ABSTRACT
CONTENTS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 960 The Science Behind Ground-Water Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961
Objectives of Ground-Water Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961 Regulatory Compliance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961 Non-Regulatory Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 962 Collecting “Representative” Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 962
Ground-Water Sampling and Data Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963 Meeting DQOs: A Superfund Project as an Example . . . . . . . . . . . . . . . . . . . . . . . 964
Factors Affecting the Representative Nature of Ground-Water Samples . . . . . . . . . 965 Factors Related to Formation and Well Hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . 965
Understanding Ground-Water Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965 Hydraulics and Water Chemistry Between Sampling Events . . . . . . . . . . . . . . 967
Factors Related to Sampling Point Placement, Design, Installation, and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 969
Three-Dimensional Placement of the Sampling Point . . . . . . . . . . . . . . . . . . . . . 969 Sampling Point Installation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 970 Poor Well Design and Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973 Inadequate or Improper Well Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976 Well Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976
Geochemical Changes in Ground-Water Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 976 Pressure Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977 Temperature Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 978 Entrainment of Artifactual Particulate Matter During Purging and Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 979
Agitation and Aeration of Water Samples During Collection . . . . . . . . . . . . . . 984 The Ground-Water Sampling and Analysis Plan (SAP): A Road Map to Field
Sampling Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 987 Objectives of the SAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 987 Preparation of the SAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 987
Selection of Field Protocols to be Incorporated into the SAP . . . . . . . . . . . . . . . . 988 Well Headspace Screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 988 Water-Level and Product-Thickness Measurement . . . . . . . . . . . . . . . . . . . . . . . 989 Field Quality Assurance and Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 991 Purging and Sampling Device Selection and Operation . . . . . . . . . . . . . . . . . . . 996 Sampling Point Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1035 Field Measurement of Water-Quality Indicator Parameters and Turbidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1056
Sample Pretreatment Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1062 Field Equipment Cleaning Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079 Documenting a Sampling Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080
Conducting a Ground-Water Sampling Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086 Field Preparation for a Ground-Water Sampling Event . . . . . . . . . . . . . . . . . . . . . . . 1087
Site Orientation and Sampling Event Preparation . . . . . . . . . . . . . . . . . . . . . . . . . 1087 Conducting the Sampling Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087
Sampling Point Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087 Well Headspace Screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1088 Water-Level Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1089 Well Purging and Field Parameter Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 1089 Sample Collection Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1090
Order of Container Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1090 Sample Collection Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1092 Protocols for Collecting Field QC Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094 Ground-Water Sample Pretreatment Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 1097 Physical and Chemical Preservation Procedures for Samples . . . . . . . . . . . . . 1100 Preparation of Sample Containers for Shipment . . . . . . . . . . . . . . . . . . . . . . . . . 1100 Cleanup of the Work Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1102 Delivery or Shipment of Samples to the Laboratory . . . . . . . . . . . . . . . . . . . . . 1102
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1102
Ground-water sampling is a key component of any effective ground-water monitoring program and most environmental site-characterization programs. Developing an effective ground-water sampling program requires an understanding of a variety of factors that can affect the integrity of samples collected from ground-water monitoring wells or other ground-water sampling points and the quality of analytical results or other data generated from those samples. These factors include formation and well hydraulics; sampling point placement, design, installation, and maintenance; purging practices; purging and sampling device selection and operation; and sample collection, pretreatment, and handling procedures. This chapter provides the reader with a detailed discussion of these factors and the processes that occur in a monitoring well between sampling events and during sample collection activities. Incorporating this knowledge should allow readers to make sound technical decisions regarding the choice of sampling procedures to meet the site-specific objectives of a ground-water monitoring or environmental site-characterization program.
