Information Update August 2013
Purpose of this update
The purpose of this newsletter is to update residents on Council's progress with planning and consenting of the Picton Sewerage Upgrade, which will extend from the Waitohi Domain in Picton to the Waikawa foreshore. In particular, the reasons why the existing sewerage system needs to be upgraded, the proposed solution and the expected benefits to the local community are discussed. Further advice on a number of key questions is also provided including:
Why is the upgrade needed?
- What will the upgraded system consist of?
- What consultation has been carried out?
- What further consultation will be carried out?
- What work has Council carried out since the last update in August 2011?
- What are the results of the Assessments of Environmental Effects prepared to support consents applications for construction, site designations and overflow discharges from pump stations?
- What are the main consents being applied for?
- What is the proposed construction programme?
Why does the existing sewer system need to be upgraded?
Although waterborne sewer systems like that in Picton provide a convenient, safe and effective means of conveying sewage to a centralised treatment plant and disposal point, they do suffer from elevated flows during storms which can exceed capacity and cause overflows. The waterborne system is still considered the most practicable option for Picton and Waikawa. The topography and density of housing does not suit onsite treatment and disposal of household sewage.
During heavy rain, the stormwater and groundwater components of the flow in the sewers is several times greater than the flow of sewage from dwellings, businesses, schools and other premises. Stormwater and groundwater entering the sewers during storm events governs the design of the capacity of the system.
The main issues with regard to the existing system are:
- Penetration of groundwater into the sewer network through cracks in pipes when groundwater level rises
- Entry of rainwater into sewers from unauthorised connections
- Sewage overflows to the surrounding environment during heavy rain
- The majority of the existing trunk sewers and pump stations are under capacity and some parts are failing.
The Picton trunk sewer is shown in Figure 1.
The proposed solution
Council proposes undertaking a number of actions to repair and upgrade Picton sewerage as follows:
- Continue with efforts to remove any stormwater connections to the sewer and repair and replace failing sewer pipes
- Replace sewage pump stations at Dublin Street, Surrey Street and Fishermans Reserve
- Upgrade sewage pump stations at Beach Road and Waikawa Wharf
- Construct a new sewage Bypass Treatment Facility at Dublin Street to treat flows in excess of what can be treated at the Picton Sewage Treatment Plant (Picton STP). The treated discharge from the Bypass Treatment Facility will be pumped to the same harbour outfall that is used by the Picton STP
- Replace almost all of the trunk sewer
- Construct new and utilise existing overflow pipes and structures to control and discharge wet weather overflows from the sewer network.
The principal benefits of the Picton Sewerage Upgrade project will be:
- A reduction in the frequency, duration and volume of sewage overflows
- A reduction in the risk to public health from contact with contaminated water
- An improvement in water quality and the marine environment
- An increase in the capacity of the system
- Provision for the future growth of Picton and Waikawa.
What will the upgraded system consist of?
System capacity design criteria
The completed upgrade will generally increase the capacity of the sewer system to meet future design flows and wet weather events. The upgrading will significantly reduce, but not completely eliminate, overflows of sewage. It is impractical to build a sewer system that never overflows, but it is possible to increase capacity to give an acceptable standard of performance. The proposed upgrading will provide a level of performance that is high when compared to the frequency of sewage overflows in other towns and cities in New Zealand.
Computer modelling of the sewer network has provided estimates of the flows for various size storms. Storm size is expressed in terms of the average recurrence interval (ARI). For example, a 5 year ARI is a storm that is expected to occur once in 5 years.
Currently the Picton sewer system overflows, due to wet weather events, 2.8 times per year on average.
It is proposed to upgrade the trunk sewer to meet a 20 year ARI storm event except for the Beach Road Pump Station which will be designed to meet a 5 year ARI. Beach Road Pump Station overflows to open water outside the Waikawa Marina breakwater, which is less environmentally sensitive than the other pump station overflow points at Waikawa foreshore, Picton Marina and the Waitohi Stream.
The Picton STP utilises a biological treatment process which is robust but there is a limit to the maximum flow the plant can handle before treatment is adversely affected. For this reason the peak flow is restricted and flows in excess of this will be treated at the proposed Bypass Treatment Facility at the Dublin Street Pump Station and then pumped to the same harbour outfall that the Picton STP discharges to. Flows in excess of the Dublin Street Pump Station's capacity will overflow to Waitohi Stream.
