The Mesa County Planning Commission is set to take up a United Companies proposal to operaate a gravel pit on 90 acres at the southeast corner of 32 1/2 and D 1/2 roads. United tells the Daily Sentinel quality deposits of aggregate are becoming difficult to find in the Grand Valley and this one could be mined for as many as 20 years. Opponents say the site is adjacent to an elementary school and close to homes, creating safety concerns, decreased property values and problems with noise and dust.