March/April 2014
Knowing how to read your stormwater test results can help identify problem areas and direct your prevention and remediation efforts, but some basic practices are essential for almost every yard.
By Lindsay Maine and Todd Peterson
Like many industrial facilities, your scrapyard is exposed to rain, and you’re prepared to manage the stormwater to comply with environmental laws and improve water quality. You have the basic components of a stormwater program: a stormwater pollution prevention plan and best management practices such as paving yard surfaces, covering oily material, and containing fine material. When you see your stormwater test results, however, you’re still not reaching the required levels of water quality. So now what do you do?
It might seem daunting—or even impossible—to comply with increasingly stringent stormwater regulations, which for a given facility could include federal benchmarks and/or local effluent goals. Concentrating on the likely sources of potential pollutants can help focus your efforts, allowing you to effectively select and deploy the BMPs that have the best chance of achieving your goals. Here’s a look at what the most common stormwater tests are measuring, where those pollutants are most likely coming from in a scrap operation, and which BMPs can help.
The current in your current. Specific conductance is a measure of water’s ability to conduct current. Testing for SC, usually done with a handheld meter, is a low-cost way to get an indirect estimate of the sample’s dissolved solids. Limits on dissolved solids can vary according to jurisdiction, but for reference, it’s helpful to know that the U.S. Environmental Protection Agency’s (Washington, D.C.) benchmark for SC is 200 micromhos per centimeter (usually written as µmhos/cm); deionized water is approximately 0 to 1 µmhos/cm; and seawater is approximately 55,000 µmhos/cm. Rainfall tends to have incredibly low SC; thus, nearly all conductivity measured in the stormwater leaving a scrapyard typically is attributed to dissolved materials from the yard’s operations.
A higher-than-desired SC result can come from just about anything in a scrapyard that’s exposed to stormwater and fully or partially dissolves in water, such as dirt, debris, waste fluids, and water-treatment chemicals such as metal precipitants, which precipitate metals from the water. Careful housekeeping in the form of prompt and thorough spill response, sweeping up fine particulates, and covering or containing materials that are likely to contribute to specific conductance is the best way to bring SC numbers down to desired levels. If the rainwater never hits a specific material, that material can’t dissolve and increase conductance.
Acids and antacids. The pH of a sample is a measure of the negative logarithm of its hydrogen ion concentration. The pH scale is from zero to 14: Water with a pH of 7 is neutral, less than 7 is acidic, and greater than 7 is basic. The EPA benchmark range for pH is 6.5 to 8.5. Acidic water could be contaminated with leaking battery acids, some cleaners, or the mishandling of sampling kits that have a small amount of acid preservative. Water that’s basic could contain antifreeze or could have come into contact with recently paved surfaces or broken concrete.
The best controls for pH levels that are too low or too high are to cover recently paved surfaces or divert water around them, use pH-balanced cleaners, allow coatings such as epoxy sufficient curing time, and store batteries in containers that are covered and have secondary containment to protect against spills. Also, note that some chemical stormwater treatments adjust pH upward to improve contaminant removal. If this is the case in your yard, you might need to readjust the pH level before you discharge the water.
Solid problems. Total suspended solids, as its name suggests, is a measure of the solids in the water. This measurement is taken by filtering the sample and drying and massing the residue that remains in the filter. If your yard’s stormwater has metal contamination, you are likely to find that a significant proportion of it comes from solids, not from metals dissolved in the water. The EPA benchmark value for TSS is 100 milligrams per liter of water, which most yards should find fairly easy to achieve. That said, removing more solids—down to 10 mg/L—can help you achieve the EPA benchmarks for various metals. Turbidity meters are a good, inexpensive way to get a sense of your TSS. We have found that samples with turbidities lower than 10 tend to have little metal contamination.
Anything that can be picked up in the flow of water across your yard, such as sediment, debris, metal fines, and waste fluids, can become a suspended solid. The best solution is to prevent the solids from getting into the water in the first place through housekeeping measures, capturing them upstream, allowing them to settle, or filtration/treatment. If you can keep the solids out of the water, you don’t have to worry about removing them downstream. This is especially true of the finer particles that settling or media filtration might struggle to remove.
If you’re thinking of adding filtration to your stormwater system to help capture solids, it’s helpful to understand the size of the suspended solids your discharges typically contain. Water laboratories can provide insight into particle size distribution if you don’t have the resources to do so in house. Solids larger than 1,000 microns are likely to settle out via gravity alone, given time and lack of disturbance. Sand filtration can filter solids as small as 50 to 100 microns, although this will depend on factors that include the size of the filtration unit, pressure, flow rate, and the filtering media used: manufactured #20 sand versus golf course sand, for example.
Most scrapyards will find that a significant proportion of their solids consists of particles as small as 5 microns or less, down to the sub-micron level. Cartridge or, potentially, membrane filtration can filter solids that small, or you can pursue flocculation—increasing the mean particle size.
Organics and oxygen. Chemical oxygen demand, a measure of the oxygen required to fully oxidize the contaminants in the sample, indirectly measures the organic materials and organic chemicals present. The EPA benchmark for COD is 100 mg/L. Contaminants that might contribute to a high COD measurement are waste fluids, solvents, trash, and organic material from nearby trees or shrubs.
