Drilling,Logging & Sampling At Contaminated Sites
DEPARTMENT OF TOXIC SUBSTANCES CONTROLCALIFORNIA ENVIRONMENTAL PROTECTION AGENCYDRILLING, LOGGING, AND SAMPLING ATCONTAMINATED SITESJune 2013Edmund G. Brown Jr.GovernorState of CaliforniaMatthew RodriquezSecretaryCalifornia Environmental Protection AgencyDeborah RaphaelDirectorDepartment of Toxic Substances ControlThe California Environmental ProtectionAgency:Department of Toxic Substances ControlState Water Resources Control BoardCalRecycleAir Resources BoardDepartment of Pesticide RegulationOffice of Environmental Health HazardAssessment
FOREWORDThe California Environmental Protection Agency (Cal/EPA) is charged with theresponsibility of protecting the state’s environment. Within Cal/EPA, the Department ofToxic Substances Control (DTSC) has the responsibility for managing the State’sHazardous Waste and Cleanup programs to protect human health and the environment.The State Water Resources Control Board and Regional Water Quality Control Boards(RWQCB), also part of Cal/EPA, have the responsibility for coordination and control ofwater quality, including the protection of the beneficial uses of the waters of the state.Therefore, RWQCB and DTSC work closely together in protecting the environment.To aid in characterizing and remediating contaminated sites, DTSC has developedseveral guidance documents and recommended procedures for use by its staff, localgovernmental agencies, responsible parties, and their contractors. This document (andthe document it supersedes) has been prepared by the Geological Services Branchstaff to provide guidelines for drilling, logging and sampling soil at contaminated sites.The Geological Services Branch within DTSC provides geologic assistance, training andguidance to DTSC staff.This document supersedes the July 1995 Cal/EPA document titled:Drilling, Coring, Logging and Sampling at Hazardous Substances Release SitesTrade names or commercial products are occasionally used by name within thisdocument. Such use does not constitute Cal/EPA endorsement or recommendationand is only meant for clarification purposes.Comments and suggestions for improvement of Drilling, Logging and Sampling Soils atContaminated Sites should be submitted to:Dot Lofstrom, PGDepartment of Toxic Substances Control8800 Cal Center DriveSacramento, California 95826Dot.Lofstrom@dtsc.ca.govi
ACKNOWLEDGMENTSPreparation of this guidance document was achieved through the efforts of manyindividuals. The following people had primary responsibility for research, editing, andwriting: Dot Lofstrom, PGRandy Adams, PG, CEGAlice Campbell, PG, CEG, CHGJohn Karachewski, PG, CHGJerod Randall, PGThe support and encouragement of Karen Baker, Chief, Geological Services Branch,was fundamental to the success of this project.This guidance has benefited greatly through input received from several sources,including the following DTSC staff: Eileen Hughes and Thomas Skaug.Administrative support was provided by Sarah Berry, Rosa Boyer, and Shannon Garrett.The revised guidance relies heavily on the work of the authors of the original guidance.Their contributions continue to be appreciated. The primary authors of the originaldocument include: Steve BelluominiBill OwenJohn WoodlingFunding for this guidance document was provided by a USEPA CERCLA Section 128(a) State Implementation Support Grant.ii
TABLE OF CONTENTS1.0INTRODUCTION . 12.0SUBSURFACE BORING PROGRAM . 22.1 Continuous Cores . 22.2 Geophysical Techniques . 32.3 Borehole Decommissioning and Sealing . 32.4 Confining Layers . 43.0BOREHOLE DRILLING METHODS . 53.1 Direct Air Rotary . 53.2 Direct Mud Rotary . 73.3 Hollow-Stem Auger . 83.4 Sonic (Vibratory). 93.5 Direct Push Technologies . 103.6 Hand Auger . 114.0SOIL SAMPLING . 125.0LOGGING OF SOILS . 135.1 Logging Boreholes . 145.1.1 Boring Log Descriptions Using the USCS . 145.1.2 Special Case of Soils with Cobbles and Boulders . 155.2 Field Classification of Coarse-Grained Soils . 165.2.1 Particle Distribution Rules . 165.2.2 Particle Size . 175.3 Field Classification of Fine-Grained Soils . 195.4 USDA Soil Classification . 226.0TEST PIT AND TRENCH LOGGING USING THE USCS. 247.0REFERENCES . 25APPENDICES . 26APPENDIX A . 27APPENDIX B . 31APPENDIX C . 40APPENDIX D . 42iii
1.0 INTRODUCTIONThis document provides guidelines for drilling, sampling and describing soil fromboreholes drilled to characterize contaminated sites. The information in this documentprovides a brief description of various drilling methods, soil sampling, and a summary ofthe Unified Soil Classification System (USCS) and American Society for Testing andMaterials (ASTM) D 2488 - “Standard Practice for Description and Identification of Soils,Visual-Manual Procedure” used for describing soil and creating boring and trenchinglogs.This document revises and replaces the previously published “Drilling, Coring, Samplingand Logging at Hazardous Substance Release Sites” (Cal/EPA 1995). Therecommendations are a subset of the site characterization process as outlined in therecently revised “Guidelines for Planning and Implementing GroundwaterCharacterization of Contaminated Sites” (Cal/EPA 2012a).ApplicationDrilling, trenching, and sampling provide a means to directly observe subsurface soilsand rock. With this information, geology and hydrogeology can be characterized,contamination defined, and remedies designed to mitigate environmental contamination.Geologists describe soil based on visual examination and manual tests, and write thisdescription for a boring/trench log using USCS terminology. A detailed description ofthe USCS is provided in the Engineering Geology Field Manual (US Bureau ofReclamation, 1998) and