Problem with searches on site for new office

[insurance_jon]

Was about to complete on the purchase of a derilict house and land adjacent to our office, and the plan was to build new offices and apts on it and move next door. BUT one of the searches shows a surface water (not main) sewer running through the garden between our office and the house in the middle of the plot. Waiting for a response from the waterboard as to how big a problem this is, but your thoughts and experiences are appreciated.