Low Impact Development and Why it Matters

It has been called green infrastructure, conservation design, sustainable storm water design, natural stormwater management, and rain management but Low Impact Development, LID, seems to be the term that has taken hold in the United States for the site level actions and strategies. LID is a strategy of stormwater management emphasizing conservation and natural features combined with small scale stormwater controls to mimic as closely as possible the natural hydraulic properties of a site. The idea is to move water slowly through open conveyance systems and use distributed stormwater retention in open unpaved areas to allow infiltration of rain water into the earth. This reduces the quantity and velocity of stormwater as it leaves a site reducing the damage that uncontrolled stormwater runoff can cause when we change the amount of impervious surfaces a site has by building roads, sidewalks, playgrounds, and structures and compacting soil.

Traditional development practices cover large areas of the ground with impervious surfaces such as roads, driveways, sidewalks and buildings. These paved and impervious surfaces prevent rainwater from infiltrating into the ground, causing it to run off site at velocities and volumes that are much higher than would naturally occur. The collective force of such rainwater scours streams erodes stream banks resulting in large quantities of sediment and other pollutants entering streams, rivers, estuaries and bays every time it rains or snow melts. The US EPA believes that sediment and nutrient pollutions contained in runoff from urban areas is the largest source of water quality impairments to estuaries (areas near the coast where seawater mixes with freshwater) in the United States and has turned its water quality focus on these areas starting with the Chesapeake Bay Watershed and moving forward with the Gulf Coast estuaries.

Groundwater is recharged from rain and sources of surface infiltration. In many areas where development has occurred, we pump the groundwater for drinking water supplies (both public and private) and create barriers to rain infiltration by paving significant portion of the urban and suburban landscape as well as allowing if not encouraging storm water to leave a site as quickly as possible reducing the time that rainwater has to infiltrate the remaining soil and percolate into the subsurface. If we do not allow adequate rain water infiltration we will deplete the groundwater aquifers as we continue to pump water from wells. The U.S. Geological Survey’s (USGS) Groundwater Resources Program has found that the volume of groundwater stored in the earth is decreasing in many regions of the United States, and if this continues we could deplete our groundwater. We are running a groundwater deficit in many parts of our country, though we have adequate rainfall. LID can help by increasing water infiltration and reducing runoff.

In addition to the problems caused by stormwater and non point source runoff, many older cities (including many of the largest cities in the United States), have combined sewage and storm water systems which results in the storm water runoff overflowing the combined sewer system during storm events and diluted, but nonetheless raw sewage being released to rivers and estuaries. This is an ongoing problem in Baltimore and at Blue Planes in Washington DC as well as other cities throughout the nation. In the late 20th century, most cities that attempted to reduce sewer overflows did so by separating combined sewers, expanding treatment capacity, expanding storage within the sewer system, or by replacing broken or decaying pipes. San Francisco and many other cities have taken all of these steps, but still have much more that needs to be done. It is unfortunate that more of the stimulus dollars were not spent to repair expand and improve the waste water treatment facilities in our oldest cities instead of pursuing $54 billion in direct loans and loan guarantees to green energy companies. Repairs and improvements to our waste water treatment systems would have served our nation for several generations rather than been wasted on unproven technology or enriching favored entrepreneurs.

Managing rain water and snow melt is at the heart of LID. Rain water and storm water management under LID is landscape based and not particularly new. At the larger regional or watershed scale, green infrastructure is the interconnected network of preserved or restored natural lands and waters that provide essential environmental functions. Large-scale green infrastructure may include habitat corridors and water resource protection. At the community and neighborhood scale, green infrastructure incorporates planning and design approaches such as compact, mixed-use development, parking reduction strategies and urban forestry that reduces impervious surfaces and creates walkable, attractive communities.

At the site scale, green infrastructure is LID and mimics natural systems by utilizing permeable surfaces to absorb storm water back into the ground (infiltration), using trees and other natural vegetation to convert it to water vapor (evapotranspiration) and using rain barrels or cisterns to capture and reuse storm water. These natural processes manage storm water runoff in a way that maintains or restores the site’s natural hydrology, allowing groundwater to recharge. Site-level green infrastructure is LID, and can include rain gardens, porous pavements, green roofs, infiltration planters, trees and tree boxes and rainwater harvesting for non-potable uses such as toilet flushing and landscape irrigation. LID not only reduces the velocity and quantity of runoff protecting our streams, rivers, lakes and estuaries, it is essential to allow the recharge of groundwater.