Trunk sewer pipeline
Approximately 5 km of pipeline will be installed to replace the bulk of the existing trunk sewer. The final decision on which existing sewers will be retained will be made during detailed design. The trunk sewer can be considered in three main sections with overall approximate lengths as follows:
- Surrey Street Pump Station to Dublin Street Pump Station -1,030 m total length
- Beach Road Pump Station to Surrey Street Pump Station -3,250 m total length
- Waikawa Wharf Pump Station to Beach Road Pump Station -1,000 m total length
- The pipeline will be constructed mostly along roads between Waikawa and Picton except:
- A section of approximately 540 m along the foreshore in private property between Waikawa Road and Beach Road Pump Station
- A section of approximately 940 m through Victoria Domain and Memorial Park from Leicester Street to Surrey Street.
Pumping mains are proposed to be constructed of continuously welded polyethylene (PE) pipe. Gravity mains are proposed to be polyvinyl chloride (PVC) and/or PE pipe.
Most of the pipeline will be installed using open trenches. Trenchless methods will be used where necessary eg; to avoid disruption to the railway line.
The five existing pump stations on the trunk sewer are to be progressively refurbished or replaced. The table below shows a summary of the works to be carried out at each site. The locations of the new and upgraded pump stations are shown on individual maps in Attachment A.
|Summary of Works
New pump station, valve chamber, bypass treatment facility, biofilter for odour treatment, plant and services buildings and standby diesel generator. The existing pump station will be cleaned out and demolished to ground level and the area restored.
Located approximately 40 m east of the existing pump station in Waitohi Domain on Dublin Street.
New pump station, valve chamber and 25,000 litre underground overflow storage tank.
Located adjacent to existing pump station (which will be cleaned out, demolished to ground level and the area restored and replanted).
New pump station, valve chamber, biofilter for odour treatment, plant and services buildings and a standby diesel generator.
Located immediately to south of existing pump station (which will be cleaned out, demolished to ground level and the area will be incorporated into the new pump station site).
Upgrade of the existing pump station with new underground overflow storage tank (120,000 litre capacity).
The storage tank will be located in a car park of the nearby marina 80 m from the pump station.
Upgrade of the existing pump station with new underground overflow storage tank (25,000 litre capacity).
Storage tank located 20 m from the pump station.
What consultation has been carried out to date?
In 2007 Council invited members from key stakeholder groups to join the Picton Sewerage Consultative
Working Group (CWG). Council also advertised for interested parties or individuals to join. A collaborative approach to consultation is favoured by Council where community and institutional representatives are informed of the key issues and options, have time to solicit the views of their organisation's members and are able to ultimately make a recommendation to Council regarding aspects of the project. This group met on several occasions prior to lodging the consents application for the new Picton STP treated effluent outfall.
The first CWG meeting held on 2 November 2007 provided background and issues in regard to the Picton Sewerage Scheme and upgrading options. Subsequent CWG meetings focussed on options for treatment and discharge. The CWG gave support to the continuation of a high degree of treatment and discharge of the treated effluent to Picton Harbour. This support was based on the results of extensive environmental and human health studies.
It wasn't until the 5 CWG meeting held on 17 August 2011 that the trunk sewer and pump station upgrading was the primary topic. Discussion included design standards for sewage overflows, the environmental effects of overflows and consenting issues. A positive response to the proposed sewerage upgrading was received from the CWG at this meeting.
Council also sent out a public information brochure in August 2011 explaining the proposed upgrading works and the consents and designations that would be required. Articles also appeared in the Marlborough Express and the Picton Community newspaper at the same time. An explanation of the Picton Sewerage Upgrade was also posted on Council's website in August 2011.
Landscape plans for the new Dublin Street and Surrey Street Pump Station sites have been prepared in consultation with Port Marlborough, Council's Rivers and Drainage Section and the Department of Conservation. Council's Reserves Section was also involved with the Surrey Street Pump Station landscape plans.
More recently Council has held a Consultative Working Group meeting (meeting No.6 held on 15 July 2013), met with a Te Atiawa resource management officer on the 19 July 2013 and discussed the project in some detail with Council staff in the Rivers and Drainage Section and the Reserves Section.
