Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff (2019)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

92 This chapter shows the state DOT how to construct a cost and effectiveness analysis for BMPs. It provides guidance to state DOTs for determining the cost of complying with TMDL requirements and to compare those costs to the value of the expected benefits. The cost of com- pliance is related to the number of BMPs required and the whole life cost of each facility (capital and maintenance). The cost is also affected by the volume of runoff treated by each BMP and how these costs might be affected by increasing BMP size. This chapter also provides guidance on determining unit cost for common types of BMPs for select constituents. It then describes how to value benefits associated with the improvement in receiving water quality, which is an exceedingly challenging task. Finally, a brief discussion is provided on watershed-based approaches to meeting water quality standards that include contributing to the funding of BMPs not located in the highway right-of-way. Estimating Cost of Compliance Number of Best Management Practices Required Estimating the number of BMPs required to achieve regulatory compliance can be done in a couple of ways. As a first approximation, the state DOT should assume that BMP implemen- tation may be required at every outfall, a location where runoff leaves the right-of-way or is discharged to a receiving water. In areas covered by MS4 permits, departments should have developed a map of all storm drain outfalls. These maps can be used to determine exactly how many outfalls are present in the subject watershed and the potential number of BMPs required, assuming one BMP per outfall. For areas outside of the permitted ranges, the state DOT may have to do a survey to determine the number of outfalls and their locations. However, such a survey should be one of the initial steps in watershed planning. A second approach, which would provide a more accurate estimate, requires that a corridor study be performed. A corridor study is a field study to document in detail the characteristics of each outfall including area served. The focus is on determining available space to install potential BMPs, whether safe access is available to construct and maintain new BMPs, and the available hydraulic head. In many cases, it is obvious that implementing a BMP at a given location is not technically feasible, especially in urban areas with limited right-of-way and sections of elevated freeway. The corridor study may produce a more refined estimate of what is feasible and what types of BMPs can be implemented at each outfall in the watershed. Best Management Practice Cost Several previous NCHRP projects have involved developing costs of BMP implementation. Partic- ular care should be taken when using these cost tools because site-specific characteristics may increase C H A P T E R 7 Best Management Practice Cost and Effectiveness Analysis

Best Management Practice Cost and Effectiveness Analysis 93 these costs significantly. For instance, utility conflicts can be a significant cost component and, where space is limited, additional costs may also be associated with material delivery and storage. Table 46 from NCHRP Research Report 840: A Watershed Approach to Mitigating Stormwater Impacts (Weinstein et al. 2017) provides unit cost data for various BMPs for both new con- struction and retrofit. New construction includes the cost of constructing a BMP as part of any new highway project, while retrofit is the cost of constructing a stand-alone BMP in an existing highway system. Retrofit is defined as a stand-alone BMP construction, while new construction consists of major reconstruction, as well as new roadways. As expected, construction of BMPs as part of new or major reconstruction projects is substantially more cost-effective than a stand- alone retrofit, since economies of scale are realized when the BMPs serve larger drainage areas. NCHRP has also funded two projects that developed tools to provide more detailed cost information for various BMP options. These studies include NCHRP Report 792: Long-Term Performance and Life-Cycle Costs of Stormwater Best Management Practices and NCHRP Report 778: Bridge Stormwater Runoff Analysis and Treatment Options (Taylor et al. 2014A, Taylor et al. 2014B). These BMP evaluation tools calculate both capital, as well as operation and maintenance costs based on a variety of factors including climate, BMP size, and level of maintenance anticipated. Tools are available for the following BMPs: • Bioretention • Dry detention • Filter strips • PFC pavement • Sand filters • Swale • Wet pond These tools are available at http://www.trb.org/main/blurbs/171471.aspx. To access the tools from this website, the user can download an ISO CD-ROM image and then burn a CD-ROM. Appendix F of NCHRP Report 792: Long-Term Performance and Life-Cycle Costs of Stormwater Best Management Practices provides guidance on the use of the tools (Taylor et al. 2014A). According to Taylor et al. (2014B), the tools can be used for the following: 1. Evaluate volume and pollutant load reduction in comparison to baseline conditions and/or performance targets and standards. The tools can be used to estimate the volume and pollutant load reduction (i.e., percent reduction of runoff volume and loads compared to the baseline condition without controls) for a wide range of potential BMP configurations. The results from the tools can also be compared directly to project goals or regulatory require- ments, such as TMDL implementation plans or volume-reduction goals. Design parameters can be adjusted in the tools to improve BMP performance and to meet project goals. BMP Cost per drainage area (BMP serving less than 3 acres) ($/ac) Cost per drainage area (BMP serving more than 3 acres) ($/ac) New Construction ($) Retrofit ($) New Construction ($) Retrofit ($) Sand filter Cartridge filter Swale Strip Bioretention Extended detention Wet pond Wetland 87,953 163,884 19,499 11,147 24,458 29,184 32,631 32,770 113,835 201,521 37,460 30,940 35,380 58,843 52,051 52,273 48,136 153,039 2,287 1,890 13,961 9,662 12,109 13,713 62,301 188,186 4,394 5,247 20,196 19,482 20,911 21,874 Table 46. Example area-weighted BMP costs (Source: Weinstein et al. 2017).