The difficulty with LID is compliance and maintenance. Federal Clean Water Act requirements, such as the Combined Sewer Overflow (CSO) Control Policy and National Pollutant Discharge Elimination System (NPDES) permit program, do not allow for deviance from traditional control strategies. EPA guidance which encourages LID and green infrastructure to manage storm water is inconsistent with permit requirements under NPDES that call for more conventional methods of stormwater management.
NPDES regulations require development and implementation of a municipal separate storm sewer system (MS4) program to address post-construction runoff from newly developed and redeveloped areas. Investments in stormwater management and wastewater treatment plants are driven by compliance with regulations, which do not allow local policy makers to implement watershed-based or decentralized LID infrastructure solutions that may not yet have the data necessary to demonstrate performance and receive regulatory credit under a permit. Within the Chesapeake Bay Watershed the Chesapeake Bay Model provides credit under the Watershed Implementation Plans for LID retrofits, but not all practices are credited appropriately (both because of the amount of time needed for these practices to show long-term performance, as well as limitations in historic data collection). LID is by its nature a distributed design involving, rain gardens, porous pavements, green roofs, planters and rainwater harvesting require ongoing maintenance of the plants, replanting after severe winters or prolonged droughts, weeding, and clearing of porous pavements. There does not yet exist a method of ensuring that these features are maintained appropriately to continue functioning over time and that any repairs or replacements are done with LID in mind.

The Quantico Watershed Study and the Chesapeake Bay TMDL

On June 23, 2011 I attended the Prince William Department of Public Works meeting to hear the results of the recently completed Quantico Watershed Study . Warren High from the County’s engineering consultants, MACTEC, presented the results. The study was used to assess the current stream conditions, examine existing storm water management facilities, and to identify future Capital Improvement Projects. They used a standardized system of scoring streams and stormwater basins, ponds and retention ponds called RSAT. http://www.stormwatercenter.net/monitoring%20and%20assessment/rsat/smrc%20rsat.pdf The meeting was attended mostly by representatives of community groups and elected and appointed officials of Quantico Bay area who have fought long and hard to try to restore the Quantico Bay that suffers from excessive sedimentation and hydrilla, an invasive aquatic plant. http://web.ead.anl.gov/ecorisk/case/docs/FINAL_Quantico_Creek_Risk_Screening.pdf

Prince William County at the edge of the greater Washington DC metropolitan area, is part of the greater Chesapeake Bay watershed and has 10 major watersheds of its own covering 360 square miles that are in turn subdivided into 222 sub water sheds. The Quantico Watershed Study is the forth watershed study to be completed. The watershed studies evaluate CIP Planning and Storm Water Management Facilities, Regulatory Compliance with federal and state regulations including EPA, CWA, VA DCR and DEQ and the Army Corp of Engineers. The studies typically examine a small number of sub-watersheds to characterize the watershed as a whole. The Quantico study examined six sub-watersheds that included Quantico Creek, South Fork, Dewey’s Creek and Swans Creek. The elevations of the sub-watersheds range from sea level to 450 feet elevation and cover an area occupied by Prince William Forest Park at the northwestern most portion of the watershed to Quantico Marine Corp Base and Dumfries as well as several residential neighborhoods.

MACTEC found culverts impeding fish passage, supercharging the water flow resulting in the scrubbing the soil during rain events. There were mid channel bars caused by woody debris, lawn cuttings and trash. Utility corridors and low head dams where corridor encroachment had occurred due to the lack of a riparian buffer which has lead to severe bank erosion of 2-3 feet per year. Swans Creek has 30 foot cuts and the extreme erosion has almost buried the stream. Every time there is a storm event all the soil is mobilized. Depositing of eroded soil and sedimentation are filling in the estuary.

MACTEC recommends several steps to increase the stormwater retention volume and detention time to prevent further sedimentation in Quantico Bay. Legacy stormwater retention ponds were designed to discharge at a “2 year storm rate” unfortunately streams are shaped by 1 ½ year storm rates so that all the existing retention ponds are shaping our creeks and streams. So the most basic recommendation is that the on-site stormwater capture and retention needs to be beefed up to slow the discharge rate and capture the first flush pollutants. The older holding basins do not do that, but are nonetheless in compliance with the design standards that were in effect when they were built. Larger basins could slow the flow, provide wildlife habitat and increase groundwater infiltration and recharge.

