Major maintenance Adegeest

Sewer work on Diepenbrocklaan has resumed. Last week, the work was halted after unknown construction materials were found beneath the pavement. 

The unknown construction materials have been packed up and will be examined further elsewhere. The materials will be disposed of in accordance with the applicable laws and regulations. 

If you have any questions about the construction work, please contact site manager Martine van Lopik of the contractor AW Groep. You can reach her by phone at 085 109 12 53 or via the chat feature in the BouwApp. For questions for the municipality of Voorschoten, please email adegeest@voorschoten.nl.

Today, during sewer construction work on Diepenbrocklaan, contractor AW Groep discovered unknown construction materials beneath the pavement. The municipality of Voorschoten is having the composition of these materials analyzed. Work on Diepenbrocklaan has been suspended. Elsewhere in the Adegeest neighborhood, sewer construction work is continuing as usual.

The unknown construction materials are being secured on site. Fences with locks are being erected around the secured materials. An independent consulting firm will begin a comprehensive investigation into the properties of the unknown construction materials as soon as possible. Once it is clear what these materials are, they will be disposed of in accordance with applicable laws and regulations.

The Municipality of Voorschoten does not want to take any risks. The safety and health of local residents and AW Groep employees are the top priority. That is why the investigation and additional measures are being taken. Furthermore, further investigations are being conducted at various locations on Diepenbrocklaan to determine the presence of unknown construction materials. The results of the investigation may affect the scheduling of the sewer work.

If you have any questions about the construction work, please contact site manager Martine van Lopik of the contractor AW Groep. You can reach her by phone at 085 109 12 53 or via the chat feature in the BouwApp. For questions for the municipality of Voorschoten, please email adegeest@voorschoten.nl.

On June 30, the engineering firm Sweco and the municipality of Voorschoten organized a community meeting about the sewer renovation in the Adegeest neighborhood. You can find the PowerPoint presentation in the documents at the bottom of this page.

Alert Monitoring specializes in monitoring the construction environment. At the end of July, the company will begin preliminary surveys in the backyards of residents in Adegeest. Alert Monitoring will start at the locations where AW Infrabouw will resume major maintenance on the sewer system after the construction industry’s summer break. These locations are on Franz Lisztlaan, Diepenbrocklaan, and Offenbachlaan. Residents will receive a door-to-door letter shortly.

Residents of Adegeest are concerned about old sewer pipes that are connected with asbestos sealant. We’d like to put those concerns to rest. These pipes are placed whole into a container lined with tarpaulin and sent to the waste processor as a single unit. They are therefore not crushed or broken up at the construction site. This also means there is no risk of asbestos contamination. Pipes connected with rubber rings, however, are crushed or broken apart.

The existing sewer system is outdated. As a result, an increasing number of problems have arisen. Partly with a view to sustainability, the municipality is switching from the existing combined sewer system to a new separated sewer system.

In a combined sewer system, stormwater and wastewater flow together through a single pipe. During heavy rainfall, the sewer system can become overloaded, causing contaminated water to enter surface water via the overflow.

A separated sewer system consists of two separate pipes. The first pipe carries wastewater to the wastewater treatment plant. The second pipe carries relatively clean stormwater directly to surface water bodies, such as canals or ditches.

In the old sewer system, the connections had subsided to such an extent that water seals (air barriers) formed between the home and the public sewer. As a result, any sewer odors were less noticeable, even if there was a problem with the ventilation in the home or if the system was porous.

With the new sewer system and the new connections, there is no longer any subsidence or water seals. If something is wrong in the home, odor issues may become more noticeable. This is because, without water seals, these odors are no longer masked. It is therefore possible that these are defects in the home that have existed for some time but are only now coming to light.

The GGD reports that residents have been complaining for some time about sewer odors in their homes. While this smells bad, it does not pose an immediate health risk. However, foul odors can affect how people feel—for example, by causing stress, headaches, or a general sense of discomfort.

A properly functioning drainage system and good ventilation in the home (ventilation grilles and/or windows open when residents are at home) are always important, including when there are complaints about odors.