various ASTM publications, as listed in Section 6.0 References.The following guidelines are presented in an effort to help responsible parties and theirconsultants select an appropriate drilling method for site characterization andremediation. Additionally, this guidance summarizes the USCS to assist in completingaccurate and complete boring logs for environmental investigations and remedialdesign.LimitationsIt is the obligation of the responsible parties and qualified professionals performing thesite investigations and remedial design to consult with pertinent regulatory agencies,identify all requirements, and meet them appropriately.This document discusses broad categories of methods and devices that can be used indrilling and sampling investigations. It does not define specific operating procedures fordrilling and sampling. Nor does this document propose guidelines for every availabledrilling method or sampling device. The qualified professional in charge of the fieldinvestigation should specify the methods, equipment, and operating procedures in awork plan and document any significant changes that were implemented in the field.This document does not supersede existing statutes and regulations. Federal, stateand local regulations, statutes, and ordinances should be identified and sitecharacterization and remedial design activities performed in accordance with the moststringent of these requirements where applicable or relevant and appropriate.1
2.0 SUBSURFACE BORING PROGRAMBorehole information is used to characterize the subsurface and identify potentialcontaminant migration pathways. When there is little or no information about a site,reconnaissance or screening level investigations are frequently used prior to launchinga subsurface boring program. In comparison to past practices, groundwater monitoringwells are used less often for characterization and are more often installed for long-termmonitoring of known plume areas, as sentry wells, and for performance monitoring ofremedial actions. Data collected from screening level investigations are used to focusthe efforts of subsequent detailed studies. For example, grab-groundwater samplesmay be collected during initial investigations to determine the extent of groundwatercontamination before installing monitoring wells.Borings are typically drilled to obtain various types of samples, including: lithologic,geotechnical, soil gas, soil, sediment, and groundwater samples. The number, location,and spacing of borings should be based on the Conceptual Site Model (CSM), whichevolves as data are acquired. Decision rules of the data quality objectives (DQOs)process ensure that the data are acceptable for decision-making.Boreholes should be spaced closely enough so that accurate cross-sections can beconstructed in order to understand site geology and to evaluate potential contaminantmigration pathways. The number of borings will depend on the complexity of thesubsurface, including: the lateral/vertical continuity and geometry of geologic units; thepresence of faults or fractures; and the identification of preferential pathways (such assand/gravel lenses, utility trenches, and channel deposits) for contaminant migration.Accurate location data of samples, borings, and wells are necessary for delineation ofareal and three-dimensional contaminant distribution and hydrogeologicalcharacteristics. All boreholes should be accurately located with reference to apermanent or semi-permanent feature onsite, and all monitoring wells should beprofessionally surveyed. DTSC recommends following the California State WaterBoard’s Geotracker requirements for surveying and reporting of electronic geographicinformation. Detailed information can be found on the State Water Board’s GeoTrackerwebsite. In general, transient or one-time sampling points (such as direct pushtechnologies, piezometers, or grab samples) do not need to be professionally surveyedand Global Positioning System (GPS) coordinates will suffice.2.1 Continuous CoresOne or more boreholes per site should be drilled for the purpose of collectingcontinuous cores to accurately describe the physical soil properties and to identify thesubsurface stratigraphy. The locations for these designated boreholes should bechosen to represent the lithologic variation over the entire study area, and a completeboring log prepared as described below. Photographs of representative samples shouldbe taken and included in field reports. Core samples may be archived for laterevaluation, providing proper care is taken in handling potentially contaminated cores.2
2.2 Geophysical TechniquesGeophysical techniques can be used to plan and supplement the drilling program.Application of Borehole Geophysics at Contaminated Sites (Cal/EPA 2012b) containsguidance for the use of surface geophysical techniques and data acquisition.2.3 Borehole Decommissioning and SealingAny boring that will not be completed as a monitoring well should be decommissionedby sealing it to avoid creating a conduit for contaminant migration, either from thesurface to the subsurface or between subsurface units. The objective of sealing aborehole is to prevent migration of contaminants through the borehole. The verticalpermeability of the sealed borehole should be equal to or less than the natural verticalpermeability of the surrounding geologic formation (USEPA 1997). This is usuallyaccomplished by filling the boring with a grout made of cement or bentonite slurry. Dryproducts such as bentonite powder may be used but should be hydrated at the surfacefirst. The slurry is then pumped into the borehole through a rigid pipe (tremie pipe),often under pressure. The bottom