The sewer is to be supplied with water from the reservoir, and by means of gates and levels three or four feet of water is to be kept standing in the sewer are to be the wash and bath houses for the whole prison, having stationary tubs with drainage into the sewer. The plan provides for surface drainage from the kitchens and into the mains ewer, so that all the filth and offal of the prison passes through the sewer and into the river. Water for drinking and culinary purposes is to be supplied the prison and post by meanest of cast-iron pipe and hydrants. The pipes from the reservoir to the 90-foot avenue to be 8 inches in diameter, and thence through the center of the 90-foot avenue, 4 inches in diameter. When the reservoir is full there will be from 22 to 35 feet head, which is sufficient to force the water through 400 feet of fine hose attached to hydrant and extinguish any fire within the prison or barracks. The following is an estimate of the cost of the proposed improvement: 160 feet 6-inch cast-iron suction pipe, at $3 per linear foot, $480; 800 feet 8-inch cast-iron main supply pipe, at $4. 25 per linear foot, $3,400; 4,400 feet 4-inch cast-iron supply pipe, at $1. 75, $7,700; 20 hydrants, at $40 each, $800; 1 Worthington duplex pump (400 gallons per minute), boiler, &c., complete, $1,650; total, $14, 030. Fifteen hundred perches masonry in reservoir, at $3. 50 per perch, $5,250; concrete bottom and cementing face of inner wall, $1,000; 550 perches masonry in sewer, at $2. 50 per perch, $1,275; total, $7,525. To be reduced two-thirds by rebel labor, &c., to about $2,500. Grand total, $16,530.

It is proposed that the prisoners and troops quarry the stone, dig the trenches for pipe and sewer, tend the masons and do all the manual labor required. The stone can be quarried on the island and hauled by Government teams. This will reduce the estimate for the reservoir and sewer by at least two-thirds as above given. If the Quartermaster-General and the Commissary-General of Prisoners of war agree, it is proposed that the privies, the wash and bath houses, and the supply of water for the rebel hospital (which is near the reservoir) be constructed at the expense of the prison fund. The above estimate does not include the cost of the above work, which will probably amount to $5,000.

It is believed that when bids are received the cast-iron pipe can be furnished considerably lower than the estimate. I believe the whole expenditure of quartermaster's funds will not exceed $17,000. The work may be done for $15,000. If the plan and recommendation are approved and the work ordered, I will immediately cause an accurate and detailed plan and estimate to be made and forwarded for your approval. I am satisfied that such a plan of water-works, sewerage, and drainage is absolutely indispensable, and believe the one submitted to be adequate and as economical as can be desired.

Very respectfully, your obedient servant,

C. A. REYNOLDS,

Captain and Assistant Quartermaster.

[Indorsement.]

I fully concur in the above. In my judgment the object proposed is indispensably necessary.

Very respectfully,

A. M. CLARK,

Surgeon and Acting Medical Inspector of Prisoners of War.