Browsing Hydrology and Water Resources in Arizona and the Southwest, Volume 20 (1990) by Title
Now showing items 9-12 of 12
Site Investigation of Underground Storage Tank ContaminationNew regulations concerning the management of underground storage tanks (USTs) have resulted in increased awareness of environmental contamination resulting from leaking USTs. The objective of the typical underground storage tank investigation is to determine if any subsurface contamination has occurred as a result of tank or product line leakage, fuel spills or overfills. Soil contamination at underground storage tank sites is usually discovered during the removal and replacement of USTs. Techniques that can be used to detect the presence of soil contamination adjacent to existing USTs include soil vapor analysis, exploratory boring, and soil and ground water sampling. The lateral and vertical extent of contamination must be determined at any site which contains detectable quantities of contamination. Two common methods for determining the extent of contamination are over-excavation and borehole drilling and sampling. Boring design and location considerations include number of borings, borehole depth and spacing, and site sub -surface conditions. Differentiation between perched sub -surface water and aquifers is critical. Once an appropriate boring plan has been established, then a sampling and analysis plan must be adopted that meets the needs of the particular investigation. The determination of the extent of contamination at an underground storage tank site is the first step leading to site closure and remediation.
Site Remediation of Underground Storage Tank ContaminationRemedial techniques for sub-surface soil and water contamination are dependent on the lateral and vertical extent of petroleum hydrocarbon contamination and the type of petroleum hydrocarbons which have been released into the sub-surface. Specific remedial technologies are required for diesel fuel and heavy oils compared to the more volatile gasoline compounds. Available remedial technologies for vadose zone contamination include excavation and treatment; soil vapor extraction and possible vapor burning; bioremediation; and chemical treatment. Remedial technologies for ground-water contamination include water recovery, contaminant volatilization, carbon adsorption, bioremediation and water reinjection. Specialized apparatuses are utilized when petroleum hydrocarbon product floating on the water table surface must be separated from the ground water. A number of hydrologic considerations must be evaluated prior to any remediation scenario. These considerations include geologic characterization of the sub-surface soil matrix, and aquifer.
A Taxonomy of Small Watershed Rainfall-RunoffA study of over 11,000 event rainfall and associated direct runoff events from 100 small watersheds was done, in a search for distinct patterns of runoff response and/or association with land type. The results show unexpected variety in the geometry and scale of the rainfall -runoff response. Groupings of similar response type and magnitude were made, and the associations with vegetative cover were tested. Five separate response groups were identified as follows: 1) Inactive, characterized by no recorded responses to any rainstorm in an extended period of record; 2) Complacent, characterized by a very small part of the rainfall (ca 0.1 to 3 percent) being converted to direct runoff, often as a linear response; 3) Standard behavior, the expected "textbook" response common to agricultural lands and humid sites, and in which the runoff slope increases with increasing rainfall, and the scale of runoff far exceeds the complacent response; 4) Violent behavior, in which an abstraction threshold of 2 -6 cm clearly precedes a sudden high response; and 5) Abrupt response in which a very high portion of the rainfall is converted to event runoff without appreciable abstraction, as typified by extensively urbanized drainages. The responses and the group identifications were parameterized by a simple broken -line linear rainfall-runoff equation, and a dichotomous key based on coefficient values is proposed. Only mild associations between response type or coefficient values and the four vegetative covers (Forest, Range, Agriculture, and Urban) were found. The variety of hydrologic behavior on forested watersheds encompassed that of the other three land types.
Use of Biotoxicity Tests for Estimating Impact of Stormwaters on Aquatic LifeA test protocol was evaluated for estimating the acute toxicity of urban stormwater runoff to aquatic life. Potential deleterious effects of storm flows on the aquatic community of small artificial impoundments were examined by application of short-term bioassays. Definitive, static renewal, acute toxicity tests were performed using the fathead minnow, Pimephales promelas, and the crustacean, Daphnia magna. The feasibility study indicated that short-term bioassays may provide an alternative to individual chemical constituent measurements and comparisons to numerical water quality criteria for protection of aquatic life. Biotoxicity tests may identify synergistic interactions to chemicals which individually meet specific water quality criteria but collectively lead to toxicity.