Coastal areas are particularly vulnerable to pollution. Streams, tidal flats, wetlands, and shore waters form a rich, but sensitive, ecosystem, and man-made pollution can have devastating effects on the life forms that inhabit that coastal zone. One of the biggest threats to that coastal web of life is simple runoff — stormwater that falls on roofs, lawns, or roads, then flows into sewers and makes its way to streams or directly into the ocean. Ordinary road runoff is bad enough — tainted with gasoline, oil, brake and transmission fluid, metals, and other toxins. But even worse is the problem of "combined flows." In many municipalities, stormwater shares a pipe with sewage; when there's a lot of rain, sewage treatment plants are overwhelmed and raw, untreated sewage overflows into the local waterways or into the ocean. New York City, Washington, D.C., and many other East Coast cities are plagued by sewage overflows. "New York's system — like those in hundreds of others cities — combines rainwater runoff with sewage ... New York’s sewage system overflows essentially every other time it rains," the New York Times reported in November of 2009 (" As Sewers Fill, Waste Poisons Waterways," by Charles Duhigg). Smaller cities are also prone to the problem: on December 13, for instance, Fox TV's Channel 10 in Mobile, Alabama ran a short, routine report about a rainstorm that sent more than 12,000 gallons of raw sewage into the Bayou le Batre (" Heavy rainfall causes sewage overflows," by Blanton Box). As development eliminates more and more acres of natural landscape and replaces soil and vegetation with urban "hardscape" (roofs and paving), the runoff and sewage overflow problem grows more intense. In response, states and communities are moving to require a new approach to stormwater — an approach that seeks to detain rain on the site where it falls and allow the water to seep into the earth, as it would in an undisturbed natural landscape. Called "Low Impact Development" or "Environmental Site Design," the advanced method relies on technologies such as permeable paving and natural "rain gardens" rather than on catch-basins and pipes. Maryland passed legislation in 2007 requiring all new development and construction to apply Environmental Site Design methods, according to a state website; final regulations to implement the policy were published in May. And while Maryland is a leader in the Low Impact Development arena – Prince George's County, Maryland, created the first comprehensive manual for the technique (9 MB PDF download) -- other states are moving the same way. North Carolina, for example, also has new stormwater regulations for coastal sites which require stormwater to be contained and managed on site. To manage rainwater on site, one of the prime tools in the builder's or developer's toolkit is "pervious" or permeable paving. Whether made with poured concrete, asphalt, or pavers, permeable paving systems allow rainwater to flow through and percolate into the ground, instead of flooding into sewers. In fact, the porous materials don't just permit flow: microbes and funguses that grow within the pores of the material and in the gravel sub-base are able to capture and break down many pollutants, helping to purify the rain and runoff before it passes into the local groundwater. The storage and slow release of the water evens out local stream flows, preventing flooding and "scouring" during rain events, while slowly feeding the streams so that they don't dry out between storms — thus maintaining the natural, pre-development stream environment. The US EPA has installed three types of pervious paving at an EPA facility in Edison, New Jersey, and plans a long-term study of the system's performance. Scientific American covers the Edison test (" EPA tests porous pavement to combat contaminated rain runoff," by Larry Greenemeier), and the Agency has published an official statement on the project (" EPA's New Green Parking Lot Allows Scientists to Study Permeable Surfaces That May Help the Environment"). But there's already plenty of data about the performance of pervious materials — enough that authorities are starting to consider it as a first-line option for builders and developers. In South Bethany, Delaware, for instance, city officials are looking at pervious concrete as one acceptable means to satisfy a new town requirement for permeable landscaping for homes near the beach, reports the Bethany Coastal Point (" New concrete type gets perking in South Bethany," by Monica Scott). Pervious concrete's water-draining capacity is impressive. In this YouTube video, a demonstration parking lot at the University of New Hampshire drinks down 1500 gallons of water in under two minutes. As more and more concrete companies get trained on the technology, pervious concrete is becoming more widely available. And the material itself is advancing, according to engineer Matt Offenberg of Rinker Materials (a major supplier of concrete admixtures). On his blog, Offenberg says that with the use of appropriate admixtures to enhance the mix, pervious concrete is evolving from a "lumpy, sticky paste" with "little workability" into a "flowable, workable, slump-able material (" Modern Vs. Meatball Pervious Concrete"). In this YouTube video, workers place a mix stiffened with Forta Corporation's "GreenNet" reinforcing fiber admixture. For more information on pervious concrete, check out the website of pervious concrete specialists PCI Systems, LLC, and take a look at the pervious concrete section of concrete industry website concretenetwork.com.