Wireless Real-Time Soil Data from Stevens Hydra Probe Soil Sensors Used In Contaminated Soil Cleanup Operation
Written by Keith Bellingham
Up until the early 1970s when The US Congress passed The Clean Water Act, industrial chemicals and petroleum products were routinely dumped onto the ground or poured down wells. In those days, few people understood groundwater hydrology, and disposing of chemical waste underground seemed like a safe and easy solution.
Depending on the chemistry, underground pollution can linger for centuries, contaminating the aquifers that people rely on for drinking water. Not only is the groundwater threatened, but aquifers discharge into streams, rivers and lakes, devastating ecosystems and endangering the people that live and work near the compromised water body. Cleanup of contaminated soil and groundwater was extremely expensive, and often times ineffective.
Starting in the 1980s, new techniques for remediating contaminated soil started to emerge. Some of the techniques included underground barriers that decontaminate the pollution as groundwater passed through it. Other techniques such as bioremediation (using microbes) and phytoremediation (using plants) showed promise. In the 1990s, a lot of research was carried out, and new and better ways of treating contaminated soil with bacteria, plants and fungus appeared in the scientific literature.
The Stevens Hydra Probe II, currently being used in soil remediation projects
Today, there are many success stories involving the cleanup of contaminated soil and there are more research institutions and private companies continuing to develop better and more cost effective ways to restore contaminated soil. One such success story is the work of Environ International Corporation (ENVIRON) with a data acquisition network provided by Stevens Water Monitoring Systems. Environ is an environmental consulting company performing assessment/remediation services for clients worldwide.
Soil remediation site, with contaminated soil contained under the black plastic cover. Shown is a radio node housed in a NEMA-4 box, with connected Hydra Probe soil sensors
ENVIRON’s work includes ongoing research to develop new methods in bioremediation of contaminated soils. Bioremediation is the practice of using microorganisms such as bacteria and fungi to decompose chemical pollutants in contaminated soils.
Bacteria and Fungi use the pollution as a food source. Maintaining the habitat in the soil to optimize the biochemical reaction is critical and involves constant monitoring of soil moisture and temperature. Contaminated soils are collected and contained. The contaminated soils then are outfitted with irrigation and aeration as well as Stevens Hydra Probe Soil Sensors.
All organisms including people need food which provides energy and nutrients. The food first needs to be metabolized so that it can be converted to energy and materials for cell growth. When an organism digests the food, it chemically takes the food apart one molecule at a time by breaking and making chemical bonds. When a chemical bond is broken, the organism needs to get rid of extra electrons.
Organisms get rid of the extra electrons using electron acceptors. The chemical removal of these extra electrons is respiration or breathing. All organisms need food and need to breath in some fashion.
There are two types of respiration: aerobic and anaerobic. Aerobic biochemical reactions use oxygen as an electron acceptor, and anaerobic organisms don’t use oxygen as an electron acceptor, but use other compounds such as sulfates and phosphates.
Animals, some bacteria and fungi are aerobic, while other kinds of bacteria are anaerobic. Generally, aerobic microorganisms will decompose petroleum hydrocarbons, glycols, and explosives. Anaerobic microorganisms will decompose chemicals that contain halogens such as pesticides, dry cleaning chemicals, and chlorinated solvents.
ENVIRON is treating chlorinated pesticides both anaerobically and aerobically using an innovative new approach. The pesticide dichlorodiphenyltrichloroethane (DDT) and other chlorinated compounds are lethal to pests because they shut down an organism’s nervous system.
Generally, aerobic bacteria will not decompose chlorinated compounds. One of the methods ENVIRON is using to decompose the DDT is called CVSR (Controlled Vadose-Zone Saturation Remediation). CVSR employs anaerobic microorganisms which do not require oxygen and in fact thrive in an oxygen deficient environment.
In order to maintain anaerobic conditions in the CVSR areas, the soils are irrigated to or near saturation (40 to 50%). The CVSR areas are also dosed with a lactate electron donor / energy source prior to the irrigation to promote microorganism growth. While the upper contaminated soil needs to stay at or near saturation, it is important that the soil moisture levels below the treatment areas stay below the field capacity (25 to 30%).
CVSR (Controlled Vadose-Zone Saturation Remediation) area with soil irrigation piping
Keeping the soil moisture below the treatment area below field capacity will prevent the toxins from leaching downward, contaminating the underlying aquifer. Soil moisture data from the Stevens Hydra Probe helps ensure that the soil moisture levels at the various depths stay at the optimal moisture level, allowing the anaerobic microorganism community to thrive while preventing the downward leaching.
Installing the Hydra Probe into a soil remediation pile
The second method ENVIRON is using to remediate the chlorinated pesticide contaminated soil is a new, innovative aerobic process utilizing fungus. Because fungi organisms don’t have a nervous system, chlorinated pesticides will not be toxic to white rot fungus (WRF).
ENVIRON’s research involves using WRF to decompose the pesticides under aerobic conditions in biopiles. The soil moisture in the biopiles are maintained at a constant 30%. In addition to maintaining the soil moisture at 30%, the biopiles are also aerated with blowers. The Stevens Hydra Probe helps ensure that the soil moisture is kept at the optimal level.
ENVIRON is operating a total of nine stations with two or three Hydra Probe in each station. Five of the stations are aerobic biopiles containing the WRF, and four of the stations are anaerobic CVSR. The Hydra Probes are configured to be digital RS485 half duplex. The first RS485 bus reaches four CVSR stations consisting of 14 Hydra Probes. The second RS485 Bus contains 10 Hydra Probes in the aerobic biopiles (two probes per pile) and is connected wirelessly to the first bus using 900 MHz Spread Spectrum Technology. The Master Radio as well as the RS485 bus are connected to a cell modem. A Python script running on a virtual server polls the data from the sensors and exports them to the Stevens-Connect website.
The Stevens-Connect service is now available from Stevens Water Monitoring Systems and is ideal for this and other applications involving real-time data acquisition exported to a website. The Stevens-Connect website includes an easy-to-use graphing feature that allows the user to easily display historical data and compare it to real time data. This tool helps hydrologists and engineers to quickly evaluate large amounts of data while having the power to select certain parameters. In addition to the advanced graphing feature, Stevens-Connect can also store site data such as pictures and text.
Real-time soil moisture data being reported to password-protected ENVIRON website by Stevens-Connect data service
The blending of data acquisition technology provided by Stevens and the biochemical remediation technology provided by ENVIRON represents an economical and effective solution for contaminated soils.