Housekeeping (especially sweeping), upstream capture, and filtration are the best options for reducing the stormwater effluent’s COD. One action that can raise COD levels, however, is holding stormwater too long between storms. Doing so allows bacteria to grow or reproduce and allows organic debris to break down further. Both processes use up oxygen in the water, which increases its oxygen demand. Holding water also can give metals the exposure and time to dissolve further, contributing to higher metal measurements. If your yard has retention basins, sumps, or clarifiers, it’s a good idea to discharge all of the water from an event or reuse it on site for dust control.
When oil and water mix. The oil and grease measurement is self-explanatory. The EPA benchmark for these materials is 15 mg/L. What might not be obvious is that oil and grease also are potential sources of the metals showing up in your water. Although newer oils are relatively clean, as machines operate and wear down, metal fragments get into the oil. The oils’ high temperature, friction, and resonance time in the machine environment will dissolve metals as well.
The best BMP for oil and grease is to prevent stormwater from coming in contact with oily materials. Always store items like motor blocks, scrap equipment, and sealed units in closed containers or those covered by an overhead structure or tarp. Also, clean up oil spills immediately and completely. To capture oil and grease in stormwater, install absorbent booms and carbon filter cloth upstream in water flow pathways. Positioning the booms as chevrons and lining the filter cloth with sandbags can encourage water to flow through the devices, which will capture both oils and sediment. Filtration media and cartridge filters also will capture oils and greases, but large amounts of those materials will quickly clog or slime the filters.
Subtle Sources of Metals
When tests identify high levels of specific metals in your yard’s stormwater, your instinct might be to look at the material you’re recycling. That’s certainly one likely source, but it’s not the only one. The contamination might be coming from fluids, vehicles, equipment, and even materials used to control other contaminants.
Copper, for example, can be coming from copper bales or other copper scrap, especially if you’re scraping that material across the ground and creating fines. But it’s also in waste fluids and in brake pads and linings, from both the vehicles and equipment in your yard and the end-of-life vehicles you’re processing. Aquatic organisms are very sensitive to copper, which is why the EPA benchmark of 0.020 mg/L is so low. Housekeeping (especially sweeping and covering scrap materials), diversion, and filtration are the best BMPs to address copper in stormwater.
Sources of aluminum include waste fluids, soil and dirt, paint, scrap fines such as shavings and turnings, and zeolite, an absorbent material used to clean up spills (and an element in some cat litter). Housekeeping and filtration are the best BMPs for addressing aluminum in stormwater. Also, when you put absorbent on top of a spill, work it into the spill vigorously, then sweep it up right away. Otherwise, you could be turning an oil or grease problem into an aluminum problem.
Iron in your stormwater could come from waste fluids, soil and dirt, and scrap, especially turnings, borings, and rust. Ferrous scrap that comes in large, intact pieces most likely is not the culprit. It’s the residues, rusts, particulates, and debris that accompany the scrap—pieces that are small enough to be picked up and transported by water or be dissolved in water—that are going to contaminate the water.
Manage these ferrous fines through constant sweeping and housekeeping. Also, keep in mind that many structures in and around the yard are made of steel. Reduce the susceptibility of that material to contribute to a stormwater problem by painting or epoxy-coating these structures to prevent rusting.
Waste fluids and paint are the main sources of lead. If you’re adequately protecting your stormwater from waste fluids—both oils and water-soluble fluids—and degraded lead-based paints, you’re less likely to have a stormwater lead issue. Similarly, if tests do find excess lead levels, focus on fluid management rather than lead scrap as the culprit. That being said, it’s still a good BMP to store lead scrap and leaded wheel weights in a covered container with secondary containment.
Zinc, like copper, is a serious aquatic pollutant. Scrapyard sources of zinc are primarily waste fluids and anything galvanized, especially the roll of galvanized fencing you might be using to sweep or push material. Dragging and scraping that material or zinc-containing scrap creates fines that, once created, are difficult to keep out of the water system.
Common Sources and Solutions
Scrapyards must monitor their stormwater for a variety of potential pollutants, but many of these materials come from the same few sources—and the methods for controlling them are the same as well. Once you’ve paved your operating areas, covered and contained problematic scrap material, and installed mechanisms to capture pollutants before they enter the stormwater or to treat them once they do, the best preventive BMP you can implement is thorough and consistent housekeeping, especially sweeping. If fines, dirt, debris, and similar pollutants don’t get hit by water, they won’t have the opportunity to contaminate it. Similarly, waste fluids can contaminate your stormwater not only with oil and grease, but also with nearly all the metals for which we monitor. To reduce those problems, clean up oil spills and contain and cover oily scrap.
Once materials show up in the stormwater, we have to get them out. It’s almost always easier—and most likely less costly—to prevent contamination upstream, and doing so will prolong the life of your filtration equipment. By understanding the sources of the contamination, we can focus our efforts on the strategies that will make the biggest difference and produce better effluent water quality.
Lindsay Maine is the environmental manager and Todd Peterson is a chemist for SA Recycling (Orange, Calif.).
Knowing how to read your stormwater test results can help identify problem areas and direct your prevention and remediation efforts, but some basic practices are essential for almost every yard.