Prepare Now for Wet Weather

Nov. 1, 2001
Yes, I know: It’s still fall and the big storms are still a month or two away. No erosion. No mud. No wet-weather blues. Thanksgiving and the December holidays are on the horizon, but on the whole it’s time to take it easy, watch the days grow shorter, and watch that tonnage roll in.But it’s also a great time–and the sooner the better–to prepare for winter. It will be here before you know it.Surface DrainageDrainage is a broad topic that includes culverts, ditches, downdrains, and even general site grading. Any initial effort to improve your site’s drainage should begin with correcting problems that occurred this past winter. Most common are ditches or culverts that were too flat, were too small, or had plugged with litter, sediment, or vegetation. Get those things cleaned ASAP.
Sometimes simple hand-cleaning of litter and/or vegetation will suffice. In more extreme cases, a motor grader or a backhoe might be needed to clean ditches. If overgrown vegetation is the only problem, however, mowing is usually preferred over regrading because the plant’s root system isn’t disturbed–and that means less erosion next winter.Another common drainage problem is ponding. Because landfills are built in relatively flat lifts and because of differential settlement of the underlying waste, many landfills have ponding problems. A settled, ponded area on your landfill is like having a mouthful of (too) hot coffee: No matter what you do next, it isn’t going to be good.Typically, ponding is a result of flat slopes or underlying settlement. Unfortunately, once ponding occurs, the ponded water will saturate the waste below, causing more settlement. It’s a vicious cycle. Filling the settled area with more waste or soil can provide a short-term fix. But the additional weight might also accelerate future settlement. So what’s the answer?The best defense against ponding problems is to maintain enough slope on each lift (in the first place) so that no ponding occurs. And when a pond does occur, get it filled as soon as possible to minimize percolation into the underlying waste. Finally, if a certain area of ponding becomes chronic, you might have to modify your fill sequence plan, steepening the slope as necessary to maintain drainage.These options all assume that there is a good solution available. But of course that’s not always the case. For example, suppose your landfill is a canyon fill, with a working area 600 ft. long and 200 ft. wide. And unfortunately, the last lift of waste was placed at only a 1% slope–much too flat for good drainage. What’s more, your wastestream is too small to enable you to place an entire new lift (at 3%) across the landfill before winter. But rather than scramble from now until the rain starts and then let water pond wherever it ponds, you decide to focus your effort on establishing a “planned” failure. This might mean establishing an accessible pumping location to enable you to easily remove water as it ponds. You might even be able to line the footprint of the “pond” area with clayey soil so that it won’t leak into the underlying waste.Now hold on just a minute while I set the record straight. I’m not advocating that you should plan to have surface water pond on your landfill. Certainly it’s best to get it to run off if possible. But sometimes, for whatever reason, that’s not possible. And in those cases, when there is no good solution, you might be left with choosing from among the best of the “worst” solutions.When that happens, a planned drainage problem is still better than an unplanned one. Also, if you know you’re going to have a drainage problem, letting others (including the regulators) know early on can help keep everyone on the same team. It might even turn up some surprise solutions. In any event, if your landfill’s drainage system has to make a “crash landing,” it’s still best to choose the location.ErosionSimilar to drainage, the term erosion covers a lot of ground. Let’s limit our discussion to the erosion that occurs on the sideslope of a landfill.Sometimes slope erosion is caused by a combination of steep slopes, long slopes, and soils that erode easily. These are fundamental issues you can address by changing the design of the slopes. Make them flatter, install periodic drainage benches, and/or stabilize the slopes with vegetation or some type of erosion control material.A more common cause of slope erosion occurs when runoff flows from the top of the landfill, uncontrolled, over the edge and down the slope. If your landfill suffers from this problem, perk up: The solution is cheap and easy.By installing one or more downdrains, you can carry that water down the slope and safely away. When it comes to downdrains, you have a variety of choices ranging from corrugated metal pipe to HDPE-lined swales. With any system, it’s important to be sure that it can collect the water (without leakage), can be designed to carry the maximum flow, and can release it safely without eroding or overloading the ditch at the bottom of the slope.As effective and economical as downdrains are, it’s surprising that more landfill don’t use them. AccessWet-weather access is a simple three-step process. Trucks come in. Trucks go out. Trucks don’t get stuck. But obviously it only appears that simple when it’s working. In the real world, there’s a lot more to it.Safe, reliable wet-weather access starts with good planning. Usually that means creating a plan that shows the location of the roads, tipping pads, soil haul roads, and other necessary access roads (i.e., to the groundwater monitoring wells). This plan can be a formal set of drawings that’s signed, sealed, and delivered. However, it is just as often a copy of the latest topographic map of the landfill whereon the manager or site engineer hand-draws the roads and tipping pads, checks fill volumes with a planimeter, and tacks it to the wall. It’s cheap, it’s simple, it’s … the plan.If you took care last winter to identify and mark specific access problem areas, your task is simply one of repair. If you don’t remember where you had access problems, however, or if the topography of your landfill has changed a lot since last winter, locating those problem areas might be more difficult. For those unengineered projects (e.g., the scraper’s haul road), you might want to have a surveyor check any questionable areas–just to make sure they drain properly.Want to put a handle on wet-weather preparation? Start off by identifying past problems. Be sure to ask the landfill crew where the problems were.Next, prioritize what needs to be done before the wet season. Be realistic about what you can actually get finished before winter.Finally, assign tasks. One of the best tools for getting ready for next winter is a punch list. (No, this isn’t a list of who to punch if the landfill’s not ready for winter.) With a detailed winter prep list, you aren’t likely to forget some important item. Nor are you apt to arrive at the threshold of next winter unprepared.

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