A treasurer and the state treasurer are authorized to deposit in a public depositary any public funds available for investment and secured by collateral in accordance with the provisions of this chapter, and receive interest thereon. The authority provided by this section is additional to any authority now or hereafter provided by law for the investment or deposit of public funds by any such treasurer: PROVIDED, That in no case shall the aggregate of demand and investment deposits of public funds by any such treasurer in any one public depositary exceed at any time the net worth of that depositary. If a public depositary's net worth is reduced, a treasurer and the state treasurer may allow public funds on deposit in excess of the reduced net worth to remain until maturity upon pledging by the depositary of eligible securities valued at market value in an amount at least equal to the amount of the excess deposits. The collateral shall be segregated as provided in RCW
39.58.050. If the additional securities required by this section are not pledged by the depositary, the depositary shall permit withdrawal prior to maturity by the treasurer of deposits, including accrued interest, in accordance with applicable statutes and governmental regulations.