REVIEW NOTES on Hahn’s “Proposed Revisions to Groundwater Monitoring Program, NW Natural – Gasco Facility, 7900 NW St. Helens Road, Portland, Oregon” letter dated March 9, 2012

The letter proposes changes to the quarterly/semi-annual sampling program Hahn is conducting for NW Natural on the Gasco and Siltronic sites.

In reviewing the recommendations I treated non-detects where ½-MRL and “J-flagged” detections greater than the lowest screening criteria as detections.

Cyanide

•  Removing amenable and WAD cyanide from program – OK based on DEQ determinations made previously and communicated in September 22, 2011 comments to Revised Interim Design.

General Chemistry

•  From a risk-based and source control perspective general chemistry parameters are OK to remove from the monitoring program

•  Sampling for these parameters and calcium, magnesium, potassium, and sodium should continue at wells included in the performance monitoring program.

Metals

In general, from a risk-based and source control perspective calcium, magnesium, potassium, and sodium are OK to remove from the monitoring program. Comments on remaining analytes are provided below.

Antimony

•  Hahn & MFA account for 572 data combined points; 439 associated with Hahn & 133 with MFA

•  Hahn samples detected [An] once at two locations above the lowest screening value (i.e., MCL = 0.006 mg/L

•  Detected [An] and ½-MRLs for MFA samples exceeded MCL for all samples

Need to further evaluate by checking Hahn & MFA data at jointly sampled installations.

Barium

•  430 data points associated with work completed by Hahn

•  430 detections with [Ba] < lowest screening criterion of 1.0 mg/L (i.e., 10/11 DEQ organism only AWQC)

•  100% detections < AWQC, 0% exceedances

Beryillium

•  423 data points associated with work completed by Hahn

•  17 data points where detected [Be], [1/2-MRL Be], and/or “J-flagged” [Be] are greater than lowest screening value of 0.004 ug/L (i.e., MCL)

•  4% exceedances

Selenium

•  Hahn & MFA account for 586 data combined points; 464 associated with Hahn & 122 with MFA

•  Detected and/or estimated [Se] and ½-MRL for Hahn samples exceed lowest screening criterion (i.e., chronic EPA NRWQC = 0.005 mg/L) in 27 samples, and one sample exceeds all criteria except highest

•  Selenium was not detected in any MFA sample, however ½-MRL (0.010 mg/L) is greater than then the chronic EPA NRWQC (0.005 mg/L)

Need to further evaluate by checking Hahn & MFA data at jointly sampled installations.

Thallium

•  423 data points associated with work completed by Hahn

•  Detected [Th] and/or ½-MRL exceed lowest screening criterion (i.e., MCL = 0.002 mg/L) in 18 samples

•  4% exceedances