To report a sewer odor, please contact Martine, the environmental manager at contractor AW Groep. You can reach Martine via the BouwApp, by phone at 085 109 12 53, or by email at adegeest@projectmail.nl.

The contractor is investigating whether the problem is caused by an improper connection between the public section of the sewer and the section owned by the resident. The contractor is inspecting this all the way down to the crawl space under the house. If the connection is broken or damaged, it will be repaired immediately.

If the connection is in good working order, then the responsibility for any sewer odor lies with the homeowner. In that case, we recommend that you contact a plumber or a drain-cleaning company.

These specialists can check whether the ventilation in your home is working properly or if the system in your home is leaky. They can also determine whether the vent leading to the roof or the gutter is clogged or not properly connected.

The “ executive board ” is committed to providing residents with the best possible support. We have reached an agreement with Freek van Os to offer a discounted rate for group requests (per four homes). This involves an inspection/assessment (smoke test) to evaluate the quality of the home’s indoor ventilation system.

The inspection costs 240 euros per home. If four homes sign up at the same time, the inspection costs 200 euros per home. That’s because the contractor won’t charge the 40-euro call-out fee in that case. You don’t have to find three other homeowners yourself! The contractor collects and consolidates all the requests.

Would you like to take advantage of this offer? Please contact Martine, the site manager at contractor AW Groep. You can do so via the BouwApp, by phone at 085 109 12 53, or by email at adegeest@projectmail.nl.

The plumber or drain-cleaning company will investigate the sewer odor. If it turns out that the cause is, in fact, an improper connection between the public portion of the sewer and the owner’s portion, you can recover the costs of the investigation.

To seek reimbursement, you must file a notice of liability. On the “Holding the Municipality Liable” webpage, you can find out what information we need. Unfortunately, without that information, we cannot process your report.

Unfortunately, it is not possible to replace the sewer system in peatland areas without some degree of ground subsidence. Based on experience gained from projects in peatland areas elsewhere in the country, and the resulting recommendations from external consultants, the municipality determined that the work could be carried out safely using the current method.

Together with experts, we are now investigating why the actual situation is turning out differently and what measures are needed to continue the work as safely as possible. The municipality is doing everything in its power to minimize ground subsidence so that it causes as little damage as possible to residents of the Adegeest neighborhood.

Sometimes it is technically necessary for groundwater pumps to continue running outside of normal operating hours, for example, to prevent soil instability. Shutting them down temporarily can cause water to flow back, leading to additional subsidence.

We understand the concerns about these pumps running for extended periods. To minimize disruption, the contractor continues to seek the most balanced approach possible to dewatering operations.

In January 2026, residents of three homes on Brucknerlaan experienced damage to their sewer lines. An on-site inspection revealed significant variation in the thickness of the peat layer. Fortunately, no sewer pipes broke, but the connectors for the house connections had slipped off the pipes. The contractor repaired the issue immediately.

The cost of the repair work will be covered by the project budget. Therefore, residents will not be responsible for these costs.

In January 2026, while removing the sewer line, a drinking water pipe that was buried too close to the existing sewer line was struck. This caused a crack. The leak was immediately reported to Dunea, which repaired it within two hours of receiving the report.

In addition to the sewer pipes, there are also utility lines buried in the ground—namely, gas, water, and electricity. Liander conducted additional surveys in the neighborhood regarding these utilities.

Liander has determined that the current method for major maintenance on the sewer system and roads is safe. These are pipes with very strong connections, mostly made of polyethylene. Nevertheless, we continue to monitor these connections on an ongoing basis.

Due to the construction work, some tiles in your yard may be uneven, or you may have difficulty accessing the yard. We can understand that you might find such a situation unsafe.

Are you experiencing this issue? Please report it at the contractor’s site office, via the BouwApp chat feature, or by calling the emergency hotline. The contractor can then assess the situation and help you find a solution.

In January 2026, the municipality hired the engineering firm Sweco to analyze the work method. We also asked the firm to propose improvements to the work method so that the follow-up work can be carried out with minimal damage.

