This industrial facility site is handles prefabrication of sheet metal, mechanical piping, and plumbing equipment. The site consists of 3.16 acres, of which 1.47 acres contains industrial activities generating stormwater runoff and is covered under the Washington State Industrial Stormwater General Permit (ISGP).

SoundEarth services included preparation of the Engineer Report, treatment system design, cost estimation, construction document development, conveyance upgrades, outfall analysis and relocation, treatment feasibility evaluation and Best Management Practice (BMP) installation, construction quality assurance and oversight, site survey and facility mapping, stormwater conveyance investigation, and O&M plan development.

In response to permit benchmark exceedances, the stormwater system was modified and upgraded to meet the treatment BMP requirements of the ISGP. A feasibility study was performed to determine the best-fit solution meeting the client needs for a small footprint, cost effective, NPDES permit complaint stormwater treatment BMP. The solution included retrofitting the existing stormwater infrastructure and site drainage by plugging a stormwater outfall pipe, redirecting the conveyance piping to combine both drainage areas to one outfall, retrofitting the existing outfall by adding an inline pump vault to direct untreated stormwater to the above ground treatment BMP. The team provided a turn-key solution for this treatment BMPs from conceptual design to commissioning.

SoundEarth staff created a modular design of above-ground GRATTIX box treatment systems, which allowed for reduced installation and maintenance costs and ability to deploy additional treatment boxes if needed. Runoff from the facility is collected and pumped to above-ground GRATTIX box treatment system which consist of a low impact designed bio-retention and multimedia filtration unit, where sediment, metals and hydrocarbons are removed from stormwater. Our design reduced contaminant loads to permissible levels. SoundEarth staff also provided construction oversight and commissioning.