Paper No. 6
Presentation Time: 3:00 PM
HETEROGENEITY OF GROUNDWATER QUALITY WITHIN A WATER SUPPLY AQUIFER AFFECTED BY ROAD SALT CHEMICALS
HON, Rudolph1, DILLON, Peter
2, DUGGAN, Amanda M.
1, MCINNIS, John R.
2 and CLABBY, Peter A.
1, (1)Earth & Environmental Sciences, Boston College, 140 Commonwealth Ave, Chestnut Hill, MA 02467, (2)Norwell Water Department, Town of Norwell, 345 Main Street, Norwell, MA 02061, rudy.hon@bc.edu
Increasing concentrations of chlorides in natural waters where road salts are used to control winter icing conditions suggest retentions of dissolved road salts within the nearby watersheds. Our previous work indicates that as much as 74% of salt is retained within the suburban watersheds and perhaps as much as 95% of salt is retained in the rural watersheds. To investigate the impact of road salting on ground waters in a producing aquifer we designed an experiment to monitor groundwater quality at three different depths near an active pumping well: shallow, medium, and deep. The sensors were installed in March 2011 near well PWS-1 in the Town of Norwell in SE Massachusetts. PWS-1 is located along a stream draining a small area (0.95 sq mi) with medium road density, multilane roads, and a shopping mall. Historical data of chloride concentrations in PWS-1 water from the 1970’s to present records a gradual rise in salinity from 20 mg/kg in 1970’s, 50 mg/kg in 1990’s, 80 mg/kg in 2000, 110 mg/kg and higher in the most recent years.
All three sensors (Aqua TROLL 200) are set to continually record water depth, temperature, and specific conductance at 15 minute intervals. The monitoring system is remotely accessible over the internet and stored data are periodically downloaded to a local computer. Specific conductance is converted into chloride concentrations by a conversion equation with linear coefficients calculated from a set of simultaneous pairs of chloride analytical data and sp. cond. measurements. Over the past 125 days (March to July 2011), Cl concentrations in the shallow zone increased from 152 to 254 mg/kg, in the medium depth zone from 225 to 246 mg/kg and in the deepest horizon only slightly from 144 to 156 mg/kg.
The producing aquifer is a dynamic system with a heterogenous distribution of chloride concentrations along the vertical profile with rapidly changing chloride concentrations with time, increasing up to 100 mg/kg in 125 days.
