Miljøprojekt Nr. 1193 – Termisk assisteret oprensning af høfdedepotet, Høfde 42, Harboøre Tange

Termisk assisteret oprensning af høfdedepotet, Høfde 42, Harboøre Tange

Summary and conclusions

On behalf of the Danish Environmental Protection Agency and Ringkjøbing County the consultants NIRAS and TerraTherm have completed a preliminary evaluation of the possibilities of applying thermally assisted remediation methods for the removal of sediment and ground water pollution in and around the dumpsite located at “Høfde 42”, Harboøre Tange in Denmark.

The present report describes the following activities:

Literature studies of thermal methods in relation to the pollution of the dumpsite at “Høfde 42”
Treatability tests with thermal methods on water and sediment from the dumpsite at “Høfde 42”
Selection of the most suitable thermal solutions and description of a full scale remediation
Description of a possible pilot project.

The aim of the literature study was to survey past results obtained by thermal methods applied at locations equivalent to “Høfde 42”. The study identified more than 700 references, of which 33 are utilized. Furthermore, the report and article database of TerraTherms is included.

In outline the following can be concluded on the basis of the implemented literature study.

There is no field data available on thermal remediation methods for substances equivalent to those at “Høfde 42”. However, similar projects suggest a considerable remediation effect.
The phosphoric insecticides found at “Høfde 42” are not highly energized, and the substances can be degraded by hydrolysis at less than 100 degrees Celsius, if submitted to an environment with a specific pH value.
By-products from the degradation of phosphoric insecticides have proven problematic, and prospective thermal prevention measures will have to manage those as well.
Equipment materials for drilling and safety installations are critical due to the risk of corrosion.
It is estimated that the working environment during the remediation procedure can be secured by means of standard procedures and a job specific analysis.
The risk of substance spreading can be minimised by well-known methods (pneumatic and hydraulic control).
Phosphoric insecticides such as parathion and methyl parathion have proven thermally unstable, and it must be determined, whether there is any danger of explosion in connection with thermal remediation of the dumpsite at “Høfde 42”.
Thermal methods seem very promising for remediation the dumpsite. A thermal remediation can possibly be carried out at a temperature below or at 100 degrees Celsius.
The patent conditions surrounding the use of thermal remediation in Denmark are clear and manageable.

Based on information from literature studies treatability tests have been carried out in order to expose a series of physical characteristics, pH buffer capacity, degeneration rates as a function of pH value and temperature as well as leaching and removal of selected substances by heating and flushing. Furthermore, gas and heat degeneration due to the increase in temperature have been examined in a screened test.

The treatability tests showed the following remediation efficiencies:

That thermal treatment at 300 oC will result in complete removal of the measured organic substances and an approximately 85 % reduction of the Hg levels.
That a temperature rise to 100 oC and steam flushing will result in a considerable reduction of the concentrations of the Chemicals Of Concern, COC, i.e. 92 % for ethyl parathion and a reduction below the level of detection in the remaining substances. The expected effect at field scale is even bigger, and ethyl parathion can probably be eliminated totally by extensive treatment. It must be noted, that this treatment does not, however, reduce the concentration of Hg in the sediment.
That a temperature rise to 90 oC and flushing with hot water will result in a reduction of the concentrations of COC, i.e. 81 % for ethyl parathion and a reduction below the level of detection in the remaining substances. The expected effect at field scale is even bigger, and ethyl parathion can probably be eliminated totally by extensive treatment. It must be noted, that this treatment does not, however, reduce the concentration of Hg in the sediment.
That a temperature rise to 70 oC and a flushing with 10 pore volumes of warm water caused a reduction of COC, i.e. reduction of concentrations between 22 and 60 % in the reactor tests. The remediation efficiency was the lowest for ethyl parathion, which occurs in the largest concentrations (reduction from 3.700 to 2.900 mg/kg TS).

Moreover, the treatability tests confirm that the thermal methods entail a risk of production of unwanted gasses and a potential risk of explosion in the sediment matrix.

Gas readings show a possible formation of inorganic gasses during the hydrolysis and thermal treatment. VOC, H2S, SO2, NO and CO will be released or generated. As such, a thorough pneumatic control is vital during possible future remediation.
The monitoring of the temperature in the oven and reactor respectively does not show any immediate signs of distinctive exothermic processes during the tests. Consequently, NIRAS has consulted Cheminova regarding the company’s experiences concerning the stability of parathion, methyl-parathion etc. during heating. Furthermore, the temperature readings carried out during the reactor tests have been discussed. Cheminova recommends that a small series of supplementing calorimeter tests with heavily polluted sediment from the “Høfde 42” is carried out.

Based on the results of the treatability tests, 16 possible remediation scenarios have been listed. The scenarios include both treatments above and under the straddled argillaceous stratification at the location as well as outside and inside of the established cap by means of various thermal methods.

An analysis of the respective scenarios has been carried out with consideration of e.g. the polluted mass removed, risk reduction and relative cost.

Consequently it is estimated, that the most favourable solution in terms of remediation, economy and practicability will be to use a remediation scenario consisting of thermal treatment within the established cap at a minimum of 90 oC below the straddled argillaceous stratification and thermal treatment at 100 oC above the straddled argillaceous stratification.

Such a remediation can be obtained either by circulation of hot water and ISTD or by injection of steam in both layers. As remediation by steam is well tested and developed at full scale in Denmark, and furthermore because it is considered to be less costly in the present case, this solution has been selected as remediation concept.

Subsequently the selected thermal solution will be described at a full scale level. The design and the main parts of the strategy are presented, and the expected amount of resources in terms of e.g. energy is estimated. Furthermore a price estimate of the expenses connected to the implementation of the presented thermal solution as well as the expected remediation efficiency, critical elements and uncertainties are presented.

Finally a recommendation for activities in the second phase of the project will be given. A preliminary design for a possible future pilot programme is drafted, and the remediation strategy, a possible monitoring program and the expected consumption of resources of a pilot programme is presented.

A price estimate of the cost level of the described pilot program and further re¬commendations for supplementing activities together with the result of the pilot programme will enable an improved basis for the design of a future full scale remediation treatment.

Appendix 1 ISTD describes an alternative to pilot-program and full-scale remediation by use of steam. A price estimate and further recommendations for supplementary activities for the ISTD remediation are also described.