Pond Concern

DocumentThis pond is used by the City of Manassas for industrial process water from Micron as storage in times of high demand on the sewer lines into Upper Occoquan Sewer Authority (UOSA) system.  The pond keeps the City within it's  daily capacity limit of 8.6 million gallons a day within the UOSA system.

The following are actions taken by the City of Manassas to ascertain and correct the odor issue at the pond.

Update June 30, 2021

Installation of the liner and the aerators has been completed and everything is now ready to be tested.

In order to test the aerators, there must be 5 feet of water in the pond.  The City will begin the filling operation on Tuesday, July 6, 2021.  Once testing is completed we will drain the pond and return it to normal operations until it is needed to divert future flows.  We currently estimate the process of filling, testing, and draining to take approximately 4 weeks.

Updated Activities -- August 6, 2020

We apologize for the delay in updating this information.  Much work has taken place and completion is expected within the next 60 days.

  • Notice to proceed with construction of the liner project was given to the contractor in November 2019.
  • Through the end of 2019, the City reviewed and approved the contractor’s submittal for materials and construction to ensure they were correct to the design plans.  The contractor began their survey work mobilized their construction equipment to the site.
  • Active construction began in early 2020.  Construction includes removing all the vegetation, installing concrete channels so the pond is more easily drained through the pump station and the installation of aerators.  These aerators are an important addition as they will prevent stagnant water and better mix the chemical treatment to prevent the creation of any odors.
  • Construction will also include removal of the cascade outfall channel where water currently enters the pond and installation of an in-line pipe at the opposite end of the pond (furthest from Winter’s Branch) to eliminate another possible source of odor creation and make operation of the pond more efficient.
  • During construction in February, groundwater was encountered during excavation that had not been observed before.  Out of an abundance of caution, we had our engineers design a solution to remove this groundwater so to remove any possible conflict with the new liner system to be installed.
  • Kimley-Horn designed an underdrain system to be installed under the liner which will channel any groundwater to a separate structure to be pumped out as needed.
  • In April, the contractor began installing the underdrain system.  They also began installing the new concrete channel as well as pouring the concrete foundation pads for the new aerators.
  • During May and June, the contractor has completed shaping and compacting the slopes in preparation for the liner.  All concrete work has been completed and the aerators have been installed onto their concrete pads.  These aerators will be able to move up and down depending upon the water level in the pond.
  • During July, the contractor has been installing all of the electrical conduit and connections to the aerators.   The groundwater pump has been installed and work continues on final grading in the bottom of the pond.
  • We expect the installation of the liner to begin before the end of August.  This is the last major piece of construction to occur before the project is complete.
Updated Activities - August 6, 2019

  • The pond has been empty for many months as we have worked on developing construction plans for lining the pond.
  • The lining project is currently out to bid and bids are due August 15. The bid process was slightly delayed in order to include aerators as part of the plans and specifications. Once bids are received, it normally takes about 30 days to review the bids, execute a contract with the successful bidder, and issue a notice to proceed.
  • Once a notice to proceed is issued to begin the work, the project should be completed within 150 days barring any unforeseen circumstances.
  • The City has just completed purchasing additional wastewater capacity at the UOSA treatment plant. We have added 500,000 gallons of capacity which will help to minimize future use of this pond.

Updated Activities - March 22, 2019

  • Kimley-Horn has completed the final draft of their design and technical specifications. They are addressing a few final City comments and the City will receive 100% complete plans and specifications next week.
  • The current schedule calls for bids to be advertised beginning the week of April 8. Projects of this nature typically advertise for 30 days so the City expects bids to be due approximately May 10. Once bids are received, it usually takes two to four weeks to finalize and sign contracts, which means the contractor should begin their work by early June.
  • Once the exact schedule with specific dates is finalized, we will post that information on this page.

Updated Activities - Feb. 1, 2019

  • Kimley-Horn has completed its technical report regarding the potential source of odors. You can read the report here. While we believe we knew the potential sources of odor, we directed Kimley-Horn to look holistically at the entire system in the area, which included the pond, the sewer trunk line along Winter’s Branch, and the Winter’s Branch Pump Station that is operated by UOSA. The report confirms the following:
  • The main source of the odor appears to be the formation of hydrogen sulfide.
  • Testing has verified sulfides are not part of the industrial process water coming from Micron.
  • Hydrogen sulfide is being formed from the biological reaction of sulfates made worse by the presence of organic material (grass, vegetation, etc.) primarily in the pond.
  • The sewer trunk line along Winter’s Branch has surcharging conditions which inhibits the ability of sewer gas to reach the pump station. This is the likely cause of odors coming up through the sewer lines and manholes in the surrounding neighborhoods.
  • The UOSA pump station does not appear to be a contributing factor to this odor issue.
  • Aerial surveying of the pond has been completed and the survey documentation has been provided to Kimley-Horn to complete the final design of the pond liner. We will have a draft set of construction documents and technical specifications to review by February 18. Once we receive and review, we will be able to establish a definitive schedule for bidding and construction of the improvements.

