EXAMINATION OF PVC IN A 'TOP CAP'
APPLICATION

Samuel B. Levin and Mark D. Hammond

REFERENCE: Levin, S. B. and Hammond, M. D., "Examination of PVC in a 'Top Cap' Application," Geosynthetic Testing for Waste Containment Applications, ASTM STP 1081, Robert M. Koerner, Ed., American Society for Testing and Materials, Philadelphia, 1990.

ABSTRACT: The PVC liner installed over Phase I of the Dyer Boulevard Landfill provides us with an opportunity to examine the material after 5+ years of exposure to landfill gas and other environmental stresses in a top cap application. Test results for samples extracted from the cap are compared to test results obtained at the time of installation, to material properties included within the original material specification, and to material properties from a 'control' sample of excess PVC material from this closure project kept in a warehouse since 1983/84.

KEYWORDS: landfill closure, landfill lining, geosynthetics performance

INTRODUCTION

The Dyer Boulevard Landfill services all of Palm Beach County, Florida. It is located over the Turnpike Aquifer, an important local source of drinking water. When initially opened in 1968, it was one of several unlined landfills operated within the County. With time, it became a major disposal area for both municipal solid waste and sewage sludge.

In late 1970's, evidence of contamination of the shallow aquifer surrounding this high rise landfill was observed within the site's monitoring network. Under the terms of a consent agreement between Palm Beach County and the Florida Department of Environmental Regulation, executed in 1982, it was agreed that:

The Phase I (unlined) landfill was to be closed in an environmentally sound manner.

A new lined landfill was to be developed to provide for future solid waste disposal capacity.

An alternative means of wastewater treatment plant sludge and septic tank pumpings disposal was to be utilized.

Post, Buckley, Schuh & Jernigan, Inc. (PBS&J) was selected by Palm Beach County, and subsequently by the Solid Waste Authority of Palm Beach County (SWA) when it assumed responsibility for the landfill in 1983, to develop the closure design for the existing 190 acres ± of landfill cells in Phase I.

The closure design developed for the site included a low permeability 'top cap', well vegetated side slopes, and an integrated drainage system to capture and remove surface runoff, reducing percolation and subsequent leachate generation. The top cap was designed for installation over slopes of less than 10 percent, based on water balance calculations which indicated that only minimal percolation was anticipated through well vegetated landfill side slopes.

The selection of a liner material for use in the top cap at the Dyer Boulevard Landfill proved to be an arduous task, with properties of various materials reported in differing units, or obtained using differing test methods. Suppliers assisted in the selection process by noting the superior properties of some liner materials relative to competing materials. Plasticizer loss, ultraviolet degradation, questionable chemical resistance with respect to landfill gas exposure, and more limited elongation properties were cited as reasons to consider materials other than PVC. Environmental stress cracking, seaming difficulties, and poor strength characteristics upon exposure to bidirectional forces were cited as reasons to consider materials other than High Density Polyethylene (HDPE). 

PURPOSE AND SCOPE

During the past several years, geosynthetics testing has matured to the point at which properties of virgin materials ' are widely available and in many cases readily comparable. Data concerning the properties of liner materials which have been in service remain scarce, although there is a growing body of information concerning exposure in the laboratory to simulated in-service environments [1], [2].

The top cap material in-service at Dyer Boulevard provides an opportunity to examine the properties of material which has been in service for over five years. Properties of this material will be compared to the properties determined by quality assurance testing during its manufacture and installation, in an attempt to assess the change in properties resulting from material exposure. Excess material stored in a warehouse since its purchase in 1983/84 will serve as a control.

DESIGN AND SPECIFICATIONS

The site closure design included the placement of PVC sheet, soil bedding and cover material, a passive landfill gas venting system, drainage improvements, and seeding, mulching and sodding of the completed landfill. A typical cross section through the final cover is provided in Figure 1. Physical properties specified for the 20 mil PVC liner are presented in Table 1. Tensile strength at the seam was required to be at least 80 percent of that of the parent material, or 1760 psi. Also required in the specification was the sampling and testing of the production run for tensile strength and elongation at break.

