1.1 本指南涵盖了地表地球物理方法的选择，通常适用于地质、岩土、水文和环境现场调查以及随后的现场特征，以及法医和考古应用。这些地球物理方法很少是现场调查中使用的唯一方法，通常用于预筛选，以指导如何以及在何处进行钻探、取样或其他有针对性的现场测试。本指南未描述进行地球物理调查的具体程序。已经为许多地表地球物理方法制定了单独的指南。 1.2 地面地球物理方法可以直接和间接测量土壤、岩石、孔隙流体以及埋藏物体的物理财产。 1.3 本指南概述了适用于地表地球物理方法的应用。它不涉及具体方法、现场程序或数据解释的理论细节。为此目的，包括了许多参考文献，这些参考文献被视为本指南的重要组成部分。建议本指南的用户熟悉引用的参考文献 ( 1- 27 ) 2. 和辅助线 D420型 , D5730型 , D5753型 , 第5777页 , D6285型 , D6430型 , D6431型 , D6432型 , D6820型 , 第7046页 和 第7128页 ，以及实践 D5088型 , D5608型 , 第6235页 和测试方法 D4428/D4428米 , D7400/D7400米 和 第57页 . 1.4 为了获得具体地球物理方法的详细信息，应参考ASTM标准、其他出版物以及本指南中引用的参考文献。 1.5 地球物理调查的成功取决于许多因素。最重要的因素之一是负责规划、执行调查和解释数据的人员的能力。对该方法的理论、现场程序和解释的理解以及对现场地质的理解是成功完成勘测所必需的。 没有专业培训或经验的人员应谨慎使用地球物理方法，并应寻求合格专业人员的帮助。本标准中所有提及的“合格专业人员”均指具有适当经验的个人（如工程师、土壤科学家、地球物理学家、工程地质学家或地质学家），如果当地法规要求，还包括适用的认证、执照或注册。术语“工程”必须理解为与该合格专业人员的实践或活动相关。 1.6 单位- 以国际单位制表示的值应视为标准值。括号中给出的值仅供参考，不视为标准值。以SI以外的单位报告试验结果不得视为不符合本标准。 1.7 本指南提供了有组织的信息收集或一系列选项，不建议采取具体行动。本文件不能代替教育或经验，应结合专业判断使用。并非本指南的所有方面都适用于所有情况。 本ASTM标准不代表或取代必须判断给定专业服务是否充分的谨慎标准，也不应在不考虑项目的许多独特方面的情况下应用本文件。本文件标题中的“标准”一词仅表示该文件已通过ASTM共识程序获得批准。 1.8 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践，并确定监管限制的适用性。 1.9 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《国际标准、指南和建议制定原则决定》中确立的国际公认标准化原则制定的。 =====意义和用途====== 5.1 本指南适用于 表1 中使用的评级系统 表1 当与应用于相同应用的其他方法相比时，基于每种方法在平均场条件下产生结果的能力。 “A”等级表示首选方法，“B”等级表示备选方法。可能有一个或多个方法可以成功应用。也可能有一种或多种方法以较低的成本在技术上取得成功。必须根据目标的规模和设置选择最合适的方法。最终选择必须考虑现场具体条件和项目目标；因此，让一名合格的专业人员对所选方法做出最终决定至关重要。 5.1.1 Benson等人 ( 1. ) 提供了地球物理学应用于环境问题的早期指南之一。 5.1.2 病房 ( 2. ) 是一个三卷的概要，涉及应用于岩土和环境问题的地球物理方法。 5.1.3 巴特勒 ( 3. ) 提供了近地表地球物理方法的详细技术解释，并包括几个详细的案例历史。 5.1.4 美国陆军工程兵团手册 ( 4. ) 提供了工程和环境调查地球物理勘探方法的介绍性章节。本手册可从美国工程兵团网站免费下载。 5.1.5 奥尔霍夫特 ( 5. ) 提供了一个专家系统，用于帮助选择在危险废物现场使用的地球物理方法。 5.1.6 美国环保局 ( 6. ) 提供了一份关于地球物理方法在受污染场地使用的理论和使用的优秀文献综述。 5.2 地球物理测量简介: 5.2.1 地球物理测量提供了一种绘制一个或多个物理财产横向和纵向变化的方法，或监测条件的时间变化，或两者兼而有之。在缺乏有关现场的事先信息的情况下，勘测级地球物理调查可能适合作为精细调查的先导。 影响现场调查结果准确性的主要因素是测试地点的数量。如果样本数量太少，可能会导致空间采样不足，无法充分描述现场的条件。这些采样点之间的插值可能很困难，并可能导致不准确的现场特征。 5.2.2 地球物理测量通常可以相对快速地进行，侵入性最小，并且可以在已知控制点之间进行插值。可以使用某些地球物理方法以高达数公里/小时（mph）的速度获得连续数据采集。 在某些情况下，整个现场覆盖在经济上是可行的。由于样品密度更大，地球物理方法可用于定义背景（环境）条件和检测异常条件，从而比单独使用钻孔或测深更准确地确定现场特征。地球物理测量设计考虑因素因测量的预期分布而不同。可以沿着单个样条收集数据，以调查线性特征（大坝、堤坝、道路），同时需要多个样条或三维测量几何图形来确定较大场地和非- 线性目标。这些地球物理方法对于在详细规划进一步现场调查（如其他钻探、取样和测试方法）之前预先筛选大型现场尤为重要。 5.3 要成功进行地球物理测量，必须存在材料财产的对比。 5.3.1 地球物理方法测量土壤、岩石和孔隙流体的物理、电气或化学财产。要检测异常情况、土壤与岩石的接触、无机污染物的存在或埋地滚筒，必须在测量的属性中进行对比。例如，要检测的目标或要定义的地质特征必须具有与“背景”条件显著不同的财产。 5.3.2 例如，含水层中淡水和盐水之间的界面可以通过孔隙流体电财产的差异来检测。土壤和未风化基岩之间的接触可以通过材料声速的差异来检测。在某些情况下，测量的物理财产差异可能太小，无法通过地球物理方法进行异常检测。 5.3.3 由于土壤和岩石的物理财产变化很大，有些甚至有许多数量级，因此这些财产中的一个或多个通常对应于地质不连续性； 因此，由地球物理方法确定的边界通常与地质边界重合，并且由地球物理数据产生的横截面可能与地质横截面相似，尽管两者不一定相同。 5.4 在以下情况下，应使用地球物理方法: 5.4.1 地表地球物理方法可以并且应该在现场调查计划的早期使用，以帮助识别背景条件以及异常条件，从而可以定位钻孔、测深和采样点，以代表现场条件并调查异常情况。 初始研究完成后，也可在现场调查计划中稍后使用地球物理方法，以确认和改进现场调查结果，并在其他测量之间提供填充数据。一般场地知识（例如，基岩深度、场地使用历史）是设计地球物理勘测的有用前提。 5.4.2 如果明确了调查目标，地球物理调查的成功程度就会提高。在某些情况下，当调查发现有关现场条件的新数据或未知数据时，目标可能会被细化。应将更改或增加技术方法的灵活性纳入计划，以说明随着现场调查的进行，现场条件解释的变化。 5.5 剖面和测深测量: 5.5.1 通过台站或连续测量进行的剖面分析提供了一种评估地下条件横向变化的方法。 5.5.2 测深提供了一种评估地质层或其他目标深度和厚度的方法。大多数地表地球物理探测测量可以分辨三层甚至四层。 5.6 数据的易用性和解释性: 5.6.1 应用地球物理的理论是定量的，然而，在应用中，地球物理方法往往会产生定性的解释。 5.6.2 一些地球物理方法提供了可在现场进行初步解释的数据，例如，探地雷达（GPR）、频域电磁剖面、直流（DC）电阻率剖面、磁剖面和金属探测器剖面。 通常可以在现场创建GPR异常图或EM（电磁）、电阻率、磁性或金属探测器数据的等高线图。 5.6.3 一些方法（例如，时域电磁学和直流电阻率测深、地震折射、地震反射和重力）要求在进行任何定量解释之前对数据进行处理。 5.6.4 应谨慎对待现场数据的任何初步解释。此类初步分析应通过与已知控制点（如钻孔或露头）的其他信息的相关性进行确认。 这种初步分析在数据处理后会发生变化，并且主要作为质量控制（QC）的手段进行。 5.6.5 正是对所有现场数据的解释和整合，为现场特征化提供了有用的信息。将原始数据转换为有用信息是一个增值过程，经验丰富的专业人员通过仔细分析实现了这一过程。此类分析必须由称职的专业人员进行，以确保解释符合地质和水文条件。 5.7 应用程序讨论- 中列出的应用程序 表1 如下所述。 5.7.1 自然地质和水文条件: 5.7.1.1 土壤/未固结层- 该应用包括确定松散层的深度、厚度和面积范围。这些层可以是不连续的或包括各种材料的透镜。由于与相邻材料相比，这些层的物理财产不同，因此可以检测到。 