Updated Activities - December 10, 2018

  • Flow data for the main trunk line have been received and analyzed by Kimley-Horn, and the data has been programmed into the modeling software. The data shows that there is “surcharging” in the main line. Surcharging is a condition where flow exceeds the capacity of the pipe and will slightly back up the line. When you have surcharged conditions, sewer odors that normally stay contained in the pipe are blocked from traveling through the system to the UOSA facilities. Surcharging conditions can be a contributing factor to odors escaping in to the neighborhood.
  • Now that surcharging conditions have been confirmed, we need to perform additional analysis to determine the best options to resolve these conditions and eliminate the potential for surcharging to occur.
  • We expect to have a preliminary report regarding the odor issues from Kimley-Horn to share in our January update. We will post it on this website.
  • Aerial surveying of the pond is currently scheduled for the week of Dec. 17 weather permitting. We should have the completed survey and data needed for pond liner design within about two weeks after the field work. The survey data is the last major piece of information needed to complete the design of the liner and prepare the construction documents for bidding. Once this information is received, we should be able to set the schedule for completion of the documents, bidding, and construction.

Updated Activities – November 1, 2018

  • All industrial process water from Micron has been drained from the pond. City staff has been scraping the bottom of the pond to consolidate all organic material to be removed. In addition, all of the sides of the pond have been cut back of vegetation. Any pockets of water remaining are from recent rains and will evaporate.
  • Final test results from additional sampling should be received within the next two weeks. Once received, Kimley-Horn will analyze these results for problem identification and solutions.
  • Flow meters were installed for three weeks and are being removed this week. The data collected will be evaluated by the consultants and programmed into the trunk line model being developed.
  • Preliminary detail information for the new pond liner has been received from Kimley-Horn. Additional design and computations are needed before beginning work on construction documents. This work continues to move forward.

Updated Activities – October 5, 2018

  • Additional sampling for sulfides at Micron is underway. Kimley-Horn is waiting for these results to add to their analysis. Micron has also provided additional pH test results to our consultants. The City will begin sulfide testing next week. There was a slight delay with establishing the testing protocols to ensure accurate sampling from our system, but this has been resolved and sampling and testing will now begin.
  • The City has been actively draining the pond and currently less than one foot of water remains. Barring any weather issues, we will continue draining the pond and expect the pond to be essentially empty by the end of next week.
  • Kimley-Horn has begun an initial trunk line model to understand how the main sewer lines along Winter’s Branch are operating. The City will be installing flow meters at various points within the line to collect flow and volume data. This information will assist with the trunk line modeling and help determine how sewer gas should be flowing and if there are flow issues that may be blocking the sewer gas and causing it to back up in the system.
  • Kimley-Horn will be providing a preliminary layout of the proposed new pond liner next week for City review. The detailed schedule is still being refined. The preliminary draft schedule calls for construction and bid documents to be ready for bid by the beginning of January. Some of the known challenges include the following:
    • There is a lead time in obtaining the lining materials of as much as 8 weeks. A contractor will not order materials until a construction contract is in place.
    • Public procurement laws require the City to go through a bidding process in order to complete this work which adds time to the schedule.
    • Cold temperatures affect the installation of the liner. Temperatures below 40 degrees Fahrenheit cause issues with unrolling and placement of the liner as well as the welding of the seams to insure proper installation. Once properly installed, temperature does not affect the operation or effectiveness of the liner.
  • We continue to work with Kimley-Horn on compressing the schedule to be able to achieve liner installation as soon as possible, but it will likely be Spring 2019 before we can effectively complete the lining process. It is our current belief that once construction begins, the liner can be installed within approximately 60 days.

Week of September 17

  • Retained on-call engineering firm Kimley-Horn to help investigate odor issue and determine solutions. Kimley-Horn to look at all aspects related to the area including the pond, the sewer lines in the area, and the UOSA pump station.
  • Kimley-Horn and city staff met on Sept. 18, 2018 and discussed the issues. The following took place:
    • Met with Micron staff and toured effluent operations. Reviewed Micron process and asked for additional sampling to investigate for sulfides – a key indicator of odor potential. Micron volunteered to conduct this additional sampling.
    • Toured pond and reviewed its operation with staff.
    • Examined new City odor-control station adjacent to pond.
    • Examined main sewer trunk line along Winter’s Branch and visually examined multiple manholes.
    • Toured the UOSA pump station and visually examined sewer flows entering into the station.
    • Visited the adjoining neighborhood including Shannon Lane, Sandy Court, and Battlefield Drive.
  • Kimley-Horn identified additional sampling/testing for the City for sulfides at both the pond and from the main sewer trunk line. City is setting up sampling with our contracted lab and expects to begin collecting samples next week. Micron is taking its samples next week as well.
  • Design drawings from UOSA and technical specifications of the aerators currently being used in the pond were sent to Kimley-Horn. As-built drawing information as well as measured elevations of the main sewer trunk line were sent to Kimley-Horn.
  • We are currently draining the pond using our new pump station and force main into the UOSA system. This is being regulated at a rate of approximately 1 million gallons per day. We will continue draining the pond as long as weather conditions permit.
  • Updated the City’s web page with this information and created a “Notify Me” sign up for citizens to receive updated information.
  • Kimley-Horn is also the engineer designing the proposed pond lining project. Installing a liner in the pond will eliminate the vegetative growth and eliminate the main source of biological reaction in the pond that contributes to odor issues. We will have a timeline for completion of their design by Sept. 28, 2018 to include in the next update. This project will still need to be bid and constructed once the pond has been completely drained.

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