Sub-Regional Operating Group
Glendale, Mesa, Phoenix, Scottsdale, and Tempe, Arizona
The Sub-Regional Operating Group (SROG) is a five-city partnership formed to facilitate the
joint ownership and operation of a wastewater conveyance and treatment system in the Phoenix
metropolitan area. The cities of Glendale, Mesa, Phoenix, Scottsdale, and Tempe are party to
this partnership, which applies to a jointly owned regional wastewater treatment plant (WWTP)
and two major interceptors. These two interceptors, Salt River Outfall (SRO) and Southern
Avenue Interceptor (SAI), run parallel, east-west collecting wastewater to be ultimately
conveyed to the regional 91st Avenue WWTP, located in the southwest corner of the Phoenix
area. The SRO and SAI interceptors are each over 20 miles long with pipe sizes ranging from 48
to 90 inches in diameter. As a result of wastewater temperature, travel time, and development,
the numbers of odor complaints are rising from residents near the interceptors. SROG conducted
odor studies for both interceptors in the year 2003. The studies recommended implementation of
odor control facilities to exhaust and treat the headspace foul air at several locations along the
interceptors. Odor control measures are in the concept stage and have not yet been implemented.
In recent studies, between 2005 and 2007, SROG has identified hydraulic capacity limitations in
the SRO and SAI interceptors that may compromise their conveyance efficiency under both dryand
wet-weather conditions. A study is currently being conducted to identify regional
municipality specific solutions to manage the interceptor capacity issues. The solution is
anticipated to include a combination of measures aimed at reducing inflow and facilities that will
permit a controlled discharge of wastewater into the interceptors. As a result, a relatively steady
wastewater flow is expected to be achieved in the interceptors. This new flow regime and its
impact on pipe headspace air volume are discussed in the paper.
Wastewater flow variations in a sewer pipe go accompanied with fluctuations of the headspace
air volume. These volume fluctuations increase the potential for sewer headspace pressurization
during wastewater level rises, increasing the potential for odor release out of the interceptor
(sewer out-gassing). The paper concludes that wastewater and rainfall derived inflow and
infiltration (RDII) management programs, typically focused on optimizing the hydraulic capacity
of collection systems, should be expanded to include an assessment of their impact on odor
release potential along the collection system. Odor generation and headspace air transport
modeling should be run in parallel with the system hydraulic model so that appropriate decisions
can be made to solve sewer pipe flow capacity and odor release issues in a concerted effort.
Metric Used:
Posted: May 3rd, 2011 | Filed under: >1M, Sanitary Sewer, Waste Water Treatment | Tags: Improved Air Quality, Improved Customer Relations, Maximize Collection System Performance, Reduced Odors | 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.
Metric Used:
Posted: August 24th, 2010 | Filed under: Stormwater | Tags: Decreased Pollutants, Improved Air Quality, Improved Stormwater Management, Recharge Groundwater, Reduced Runoff | No Comments »