sodium hydroxide contamination of soil

[imagineero]

Well.... My long weekend hasn't started out all that great, so I thought I'd consult the brains trust at TFP to see if it can be improved!

A friend contacted me to say that their grass and hedges were dying off, and that they'd had the exterior of their house washed the week before. A few days after having the exterior washed, their power went out for two days, and the service drop had to be reconnected due to corrosion. So I asked a few questions, then got in touch with the guy who did the house cleaning and the answers were not encouraging.

• Two story house, with a terracotta tile roof, long concrete drive and exterior concrete pathways all round the house, plus some stairs.
• Hedges wrap around maybe 30% of the house, lawn is up against the concrete pathways/drive
• Contractor sprayed the entire house, driveway and paths with 12.5% sodium hydroxide and a surfactant with water at a ratio of 1:9 (1.25% NaOH according to him?)
• Am I right in thinking this solution is 12,500ppm chlorine(!)?
• Solution left on for approx 5 min then hosed off with a garden hose. No neutralising or capturing of the runoff, no attempt made to reduce overspray
• Contractor in business less than a year, quite a few negative feedbacks online re: plants dying off

My friends are in a ****** position in life at the moment (who isn't lately?) and are hoping to list the house for sale and sell before christmas as the husband lost his job after being injured and they can no longer meet their mortgage obligations. They got the guy in to tidy the house up to make it presentable for sale, so very limited time to remediate the issue. I'm an arborist, which is why they gave me a ring to ask for help - though maybe a little too late. My immediate guesses are;

• I have a soil PH test kit which I use for work, I might try to test the affected dead areas of grass and see how they are for PH which is critical for plant nutrient uptake.
• Can I realistically test soil chlorine with my pool test kit? No idea and have never needed to do this before.
• I'm thinking the contamination would quickly sort itself out, though the house doesn't have a great sun aspect.
• If the soil is good, I'm thinking to try and re-seed affected areas and aggressively fertilise/water. It's spring in Australia.
• If the soil is still contaminated, I'm guessing daily watering will help?
• Water is the only thing that comes to mind to help the affected hedges
• They realistically have less than 2 weeks to make the place presentable
• Screw the guy that did this. I'm not going to send him a christmas card
• My friends are really nice and don't deserve to have this in their life

Any and all advice appreciated.

 

[JamesW]

Do you mean sodium hypochlorite?

If yes, how many total gallons were used?

 

[Dirk]

I don't see how anything is going to be fixed in two weeks, short of all new plants. That's about all I have, considering I have no idea what the housing market is like in Oz (I just learned that. Did I use it right? ).

Here, that would be bad, but wouldn't likely affect the house sale or asking price all that much, if at all. Buyer's here expect to be doing some or a lot of remodeling, and landscaping is part of that. The notion of fixing a house all up for the next owner is not really applied anymore here (in California, anyway). Remediate the soil as best you can. Not sure what else you could do but use water for that. The chlorine is likely already gone. Fertilize. Then, if you can get even a little bit of green to spout on the affected plants, the seller's realtor can point to that, disclose what happened re the house cleaning, but assure the buyer and their realtor that the plants will all come back, and the damage is temporary (new growth is an indicator that the plant is on the mend).

Or rip out and replace all affected plants and cover the dirt with a nice looking mulch. Doing that right before a sale is still done here often to mask a neglected garden.

 

[imagineero]

Do you mean sodium hypochlorite?

If yes, how many total gallons were used?

The guy did specifically say hydroxide, but then he also said "pool chlorine", which means hypochlorite generally in australia. I saw no signs of speckling/salts anywhere on the house. I have no idea how what sort of volume of chemical was applied, or the volume of tap water used to wash it off... but I can get in touch with the guy and ask. He was pretty forthcoming with information, but didn't seem to have much of an idea of what he was doing. He mixes the chlorine with water in a tank on his truck and then applies it with a pump in an amount that "covers the entire surface", then washes it off with a garden house "until it's washed off". He was pretty specific about the 12.5% and the 1:9 ration with water, but could well be simply incorrect about hydroxide vs hypochlorite.

 

[Dirk]

Wow, yah, that was an extreme dose. Power washing with water would have been enough for a home sale... bummer.

 

[JoyfulNoise]

Sounds like he was using sodium hypochlorite and not hydroxide. Sodium hydroxide (aka, lye) would be very dangerous to spray around wildly and would cause a lot of damage to surfaces. The mist would cause severe eye irritation and possibly skin burns. Also, sodium hypochlorite (pool chlorine) is readily available as a 12.5% solution while lye is typically a solid compound that you mix in water.

My guess is the overspray of the hypochlorite killed the vegetation. Chlorine is neutralized fairly rapidly in soil within the first few inches. Now it will damage (kill) the soil biome which is a long term problem. But "splashing" bleach onto leaves and plants will definitely kill them.

As @Dirk said, time to start replanting...,