Do I have DNAPL at my site?
It is difficult to verify the presence of DNAPL through direct observation. A common practice is to estimate the presence of DNAPLs indirectly by applying the “1 percent of solubility” rule-of-thumb (EPA, 1992).
Under this approach, DNAPL is suspected to be present when the concentration of a chemical in groundwater is greater than 1 percent of its pure-phase solubility. For example, PCE is inferred to be present as a DNAPL when the concentration of PCE is greater than 2,000 micrograms per liter (μg/L) in the dissolved phase (1 percent of its pure-phase solubility of 200,000 μg/L).
Suspected DNAPL Thresholds Based on Solubility Relative to 1 Percent of Aqueous Solubility
| Chlorinated Solvent (CAS Number) |
Aqueous Solubility |
1% of Aqueous Solubility |
| PCE (127-18-4) |
200,000 |
2,000 |
| TCE (79-01-6) |
1,472,000 |
14,720 |
| cis-1,2-DCE (156-59-2) |
3,500,000 |
35,000 |
| trans-1,2-DCE (156-60-5) |
6,300,000 |
63,000 |
| 1,1-DCE (75-35-4) |
2,250,000 |
22,500 |
| Vinyl Chloride (75-01-4) |
8,800,000 |
88,000 |
| 1,1,1-TCA (71-55-6) |
1,334,000 |
13,340 |
| 1,1,2-TCA (79-00-5) |
4,420,000 |
44,200 |
| 1,2-DCA (107-06-2) |
8,524,000 1 |
85,240 |
| 1,1-DCA (75-34-3) |
5,057,000 |
50,570 |
| Chloroethane (75-00-3) |
5,678,000 1 |
56,780 |
| Carbon Tetrachloride (56-23-5) |
793,000 |
7,930 |
| Chloroform (67-66-3) |
7,920,000 |
79,200 |
| Methylene Chloride (75-09-2) |
1,030,000 |
10,300 |
| Chloromethane (74-87-3) |
5,325,000 |
53,250 |
Notes:
- The reference temperature is 20 oC for the properties of these compounds.
- Source for Aqueous Solubility: EPA. 2004. In Situ Thermal Treatment of Chlorinated Solvents – Fundamentals and Field Applications. EPA 542-R-04-010.
- Source for 1 Percent Rule-of-Thumb: EPA. 1992. Estimating Potential for Occurrence of DNAPL at Superfund Sites. OSWER Publication 9355.4-07FS. NTIS Order Number PB92963338CDH.
Abbreviations:
DCA – Dichloroethane
DCE – Dichloroethene
PCE – Tetrachloroethene
TCA – Trichloroethane
TCE – Trichloroethene
