Philadelphia Water Department (PWD)
The Philadelphia Water Department (PWD) is currently evaluating the implementation of
various combined sewer overflow (CSO) control alternatives. This includes traditional
engineering approaches that rely on physical infrastructure (e.g., building large diameter
tunnels), as well as more “natural” approaches that rely on “green infrastructure” techniques
(e.g., vegetated bioswales, permeable pavement).This report provides a Triple Bottom Lineoriented
benefit-cost assessment of the CSO control alternatives under consideration by PWD.
The focus is on the benefits and external costs of the alternatives. The key finding of this report
is that the green infrastructure approaches generate a broader and more valuable array of
environmental, public health, and social benefits than do traditional CSO control strategies.
Benefits of green infrastructure evaluated and monetized include: Improved recreation
opportunities, increased property values, reduced heat-stress related fatalities, improved air and
water quality, green jobs, reduced energy use, and reduced disruption due to construction and
Posted: May 20th, 2011 | Filed under: >1M, Sanitary Sewer, Stormwater, Waste Water Treatment, Water Treatment | Tags: Combined Sewer Overflow (CSO) Control, Environmental Impact, Green Infrastructure, Improved Customer Relations, Improved Public Health, Improved Stormwater Management, Low Impact Development, Permeable Pavement, Plant Sustainability, Rain Gardens, Vegetated Bioswales | No Comments »
The past five years has seen a renewed interest in the use of stormwater best management
practices (BMPs) that incorporate vegetation and/or are designed to mimic the functions
provided by the natural vegetative cover. A variety of terms (e.g., green infrastructure, low
impact development) are used to describe this wide range of BMPs, but the common
denominator is that they all reduce the total annual runoff volume using rainfall interception, soil
infiltration, evaporation, transpiration, engineered infiltration, and/or extended filtration. This
paper explores some of the recent state and local approaches toward using these practices,
collectively referred to here as green stormwater BMPs.
The concept of using green stormwater BMPs to reduce and treat stormwater runoff is not a new
one. The recent interest in these BMPs is perhaps a result of the realization that the conventional
approach has not been successful in terms of improving the quality of our receiving waters and
achieving pollutant reduction and ecological restoration goals. It may also be due to the
realization that green stormwater BMPs provide so many secondary benefits, such as air quality
improvement, regulation of air temperature, aesthetic appeal, and wildlife habitat.
Even where interest in these BMPs is high, actual application of green stormwater BMPs has
been somewhat limited by barriers such as conflicting local code and ordinance language,
skepticism about new approaches by developers and local officials, and a lack of technical
guidance or good data on performance. The latest approaches taken by communities to “green”
stormwater begin to address some of these barriers and seek to promote better stormwater design
and management. The following three strategies are summarized in this paper, and are
supplemented with specific examples from around the country:
1. Adopting new stormwater criteria that focus on runoff reduction
2. Developing credit systems that provide incentives for using green stormwater BMPs, and
3. Improving BMP designs to increase pollutant removal performance
Several east coast states are leading the charge to promote green stormwater BMPs for
stormwater treatment using a runoff reduction approach. The states of Georgia, Virginia, and
Delaware are all in the process of revising their stormwater regulations and/or design manuals
and are highly interested in promoting the concept of natural systems for stormwater treatment.
A brief overview of this approach and status of the work in each state is provided in this paper.
A number of states and local governments have adopted stormwater credit systems as part of
their stormwater management programs that encourage the use of green stormwater BMPs by
reducing the size and cost of structural BMPs needed based on the runoff reduction or pollutant
removal benefits provided by green stormwater BMPs. Although the details of each system vary,
the most effective credit systems specify minimum criteria to be met to be eligible for the credit,
and provide simple guidance on how to calculate the credit. These credit systems directly
translate into cost savings to the developer by reducing the size of storm water storage and
conveyance systems required. Some examples of innovative stormwater credit systems from
around the country are described in this paper.
The current menu of stormwater BMPs is not capable of reducing nutrients and other pollutants
to urban land targets for pollutant loads in the Chesapeake Bay watershed and other regions of
the country. There are several reasons why communities get such modest pollutant reduction
from the stormwater BMPs they require at new development projects. For example, they often
accept BMPs that have low or negligible removal rates on a significant proportion of their
development sites, they do not encourage green stormwater BMPs because they lack detailed
design criteria or defined pollutant removal rates, and the BMPs used often achieve lower
performance than expected due to poor design, installation or maintenance of practices in the real
world. Two recent initiatives to improve pollutant removal performance through enhanced BMP
design are described in this paper.
Posted: August 24th, 2010 | Filed under: Stormwater | Tags: Decreased Pollutants, Improved Air Quality, Improved Stormwater Management, Recharge Groundwater, Reduced Runoff | No Comments »