Influence of co-disposing oil and gas exploration and production waste and municipal solid waste on hydraulic conductivity
Date
2022
Authors
Karimi, Sajjad, author
Bareither, Christopher, advisor
Scalia, Joseph, advisor
Sharvelle, Sybil, committee member
von Fischer, Joe, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
The most common method of municipal solid waste (MSW) disposal in the U.S. is still landfilling. Co-disposal of MSW with other non-MSWs in solid waste landfills requires engineering design to reduce the risks associated with the stability and functionality of solid waste landfills. Hydraulic conductivity is one of the engineering parameters required to assess the stability of a landfill. This study evaluated the effects of addition of oil and gas exploration and production wastes (E&PW) to municipal solid waste (MSW) landfills on hydraulic behavior of mixed waste. Hydraulic conductivity of solid waste is a function of vertical stress, waste composition, mixture ratio of MSW to E&PW based on total mass (e.g., 20% MSW + 80% E&PW), and mixing methods. A series of laboratory experiments were conducted to assess the impacts of these factors on the hydraulic conductivity of solid waste. Exploration and production waste was prepared to two moisture contents for laboratory testing: (i) as-received, which had a dry weight water content of 18%; and (ii) wet, which had a target moisture content of 32% to 36%. Wet E&PW prepared to the water content threshold represented the upper bound of water content for which the HMW met regulations for direct disposal in an MSW landfill. Hydraulic conductivity of the as-received E&PW measured in a large-scale permeameter decreased from 7.3×10-5 m/s to 1.1×10-8 m/s with an increase in vertical stress from 1 kPa to 394 kPa. The ks of as-received E&PW in small scale a small-scale permeameter reduced from 1.2×10-7 to 1×10-9 m/s with increasing stress to 50 kPa, and then ks stabilized at 7.5×10-10 m/s with increasing effective stress to 400 kPa. Although ks of the small-scale E&PW specimen was two to three orders-of-magnitude lower relative to the large-scale specimen as a function of vertical stress, the data align when evaluating ks as a function of dry unit weight. This indicated similar response of small-scale and large-scale specimens to hydraulic conductivity with respect to dry unit weight. The effects of E&PW hydration can be observed via the wet E&PW. The initial dry unit weight of the wet E&PW specimen was approximately 14 kN/m3, with a ks similar to the trend in ks versus dry unit weight for the as-received (dryer) E&PW specimen. However, ks of the wet E&PW specimen reduced two orders of magnitude (6.6×10-6 m/s to 5.4×10-9 m/s) as the effective vertical stress was increased to 17 kPa and dry unit weight increased to 15 kN/m3. Subsequently, ks of the wet E&PW decreased one order of magnitude to 2.8×10-10 m/s as vertical effective stress was increased from 17 kPa to 389 kPa. The ks of the wet E&PW specimen was two orders of magnitude lower than as-received E&PW under 394 kPa effective vertical stress. The overall trends for all E&PW mixture ratios for both the as-received and wet E&PW were similar, and exhibited an as-expected decrease in hydraulic conductivity with increasing vertical effective stress. Hydraulic conductivity for MSW-E&PW mixtures with 20% and 40% E&PW contents reduced from 3×10-5 m/s to 1×10-7 m/s under effective vertical stress ranged from 0 to 400 kPa. An increase in the mixture ratio above 60% resulted in an additional order-of-magnitude decrease in ks to 1×10-8 m/s as vertical effective stress increased above 200 kPa. The lowest ks at each stress level was measured for MSW mixed with 80% wet E&PW. Findings from this study indicate that addition of an E&PW did not change the hydraulic behavior of MSW. Mixture of E&PW and MSW creates a waste matrix such that hydraulic behavior still is controlled by MSW components at low stresses (and low dry densities). However, if vertical stress exceeds 50 kPa, mixtures of MSW + 80% (and above) E&PW were observed to produce a low permeability (i.e., ks < 1×10-9 m/s). If the E&PW is disposed in discrete layers without rigorous mixing with MSW, increasing vertical stress may substantially reduce the E&PW hydraulic conductivity producing water and vapor barriers within the landfill. These findings represent the specific E&PW tested in this study, however, when combined with other data in the literature, illustrate the need for establishing mixture ratio thresholds and intentionally co-disposing E&PWs.
Description
Rights Access
Subject
high moisture waste
landfill
solid waste
hydraulic conductivity
co-disposing
oil and gas exploration and production waste