vary considerably even when the same effluent limit is targeted. Alum dosages for plants targeting a 1 mg/L effluent TP limit averaged a molar Al:P ratio of 2.2:1, which translates into an alum:P ratio of about 21:1. This dosage, thus, was assumed as a medium estimate for calculating alum use. It is noted, however, that due to the variability of effluent conditions, required alum dosages could be much higher. Some plants in the aforementioned study required dosage rates of almost twice the average value. Thus, in subsequent calculations in the analysis, a high estimate for alum use is calculated by doubling the alum amount used in the medium estimate.
Multiplying the alum:P ratio of 21 by the number of pounds per day needing removal results in the daily alum dose required, from which the annual alum dose is calculated. Annual dosages of alum are divided by 5.3 to arrive at the number of gallons of alum solution required. This value is multiplied by the price of alum to estimate the annual cost of alum required for each North Bosque WWTP, as reported in Table 5. A cost of $0.46 per gallon of alum solution was used in this analysis, based on a price quotation from General Chemical for bulk alum solution delivered to the North Bosque region of Texas.23
Other O&M Expenses
Use of alum for phosphorus removal creates greater amounts of sludge, which must be disposed of. Sludge removal costs in this analysis are assumed to be proportional to the production of additional sludge, which is assumed to be proportional to the quantity of alum used. Thus, sludge removal cost in this analysis equals CDM’s sludge removal estimate multiplied by the fraction AlumT/AlumC, where AlumT is the amount of alum required as estimated in this report and AlumC is the amount of alum estimated in the CDM report. Other O&M expenses include polymer, maintenance, electricity, and labor. Cost estimates developed by CDM (2001) for these items are used in this analysis. Some of these items, especially polymer, could be influenced by the amount of alum required. Following conservative principles, however, this analysis does not reduce any of the other O&M expenses estimated by CDM (2001). Table 6 presents a summary of annual O&M expense for the six North Bosque WWTPs.
Capital Costs Capital costs consist of one-time expenses associated with physical plant upgrades or retrofits required for phosphorus removal. Capital costs estimated in CDM (2001) are also used in this analysis with the exception that the cost of a two meter belt press and
23 This price is consistent with other analyses. Miertschin (1999), for instance, assumes a price per pound of bulk liquid alum at $0.10 per pound, which translates into a cost of $0.53 per gallon of bulk liquid. An analysis of P removal at a Kerville, Texas plant used a cost of $0.37 per gallon of bulk liquid alum. CDM (2001) assumed a cost of $1.00 per pound for liquid alum, a price that would apply for purchases of small quantities. Prices for bulk purchases are considered more ap- propriate for this analysis.
19 Economic and Environmental Implications of Phosphorus Controls
Table 6 Annual Expense (Medium Estimate) for Phosphorus Removal at North Bosque River WWTPs Stephenville Hico Iredell Meridian Clifton Valley Mills Total/Avg. Annual O&M Expense Alum cost ($) 14,911 1,335 307 5,169 3,168 1,070 25,960 Sludge disp. cost ($/yr) 3,061 274 60 1,172 241 212 5,020 Other O&M expense ($/yr) 46,760 7,610 7,215 24,849 11,590 18,880 116,904 Total O&M ($/yr) 64,731 9,219 7,582 31,191 14,999 20,161 147,883 Capital Costs Capital costs ($) 441,735 464,000 445,000 1,287,000 550,000 538,000 3,725,735 Capital service cost ($/yr) 26,822 28,174 27,021 78,147 33,396 32,668 226,228 Total annual expense 91,554 37,393 34,603 109,338 48,395 52,829 374,111
associated expenses was not included in the Stephenville estimate, because the City of Stephenville has recently contracted for the purchase of a two meter belt press. Capital costs for infrastructure improvements at WWTPs are typically financed through the issuance of municipal bonds. It is probable that funds could be secured through EPA’s state revolving fund (SRF), as administered through the Texas Water Development Board (TWDB). SRF loan rates are subsidized and are approximately one percentage point lower than market municipal bond rates. As of November 15, 2002, the published rate for insured loans was 3.3 percent, while the rate for non-rated loans was 3.6 percent. An interest rate of 3.6 percent and a loan term of 25 years were used to calculate annual loan payments (capital service costs) for this analysis. One time capital costs and associated annual capital service costs are reported in Table 6. Total annual P removal expense is the summation of annual O&M expense and annual capital service cost, and is also reported in Table 6.
Table 6 reveals that annual O&M expense varies considerably among North Bosque WWTPs, ranging from $7,600 for Iredell, the smallest of the plants, to an estimated $64,800 for Stephenville, which operates the largest facility. Capital costs for P removal retrofits, however, do not bear an ostensible relationship to plant flows or community population. In fact, capital costs are relatively similar for five of the six plants, despite great variations in flow. Capital costs for the Stephenville, Hico, Iredell, Clifton, and Valley Mills plants all range between $440,000 and $550,000. Capital service costs on these amounts range between $26,800 and $32,700 annually. Due to site-specific factors, costs for capital improvements are substantially higher for the Meridian plant at $1.29 million, while its capital service cost on this amount would be about $78,000. Capital service costs constitute a substantial portion of total annual costs for phosphorus removal, ranging from 23 percent at Stephenville to 78 percent for Iredell. Because capital service costs are high and apparently not correlated with plant flow, the smaller WWTPs bear a much higher cost per unit of phosphorus removed, than the Stephenville plant.
Affordability The affordability of phosphorus controls is of undoubted interest to North Bosque communities and regulatory agencies. Table 7 presents an affordability analysis of P removal for the six North Bosque communities. Three estimates (medium, high, and
20 Economic and Environmental Implications of Phosphorus Controls
midpoint) are presented in order to acknowledge that there is a great deal of uncertainty in cost estimates. The medium estimate involves the methodology heretofore presented. A high estimate is also calculated, which adjusts the medium estimate in two ways. First, alum costs and additional sludge removal expense were doubled, since it is possible that alum dosage rates could be as much as twice as high as the average rate selected for the medium estimate. Secondly, capital costs were increased by 78 percent. The increase in capital costs for the high estimate is based on a recent purchase of a two-meter belt press by the City of Stephenville. The contracted purchase price for the belt press and associated costs purchased by the City of Stephenville was 78 percent higher than the cost estimate for these costs developed by CDM (2001). Thus, there is some rationale that actual costs for all capital purchases might be higher than CDM estimates by a similar percentage. It is considered probable that actual annual costs for P removal might lie somewhere between the medium and high estimates and that this is a conservative reasonable range into which actual P removal costs might fall. A midpoint estimate is developed for total P removal costs, which is the average (or midpoint) of the medium and high estimates for total P removal costs. (To simplify the presentation, cost-effectiveness ratios and trading scenarios developed later in the analysis use only midpoint estimates.)
Table 7 Cost and Affordability of Phosphorus Controls for North Bosque River Communities Stephenville Hico Iredell Meridian Clifton Valley Mills Total/Avg.a Avg. residential bill ($/mo)b 20.69 12.00 15.14 18.64 22.00 8.00 16.08 Medium Estimate Total cost ($/yr) 91,554 37,393 34,603 109,338 48,395 52,829 374,111 Cost / res. hookup ($/yr) 11.61 58.74 189.67 113.47 29.53 97.32 35.78 Cost / res. hookup ($/mo) 0.97 4.90 15.81 9.46 2.46 8.11 2.98 Percent of average bill 5% 41% 104% 51% 11% 101% 19% Cost / person ($/yr) 4.23 20.93 94.31 44.37 10.30 39.26 11.94 High Estimate Total cost ($/yr) 130,506 61,041 56,105 176,807 77,926 79,663 582,048 Cost / res. hookup ($/yr) 16.56 95.89 307.54 183.49 47.55 146.76 55.88 Cost / res. hookup ($/mo) 1.38 7.99 25.63 15.29 3.96 12.23 4.66 Percent of average bill 7% 67% 169% 82% 18% 153% 29% Cost / person ($/yr) 6.03 34.17 152.91 71.75 16.59 59.20 18.57 Midpoint Estimate Total cost ($/yr) 111,030 49,217 45,354 143,072 63,161 66,246 478,080 Cost / res. hookup ($/yr) 14.09 77.32 248.60 148.48 38.54 122.04 45.83 Cost / res. hookup ($/mo) 1.17 6.44 20.72 12.37 3.21 10.17 3.82 Percent of average bill 6% 54% 137% 66% 15% 127% 24% Cost / person ($/yr) 5.13 27.55 123.61 58.06 13.44 49.23 15.25
a. Except for total cost, all values are averages, weighted by number of hookups or population. b. Based on billing information for early 2002.