5.7.1.2 岩石层- 该应用包括确定不同岩层之间的接触，例如，花岗岩上的石灰岩或页岩上的砂岩、不连续层面、不整合面和这些岩层的厚度。 根据岩层的物理财产、深度和厚度，可以使用几种地球物理方法来描绘岩层。 5.7.1.3 至基岩的深度- 该应用包括确定松散覆盖层覆盖的合格岩石顶部的深度。地球物理方法的选择取决于岩石和上覆材料之间是否存在物理性质对比。在岩石顶部风化或高度断裂的区域，岩石顶部可能难以确定。高度不规则的岩石表面可能会带来额外的问题。 5.7.1.4 地下水位深度- 该应用包括确定地下单元完全饱和的深度。由于饱和条件引起的物理财产变化，可以检测到地下水位（饱和区顶部）。探测地下水位的能力可能取决于地下水位发生的地质单元。地震方法可用于检测大多数松散材料的地下水位；电、电磁或GPR方法可用于检测固结或松散材料中的地下水位。 5.7.1. 5. 裂缝和断层带- 该应用包括节理、裂缝和断层的位置和特征。这些特征从单个节理和断裂带到更大的区域结构特征。节理、裂缝和断层带可能是干燥的、流体填充的或填充有粘土或风化岩石。这些特征的可检测性随着特征的大小以及不同孔隙流体或导电填充材料的存在而增加。 5.7.1.6 空隙和沉孔- 该应用包括岩溶特征，如岩石中的风化洼地、开阔地、水- 填充或沉积物填充的沉坑、空洞或更大的洞穴系统。在许多情况下，所关注的目标可能超出某些或所有地表地球物理方法的有效分辨率或深度范围；然而，深洞通常显示出其存在于近地表的迹象，可以使用浅层地球物理数据进行解释。对于所有地表地球物理方法，探测给定尺寸空洞的能力随着深度的增加而降低。 5.7.1.7 土壤和岩石财产- 该应用是指测量土壤和岩石的物理财产，例如弹性、塑性和电性。 所选择的地球物理方法将由待测量的具体性质决定。应参考与这些财产相关的ASTM标准。例如，《指南》中讨论了岩石的撕裂性和声速 第5777页 ，测试方法中沿单个钻孔测得的波速 D7400/D7400米 以及试验方法中的钻孔之间 D4428/D4428米 测试方法中讨论了土壤电阻率测量 第57页 指南中讨论了钻孔中的密度、孔隙度测量和地震速度测量 D5753型 . 5.7.1.8 大坝和泻湖泄漏- 该应用涉及沿着优先流动路径从大坝或泻湖泄漏的流体的检测和绘图。 应用地表地球物理方法探测泄漏取决于是否存在局部流动或电导率差异。 5.7.2 无机污染物: 5.7.2.1 垃圾填埋场渗滤液- 该应用包括所有类型的垃圾处理场，其中主要渗滤液可能是无机的和导电的。这包括城市垃圾填埋场、危险废物场和矿山尾矿。无机污染物可以使用电学或电磁地球物理方法检测。 5.7.2.2 盐水入侵- 盐水入侵是指盐水流入淡水含水层，虽然这主要是一个沿海问题，但它可以自然发生在内陆含水层，也可以是人为造成的- 造成污染，例如盐水池。盐水具有很强的导电性，可以通过直流电阻率和电磁法进行检测。可以绘制盐水/淡水界面的横向边界，并估计盐水的深度。 5.7.2.3 土壤盐度- 土壤盐分是指土壤中的盐分浓度达到影响作物生长和产量的水平。直流电阻率和电磁传导率测量提供了在大面积和不同深度测量土壤盐度的方法。 5.7.3 有机污染物: 5.7.3.1 轻质非水相液体（LNAPL）- 该应用包括以离散的、可测量的污染物形式存在的石油产品，其浓度大于其在水中的溶解度。污染物比水轻，“漂浮”在多孔介质中的非承压含水层表面。它们在断裂土壤或岩石中出现的几何结构更为复杂，也不太明确。LNAPL溶解在水中，并作为溶解污染物羽流的来源（见溶解有机污染物）。在某些情况下可以检测到LNAPL，因为其电财产与地下水不同； 如果存在足够数量的地下水，则会降低地下水面；而且，它可以改变土壤的毛管财产。 5.7.3.2 致密非水相液体（DNAPL）: (1) 该应用包括氯化有机溶剂和其他污染物，这些污染物以离散的、可测量的污染物相存在，其浓度大于其在水中的溶解度。污染物比水密度更大，“下沉”到地下水位以下。DNAPL在地下的分布很复杂，受重力和地下物质的毛细财产控制，而不是受地下水流动方向控制。 DNAPL溶解在水中，并作为溶解的污染物羽流的来源（参见溶解的有机污染物）。此外，“残留”DNAPL（迁移过程中留下的固定污染物）也可以作为溶解有机污染物的来源。DNAPL的残余浓度不会显著改变大多数地球物理方法测量的财产。 (2) 一些DNAPL具有介电财产，如果在引入DNAPL之前进行时间测量，以与存在DNAPL之后存在的财产进行比较，则可以使用GPR进行检测；因此，GPR可用于监测修复期间DNAPL的移动。 (3) 中列出的地球物理方法 表1 在自然地质和水文条件下，适合描述场地的水文地质特征；因此，可以根据对现场地质的理解，尝试预测DNAPL的发生和分布。 5.7.3.3 溶解相: (1) 该应用包括溶解在地下水中的燃料、溶剂和其他有机污染物。来源可能是LNAPL或DNAPL的泄漏和溢出，也可能是污染物到达地下水时溶解的小体积泄漏和溢出。 (2) 地下水中的溶解有机污染物浓度非常低（十亿分之一），是监管关注的问题。 可通过大多数地球物理方法测量的溶解有机羽流的财产与可检测的环境地下水的性质差别不大。一些有机污染物，如酒精，是高度可溶的，即使在高浓度下也无法检测到。 (3) 当已经确定了溶解有机污染物的来源时，可以使用地球物理方法来描述场地的水文地质特征，以便确定溶解羽流的迁移路径。本指南中与地质和水文条件相关的章节讨论了适当的方法。 5.7.4 人造埋藏物: 5.7.4.1 公用设施- 此应用程序包括非常广泛的目标，包括管道、电缆和公用设施。幸运的是，大多数公用设施都埋在地表附近，因此相对容易探测到目标。选择的地球物理方法将取决于管道或公用设施的材料（黑色或有色金属或非金属材料）。非金属设施，即混凝土或塑料，有时可以用探地雷达探测到。 5.7.4.2 地下储罐和桶- 该应用包括地下储罐（UST）和桶。 由于大多数地下储罐都很大（超过2000升（500加仑）），埋得很浅，而且通常由钢制成，因此它们相对容易探测。如果储罐由非金属材料（例如混凝土或玻璃纤维）制成，则更难检测。各种尺寸（通常为4至200L（1至55gal））的桶由非金属或金属材料制成。虽然可以检测到鼓组，但单个200-L（55加仑）鼓和较小的鼓更难定位。 5.7.4.3 未爆炸弹药- 这种应用包括各种设计用于爆炸的材料，如炸弹、地雷和杀伤人员武器。 未爆弹药的大小从几厘米到米不等，由多种金属和其他材料制成。未爆弹药的形状、大小、深度、成分和方位会限制其可探测性。 5.7.4.4 废弃油井- 该应用包括废弃的井，这些井可能未加套管或用钢、PVC或混凝土套管。废弃井可通过各种方法进行检测，具体取决于施工、相关地面坑和其他设施、泄漏液体和废弃方法。指导 D6285型 提供了地球物理和其他方法来定位废弃井的讨论。 5.7.4.5 填埋场和沟渠边界- 该应用包括填埋场、坑和沟渠。由于金属的存在，可以检测到含有掩埋金属材料的那些。有时可以通过电导率的变化、地下层的扰动或填充材料的存在来检测沟槽和坑的边界。确定填埋场或沟渠底部的深度比确定横向边界要困难得多。 5.7.4.6 法医学- 该应用包括埋体和各种金属和非金属物体。 这些物体有时可以直接检测到，也可以通过扰动土壤条件间接检测到。 5.7.4.7 考古特征- 该应用包括广泛的目标，包括石头基础、墙壁、道路、火坑、洞穴和坟墓，以及金属和非金属物体。这些目标和物体有时可以直接检测到，也可以通过土壤条件的变化间接检测到。

