Policy support regarding PFAS in subsurface and sediments

Following on from a number of incidents such as the industrial PFOA and GenX discharges and a PFOS incident at Schiphol, there has been a significant increase in 2018 in interest from the dredging and earthmoving sector in the group of more than 6000 per- and polyfluoroalkyl substances (PFAS). Because these substances have not been measured in soil and dredged material until now and there were no applicable standards, the duty of care applied. The elaboration of this duty of care is embodied in the PFAS Temporary Action Framework (THK) that has been in force since July 2019. The first version of the THK led to so many operational problems that an updated THK was published in the autumn of 2019 and again in June 2020. On the basis of the available knowledge, this gradually opened up more possibilities for the use and distribution of soil and dredged material. A definitive action framework for PFAS is expected in late 2020 but the discussion about PFAS is expected to have a broader impact on the re-use of soil and dredged material and it will take shape after 2020.

Deltares has been involved with the THK since September 2019. Deltares is primarily involved in support for the policy for the use and distribution of soil and dredged material in the water system. This relates to: the use of soil and dredged material in deep lakes, their use in surface water such as parts of dikes located in the surface water and the distribution of dredged material at sea.

Provisional levels of re-pollution for nationally managed waters

In November 2019, Deltares, working with Rijkswaterstaat, derived the PFAS re-pollution levels (HVN) for aquatic soils in the nationally managed waters, and therefore set a standard for the reduction of the depth of lakes with direct connections to the nationally managed waters.

When the THK was drafted in July 2019, no HVN had yet been derived for PFAS. An HVN refers to the level of pollution in sediment deposited on a water bed; this level of pollution is a given. The HVN can be used to demonstrate that the use of dredged material complies, in principle, with the standstill principle (in other words, there is no deterioration in the situation). That makes it possible to fulfil the duty of care.

Data for the PFAS levels of suspended matter in water are used to derive an HVN for the sediment. The HVNs for the list of substances in the prevailing Dutch Soil Quality Decree (Bbk) have been derived on the basis of a 95th percentile or 10 years of suspended-matter-quality data at the Lobith monitoring location. That will not be possible in the short term for PFAS and the provisional HVN has been derived using the data about PFAS levels in the suspended matter in nationally managed waters (2018-2019). Because the database differs in that it covers a shorter period and other locations, a more conservative value – an 80th percentile – has been adopted on precautionary grounds.

PFOS as an exception
The historical data for PFOS showed that the 2018/2019 database that was used contained lower concentrations than a full database for the past ten years would contain. The HVN for PFOS is therefore not based on an 80th percentile but on a 95th percentile, as is usual for the normal derivation of an HVN.

Leaching from soil

For the purposes of the amendment in the summer of 2020, Deltares worked with the National Institute of Public Health and the Environment (RIVM) on the leaching of PFAS from soil from dry land, dredged material and floodplain soils. It was assumed that there could be more leaching from soil taken from dry land when it was used in surface water because soil is not continuously in equilibrium with water and because the sources of pollution in soil are not the same as those in dredged material. This study showed that, given the same total concentrations, leaching in batch tests was the same for soil from dry land, dredged material and floodplain soils. The research report, together with the data, can be downloaded from RIVM.(in Dutch)

Proposal for PFAS re-pollution level in dredged material from regional waters

In addition to the leaching study, Deltares also determined a PFAS re-pollution level for regional waters (in Dutch) . The HVN for the Rhine Distributaries (Deltares report November 2019, in Dutch) was also declared applicable to the whole of the Netherlands but the thinking for PFAS was that this would allow too much latitude for the regional deep lakes. An HVN for regional waters does more justice to the standstill principle in deep lakes, where the process of reducing the depth of the waters has already begun. The change in the THK in the summer of 2020 leaves no room for new initiatives.

There are three PFAS compounds that are clearly present in higher concentrations than the other PFAS: PFOS, EtFOSAA and, to a lesser extent, PFOA. No standard has been established as yet for EtFOSAA but it is widely found in amounts similar to PFOS. The pattern for PFOS is more diffuse and the pattern for EtFOSAA is slightly more patchy.

A large database with water bed measurements in regional waters, rather than measurements of suspended matter, was used to derive the HVN for regional waters. Seventeen of the twenty-one water authorities contributed to the database and the amount of data is large enough for a representative picture. However, the national database suffers from a number of limitations: the Rhine West water authorities dominate the database because they have supplied much more data. In addition, the concentrations in Rhine West are clearly higher than in the other catchment areas. That is why Deltares has elaborated two possible options in the memorandum: 1) one national value and 2) a separate value for Rhine West and the other catchment areas.

Because the database is representative for the whole of the Netherlands to only a limited extent, a conservative 80th percentile has been recommended in line with temporary HVNs and temporary background values. Splitting the database eliminates both limitations: the amounts of data in Rhine West and in the other catchment areas are more evenly distributed and there is much less regional variation in the measured concentrations. Because the amount of data (at least a few hundred measuring points) is adequate, the usual 95th percentile value has been recommended for a split database. The numbers are presented in detail in the report.

Towards a definitive framework

There are plans to include PFAS definitively as a ‘standard’ substance in the Soil Quality Regulation in late 2020. This means that there will have to be a well-founded value for all the different applications. Deltares will contribute here in the latter half of 2020 by:

proposing a maximum value for distribution in saline waters;
deriving an updated HVN for nationally managed waters;
producing the additional values required for the other applications (use in sand mining lakes, ‘general’ application in surface water).