Hazgard 250 - Underground Fuel Tanks

LOCATION: Port Hadlock, Washington

TIMEFRAME: November 15th / January 20th SCOPE OF WORK: Layfield supplied and directed the installation of Hazgard 250 geomembrane to encapsulate 2 underground fuel tanks.

PROJECT PARTNERS Owner: Kroger Foods Installation: Evergreen Environmental and Layfield Environmental Material supplier: Layfield Environmental Systems

Challenge

The challenge was to directly create a full containment of an excavation 24' wide x 42' long x 14' to keep both gasoline tanks contained from leaking into ground water as well as prevent surface water from entering the containment. Further challenge was noted in completing the installation during the rainy season of the Pacific Northwest.

Solution

The solution involved getting as much information on how the site could be prepared in advance, and then considering the logistics of how this liner would be backfilled.

We established with the contractor that the liner system would be installed in two phases. The first phase involved lining the bottom and sides with a one piece liner so the contractor was able to install the tanks on top of this liner and backfill up to the where the second liner would go over top. During the pre-bid the contractor had said they could dig the excavation with vertical walls 4' deep from the bottom, then they would follow regulations to run outward the remaining 16’ at a 1:1 slope. Based on this, Layfield concluded that our liner size be set on fitting the 4’ vertical and then up and outward at 1:1 slope 7’, then we would have the contractor backfill the excavation such that we could run the liner back towards the center at a 1:1 slope another 7’ and then have 5’ of liner to pull to the center. Based on this we figured the bottom panel had to be 73’ x 87’.

For the second phase we wanted our lid to go sufficiently out from the sides, so we made the “Lid” 6’ wider than the planned excavation. We also figured we would take advantage of using cut-offs from the site from the same risers that we would later have to seal around to take back to our shop to use as forms for pipe boots.

Results

With order in hand we made the liner, yet when the contractor completed the installation the hole was significantly larger on one end. Fortunately we had prepared some extra length in the liner size to account for field error and it paid off.

For lining the first phase, there was no substitute for a good thick nonwoven to protect a liner excavation. The soils in the site were terrible, so it was a big comfort to have our LP 16 Geotextile down as a cushion fabric on which to lay the Hazgard 250 Geomembrane.

When it came to putting out the liner, the Layfield Supervisor Technician showed the contractor how to use their equipment and labor to pick-up the liner and center it in the excavation. Once we centered the liner in the excavation we were able to stake the edges of the liner outside the excavation. Next we installed another layer of LP 16 Geotextile on top of the Hazgard 250 Geomembrane, then the contractor was able to backfill.

The backfill did not go as planned, but with regular communication with the contractor we were able to review changes proposed to insure the sides of the liner could be brought in sufficiently to the center of the tanks, and the lid would adequately cover the top.

As the contractor completed the backfill of the bottom liner system, the Layfield Project Manager took particular care to review with the contractor’s site supervisor that all leading edges of the liner system were pulled up and towards the center.
Once the top lid went on, the Layfield Project Manager along with the supervisor, reviewed the edges to ensure they were at an equal distance from the tank installation, as well as maintain that the liner would shed water as opposed to holding it.
Upon completion of Layfield’s work, the contractor was very happy with the overall performance and attention to detail.

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