Indiana Department of Environmental Management
Office of Land Quality
100 North Senate Avenue
Indianapolis, IN 46204-2241
OLQ PH: (317) 232-8941
Title: Sampling and Analysis of Ground Water for Metals at Remediation Sites
Identification Number: WASTE-0057-NPD
Date Originally Effective: March 17, 2005
Dates Revised: None
Other Policies Repealed or Amended: None
Brief Description of Subject Matter:
Provides background information for using unfiltered ground water sampling for metals at remediation sites, also, outlines the ground water sampling methods for water supply wells, monitoring wells and boreholes. Guidance applies to those sites being remediated under the following programs in the Remediation Services Branch of the Office of Land Quality: Voluntary Remediation Program, Leaking Underground Storage Tanks, Federal Cleanup Programs, State Cleanup Programs, RCRA Corrective Action, and Site Assessments & Brownfields as well as Environmental Emergency Responses. This guidance does not apply to those sites in the Solid Waste Permits or Hazardous Waste Permits programs.
Citations Affected: 40 CFR 264, Subpart F, as incorporated by reference in 329 IAC 3-1-9
This nonrule policy document is intended solely as guidance and does not have the effect of law or represent formal Indiana Department of Environmental Management (IDEM) decisions or final actions. This nonrule policy document shall be used in conjunction with applicable laws. It does not replace applicable laws, and if it conflicts with these laws, the laws shall control. This nonrule policy document may be put into effect by IDEM 30 days after presentation to the appropriate board. Pursuant to IC 13-14-11.5, this policy will be available for public inspection for at least 45 days prior to presentation to the appropriate board. If the nonrule policy is presented to more than one board, it will be effective 30 days after presentation to the last. IDEM will submit the policy to the Indiana Register for publication. Revisions to the policy will follow the same procedure of presentation to the board and publication.
Sampling and Analysis of Ground Water for Metals at Remediation Sites
Over the years there has been debate regarding the merits of using filtered vs. non-filtered samples for the analysis of metals in ground water. The primary considerations are: the turbidity of a sample; the type of well (e.g. drinking water vs. monitoring well vs. direct push); and whether total or dissolved metals are the parameters of concern, e.g. monitoring for health risk vs. leak detection.
This guidance briefly provides background information for using unfiltered ground water sampling for metals at remediation sites. It then outlines the ground water sampling methods for water supply wells, monitoring wells and boreholes. This guidance applies to those sites being remediated under the following programs in the Remediation Services Branch of the Office of Land Quality: Voluntary Remediation Program, Leaking Underground Storage Tanks, Federal Cleanup Programs, State Cleanup Programs, RCRA Corrective Action, and Site Assessments & Brownfields as well as Environmental Emergency Responses. This guidance does not apply to those sites in the Solid Waste Permits or Hazardous Waste Permits programs.
Historically, ground water samples have been filtered as a means of excluding naturally occurring metals and non-mobile organics that were sorbed to aquifer matrix elements (i.e. suspended solids, colloids, etc.), and to ensure that only site-related inorganic contaminants were evaluated. A growing body of evidence indicates that sample filtration may not achieve this goal, and may instead alter the characteristics of site-related hazardous constituents in a ground water sample.
Sample agitation, aeration, and rapid purge and sample rates, which exceed 1.0 liter/minute or cause a drawdown of more than 0.3 feet, may induce physical and chemical changes in a sample. These changes may include induced turbidity, exposure of fresh suspended sorptive surfaces (capable of adsorbing dissolved contaminants), mixing (may cause dilution), oxidation, and other changes in metal speciation. Any of these could affect sample analysis in the laboratory (Luftig, 2003).
Proper sampling techniques minimizes induced turbidity and the need for filtering and, thus, does not alter the sample. Filtration may cause a number of unintended changes (oxidation, aeration, etc.) to occur by introducing artifacts to the analytical results, which may be misleading (Puls and Barcelona, 1996). Filtering a ground water sample may remove contaminants that exist in the dissolved and mobile phase or remove colloidal particles that are known to be mobile in certain ground water conditions and may be important to the transport of hydrophobic contaminants and metals. The resulting sample analysis will produce false negatives and not accurately reflect the true concentrations for these contaminants. In comparison, proper sampling techniques that minimize stress to the well/aquifer interface should achieve acceptably low levels of induced turbidity without the risk of altering the sample by filtering (Luftig, 2003).
U.S. EPA and several states recommend testing unfiltered ground water samples for metals (U.S. EPA, 1992). The analysis of filtered samples for ground water without also including the analysis of unfiltered (totals) samples is rarely considered acceptable (U.S. EPA, 1998).
Filtration cannot correct improper sampling technique nor is it a "cure" for improperly built/developed wells that produce turbid samples (O'Toole, 1988). As a result, sample filtration is an unacceptable alternative to proper sampling methods.
Ground Water Sampling at Remediation Sites
The following minimum conditions should be met to ensure that ground water samples are representative and of sufficient quality for the intended data use.
- The sample location is in the appropriate area;
- The sample comes from the appropriate depth;
- If taken from a well, the well is properly constructed according to 312 IAC 13;
- If taken from a well, the is well properly developed according to 312 IAC 13; and
- The sampling method will yield a representative sample.