The affordability of P removal is calculated by dividing costs by the number of residential hookups or by the population of each community. The annual cost for P removal per residential hookup (one residential hookup is most often one household) was calculated by dividing the residential portion of sewer use (Table 3) by the number of residential hookups to arrive at an annual per hookup cost. Annual costs were then divided by 12 to estimate the monthly residential hookup cost. Since sewer
21 Economic and Environmental Implications of Phosphorus Controls
charges are billed monthly, this cost represents the estimated cost increase for sewer service due to P control that an average household might see reflected on its monthly municipal utility bill. This analysis assumes that the costs for P removal will be distributed to sewer accounts in proportion to usage. This may or may not be the case in actual practice, which cannot be determined a priori. Current rate structures for North Bosque communities either treat commercial and residential accounts equally, or else charge commercial accounts higher rates (see Table 4).24
Midpoint estimates for phosphorus control range from $1.16 per month for Stephenville households to $20.70 per months for Iredell households. As indicated earlier in the analyses, this great difference in costs is due, in large part, to high capital costs being divided by a much smaller number of residential accounts in the smaller communities. While absolute affordability is a subjective concept, it can be said that phosphorus removal is much less affordable for small North Bosque communities than for Stephenville. Figure 5 depicts the medium and high estimates for monthly per household costs for P removal for North Bosque communities, thereby indicating reasonable ranges into which actual costs might fall. Figure 5 also orders North Bosque communities from largest to smallest thereby graphically illustrating the generally inverse relationship between phosphorus removal unit costs and WWTP size.
Figure 5 Per household cost of North Bosque River TMDL phosphorus control limits ($/month)
24 This suggests that residential accounts would not be charged proportionately more per unit of use for P removal than commercial accounts, suggesting that reported affordability values are not overestimates, but could be underestimates, if commercial accounts were charged proportionately more per unit use than residential accounts.
22 Economic and Environmental Implications of Phosphorus Controls
Table 7 also reports P removal costs for residential accounts as a percent increase from current average monthly sewer bills. In 2002, monthly sewer bills for residential hookups ranged from $8.00 to $22.00 (Table 7). Percent increases based on midpoint estimates, from current monthly charges, as reported in Table 7, range from 6 percent for Stephenville to 137 percent for Iredell.
Per person costs for phosphorus removal were also calculated by dividing the summation of the single family residential and multi-unit residential sewer use (Table 3) by the population of the community, as reported in the year 2000 U.S. Census. Per person costs for phosphorus removal (midpoint estimates) range from $5 per year for Stephenville residents to $124 per year for Iredell residents (Table 7). Figure 6 graphically depicts the relationship between per person cost ranges (medium and high estimates are graphed) for phosphorus removal by community, ordered from largest to smallest. This analysis also demonstrates that phosphorus removal is less affordable, i.e., more expensive on a per person basis, for small communities than for large communities with proportionately larger effluent flows.
Figure 6 Per capita cost of North Bosque river TMDL phosphorus control limits ($/year)
Effectiveness Measures
Basis for Effectiveness Measures The obvious purpose of implementing environmental control measures is to reduce or eliminate a water quality impairment. Environmental impairments (e.g., fish kills,
23 Economic and Environmental Implications of Phosphorus Controls
algal blooms, and reduced biodiversity) are the result of complex anthropogenic physical and/or chemical alterations to water bodies. Within a TMDL context, impairment occurs when a designated use (e.g., support of aquatic life or contact recreation) of a water body is not supported. States are charged with developing water quality criteria that protect designated uses for different types of water bodies. When a water quality criterion is exceeded thereby threatening or impairing a designated use, the water body may be placed on a state impaired waters list (303d list). Effectiveness, thus, within a TMDL context, can be considered an improvement in a water quality measure not meeting a state water quality criterion.
This analysis develops three phosphorus-based effectiveness measures: 1) load reductions, 2) reduction in median concentrations at the outfall (or just downstream) of each WWTP, and 3) reduction in median concentration-miles. Reductions in absolute loads was chosen because impairment in Lake Waco may be highly correlated with the P concentrations in the lake, which, in turn, are determined by total load entering the lake, regardless of the source of the P or its ambient concentration in various stream segments.
Ambient P concentration (as opposed to load) is considered a more appropriate impairment measure in the river because growth of algae in rivers has been shown to correlate with P concentrations when P is the limiting nutrient. Ambient P concentrations are highly dependent on both the loads entering the stream and streamflow, which constitute the numerator and the denominator of the concentration measure, respectively. Large loads, thus, would not produce high concentrations if diluted by high flows. In addition, spikes in nutrient loads associated with large runoff events may not contribute to algal growth because storm flows 1) are turbid, providing no light for plant growth and 2) travel fast, thereby scouring attached algae and flushing it, along with suspended algae, downstream. Thus, high mean (flow weighted) concentrations do not necessarily correlate well to stream impairment, if most of the load is the result of storm flow. Median P concentrations, however, better typify normal baseline conditions of the river, which largely determine algal growth. Thus, median P concentrations were chosen for effectiveness measures rather than mean values, which can be greatly influenced by spikes in nutrient loads caused by infrequent storm events.
Changes in median P concentrations resulting from WWTP effluent are strictly relevant for the point in the stream just downstream of WWTP outfalls, which are generally located downstream from the communities they service.25 Taking a broader perspective, it can be argued that phosphorus emitted into the river might not only impair a small area of the river downstream from the outfall but may also potentially impair any downstream location in the river. This argument is supported by the conservative nature of P, i.e., although P may change between organic and inorganic forms as it travels down a river (often referred to as nutrient spiraling), it does not volatilize, as does nitrogen. In order to develop an effectiveness measure consistent with this broader perspective, the impact of reductions in WWTP P emissions on median P concentrations at all points downstream of the outfall was assessed and
25 A small portion of Stephenville’s WWTP effluent, however, is pumped upstream to a city park, from which it flows through part of the city.
24 Economic and Environmental Implications of Phosphorus Controls
integrated into one effectiveness measure, referred to as reduction in concentration- miles. The mathematical derivation of the concentration-miles effectiveness measure is presented in Appendix D. Simply put, the concentration-mile effectiveness measure sums P concentrations resulting from a WWTPs effluent for all miles downstream of the plant outfall.
In practice, water quality effectiveness may be measured in a variety of ways, even for one constituent, e.g., total phosphorus. Reductions in total phosphorus emissions, for instance, can be measured in terms of loads, time-weighted concentrations, flow weighted-concentrations, and median concentrations. The theoretically best impairment measures would be those most highly correlated with impairment. The extent of available data, however, often predicates the formulation of effectiveness measures. Time-weighted P concentrations have been deemed to adequately summarize potential river impairment (Santhi et al., 2001a, 2001b).26 In the present study, median concentrations were selected for effectiveness measures, and were defined as median loads divided by median flows. This formulation allowed us to subtract WWTP loads from river loads and WWTP flows from river flows to assess WWTP impact, while using time-weighted concentrations would not have allowed such an analysis.
While the correlation of nutrient enrichment in streams to steam impairment remains a challenge (Anderson, Glibert, and Burkholder, 2002), the two effectiveness measures incorporating median P concentrations provide a basis for comparing the relative effectiveness of P reductions at the six North Bosque WWTPs on river impairment. As previously indicated, reductions in load may be more relevant from the perspective of Lake Waco impairment than for river impairment.
Analysis
Load Reduction
Phosphorus reduction effectiveness measures are presented in Table 8. Environmental effectiveness in terms of load reduction is presented in units of pounds removed per day (also presented in Table 5). Table 8 indicated that P removal meeting a 1 mg/L limit at the Stephenville plant would remove approximately 3 times the TP as for the Meridian plant, and 5 times, 11 times, 14 times, and 49 times the amount of TP as for the Clifton, Valley Mills, Hico, and Iredell plants, respectively, assuming these plants were also held to a 1 mg/L TP limit.
26 Santhi et al. (2001a) simulated the effects of combinations of control measures (included phospho- rus controls at WWTPs) on ambient P concentrations in the North Bosque River. Daily time step iterations allowed the easy calculation of control measure impact on time-weighted concentra- tions. In this study, actual measured WWTP and river flows and loads were employed. Since WWTP and river data dates did not match, nor did we simulate phosphorus control under various environmental conditions, we could not calculate WWTP impacts on time-weighted P concentra- tions. In our assessment of effectiveness measures, however, we found that our calculated median concentrations (median loads / median flows) for river conditions reasonably approximated time- weighted concentrations as well as observed median concentrations.
