June 21, 2018

Emily Stockwell Coauthors Article on Thermal Monitoring of Natural Source Zone Depletion for the Groundwater Monitoring and Remediation Journal

Emily Stockwell (Colorado) coauthored an article entitled "Thermal Monitoring of Natural Source Zone Depletion" published in the National Groundwater Association's (NGWA) journal, Groundwater Monitoring and Remediation, on May 3, 2018. Her co-authors were Kayvan Karimi Askarani, Keith R. Piontek, and Tom C. Sale.

Emily's experience includes investigating and characterizing sites contaminated with light non-aqueous phase liquids (LNAPL), dense non-aqueous phase liquids (DNAPL), and metals. Emily has assisted in selecting, implementing, and evaluating remediation strategies for these sites including soil vapor extraction (SVE), in-situ chemical oxidation (ISCO), enhanced in-situ bioremediation (EISB), and monitored natural attenuation (MNA). She has also evaluated the effectiveness of pump and treat and air sparging remediation systems. Emily has extensive experience evaluating natural source zone depletion (NSZD) at LNAPL impacted sites.

Groundwater Monitoring and Remediation is a quarterly journal that offers application oriented, fully peer-reviewed papers and articles from the practitioner's perspective. Each issue features information on treatment technology as well as EPA updates, news briefs, industry announcements, equipment news, professional services, annual directories, and buyer's guides.

NGWA is a community of groundwater professionals working together to advance groundwater knowledge and the success of its members through education and outreach; advocacy; cooperation; information exchange; and enhancement of professional practices.


Natural depletion of subsurface petroleum liquids releases energy in the form of heat. The rate of natural source zone depletion (NSZD) can be derived from subsurface temperature data. An energy balance is performed to resolve NSZD‐generated energy in terms of W/m2. Biodegradation rates are resolved by dividing the NSZD energy by the heat of reaction in joules/mol. Required temperature data are collected using data loggers, wireless connections, and automated data storage and analysis. Continuous thermal resolution of monthly NSZD rates at a field site indicates that apparent monthly NSZD rates vary through time, ranging from 10,000 to 77,000 L/ha/year. Temporal variations in observed apparent NSZD rates are attributed to processes governing the conversion of CH4 to CO2, as opposed to the actual rates of NSZD. Given a year or more of continuous NSZD rate data, it is anticipated that positive and negative biases in apparent NSZD rates will average out, and averaged apparent NSZD rates will converge to true NSZD rates. An 8.4% difference between average apparent NSZD rates over a 31‐month period using the thermal monitoring method and seven rounds of CO2 efflux measurements using CO2 traps supports the validity of both CO2 trap and thermal monitoring methods. A promising aspect of thermal monitoring methods is that continuous data provide a rigorous approach to resolving the true mean NSZD rates as compared to temporally sparse CO2 trap NSZD rate measurements. Overall, a vision is advanced of real‐time sensor‐based groundwater monitoring that can provide better data at lower costs and with greater safety, security, and sustainability.

More Information

Learn more about the article: https://onlinelibrary.wiley.com/doi/full/10.1111/gwmr.12286.
For consultation regarding natural source zone depletion, contact Emily at This email address is being protected from spambots. You need JavaScript enabled to view it..
Learn more about Emily at: https://www.linkedin.com/in/emily-stockwell-aba8a730/

Geosyntec Consultants
Geosyntec is a consulting and engineering firm that works with private and public sector clients to address new ventures and complex problems involving our environment, natural resources, and civil infrastructure.

Follow Us