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Citv of Nashua, Public Works Division
i f
Board of Public Works Meeting Date: December 29, 2016
Noelle Osborne, Operations Supervisor
Wastewater Department
Wet Weather Facility Evaluation
To approve a contract to Wright Pierce for professional services for a complete
evaluation of the wet weather facility in an amount not to exceed $35,100.
Funding will be through: Department: 169 Wastewater; Fund: Wastewater;
Account Classification: 53 — Professional & Technical Services.
Wright Pierce Scope of Work and Fee.
The Nashua Wastewater Treatment Facility (NWTF) has a Wet Weather
Treatment Facility (WWTF) that treats high flow conditions during storm
events that are in excess of the design capacity of the plant. The WWTF was
constructed and put into operation in 2009. This facility only operates when
flows exceed 5OMGD to the main plant, causing very infrequent operation.
The facility can run an average of 10 times a year for a brief period of time
(less than 12 hours at a time, depending on the storm flow). With infrequent
operation, it is difficult to test, trouble shoot and determine appropriate
corrections. Over the years the operational components have failed to work
worked properly. The EPA has recently stated to the City that they do not
consider our Consent Decree for CSO abatement complete until this facility is
fully functioning. Since the WWTF is complex and has many processes
ongoing when in operation, it needs to be evaluated by a qualified engineering
firm to determine the appropriate corrective action.
In addition to operational difficulties, there has been an overflow at a manhole
outside of the WWTF for 2 consecutive years. This manhole is for an
incoming interceptor and has an inner diameter vortex in it that is suspected to
not be able to handle excessive flows, causing a backup to ground surface.
The NWTF would like to use the services of Wright Pierce to evaluate our
ongoing issues with this facility. The intent is for them to begin by looking at
the design of the facility and evaluate the influent flows and hydraulics of the
interceptor vortex. From there, the City will determine what the appropriate
next stage will be and how to best approach the WWTF evaluation. Wright
Pierce has been used for numerous projects at the NWTF over the past 5 years.
They have a good understanding of the entire plant and are well qualified to
evaluate and provide the corrective actions needed.
Wright Pierce has provided a total cost of $35,100 which the City proposes to
