Lemon Lane Final Report
June, 2001
1.0 Introduction | 2.0 Site Description and History | 3.0 Remediation Planning | 4.0 Changes to Original Work Plan | 5.0 Sampling Activities | 6.0 Preparation of Iterim Cap Surface | 7.0 Intallation of the Geosynthetic Clay Barrier | 8.0 Placement of Geomembrane and Geonet | 9.0 Placement of Vegetative Support Zone | 10.0 Site Surface Water Controls | 11.0 Site Restoration | 12.0 Data Validation | Photos
9.0 PLACEMENT OF VEGETATIVE SUPPORT ZONE
9.1 Inspection and Quality Control
The function of the vegetative support zone is to promote vegetation, minimize
erosion, promote drainage and protect the cap barrier materials. Design details in
the WP require that the support zone consist of 6 inches of topsoil and 18 inches of
cover soil over the geonet drainage composite system. These two zones were
constructed separately. The soil characteristics for the cover soil require a medium
textured material containing sufficient sand to allow drainage to occur and sufficient
clay/silt to allow some water to be retained for vegetation support. Samples were
taken of the cover soil at the source prior to excavation and transportation to the site
for placement. The samples were sent to Golder Associates for analysis and
approval for use as cover soil. The results are reported in PSARA Construction
Certification Report contained in Appendix F.
9.2 Placement of Cover Soil
The 18 inches of cover soil were obtained from Hanna Trucking and met the
specifications for cover soil as identified in the Final Cap Design Report. Cover soil
was delivered to the site in over-the-road tri-axle dump trucks, dumped loose on the
slopes, and spread over the slopes by a Komatsu D65 dozer. Truck access to the
cap area was over two culverts installed to cross over the perimeter channels on the
east and the northwest. Support soil was placed in one loose uncompacted lift.
Care was taken to insure that both the dump trucks unloading soil and the dozer
spreading the soil tracked only over previously spread cover soil that was not less
than 12 inches thick. No density specification was provided in the project
specifications and no formal density testing was performed. Since cover soil was
placed and spread over the entire landfill, construction traffic was fairly uniform over
the entire landfill. As a result, construction traffic provided adequate compaction to
ensure the stability of the cover soil layer. The cover soil terminated at the edge of
the cap into a geotextile fabric that was placed between the cover soil and the riprap.
The geotextile prevents cover soil from eroding into the riprap.
Both Golder and PSARA representatives provided oversight and certification
inspection services for the placement of the vegetative support zone soils over the
geomembrane/geonet system. Continuous inspection of cover soil placement was
performed in order to insure that construction equipment did not drive directly on the
geonet drainage layer, and that wrinkles in the geonet were minimized.
Once the 18 inches of support zone soil was in place, purchased topsoil was brought
to the site using the same tri-axle dump trucks to complete the vegetative support
zone. Prior to delivery the topsoil was analyzed to insure it met the topsoil
specification stated in the Final Design Report. The same process for spreading the
support zone soil was used for the topsoil.
Survey certification of the thickness of cover soil was performed by SNA using the
same 50 ft. by 50 ft. grid system that was used to verify the thickness of the cushion
soil. A tabulated summary of survey results is included on Figure 9. This table was
prepared by SNA and shows a cover soil thickness of at least 24 inches at all 50 ft.
by 50 ft. grid points on or within the LOO except at point number 159. At this point
the cover soil was only 1.6 feet. This deficiency in thickness will be corrected in the
spring of 2001 when the weather permits. This table also lists the final elevations at
these grid locations.
PSARA's certification letter describing cover soil placement and the integrity of the
geomembrane/geonet system is presented in Appendix G of this report. In summary,
the letter states that the cover soil layer was placed in general accordance with the
project specifications. No visible damage was observed to the geonet drainage
composite or the underlying geomembrane liner as a result of soil placement or the
movement of construction equipment on the cap.
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