The words that cause the trouble
Regularly, periodically, as required, as needed, when necessary and routinely are the six offenders. Each of them looks like a frequency and none of them is one. A bidder pricing conservatively reads them as often; a bidder pricing competitively reads them as rarely, and both are being reasonable. The resulting quotes are not comparable, and the eventual disagreement has no document to resolve it. The cost of the vagueness lands entirely on the buyer, since the contractor priced exactly what they read.
The fix is arithmetic. Replace each with a number and a period: three times per week, once per fortnight, four times per year. If you genuinely do not know how often something should happen, that is a question to answer before issuing the scope, not one to leave in it. Asking bidders to propose a frequency is legitimate; leaving the word vague and hoping is not.
