FFB_Sewer_Service_Report_Memo.pdf

Fairbanks Federal Building Sewer

To: Mike Heidenreich, ECH Architecture, P.S. 3900 Arctic Blvd., Suite 204 From: Matt Stephl, P.E. Anchorage, Alaska 99503 Subject: Sewer Service Condition and Trenchless Repair Ph: 907-562-1468 Project: Fairbanks Federal Building (FFB) Sewer mstephl@stephleng.com Date: September 27, 2017

SECTION 1

PURPOSE AND BACKGROUND

Purpose The purpose of this memorandum is to describe the condition of the sewer pipes serving two federal government buildings in Fairbanks and to provide recommendations for trenchless pipe repairs where appropriate.

Background The General Services Administration (GSA) operates two buildings in Fairbanks called the Fairbanks Federal Main Building (FFB Main Building) and the Fairbanks Annex Building (FFB Annex). The buildings were constructed in 1979. The FFB Main Building has three floors as well as a partial basement level.

There are no known problems associated with the FFB Main Building sewer. The sewer line from the FFB Annex is tied into an old wooden stave drain from the WWII Army base days. The FFB Annex sewer line does not drain properly, freezes every winter and has backup problems. The two sewer lines come together in a manhole (named MH-2) at the northwest corner of the property and thereafter discharge into the Fairbanks sewer system.

SECTION 2

EXISTING PIPE CONDITION

Pipe Inspection and Survey Method A closed-circuit television (CCTV) inspection of the two project pipes was completed on September 21, 2017 by Alaska Stormwater Maintenance, Inc. Richard Bailey with Stephl Engineering LLC was at the site during the inspection work. A video recording of the inspections was completed. The video data is provided as an attachment to this report.

Stutzmann Engineering Associates, Inc. staff were tasked with completing a survey of the project site and the two project sewer pipes. Their survey staff were at the site during the CCTV inspection work. A sonde transmitter was attached to the CCTV camera. The sonde used on this project was a miniature transmitter that was battery operated and omitted a specific frequency that the above-ground locator could receive. As the camera and sonde traveled along the sewer pipe, the receiver equipment was used to identify the location and depth of the sonde inside the pipes. The surveyor’s recorded the pipe location information being transmitted by the sonde.

FFB Annex Sewer Pipe Condition Overall, the 4-inch sewer pipe serving the FFB Annex is considered to be in poor condition due to sags in the first 115 feet from the building and also due to the woodstave pipe section showing signs of mailto:mstephl@stephleng.com AutommeNCircosta Text Box FFB Sewer Service Condition Report Memo deterioration. A sag in a sewer pipe is defined as an area where the actual location of the pipe invert is at a lower elevation than it should be.

The existing 4-inch sewer pipe runs from the FFB Annex to MH-2 and is approximately 255 feet long. It is constructed with woodstave pipe and ductile iron pipe. A cleanout is located in the sewer pipe at approximately 140 feet upstream of MH-2. There is approximately five feet of soil cover over the pipe.

The entire 4-inch sewer is located under pavement in the building parking lot.

The CCTV inspection on September 21 was accomplished with a 2-inch diameter push camera. A “push camera” is attached to the end of a stiff rod and pushed into the pipe by hand. The pipe contained debris and grease buildup, and the pipe was partially cleaned by flushing and jetting prior to completing the CCTV inspection. The inspection was performed from both ends of the 4-inch pipe. Access was via MH-2 at the downstream end and a cleanout at the upstream end.

Fairbanks Federal Building Site (courtesy of Google Earth)

Upstream Inspection From MH-2 the camera was pushed upstream for 134 feet until it was stopped by a large chunk of debris that was either a rock or a piece of concrete. The upstream inspection was stopped approximately five feet short of the cleanout. In this 134-foot distance, the pipe consisted entirely of 4-inch woodstave and the invert grade was fairly uniform and appeared to slope downhill toward MH-2. The wood pipe had splinters hanging off of the interior and in some places the wood staves appeared to be damaged. The woodstave pipe was round and no indication of collapsing was observed. Debris up to 1-inch deep

Federal Building Site Plan (sewer pipes shown in yellow) consisting of gravel and other miscellaneous debris was observed along the entire 134-foot distance.

Places with grease buildup up to ½-inch thick were observed along the entire 134-foot inspection.

Downstream Inspection From the cleanout located just inside of the building exterior wall the camera was pushed approximately 115 feet downstream until it reached the mid-point cleanout. This portion of the sewer service is constructed with 4-inch ductile iron or cast-iron pipe. The camera went underwater numerous times during the CCTV inspection. This is an indication that the invert grade has sags in it. It should be noted that the asphalt surface above this section of the 4-inch sewer was heaved and sunken and showed signs of distress.

FFB Main Building Sewer Pipe Condition Overall, the 6-inch sewer pipe serving the FFB Main Building is considered to be in fair condition.