94 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff 2. Quickly compare several BMPs for a given drainage area. Once project location and tribu- tary area has been established, the tools can be used to evaluate BMP types, configurations, performance, and costs to provide an understanding of the varying sizing and pollutant removal capabilities of the BMP types and to aid in choosing the most appropriate, cost- effective BMP for a given site. 3. Evaluate performance relationships and sensitivities of design parameters. The tool pro- vides the ability to adjust design parameters and to obtain near-immediate estimates of long-term performance (i.e., without requiring the delay to set up and run a continuous simulation model). This functionality can be used to evaluate performance relationships and sensitivities, as well as to understand how changing design parameters affect project costs. For example, the water quality benefits of increasing BMP sizing to provide 90 percent average annual runoff capture instead of 80 percent can be compared alongside the BMP costs to assess whether there is a proportional benefit to increasing the average annual runoff capture. BMP sizing can also be adjusted to assess the volume and pollutants being captured and treated by the BMP versus the volume and pollutants that bypass or overflow the BMP. The organization of the tools is provided in Table 47. This table also describes the inputs that can be modified for site-specific locations. Best Management Practice Sizing The amount of runoff that must be treated is largely a function of the amount of load reduc- tion required for the POC. The set of tools described above calculate the load reduction in pounds per year (or colony-forming units per year for bacterial constituents), as well as the percent annual load reduction. These values can be compared to the TMDL requirements to determine whether the BMP achieves the necessary reduction. The size of the BMP can then be either increased or decreased to match the regulatory requirement. Incremental Costs Associated with Increasing Best Management Practice Size The BMP evaluation tool automatically recalculates the capital and maintenance costs when the user specifies a larger treatment volume for the BMP. The capital costs are based on unit costs for the typical components of each BMP. These costs can also be modified by the user to include Input Form Worksheet Name Summary of User Inputs and Results Project Location and Climate Selection Project Location Specify project location. View default climate parameters. Override default climate parameters, as needed. Project Options Project Options View and edit pollutant concentrations. Select primary cost inputs. Capital Costs (Hidden) Capital Costs Optionally view capital costs sheet and override defaults. Maintenance Costs (Hidden) Maintenance Costs Optionally view maintenance costs sheet and override defaults. Tributary Area Attributes Project Design Specify tributary area characteristics. View reference information related to precipitation and runoff volumes. BMP Design Parameters Project Design Specify BMP design parameters. View and edit default and additional design parameters. Results Summary Report Results Summary Report View summary of performance results in tabular and graphical format. Supporting Data Supporting Data View underlying model results data used by the tool to provide performance estimates. Whole Life-Cycle Costs Summary Whole Life-Cycle Costs Summary View the whole life-cycle costs results in tabular and graphical format. Table 47. Organization of the tools.

