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.

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.

City of Broken Arrow Vets LID Practices Manual

If you've not seen it yet, the City of Broken Arrow is in the process of vetting its Draft “Living Green Low Impact Development recommended Practices for Certification Manual ”. The following summarizes the Manual and is taken from the same:

Jeff Bigby, with the City of Broken Arrow, will be conducting two roundtable meetings on November 30 and December 3 . They are both open to the public! If you are interested in Broken Arrow's proposed policy, and want to hear what developers and consultants think, please come. The one at 11:30 to 1:00 on November 30 is a regular meeting of the BA Builders\Developers Council. The meeting from 1:30 to 3:30 on December 3 rd is a separate engineers\consultants roundtable entirely devoted to the LID program . They are requesting comments on the draft manual on a card to be distributed the meetings.

While certification programs like the one proposed by the City of Broken Arrow are used in other parts of the country, they are new to Oklahoma. To my knowledge this will be the first LID certification program in the state, other than the national LEED and Green Globes standards. (Correct me if you know otherwise!) As such, it stands to become a template for many other communities that are looking to implement similar programs.

Defining LID

I've had several people ask me, after reviewing this blog, what exactly in Low Impact Development? And though we've attempted to shortly define the concept in our introduction, I liked this more lengthy description of LID from the Low Impact Development Center, Inc..

"LID is an innovative stormwater management approach with a basic principle that is modeled after nature: manage rainfall at the source using uniformly distributed decentralized micro-scale controls. LID's goal is to mimic a site's predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source. Techniques are based on the premise that stormwater management should not be seen as stormwater disposal. Instead of conveying and managing / treating stormwater in large end-of-pipe facilities located at the bottom of drainage areas, LID addresses stormwater through small landscape (as well as process or structural, my addition) features located at the lot level.

LID controls can be incorporated into almost every section of urban and suburban environments including open space, rooftops, streetscapes, parking lots, sidewalks, and medians. This versatile approach can be applied equally well to new development, urban retrofits, and redevelopment / revitalization projects. LID provides numerous benefits and advantages over conventional stormwater management approaches. The major benefits of LID include being a more environmentally and economically sustainable way to address the adverse impacts of urbanization. By managing runoff close to its source though intelligent site design, LID can enhance the local environment, protect public health, and improve community livability."

More information from The Low Impact Development Center, Inc. is available from their website at www.lowimpactdevelopment.org.

New Public LID Projects for Tulsa, Norman

Part of the American Recovery and and Reinvestment Act of 2009 (ARRA) included provisions for clean water projects in Oklahoma. All in all, Oklahoma was granted access to $31,662,100 in funds to improve water quality within the state. One of the stipulations of the ARRA is that 20% of these funds, or about $6.3MM, be used for "green" infrastructure projects.


Three projects that have been funded as part of the "green reserve" are an experimental green roof at the National Weather Center in Norman, Oklahoma, redevelopment of the dry pools into roof gardens at the downtown Tulsa City/County Library, and development of raingardens at the Tulsa City/County Library location in Sperry.



At the National Weather Center, a section of roof has been set apart for installation of a green roof system. The purpose of this roof section, as with many aspects of the NWC, is to educate the public. According the Oklahoma Water Resources Board, "Wide spread adoption of green roof technology remains absent in Oklahoma due to a limited local knowledge. This roof will be the first step to correct market deficiencies through knowledge creation and dissemination."


At the Tulsa City/County downtown library, we've all seen the "reflecting pools" located south of the library in the roof of the parking garage. The pools have been dry for as long as I can remember due to maintenance and structural issues and are something of an embarrassment, considering their location next to the Convention Center. The new green roof garden will be an asset and far more aesthetically pleasing.



The last LID project currently funded is installation of raingardens at the Sperry library. Sperry has had significant flooding issues in the past and the library continues to have a wet spot outside the front door. Why not a raingarden? This installation should address about 50% of the runoff from the facility and provide an educational opportunity as well.

