mdu.com, under the Investors tab.
For second quarter of 2021, we delivered earnings of $100.2 million or $0.50 per share compared to second quarter 2020 earnings of $99.7 million or also $0.50 per share.
During the quarter, our results were impacted by higher stock-based compensation and healthcare costs of approximately $4.2 million after tax.
Further impacting our second quarter consolidated results was a $5.4 million lower investment returns on certain benefit plans compared to the same quarter in 2020.
While these items had an impact on the quarter's results, all of our operations performed very well throughout the first six months of the year, growing consolidated revenues by 3.5% and increasing earnings $27.5 million year-to-date.
Our utility business are $9.6 million for the second quarter compared to earnings of $11.2 million in the second quarter of 2020.
For the Electric Utilities segment, reported earnings of $10.3 million for the quarter compared to $12.2 million for the same period in 2020.
Partially offsetting the decrease was higher adjusted gross margin driven by a 6.9% increase in retail sales volumes.
Our natural gas utility segment reported a seasonal loss of $700,000, improved from a seasonal loss of $1 million for the same period in 2020.
Adjusted gross margin increased during the quarter from approved rate recovery and 2% customer growth.
The pipeline business had earnings of $9.2 million in the second quarter compared to $9 million in the second quarter of 2020.
Construction services reported record second quarter earnings of $28.9 million compared to the prior year's record of $27.9 million.
Revenues increased 6% on a year-over-year basis to second quarter -- to a second quarter record of $525.6 million.
Our construction materials business reported second quarter earnings of $51.4 million compared to the prior year's $53 million in the second quarter.
Revenues increased 2% to $633.8 million.
We now have approximately 1.15 million customers across our electric and natural gas utility businesses.
We continue to expect strong customer growth across our service territory, outpacing the national average and in the range between 1% and 2% compounded annually.
Our generation portfolio in regards to nameplate capacity prior to the commencement of the retirements -- these retirements was 48% coal and will decrease to 31% in 2023 upon completion of the proposed Heskett IV natural gas-fired peaking unit.
The project involves constructing approximately 60 miles of 12-inch pipeline from our existing facilities at Mapleton, North Dakota to Wahpeton.
It will add 20 million cubic feet per day of natural gas capacity and is expected to cost approximately $75 million.
This $260 million project will add 250 million cubic feet of daily natural gas transportation capacity to our system, bringing WBI's total pipeline capacity to more than 2.4 Bcf per day, while helping to reduce natural gas flaring in the region and allowing Bakken producers to move natural gas to market.
CSG reported record second quarter revenues and earnings and an all-time record backlog now standing at $1.32 billion as of the end of June.
As a reminder, revenue guidance at this business for 2021 continues to be in the range of $2.1 billion to $2.3 billion, with margins comparable to or slightly higher than 2020 levels.
Construction materials reported backlog at the end of the quarter at $912 million, an increase of over 4% from the prior year.
Revenue guidance for this business is also in the range of $2.1 billion to $2.3 billion, with margins comparable to our 2020 levels.
With combined construction backlog at an all-time record at $2.23 billion as of June 30, we believe we are well positioned to take advantage of these multiyear growth opportunities.
While we believe these infrastructure proposals will provide additional opportunities to some of our core areas of business, such as surface transportation improvements, renewable energy, power grid modernization, broadband and much more, these infrastructure proposals are not included in our earnings per share guidance of $2 to $2.15 for this year of 2021 or in our 5-year capital investment plan for that matter as well.
For the last 83 consecutive years, we provided a competitive dividend for our shareholders and have been increasing it for the last 30 years.

Summary:
mdu.com, under the Investors tab.
For second quarter of 2021, we delivered earnings of $100.2 million or $0.50 per share compared to second quarter 2020 earnings of $99.7 million or also $0.50 per share.
The pipeline business had earnings of $9.2 million in the second quarter compared to $9 million in the second quarter of 2020.
As a reminder, revenue guidance at this business for 2021 continues to be in the range of $2.1 billion to $2.3 billion, with margins comparable to or slightly higher than 2020 levels.
Revenue guidance for this business is also in the range of $2.1 billion to $2.3 billion, with margins comparable to our 2020 levels.
While we believe these infrastructure proposals will provide additional opportunities to some of our core areas of business, such as surface transportation improvements, renewable energy, power grid modernization, broadband and much more, these infrastructure proposals are not included in our earnings per share guidance of $2 to $2.15 for this year of 2021 or in our 5-year capital investment plan for that matter as well.