This staff report requests authorization for amending the existing contract with the Howard Ridley Company under Quotation No. 2002-062 for the Internal Rehabilitation of Reservoir No. 2 by increasing the contract amount by $90,000 to a total of $194,453.50. The increase in the contract cost will cover work to address conditions that were unknown prior to initiating this project.

Reservoir No. 2 is a concrete lined reservoir with an under drain system and a structural cover supported by timber columns. The reservoir was originally constructed in 1933. The reinforced concrete lining was poured in slabs with flexible material placed in the construction joints between slabs to allow for normal expansion and movement without allowing leaks to develop at the joints. Joints also exist around the perimeter of the roof column pile caps where the floor slab was poured around them. Repair and maintenance work has been undertaken periodically as required during the almost seventy year life of the reservoir.

Repair work to the construction joints and concrete slabs occurred sometime in the late 1950's or early 1960's. A thin veneer of concrete or plaster was placed on the floor and side wall slabs of the reservoir. Additional flexible sealer of the type used in the original construction (coal tar) was poured into the joints. The evidence of this work has been visually apparent in the reservoir although no project records exist for the work. Some fine cracks were visible in the floor slabs where small patches of the plaster layer had come up. The flexible material in the slab joints had subsided or settled deeply into the joint in some areas of the slab joints.

Monitoring of the under drain system had shown that flow through the bottom of the reservoir into the drain system increases substantially as the water level of the reservoir increased. Seeding with cement, broadcast on the water surface, did diminish flow in the under drain. Subsequent draining and filling during routine inspection and cleaning would apparently eradicate the beneficial effects of the seeding as the under drain flow returned to former flow rates.

Water quality problems related to difficulty in maintaining chlorine residuals were noted. Episodes of nitrification appeared to be linked to water in residence beneath the plaster veneer layer.

The seeding of the reservoir with cement had not identified any specific leakage site(s) in either the slab joints or the concrete slabs. The plaster veneer covered most of the floor and side walls so that the potential existence and the extent of the cracks in the slabs were speculative. The decision was made to remove the veneer covering the slabs and repair any cracks that were found and to replace the sealing material in the slab construction joints.

A Request for Quotation (RFQ) was issued and the Howard Ridley Company was the low quote at $104,453.50. The next lowest bidder was almost 43% more. The most significant cost item in the quotation was $70,100 for sandblasting the plaster veneer layer from the cement slabs. Once this layer was removed, a clear picture of the condition of the floor and wall slabs was available.

The method specified in the RFQ for crack repair was routing out the crack and then filling the void with joint material as if it was a constructed joint. If this method is applied to cracks near a joint, then the void to be filled after the routing will be wider than the joint material is rated to seal. The cracks near existing joints will have to be sealed by pressure injection of epoxy to the full depth of the crack in the slab. Thirty five column bases with adjacent cracks and about 75 linear feet of cracks near and parallel to the slab joints will require this method of repair at a cost of $3,800.

The spalls are the result of pieces of expansive aggregate that were part of the original cement pour for the slabs. The individual pieces of aggregate absorb water over time and eventually swell and spall off the surface concrete above them. This can eventually lead to penetration of the slab and direct leakage. The repair method is to chisel out the damaged concrete and defective piece of aggregate and then fill the depression with a cement epoxy to restore the surface. This is a relatively large number of spalls, but it reflects the source and quality of the aggregate used in 1933. The cost to repair the spalls is $22,375.00.

Reservoir No. 2 provides 75% of the total storage for Zone 2 and is a key element in providing water on the hillside for all residents above Zone 1. Constructed in 1933, it has provided reliable service with reasonable maintenance being performed as required. The current project scope was intended to address measured leakage and water quality problems that appeared to be linked to the joints and to the cracking and flaking plaster layer on the floor.

When the contractor entered the reservoir and completed the removal of the plaster veneer coating, the full extent of the condition of the slab was clear where it hadn't been possible to see it before. Each identified problem has a specific proposed remedy which is time tested and has been successful at other locations in water storage reservoirs. The actual methods being proposed for repair of the slabs may seem similar in concept to what was done in the original 1950's repair. However, the methods and/or materials being used are truly advanced and have only been available in the last 20 years. Pursuing the additional work as outlined will return the reservoir to full function, allow for an enforceable warranty on the repair work and extend the useful life of the reservoir well into the future.

Approval of this amendment to the contract will allow the work to proceed in a timely manner and be completed before the high water use months of the Summer come on.

This amendment will increase the contract amount by $90,000. The funding will come from within the existing BWP Water Division CIP budget and will not require a budget amendment.

Staff recommends that the City Council adopt the proposed resolution entitled: