Case Study Palermo Well Field Use of Stable Isotopes Tumwater, Washington

Transcription

1 Case Study Palermo Well Field Use of Stable Isotopes Tumwater, Washington Prepared by Bernie Zavala U.S. Environmental Protection Agency Region 10 For The U.S. EPA Technical Support Project San Antonio, Texas November 18, 2009

2 Overview of the Presentation Questions regarding the Conceptual Site Model (CSM) Is PCE degrading to TCE in the Palermo valley? Or is TCE in the Palermo valley from another source? Why Stable Isotopes were used at the Palermo well field Data Results Redevelopment of existing CSM using Compound Specific Isotope Analysis (CSIA) Conclusions / Observations / Take home message

3 CSM- Source area locations and how they may be impacting the Well Field Southgate Dry Cleaners (PCE) WDOT Testing Lab (TCE) Trosper Road & Littlerock Road (TCE)

4

5 CSM- Site Hydrogeology Glacial Deposits, outwash sands and till Deschutes River valley, consisting of gravel, sands, silts and clay

6

7 CSM- Groundwater flow direction & TCE / PCE concentrations Groundwater flows southwest to northeast towards the Deschutes River & the Palermo well field TCE detections of 20 ug/l in MWs downgradient of WDOT PCE detections of 40 ug/l in 2-MWs downgradient of the dry cleaners TCE is only VOC detected above the MCL in the Palermo well field with no detections of PCE.

8

9

10 Why stable isotopes were used at the Palermo Well Field These stable isotopes are inherently stable unless a process occurs that will act on one of the isotopes to undergo enrichment or depletion. This process is called fractionation. Direct measurements of carbon isotope ratio s of 13 C/ 12 C can be determined in the laboratory and this can also determine if degradation is occurring for PCE or TCE. Sample collection for stable isotopes is similar to volatiles, both were collected at the same time. Limits of quantitation for CSIA were estimated as 20 ug/l for TCE and 30 ug/l for PCE, Lawrence Berkeley National Laboratory using a purge-and-trap apparatus combined with a GC-IRMS system.

11 Background information on Stable Isotopes for Carbon Naturally occurring isotopes of carbon are 12, 13 & 14. Carbon-14 is unstable. CSIA or stable isotopic analysis involves determining the ration of 13 C/ 12 C and are express in an δ(delta) notation in units of per mil or per thousand. A reference standard for carbon has a value of 0. A positive value is a heavy isotope compared to the standard. For example, a δ 13 C value of -26 per mil means that the 13 C/ 12 C ratio of the sample is 26 parts per thousand or 2.6% lower than the standard.

12 Question: Is PCE degrading to TCE in the Palermo valley?

13 Biannual ground water sampling event was conducted during the spring of 2006 and EPA sampled additional monitoring wells and also sampled for stable isotopes or performed a Compound Specific Isotope Analysis (CSIA) of the groundwater.

14 Taken from Vlassopoulos, (May 2006)

15 Results of CSIA for TCE Taken from Vlassopoulos, (May 2006)

16 Data taken from Parametrix January 2008

17 Taken from Vlassopoulos, (May 2006)

18 The ground water sampling results reveals the following: The PCE isotope data at the Southgate Dry Cleaners was -33 per mil. The TCE isotope data at WDOT Lab was - 26 per mil. The TCE isotope data near Trosper and Littlerock road was -26 per mil. The TCE isotope data within the Palermo valley or near the well field was -26 per mil.

19 Conclusions Minimal amount of degradation has taken place for PCE & TCE. The carbon isotope ratio were the same near WDOT Lab and the property once owned by WDOT at Trosper and littlerock road (-26 per mil). The carbon ratio near the Tumwater wellfield was (-26 per mil). EPA believes that WDOT is responsible for the TCE at the Tumwater wellfield.

20 Take Home Message Use multi-lines of evidence for the development for the CSM. Go out to the site, either conduct the sampling or observe key locations. CSIA is appropriate for use if specific site conditions are met.

21 References Parametrix, Groundwater Long-Term Monitoring 2007 Annual Report, January 2008 Vlassopoulos, Dimitri, Expert Report, U.S. VS Washington State Department of Transportation, May 2006