Recycling Center Exceeds Regulations With Advanced LID
Since 1995, Ben’s Recycling center in Oceanside, CA, has been taking waste and unwanted electronics safely off customers’ hands. The facility needed to expand; the proposed new facility would be a state-of-the-art indoor recycling center located around the corner from the recycling center’s current location. The drainage area of concern was approximately 30,000 square feet or 0.68 acre.
Dan Kwak of Ben’s Recycling contacted Zach Kent of Modular Wetlands in October 2008 to discuss his concerns and possible solutions. Ben’s Recycling is mandated to be in compliance with NPDES Phase I stormwater regulations, but Kwak and the facility owner expressed their desire to implement an advanced stormwater treatment system with capabilities vastly exceeding these regulations.
Several existing site constraints limited the choice of available BMPs. The main challenge was no sub-surface drainage infrastructure on the property or in the street. Runoff could be conveyed offsite only by sheet flow from the current ribbon gutter. The existing grading of the site dictated that runoff flow to the far northeast corner of the property, then to the street through a ribbon gutter located along the west side of the property, which eventually discharged directly into the San Luis Rey River.
|Installing Modular Wetland System catch basin
A significant portion of the property’s drainage area is rooftops, while the remaining area is paved. This site is 100% impervious. The recycling facility activities take place indoors, therefore yielding a significantly lower pollutant loading concentration than traditional outdoor recycling facilities. However, the loading and unloading of recyclables generates some level of pollution in the parking lot, and Ben’s Recycling requested advanced treatment for this area. Anticipated pollutants include heavy metals, nutrients, organic compounds, sediments, trash and debris, oxygen-demanding substances, and oils and grease.
All industrial facilities are required under Phase I to treat stormwater discharge. The runoff from this site flows to the San Luis Rey River and Pacific Ocean. These waterways are on the 303(d) list due to impairment by chloride, total dissolved solids, and bacteria indicators.
After an in-depth analysis, it was determined that the soils on the site had appropriate infiltration rates, making this an ideal candidate for an advanced infiltration system. The soil is A type, TuB–Tujunga sand, with infiltration rates starting at 5.95 inches per hour. Given this information and the above limitations, the best solution was determined to be a treatment train BMP incorporating screening, hydrodynamic separation, media filtration, and biological filtration followed by storage and infiltration.
The existing paved area in the northeast corner of the property was turned into a landscape area containing the custom-designed Modular Wetland System–Linear with patented underground wetland chamber. Given the grading of the site, runoff flows directly to a custom-designed 4-cubic-foot grate-type catch basin. This catch basin contains the first three stages of treatment: screening, separation, and media filtration (BioMediaGREEN).
Following the media filtration, the water discharges out of a series of specially designed perforated pipes into the subsurface flow wetland, where it is infiltrated back into native soils. This system uses a specialty wetland media with more void space (48%) than traditional rock backfill (40%).
This system was designed to capture, store, and infiltrate up to 4,407 cubic feet of runoff over a 24-hour storm event (static capacity is 979 cubic feet). The capacity of the system vastly exceeds the calculated water-quality volume of 1,481 cubic feet for the drainage area.
This solution provides heightened treatment compared to other options. The design allows for gradual recharge into native soil, protects ground water, and prevents runoff from leaving the site, therefore avoiding future pollutant testing while protecting the downstream impaired bodies of water. Another option was to capture and hold the treated runoff in a catch basin and then pump out the water. This option would have been much more expensive and time consuming for the owner.
Over the past year no runoff has been observed leaving the site. “I am very happy with how the system has performed. Even better, the annual maintenance is cost is only $600,” says Kwak.