What further consultation will be carried out?
Further consultation is proposed as follows:
- Council website update and information in the newspaper
- Information update to neighbours to the pump stations
- Information updates to Marlborough Roads, New Zealand Transport Authority (NZTA) and KiwiRail
Further consultation will be carried out through the life of the project.
What work has Council carried out since the last update in August 2011?
Since August 2011, Council has continued to progress the upgrading works as follows:
- The new treated effluent outfall on the west side of Picton Harbour, north of the log yard entrance is now operational. The old Kaipupu Point pipeline and outfall structure has been removed
- The preliminary design of the upgraded trunk sewer between the Dublin Street and Waikawa Wharf Pump Stations has been completed and an initial alignment proposed which essentially follows the existing pipeline
- A review of population growth in Picton and Waikawa has been carried out which allows for a long term increase of about 3000 persons. The majority of the future growth is expected to occur in Waikawa and can be largely accommodated within the existing urban residential zone
- The Picton sewerage model developed by Council has been updated to reflect the outcomes of the population growth review. The proposed sewer and pump station design capacity is a considerable improvement on the current situation
- Draft consent applications for construction, site designation and operation have been prepared. These will be finalised after the next round of community consultation is completed
- A draft Construction Management Plan has been prepared to support consent applications for construction activities
- Council has obtained general agreement with the various affected groups within Council regarding temporary construction management areas.
What are the results of the Assessments of Environmental Effects?
Key effects during construction
Construction will take place along a corridor from Dublin Street to Waikawa Wharf. The route includes roads, private property and reserve land. Refer to figure 1 above. In addition to the construction activities at pump stations, overflow tanks and pipelines, the contractor will require areas to store and fabricate materials, weld pipelines and house offices for works on the project and is likely to use all of the temporary construction management areas, shown on the pump station plans in attachment A and the plans in attachment C, for that purpose.
The results of the assessment of environmental effects show that the main issues in relation to construction will be:
- Temporary disruption to traffic and pedestriansThere will be some temporary disruption to road users, particularly during construction of sewers in roads.
The contractor's construction methodology and programme will need to take into account holiday traffic and the requirements of road users and pedestrians. Traffic Management Plans will be prepared by the contractor for approval by Marlborough Roads. Traffic Management Plans will address entry to the work sites and the safety of road users, pedestrians and construction workers.
The contractor will be required to regularly notify the public in areas of impending construction activities and communicate with residents about the project.
- Temporary noise, vibration and dustDust will be readily managed on the construction sites given the small volume of earthworks required.
The installation of piles can cause noise and vibration. Piles are likely to be required for the foundations of new structures at Dublin Street, Surrey Street and possibly Fishermans Reserve Pump Stations. Sheet piles will likely be used for supporting the ground around deep structures at pump stations, overflow tanks and deeper pipelines. Sheet piles are driven into the ground which causes noise and some vibration. The overflow tanks may also require ground improvement which could involve techniques that cause temporary vibration (e.g. vibro-compaction). People living or working in adjacent properties may also experience some noise and vibration from heavy machinery during excavation and construction.
These effects will be managed by the contractor to reduce nuisance to neighbours. Noise will be managed in accordance with New Zealand Standard Acoustics-Construction Noise (NZS 6803:1999). The effects of vibration will be managed through the requirements of the contract specification to mitigate any adverse effects on neighbouring buildings and land. Investigations have already been carried out on the soils at each pump station for engineering design.
The contractor will communicate with neighbours before commencement of work and throughout the project. Neighbours will be advised in advance of work that may be noisy or cause vibration.
- Temporary effects of sediment discharges during dewateringThe discharge from dewatering of construction works will in most cases be via the stormwater system which will in turn discharge to streams or directly to coastal water. The contractor will be required to provide appropriate treatment of dewatering flows before discharge to minimise the carryover of sediments which could have an adverse effect.
Key effects following construction
The key effects of the Picton sewerage scheme following upgrade are considered to be:
Visual and aesthetic
The Surrey Street Pump Station will be constructed adjacent to the existing pump station. The Dublin Street Pump Station will be built approximately 40 m east of the existing pump station. These proposed new pump stations are larger than existing stations and without any screening or landscaping will be plainly visible from all aspects.
