What type of surgery is done for broad based disc bulge at l4, L5 and facet hypertophy at l4-s1 causing back and leg pain if sugical route is taken?

Decompression. I would first ask if you have had physical therapy, chiropractic care, injections, massage, accupuncture. If not, you should consider it as it might completely resolve your symptoms. These are all relatively benign, easy options. If they don't work to improve your symptoms, then you have no choice. Speak to your surgeon to discuss all your appropriate options.
Disc Bulge. The surgical management of nerve root compression in the lumbar spine is a decompressive laminectomy procedure (removing part or all of the roof of the spinal canal). This can achieved with an open surgical approach or minimally invasive surgery. For single level (one area) disease either procedure is beneficial and can have good outcomes. Speak to your spine surgeon about surgical options.