“Avoidable Complications Due to Landfill Liquids Pumping System Designs”

The most important decisions that impact the success of a landfill occur during the initial design phase.  The initial design of the landfill, cell or the expansion, has a significant impact on the long-term success of the landfill. It can have regulatory compliance as well as significant operational cost or operational efficiency implications, which can impact the long-term sustainability of the landfill. Because of the challenges that a large number of landfills are still facing with their leachate pumping systems, EPG Companies has developed presentations to address complications in landfill leachate and condensate pumping systems. The content of the presentations is based on a) actual conditions that our support teams are regularly coming across on landfills and b) the hundreds of new landfill or new cell designs that our Application Specialists are reviewing every year when we are asked to provide pumping equipment quotes for the projects.

The goal of this presentation is to create awareness of design oversights or best practices that could lower down time of the liquid pumping systems and minimize operational cost due to maintenance of the leachate pumping systems.

Who is it for?

These trainings/webinars are suitable for:

a) Engineers who are working for private consulting firms, private solid waste companies, public municipalities, waste management authorities, doing landfill designs, or cell expansion designs that require leachate pumping systems to either a) keep the landfill compliant with leachate levels, odor or methane emission regulatory requirements, or b) dewater gas wells for the purpose of methane gas extraction for LFGTE projects.

b) Quality Control consultants or engineers who are inspecting the installation of electric or air powered leachate pumping systems on landfills, that were installed for the purposes listed above.

c) Landfill general managers, operations managers, technicians or third-party support and services personnel who are managing landfills or providing services to landfills to maintain their leachate pumping systems.

The following are common design complications that we are frequently coming across. Each section will address the cause and the recommended alternatives as food for thought. Sections 1-5 address electric pump conditions, while sections 6-9 address pneumatic pump conditions.

1)            Designing pumps for too high of flow rates

Pumps are often selected for 100-year storm event flow rates. The result is a pump installed that is significantly larger than what is really required for day-to-day operations. Larger pumps result in higher liquid velocity into the sump, pulling in more particulate matter that could clog the infiltration area as well as the pump, reducing flow rate. Rapid dewatering of the sump infiltration area could lead to an increase in biological growth. It has been proven in water well design that extended pump run cycles and low velocity reduce or delay incrustation and infiltration of fine solids, and in doing so, maximize the efficiency of the overall liquid pumping system.

2)            Pump Performance Curve(s) vs System Head Curve Analysis

One of the most common reasons for low flow or “no” flow, is due to liquid pumping systems not being designed based on the complete system head curve. When the force main is undersized, we see “no” flow or low flow due to the pumps pumping against each other. We also often see that when another pump is added to the system, that the present system flow rate drops. Another problem is the force main being oversized, causing the pumps not to operate at their optimal level, which has the potential to reduce the life of the pump.

3)            Specifications or drawings being copied from site to site

EPG’s Applications Specialists have collaborated with engineers on over 10,000 landfill projects. We see numerous examples every day of specifications or drawings being copied from project to project, often without updating all the specifications or aligning the written specifications with the drawings. An obvious consequence is the time that will be wasted for engineers to answer questions from suppliers and contractors, asking for clarifications. A bigger concern is design errors being carried over from project to project, or designs not being optimized for a new site/project. This sometimes results in delays in the implementation stage of the project, or worse, an ineffective pumping system being installed.

4)            Landfill Gas Effect

Vacuum conditions or positive pressure conditions could have a significant impact on a landfill’s regulatory compliance and reduce the life of the electric pumps. Operating an electric pump, with a level sensor as input, under vacuum could cause increased liquid levels on the liner, delay the pumps from starting and delay high level alarms. On the other hand, operating an electric pump, with a level sensor as input, under positive pressure could cause pumps to start prematurely, pumps could run dry or could result in false high-level alarms.

5)            Components often overlooked in electric pump system design

Designs often do not include a few basic necessities. One is not having pressure gauges installed on the discharge lines of the pump. Pressure readings are the most effective tool in doing a root cause analysis of an ineffective liquid pumping system. Less time being spent identifying the cause of an issue results in higher up time, and getting liquid levels back to desired levels. The components could also be used to identify the need for scheduled preventative maintenance of pumps, which would limit downtime of the liquid pumping system, and save the landfill time and money, not to mention, staying in compliance.

6)            Piping Configurations

Incorrect pipework configuration is one of the most complicated causes of pneumatic pumps stalling and is very difficult to identify. Stalling could be due to the pipe configuration not being specified with enough details, pipe configuration left up to the contractor for interpretation, design errors or installation errors. Pipework is often configured with pumps pumping against each other from opposite ends of Tees, leaving some pumps overpowered (stalled)!

The second challenge of pipework configurations are airlocks. High points are caused by changes in the discharge force main elevation. They can cause reduced flow, or pumps stalling. The cause is often difficult to identify and expensive to fix.

7)            Corrosion and Precipitation

Chloride is the major cause of corrosive attacks on Stainless Steel in leachate/condensate system piping. Chloride attack is characterized by pitting and eventually perforates tubes. 304 grade stainless steel is not really suitable as it is significantly more susceptible to corrosion by chloride! Corrosive attack on 316 Stainless Steel due to chloride in leachate, is extremely rare. The pitting, due to corrosion that is often seen on 304 Stainless Steel, accelerates the forming of precipitation/scaling which could cause higher frequency of pump stalling and maintenance required, and ultimately increase a site’s operational cost, while also reducing gas extraction.

8)            Air in discharge line

Air in the liquid discharge line, in itself, is often not considered to be a problem, but it can have significant implications that are often not linked to the air as the cause of the problem. Air in the discharge line could be caused by faulty or not well tuned pumps, or poorly designed pumps. Air in the discharge line accelerates scaling in the liquid discharge piping, and could possibly cause airlocks and increased back pressure which could potentially cause a number of other pumps on the line to stall.

9)            Impact of Landfill Gas Effect in Condensate Sumps

Vacuum conditions, due to gas extraction from gas wells, has the potential of placing the condensate sump under a vacuum. Operating a Pneumatic Pump under vacuum will cause an elevated liquid level before pumping can occur, resulting in increased liquid levels in the condensate sump. Most modern design packages can account for this resulting in the inflow and outflow from the condensate sump being high enough above the potential liquid levels. However, when field services teams take over landfills that were previously managed by another companies, they don’t know if the system was design correctly and have to consider gas effect as one of the potential reasons why there could be elevated liquid levels in the condensate sump.

10)          Components often overlooked in pneumatic system design

Pneumatic pump system designs often do not include a few basic components since they are not considered necessary for day to day operation. Examples of these are air release valves, test valves, non-return/isolation valves and minimum pressure valves. Although none of these are required for a pneumatic system to operate under normal conditions, these components could address symptoms in a few scenarios that could prevent a number of pumps from stalling. When pumps do stall, identifying the primary cause of the problem could be time-consuming and costly.