Thursday, December 10, 2009

Turbidity Limit on Construction Phase SW Challenged

from Inside EPA Water Policy Report - 12/7/2009

Key Republican lawmakers are slamming EPA’s just-signed regulation governing stormwater discharges from construction sites, saying it is far too costly for the environmental benefits derived. EPA’s rule is in the top five least cost-effective regulations, across all federal agencies, since the White House Office of Management & Budget (OMB) began tracking such figures in 1992, according to industry’s review of OMB’s records.

“I am extremely concerned about the impact this rule will have on economic recovery in the U.S.,” Sen. James Inhofe (R-OK), ranking member of the Senate environment committee, said in a statement to Inside EPA.

At issue is EPA’s just-signed, court-ordered rule governing stormwater runoff from construction sites. EPA included in the rule a numeric limit for turbidity prompting industry criticism because it will cost almost $1 billion per year to fully implement. (Note: This is a significant change from previous regulations, which said that certain practices must be followed, but did not specify outcomes.)

The construction and development sector effluent limitations guideline phases in a numeric limit of 280 nephelometric turbidity units (NTUs), a unit of turbidity, and requires “passive” filtering technologies to meet the standard. (What does 280 NTU look like? See the image below:)
Inhofe singles out in particular the controversial numeric turbidity limit in the regulation for criticism. “[T]he rule sets an arbitrary ‘turbidity’ benchmark that will be extremely cost burdensome for builders to achieve, especially with the current limited technology. It also provides yet another tool for environmentalists to delay or stop important development and transportation projects through frivolous litigation,” Inhofe said.

Although EPA is only requiring passive treatment systems in the rule, industry fears that in many parts of the country, the active systems will be needed to meet the numeric turbidity limit. Further, industry argues concerns about liability will force the use of active treatment because passive treatment systems can vary in effectiveness based on circumstances, potentially putting construction site discharges in violation of the law.

Wednesday, December 9, 2009

EPA Technical Guidance for Federal Facilities Out

New technical guidance from EPA came out last week. This particular piece applies to federal government facilities and puts more teeth to federal facility directives that have been out for a while. And while you might think that you don't deal with federal facilities, many municipalities and county offices actually do.

This guidance applies to "any building that is constructed, renovated, leased, or purchased in part or in whole for use by the Federal Government". It also specifies that the guidance applies to facilities with a footprint of greater than 5,000 square feet (sf) - this "includes all land areas that are disturbed as part of the project". This means it applies to the entire cleared construction area even if the structure is tiny or only remodeled.

Overall, about half the document is the "why" of LID. The rest is about implementing LID. A surprising amount of the implementation portion is dedicated to development of the design precipitation event, as discussed below.

The document provides two options for determining the volume of water to be retained on site. In the first option, the design storm (95% 24-hour event) must be fully retained on site. The document provides guidance on development of the 95% 24-hour event depth with several helpful examples.

In the second option, the post-construction hydrology must be equal to the pre-construction hydrology. It provides a site-specific approach to runoff control, rather than the first option which provides a more generalized approach.

Both options provide for a variety of methods to be used in converting rainfall to runoff. Direct Determination, TR-55, Rational Method, and SWMM are compared in the text.

The document provides some limited criteria regarding BMP design as well (Appendix A). It specifically addresses design of bioretention areas, with and without underdrains, using Horton's equation to assess infiltration and storage. Similar methods are used to assess green roofs and permeable pavers.

The main body of the document also notes cisterns and reuse as options for retention but addresses only infiltration BMPs in its analysis.

While I'm glad to see some guidance provided for federal LID development - there's still a lot to be desired in terms of design criteria. Given, federal facilities span the continent and the world, so its nearly impossible to provide criteria that would apply to every site. This document gives some basics for implementing three common LID techniques every stormwater engineer should have in their toolbox.