On November 23, 2009, EPA released the final Construction & Development Effluent Limit Guidelines (C&D ELG). The final C&D ELG will impact all construction sites disturbing more than one acre by imposing non-numeric effluent limitations. More importantly, the C&D ELG will impose numeric effluent limits for the first time on all construction disturbing more than 10 acres within approximately 4 years. Most construction sites will need to use Passive Treatment Systems (PTS) to achieve those limits rather than the typical erosion and sediment control measures currently in use. EPA estimates as many as 21,000 construction sites annually would need to meet those numeric limit standards.
In the past, sediment control practices have generally been designed based upon a rule of thumb. Many states rely on 1800 ft3/acre of drainage (or disturbed acre), which doesn’t take into consideration the discharge quality. In fact, a sediment control measure can have an 80% settling efficiency and still produce a turbid (muddy) discharge. With this in mind, EPA has been struggling since early 2000 to establish a C&D ELG, with prodding from environmental groups.
In November 2008, EPA published a draft C&D ELG that set the ELG (turbidity) at 13 Nephelometric Turbidity Units (NTUs) for sites that disturbed 30 acres or more, were located in areas of the country with high rainfall intensity, and located on soils that had at least 10% clay. That incredibly low turbidity limit (13 NTUs) severely limited the stormwater treatment options to Active Treatment Systems (ATS) that, simply put, look and function like small waste water treatment plants. EPA requested public comment on the draft rule and requested additional data on the cost benefit analysis, treatment feasibility, and other components. Concerns mounted as those affected began questioning the draft rule, particularly the feasibility of achieving the 13 NTU discharge standard.
EPA published the final C&D ELG in November 2009 with major revisions based on the comments received. EPA chose to greatly simplify the rule and increase the numeric standard. Below is a summary of the final rule:
- All construction projects must install best practicable control technologies.
- Sediment basins and other impoundments must be dewatered from the surface.
- The ELG has been set at 280 NTUs. This limit is a daily maximum average, based upon sampling for storms up to the 2 yr, 24 hr storm. Discharges from storm events greater than the 2 yr, 24 hr are not required to meet the ELG.
- Discharges from construction sites must meet an effluent limitation guideline as follows:
- Within 18 months of the effective date of the rule (August 2011), sites disturbing 20 acres or more must meet the ELG.
- Within 4 years of the effective date of the rule, sites disturbing 10 acres or more must meet the ELG.
- For both scenarios above, the size limitations apply to “larger common plans of development” like subdivisions with multiple small lots.
Each state will need to marry the final C&D ELG with their existing monitoring plans, which will be a huge task. Additionally, EPA has noted that as each state’s construction stormwater permit comes up for renewal, these requirements must be inserted. EPA is the permitting authority in four states. Their general permit is due to expire in June 2011 and will be reissued with the ELG requirements in it at that time. Interestingly, North Carolina’s permit was in the midst of renewal when the ELG rule was finalized, and EPA only allowed their permit to be renewed for 18 months (through August 2011). After that date, the reissued permit must include the ELG requirements.
As indicated earlier in this blog, PTS will generally be required to meet the numeric standard of 280 NTUs. A PTS incorporates a flocculant with a standard construction site practice. An example of a PTS is a jute-lined ditch that has been impregnated with polyacrylamide (PAM). Design components that must be considered include mixing zones and settling zones. At this point, we don’t have design tools that dictate the amount flocculant to be used on a site. Flocculants and soils must be matched (not every flocculant works on every soil), and the applications tweaked in the field for peak performance. Then the flocculant must be reapplied after rain events.
You can expect to have the ELG requirements inserted into the permit language if your state’s permit expires before August 2011. If, however, your permit was reissued before the rule was finalized and without the ELG language in it, EPA could administratively open the permit to have the language inserted into it. I suspect that between June 2011 (when EPA’s Construction General Stormwater permit expires) and August 2011 (the deadline to begin implementing the ELG) some permits may be administratively opened. That option is certainly possible.
If you have any questions about the C&D ELG, how it may impact an upcoming project, and how you can meet the numeric standard, contact CEC’s Nashville office at (800) 763-2326.
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