General Contractor Crabtree Construction Company, Inc., purchased 3.32 million square feet of PVC material, Product Number 1951, manufactured by Dynamit Nobel of America, Inc. and fabricated by the Watersaver Company, Inc. The surface of the subgrade prepared as liner bedding was treated with Hyvar X-L Herbicide prior to placement and seaming of the liner panels. The coarse grained sand used for liner bedding and backfill was obtained by dredge from a near site borrow area.

One hundred and sixty-six panels of PVC, most of which measured 400 feet by 70 feet, were installed by Wright/Kohli Construction Company, a specialty liner subcontractor. Watersaver WS-70 splicing solvent was used for seaming the panels together.

TABLE 1 -- Specified Physical Properties for 20 Mil PVC
Physical Property	Value	ASTM Test
Thickness	+/- 10%	D 1593
Specific Gravity	1.24 - 1.30	D 792
Tensile Strength	2200 psi	D 882 or D 412
Elongation	300%	D 882 or D 412
100% Modulus	1000 psi	D 882
Graves Tear	270 lbs/in	D 1004
Water Extraction	0.35% (max)	D 1239
Volatility	0.70% (max)	D 1203
Impact Cold Crack	-20ºF	D 1790
Dimensional Stability	5% max @ 212ºF	D 1204-54

 

 

 

 

 

 

 

 

 

 

 

 

 

PVC SHEET (LINER) TESTING

Testing of the properties of the PVC sheet installed over the Dyer Boulevard landfill included:

Quality control (QC) testing of the parent material at the time of manufacture by Dynamit Nobel of America, Inc.

Non destructive (air lance) testing of all field seams during the time of installation.

Destructive testing of the parent material, factory and field seam samples obtained throughout the ten month installation period.

Table 2 provides a summary of the manufacturer's QC data. Please note that the data presented is the average for a number of rolls tested. One sample was obtained for testing purposes for each 86,000 square feet of manufactured product.

TABLE 2 -- Manufacturer's QC Dataa
	ASTM	Manufacturer's	Test Result	Test Result	Test Result	Test Result
Properties	Test Method	Specification	(Ave.11 Rolls)	(Ave.6 Rolls)	(Ave.13 Rollsb)	(Ave.7 Rolls)
Thickness (mils)	D-1593	20 +/- 5%	19.9	19.5	19.8	19.9
Specific Gravity	D-792	1.23	1.25	1.25	1.25	1.25
(min.)
Tensile Strength	D-882	2400	MD 2999	MD 2836	MD 2487	MD 2977
(psi)			TD 2768	TD 2692	TD 2464	TD 2781
Modulus @ 100%	D-882	1000	MD 1446	MD 1270	MD 1384	MD 1291
Elong. (psi min.)			TD 1333	TD 1202	TD 1332	TD 1203
Elongation, % min.	D-882	300	MD 414	MD 423	MD 336	MD 453
			TD 426	TD 435	TD 354	TD 449
Tear Strength (lbs.)	D-1004	5.5	MD 7.46	Not	8.51	Not
			TD 7.92	Reported	9.18	Reported
Low Temperature	D-1790	-20	Pass	Pass	Pass	Pass
Impact ?F
Volatile Loss max.	D-1203	1	0.79	0.70%	0.87%	1.13%
(@70?C for 24 hrs.)
Water extraction,	D-1239	0.3	0.08	0.18	0.15	0.3
% Loss max
(1040F, for 24 hrs.)
Dimensional Stability	D-1204	±5.0	MD -1.8	MD -1.8	MD -1.8	MD -1.27
% change, max.			TD 0.6	TD 1.7	TD 0.86	TD 0.51
212?F for 15 min.
a Provided by the Watersaver Company, Inc.					MD - Machine Dire
b Number of rolls tested estimated based upon reported material weight.					TD - Transverse D

Destructive testing of field samples taken throughout the liner installation process was performed by QC Metallurgical Inc., Hollywood, Florida. A total of 236 tensile strength tests were performed on field samples. These test results are summarized in Table 3. All tensile tests were performed in shear.