1.1 This guide covers the selection of surface geophysical methods, as commonly applied to geologic, geotechnical, hydrologic, and environmental site investigations and subsequent site characterization, as well as forensic and archaeological applications. These geophysical methods are rarely the sole method used in the site investigation and are often used for pre-screening to guide how and where drilling, sampling or other targeted in situ testing are conducted. This guide does not describe the specific procedures for conducting geophysical surveys. Individual guides have been developed for many surface geophysical methods. 1.2 Surface geophysical methods yield direct and indirect measurements of the physical properties of soil and rock and pore fluids, as well as buried objects. 1.3 This guide provides an overview of applications for which surface geophysical methods are appropriate. It does not address the details of the theory underlying specific methods, field procedures, or interpretation of the data. Numerous references are included for that purpose and are considered an essential part of this guide. It is recommended that the user of this guide be familiar with the references cited ( 1- 27 ) 2 and with Guides D420 , D5730 , D5753 , D5777 , D6285 , D6430 , D6431 , D6432 , D6820 , D7046 , and D7128 , as well as Practices D5088 , D5608 , D6235 , and Test Methods D4428/D4428M , D7400/D7400M , and G57 . 1.4 To obtain detailed information on specific geophysical methods, ASTM standards, other publications, and references cited in this guide, should be consulted. 1.5 The success of a geophysical survey is dependent upon many factors. One of the most important factors is the competence of the person(s) responsible for planning, carrying out the survey, and interpreting the data. An understanding of the method's theory, field procedures, and interpretation along with an understanding of the site geology, is necessary to successfully complete a survey. Personnel not having specialized training or experience should be cautious about using geophysical methods and should solicit assistance from qualified professionals. All references in this standard to the “qualified professional” refers to individuals (such as engineers, soil scientists, geophysicists, engineering geologists or geologists), who have the appropriate experience and, if required by local regulations, applicable certification, licensure or registration. The term “engineering” must be understood to be associated with the practices or activities of that qualified professional. 1.6 Units— The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only and are not considered standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard. 1.7 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word “Standard” in the title of this document means only that the document has been approved through the ASTM consensus process. 1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 This guide applies to commonly used surface geophysical methods for those applications listed in Table 1 . The rating system used in Table 1 is based upon the ability of each method to produce results under average field conditions when compared to other methods applied to the same application. An “A” rating implies a preferred method and a “B” rating implies an alternate method. There may be a single method or multiple methods that can be successfully applied. There may also be a method or methods that will be successful technically at a lower cost. Selection of the most appropriate method(s) must be made based on the scale and setting of the target. The final selection must be made considering site specific conditions and project objectives; therefore, it is critical to have a qualified professional make the final decision as to the method(s) selected. 5.1.1 Benson et al ( 1 ) provides one of the earlier guides to the application of geophysics to environmental problems. 5.1.2 Ward ( 2 ) is a three-volume compendium that deals with geophysical methods applied to geotechnical and environmental problems. 