Proper Disposal of Drilling Waste
All that Dirt You Drill Up Has to Go Somewhere
Particularly on environmental investigation/remedition sites, dealing with all that waste is a thankless task. While the well installations and sub-surface samples provide useful data to move along project objectives, the disposal of the soil and water often is no more than an inconvenient afterthought. Regardless of how non-gratifying the process may be, it easily can amount to an additional 10 percent to 25 percent on top of the drilling budget. Initial anxiety over waste-handling typically stems from simply trying to figure out how much waste will be generated. WDC (WDC Exploration & Wells, Sacramento, Calif.) always has felt that knowledge is power, which is why we’ve always kept our “Volume Calculator” prominently displayed on our Web site (www.wdcexploration.com/tools/volume.xls). But the raw numbers are just the first step. Figuring out the containment configuration, staging, transport, etc., usually brings on the next stage of consternation. Do not fear this step.
Drums vs. Bins: The Epic Battle
Drums are not cheap, they take up a lot of space, and when they’re full, they’re heavy. They have to be dealt with individually. There are many reasons not to use drums. Drums are only a convenient containment method if you’re not going to need a lot of them. But what’s the magic number where drums become more trouble than they’re worth? Drillers tend to preface most answers to any question with, “Well, that depends …,” and this situation is no different. Maybe there’s plenty of room for hundreds of drums, and you know a company that will transport and dispose of them really cheap. Great – use drums.
More often than not, however, a roll-off bin is the way to go, and you might be surprised to find that a bin still is more cost-effective even if you’re only going to fill it to 30 percent of its capacity. The graph below plots a simulated comparison for total cost of containment and disposal. This scenario assumes $160 per drum (includes the drum itself, plus disposal). Bin costs are a little more complicated. You have the cost of delivery, bin rental, a forklift and hopper to get the soil from the drill site to the bin, off-hauling to a landfill, and disposal fees. Variables affected by time (bin rental and the forklift rental) assume 1.2 cubic yards of soil generated per day (100 linear ft. of 8-in. hole – a reasonable drilling assumption). Bin transport assumes eight hours per trip. Neither the drums nor bin cost calculations include profiling cost. In this simulation, the magic number is 16 drums. Any more than 16 drums and a bin is cheaper. Putting the cost aspect aside, we’ve found that somewhere between 20 drums to 30 drums is where it starts to be really inconvenient from a schlepping-them-about-the-site-and-figuring-out-where-to-put-them perspective.
Waste-handling isn’t fun. It’s expensive. It’s annoying. But it isn’t going to deal with itself. Like anything, a little bit of planning goes a long way. There is no worse feeling in the world than that twinge you feel a week before a job is supposed to start, and everything is firmed up and dialed-in, and then someone asks the one question that hasn’t come up (but should have): “What are we doing with the spoils?” Plan ahead; waste-handling isn’t that bad.
Dealing with liquid materials is by far the most difficult and potentially costly aspect of drilling waste management, due to the difficulty in determining how much liquid will be generated (i.e. from drilling and development). Usually, the best management practice for handling large volumes of liquid is to discharge clean fluids (non-contaminated/non-turbid) to a storm sewer at or near the site. Hauling liquid from the site gets expensive, and is hard to budget since the total volume is variable. Development and formation water may be loaded with natural sediment, so it needs to be separated before it can be discharged. Additionally, with environmental sites, contamination is a barrier to discharge. If a site is in the remediation phase, a water treatment system may be in use. If the permit allows, the system can be an effective means to treat the liquid. If not, a portable treatment system can be an effective alternative, and can provide some cost savings in lieu of hauling and disposal. Yes, you will need to get a waste discharge permit, and some sanitary districts are easier to deal with than others.
If you are drilling mud rotary, you can calculate how much drilling fluid will theoretically be needed or generated (remember the volume calculator tool on the WDC Web site). A good rule of thumb for mud is to calculate the final borehole volume and multiply by three. This factor will compensate for the mud tank volume and any thinning of the drilling fluid that may be required prior to well construction. Drilling mud can be either solidified and treated like the rest of your soil/solids, or flocculated and separated into the bentonite and water. Sometimes it is easier to just have it hauled with a vacuum truck. Pricey, yes, but getting the mud off the site quickly often is worth it. If you are going to solidify or flocculate, make sure that your containment has plenty of excess volume. The amendments that facilitate these processes need to make contact with all of the mud. The two most important elements in any chemical reaction are residence time and surface area. The latter is cheaper than the former.
Other drilling methods will generate excess water during operations. Air rotary below the water table and sonic are the two biggest offenders. Yes, you heard right – sonic. It is not a no-waste method, contrary to popular wishful thinking. Unless you explicitly specify “dry” sonic to the driller, he may use water to wash in over-ride casing and to cool his bit. Because the cuttings and water (added or formation) return to the surface together, they need to be separated. It is best to collect everything in a hopper as it surfaces, and separate somewhere else rather than slow down the drilling (time is money). In this case, phase-separator bins instead of standard roll-offs are worth the extra rental cost. Don’t forget to buy extra sediment filters.
If you are anticipating a significant amount of development water, a fixed-axle T-Tank is the way to go. T-Tanks have roughly 21,000 gallons of capacity. The time it takes to fill the tank is more than enough time for the sediments to settle out. Clear water is siphoned off the top and delivered to whatever discharge point you have set up (remember: permit, permit, permit). Beware: 4,000- and 6,500-gallon poly tanks are relatively cheap and easy to rent, but they are extremely difficult (read: expensive) to clean afterward, because they are a confined space. Regardless of what type of tank you use (21,000-gallon steel tank or the smaller poly tanks), clean-out is a classic, budget-busting “oh by the way …” process. In addition to paying someone to clean out the tank, the residual sediment will have to be hauled off and disposed properly (note: analytical testing required). Like untreated drilling mud, it is considered a sludge, and cannot be taken as Class III ADC (alternate daily cover) by your friendly local landfill. Make sure your waste-handling budget includes a vacuum-truck round-trip and sludge disposal at a licensed facility.
When performing an aquifer test, you may be able to discharge directly to the storm sewer, as the well should have been completely developed by this point (note: do not forget about a waste discharge permit. Also, analytical testing will be required as part of the process). If you still have significant sediment, get out your Driscoll Second Edition, and take a quick refresher on screen and filter pack design, or consultant a hydrogeologist knowledgeable in well design.
Now you are set. You know how to deal with the soil and liquid waste. Summer’s here, so what are you waiting for? Let’s get turning to the right.