![\"\"](\"https:\/\/www.envguide.com\/wp-content\/uploads\/2018\/01\/1-7-300x225.jpg\")
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The SAP should be written by an experienced practitioner who has relevant field experience and who can identify potential sources of error and bias in each component of the ground-water sample collection process. Implementation of a comprehensive and well thought out SAP should ensure that ground-water sample collection procedures are consistent from one sampling event to the next, thus reducing the potential for sampling team related error and bias.<\/p>\n
The SAP details specific standard operating procedures for a number of work tasks to be implemented during the sampling event. While preparing the SAP, a great deal of thought needs to go into the selection of protocols for each of the work tasks most appropriate for any individual site. This includes methods and equipment for wellhead screening, water-level and product-thickness measurement, field quality assurance (QA) and quality control (QC), sampling point purging and sample collection, field parameter measurement, and field equipment decontamination.<\/p>\n
Well Headspace Screening<\/p>\n\t\t\t\t\t<\/div>\n
The first task implemented by the sampling team at each sampling point is opening the well and screening the headspace above the water column in the well for the presence of volatile or combustible gases and vapors. FID(flame ionization detector), PID (photoionization detector) or other flammable vapors may be used for well headspace screening and their applications.<\/p>\n
![\"Wellhead](\"https:\/\/www.envguide.com\/wp-content\/uploads\/2018\/01\/2-1.jpg\")
Wellhead screen with PID<\/p><\/div>
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Water-Level and Product-Thickness Measurement<\/p>\n\t\t\t\t\t<\/div>\n
Following well headspace screening, the next task is to take water-level or product thickness measurements. These measurements must be taken in all sampling points prior to any purging and sampling activities, to ensure that the data are collected under as close to the same environmental and atmospheric conditions as possible. This is of particular concern when taking water-level measurements, which are potentially affected by a number of environmental variables including changes in ambient air pressure (especially problematic for shallow, unconfined formations), tides, changes in levels of nearby rivers, precipitation events, and operation of nearby pumping wells.<\/p>\n
![\"Water](\"https:\/\/www.envguide.com\/wp-content\/uploads\/2018\/01\/3-1-300x197.jpg\")
Water level measurement<\/p><\/div>\n
Field Quality Assurance and Quality Control<\/p>\n\t\t\t\t\t<\/div>\n
Below table summarizes the key administrative and field elements of a field QA program for ground-water sampling.<\/p>\n
Administrative Elements<\/p>\n\t\t\t\t\t<\/div>\n\t \n\t\t
Field Elements<\/p>\n\t\t\t\t\t<\/div>\n\t \n\t\t
Table below presents a list of the various QC samples that may be included in a field QC program, with the typical frequency of collection for each type of sample.<\/p>\n
Type of QC Sample Recommended Frequency of Collection<\/p>\n\t\t\t\t\t<\/div>\n
| Trip blank<\/td>\n | One per shipment per day per laboratory<\/td>\n<\/tr>\n |
| Temperature blank<\/td>\n | One per shipping container<\/td>\n<\/tr>\n |
| Field blank<\/td>\n | One per waste management unit<\/td>\n<\/tr>\n |
| Equipment blank<\/td>\n | One for every ten sampling points<\/td>\n<\/tr>\n |
| Blind duplicate sample<\/td>\n | One for every ten sampling points<\/td>\n<\/tr>\n |
| Spiked sample<\/td>\n | One for every ten samples submitted for analysis<\/td>\n<\/tr>\n |
| Field split sample<\/td>\n | Variable, but at least one upgradient location and two downgradient locations should be sampled<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n\t\t\t\t\t\t Purging and Sampling Device Selection and Operation<\/p>\n\t\t\t\t\t<\/div>\n Many devices are available for purging and sampling ground water. The SAP must include a description of the devices selected for use on a task-specific basis.ASTM Standard D6634 summarized selection criteria in more detail:<\/p>\n\t \n\t\t \n\t\t\n
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