25 Economic and Environmental Implications of Phosphorus Controls
Table 8 Phosphorus Control Effectiveness for North Bosque River Communities Stephen- Valley Hico Iredell Meridian Clifton ville Mills River sampling site # BO040 BO070 BO080 BO085 BO090 BO100 Load Reduction TP removed (lb/day) 22.38 2.00 0.46 7.76 4.75 1.61 Percent of Stephenville effectiveness 100% 9% 2% 35% 21% 7% Stephenville eff. / other WWTP eff. 111493 514 Reduction in Median Concentrations Median concentration above WWTP (µg/L) 1,151 292 165 110 104 92 Median concentration below WWTP (µg/L) 1,631 300 167 146 125 96 Median conc. below WWTP after P removal (µg/L) 1,025 293 165 117 111 93 Reduction in median conc. due to P control (µg/L) 605.5 6.8 1.6 28.5 14.5 3.7 Percent of Stephenville effectiveness 100.0% 1.1% 0.3% 4.7% 2.4% 0.6% Stephenville eff. / other WWTP eff. 1 89 388 21 42 164 Reduction in Concentration-Miles Stephenville reach (21.8 miles) (µg/L) 4,156 Hico reach (15.8 miles) (µg/L) 1,220 109 Iredell reach (19.4 miles) (µg/L) 1,545 138 32 Meridian reach (14.7 miles) (µg/L) 1,205 108 25 418 Clifton reach (13.1 miles) (µg/L) 8747818303186 Valley Mills reach (18.8 miles) (µg/L) 1,014 91 21 352 216 73 Total (103 miles) (µg/L) 10,015 524 96 1,072 401 73 Percent of Stephenville effectiveness 100.0% 5.2% 1.0% 10.7% 4.0% 0.7% Stephenville eff. / other WWTP eff. 119105925138
Reduction in Median Concentrations
The second and third effectiveness measures assessed (reduction in median ambient concentrations and reduction in concentration-miles) require streamflow data as well as WWTP flows and P loads. Table 9 provides median flows, P loads, and concentrations for the North Bosque River. In addition, median effluent flows, P concentrations, current P loads, and P loads removed for the P removal scenario for North Bosque WWTPs are reported. Based on Table 9 data, the second section in Table 8 shows P reduction effectiveness for the six plants in terms of reductions in ambient median concentrations downstream from the WWTP. Ambient concentration is regarded as a better indicator of river impairment than load, especially since river flows vary markedly among the six WWTPs. A given load emitted into a small (low flow) stream, for instance, would be expected to have a much greater impact on impairment than the same load emitted into a large (high flow) river.
Sampling sites measuring phosphorus concentrations and flows were located upstream of the Hico, Clifton, and Valley Mills WWTPs, and downstream of the Stephenville WWTP. For Hico, Clifton, and Valley Mills, median river concentrations upstream of the WWTP were found by dividing median loads by median flows; while median river concentrations below WWTPs were found by summing river and WWTP median loads and dividing by the sum of river and WWTP flows. For the Stephenville plant, median river concentration upstream of the WWTP was found by subtracting median WWTP load from median river load and dividing by median
26 Economic and Environmental Implications of Phosphorus Controls
Table 9 Median Flows,a TP Loads, and TP Concentrations for North Bosque River and WWTPs Stephenville Hico Iredell Meridian Clifton Valley Mills River Data Sampling site # BO040 BO070 BO080 BO085 BO090 BO100 Median P load (kg/d) 23.2 38.8 21.3 13.7 12.5 17.2 Median river flow (m3/d) 14,211 132,890 128,955 124,120 120,460 187,497 Median P concentration (µg/L) 1,631 292 165 110 104 92 WWTP Data Median P conc. (1993-2002) (µg/L) 2.60 3.66 2.90 3.43 2.23 3.16 Median flow (2001) (mgd) 1.24 0.08 0.03 0.36 0.32 0.08 Median P load (kg/d) 12.22 1.15 0.27 4.61 2.70 0.92 Median P load removed (kg/d) 8.60 0.91 0.20 3.57 1.77 0.70
a. Median river flow and load data were calculated from automatic and grab sampler samples collected by TIAER from 1996 through 2001. Flow data was not available for site BO080 and BO085. Estimated median flows for these sites are interpolations of median flows between sites BO070 and BO100 based on river miles.
river flow minus median WWTP flow. Median ambient P concentration after P removal was calculated by subtracting median P loads removed at WWTPs from the sum of river and WWTP loads and dividing by the sum of river and WWTP flows. Reductions in median river concentrations due to P removal were found by subtracting after-removal median concentrations from before-removal median concentrations.
Reductions in P concentrations due to P control vary tremendously among the six North Bosque WWTPs, ranging from 606 µg/L at Stephenville to 1.6 µg/L at Iredell. The impact of P control on ambient concentration is especially large for Stephenville not only because it produces the largest P load, but because it is located at the headwater area of the watershed, where median streamflow is much lower than for other sites (see Table 9). Consequently, when effectiveness is measured in terms of the impact on ambient concentration, removal at the Stephenville plant is 21 times more effective than the Meridian plant and 388 times more effective than at the Iredell plant. These multiples (Stephenville effectiveness/other WWTP effectiveness) for concentration reduction are over six times higher than those for load reduction.
Reduction in Concentration-Miles
The final effectiveness measure, reduction in concentration-miles, measure and integrates (adds up) the effect of WWTP P reductions for every mile downstream of the WWTP. Other things being equal, the further upstream a plant is located, the more river-miles it can potentially affect. Thus, for a given load, effectiveness measures are larger for upstream WWTPs versus more downstream WWTPs. As a phosphorus load from a WWTP moves downstream, the load is modeled to remain the same since phosphorus is a “conservative” element that does not volatilize.27 Streamflow, however, varies greatly, generally increasing as it travels downstream. Thus, the numerator forming the concentration ratio (load/flow) remains the same, whereas
27 Phosphorus can be locked up in sediment, however, sediment can also be eroded and phosphorus thereby released. We assume there is no net long-term accumulation of phosphorus in sediment.
27 Economic and Environmental Implications of Phosphorus Controls
the denominator changes. Mathematical derivation of the concentration-mile effectiveness measure is presented in Appendix D.
The third section of Table 8 presents reduction in concentration-miles by reach for the six North Bosque WWTPs and the total reduction in concentration-miles. GPS coordinates for WWTPs and a GIS routine were employed to calculate river-miles between the WWTPs. The Stephenville reach is defined as the river reach between the Stephenville WWTP and the next downstream WWTP (the Hico WWTP). Subsequent reaches are defined in a similar manner. The last reach (Valley Mills reach) extends from the Valley Mills WWTP to the mouth of the North Bosque River at Lake Waco. Because the Stephenville WWTP is the most upstream of the six WWTPs, its phosphorus reductions are assumed effective in reducing P concentration for all six defined reaches. The next downstream WWTP, the Hico plant, reduces P concentrations for the remaining five downstream reaches. The Valley Mills WWTP (the most downstream plant) reduces P concentrations only for the final (Valley Mills) reach. Concentration-mile values are summed over all applicable reaches for each WWTP to obtain total reductions in concentration-miles.
It is not surprising that the concentration-mile value obtained for the Stephenville WWTP is much greater than for the other plants because it 1) produces the greatest load, 2) is the most upstream of the six plants, and 3) median flows are very low in the uppermost reach, producing high concentrations. The smallest concentration-mile value is calculated for the Valley Mills WWTP, in large part because it is the furthest downstream of the six WWTPs, thus, its P reductions would apply only to the final (Valley Mills) reach. Although the Iredell plant produces the smallest plant flow and lowest P load, it is not the least effective of the six plants considered, because its effectiveness extends over four river reaches (see Table 8). The Stephenville WWTP is 9 times more effective in reducing concentration-miles values than the Meridian plant and 138 times more effective than the Valley Mills WWTP. Cost-Effectiveness A relevant measure for policy makers and communities to consider is the cost- effectiveness of phosphorus removal for the six plants. While bearing some resemblance to the affordability analysis, cost-effectiveness ratios measure the cost per unit improvement in an environmental effectiveness measure. Thus, for this analysis, costs of phosphorus control for the six plants were divided by their associated environmental effectiveness measures.
Table 10 presents midpoint cost estimates for phosphorus removal at North Bosque WWTPs, the three environmental effectiveness measures previously defined, and cost-effectiveness values for the three effectiveness measures. The first line of values in the cost-effectiveness section of Table 10 indicates that phosphorus removal at the Stephenville WWTP would cost $14/lb., whereas the cost of removal at other WWTPs is considerably higher: $36/lb for Clifton, $50/lb for Meridian, $67/lb for Hico, $113/ lb for Valley Mills, and $269/lb for Iredell. The second line in the cost-effectiveness section of Table 10 shows cost-effectiveness in terms of dollars per 1 µg/L reduction of ambient P concentrations just downstream of each WWTP. Costs range from $183
28 Economic and Environmental Implications of Phosphorus Controls
per µg/L reduction for Stephenville to $29,000 per µg/L reduction in P concentration downstream of the Iredell WWTP. The third line in the cost-effectiveness section of Table 10 presents cost-effectiveness ratios in terms of dollars per 1 µg/L reduction in concentration-miles, as previously defined. Costs per µg/L reductions in concentration-miles range from $11 per µg/L reduction for Stephenville to $910 per µg/L reduction at the Valley Mills plant.
