The scale and type of equipment used in the recycling sector produce unique challenges and opportunities for stormwater management. Additionally, in response to changing permit conditions, the recycling sector has continued to evolve, embracing and implementing practices that result in better water resource management and stronger stormwater pollution control.
This article prescribes an approach for stormwater management and pollution control in the recycling sector and incorporates suggested environmental management philosophies and best management practices (BPMs) by scrap recycling facility operators from around North America.
Most scrap recycling facilities operate under a general industrial stormwater permit requiring the facility to implement a stormwater pollution prevention plan (SWPPP) that describes operational, structural and treatment BMPs that minimize stormwater pollution. Most general industrial permits also set forth numeric “benchmark” water quality concentrations to help facilities measure their BMPs’ efficacy and require facilities to monitor and report effluent pollutant concentrations.
Stormwater chemistry is complex. Here are some stormwater chemistry terms and principles that may help to demystify stormwater permits and pollutants.
water – a solvent that will dissolve solid materials. Theoretically, only pure water (H2O) is released as rain. When rain hits a surface and runs off, it is considered stormwater. Stormwater contains pure water and other chemicals that it touches while falling through the atmosphere or flowing across or into the ground. The amount of material that it picks up is measured in units such as milligrams per liter (mg/L.)
conversion factors – understanding the conventional units for stormwater is important. Milligrams per liter (mg/L) equals parts per million; one part per million is one drop in half a barrel of water. Micrograms per liter (ug/L) equals parts per billion; one part per billion is one drop in 500 barrels of water. A milligram per liter is 1,000 times greater than a microgram per liter.
pH – a measure of the relative ratio of acidity in water. Generally the lower the pH, the more readily solids, including metals, will dissolve in water. The normal allowable pH range for stormwater is 6.5 to 8.5. Water that has a pH greater than seven is alkaline. Water that has a pH less than seven is acidic, and water that has a pH of less than about 4.5 is usually devoid of fish. Low pH stormwater can be caused by acid rain or by contact with acids (such as battery acid or carbonated beverages) in recycling yards. Low pH also can indicate the presence of decomposing organic materials. Stormwater with high pH is less common in the recycling sector but can be caused by erosion of alkaline soils or detergents.
oil and grease – a measure of a variety of substances, including fuels, motor oil, lubricating oil, hydraulic oil and animal-derived fats. Water-soluble oils contained on metal turnings, borings and stampings also release oils that are detected in this pollutant category. Not all oils result in visible oil sheen; water-soluble oils, such as those draining from turnings and borings, may appear milky when mixed with stormwater in combination with some oil sheen. Water-soluble oils will not be removed by stormwater separators but may be partially removed by media filtration treatment processes.
total suspended solids (TSS) – a measure of the particulate fraction of stormwater, usually in units of milligrams per liter. Typical untreated stormwater runoff from recycling facilities ranges from 100 to 1,000 mg/L TSS.
metals – a broad class of elements that are generally solid at room temperature. Examples include sodium, calcium, magnesium, aluminum, iron, lead, zinc and copper. Some metals exhibit toxic effects to aquatic organisms in natural waters. Many of these metals have numeric standards associated with them that indicate how much of the metal is acceptable—the term “benchmark” is commonly used. Generally concentrations of metals that are allowed in drinking water are higher than concentrations tolerated in natural water systems. Metals may be presented in terms of either mg/L or ug/L. Be careful to know the difference. Generally, metals in stormwater are present at much lower concentrations than TSS. TSS concentration may be 100 mg/L while the concentration of a metal in that stormwater is 100 ug/L – a thousand times lower. Generally metals water quality standards are much harder to achieve than TSS standards.
dissolved metals – a measure of the amount of metals and other chemicals that will pass through a 0.45-micrometer glass fiber filter. A human hair is in the range of 30 micrometers, or almost 70 times larger than the largest dissolved metal. Dissolved metals can be very small metal particles, complexed with other solid materials in the water, or ionized within the matrix of the pure water molecules themselves. The form and amount of a metal in stormwater is a function of many factors, including temperature, pH, chemical composition and concentration. Conditions that favor separation of one metal from the water may aggravate separation of other metals.
Metals concentrations in recycling facility stormwater are often loosely correlated with TSS concentrations. The suspended solid particulates themselves usually contain metals, so removing the solids also can remove metals. Getting to very low concentrations is usually achieved by removing particulate and dissolved forms of the metal.