Defects observed included a sag in the first 10 feet from MH-2 and the woodstave pipe showed signs of deterioration. The pipe appears to be functioning adequately at this time. However, it is nearing the end of its useful life based on the deterioration observed.

The 6-inch sewer pipe from the FFB Main Building is approximately 290 feet long and is not known to freeze or have sewer backup problems. The 6-inch sewer is constructed with woodstave pipe. A cleanout is located at approximately 174 feet upstream of MH-2. A second cleanout is located just outside of the FFB Main Building wall. The pipe is mostly located under a yard area. The soil cover is estimated to be approximately three to eight feet in depth. This pipe was inspected with a CCTV camera mounted on wheels. The camera was inserted into the pipe in MH-2, traveled upstream and was able to observe the entire pipe length. The camera also traveled another 100 feet inside the building and observed the 6-inch interior pipe as well.

A sag was observed in the 6-inch pipe. The sag starts at MH-2 and ends approximately eight feet from MH-2. The invert of the sag is approximately three inches below normal at the deepest point.

3-inch deep sag upstream from MH-2

Splintered and delaminating wood slats at 1:00 position

The interior of the 6-inch woodstave pipe is deteriorating. Splinters of wood were observed hanging or protruding off the wood slats and reaching into the flow line. This is a common characteristic of woodstave pipe that has been subjected to either high pressure interior cleaning, jetting or sewer snaking work. In a few places slats that were broken and partially protruding into the pipe interior were observed. At the woodstave joints, some gaps up to ¾” wide were observed. This is an indication that the pipe sections are not completely butted or pushed into each other. None of the joints were offset.

The 6-inch pipe is not failing structurally at this time. No collapsed sections were observed. The grade of the pipe invert is fairly uniform. No serious grade breaks were observed (except for the sag near MH-2).

Sewage was observed to flow along the pipe invert at a fairly rapid rate, an indication that the pipe has a relatively steep slope.

Manhole 2 Condition Overall MH-2 was observed to be in poor condition. The precast concrete manhole sections were separated at the joints and significant mortar loss was occurring on the manhole walls. The mortar that was used to construct the invert, shelf and beaver slide was deteriorating and causing sewage debris to collect in the manhole. One of the incoming pipe connections was missing mortar. No significant cracking, broken sections or structural failure were observed.

SECTION 3

RECOMMENDED UPGRADES

FFB Annex Sewer Pipe It is recommended that the 4-inch sewer from the FFB Annex be removed and replaced with a new sewer pipe that is properly graded to a uniform slope and is insulated and protected from freezing. The existing pipe has sags and bellies and the woodstave portion of the pipe is deteriorating and is at the end of its useful life. The 4-inch pipe has approximately five feet of soil cover and is located in a parking lot that is plowed all winter. The amount of insulation around the pipe is unknown. It is assumed that the poor flow velocity through the pipe in conjunction with the shallow soil cover is contributing to the annual freezing and backup problems.

FFB Main Building Sewer Pipe It is recommended that the 6-inch sewer from the FFB Main Building be upgraded by fixing the sag near MH-2 and by rehabilitating the entire 290-foot-long sewer with a cured-in-place-pipe (CIPP) liner. Excavation work would be done to repair the eight-foot long sag near MH-2. This excavation work would be completed in conjunction with the excavation work proposed for replacing the 4-inch sewer to the Annex building and replacing MH-2.

Using a CIPP liner to rehabilitate the 6-inch woodstave pipe is a common practice. There are three sewer CIPP installers in Alaska who would be capable of doing this work. The liner should be designed for a fully-deteriorated condition. It is assumed that the wood host pipe over the long-term could completely deteriorate.

The woodstave host pipe should be prepared properly prior to installing the liner. This would include using a robotic cutter to remove stiff wood splinters that may create an unwanted bulge in the new liner surface.

CIPP lining is the most popular sewer pipe rehabilitation method in use today. The liner is constructed of a soft fabric tube that is impregnated with resin. After the tube is inserted into the host pipe it is inflated with water or air and cured until hard. A CIPP liner will conform to the shape of the host pipe wall. The host pipe is taken out of service during the lining work. Either the flow must be shut off (on a weekend, for example) or bypass pumping is required.

It is estimated that a 290-foot-long, 6-inch diameter CIPP liner installation for this application would cost approximately $40,000 to construct. This estimated cost includes host pipe preparation work. It is assumed that the work would involve two days of mobilization and demobilization and one day to prepare the pipe and one day to install the CIPP liner. It is assumed that the lining work would occur over a weekend when the building sewer could be plugged and taken out of service. The estimated cost does not include repairing the sagged pipe section at MH-2 and does not include engineering design and construction support services.

CIPP liner in a woodstave sewer pipe at the University of Alaska Fairbanks

Manhole 2 It is recommended that the existing MH-2 be completely removed and a new modern insulated precast manhole be installed. Excavation work would be completed to repair both pipes entering the manhole. Therefore, it would be cost-effective to replace the manhole at the same time.