DETAILED THIRD-PARTY INDUSTRY ANALYSIS
A white paper presented the recent International Water Conference (IWC) details urgent and widespread need for wastewater solutions in the Marcellus region:
“The Marcellus Shale Formation is estimated to contain over 168 trillion cubic feet of natural gas. Due to the depth and compact nature of this formation, horizontal drilling with follow-up hydrofracturing of the formation using a mixture of high pressure water and sand is required to achieve economic gas production. From 2 to 8 million gallons of water, mixed with sand and various additives, is required to completion fracture each horizontal deep well. Following hydrofracture, free (or “flowback”) water must be removed from the well – generally 10% – 20% is recovered. Recent developments permit the recycling of flowback water, with minimal treatment, as hydrofracture makeup water.
Once a Marcellus gas well has been drilled and hydrofractured, “production” wastewater is produced for the 15 to 20-year life of the well at rates from 400 to 4,000 gallons per day. In 2016, with an estimated 30,000 wells in production, an estimated 60 million gallons per day of production wastewater was generated.
Production wastewater is “dispersed” – the wells producing it are geographically spread over wide areas with low daily flows. Management of this wastewater requires well site tankage and tank truck based collection to convey it to either transshipping locations for transport to injection wells, out of state treatment, or to central resource recovery facilities.
In contrast to production wastewaters from other gas shale plays, Marcellus production wastewater has a very high level of dissolved solids with large amounts of barium, calcium, magnesium, sodium, and strontium chlorides; with many other constituents, such as bromine and lithium, present in lesser quantities.
The table below is a typical analysis of a Marcellus Production Wastewater. Note that chemical analysis of Marcellus production wastewaters presents a challenge to analytical laboratories due to the high dissolved solids content.
TABLE 1: Marcellus Production Wastewater
|Parameter as mg/l||Result|
|Chemical Oxygen Demand||8,000|
PAST AND CURRENT TECHNOLOGY
Past and current practice for disposal of flowback and production wastewaters has included use as a roadway deicer in winter and dust control agent in the summer, discharge to surface waters via publicly owned treatment works (POTW), treatment with direct discharge to stream, and treatment with recycle as hydrofracture makeup water.
ROADWAY DEICER/ DUST CONTROL
Gas well production wastewaters have been generated and disposed of in Pennsylvania for over 100 years. In the past, the majority of these wastewaters were either dumped around the producing well or used for roadway deicing and dust control. The advent of environmental regulation has correctly eliminated these disposal practices.
DISCHARGE VIA POTW (Publicly Owned Treatment Plants)
Prior to the Marcellus shale development, a substantial amount of gas well production wastewater was disposed of via POTW with subsequent discharge to surface waters. This did not result in any major problems as non-Marcellus gas well production wastewaters are low volume and contain much lower amounts of barium and strontium than Marcellus wastewaters. In 2008, the rapid increase in Marcellus wastewater production and disposal via POTW that the Monongahela River was severely impacted, dissolved solids levels increasing by a factor of more than two. This prompted the PA Department of Environmental Protection (PADEP) to ban disposal of Marcellus wastewaters by almost all POTW. Currently less than ten (10) POTW are permitted for gas well wastewater disposal and continue to accept limited amounts of gas well wastewaters. Some specific problems noted by POTW accepting Marcellus gas well wastewaters include increased sludge generation, increased barium content in produced sludge leading to concerns as to a potential hazardous waste designation, and flotation of sludge in final clarifiers.
TREATMENT WITH DISCHARGE
Prior to development of the Marcellus shale, several facilities existed for chemical treatment of gas well wastewaters with direct discharge to stream. These facilities use chemical precipitation with calcium hydroxide to remove suspended solids and some dissolved metals. The PADEP has prohibited discharge of additional, or new, high dissolved solids (over 500 mg/l) wastewaters into waters of the Commonwealth. This prohibition has restricted these facilities to treat no more than historical flows, estimated at 1.5 mg/d, and dissolved solids loading, which existed prior to the regulation change. These facilities face an additional challenge if Marcellus wastewaters are to be treated in that as their discharge permits are renewed, or modified, they must comply with an effluent limitation of 10 mg/l maximum for both barium and strontium.
