On June 9, 2013, at 0920 eastern daylight time, a Cessna 170, N2585V, was substantially damaged during a forced landing following a total loss of engine power while on landing approach to Robertson Field (4B8), Plainville, Connecticut. The private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which originated from Meriden Markham Municipal Airport (MMK) Meriden, Connecticut. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. According to the pilot, the airplane was on the left downwind leg of the airport traffic pattern for landing on Runway 02. He described as he reduced power, and incrementally increased the flap settings to 10, 20 and 30 degrees; all on the downwind leg. The pilot stated he applied carburetor heat when he increased the flap setting to 20 degrees. At 80 miles per hour, with 30 degrees of flaps extended, and prior to turning to the base leg of the traffic pattern, the engine experienced a total loss of power. The pilot stated that the airplane lacked the altitude and airspeed to glide to the runway from the point of the engine failure, and elected to land the airplane in wetlands on the east side of the runway; beyond the approach end. The pilot of another airplane in the airport traffic pattern at the time of the accident stated that his airplane was ahead of the accident airplane, on a left base for landing on runway 02, when the accident airplane appeared beneath his, and inside of his base-leg turn for the same runway. He described and diagramed how the airplane crossed the extended runway centerline from west to east, flew past and north of the approach end of the runway, and crashed in wooded wetlands east of the runway, abeam the runway numbers. The pilot held a private pilot certificate with a rating for airplane single-engine land. His most recent Federal Aviation Administration (FAA) third class medical certificate was issued in December 2012. The pilot reported 407 total hours of flight experience, 56 hours of which were in the accident airplane make and model. The airplane was recovered and examined by an FAA inspector on June 10, 2013. The fuel system was sumped from three points, and each sample contained a significant quantity of water. The fuel system was drained, the airplane was serviced with fresh fuel, and an engine start was initiated. The engine started immediately, accelerated smoothly and ran continuously without interruption. Examination of the seals around the fuel caps revealed that they were unserviceable, and no longer functioned as designed. Examination of rainfall totals revealed that over 3 inches of rain fell between the flight previous to the accident flight and the day of the accident.