Water Supply Well Sampling Methodology (Metals)
Conditions 1 through 4 may be unknown or uncertain when sampling an existing water supply well. One certainty, though, is people, plants, and/or animals are in contact with or drinking the water from that well. To obtain a representative ground water sample in this situation:
- If there is an aerator at the sampling point, remove it.
- Either shut down or bypass treatment systems (e.g. softener, reverse osmosis, carbon filtration, etc).
- Completely purge the storage tank until fresh ground water comes from the tap. This may take several minutes, depending on the volume of the storage tank and flow rate. Typically a fifteen-minute purge time is utilized.
- Collect the sample and preserve (acidify) it without filtration.
Monitoring Well Sampling Methodology (Metals)
If conditions 1 through 4 can be met, then sampling may proceed. If one or more of the conditions is not met, then the well probably should not be used for ground water sampling, (however, the well may be suitable for other purposes, such as determining ground water elevation). Proper sampling technique involves gathering samples that more accurately represent the mobile composition of ground waters (Matanoski, and Murarka, 1997). Bailers increase turbidity while purging and sampling and should be avoided when sampling for metals (Yeskis and Zavala, 2002).
Low-flow, low-stress purging and sampling (micro-purge sampling) has been shown to significantly reduce induced turbidity problems. This method may prove particularly valuable with low permeability sediments and highly turbid ground water (OLQ Geological Services, 2003). For example, micro-purge sampling was approved for a landfill in Indiana, with very high turbidity. The turbidity dropped from over 40,000 NTUs (nephelometric turbidity units) to 6 or less (OLQ Geological Services, 1998).
- A review of micro-purge sampling, listing advantages and disadvantages of the technique [PDF]
- The complete text for using Micro-Purge Sampling for Monitoring Wells [PDF]
Sometimes, a well may be properly installed, developed and sampled; yet turbidity is high. In this situation field-filtered samples may be taken but only in conjunction with unfiltered samples to determine if particle size and mobility affect the results. A large difference between unfiltered and filtered samples does not preclude the use of unfiltered data for risk assessment decisions (Puls and Barcelona, 1989).
Sample filtration may be used if the OLQ determines that conditions 1 through 4 are met and that micro-purge sampling does not reduce turbidity to <10 NTU (Yeskis and Zavala, 2002). (The project chemist should be consulted to determine if proper water quality screening and sampling techniques have been conducted. Also, the project geologist should be consulted to determine if proper well construction and development occurred). When filtration is necessary, a 10 m in-line filter should be used to minimize contact with air and avoid metals precipitation (Yeskis and Zavala, 2002). This recommendation is similar to what other states suggest. Also, a filter pore size of 10 m approximates the efficiency of a common household filter. The filter should be allowed to acclimate before a sample is collected.
Approximately 500 to 1000 ml of water should pass through the filter (depending on manufacturer's recommendation) before a sample is collected and preserved. If volatile organic compounds are also to be collected, they should be collected first and metals last.
Other filter sizes may be appropriate but their usage should be predetermined based on several factors such as, grain-size distribution, ground water flow and velocity, mineralogy, and the project Data Quality Objectives (DQO). The changing of filter media pore size may limit the comparability of the data obtained with other data sets from a site, region, or aquifer and the DQOs should be taken into consideration (Yeskis and Zavala, 2002).
Borehole Sampling Methodology (Metals)
Boreholes should meet the first two conditions, (appropriate sample location and sample depth); however, they will probably not meet the conditions of proper construction and development. Nevertheless, the same considerations and procedures for monitoring well sampling and sample treatment should be followed. When sampling boreholes, particular care needs to be taken to ensure that samples do not include:
- Drilling fluids;
- Soil materials sloughed from upper horizons; and
- Water or other fluids encountered in other zones during drilling (cross contamination).
Following these steps for micro-purge sampling should reduce the turbidity and, thus, the need for field filtration.
Indiana Administrative Code, 1999. 312 IAC 13 Article 13 Water Well Drillers
Luftig, S.D. 2003. Draft Guidance, National Guidance on Field Filtration of Ground Water Samples from Monitoring Wells for Superfund Site Assessment U.S. EPA
Matanoski, G. M. and I. P. Murarka, 1997. To Filter, or Not to Filter; That is the Question. Letter to Carol M. Browner, Administrator EPA EPA-SAB-EEC-LTR-97-011
OLQ Geological Services, 1998. Technical Memorandum. Short Review of the Micro-Purging Option for Monitoring Wells
OLQ Geological Services, 2003. Technical Memorandum. Micro-Purge Sampling for Monitoring Wells
O'Toole, M. J., 1988. New York State Department of Environmental Conservation Technical and Administrative Guidance Memorandum #4015. Policy Regarding Alteration of Ground Water Samples Collected for Metals Analysis
Puls, R. W. and M. J. Barcelona, 1989. Ground Water Sampling for Metals Analyses EPA/540/4-89/001
Puls, R. W. and M. J. Barcelona, 1996. Low-Flow (Minimal Drawdown) Ground Water-Water Sampling Procedures EPA/540/S-95/504
U.S. EPA, 1992. RCRA Ground-Water Monitoring: Draft Technical Guidance
U.S. EPA, 1998. RCRA QAPP
Yeskis, D. and B. Zavala, 2002. Ground-Water Sampling Guidelines for Superfund and RCRA Project Managers EPA 542-S-02-001