In response, the municipality began a trial of an improved method, in which we keep the water in the ground for as long as possible so that it remains in the peat layer or returns to it as quickly as possible. We conducted this trial between two green belts at the end of Brucknerlaan. The initial measurements were positive. We did not observe any unexpected soil subsidence.

In February 2026, work continued on Van Beethovenlaan. There, too, we began testing the improved work method. A letter to residents was distributed regarding this. You can find it at the bottom of this page. At this location, we are encountering more sand and no peat. Consequently, no subsidence has been observed, but we will continue to monitor the soil.

Fugro conducted a soil investigation for the tender for the sewer work in Adegeest. Based on Fugro’s recommendations, we outlined the work procedure in the contract with the contractor.

Following the first liability claims in 2025, the approach was adjusted based on advice from the engineering firm Sweco and in consultation with the Rijnland Water Board: by shortening the work site, the period during which groundwater was extracted was reduced.

The modified method worked as expected, until the damage occurred on Brucknerlaan. We then halted the work and asked Sweco to propose a method that is even better suited to the nature of the soil.

In March 2026, the engineering firm Movares reviewed Sweco’s proposed measures and approved them. The contractor is therefore continuing the work based on a procedure that has been reviewed by three parties.

There will be no independent claims office. The municipality will remain the point of contact for liability claims. These liability claims will be handled by the independent claims assessment firm Lengkeek.

Damages that can be proven to have been caused directly by the sewer work will be compensated. The municipality will primarily follow the advice provided by the independent claims adjuster Lengkeek. Anyone is free to have a second opinion prepared at their own expense.

Claims covered by insurance will be paid by the insurer Centraal Beheer. Other damages will be covered on a provisional basis through the municipality’s project budget. 

The section of gravel road (a mix of sand and stones) was installed because we will be renovating (paving) Bachlaan last. We are doing this last because we do not need to replace any sewer lines on Bachlaan and because it is a major thoroughfare.

Once all the work in the neighborhood is complete, we will redesign Bachlaan so that residents can easily follow a detour through the neighborhood.

If we were to pave that section of the gravel road right now, Bachlaan would have to be partially closed, and traffic would therefore be rerouted through the neighborhood. That would cause problems because construction is still underway everywhere.

An elevated concentration of gasoline was detected near the gas station on Van Beethovenlaan. We have notified the Environmental Agency and submitted a request, along with an action plan, to proceed with further steps.

The Environmental Agency has approved the action plan, so we can resume work. Remediation is not necessary. We will inform the stakeholders as soon as possible.

The service road will remain accessible to the stores on a “half-and-half” basis. We will be in direct contact with the store owners throughout the construction work. Barring unforeseen circumstances, the work will continue for several more weeks.

Rainwater is collected in the storm sewer system, which is connected to the wadis and ultimately to the waterways as well. Where technically feasible, stormwater drainage tiles were installed in the renovated streets. Each resident was also offered a rain barrel. The contractor has since delivered the rain barrels to the residents who wished to use them.

Residents who would still like to receive a rain barrel or, if technically feasible, have a rainwater drainage tile installed can let the environmental manager know during the weekly walk-in office hours or by emailing adegeest@voorschoten.nl.

The STOMP principle refers to the order of five modes of transportation used to depict a new traffic situation:

1. Steps (pedestrian)
2. Pedaling (cyclist)
3. Public Transportation
4. Mobility as a Service (bike-sharing and car-sharing)
5. Private car

In addition to this guideline, the design also takes into account the accessibility of emergency services, such as ambulances and the fire department.

Preliminary Design 

A preliminary design is the first drawing created during the design process. A key objective is to translate requirements into a visual representation. During the development of the preliminary design for Adegeest, there was an opportunity for collaboration (co-production) between residents and the municipality.

Final Design

A final design is the phase that follows the preliminary design and meets the requirements of a construction drawing. Carefully verifying and calculating dimensions and the associated costs clarifies what is and isn’t feasible in practice. This allows for a more realistic design to be drawn up. A final design also specifies the various materials to be used. It is therefore more detailed than a preliminary design. The client ( municipal council ) is informed about the final design.

Detailed Design 

A construction drawing is a detailed drawing. It follows the final design and serves as a guide for the contractor who will carry out the work.