Arsenic mobilization is an unfavorable side effect of biostimulation for the remediation of some TCE contaminated aquifers. The effect of biostimulation on arsenic mobilization was evaluated in 2 m x 15 cm aquifer material columns designed to study TCE bioremediation.  They were treated with whey or a commercially available lactate and emulsified oil product (Newman Zone®, Remediation & Natural Attenuation Service, Inc.), with and without the addition of a TCE dehalogenating mixed microbial culture.  The glass columns were sampled by coring in lifts ranging in thickness from 7.6 cm near the top to 30 cm lower in the columns. Under reducing conditions, the mobility of arsenic was greater in whey columns compared to emulsified oil and control columns. There was no significant relationship between iron reduction and arsenic release. Variation in As(III) levels within the whey columns were correlated with the levels of sulfate and sulfate reduction with depth.  Quantitative PCR was used to determine the density of arrA and dsrA functional genes in both the whey columns. The results illustrated that the dsrA copy numbers were relatively high in the first whey column lifts indicating greater sulfate reduction capacity than in the rest of the column. As(III) concentrations changed with depth through the column but the arrA gene concentrations were frequently below detection preventing correlation between As(III) and the aarA gene population density with depth. A future study will focus on understanding the relationship between sulfate reduction and arsenic release in biostimulated environments.