Ground-water data in Orange County and adjacent counties, Texas, 1985-90

Abstract

The lower unit of the Chicot aquifer is a major source of freshwater for Orange County, Texas. In 1989, the average rate of ground-water withdrawal from the lower unit of the Chicot aquifer in Orange County for municipal and industrial use was 13.8 million gallons per day, a substantial decrease from the historical high of 23.1 million gallons per day in 1972. The average withdrawal for industrial use decreased substantially from 14.4 million gallons per day during 1963-84 to 6.9 million gallons per day during 1985-89. The average withdrawal for municipal use during 1985?89 was 6.8 million gallons per day, similar to the average withdrawal of 5.8 million gallons per day during 1963-84. Water levels in wells in most of the study area rose during 1985?90. The largest rise in water levels was more than 10 feet in parts of Orange and Pinehurst, north of site B (one of three areas of ground-water withdrawal for industrial use), while the largest decline in water levels was a localized decline of more than 60 feet at site C in south-central Orange County (also an area of withdrawal for industrial use). Chemical analyses of ground-water samples from the lower Chicot aquifer during 1985-90 indicate that the aquifer contained mostly freshwater (dissolved solids concentrations less than 1,000 milligrams per liter). Dissolved chloride concentrations remained relatively constant in most wells during 1985-90 but could vary greatly between wells within short distances. Saline-water encroachment continued to occur during 1985?89 but at a slower rate than in the 1970s and early 1980s. On the basis of chemical data collected during 1985?89, a relation was determined between specific conductance and dissolved chloride concentration that can be used to estimate dissolved chloride by multiplying the specific conductance by different factors for low or high conductances.