Permeable Pavement for Oklahoma

Over the past few years I've fielded a number of questions about the use of permeable pavement in Oklahoma. Permeable pavements are an alternative to conventional concrete and asphalt paving that allow for infiltration of stormwater through the pavement and into a subsurface storage area or drain. Recently, there have been some significant installations, including Chicago's U.S. Cellular Field parking lot consisting of 6 acres of interlocking pavers. Its important to look into the advantages and limitations for its use on local sites.

Initially, I began by looking into the ratings for permeable pavement provided by the EPA. EPA showed permeable pavements to have a failure rate of about 75%1,2. That was not encouraging. I looked into the studies behind these findings and found that they were from 1992. Well, a lot has happened in the LID world since 1992, so what about more recent studies?

My inquiries took me to states like North Carolina and Georgia, where water quality regulation is intense, and to the EPA's LID Development Center in Portland, Oregon. As you may know, some advantage of permeable pavement include:

* The lifespan of a northern parking lot is typically 15 years for conventional pavements due to freeze/thaw stress, which is also common in Oklahoma. Porous asphalt or concrete parking lots can have a lifespan of more than 30 years because saturation during freeze/thaw is reduced3.

* Permeable pavement transforms areas that were a source of stormwater runoff to a system that can reduce or eliminate runoff that would have been generated from traditional paving. Studies show stormwater retention rates ranging from 25-100% depending upon storm intensity. http://www.thewaterchannel.tv/index.php?option=com_hwdvideoshare&task=viewvideo&Itemid=53&video_id=349

* Permeable pavement can reduce the amount of pollutants in stormwater runoff and can address suspended solids (high removal rates), acid rain (some types effective), phosphorous (moderate removal), nitrogen (moderate removal), and metals pollution (best in vegetated systems).

So what's not to like? There are some drawbacks and limitations to use including:

* Permeable pavement is not recommended, or in some states even allowed, where surface soils are silt or clay. That's most of northeastern Oklahoma. Generally, permeable pavement is only recommended in areas with sandy surface soil, like the western part of the State, or where stormwater has been pretreated.

* Even when properly sited, maintenance requirements are critical for the success of permeable pavement. Proper maintenance includes vacuum sweeping or high-pressure water washing at regular intervals and inspections after each storm. If you can't commit to maintenance, there are better options.

* Porous pavement has reduced strength compared to conventional materials and isn't appropriate for applications with high volumes, high speeds, or heavy loads.

So how might permeable pavement be used in Oklahoma? Walkways, driveways, alleyways, and overflow parking are some options. And consideration should be given to preventing sediment from reaching the pavement, especially during construction, which can trouble a pavement system before it's even in use.

Finally, we have a responsibility to put our best foot forward for LID as these topics are being introduced in local communities, to hit the ground with practices we know have positive reproducible results. Who wants to hear, "More of my tax dollars gone to waste." again? The future of LID is in our hands!

1 Schueler, T.R., P.A. Kumble and M.A. Heraty. 1992. A Current Assessment of Urban Best Management Practices. Metropolitan Washington Council of Governments, Washington, DC.

2 J. Galli. 1992. Analysis of Urban BMP Performance and Longevity In Prince George's County, Maryland. Prepared for Department of Environmental Resources, Prince George's County, MD.

3 Gunderson, J., Pervious Pavements: New Findings About Their Functionality and Performance in Cold Climates, Stormwater, September 2008.

Canopy Economics - The Power of Trees

During a news conference seven years ago this week, American Forests (americanforests.org) unveiled one my favorite studies - it showed that urban tree deficits were costing tax payers billions of dollars each year in air and water benefits. At that point, San Antonio, Texas, Charlotte, North Carolina and San Diego, California joined in as the first cities in the nation to take action to reverse the tree loss trend by incorporating tree cover data into their infrastructure database - considering trees on the same level as roads, bridges, and treatment plants.

The connection between tree canopy and stormwater may not be immediately clear. Trees reduce the volume of stormwater runoff by capturing some rain on their leaves and branches, which then evaporates back into the atmosphere. Other water infiltrates into the soil rather than running off the land, which must be managed. For example, San Antonio’s urban forest manages 974 million cubic feet of stormwater, valued at $624 million using a $0.64 per cubic foot value based on local engineering, construction, and land costs (Pape-Dawson Engineers).

