It's pretty unbelievable to find 1000 year old treasure 6 inches beneath the surface - natural composting over 10 centuries could typically be as much as ten feet in a wooded area, so treasure would only be so near to the surface in exposed land that is regularly cultivated.
Based on house price inflation since Martin said they'd bought their house in 1985, this should be set around 2005. Somewhat strangely he is driving a much more modern car, circa 2015, and yet the house decor and appliances appear to be 1970's or 80's!