In collaboration with Judy Daniels from Soil Sage
With 121,577 wells distributed in approximately 9.5 million acres, Colorado accounts for just over 4% of U.S. total crude oil production and 3% of the nation’s economically recoverable crude oil reserves (2,3). It also has the most comprehensive natural gas and oil regulations in the country. Operators are required to submit permits for approval before beginning exploration. Part of that initial permit process outlines the reclamation obligations for the site once it is decommissioned. Each site shall be reclaimed to its original condition or final land use that restores the soil system and ensure the target revegetation rate is at least 80% of the original vegetative cover for native and croplands.
Once the reclamation work is complete, the state compliance body audits the area using traditional ecological on-ground assessments like transect, quadrants, and percent cover vegetation sampling methods. However, these methods are constrained by the sampling design and individual interpretations, only providing information about the number and distribution along a fixed area. There’s also a limited number of inspectors and thousands of mining sites across the state, which creates a bottleneck and raises the need for reclamation consultants.
Dr. Judy Daniels, Geospatial Soil Scientist and CEO of Soil Sage, is a reclamation specialist who architects reclamation plans for extraction sites in Colorado. It is Dr. Daniels’ mission to alleviate these compliance issues by integrating drone mapping to provide time-series evidence of sustained vegetation recovery across the season. In this way, she can provide time savings with an even more holistic picture of the reclamation process than is possible with visual inspections.
The process
The reclamation process begins with a site evaluation. The evaluation gathers information about the initial environmental soil and vegetation conditions, and landscape properties that include elevation, slope, contours, compaction, and hydrologic characteristics to assess stormwater and erosion issues. The data is collected using drone mounted sensors and GPS ground sampling. The information is then processed, analyzed, and interpreted into a reclamation plan. The plan is based on site-specific environmental solutions that aim to improve the reclamation processes that foster ecosystem recovery. These recommendations align with the ecological characteristics of the soil and vegetation systems allowing the process to exceed the state’s regulatory compliance for closure.
The hardware
In order to get a full representation of the vegetation cover across both the undisturbed natural space (reclamation reference) and the reclaimed area, Dr. Daniels flew a Phantom 4 drone with the 1-inch CMOS sensor paired with a MicaSense series RedEdge in spring 2021, and a Matrice 300 drone with the DJI P1 paired with a MicaSense series RedEdge-MX in the fall, over the reclamation site in Weld County, Colorado.
The distinct advantage of gathering both datasets simultaneously proved to be a critical time-saving element. In addition, the ability to calibrate the data was key, as the site would be flown multiple times, and the vegetation change over time would be analyzed. The robust radiometric calibration workflow using the DLS2 and the calibrated reflectance panel (CRP) enabled this time series analysis.
The analysis
Esri’s Drone2Map was used to process and analyze the multispectral data. The result was a vegetation cover assessment that demonstrated the percent vegetation cover using both NDVI and NDRE indices. An additional analysis and an on-the-ground inventory of species were required to define the appropriate cover types, e.g., vegetation versus non-vegetation parameters within the disturbance extent. These analyses provided the basis for the vegetation target percent recovery.
The remotely sensed imagery provides frequent, site-wide vegetative analyses to inform the operator, and ultimately state inspectors, on the reclamation progress. This repeatability is important because the vegetation monitoring needs to be conducted at a frequency that allows the operator to rapidly detect and respond to issues, such as soil erosion, revegetation standards, and crop efficacy.
The results
These data were collected during the spring (May 2021) and fall (August 2021) flights and depicts the vegetation difference at the two different time intervals. The May NDVI/NDRE imagery (Figures 1-2) indicates a significant amount of vegetative growth following the wet spring season.
The second dataset (Figures 4-5) indicates the vegetation coverage from the dry summer months and shows a lower threshold value for revegetation within the reference extent. Even though the vegetation coverage varied depending on season, in both instances, the site met the regulatory requirement for permit closure.
The sequence of temporal imagery indicated that the reclamation processes facilitated revegetation that surpassed the native vegetation within the reference extent. It also allowed the operator to submit the request to the state regulator for closure after the active growing season ended.
The ability to use NDVI and NDRE in this manner allowed state regulators to approve sites based on data, reducing the need for individual site visits. Adoption of this method proved crucial for sites that are co-developed with agricultural fields where the regulator may visit the field after harvest when the vegetative cover is nonexistent versus several days before when it would have met the required recovery.
In the end, the aerial data captured with the RedEdge-MX was highly beneficial for monitoring and measuring the reclamation process at this site. Moving forward, Dr. Daniels will be able to replicate this process for thousands of sites across the state, helping companies efficiently and effectively achieve compliance with regulatory laws. As stricter environmental regulations are implemented across a variety of geographies and industries, the need for this type of in-depth analysis and reporting for reclamation sites is becoming more and more valuable.
References
- Colorado Natural Gas and Oil, 2018. American Petroleum Institute (API). Digital Media | DM2018-052 | 11.14