Proposed landscape plans for the new Dublin Street and Surrey Street Pump Stations have been prepared with plantings to screen and soften the appearance of the new structures on the site, ensuring that they do not appear as simple utilitarian structures (see draft landscape plans in Attachment B). Overall the landscaping will ensure that the new pump stations will not give rise to any significant adverse visual effects and in the case of Surrey Street will not be incongruent with the established residential setting.
A significant portion of Fishermans Reserve will have to be cleared to construct the new pump station and overflow storage tank. When construction is completed, Fishermans Reserve will be replanted.
Changes to the visual appearance of the Waikawa Wharf Pump Station will be relatively minor. The timber fence will probably be replaced with bollards to protect the installation from vehicles. Any plants removed to carry out the upgrade will be replaced. Beach Road Pump Station is on a compact site near the entrance to Waikawa Marina. There will be little if any space for plantings following the upgrade. Consideration will be given to the visual appearance of the above ground structures.
The longer sewage remains in sewers and pump stations, the greater the potential for the release of odour. The catchments of the Fishermans Reserve and Waikawa Wharf Pump Stations are small, hence there is a low risk of odour. The Beach Road Pump Station catchment is larger and there is a small risk of odour. Sewage can take some considerable time to be pumped through the long pipeline from Beach Road Pump Station, up Beach Road and Waikawa Road to the high point near Ranui Street. Sewage is released to the gravity sewer at this point and, as it flows in sewers to Surrey Street Pump Station, can emit odour and for this reason a chemical that controls odour is dosed at the Beach Road Pump Station. The chemical is safe to use and presents no health risks.
Surrey Street and Dublin Street Pump Stations require odour control and will be fitted with extraction fans and biofilters to treat odour. The biofilters are large beds of a mixture of bark and soil. The odorous air is blown into the bottom of the filter through a network of perforated ducts. The odour is treated as it rises through the bark and soil.
Noise and vibration
Steps will be taken to minimise operational noise. The pumps will be located underground and this is effective at controlling noise from them. Biofilter fans will be housed within purpose built facilities which will control noise. The new pump stations at Dublin Street and Surrey Street will include a generator for back-up power supply in the event of an outage. The generators will produce some low level noise. Generators will be test run during the day to minimise any nuisance.
The Bypass Treatment Facility at Dublin Street will make some low level noise during operation however it will normally only operate during heavy rain when the flow of sewage exceeds the capacity of the Picton Sewage Treatment Plant. Test running will be carried out during the day.
Access and traffic generation
Once constructed traffic movements to and from the pump stations will be associated with visits by Council staff and contractors for operational and maintenance activities as required.
Discharge of sewage overflows from the upgraded sewer network
The key issues are considered to be:
Ecological effects of overflows
The potential for environmental effects from overflows will be mitigated because:
- There will be a significantly reduced frequency, duration and volume of wet weather overflows as a result of the upgrade
- The sewage is domestic/commercial based (ie; no heavy industrial activities)
- The sewage will be diluted due to rainfall derived inflows of groundwater and stormwater to sewers prior to overflow
- The overflow discharge will mix with the receiving waters and further dilute any contaminants.
Differentiating the ecological effects between sewage overflows and stormwater is difficult as most sewage overflows occur during significant rainfall when there are also high stormwater flows. Stormwater carries contaminants from the urban area and from the surrounding bush clad hills.
Waterways that Dublin Street, Fishermans Reserve and Surrey Street Pump Stations overflow to are not considered to have any particular ecological values. Untreated wet weather overflows will coincide with heavy rain and will be significantly diluted with flood flows in the receiving streams. These flows will assist with rapid transport and dispersion of contaminants along the waterway and into coastal waters. It is considered that the effects of infrequent, short term discharges will be less than minor on ecological values and no residual effects will occur.
It is considered that the risk of exposure to contaminants from the overflows on the marine ecosystem (including benthic communities, fish, marine mammals and birds) of Picton Harbour and Waikawa Bay will be very low. The effects of the infrequent wet weather overflows on the ecology of Picton Harbour and Waikawa Bay will be minor.
Effects of wet weather overflows on public health
There are a wide variety of potentially pathogenic (disease-causing) organisms in sewage, including viruses, bacteria and parasites. The actual presence of these organisms in sewage is dependent on the prevalence and incidence of disease in the local population. The Picton/Waikawa community health profile can be considered typical of many smaller communities in New Zealand however the area is a favoured tourist destination which may have a seasonal impact on the outbreaks of infectious enteric diseases.