Best Management Practice Cost and Effectiveness Analysis 95 site-specific cost data. An example of the detail in the capital cost determination is provided by the following list of items included for bioretention facilities: • Mobilization • Clearing and grubbing • Planting media • Pea gravel • Gravel • Mulch • Slotted PVC underdrain pipe • Excavation and grading • Hauling and disposal of excavated material • Finish grading (yd2) • Bioretention vegetation (ft2) • Hydroseed (ft2) • 18”-square trench (LF) • Dewatering • Inflow structure(s) • Overflow structure (concrete or rock riprap) • Metal beam guardrail • Conveyance Unit Cost Data by Best Management Practice and by Constituent The BMP tools also provide unit cost data for each constituent based on the mass removed. The cost data ($/lb for most constituents and $/1012 colony-forming units for bacteria) are based on the volume treated and the removal efficiency of the BMP for that constituent. These cost data allows for easy comparison of the economics of each of the feasible BMPs for a given site and the selection of the most cost-effective treatment option. Total State DOT Cost for Compliance There are two procedures for determining a state DOT’s cost of complying with TMDL requirements. The first procedure is a simple method for getting an initial estimate. In this case, the state DOT would use the number of outfalls—based on its NPDES inventory—to estimate the number of BMPs required (assuming one BMP per outfall) and then use the unit cost data provided by NCHRP Research Report 840: A Watershed Approach to Mitigating Stormwater Impacts to estimate total cost (Weinstein et al. 2017). The more accurate approach to estimating cost for compliance is to conduct a corridor study to determine the number and type of BMPs required that can be feasibly implemented within the highway right-of-way at each outfall based on hydraulic head, available space, soil type, and other factors. The state DOT can then use the BMP evaluation tools developed by NCHRP to produce detailed whole life-cycle cost estimates, as well as unit costs to determine the optimum BMP imple- mentation strategy. This latter approach, although significantly more expensive, would carry much more weight with regulatory agencies due to the detailed and site-specific nature of the estimates. Quantifying Benefits Associated with Achieving Water Quality Standards Quantifying the benefits and assigning a dollar value to improving water quality is a very chal- lenging exercise that most state DOTs may find too onerous to pursue. However, this section provides an overview of the process should circumstances require such an effort. The following

96 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff description is drawn largely from Guidelines for Preparing Economic Analyses (National Center for Environmental Economics 2014). Economic valuation is based on the traditional economic theory of human behavior and pref- erences, which centers on the concept of “utility”—or “satisfaction” or “welfare”—that people realize from goods and services, both market and nonmarket. Different levels and combina- tions of goods and services afford different levels of utility for any one person. Because different people have different preferences, different sets of goods and services appeal to different people. Utility is inherently subjective and cannot be measured directly. Therefore, to give “value” an operational definition, it must be expressed in a quantifiable metric. Money generally is used as the metric. A marginal abatement cost curve compares the cost of actions to reduce pollutant discharge to the marginal damages, which, in this case, is the impairment leading to a TMDL. As the dam- ages are reduced to zero, the expectation is that the cost to achieve this may rise dramatically. Ideally, it is preferable to not spend more on mitigation than the benefits achieved by reducing damages. This point is shown as e* in Figure 27. However, many environmental goods and services, such as air quality and biological diversity, are not traded in markets. The challenge of valuing nonmarket goods that do not have prices is to relate them to one or more market goods that do. Assigning prices can be done either by determining how the nonmarket good contributes to the production of one or more market goods (often in combination with other market good inputs) or by observing the trade-offs people make between nonmarket goods and market goods. Figure 27. Marginal Abatement Cost Curve (MAC = marginal abatement cost; MD = marginal damages) (Modified from National Center for Environmental Economics 2014).

Best Management Practice Cost and Effectiveness Analysis 97 One way or another, this comparison is what revealed and stated preference valuation methods are designed to do. The economic valuation of an environmental improvement is the dollar value of the private goods and services that individuals would be willing to trade for the improvement at prevailing market prices. The willingness to trade compensation for goods or services can be measured either as “willingness to pay” or “willingness to accept.” Willingness to pay is the maximum amount of money an individual would voluntarily pay to obtain an improve- ment. Willingness to accept is the least amount of money an individual would accept to forgo the improvement. Table 48 summarizes the types of benefits that might be realized by improv- ing environmental quality and provides the commonly used valuation method. Note that stated preference (i.e., a public survey) is a method that can be used to value most potential benefits. Table 48. Types of benefits associated with environmental policies (Source: National Center for Environmental Economics 2014).

