Appraisal of shallow ground-water resources, Pueblo Army Depot, Colorado

Abstract

The water supply for the Pueblo Army Depot, 15 miles east of Pueblo, Colo., is obtained from wells that tap an aquifer in terrace alluvium. Withdrawals have resulted in a water-level decline of 27 feet, which adversely affects the discharge rate ot individual wells. Furthermore, excessive pumpage has resulted in progressive deterioration o f water quality. Over a 20-year period, hardness has increased from 70 milligrams per i er to 135 milligrams per liter and dissolved-solids content has increased from 250 milligrams per liter to 370 milligrams per 1i ter.Two new supply wells were drilled in the southern part of the Depot and were tested to determine aquifer properties and probable production rate. The hydraulic conductivity determined from these tests ranged from about 350 to nearly 600 gallons per day per square foot. The transmissivity for the full thi c kness of the aquifer is in ~he range of 7,500 to 12,000 gallons per day per foot.The two new s upply wel ls can be pumped at a combined rat e of about 140 gallons pe r minute. If pumpage in the existing well field is reduced by the same amount, some re co ve ry of water levels in the field will occur and th e trend in wat e r quality deterioration may slow or e ven reverse.

Geohydrology and ground-water quality at the Pueblo Depot activity landfill near Pueblo, Colorado

“…The second phase consisted of the collection of ground-water samples and of the measurement of water levels. The hydraulic and storage properties of the unconfined aquifer were determined during a previous investigation (Welder and Hurr, 1971 18) and an explanation of the system of designating local well number is provided in the "System of Numbering Wells" subsection in the "Supplemental Data" section at the back of this report. Five monitor wells and the four piezometers were installed using a hollow-stem auger that had a 3.25-in.…”

“…Because it is an erosional surface, it is irregular and slopes vary locally. Welder and Hurr's (1971) Bedrock is exposed in the sides of the mesa, south of the landfill.…”

“…The hydraulic and storage properties of the unconfined aquifer at the landfill that are described in this report are based partly on the results of aquifer tests described by Welder and Hurr (1971) The storage properties of an aquifer (storage coefficient and specific yield) are used in determining the response of an aquifer to transient flow conditions. The porosity of the upland alluvial terrace deposits is used to estimate ground-water velocity.…”

“…The porosity of the upland alluvial terrace deposits is used to estimate ground-water velocity. The storage coefficient of the upland alluvial terrace deposits was determined by Welder and Hurr (1971) to range between 0.00016 and 0.00033. Because of the short duration of the aquifer tests, these values were assumed to represent the storage properties of the semiconfined gravels.…”

“…Regional ground-water flow at the Pueblo Depot Activity landfill, as indicated by the water-table map developed by Welder and Hurr (1971), is toward the south-southeast. The regional hydraulic gradient is disturbed in the vicinity of supply wells and at discharge areas near the edge of the upland alluvial terrace deposits.…”