April 21 2016 Page z
20160421 Ph Nl Stage lf LFG Prapasal (revised).dacx 3066,06
Task 2 Dewatering System Conceptual Design
For Task 2, Sanborn Head will prepare a conceptual design and an opinion of cost for
removing liquid from LFG extraction wells in the closed, unlined landfill as well as Phases I
and II of the active, lined Jandfill. We understand that the City will be providing liquid level
measurements from the existing LFG wells for our review. We envision that the liquid
removal system will be composed of a series of submersible, air-powered pumps installed
in the wells and connected to force main pipes that discharge to leachate collection system
(LCS) risers along the perimeter of the lined landfill. Considering the number of wells
(some of which may be replaced or extended as the active Jandfill is Filled) and the potential
volume of liquid to be removed, a manifold system with quick disconnects will be designed
to provide compressed air to the pumps and connections to a drain for the pump discharge.
The design will include a dedicated pump for each well.
As part of this task, Sanborn Head will evaluate the existing air compressor located at the
Landfill Gas-to-Energy (LFGTE) facility to assess its potential in supporting the dewatering
system. The evaluation will include the air compressor and air drier (needed to limit
potential for freezing of the distribution lines), and power requirements for the electrical
equipment.
The conceptual design of the dewatering system will be presented on engineering drawings
provided electronically to the City. The engineering drawings will illustrate the air
compressor and drier layout, the manifold systems for the compressed air and liquid
discharge lines, and details that depict the pipe installation and connection details. In
addition, the design will include modifications to the LCS risers and to the well risers to
accommodate the following components: (i) LFG control wellhead; (ii) liquid removal
pump; and (iii) pneumatic liquid head monitor. The pneumatic liquid head monitor
provides a means to measure the head of liquid in the extraction well without disabling the
extraction oy pumping system. Technical specifications for materials and equipment will
be presented on the engineering drawings, and an opinion of cost based on the conceptual
design will be provided to the City.
We propose a conference call with the City as part of this task to discuss the design of the
dewatering system, opinion of cost, and steps for moving forward should the City elect to
proceed.
Task 3 GCCS Expansion in Phase li, Stage 0
Under this task, Sanborn Head will work with the City to design the next expansion to the
GCCS in Phase II, Stage II of the active landfill, We understand, based on discussions with
you, that the design is likely to include six new LFG collection trenches, one surface LFG
collection trench, and associated lateral conveyance piping and connections to the existing
GCCS. We anticipate our services to include the preparation of construction-level
drawings, technical specifications, bid item definitions, an opinion of cost for the project,
and a New Hampshire Department of Environmental Services (NHDES) Type II Permit
Modification application form with a narrative describing the proposed construction. The
drawings will be signed and sealed by a professional engineer licensed in the State of New
SANBORN |) HEAD
