1、American Petroleum Institute API PUBL*4643 96 = 0732290 0559284 T5T Estimation of Infiltration and Recharge for Environmental Site Assessment t ,alth anc Environmen, Publication Number 4643 July 1996 Sciences Departmen, API PUBL*Lib43 96 0732290 0559285 996 One of the most significant long-term tren
2、ds affecting the future vitality of the petroleum industry is the publics concerns about the environment. Recognizing this trend, API member companies have developed a positive, forward-looking strategy called STEP: Strategies for Todays Environmental Partnership. This program aims to address public
3、 concerns by improving our industrys environmental, health and safety performance; documenting performance improvements; and communicating them to the public. The foundation of STEP is the API Environmental Mission and Guiding Environmental Principles. API ENVIRONMENTAL MISSION AND GUIDING ENVIRONME
4、NTAL PRINCIPLES The members of the American Petroleum Institute are dedicated to continuous efforts to improve the compatibility of our operations with the environment while economically developing energy resources and supplying high quality products and services to consumers. The members recognize
5、the importance of efficiently meeting societys needs and our responsibility to work with the public, the government, and others to develop and to use natural resources in an environmentally sound manner while protecting the health and safety of our employees and the public. To meet these responsibil
6、ities, API members pledge to manage our businesses according to these principles: To recognize and to respond to community concerns about our raw materials, products and operations. To operate our plants and facilities, and to handle our raw materials and products in a manner that protects the envir
7、onment, and the safety and health of our employees and the public. To make safety, health and environmental considerations a priority in our planning, and our development of new products and processes. To advise promptly, appropriate officials, employees, customers and the public of information on s
8、ignificant industry-related safety, health and environmental hazards, and to recommend protective measures. To counsel customers, transporters and others in the safe use, transportation and disposal of our raw materials, products and waste materials. To economically develop and produce natural resou
9、rces and to conserve those resources by using energy efficiently. To extend knowledge by conducting or supporting research on the safety, health and environmental effects of our raw materials, products, processes and waste materials. To commit to reduce overall emission and waste generation. To work
10、 with others to resolve problems created by handling and disposal of hazardous substances from our operations. To participate with government and others in creating responsible laws, regulations and standards to safeguard the community, workplace and environment. To promote these principles and prac
11、tices by sharing experiences and offering assistance to others who produce, handle, use, transport or dispose of similar raw materials, petroleum products and wastes. API PUBL+4643 96 D 0732290 0557286 822 = Estimation of Infiltration and Recharge for Environmental Site Assessment Health and Environ
12、mental Sciences Department API PUBLICATION NUMBER 4643 PREPARED UNDER CONTRACT BY: DANIEL B. STEPHENS (2) describe, compare, and contrast estimation techniques applicable for assessing petroleum hydrocarbon or salt-impacted sites; (3) compile site-specific recharge estimates from sites throughout th
13、e country; and (4) identify areas for further research. A literature search revealed dozens of methods, both physical and chemical, to quantify recharge in humid and dry climates. For determining site-specific recharge estimates, techniques that rely on very local measurements are more appropriate.
