See SCS Engineers Landfill Construction Services
Marion County has awarded SCS the planning, designing, permitting, bid phase services, construction quality assurance (CQA) services, and construction contract management for the approximately 50-acre baseline landfill cell No. 3 closure. The County sought a firm specializing in solid waste, with landfill closure experience in Florida to provide the required design and permitting services, and with the in-house capability to conduct the construction quality assurance (CQA) services required during construction. The entire project is estimated to take three years to complete, with construction spanning multiple rainy seasons.
Weather-related issues during closure construction are one of the critical factors to address. An overly aggressive contractor could strip too large of an existing vegetative area, try to place too much protective cover material over the barrier layer system; either can potentially cause significant erosion during rain events.
The County’s concern about CQA is to prevent placing the protective cover material over the newly installed barrier layer system. Should an unqualified contractor replace the protective cover material on the barrier layer, it will increase construction time and increase the potential for damage to the system. This damage is often not found until the contractor has demobilized from the site, and the facility begins to conduct the required surface emissions monitoring. The resulting repairs to the barrier layer are often a cost the owner incurs, not the contractor.
Based on decades of experience designing, building, and operating landfills, the SCS CQA professionals prevent these types of construction mistakes. Working closely with contractors to ensure construction events are thought through to the operations phases while providing recommendations if the construction plan may encounter potential issues.
“Our entire team is excited to have the opportunity to continue serving Marion County, especially with a project of this magnitude and importance to Marion County,” said Shane Fischer, a vice president with the SCS team. “Our professionals are committed to delivering the highest quality engineering and construction services possible for the long-term success of the project.”
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Sometimes geosynthetic material specifications for a specific project, i.e., lining system or final cover system, is a performance-based specification which does not specify the type of product for use in construction. What does the engineer need to do when the selected contractor submits a product for approval in accordance with a performance-based specification? What should the engineer do when the owner purchases the material and identifies a product for use based on the performance-based specification?
Specifications that SCS has prepared are performance-based and include a qualifying procedure whether the product is introduced by a contractor or owner. This qualifying procedure is specifically left to the engineer to carry out by laboratory testing of typical samples of the specific product for use in construction. Typical reported values by the manufacturer or test results submitted by the contractor or owner are not acceptable under these procedures. Since the engineer is taking the liability of accepting a specific type of product for his or her project, the engineer should have the right to perform laboratory testing before the product is approved for use in the project, that only makes sense in the world of taking liabilities!
The testing performed by the engineer for qualifying a product do not count toward conformance testing of materials delivered to the site. The qualifying procedures are solely for accepting a certain type of product to be used in the project, but the specific rolls of pre-qualified product manufactured for use in engineer’s project must go through the required conformance testing specified in the specifications before use in the project.
The process of qualifying a product, ordering the qualified product, and performing conformance testing on the pre-qualified materials takes time. Engineers need to consider the amount of time necessary for the involved stages of approval into the construction schedule. If using material purchased by the owner, the owner needs to keep the timeline in mind to allow the engineer to carry out all necessary testing for the approvals to be in place before construction begins.
Repeating the qualifying procedure for a product from one project to the next depends on how the performance-based specification is written. Sometimes, the engineer accepts a product that was qualified for use in a prior project as long as the product has not changed since last used in accordance with statements by the manufacturer. If the performance-based specification includes such options, SCS highly recommends identifying the period between a prior project and the next project in the specification. In some cases, this means the product must go through a qualifying process even if it has not changed for many years but the previous set of qualifying data is older than a certain number of years. The period is based on the engineer’s judgment, but most professionals normally use five years in their specifications. During a five-year period, if the product changes or there are indications that the product might have changed due to recorded changes in certain reported values by the manufacturer, the qualifying process must be followed irrespective of the number of years passed since a recent past project to maintain quality and minimize risk.
Questions? Contact the author, Ali Khatami.
The primary role of gas collection system laterals is conveying landfill gas to the final destination in the system; however, lateral pipes are also used to convey condensate in the system to a collection point such as a condensate sump. Between the gas collection laterals and the condensate sump, there are gas headers that provide vacuum to the laterals. Condensate sumps are primarily connected to gas headers for effective management of condensate in the system.
On many occasions, gas headers are installed over the landfill surface, where condensate sumps have to be constructed as well. This type design could potentially create issues during construction of the final cover system in the area. On numerous occasions, the condensate sump sticking up above the surface is too short causing the sump to be extended during the final cover construction.
The gas system in the area must be taken out of service to extend the condensate sump. Such interruptions are never welcome because odors or lack of gas productivity can cause serious issues for operators. Also, waste settlements at or around the condensate sump can cause other issues that must then be addressed during construction of the final cover. Furthermore, if the gas header connected to the condensate sump ends up in the middle of the waste column with tens of feet of waste above the gas header, there is the risk of the gas header collapsing under the waste surcharge load and causing issues in the flow of gas and condensate in the system.
Avoid problems by allowing for constructing the gas header and condensate sumps in the landfill perimeter berm.
There are major benefits when the gas headers and condensate sumps are located outside of the waste. First, settlement issues are avoided and secondly potential gas header collapse is averted because they are not situated below many tons of waste. Construction of the condensate sumps to the correct and final height is accomplished while avoiding any final cover construction delays because of issues with the condensate sump locations. In addition to these benefits, the condensate sumps are readily accessible for maintenance.
Under certain conditions construction of the perimeter, berm needs to be carried out in advance of construction of certain disposal cells to position the gas header and condensate sumps in the berm. The design adds to the planning time and requires close coordination with a landfill engineer, but the return is worth every penny.
Contact Dr. Khatami to learn more about the specific conditions that can increase your ROI.
