The Moana Hot Springs, located in NE¼ Sec. 26, T19N, R19E, in southwestern Reno, support the largest low-to-moderate temperature, direct-use development in Nevada. The springs have not flowed at the surface since the early 1980s; however, some of the wells drilled in the surrounding area maintain an artesian head. The springs were the discharge point for an area of thermal groundwater that has been used for a spa, swimming pool, and home heating for nearly 100 years. Recent use for home space heating began in the 1960s. The area today is predominantly residential. We estimate that the area of thermal groundwater encompasses at least 9 km2. Depths to the resource range from <50 to 240 m (e.g., McKay and others, 1995). In this area there are more than 250 wells, ranging in depth from 3 to 304.8 m, that access geothermal fluids for space heating. More than 300 residences are heated either by use of individual wells or a distrct heating system. Also heated are churches, apartments, a county swimming pool, and a casino. Residential and commercial development is concentrated in Sections 23 through 27, T19N, R19E (Flynn, 2001). ( figure).
The Moana Hot Springs were formerly the site of a spa that could be reached from downtown Reno by a streetcar line built in 1907 (Nevada State Journal, January 2, 1977). The swimming pool was also supplied for a long time with heated water from a well in the vicinity, and water was mixed directly with city water to maintain a specified pool temperature. This operation was terminated because of production problems with the well and water quality. Several homes in the area have used the thermal waters for over 60 years, although the number of wells increased markedly in the 1970s and 80s as the Reno residential area expanded. Numerous homes and three commercial establishments now use the geothermal waters for space heating; other uses include the heating of domestic hot water and water for swimming pools. Most of the systems use down-hole heat exchangers, and circulate city water through finned-tube baseboard heaters. Thermostatically controlled pumps are installed in most systems. Of the 162 lots that have access to the district heating systems in Manzanita and Warren Estates, 110 residences have paying customers, with the other homeowners declining the use of the resource. Fluid is delivered to the residences at 140 to 160°F (pers. comm. with Dennis Trexler, summer 2006). Bateman and Scheibach (1975) discuss the early use of the Moana geothermal waters in more detail, and maps by Garside (1983) and in Trexler and others (1982) show the area of geothermal development to that time. Jacobson and Johnson (1991) presented a more recent summary of the geohydrology.
Location of the Moana thermal system is thought to be controlled by northerly striking faults that parallel the front of the Carson Range to the west (Flynn and Ghusn, 1984; Bateman and Scheibach, 1975; Bonham and Bingler, 1973). Several faults in this area cut glacial outwash deposits of Illinoian age (E.C. Bingler, oral commun., 1977). It has also been noted that there is a striking north-south alignment of those wells with artesian head (past and present) and that the alignment may mark a fault trace (Bateman and Scheibach, 1975).
Although thermal groundwater has been encountered in wells over an area of several square kilometers ( figure), the highest temperatures, as well as the area of maximum use for space and domestic hot water heating, is concentrated in an area slightly over 5 km2. ( figure). The wells in the Sweetwater Drive-Manzanita Lane area (SE¼ NE¼ Sec. 26, Tl9N, R19E) are usually 30-90 m deep and many have temperatures of 71-85°C. The resource temperature of the Warren Properties district heating system is reported to be 99°C (Rafferty, 1989). To both the north and west of this area, it has been necessary to drill deeper wells to encounter thermal waters. Since 1995, well drilling has all but stopped due to depressed cost of natural gas and the expenses associated with drilling and the completion of both production and injection geothermal wells, but there has been a renewed interest in geothermal direct use with a recent rise in the cost of natural gas (Flynn, 2001, p. 7).
There are few indications of subsurface hot water north of Virginia Lake, although subsurface temperatures of 48°C were found at the Veterans Hospital 1.5 km northeast of Virginia Lake (Nork, 1985). In the Moana area, the hot waters encountered in drilling are associated with a "blue" clay zone that directly overlies the Tertiary bedrock units here and may be up to 46 m thick. The hot water is not generally found above this "blue" clay zone (Bateman and Scheibach, 1975). Flynn and Ghusn (1984) reported that the blue clay, a smectite clay, represents hydrothermal alteration of Tertiary rhyodacite. If the water moves upward through faults in the bedrock, this clay zone may act as a relatively impermeable cap, forcing the water to diffuse laterally (and vertically) away from the fault zone. Noticeable increases in water temperature were observed when certain wells were drilled through the contact between the clay and underlying bedrock. The existence of an artesian head only in wells drilled along a certain alignment, presumably a fault, may further support this theory of near-surface operation of the system. Wells drilled into or through the clay at some distance from such an input zone would tend not to display artesian conditions due to the hydraulic head loss involved in moving water laterally through the clays and andesite.
Water temperatures encountered at depths greater than 30 m range from 75 to 96°C. Deeper wells do not in general have the highest temperatures, suggesting that temperatures deep within the system may not be appreciably greater than those encountered nearer to the surface. This figure shows temperature profiles of several wells within the area. Although variable, the pattern of a leveling off of temperature with depth can be clearly observed (Bateman and Scheibach, 1975).
Photos
Drilling geothermal well at 2690 Monterey Circle.
Pool at Mark Twain Motel, S. Virginia St. - geothermally heated, Geothermal Reno.
Well no.1 drilling in the Moana area of Reno.
Warren Estates Production Well No. 1 during drilling in March, 1982 in the Moana geothermal area of SW Reno.