Table 10 Cost-Effectiveness of Phosphorus Removal at North Bosque River WWTPs Stephen- Valley Hico Iredell Meridian Clifton ville Mills Total cost (midpoint estimate ($/yr) 111,030 49,217 45,354 143,072 63,161 66,246 Effectiveness Load reduction (lb/yr) 8,174 732 168 2,834 1,737 586 Reduction in river concentration at WWTP outfall (µg/L) 6057228154 Reduction in concentration-miles for entire river (µg/L) 10,015 524 96 1,072 401 73 Cost-Effectiveness Load reduction ($/lb) 14 67 269 50 36 113 Reduction in river conc. at WWTP outfall ($/µg/L) 183 7,235 29,047 5,023 4,347 17,899 Reduction in concentration-miles for entire river ($/µg/L) 11 94 475 133 157 910 Cost-Effectiveness (Stephenville = 1) Load reduction 1.0 5.0 19.8 3.7 2.7 8.3 Reduction in river concentration at WWTP outfall 1.0 39.5 158.4 27.4 23.7 97.6 Reduction in concentration-miles for entire river 1.0 8.5 42.8 12.0 14.2 82.1
For all cost-effectiveness measures, the Stephenville WWTP is by far the most cost- effective of the six North Bosque plants in removing phosphorus. The final section of Table 10 presents effectiveness values as multiples of Stephenville’s effectiveness. The first line of the final section of Table 10 indicates that the cost per pound of phosphorus removed at the five smaller WWTPs ranges from 2.7 times Stephenville’s cost (Clifton) to 20 times Stephenville’s cost (Iredell). The second line of the final section of Table 10 indicates that the costs per µg/L reduction in ambient P concentration for the five smaller WWTPs range from 24 times Stephenville’s cost (Clifton) to 158 times Stephenville’s cost (Iredell). The large reductions possible at the Stephenville plant and economies of scale in phosphorus removal combined with low median streamflows at Stephenville account for these high multiples.28 The last line of Table 10 indicates that the cost per concentration-mile reduction of P removal at the five smaller WWTPs ranges from 9 times Stephenville’s cost (Hico) to 82 times Stephenville’s cost (Valley Mills). Trading Implications The trading of effluent reduction obligations (or emission “rights” or “credits”) is sometimes recommended when compliance costs between entities varies markedly,
28 In addition, the Stephenville WWTP already has the necessary filters and has recently purchased a belt press, thereby lowering required capital costs. Even without these existing infrastructure ad- vantages, however, the Stephenville WWTP would be significantly more cost-effective in remov- ing P than the other North Bosque WWTPs.
29 Economic and Environmental Implications of Phosphorus Controls
as they do for the North Bosque WWTPs. For a trading program to be successful, a number of conditions must apply. First, there must be substantive difference in compliance costs at the margin. Second, all potential trading entities must be given a verifiable and enforceable pollution reduction obligation. Third, trades must be permitted and an administrative system tracking trades and verifying compliance must be in place. Fourth, control measures for all entities involved in potential trading should impact a common effectiveness measure. It is also desirable that the unit of trade be closely correlated with remediation of an impairment. There is some precedent for trading nutrient loads among WWTPs and other entities. In theory, trades could be structured for units of other effectiveness measures, such as reduction in in-stream concentration, or reduction in concentration-miles, although precedent for trading of this type is currently lacking. Trading loads has the advantage that it is a relatively simple concept and, in many situations, particularly in case of lakes and estuaries, the total load entering the water body may correlate reasonably well with impairment of the water body targeted for remediation. The trading analysis in this report confines itself to the trading of phosphorus loads between North Bosque River WWTPs.
Trades Between Stephenville and One Other North Bosque WWTP Table 11 quantifies the additional phosphorus removal at the Stephenville WWTP needed to meet a 1 mg/L P reduction obligation at one of the other North Bosque WWTPs. Table 11 also presents estimated Al:P molar ratios assumed to be required to meet a lower effluent standard at the Stephenville plant. It is assumed that higher P removal rates at the Stephenville plant will require higher molar ratio alum dosages. Specifically, it is assumed that the Al:P molar ratio must increase by one-tenth (0.1) for every one-tenth mg/L reduction in target effluent TP concentration.29 The amount of alum required at the Stephenville plant to make additional reductions beyond 1 mg/ L TP increases exponentially because both the required P removal and the assumed Al:P molar removal ratio increase. The cost of alum and associated sludge removal expense at the Stephenville plant, however, is only a small fraction of total P removal cost. Table 11 presents medium, high, and midpoint estimates for cost of additional P removal at the Stephenville WWTP, as well as the midpoint P removal cost for each of the five smaller WWTPs assuming they pursued phosphorus removal on their own.
Table 11 shows that the cost to Stephenville of additional P removal is much smaller than if the other plants were to engage in phosphorus removal on their own. P removal to 1 mg/L at the Iredell WWTP, for instance, is estimated to cost $45,400 annually, whereas the midpoint cost to the Stephenville plant for an equivalent amount of phosphorus reduction is estimated at only $947 annually. Thus, if a 1 mg/ L TP effluent limit were placed on Iredell, it would be of mutual benefit to both Iredell and Stephenville for Iredell to purchase a portion of Stephenville’s phosphorus
29 For example, it is assumed that meeting a 1 mg/L TP effluent limit would require an Al:P molar ratio of 2.1, whereas meeting a 0.9 mg/L TP effluent limit is assumed to require an Al:P molar ratio of 2.2.
30 Economic and Environmental Implications of Phosphorus Controls
Table 11 Additional P Removal at Stephenville WWTP Equivalent to Meeting 1 mg/L Standard for WWTPs at Other Bosque Communities Hico Iredell Meridian Clifton Valley Mills Target conc. needed at S’ville WWTP (mg/L) 0.839 0.964 0.382 0.639 0.873 Assumed avg. conc. (mg/L) 0.609 0.734 0.152 0.409 0.643 Additional TP Removed at S’ville mg/L 0.16 0.04 0.62 0.36 0.13 lb/day 1.84 0.41 7.07 4.13 1.45 Add’l percent removal required 6% 1% 23% 13% 5% Total percent removal (S’ville WWTP) 77% 73% 94% 85% 76% Molar ratio assumed (Al:P) 2.36 2.24 2.82 2.56 2.33 Add’l alum cost ($/yr) 2,402 524 10,226 5,646 1,883 Add’l sludge handling cost ($/yr) 493 108 2,099 1,159 386 Alum & Assoc. Expenses ($/yr) Medium estimate 2,895 632 12,324 6,805 2,269 High estimate 5,790 1,263 24,649 13,611 4,538 Midpoint estimate (removal at S’ville) 4,342 947 18,487 10,208 3,404 Midpoint phosphorus removal expense 49,217 45,354 143,072 63,161 66,246 (own removal) Cost Effectiveness ($/lb) Stephenville WWTP 6.47 6.29 7.16 6.77 6.42 Own removal 67 269 50 36 113
emission “right” or “credit” for a price somewhere between $947 and $45,400 annually.
The last section in Table 11 presents P removal costs at WWTPs in terms of dollars per pound of phosphorus removed (one of the cost-effectiveness measures previously described). Values indicate that the cost for the five smaller WWTPs of P removal at their own plants ranges from $36/lb to $269/lb. The additional cost to the Stephenville plant, of removing equivalent amounts of phosphorus would range from $6.29/lb to $7.16/lb. This analysis highlights the economies that can be realized when Stephenville removes additional phosphorus in lieu of one of the smaller plants removing it on its own.
Even though Stephenville is by far the largest of the six North Bosque WWTPs, its capacity to remove additional phosphorus is limited. A conservative assumption is that the Stephenville plant might consistently meet effluent targets down to 0.5 mg/ L, but not lower. If this is the case, then the first line of Table 11 indicates that the Stephenville plant would not be able to meet Meridian’s load reduction obligation as well as its own, since it would need to target a TP effluent concentration of 0.38 mg/L (less than 0.5 mg/L).
Trades Between Stephenville and Multiple Smaller WWTPs The analysis in Table 11 assumes that the Stephenville plant would be meeting the P reduction obligation of one other North Bosque WWTPs. The Stephenville WWTP,
31 Economic and Environmental Implications of Phosphorus Controls
however, has sufficient capacity to meet the entire P reduction obligations of the three smallest North Bosque River WWTPs.30 Doing so would enable the P reduction obligations of all North Bosque WWTPs combined to be achieved at minimum cost. This analysis assumes that this most efficient allocation of P reduction would be accomplished through trades (as previously described), although the same total load reduction could be achieved by an initial reduction obligation for Stephenville lower than 1 mg/L, while other North Bosque WWTPs could be relieved of P reduction obligations. Table 12 presents results of a trading scenario that would achieve the P reduction obligations of all North Bosque WWTPs at least cost.
Table 12 Effect on Stephenville WWTP of Trades with Iredell, Valley Mills, and Hico WWTPs Stephenville After Trade After Trade After Trade (before with with with trading) Iredell Valley Mills Hico Phosphorus Removal (lb/day) Required removal at each WWTP 19.75 0.41 1.45 1.84 Actual removal at Stephenville 22.38 22.79 24.24 26.08 Phosphorus Conc. at Stephenville (mg/L) Required concentration limits 1.00 0.96 0.84 0.68 Average concentration 0.77 0.73 0.61 0.45 Percent Removal - Stephenville Additional - 1.3% 4.7% 6.0% Cumulative 71% 73% 77% 83% Molar ratio assumed (Al:P) 2.20 2.24 2.36 2.52 Alum Dose Required (gal/yr) Total (cumulative) 32,290 33,425 37,570 43,164 Additional 32,290 1,135 4,146 5,594 Alum Expenses ($/yr) Add’l alum cost 14,911 524 1,914 2,583 Add’l sludge handling cost 3,061 108 393 530 Add’l Alum & Assoc. Expenses ($/yr) Medium estimate 17,971 632 2,307 3,113 High estimate 35,943 1,263 4,615 6,227 Midpoint estimate 26,957 947 3,461 4,670 Cost-Effectiveness of Add’l P Removal ($/lb) Trading scenario (additional cost for Stephenville) - 6.29 6.53 6.96 Own removal (no trade scenario) 14 269 113 67 Average cost for Stephenville 13.58 13.45 13.04 12.61
To obtain the most economically efficient outcome, we assume Stephenville will trade with the WWTP with the most costly (least cost-effective) P removal first, and continue to make trades with WWTPs with the next most costly P removal until its trading capacity has been exhausted. Trading in this manner results in a trade with Iredell first, for its entire P removal obligation, and then trades with Valley Mills and
30 If Stephenville were to remove TP to a concentration of 0.5 mg/L (the lowest level assumed achiev- able), then it could remove an additional 5.7 lb P/day over and above the amount needed to meet the 1.0 mg/L limit. The 1 mg/L P limit for the three smallest North Bosque WWTPs would neces- sitate the removal of 3.7 lb P/day. Thus, Stephenville has sufficient P removal capacity to meet the P removal requirements of the three smallest North Bosque WWTPs.