Iron and aluminum are present in elevated concentrations in the soil in many parts of North America. As a result, erosion control to prevent sediment from unpaved areas from getting into stormwater can be a strong BMP to reduce stormwater concentrations of these metals.
chemical oxygen demand (COD) – COD is not a pollutant itself but a laboratory measure of how much oxygen organisms will consume while degrading organic material in the water. Oxygen-demanding substances are most often organic in nature (meaning they contain materials that once were alive—petroleum, oils, detritus, alcohols, sugar, etc.) When these organic materials enter natural water systems, microorganisms that are ubiquitous “feed” on the organic materials, breaking down the organics to simpler compounds. These microorganisms are efficient eaters and consume the oxygen in the water during the decomposition process, competing with fish for the same oxygen. One-quarter pound of sugar in 280 gallons of stormwater will contaminate that stormwater to the COD benchmark of 120 mg/L. A little sugar, oil or antifreeze goes a long way!
More information on stormwater pollutants can be found at www.stormwaterx.com/Resources/IndustrialPollutants.aspx.
Increasingly, permits (including the proposed 2013 U.S. Environmental Protection Agency Multi-Sector General Permit and some state permits, such as those in California, Oregon, Washington, Colorado and Ohio) are requiring active responses to benchmark excursions.
Mandatory renewal or extension of the general permits has trended toward more stringent standards and a higher level of public accountability.
Stormwater control infrastructure
Many scrap recycling and other industrial facilities are operating on infrastructure that was designed and installed more than 30 years ago, before the Clean Water Act and industrial stormwater permits existed. Facilities may have a conveyance system that is antiquated or may not have a stormwater conveyance system at all. Proper stormwater conveyance may be underappreciated with regard to the impact it has on stormwater quality.
Recycling operations are best performed on a level or gently sloping paved surface. While pavement generates more stormwater runoff than unpaved surfaces, pavement also prevents soil erosion that is a major source of suspended solids and metals. (See the sidebar on stormwater chemistry) A paved surface with a network of drain inlets or trench drains adjacent to processing areas, along with vacuum sweeping to keep accumulated metal fines off the pavement, is a strong stormwater BMP. Dry weather runoff from processing areas may contain highly concentrated pollutants, such as oil and sugars, that can contaminate stormwater when it rains or can generate spikes in measured pollutant concentrations well in excess of the benchmarks. A program to vacuum or mop up liquid concentrates should be undertaken at all facilities generating this type of pollutant.
Where feasible, uncontaminated stormwater from roofs and administrative buildings should be diverted from processing areas or infiltrated to the ground.
“We operate an 8.7-acre asphalted and bermed scrap metal processing facility along Puget Sound in Washington state,” says Nick Nickolas, environmental manager, Calbag Metals Co., Tacoma, Washington. “All stormwater from the site is collected through a network of drain inlets and storm drains and conveyed to a stormwater separator, stormwater detention and a multimedia gravity filtration treatment system. Filtered stormwater is released to Puget Sound.”
Nickolas adds, “The pavement makes it easier for our staff to control the amount of solids entering the catch basins and connecting pipes.”
Nickolas says the BMPs Calbag Metals uses include:
- operating its mechanical vacuum sweeper as often as possible outside, weather permitting;
- replacing catch basin inserts, straw waddles, straw bales and oil absorbent booms when no longer effective;
- cleaning the stormwater separator (two to three times per year) to allow it to function properly;
- annual cleaning of the storage tanks to remove solids that have settled out; and
- regularly removing accumulated pollutants from its stormwater filter and topping it with new filter media.
“In addition to these BMPs we have added filter media to our warehouse roof exhaust fans and added a mister over the baler to eliminate dust during baling of copper radiators,” Nickolas says. “All of these additions have been effective in reducing our effluent numbers and putting us under benchmark in most cases.”
Best stormwater practices for facilities that do not have paved yards dictate limiting movement of mobile equipment and trucks to paved processing corridors within the facility. Unpaved facilities should be designed with lined channels, ditches or storm drains to divert stormwater away from scrap materials. Standing water should be minimized except for ponds and separators designed to remove oil, sediment and floatables.
Oily scrap and turnings, borings and stampings should be handled and processed on paved surfaces and should have dedicated oil sumps and stormwater separators that are cleaned often. Many coolants coating turnings and borings contain water-soluble oils. Extra care should be used to isolate these materials and prevent them from contacting stormwater. Balers used for turnings should be located indoors and should have sumps that are vacuumed out regularly.
