Landfill slopes that have reached final grades, or will receive waste in the distant future have maintenance challenges. Environmental elements continually affect surface conditions, and remedial work is required routinely to prevent negative outcomes of exposed slopes. Consider using a geomembrane temporary cap to address much of the maintenance. Here’s a list showing how the cap can help:
Landfill Maintenance Challenge
With Geomembrane Temporary Cap
The significant maintenance savings by using a temporary cap make the payoff period for the investment attractive. Based on my experience and site variations, the return on investment is usually three to six years. The period is considerably shorter if your landfill does not have a leachate disposal or treatment system, or deep injection well. The difference is the high cost to have the leachate hauled away.
Temporary caps potentially reduce routine maintenance work, leaving operation staff available for other tasks. The cap provides peace of mind that slopes remain in compliance; regulators don’t need to report non-compliance conditions of exposed slopes during inspection events.
After completing 25 temporary cap projects in the U.S. Southeast alone, we highly recommend using a thick geomembrane. It’s tempting to try to save money using a thinner geomembrane, such as 12 mils or 20 mils, but these can damage more easily and will negatively affect your return. The majority of SCS clients chose to use the recommended 40 mils thick geomembrane, which will survive severe weather conditions.
Ballasting the geomembrane and using the right materials for ballasting is significantly important. We recommend using ultraviolet (UV) resistant rope and sandbags, a tried and true system. UV resistant straps are a decent replacement for ropes. Anchoring mechanisms are also important. We typically recommend using 4×4 treated wood posts at 10-ft spacing, installed in anchor trenches, and tied to ballasting ropes. Depending on the site and operator’s preference, the supporting architecture may be to lay the post horizontally, while tied to the ballasting ropes, at the bottom of the anchor trench buried in the anchor trench’s backfill material.
Over the years, landfill operators have experienced the savings and value that temporary caps bring to landfill operating budgets, and we’re placing more temporary caps every year. If considering this option, SCS can assist you by evaluating the slopes at your site for the caps. We’ll also prepare estimates for the purchase of material and installation costs and estimated time of recovery for your project.
About the Author: Ali Khatami, Ph.D., PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Elevated Temperature Landfills, plus Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering.
Learn more at Landfill Engineering
Leachate seeps from relatively wet landfills are a fact of life for some operators. Leachate seeps increase in intensity and frequency after a storm, and you’re wondering, how many seeps today; are they reaching the stormwater ditches, detention ponds, or wetlands?
We all deal with daily job challenges, but why not prepare better for this particular problem, given the consequences? Sitting back and waiting for a seep to appear and then scrambling to come up with a solution is obsolete and can be costly.
The timing of handling leachate seeps is as vital as submitting compliance data to regulatory agencies on time. Rapid mitigation of leachate seeps is of ample problem before it turns into a compliance issue and exposing yourself to scrutiny by regulators. We all know that no compliance officer at the corporate office wants to hear from a facility the news of another compliance issue. To get a handle on managing leachate seeps, today’s operator has an arsenal of controls suited for different stages of a landfill’s operation. These controls may vary from the dry season to the wet season, as well.
As the landfill operator, you review the facility operation plan prepared by your engineer from the back to the front to make sure the document addresses all operations. The same document can also include descriptions of seep management controls. You simply request written solutions from your engineer, incorporating controls and guidelines into your operations plan. Your staff now has immediate means to combat the problem following the site operator’s direction using these pre-established guidelines.
With the controls in your facility operations plan, regulatory agencies won’t need to ask for the information. The operations plan has put forward a set of guidelines for the management of leachate seeps in your operations plan, and they became aware of these guidelines during the review of your document submitted to their office as part of intermittent or a renewal submittal. Inspectors are aware that your staff follows the guidelines when necessary; otherwise, non-compliance issues arise. Having an inspector observe a seep closing in on a stormwater ditch isn’t going to do much for your landfill’s standing. The regulators are well informed and understand leachate seep prevention. They will work with you during the implementation of remediation measures based on the guidelines in the facility operations plan.