32 Economic and Environmental Implications of Phosphorus Controls finally Hico, for their P removal obligations.31 The first line of Table 12 shows the P load reduction needed for each WWTP to meet a 1 mg/L P effluent target. The second line presents the actual P removal that would be expected at the Stephenville WWTP, which is more than the required amount because we assume that actual P concentrations will be 0.23 mg/L less than the required concentrations in order to consistently meet targets. Required P reduction obligations at each trading North Bosque WWTP are cumulatively added to Stephenville’s actual P reduction to arrive at Stephenville’s actual P reduction after trading with each WWTP.
The second section of Table 12 shows the concentration limits that would be required of Stephenville in order to remove an amount of phosphorus equivalent to that required for itself and its WWTP trading partners; and average actual concentrations that would be expected in order to consistently meet those limits. Actual concentrations are assumed to average 0.23 mg/L less than the required concentration limits based on empirical industry studies. Required concentration limits for Stephenville would need to be reduced from 1 mg/L TP to 0.96 mg/L, 0.84 mg/L, and 0.68 mg/L TP after trading with Iredell, Valley Mills, and Hico, respectively, while it is expected that actual average concentrations would be reduced from 0.77 mg/L to 0.73 mg/L, 0.61 mg/L, and 0.45 mg/L. Trading stops after the trade with Hico because there is not enough additional P removal capacity at the Stephenville plant to support trades with other North Bosque WWTPs.32
The third section of Table 12 shows the additional percent removal needed at the Stephenville WWTP to remove an additional amount of phosphorus equivalent to that required for the trading plant. The cumulative percent removal which would need to be achieved at the Stephenville plant is also shown. The Stephenville WWTP would need to reduce P loads by an additional 1.3 percent to make up for phosphorus removal at the small Iredell plant, an additional 4.7 percent for the Valley Mills plant, and an additional 6.0 percent for the Hico plant. These trades would increase P removal at the Stephenville plant from 71 percent to 73 percent, 77 percent, and 83 percent, respectively, after trades with Iredell, Valley Mills, and Hico.
Table 12 also shows the Al:P molar ratios that are assumed to be necessary for removal at successively higher rates. The required molar ratio is assumed to increase after trades with Iredell, Valley Mills, and Hico in accordance with observed relationships between ending TP concentrations and the Al:P molar ratios required to reach those concentrations, as previously discussed. The total (cumulative) amount of alum required for the specified removal rates is found by multiplying the Al:P molar ratio by the amount of P removed (line 2) and appropriate conversion ratios. The
31 Trading between Stephenville and another North Bosque WWTP for only part of its P reduction obligation would not be cost-effective if it is assumed that the fixed costs associated with P remov- al would need to be incurred for even small reductions in P loads.
32 The trading of P credits between the Meridian WWTP and another North Bosque WWTPs was also considered, however, there is insufficient P removal capacity at the Stephenville and Meridian WWTPs combined (assuming that 0.5 mg/L is the lowest concentration that can be consistently achieved) to meet the 1.0 mg/L P reduction requirements of the remaining four North Bosque WWTPs. Thus, trades between the Stephenville WWTP and the three smallest WWTPs is the op- timal (least cost) solution within the constraints considered here.
33 Economic and Environmental Implications of Phosphorus Controls
additional amount of alum required for each trade is found by subtracting the amount of alum needed after trading from the amount needed before trading.
The cost of additional P removal at the Stephenville WWTP is assumed to consist solely of the cost of additional alum and sludge removal expense, both of which are a function of the additional amount of alum used.33 The medium estimate assumes that additional alum solution is purchased for $0.46 per gallon and that additional sludge removal expense amounts to 9.5 cents per additional gallon of alum used.34 The high estimate assumes double the additional alum and sludge handling cost, based on a conservative assumption that twice the alum may be required to achieve target effluent concentrations. The midpoint estimate is the average of the medium and high estimates. The midpoint cost estimates for the additional P removal needed for trades with Iredell, Valley Mills, and Hico are $947, $3,461, and $4,670, respectively.
The last section of Table 12 presents cost-effectiveness ratios ($/lb) for additional P removal. The first line presents the cost-effectiveness of additional amounts of P removal for the Stephenville plant; the second line shows cost-effectiveness ratios for each trading WWTP assuming that each community removed phosphorus at its own WWTP. Comparison of the first two lines of the last section of Table 12 illustrates the great gains in economic efficiency that are achievable by the Stephenville WWTP removing additional P in lieu of each WWTP removing P independently. For example, the cost to Stephenville would be $6.29/lb for additional P removal equivalent to Iredell’s obligation, $6.53/lb for Valley Mills’ obligation, and $6.96/lb for Hico’s obligation, whereas removal at the smaller plants would cost $269/lb, $113/lb, and $67/lb, respectively. Costs increase for additional removal increments at Stephenville because we assume that the Al:P molar ratio must be increased for higher levels of removal. The last line in Table 12 shows that although the marginal costs of removal increase, the average cost per pound of P removed at the Stephenville WWTP decreases. Average cost per pound decreases because high capital costs are distributed over more pounds of removal.
Table 13 compares the most economical trading scenario for the North Bosque WWTPs (trades between Stephenville, Iredell, Valley Mills, and Hico) with the no trading scenario, and illustrates the win-win nature of trading. The total (midpoint estimate) costs of P removal without trading, P removal with trading, and the difference are presented in the first three lines of Table 13 for the six North Bosque WWTPs. The first section of Table 13 pertains only to the costs of P removal irrespective of any transfer of funds that may occur as a result of trading. Although Stephenville would incur additional expenses of $9,000 as a result of additional removal from trades with Iredell, Valley Mills, and Hico; these three smaller communities would be relieved of the entire amount of their P removal expense totaling $161,000. Net savings, thus, as the result of trading for the four trading
33 We assume that P reduction facilities would be constructed at the Stephenville WWTP with enough excess capacity to allow the amounts of additional removal here assumed for the three trades, without requiring additional capital expenses for items such as additional feeding equip- ment and storage tanks.
34 This sludge handling cost is derived from estimates published in the CDM (2001) report.
34 Economic and Environmental Implications of Phosphorus Controls
WWTPs is $152,000 annually. Because Meridian and Clifton do not trade under the optimal trading scenario, their costs do not change.
Table 13 Comparison of Optimal Trading Scenario with No Trading Scenario, North Bosque River WWTPs Stephen- Valley Total/ Hico Iredell Meridian Clifton ville Mills Avg. Trading with Stephenville - Yes Yes No No Yes Total Cost (Midpoint Estimates) ($/yr) Without trading 111,030 49,217 45,354 143,072 63,161 66,246 478,080 With trading 120,108 0 0 143,072 63,161 0 326,341 Difference 9,078 (49,217) (45,354) 0 0 (66,246) (151,739) Costs and Benefits of Trading Assuming Trades at $13.58/lb TP Removed ($/yr) Costs 9,078 9,112 2,047 n/a n/a 7,199 27,436 Benefits 18,358 49,217 45,354 n/a n/a 66,246 179,175 Net benefits 9,279 40,105 43,307 n/a n/a 59,048 151,739 Per Person Analysis ($/yr) P control without trading 5.13 27.55 123.61 58.06 13.44 49.23 15.25 P control with trading 4.70 5.10 5.58 58.06 13.44 5.35 10.16 Per Household Analysis ($/mo) Monthly sewer bill (without P control) 20.69 12.00 15.14 18.64 22.00 8.00 16.08 P control without trading 1.17 6.44 20.72 12.37 3.21 10.17 3.82 P control with trading 1.08 1.19 0.94 12.37 3.21 1.11 2.32 Percent increase without trading 6% 54% 137% 66% 15% 127% 24% Percent increase with trading 5% 10% 6% 66% 15% 14% 14%
The second section of Table 13 assumes that the Stephenville WWTPs will sell P emission “rights” to the Iredell, Valley Mills, and Hico WWTPs for a price of $13.58/ lb P removed. A price of $13.58 was chosen because it is the average cost of P removal for Stephenville without trading (see Table 12) and incorporates both the fixed (capital) cost and variable (operational) costs of removal. Under this scenario, although Stephenville would incur additional expenses of $9,100 annually to remove additional P equivalent to Iredell’s, Valley Mills’, and Hico’s obligations, it would collect fees or payments from these communities totaling $18,400 annually, thereby gaining net benefits of $9,300. Iredell would save $45,300 annually in P removal costs while paying $2,000 by contracting out its phosphorus removal obligation to Stephenville, resulting in net benefits of $43,300. The Valley Mills WWTP would achieve net savings of $59,000 annually, while the Hico plant would save $40,100 annually by contracting their phosphorus removal obligation to Stephenville. Altogether, benefits of $152,000 would accrue, while each trading WWTP would gain substantial net benefits.