The upgraded sewerage scheme will overflow at or near the five pump stations on the trunk sewer when capacity is exceeded during heavy rainfall. Beach Road and Waikawa Wharf Pump Stations overflow to Waikawa Bay, the Waikawa Wharf overflow being the more sensitive discharge point on the Waikawa Foreshore through an existing stormwater pipe. Surrey Street and Fishermans Reserve Pump Stations discharge to streams close to Picton Marina. Dublin Street Pump Station overflows to Waitohi Stream which passes though culverts under the rail yards to Picton Harbour.
Discharges of sewage overflows can increase health risks to those engaged in contact recreation. The consumption of shellfish contaminated by sewage overflows is also a health concern, although the gathering of shellfish near urban areas is discouraged, for example the Ministry for Primary Industry recommends avoiding collecting shellfish from areas where pipes or culverts run down to the beach or from areas where sewage or storm water is discharged or areas with houses nearby. Despite this warning some people may still gather shellfish in Picton Harbour and Waikawa Bay.
Dublin Street Pump Station overflow will be to the Waitohi Stream on the downstream side of the Dublin Street Bridge. The short section of stream has been modified and is not typically used for contact recreation. Neither the waterway near the Fishermans Reserve Pump Station, nor the Memorial Stream adjacent to Surrey Street Pump Station, has any recognised recreational values.
The likelihood of public contact with these receiving waters during periods of high stormwater flow, when wet weather overflows occur, is very low.
Improvements to public health as a result of the sewerage upgrading
The sewerage upgrade will result in a significant reduction in untreated wet weather overflows to the environment and when wet weather overflows do occur, they will be controlled to specific points of discharge to water to reduce the risk of human contact. While it is not possible to quantify the reduction in health risk associated with the upgrade, the following should be noted:
- The upgrading includes provision for a high flow Bypass Treatment Facility at the Dublin Street Pump Station to reduce concentrations of microorganisms, including those that are pathogenic, using UV (ultraviolet) disinfection. The screened and disinfected effluent will then be discharged to the same outfall that the Picton STP discharges to. This outfall discharges into deep water in a part of the harbour which is away from recreational activities and well separated from the Picton Foreshore.
- The Beach Road Pump Station will be designed for a 5 year ARI storm as the associated overflow point is in open water outside the Waikawa Marina. A higher 20 year ARI flow design will be used for the Waikawa Wharf Pump Station (which overflows to Waikawa Bay Foreshore), and for both the Surrey Street and Fishermans Reserve Pump Stations which overflow to local waterways and then to Picton Marina. These are considered to be more sensitive receiving environments with respect to public health risk. Dublin Street Pump Station will be designed for a 20 year ARI as overflows will enter Waitohi Stream and then Picton Harbour.
- There will be significantly reduced frequencies, durations and volumes of wet weather overflow discharges occurring following completion of the upgrade. Given the increased capacity there will be extended periods when untreated wet weather overflows are unlikely to occur.
- Any wet weather overflows that do occur will mix with flood flows in waterways and be diluted with coastal water which will quickly reduce contaminant concentrations to low levels. None of the coastal locations where the wet weather overflows occur are suitable for shellfish gathering.
- Council has an Overflow Response Plan which includes assessing overflow volumes and taking action as necessary to alert the public of the potential health effects.
Te Atiawa Manawhenua Ki Te Tau Ihu Trust (Te Atiawa) holds Rangatiratanga over the lands and waters that are affected by the Picton sewerage scheme. Council has consulted with Te Atiawa through the Consultative Working Group (CWG) and through separate meetings.
In respect to the new outfall in Picton Harbour, Te Atiawa advised that the discharge of effluent to water was abhorrent to its cultural values and tikanga but also recognised that there were difficulties with alternative options for discharge to land. More recent consultation has been about the trunk sewer upgrade and wet weather overflows. Te Atiawa's view on discharges of sewage has been taken into account when setting high design standards which will substantially reduce the frequency of overflows during rainfall.
The discharge of untreated sewage can change the visual amenity of the receiving water due to the contaminants discharged. Potential visual effects include floating scums, slicks and foams or reduced clarity and change in colour. There is also a low potential for odours.
