Plymouth Reservoir Dam, also known as the Thomaston Reservoir Dam, consists of an earth embankment structure with a maximum height of 25 feet and a total length of 730 feet including a 31.7 foot long concrete and stone masonry overflow spillway located 200 feet from the right end of the dam. The outlet works, located to the left of the spillway, consist of a 12-inch supply main and 10-inch low level outlet or blowoff through the dam, and an upstream gatehouse. Based on the visual inspection, the dam is judged to be in fair condition. Features that could affect the future integrity of the dam are downstream seepage, the lack of riprap slope protection on the upstream slope above the waterline and settlement of existing riprap, the unknown working condition of the intake gates, and the downstream location of the control valve on the low level outlet or blowoff. The Test Flood inflow of 600 cfs results in a Test Flood routed outflow of 390 cfs that would just reach the top of the dam. The spillway capacity is 410 cfs or 105 percent of the Test Flood routed outlfow.

The Middle Pond Dam consists of an earth embankment and stone masonry structure with a maximum height of 10 feet a top width of 10 feet and a total length of 535 feet including overflow spillways of 21 feet and 29 feet located near the left end of the dam. A low earthen dike with a maximum height of about 3 feet, a top width of about 5 feet and a length of about 200 feet is located about 150 feet to the left of the dam. Based on the visual inspection, the dam is judged to be in very poor condition. Features that could affect the future integrity of the dam are continued erosion of the upstream slope and crest, trees and stumps on the slopes, seepage through the dam, decreased spillway capacity due to blocking off the right spillway, deterioration of the right spillway, and lack of an operable outlet works. With the right spillway blocked the total spillway capacity of 430 cfs is equal to 17 percent of the Test Flood outflow. With the right spillway restored, the total spillway capacity of 550 cfs would be equal to 22 percent of the Test Flood outflow.

The Thurston Pond Dam, also known as the New Dam, consists of an earth embankment with a stone masonry overflow spillway located at the right end of the dam, and outlet works located at the right abutment. The total length of the dam, including the spillway section, is 510 feet and the maximum height is 20 feet. The stone masonry overflow spillway section has an upstream earth embankment of unknown section, a concrete cap and a batter of 6 inches per vertical foot on the downstream face. The outlet works consist of a concrete intake structure with inlet and outlet gates which can discharge water through a 24-inch concrete pipe to downstream locations or through an 18-inch concrete pipe into the stream below the dam. The dam impounds Thurston Pond, which is used for industrial water supply. Based on the visual inspection, the dam is judged to be in poor condition. Features that could affect the future integrity of the dam are continued erosion of the earth embankment, the presence of trees on the dam, the deterioration of the stone masonry overflow spillway, and inadequate spillway capacity to pass the Test Flood Outflow. The spillway capacity is 2,500 cfs or 37 percent of the Test Flood Outflow.

Park Pond Dam, located at the eastern end of the pond, consists of an earth embankment with a maximum height of 20 feet and a top width which varies from 8 feet to 15 feet. The dam is 420 feet long and has a 19.9 foot concrete spillway at the left end. A diversion channel from an adjacent watershed connects to the spillway approach channel. The impoundment has a maximum storage capacity of 1,100 Acre-Feet. The dike, located at the northwestern end of the pond, consists of an earth embankment with a paved roadway along the crest. The dike has a maximum height of 7 feet, a top width of 21 feet, and a length of about 80 feet. Based on the visual inspection, the dam is judged to be in poor condition and the dike in fair condition. Features which could affect the future integrity of the dam are trees and brush on the embankment; seepage through the embankment; erosion of the downstream slope; deterioration of the spillway approach channel wall and the spillway weir; the accumulation of debris in the spillway and approach and discharge channels; the location of the low level control valve downstream of the dam and lack of erosion protection on the dike. The spillway capacity with water level at the top of the dam and the dike is 310 cfs or 58 percent of the Test Flood routed outflow. The Test Flood would overtop the dam and dike by 0.3 feet.

The Pin Shop Pond Dam consists of an earth embankment with a 100 fokot long stone masonry overflow spillway located at the left end of the dam. Teh dam has a total length of 400 feet and a miximum height of 23 feet. The outlet works located to the left of the spillway consistk of an intake sluice gate which discharges into a stone masonry and concrete structure. A 16-inch gate valve drains the structure and discharges downstream of the spillway, A conduit to a downstream industrial complex is plugged with concrete. Based on the visual inspection, the dam is judged to be in poor condition. The future integrity of the dam can be affected by the lack of slope protection on the upstream slope, and continued erosion of the upstream and downstream slopes; trees on the embankment; continued undermining of the spillway apron; vegetation growing in open joints of the stone masonry training walls; the poor condition of the outlet works; and indagequate spillway capacity. The spillway has a capacity of 3,200 cfs and is capable of discharging 34 percent of the Test Flood outflow.