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    Ken
    Resolving Lead in Groundwater Due to Turbidity
    Topic posted May 25, 2011 by KenMember, last edited January 19, 2012
    1136 Views, 8 Comments
    Title:
    Resolving Lead in Groundwater Due to Turbidity
    Content:

    We have a site (in NJ), with low levels of lead in groundwater but which exceed the applicable standard.  Filtered samples (not admissable for compliance) do not have similar concentrations of lead, indicating the metal is likely due to turbidity/colloids and are not actually dissolved in groundwater.

    Typically we resolve these situations with a variety of sampling/well installation techniques designed to reduce turbidity, however, recent rule changes in NJ allow the use of professional judgement or relevant guidance from EPA or other states.So I am asking for input from non-NJ consultants - how does your state address the metals in groundwater/turbidity issue and the use of filtered samples to acheive compliance. 

    Your feedback and regulatory citations are appreciated!

     

     

    Comment

     

    • John Davis
      posted May 25, 2011 by John DavisMember

      I have run into this issue in both North Carolina and in Georgia.  We use quiesent sampling techniques to get around the metals in (sediment) ground water problem.  After the well is installed and completly developed, we would purge the well and then let it sit overnight (24 hr) before we sample the well.  Collect the first dip samples being very careful not to surge the well.  We would not let the bailer get completly submerged.  The lead in water problem went away and the regulators were happy.

    • Steve Kirschner
      posted May 25, 2011 by Steve KirschnerMember

      Ohio uses 20 NTUs as a threshold for filtering.  Check out the VAP Technical Guidance Compendium doc VA30007.09.011.  There are some other critierum you need to meet.

      We have also had success using Hydrasleeves for turbidity/metals issues.

    • Bill E.
      posted May 25, 2011 by Bill E.Member

      In Illinois, I've used low-flow (<0.5 L/m) purging and sampling as an effective means to reduce turbidity.  Purge until water quality parameters have stabilized (pH, conductivity, temperature, dissolved oxygen), then collect sample.  Groundwater almost always stays clear.  The elevated metals usually go away.  I haven't encountered any problems with Illinois regulators (yet).  This method also reduces the amount of purged water generated, reducing disposal costs.  Check out ASTM D 6771-02.  Also USEPA publication "Low-Flow (Minimal Drawdown) Ground-water Sampling Procedures", authored by Puls and Barcelona, EPA/540/S-95/504, April 1996.

    • RobE
      posted May 25, 2011 by RobESuper Contributor

      We often use professional judgement with this regard in cases where turbidity is an obvious issue (e.g. sample collected from temporary well point).

      You asked for regulatory cites,so in Oregon, and with regard to Leaking UST sites: 

      OAR 340-122-0218(c) Sampling and Analysis: "Groundwater samples collected for the purpose of testing for lead must be filtered immediately upon collection using a 0.45 micron filter and analyzed for dissolved lead".

      When sampling from a well (and for non LUST Sites), we will use low flow purging and sampling to reduce sampling-induced turbidity to a minimum.

    • Show/Hide Replies
      Dan Fluman
      posted May 25, 2011 by Dan FlumanMember

      We use dedicated 3/16" TFE tubing which has had the bottom plugged and is perforated at an interval of 3-5' above the bottom of the casing.  We sample using a peristoltic pump at <1L/minute which goes through a flow-through cell where the instrument probes are housed.  We monitor until the field measurements have stabilized.  Once this has occured (3-5 minutes), we alllow the line to purge at a very slow rate and then draw our samples.  Metals are drawn first, VOCs/SVOCs second and the remainder are drawn at a higher flow rate.  All-in-all, about 15 minutes from setup, collect, breakdown and move onto the next well. 

      • Dan Fluman
        posted May 25, 2011 by Dan FlumanMember

        We have been doing this since 1994.  It seems to work out well, except that the wells require redevelopment every 5 years of so.

         

    • Emily B
      posted May 25, 2011 by Emily BContributor

      Low-flow is acceptable in Michigan (I'll have to look up the regulatory citation), and that usually eliminates the turbidity issue. 

      Just thinking of what I've observed in the field, if you aren't able to filter, you may be able to decant (especially with metals, since they won't volatilize).  I've noticed through a day of sampling that suspended solids will settle out by the afternoon in a turbid morning sample.  Disclaimer: I haven't tried this or run it by regulators but it seems like it could be a reasonable solution.  

      My approach would be to fill an unpreserved larger bottle (say, 1 L) and leave it undisturbed in your cooler for a while (few hours).  Then, either with a careful pour or a verly slowly pumping peristaltic pump, you could transfer the water to your metals containers leaving most of the sediment behind.

    • MaxEng
      posted May 25, 2011 by MaxEngElite Contributor

      Ohio's guidance document for groundwater investigations is currently undergoing revision, and the revisions are subject to public comment.  See them at http://www.epa.ohio.gov/ddagw/tgmweb.aspx

      I've had lots of problems through the years with lead in turbid wells.  Dedicated low-flow pumps (bladder pumps) are the best way to deal with the problem in my experience.  Be patient and allow turbidity to reach less than 5 NTU and you shouldn't have too many problems with suspended lead.  Dedicated pumps really help get the turbidity down.  The initial cost of installation is usually made up pretty quickly by the fact you don't need to purge as long to bring turbidity down (just the act of placing a pump into a turbid well can kick up sediment that can take a long time to clear up).