WSP00601 - Laserfiche WebLink

Home Browse Search

N N is about 12,700 tons, or about 102,000 tons for ..::::. 1986-93. The 102,000 tons represents only the CJt decrease in dissolved-solids load from the Grand Valley in 1986-93. That load decrease also seems plausible when comparejj to the projected decreases in dissolved-solids load for the Grand Valley Unit. Neither of the previously stated decreases in annual dissolved-solids loads alStation 09163500 for 1986-93 should be interpreted as jjirect measures of salinity decreases in the Colorado River that are attributable to the salinity-control projects. However, after account- ing for the trend in annual loads in the Colorado River upstream from the GranQ Valley (station 09095500), there seems to be evidence that decreases in the annual dissolved-solids loads in the Colorado River down- stream from the Grand Valley (station 09163500) during 1986-93 were, in part, caused by salinity- control projects. TREND ANALYSIS FOR THE WHITE RIVER Preliminary analysis of data for water years 1978-84 indicated'that plugging of the three wells on Meeker Dome in 1980-81 had caused a decrease in dissolved solids in the White River (CH2M Hill, 1982; Burellu of Reclamation, 1985b). The saline ground water that was discharging from the wells had high chloride and sodium concentrations, and there were marked decreases in concentrations of those ions. Trend tests on chloride and sodium data collected at three gaging stations on the White River in the Meeker Dome area were used to statistically verify the initial conclusions about the effects of the well plugging in 1980-81 and to verify that the well plug- ging has remained effectiye since 1984. Data collected at three gaging stations were tested: station 09304200 White River above Coal treek; station 09304600 White River at Meeker; <lnd station 09304800 White River below Meeker (fig, 2). Station 09304200 is upstream from Meeker Dome and is a background site relative to the project. Station 09304600 is down- stream from Meeker Dome, and all effects on water quality from ground-water discharge from Meeker Dome were assumed to be between stations 09304200 and 09304600. Station 09304800 was the outflow site for the Meeker Dom\\ Unit study, and dissolved- solids and major-ion concentrations were affected by natural and agricultural inflows between Meeker and this station. The period examined for trend tests was 1973-92. Sampling frequency has varied during the period of study, as is apparent in the chloride and sodium data collected at stations 09304200 and 09304800 (figs. 11 and 12). There was a period of intensive sampling from July 1978 through September 1984 at stations 09304200 and 09304600 and from July 1978 through September 1983 at station 09304800, when samples were collected approximately weekly by the USGS for studies of the Meeker Dome Unit. Sampling was done on a quarterly basis in water years 1988-92 at stations 09304200 and 09304800. No chloride and sodium data were collected at station 09304600 after 1984 until water year 1995. Three sets of concurrent samples were collected in water year 1995 during November to early March at the three stations to con- firm that chloride and sodium concentrations had not changed since 1992. Three sets of samples also were collected at station 09304500, White River near Meeker (adjacent to Meeker Dome, fig. 2), concur- rently with sampling at the other three stations in water year 1995 for comparative purposes with samples col- lected at station 09304600. A review of figure 11 indicates that chloride and sodium concentrations have not changed at the background station 09304200, except for an anomalous fluctuation in water year 1982. By contrast, review of figure 12 indicates a large change in chloride and sodium at station 09304800 after completion of well plugging in 1981. Step-trend tests were done to statis- tically verify those observations for stations 09304200 and 09304800, and trend tests also were done for station 09304600. Step-trend tests were done by dividing the chloride and sodium data into four periods during 1973-92. Data collected before July 1981 were in the pre-project period (PRE); data collected from July 1981 through March 1982 were in the transition period (TRANS); data collected from April 1982 through December 1984 were in the first post-project period (POST!); and data collected from May 1987 through September 1992 were in the second post-project period (POST2). The TRANS period was when existing saline ground water that had flowed through the wells prior to the well plugging was drain- ing from the aquifer at Meeker Dome (Bureau of Reclamation, 1985b). Only stations 09304200 and 09304800 had data for the POST2 period. There virtually were no chloride and sodium data collected between the POST! and POST2 periods. TREND ANALYSIS FOR THE WHITE RIVER 31