The third section of Table 13 compares P control costs on a per person basis with and without trading. For the trading scenario depicted, annual per person costs of P removal at Stephenville would decline from $5.13 annually without trading to $4.70 annually with trading, Iredell’s per person costs would decline from $124 without trading to $5.58 with trading, Valley Mills’ per person P removal costs would decline from $49 to $5.35 with trading, while Hico’s cost would decline from $27 to $5.10 per
35 Economic and Environmental Implications of Phosphorus Controls
person annually with trading. P removal costs for the Meridian and Clifton residents would not change because these WWTPs do not trade under the optimal trading scenario due to insufficient P removal capacity. It is noteworthy that post trading P removal costs for the 4 trading WWTPs are quite equitably distributed on a per person basis: $4.70, $5.10, $5.58, and $5.35 for the Stephenville, Hico, Iredell, and Valley Mills plants, respectively.
The final section of Table 13 presents P removal costs in terms of their impact on monthly single-family residential sewer bills—terms that are familiar to residential ratepayers. This section first presents average current (2002) residential monthly sewer bills for the six North Bosque communities, then shows the impact of estimated P removal costs on monthly residential sewer bills without and with trading. P removal costs under the trading scenario, again, appear quite equitably distributed among the trading WWTPs on a household basis: $1.08, $1.19, $0.92, and $1.11 per month for Stephenville, Hico, Iredell, and Valley Mills households, respectively. The final two lines in Table 13 present P removal costs with and without trading as a percentage increase in monthly single-family residential sewer bills. Without trading, P removal costs could raise total month residential sewer bills quite dramatically for the smaller North Bosque communities, as much as 137 percent for Iredell households. Under the trading scenario, however, monthly sewer bills would rise only modestly for the trading WWTPs: 5 percent for Stephenville households, 10 percent for Hico households, 6 percent for Iredell households and 14 percent for Valley Mills households. For the non-trading WWTPs, P removal is estimated to increase monthly sewer bills by 15 percent for Clifton households and 66 percent for Meridian households. Conclusions The analysis presented in Table 13 suggests that if all North Bosque River WWTPs were required to attain phosphorus concentrations of 1 mg/L, that effluent trading would be an attractive option, saving North Bosque communities a total of $152,000 annually. Under the optimal trading scenario and the price of P credits here assumed, the greatest beneficiaries would be the three small communities trading with Stephenville—Iredell, Valley Mills, and Hico. These communities would benefit greatly because P removal costs at their own WWTPs is very high on a per pound or per person basis. The City of Stephenville would also benefit under a trading scenario because it would receive payment for its P removal services well in excess of the additional P removal costs it would incur. The Cities of Clifton and Meridian would be unaffected under the optimal trading scenario here depicted because these communities would not trade and would, therefore, need to remove phosphorus at their own plants. Addendum On December 13, 2002, the TCEQ approved an implementation plan for the North Bosque River TMDLs (TCEQ, 2002).35 In addition to specifying dairy waste control actions and management measures, a key component of the plan is the
36 Economic and Environmental Implications of Phosphorus Controls
implementation of municipal WWTP effluent limits. Phase I of the plan specifies initial load allocations for the six existing WWTPs analyzed in this report plus a planned facility at Cransfill’s Gap, a small community of less than 200 people located at the headwaters of Meridian Creek currently serviced by septic systems. These load allocations are based on the load that would be generated by WWTPs discharging effluent at fully permitted levels with TP concentrations of 1 mg/L plus a future growth allocation of 829.5 kg/yr, which is partially distributed among the WWTPs (TCEQ, 2002). Phase II of the implementation plan for North Bosque River WWTPs commences after Phase I load allocations have been reached. For Phase II of the implementation plan, communities are given a choice of complying with either a load limit, or a concentration limit of 1 mg/L TP. These control actions depart from the assumptions employed throughout this report and in WWTP P control scenarios simulated in Santhi et al. (2001a). Load limits (and therefore implied concentration limits) under the implementation plan are considerably higher than those assumed in this report because they are based on permitted WWTP flows rather than actual flows.
Table 14 presents actual current loads, loads based on permitted flow assuming an effluent TP concentration of 1 mg/L, and TCEQ Phase I initial load allocations. The difference between actual current loads and TCEQ Phase I load allocations is also calculated. Table 14 indicates that both the Stephenville and Meridian WWTPs are currently over TCEQ Phase I load allocations, while the other WWTPs are under their allocations. Table 1, thus, suggests that the Cities of Stephenville and Meridian may need to implement near-term phosphorus controls in order to satisfy TCEQ requirements. Because of the smaller reductions implied under the TCEQ plan (as opposed to the assumptions in this report), the Stephenville WWTP, however, could easily meet both its own phosphorus reductions and those of Meridian with the conventional P control measures assessed in this report. Thus, there is opportunity for the trading of phosphorus ‘credits’ between the Cities of Stephenville and Meridian in order to reduce the total cost of compliance for both cities.
Table 14 Analysis of TCEQ’s TMDL Load Allocations
Stephen- Hico Iredell Meridian Clifton Valley Cranfills Allowance ville Mills Gap for Growth Total Permitted flow (mgd) 3.000 0.200 0.050 0.450 0.650 0.360 0.040 0.225 4.975 Mean WWTP flow (mgd)a 1.373 0.087 0.025 0.360 0.328 0.081 2.254 Mean effluent TP conc. (mg/L)b 2.69 3.52 2.96 3.36 2.40 3.14 3.01 Load Analysis (lb/day) Current loads 30.8 2.6 0.6 10.1 6.5 2.1 0.0 52.7 Calculated TCEQ loads before 25.0 1.7 0.4 3.7 5.4 3.0 0.3 1.9 41.5 future growth allocationc TCEQ initial load allocationd 25.4 3.2 1.7 5.9 7.0 3.0 0.4 1.8 48.4 Amount over (under) allocation 5.4 (0.6) (1.1) 4.2 (0.5) (0.9) n/a (1.8) 4.3
a. Based on monthly self-reported values for 2001. b. Based on grab Samples collected from 1993 to 2002. c. These values were calculated based on TCEQ’s methodology (TCEQ, 2002) of allowing a load equivalent to that which would occur given permitted effluent flows containing 1 mg/L TP, but do not include allowances for future growth, which were subsequently added by TCEQ. d. Includes allowances for future growth.
35 The Texas State Soil and Water Conservation Board also approved the Implementation Plan at its January 16, 2003 meeting.
37 Economic and Environmental Implications of Phosphorus Controls
38 References
Anderson, Donald M., Patricia M. Glibert, and JoAnn M. Burkholder. 2002. Harmful Algal Blooms and Eutrophication: Nutrient Sources, Composition, and Consequences. Estuaries. Vol. 25, No 4b, p. 704-725 (August).
Camp Dresser & McKee. 2001. North Bosque River Phosphorus Removal Study for Six Wastewater Treat- ment Plants. Prepared for the Brazos River Authority.
Chesapeake Bay Program. 2001. Chesapeake 2000 and the Bay: Where are We and Where are We Going?
County of Dane. 2002. What Kind of lakes are the Yahara Lakes? Dane County Lake Management, Wis- consin.
Environment Canada. 2001. The Great Lakes Water Quality Agreement: A History of the Agreement. Envi- ronment Canada, Ontario, Canada.
Europa. 2000. Implementation of Council Directive 91/271/EEC of 21 May 1991 concerning urban waste wa- ter treatment, as amended by Commission Directive 98/15/EC of 27 February 1998. European Commis- sion.
Europa. 2002. Second Implementation Report: Commission report - Implementation of Council Directive 91/ 271/EEC of 21 May 1991 concerning urban waste water treatment, as amended by Commission Directive 98/15/EC of 27 February 1998. European Commission.
EEA. 2001. Nitrogen and Phosphorus in river stations by river size and catchment type. YIR01WQ1, Euro- pean Environment Agency, European Commission.
EPA. 2000a. Progress in Water Quality: An Evaluation of the National Investment in Municipal Wastewater Treatment. Office of Wastewater Management.
EPA. 2000b. Nation Water Quality Report2000 Report to Congress. EPA-841-R-02-001. Office of Water, Washington D.C.
EPA. 1997. Chesapeake Bay nutrient reduction progress and future directions. EPA-903-R-97-030. USEPA, Washington D.C.
EPA. 1987a. Handbook: Retrofitting POTWs for Phosphorus Removal in the Chesapeake Bay Drainage Basin. Water Engineering Research Laboratory, Center for Environmental Research Information; EPA Office of Research and Development, Cincinnati, OH.
EPA. 1987b. Design manual: phosphorus removal. EPA-625-1-87/001.
EPA, 1980. Phosphorus Removal in Lower Great Lakes Municipal Treatment Plants. Municipal Environ- mental Research Laboratory, Office of Research and Development; EPA, Cincinnati, OH.