5.1.3 Butler ( 3 ) provides detailed technical explanations of near-surface geophysical methods and includes several detailed case histories. 5.1.4 The U.S. Army Corps of Engineers manual ( 4 ) provides introductory chapters for the methods of Geophysical Exploration for Engineering and Environmental Investigations. This manual can be downloaded for no charge from the Corps of Engineers website. 5.1.5 Olhoeft ( 5 ) provides an expert system for helping select geophysical methods to be used at hazardous waste sites. 5.1.6 The U.S. EPA ( 6 ) provides an excellent literature review of the theory and use of geophysical methods for use at contaminated sites. 5.2 An Introduction to Geophysical Measurements: 5.2.1 Geophysical measurements provide a means of mapping lateral and vertical variations of one or more physical properties or monitoring temporal changes in conditions, or both. In the absence of prior information about the site, reconnaissance-level geophysical investigations may be appropriate as a precursor to refined surveys. A primary factor affecting the accuracy of site investigation results is the number of test locations. Insufficient spatial sampling to adequately characterize the conditions at a site can result if the number of samples is too small. Interpolation between these sample points may be difficult and may lead to an inaccurate site characterization. 5.2.2 Geophysical measurements generally can be made relatively quickly, are minimally intrusive, and enable interpolation between known points of control. Continuous data acquisition can be obtained with certain geophysical methods at speeds up to several km/h (mph). In some cases, total site coverage is economically possible. Because of the greater sample density, geophysical methods can be used to define background (ambient) conditions and detect anomalous conditions resulting in a more accurate site characterization than using borings or soundings alone. Geophysical survey design considerations vary according to the intended distribution of measurements. Data may be collected along individual transects to investigate linear features (dams, levees, roadways), while multiple transects or 3D survey geometries are required to identify areal trends over larger sites and non-linear targets. These geophysical methods are especially important to pre-screen large sites prior to detailed planning of further site investigation such as other drilling, sampling and testing methods. 5.3 A contrast in material properties must be present for geophysical measurements to be successful. 5.3.1 Geophysical methods measure the physical, electrical, or chemical properties of soil, rock, and pore fluids. To detect an anomaly, a soil to rock contact, the presence of inorganic contaminants, or a buried drum, there must be a contrast in the property being measured. For example, the target to be detected or geologic feature to be defined must have properties significantly different from “background” conditions. 5.3.2 For example, the interface between fresh water and saltwater in an aquifer can be detected by the differences in electrical properties of the pore fluids. The contact between soil and unweathered bedrock can be detected by the differences in acoustic velocity of the materials. In some cases, the differences in measured physical properties may be too small for anomaly detection by geophysical methods. 5.3.3 Because physical properties of soil and rock vary widely, some by many orders of magnitude, one or more of these properties usually will correspond to a geologic discontinuity; therefore, boundaries determined by the geophysical methods will usually coincide with geological boundaries, and a cross-section produced from the geophysical data may resemble a geological cross-section, although the two are not necessarily identical. 