The family moved to Spalding in south Lincolnshire in 1739, after his father became engineer for the drainage works at Deeping Fen.
[2] Grundy was involved with major projects at Grimsthorpe between 1746 and 1752 which included an earth dam to create an artificial lake, and returned there intermittently over the next 20 years.
In 1762 he became the collector of the Land Tax in Spalding district, which although it only occupied him for a few weeks each year, earned him more money than his salary from Deeping Fen.
He continued to act as consultant for Deeping Fen during this time, and also oversaw the construction of the first of the docks at Hull, the largest in England when it was completed in 1778.
His biggest achievement in this period was the production of his Report Books, running to 12 volumes and 4,000 pages, with details of all his projects, except the works for Deeping Fen.
Later, Grundy sent the working drawings for the terminal sluice into the Humber to Smeaton, who made some suggestions and drew up a bill of materials.
He then produced detailed plans, which formed the basis for an Act of Parliament, and stayed in London during March and April 1769 to ensure the bill was passed.
One change to the original scheme was his decision to add a drainage mill at Sturton, to lift water from the Mother Drain into the Trent.
They were bought by Sir Joseph Banks, who was president of the Royal Society, in 1793, and the loose reports were bound into a further five volumes.
In addition to Grundy's reports, the volumes contain carefully drawn diagrams and plans, together with copies of estimates, minutes of meetings, and other details of his schemes.