of the tremie pipe is placed into the bottom of theopen hole, and is kept below the surface of the slurry as the grout fills the hole. Someborings may need to be overdrilled before being filled with grout. Boringdecommissioning should be performed in compliance with California Department ofWater Resources’ Water Well Standards, Bulletin 74-81 and Bulletin 74-90.Additionally, county ordinances and regulations should be consulted to ensurecompliance with local agency concerns.Direct Push Technology (DPT) Decommissioning. If the borehole was created with aDPT method, the resultant borehole may be too small in diameter to push grout throughit. Several methods are available for decommissioning DPT holes, but the methodchosen should be capable of backfilling the hole completely with grout or bentoniteslurry, from bottom to top and without gaps (USEPA 2005).Retraction Grouting. Retraction grouting allows for DPT rods to act as a tremie pipe forgrout that is either poured or pumped down the hole, ensuring a complete seal of theborehole. Retraction grouting typically involves pumping a high-solids bentonite slurryor a neat cement grout through the rod and tool string and out the bottom of thesampling tool as the tool is withdrawn from the hole. To use this method, a port isneeded at the end or sides of the tool and/or an expendable tip is necessary on theterminal end of the tool through which the grout can be pumped. Because the hole isgrouted as the tool is withdrawn, this method ensures that the borehole is sealedthroughout its length. Retraction grouting is generally considered the most reliableborehole sealing technique (USEPA 1997; USEPA 2005).Re-entry Grouting. Re-entry grouting typically involves pumping grout through a tremiepipe inserted into the borehole immediately following withdrawal of the rod string.Alternatively, the rod string may be reinstalled in the borehole without the sampling tool,so that grout may be pumped through the open rods. The grout should be pumpedcontinuously from the bottom of the hole to the top as the tremie pipe (or rod string) iswithdrawn to avoid gaps and bridging. Typically, re-entry grouting is effective only if theborehole remains open until tremie pipe or rods can be extended to the bottom of the3
borehole. If a portion of the borehole collapses, the tremie pipe or rods will notpenetrate to the total depth of the borehole. In this situation, it may be necessary to putan expendable tip on the end of the rod string. The rods are then pushed through soilbridges to the bottom of the borehole. The probe rods are withdrawn slightly, and theexpendable tip is knocked out by lowering a small diameter steel rod inside the directpush rods. Alternatively, the tip may be blown off by applying pressure with the groutpump. Grout is then pumped through the direct push rods as they are withdrawn fromthe borehole. Re-entry grouting may not provide a reliable seal if the DPT rods do notfollow the original borehole. In most circumstances, the original borehole will providethe path of least resistance and this will not be a concern (USEPA 1997; USEPA 2005).Both re-entry grouting and retraction grouting can be successfully used with DPT, conepenetrometer tests (CPTs), and sonic drilling.2.4 Confining LayersIn some situations, it may be necessary to drill through actual or possible confininglayers at a site. Extreme care should be taken when drilling into confining units so thatthe borehole does not create a pathway for the migration of contaminants betweenupper and lower hydraulically-separated zones. Particular care should be taken ifdense, non-aqueous phase liquids (DNAPLs) areExtreme care should bepresent. In all cases, the investigator should preventtaken when drilling intomobilization of DNAPLs when drilling boreholes.confining units so that theResponsible parties should obtain approval of the leadregulatory agency prior to implementing a plan to drillborehole does not create athrough a possible confining layer. There are at least twopathway for the migration ofapproaches for drilling through confining layers. Basedcontaminants between upperon site-specific conditions, one or both of theseand lower hydraulicallyapproaches may be appropriate:separated zones. Install initial boreholes on the perimeter of the site,in less-contaminated or uncontaminated areas, toallow characterization of the lower units. Boreholes may be drilled through thepossible confining layer to characterize the geology of the site providing theboreholes are located upgradient of the source of DNAPL or a dissolved-phaseplume. Drill the boreholes using techniques that minimize the danger of crosscontamination between water-bearing zones. Such techniques typically involvedrilling a borehole partially into the possible confining layer, installing an exteriorconductor casing, sealing the annular space in the cased portion of the borehole,and drilling a smaller-diameter borehole through the confining layer.DPT methods that may penetrate confining layers include: single-wall and dual-walledprobes; DPT well installation (dual-walled only); real-time measurement tools (such asCPTs, Membrane Interphase Probes [MIPs]); and, sampling tools such asHydropunch . Sonic drilling, using dual-walled methods, is similar in approach. In4
each case, proper grouting protocols and materials should be used to minimize thepotential for cross-contamination between water-bearing zones. When penetratingconfining layers or source zones, dual tube direct push installations (analogous toconductor casing) may be prudent. Detailed information regarding sealing DPTboreholes is prov
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