5.4 Geophysical methods should be used in the following instances: 5.4.1 Surface geophysical methods can and should be used early in a site investigation program to aid in identifying background conditions, as well as anomalous conditions so that borings, soundings, and sampling points can be located to be representative of site conditions and to investigate anomalies. Geophysical methods also can be used later in the site investigation program after an initial study is completed to confirm and improve the site investigation findings and provide fill-in data between other measurements. General site knowledge (for example, depth to bedrock, site use history) is a useful precursor for designing a geophysical survey. 5.4.2 The level of success of a geophysical survey is improved if the survey objectives are well defined. In some cases, the objective may be refined as the survey uncovers new or unknown data about the site conditions. The flexibility to change or add to the technical approach should be built into the program to account for changes in interpretation of site conditions as a site investigation progresses. 5.5 Profiling and Sounding Measurements: 5.5.1 Profiling by stations or by continuous measurements provides a means of assessing lateral changes in subsurface conditions. 5.5.2 Soundings provide a means of assessing depth and thickness of geologic layers or other targets. Most surface geophysical sounding measurements can resolve three and possibly four layers. 5.6 Ease of Use and Interpretation of Data: 5.6.1 The theory of applied geophysics is quantitative, however, in application, geophysical methods often yield interpretations that are qualitative. 5.6.2 Some geophysical methods provide data from which a preliminary interpretation can be made in the field, for example, ground penetrating radar (GPR), frequency domain electromagnetic profiling, direct current (DC) resistivity profiling, magnetic profiling, and metal detector profiling. A map of GPR anomalies or a contour map of the EM (electromagnetic), resistivity, magnetic or metal detector data often can be created in the field. 5.6.3 Some methods, (for example, time domain electromagnetics and DC resistivity soundings, seismic refraction, seismic reflection, and gravity), require that the data be processed before any quantitative interpretation can be done. 5.6.4 Any preliminary interpretation of field data should be treated with caution. Such preliminary analysis should be confirmed by correlation with other information from known points of control, such as borings or outcrops. Such preliminary analysis is subject to change after data processing and is performed mostly as a means of quality control (QC). 5.6.5 It is the interpretation and integration of all site data that results in useful information for site characterization. The conversion of raw data to useful information is a value-added process that experienced professionals achieve by careful analysis. Such analysis must be conducted by a competent professional to ensure that the interpretation is consistent with geologic and hydrologic conditions. 5.7 Discussion of Applications— Applications listed in Table 1 are discussed below. 5.7.1 Natural Geologic and Hydrologic Conditions: 5.7.1.1 Soil/Unconsolidated Layers— This application includes determining the depth to, thickness of, and areal extent of unconsolidated layers. These layers may be discontinuous or include lenses of various materials. These layers can be detected because of differences in their physical properties as compared to adjacent materials. 