Living Capital Planning Tools

INTRODUCTION Clean Water Services (CWS) operates four WRRFs that are expanded and improved through a ~$40 million yearly capital budget. The goal of the CWS capital planning approach is to have a level capital outlay year to year. Capital expenditures are reprioritized yearly to achieve this goal and to ensure that processes are expanded only as they reach capacity. Typical master planning approaches are updated only about every five years. A 'living' capital plan allows CWS to adapt to changes in critical assumptions that drive planning timelines and proactively manage capital expenditures. This paper presents the CWS approach to creating and managing a living capital plan and summarizes the benefits. OVERVIEW The first integrated capital planning tool was developed for the Durham WRRF in 2020 with Carollo and Jacobs, the consultants for the most recent Durham master plan project (Figure 1). As part of the ongoing West Basin master plan, work is underway with Carollo to develop the tool for the three interconnected West Basin facilities, which include Rock Creek, Hillsboro and Forest Grove (Figure 1). The initial pieces of the tool are developed in collaboration with consultants but the final product is owned and managed by CWS. The goal of the living capital planning tool is that it's updated every year and should improve and evolve over time. OUTCOMES FLOW AND LOAD PROJECTIONS Flow and load projections are developed from base assumptions in the flow and load spreadsheet. The process of building the spreadsheet provided CWS with a comprehensive understanding of all the critical assumptions used to generate the projections, making it easier to evaluate those assumptions over time. Alternate planning scenarios were also created based on differing growth assumptions for the Durham WRRF, and flow diversion alternatives for the West Basin WRRFs. Historic flows and loads are evaluated annually and compared to projections. Tracking observations against planning numbers makes it evident when revisions are necessary (Figures 2 and 3). While the intention is not to revise the projections every year, the spreadsheet tool and yearly evaluation process is meant to make the effort for revising projections more efficient when needed. PROCESS PERFORMANCE AND DESIGN CRITERIA Design criteria, which set the capacity of the unit processes (e.g. solids loading rate), and process performance criteria, which are assumptions based on operational observations (e.g. percent removal, solids capture, sludge volume index) are also evaluated yearly. The data validation and process capacity spreadsheets gather process performance assumptions and design criteria from the master plan and compare them to historical observations. This comparison determines when unit processes are approaching capacity triggers and identifies when unit processes should be optimized due to declining performance. One example of a process performance parameter (capture in the primary solids thickening process, Figure 4) that drove the capital planning timeline for secondary treatment (Figure 5) is illustrated here. Lower solids thickening capture sends additional solids loads to the secondary process, decreasing its treatment capacity. Just this single assumption changed the secondary capacity trigger year by 4 years (Figure 5). With projects at four WRRFs to phase, improving this 4-year discrepancy in secondary capacity allows capital outlay to be phased more effectively. MASS BALANCE SPREADSHEET VERUS PROCESS SIMULATOR CWS uses both a process simulator and a spreadsheet mass balance model to create solids projections for its West Basin WRRFs. The mass balance spreadsheet can be used to quickly evaluate scenarios that require a lower level of sensitivity and to identify scenarios that could have a major impact to timelines. This simpler, quicker approach is beneficial with the three interconnected West Basin treatment facilities as running a process simulator with all three WRRFs connected is complex and prohibitively slow. However, the process simulator generates more detailed predictions within each individual facility that are beneficial for informing comprehensive planning evaluations. Table 1 compares CWS experiences using these tools. CWS aims to extend both approaches to its East Basin capital planning system to take advantage of their complementary strengths. LESSONS LEARNED The living capital planning approach means that planning is not confined to periodic, consultant-lead master planning efforts. Tracking of flows and loads and other critical assumptions yearly against master planning values has provided valuable insights into when capacity and capital planning shifts are needed. It also daylights areas of conservatism or risk as capacity triggers are reached. Even if a utility is not running models or doing the projections themselves, tracking assumptions against reality is beneficial and achievable for any utility. Other benefits: Having ownership over the data and tools gives CWS the independence to quickly evaluate new scenarios (e.g. impact of a new large industrial user or shifts in population growth). Daylighting and tracking assumptions also aids in documenting the information that drives capital planning decisions. The integrated tool makes capital planning information more accessible to a wider range of CWS stakeholders from executive managers to operators.