×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Arsenic Results - Differences among Approved Analytical Methods?

Arsenic Results - Differences among Approved Analytical Methods?

Arsenic Results - Differences among Approved Analytical Methods?

(OP)
My question concerns differences in Arsinic levels using EPA approved analytical methods. The water system serves < 10,000 and is in NJ (As MCL is 0.005 mg/l)

Three years ago, As testing was done and Std Method 3113 B was used. Of the 4 source wells, 1 was clearly over the MCL (>0.010 mg/l) 1 was just over (around 0.0056 mg/l) and 2 wells were below the MCL (<0.004 mg/l). 1st quarter 2006 testing was performed using EPA 200.8. All results are approximately 2x the 2003 results; so instead of treating two wells it looks like all four will require treatment.

I can’t believe there that much variation between approved analytic methods, but, to be frank, I don’t know. I’ve called the testing lab twice last week and asked this via voicemail, but no one is getting back to me.

With all that as background information, my question is:

Can the differences between the 2003 and 1st quarter 2006 results be attributed to the difference in the analytical methods used?

RE: Arsenic Results - Differences among Approved Analytical Methods?

I can't say for sure for arsenic, but it may be like ammonia which can be reported as total ammonia or as ammonia nitrogen (NH3-N).  The molecular weight of arsenic acid H3AsO4 is 147 about twice the 75 for As.  You must also make sure which format the MCL is in.  It may be worth looking into.

RE: Arsenic Results - Differences among Approved Analytical Methods?

Method 200.8 is more sensitive to the valence state of the As (must be oxidized to +5), so sample preparation is critical for accurate results.  See footnote 14 at http://www.epa.gov/OGWDW/methods/inch_tbl.html

But, you really need to have more testing done, with split samples going to different labs. Maybe even split 4-ways & have done by both methods to settle the issue.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources