For arsenic speciation in ground water a lots of work have been carried out and published by NGRI, Hyderabad. For information regarding your problem kindly contact :
Director, National Geophysical Research Institute, Uppal Road, Hyderabad, India.
I dont know exactly where you can do it in India, you can search where the following facilties are avaiable: ICP-MS or GF-AAS, NAA and Counting facility.