The Stormwater Management StormFilter
When the Environmental Protection Agency (EPA) threatened to put shipyards in the Coos Bay Estuary on the National Priorities List of hazardous waste sites, the Charleston Marina Complex, responded quickly. The EPA and Oregon Department of Environmental Quality (DEQ) determined that the area surrounding the Complex’s boatyard was contaminated with heavy metals, poly-aromatic hydrocarbons and tributyl tin.
The agencies issued a consent order requiring development and implementation of an action plan. With the help of a multi-disciplinary team, a combination of source controls, and a passive stormwater filtration best management practice (BMP), the Complex met the agencies’ terms and reduced stormwater runoff pollutant levels to be compliant with permit requirements.
The marina complex is located on the South Slough National Estuarine Research Reserve and home to populations of clams, oysters, fish and birds. The Complex owners were concerned about protecting the estuary from current contaminants on the boatyard site and reducing human health risks.
Activities at the 4.5-acre facility encompass boat construction and reconstruction, including cleaning, preparation, painting and outfitting vessels. The site also has several businesses servicing the yard, tenant boat storage and work areas, two marine ways and a boat washing area.
Hart Crowser of Seattle, Wash., a design engineering firm, recommended removing contaminated sediment from the intertidal areas around the marine railways to address historical pollutants deposited before the 1986 purchase by the marina complex. Hart Crowser also suggested paving upland areas with asphalt and concrete to prevent soil erosion and to make cleaning the yard easier.
To meet Oregon 1200Z General Industrial Stormwater Permit requirements, the Complex made a number of site enhancements to better control stormwater discharge by: re-grading and curbing to control runoff, improving the stormwater collection system , installing three passive stormwater treatment systems and replacing five existing stormwater outfalls with three new outfalls .
The stormwater filtration systems treat site runoff and remove toxic pollutants including zinc, copper, lead and sediment that are regularly generated by vehicle traffic and boat maintenance activities conducted in the yard.
Typically the size of the filtration systems is calculated based on the area’s design storm guidelines, but Coos Bay had not established them. The projected pollutant loading and required removal rates usually determine the number of filter cartridges, but paving had changed the pollutant generation and transport characteristics of the site, making estimation of future loading difficult.
Using historic effluent data for the boatyard and criteria from similar sites, Contech sized the filtration systems for the first flush flow, which is typically the most heavily pollutant-laden runoff. They also applied a stepped approach to the system sizing process to allow for later system adjustments that would accommodate changing site conditions and allow the facility to continuously meet stormwater permit requirements.
To collect runoff, engineers chose the Stormwater Management StormFilter®, which consists of a vault that houses rechargeable, media-filled, filter cartridges. During a storm, stormwater percolates through the cartridges, where the media traps particulates and removes pollutants such as oil and heavy metals. A layered zeolite-perlite media provides filtration of these sediments and chemically removes soluble heavy metals by cation exchange. Each system has an internal high flow bypass that allows runoff from storm events exceeding the system flow capacity to bypass treatment.
To help Charleston Boatyard understand performance of the site improvements, Contech Stormwater Solutions staged a simulated stormwater runoff event to evaluate the filtration systems under first flush conditions. The test also permitted evaluation of alternative cartridge media to remove common boatyard pollutants. Selecting an active drainage area associated with typical boatyard activities for the simulation, the company used fanning sprinklers and a spray hose, each discharging an average of 4 to 5 gallons of water per minute.
The Complex analyzed influent samples to confirm that the chemical makeup represented activities conducted at the site. Contech engineers used samples in media performance column tests and gathered data to determine an effective filter cartridge configuration for small boatyards and shipyards.
Effluent data showed that Contech’s zeolite-perlite media and CSF® leaf media are effective for reducing stormwater pollutants common to shipyards and boatyards. The medias remove both particulate and soluble pollutants. Data also showed that use of finer-grade media increases the removal efficiency of the filter cartridges for total suspended solids (TSS) and metals.
Since completing the site improvements and installation of the filtration systems in late 2002, the Charleston Boatyard is meeting its permit requirements. Data collected by the boatyard from four storm events reflect removal rates of up to 81% copper, 86% lead, 84% zinc, and 92% TSS, validating the selection of this stormwater BMP.
“I care deeply about the environment. I am proud that the Charleston Boatyard is contributing to the preservation of this treasure. We believe we are one of a handful of boatyards in the state and nation that are outwardly proactive in regard to protection of the environment,” said Donald Yost, manager of the Charleston Marina Complex.
The Stormwater Management StormFilter