Storm Water – Kevin D.

Stormwater Infiltration in the Planning Process—Perilous Pitfalls

For any land development project, proper collection, conveyance, and treatment of stormwater runoff is essential to minimize the impacts of increased stormwater flows and pollutant loads that result from conversion of natural, vegetated land to hard surfaces, such as roads, parking lots, and building rooftops.  With the advent several years ago of NYSDEC’s requirement for development projects to reduce the volume of runoff generated by the 90% occurrence rainfall event after construction completion, the “runoff reduction volume” (“RRv”), through implementation of green stormwater infrastructure (“GSI”) practices that utilize treatment methods including infiltration into underlying soils, evaporation, and plant uptake, stormwater management practices (“SMPs”) such as infiltration basins, bioretention areas, and drywells have experienced increased utility. 

As an environmental engineer routinely involved in reviewing stormwater pollution prevention plans (“SWPPPs”) for proposed development projects, when I see infiltration SMPs proposed, alarm bells ring in my head!  It’s not that infiltration SMPs do not effectively remove pollutants from stormwater and recharge groundwater.  When properly implemented design, construction methods, and maintenance are utilized, they are fantastic for stormwater treatment, however, there are numerous potential pitfalls in such proper implementation.  NYSDEC has rigorous design requirements for infiltration SMPs to promote effective stormwater treatment, including soil infiltration rate testing, soil characterization, pre-treatment requirements, and separation distance from seasonally high groundwater or bedrock.  Construction methods need to ensure that the soils underlying an infiltration SMP are protected and not compacted by construction equipment or clogged through use as sediment basins during construction.  Long-term maintenance practices, including maintaining vegetative growth in bioretention areas, removing decaying plant matter and trash, and sediment removal from pre-treatment areas are essential for infiltration SMPs to remain perpetually effective.   

Due to the myriad of potential pitfalls, whenever I review a SWPPP for a proposed development as part of the SEQR process here in New York State and see infiltration SMPs proposed to achieve RRv and treat stormwater, I analyze the soil testing, design, proposed construction methods, and proposed long-term maintenance with a fine tooth comb.  All too often, I find improper soil testing techniques used, failures to meet NYSDEC’s design standards, and absolutely no plan for long-term maintenance, all of which are pitfalls that can lead to infiltration SMPs failing and our precious waterways degrading through increased stormwater pollution loads.

Kevin Draganchuk, P.E., BCEE

President and Principal Engineer, CEA Engineers, P.C.

Board Certified Environmental Engineer – Water Supply and Wastewater Specialty

Phone: 845-372-9674