A reliable engineer will suggest, even emphasize, these measures to clients. You, as the operator, are not only prepared, your site engineer and staff are too. Significant unexpected expenses associated with managing leachate seeps are a thing of the past, and inspectors can be confident that your management of leachate control is appropriate.
About the Author: Ali Khatami, Ph.D., PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering.
Learn more at Landfill Engineering
Equipped with wheels, the pumps roll down the riser pipe positioned in the horizontal portion of the pipe at the bottom of the sump. A discharge line from the pump extends up through the riser pipe, and after exiting the riser pipe at the top of the berm, connects to a leachate force main in the perimeter berm.
Maintenance of Submersible Pumps
To access the pump, the entire pump assembly, including the power cable connected to the pump, level control leads, discharge line, and the pump is removed from the riser pipe. The entire pump assembly is usually soiled with leachate and slime sticking to pipes, lines, and the pump while submerged.
Depending on the depth of the landfill from the top of the perimeter berm, the discharge lines could be long. A technician is handling the extraction of a long and heavy pipe, connected to a heavy pump at the lower end of the pipe to extract it from the rise pipe may have trouble.
A well-trained maintenance technician, particularly in the safety aspects involved in submersible pump maintenance is necessary. When removing a submersible pump for maintenance, having more than one technician is safer, and could be more cost-effective. Environmental aspects of maintenance work are also important, for example, the structure located at the top of the berm, where the riser pipes and leachate piping are located, should remain watertight. Otherwise, during maintenance, the liquids generated will escape into the berm structure and the environment.
If a landfill’s depth, to the bottom of the disposal cell, is less than the water column vacuum pressure (for practical purposes assume less than 15 ft.), self-priming pumps may be a feasible replacement for specialized submersible pumps.
Self-priming pumps come in all sizes, are less expensive than the submersible pumps, and install easily inside the structure at the top of the perimeter berm using a 2-inch line extended to the bottom of the riser pipe for leachate removal.
Maintenance of self-priming pumps is significantly less cumbersome than submersible pumps. One technician can handle replacement or maintenance of the pump in a shorter period. The work is not necessarily as dirty a job either, because the technician is not handling significant amounts of leachate and slime.
Self-priming pumps are designed to prime easily after each maintenance session. On the pump is a check valve on the intake, and another near the bottom of the leachate removal pipe. The check values prevent any liquid inside the pump and the pipe from flowing back down to the sump when the pump is off. This benefit also prevents the need to prime the pump when it cycles back on.
Self-priming pumps are useful for double-lining systems equipped with a secondary sump and a primary sump. In areas where freezing conditions occur, the pumps can be used as long as the pumps, and the exposed piping is located inside an enclosed housing to prevent frost damage.
I’ve used self-priming pumps in applicable designs with sufficient performance. Even when utilized in very large pumping networks the results are as good. Testimonials from my clients regarding ease of maintenance and lower capital costs for system construction are positive.
After more than 20 years, that’s a good track record for continued use in the future.
About the Author
Ali Khatami, PhD, PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has over 40 years of research and professional experience in mechanical, structural, and civil engineering.
One of the most important regulatory requirements on landfill bottom lining system drainage layer is that the maximum head of leachate over the liner should not exceed 1 ft. When this requirement was developed, the consensus was that the drainage layer consisted of granular materials. Later, when geonets and geocomposites entered the market, the unwritten consensus among solid waste engineers and regulators was that the maximum head of leachate at the base should not exceed the thickness of the geonet or geocomposite drainage layer.
With that in mind, the reduction in hydraulic transmissivity of geocomposite laid over steeper slopes can adversely affect the maximum leachate head over the liner. When hydraulic transmissivity value reduces due to steeper slope at the base, the hydraulic conductivity reduces in turn as well. Reducing hydraulic conductivity results in an increase in the maximum head of leachate passing through the geocomposite.
Read Dr. Ali Khatami’s design advice for cell base slopes under these circumstances to maximize hydraulic transmissivity; recently published in the winter edition of Talking Trash.