Lowes, Gilford NH Slope Stabilization:
During the 2006 growing season .Certified Erosion Control- NH (CEC) successfully stabilized a four and a half acre,
terraced two to one slope using a Compost Storm Water Blanket with Filtrexx Lockdown Netting.
In 2005 construction began on a new Lowes in Gilford, NH. The project would include the construction of the Lowes Box store and 2
pads for future development. The site had historically been a strip mall with several smaller stores and one large box store. The
plan was to lower this lot and expand it in size. The cut required was significant, resulting in a four and a half acre, two to one terraced slope.Busby Construction began the excavation portion of the project in the summer of 2005 with an original construction sequence calling for the slope to be graded and stabilized after constructing the building pad. In the fall of 2005 a heavy rain event produced a
plume of sediment from the site, causing the EPA to levy a significant fine against Busby Construction, the primary excavation contractor for the project.
Early in 2006 Michael Redding, an engineer from GeoInsight Inc. was hired by Busby Construction to develop a SWPPP that would address the difficult site. CEC-NH worked closely with GeoInsight to develop a strategy to treat and filter sediment laden waters on site that would gain approval at the state level. Preliminary testing included filtering dirty water through several different types of
sediment barriers, including Siltfence and Filtrexx filtersoxx. It became clear that due to the characteristics of the soils on site and the area available for developing a treatment train that deflocculating polymers would be required to meet EPA water quality standards under the current construction sequence. Further field testing proved that this method would be expensive and could be easily overwhelmed during a large rain event. The focus of the plan turned to the construction sequence to solve the problem.
The early spring of 2006 proved to be unseasonably dry and the soils on the building pad proved to have good infiltration qualities.
Busby used the pad are as a sedimentation pond and switched their focus toward bringing the slope to finish grade and stabilizing those grades as soon as they were completed. This allowed Busby to utilize the building pad to store and infiltrate runoff water onsite as long as possible, eliminating the need for the use of polymers to improve water quality. CEC-NH proposed using a combination of the Compost Storm Water Blanket with Filtrexx Lockdown netting. Because the Compost Storm Water Blanket is applied pneumatically to the surface of the slope without the additional loam, Busby Construction could concentrate on cutting grades and removing the large amount of soil needed to create the finished grades. Busby sought and won approval to use compost blankets in lieu of traditional loam and seed with woven erosion control blankets.
CEC-NH worked closely with Busby Construction Inc. as they began cutting finished grades on the slope. The slope was built at a 2:1
grade with two steps or terraces. As Busby completed a section, CEC-NH would follow installing Lockdown Netting and compost blanket. The blanket material was seeded with NH slope 44 as specified in the original specifications; the seed rate was increased to 10 lbs. /1000 to meet the Filtrexx recommendation. NH Slope 44 is a mixture of, Creeping Red Fescue, Catalina Perennial Rye, Alsike Clover, Birdsfoot Trefoil, and Red Top. Compost blankets quickly begin to integrate with the existing soils and provide an excellent medium for seed germination.
In May of 2006 the "Mother's Day" flood dropped over 9 inches of rain on the partially completed slope. Despite limited germination,
the Compost Storm Water Blanket held, with the exception of that portion that was installed within hours before the rains started.
This project is an excellent example of how a well-planned and implemented SWPPP can reduce costs and keep a project on schedule, in compliance with state and federal regulations. The best evidence of this success is that even though the site experienced one of the most significant storm events of recent history in NH, no polymers were required to keep the site in compliance. One final effect the Compost Storm Water Blankets had on this project involved the question of stability. On October 17,
2006 Ridgely Mauck, Administrator of the NH Department of Environmental Services, Alteration of Terrain program responded to the
question, "Once the compost blanket is installed, does the state consider the site stabilized".
Administrator Mauck's answer was: "I have reviewed Section 5.2.1 Filtrexx Compost Storm Water Blanket™ (CSWB) of the Filtrexx®
Standard Specifications and Design Manual – Version 5.0, and determined that CSWBs installed in accordance with the referenced
specifications would meet NHDES criteria for the post construction stabilization of a site." This meant that, once all of the exposed
areas were blanketed, Busby Construction's bond on the project could be released that fall rather than waiting for the spring as
expected. The Compost Storm Water Blanket represented a significant cost savings for the contractor over the originally proposed
topsoil, blanket, seed solution, especially when considering the costs of equipment to spread topsoil on difficult slopes like the ones at the Gilford Lowes. These features make the Compost Storm Water Blanket the premier solution for slope stabilization