14、Such techniques include lysimeters, chemical tracers, the Darcy flux and plane of ES-1 API PUBLW4643 96 = 0732290 0559297 608 zero flux methods, one dimensional soil-water balances and soil-water models, and soil temperature methods based on near-surface soil temperature gradients. The most accurate
15、 (and often most costly) approach to estimating recharge in any climate uses soil lysimeters to collect deep percolating soil water that eventually would reach the water table. In humid climates, reasonably accurate recharge rates can be obtained from water balance calculations in the vadose zone, p
16、rovided that the period of accounting is weekly or more frequently. Vadose zone chemical tracers may provide more accurate estimates in dry climates for low to moderate cost. SUMMARY OF RECHARGE ESTIMATES Recharge estimates were gathered from the open literature and through requests for information
17、from U.S. Geological Survey district offices throughout the country. These data were compiled to (1) identify key studies and sources of information on recharge estimates throughout the U.S., (2) understand which techniques are being applied in various hydrogeologic and climatic settings, (3) determ
18、ine the frequency with which the various techniques are being applied, and (4) develop a database for future statistical analysis. The recharge estimates are tabulated for watersheds throughout the country. Information for each recharge study area includes climatological data, site physiography, and
19、 general soil characteristics. The recharge estimates are organized according to major surface drainage basins within geographic regions (Appendix A, Table A-1) and estimation technique (Appendix A, Table A-2). As indicated in these tables, the most frequently applied methods to quantify recharge ar
20、e the soil-water balance techniques and stream flow analyses. In addition, examination of the data reveals that within any climatic region individual studies ES-2 - API PUBLS4b43 76 0732290 0559298 544 m produce a wide variation in the recharge estimates. This variation may be attributed to differen
21、ces in the scales of investigations. METHODS TO QUANTIFY DIFFUSE NATURAL RECHARGE Physical methods described in this report include both direct and indirect methods. The only direct method of measuring recharge is lysimetry, which is costly and requires lengthy data collection periods. Indirect meth
22、ods described in this report include: Soil-water balance Darcy flux Plane of zero flux Soil temperature Electromagnetic Groundwater basin outflow Water-level fluctuation Stream gauging The soil-water balance method is one of the mos. widely used indirect estimation techniques. However, the accuracy
23、of this method depends upon the accuracy of estimates of its component parameters (runoff, infiltration, evapotranspiration and storage), which sometimes are poorly known or exhibit significant variability at a site. The greatest uncertainty lies in estimating evapotranspiration. Data compiled in th
24、is report indicate that recharge estimates using the soil-water balance method can vary over two orders of magnitude over large areas. However, this method may be suitable for small sites in humid or temperate regions where parameters that rely on climatic data are known to have low variability. Sev
25、eral vadose zone field test methods and equations needed to measure or calculate the component parameters of the water balance equation are discussed. ES-3 API PUBLU4643 96 0732290 0559299 480 W The Darcy flux and plane of zero flux methods provide useful estimates when resources are available to co
26、llect a sufficient number of field measurements. These methods require measurements of vadose zone moisture content and hydraulic conductivity over the seasonal range of site-specific soil moisture conditions. The soil temperature, electromagnetic, groundwater basin outflow, water-level fluctuation,
27、 and streamflow methods provide regionally averaged estimates of diffuse recharge. These methods may be most useful when the regional hydrogeology (.e., the location of recharge areas and aquifer boundaries, storage and outflows, etc.) is well understood. Chemical methods for estimating diffuse rech
28、arge are subdivided into those requiring measurements in either the vadose or saturated zones. Where project resources permit, chemical methods may provide better estimates of long-term recharge because they reflect recharge conditions over long periods of time. Vadose zone chemical tracer methods t
29、rack the movement of stable and radioactive isotopes. Chemical methods described in this report include the chloride mass balance method and those using tritium, chlorine-36, and stable isotopes as tracers. Chemical tracer techniques in the saturated zone determine the age of ground- water, which in
30、 turn permits calculation of groundwater travel time. Where recharge to an aquifer occurs primarily by direct local recharge, the age of the groundwater is related to local recharge. Chemical tracers used in aquifers include tritium, chlorofluorocarbons, krypton-85, carbon-1 4, and chlorine-36. Math
31、ematical models (soil-water and groundwater) are best suited to predict recharge when the physical properties of the soil and groundwater are well characterized. The water balance models typically require site-specific climatic data for precipitation, temperature and solar radiation; soil characteri
