Manual for Soil Analysis-Monitoring and Assessing Soil Bioremediation Phần 2 doc

22 A. Paetz, B.-M. Wilke

Sampling locations should be determined with an appropriate degree of

accuracy. Because it may be necessary to vary the actual location away from

the predetermined location because of the presence of obstructions, it may

be preferable to do the accurate surveying of sampling locations once the

sampling exercise is completed or as it progresses. Surface levels can be

determined at the same time.

When investigating abandoned industrial, waste disposal, or other po￾tentially contaminated sites, the horizontal and vertical location of sam￾pling points or probing points should be recorded. The location of sampling

points should be marked before sampling begins using poles/markers with

color sprays. Color sprays should not be used if soil air has to be sampled.

Preparation of the Sampling Site

Depending on the objective of the investigation, a sampling pattern is

chosen at the design stage and is then applied in the field. Within the

range of patterns are some very complex ones developed with the help of

computer-aided statistics. Preparation for sampling with the use of such

patterns, e.g., location of desired sampling points on the ground, can be

very time-consuming, especially when samples are to be obtained by bor￾ing/drilling techniques or from trial pits. Preparation of the site includes,

for example, removal of superficial deposits (e.g., uncontrolled deposition

of urban wastes), establishment of safety measures, installation of mea￾surement devices (if field tests are carried out together with sampling), as

well as exactly locating the sampling points. In many cases, preparation

of the site takes longer than the actual sampling procedures. Both during

and on completion of sampling all necessary measures must be taken to

avoid hazards to the health and safety of anyone entering the site, and to

the environment.

Barriers to Sampling

It may not be possible to sample at a planned location due to a variety

of reasons (e.g., trees, large rocks, buildings, buried foundations or public

utility services, difficulties of access) and contingency plans for dealingwith

such situations should be made in advance. The action to take will depend

on the circumstances. The investigator may ignore the unavailable point

or follow predetermined rules for choosing a nearby substitute location

(e.g., alternative position within 10% of grid spacing or paired sampling

along grid lines on either side the obstruction). Ad hoc decisions made in

the field can lead to bias. An attempt should be made when mapping out

the site to identify such obstructions in advance of actual field work. In all

cases when a sampling point has to be relocated, this fact, and the reasons

for relocation, should be clearly indicated in the report.

1 Soil Sampling and Storage 23

Preliminary investigations as described in Sect. 1.3.2 should provide as

much detail as possible about conditions expected to exist on the site and

should therefore guide the design and execution of the sampling program.

However, such investigations cannot totally prevent the danger of misin￾terpretation of the results of borings, and the selection of sampling points

should take this into account.

Depth of Sampling

No general recommendation can be given on the depths at which samples

should be taken or on the final depths to which trial pits or boring/drilling

should extend. This depends on the objectives and might be subject to

change during a running program. Investigation of soil for chemical char￾acteristics can be divided into two general types:

1. The investigation of agricultural and similar near-natural sites, where

information is required mostly on the topsoil or plowed horizon or arable

zone but often over an extended area.

2. The investigation of sites which are known or suspected to be contami￾nated, where information is required from deeper layers, sometimes to

a depth of several tens of meters, the extent of the area usually being

rather small compared to agricultural sites.

A mixture of both cases is realized in so-called “soil-monitoring sites,”

which represent larger areas of homogeneous soil development and in most

cases are established to monitor environmental effects to the complete

profile over a long-term scale. A precise description should be made of

all soil horizons or layers encountered during the sampling exercise and

included in the report.

If a profile is to be sampled, care should be taken that every horizon/layer

of interest is sampled and that different horizons/layers are not mixed. In

general, contaminated sites should be sampled horizon by horizon unless

stated otherwise by the client. Care should be taken in a site investigation

to ensure that pathways for migration of contamination are not created,

particularly where impermeable strata may be penetrated.

When trial pits are used it may be appropriate to sample from more

than one site. A depth-related sampling program is based on a number

of conventions, depending on the project. It is not as representative with

regard to the soil as a horizon-related sampling program can be. The

mode of sampling from each depth should be carefully specified; e.g., the

maximum depth range (usually not more than 0.1 m) and how horizontal

variations are to be dealt with.

The total depth reached, the thickness of the horizons/layers penetrated,

and the depth from which the samples are obtained should be recorded. All

24 A. Paetz, B.-M. Wilke

data should be recorded in meters below surface. The soil depth should be

measured from the ground surface with the thickness of the humus litter

layer recorded separately.

Mountain regions or hilly areas with pronounced slopes require special

consideration. For slopes of 10◦ and greater, vertical drilling lengths should

be extended according to the cosine rule in order to maintain constant

slope-parallel thicknesses of soil layers. The extension factor is 1/ cos of

slope. Without correction, for example, the error will be 2% at a slope of

11.5◦.

Timing of Investigation

In some circumstances, it may be necessary to restrict sampling to specific

periods of the year. For example, if the characteristic or substance to be

determined is likely to be affected by seasonal factors or human activities

(weather, soil conditioning/fertilization, use of plant protecting agents), this

should be taken into account in the design of the sampling program. This is

particularly important where monitoring continues for several months or

years or is repeated periodically, and therefore requires similar conditions

every time sampling is carried out.

Sample Quantity

At least 1,000 g of fine soil should be obtained for chemical analysis. This

figure applies both to single samples and composite samples, in the latter

case after sufficient homogenization. Samples obtained to serve as reference

material or to be stored in a soil specimen bank should be of larger size,

usually larger than 2,000 g.

Where the sampling of soil involves the separation of oversized material

(i.e., mineral grains, sand, pebbles, and all other materials) due to very

coarse-grained or heterogeneous soil conditions, the material removed

shall be weighed or estimated and recorded and described to enable the

analytical results to be given with reference to the composition of the

original sample. These procedures should be carried out in accordance

with ISO 11464 (1994).

Details on the amount of sample materials needed for determination

of specific physical soil parameters are given in the respective methods

(Chap. 2). In particular, the determination of the particle size distribution

may need a very large mass of soil material. The actual mass required will

usually depend on the largest grain size to be determined (see ISO 11277

1998). The quantity of soil sample needed for biological or ecotoxicological

investigations is highly dependent on the aim of the investigation and the

related soil organisms.