5.7.1.2 Rock Layers— This application includes determining the contact between different rock layers, for example, limestone over granite or sandstone over shale, discontinuous bedding planes, and unconformities and the thicknesses of these layers. Several geophysical methods can be used to delineate rock layers depending on the physical properties and the depths and thicknesses of the layers. 5.7.1.3 Depth to Bedrock— This application includes determining depth to the top of competent rock covered by unconsolidated overburden. The choice of geophysical method depends on whether there is a physical property contrast between the rock and the overlying material. In areas where the top of rock is weathered or highly fractured, top of rock may be difficult to determine. Highly irregular rock surfaces may present additional problems. 5.7.1.4 Depth to Water Table— This application includes determining the depth at which a subsurface unit is fully saturated. The water table (top of the saturated zone) can be detected because of the changes in physical properties that are caused by saturated conditions. The ability to detect the water table may depend on the geologic unit in which it occurs. Seismic methods can be used to detect the water table in most unconsolidated materials; electrical, electromagnetic, or GPR methods may be used to detect the water table in either consolidated or unconsolidated materials. 5.7.1.5 Fractures and Fault Zones— This application includes the location and characterization of joints, fractures, and faults. These features range from individual joints and fracture zones to larger regional structural features. Joints, fractures and fault zones may be dry, fluid-filled or filled with clays or weathered rock. The detectability of these features increases with the size of the feature and with the presence of distinctive pore fluids or conductive fill material. 5.7.1.6 Voids and Sinkholes— This application includes karst features, such as weathered depressions in rock, open, water-filled, or sediment-filled sinkholes, and cavities or larger cave systems. In many cases, the target of concern may be beyond the effective resolution or depth range of some or all of the surface geophysical methods; however, deep cavities often show signs of their presence in the near surface and may be interpreted using shallow geophysical data. The ability to detect a given size cavity decreases with increasing depth for all surface geophysical methods. 5.7.1.7 Soil and Rock Properties— This application refers to the measurement of the physical properties of soil and rock, for example, elastic, plastic, and electrical. The geophysical method selected will be determined by the specific property to be measured. ASTM standards pertinent to those properties should be consulted. For example, rippability and acoustic velocities of rock are discussed in Guide D5777 , the wave velocities measured down a single borehole in Test Method D7400/D7400M and between boreholes in Test Methods D4428/D4428M . Soil resistivity measurements are discussed in Test Method G57 . Density, porosity measurements and seismic velocity measurements in boreholes are discussed in Guide D5753 . 5.7.1.8 Dam and Lagoon Leakage— This application refers to the detection and mapping of fluids leaking along preferential flow pathways from a dam or lagoon. The application of surface geophysical methods to detect leakage is contingent upon the presence of localized flow or difference in conductivity. 