Urbanizing watersheds across the Northeast can have a major problem with too much water entering the supply source from all the wrong places. Instead of precipitation recharging groundwater and surface water supplies, it gets routed over paved surfaces and enters as stormwater. So it has been for Pennichuck Water Works (PWW) Corporation, an investor owned utility that supplies drinking water to the communities of Nashua, Amherst, Merrimack and Milford, NH among others.

One of the primary challenges in urbanized watersheds is trying to undo damage that may have started more than 50 years ago, as it did in the Pennichuck brook watershed that was occupied by a major arterial roadway that brought intense development years ago.


Pennichuck Water Works Corporation has been working hard over the last 15 years to overcome the impacts of urbanization by using Low Impact Development (LID) techniques with both new and redevelopment projects. One challenge has been encouraging developers and their engineers to use better development techniques such as biofilters and porous asphalt, so a demonstration project was borne.

Working with the owner of a 2-acre commercial mall next to Pennichuck Brook, CEI assisted PWW in creating a demonstration project at the aptly named “Pennichuck Square” containing a dozen retailers and occupying nearly all of the    2-acre site with impervious roofs and asphalt. Construction took place during the Summer of 2005 and took approximately 5 weeks. CEI was able to design a construction schedule to meet the business owners’ needs while completing the project on-time and on-budget.

CEI used multiple LID elements, including a large biofilter, raingardens, a wet pond and dry wells for roof leaders and leaching catch basins for areas that commonly flood. As a result, stormwater runoff from the site has been reduced by 88%, nearly eliminating pollution into the brook from the site and instead treating and recharging water through natural cleansing. A side benefit was reduced flooding for the landowner and the resident businesses.