The findings from American Forests showed that San Antonio had 27 percent tree canopy, seven percent open space, 64 percent impervious/bare urban land, and one percent water. However, if tree cover were increased from 27 to 35 percent citywide, 2.5 million pounds more air pollutants would be removed each year and stormwater runoff would be reduced by 103 million cubic feet during an average 2-year, 24-hour storm event. This service would be worth an additional $200 million in avoided stormwater facility construction.

"Flooding in San Antonio is an age-old issue," said Carol Haywood, a planner with San Antonio's neighborhood and urban design department. "Most folks think we need more concrete culverts to simply whisk the water away as fast as possible. We will use this green (infrastructure) data to model and demonstrate the ability of trees to perform a similar function without adding new concrete."

For its part, the City of Tulsa began a tree planting program in 2007, after that year's devastating ice storm. For comparison, that storm destroyed or damaged as many trees as Up With Trees had planted in its entire 30 year history. Since that time over 5,000 trees have been replanted, with a goal of 20,000 trees by 2010 through ReGreen Tulsa. The City, through its Tree Advisory Oversight Committee, seeks to increase tree canopy by 3% year over year through 2013. Overall, the American Forests recommend 35% canopy coverage in urban areas.

When municipalities are looking to control long-term stormwater infrastructure costs, it should be clear that canopy cover can be a key element. What if we designed for the 2-year 24-hour event with both concrete and canopy? How much less would taxpayers have to spend? And how much more we would enjoy our new public infrastructure.

Tulsa Raingardens: The Clyde Home

This week we're featuring a local raingarden designed and installed by Tony and Jen Clyde in midtown Tulsa. I've been talking with Tony about his raingarden plans for a couple of years now. Their garden was planted in the summer of 2008, so I was curious as to how it was coming along. The answer is, "Great!", as you can see from these photos.


Tony designed this raingarden to address runoff from one section of their home encompassing about 170 square feet of roof. The location sits off the southwest corner of the home, in full sun, and is just off a stone sitting area. To begin his garden design, Tony performed a permeability test at the proposed raingarden location and found he had loamy soil with good infiltration.



The roof section selected for this garden has two downspouts that were disconnected from the storm sewer and rerouted, as shown in these photos. The first shows the downspout connection. The second photo shows the inlet into the raingarden.


Tony then began to dig out the raingarden. He excavated about 1.5 cubic yards of dirt, which has since been used in other yard projects. The garden is kidney-shaped, measuring about 4.5' x 10', or 45 square feet, and is 6" deep.


As an overflow outlet, a rut left by a utility truck was purposefully not filled in. The rut is barely noticeable in the grassy yard but functions regardless, channelling water out of the raingarden and into the street (and storm sewer) during high rainfall events. The overflow is located in the bottom left corner of this photo. Every raingarden needs an overflow.


The garden was then planted with facultative wetland plants - that is, plants that can handle periodic flooding. For this garden, Tony selected swamp milkweed, swamp verbena, sawtooth sunflower, and leadplant. The plants were obtained from Pine Ridge Gardens in Arkansas, which specializes in native plant materials. The plants were shipped directly to his home and cost about $110. To finish it off, Tony selected a good cypress mulch.

When I visited, there were numerous different species of butterflies and bees present. Although the plants were not chosen to attract pollinators, it is certainly effective. The garden looks like a natural, but planned, part of the landscape.

I asked Tony about comments from neighbors. He said the most common have been regarding the garden's attractiveness. But he did tell about one visitor who remarked, "You know your pond doesn't hold water." Some things take a while to catch on. :)

Dealing with Off-site Runoff

I remember the first big storm that occurred after we moved into our current home: a river carved its way under the fence and through the newly sodded backyard. Where did it come from? A peek over the fence showed me something I hadn't noticed before. The adjacent backyard was a concrete slab, funnelling runoff from the house, outbuildings, and pavement through our yard. Granted, it wasn't my neighbor's fault. The problem had been there for decades and they inherited it just like us.

