Premium
Field vs. Lab Alkalinity and pH: Effects on Ion Balance and Calcite Saturation Index
Author(s) -
Shaver Robert B.
Publication year - 1993
Publication title -
groundwater monitoring and remediation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 47
eISSN - 1745-6592
pISSN - 1069-3629
DOI - 10.1111/j.1745-6592.1993.tb00441.x
Subject(s) - calcite , saturation (graph theory) , chemistry , alkalinity , mineralogy , analytical chemistry (journal) , environmental chemistry , mathematics , organic chemistry , combinatorics
Ground water samples for a hydrochemical investigation were collected from 92 observation wells completed in a shallow, unconfined aquifer in southeastern North Dakota. The samples showed predominantly an increase in HCO 3 ‐ (positive bias) and both a pH decrease (positive bias) and a pH increase (negative bias) from field to lab. Positive pH bias generally was associated with ground water characterized by dissolved‐solids concentrations less than 400 mg/L. Negative pH bias generally was associated with ground water characterized by dissolvedsolids concentrations greater than 400 mg/L. Observed HCO 3 ‐ bias from field to lab slightly distorted ion balance distribution. Excess anions greater than 2 percent generally corresponded to increased HCO 3 ‐ from field to lab. Observed HCO 3 ‐ and pH bias significantly distorted the distribution of calcite saturation indices. Samples with dissolved‐solids concentrations less than 400 mg/L that generally showed a positive pH bias had a mean change in calcite saturation index of ‐0.214 (toward undersaturation). Samples with dissolved‐solids concentrations greater than 400 mg/L that generally showed a negative pH bias had a mean change in calcite saturation of +0.132 (toward over saturation). Calcite saturation indices were much more sensitive to observed pH bias than to observed HCO 3 ‐ bias. Linear regression analysis indicates % percent of the variability in calcite saturation index change from field to lab is attributed to change in pH from field to lab. Field pH should be used to compute calcite saturation index.