TREATMENT WITH RECYCLE AS HYDROFRACTURE MAKEUP WATER
Since start of Marcellus development, several facilities have been constructed which treat gas well wastewaters by precipitation using sulfate to lock up barium and strontium followed by calcium hydroxide for general metals removal. The resulting clear brine is then returned to gas well drillers for use as hydrofracture makeup water. There is a substantial debate as to what standards are needed for reuse of treated water as hydrofracture makeup water. The following Table 2, Recycle Criteria, summaries some generally accepted recycle criteria. Table 2, Recycle Criteria Parameter Criteria pH 6.0 to 8.0 maximum total hardness 2,5000 mg/l as CaCO3 maximum calcium hardness 350 mg/l as CaCO3 maximum total iron 2 to 20 mg/l maximum sulfate 100 mg/l maximum dissolved solids 40,000 to 150,000 mg/l Note that these criteria are usually achieved by precipitation treatment of the Marcellus wastewater followed by a high rate of dilution with fresh water. Major problems with this approach include a large volume of mixed sludge to be landfilled and the potential to become water logged as Marcellus hydrofracture activity is replaced by production operations.
Various promoters have advanced use of total evaporation with production of a condensate as a viable means to dispose of Marcellus wastewater. Evaporation has two major problems. Evaporation of Marcellus wastewaters produces a solid material for disposal which, if the barium content is not removed or chemically rendered insoluble, will often test out as a USEPA Toxic Characteristic Leach Procedure (TCLP) test hazardous waste due to soluble barium content. This specific problem has been demonstrated by operation of a total evaporation pilot facility where the produced solids were determined to be a TCLP hazardous waste due to soluble barium content. The other problem with total evaporation is the amount and chemical composition of the solid material produced and how to manage it. Based on the typical Marcellus wastewater, pretreated for barium removal, evaporation of 250,000 gallons would produce 397,823 pounds (approximately 200 tons) of a mixture of residual salts. Some of these salts, such as calcium chloride, are deliquescent; all are very soluble in water as shown in the following Table 3, Residual Salts Solubility – barium chloride 37.5 g/100 ml calcium chloride 74.5 g/100 ml lithium chloride 63.7 g/100 ml magnesium chloride 54.3 g/100 ml sodium chloride 35.7 g/100 ml strontium chloride 53.8 g/100 ml Based on the solubility of these salts, disposal of the residual salt mixture from total evaporation treatment in a landfill of any kind would appear to be impractical due to their ready formation of liquid salt solutions on contact with water or moisture. While use of the residual salts for roadway deicing has been proposed, this appears to be ruled out by the regulation of strontium in aqueous effluent at a maximum of 10 mg/l and would also present substantial logistics problems.
CHEMICAL PRECIPITATION TO SALT BRINE
Chemical precipitation of barium, calcium, magnesium, and strontium from Marcellus wastewater results in production of a sodium chloride brine, which could be utilized for roadway deicing if other toxic constituents were at suitable levels. This brine could also be evaporated to produce a solid sodium chloride that may be suitable for other uses. Drawbacks include generation of very large amounts of mixed sludge requiring landfill disposal and a substantial logistics problem.
DEEP WELL INJECTION
Currently, a substantial amount of Marcellus wastewater is disposed of by deep well injection, with most of the injection wells being located in Ohio. This disposal method has two problems, the first being simply that the wastewater has to be transported considerable distances by tank truck or rail tank car to the injection well site. Transportation costs on the order of $0.05 to $0.25/gallon have been reported. A second problem has been that several deep well injection sites being linked to earthquakes. The Ohio EPA has responded by shutting several injection wells down and restricting both the amount of wastewater that can be injected and development of additional wells.”