A number of people have similar experiences, though, when neighbors add on or developers substitute McMansions for bungalows. New guidance being developed by the City should address some of those infill issues, but what can you do about "run-on" short of legal action? In this case we looked at redirecting the river and decreasing its energy. And the application may give you ideas about how to handle your own off-site problem.

First, we talked with our neighbors about what we were observing. They made some changes to their yard, including switching two parking spaces to loose gravel. Tremendous! And it looks great too.

On our side of the fence, we used recycled concrete, which came from tearing out our own paved yard, to provide energy dissipation for the flow entering from the fenceline. Basically, that means putting something in the way of the stream to smack it around and is provided by the larger stone in the middle of the garden to the left. We then used the same materials to edge a planting bed along the fence and provided spaces between the concrete to allow water flow. The water then enters a horizontal gravel filter, made up of river rock, which dissipates the flow further and allows it to pass through the yard without being seen. The filter also acts as a walkway from the house to the play yard. On the downstream side of the walkway, I added a raingarden that is a few inches lower than the gravel bed.

Overall, the system dissipates the energy of the water entering the yard, filters the water, conveys it, and provides some infiltration. Afterwards, water exits into the alley. During high rainfall events, water flows through this system as well as overflows to the yard and a shallow lined channel directly to the alley.

I mentioned the design to someone recently and they asked "Isn't that just a walkway?" And I thought, "Yes, and No." I'll highlight again that stormwater controls don't have to look different, they just have to work different. And if it is mistaken for a walkway, great. That tells me its a job well done.

What's Up With Rats?

It seems each time I talk about raingardens, someone has to ask about vermin. You know, squirrels without the cute fuzzy tails: rats and mice. The question is usually, "Do raingardens bring in vermin?". My standard answer is, "No". But after hearing it so many times, I decided to get some additional advice on the topic.

I talked with both a horticulturist and a biologist about this question. On my list were Jay Ross, Horticulture Curator at the Tulsa Zoo, and Stephanie Rainwater, a biologist at URS. Jay and Stephanie both noted that any garden with dense vegetation can provide a nesting area for all types of critters, from songbirds to cats to, you know. The key to what critters you attract is what food supply is nearby. If you have insects, you should get birds that eat insects, and so on.

In the public arena, a community might consider whether the garden is located near areas of animal feeding (advised or not), such as a duck pond or petting zoo. Likewise the residential homeowner should consider whether they leave dog, cat, or bird food where other animals can access it. In my own yard, I've found the compost heap to be a problem.

But are there features that make raingardens uniquely less prone to being used by vermin than other landscaping? The answer is yes. Raingardens are designed to flood - every time it rains. There aren't a lot of critters that will put up with being flooded on a regular basis - they'll pick somewhere else to nest.

So, what does all this mean? Raingardens should be less likely to house these unwanted guests than other types of gardens and landscaping, a fact that should encourage others to bring stormwater controls into their landscaping.

Rainwater Harvesting: How Much is Enough?

This week's poll has to do with what people want to use rainwater collection for, whether it be watering lawns or running the commode. Even ambitious LIDers won't be using rainwater to wash clothes anytime soon b/c they don't have dual plumbing systems (potable/non-potable) in their homes. So that leaves most us looking at outside uses, watering the lawn and the like.

Rain barrels are becoming more and more popular. But it seems the minute most people put one in they want it bigger: a 55-gallon barrel doesn't go very far. How far you might ask? Well, I use a 55-gallon barrel for air conditioner condensate collection and am able to water my container plants for about week from one barrel. How much water do you need?

A traditional lawn needs about 1-inch of water per week during the summer. That's 0.623 gallons per week per square foot. (Sometimes I just call it a half-gallon per foot to make it easy.) If you have a lawn that is 20' x 50', that's 1,000 square feet of lawn. It would take 623 gallons of water per week. During the summer, let's say that it doesn't rain for a month. Over those four weeks your lawn would need 4 x 623 gallons = 2,480 gallons. If your lawn is bigger, you'll need more, maybe much more!

