These FAQs are designed to provide a better understanding of the proceedings – water extraction & desalination – of HDDW. On this page you’ll find the frequently asked questions and answers.

Water extraction

How long can a water well be when made with HDDW technology?
A horizontal drilling can be more than 1,5 km. Depending on the used filter materials, the well can be made with  a length up to 1 km. Depending on the soil this length generates a huge capacity, thanks to the gravel pack around the filter. In general, because of our special HDD technique, a HDDW will be a few hundred meters.

In which cases should we prefer a HDDW instead of the conventional vertical wells?For several projects we have made feasibility studies together with the research institute of the Dutch drinking water companies KWR Watercycle Research Institute, which indicated that one HDDW can compete with 5 to 10 vertical wells. It depends largely on soil, depth and capacity. We would be happy if we can make a comparison for your case.

How does HDDW influence the ground water level?
Horizontal wells influence the groundwaterlevel during the process of groundwater extraction less than a series of vertical wells with the same capacity. This has been calculated by our partner in Denmark, Orbicon for a HDDW project near Copenhagen for their client HOFOR. The reason is that vertical wells have a big influence on the ground water level in the direct vicinity of their location. A HDDW extracts the water more smoothly over a bigger area. Due to this effect you can increase capacity with HDDW and keep the same ground water level for permit reasons.

Why is the water quality of a HDDW well good?
Our standards are drinking water wells, which have a high quality. We develop the well by flushing large amounts of water through it under high pressure, which also affects the gravel pack.The filter is clean and permeable afterwards. Furthermore, we use high quality materials from selected suppliers and perform several quality checks during construction.

What is so innovative about an HDDW?
We are world expert in Horizontal Directional Drilling (www.hddsolution.com). We have been pioneers in drilling in Europe for more than 30 years now. For HDD drill, the construction of the gravel pack is the innovation. We need to remove the drilling fluid and fill the borehole with sand or gravel at the same time at a high speed. Low speed causes high costs. However, we have developed a method that works well, after several years of research together with acknowledged partner

What is the biggest market for this technology in your view
We have identified large opportunities for the intake of seawater for desalination plants. These seawater filtration projects are huge and face problems with the quality of the water intake to the Reverse Osmosis systems. HDDW can increase the purity of the influent up to a factor 7.

Desalination

What is the function of HDDW for a desalination plant?
With an HDDW it is possible to extract seawater for  the desalination plant under the seabed. During this process of desalination of seawater, the seabed acts as a filter around the HDDW, thus preventing the inflow of coarse and undesirable material. Fine material, such as sand, is impeded by the gravel pack and well screen. Furthermore, the quality of the extracted water is stable.

What is the impact on the aquatic environment?
The HDDW is located under the seabed. The filter through which the water enters the pipe is very long. Therefore the velocity of the water at the seabed is low. This low velocity of water inflow means that the surrounding flora and fauna are not adversely affected by the water extraction.

What can you say about the quality of the raw water?
Water can be extracted from a single aquifer (also read: aquifer storage). In addition, both the residence time under the seabed and the response time to changes in the surroundings are longer than with a subsurface intake. Research has indicated that the turbidity for a HDDW intake is up to 7 times lower than water extracted with the conventional methods.

How does an HDDW intake cope with the high capacity of a desalination plant?
First of all, the geological conditions need to be sufficient to provide the water. The permeability of the seabed is the most important factor. Dependent on the desired capacity, the length and amount of HDDW’s can be determined. The capacity per HDDW is maximized by preventing sand delivery by installing a gravel pack. So huge capacities are possible.

What can you say about the cost of a HDDW plant intake?
The Total Cost of Ownership for HDDW is lower than for vertical beach wells and open intakes. For open intakes, large installations for pretreatment of the water are needed and chemicals need to be added to prevent biofouling of the system. With HDDW these installations can be reduced significantly or in some cases even omitted. These operational advantages weigh up against the higher investment needed for HDDW compared to an open intake. Compared to vertical beach wells, less wells are needed to reach the same capacity. This means less pumps, piping and installations, reducing costs for investments, energy and maintenance for all HDD applications.

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