Att HAVO Construction Phasing Memo

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Re:

David Sacamano, PLSA, ALSA - Otak
Justin Meeks, PE

Date:
November 19, 2024
Project No.: 23.0544
Project Title: HAVO Rainwater Catchment
Construction Phasing - 326181

HAVO Construction Phasing

Construction phasing for the rainwater catchment areas include improvements to Ground Catchments 1 and 2, demolition and construction for Buildings 241 and 43. Based on monthly precipitation data provided by HAVO staff for the years 2007 to 2022, the months May through September have the lowest rates of rainfall. Martin/Martin performed water analysis to estimate impacts to the raw water storage of the Park during construction. Water analysis used precipitation data from 2010, which had the lowest annual rainfall during the period provided. Analysis also used a 20% increase in average monthly water use, as calculated from meter data provided by HAVO staff for the years 2018 to 2022. The 20% increase in water use was assumed to correlate with a 20% increase in visitation. The water analysis assumed that improvements to Ground Catchment 1 would take around six (6) months, and the demolition and construction of the buildings to take one (1) year per building. The analysis was completed using the 2010 low precipitation conditions, 20% increase in demand/visitation, and construction schedule to be conservative. The analysis predicted that the construction on GC1, Building 241, and 43 can be completed in any order if a single structure is offline at a time. It is predicted that up to two of these structures can be taken offline simultaneously while maintaining sufficient water production throughout construction. It is predicted HAVO can have GC1 be offline at the same time as either of the rainshed buildings or have both buildings under construction simultaneously. Having all three structures offline, the evaluation showed that there would not be enough raw water production and service could not be maintained. The evaluation showed that with only two structures offline simultaneously, water production could be maintained throughout construction regardless of the season when construction commences.
The following recommendations were developed for implementation prior to starting construction, regardless of seasonality or sequencing:
• Install new Splitter box and 24 pipe to GC2
• Direct all rain catchment from Building 241 and Building 43 to GC2 prior to starting construction of GC1 to minimize pumping between reservoirs and water wasted to drain GC1