EPA. 1976. Process design manual for phosphorus removal. EPA 625-1-76-001a.
Imperial, Mark. 2000. Tahoe Regional Planning Agency: The Evolution of Collaboration. Prepared by School of Public and Environmental Affairs, University of Indiana, Bloomington, IN.
Lee, G.F. and R.A. Jones. 1998. The North American Experience in Eutrophication Control Through Phosphorus Management. In: Proc. Int. Conf. Phosphate, Water and Quality of Life. Paris, France.
Litke, D. W. 1999. Review of Phosphorus Control Measures in the United States and Their Effects on Water Quality. Water-Resources Investigations Report 99-4007. USGS, Denver, CO.
39 Economic and Environmental Implications of Phosphorus Controls
Metcalf and Eddy, Inc. 1991. Wastewater Engineering: Treatment, Disposal, and Reuse, 3rd Ed., McGraw- Hill, Inc., New York, NY.
Miertschin, James. 1999. Cost for Phosphorus Removal. Prepared for the Texas Institute for Applied En- vironmental Research.
Minnesota Pollution Control Agency. 1997. Pollutant Trading for Water Quality Improvement: A Policy Evaluation. Water Quality Division.
Resource Strategies. 1999. Analysis of Phosphorus Control Costs and Effectiveness for Point and Nonpoint Sources in the Fox-Wolf Basin. Prepared for Fox-Wolf Basin 2000. Resource Strategies Inc, Madison, WI.
Santhi, C., J.G. Arnold, J.R. Williams, L.M. Hauck, and W.A. Dugas. 2001a. Application of a water- shed model to evaluate effects on point and nonpoint pollution. Transactions of American Society of Agricultural Engineers - Soil & Water 44(6):1559-1570.
Santhi, C., J.G. Arnold, J.R. Williams, W.A. Dugas, R. Srinivasan, and L.M. Hauck. 2001b. Validation of the SWAT model on a large river basin with point and nonpoint sources. Journal of American Wa- ter Resources Association 37(5):1169-1188.
Texas Commission on Environmental Quality. 2002. An Implementation Plan for Soluble Reactive Phos- phorus in the North Bosque River Watershed: For Segments 1226 and 1255.
Texas Natural Resources Conservation Commission (TNRCC). 2001. Two Total Maximum Daily Loads for Phosphorus in the North Bosque River.
University of Washington. 1996. 1955, “Rescue of Lake Stinko”. In Pathbreakers. Office of Research, Seattle, WA.
VDEC. 2001. Draft of the Lake Champlain Phosphorus TMDL. September 2001. Vermont Agency of Natural Resources, Dept. of Environmental Conservation, Waterbury, VT.
40 APPENDIX A Texas Regulation Impacting Phosphorus Control
30 TAC Chapter 311 Watershed Rules Texas Watershed Rules Chapter 311 has 7 subchapters specifically protecting the water bodies listed below:
• Lakes Travis and Austin • Lakes Inks and Buchanan • Clear lake watershed • Colorado River (segment 1428) • Lakes Lyndon B.Johnson and Marble Falls • Lakes Worth, Eagle Mountain, Bridgeport, Cedar Creek, Arlington, Benbrook and Richland-Chambers
Chapter 311 rules specify specific additional water protection measures must be undertaken for these water bodies. These measures range from the prohibition of direct WWTP discharge to a water body (such as for Lakes Travis and Austin) to the requirement of phosphorus effluent limits in the TPDES permits of WWTPs who may discharge into specified water bodies or their tributaries (such as a specified 1 mg/ P limit for WWTPs discharging to segments 1427 and 1428 of the Colorado river). TCEQ’s Antidegradation Policy The TCEQ’s antidegradation policies in TAC Chapter 307 specify that:
• Existing uses will be maintained • Activities that lead to the degradation of water quality are only allowed if necessary for important social and economic development, and only if the resulting water quality is sufficient to protect existing uses • Quality of Outstanding National Resource waters will be maintained
TCEQ’s antidegradation policy implies that a water body should not be subject to water quality degradation, except when any necessary degradation (for important economic and social development) does not threaten the attainment and protection of the water body’s existing uses.
41 Economic and Environmental Implications of Phosphorus Control
The 75%-90% Rule 30 TAC §305.126 (2002) (Additional Standard Permit Conditions for Waste Discharge Permits)
The code pertaining to the 75 percent-90 percent rule states:
Whenever flow measurements for any sewage treatment plant facility in the state reaches 75 percent of the permitted average daily or annual average flow for three consecutive months, the permittee must initiate engineering and financial planning for expansion and/or upgrading of the wastewater treatment and/or collection facilities. Whenever the average daily or annual average flow reaches 90 percent of the permitted average daily flow for three consecutive months, the permittee shall obtain necessary authorization from the commission to commence construction of the necessary additional treatment and/or collection facilities.
In essence, the rule implies that if, in the course of its mandatory monthly reports of effluent levels, a wastewater treatment plant documents that it has been discharging for three months in a row at an average daily rate of greater than 75 percent of their permitted flow, they must initiate a planning process for plant expansion to deal with these higher flows, as well as starting the process to secure financing for this expansion. These processes are undertaken so that when the permittee violates the 90 percent average daily flow limit for three consecutive months, the plans and finance will be in place to allow the immediate start of the construction necessary to expand capacity to accommodate a new and higher permitted flow. Communities typically choose to expand capacity by at least 50 to 100 percent due to the large capital costs involved in wastewater treatment plant construction. The rule allows for exemptions to the 75 percent limit to be granted by the executive director where factors other than population growth are deemed to have caused the violation (e.g. three months of well above average precipitation and no significant population growth). TCEQ has rarely acted on the 90 percent limit because as population growth forces a plant’s average daily flows over the 75 percent limit, it will in all likelihood start violating other of its permit effluent limits, leading it to expand capacity before it reaches the 90 percent limit. Furthermore, violations of effluent limits per se are not enforceable, because the discharge of water (and other constituents not considered pollutants) does not constitute a violation of the law. Violation of Permit Effluent Limits The TCEQ’s TPDES follows the federal regulations for violations of Permit Effluent Limits. Title 40, Chapter I, Subchapter D, Part 123, Subpart C, Appendix A to @ 123.45 states that for violations of Group I pollutants, which included nutrients, the following criteria should followed:
Violations of monthly average effluent limits which exceed or equal the product of the Technical Review Criteria (TRC) times the effluent limit, and which occur two months on a six month period must be reported. … Chronic
42 Appendix A Texas Regulation Impacting Phosphorus Control
violations must be reported…if the monthly average permit levels are exceeded any four months in a six-month period.
The TRC for Group I pollutants is currently set at 1.4.
The rules in Appendix A to 123.45 thus state that a ‘violation’ of monthly permit effluent limits occurs when a wastewater treatment plant states that it was more than 40 percent over a specified effluent limit for two months out of the preceding six months (e.g. for a TP effluent limit of 1 mg/L, a violation would occur if TP exceeded 1.4 mg/L in any two out of the previous six months). A ‘chronic violation’ occurs when the WWTP reports it was over (by any amount) its specified effluent limit in four of the previous six months.
43 Economic and Environmental Implications of Phosphorus Control
44 APPENDIX B Derivation of Adjusted Effluent Phosphorus Concentrations
Assuming that an effluent limit (L) is just met every day, then the amount of phosphorus removal (R) can be specified as: n () (1) Rx= ∑ i – L i = 1 where xi = average daily phosphorus concentration (mg/L), and n = number of days in time period.
Equation 1 can be rewritten as: n (2) Rx= ∑ i – nL i = 1 n ∑ xi i = 1 (3) = n------– L n
(4) = nx()– L where x is the mean effluent concentration.
Thus, it can be seen that subtracting the effluent limit from the mean concentration (x ) and multiplying the difference by n also yields the amount of phosphorus removed, and is equivalent to equation 1. < However, no phosphorus is removed when xi L because, in this case, the phosphorus concentration is already below the limit. Therefore, the amount of phosphorus actually removed (Rˆ ) is: m ˆ () (5) R = ∑ xi – L i = 1 > < where m = number of days where xi L . Hence mn.
45 Economic and environmental Implications of Phosphorus Control
Equation 5 can be rewritten as:
(6) Rˆ = mx()ˆ – L m ∑ xi i = 1 where xˆ = ------. m Rˆ will always be greater than or equal to R.
The adjusted concentration()x˜ is calculated so that it will yield the actual amount of phosphorus removed()Rˆ when the difference()x˜ – L is multiplied by the number of days in the time period (n). Thus,
(7) nx()˜ – L ==Rˆ mx()ˆ – L
Thus, m (8) x˜ = ---- ()xˆ – L + L n
x˜ will always be greater than or equal to xˆ .
The calculation of x˜ permits convenient calculation of the estimated amount of phosphorus removal that is equivalent to the amount that would be calculated using disaggregate (daily) concentration data, and assuming that each daily concentration were reduced to 1 mg/L. The value of x˜ would be significantly higher than the value of xx in cases where is close to L and where the variance of x is high. Where this is not the case and in this analysis, adjusted concentrations are not appreciably different than unadjusted concentrations.