Open channel recommendations were the other major area that MACTEC felt needs to be addressed. These include infrastructure repair, debris removal channel restoration or enhancements, riparian buffer restoration and finally preservation and monitoring of the enhancements. Overall, MACTEC identified 30 open channel problems and 16 stormwater basin maintenance problems in the 6 sub-watersheds and estimates that these improvements and repairs will cost $15.7 million. Stabilizing the stream beds to slow the catastrophic erosion rate of 2-3 feet per year to a more natural erosion rate in the area of Prince William Estates and Dewey’s Creek is the only way to ameliorate the rate of sedimentation in the Quantico Bay. The only way to restore the bay would be first to stabilize the up-stream stream beds and then dredge the bay. While a certain amount of erosion is entirely natural and is part of the natural cycle, development, pavement, destruction of the riparian buffers have resulted in extreme erosion.

Most of the repairs recommended by MACTEC are to address the open channel problems and will have to be maintained and monitored. These are the costs to address just one of the ten watershed basins in Prince William County Virginia. estimating total costs for the entire county from that number is hundreds of millions of dollars. In thinking about how to finance and maintain theses improvements, credit trading and sale of credits for the EPA mandated TMDL seems one source (beyond a direct surcharge tax on property) for funding these improvements. If these types of improvements could be quantified within the Chesapeake Bay Model modules for compliance with the TMDL targets there might be a way to fund some of these activities without resorting to command and control regulatory model so popular to the north of us. Unlike MS4 (municipal separate storm sewage system) and waste water treatment plant permits which have measured results that can be traded, these would have to be given “model credit” for open channel recommendations, on-site stormwater capture and detention etc. if they are to be traded, but like farm BMPs are probably low lying fruit. It might be possible to utilize the Scenario Builder within the Chesapeake Bay model to generate simulations to quantify watershed restoration.

Local Stormwater Management in the Chesapeake Bay Watershed

Winter is coming and so the woods on the back seven acres of my land are easily accessible and I can walk to the stream behind my house. My intension was simply to collect the trash that accumulated in the area since spring, but I am bothered by the erosion I observe in the stream bank. It is not noticeably different from the spring, but certainly there has been some impact to the area and I can only guess it is from paving the road in my neighborhood. It is a private road about 2 miles long that is maintained by the 34 property owners who live in our neighborhood. During big storms it is clear that the stormwater runoff is inadequately controlled by the ditch that runs along side the road and terminates on the crest of the hill down to the stream. Yet, the challenge is to get a group of rugged individualists to spend money to address a problem only two homeowners see and care about.

It is my understanding the road was built by the developer of the lots in 2004. I bought my home from a bank in 2007 so I rely on information from my neighbors. Stormwater management for the development of the road and for the road itself was not regulated within the rural crescent (the area within Prince William County that requires 10 acres per home with some limitations and loopholes). On January 29, 2005 Virginia Soil & Water Conservation Board & Department of Conservation & Recreation responsible for municipal separate stormwater sewage systems, MS4s, and Construction General Permits for stormwater. The DCR did not issue regulations until December 9, 2009 when they adopted the Final Regulations Parts I, II, and III Virginia Stormwater Management Program (VSMP) Permit Regulations, but then just over a month later on January 14, 2010 the DCR suspended the regulations and convened hearings.

Though the DCR retains regulatory responsibility for the MS4 and Construction and General Permits for managing storm water, localities with MS4 permits and localities within the Chesapeake Bay Protected Area must adopt a local stormwater management programs to comply with the requirements of the Chesapeake Bay Act and the US EPA mandated TMDL. These elements will have to be incorporated in to the environmental chapter for the Prince William County comprehensive plan. Part of the challenge is to have the plan or requirements reach in a reasonable manner the stormwater management of our community and other communities like us. To meet the requirements of the EPA TMDL we need to reduce nutrient pollution from all existing sources, not just ban new development and increase regulation on point source polluters. Though I do not know if it will be reasonable, the obvious solution is to tie obtaining permits to maintain and repave the road with installing stormwater best management practices, BMPs, to ameliorate the excessive flow of water during storms.