98 Approaches for Determining and Complying with TMDL Requirements Related to Roadway Stormwater Runoff Only a few benefits can be assessed based on actual cost. One analysis that is somewhat com- mon in the literature is to value the benefits of achieving bacterial water quality standards for contact recreation. A good example is the 400+ page Cost–Benefit Analysis: San Diego Region Bacteria Total Maximum Daily Loads (https://www.waterboards.ca.gov/sandiego/water_issues/ programs/basin_plan/docs/issue3/Final_CBA.pdf) (Environmental Incentives 2017). The San Diego analysis considered the following: • Avoided illnesses: The value to individuals of avoiding infectious illness, including gastro- intestinal illness. Benefits include reducing medical expenditures, regaining lost work days, and alleviating discomfort. The analysis was conducting using a unique data set, namely, a first-of- its-kind Surfer Health Study that quantifies the existing risk of illness among San Diego County surfers entering the ocean within the 72-hr period following a rain event (available at http:// ftp.sccwrp.org/pub/download/DOCUMENTS/TechnicalReports/943_SurferHealthStudy.pdf) (Schiff et al. 2016). • Additional beach trips: The value of regaining trips to the beach due to reduced beach closure days and water quality advisories for a broad group of recreation activities. The analysis uses local data on beach usage and thorough beach attendance modeling to project the increased beach usage estimated to result from improved water quality following rain events. • Co-benefits: The additional benefits—such as carbon sequestration, air quality, wildfire risk, and other pollutant removal from water—resulting from BMPs implemented to reduce bacteria loads. It is clear from the scope of the benefits considered and the substantial data requirements that substantial costs may be incurred to make a defensible estimate of benefits. To be credible, a wide range of stakeholders should also be involved in the analysis; therefore, this effort is not suitable for a state DOT go-it-alone exercise. Alternative Strategies The cost-effectiveness of alternative strategies to implementing BMPs in the highway right- of-way has been extensively explored by Weinstein et al. (2017). They report that: Implementing stormwater best management practices (BMPs) to manage stormwater runoff quality and quantity can be quite challenging for roadway drainage designers. DOTs face unique limitations and design challenges due to the linear nature of the road network and limited space within the right- of-way for stormwater management. This is particularly true in urban and ultra-urban areas that are built out and have limited land available to purchase additional right-of-way for stormwater manage- ment or in areas with unique physical or political geographic features (such as soil, topography, or political boundaries that restrict mitigation options). Even when these challenges do not exist, there is a growing need to think beyond the right-of-way and within the watershed to determine the best and most cost-effective option to mitigate the impact of particular stormwater stressors or pollutants to ensure that it provides the greatest water quality and ecosystem benefit while preserving the stewardship of public funds. Addressing stormwater issues in a project-by-project fashion can be very inefficient and much less effective in addressing important water- shed water quality and ecosystem issues. In constrained sites, this can result in very expensive and often unsustainable treatment alternatives. The goal of the watershed-based approach to mitigate stormwater impacts is to allow DOTs to identify environmentally superior alternatives for compliance within existing and emerging regulations. In many cases, meeting cost-effective pollutant reduction goals may be more achievable with strategies other than constructing BMPs within the highway right-of-way. This may be true in situations where there is limited space (especially in urban areas) or where the POC is poorly controlled by existing BMPs (e.g., nitrogen). In these cases, partnering with other stakeholders through cooperative agreements to implement BMPs in other locations in the watershed may

Best Management Practice Cost and Effectiveness Analysis 99 be the most cost-effective alternative. Examples of strategies include payment in lieu and cost- sharing BMP implementation within the watershed but outside the highway right-of-way. A payment in lieu strategy consists of making a payment to a municipal or regional authority instead of implementing and maintaining a BMP by the state DOT. The authority then uses the money in the fund to implement regional BMPs in locations that are most suitable for address- ing the water quality impairment. This approach has the advantage of simply writing a check, and then no further action is required by the state DOT. Departments can also consider several variations of constructing and operating BMPs out- side the right-of-way with other watershed stakeholders. This approach might include sharing both construction and maintenance costs based on the relative contribution of each stakeholder to the water quality impairment. There have also been instances where the state DOT designed and built BMPs outside the right-of-way and then transferred ownership to other parties for long-term maintenance. Texas DOT has successfully executed this approach for at least one regional BMP in the Austin, Texas, area. Payment in lieu, collaborative partnerships, and other watershed-based approaches are dis- cussed in detail in Chapter 8.