Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 11.2
SAMPLE PRESERVATION AND HOLD TIMES

11.2 SAMPLE PRESERVATION AND HOLD TIMES

This section presents the recommended sample preservation for soil and water sample collection. Always consult with the laboratory when planning fieldwork to ensure that the proper sample containers and preservatives are used. Tables 11-A and 11-B, provided in the Appendices, present the recommended preservation and hold times for soil and groundwater, respectively.

Sample preservation consists of methods to assure the samples analyzed in the laboratory are representative of the field conditions. Preservation methods may include maintaining sample temperatures, analyzing the samples within recommended hold times or using chemicals (such as HCl or nitric acid [HNO3]) to stabilize the target contaminants by altering the sample chemistry.

Several potential difficulties associated with field preservation techniques include: sampling gravely soil matrix (if using EnCore® type samplers), spillage or evaporation of pre-weighed chemical preservatives, shipping restrictions involving chemical preservatives, or potential chemical reactions between calcareous particles and HCl preservative.

11.2.1 Sample Temperature

Upon collection and sealing of sample containers, immediately begin the cooling process in the field by placing the sample containers in an insulated cooler containing water ice or frozen gel packs. Use of water ice is generally considered by the HEER Office to be more efficient to rapidly cool samples, and may be especially important for use with samples for volatile analyses, when feasible. Maintain the temperature of the sample containers at less than or equal to 6 degrees Celsius (°C) from the time of collection through the delivery to the analytical laboratory.

The National Environmental Laboratory Accreditation Conference (NELAC) states that samples which require thermal preservation shall be considered acceptable if the arrival temperature is within 2°C of the required temperature or the method specified range. For samples with a temperature requirement of 4°C, an arrival temperature from 0°C and 6°C meets specifications. Samples that are delivered to the laboratory on the same day that they are collected may not meet these criteria. In these cases, the samples are considered acceptable if there is evidence that the chilling process has begun, such as arrival at the analytical laboratory on ice.

11.2.2 Chemical Preservation

When employing chemical preservation, add the chemical reagents to the sample containers prior to mobilizing to the field, or request sample containers with pre-measured chemical reagents from the analytical laboratory. Carefully place the soil or groundwater samples into the sample containers to minimize loss of chemical preservative as well as volatile constituents in the sample (i.e., do not overfill water sample containers or leave the cap off a jar containing methanol for soil samples).

Some commonly used preservation chemicals may react with the sample media. For example, calcareous soil may react with sodium bisulfate; turbid groundwater collected from a coral aquifer formation may react with hydrochloric acid. If the sample media reacts with the chemical preservative, volatile organic constituents may be lost due to effervescence during sample collection, so an alternative preservation method or no chemical preservation may be needed.

The use of chemical preservatives for fieldwork in Hawai`i presents challenges when shipping preserved samples between islands or to the mainland (see Subsection 11.4 for additional details on shipping preservatives).

Some samples collected for specific analysis, such as dissolved metals in groundwater, may require pre-treatment prior to collection, as well as preservation (see Section 6.0).

11.2.3 Sample Hold Times

The soil and water samples should be analyzed as soon as possible after collection. Hold times are the maximum allowable times that a sample, or any subsample generated from the bulk sample, may be held before analysis. Several methods provide guidelines for both the hold time until extraction (denoted by "E" on Tables 11-A and 11-B in the Appendices) and the hold time after extraction until analysis (denoted by an "A" on the Tables).

Results from samples analyzed past the hold times may or may not be usable, depending upon the DQO set forth in the SAP. At a minimum, the results from analyses conducted past the recommending hold times should be interpreted as minimum concentrations.

Volatile Soil Samples

The sample collection and preparation methods in EPA Method 5035 and 5035A include short hold times, ranging from 48 hours up to 14 days (if samples are chemically preserved in the field at the time of collection). The following presents the preservation and associated hold times for volatile soil samples:

  • Unpreserved soil samples collected with EnCore® samplers (or equivalent device) and stored at 4°C must be analyzed within 48 hours from the time of sample collection. Samplers are transported to the laboratory where the cap is opened and the undisturbed sample is immediately placed in the appropriate preservation fluid prior to analysis.
  • Unpreserved soil samples collected with EnCore® samplers (or equivalent device) and immediately frozen on dry ice in the field to less than negative 7°C may be analyzed within 7 days from the time of sample collection. EPA Region IX has approved, on a limited basis, this modification of the method allowing for the freezing of samples for up to 7 days from sampling date to analysis (USEPA, 2005b).
  • Unpreserved soil samples collected with EnCore® samplers (or other similar sampling device capable of providing a pre-determined mass of soil) and immediately extruded into a glass jar containing laboratory grade water must be analyzed within 14 days from the time of sample collection only if the samples are delivered to the laboratory and frozen within 48 hours of collection. Sample container breakage may be a concern when using this approach since the glass jars are not intended to contain freezing liquids. If employing this approach, consider collecting additional sample volumes at each sample location to account for breakage.
  • Preserved soil samples collected with EnCore® samplers (or other similar sampling device capable of providing a pre-determined mass of soil) and immediately extruded into a glass jar containing sodium bisulfate preservative must be analyzed within 14 days from the time of sample collection. This approach is appropriate for non-calcareous soils and a field check to determine whether the soil is calcareous is recommended (calcareous formations are commonly encountered when performing fieldwork in Hawai`i). The use of sodium bisulfate as a preservative should be discussed with the analytical laboratory since it may cause laboratory instrument problems requiring frequent recalibration.
  • Preserved soil samples collected with EnCore® samplers (or other similar sampling device capable of providing a pre-determined mass of soil) and immediately extruded into a glass jar containing methanol must be analyzed within 14 days from the time of sample collection. This approach is appropriate if high levels of contaminants are suspected, as well as for any contaminants for which lab reporting limits below applicable HEER Office Environmental Action Levels (EALs) can be achieved (HDOH, 2008). In this application, methanol acts as the preservative as well as the extraction solvent and a limited volume of methanol is introduced directly into the laboratory instrument. As such, the dilution and the reporting limits are higher than with other preservation and extraction approaches. In some cases, the laboratory may be able achieve lower reporting limits for specific contaminants preserved in methanol by using additional analytical techniques, so consultation with the laboratory is recommended.