facilities; supporting our operations, including maintenance and improvements of our infrastructure; supporting our sales and marketing activities, including support of legislative and regulatory initiatives; financing vehicles for our customers; any investments in other entities; any mergers or acquisitions, including acquisitions to expand our RNG production capacity; pursuing market expansion as opportunities arise, including geographically and to new customer markets; and to fund other activities or pursuits and for other general corporate purposes.
Our business plan originally called for approximately $27.5 million in capital expenditures in 2021. These capital expenditures primarily relate to the construction of fueling stations, IT software and equipment and LNG plant costs, and we expect to fund these expenditures primarily through cash on hand and cash generated from operations. As a result of the Fuel Agreement with Amazon Logistics, Inc., we expect to deploy an additional $45.0 million to $60.0 million in capital expenditures to build fueling stations during the year ended December 31, 2021 that will support RNG fueling volume contracted to Amazon Logistics, Inc. We may fund up to $45.0 million of these expenditures through our SG Credit Agreement. Further, in 2021 we anticipate deploying up to approximately $100.0 million to develop ADG RNG production facilities. To that end, we contributed $50.2 million to the bpJV during the three months ended June 30, 2021.
In addition, NG Advantage may spend up to $0.4 million in 2021 to purchase additional equipment in support of its operations and customer contracts. Although NG Advantage has sought financing from third parties for capital expenditures, we have provided and may continue to provide financing for these capital expenditures.
We had total indebtedness, consisting of our debt and finance leases, of approximately $41.7 million in principal amount as of June 30, 2021, of which approximately $2.0 million, $14.2 million, $10.0 million, $5.5 million, $1.7 million, and $8.3 million is expected to become due in 2021, 2022, 2023, 2024, 2025 and thereafter, respectively. We expect our total interest payment obligations relating to this indebtedness to be approximately $2.3 million in 2021, $1.0 million of which had been paid when due as of June 30, 2021. We plan to and believe we are able to make all expected principal and interest payments in the next 12 months.
We also have indebtedness, including the amount representing interest, from our operating leases of approximately $50.3 million as of June 30, 2021, of which approximately $2.6 million, $5.5 million, $5.4 million, $5.4 million, $5.3 million and $26.1 million is expected to become due in 2021, 2022, 2023, 2024, 2025 and thereafter, respectively.
In addition, in connection with implementing our Zero Now truck financing program, we have entered into agreements that permit us to incur a material amount of additional debt on a delayed draw basis and obligate us to make interest and other fee payments that vary in amount depending on the outstanding principal of this debt and certain other factors; none of this potential debt nor the related interest and other payments are included in the foregoing estimates, other than the principal amount of $9.5 million drawn as of June 30, 2021.
We intend to make payments under our various debt instruments when due and pursue opportunities for earlier repayment and/or refinancing if and when these opportunities arise. Although we believe we have sufficient liquidity and capital resources to repay our debt coming due in the next 12 months, we may elect to suspend, or limit repurchases under, our share repurchase program or pursue alternatives, such as refinancing, or debt or equity offerings, to increase our cash management flexibility.
Sources of Cash
Historically, our principal sources of liquidity have consisted of cash on hand; cash provided by our operations, including, if available, AFTC and other government credits, grants and incentives; cash provided by financing activities; and sales of assets. As of June 30, 2021, we had total cash and cash equivalents and short-term investments of $254.2 million, compared to $138.5 million as of December 31, 2020.
We expect cash provided by our operating activities to fluctuate depending on our operating results, which can be affected by the factors described above, as well as the other factors described in this MD&A and Part II, Item 1A. “Risk Factors” of this report.