So, here's where reason kicks in. Are you ready for a 2,500 gallon (or larger) tank? Do you have the space? (A 2,500 gallon-tank is about 8 feet in diameter and 7 feet tall.) Does your neighborhood allow these kinds of appurtenances?

There are a number of factors to consider when evaluating "How Much is Enough?". Maybe for you it is a rain barrel to refill the fish pond, maybe it's finding out if the old cistern in the backyard still holds water, or maybe its having a system engineered for your specific needs. Whatever you decide, there's an opportunity every time the rain falls.

Kill Before You Till

Is this a familiar sight? Bermuda grass is the bane of this gardener. Typically, directions for development of raingardens in native soil are to check permeability, clear the site, till in compost, and plant. But digging up sod in Illinois is different than removing the grass in Oklahoma.

Our primary grass seems to be Bermuda and it is invasive! Bermuda spreads not only by seeds but also by runners above and below ground. It can overtake over a foot of garden in a growing season. So, simply taking off the top layer of sod won't do. You have to kill it.

But how? I checked with the County Extension Office office for some direction. And their advice confirmed my anecdotal experience: Bermuda is tough stuff. You can try thermal sterilization of soil - putting down black plastic and allowing the sun's heat to kill everthing off. This kills the surface plants but doesn't address the deeper roots, which can be six inches or more below the surface. This also kills plants by depriving them of sunlight, but Bermuda can stay dormant under the soil for an extended period of time. I've also tried herbicides, which seem to work for a while, but Bermuda always seems to come back.

Bermuda, it seems, must be killed and killed again. They say up to 6 or 7 sprayings over time are necessary to really eradicate Bermuda from a proposed plot. And that takes planning ahead, about a growing season ahead, of when you want to plant.

And because it continues to spread from the outside, placing a good quality edge to 6 inches beneath the soil (not extending above the ground) will help minimize root intrusion. Surface runners take a hands-on approach. After all that, you should have a garden that is much easier to maintain. But it takes some time and planning (and a bit of grass-killer).

Traveling LID: Florida

As you may have guessed, I have to make note of LID applications wherever we travel. We took a family vacation to Sanibel and encountered these raingardens in a small county park northeast of Ft. Myers. We went to watch manatees, which we didn't see, but we found multiple raingardens!

Much of Florida is condusive to bioretention, a fancy word for raingardens, because of its sandy soils and high infiltration rates. As you can see in these photos, the surrounding landscape has been graded to form a depression. This is where rainwater collects. Plants within the depression have been selected that can withstand periods of standing water, or inundation. And the water is allowed to infiltrate, or seep into, the soil.

Some of the things I liked about this park were the number and variety of raingardens present - in the parking lot, at the entrance, and scattered throughout. They also provided educational signs, which I don't have photos of. I also liked that they made use of a range of vegetation, from trees that look like they've been there forever (and they may well have) to bushes and groundcover. Its not obviously a stormwater treatment system but fits attractively into the overall landscape. Kudos!

Who Designs Raingardens?

I was recently asked to come out and look over a new raingarden that had been designed by a reputable local landscape architecture firm. But I had been asked to take a look because it really didn't seem to the owner (a public entity) to fit the definition of a raingarden. Sure enough, the garden fit right into the profile of the slope, and did not provide a means of detention or opportunity for infiltration. I checked the design drawings which provided a planting plan with a note to set the garden six inches below the surrounding surface - not a bad start but not really a raingarden design. But it made me think again about a question I had received previously - who designs raingardens and why?

I checked with the Board of Professional Engineers for Oklahoma and the Board for Landscape Architects. And there is some confusion. Apparently there is joint commission that discusses and decides on such issues and I recommended that this could be a good question to consider. The feedback I received was that landscape architects should develop and stamp landscaping plans. But because LID features are designed, or should be designed, for stormwater collection, conveyance or treatment, the sizing and hydrology (how much water and where it goes) should be stamped by an engineer. Ah, interdisciplinary design. We get to all work together. Now, if we just would.