Use a Turbidimeter for detection of high Suspended solids concentration (sand and Silica). Normally, the first run off will be highly charged with SS. After a while you could expect a drop in SS and the TDS will be also low as dilution come into effect.
You are right, safety first. My concern is mainly, if it is a normal practice to insulate rotary equipment like pumps whit high maintainability requirements.
My client is requesting pumps insulation for personal protection for services above 60 C. Where can I find solid arguments against it. It is too expensive.