High Radon‐222 (222Rn) concentrations exist in ground water from most granitic rocks in Maine. Some values exceed the suggested limit of 500 pCi/1 (E.P.A., 1976) by more than 100 times. Although high values (x̄= 22,100 pCi/1) are conclusively linked with the granites, high values are also present in ground water in metasedimentary rocks from sillimanite‐ (x̄= 13,630 pCi/1) and sillimanite‐orthoclase zone metamorphic terrains. Metamorphic (anatectic) pegmatites with hydrothermally introduced uranium are thought to be the source of radon in high grade terrain. At lower grade (chlorite to staurolite), no relationship exists between 222Rn content and metamorphic grade, although each rock formation has a somewhat characteristic 222Rn range from ground water, ranges which overlap. Considerable local 222Rn variations exist within the same rock body, reflecting local geologic and hydrologic conditions. Data on well depth, type of well, well yield, overburden type and thickness, and water chemistry show that 222Rn may increase slightly with well depth up to 50 to 75 m and is essentially constant thereafter. Low yield wells, generally associated with areas of thin overburden, tend to have higher 222Rn values than high yield wells, normally associated with thick sand and gravel overburdens. 222Rn concentrations decrease with increasing sodium concentrations, suggesting that low 222Rn wells are closely linked with surface waters. No other chemical parameter (Na, K, Ca, Mg, Fe, Mn, Zn, and Cu) correlates with 222Rn content within a single rock unit.

In the solution of nonlinear parabolic partial differentiM equations, such as the Richards equation, classical implicit schemes often oscillate and fail to converge. A fully implicit scheme has been developed along with a functional iteration method for solving the system of nonlinear difference equations. Newton's iteration technique is mathematically the most preferable of all functional iteration methods because of its quadratic convergence. The Richards equation, Newton-linearized with respect to relative permeability and saturation as functions of capillary pressure, is particularly aided by this new approach for problems in which saturations vary rapidly with time (infiltration fronts, cone of depression near a well bore, and so forth). Although the computing time is almost twice as long for a time step with Newton's iteration scheme, the smaller time truncation than that of classical implicit schemes and the stability in cases in which classical schemes are unstable permit the use of much larger time steps. To demonstrate the method, heterogeneous (layered) soil systems are used to simulate sharp infiltration fronts caused by ponding at the soil surface. When water filters into or through a soil, it replaces or is replaced by air. It may often bepossible to ignore the flow of the air phase because of the relatively small resistance to the flow of air. This assumption is made in the present paper so that the analysis of fluid flow in a soil saturated partially with water and partially with air reduces to one-phase flow, i.e., flow of water only. In such cases it is convenient to consider the pressure of the air to be constant everywhere and usually atmospheric [Corey, 1969]. Under these conditions the Richards equation [Richards, 1931], a combination of continuity and Darcy's law for the water phase only, applies. The present paper proposes a numerical scheme for a two-dimensional x, z or r, z form of the Richards equation (equation 1) suitable for infiltration problems in heterogeneous (layered) and anisotropic soils. A comparison of numerical and experimental results will be made in a subsequent paper along with a demonstration of solutions to practical problems. To date one-dimensional numerical results of the Richards equation are numerous and have been reviewed by Freeze [1969]. Two-dimensionM applications are less numerous. Most of them relate to 'free surface' flow problems integrating the saturated and unsaturated zones into a hydrodynamic unity [Rubin, 1968; Hornberger et al., 1969; Taylor and Luthin, 1969; Cooley, 1970; Verma and Brutsaert, 1970]. A unique threedimensional model was constructed (R. A. Freeze, unpublished report, 1970) for the treatment of saturated-unsaturated transient flow in small nonhomogeneous anisotropic geologic basins. In all of the preceding studies except that of Freeze (unpublished report, 1970) homogeneous soils are used in the analysis. All two-dimensional studies are restricted to cases in which saturations vary rather smoothly in space and time; i.e., sharp infiltra...

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The applicability of the Monte Carlo simulation technique to water quality modeling is demonstrated with the aid of a simple Streeter‐Phelps model. The model accounts for the stochasticity of the input parameters. Triangular probability density functions are shown to be useful in case insufficient information is available to define meaningful frequency distributions of input parameters. The model output is presented as probability distributions of stream quality parameters.

Two processes were investigated in the laboratory to determine their efficiency for removing radon from household water supplies. Granular activated carbon (GAC) adsorption was found to be extremely effective as a result of an adsorption‐decay steady state that is established quickly and continues for years. Because bed replacement is not a factor for practical purposes, GAC is the most cost‐effective process for radon removal. The GAC bed, however, adsorbs radon progeny as the radon decays, and it becomes a source of gamma radiation. This problem is believed to be manageable for the vast majority of potential applications. Diffused bubble aeration was found to be as effective as GAC, with removals of greater than 99 percent being practical. Although more costly than GAC, aeration does not have the problem of gamma activity buildup.