Frequently asked questions application granulite Saskerleidam

Last update: November 20, 2025

The Recreatieschap Alkmaarder- en Uitgeestermeer (RAUM) is currently carrying out a project in the Alkmaardermeer near the Saskerleidam. The project consists of creating a lee zone on the south side of the Saskerleidam to prevent further erosion of the Saskerleidam. The lee zone will also be made nature-friendly, which will contribute to the ecological water quality of the Alkmaardermeer. Below are frequently asked questions and answers about the application of granulite. For more information about the project, visit the RAUM website: Bank and nature development Saskerleidam - Projects - Alkmaarder and Uitgeestermeer lake. 

What is HHNK's role in the project?

The State Water Board is a permit issuer and supervisor. HHNK has given permission under additional Requirements for the construction of a dam containing a core of granulite. HHNK is not an initiator of the project. Because of the boost to ecological water quality, HHNK is contributing financially.

What is granulite?

Granulite is fine material created from the crushing of natural stone. The natural stone is granite from Scotland and a metamorphic sandstone from Norway. The natural stone is crushed to serve as aggregate for asphalt and concrete. Grains of minimal size are needed for asphalt and concrete, but crushing also produces finer material as a residual product. The granules for the asphalt and concrete are washed with water. In this water there is fine material. After separating the water from the fine material, granulite remains.

Why is there so much focus on the application of granulite?

Granulite has previously been widely used elsewhere in the Netherlands to deepen sand extraction pits. The deepening of deep sand extraction pits is also a measure to improve ecological water quality. During the implementation of the deepening of these sand extraction ponds, concerns arose about the presence of polyacrylamide and the formation of acrylamide. The use of granulite was widely reported in the national press. In the separation process to remove the finest dust from the wash water, a flocculant (flocculant) is used. The flocculant causes the fine dust to clump together and settle faster. This flocculant consists of polyacrylamide. The polyacrylamide can potentially break down into acrylamide which has been classified as a carcinogen. In response to all the media attention and concerns, the Ministry of Infrastructure and Water Management commissioned studies. Many surface water and groundwater samples and laboratory analyses were conducted at multiple sites for both polyacrylamide and acrylamide. In none of the samples was polyacrylamide or acrylamide detected above detection limits below drinking water standards. Despite the positive results of the study, concerns have not been allayed and granulite continues to receive considerable media attention.

What kind of substance is acrylamide?

Acrylamide is a substance that is usually created when starchy products such as potatoes, grains and coffee beans (among others) are roasted. It is found in foods such as French fries, potato chips, bread, rusks, cookies, toast, breakfast cereals and coffee. Acrylamide has been identified as a substance of very high concern because of its carcinogenic properties. Standards for acrylamide have been established for food products and drinking water from a public health perspective to limit human exposure to this substance. Acrylamide dissolves well in water but it also rapidly breaks down into carbon dioxide (CO2) and ammonium (NH4). 

Why does HHNK allow the use of granulate? 

HHNK initially had the same concerns regarding granulite and the possible release of acrylamide. Indeed, for water quality reasons, it is undesirable for acrylamide to be released into surface water. On the other hand, the source of granulite is a clean material in which it is unlikely that other pollutants such as PFAS (Poly- and perfluoroacyl substances) or PAH (Polycyclic Aromatic Hydrocarbons) are present. In soil that is being reused, for example, it is more likely that a contaminant will be overlooked. Because of concerns about acrylamide, HHNK required the applicant to have the granulate tested for the presence of polyacrylamide and acrylamide before it could be applied in the Alkmaardermeer. This batch inspection showed that the amount of polyacrylamide and acrylamide is so low that it is not measurable. The fact that it has not been analytically demonstrated gives HHNK sufficient assurance that the application of granulite will not lead to contamination of the surface water with acrylamide. The granulite for the Saskerle Dam is thus of a quality that is freely applicable on land and in surface water. 

Can the work continue? 

Yes, the tailoring order has been issued by HHNK for this purpose. We are supervising the work. The project is also part of the Water Framework Directive (WFD) goals to be achieved. So HHNK also has an interest in ensuring that the material does not leach acrylamide. 

Does HHNK measure whether acrylamide is released into the water? 

Yes, the supervisors of HHNK monitor the work and take water samples at various times during the application of the granulite. On October 2, 2025, measurements were taken of the dust cloud created after stormy winds. None of the measurements showed acrylamide above the detection limit or the drinking water standard.

How is the granulate prevented from spreading throughout the lake? 

The work with granulite involves making the dam creating a dammed bay. The dam will eventually be lined with clay, a geotextile, railroad ballast and poured stone, and on the inside a nature-friendly bank with a grass mat on top of the dam. In particular, the clay cover on the granulite core prevents the granulite from being in direct contact with surface water.

In late September and early October 2025, part of the granulite dam is not yet capped. Why not?

There has been a delay in the supply of clay to cover the remaining granulite core. The current situation is temporary but temporary measures are being considered.

In late September and early October 2025, a cloud of dust formed in the water. Is this granulite and is it dangerous?

We do not rule out the possibility that the dust cloud in the water contains granulite. Not all of the applied granulite within the natural development area had been finished with clay by October 2025. Due to the lack of the clay cover, granulite may swirl up due to wave action and thus enter the surface water in suspension. The dust cloud may also come from the applied clay. In order to determine whether acrylamide is present in the dust cloud, HHNK again conducted monitoring measurements on October 2. These measurements also showed no acrylamide. The dust does temporarily reduce sunlight in the surface water. This hinders the development of aquatic species. The dust cloud is mainly in the dammed section that will eventually receive a nature-friendly design and will contribute to an improvement of the aquatic ecology.

What is being done to prevent the formation of the dust cloud?

The RAUM is responsible for taking action. The dust cloud is mainly located in the dammed section that will eventually be further deepened and nature-friendly. Through an opening between the new dam and the existing Saskerleidam, the dust cloud can also spread to the Alkmaardermeer. This is a temporary situation but for water quality and aquatic organisms (aquatic flora and fauna) the turbidity is undesirable. The dam and nature-friendly zone are expected to be completed by mid-March 2027. To prevent turbidity until then, the contractor will apply sand from the Alkmaardermeer to the dam which has not yet been completed. The opening to the dammed area will also be reduced or temporarily closed. To prevent erosion of the deposited sand, a design for a breakwater made of rock is also currently being worked on. The breakwater was not yet foreseen in the original design.

Will the entire expansion of Saskerleidameiland be made of granulate? 

No, granulite is only used in the core of the dam on the outside of the dammed section. The section behind the dam will be filled with dredging from the surrounding area, mostly from Uitgeester- and Alkmaardermeer itself and from the Zaan. The water board and the recreation board are still discussing this. Here, too, we test the dredging against current legislation and the WFD targets to be achieved. The water quality must never deteriorate, only improve.