Retrospective Analysis of Above Grade Stormwater Treatment System Operating and Maintenance Costs

Abstract: Washington State’s stringent industrial stormwater general permit (ISGP) requirements have driven many facility owners and operators to install stormwater treatment systems. Washington’s ISGP has low benchmarks for copper and zinc and a compliance structure that can require installation of stormwater treatment in as little as 1 year. Space-limited waterfront facilities often install engineered aboveground treatment systems due to limitations associated with high groundwater tables and limited available space for traditional in-ground passive systems. Typical treatment system alternatives analysis includes site-specific review of the following selection criteria:

1. Ability of the treatment system to consistently meet benchmarks
2. Treatment system footprint/location
3. Capital cost
4. Operation and maintenance (O&M) cost/effort

Most of these factors are known and directly comparable prior to system installation. However, it can be difficult to estimate, compare, and evaluate lifetime O&M needs and costs and to extrapolate these factors over the system’s lifespan. Therefore, O&M considerations are typically given less credence than other evaluation criteria.

This paper will evaluate actual treatment system O&M requirements and cost data for 17 end-of-pipe treatment systems installed at four different container terminals in Washington to better understand true costs of treatment system O&M. It will focus on facilities operated by SSA Terminals (SSAT) in Seattle and Tacoma to limit variability in industrial activities and housekeeping practices among different facility operators and different weather patterns among different geographic regions. Treatment systems installed at SSAT container terminal facilities include nine chitosan-enhanced sand filtration (CESF) treatment systems and two different types of engineered passive filtration treatment systems. At SSAT's Terminal 18, treated stormwater from all three different treatment systems has consistently met ISGP benchmarks, proving that with proper maintenance, each system can achieve benchmarks.

SSAT’s actual annual O&M cost and maintenance frequency will be compared to cost ranges estimated using manufacturer-recommended maintenance frequency ranges for a typical industrial facility to evaluate the accuracy of extrapolating manufacturer recommendations to container terminal facilities. This paper will also evaluate variables affecting maintenance frequency for treatment systems of the same type, including basin operations, operational intensity/influent stormwater characteristics, pretreatment type and characteristics, and degree of implementation of operational best management practices. From this evaluation, the paper will extrapolate updated lifetime treatment system O&M cost ranges and the most important variables affecting these cost ranges. Qualitative factors, such as ease of performing maintenance, will also be discussed.

An improved understanding of lifetime O&M costs and maintenance needs associated with common treatment system alternatives will help port facility owners, tenants, and stormwater engineers make informed decisions regarding treatment system life cycle costs and maintenance needs, improving alternatives evaluations at other facilities. A more complete understanding of maintenance needs, costs, and frequency can also help treatment system operators allocate funds and resources necessary to maintain treatment system performance and maximize treatment media lifespan. Finally, the authors will provide recommendations for current treatment system operators regarding best practices to both reduce treatment system operational costs and prolong the performance capabilities of passive treatment systems.

How does this project / topic contribute to the advancement of the industry and profession?: This project contributes to the advancement of the industry because it provides a retrospective analysis of treatment system life cycle costs for a variety of full-scale treatment systems installed at fully operational container terminals. It provides a critical point of reference to manufacturer data extrapolated from lab-and pilot-test installations under relatively controlled conditions. This paper will benefit other Washington permit holders and will benefit Port engineers in areas of the country where stormwater treatment requirements are becoming more rigorous and trending toward installation of more robust treatment systems.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: SSAT and its consultants have collected a wealth of information regarding SSAT operations and treatment system performance since 2019, following initial design and installation of the first treatment systems at SSAT Terminal 18 at the Port of Seattle. This paper evaluates operational data and treatment system performance to reach credible conclusions regarding best practices for treatment system O&M at container terminals and other transportation facilities with similar operations. Novel adaptive management approaches to maintain treatment system performance will be identified and explored.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: At the time of treatment system installation, very little published data was available from facilities with similar operational characteristics that could be used to assess O&M costs and requirements during alternatives analysis. Treatment systems were selected using vendor-provided performance data, treatment system footprint, and capital cost, with less emphasis on O&M needs and costs. Over the last 5 years, SSAT and its consultants have performed data analysis and adaptive management to ensure that effluent consistently meets permit benchmarks post-treatment, regardless of treatment system type. This retrospective provides a useful reference for operators of similar treatment systems and facilities.

Who is the target audience for this paper?: The target audiences of this paper are civil engineers, environmental engineers, stormwater regulators, industrial facility owners, port authorities, and terminal operators who would like to better understand factors influencing O&M costs and requirements for engineered treatment systems.