TABLE 3 -- Summary of Tensile Test Data for Field Samples of PVC when Installed
		Specified Values	Range of Results	Average Value	Sample
Sample Type	Sample Quantity	(psi)	(psi)	(psi)	Standard Deviation
Field Seam in Shear	195	1760	1490 - 2550	1937	165
Factory Seam in Shear	30	1760	1825 - 2568	2132	186
Parent Material	11	2200	2040 - 4750	2857	712

LINER RESAMPLING/TESTING PROGRAM

In December, 1989, the soil overburden was carefully removed from the top cap in several locations of the Phase I area to expose the liner material. According to the Solid Waste Authority's manager of landfills, the exposed material appeared to exhibit few signs of degradation upon visual inspection.

The surface of the material exhibited minor undulations, a few millimeters in size, where the material apparently elongated to conform to the surfaces of soil particles. The samples were highly pliable, exhibiting no apparent brittleness.

Eight coupons of the parent material and one field seam coupon were sliced from the cap by the Solid Waste Authority's manager of landfills. Added to the package of nine samples was a coupon sliced from a factory panel of PVC stored by the Solid Waste Authority as surplus in a warehouse since its purchase in 1983/84 for capping the Phase I Dyer Boulevard site. The ten samples were transmitted to Geosyntec, Inc., Boynton Beach, Florida for laboratory testing.

A summary of test results for these samples is provided in Table 4. The tests were selected to correspond with tests performed by the manufacturer in 1984. Low temperature impact testing was not performed due to its limited applicability to the sub-tropical West Palm Beach environment. Dimensional stability was not determined due to an insufficient quantity of sample material.

TABLE 4 -- Liner Resampling/Testing Program
	Specific	Tensile	Modulus @ 100%	Elongation	Tear	Volatile Loss	Water Extraction
	Gravity	Strength	Elongation	(%)	Strength	(%)	(%)
		(psi)	(psi)		(lbs.)
ASTM
Test Method	0-792	0-882	D-882	0-682	D-1004	D-1203	D-1239
Field Seam	N/A	2204 shear	N/A	407	N/A	N/A	N/A
		1140 peel
Field Panel 1	1.265	MD TD	MD TD	MD TD	MD TD
		2744 2642	1865 1721	341 381	10.1 9.3	1.33	2.81
Field Panel 2	1.282	MD TD	MD TD	MD TD	MD TD
		3072 2642	1865 1721	341 381	10.1 9.3	0.4	1.08
Field Panel 3	1.267	MD TD	MD TD	MD TD	MD TD
		2740 2544	1968 1828	341 334	9.9 9.6	1.41	2.06
Field Panel 4	1.264	MD TD	MD TD	MD TD	MD TD
		2614 2633	2043 1904	340 324	9.5 9.8	2.02	1.85
Field Panel 5	1.267	MD TD	MD TD	MD TD	MD TD
		2634 2327	1884 1879	311 309	9.5 8.6	3.26	1.99
Field Panel 6	1.252	MD TD	MD TD	MD TD	MD TD
		2496 2360	1667 1794	356 270	8.8 8.9	4.23	2.63
Field Panel 7	1.27	MD TD	MD TD	MD TD	MD TD
		2446 2149	1746 1672	309 331	9.2 8.5	0.85	1.69
Field Panel 8	1.278	MD TD	MD TD	MD TD	MD TD
		2627 2628	1763 1781	362 345	8.9 8.6	0.96	2.58
Warehouse	1.279	MD TD	MD TD	MD TD	MD TD
Panel		2662 2439	1557 1476	429.4 417.4	8.3 7.8	0.78	1.29
						MD - Machine Direction
						TD - Transverse Direction

COMPARISON/EVALUATION OF TEST RESULTS

An insufficient number of field seam samples (one) and warehouse parent material samples (one) were retested to provide for a reliable comparison of test results. Data from the testing of these samples is provided for information only. Emphasis will be placed on comparing the data from the factory QC parent material test results with testing of the eight parent material samples obtained in December, 1989. This data is presented for comparison in Table 5.

TABLE 5 -- Summary of Test Results
		Parent Material (Manufacturer's	Parent Material	Parent Material (field samples
		QC Data)a	(from Warehouse)	December 1989)
Specific Gravity	Range	1.26 - 1.25		1.25 - 1.28
	Ave.	1.25	1.28	1.27
Tensile Strength	MD Range	2487 -2999	2662	2498 - 3072
(psi)	Ave.	2789		2672
	TD Range	2464 - 2781	2439	2149 - 2725,
	Ave.	2651		2502