Council has recognised that areas with high amenity values including Waikawa Bay Foreshore, Picton Foreshore and Picton Marina require greater protection from overflows of sewage. A 20 year design ARI has been adopted for pump stations with overflows to these areas.
Any temporary effects on the amenity values of the affected waterways and coastal marine areas will be minor given:
- The high dilutions expected from inflows of groundwater and stormwater to sewers prior to discharge
- The proposed screening and UV disinfection of the wet weather flows in excess of the Picton Sewage Treatment Plant's capacity (up to a 20 year design ARI) at the Dublin Street Pump Station, with discharge to the Picton Harbour outfall
- The significantly reduced frequency, duration and volumes of wet weather overflow discharges
- The significant mixing with the receiving waters, which are likely to be discoloured, as a result of stormwater flows during heavy rainfall.
Summary of effects of discharges
The increase in capacity of Picton sewerage will have a positive environmental outcome, as it will result in a significantly lower incidence of discharges of sewage to waterways and the coastal marine area. The environmental and public health effects of these occasional discharges will be less than minor and will only occur during heavy rainfall when dilution will be significant and the likelihood of contact recreation will be very low.
What consents and designations will be applied for?
Council will be applying for consents to construct and operate the new and upgraded pump stations and sewer pipelines. It is also proposing to designate the land occupied by the new and upgraded pump stations and the pipeline in Memorial Park and Victoria Domain. The designations would be recorded on maps in the Marlborough Sounds Resource Management Plan so it is clear where the infrastructure is located and what its function is.
Consents will be required by Council for the use of the Temporary Construction Management Areas in reserves, construction of the new pump stations (discharges of groundwater and sediment from excavations to land or water), as well as pipeline works close to streams and the coastal marine area.
Application will be made for resource consents for discharge of wet weather sewage overflows to surface water and coastal water at the following locations:
- Waikawa Bay near Waikawa Wharf
- Waikawa Bay outside the breakwater at Waikawa Marina
- Memorial Stream at Surrey Street
- an unnamed waterway within Fishermans Reserve
- Waitohi Stream near Dublin Street
Description of the works and proposed programme
|Description of Work
|Replacement of the existing outfall pipeline now completed and operational.
Replacement of the existing Dublin Street Pump Station with a pump station consisting of three separate pumping units and a treatment facility (to be known as the Bypass Treatment Facility or BTF) to treat flows in excess of the Picton Sewage Treatment Plant's capacity. The three pumping units are:
Main pumps which pump sewage preferentially to Picton Sewage Treatment Plant.
Bypass pumps which pump flows that are in excess of the Picton Sewage Treatment Plant's capacity, and up to the 20 year ARI, to the Bypass Treatment Facility (BTF).
Outfall pumps which pump flows from the Bypass Treatment Facility to the Picton Harbour outfall (the same outfall the Picton Sewage Treatment Plant discharges to).
This stage includes the new gravity trunk sewer in Waikawa Road from High Street, across Auckland Street and along Dublin Street to the Dublin Street Pump Station. A new gravity sewer will also be required in Dublin Street from York Street to the new pump station.
Replacement of Fishermans Reserve Pump Station, the construction of an underground overflow storage tank and new pumping main. Replacement of Surrey Street Pump Station with a new pump station.
This stage includes the new gravity trunk sewer in Waikawa Road from a point near Ranui Street to Leicester Street, along Leicester Street to Victoria Domain and then beside Memorial Stram to the Surrey Street Pump Station. A new pumping main will also be installed from Surrey Street Pump Station along Surrey Street and Waikawa Road to High Street.
Upgrading of the existing Beach Road Pump Station, which is located near the entrance to Waikawa Marina, and the construction of an underground overflow storage tank in Waikawa Marina carpark.
This stage includes the replacement of most of the gravity sewer from Waikawa Road near Findlay Grove and around the coast to the Beach Road Pump Station. A new pumping main will also be installed from Beach Road Pump Station up Beach Road and along Waikawa Road to a point near Ranui Street.
Upgrading of the existing Waikawa Wharf Pump Station including construction of an underground overflow storage tank in the Waikawa Foreshore Reserve carpark. The pumping main from this pump station is likely to be replaced. A final decision will be made during detailed design.