New Zealand scrap company installs stormwater treatment system

A metal recycling facility in Christchurch, New Zealand, voluntarily installed stormwater treatment best management practices (BMPs) to demonstrate its commitment to raising environmental protection standards within the metal recycling industry in that country. The facility owners proactively installed stormwater treatment at its 1.5-acre facility, establishing a new benchmark for industrial stormwater quality under New Zealand’s Resource Management Act 1991.

Industrial facilities in the United States are subject to similar stormwater discharge regulations and monitoring under the National Pollutant Discharge Elimination System (NPDES) permit program as mandated by the Clean Water Act. In the United States, these regulations typically are administered by individual states. In the case of the facility in New Zealand, monitoring and enforcement fall under the purvey of a city council. What is unusual about this facility in New Zealand is that the owner went the extra distance to ensure the environmental impact of the business operations was minimized to the greatest extent possible, meeting local discharge requirements in the process, and Christchurch City Council took notice.

The facility

Established in 1989, Metalcorp NZ Ltd. is a family-owned business that operates from two branches within the South Island of New Zealand. The primary function of Metalcorp is to collect and process ferrous and nonferrous scrap into the raw materials that other industries require to produce new products for domestic and international markets. Such facilities in the developed world are subject to varying degrees of stormwater pollutant discharge regulations. Metalcorp is no exception, yet the company is exceptional for its regard for the environment and the community. As a long-term member of the New Zealand Association of Metal Recyclers, Metalcorp demonstrated its commitment to raising the environmental protection standards within the metal recycling industry by proactively installing a series of stormwater treatment BMPs at one of its sites.

The compliance drivers

While Metalcorp was proactive in installing stormwater treatment to ensure that the company’s pollutant discharge was clean, it also was subject to stormwater compliance regulations outlined in Section 15 of New Zealand’s Resource Management Act. These regulations and the enforcement network, Environment Canterbury (ECan) of New Zealand, are analogous to the Clean Water Act and the Environmental Protection Agency’s (EPA) NPDES permit program in the United States. Just as each U.S. state is given general guidelines to enforce stormwater discharge limits through a permit system under the Clean Water Act, each regional council in New Zealand has guidelines to follow when tailoring monitoring and enforcement to their regions. Because Metalcorp is in Christchurch City Council’s jurisdiction, compliance officers from Stormwater Audit, the compliance arm of the Council, monitored Metalcorp’s stormwater discharge compliance.

Pollutants of concern: sediment and heavy metals

Routine monitoring action by the Christchurch City Council revealed that the facility had exceeded trigger levels for stormwater discharge of aluminum, copper, zinc, lead and magnesium. The trigger levels for Metalcorp were based on local regulations that set the levels required to be higher quality than drinking water—levels that are unnecessarily stringent for stormwater runoff. Despite being subject to this exceedingly high bar for stormwater quality, Metalcorp decided to proactively implement BMPs to bring the pollutant discharge levels down closer to trigger levels.

Photo courtesy of StormwateRx

The treatment solution: gravity separation inline, upstream of media filtration

Not finding stormwater specialists within New Zealand willing to provide assurances that their products would meet the trigger levels if monitored, Metalcorp sought help from StormwateRx LLC, a United States-based stormwater treatment engineering and treatment equipment company. Korina Kirk, president of Metalcorp, met Calvin Noling, general manager of StormwateRx, which is based in Portland, Oregon, at the 2018 Institute of Scrap Recycling Industries (ISRI) Annual Convention.

In 2019, resulting from a few months of site-specific retrofit design and site planning with StormwateRx engineers, Metalcorp installed a Clara 25C gravity separator upstream of an Aquip 110SBE media filter in its Christchurch facility. This combination of technologies provided oil and total suspended solids pretreatment followed by particulate and soluble metals removal—a strategy commonly employed at top-tier scrap recycling facilities in the U.S.

The results

Metalcorp ran the StormwateRx units for an entire year before collecting and testing samples. The company submitted the test results to Stormwater Audits, a branch of New Zealand’s governing entity Christchurch City Council. The results demonstrated that Clara effectively removed bulk solids and metals, with Aquip further filtering the effluent. These BMPs together brought total suspended solids, aluminum, cadmium and chromium below the exceedingly low trigger levels while also significantly reducing copper, lead and zinc by greater than 98 percent. All of the treated stormwater quality values were below U.S. EPA benchmark standards for the multisector general permit and industrial stormwater general permits.

Based on the results, which assume 1.3 acres for C1-C3 and 26 inches average rainfall for Christchurch, the Christchurch City Council calculated that Clara and Aquip are mitigating an estimated 1,224 pounds of chemical oxygen demand, 2 tons of solids, 35 pounds of aluminum, 4.4 pounds each of copper and lead and 110 pounds of zinc per year from Halswell Junction Outfall, the watershed most affected by runoff from the Metalcorp facility. As the Council Advisor put it: “Not quite drinking water quality, but nearly!”

*All New Zealand metals parameters measured as acid extractable.

**2020 Draft US EPA MSG Permit, freshwater discharge, metals values as total with assumed receiving water hardness of 250 mg/L.

This case study was submitted by StormwateRx LLC, Portland, Oregon. More information is available at www.stormwaterx.com.