20051216 Ver 2_More Info Received_20100517

JMcGM
A S S O C I A T E S
May 12, 2010
Mr. Ian McMillan
401 Permitting Unit
1650 Mail Service Center
Raleigh, North Carolina 27699-1650
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MAY 17 2010
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NIETi M AW STORWATU SRII O
RE: 401 Water Quality Certification
East Yancey Water and Sewer District
Sewer System Improvements
Yancey County, North Carolina
Dear Mr. McMillian:
This letter is a response to a request for additional information on the above referenced
project, received on April 12, 2010 from Roger Edwards, Regional Supervisor in the North
Carolina Department of Environment and Natural Resources Asheville Regional Office
(DENR-ARO). Yancey County has requested that we respond to the Department's letter. The
request for additional information comes from the suggestion from the North Carolina Wildlife
Resources Commission to utilize horizontal directional drilling (HDD) techniques for the creek
crossings in the East Yancey project. McGill Associates constantly evaluates the use of this
technology for all projects involving stream crossings. We would like to take this opportunity
to explain the reasons this technique is not appropriate for these sites with the current state of
the HDD industry and equipment.
While Horizontal Directional Drilling has been utilized by other industries such as
telecommunications and gas for some time, it has a shorter history with other types of utilities.
McGill Associates has utilized HDD for the installation of water lines and force mains under
creeks and rivers for some time, when the topography and other conditions are appropriate. It
certainly can have a lessened impact from a land and waterway disturbance standpoint with the
added benefit of streamlining the permitting process. It has become our standard installation
method for projects in which the pipe is under pressure and grades are not critical, such as
water and sewer force mains.
Without question, where appropriate and reasonable, horizontal directional drilling can
lessen the impact to stream bottoms and banks. But there are other impacts associated with
HDD that can be detrimental to streams. A crossing with HDD requires excavation of both a
launch pit and receiving pit. Depending on depth and terrain, both these pits can be large and
deep, requiring the stockpiling of excavated material adjacent to the stream. While proper
erosion control measures can minimize any issues, a large storm event with a mound of soil
material next to the stream has the potential to create a larger sedimentation problem than a
properly installed conventional creek crossing. A conventional creek crossing has an impact
E n g i n e e r i n g P l a n n i n g F i n a n c e
McGill AAsociale.S'. P.A. - P.O. Box 2259. Asheville. NC 28802 - 55 Broad Slreel. Asheville, NC 28801
S28-252-0575 - Fax: [phone]
Mr. Ian McMillan
May 12, 2010
Page 2
only on the width of the work area necessary for the pipe installation. In addition, the actual
work time involved in working adjacent or
in the creek can be significantly less for conventional installation techniques. Due to the flow
characteristics of both Little Crabtree Creek and Ayles Creek, any minor sedimentation
problems will quickly be dissipated.
Unfortunately, current HDD equipment is limited in the ability to maintain a uniform
alignment and grade. Even the most expensive drilling equipment has difficulty keeping the
pipe alignment of the pilot bit straight with minimum deflections, especially in less than ideal
conditions. And even with a relatively straight pilot bore, the reaming and pullback operation
is easily deflected off course, creating dips and valleys in the final pipe alignment. These
issues are well known within the field and have been noted on many projects. Obviously, pipe
deflections are not a problem with pipes under pressure, but with gravity sewer line this leads
to solids deposition pipe blockages, and eventually, sewer overflows. Since the sewer lines in
question are adjacent to water bodies, this is a public health concern and a maintenance issue
for those responsible for the sewer system.
Because of the difficulties mentioned, attempts to install gravity sewer by HDD are
generally limited to areas where soil conditions are known and better suited for drilling and
maintaining alignments and grades and also where gravity sewer line grades are 2 percent or
greater, allowing for some fluctuation of the pipe and still maintaining flow. Rocky conditions
and areas where there is the presence of both soft and hard materials in the bore are the most
likely to create problems. Case studies in the past by trenchless technology societies and
utilities have shown that gravity sewer line installations under poor conditions are likely to not
be successful.
