Methane in Water, conversion between mg/l and percentage by volume

Link to this: http://williamahuston.blogspot.com/2013/11/methane-in-water-conversion-between-mgl.html
   

I was looking at some water test results, and it seems others (besides me!)
are confused by the difference between mg/l of dissolved methane
in water, and percentage of dissolved methane by volume.

 
Here is a handy table which helps you to convert between these.
(see below).

Let us assume we are at room temp (77'F) at a little above sea level.

It turns out that

10 mg/l is ~2%

28 mg/l is ~5%

63 mg/l is about 10%

• Below 7mg/l (about 1%) is considered safe and nominal. 
• 5% is the saturation point where bubbles will be observed (flammable).
• 10% is dangerously explosive.

10%-11% was the level seen in several homes in Franklin Forks PA.
 

This is some of the highest concentrations ever observed, anywhere, because of the methane is much higher than this, it just bubbles out immediately (because water is about 1,590x more dense) and it will do something like this:

http://www.youtube.com/watch?v=Kf_RxSuu9IA

  ----- the calculation and table ----

Metric system for volume/mass is based on the physical constants of water.
Water is 1000 g/l by definition = 1kg/l = 1,000,000 mg/l.

Methane is about 0.63 g/l at 25'C (77'F) and 0.978 ATM (a little above sea level). 
http://answers.yahoo.com/question/index?qid=20110224194358AAkQ5Ug

So to convert from P (percent of volume) of dissolved methane in water to mg, use
N = P * 6.3.

So a liter of pure methane at room temp and about sea level would be
N = 100 * 6.3 = 630 mg

From this we can create these charts.
TABLE 1 goes from 0% dissolved to 100% in 5% steps.
TABLE 2 goes from 0% to 20% in 1% steps. (This is the region we are most interested in).

TABLE 1 percentage dissolved methane by volume in 1L water mass of dissolved methane (mg) 0% (pure water) 0.0 5 31.5 10 63.0 15 94.5 20 126.0 25 157.5 30 189.0 35 220.5 40 252.0 45 283.5 50 315.0 55 346.5 60 378.0 65 409.5 70 441.0 75 472.5 80 504.0 85 535.5 90 567.0 95 598.5 100% (pure methane) 630.0

TABLE 2 percentage dissolved methane by volume in 1 liter water mass of dissolved methane (mg) notes 0 0.0 1 6.3 DEP considers under 7mg/l acceptable and safe, or about 1% 2 12.6 3 18.9 4 25.2 5 31.5 28 mg/l is considered the saturation point of water, where methane will bubble out ~5% by volume 6 37.8 7 44.1 8 50.4 9 56.7 10 63.0 Tammy Mannings was 58.4 mg/l 3-6-2012, which is ~10% methane 11 69.3 Unlikely to find dissolved methane in water greater than this. 12 75.6 13 81.9 14 88.2 15 94.5 16 100.8 17 107.1 18 113.4 19 119.7 20 126.0

So lets say our water test results are 64 mg/l of methane in water.
Finding the nearest entry in either chart shows that the nearest entry
is 63.0 which is about 10% methane.

I hope this is helpful -- BH