The use of “landfarming” for the disposal of waste materials from the oil exploration and production industry to encourage the formation of more stable topsoil on re-contoured sandy dunes and the growth of pasture has increased the agronomic value of the land ten-fold.
The Taranaki Regional Council has issued resource consents for this work to be carried out on some areas of South Taranaki coastal land. Specialist landfarming operators and contractors do the work. It has been a hot topic in the region – criticised in the past because of a public perception that the drilling waste (rock cuttings, drilling mud and produced fluids) would contaminate the soil with hydrocarbons and heavy metals, but repeated trial work has shown that is not the case.
The coastal country in South Taranaki is largely exposed sand dunes with a limited and patchy ground cover from which livestock cannot gain much substance and energy. In summer prevailing winds reduced the feed content of pasture even further.
A key benefit of landfarming is the opportunity to re-contour the land to reduce the dune highs and filling the topographic lows. The oilfield solid and liquid waste is then spread to a thickness of between 50-100 mm. This waste is tilled into the underlying contoured sand to a depth of 250mm. The existing windrowed top soil is then replaced to cover the sand waste mix. Final levelling is followed by fertiliser applications and pasture seeds are sown.
Waste Remediation Services Ltd. (WRS) uses a 20-tonne digger, agricultural tractors and hydraulic trailers to carry out the work. Although there has been a slowdown in oil and gas exploration in Taranaki, WRS has still had significant volumes of oilfield waste from wellsite cleanups to keep them busy over the last couple of years.
The main constituents of the drilling muds are bentonite (clay), barite ( barium sulphate) and potassium chloride (KCL).
Soil scientist Doug Edmeades of AgKnowledge was commissioned by the Taranaki Regional Council to consider the current soil fertility of modified soils on land farms with respect to growing clover-based pasture for dairy cows. He was also asked about the heavy metal and barium concentrations in the soils and pastures and whether there were any implications for soil, pasture and animal health and production. Finally he was asked to show if there were any petrochemical residues in the soils and pasture, which might affect soil, plant and animal health.
After soil and pasture sampling and testing in commercial laboratories, Edmeades came to the conclusion, in a report to the TRC, that these modified soils were “fit-for-purpose”. The concentrations of nutrients (macro and micro), heavy metals and soluble salts in these soils and pasture were similar to normal New Zealand soils. The form of barium present was the environmentally benign barite, and there was no evidence of accumulation of petrochemical residues. Edmeades later told NZ Farmers Weekly that when he initially agreed to do the report, he was uncertain what the tests would reveal. “But the amazing thing about these sites is they are so damn normal.” He also identified worm casts on the sites he visited as “the canary in the mine” indicating that healthy ecosystems had re-established in the soils.
Another report, Biological Response of Earthworms and Soil Microbes Associated With Drilling Mud Wastes, by Landcare Research, included both the results of new investigations into drilling muds, and a review of relevant international scientific literature. Its findings said the environmental effects of drilling mud could be explained by the amount of salt present in the mixtures. While extremely high levels of hydrocarbons were found to knock back earthworm populations, no mortality was observed at levels even double those that bio-remediation sites were allowed to apply. Thus there was a good measure of protection.
The bio-remediation process resulted in marked and rapid reduction in hydrocarbon levels – 80% to 90% within two months, in some cases. Hydrocarbons were found to enhance soil microbial activity at all except the highest concentrations tested – far above permitted levels.
“The report tells us that the conditions we impose on drilling waste remediation at landfarms are more than adequate to safeguard natural soil degradation processes and re-establishment of earthworm populations,” Taranaki Regional Council said.
A report published by the Ministry for Primary Industries in late 2014 found no evidence that milk was being contaminated on farms where drilling waste had previously been bio-remediated or otherwise disposed of. The report was based on tests of milk from 17 Taranaki dairy farms where drilling waste has previously been bio-remediated in the ‘landfarming’ process, or disposed of in a mix-bury-cover process.
For comparison, milk was also tested from three control farms outside the region. Testing at an extremely high level of sensitivity was carried out for a wide range of compounds or families of compounds generally associated with hydrocarbon drilling. Among the results were a few substances detected that were at a level that do not represent a risk to consumers and within the range of detection reported from overseas and from elsewhere in New Zealand. A limited number of compounds were detected in some samples and none at all in a wide range of samples. Some compounds were detected from control farms also, so could not have originated from bio-remediation alone. MPI said will testing would continue, milk was a highly sensitive food and there would be little point in testing meat or other agricultural products as well.
Taranaki Regional Council’s director, environmental quality, Gary Bedford, said the MPI report brought reassurance and objective, fact-based evidence to inform discussions over the potential effects of landfarming. Some people had argued that allowing animals to graze on reinstated landfarm sites might give rise to tainted or polluted milk or meat. “But no facts or plausible rationale supporting this concern have ever been offered, to the knowledge of council officers,” he said. “Everyone can welcome this new report, which provides hard data to confirm there is no cause for concern.”
“Bio-remediation takes place in specified areas on a property, separate from other farming activities. Consent conditions require full rehabilitation so that the soil meets New Zealand agriculture guidelines. Notably, the practice turns scrubby, windblown, sandy paddocks into fertile and highly productive pasture of much greater productivity and value, with minimal ecological disturbance. Those who take the time to understand the process and the science will understand that landfarming really is a win-win proposition.”
WRS Operations Manager Keith Brodie says their consents enable them to “accept production station wastes – mostly “produced water” from producing wells that are under maintenance and work overs and impacted soils from well site remediation projects. We also receive waste on an intermittent pattern and only spread this (the actual landfarming) on a campaign basis when we have sufficient waste in storage to make the whole process practicable and economic. To enable this storing up to occur waste accepted to either of the sites is placed into HDPE or FFP impermeable lined pits each of approx. 350m3. At both sites we have 3 pits, thus total stored capacity is around 1000 m3 – this requires an area of 10,000 m2 (1 Ha) be prepared prior to the commencement of spreading.
In mid-2013, before the Edmeades, MPI and Landcare published reports, Fonterra changed its policy and said it would not collect milk from any “new” landfarms. It said it was 100% confident there were no food safety issues from cows grazing on bio-remediated land, but that testing of milk for hydrocarbons was costing $80,000 a year. It would continue to collect milk from six pre-existing landfarms and since that date all bio-remediation had been carried out on dry-stock properties or parts of dairy farms where only replacement stock were grazed.