Our soil conditions on the East Yancey project are typical of many mountain locations,
which are either solid rock, `cobbles' (small to medium loose rocks) or a mixture of both.
Also, due to grade issues, most all of our creek crossings are less than 1 percent grade. Both
of these factors make an attempt to install gravity sewer by directional drilling likely to fail
and a poor construction approach.
HDD sewer line installation in this type of environment will likely result in failed
attempts which would then have to be installed as a conventional installation. The resultant
delays for permitting, all while the Contractor is on the project and stopped from working, is
impractical from a contract administration standpoint.
Another difficulty with HDD pipe installation where grade is so critical is the cover
requirements. On past projects, when using HDD for water or sewer force main installation,
both U.S. Fish and Wildlife Service and North Carolina Wildlife Resources Commission have
requested that the utility line be installed up to 30 feet below the creek or river bed due to
concerns about `frac outs', which is drilling fluid escaping through rock crevices into the
Mr. Ian McMillan
May 12, 2010
Page 3
water flow. While we have considered the risks minimal and the depth requirements excessive
at times, McGill Associates has attempted to maintain significantly more depth for HDD
projects than with conventional installation techniques. This is obviously an issue for gravity
sewer line and in the case of the East Yancey project, extra depth requirements cannot be
obtained and maintain gravity sewer flow for the rest of the project.
Other alternatives that were considered for the project but were rejected for various
reasons include the following:
• Siphons are used for creek and river crossings but require a high, sustained
flow to maintain the siphon. Flows for the East Yancey project are going to be
small at first and no large-scale growth or increase in flow is expected in the
future to allow the use of siphons.
• Traditional bore and jack installation of encasement pipe such as used under
highways will not work under creek crossings for the same reasons as HDD -
rocky conditions preventing a successful installation. There is also the additional
factor to boring under a water body risking creating a route for the stream flow
to divert into the bore hole, risking the safety of the contractors and damaging
the creek bottom.
• Micro tunneling or rock bores are an extremely expensive technique, usually
reserved for pipe installation in congested urban settings. In addition, all the
safety concerns and threats to the stream bed that apply to traditional bore and
jack techniques, also apply to this method.
• Aerial crossings have been used in the past, allowing most of the construction to
be done outside the waterway. However, grade issues, the higher risk of aerial
pipes during flooding and the increased maintenance of the crossings required to
keep them free of debris eliminate their use for most of this project.
• Pump stations may be used to eliminate water crossings. However, 15 pump
stations are unrealistic from a public health risk, cost, and maintenance
standpoint.
After multiple internal meetings on this subject, which included project engineers, field
personnel, and the input of Forrest Westall in our office for guidance on regulatory issues,
McGill Associates believes that permitting the gravity sewer line crossings as sub-aqueous
crossings, installed by conventional construction methods and current best management
practices for erosion and sedimentation control is the best alternative at this time. We
continually monitor new technology in the construction industry and look forward to the time
techniques are developed that will allow us to avoid working in the water for crossings. That
will both reduce the impact on the habitats and simplify the approval process greatly.
Mr. Ian McMillan
May 12, 2010
Page 4
We hope this answers any questions about why horizontal directional drilling is not a
viable alternative for this project. If there are any further questions on the project, please
contact our office at any time.
Sincerely,
McGILL,
TES, P.A.

Technician
cc: Nathan Bennett, Yancey County Manager
Roger Edwards, Regional Supervisor, Asheville Region, DWQ
Chuck Crawford, Surface Water Protection Section, Asheville Region
Dave Baker, US Army Corps of Engineers
Bryan Tompkins, US Fish and Wildlife Service
Dave McHenry, NC Wildlife Resources Commission
Harry Buckner, PE, McGill Associates, P.A.
Randy Hintz, PE, McGill Associates, P.A.
Forrest Westall, PE, McGill Associates, P.A.
01743/collection system/letters/iml2may10_401 Cert.doc