By Sue McCraven
If it rains where you work, you need to know about the National Pollutant Discharge Elimination System (NPDES). The same goes for anyone who discharges process water from his or her manufacturing operations. Because all precasters use potable water to make concrete, each plant must make sure it is NPDES-compliant (plants that discharge directly to municipal sanitary sewer systems do not require NPDES permits).
NPDES’s function is to protect surface waters from water-borne industry pollutants through the enforcement of effluent limits. Most NPDES permits are administered by state environmental agencies.
Why should you care?
Why should a precast concrete producer care about how rainwater flows in the yard or where plant process water ends up?
- There are significant U.S. Environmental Protection Agency (EPA) fines for violations of NPDES, created through a 1972 amendment to the Federal Water Pollution Control Act.
- Concrete manufacturing facilities are identified under NAICS 327390 (SIC 3272) as an industry that must meet NPDES compliance. There is no ambiguity in the law about the producer’s responsibilities.
- The Clean Air Act authorized the EPA to enforce NPDES, and EPA’s province has grown.
- Most of us know that in the last five years the EPA has been given greater authority to enforce more stringent and expansive interpretations of existing statutes. New, tougher air and water quality regulations can be expected across all industries.
- Most states enforce their own versions of NPDES (some include groundwater pollution) and can promulgate water quality regulations that are even more onerous and restrictive than federal standards.
- Once stormwater mixes with a plant’s process water, it is categorized as process water and must meet strict pollutant limits with significant monetary penalties for noncompliance.
U. S. concrete manufacturing facilities cannot pollute navigable waters under NPDES. If “navigable” makes you think only of large tankers on the Mississippi River or the Great Lakes, you might be off the mark. In addition to commercial shipping waterways, “navigable” means any surface water – like lakes and streams – but the term legally encompasses any body of water that can be used for “recreation” or is home to fish and aquatic life. So you might dismiss a narrow, shallow and garbage-strewn drainage channel near your business, but if it contains aquatic organisms or children play in its waters, it qualifies under NPDES. When we think of “navigable” or “surface waters” we need to think of “fishable, swimmable” and recreational possibilities.
Under NPDES language, a precast concrete plant is a “point source” for water pollution. Permits require that plants establish a stormwater pollution prevention plan that incorporates best available management practices.
Precasters are relatively lucky in the arena of environmental law. Precast concrete production crews don’t work with really nasty chemicals or lots of hazardous substances (though wet concrete is considered hazardous to skin) that are common in other manufacturing sectors. But there are six potential water-polluting substances from concrete production that are of concern to the EPA:
- Oil and grease: 10 mg/L daily maximum
- pH level: between 6 and 9
- Iron: 1 mg/L daily maximum
- Total Suspended Solids (TSS): 50 mg/L daily maximum
- Total Dissolved Solids (TDS)
- Chemical oxygen demand: 30 mg/L monthly average
To get an idea of typical pollutant discharges in the precast industry, Table 1 provides the results from two years of monitoring pH and TSS levels at 15 precast concrete plants.
EPA’s effluent limitation guidelines for concrete manufacturing facilities, using the best practicable control technologies that are currently available (BPTs), are:
- TSS: Not to exceed 50 mg/L
- pH: Within the range 6.0 to 9.0 su
You can see that, when all 15 plants are assessed together, the table’s mean value for these two pollutants met EPA’s BPT limit guidelines for one monitoring period (highlighted in red) and that there exists a broad range of pH and TSS discharge values among producers. It is likely that these data are representative of precast concrete plants in general.
Control, recycle and eliminate site drainage
Precasters are encouraged to do the following:
- Control site drainage (waters associated with washout; dust-control; manufacturing; maintenance for mixers, vehicles, formwork and equipment; and yard products and materials exposed to rainwater)
- Recycle manufacturing process water and byproducts
- Treat process water to meet effluent discharge limits
- Monitor pollutant limits
- Apply for applicable state permits or certificates of coverage (COCs) for stormwater and process water
There are many strategies for precast manufacturers to control and prevent water pollution. Articles published by the National Precast Concrete Association provide additional information on NPDES and process water issues.
Sue McCraven, NPCA technical consultant and Precast Solutions editor, is a civil and environmental engineer.