5.7.2 Inorganic Contaminants: 5.7.2.1 Landfill Leachate— This application includes all types of waste disposal sites in which the primary leachate is likely to be inorganic and electrically conductive. This includes municipal landfill sites, hazardous waste sites, and mine tailings. Inorganic contaminants can be detected using electrical or electromagnetic geophysical methods. 5.7.2.2 Saltwater Intrusion— Saltwater intrusion refers to movement of saline water into fresh water aquifers, and although this is primarily a coastal problem, it can occur naturally in inland aquifers or by man-made contamination, for example, brine ponds. Saline water is highly conductive and can be detected by DC resistivity and electromagnetic methods. The lateral boundary of the saltwater/fresh water interface can be mapped and the depth of the saline water estimated. 5.7.2.3 Soil Salinity— Soil salinity is a condition in which salt concentrations within soils have reached levels affecting the growth and yields of crops. DC resistivity and electromagnetic conductivity measurements provide means for measuring the soil salinity over a large area and at various depths. 5.7.3 Organic Contaminants: 5.7.3.1 Light, Nonaqueous Phase Liquids (LNAPL)— This application includes petroleum products present as discrete, measurable contaminants with concentrations greater than their solubility in water. The contaminants are lighter than water and “float” on the surface of an unconfined aquifer in porous media. The geometry of their occurrence in fractured soil or rock is more complex and less well defined. LNAPL dissolves into water and acts as a source of dissolved contaminant plumes (see dissolved organic contaminants). LNAPL can be detected in some cases because its electrical properties are different from those of ground water; it depresses the ground water surface if present in sufficient quantities; and, it can alter the capillary properties of soil. 5.7.3.2 Dense, Nonaqueous Phase Liquids (DNAPL): (1) This application includes chlorinated organic solvents and other contaminants that are present as a discrete, measurable contaminant phase with concentrations greater than their solubility in water. The contaminants are denser than water and “sink” below the water table. The distribution of DNAPL in the subsurface is complex and is controlled by gravity and the capillary properties of subsurface materials, rather than by ground water flow direction. DNAPL dissolves into water and acts as a source of dissolved contaminant plumes (see dissolved organic contaminants). Moreover,“ residual” DNAPL (immobile contaminant left behind during migration) also can act as a source of dissolved organic contamination. Residual concentrations of DNAPL do not significantly alter the properties measured by most geophysical methods. (2) Some DNAPLs have dielectric properties that may allow their detection using GPR if temporal measurements are made before the DNAPL is introduced to compare with properties that exist after the DNAPL is present; thus, GPR may be useful to monitor the movement of DNAPL during remediation. (3) The geophysical methods listed in Table 1 under natural geologic and hydrologic conditions are appropriate to characterize the hydrogeology of a site; therefore, an attempt can be made to predict DNAPL occurrence and distribution based upon an understanding of site geology. 