46 APPENDIX C Chemistry of Phosphorus Removal by Alum Addition
3- One of the most reliable and well studied methods for removing phosphate (PO4 ) load from a wastewater stream is the addition of alum and the subsequent settling and removal of insoluble aluminum phosphate. Chemistry of Alum and Phosphorus 3- Aluminum (Al) ions react with PO4 in order to create relatively insoluble aluminum phosphate:
(1) 3+ + 3− → Al PO4 AlPO4
The above formula implies that 1 molecule of Al ion will precipitate one molecule of phosphate. However, there are many conflicting interactions in wastewater, therefore dosages are usually established on the basis of bench-scale tests. A review of the literature reveals that actual Al:P ratios used at WWTPs, which remove P by alum addition are much higher than the theoretical 1:1 ratio (CDM, 2001; Metcalf and Eddy, 1991). An EPA (1987) study revealed that the average Al:P ratio required in plants targeting a 1 mg/L effluent TP limit was, in fact, 2.2:1. Based on this and other studies, we assume an Al:P ratio of 2.2:1 will be necessary at all North Bosque WWTPs to achieve effluent TP concentrations of 1 mg/L.
Based on grab samples (n = 62) collected by TIAER over a three year period (1998- 3- 2001), PO4 averages about 88 percent of TP measurements. Therefore, at best it would seem that only 88 percent of TP could be removed by alum addition according to the reaction expressed in equation (1). However, flocculation created by alum addition also settles out particulate phosphorus (Metcalf and Eddy, 1991).
Alum is the common name for the aluminum salt with the formula:
(2) Al2(SO4)3(14H2O)
Upon disassociation, each molecule of salt releases two ions of Al3+ which can ideally precipitate 2 ions of PO43-:
→ 2- (3) Al2(SO4)3(14H2O) 2 Al3+ + 3SO4 + 14H2O
47 Economic and Environmental Implications of Phosphorus Control
As stated above, this perfect stoichiometric theoretical 1:1 ratio of Al to P is not realized in actual practice and, hence, we have adopted a relationship of 2.2:1 Al to P.
It is possible to mix one’s own alum solution by adding dry alum to water, however, this is somewhat difficult to do, exposes workers to the hazards of alum dust, and is time consuming. For this reason facilities often choose to use alum already prepared in solution. Alum solutions can come in different strengths. Miertschin (1999) refers to bulk delivery of 4500 gallon loads of 50 percent alum solution. Metcalf and Eddy (1991) report the density of liquid alum as 10.7 lb/gallon. CDM (2001) uses a 48 percent alum solution with a density of 11.1 lb/gallon in their design criterions. General Chemical a vendor of liquid alum, also characterized their product as 48 percent alum with 11.1 lb per gallon wet and 5.4 lb per gallon dry (Hummel, 2002). Using the design criterion of CDM confirmed by General Chemical the weight of alum per gallon is:
lbs alum lbs alum solution 5.33 lbs alum (4) 0.48 × 11.1 = lbs alum solution gallon alum solution gallon alum solution
The weight of aluminum per gallon of alum solution is based on the chemical formula for alum (equation 2). The molecular weight of alum is 594 and the molecular weight of aluminum is 26.98. Hence, the weight of aluminum per gallon of alum solution is:
(5)
5.33 lbs alum × 2 moles Al × 26.98 g Al × mole alum = 0.484 lb Al gallon alum solution mole alum mole Al 594 g alum gallon alum solution
The weight of Al required to precipitate a given weight of P is again based on the molecular weights of the two substances and their stoichiometric relationship of 1 mole of Al per mole of P. The molecular weight of P is 30.97 so the ratio of the weights of Al/P is equal to 26.98/30.97, or 0.87 lb Al/lb P. However, as stated in our conservative assumptions, we do not assume a perfect one to one reaction ratio, but rather a 2.2 to one reaction ratio, hence the alum dosage is determined thusly:
0.87 lb Al gallon alum solution 3.955 gallon alum solution (6) 2.2 × × = lb P 0.484 lb Al lb P
The above calculation gives a ratio of alum to P (lb/lb) of:
(7) 3.955 gallon alum solution × 5.33lb alum = 21.08 lb alum lb P gallon alum soultion lb P
48 Appendix C Chemistry of Phosphorus Removal by Alum Addition
Determining Alum Dose for a Specific Wastestream At this point it is possible to determine the amount of alum solution required based on the amount of P one wants removed from the waste stream. For example, the adjusted mean TP concentration for the Stephenville effluent was 2.73 mg/L. In order to meet our target effluent of 0.77 mg/L then 1.96 mg/L TP must be removed (2.73 - 0.77 = 1.96). The total waste stream had a mean flow rate of 1.37 million gallons per day (mgd). Hence the total amount of P to be removed per day would be 22.4 lb P:
× 6 × −6 (8) 1.37 Mgal × 1.96 mg P × 3.78 10 l × 2.205 10 lb P = 22.4 lb P day l Mgal mgP day
Using the previously derived value of 3.955 gallons of alum solution required per pound of P removed (equation 6), the alum dose required to remove the amount of TP in equation (8) would be:
(9) 22 .4 lb P × 3.955 gal alum solution = 88.6 gal alum solution day lbP day
The total cost for alum per year, based on a $0.462 cost per gallon of alum solution, would be $14,900 per year:
(10) 365 days × 88.6 gal alum solution × $0.462 = $14,900 year day gallon alum soultion year
This costs is substantially below CDM’s (2001) estimated alum cost of $144,500/yr. Even when costs are doubled (to $29,800), to reflect the possibility that the molar Al:P ratio could be as high as 4.4:1, costs are well below the CDM estimate. The CDM (2001) estimate, however, was based on an aeration basin effluent of 4.5 ppm TP, versus a measured (adjusted) TP effluent concentration of 2.7 ppm; an effluent flow matching the plant flow capacity of 3.0 mgd, versus a self-reported average actual flow of 1.4 mgd; and a $1.00/gallon price for alum solution, whereas the quoted price of bulk alum solution used in this analysis was $0.46/gallon. The measured values and quoted alum price used in this analysis are intended to estimate actual near-term alum costs, which are more appropriate for determining affordability measures, such as cost/person/yr. References
Camp Dresser & McKee. 2001. North Bosque River Phosphorus Removal Study for Six Wastewater Treatment Plants. Prepared for the Brazos River Authority.
EPA. 1987. Design manual: phosphorus removal. EPA/625/1-87/001.
Hummel, H. C. 2002. Personal Conversation. General Chemical (1-800-631-8050)
49 Economic and Environmental Implications of Phosphorus Control
Metcalf and Eddy, Inc. 1991. Wastewater Engineering: Treatment, Disposal, and Reuse, 3rd Ed., McGraw- Hill, Inc., New York, NY.
Miertschin, James. 1999. Cost for Phosphorus Removal. Prepared for the Texas Institute for Applied Environmental Research.
50 APPENDIX D Derivation of Concentration-Mile Effectiveness Measure
Reduction in average ambient P concentration at WWTP i at outfall j (Cij) as a result of phosphorus control is found by dividing the P load removed by WWTP i (Li) by the streamflow at the outfall j (Fj). Thus,
Li (1) Cij = ---- Fj
We assume that the reduction in P load would reduce P concentrations at all points downstream from the outfall. The load reduction from WWTP i traveling down the river (Li) is assumed to remain constant. Flows, however, change at different locations of the river. The average change (or difference) in flow at a point one mile downstream from a given point in a river reach between outfall j and j+1 (Dj) is estimated as:
Fj + 1 – Fj (2) Dj = ------mj where Dj = average per mile change in streamflow between outfall j and outfall j+1, Fj = river flow at WWTP outfall j, Fj+1 = river flow at the next downstream WWTP outfall (i+1), and mj = distance in river miles between i and i+1.
Thus, the concentration reduction resulting from phosphorus control at WWTP i one mile downstream of outfall j is estimated to be:
Li (3) ------Fj + Dj
Summing estimated concentrations over discreet mile intervals for the reach bounded by outfall j and outfall j+1 (hereafter referred to as reach j) for the load generated by WWTP i yields:
m j Li (4) CM = ∑ ------ij F + D x x = 1 j j where CMij = the concentration-mile reduction in ambient P concentration for load reduction i,reach j,
51 Economic and environmental Implications of Phosphorus Control
x = the river mile for reach j (x = 1 ... mj), and the other variables are defined as before.
A more elegant and precise method of finding the concentration-mile reduction for load reduction i, reach j is by means of integral calculus, where:
m j Li (5) CMij = ∫ ------dx 0 Fj + Djx
Solving equation 5 yields:
m Li []j (6) CMij = ------ln Fj + Djx Dj 0
When evaluated from 0 to mi, equation 6 yields: L i {} (7) CMij = ------ln Fj + Djmj – ln Fj Dj
Li Fj + Djmj (8) = ------ln------DjFj
Reduction in concentration-miles associated with phosphorus control at WWTP i for all downstream reaches (CMi) is found by summing reductions in concentration- miles (CMij) over all downstream reaches (j). Thus: ∑ (9) CMi = CMij , for all applicable j. j
In this manner, reductions in concentration-miles (CMi) can be calculated and compared among various WWTPs located on a particular river. For a given load, WWTPs that are located upstream will have greater CM values than those located downstream, because their loads would flow through more river reaches.
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