Natural systems like our land and stream respond to runoff volumes, frequencies, durations and temperatures. Even though “pollutant” is defined broadly by the EPA in the Clean Water Act to include virtually every imaginable substance added to surface waters, including heat, it does not include water volume. A more straightforward way to regulate stormwater contributions to the Chesapeake Bay Watershed impairment would be to use flow or possibly something like impervious cover, as a measure of stormwater loading and then require BMPs based on the amount of pavement. Flow of stormwater is easier to monitor, model, and even approximate rather than the complicated modeling of the loadings of individual contaminants in stormwater effluent. Using BMPs to simply reduce stormwater flow will automatically achieve reductions in pollutant loading. Moreover, flow is itself responsible for erosion and sedimentation that is damaging our streams and rivers within the watershed.

Municipal Separate Storm Sewer Systems

The federal 1987 Water Quality Act (WQA) was an amendment to the Clean Water Act, requiring that EPA issue National Pollutant Discharge Elimination System (NPDES) permits for storm water discharges that were permitted prior to February 4, 1987, or associated with industrial activity, or from Municipal Separate Storm Sewer Systems (MS4s) serving a population of 100,000 or more, or judged by the permitting authority to be significant sources of pollutants or which contribute to a violation of a water quality standard.

The storm water program also includes a Phase II, which phased in regulation of some smaller dischargers than previously regulated. These regulations require storm water permits by March 10, 2003 for numerous small MS4s, construction sites of one to five acres, and industrial facilities owned or operated by small MS4s which were previously exempted under the Intermodal Surface Transportation Efficiency Act. Until now only a portion of the small MS4s have been regulated under Phase II.

The universe of small MS4s is quite large since it includes every storm water collection system in every community except for those medium and large MS4s regulated under the first phase of the storm water program. There are thousands of them. Only a portion of small MS4s have been regulated d by the Stormwater Phase II Final Rule, either by being located near an urban area having high population density or designation by the NPDES permitting authority because the MS4 or drainage ditch discharges to sensitive waters.

As was stated in Executive Order 13508 -Strategy for Restoring and Protecting the Chesapeake Bay Watershed Public Comment Response dated May 12, 2010: EPA will initiate rulemaking to increase coverage and raise standards for CAFOs, municipal stormwater, and new dischargers of pollution. The EPA representative at the Public Hearing in Annandale, VA stated that EPA expects that it will promulgate new Chesapeake Bay specific regulations expanding the reach of MS4 point source regulations to ensure compliance with the total maximum daily load, TMDL, numerical limit imposed by EPA.

Polluted stormwater runoff is commonly transported through Municipal Separate Storm Sewer Systems (MS4s), from which it is often discharged untreated into local water bodies. To prevent harmful pollutants from being washed or dumped into an MS4, operators must obtain a NPDES permit and develop a stormwater management program. In the smallest MS4s a stormwater management program consists of modest activities like education, best management practices, BMPs to control flow and run off.

On December 28, 2009, EPA issued a Federal Register Notice announcing EPA's initiation rulemaking to strengthen its stormwater program. EPA is now soliciting input on potential rules and regulations relating to the Chesapeake Bay watershed, with several public “listening sessions” to be held in October and November 2010, and an interactive Webcast scheduled for November 16, 2010, 1 p.m. to 4 p.m. EST, Visit http://www.epa.gov/npdes/stormwater/rulemaking to register to participate in the Webcast.

The intent of the new regulations is to control and manage stormwater discharges not currently regulated that are causing or contributing to water quality impairments in the Bay watershed. That is pretty much every drop of stormwater in the Chesapeake Bay watershed. This would require additional measures, such as BMPs and change in flow patterns targeting ( but not limited to) nitrogen, phosphorus, and sediment in the Chesapeake Bay Watershed, According to the Federal register these rules would require the retrofit of stormwater controls for existing developments; and applying specific performance standards to discharges from new and retrofitted stormwater systems within the watershed. EPA is also seeking input on whether to consider specific evaluation, tracking, or reporting elements.

That modest announcement will probably impact all homeowners throughout the Chesapeake Bay watershed. The success of any changes in stormwater regulations in protecting the environment will depend on notification of and the compliance of individual homeowners, homeowner associations and communities. For the individual homeowner the regulations will have to be clear, fair and easily understood by a layman reading them and county and community staff will have to be informed and informative. Compliance with the regulations will suffer if no one is ever aware of them, the building department will issue roadwork permits with out ensuring compliance with MS4 regulations or the regulations are, or are perceived, to be excessively costly or burdensome and without environmental benefit.