For outdoor operations, only separators specifically designed for stormwater applications should be used; these devices are designed specifically to prevent washout of accumulated pollutants during storm events. Unpaved or very large facilities may benefit from a detention pond or wetland that will allow entrained erosive soils to settle out before the stormwater is released.
Stormwater can be reused on site, such as for cooling water for shredders or for dust control. This can be accomplished by incorporating on-site storage or detention. Except in the most arid regions, insufficient detention volume will be available to reuse all stormwater, but reuse should be considered for the freshwater offset and stormwater discharge reduction. Keep in mind, however, that dirty stormwater that is applied for evaporative processes, such as shredder cooling and dust control, will leave behind a salt film with even higher concentration of pollutants that can wash off during the next storm event.
“Davis Industries operates a 23-acre partially paved recycling facility in Lorton, Virginia,” says Bill Bukevicz, executive vice president of Davis Industries. “Our ferrous and nonferrous processing [equipment] includes a 1,700-ton shear, eddy/ISS (induction sensor sorter) nonferrous system, baler and an 80x104 wet shredder.”
He continues, “One of our practices is to divert all runoff to a central retention pond that also serves as a cooling water supply for our wet shredder. During normal operations, we evaporate 20,000 to 30,000 gallons per day of stormwater through the shredder.
“We have numerous other stormwater pollution control measures in place—housekeeping, yard organization and employee training are all key aspects of our environmental management philosophy,” Bukevicz says.
“Finally, Davis Industries has invested in an industrial stormwater treatment system to purify any stormwater that is released from our facility,” he continues. “The treatment system is designed to remove suspended solids and total recoverable metals prior to discharging into the environment.”
Pollutant control philosophy
The phrase “oil, dirt, dissolved” is a stormwater pollution control philosophy that yard operators can adhere to when designing operations to prevent stormwater pollution or when designing stormwater treatment controls. From a stormwater pollution prevention and treatment perspective, the presence of oil aggravates reduction of total suspended solids and turbidity, metals and chemical oxygen demand (COD), rendering BMPs that target these pollutants less effective, more labor intensive and more expensive. Similarly, the presence of particulates or dirt in stormwater can cause pH swings and render technologies designed for dissolved pollutants removal less efficient.
Therefore, additional BMPs to generally consider are:
Oil control. Keep recyclables that contain oil (motors, turnings, stampings, borings, etc.) separate from other materials, elevated and away from stormwater flows. These materials should be covered or kept in a segregated bunker with perimeter drains and a dedicated stormwater separator near the point of generation. Use hay bales at the perimeter of oily materials to absorb free oil; keep the bales fresh. Alternatively, use oil sorbent booms around oily materials and replace them whenever they become discolored. Oil that gets released into the stormwater conveyance system may become mechanically emulsified if the stormwater is subjected to strong currents or if the water is pumped, which is difficult to separate or to remove from stormwater.
Dirt control. Minimizing erosion, capturing sediment and removing solids from work surfaces is a good approach to reduce suspended solids and metals concentrations in stormwater. As mentioned, facilities that do not have paved yards should limit movement of mobile equipment and trucks to paved processing corridors.
Storing nonferrous metals indoors or installing a partial roof over certain areas of the facility is a recommended stormwater BMP. Covering these areas minimizes stormwater contact with heavy metals, including copper, zinc and lead. Work aisles should be kept well-swept to minimize tracking particulates on vehicle tires.
Dissolved pollutants control. Removal of dissolved metals and other pollutants, such as COD, can be achieved through stormwater treatment methods, including adsorptive filtration, biofiltration or ion exchange.
Enhanced filtration processes can concurrently remove particulate and dissolved pollutants through a combination of straining, filtration, complexing, adsorption, absorption, microsedimentation and biodegradation without the use of chemicals or power other than for pumping.
The recycling sector has earned its reputation as an industry on the forefront of natural resource conservation and materials reuse. But for recycling businesses that must comply with increasingly stringent stormwater permits, figuring out how to upgrade their stormwater management practices may seem daunting. Implementing stormwater infrastructure improvements, such as selective paving and stormwater drainage, and using BMPs following the “oil, dirt, dissolved” design principle can simplify the task and improve stormwater quality in a cost-efficient manner.
Calvin Noling is a principal engineer and founder of StormwateRx LLC, a Portland, Oregon-based company that designs, manufactures, installs and maintains industrial stormwater treatment systems for customers throughout North America.