32、stics data including porosity and moisture retention characteristics; or a limited set of soil characteristics ES-4 API PUBL*:4643 96 O732290 O559300 T22 parameters, including field capacity, wilting point, saturated moisture content, and organic matter content. The soil-water balance model HELP (Sc
33、hroeder et al., 1994) was reviewed as a tool for estimating recharge rate. If recharge rates are low and the period of soil- water balance accounting is too long, then HELP (and other soil-water balance models) are likely to underestimate recharge because they only roughly approximate the physics of
34、 unsaturated flow. However, at one arid-climate field site, HELP-generated recharge estimates compared favorably to independent estimates using the Darcy flux method and the chloride mass balance technique. CHOOSING AN APPROPRIATE RECHARGE ESTIMATION TECHNIQUE No universally acceptable methods to co
35、mpute diffuse recharge can be applied to all sites. The method selected will depend on the site geology, soil characteristics, depth to the water table, vegetative cover, and climatic conditions, along with factors such as time constraints, available budget, and the importance of recharge to the suc
36、cess of the project. Section 4 of this report provides a guide to the appropriate selection of recharge estimation techniques based on optimal site characteristics, cost and relative accuracy. In most cases, a limited project budget requires use of a less sophisticated technique. In such cases, one
37、must accept some uncertainty in a site-specific recharge estimate and must attempt to understand the degree of that uncertainty. However, no comprehensive uncertainty analysis exists for the techniques described in this report. When time and budget are limited, one can refer to estimates contained i
38、n reports by the US. Geological Survey or state and local water resource or geological surveys. Where site-specific measurements are required but resources are limited, ES-5 API PUBL*4b43 b m 0732290 0559303 969 m one may consider an approach using a one-time data collection such as a Darcy flux ana
39、lysis based on laboratory or field measurements of the deep vadose zone hydraulic properties or chemical tracer sampling of the vadose zone. If resources are available, it is desirable to use both a physical and chemical method at the site. FUTURE RESEARCH This study revealed several areas in which
40、further research is needed, as outlined below: The reliability of some of the key methods to quantify recharge, especially in dry climates, needs to be improved. One example where considerable improvement could be achieved is in critically evaluating assumptions in the widely used chloride mass bala
41、nce method. Methods are needed to rapidly address the nature of spatial variability in recharge over large areas. In particular, methods for quantifying the contribution of flow through macropores are needed. A better understanding of recharge method uncertainty in various hydrogeologic and climatic
42、 settings is needed. Additional comparison studies of the low-cost, simpler estimation techniques with more rigorous measurement systems, under a variety of conditions, would provide useful uncertainty data on recharge estimates used in risk-based corrective action and other site-modeling efforts. A
43、 statistical analysis of the database compiled for this study may identify a correlation between precipitation and recharge for various physiographic provinces and climatic regions. ES-6 API PUBLX4643 96 W 0732290 0559302 AT5 = Section 1 Introduction API PUBLX4643 96 0732290 0559303 731 = Section 1
44、INTRODUCTION Chemicals released into the vadose zone, from either accidental spills or wastes managed on the land, may migrate to groundwater, depending upon the nature of the release, design of the waste management facility, properties of the chemical, vadose zone characteristics, and leaching pote
45、ntial. Typically, quantitative analyses are required to assess whether such contaminant releases or leachate pose a threat to human health and the environment. For example, in promulgating the 1 990 Toxicity Characteristic (TC) Rule, the U.S. Environmental Protection Agency (EPA) used a computer cod
46、e called EPACML (EPAs Composite Model for Landfills) to estimate the potential human exposure to chemicals inappropriately disposed of in municipal landfills. Such chemical fate and transport analyses are an integral component of risk assessments required at sites remediated under the Comprehensive
47、Environmental Response, Compensation and Liability Act (CERCLA). Similar computations are required in designing land treatment facilities for petroleum-contaminated soils and in evaluating risk-based alternatives at sites of fuel releases into the soil. There are many analytical and numerical method
48、s available to determine the mass flux of chemicals migrating by liquid-phase advection through the vadose zone into an aquifer. In virtually all instances, recharge is a key data need that must be prescribed in these calculations. Unfortunately, because of the difficulty in obtaining recharge value
49、s at a specific site, many analysts simply estimate the recharge rate based on their professional judgment, or they use model-embedded default parameters that are generally conservative for their purpose. A probabilistic approach such as a Monte Carlo analysis is sometimes used in risk assessments to address uncertainty in parameters. The probability of occurrence of a particular outcome is developed by making dozens or hundreds of calculations, each with a 1-1 - API PUBLm4643 96 O732290 0559304 678 W different set of parameters chosen at random and o