5.7.3.3 Dissolved Phase: (1) This application includes fuels, solvents, and other organic contaminants dissolved in ground water. Sources can be leaks and spills of LNAPL or DNAPL or can be leaks and spills of such small volume that the contaminant is dissolved as it reaches ground water. (2) Dissolved organic contaminants are of regulatory concern at very low concentrations (parts per billion) in ground water. The properties of the dissolved organic plumes that can be measured by most geophysical methods are not sufficiently different from those of ambient ground water to be detectable. Some organic contaminants, such as alcohol, are highly soluble, and are not detectable even at high concentrations. (3) When sources of dissolved organic contaminants have been identified, geophysical methods can be used to characterize the hydrogeology of a site so that pathways for migration of dissolved plumes can be identified. The appropriate methods are discussed in the sections of this guide that pertain to geologic and hydrologic conditions. 5.7.4 Man-Made Buried Objects: 5.7.4.1 Utilities— This application includes a very wide range of targets including pipes, cables, and utilities. Fortunately, most utilities are buried near the ground surface, making them relatively easy targets to detect. The geophysical method selected will depend on the material of which the pipes or utilities are made (ferrous or nonferrous metals or nonmetallic materials). Nonmetallic utilities, that is, concrete or plastic, can sometimes be detected with GPR. 5.7.4.2 Underground Storage Tanks and Drums— This application includes underground storage tanks (UST) and drums. Since most underground storage tanks are large (more than 2000 L (500 gal)), buried shallow, and often made of steel, they are relatively easy to detect. If the tank is made of non-metallic material (for example, concrete or fiberglass), it is more difficult to detect. Drums of various sizes (typically 4 to 200 L (1 to 55 gal)) are manufactured from either non-metallic or metallic materials. While groups of drums may be detected, a single 200-L (55-gal) drum and smaller drums are more difficult to locate. 5.7.4.3 Unexploded Ordnance (UXO)— This application includes a wide range of materials that were designed to explode, such as bombs, mines, and antipersonnel weapons. UXO occur in a variety of sizes from a few centimeters to meters and are made of a wide variety of metals and other materials. Shape, size, depth, composition and orientation of the UXO can limit detectability. 5.7.4.4 Abandoned Wells— This application includes abandoned wells that may be uncased or cased with steel, PVC, or concrete. Abandoned wells can be detected by various methods depending upon construction, associated surface pits and other facilities, leaking fluids, and the method of abandonment. Guide D6285 provides a discussion of geophysical and other methods to locate abandoned wells. 5.7.4.5 Landfill and Trench Boundaries— This application includes landfills, pits, and trenches. Those that contain buried metallic materials can be detected because of the presence of the metal. Boundaries of trenches and pits can sometimes be detected by changes in electrical conductivity, disturbance of subsurface layers, or the presence of fill material. Determining the depth to the bottom of a landfill or trench is much more difficult than defining the lateral boundaries. 5.7.4.6 Forensics— This application includes buried bodies and a variety of metallic and nonmetallic objects. These objects can sometimes be detected directly or may be detected indirectly by disturbed soil conditions. 5.7.4.7 Archaeological Features— This application includes a wide range of targets, including stone foundations, walls, roads, fire pits, caves, and graves, as well as metallic and nonmetallic objects. These targets and objects can sometimes be detected directly or may be detected indirectly by changes in soil conditions.