Soil and Water Contamination - how long after a wastewater treatment plant is decommissioned does the surrounding area remain contaminated?

  • bones
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Soil and Water Contamination - how long after a wastewater treatment plant is decommissioned does the surrounding area remain contaminated?

Would like an idea of how long after a wastewater treatment plant is decommissioned does the surrounding area remain contaminated.

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I work for a NGO which as part of our work does experiential education programs relating to issues faced in developing countries, such as poverty, water quality/scarcity, Aids etc. We need to redevelop part of our site for one of these programs, however the area we want to use is next to an old wastewater treatment plant - unused for around 20 years. Given that the plant likely only served domestic wastewater, should we be concerned about soil contamination? Do we need to get the soil tested for pathogens/contaminants?

Also, there is a well in the area which we want to use which would be great to include in the simulation program but again concerned about water contamination. Even if it's groundwater I am aware that we should implement ongoing water testing if we are going to use the water in the well, but would like to know whether this well might be in anyway have remaining contamination from the wastewater treatment plant.
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Re: Soil and Water Contamination - how long after a wastewater treatment plant is decommissioned does the surrounding area remain contaminated?

Hi Nigel,

What kind of wastewater treatment plant was it and in which country? Was it properly decomissioned or just "left to rot"? Do you have some photos of it? If it was a half-decent WWTP then it should not have leaked into the groundwater but delivered its effluent into a surface water body... (which is then more likely to be polluted than your groundwater if the treatment plant wasn't working well). But 20 years on you should be quite safe, I would assume.

But please tell us more about this decommissioned WWTP, and why it was taken out of service?
Are there also still piles of sewage sludge stored on the site perhaps (which could have caused groundwater pollution)?

Do you have a budget for testing the quality of the groundwater in the area?

And what did you mean by "simulation program"?
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Elisabeth

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  • bones
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Re: Soil and Water Contamination - how long after a wastewater treatment plant is decommissioned does the surrounding area remain contaminated?

I'm in Hong Kong, the site is an old army barracks site, so suspect only domestic wastewater? As such it's a fairly small system, three stage, a primary settlement tank (~50m2) feeding two circular gravel filters (13 m dia each) and finally discharging into 4, what I would think were soakage beds, but the plan I'm looking at has them labelled as a 'pond' (~ 100 m2). It is adjacent to a stream, so is possible that that was the discharge point. Also the system is within 200 m of the original coastline and is pretty much at sea level.

I doubt that it was decommissioned properly, the soakage beds are definitely not empty, but that could just be 20 years of leaf litter. The system was decommissioned when a reticulated wastewater system was installed in the area, which was prior to the military leaving the site in 1994.

Image 1 is of the primary septic tank. This actually appears to be a three stage system with, a primary settling tank (maybe) located behind the structure. Within the structure there are 5 tanks (I guess the were operating in parallel?) And under the white profiled metal in the foreground is one (maybe 2) final tanks, with an outlet chamber on either side (you can see the rusted metal covering of one).

Image 2 shows, what I'm assuming were gravel filters, one in the foreground and one in the background. I was told by one of my directors that they used a central pivot sprinkler to apply the wastewater onto this area, but I don't know how he knows that?

Image 3 shows the final soakage ponds. The stream is located just behind the ponds, hidden by the trees in this photo.

Image 4 is the area that we want to use, you can see the WWTP on the left, with the well that we are interested in using at the top left. The ground of this area is about 1 meter above the current level of the soakage pond.

Simulation Program - meaning an experiential education program. So instead of providing a lecture on the issues surrounding access to water is some developing country contexts, we get the students to 'play a game', where they are living a poor rural village and have to collect water for the household before they can go to school ...

Our current desire to get clarity on this is that we are in discussion with a potential donor who in interested in providing some financial assistance in this area (We are an NGO). I am waiting to hear back from a lab to see what (if any) testing they recommend, and a quote, but thought it prudent to get some independent expert advise.

Hope this clarifies and answers you questions.
Thank you for your assistance in this matter.

Regards
Nigel Langdon
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